Marita Christmansson

A case study of a principally new way of materials kitting - an evaluation of time consumption and physical workload

Abstract This article presents a materials kitting case study, using an alternative method for materials kitting: the traditional picker-to-material principle was replaced with a material-to-picker approach. The study was made in a materials supply workshop of an automobile plant shortly after this kitting process had been introduced. The materials kitting was video recorded and the material pickers’ physical exposure was assessed using ambulatory equipment to make an integrated registration of muscular activity, work postures and movements. The material pickers assessed work situations perceived as physically stressful. The materials kitting showed improved productivity as compared with other kitting methods. The study indicated that the work situation offered pickers low levels of physical exposure. The picking work was rather light but involved great repetitiveness in arm movements. The material pickers experienced the work as repetitive and having some physically stressful work situations. The integrated analyses showed: (1) that exposure in picking operations was similar to, but could be distinguished from, other work activities and (2) that picking from one type of storage package, Euro pallets, resulted in higher exposure than picking from plastic containers. More studies are needed on the implications of exposure levels in materials picking. Relevance to industry In the car industry, customer demands and manufacturers’ strategies result in the handling of many components in production systems. Materials kitting is one way to handle this and reduce costs for space and materials in progress. Traditional kitting methods are time consuming, and work-related musculoskeletal problems are common.

Task design, psycho-social work climate and upper extremity pain disorders – effects of an organisational redesign on manual repetitive assembly jobs

A company redesign was carried out to improve production efficiency and minimise the prevalence of work-related musculoskeletal disorders and sick leave. The redesign was evaluated on the basis of studies of assembly workers before (17 workers) and after (12 workers) the redesign. The redesign resulted in more varied, less repetitive, and more autonomous assembly jobs. The psycho-social work climate was both improved and impaired. A medical examination showed that eight of 17 workers before and nine of 12 workers after the redesign suffered from upper extremity pain disorders. Neither the production goals nor the goals of the redesign were fulfilled. Our conclusion was that the increased task variation and impaired psycho-social work climate, combined with a lack of skill and competence, actually increased the physical stress, risk for disorders and difficulties in fulfilling the production goals.

Evaluation of ergonomics in a virtual manufacturing process

This paper presents a study of the evaluation of ergonomics using virtual tools in a pre-production phase when verifying the manual assembly of the XC90 car model at the Volvo Car Corporation. The case study focused especially on the verification of visual demands in assembly work due to its complexity. The virtual development process was mapped in observations of the use of virtual tools and interviews with actors involved in the verification. Results show that computer manikins are viable tools in verifying ergonomics early in a development process and that they help to detect many problems prior to physical pre-series. There are, however, substantial improvement potentials, both in the software itself and, even more, in the process of using virtual tools. The study identified several factors that can increase the reliability of the results of computer manikin simulations (e.g. participative ergonomics and documentation issues). The special focus on visual demands shows the need of basic knowledge about human behaviour for making valid simulations. This case study stresses the need for knowledge about simulations in both analysis and interpretations in order to achieve maximum output from a virtual manufacturing process.

Modified method time measurements for ergonomic planning of production systems in the manufacturing industry

The paper reports on an evaluation of a method called ErgoSAM. This method is based on SAM, a higher-level method-time-measurement (MTM) system, and is for use by production planners, e.g. production engineers. In addition to the SAM information, the ErgoSAM method considers information on weight handled or forces applied and work zone. The method is designed to predict the physical demands of work postures, force and repetitivity, according to a scientific model, the Cube model. In co-operation with the Volvo Car Corporation, six work-stations of an assembly line were analysed by a production engineer using ErgoSAM. The total assembly time analysed was about 17 minutes. The results were compared to results from ergonomic analyses made by an ergonomist using the Volvo Car Corporations standards. The results showed that ErgoSAM predicts work situations of high physical stress for the workers. However, the method does not consider stressful positions for the hand, wrist and neck or mental stress. The production engineer judged the ErgoSAM analyses to require about 5% more time than SAM analyses alone. It is concluded that the method shows considerable promise for predicting physically stressful work situations, but needs to be further evaluated and refined.

Methodological Differences Using a Computer Manikin in Two Case Studies: Bus and Space Module Design

The computer manikin software Jack™ was used in two different case studies analyzing ergonomics. A comparison was made on how Jack was used in the two case studies. In the first, Jack was used in the design phase of a new Volvo bus model. A group was formed to work with a special part of the bus chassis design, namely cables and tubes. The group aimed to create an ergonomically correct and efficient assembly production. The group consisted of designers, production engineers and researchers. Jack was used late in this process for analysis of assembly work situations resulting from the design. In the second case study, an analysis was carried out in the preliminary design phase of the Cupola, a European Space Agency (ESA) module for manned space flights for the International Space Station (ISS). In this study, Jack was used early in the design process before any flight hardware production. When comparing the two studies, differences were found regarding the approach of the mimics of zero-gravity activities relative shop floor assembly work, and also of the modeling of Jack body postures. Animations were found more useful in the zero-gravity environment. Beside the treatment of co-ordinate systems, the process of file transfer was almost identical. In both case studies benefits of the use of Jack analysis, and resulting design impact according to this, seem to be equal despite when the analysis were carried out in the design process.