Flow time in a human-robot collaborative assembly process: Performance evaluation, system properties, and a case study

In this article, an analytical method is introduced to evaluate the flow time of an assembly process with collaborative robots. In such a process, an operator and a collaborative robot can independently carry out preparation tasks first, then they work jointly to finish the assembly operations. To study the productivity performance of such systems, a stochastic process model is developed, where the joint work is modeled as an assembly merge process, and the task times of all operation steps are described by phase-type distributions. Closed-form solutions of system performance, such as flow time expectation and variability, as well as service rate, are derived analytically. The system properties of monotonicity, work allocation, and bottleneck identification are investigated. In addition, a case study is introduced to evaluate the performance of a front panel assembly process in automotive manufacturing.