Ergonomical study on refrigerated cabinet

1. Original Article Proceedings of IDMME - Virtual Concept 2008
Beijing, China, October 8 – 10, 2008
Virtual Ergonomic analyses to optimize
refrigerated display units design
Giorgio Colombo 1, Giorgio De Ponti 2, and Caterina Rizzi 3
(1) : Dipartimento di Meccanica (2) : Innovation Centre - Epta Group
Via G. La Masa, 24 – 20153 Milano - Italy V.le Liguria 2/18 20068 - Peschiera Borromeo (MI) - Italy
Tel. +39 02 23998259/Fax+39 02 23998202 Tel: +39 02 55308269/Fax +39 02 55303193
E-mail: giorgio.colombo@polimi.it E-mail: giorgio.DePonti@epta-group.com
(3) : Dipartimento di Ingegneria Industriale
Viale G. Marconi, n. 5 – 24044 Dalmine (BG) - Italy
Tel. +39 035 2052075/Fax+39 035 2052077
E-mail : caterina.rizzi@unibg.it
Abstract: This paper presents a methodological approach to (http://www.plm.automation.siemens.com) and Safework
evaluate ergonomic issues of refrigerated display units. It is (http://www.safework.com/); they can be used to define
based on the use and integration of virtual human models with complex scenes with virtual manikins and objects and
virtual prototyping techniques in order to support and optimize simulate many tasks.
the product development process. The methodology have been Applications in ergonomics were immediately subsequent, as
experimented simulating the behavior of two users’ categories demonstrated by research activities described in [KG], [CP],
(customers and operators), which have different roles, needs, [FL], [BL], [BH] [CG] and [SO] and refer to various areas,
and ways of interaction with the machinery. Regarding but especially to automotive and aerospace.
customers, aspects related to reach capability and visibility In this paper, we focused the attention on virtual human
have been analyzed and quantified. For the operators, two modeling as a tool to integrate virtual prototyping and to
typical tasks have been analyzed (loading a unit and serving a carry out ergonomic analysis during the first phases of
customer) evaluating postures and movements respect to product development process. Thus, main goal has been to
requirements established by international standards to reduce verify the potentiality and usefulness of ergonomics analysis
health risks. Ergonomic simulations have been carried out using virtual human to predict and study the behavior of
varying unit type and configuration (number and types of users’ categories which have different roles, needs, and ways
shelves, etc.), manikins’ size and packed food (sizes and of interaction with the product. Industrial sector considered
weight). refers to refrigerated display units for supermarket and in
collaboration with a producer we develop a methodology to
Key words: Ergonomics, Virtual Human, Refrigerated carry out ergonomic analyses in a virtual environment to
display units, Visibility, Reach capability. support and optimize the design process.
In the following, we first describe the context of interest, the
methodological approach and finally the ergonomics
1- Introduction simulations and their evaluation. To model virtual humans
and realize simulations we adopted the commercial software
Virtual engineering approach, and in general virtualization, has package Jack [BP].
been revealed to be one of the main trends of research during
these last decades [FH]. Various techniques and tools,
especially for simulation tasks, have been developed to support 2- Products and users
both products and processes during their life-cycle, from
concept to disposal. In this context, the use of realistic models As said the main goal has been to experiment the use of
for human body is attracting more and more interest in virtual human and define a strategy/methodology to carry out
different domains since the applications can be various and ergonomic analyses for refrigerated display units.
important within the product development process [SO]. Refrigerated display units considered in this work are
Digital human modeling started in the 1960s and at present, produced by the involved company in different types:
several frameworks with human models of different
complexity are available, such as Ramsis (www.human- Traditional cabinets with horizontal refrigerated display
solution.com) ManniquinPRO (www.nexgenergo.com), Jack units in two different versions: serve-over and self-
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2. IDMME - Virtual Concept 2008 Virtual ergonomic analyses to optimize refrigerated display unit design
service; these groups. For example, customers should easily access
Vertical and semi-vertical chiller units to conserve and food packages, while supermarket operators need also to
display fresh products; execute repetitive tasks (e.g., loading a shelf) with postures
Vertical and horizontal freezer units for optimum and movements as safely as possible without causing
conservation of frozen products. musculoskeletal disorders and health risks. This means that
the designer should also assess postures and movements to
Following figures show some examples, and precisely, Fig 1 a ensure a complete and healthy use of the refrigerated unit.
small vertical unit for fresh products (A), another one for
frozen product (B), a cabinet with horizontal refrigerated self-
service display unit (C), a mixed configuration (D) and, finally, 2- The adopted methodology
an horizontal serve-over horizontal display.
The basic idea has been to identify a step-by-step roadmap
that can be adopted by the designer to evaluate the
ergonomic aspects and analyze alternative configurations.
