Kollmorgen robotic symposium presentation-motor design impacts on the optimization of robotic systems

Motor Design Impacts on the
Optimization of Robotic Systems
Tom Wood – Kollmorgen Electromate Robotics Symposium
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Enabling Innovators
To Make The World A
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Agenda Overview
• Why are we here ?
• Why Frameless?
• What are the motor
topology differences ?
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Agenda Overview
• 3 Important Concepts
–D2L Rule
–Kt (Torque Sensitivity or
‘Torque Constant’)
–Km Factor (also called
‘Motor Size Constant’)
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Agenda Overview
• Robotic Application Review
• Deep Dive into Collaborative
Joint Design
• Speed/Torque Curves
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Why are we here ?
• Industrial Robotics Marketplace
• “Made in China 2025”
• $30B Global Market - Source IFR
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Why Frameless ?
• Performance
– No mechanical compliance – Direct Drive
– Smooth motion
– Highest Torque for volume
• Smallest footprint for performance,
minimal machine impact
• Reduced maintenance
• Efficiency increased
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Typical Form Factors – Quick Comparison
Classic ‘Torque’
Motor Shape
Classic ‘Servo’
Motor Shape
Stationary wound
armature Rotating permanent
magnet field
Stationary wound
armature
Rotating
permanent
magnet field
COMPARING ‘TORQUE’ VS. ‘SERVO’
FRAMELESS MOTOR FORM FACTORS
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A Closer Look at a Typical ‘Torque’ Shape Factor
Large
armature OD
Short winding
end turns Short axial
stack length
High pole count
Large rotor bore 
Thin OD/ID cross
section
Thin rotor hub wall
with mounting option
flexibility
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What do we mean by Pole Count ?
2 Pole Design
1 North – 1 South
1 Pole Pair
4 Pole Design 8 Pole Design
2 N – 2 S 4 N – 4S
2 Pole Pairs 4 Pole Pairs
N S
S N
N
S
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A Closer Look at a Typical ‘Servo’ Shape Factor
Lower pole count
Smaller rotor bore 
Longer axial
stack length
Longer winding
end turns
Thicker OD/ID cross section
Rotor hub wall similar
Smaller armature OD
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Performance
Parameter
Speed Low (<2000 rpm) High ( >1000 rpm)
Motion Slow, smooth, precise Fast, rapid accel/decel
Continuous Torque High Low
Typical applications
Precision robotics,
indexing, pointing,
tracking
Spindle, missile fin,
general automation,
Down-hole
Other applications Direct Drive, Printing, Packaging, Converting
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• D2L Rule
Continuous Torque
Capacity is Directly
Proportional to
Length:
2 x Length = 2 x TC
But …
Doubling the
Diameter (Moment
Arm) Squares the
Continuous Torque
Capacity
2 x Diameter = (TC)2
From
From
To
To
2x
2x
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• Kt (Torque Constant or Torque Sensitivity)
Kt = Unit Torque Output
Unit Current Input
Example: N-m / Amp RMS
Kt is Determined by:
- Number of Turns per Coil in the Copper Winding
- Density of the Magnetic Field in the Air Gap
(Number of Magnetic Flux Lines Crossing Through
the Winding Turns)
IMPORTANT MOTOR CONCEPTS
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How does this relate the Ke (BEMF Constant) ?
They are proportional.
Ke = Volts
_________________________________________________________________________________________________
Unit of Rotational Speed – RPM [or Rad/sec]
Example: V / 1000 RPM
FYI - If working in SI units, these numbers are
identical, Kt in Nm/A = Ke in V-sec / rad
• Kt (Torque Constant or Torque Sensitivity)
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Km = Kt /
Km factor describe how much Kt is
generated by magnetic flux rather than
copper winding turns
Km factor directly influences a motor’s:
- Continuous torque capacity
- Efficiency at various Speed / Torque ranges
√ Rm
• Km Factor (Torque produced as a function of heat)
Km = N-m / √ watt --- Figure of Merit
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Output Power
I2R
Loss
Freq.
