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Original Article Proceedings of IDMME - Virtual Concept 2008 Beijing, China, October 8 – 10, 2008

Paper Number -1- Copyright of IDMME - Virtual Concept

Virtual Ergonomic analyses to optimize refrigerated display units design

Giorgio Colombo 1, Giorgio De Ponti 2, and Caterina Rizzi 3

(1) : Dipartimento di Meccanica Via G. La Masa, 24 – 20153 Milano - Italy

Tel. +39 02 23998259/Fax+39 02 23998202 E-mail: [email protected]

(2) : Innovation Centre - Epta Group V.le Liguria 2/18 20068 - Peschiera Borromeo (MI) - Italy

Tel: +39 02 55308269/Fax +39 02 55303193 E-mail: [email protected]

(3) : Dipartimento di Ingegneria Industriale

Viale G. Marconi, n. 5 – 24044 Dalmine (BG) - Italy Tel. +39 035 2052075/Fax+39 035 2052077

E-mail : [email protected]

Abstract: This paper presents a methodological approach to evaluate ergonomic issues of refrigerated display units. It is based on the use and integration of virtual human models with virtual prototyping techniques in order to support and optimize the product development process. The methodology have been experimented simulating the behavior of two users’ categories (customers and operators), which have different roles, needs, and ways of interaction with the machinery. Regarding customers, aspects related to reach capability and visibility have been analyzed and quantified. For the operators, two typical tasks have been analyzed (loading a unit and serving a customer) evaluating postures and movements respect to requirements established by international standards to reduce health risks. Ergonomic simulations have been carried out varying unit type and configuration (number and types of shelves, etc.), manikins’ size and packed food (sizes and weight). Key words: Ergonomics, Virtual Human, Refrigerated display units, Visibility, Reach capability.

1- Introduction

Virtual engineering approach, and in general virtualization, has 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 both products and processes during their life-cycle, from concept to disposal. In this context, the use of realistic models for human body is attracting more and more interest in different domains since the applications can be various and important within the product development process [SO]. Digital human modeling started in the 1960s and at present, several frameworks with human models of different complexity are available, such as Ramsis (www.human-solution.com) ManniquinPRO (www.nexgenergo.com), Jack

(http://www.plm.automation.siemens.com) and Safework (http://www.safework.com/); they can be used to define complex scenes with virtual manikins and objects and simulate many tasks. Applications in ergonomics were immediately subsequent, as demonstrated by research activities described in [KG], [CP], [FL], [BL], [BH] [CG] and [SO] and refer to various areas, but especially to automotive and aerospace. In this paper, we focused the attention on virtual human modeling as a tool to integrate virtual prototyping and to carry out ergonomic analysis during the first phases of product development process. Thus, main goal has been to verify the potentiality and usefulness of ergonomics analysis using virtual human to predict and study the behavior of users’ categories which have different roles, needs, and ways of interaction with the product. Industrial sector considered refers to refrigerated display units for supermarket and in collaboration with a producer we develop a methodology to carry out ergonomic analyses in a virtual environment to support and optimize the design process. In the following, we first describe the context of interest, the methodological approach and finally the ergonomics simulations and their evaluation. To model virtual humans and realize simulations we adopted the commercial software package Jack [BP].

2- Products and users

As said the main goal has been to experiment the use of virtual human and define a strategy/methodology to carry out ergonomic analyses for refrigerated display units. Refrigerated display units considered in this work are produced by the involved company in different types: Traditional cabinets with horizontal refrigerated display

units in two different versions: serve-over and self-

IDMME - Virtual Concept 2008 Virtual ergonomic analyses to optimize refrigerated display unit design

Paper Number -2- Copyright IDMME - Virtual Concept

service; Vertical and semi-vertical chiller units to conserve and

display fresh products; Vertical and horizontal freezer units for optimum

conservation of frozen products. Following figures show some examples, and precisely, Fig 1 a 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, an horizontal serve-over horizontal display.

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C D

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Figure 1: Refrigerated units (Images courtesy Epta Group).

The refrigerated units can display various types of packed food, fresh or frozen, characterized by different packages (rigid, semi-rigid, and soft), dimensions and weight (Fig. 2).

Figure 2: Example of packed food.

