Pt on robats & robotics

PROJECT REPORT AIM ROBOTS AND ROBOTICS INTRODUCTION For a very long time man has dreamt of mechanical slaves of great strength which could carry out wonderful tasks for him. The story of Alladin and the Wonderful Lamp is popular throughout the world. When the lamp was rubbed, a genie appeared and carried out the wishes at a command. While this story expresses the benefits of having such a wonderful mechanical slave, it also points out the danger of such a powerful device falling into evil hands. Indian mythology too is full of stories of princes and magicians who acquired the power to control similar mechanical slaves and devices. The great epics Ramayana and Mahabharata speak about similar gigantic and magical powers. Krishna could lift a mountain and could balance it on his little finger. Hanuman could fly in the air while carrying a mountain. The arrows and weapons described in the air while carrying a mountain. The arrows and weapons described in the Ramayana and the Mahabharata are said to possess magical powers. Stories and epics of these types are common in other counties as well. Since prehistoric times, man has been fascinated by mechanical men, extraordinary beings and other creatures. There is historical evidence to show that priests in Egyptian temples built mechanical arms and statues of their gods, which they could operate secretly so as to pretend that they were acting under the direct inspiration of God. The priests wished to use such machines to impress the faithful or to coerce the unfaithful. When a mammoth God breathed smoke and flames, waved its hands at the primitive people and commanded them to obey, it certainly made a deep impression. Heron of Alexandria, the ancient Greek mathematician and engineer who invented the fountain that bears his name, has left the description of two artful methods, which enabled the Egyptian priests to take in worshippers by their ‘miracles’. Fig. 1 shows one such device consisting of a hollow metal altar, which stood in front of the temple doors. The mechanism, hidden beneath the flagstones, caused the temple doors to open as if by God’s will. When incense was burned, the heated air inside the hollow altar exerted a pressure on the water in the vessel hidden below the floor, causing it to flow through a pipe into a bucket. The bucket descended due to the additional weight and set in motion the door-opening mechanism (see Fig. 2). The worshippers saw what they thought to be a miracle-the temple doors swung open of their own accord as soon as incense and prayers were offered by the priests. They, naturally, knew nothing about the hidden mechanism. Another fake miracle, which the priests staged, is explained in Fig. 3. As soon as the incense was burned, the expanding air forced more of the incense to flow out of the cistern below the floor, into the pipes concealed inside the figures of the priests. The worshippers beheld the miracle of an undying flame. However, when the priest in-charge considered the offerings too scanty, he would quietly remove the stopper in the lid of the cistern. This stopped the flow of incense, because now the expanding air could find a free outlet. This interest in mechanical men and other exotic creatures has continued even to the present day. Starting about 350 years ago, ingenious inventors designed and fabricated some strange devices. Medieval clocks mounted on the tops of churches and cathedrals often had a life-sized figure of a man, angel or devil that struck the hours on a bell with a mace. These were refined as time went by and they became more intricate. Jaganmohan Palace in Mysore and the Salar Jung Museum in Hyderabad have such clocks even today. Around 170, a bird organ was invented. The device is shown in Fig. 4 a. The bird could generate a selected set of bird-whistles and the head, beak and wings could move realistically. The device was worked by cams and levers with a clockwork mechanism (see Fig. 4.b). In the year 1738, an automated flute player was constructed and demonstrated by Jacuqes de Vaucanson in Paris. The flute player was dressed in musician’s clothes. It held a flute to its lips blew air across the flute and manipulated its fingers to control the ports of the flute. The player was driven by a musical-box type drum and operated by compressed air) see Fig.5). Henri Maillardet built an incredible automation, which could write and draw pictures, in London around 1805. This automation consisted of a very complicated and versatile clockwork mechanism. It could draw the picture of a ship in about five minutes. The picture of the ship consisted of three decks, portholes and all the necessary lines and details. The automation could also write a five-line poem in French. Fig. 6 is a sketch of this writing automation. Even though there were several robot-like mechanisms in earlier times, it was Karel Capek, a Czechoslovakian playwright who coined the word ‘robot’ and used it in his play Rossum’s Universal Robots (R.U.R.), written in the year 1921. In this play, factory-manufactured pseudo-men work side-by-side with human beings. These mechanical men could initiate action on their own. They could think and observe; they realized that the human master was exploiting them and rebelled against him, destroying everything around. In the Czech language robota means slave labour or rather compulsory service or labour provided by a worker. It is because of this characterization of a robot in Capek’s play that people began to visualize a robot as a monstrous human-like machine, something to be afraid of. Such fear is depicted in Mary Shelley’s Frankenstein. In the public mind, ever since, a robot has been mechanical humanoid, tireless and somewhat sinister. Perhaps it was not Capek’s work directly, but its influence on Lang’s movie Metropolis in the year 1926 that introduced the term robot into popular usage. Although the initial thinking about robots took place in the 1920s, practical scientific work on robots did not take place for nearly 40 years after that. However, the word robot kept appearing in science fiction stories and movies. Sir Isaac Asimov, the famous science fiction storywriter, has written numerous stories about robots. The robot of Asimov’s stories is a benevolent, friendly creature, always prepared to help its human master and is even ready to sacrifice its own existence in order to protect its human master. It was in the 1960s that Charles Devol and Joseph Engleburger of USA developed the first computer-controlled robot and demonstrated how robots could be made use of in industries. However, people doubted whether robots could prove practical at all! Indeed they were looking at robots with scepticism and ridicule. The movie Modern Times with Charlie Chaplin as the main character, made during that period, depicted such an attitude towards robots. Robots could not yet be used for practical purposes mainly because of their large size and high cost. In the 1980s, with the advent of microelectronics and microcomputers, computers became drastically smaller and their cost came down considerably. The result was that robots have been successfully employed in industries since then. With the success made by engineers and scientists in using robots for several industrial applications, people now began to ask: “ Will the robots replace human beings?” “Will not robots create large-scale unemployment?” Such fears were mainly due to ignorance and lack of understanding of robots. Fears about unemployment were there even during the first industrial revolution. When computers came on the scene people were apprehensive of computers creating large-scale unemployment. However, time has shown that such fears were unfounded. A careful study of the social and economic aspects of robots will reveal that instead of creating unemployment, robots will help create more job opportunities in the skilled category. Even if we grant that robots will replace human beings, no one can deny or protest against the use of robots when they are used in situations, which are uncomfortable or unpleasant or hazardous to human beings. Some examples are like working in very hot or very cold regions; doing welding or spray painting jobs where there are toxic fumes; handling radioactive chemicals as is don in nuclear power stations; or cleaning sewers and gutters. Robots are best suited to replace humans in doing hazardous, repetitive, monotonous tasks. Workers displaced by robots are sure to find new and better occupations. There is a virtually unlimited amount of work that needs to be done in eliminating poverty, hunger and disease throughout the world. We need to develop renewable energy resources, clean up the environment, rebuild our cities and villages, exploit the oceans, explore the planets and possibly colonise outer space. The new age of robots will open many new possibilities. What we humans can achieve in the future is limited only by our imagination and courage to act. ROBOTS AND ROBOTICS What is a robot? Different persons may have different concepts of robots. When we examine the robot-like devices of earlier times and compare them to the present-day robot we get a completely different picture of a robot. The wonderful lamp of Alladin leads us to believe that this robot-like device is a gadget, which has magical powers. But this robot-like gadget is fictional. The mechanical arms and statues used by the Egyptian priests made us believe that a robot resembled a human being, or at least his arms did. The mechanisms that opened the temple doors tell us that a robot is a mechanical contraption (hidden of course). The bird organ, the automated flute player, etc. give the impression that a robot is made of levers and cams and that sometimes a human appearance is given to impress the viewers. Karel Capek’s robot is a monstrous human-like machine. The picture of a robot in a science fiction movie shows a machine resembling the human and capable of tremendous memory and intelligence. In the present times, some people will accept that a vacuum cleaner or an automatic washing machine is a robot. Many contend that a machine becomes a robot when it can perform physical tasks without human intervention. What actually is robot? When different persons have different concepts of robots, the only way of deciding what really is a robot is to look for a definition of the term robot. The dictionary meaning of a robot is that it is an automatic apparatus or device that performs functions ordinarily ascribed to human beings or operates with what appears to be almost-human intelligence. It is interesting to observe that this meaning does not give a human shape to the robot. In order to dramatize the fact that the robot does the work of a human being, a human shape is given to the robot in science fiction stories and movies. The human shape is irrelevant as far as the functions of the robot are concerned. The Robot Institute a America, which is an association of several robot manufacturers, gives the following definition of an industrial robot (an industrial robot is a robot that is used in industries or manufacturing concerns): “An industrial robot is a reprogrammable, multifunctional manipulator designed to move material, parts, tools, or specialized devices through variable programmed motions for the performance of a variety of tasks.” The key word in this definition is ‘reprogrammable’. This means that a robot is capable of being reprogrammed. This feature is the one that distinguishes it from a fixed automation. A fixed automation is designed to do one, and only one, specific task. If the specifications of the tasks change even slightly, the fixed automation becomes in capable of performing the task it was designed to perform according to one fixed specification. However, a robot can be reprogrammed to perform even when the specifications are changed drastically. The original program is simply erased and the new program takes care of the changed tasks. The characteristic that a robot can be reprogrammed to handle a variety of tasks, makes the robot a flexible device. Because of the flexibility offered by