Loss
Output Power
I2R
Loss
Freq.
Loss
Heat
Input Power
Reduced
Heat
Increased Performance & Efficiency
Motor
Winding,
Pole Count,
Magnetics
Design –
Optimization
Lead to:
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I2R losses result from current flowing through resistive
copper winding, creating a wasteful voltage drop.
Largest loss impact occurs when torque load and
current draw is high.
Increased Km factor reduces I2R losses because same
Kt is achieved with lower winding resistance.
• I2R Losses -- (Copper Losses)
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Hysteresis and Eddy Current losses occur in the iron (flux-
carrying) parts of the motor’s magnetic circuit, generating heat
and wasting current. Iron losses are directly proportional to
shaft speed (pole frequency).
Motor Pole Freq. = Mech. Revs X # of Pole Pairs
Largest loss impact occurs when operating speed (pole
frequency) is high.
Lower Km factor generally equates to lower pole count and
lower magnetic flux density levels in motor steel, which result in
reduced frequency-related losses.
• Frequency Losses -- (Iron Losses)
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• Km Factor Influence
More Kt due to winding
turns rather than
magnetic flux
Typically fewer poles
Lower Tc capacity
Lower frequency-related
losses
More Kt due to magnetic
flux rather than winding
turns
Typically more poles
Higher Tc capacity
Lower I2R losses
Lower Km Higher Km
Km SCALE
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To maximize efficiency at a specific speed and
torque operating point, I2R losses and frequency
losses are ideally balanced:
I2R
Losses
Frequency
Losses

For any motor, this ideal condition theoretically
occurs at approximately:
15-20% of maximum torque capacity
80-85% of maximum speed capacity
• Motor Efficiency
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Ideal balanced condition is difficult to achieve unless motor
operates at a single continuous speed & torque and the motor
is optimally designed for that specific load point.
In most real world applications where speed and torque
points vary over the machine duty cycle, the most reasonable
approach is to optimize the motor design based on:
- RMS calculation for the entire duty cycle to determine
average speed and torque the motor will need to provide
- Confirm that adequate Voltage, Current, and Thermal
Margins are met at the worst-case load operating conditions
• Motor Efficiency
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Dominated by I2R losses: - Usually occurs at High
Torque, Low Speed operation
- Motor is undersized, Pole
Count probably too low
- Need higher Km solution to
maximize efficiency
I2R
Frequency
Dominated by Frequency Losses: - Usually occurs at Low Torque,
High Speed operation
- Motor is Oversized, Pole
Count probably too high
- Need lower Km solution to
maximize efficiency

I2R
Frequency
• General sizing conclusions at specific load condition
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Kollmorgen’s Value
• Optimized Capabilities
• Smaller, Lighter & Faster Robots
• Speed to Market
24
1
2
3
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Collaborative Robotics
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Robotic Application:
Collaborative Articulated Robotic Joint
Motor Type: Frameless Pancake Torque Motor driving HD® Gearing
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Surgical Robotics
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Surgical Robotics
Motor Types: Frameless Torque Motor, Conventional Servo
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Specialty & Extreme Robots
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30 DOF Robotic Joints, 4 Sizes
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Articulated Robot Joint
NREC – CHIMP Robot Nugget Joint
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Multiple Robotic Joints
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Mobile Robotics
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Propulsion Drive Wheels
Motor Type: Optimized design, conventional housed servo motors
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Agricultural Robotics
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Motor Type: Optimized design, conventional housed servo motors
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Multi-Generations Mars Rover
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Articulated Robotic Joint, Cryogenic Cooling
Motor Type: Frameless Pancake Torque Motor
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Medical Rehab / Exo-Skeletons
