Ann-Christine Falck

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.

Proactive assessment of basic complexity in manual assembly: development of a tool to predict and control operator-induced quality errors

A major challenge for manufacturing companies today is to manage a huge amount of product variants and build options at the same time in manufacturing engineering and in production. The overall complexity and risk of quality errors in manual assembly will increase placing high demands on the operators who must manage many different tasks in current production. Therefore, methods for decreasing and controlling assembly complexity are urgent because managing complex product and installation conditions will result in distinct competitive advantages. The objective of this paper is to present a method for predictive assessment of basic manual assembly complexity and explain how included complexity criteria were arrived at. The verified method includes 16 high complexity and 16 low complexity criteria to aid designers in preventing costly errors during assembly and create good basic assembly conditions in early design phases of new manufacturing concepts.

Operator Related Causes for Low Correlation Between Cat Simulations and Physical Results

The objective of this study was to explore correlation between CAT (Computer Aided Tolerancing) simulation and physically measured results in running production with focus on operator dependant factors. Therefore, the manual assembly of 25 different system solutions (locating scheme, tolerances, fasteners etc for a part) was analyzed. The study has been performed in the automotive industry and the system solutions are from 3 different cars in 2 different factories, all manual assembly in a paced line. The analysis shows several interesting results; in running production 33% of the measurements are not ok although 28% had their tolerance zone adjusted according to the measured results to make them ok. The conclusion is that the CAT simulations do not predict all the variation and therefore additional factors need to be included to enable accuracy improvement. Further relationships between additional factors such as operator influence and bad geometrical quality can be proven. A short term solution is suggested as well as a long term solution involving the need for development of additional functions in CAT tools, the overall goal being to decrease the difference between simulation results and actual physical results.

Robust design and geometry assurance considering assembly ergonomics

The objective of this study was to explore how assembly ergonomics issues were regarded by geometry engineers. Therefore, 21 geometry engineers in two manufacturing companies were interviewed. Their answers show good awareness of the implications of poor assembly ergonomics but appropriate working procedures and support in CAT (Computer Aided Tolerancing) tool are missing. 95% of the respondents would like to add consideration to assembly ergonomics in their CAT simulation. Based on this study a number of assembly factors that need to be included and considered in locating scheme definition and geometric stability analysis are identified and presented. Altogether, the results show a need for organizational change and CAT tool development.

Early Risk Identification and Cost-Benefit Analyses through Ergonomics Simulation

For cost-beneficial reasons simulations with computer manikins have been increasingly used in the automotive industry for prediction of ergonomics problems before the product and work place exist in physical form. The main purpose of ergonomics simulations is to apply biomechanical models and data to assess the acceptability of the physical work load, e.g. working postures, visibility, clearance etc., which could result in requirements to change the design of the product. The aim is to improve ergonomics conditions in manual assembly and to promote a better product quality through improved assemblability (ease of assembly). Many studies have shown a clear correlation between assembly ergonomics and product quality and that poor assembly ergonomics result in impaired product quality and in decreased productivity. Nevertheless, there are remaining difficulties in achieving acceptance for changes of product and production solutions because of poor assembly ergonomics. A recent study in the Swedish automotive industry showed that huge savings and increased profit margins can be obtained by eliminating ergonomics risk concepts in the very early product development process. The study confirmed a strong relation between poor ergonomics assembly solutions and quality errors of the product (car). There was a substantially increased risk for quality errors and increased costs for corrective measures of the product for assembly items of high and moderate physical work load compared to assembly items of low work load. The quality risk was increased 3 and 3.7 times, respectively. The overall cost for corrective measures in the assembly plant and for factory complete cars was 8.7 and 8.2 times higher for assembly items of high and medium physical work load compared to items of low physical work load. The purpose of this paper is to demonstrate the need for ergonomics simulations of potentially harmful assembly concepts in combination with cost-benefit analyses of conceivable system solutions based on calculation of costs for quality errors related to poor ergonomics and poor assemblability. The intended end result of this research is a model by application of which it is possible to calculate the cost for quality losses and health effects due to poor ergonomics and compare it with the cost for improving the ergonomics with designers, manufacturing engineers and ergonomists as main users.