The design of such a machinery should accommodate the full range of users during its life-cycle; i.e., from workers like fitters and maintenance men to the final users. We focus the attention on the last category that can be further subdivided into two groups: customers and supermarket operators. Different ergonomics aspects have to be analyzed according to

these groups. For example, customers should easily access food packages, while supermarket operators need also to execute repetitive tasks (e.g., loading a shelf) with postures and movements as safely as possible without causing musculoskeletal disorders and health risks. This means that the designer should also assess postures and movements to ensure a complete and healthy use of the refrigerated unit.

2- The adopted methodology

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 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 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 them and with current national and international standards.

Concerning the step 1, we first analysis the mentioned types of refrigerated unit to identify main product families and 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 cabinet with horizontal refrigerated self-service display unit, and Figure 5 a configuration comprising both vertical and horizontal freezer units. Similarly, the second library includes a set of 3D parametric models that represents a wide range of products having generally weight less than 1kg and easily adaptable to the specific refrigerated unit. Fig. 6 shows some examples, from



a two-yogurt package to a milk package.

Figure 3: Vertical unit for fresh products.

Figure 4: Cabinet with horizontal refrigerated display unit.

Figure 5: Mixed configuration.

Two‐yogurts package Deli meats package

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 6: Considered virtual humans.

Table 1: Manikins anthropometric measures.



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 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 units. The first refrigerated unit analyzed is a small vertical unit with five shelves: the first at 1115 mm from ground and the last one at 295 mm (see Fig. 3). Figures 7 and 8 show respectively the postures obtained for a female 50thile and a disabled male to evaluate product accessibility for each shelf. 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 7: Vertical unit - Female 50thile.

Figure 7: Vertical unit - Disable 50thile.

Table 2: Reach values for vertical unit.

The second vertical unit has a structure similar to the previous one but it is higher and has five shelves deeper and larger. Figure 8 portrays a comparison of manikins’ product accessibility identified for lowest shelf and corresponding visibility.

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.



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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 unit parts that limit food packages visibility. Table 3 shows results of the ergonomics analysis where the values are related to width of the chest assuming as origin of the coordinate system the one shown in Fig. 4.

Table 3: Reach values for cabinet with horizontal unit.

Figure 10 portrays the corresponding manikins’ postures for the above listed values.

Figure 10: Comparison among the manikins.

Finally, we perform both reach and visibility analysis for the mixed configuration (see Fig. 5). Figure 11 portrays postures obtained for the woman 50th percentile, while Figure 12 the

histogram summarizing results organized by percentile. The geometry of the refrigerated unit limits the accessibility of highest shelves to all manikins, especially the smallest ones. This is manly due to the presence of the chest. Better results can be reached reducing its width.

Figure 11: Mixed configuration - Female 50thile.

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1st shelf 2nd shelf 3rd shelfChest Width Chest Depth

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 refer to the European Standard UNI-EN 1005-4:2005 [UE1] and UNI EN 1005-5:2007 [UE2]. The standard uses a number of zones to evaluate these aspects and defines values acceptable for low and high



frequency movement related to trunk, upper arms, neck, and so on. As an example, Figure 13 shows mentioned zones for the upper arm posture.

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 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 packages) located at the end of the chest at the farthest edge. One can note that varying the position and the weight the

percentage of worker population decreases appreciably for the ankle, while the other values remain stable. 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.

Figure 15: Loading task varying products’ weight.

Table 3: Comparison defined posture with standards rules.

Since some values are not acceptable, other simulations have



been performed varying the height (H) and width (W) of the chest in order to find a configuration that meets the regulations. Figure 16 shows a configuration with height equal to 460 mm and width 750mm where data related to ankle improve.

Figure 16: Loading task for the new configuration.

The second test case regards a horizontal serve-over display 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 17: Postures for the horizontal serve-over display unit.

4- Final Considerations

Figure 18 summarizes the step-by-step roadmap developed for ergonomics analysis of refrigerated units. The designer can adopt it since the early stages of the product development process and it has been mainly conceived for analysis related to customer and operators/machinery interaction. It has been experimented with five types of refrigerated unit representing main product families and characterized by different configurations of the shelves and customer/operator interaction modes. Regarding customers, quantitative data acquired for reach capacity and visibility are organized in tables and histograms allowing the designer to evaluate rapidly not only the specific machinery but also to compare different types of refrigerated units respect to packed food accessibility and expository space.

