Ikuro Iimura

Suppression of Micro Stick-Slip Vibrations in Hydraulic Servo-System

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.

Hydraulic Servo System With Mechanically Adjustable Compliance

This paper deals with a hydraulic servo system with compliance control for the operation in an environment with frequent machine-human interaction. The compliance is mechanically adjusted in the present hydraulic system by changing the neutral position of the bridge valves between the full opening and the full closing states. The mathematical model of the system is first derived, and the static and the dynamic behavior of the system are investigated through numerical simulation. Since the present system exhibits a strong nonlinear characteristic in the operating condition of large compliance, a nonlinear controller is designed with the feedback linearization technique. In the operating condition of small compliance, on the other hand, a conventional linear control is applicable as usual hydraulic control systems. The performance of the present control system is investigated through both numerical simulation and experiment, justifying that the present hydraulic servo system continuously adapts its performance between a rigid positioning against disturbances and a compliant positioning to prevent damage to obstacles on the path.