538 Cycle-to-Cycle Feedback Control and its Application to Sheet Metal Forming

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In-process control of metal forming processes is often difficult owing to the lack of access to shape during the process and the lack of control inputs to the process. Consequently, such processes are usually left to statistical process control methods, which only identify problems without specifying solutions. The use of feedback control on a cycle to cycle basis (i. e. measurement and control between process cycles) has the prospect of improving over statistical monitoring without incurring the limitations of high-bandwidth in-process feedback. Simple single input-single output systems of this type have been analyzed and implemented at MIT on both simple metal bending and plastic molding processes with encouraging results. These include rejection of mean value errors and bounded changes in process variance. In this paper we address the extension of cycle to cycle control to the multivariable case, with an eye to a three-dimensional sheet forming shape control problem. This problem arises from the effort at MIT to control a process with a reconfigurable tool surface. With thousands of degrees of freedom, the choice of a suitable control algorithm is vital.