Thanks to the library of the 3D parametric model, it is quite easy to modify meaningful dimensions of the unit or shelves (sizes, location, and number) to find better ergonomic 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 order to satisfy national and international regulations and advanced analysis tools, like TAT toolkit, have to be adopted.

Figure 18: Roadmap for refrigerated unit ergonomics analysis.

CONCLUSIONS

This paper focuses the attention on a methodological 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 context different from traditional ones (automotive or aerospace). It has been developed a methodology to perform and analyze ergonomics of refrigerated units that has been tested with the involved company considering a number of refrigerated units covering possible configurations and human-machine interactions: customer-machinery, operator-machinery and customer-operator. Our objective has been primarily methodological. The definition of the virtual environment and the planning of the simulations are not particularly complex. On the other hand, it can be a little more difficult defining the correct position and posture of the virtual human and this can lead to wrong results. Quantitative data derived from simulations permitted the designers to evaluate ergonomics performances and study alternative configurations more compliant with standard rules.



Future activities have been already planned. The approach will be extended to analyze maintenance tasks and study a solution suitable for different types of refrigerated units.

ACKNOWLEDGEMENTS

The authors would like to thank Dario Cimini, Fabio Arizzi e Rosario and Assenza Rosario for their contribution in developing simulations.

7- References

[BH] Bäckstrand G., Högberg D., De Vin L.J., Case K. and Piamonte P. Ergonomics Analysis In A Virtual Environment. In International Journal of Manufacturing Research, 2(2): 198-208, 2007. [BL] Berger U., Lepratti R., Otte H. Application of digital human modelling concepts for automotive production. In TMCE 2004, Lausanne-CH, pp. 365-373, 2004. [BP] Badler N., Phillips C., Webber B. Simulating Humans: Computer Graphics Animation and Control. New York, Oxford University Press, 1993. [CG] Colombo G. and Cugini U. Virtual Humans and Prototypes to Evaluate Ergonomics and Safety. In Journal of Engineering Design, 16(2): 195-203, 2005. [CP] Case K., Porter J.M., Bonney and M.C. SAMMIE: a man and workplace modelling system. In Computer Aided Ergonomics, 31-56, 1990. [DH] Delle man N.J., Haslegrave C.M., Chaffin D.B. Working Postures and Movements – Tools for Evaluation and Engineering. Taylor & Francis, London / CRC Press, Boca Raton, FL, USA, 2004. [EF] European Foundation for the Improvement of Living and Working Conditions, Third European Survey on Working Conditions 2000, 2001. [FH] Fokkema J.T., Horvath I.,Challenges and answers for competitive engineering, in Tools and Methods of Competitive Engineering. In TMCE 2008,Izmir (Turkey), Ed. Horvath I. and Rusak Z., 1: 3-18, 2008. [FL] Feyen R., Liu Y., Chaffin D., Jemmerson G., Joseph B. Computer-aided ergonomics: a case study of incorporating ergonomics analyses into workplace design. In Applied Ergonomics, 31: 291-300, 2000. [JK] JACK Training Manual, Siemens UGS PLM Solutions, 2007. [KG] Karwowski W., Genaidy A.M., Asfour S.S. Computer Aided Ergonomics. In Taylor & Francis, 1990. [SO] Sundin A., Örtengren R. Digital human modeling for CAE applications. Handbook of human factors and ergonomics, Chapter 39, Ed. G. Salvendy, 2004. [UE1] UNI-EN 1005-4:2005:E, Safety of machinery – Human physical performance – Part 4: Evaluation of working postures and movements in relation to machinery, European Community for Standardization, May 2005.

[UE2] UNI-EN 1005-5:2007:E, Safety of machinery – Human physical performance – Part 5: Risk assessment for repetitive handling at high frequency, European Community for Standardization, February 2007.

huceid p116

Design

virtual ergonomic analyses

virtual manikins

virtual humanhave

virtual humansand

refrigerated unit

idmme virtual concept

ergonomic simulations

horizontal freezer units