Optimal multi-degree cyclic scheduling of multiple robots without overlapping in robotic flowshops with parallel machines

Xin Li, Tung Sun Chan, Sai Ho Chung

Research output: Journal article publicationJournal articleAcademic researchpeer-review

15 Citations (Scopus)


This paper considers scheduling robotic flowshops with parallel machines and multiple robots. Robots share the same track and cannot crossover each other. To avoid conflicts among robots, the principle without overlapping is applied. Identical parts with time window constraints are produced. It is challenging to obtain better cyclic schedules to improve the throughput. Moreover, multi-degree cycles are considered to obtain better schedules comparing to simple cycles, i.e. 1-degree cycles. To our knowledge, this is the first work to deal with the multi-degree cyclic scheduling in this complicated scenario. This is the main contribution of this research. The objective is to maximize the throughput of the flowshop by obtaining optimal schedules. As for given degree cycles, it is equivalent to minimizing the cycle time. Operations in robotic flowshops considering multi-degree cycles are analyzed in detail. Based on the analyses, a mixed integer linear programming model is formulated for this challengeable problem. A numerical example modified from the previous work is used to illustrate the model proposed, which is solved by CPLEX. Results show the benefits of the model, especially considering multi-degree cycles.
Original languageEnglish
Pages (from-to)62-75
Number of pages14
JournalJournal of Manufacturing Systems
Publication statusPublished - 1 Jan 2015


  • Mixed integer linear programming
  • Multi-degree cycles
  • Multiple hoists without overlapping
  • Parallel machines
  • Robotic cells

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Industrial and Manufacturing Engineering
  • Hardware and Architecture
  • Software

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