Design of assembly lines with the concurrent consideration of productivity and upper extremity musculoskeletal disorders using linear models

Abstract

The productivity of assembly lines is considerably affected by the health condition of assembly workers, and work-related musculoskeletal disorders (WMSDs) are common occupational diseases among assembly workers due to repetitive motions or heavy working loads. The conventional approaches to decreasing WMSD risks in the assembly lines include slowing the work-pace or applying job rotations. These adjustments usually focus on individual assembly workers at the station level but not the work allocation among the workers at the whole assembly line level, and thus may decrease the line productivity. To avoid these negative effects, some research started considering ergonomic characteristics at the line level, such as balancing ergonomic burdens by proper work assignment among workers. These previous studies incorporated physical grip demands or processing time overload into non-linear assembly line design problems, and used heuristic solution methods. This paper presents a methodology that explicitly integrates ergonomic measures for upper extremities into linear assembly line design problems. As the ergonomic measures, this research considers a guideline of Threshold Limit Value (TLV) from American Conference of Industrial Hygienists. Linear models are developed to link work-worker assignment to the measures of hand activity and hand-arm vibration. As productivity measures, conventional assembly line design criteria are considered, such as cycle time and the number of workers. These linear models allow ergonomic and productivity measures to be integrated as a mixed-integer programming model for assembly line design. In addition, these linearization methods can be generalized in order to incorporate ergonomic measures in tabulated forms into assembly line design problems.The analysis of the result shows the new model can effectively control the exposure levels in the upper extremity by proper work assignment compared to the conventional approaches, and does not decrease production rates considerably. This research also shows the potential to reduce the need of numerous task adjustments after assembly line design in traditional trial-and-error based assembly task adjustment. ACKNOWLEDGEMENTS

Productivity and ergonomic risk in human based production systems: A job-rotation scheduling model

“…Traditionally, assembly task assignment and ergonomic evaluations are carried out independently (Xu et al, 2012). Few researches jointly consider physical demands and completion time of tasks in assignment problems, and solve them using heuristic methods (Carnahan et al, 2000a(Carnahan et al, , 2000bChoi, 2009;Otto and Scholl, 2011).…”

“…Despite this, previously the influence of human behavior on production system performance has been underestimated. Ergonomic studies and human reliability measures have been widely investigated for production and safety related issues separately (Xu et al, 2012). Models are still far from being considered experienced and reliable, since an appropriate and complete description of human behavior is a complex task which has not yet been fully addressed.…”

A better way of fitting clips? A comparative study with respect to physical workload

“…Many of these tasks are performed manually, with the bare hand or using a tool, powered or unpowered . In view of the repetitiveness of the movements, of the level of force required to perform an action, of extreme joint amplitudes and/or of activity maintained for long periods, neck and upper limb pain or indeed musculoskeletal disorders occur frequently in the workers performing such tasks (Ferguson et al, 2013(Ferguson et al, , 2012Jansen et al, 2012;Xu et al, 2012;Spallek et al, 2010;Nordander et al, 2009;Landau et al, 2008;Buckle and Devereux, 2002;Silverstein et al, 2002;Sluiter et al, 2001;Fransson-Hall et al, 1995). In ergonomics, workplace exposure to such physical workload is often evaluated by measuring muscular activity, which has been correlated with pain or musculoskeletal disorder symptoms (Ferguson et al, 2012;Porter et al, 2010;Bao et al, 2009;Ostensvik et al, 2009;Southard et al, 2007).…”

Conceptual Framework of Lean Ergonomics for Assembly Process: PDCA Approach

“…Recent studies show that many researchers had tried to improve the integration of ergonomic and lean manufacturing for productivity improvement. Besides, many articles found that hidden wastes in lean manufacturing had significant correlated to the human factors [33][34][35]. Ergonomics injuries and illnesses such as carpal tunnel syndrome, tendinitis and musculoskeletal disorders (MSDs) rate are increasing which cut across all industries and occupations.…”