Integrating process planning and control for flexible production systems

The requirements for custom-oriented production lead to demands for increasingly flexible production processes. Flexibility can be interpreted at different time-scales. Object-oriented modeling supports long time-scale flexibility by simplifying the introduction of different equipment within the system without extensive reprogramming of the control system. Distributed product specification, where each (type of) product is specified independently of any other product that may be simultaneously produced, supports medium time-scale flexibility with feasible introduction of new products. Automatic synthesis of control laws, by use of the supervisory control theory, permits on-line recalculation of the control policies and thus supports short time-scale flexibility. We describe an integrated approach to increase flexibility of production-system control, where given a set of object-oriented resource models, and a set of distributed product specifications control-laws are automatically synthesized. Implementation-wise the approach is centered around a database holding all relevant information, such as the product specifications, the current states of the resources, etc.