Increasing the degree of automation in a production system: Consequences for the physical workload
Introduction
During the last decades, various efforts have been made to improve working conditions, as well as efficiency in the production systems. In spite of such efforts, work-related musculoskeletal disorders are still very common (Bernard, 1997; Official Statistics of Sweden, 2000; Coury, 1999; NRC, 2001). Such disorders often lead to prolonged sick-leave periods, disability pensions and decreased life quality (Pålsson et al., 1998). The economical consequences are huge, e.g. 0.5–2% of the gross national products in the different Nordic countries (Toomingas, 1998; Johansson, 2000; Norlund et al., 2000). In the United States the annual cost for the society amounts to 13 billion USD (NIOSH, 1996).
The lack of success of ergonomic interventions is probably due to the shortage of knowledge concerning ergonomic consequences of changes in production systems (Westgaard and Winkel, 1997). For example, one obstacle has been the lack of suitable methods to measure physical exposure as a consequence of the interventions. However, several ‘field methods’ are now available (Hansson et al., 1997, Hansson et al., 2000a; Stål et al., 2000; Unge Byström et al., 2002; Juul-Kristensen et al., 2002). Hence, case studies of ergonomic interventions should now be possible to carry out in a more conclusive and feasible way (Cole et al., 2003). The need of such studies are obvious—especially such studies that in some ways also relate to various types of tangible technical dimensions. For example, these can be choice of layouts and materials feeding techniques, work group size and organisation.
When investigating the infliction of ergonomic interventions on the human being, it is essential that the achieved data are in a suitable form to be able to link them to the actual production system design. Especially so, concerning the fact that there is an inarticulate zone as to what is considered as ‘healthy’ or ‘unhealthy’ work within the manufacturing industry.
During recent years, a number of ergonomic recommendations and regulations, national (e.g. Kilbom, 1994; AFS, 1998:1; ACGIH, 2001), as well as international (e.g. European Committee for standardization, 1996; ISO11226, 2000), have been introduced. However, these recommendations and regulations are not fully implemented and are in practice seldom used as a tool for the actual design of production systems. A more proactive and technically based type of ergonomic interventions are actually called for. This article will to some extent illuminate these issues.
This case study was conducted at a plant processing wooden boards for parquet flooring in the south of Sweden. There is, for several years, an ongoing stepwise mechanisation/automation of the manufacturing process aiming at improved manufacturing efficiency and product quality as well as improved ergonomic conditions. As a result, three different production lines are used simultaneously, each of them representing the state of art of mechanisation/automation at the time when they were designed and introduced. Consequently, they comprise different technical and ergonomic measures for efficiency and work conditions. In fact, these three generations of production lines represent different stages of an evolution from a manual towards an automated manufacturing process. Thus, this case study offers an unique possibility to assess the ergonomic effects of tangible technical evolution.
Accordingly, the main aim of this case study is to quantify and evaluate eventual change in physical workload in the form of muscular load as well as work postures and movements in the neck and the upper extremities, as a consequence of the stepwise technical development of the three generations of production system designs.
Section snippets
Production system design
On an overarching level, the production systems in the company process wooden boards for parquet flooring. The production systems studied consisted of three production lines; (1) the manual line, (2) the semi-automated line and (3) the automated line.
The manual line is the oldest production line (Table 1; Fig. 1A). The work is organised along two parallel conveyors with a production rate of 2 slats/s each. Four workstations are organised along each conveyor, thus attended by in total eight
Study design
The study base comprised all 152 currant female operators at the Hardwood Grading Department. They were all interviewed and had a physical examination of neck and upper limb.
For quantifying the physical workload direct technical measurements were performed. Five unique work tasks were chosen, i.e. for the manual line ‘inspection and sorting by surface’, ‘inspection and sorting by edges’ and ‘piling’ and for the semi-automated line ‘inspection and sorting by surface’ and ‘inspection and sorting
Operators
The mean age for the 152 operators was 38.5 (range 20–61) years and the mean employment time was 9.8 (0.25–38) years. Their work schedules were based on two- and three shift as well as work only night time.
By a structured interview, data on subjective complaints were registered for the last 12 months as well as for the last 7 days (Kuorinka et al., 1987). Further, a standardised physical examination of the neck and upper extremity was performed (Ohlsson et al., 1994a). Diagnoses were decided on
General
There were no systematic differences between the right and left side comparing the different tasks between the lines. Hence, only the results from the right side are presented. However, all data are available on our web http://www.ymed.lu.se/papers/appendix/Increasingautomation.pdf.