The proposed methodology is based on the use of 3D
parametric models and ergonomic simulations with virtual
humans. It requires five main steps:
1. Model the virtual environment. The ergonomic tester
selects from the libraries the refrigerated unit and the
A B food package s/he wants to analyze, and properly sets
the meaningful dimensions.
2. Select virtual manikins. According to users’ group, a
set of manikins are selected from the anthropometrics
databases integrated within the system adopted, in our
case Jack.
3. Insert manikin into the virtual testing environment.
Manikin is located in front of the refrigerated unit and
postures are defined in relation to the ergonomic
C D analysis.
4. Plan and execute ergonomic simulations. According to
the goal of ergonomics analysis (e.g., reach or visibility),
the tester plans and assigns postures and movements to
the virtual human.
5. Evaluate results. During this step, results obtained for
each virtual human are evaluated and compared among
E them and with current national and international
Figure 1: Refrigerated units (Images courtesy Epta Group). standards.
The refrigerated units can display various types of packed Concerning the step 1, we first analysis the mentioned types
food, fresh or frozen, characterized by different packages of refrigerated unit to identify main product families and
(rigid, semi-rigid, and soft), dimensions and weight (Fig. 2). parts involved in the ergonomic analysis, such as unit overall
dimensions, shelves position and sizes. Thus to optimize the
analyses and the development of new products, we
developed two libraries: one for the refrigerated units and
another one for packed food. The first library includes the 3D
parametric models, which are archetypes of refrigerated units
and represents the product families like those ones shown in
Figure 1. Each 3D model is a simplified representation of the
product where components specifically involved in the
ergonomics analysis have been parameterized to be easily
modifiable; examples are shelves sizes (length and width),
positions (height from ground) and number.
Figure 3 shows the simplified model and meaningful sizes of
a vertical unit for fresh products, Figure 4 the model of a
Figure 2: Example of packed food. cabinet with horizontal refrigerated self-service display unit,
and Figure 5 a configuration comprising both vertical and
The design of such a machinery should accommodate the full
horizontal freezer units.
range of users during its life-cycle; i.e., from workers like
Similarly, the second library includes a set of 3D parametric
fitters and maintenance men to the final users. We focus the
models that represents a wide range of products having
attention on the last category that can be further subdivided
generally weight less than 1kg and easily adaptable to the
into two groups: customers and supermarket operators.
specific refrigerated unit. Fig. 6 shows some examples, from
Different ergonomics aspects have to be analyzed according to
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3. IDMME - Virtual Concept 2008 Virtual ergonomic analyses to optimize refrigerated display unit design
a two-yogurt package to a milk package.
Two‐yogurts package Deli meats package
Figure 3: Vertical unit for fresh products.
Milk package
Figure 5: Consumer’s products.
Regarding step 2, two sets of virtual manikin has been
selected: one representing the consumers’ population and
another one representing the intended operators of the
refrigerated units. In agreement with the involved company,
the first set comprises 6 manikins: 2 female (5th and 50th
percentiles), two male (50th and 95th percentiles) and two
manikins (female and male 50th percentile) sitting on a wheel
chair representing disabled people. The second set consists of
two manikins corresponding to a 50th percentile female and a
50th percentile male.
Figure 6 shows the selected virtual humans and Table 1
summarizes corresponding anthropometric measures.
Figure 4: Cabinet with horizontal refrigerated display unit.
Figure 6: Considered virtual humans.
Figure 5: Mixed configuration.
Table 1: Manikins anthropometric measures.
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4. IDMME - Virtual Concept 2008 Virtual ergonomic analyses to optimize refrigerated display unit design
3- Ergonomics analyses
To verify potential of ergonomic analyses with virtual human,
simulations have been performed for the different types of
refrigerated units included in the library, varying parameters
such as shelves positions and number. Simulations have been
planned taking account the different needs of the final end-
users and, when necessary, of the international standards for
machinery workers.
3.1 – Costumer’s p.o.v.
From the consumer’s p.o.v., main ergonomics aspects concern
reach capability and visibility of food packages placed over the
shelves. As packed food, we have considered a two-yogurt
package, a can, and a milk package varying the sizes according
to the shelves ones. As said, we have selected six manikins
from the anthropometric database, two of which representing a Figure 7: Vertical unit - Disable 50thile.
disabled female and a disabled male. In the following we
illustrate the procedure adopted.
In this case, there are no specific standards for the posture;
therefore, manikins are initially located in front of the
refrigerated unit. For each size of the manikin, the analyses
have been conducted following a procedure to identify if s/he
can reach the product, the corresponding postures and
visibility. In agreement with the company, the results have
been quantified calculating the farthest distance reachable from
the left border of each shelf and respect to the center of
manikin hand. This permits to evaluate product and shelves
accessibility with regard to the different percentiles. In the
following we present results obtained for some of analyzed Table 2: Reach values for vertical unit.
units.