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Exo-Skeleton, Prosthetic Robotic Joint
Motor Type: Frameless Pancake Torque Motor
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Collaborative Robotics
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• Payload capacity – Typically 3, 5, 10 Kg
• Speed – Design limited based on “how safe” …
• Thermal management – “Touch-proof”,
Machine design limitations of gearing,
feedback, etc
• Gearing considerations – Need to minimize
reflected inertia in a highly variable and
dynamic system. Mechanical efficiency, heat
generation, system life all reflect on gearing
type and ratio to be chosen
DEEP DIVE – Collaborative, Articulated Joint Design
• Joint Design Considerations
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• Typical Motor with Class F insulation system
has 155 C max winding temperature
• 155 C equates to nominal 140 C in close
proximity to encoder / gearing design elements
• Solutions:
Increase thermal heat sink mass
Increase distance to encoder / gearing [longer thermal
path = increased weight]
Reduce maximum winding temperatures
• Joint Design Considerations
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Harmonic Drive® Gearing
“Collaborative” Type Robot
• Harmonic Drive® Gearing
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• Efficiency seems low but when taking into
account the dynamics to weight this gearing is
uniquely qualified for these types of joints
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• True zero backlash – modest stiffness but
advanced position loop control algorithms
easily stabilize high dynamic reflected loads
when using high ratios
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• Driving with classical torque motor suffers
performance penalty at higher speeds
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What if you had:
A motor series that was designed to
be optimized for mating up with the
various Harmonic Drive® Gearing
sizes?
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What if you had:
A motor series that was designed to
be optimized for mating up with the
various Harmonic Drive® Gearing
sizes?
You would be able to:
Create robotic joints that were
optimized for performance in
collaborative style robotics
applications
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• High torque density that results in the shortest
and lightest possible electromagnetics package
• Optimized for easiest installation into Harmonic
Drive® Gearing designs
• Windings optimized for speed and torques
required in 3,5 and 10 kg collaborative robot
applications @ 48 VDC bus voltage
• Designed to perform while not exceeding 80
degrees C safety standard
• Cost optimized for Cobot market
• BMS Family Motors
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• BMS-1601-A with 14
• Motors are designed specifically
to fit with Harmonic Drive® Sizes
• BMS Family Motors
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Kollmorgen BMS
Frameless Motor
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Robotics Joint Motor Performance Considerations
Mechanical
Units BMS-1601-A TBMS-6013-A
O.D. Armature
in 2.362 2.375
mm 59.99 60.33
Stack Length
in 0.520 0.500
mm 13.21 12.70
Endturn (Lead Side)
in 0.270 0.400
mm 6.86 10.16
Endturn (Non-Lead Side)
in 0.150 0.200
mm 3.81 5.08
Total Armature Length
in 0.940 1.100
mm 23.88 27.94
Rotor Thru-Bore
in 1.182 1.130
mm 30.02 28.70
Jm Kg*m^2 1.54E-05 1.41E-05
Poles - 16 12
Weight (Total)
lbs 0.488 0.485
grams 221 220
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TBMS-6013-A
155 C
Winding
Temp
.290 Nm @
4000 rpm
121.5 watts
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TBMS-6013-A
80 C
Winding
Temp
.070 Nm @
4000 rpm
29.3 watts
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BMS-1601-A
155 C
Winding
Temp
.410 Nm @
4000 rpm
171.7 watts
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BMS-1601-A
80 C Winding
Temp
.240 Nm @
4000 rpm
100.5 watts
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Performance Units BMS-1601-A TBMS-6013-A
155 C Torque @ 4000 rpm Nm 0.410 .290
80 C Torque @ 4000 rpm Nm 0.240 .070
155 C Power @ 4000 rpm watts 172 122
80 C Power @ 4000 rpm watts 101 30
• Motor Performance Comparison Summary
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Electromate Robotics Symposium
Enabling Innovators
To Make The World A
Better Place
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Kollmorgen robotic symposium presentation-motor design impacts on the optimization of robotic systems