Dual-stage Soft Landing for a Pick-and-place Manipulator

In this paper we document a systematic solution to a particular motion control problem called soft landing encountered in the design of pick-and-place machines for the semiconductor industry. The problem has already been studied for a single actuator, and a solution for the case of voice-coil motors has already been implemented in commercial drivers. Here we investigate a more complex setup consisting of two translation stages, which make the problem over-actuated; furthermore, the inner stage (actuated by a voice coil motor) is preloaded with a weight- compensating spring. Our systematic approach is based on the concept of reaction force observer. Its functionality is demonstrated using numerical simulations and laboratory experiments. We compare the proposed method with a baseline solution based on a simple extension of an existing method. A related Simulink model and Matlab scripts are available for free download to help reproduce the results.