robots, manufacturing systems which use robots are called Flexible Manufacturing Systems (FMS). Karel Capek was responsible for introducing the word robot. Sir Isaac Asimov is the one who coined the word robotics. According to Asimov, robotics is the science of dealing with robots. Hence robotics involves a scientific study of robots. The study includes design, selection of materials of proper quality for the components, fabrication, the study of various motors required for moving the components, design of electronic circuits, computers and computer programming, and control of robots. Since robots and robotics are still in the developing stages, a considerable amount of research is required and is being pursued. Robotics involves various disciplines-mechanical engineering, material science, electronics, computer science, computer engineering, and control system, to name just a few. Depending on the area in which robots are to be used, robotics includes disciplines such as biology, medical science psychology, agriculture, mining, outer space engineering, etc. Basically, there are two types of robots: fixed and mobile. A fixed robot is attached to a stationary platform. A sketch of an industrial robot can be seen in Fig. 23 on p.34. A fixed robot is analogous to a human standing or sitting in one fixed location while doing his work with his hands. A mobile robot moves from place to place. Mobility is given to robots by providing wheels or legs or other crawling mechanisms. Fig. 25 on p 36 shows the sketch of a mobile robot. A mobile robot can be given a human shape, but the actual shape has nothing to do with the actual functions of the robot. Wheeled locomotion is good for smooth terrains. For rugged terrain, legged locomotion is preferable. A mobile robot should have at least three wheels or legs for stability. COMPONENTS OF AN INDUSTRIAL ROBOT TYPES: - Let us now se how a robot if fabricated. Let us look at the various components that constitute a robot. When we examine the various tasks that are performed in an industry, we observe that the human hands do the majority of work, with the person standing or sitting in one fixed location. The human being performs the tasks assigned to him with the help of five major parts of his body. First, he uses his arm, which is made up of joints and links. Second, he uses his palm and fingers. Third, he uses his muscle power to move the arm and palm and fingers. Fourthly, he uses his brain to control the movements of his arm and palm and fingers. Finally, he uses his senses (or rather the sense organs) –the eyes, ears, and sense of touch (skin), to provide valuable information to the brain in controlling the actions of the various parts. The use of the other sense organs, the nose and tongue is less common. Analogously, the industrial robot consists of five major components. These five components are described next. Component 1: The Manipulator -- Analogous to the human arm, the industrial robot consists of what is called a manipulator having several joints and links. The number of joints and links to be provided depends on the type of work required of the robot. This number is related to the number of independent motions required of the robot. For example, if there is only one joint and only one link, there can be movement in only one joint and only one link; there can be movement in only one direction. If the movement is linear, that is along a straight line and we can reach points only on this straight line. Further, the distance that can be travelled along this straight line will depend on the length of the link. On the other hand, if the joint moves in a rotary fashion, as in the case of the joints of the human arm, the tip of the link goes along the arc of a circle and only points on this arc can be reached by the link, Now, if we have two joints and two links and if the two have linear motions such that the two motions are mutually perpendicular, the combined motion will be such that any point in a rectangular region can be reached. The number of independent motions is technically termed number of degrees of freedom. Let us now examine how many degrees of freedom are required to uniquely specify the location of a three-dimensional rigid body in space. Three coordinates can specify the centre of gravity of the rigid body. The rigid body can have an arbitrary orientation; it can rotate about the x-axis; it can rotate about the y-axis; and it can rotate about the z-axis. As an illustration, let us suppose that there is an object on a table in a room (see Fig. 7). Let us assume that one corner on the floor is taken as the origin of the three-dimensional co-ordinate system. To reach the centre of gravity of the object on the table, we can move along three mutually perpendicular directions (called the x-axis along one edge of the wall on the floor, the y-axis along another edge of the wall on the floor, and the z-axis along the vertical direction given by the intersection of the two walls at the origin). The orientation of the object is defined by three rotations about the x-axis, the y-axis and the z-axis. Thus the position and orientation of the object is described in terms of six-co-ordinates or six movements, which are dependent. In other words a rigid body in space is uniquely described in terms of six degrees of freedom. Therefore, a general purpose industrial robot must have six degrees of freedom. It must have six joints and six links. The lengths of the links are decided by the extent of the volume in which the robot must work. It is of interest to observe that the human arm has got six degrees of freedom. The shoulder joint has two degrees of freedom, the elbow joint has one degree of freedom, and the wrist joint has got three degrees of freedom. Because of the six degrees of freedom it possesses, the human arm can handle an object (within the reach of the arm) having an arbitrary position and orientation. All the joints of the human arm are rotary in nature. A rotary joint is also termed as a revolute joint. At industrial robot can be designed to have either rotary joints or to have linear joints (joints that move in a straight line). A linear joint is technically called a prismatic joint. It is possible to reach an arbitrary point in three-dimensional space or using three independent linear joints or three independent dependent rotary joints or three independent joints which are combinations of liner and rotary joints. However, an arbitrary orientation can be realized only through three mutually perpendicular (independent) rotary joints. This arbitrary orientation cannot be realized by means of linear joints or by means of combinations of linear and rotary joints. In view of this, of the six degrees of freedom required for a general-purpose robot manipulator, the final three joints must necessarily be only three mutually perpendicular (independent) rotary joints. The remaining three joints can be combinations of linear and rotary joints. Depending upon the number of linear joints (or equivalently the number of rotary joints used), the manipulator is categorized into different types. Cartesian Robot Manipulator: The Cartesian robot manipulator has three linear joints and three rotary joints. The movements of the three linear joints are in mutually perpendicular directions. The first three linear joints of the Cartesian manipulator are shown in Fig. 8. This type of manipulator has a small work space (work space is defined as the set of all points that can be reached by the robot manipulator). Cartesian manipulators have a high degree of mechanical rigidity. These are capable of reaching the specified point with a high degree of accuracy. Accordingly, Cartesian manipulators are used in situations in which great accuracy is called for. Cylindrical Robot Manipulator: This type of robot manipulator consists of two linear joints and one rotary joint; the other three joints are, of course, rotary in nature. Fig. 9 is a sketch of the first three joints of a cylindrical robot manipulator. The workspace of this robot is larger than that of the Cartesian robots. Cylindrical robots are best suited for what are called pick-and-place operations. These operations involve picking up an object from a specified position and placing it at another specified position. The mechanical rigidity of this type of robot is slightly lower than that of the Cartesian robot. Spherical Robot Manipulator: In addition to the final three rotary joints, a spherical robot manipulator consists of one linear joint and two rotary joints. Fig. 10 is a sketch of a spherical robot. Spherical robots have a larger workspace and a lower degree of mechanical rigidity when compared to cylindrical robots. Horizontal Articulated Robot: This type of robot manipulator has two rotary joints and one vertically moving linear joint as illustrated in Fig. 11. The final (three) joints are necessarily rotary. The workspace of this type of robot is smaller than that of the spherical robot, but larger than that of the Cartesian or the cylindrical robot. This type of robot is appropriate for assembly operations (that is joining together individual components to make a final product). Vertical Articulated Robot: Apart from the final three joints, which are rotary in nature, this type of robot manipulator has only three rotary joints (Fig. 12). This type resembles the human arm because both have only rotary joints. This is the most popular type of robot. Component 2: The Endeffector -- At the end of the human arm there are the palm and fingers, with the help of which the human being can pick and hold and transfer objects from one position to another. Analogously, we have the second component of the robot, which is called the endeffector. The base of the manipulator is fixed to a base support and at its other free end, the endeffector is attached. The endeffector is expected to perform tasks normally performed by the palm and finger arrangement of the human arm. The palm and fingers of the human arm are very delicate and dexterous and are capable of several intricate holds. Some typical types of hand prehension (holds or grasps) are illustrated in Fig. 13. We hold cylindrical objects such as a glass of water or a small pipe, using a cylindrical grasp. The tip grasp enables us to hold small objects such as a pin. To carry a briefcase or a small suitcase, we use the hook grasp (also called the snap grasp). To hold a piece of chalk or a matchstick we use the palmer grasp. Spherical objects, such as a ball, are held using a spherical grasp. The lateral grasp enables us to hold objects such as a visiting card. With the present-day technological know-how, it is not yet possible to design and construct one single mechanical device that is capable of the wide range of delicate and dexterous holds possible for the human palm and fingers. Therefore, endeffectors have to be designed and constructed to suit individual needs. That is, different endeffectors are designed for different types of functions demanded of it and, therefore, there are a large number of different endeffectors. Fig. 14 illustrates an endeffector, which is finger-shaped and has an object-shaped cavity to help hold the object firmly. Fig. 15 illustrates another finger-shaped endeffector having multiple object-shaped cavities. Using this type of endeffectors, objects of different sizes are held in a firm grip at different position. Inspired by the human three-fingered grip as illustrated in Fig. 16.a, one can design a flexible gripper-enabling object such as a turbine blade to be held. Such an endeffector is shown in Fig. b. We can have multiple detachable grippers as shown in Fig. 17. The different grippers are in the form of fingertips. One gripper can be removed and another attached as and when necessary so that objects of different sizes and shapes can be handled. When objects to be held have parallel and flat edges, they can be gripped with the help of a parallel jaw gripper illustrated in Fig.18. The endeffector shown in Fig. 17 has multiple detachable grippers. If a different gripper is to be used, it takes time to detach the present gripper