Automata-based supervisory control logic design for a multi-robot assembly cell

Abstract

A complex multi-robot assembly cell should be controlled to satisfy control requirements such as obeying an assembly sequence, and freedom from deadlocks, livelocks, collisions, or wasteful behaviour. Once the control requirements are specified in a formal model such as automata or Petri nets and the specification satisfies a {\em controllability} qualification, such a specification for desirable behavior can be directly used as the control logic. When the control specification cannot prevent the system from falling into an undesirable state due to some uncontrollable events like breakdowns or alarm occurrences, the {\em supervisory control logic} should be derived by restricting the control specification further. Most studies on the modern supervisory control theory, based on the formal language theory, focus on deriving the controllable supervisory control logic, called the {\em supremal sublanguage}, from a priori given formal control specification for the desirable behavior, called the {\em legal language}. However, the most essential part of supervisory control logic design is to develop the formal control specification itself from the control requirements. While most supervisory control logic design works concentrate on logical control, a supervisory control logic for a manufacturing system should optimize the performance as well as satisfying the logical control requirements. Further, since most error recovery procedures tend to be specified by the domain knowledge of manufacturing or system engineers, we need a systematic way of incorporating such practical error recovery procedures into the supervisory control logic.

In this work, we propose a practical way of designing a supervisory control logic for a multi-robot assembly cell based on a automata-based formal control specification. The proposed method has three design phases, such as logical control logic design, performance control logic design, and error-recovery control logic design. We first ...