Friction compensation control of an electropneumatic servovalve by using an evolutionary algorithm

Abstract

A poppet-type electropneumatic servovalve developed in this study utilizes a poppet directly operated by a moving-coil actuator in the metering stage and is controlled by a digital controller. This servovalve is insensitive to air contamination and has no problem of air leakage at null, but it has relatively large friction between the O-rings installed in the peripheral grooves of the balance pistons and the valve sleeve. For friction compensation control, a static friction model that enables simulation of the stick-slip phenomena and a dynamic model that captures the friction behaviour such as presliding displacement and varying break-away force are presented. The parameters for the friction models are identified by utilizing an evolution strategy, one of the evolutionary algorithms, which is a probabilistic global search algorithm based on the model of natural evolution. These friction models are then used in designing a non-linear friction compensation controller. It is found in the experiment that the electropneumatic servovalve has almost no hysteresis and that the friction compensation control significantly improves valve performance. The experimental results of the open loop test on poppet positioning agree well with simulation results of the valve model with identified friction parameters. It is also shown that the experimental results of friction compensation control using a static friction model show a small steady state error but those using a dynamic friction model show almost no such error.

Frictional Contact Finite Element Analysis of Pneumatic Cylinders

“…According to the piston seals' installation catalogue the material is NBR (acrylonitrile butadiene rubber). The density ρ of the seal is 1.31 g/cm 3 (see Table 2). The friction coefficient µ was chosen to be 0.05.…”

“…For example, Araki et al, [2] produced linear models of servopneumatic systems. Choi et al, [3] modelled the nonlinear friction property of an electro pneumatic servo valve. The friction model had two parts: a static and a dynamic one.…”

Study of “Sticking and Restarting Phenomenon” in Electropneumatic Positioning Systems

“…So a compromise must be found between the static error and the restarting occurrence. The solutions must be included in the control strategy as in [26][27][28][29][30]. It must be noticed that the results obtained in this paper are valid for every kind of control law for which the control value does not evolve during the partial mechanical equilibrium.…”

Adaptive robust control of a high-response dual proportional solenoid valve with flow force compensation

“…5 Adaptive control (AC) was introduced into solenoid valve controllers for accurate compensation. 16,17 Garvin and Mathew 18 developed a controller for a nonlinear servo valve by root locus analogy, and Chen et al 19 synthesized a throttle valve controller with Nyquist curve. Obviously, these linear design tools cannot address nonlinearity and present poor robustness to parameter uncertainty.…”