Analysis and Design of a Valve-Controlled Hydraulic Device

Abstract

When the load of an actuator consists of a mass and friction for a valvecontrolled hydraulic device, the exact responses are obtained analytically for rectilinear inputs. As any type of input can be approximated by a connection of straight lines, the responses to various types of inputs can be calculated. An important application of the analysis is to obtain the frequency characteristics. As the sinusoidal input can be approximated by a proper trapezoid, the rectilinear inputs are applied to each straight range of the trapezoid. By this approach, the frequency characteristics for the case of considerably high frequency or heavy load for common hydraulic servos are made clear. The analytical results are shown in normalized forms and are approximated by the responses which are calculated by the equivalent transfer functions. The analytical results were verified by experiments. Another important application of the analysis is to make clear the effects of the dither applied to the spool. The wave shape of the dither is also approximated by a proper trapezoid, and the responses to the rectilinear inputs are applied to each straight range of the trapezoid. The results of calculations are represented by an equivalent transfer function, and it was made clear how the dither affects the gain and the time constant. The equivalent transfer functions are very useful to design the hydraulic servomechanism. In this paper, the design criterion which is based on the performance of the hydraulic device, particularly that of the frequency characteristics, is given.