The work, when producing slats for parquet flooring was, in general, characterised by moderate muscular loads (Table 2, Table 3, Table 4). Most of the work tasks were performed with moderate flexion of the head, with
General
Producing slats for parquet flooring implied moderate muscular loads, moderate head flexion, somewhat elevated upper arms and constant hand movements, yet these exposures involved high prevalence of musculoskeletal disorders. The exposure circumstances were most pronounced for the manual line. By the stepwise automation the physical exposure changed significantly. Thus, the semi-automated line displayed an overall decreased muscular activity. Moreover, the technical development resulted in
Acknowledgements
Ms. Lothy Granqvist, Christina Glans and Jeanette Unge gave skilful technical assistance. The case study was supported by grants from the Swedish Council for Work life Research (including the program Change@Work), the Swedish Medical Research Council, the Swedish National Institute of Working Life (Co-operative for Optimization of industrial production lines regarding Productivity and Ergonomics; COPE), the Swedish Council for Planning and Coordination of Research, the Medical Faculty of Lund
References (51)
- et al.
A triaxial accelerometer for measuring arm movements
Applied Ergonomics
(2002) - et al.
Effects of progressive levels of industrial automation on force and repetitive movements of the wrist
International Journal of Industrial Ergonomics
(2000) - et al.
Goniometer measurement and computer analysis of wrist angles and movements applied to occupational repetitive work
Journal of Electromyography and Kinesiology
(1996) - et al.
Impact of physical exposure on neck and upper limb disorders in female workers
Applied Ergonomics
(2000) - et al.
Sensitivity of trapezius electromyography to differences between work tasks—influence of gap definition and normalisation methods
Journal of Electromyography and Kinesiology
(2000) - et al.
Measurements of wrist and forearm positions and movements: effects of, and compensation for, goniometer crosstalk
Journal of Electromyography and Kinesiology
(2004) - et al.
Physical workload during manual and mechanical deboning of poultry
International Journal of Industrial Ergonomics
(2002) - et al.
Standardized Nordic questionnaire for the analyses of musculoskeletal symptoms
Applied Ergonomics
(1987) - et al.
Precision of measurements of physical workload of the shoulders and arms during standardised manual handling. Part I: surface electromyography of m. trapezius, m. infraspinatus and the forearm extensors
Journals of Electromyography and Kinesioligy
(2004) - et al.
Upper extremity muscular load during machine milking
International Journal of Industrial Ergonomics
(2000)
Guidelines for occupational musculoskeletal load as a basis for intervention: a critical review
Applied Ergonomics
Ergonomics for the Prevention of Musculoskeletal Disorders
Quantifying workload in neck shoulders and wrists in female dentists
International Archives of Occupational and Environmental Health
Interindividual variation of physical load in a work task
Scandinavian Journal of Work, Environment & Health
Methodological issues in evaluating workplace interventions to reduce work-related musculoskeletal disorders through mechanical exposure reduction
Scandinavian Journal of Work, Environment & Health
The effects of production changes on the musculoskeletal disorders in Brazil and South America
International Journal of Industrial Ergonomics
Safety of Machinery—Human Physical Performance—Part 4: Evaluation of Working Postures in Relation to Machinery
Physical exposure assessment in monotonous repetitive work—the PRIM study
Scandinavian Journal of Work, Environment & Health
Evaluation of physical workload standards and guidelines from a Nordic perspective
Scandinavian Journal of Work, Environment & Health
The influence of production systems on physiological responses measured in urine and saliva
Stress and Health
Kinematic evaluation of occupational work
Advances in Occupational Medicine and Rehabilitation
Questionnaire versus direct technical measurements in assessing postures and movements of the head, upper back, arms and hands
Scandinavian Journal of Work, Environment & Health
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2017, Applied ErgonomicsCitation Excerpt :Of the final 14 studies, two were non-randomized control trials (Guimaraes et al., 2012; Fredriksson et al., 2001), one had case-control design (Roquelaure et al., 1997), and 11 were of cross-sectional designs (Table 2). In terms of outcomes, five studies targeted MSD prevention (outcomes included measures of disability, disorders, pain, discomfort) (Balogh et al., 2006; Guimaraes et al., 2012; Fredriksson et al., 2001; Roquelaure et al., 1997; Sato and Coury, 2009), 11 studies targeted changes in exposure to physical risk factors (biomechanics, repetition, fatigue, effort exertion) (Asensio-Cuesta et al., 2012a, 2012b; Balogh et al., 2006; Carnahan et al., 2000; Diego-Mas et al., 2009; Frazer et al., 2003; Fredriksson et al., 2001; Filus and Okimorto, 2012; Roquelaure et al., 1997; Sato and Coury, 2009; Tharmmaphornphilas and Norman, 2007), and three targeted the job-rotation effect on psychosocial factors (job satisfaction) (Dawal et al., 2009; Dawal and Taha, 2007; Guimaraes et al., 2012). The indicators and tools used to evaluate the outcomes varied widely in the studies.