An Approach for Intuitive Visualization of Ergonomic Issues
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Ergonomics is the science of human work. One goal is the adaption of work to the human, thus to create better working conditions and to avoid health risks. Increasingly often, digital human models and corresponding evaluation methods are used. Due to the mass of data and the variety of possible analyses which come along with a simulation, the interpretation of the outcomes can take a long time. We introduce a new concept, which enables a quick and understandable visualization and navigation of critical ergonomic situations and their causes. There are filter mechanisms available for changing the level of detail. These enable a representation for specific target groups. Prior to the development of the concept, expert interviews were conducted to specify the user requirements. Each iteration step of the design process was evaluated in cooperation with ergonomics experts.
KeywordsOverview and glyph-based visualization Ergonomics Concept study
An important property of visualization is its interactive nature. It is necessary to consider some simulation results, analyze them, and change parameters for a better understanding. Typically, a reconsideration from another viewpoint or comparison of the several outcomes has to be conducted. Furthermore, user interaction is often needed because of the mass of data which is not perceptibly at a glance. Especially in research and industry, experts use visual analytics tools to detect ergonomic problems . Modest circumstances concerning ergonomics could increase working time and costs. During the beginning of professional ergonomics, ergonomists used life-size human models and prototypes, for example, to design vehicle interior. These days they are using computers and ergonomics software tools, such as digital human models (DHM), to visualize results for a fast processing and understanding. While some ergonomists still use tables in hard copy for their analysis, the following surveys show the importance of ergonomics software tools in all areas of product planning, manufacture, and usage. The results of a survey carried out by Wischniewski  indicate that for the majority of the sample, ergonomics tools are important today. Most of the 30 domain experts, which participated in the survey, think that these tools will take an inherent part of virtual ergonomics evaluation in the future. Another survey carried out by Muehlstedt  with 59 experts also emphasizes the importance of ergonomics tools. Especially the analysis function in the matter of visualization (as picture or video) next to measurement, and posture were considered to be relevant.
2 Potential Users and Requirements
In order to create an interactive visualization of ergonomics information, we had to determine potential users and their requirements. Often several target groups work on the same data base, but with different intension and from different angles. For this purpose we interviewed professionals in the field of ergonomics, the occupational health and safety department (HSE), and industrial engineering (IE) from Deutsche Bahn AG (German Railways). Six experts participated in this workshop. A further workshop was held at the Volkswagen AG with two experts. We identified the main groups of potential users and their requirements in moderated interviews. All things considered, we obtain three main areas. In the first area experts are responsible for planning and designing of work processes. This includes professionals of HSE, IE, as well as planers and designers. The latter define the final product design in collaboration with ergonomists, HSE, and the IE. They are also responsible for the implementation of the working system. The industrial engineers set, among other things, time standards. A further group of potential users are persons who actually produce the goods. Here, workers are responsible for the correct execution of the working task and they are assisted by the team leader. The team leader takes the responsibility for decision-making, monitoring, and advisory to maintain the quality and quantity goals in the production. The person has also to decide about the deployment. Hereby, the work requirements and individual productivities of the corresponding employee have to be matched [3, 4, 5]. The last area consists of the work council and management. The former is the representative of workers’ interests. The management deals with economic aspects. This also includes the investment costs of workplace design.
In the following, the mentioned requirements of the participants of the workshops are explained in more detail. The respondents expressed their desire for an easier handling. In general, existing ergonomics tools are too complicated, as they told us. There is a high learning curve and a new incorporation is necessary after a few months without using the corresponding software, in particular in DHMs. In order to counter these problems, explanations, such as mouse-over info boxes on all interactive elements are wanted. The second wish was a user-friendly representation of the analysis data. The design should have an eye-catching character. In their experience, most non-ergonomists aren’t interested in tables. Color coding is preferred over tables. Furthermore, as the ergonomists mentioned, intuitive and sustainable graphical user interfaces are requested to demonstrate the ergonomic-critical situation in workshops, which are held for the workers. Many workers do their work already for years in the same manner. They very often lack the understanding of the necessity of the advantages the workers obtain due to ergonomic analyses of their workplaces. In addition, a prioritization is required to set a focus on major problems, such as bending. A visualization of ergonomic data should also consider that the same data has to presented in different forms, depending on whether they talk in front of the management or the workers. In result, important ergonomic issues should be visible at a glance and additional information should be provided on demand in a simple way.
