Variable gain motion control for transient performance improvement

In this paper, we introduce variable gain controllers for linear motion systems designed to improve transient performance. In particular, we focus on the well-known tradeoff induced by integral action, which removes steady-state errors due to constant external disturbances, but deteriorates transient performance in terms of increased overshoot. We propose a switched integral controller (SIC) and a variable gain integral controller (VGIC), which both limit the integral action if the error exceeds a certain threshold and balance this tradeoff in a more desirable manner. The resulting nonlinear controller structure consist of, on the one hand, loop-shaped linear controllers, and on the other hand, the variable gain element. This structure makes the design and tuning of the variable gain controller intuitive for motion control engineers. The results are illustrated by application of the VGIC and SIC to an experimental set-up.