and attach the different gripper required for the new task. An arrangement of the endeffector, which can save the time required for changing the gripper, must have multiple grippers permanently fitted to the end of the manipulator. The endeffector can be a spray-painting gun or it can be a welding gun; the endeffector can be an electromagnetic pick-up device or it can be a vacuum suction mechanism. In this manner the endeffector can take several different forms to suit the specific type of work it is expected to do. The designer can use his imagination and ingenuity in deciding how the endeffector is to be fabricated. Component 3: The Locomotion Device -- In the case of human beings muscles provide the power for the movement of the arm, the palm and fingers. The expand and contract so that the required power is produced. For the robot the power for the movement (locomotion) is provided by motors. The motor of an automobile is run by the energy generated by the ignition of a mixture of air and petrol. The electric fan has a, motor driven by electrical energy. In a hydroelectric generating station the generator is driven by a turbine, which is powered by running water. A windmill is driven by the energy possessed by moving air. The motors used for providing locomotion in robots are of three types depending on the source of energy: electric, hydraulic or pneumatic. Electric motors are driven by electricity. Hydraulic motors are powered by pressurized liquid, usually pressurized oil, pneumatic motors are actuated by pressurized air. All the joints of the human arm are rotary in nature. However, the joints of the robot can be either rotary or linear. Electric motors give rotary motion. If required, rotary motion can be transformed to linear motion through the use of a lead screw mechanism. When the head of a screw is rotated (that is, given a rotary motion), the tip of the screw gets a linear motion. The speed at which a motor rotates (the r.p.m.) is generally high. The speed of rotation can be reduced by the use of gear trains. Locomotion devices are also known as drive units. Drive units are classified according to the type of energy source used for locomotion. Accordingly, we have three important types of drive units: electric drive, hydraulic drive and pneumatic drive. Electric drives give a rotary motion, which, if necessary, can be transformed into linear motion. Hydraulic or pneumatic drives can give rise to either rotary motion or linear motion. When hydraulic drives provide a rotary motion they are called hydraulic motors; if they give a linear motion, they are called hydraulic cylinder. Similarly we have pneumatic motors and pneumatic cylinders depending on whether they give rotary or linear motion. The drive units are coupled to the joints. Each drive unit moves the joint to which it is coupled independently. The combined motion of the various joints, and hence the various links, results in the motion of the robot manipulator. There are two ways in which the drive unit is coupled to the joint it moves. The drive unit can be connected directly to the joint shaft. In this event the drive unit is called a direct drive unit (motor). However, this makes the times we may need the joint to move at a speed different from that of the motor. In this situation, the motor is indirectly connected to the joint; thus we have an indirect drive unit (motor). The motion of the motor is transferred to the joint by transmission devices such as rods, chains, belts and gears. Fig. 19 illustrates the direct drives and indirect drives used in a typical robot. Component 4 : The Controller -- The human brain controls the actions of the human hand. In the robot there is a component which functions in a manner analogous to the human brain. The computer, more specifically a digital computer, can be compared to the human brain, because the computer possesses five important functional characteristics of the human brain. A computer is able to read. In other words, a computer is capable of grasping information. Information is fed to the computer in a coded form and the computer is able to understand the coded information. A computer is able to write. In other words, a computer is capable of giving out information. A computer has memory. It is capable of storing information (numbers, alphabets and special characters) for any length of time without loss in accuracy and can recall the required information. The amount of time required to store information or to recall information is a very small fraction of a second. A computer is able to calculate. It can do arithmetic operations-addition, subtraction, multiplication and division. The time required for adding two numbers is a very small fraction of a second. A computer is capable of taking logical decisions. Because a digital computer possesses these five capabilities, which are also possessed by the human brain, it can function as the fourth component of the robot, the controller. The digital computer (both the hardware and the software) acts as a controller to the robot. With the help of this controller, the robot is able to carry out the assigned tasks. The controller directs and controls the movement of the manipulator and the endeffector. In other words, the controller controls the motors that drive the robot links (joints). Suppose there is an object at a certain position, and the robot is required to pick up the object from its initially specified position and then to place it at a certain other position. The location of the object is known. With this information, the controller, that is the computer, calculates the amount by which each joint has to move so that the endeffector reaches the position where the object is situated. After calculating this information, the controller supplies to each motor (driving the individual joints) the appropriate amount of signal so that the joints move by the required amount and the endeffector reaches the position where the object is located. After the endeffector reaches the desired location, the controller gives an appropriate signal to the endeffector to grasp the object. Then the controller gives appropriate signals to the various motors driving the joints to move by the appropriate amount so that the final desired position is reached. Finally the controller directs the endeffector to release the object so that it is placed at the desired location. Controlling the joint to move by an appropriate amount can be accomplished accurately when the system as well as the environment is accurately known in advance. However, many-a-time the information about the system and the environment is not available in advance because there are unknown and unpredictable disturbances. The effect of unknown and unpredictable disturbances can be overcome by the use of feedback control. Here, the actual output of the actuator/motor is measured and compared with the reference input signal and the difference between the two, called the error signal, is amplified and the amplified signal is applied to the actuator/motor. The joint driven by the motor moves until the error signal becomes zero. Thereby a very accurate control is obtained even in the presence of unknown and unpredictable disturbances. A schematic diagram of a closed loop (i.e. feedback) control is shown in Fig. 20. It is interesting to note that the computer calculates the amount by which a particular joint is to be moved in a particular situation, and generates a signal to be applied to the motor driving the joint under consideration. The power contained in the signal generated by the computer is very small. But a considerable amount of power is needed to drive the motor. Since the computer by itself is unable to supply the needed power, an electronic power amplifier (also called an electronic driver circuit) is used to increase the strength of the signal generated by the computer. Furthermore, the output signal supplied by the computer is a digital signal. Most motors require that the input signal to the motor be an analogous signal. Therefore, a digital-to-analog converter (D/A converter) is used to interface the computer and the drive motor. Fig. 21 shows a schematic diagram of the arrangement used to drive a motor. Converters (digital-to-analog) and driver circuits are also used in hydraulic and pneumatic drive systems. The difference is that in these types of systems, the electrical unit moves only the valve (see Fig. 22) while an external unit such as an air pump or an oil-pump supplies the energy to the actuator. Although for all intents and purposes, the digital computers started developing in the years following World War II, robots using computers became successful only during the 1980s. This is because the computers of the earlier days were huge and very expensive. These computers used vacuum tubes, which are large. For example, a vacuum tube was to 10 cm in height and about 5 to 8 cm in diameter. When thousands of vacuum tubes were used to make the digital computer, it became very large and required a large room to house it. Further, vacuum tubes dissipated a large amount of heat and the computer required a cooler. With the advancement in electronics, transistors replaced the vacuum tubes and computers became relatively small. A transistor is approximately one-hundredth of a vacuum tube in size, but it performs the same function as that of the vacuum tube. With the advent of microelectronics, we now have a microelectronic device, which performs the same task as that of a transistor and which is so tiny that about 50,000 microelectronic device can be housed in the same volume occupied by a single vacuum tube. A transistor generates very little heat, compared with that generated by a vacuum tube. A microelectronic circuit looks very small when placed by the side of a rice grain (and the rice grain is much bigger when compared with a microelectronic circuit). The advent of microelectronics has given us microcomputers, which are very small and with low costs. One can therefore afford to use one or several microcomputers have revolutionized control methods. The present trend is to use one microcomputer for the control of an individual joint and an overall computer to control the entire manipulator and interface to the external world. When there are multiple computers available, it is possible to used parallel processing methods and many complicated computations required to solve the equations of motion can be performed in a very short time. Thereby, it becomes easy to control the motions of various joints and the endeffector. The overall computer is used as a supervisory computer to supervise and co-ordinate the functions performed by the individual microcomputers. Component 5: The Sensors -- The brain of the human being by itself cannot perform intelligent tasks. It is capable of all its attributes because it is supported by the five sense organs of the human body. These sense organs provide valuable data to the brain, which in turn understands the data after processing it. Without the data supplied by the sense organs, the brain would be incapable of intelligence. When we understand this, it is easy to see that the controller (the computer) of the robot cannot do any meaningful task, if the robot is not provided with a component analogous to the sense organs of the human body. Thus, the fifth and the most important component of the robot is the set of sensors. Sensors are nothing but measuring instruments, which measure quantities such as position, velocity, force, torque, proximity, temperature, etc. Robots, like humans, must gather extensive information about the environment and the status of the robot itself in order to function effectively. For example, a robot must be able to pick up an object; and it must know that the object has been picked up. While the manipulator (with the object held by the endeffector) is in motion, it must not drop the object, it must not collide with obstacles along the path, and the manipulator must approach the object to be handled with controlled speed in order to avoid collision. A robot must be capable of recognizing those salient