The first refrigerated unit analyzed is a small vertical unit with The second vertical unit has a structure similar to the
five shelves: the first at 1115 mm from ground and the last one previous one but it is higher and has five shelves deeper and
at 295 mm (see Fig. 3). Figures 7 and 8 show respectively the larger. Figure 8 portrays a comparison of manikins’ product
postures obtained for a female 50thile and a disabled male to accessibility identified for lowest shelf and corresponding
evaluate product accessibility for each shelf. visibility.
Table 2 summarizes results obtained for food package reach
where the values have been calculated as above mentioned.
Yellow cells highlight critical values which mainly refer to the
5th shelf and the disabled manikin. The food package can be
assessed almost by all manikins even if for some percentiles
the postures are not really comfortable.
Figure 8: Comparison of manikins’ posture for the lowest shelf.
Figure 9 shows a histogram that summarizes the percentages
of product reach calculated for each shelf.
Figure 7: Vertical unit - Female 50thile.
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5. IDMME - Virtual Concept 2008 Virtual ergonomic analyses to optimize refrigerated display unit design
FEMALE 5th ile FEMALE 50th ile MALE 50th ile histogram summarizing results organized by percentile.
The geometry of the refrigerated unit limits the accessibility
MALE 95th ile DISABLED MALE
of highest shelves to all manikins, especially the smallest
100%
ones. This is manly due to the presence of the chest. Better
90% results can be reached reducing its width.
80%
70%
60%
50%
40%
30%
20%
10%
0%
1st 2nd 3rd 4th 5th
Figure 9: Reach analysis for the vertical unit for frozen products.
From the histogram one can note that only the central shelf can
be completely accessed by all manikins, while the highest is
practically reachable only by the 95th percentile. This suggests
that the 1st shelf could be eliminated. Even if this solution
diminishes the expository space, at the same time it permits to
decrease the consumption of the energy necessary to preserve
frozen product at the right temperature.
For cabinets with horizontal self-service refrigerated display
unit, only reach analysis can be carried out since there aren’t Figure 11: Mixed configuration - Female 50thile.
unit parts that limit food packages visibility. Table 3 shows
results of the ergonomics analysis where the values are related 1st shelf 2nd shelf 3rd shelf
to width of the chest assuming as origin of the coordinate Chest Width Chest Depth
system the one shown in Fig. 4. 100%
90%
80%
70%
60%
Table 3: Reach values for cabinet with horizontal unit. 50%
40%
Figure 10 portrays the corresponding manikins’ postures for 30%
the above listed values. 20%
10%
0%
FEMALE 5th ile FEMALE 50th ile MALE 50th ile MALE 95th ile DISABLED MALE
Figure 12: Reach analysis for the mixed configuration.
3.2 – Operator’s p.o.v.
From operator’s p.o.v, ergonomics analysis concerns also the
evaluation of working postures and movements in relation to
the refrigerated unit; in fact, operators are exposed to
repetitive tasks that can cause pain and fatigue. Thus, the
engineers should design machinery paying attention also to
these aspects reducing as much as possible painful and tiring
postures and movements. Several researches have been
conducted in this field [DH] [EF] (www.cdc.gov/NIOSH/)
and national and international standards have been
established to specify requirements for postures and
movements in order to reduce health risks. In this work, we
Figure 10: Comparison among the manikins. refer to the European Standard UNI-EN 1005-4:2005 [UE1]
and UNI EN 1005-5:2007 [UE2].
Finally, we perform both reach and visibility analysis for the The standard uses a number of zones to evaluate these
mixed configuration (see Fig. 5). Figure 11 portrays postures aspects and defines values acceptable for low and high
obtained for the woman 50th percentile, while Figure 12 the
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6. IDMME - Virtual Concept 2008 Virtual ergonomic analyses to optimize refrigerated display unit design
frequency movement related to trunk, upper arms, neck, and so percentage of worker population decreases appreciably for
on. As an example, Figure 13 shows mentioned zones for the the ankle, while the other values remain stable.
upper arm posture. From the data obtained with the previous toolkit, the
identified postures have been compared with requirements
defined by European Standard UNI-EN 1005-4:2005 and
UNI EN 1005-5:2007. Table 3 shows a partial view of
numerical data used to evaluate the most critical posture
defined for a 1kg product loading (i.e. that one for the
farthest edge) with mentioned standards rules.
A B
Figure 13: Zones for upper arm posture [UE1].
