European J. Industrial Engineering, Vol. 8, No. 2, 2014 143 Copyright © 2014 Inderscience Enterprises Ltd. Optimal cyclic scheduling of a robotic flowshop with multiple part types and flexible processing times Weidong Lei and Ada Che* School of Management, Northwestern Polytechnical University, Xi’an 710072, China E-mail: leiweidong@gmail.com E-mail: ache@nwpu.edu.cn *Corresponding author Chengbin Chu Labortoire Génie Industriel, Ecole Centrale Paris, Grande Voie des Vignes, 92295, Châtenay-Malabry Cedex, France E-mail: chengbin.chu@ecp.fr Abstract: This paper proposes a branch-and-bound algorithm for cyclic scheduling of a robotic flowshop with multiple part types in which the processing times of parts can vary within their given time windows. The problem consists of two types of sequencing issues: part input sequencing and robot move sequencing. We give a formulation for the problem and propose a branch-and-bound algorithm based on the properties of the developed model. The proposed branch-and-bound algorithm consists of three nested procedures, called procedures A, B and C, respectively. Procedures A and B are mainly designed for enumerating part input sequences, while procedure C is responsible for enumerating robot move sequences. To reduce the solution space and speed up the algorithm, we derive the upper bound of the number of parts that can be serviced by the robot within a cycle. Computational results on both benchmark and randomly generated instances are reported. [Received 19 August 2011; Revised 16 February 2012; Revised 29 June 2012; Accepted 22 July 2012] Keywords: cyclic hoist scheduling; robotic flowshop; minimal part set; MPS; branch-and-bound algorithm; flexible processing times. Reference to this paper should be made as follows: Lei, W., Che, A. and Chu, C. (2014) ‘Optimal cyclic scheduling of a robotic flowshop with multiple part types and flexible processing times’, European J. Industrial Engineering, Vol. 8, No. 2, pp.143–167. Biographical notes: Weidong Lei received his BS in Information Management and Information System from Tianjin Polytechnic University, China, in 2008 and his MS in Management Science and Engineering from Northwestern Polytechnical University, China, in 2011. Currently, he is a PhD candidate at Northwestern Polytechnical University, China. His main research interest is robotic scheduling problems in advanced manufacturing systems.