On Throughput Maximization in Constant Travel-Time Robotic Cells

Abstract:  We consider the problem of scheduling operations in bufferless robotic cells that produce identical parts.  The objective is to find a cyclic sequence of robot moves that minimizes the long-run average time to produce a part, or equivalently, maximizes the throughput rate.  The robot can be moved in simple cycles that produce one unit or, in more complicated cycles, that produce multiple units.  Because one-unit cycles are the easiest to understand, implement and control, they are widely used in industry.  We analyze one-unit cycles for a class of robotic cells called constant travel-time robotic cells.  We complete a structural analysis of the class of one-unit cycles and obtain a polynomial time algorithm for finding an optimal one-unit cycle.

Constant travel-time robotic cells are used in real manufacturing operations that the authors have encountered during their interactions with companies.  The results and the analysis in this paper offer practitioners (i) a tool to experiment with and study the design of a proposed robotic cell during a prototyping exercise, (ii) a lower bound on the throughput of a robotic cell to help them make an informed assessment of the ultimate productivity level and (iii) a benchmark throughput level (for comparison purposes) for robotic cells whose operations differ slightly from those discussed in this paper.