3 State of the Art
As mentioned before (see Sect. 1), ergonomic investigations in companies are surprisingly often carried out by measuring or capturing data using paper-pencil methods and simple software support. For ergonomic reports, standardized sheets, such as the EAWS scoring sheet or simple diagrams, are applied as visualization. In addition, ergonomic maps or exposure registers are used for the documentation of an ergonomic evaluation of several work stations. The visualization of this kind of work is typically done using simple floor plan sketches or plain (Excel-) tables. A workstations can also receive a color coding according to the common standard DIN EN 614 (green, yellow, red) or separate evaluation points for a sharper disjunction .
Digital human models are becoming more and more popular  and usage is growing . The presentation of ergonomic results with software is often bounded to lists, simple dialogs, or simple graphs. An excerpt of the most common representations of ergonomic reports in digital human models can be found in Figs. 1 and 2. The introduced tools are not able to pass the above mentioned design requirements. There is no possibility to select the depth of analysis and only information about a static pose can be displayed, instead of an overall view. The current visualization in DHM does not support the user in analyzing ergonomic critical situations in an adequate way. The current presentation tends to demonstrate data in the absence of a context relation and without the possibility to change the depth and range of analyzing. Thus, there is room for improvement.
4 Related Work
Since time-oriented data is relevant in many practical situations, the visualization of such data has a long tradition  and still many recent work exists [14, 15, 16]. However, visualizations in digital human models for showing critical ergonomic situations or illustrating time-oriented processes are very limited. The concept of timelines is used in LifeLines . LifeLines was developed to create an overview over certain events in the life of a person. Therefore, the authors make investigations in hospitals, to receive facts about deseases, visits to the doctor, and so on. The presence of all import information at one stage enables the doctors to make a better prognosis about the medical condition and to offer a more suitable therapy. However, an overview of a huge amount of data can still quickly lead to confusion. LifeFlow  delivers a possibility to counteract this circumstance with event sequences (series of temporal distinct and consecutive events). Matchpad  presents an interactive glyph-based visualization for realtime sport events. The events are directly visualized in an overview, during the match. SoundRiver  makes an audio-visual mapping to illustrate sound effects from audio sources, like movies (e.g., for hearing-impaired viewers). In this way, it symbolizes the noise of an airplane as an icon with a small aircraft, for example.
5 Evaluation Procedure
6 Design Process
The initial (Fig. 3) and the final version (Fig. 4) follow Shneidermans seeking mantra “overview first, zoom and filter, then details-on-demand” . Nevertheless, our user study led to significant changes, related to the initial design.
A number of problems at the timeline (Fig. 3: dp 1) cannot be displayed at its best; i.e., a bar could overlap other bars, if they occurred nearly at the same time.
The permanent assignment of the colors to the appropriate evaluation methods was described as inconvenient, by the survey participants.
It is hard to compare the results over the time for the respective method.
There isn’t a possibility to choose a specific range, e.g., from second 5 to 20.
The duration of a single problem is not that simple to recognize from the timeline.
In order to simplify the usage, some interviewees have proposed to provide mouse-over info boxes direct at the interactive parts. We deviated from this proposal, since permanently opening boxes during navigation might be cumbersome for the users. Nevertheless, we have realized this idea by adding tooltips at the right-hand edge of the display (Fig. 4: dp 11), which are accepted generally.
In this paper, we have discussed two concepts to visualize ergonomic analysis data and to explore it. The first concept (Fig. 3) was prepared on basis of several expert interviews. We have realized the requirements of the experts, such as an intuitive handling, a first overview of all critical situations, as well as the providing of deeper information on demand. An evaluation of this prototype with experts from the field of ergonomics, visualization, and usability led to significant changes in our initial concept (Fig. 3). This demonstrates the importance of our user studies. The disadvantages of the first concept were highlighted and eliminated in several iterative loops. Furthermore, we explained why we use pictograms (see Fig. 5) and why we changed the order of certain graphical elements in the final concept, as a result of the survey.
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