features of objects and the environment and of distinguishing the intricate differences between two almost similar objects in order to identify the right object to be handled. All these and similar characteristics can be acquired by the robot through the sensors. Sensors measure the required data and the measured data is fed to the computer. The computer in turn, processes the sensor data, understands them and thereby enables the controller to control the manipulator and the endeffector in meaningful and effective manner. Computer vision (a TV camera and a computer with required data processing programs) has enhanced the capabilities of present-day robots. The TV camera looks at the object or a scene, grabs a picture frame, digitizes the picture information and the digitized data is fed to the computer. The computer processes this information and enables the robot to understand what the camera sees. Computer vision enables the robot to see objects and surrounding, understand them and thereby enable the robot to modify its actions and operations, if necessary, so that complex tasks can be handled. A Robot System: - A robot system is an arrangement of the five components of the robot interfaced properly so that the components work in a co-ordinated fashion for the effective and efficient functioning of the robot. An industrial robot system, which uses a minicomputer as a controller, is illustrated in Fig. 23. In this figure the endeffector is not shown and is to be attached to the free end of the manipulator. The locomotion devices are not visible externally. This robot system is used in an industry for doing routine jobs and therefore does not need any sensors. Fig. 24 demonstrates four types of installations of industrial robots. Fig. 25 shows a mobile robot with a few sensors. Bump detectors enable the controller to control the motion of the mobile robot so that bumps are negotiated smoothly. The television camera provides a sense of vision to the robot. The camera control unit controls the direction of vision. The range finder enables the robot to identify the location of obstacles along the path and reach the destination without colliding with the obstacle. With the help of the antenna for radio link, the robot can be controlled from a remote location by sending commands via radio transmission. APPLICATIONS OF ROBOTS Robots have become more and more popular in industrial and other fields because of three important qualities they possess. Robots are indefatigable; robots work very accurately; and robots work without any protest. A human being becomes tired after working for some time continuously. With the help of measuring instruments (sensors), robots can produce items they manufacture very accurately; a human being estimates and is therefore subject to inaccuracy. A robot faithfully executes the given command; a human being occasionally protest when asked to do a certain task and invariably asks questions, such as, quot;
Why should I do this work?quot;
Why should not this work be assigned to some other person?quot;
 APPLICATIONS OF ROBOTS IN INDUSTRIES: - Work in an industry can be broadly divided into four major categories. Robots can be advantageously used in all these types of jobs. Robots can be classified according to the type of work they perform. 1)Pick-and-Place Operation :: There are certain types of industrial jobs in which an object is required to be picked up from a specified position and placed in a particular position. A robot, which does the pick-and-place operation, is called a pick-and-place robot. Pick-and-place robots are used for machine loading and unloading, palletizing, stacking and general materials handling. 2)Point-to-Point Operation :: In the pick-and-place operation, the robot is expected to pick up an object from an initial position and place it at a final position. The initial and final positions can be different when the operation is repeated. There are operations in which work is required to be performed at several different locations. Consider, for example, the operation involved in drilling holes for a printed circuit board. A printed circuit board must have a very large number of tiny holes drilled very accurately in exactly the specified positions. Doing such a job manually will usually lead to an inaccurate product. A robot can be gainfully employed in doing the drilling operation, as it will perform the operation very accurately. A robot of this type is called a point-to-point robot. Application of point-to-point robots is in spot welding, gluing, drilling and other similar operations. In the first two categories of operations, namely pick-and-place operation and point-to-point operation, it is necessary for the robot to go from one point to the other, reaching the desired point accurately. The path traversed between two points, or the velocity with which the endeffector moves along the path, is unimportant since the robot is not expected to do any job while moving between two points. However, there are certain operations to be performed in an industry, wherein the path taken is important and the velocity with which the endeffector moves along the path is also important. In this event we have a continuous path operation. 3)Continuous Path Operation :: Consider, for example, spray-painting he walls of a room. The painting is not expected to be done continuously along the wall from one corner to the other since no paint is to be applied to the doors and windows. If we assume that the robot moves along a straight line along the wall to be painted, and if we assume that the paint is sprayed at a constant volume per unit time, in order to apply a uniform coat of paint on the wall, the robot has to move at a constant velocity. A robot, which does an operation of this type, is called a continuous path robot. The applications of continuous path robots are in paint spraying, seam welding, cutting, inspection and other similar operations. During manual spray painting, the material of the paint gives out a toxic vapour because of which the human operator has to wear a protective mask to conveyor his face and the entire body. The human being has to operate in an environment where air is present. When paint is sprayed through air, air bubbles get entrapped. If these air bubbles remain in the paint, when the surface of the paint is rubbed by an external agency, the air bubbles escape, breaking through the paint surface and exposing the surface of the material as a result of which it will deteriorate due to weather effects. In order to prevent such damage from happening later on, the human operator removes the air bubbles by applying a roller on the entire painted surface. When a robot is used for the spray painting operation, it will relieve the human being from the uncomfortable situation of having to work with the toxic paint, it will perform the operation more uniformly and further, it can work in a chamber which is evacuated beforehand. When spray painting is performed in vacuum, there is no air to get entrapped with the paint. A continuous path robot can be used for inspection of the inside surface of a motor cage for the presence of any burrs. The inside surface of a motor cage must be smooth and free of burrs in order to allow the rotor of the motor to rotate freely and safely when assembled inside the cage. The crankshaft of an engine has a very odd shape. Crankshafts are to be deburred after they are cast. A continuous path robot can perform this deburring operation. The crankshafts are placed on a conveyor belt, which is moving. TV cameras placed conveniently far above the conveyor belt look at the crank shafts and determine the position and orientation of the crankshaft, thus enabling a robot to pick up a crank shaft and load it to a machine, a continuous path robot performs the deburring operation. The deburring operation required the deburring operation. The deburring operation requires that thesurfaces be handled continuously and delicately. A continuous path robot can take care of such an operation. 4)Assembly Operation :: Finally we have the assembly operation in an industry. In making a final part, a large number of component parts of different sizes and shapes must be put together properly. A robot, which performs the assembly operations, is called an assembly robot. The robot must be capable of identifying the required part, determine its position and orientation so that the right object can be picked up with the right orientation in order to join/attach it with the other required component. Suppose a toothed wheel is to be picked up by the robot. Using a TV camera, the robot gets the picture of each component and compares it with the picture of the toothed wheel already stored in the memory of the computer. If the present picture and the stored picture of the required component match, the robot decides that the required component has been identified. Otherwise it looks at the picture of a different component. This operation is repeated until the required component is found. Sometimes two hands are required to do a certain task. In this event two robot manipulators can be used. However, a good co-ordination between the two robots is essential. ADVANTAGES OF ROBOTS IN INDUSTRIES: - In countries such as Japan and USA which are technically advanced, the number of robots in sue at present in industrial and commercial applications is increasing at the rate of about 35 per cent per annum. There are several reasons for this increasing use of robots. 1)Robots offer Reduced Cost of Production :: The cost of maintaining a robot is less than the average cost of maintaining a human being when the fringe benefits are taken into account. Robots do not get any of the fringe benefits as they are not paid any social security, workman's compensation, do not need vacations, holidays, sick leave, medical and dental benefits, maternity benefits, or retirement pay. Robots work 98 per cent of the time at assigned tasks. In other words, robots work almost 24 hours per day, 7 days a week and 12 months a year. A human can work only in shifts of 8 hours per day. Humans take coffee breaks, tea breaks, lunch breaks, dinner breaks and other time off for personal reasons. Such time off is estimated to be not less than 10 to 20 per cent of the total time. Moreover, human beings are subject to fatigue and lack of attention, particularly when doing repetitive work. Robots work without any fatigue. Frequently robots seem to repay their entire cost within 12 months. 2)Use of Robots Results in Increased Productivity :: Robots can be designed to work faster than human beings. For example, a robot does straight welding at the rate of 75cm per minute while a human being does only 25 cm per minute. Two typical spray-painting robots can complete the painting of an automobile inside and out with two coats in 90 seconds and work 20 hours per day. Even the best human spray painter takes as much as 15 to 20 minutes to complete the same job. Increased productivity means more work is completed on schedule. 3)Robots offer Improves Production Quality :: With robots, the accuracy of positioning is greater. The speed of operation is another advantage. There are cases where the weld has to be completed before the pieces distort due to the heat of the welding. With controlled accuracy and speed, welds that were difficult to perform earlier are now possible. Another example is in die-casting where the casting cycle must be strictly adhered. To robot is assisted by measuring instruments and therefore the final product is produced accurately and meets the qualities prescribed. Therefore, almost all the items produced by the robot pass the quality inspection test and the number of items rejected will be practically nil. This improved quality of production will reduce the cost of production. When a human being does the job manually, the quality of items produced will not always conform to the required specifications. It is estimated that when items are manufacture manually, the items that are rejected (because of failing in the quality inspection tests) is of the order of 30 to 50 per cent. Quality of production is very important factor in any manufacturing industry and robots provide the required quality of production. 