ارزیابی ارگونومیک کار پیچیده: به کارگیری یک رویکرد مشارکتی تعامل تصویری کامپیوتر،مطالعه در یک نمونه ازچیدن سفارش
|کد مقاله||سال انتشار||تعداد صفحات مقاله انگلیسی||ترجمه فارسی|
|6673||2000||11 صفحه PDF||سفارش دهید|
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Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : International Journal of Industrial Ergonomics, Volume 25, Issue 4, May 2000, Pages 435–445
A method for ergonomic evaluation of complex manual work was developed, based on interactive operator assessment of video recordings. The video film is displayed on the computer terminal, and the filmed operator assesses the work by clicking on virtual controls on the screen, whenever a situation inducing pain or discomfort appears. The operator marks body region and rates perceived exertion. In this way, a filmed sequence covering hours of work is condensed into a limited number of high-priority tasks. A library is formed in the computer, including task and operator identification data, ergonomic data, and pictorial information. The evaluation system, called VIDAR, was applied in an application study of manual materials handling in an automotive workshop. Results showed that the subjects after a brief instruction were able to understand and provide input to the system. The assessments were reasonably consistent in the group of operators. It was concluded that VIDAR provides data that are highly useful in a participatory process of change, and that it adds a new dimension to ergonomic evaluation of complex work. Cognitive aspects calling for further scientific study were identified. Relevance to industry Existing expert-based observation methods are sometimes difficult to apply in practice. The method described here is based on operator rather than expert assessment, which provides structured information that is relevant and useful, for instance in industrial interventions.
A basic problem in applied ergonomics is to be able to assess work situations, taking into account a complexity of exposures. Many types of jobs involve a variety of tasks, each one representing its special set of ergonomic characteristics. For instance in long cycle time assembly or in production systems involving job rotation, many different objects, tools and machinery may be handled by the individual operator over a working day. The large number of situations and the different exposures to be considered may make ergonomic evaluation extremely difficult. For instance, in automotive assembly where the operators work at several workstations, if there is a high incidence of shoulder–neck complaints, it may be hard to conclude which situations and tasks should be in focus for ergonomic intervention in the first place. In a series of studies in manufacturing industry, we have endeavored to make ergonomic assessment of long complex work sequences, as a basis for ergonomic interventions. However, we found that only to a limited extent did existing methods meet the demands encountered in practice. For instance, expert-based observation methods (e.g., OWAS, Karhu et al. (1977); PEO, Fransson-Hall et al. (1995); RULA, McAtamney and Corlett (1993)) may indeed provide useful data, but they tend to be too time consuming to be useful in routine analysis of complex tasks, particularly if these tasks are dynamic or hand intensive, such as in assembly work. For this reason, we started development of a new method for ergonomic evaluation of complex work, based on subjective reporting. Demands on this method included,
نتیجه گیری انگلیسی
4.1. Evaluation of complex work There is a typology in physical exposure assessment methods, (a) self-reports, (b) observation, (c) measurement. Each one of these types of methods has its assets and problems; see for instance analyses concerning subjective exposure assessment by Viikari-Juntura et al. (1996), and observation methods by Juul-Christensen et al. (1997). The external exposure approach relies on the assumption that if more is known about the exposure, the researcher is in a position to evaluate the work more accurately. This assumption is justified in many situations, for instance when there are established evaluation criteria to relate to, but ever so often the understanding of the basic mechanisms causing pain, disease or complaints is incomplete. Even if we were to know of the external exposure in all its detail we may be misled in such circumstances by the results of our measurements. In our group, we have worked extensively with development and application of mapping methods for external as well as internal exposure (Winkel and Westgaard, 1996), based on measurement techniques, such as goniometry, biomechanical analysis, and electromyography (e.g., Kadefors et al., 1993; Törner et al., 1994; Öberg et al., 1995). We have concluded from these studies that such methods may be extremely helpful, provided there is a hypothesis focusing precisely on the entity to be mapped. Unfortunately, physiological effect mapping often fails to shed light on the real problem at hand, because there may be no methodology allowing monitoring of the relevant variables, or the manifestation of effects may be unknown or questionable. An alternative approach in ergonomic assessment is to focus on the effect side rather than on the exposure side. The acute effects are based on external as well as internal exposures. They may be assumed relevant with respect to identifying high-risk situations with respect to development of work-related musculoskeletal disorders (WMSDs; Kuorinka and Forcier, 1995). These effects may be evaluated by mapping carried out using psychophysical techniques such as rating of perceived exertion (Borg, 1982) which provides data on the individual's subjective assessment resulting from external exposure. In order to structure and facilitate assessment of effects of exposure during manual work, questionnaire techniques have been developed and applied (e.g., Wiktorin et al., 1993; Burdorf, 1993; Johansson, 1994). Such methods make available data enlightening effects of exposure based on individual, subjective assessment. There may be some limitations as to the applicability of questionnaires in the type of situations considered in the present paper: it is complicated to design a questionnaire which makes possible reliable and expedient assessment of complex work, involving a multitude of tasks in a working day, if the goal is to identify high-strain situations linked to operation sequence, and to provide details such as location and degree of perceived pain or discomfort. The logbook or diary approach provides a related method of information acquisition where the subject reports exposures and/or acute effects as perceived over, say, a working day (Burdorf and Laan, 1991; Viikari-Juntura et al., 1996). There seem to be few studies on the validity of logbook reporting, but it is clear that valuable information can be obtained this way, providing that the subjects are motivated enough and there is a structure that facilitates data processing. Still this technique is difficult to apply so as to reflect the perceived strain during work. Also, structured interviews have been applied. An attractive asset of interviews is the open character of data collection: few presumptions have to be made by the investigator. On the other hand, open methods tend to be difficult and time consuming to evaluate, particularly if data are to be used in an organizational change process. 