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Digital control system for mechanical damping of suspended mass

In this paper we present a digital control system designed to damp the mechanical motion of a suspended mass. The control system is based on optical levers for reading the position of the mass with respect to some fixed references. The reading system was implemented by using a laser beam, produced by a commercial laser diode, and two position sensing photodiodes as components. The laser light is reflected from the suspended mass and the reflected beam is sent to the position sensing photodiode. Each beam can be used to control more than one degree of freedom of the mass by simply using a suitable optical arrangement to uncouple translation and rotational motions. The digital control system is based on both standard linear signal filtering and on a non linear section. The latter is necessary to solve particular situations, like the very large motion, a situation in which standard control system techniques are often not adequate. Moreover the control system has to take into account all the degree of freedom of the suspended mass, also to avoid the excitation of some extra resonance due to the coupling of the different motions.