4)Robots can operate in Hazardous and Hostile Environments:: Robots can operate in situations, which are either uncomfortable or dangerous for the human being to work in. The human will therefore be glad to let the robot replace him, even at the cost of creating unemployment. Some examples are loading and unloading of hot furnaces; working with toxic paints; doing welding operations where unhealthy or toxic fumes will be produce; handling radioactive chemicals; working in deep mines; working deep under the ocean; working in outer space; working in polar regions; fire-fighting. 5)Robots enable Improved Management Control :: Computer-controlled robots can carry out pre-programmed procedures with greater accuracy. In addition, they can record in the memory of the computer what is being done. The inventory of all the shop floors can be maintained in the memory of the computer. With these advantages, the manager can sit comfortably in an air-conditioned room and find out what is happening on any shop floor by recalling the information from the memory of the computer. The manager need not waste his time going from shop floor to shop floor. Thereby there is an improvement in scheduling, planning and monitoring operations. 6)Robots meet Occupational Safety and Health Administration Standards :: Since a robot obeys the commands without protest, it will meet the occupational safety and health administration standard. A human being will often violate the safety and health administration precautions (for example, by not wearing a protective helmet, not wearing protective goggles, etc). Due to the above-mentioned advantages, robots are being used increasingly in industrial applications. SHOULD ALL INDUSTRIES GO IN FOR ROBOTISATION? That a robot offers several significant advantages may lead one to the conclusion that all industries must necessarily go in for robotisation. However, this conclusion will not necessarily be a valid one. An industry must make a study of the cost-effectiveness of introducing robots for its manufacturing tasks. There are three types of manufacturing tasks. These are manufacturing by manual labour, manufacturing using hard automation and flexible automation. Hard automation is an automatic manufacturing procedure in which the manufacturing procedure in which robots is used. A study of the production volume per year and the resulting unit cost of production, for the three methods of manufacturing, determine which of the three methods for manufacturing one should choose. Fig. 2 shows a comparison of the three types of manufacturing and the dependence of unit cost of production of the volume of production per year. The production volume per year of the particular manufacturing concern decides whether it should use manual manufacturing, go in for robotisation or use hard automation. It is obvious therefore that not every manufacturing industry should go in for robotisation. APPLICATION OF ROBOTS IN THE HOME ENVIRONMENT: - Robots that are used at home are called home robots or personal robots. In technologically advanced counties, there are three types of home robots that are in use. The first type is the one that can be used as a toy or as a companion to play a game, such as checkers (draughts) or chess with. As an example of a toy-robot, we can think of doll which can be commanded to dance, walk, sing a song or laugh and cry. A child can hold the hand of a toy-robot and walk and the toy-robot walks along, takes a turn whenever the child takes a turn and stops when the child stops. One can play a game of chess with the help of a computer. On the video screen one can display a chessboard with the pictures of the various pieces (king, queen, knight, bishop, rook and pawn). The person playing chess with the robot can make his move by pressing appropriate keys on the keyboard. The corresponding move is displayed on the video screen. The robot, with the help of a built-in program, computes its best possible move and displays its corresponding move on the screen. The game can be continued until the end. The final outcome may be the human winning, the robot winning or the game ending in a draw. The robot can be programmed to play at different levels (for example, level 1 to be selected by a beginner, level 2 to be selected by a good player and level 3 to be selected by an expert). If needed, an actual robot with hands and fingers playing on an actual chessboard can replace the computer and the video terminal. When the computer actually decides the best possible move, it can command the robot to physically make the move on the real chessboard. The second type of home robot is the one used for entertainment purposes. Since this is an entertainer, any of the tricks adopted by an entertainer (a magician, for example) can be used by the robot. The robot can use such a robot. Such a robot can be used at home when there is a gathering of guests or it can be used in a supermarket to attract customers. Here is an example of an entertaining robot; it is about 75 cm tall. There is a video screen on the top. On the video screen there is the sketch of the face of a human; the face shows details such as nose, eyes, lips, teeth, etc. the robot entertains the persons in from of its as follows: A person standing in front can ask questions (the limitation on the questions is that they should be of only such a nature that a total stranger standing in front can answer by observing the questioner). The robot will answer all the questions correctly to the amazement of the bystanders. The working of the robot may be as follows: A built-in microphone receives the questions of the person in front of the robot. The microphone is connected to a tiny radio transmitter inside the body of the robot. The radio transmitter transmits the questions. A person hidden from the bystanders monitors the transmitted signals. This person observes the questioner and bystanders with the help of a pair of binoculars. After hearing the question and watching through the binoculars, he will meaningfully answer the questions. The reply is transmitted through another radio transmitter and received by another radio receiver within the body of the robot. The answers are given out through speakers in the body of the robot; when the answers are being broadcast, a computer program makes the picture on the video screen move appropriately (eyes are moved, and teeth displayed when necessary; these movements are controlled by the person hiding at a distance) and the bystanders get the illusion that the robot is answering the questions by itself. The third type of home robot resembles an industrial robot in the sense that it has manipulators with the help of which it can handle objects. This is a mobile robot mounted on wheels and controlled by a computer. It can be fitted with several sensors in order to enable it to intelligently perform certain operations. It can be commanded to perform certain chores such as fetching a newspaper from a certain point to another, taking a breakfast tray from the kitchen to a specified room to give to children busy studying. A home robot can be controlled to do several chores at home. It can be commanded to take certain things from one place to another. It can be programmed and commanded to help a child in his studies. A home robot can also be designed to act as an escort an take children from home to school and bring them back safely; the robot will permit children to cross streets only. When it is safe no do so. The home robot can also be commanded (after proper design, of course) to do several other chores such as fetching a glass of water, or cleaning a room with a vacuum cleaner. APPLICATION OF ROBOTS IN NON-MANUFACTURING AREAS: - Some of the applications of robots in non-manufacturing (non-industrial) areas are described below. 1)Australian Sheep Shearing :: One of the most interesting applications of robots is in sheep shearing. An electric clipper is carried by the robot arm and follows the contours of the sheep’s body. Sensors on the clipper determine the distance to the skin of the sheep within an accuracy of 0.005 inch (0.0125 cm). Motors on the robot are fast enough to move the clipper out of the way when the animal moves, so that the sheep is not injured. 2)Agricultural and Forestry Applications :: Robots with vision and other sensors are potentially capable of handling many agricultural tasks. Fruit picking, asparagus harvesting, robots are performing potato digging and similar activities. Robot technology could be applied to forestry for tree felling and wood gathering. 3)Radioactive Materials Handling :: Nuclear energy experiments require handling of radioactive chemicals, which can be successfully managed by robots. This relieves the human being from doing such tasks, which are hazardous, like having to handle radioactive materials in a nuclear power station. Robots can also be helpful in the disposal of radioactive wastes from nuclear plants and in maintenance work, periodic inspections and disassembly of nuclear plants. 4)Mining :: It is hazardous to work in a mine where the earth from above is prone to collapse. Robots will be very valuable in performing mining operations. 5)Undersea Exploration :: The record depth to which a man has gone down into the ocean is only 100 meters and that too with the help of special suits and special breathing apparatus. The ocean occupies Seventy per cent of the earth’s surface. The large area of the ocean has depths ranging from 2 to 6 km. With submersible robots fitted with mechanical arms and vision capability, it is possible to explore deep undersea waters and collect valuable material. Such a robot, called SCARAB, was used to retrieve the black box of the ill-fated Air India Jumbo, which exploded and went down into the ocean several years ago. Robots could help in underwater construction. They could also be used for mining of the ocean-floor minerals. A miniature robotics submarine with TV camera ad powerful lights can inspect deep-sea fauna at much lower costs compared to similar operations with human beings. Robotic submarines are also used to inspect underwater structures, pipelines and power cables. 6)Fire Fighting and Disaster Relief :: Robots, which can move, climb a ladder and lift or transfer human beings and objects would be very useful in relieving humans of dangerous tasks such as fire fighting. Robots could enter areas closed to human beings because of poisonous gas discharges during earthquakes, storms, floods, and forest fires. They could also be used in remote controlled searches for missing people, and remote surveillance of disaster conditions. 7)Space Exploration :: Space exploration and space research offer a wide field of application for robots. Robots could be of help in assembling structures in outer space and in the operation of outer space factories. Robots can maintain and service thousands of man-made celestial bodies already orbiting the earth. Planetary exploration becomes an easy task when robots are sent to other planets. The Russians had sent a self-propelled mobile robot called Lunakhod to the moon. This robot explored the surface of the moon, took lunar-earth samples, subjected them to chemical and X-ray analysis and sent the results of the experiments to Earth. The Voyager II mission of USA was successful partly because of the two on-board robots that were helping with various operations of the mission. 