DIRECT AND INDIRECT ADAPTIVE PROCESS CONTROL OF SHEET METAL FORMING

摘要

This paper compares the design, implementation and performance of direct and indirect adaptive control (AC) to improve part quality in the stamping process in the presence of disturbances. First, previous work on the design and performance of a direct AC approach (i.e., model reference adaptive control or MRAC) is summarized. The direct AC filter uses nominal process parameters, and so requires some knowledge of the process. Consequently, an indirect AC approach, which estimates process parameters on-line, was also considered. However, due to the simple proportional plus integral (PI) control structure selected, the computation of the controller gains from the estimated parameters requires an optimization procedure, which is not amenable to real-time implementation. Consequently, the indirect AC is implemented using a look-up table, with controller gains that are pre-computed off-line via optimization. The indirect AC with the look-up table is compared to the direct AC via simulations and experiments in terms of tracking performance as well as part quality, in the presence of plant variations. The indirect AC, with a sufficiently high level of discretization in the look-up table, performs well in simulations. However, due to extensive memory requirements, a smaller look-up table is used in the experiments, where it is outperformed by the direct AC.