• Journal of the Korean Society for Precision Engineering
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• v.34 no.4
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• pp.265-272
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• 2017

Velocity ripple in manufacturing processes reduces productivity and limits the precision of the product. In practice, the frequency and phase of velocity ripples always change minutely, which makes it impossible to compensate for the ripple by simply inserting an opposite feed-forward signal in the system. In this study, an active-phase compensation algorithm was developed to enable the velocity-ripple controller to track the phase change of the ripples in real time. The proposed controller can compensate for the velocity ripple whatever its cause, including disturbance by the torque ripple. The algorithm consists of three functional modules: the velocity-ripple extractor, the synchronized integrator, and the phase shifter. Experimental results showed that the proposed controller clearly reduces velocity ripples with phase variation.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1489-1494
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• 2003

A neuromuscular control system of a myoelectric prosthetic hand (PH) constitutes a nonlinear system with a dead zone whose magnitude is equal to its joint angle when the PH just grasps an object. This is because the neuromuscular control system remains an open-loop system until the PH grasps the object but it constitutes a feedback control system after the PH griped the object in which a torque induced in the fingers of the PH is fed back. To improve the transient performance of the control system, it is desirable to make the feed-forward gain as large as possible, so long as the stability of the system is not impaired. It is also desired that the control system remains stable even when the PH lifts a heavy or rigid object, because this makes the closed loop gain large and leads to the closed system unstable. According to the theory of stability analysis of nonlinear systems, we can only know the sufficient conditions that the system should be stable. Thus the nonlinear theory on stability is insufficient to be used to design the neuromuscular control system for improving its transient responses. This paper shows that the nonlinear system with a dead zone can be approximated to a linear feedback system and that well-known methods of analysis and design on linear control systems can be applicable. It is also shown through various simulation results that errors induced by approximation are practically negligible and thus the design methods are quite accurate.