8)Medical Applications :: Robots have been valuable in the areas of orthotics and prosthetics. Prosthetics is a medical specialty concerned with the artificial replacement of missing parts of the human body. In cases of persons who have lost their arms or legs due to amputation, artificial legs or arms can be provided and the manipulator can be controlled using robotic principles. Measuring the EMG (electromyograph) signals from the umamputated part of the body, and processing the electromyograph signals, the actual command given by the brain can be understood and this information can be used in controlling the artificial limb. Orthotics is concerned with providing exo-skeletal structures on an invalid arm or leg or in cases where the invalidity has been caused by the loss of nervous control due to paralysis. The exo-skeletal limb can be controlled as in the case of the artificial limb. Some prostheses and orthoses can be controlled by voice commands. Robots can also be helpful in everyday care and nursing of the disabled people or the bedridden elderly and thereby reduce the burden on the attendants. A robot being developed by the Transition Research Corporation, called HelpMate, can pick up the correct tray at the nurse’s voice command and deliver it to the patient’s bed. Surgeons are experimenting on the use of robots in brain surgery. Initial experiments were conducted not on real patients, but on a watermelon. They pellets were inserted into a watermelon and the Computer Assisted Tomography (CAT) image located these pellets precisely in three dimensions, which were communicated to the robotic arm in tool coordinates. The robotic arm was able to penetrate into the watermelon at the correct depth and locate the pellets. Based on this success, surgeons have used the robotic arm on patients and successfully performed operations. Surgeons claim that the robotic procedure reduces the time on operating table by more than 50 per cent and thus diminishes the resultant trauma. Probe placement can be made to an accuracy of 0.002 of an inch (0.004 cm). Microrobotics is currently being developed in Japan. Robots are being designed tiny enough for several of them to be accommodated in a capsule, which a patient could swallow. With nominal external controls, these robots will perform operations such as cleaning blocked arteries inside the patient’s body. Microrobots will one day be released in the fields where they will chase and destroy pests and fungus. 9)Table-Tennis Playing Robots :: In an experiment in real-time intelligent control, Russell L. Anderson has developed a ping-pong playing robot. To make the problem simple, to start with, the rules for playing the game and the dimensions of the ping-pong table are modified. The robot incorporates sensors and processing techniques as well as the techniques needed to intelligently plan the robot’s response in the fraction of a second available. Sensors measure, among other quantities, the ball’s trajectory, the velocity of the ball and the spin of the ball. Based on the measurements, the controller determines the force and angle with which the paddle should hit the ball. Having this information, the robot arm carrying the paddle successfully intercepts the ball and sends it to the other side. Further work is being done to improve the system so that the game can be played on a standard table using standard rules of the game. 10)Robotic Olympics :: The first international Robot Olympics was held in Glasgow, Scotland. Over 50 robots from Britain, USA, Russia, Japan, France, Mexico, India, Canada and Germany took part in the exhibition. The Robot Olympics will be held every two years alternating between Glasgow and other venues in various countries. Two-legged robots rocking from side to side, wheeled robots that can avoid obstacles, robots that crawl with a screwdriver were some of the tasks these exhibits could perform. The events included contests in wall climbing, obstacle avoidance, javelin throw and similar activities. At the science museum in Kensington, West London, 24 Japanese robots were exhibited. Most interesting of these were a flower-arranging robot, which could make both its arms, work in unison and a portrait-drawing robot. 11)Construction Work :: Robots can be used in reinforcement-bars assembly, bridge painting, inner and outer finishing of high-rise building, cleaning outer walls, painting, finishing concrete floors and spraying concrete on tunnel walls. 12)Robots in Defence :: Robots can gather up the wounded and reduce causalities by replacing tank crewmembers or by doing field refueling and loading guns in combat zones. Robots could be used in dangerous surveillance missions. If the enemy uses BCN (biological, chemical or nuclear) weapons, robots are in a better position to withstand the attack. 13)Robot Sentries :: A robot sentry developed in USA, can detect within a 45-metre radius the presence of anything or anybody that moves around. TEACHING ROBOTS THEIR JOBS A human starting on a new job must learn the work he is to perform. He learns the assigned tasks from generalized definitions and by observing others do the same work. The brain is responsible for the learning of the procedures to be followed. It receives vital information, such as the location and orientation of the object to be picked up and the position and orientation of the object at the destination where it is to be placed, from the sensory communicated to the hand by the brain. The sense organs provide the necessary feedback to ensure that the task is properly completed. A robot is similar to the human in as much as it can be taught to perform an assigned task. Unlike humans, the robot requires that each task is broken down into sub-units and possibly even further, until the analysis reaches the level of individual motions. In the majority of industrial applications, the robot controller is where these extremely detailed and explicit commands are made to reside. Consider, for example, the process of teaching the robot how to build a tower of two blocks. In teaching the robot, the process must be carefully separated into individual motions somewhat like the following: Move the manipulator until the gripper is directly above the first block. Lower the gripper until the block is between the gripper jaws. Close the gripper jaws. Raise the manipulator with the block held firmly in the gripper. Move the manipulator until the first block (held in the gripper) is directly above the second block. Lower the gripper until the block held in the gripper rests on top of the second block Open the gripper jaws. Move the manipulator away from the two-block tower. In addition to these eight commands, the proper velocity of the manipulator must be defined at each step. More complicated tasks require very precise velocity control, as well as the definitions of hundreds of different motions. Laying out the learning process may take a lot of time. A robot can be taught how to perform a sequence of operations. This may be done using several existing methods. Further, robot manufacturers and research workers are developing additional methods with the intention of reducing the amount of time required for the robot to learn new tasks and with the intention of simplifying the teaching methods. At present, there exist three methods by which a robot can learn a sequence of operations. MANUAL TEACHING: - In this method of teaching the robot, the human operator moves the robot through a series of points using a teach-box or teach-pendant. Fig. 27 shows the sketch of a typical teach-pendant. The teach-pendant consists of several push buttons (switches), which are connected through electrical wires to the electric drive motors driving the manipulator joints and the gripper. Each motor is associated with a pair of buttons. When one of these is depressed, the corresponding motor moves the joint in one direction; when the other is depressed, the joint is moved in the opposite direction. Fig. 28 shows a human operator using the teach-pendant to teach a robot. When appropriate push buttons are pressed in the correct sequence the robot moves according to the requirement, through a series of points, thereby completing a sequence of point get stored in the memory of the computer. In addition to these details, other necessary details such as the speed with which the motor has to move, or the duration of the pause to be given before one sub-operation is to be performed after the previous one is completed, are also stored in the memory of the computer. When the entire sequence of operations and other details are stored in the memory of the computer, the robot is ready to repeat the learnt sequence of operations. Upon an EXECUTE command, the robot will recall from the memory of the computer the taught sequence of operations and will execute the learnt sequence of operations faithfully. The robot can be commanded to repeat the same sequence of operations any number of times. The learnt sequence of operations will remain in the memory until the operator who decides that it is no longer required for further operations erases it. This method of manual teaching using the teach-pendant (box) has a serious disadvantage. The operator must look away from the robot motion to locate the proper push button to be depressed next, in order that the required joint or the endeffector is moved appropriately. Although with a lot of experience the operator can overcome this disadvantage, when a new sequence of operations is to be taught, this disadvantage is rather difficult to overcome. One sure way of overcoming the disadvantage found in manual teaching by means of a teach-pendant is to use a joystick. Fig. 29 shows a Joystick that is connected to a robot to be taught. The joystick is similar to that used by a pilot to fly an aircraft. When the joystick is used, it is moved in a particular direction in order to depress a particular switch. It is easy for the human operator to remember the different directions in which the joystick is to be moved and the corresponding switches that are activated (depressed). Using the joystick, the human operator will be able to depress appropriate switch buttons and thereby move the appropriate joint in an appropriate direction, while concentrating his attention on the actual movement of the robot. He does not have to turn away from the robot when he is to depress another switch. All he has to remember is the direction in which the stick is to be moved and this movement of the joystick can be accomplished without having to look at the stick. The stick is always in contact with the hand of the human operator; hence moving the stick in a particular direction without looking at it is easy. TEACH BY GUIDING: - In the method of manual teaching using either a teach-pendant or using a joystick, it is very difficult for a novice to quickly teach the robot a given sequence of operations. It requires a lot of trial and error on the part of the operator to complete the correct teaching operation. A method, which can overcome the trial and error nature of the manual teaching with a teach-pendant, is the manual method of teaching by guiding. This method is better described as the method of teaching by showing. In this method, the operator literally holds the robot manipulator in his hand and manually moves the robot along the desired path and through the required sequence of operations; while he is showing the required path and the required sequence of operations, the controller with the help of sensors, records the joint positions at regular intervals of time in the memory of the computer. During this period of time when the operator manually moves the robot manipulator, the robot motors are inoperative. When once the required sequence of operations is recorded, commanding the robot to repeat the taught sequence of operations in the same as in teaching with a teach-pendant. This method of teaching by guiding also has some limitations. Firstly, the operator has to overcome the weight of the robot as well as the friction that exists in the arm joints and gears. Secondly, the controller memory must be very large in order to store the information sampled at a rate of hundreds of points per second. The first of these limitations makes the method inapplicable for medium-size and large-size robots where high precision is required in the performance of a given task. The limitation may be partially overcome by the use of a balance unit, which supports the static weight of the robotic manipulator. A better method of overcoming the first limitation is to use an additional robot (a prototype model) called the master robot. The master robot is a light-weight model and does not include the motors or