Balancing collaborative human–robot assembly lines to optimise cycle time and ergonomic risk

Abstract

Human–robot collaboration can enhance productivity of production lines and reduce human ergonomic risk. The numbers and types of robots and stations in which robots are allocated need to be determined. Operations should be scheduled carefully when a human and robot work on a part in a station to obtain a feasible operation allocation with the highest efficiency and lowest ergonomic risk. A mixed-integer linear programming model, constraint programming model, and Benders decomposition algorithm were developed to analyse advantages of collaborative robots in assembly lines. An energy expenditure method was used to evaluate ergonomic risk. By scheduling and balancing collaborative human–robot assembly lines, operational advantages and scheduling constraints from human–robot collaboration were studied when immobile and mobile robots are used. Regression lines were developed that can help managers determine how many and what types of robots are best for a line and what the impact of robot mobility on robot and line performance can be. The best configuration for equipping a line with collaborative robots is when (number of robots)/(number of stations) is near .7 and about 37% of robots are mobile. Robots can be efficiently used in lines with both a small and large number of passive resources and in simple and mixed-model lines.

Keywords:

• Assembly line balancing
• human–robot collaboration
• mobile robots
• constraint programming
• Benders decomposition

Acknowledgments

The authors would like to deeply thank the referees for their valuable comments that helped to improve our paper. We thank Oleg Gusikhin for helping us better describe our balance shaft module example.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Our codes and data are available both on request and also at https://drive.google.com/file/d/1HTLOL11HH-HiBG0EhJQE0MqBr9uHHg2u/view?usp=sharing.

Additional information

Notes on contributors

Kathryn E. Stecke

Kathryn E. Stecke teaches in the Naveen Jindal School of Management at University of Texas at Dallas as the Naveen Jindal School Advisory Council Chair. She received an M.S. in Applied Mathematics and M.S. and Ph.D. in Industrial Engineering from Purdue University. She is an INFORMS Fellow, POMS Fellow, and DSI Fellow. She is founding Editor-in-Chief of both the International Journal of Flexible Manufacturing Systems and Operations Management Education Review. She was on the POMS Board of Directors (April 2006 to April 2008 and April 2014 to April 2016). She served on the INFORMS Board of Directors as Vice President from January 2003 to December 2004 and from January 1999 to December 2001. She has served as General Chair, Program Chair, and Plenary Chair of POMS, INFORMS, DSI, and other conferences. In February 2004, INFORMS compiled a list of all 475 papers that have 50 or more citations from all papers published in Management Science over the last 50 years. All of her Management Science papers are on this list. INFORMS selected 50 of these as those papers that ‘represented the most significant research published in Management Science over the last 1/2 century’. One of her papers is on this select list.

Mahdi Mokhtarzadeh

Mahdi Mokhtarzadeh is a Ph.D. student in operations management at the University of Texas at Dallas. He did his master's degree in Industrial Engineering at the University of Tehran in Iran. His research interests comprise operations management, optimisation, production planning, seru production systems, scheduling, industry 4.0, and human–robot collaboration.