An Approach to Control Input Shaping With Application to Coordinate Measuring Machines

Dimensional measurements obtained with Coordinate Measuring Machines (CMMs) are negatively affected by self-induced structural vibrations. In this paper, a control strategy that reduces the structural vibrations in a CMM is outlined and experimentally demonstrated. The control strategy, designated the Feedforward Filter, is developed by establishing the relationship between contemporary controller input shaping techniques and traditional notch filtering methods. Issues on both robustness and multiple mode vibrations are addressed. Controller input development takes place in the discrete time domain. This method provides results identical to those for optimal command input preshaping obtained through non-linear programming methods and requires considerably less computational effort. Experimental results show a 50 percent reduction in the peak-to-peak magnitude of structural vibrations as compared to unshaped bang-bang trajectories.