motion transfer devices such as gears, chins, belts, etc.; however, measuring instruments called encoders are mounted on the joints of the master robot. The links of the master robot are equal in length to those of the actual robot, which is now called the slave robot. The slave robot is the actual robot, which is required to carry out the task taught to the master robot. During the teaching process, the operator moves the master robot through the desired path of motion; a task, which is easily accomplished because the master robot is very light, and no gears are used in the master robot. The motions of the master robot are recorded in the memory. Upon and EXECUTE command, the slave robot and the master robot will faithfully reproduce the taught sequence of operations. Both the master robot and the slave robot are controlled by a common controller (computer). It is important to note that the geometric structure of the master robot and the slave robot are identical and hence the path traversed by the slave robot will be exactly the same as that of the master robot. Fig. 30 shows a robot system employing-teach-by-guiding method, using a master robot and the slave robot. Do you see how the master-slave robot system can be profitably used to control a slave robot, which is situated in a hazardous environment, by keeping the master robot in a safe environment? Another method of overcoming the first limitation of the teach-by-guiding method is to use a force sensor attached to the endeffector. Then the method of teaching will be called teach-by-guiding using a force sensor. When the operator moves the manipulator by holding the endeffector, he exerts a force on the endeffector; the force sensor measures this force and translates it into an electrical signal, which activates the robot motors and moves them in the desired direction. The advantage of this method is that the operator does not have to make a great effort to move the robot. Therefore, a higher degree of precision can be obtained in the measurements that are recorded in the expensive because of the additional sensor and associated circuits required in the teaching process. Further, the sensor is used only during the teaching process and is not required at all during the actual performance of the task. It is not economical to provide an expensive sensor only for a short period of time. In the first two manual methods of teaching, the robot arm is physically moved from point to point during the teaching period. In contrast to this, there is a method of teaching in which the robot does not move at all during the teaching period and this method is called the programming method of teaching. In this method, the robot does not move because the robot manipulator is not touched at all by the operator (or rather the programmer) during the teaching period. The teaching is not done manually but by programming. TEACHING BY PROGRAMMING: - In this method of teaching (by programming), the points in the path of motion are defined to the controller by means of mathematical equations. The path along which the endeffector is expected to go is known beforehand. This path can be described by a mathematical equation. For example if the path is a straight line in a plane, it is given by the equation y = m x + c, where x and y are co-ordinates of the points on the straight line with respect to some chosen co-ordinate axes, m is the slope of the curve (straight line) and c is the y-intercept. If the path is not a straight line, or if the path is an arbitrary curve in three-dimensional space, the path can be described similar way in terms of a mathematical equation. The path is bound by the initial and final points, which are also known. Given the mathematical equation, the co-ordinates of the points on the path can easily be computed by a computer program. A computer program can compute these points. These points can be stored in the memory of the computer. Another program enables the controller to calculate the amount and direction of movement each joint of the manipulator has to undergo; and this information can also be stored in the memory of the computer. When once the required information is stored in the memory, commanding the manipulator to execute the required sequence of operations is similar to the earlier procedure. The advantages of the programming method over the manual methods are: The programming method saves time and effort. In addition, there is no need to take the robot off production when it is to be taught a new task. Programming the new path is done off-line, while the robot is performing some regular task. Programming the new path is done off-line, while the robot is performing some regular task. A task learned by defining the co-ordinates of the points along the path can be communicated to other robots, even to some robots that are non-identical in structure. ROBOT ANALYSIS AND CONTROL The previous chapter on teaching methods for robot control may lead one to believe that it is a very simple matter to control a robot for the performance of a given task. The fact of the matter is that the accurate control of a robot manipulator is an involved process. While teaching methods do offer simple procedures for controlling a robot, these procedures do not result in an accurate control of the manipulator, because these methods do not take into account the mass, inertia and other related parameters of the links, of the motors and of the endeffector. When very accurate control of the manipulator is required, it becomes necessary to use sophisticated control methods based on a detailed analysis of the robot manipulator. These methods must take into account not only the geometric structure of the manipulator, but also the masses, inertias and other related parameters of the robot manipulator. It is beyond the scope of the present book to discuss these aspects. However, we can study a simple example of a robot to understand and appreciate the difficulty and complexity involved in analyzing and controlling a robot manipulator. Consider the simple example of a robot manipulator described in Fig. 31. The figure shows a robot manipulator having two links and two joints. The lengths of the links are l1 and l2. The two joints are fitted with motors whose axes of rotation are perpendicular to the plane of the figure. The x-y co-ordinate axes are imbedded at some convenient point on the axis of the motor driving link 1 (having length l1). There is an endeffector attached to the free end of link 2. When the two joints motors rotate, the robot manipulator moves only in the x-y plane. Hence the robot described in the figure is a two-degrees-of-freedom planar manipulator. When the links are described by the two parameters (angles) 1 and 2. 1 is defined as the angle made by the axis of link 1 with respect to the x-axis, which is taken, as a reference line to measure the angle 1. An angle measured in the counter-clockwise direction is considered positive; and an angle measured in the clockwise direction is considered negative. The position of link 2 is defined by angle 2, which is measured with respect to the axis of the link 1, as shown in the figure. The angular positions of the links, namely 1 and 2 will define the location of the endeffector. That is, the centre of the endeffector will reach the point defined by the co-ordinates (x, y) as shown in the figure. Given the joint co-ordinates, as they are called, (1, 2), it is a simple mathematical computation in terms of the link lengths l1 and l2 to compute (x, y) which are called the world co-ordinates. The problem of calculating (x, y) for a given set of (1 2) is called the forward kinematics problem. For a given (12), the solution to the forward kinematics problem is unique; that is, we get a single unique answer (x, y). It is less frequently that one would be required to solve the forward kinematics problem. In general, more frequently one would be required to solve the inverse problem. That is, given the world co-ordinates (x, y) it will be required to calculate the joint co-ordinates (1 2). This problem, for obvious reasons, is called the inverse kinematics problem. It is the inverse kinematics problem that is to be solved in the following situation. An object is places at a given location. The co-ordinates of the centre of gravity of the object are given by the pair (x1, y1), which is the world co-ordinates. In order that the robot be commanded to reach the location (x1, y1) so that it can pick up the object, one should know the joint co-ordinates (1, 2) so that the joint motors may be rotates to the corresponding angular position (1 2). That is, given (x1, y1) one would be required to calculate (1 2). It turns out that the solution to the inverse kinematics problem is not unique; that is, there will be more than one solution. Sometimes there may not be a solution at all. In order to appreciate these points, look at Figs. 32 and 33. Fig. 32 shows two configurations (arrangements of links), which reach the same endeffector position. This explains that given (x, y) the solution to the inverse kinematics problem has two solutions. Fig. 33 shows the two-degrees-of-freedom planar manipulator having length of link 2 (that is l2) less that that of link 1 (that is l1). When the two links are aligned with 2 = 0, the manipulator traces a circle with radius equal to (l1 + l2). When the two links are aligned with 1 = 180, the manipulator end traces a circle of radius equal to (l1 – l2). Thus the endeffector can reach only the points within the annular region bounded by circumferences of circles having radii (l1 + l2) and (l1 – l2). Any point outside the outer circle or inside the inner circle cannot be reached by the endeffector. In other words, if the given (x, y) is either outside the outer circle or inside the inner circle, the inverse kinematics problem has no solution. Figs. 32 and 33 have explained by physical reasoning the concepts of unique solution [note that given (1 2) there is only one solution for (x, y)], multiple (non-unique) solutions and existence of no solution. The same concepts can be mathematically explained by considering a function of a single variable such as y = x2. Given x = 2, there is only one value of y = 4, that satisfies the functional equation. Given y = 4, there are two solutions for x, namely, x = +2 or x = -2. If y is given to be –9, there is no real solution for x. When the problem is complicated for the simplest two-degrees-of-freedom manipulator, one can imagine the complexity and difficulty one encounters in a general-purpose six-degrees-of-freedom manipulator that works in a three-dimensional space. When once the angular positions of the links (1 2) are calculated in the case of the two-degrees-of-freedom manipulator, the amount of force (torque to be applied to the motors will depend on the mass (inertia) and other related parameters in order that the manipulator is positioned so that the endeffector reaches the desired position. EPILOGUE The first industrial robot was built in USA during 1959-60. However, it took another 20 years for the industry to fully develop and utilise the robot successfully for industrial applications. Gradually, the use of robots spread to other countries such as Europe and Japan. Although it was America that pioneered the development of industrial robots, at present it is Japan that employs the largest number of such robots. According to a recent report from Tokyo, the total number of industrial robots in operation worldwide is now over 700, 000. Of these Japan alone uses 61 per cent. Furthermore, 70 percent of the total robots are made in Japan. The USA, which had come out with, the world’s first robot, is today lagging behind Japan by almost a decade and uses only 8 percent of the worlds total. Why are Japan miles ahead in robotisation of its work force? This may be because Japan has a unique system of labour unions. Unlike USA and Europe, Japan does not have the system of craft unions, but has company and industry unions instead. Employers are also involved with giving technology education to their work force. So it is very easy for a Japanese