Improvement of spring forming accuracy using minimum-variance control

In this paper, we consider the control problem of spring forming machine. Helical springs are usually made of long stock wire which is fed into forming machine. A spring forming machine can force wire into a coiled shape, but the length of the produced spring is varying according to the internal stress of wire, mechanical uncertainty of the forming machine etc. To improve the accuracy of free length of spring produced by forming machine, we propose to adopt minimum-variance control strategy for each production cycle.