This paper deals with suppression of two kinds of micro stick-slip vibrations occurring in a typical computer-controlled hydraulic servo-system. The relevant system consists of a single-rod hydraulic cylinder, an electrohydraulic servo-valve and a personal computer. The discontinuous control signal from a $D/A$ converter causes a stick-slip vibration of micron order of magnitude over a wide range of the feedback gain. Increasing the feedback gain results in the other stick-slip vibration of nearly ten times larger amplitude due to the nonlinear pressure-flow characteristic of the servo-valve. The numerical simulation revealed the latter micro stick-slip vibration could be efficiently suppressed with the feedback linearization technique to compensate the nonlinearity of the servo-valve, while the former one reduced by improving the resolution of the $D/A$ converter. Validities of both the methods were also confirmed with experiment. [S0022-0434(00)00102-7]

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