Online stochastic control of dimensional quality in multistation manufacturing systems

Abstract

In the current paper, a control law is devised for flexible tooling element adjustments in a multistation manufacturing system based on the in-process product measurements and the state-space model of dimensional error flow through this system. The control law is devised so that the dimensional product quality at the end of the line is as close to the nominal as possible in the least squares sense, taking into account the measurement and process noise, as well as the accuracy of actuation of flexible tooling elements. The condition of controllability of product quality is introduced and dimensional quality variations of the product with and without the newly introduced stochastic quality control law are compared. It is proven that the newly proposed control algorithm reduces variations of dimensional product errors and that the controllability condition is beneficial to both the expected product quality as well as for its variations. Capabilities of the newly proposed method for stochastic control of dimensional quality in multistation manufacturing systems are illustrated in an example of a machining system used for the manufacturing of an automotive cylinder head by a major automotive manufacturer.