Human operator and robot resource modeling for planning purposes in assembly systems

This paper presents how robot and human resources can be modeled for planning purposes. Instead of using simplistic models such as available or unavailable resources, the method for modeling resources presented in this paper integrates parameters that are realistic and relevant for the considered assembly system. For example, a robot resource model can take into account maintenance tasks and ramp-up parameters. The framework of this modeling is based on the definition of Sequences of Operations (SOPs) and includes a formal relation between product operations and resources abilities. The main idea is to avoid the representation of long and static sequences of operations, since this typically reduces flexibility and is even intractable for large systems. To tackle this issue, relations between operations and resources are defined using only strictly necessary pre-conditions and post-conditions for each individual operation. The Sequences of Operations that permit to express the minimally restrictive behavior of an assembly system are automatically generated. Finally, the SOPs can be viewed from different angles, e.g. from a product or a resource perspective. These multiple views increase the interoperability between different engineering disciplines. Experiments have shown that, even for simple examples, obtaining the optimized assembly sequence is not an easy task. That is why a sequence planning software associated to realistic resource models, including both humans and robots, as presented in this paper, is a crucial help to increase flexibility in assembly systems that require different Levels of Automation.