4.2. The approach It should be emphasized that the present method for ergonomic evaluation of complex work sequences is not just another video-based observation method. The uniqueness of the method is that it is the filmed operator rather than an ergonomic expert who is responsible for the evaluation: this method has more in common with psychological methods such as questionnaires and structured interviews, than with expert evaluation, even though such may well be undertaken using video or computer display (e.g., Landau et al., 1996). However, VIDAR differs from standard psychophysical methods since it is built on identification rather than on recollection. The closest analogy among reported methodologies is rather the interactive use of body maps while the work is being carried out or immediately following completion of a job sequence (Corlett and Bishop, 1976; Kadefors et al., 1993). The approach of recording the filmed subject's responses to seeing himself or herself in situations displayed on the video screen, so-called “self-confrontation”, has been applied in interactive studies of human performance, particularly in therapeutic situations (for a review, see Casswell, 1983). In these studies, the question whether video recordings accurately reflect the naturally occurring behavior of the participants, has been addressed (Renne et al., 1983). Potential distortions include increased or decreased rate of focal behaviors, and changes in response magnitude. A common observation is that the subjects’ behavior changes under video filming. This may also be the case in the present application, although the filming was not aimed at evaluating the subjects’ way of work, but rather to facilitate identification of certain strenuous situations. A more significant risk may be the one called “observer drift”, which means that the standards used by the subject in the course of evaluation may change. In VIDAR, the subjects are given the opportunity to reevaluate the prioritized situations, a scheme recommended by psychologists applying self-confrontation (Maxwell and Pringle, 1983). The results from work assessment employing VIDAR will probably always deviate from those of expert-based ergonomic work analysis. In fact, these different methodological approaches entail results of different modalities. Whereas expert-based analysis may provide quanitative data that can be put in the context of ergonomic standards and regulations, subjective assessment according to VIDAR reflect the workers’ opinions and may more readily provide a base for participatory ergonomic change programs. The application study results show that the method is easy to understand and operate by practitioners. The task identifications were reasonably consistent between operators, but there were considerable individual differences in perceived rating. This is to be expected, since different persons react differently to a given ergonomic exposure, because of different physical and psychic consititution, and differences in working techniques. There may also be differences in attitudes influencing the outcome of the assessment. For these reasons, assessment of validity of the method is a complex task. The present study demonstrated some aspects of validity only. It was found that the method entailed useful ergonomic data from a group of operators. It also discriminated between tasks of different character (Table 1). On the other hand it is not known to what extent the fact that assessments were made not during but subsequent to exposure, may influence the results, or to what extent operators’ assessments comply with ergonomic expert assessment of the same tasks. Tests of validity should include prospective studies where the identifications of strenuous tasks and markings of body regions be compared to development of work-related musculoskeletal disorders. Nevertheless, mapping of workers’ opinions on the work situations to which they are exposed has an intrinsic value that should not be underestimated. 4.3. Cognitive aspects There are a number of important cognitive aspects linked to the use of VIDAR, that should be considered. An assumption made in the design of the method is that watching oneself carrying out a job enhances the possibility to create a library of the most strenuous operations to which the person is exposed at work, and to assess the degree of perceived pain or discomfort. The identification process taking place within the individual calls for scientific analysis. A related question not addressed here but certainly warranting analysis is if assessment could be made also looking at films of other persons doing tasks that are familiar to the operator. This would increase the applicability of the method, since filming time may be saved. It should be recognized that the participatory dimension may however be compromized, using this alternative approach. As touched upon above, the problem of recollection is essential for the interpretation of the results. A common technique in ergonomic studies is to ask subjects to assess workload subsequent to exposure (e.g., Corlett and Bishop, 1976; Kadefors et al., 1993). In using VIDAR, the time delay is at least as long as the length of recording, and it is assumed that the pictorial feedback helps cancelling the time delay effect. The effect of the time factor warrants further study, although it was demonstrated in the application study carried out that subjects had no difficulty to make assessments after one or two days delay. It was noted in this context that Wiktorin et al. (1996) found that subjects were able to reproduce forces reliably on laboratory equipment, mimicking those to which they were exposed in their daily work. A number of different scales have been used to assess pain and discomfort, for instance the VAS scale (Jørgensen et al., 1993; Madeleine et al., 1998). Here we chose to use the CR-10 scale; this scale is physiolocically well defined, and we have applied it previously in ergonomic research to assess pain and discomfort (Kadefors et al., 1993). The CR-10 scale as such has previously been used in analysis off line of work situations (Holzmann, 1982). The choice of scale is probably not critical for the usefulness of the method. 4.4. Limitations In a practical situation, VIDAR provides an input based on the opinion of several operators, and since the individual responses may differ depending on e.g., way of work, physical status, and psychological constitution, a certain diversity in the data acquired is to be expected. Also aspects such as mood and attitude towards work may affect the reproducibility. If the diversity is large, the reason behind should be penetrated, for instance with respect to a possibility that the exposure during work may be problematic for the more vulnerable persons. In such a case the measures to be taken would be focusing on problem solving for the individual rather than for the entire group under study. However, in most cases involving materials handling, such as in the application study reported here, the response from different operators is expected to be reasonably coherent. The present method adds to the tool box that the ergonomist and the practitioners may use in ergonomic interventions. It should be seen as a complement to existing work analysis methods. Expert-based evaluation methods will undoubtedly remain the basis for ergonomic workplace assessment. Setting and implementing standards and good practices will continue to require skilled analysts equipped with methods that makes it possible to identify and evaluate exposures. However, in workplace interventions, particularly in complex manual work, there is a need for new methods which support end-user involvement and facilitate prioritizing of the ergonomic problems. VIDAR was developed as a contribution in this regard.