worker to change from one job skill to another. A Japanese machine tool operator can be re-trained in a week to become a robot operator. Another factor was the demand for automation technology to deal with the shortage of skilled labour and the difficulty in employing blue-collar workers that have come with the aging and higher education levels of the Japanese work force. According to the Ministry of Education, 96.2 per cent of the youngsters entered high schools in 1993, and 34.5 per cent of the youngsters entered colleges or universities. Such figures point to be ‘white-colorization’ of the Japanese work force. The Ministry of Labour reports that at the end of 1992, Japan had a deficit of 1.74 million skilled labourers. Of these vacancies, approximately 600,000 were in the manufacturing industry, 400,000 in construction. Japanese industry relied on automation for help. The majority of the application of robots is in the automobile industry; mostly in welding and spray-painting operations. In India, the interest in robots and robotics started during the 1980s. Work in robotics began in advanced educational institutions and research centres. There has been interest on the part of industrial organizations in the development of robots for welding and spray-painting operations and also for electronic assembly. The future of robotics appears to be very bright. When we look at the worldwide scenario, we see that a lot of work in the field of robotics is already done. The years to come will witness further interesting work in development and research. Robotics and related subjects are in the curricula of degree programmes of educational institutions. Industries have projects to utilize the potential of robots. Governments are funding research and development projects in the area of robotics. When the two very interesting fields, robotics and artificial intelligence, are successfully and completely integrated there would be fascinating and wonderful results in the development and use of what are called intelligent robots. Artificial intelligence is better understood by its synonym ‘intelligent machines’. The object of scientists and engineers working in the area of intelligent machines is to demonstrate that machines can be built so that they possess intelligence. A machine is said to possess intelligence if it can be made to do a task which, when done by a human, will be called intelligent work. The major areas that are being pursued by scientists in the field of artificial intelligence are pattern recognition and picture processing, voice analysis and synthesis, understanding of spoken words and sentences, natural language understanding, machine translation of scripts from one language to another. Although the work in the area of artificial intelligence is said to be in its initial stages of development, considerable progress has been made in all its sub-areas mentioned above. Principles of artificial intelligence have been used to develop intelligent robot. It can be observed that the capabilities of robots increase when a larger and larger number of sensors and sensor information-processing programs are added to the robot system. Let us look at two experimental robots that have been developed in American educational institutions. The first example is a robot, which is mobile and is provided with a large number of sensors. This robot can move on its, own, from place to place. It can recognize obstacles in front with the help of ultrasonic sensors and thereby avoid obstacles while moving. The energy for this robot, for moving its motors and doing other tasks, comes from a battery (similar to an automobile battery) within the body of the robot. As is well known, the battery cannot supply energy forever. When the battery of the robot gets discharged to a sufficiently low level, sensory circuits built within the robot detect it. When this is detected, the robot stops doing whatever it doing and with the help of the TV camera it has been provided process involves going towards the nearest wall and moving parallel to the wall until it comes to an electric outlet. When it reaches the electric outlet it stops moving and turns towards the electric outlet. Then it takes out an electric outlet. Then it takes out an electric plug from within its body and plugs it into the electric outlet. After this it puts the electrical switch on; this energizes the battery-charging circuit within its body and charges its battery. The robot waits in front of the electrical outlet until the battery is completely charged. After detecting that the battery is completely charged, the robot puts off the switch to the electrical outlet, unplugs itself, puts the plug back inside its body and goes back to the place at which it detected that the battery is discharged, and continues with whatever it was doing. Another robot developed in another American educational institution is a mobile robot which is made to perform in a laboratory in which there is a table on which a number of objects such as a small cube, a large cube, a sphere, a prism, etc. are placed. Also in the room are kept a few ramps of different heights. The robot is given a command: REMOVE THE LARGE CUBE FROM THE TABLE. Upon receiving the command, the robot, which is situated on the floor, determines the height of the table with the help of sensors, and then searches for the ramp of the appropriate height. It goes towards the ramp and pushes the ramp towards the table until the higher end of the ramp aligns with the tabletop. The robot then moves up the ramp to the top of the table. With the help of its TV camera, it looks at the objects on the table, recognizes that there are two cubes and determines the location of the larger cube. It then moves the larger cube off the table, comes down the ramp, pushes the ramp back to its original position and gives a signal informing that it has completed the task assigned to it. The height of the table can be changed; the objects on the table can be changed; the command can be changed. In every case, the robot successfully completes the task assigned to it. In Japan, Mitsubishi has developed a robot to sort a fishing boat’s catch. In Italy, Digital Electric Automatic Company uses a robot that can assemble a compressor value unit from 12 different parts at the rate of 320 units per hour. In USA, robots are used to help build F-16 fighter planes. These robots can select tools from a rack, drill holes accurate to 0.005 of an inch (0.0125 cm) and machine the perimeter of 250 different parts. In England robots are used to weld frames of hospital beds. This had led to an increase in output by more than 30 per cent and also a vast difference in the quality of work. In New York, IBM has a robot that can load and unload a computer that writes codes on blank discs. The robot knows which of the four machines gets a specific blank disc, when to remove the recorded disc, how it should be labeled and which container to pack it in. In India, the Bhabha Atomic Research Centre (BARC) has developed robots for handling radioactive fuel. Robots can take care of inspection and maintenance of research and power reactors. Researchers in Japan are working on robots that can smile. They have built a robot face that can adopt expressions representing six different emotions: joy, sorrow, hatred, horror, anger and surprise. CAN ROBOTS BEHAVE ERRATICALLY AND CAUSE HARM OR EMBARRASSMENT? It is possible. You may have read a newspaper item describing a robot, which, instead of serving the customers in a hotel, poured drinks on them; or of a robot, which hit a human and killed him. Such things are possible and can be avoided by taking adequate precautions. A robot consists of several components. One or more parts can malfunction. When a robot is used in critical areas, sensors can be provided to frequently or continuously check for the correct functioning of each and every component. When a fault is detected, the faulty component can immediately be replaced by a healthy component to allow the robot to function according to the desired specification. This involves the provision of expensive sensors and sensor circuits and the storage of spare components so that the robots can readily replace a faulty component. If such precautions are taken, there is no possibility of a robot misbehaving. IS THERE AN EVENTUALITY OF ROBOTS BECOMING MASTERS OF HUMANS? WOULD ROBOTS BECOME DANGEROUS TO HUMANS? That there would arise an eventuality of robots becoming masters of humans has been suggested in Capek’s play Rossum’s Universal Robots and is being, and will continue to be, depicted in science fiction movies and stories. It is not impossible to develop such dangerous robots, but it is man who must design and build robots; and it is man who must write programs to control robots; and it is man who would have to write programs to enable a robot to assemble another robot. We must ensure here that no man would be foolish enough to design and fabricate robots and to provide them with such faculties and capabilities that the robots work against him. We know that there can be danger if powers are in the hands of wicked persons. If proper precautions are not taken beforehand, robots can be dangerous and can cause harm to human beings. Sir Isaac Asimov, the well-known science fiction storywriter, has proposed three laws of robotics, which must receive serious attention and consideration from every robot designer. These three lows are: Law 1: A robot may not injure a human being, or through inaction, allow a human to come to harm. Law 2: A robot must always obey the orders given to it by human beings (the authorized ones, of course), except where such orders conflict with the first law. Law 3: A robot must protect its own existence as long as such protection does not come in conflict with the first and second laws. Fig. 1 : Egyptian temple ‘miracle’ explained. The doors open when incense is burned on the alter Fig. 2 : Diagram showing how the temple doors swing open. Fig. 3 : Another fake miracle of the ancient priests shows how incense ‘everlastingly’ drips into the sacrificial flame. Fig. 4 a) : Bird organ Fig. 4 b) : Diagram showing how whistles are produced Fig. 5 : Diagram showing how the automated flute player works Fig. 6 : Maillardet’s (writing) automation Fig. 7 : Illustration of six degrees of freedom defining the arbitrary position and arbitrary orientation of a body. Fig. 8 : Cartesian robot manipulator Fig. 9 : Cylindrical robot manipulator Fig. 10 : Spherical robot manipulator Fig. 11 : Horizontal articulated robot manipulator Fig. 12 : Vertical articulated robot manipulator Fig. 13 : The various types of hand prehension Fig. 14 : Fingers with object-shaped cavity Fig. 15 : Fingers with multiple cavities Fig. 16 a) : The human three-fingered b) : Flexible gripper for turbine blades Fig. 17 : Two-fingered gripper with changeable fingertips Fig. 18 : Rack and pinion parallel jaw gripper Fig. 19 : A robot may have direct and indirect drive systems Fig. 20 : A typic al feedback system Fig. 21 : The computer controls the electric motor via a digital-to-analog converter and driver system Fig. 22 : A prismatic hydraulic drive unit Fig. 23 : An industrial robot system Fig. 24 : Four types of installations of industrial robots Fig. 25 : A mobile robot with a few sensors Fig. 26 : Comparison of management methods for different production volumes Fig. 27 a) : A typical teach-pendant. b) The teach-box of the PUMA robot. Fig. 28 : The use of a teach-box in manual programming Fig. 29 : Teaching a robot using a joystick to control the movement of the arm Fig. 30 : Teaching a robot the movements required to spray paint an automobile using a master robot Fig. 31 : A two-link articulated planar manipulator. Desired endeffector positions are reached by moving the two motors located at the joints Fig. 32 : The two inverse kinematics solutions. Fig. 33 : The manipulator work space

Pt on robats & robotics

Recomendados

Recomendados

Mais conteúdo relacionado

Semelhante a Pt on robats & robotics

Semelhante a Pt on robats & robotics (20)

Último

Último (20)

Pt on robats & robotics