For ergonomic analyses, we identified two typical situations:
an operator loading a vertical or horizontal unit and the
operator serving a customer. For both cases, we used the Task
Analysis Toolkit (TAT) of Jack and, in particular, the Low
Back Analysis and Static Strength Prediction [JK]. The first
permits to determine the spinal forces acting on a virtual
human's and to verify if worker’s tasks respect NIOSH
guidelines; while the second allows the designer to evaluate the
percentage of a worker population that has the strength to
perform a task based on posture, exertion requirements and
Figure 15: Loading task varying products’ weight.
anthropometry.
The first test-case refers to the horizontal refrigerator cabinet
depicted in Figure 3 and the task accomplished by 50th
percentile operator to load the chest with frozen products. We
evaluated virtual human’s postures to load products taking into
account following variables: products place within the chest
(e.g., at nearest and farthest edges of the chest and at the
middle), product weight and chest depth. This last one has been
considered to analyze alternative unit configurations that better
satisfy ergonomics standards. Figure 14 shows the postures and
results obtained with the product loaded at different locations
and using TAT toolkit.
Figure 14: Loading task.
Figure 15 portrays the results obtained varying the weight of
product from 1kg to 4kg (to simulate loading of multi Table 3: Comparison defined posture with standards rules.
packages) located at the end of the chest at the farthest edge.
One can note that varying the position and the weight the Since some values are not acceptable, other simulations have
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7. IDMME - Virtual Concept 2008 Virtual ergonomic analyses to optimize refrigerated display unit design
been performed varying the height (H) and width (W) of the Thanks to the library of the 3D parametric model, it is quite
easy to modify meaningful dimensions of the unit or shelves
chest in order to find a configuration that meets the regulations.
Figure 16 shows a configuration with height equal to 460 mm (sizes, location, and number) to find better ergonomic
and width 750mm where data related to ankle improve. performances. For this type of analysis, we do not evaluate
the comfort of customer’s posture since s/he executes the
task (access the packed product) occasionally; therefore a
limited set of system functionality can be sufficient and
adequate to perform ergonomic analyses.
This is no more valid when considering operators. Results
from customers’ ergonomics analysis (especially postures)
can constitute the starting point, but it is necessary to
evaluate the comfort and compare operators’ postures in
Figure 16: Loading task for the new configuration. order to satisfy national and international regulations and
advanced analysis tools, like TAT toolkit, have to be
The second test case regards a horizontal serve-over display adopted.
unit commonly used for fresh meats, deli or cheese. In this
case, an operator should be able to access products and serve
the customer performing the task according to regulations. We
proceeded similarly to the previous case evaluating product
reach, related postures/movements, operator working space and
the interaction with the customer. Figure 17 shows some
examples of the identified postures and of interaction
customer-operator.
Figure 18: Roadmap for refrigerated unit ergonomics analysis.
CONCLUSIONS
This paper focuses the attention on a methodological
Figure 17: Postures for the horizontal serve-over display unit. approach based on the use of 3D parametric model and
virtual humans to improve machinery ergonomics and verify
the applicability of human modeling system in an industrial
4- Final Considerations context different from traditional ones (automotive or
aerospace). It has been developed a methodology to perform
Figure 18 summarizes the step-by-step roadmap developed for
and analyze ergonomics of refrigerated units that has been
ergonomics analysis of refrigerated units. The designer can
tested with the involved company considering a number of
adopt it since the early stages of the product development
refrigerated units covering possible configurations and
process and it has been mainly conceived for analysis related to
human-machine interactions: customer-machinery, operator-
customer and operators/machinery interaction. It has been
machinery and customer-operator.
experimented with five types of refrigerated unit representing
Our objective has been primarily methodological. The
main product families and characterized by different
definition of the virtual environment and the planning of the
configurations of the shelves and customer/operator interaction
simulations are not particularly complex. On the other hand,
modes.
it can be a little more difficult defining the correct position
Regarding customers, quantitative data acquired for reach
and posture of the virtual human and this can lead to wrong
capacity and visibility are organized in tables and histograms
results. Quantitative data derived from simulations permitted
allowing the designer to evaluate rapidly not only the specific
the designers to evaluate ergonomics performances and study
machinery but also to compare different types of refrigerated
alternative configurations more compliant with standard
units respect to packed food accessibility and expository space.
rules.
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8. IDMME - Virtual Concept 2008 Virtual ergonomic analyses to optimize refrigerated display unit design
Future activities have been already planned. The approach will [UE2] UNI-EN 1005-5:2007:E, Safety of machinery –
be extended to analyze maintenance tasks and study a solution Human physical performance – Part 5: Risk assessment for
suitable for different types of refrigerated units. repetitive handling at high frequency, European Community
for Standardization, February 2007.
ACKNOWLEDGEMENTS
The authors would like to thank Dario Cimini, Fabio Arizzi e
Rosario and Assenza Rosario for their contribution in
developing simulations.
7- References
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