Steve Kihlberg

A case study evaluating the ergonomic and productivity impacts of partial automation strategies in the electronics industry

A case study is presented that evaluates the impact of partial automation strategies on productivity and ergonomics. A company partly automated its assembly and transportation functions while moving from a parallel-batch to a serial line-based production system. Data obtained from company records and key informants were combined with detailed video analysis, biomechanical modelling data and field observations of the system. The new line system was observed to have 51% higher production volumes with 21% less per product labour input and lower work-in-process levels than the old batch-cart system. Partial automation of assembly operations was seen to reduce the total repetitive assembly work at the system level by 34%. Automation of transportation reduced transport labour by 63%. The strategic decision to implement line-transportation was found to increase movement repetitiveness for operators at manual assembly stations, even though workstations were constructed with consideration to ergonomics. Average shoulder elevation at these stations increased 30% and average shoulder moment increased 14%. It is concluded that strategic decisions made by designers and managers early in the production system design phase have considerable impact on ergonomic conditions in the resulting system. Automation of transport and assembly both lead to increased productivity, but only elements related to the automatic line system also increased mechanical loads on operators and hence increased the risk for work-related disorders. Suggestions for integrating the consideration of ergonomics into production system design are made.

Job enlargement and mechanical exposure variability in cyclic assembly work

Cyclic assembly work is known to imply a high risk for musculoskeletal disorders. To have operators rotate between work tasks is believed to be one way of decreasing this risk, since it is expected to increase variation in mechanical and psychological exposures (physical and mental loads). This assumption was investigated by assessing mechanical exposure variability in three assembly tasks in an electronics assembly plant, each on a separate workstation, as well as in a ‘job enlargement’ scenario combining all three stations. Five experienced operators worked for 1 h on each station. Data on upper trapezius and forearm extensor muscle activity were obtained by means of electromyography (EMG), and working postures of the head and upper arms were assessed by inclinometry. The cycle-to-cycle variance of parameters representing the three exposure dimensions: level, frequency and duration was estimated using ANOVA algorithms for each workstation separately as well as for a balanced combination of all three. For a particular station, the variability of trapezius EMG activity levels relative to the mean was higher than for extensor EMG: between-cycles coefficients of variation (CV) about 0.15 and 0.10, respectively. A similar relationship between CV applied to the parameter describing frequency of EMG activity. Except for head inclination levels, the between-cycles CV was larger for posture parameters than for EMG. The between-cycles variance increased up to six fold in the job enlargement scenario, as compared to working at only one station. The difference in mean exposure between workstations was larger for trapezius EMG parameters than for forearm extensor EMG and postures, and hence the effect of job enlargement on exposure variability was more pronounced for the trapezius. For some stations, job enlargement even implied less cycle-to-cycle variability in forearm extensor EMG parameters than working at that station only. Whether the changes in exposure variability associated with job enlargement were sufficient to imply a decreased risk for musculoskeletal disorders is not known.

Integrating Production Engineering and Ergonomics in Production System Design

Within the framework of the COPE program, a tool is described for integrated documentation and prediction of ergonomic and technical performance in production systems. The tool is based on data on exposures and durations of tasks occurring in production. A case study is reviewed to illustrate initial efforts to implement the tool, as well as further lines of its development.

Association between Assembly Work Electromyography and Discomfort as Identified by Video-Computer Interaction

The purpose of this product is to study the correlation between self-reported and measured mechanical workload of neck and shoulder on workstations level. Six persons participated in the study, each working at six different workstations. The workstations were ranked from “lowest” to “highest” workload according to different variables. The correlations were studied on ranking order. Different types of assembly work were mainly carried out in all stations. In this work (few high workload situations, and a high degree of monotonous, repetitive work situations) one situation with a high workload could in this case be experienced as positive. The methods lead to contradicting results as regards identifying work situations with high loads. The results indicate that the methods lead to similar results as regards identifying work situations with low loads.

Relationships between Cycle Time and Mechanical Exposure within and between Individuals in Repetitive Assembly Work

Cycle time is an important parameter for both the production engineer and the ergonomist. This study focused the relationships between cycle time and another ergonomic parameter, exposure level. Mechanical exposure was assessed with EMG and inclinometry on five operators at three workstations in an assembly plant. Average cycle time and exposure level did not differ between workstations. Significant relationships between cycle time and exposure level were found in some cases at an individual level. Large between operator variability was found for both exposure levels and cycle time while the within operator variability was smaller, even across stations. This indicates that the operators used individual working methods.

Representative video recordings for synchronized collection of ergonomic and production data in an assembly system

A method has been developed for optimized representative video recordings for synchronized collection of ergonomic and engineering data in assembly systems using the same film. The method is based on random selection of both operators and starting time of the recordings during the day with some boundary conditions: fixed total recording time (30h) and an upper (3h) and lower (1h) recording time per operator. The method was tested at an electronic assembly industry. The study showed that the method has to be further developed. This development would be on basis of statistical models assessing associations between measurement resources, representativeness and precision as functions of working hours, number of work stations, manning and work rotation.