Friction compensation for a pneumatic proportional valve based on dither effect

The friction of a pneumatic proportional valve is the major reason resulting in the valve dead zone. The relation between the valve friction and the spool radial unbalanced force is analyzed, the friction compensation mechanism with high-frequency low-amplitude dither signals acting on the valve is discussed based on vibrational effects, and the friction compensator is designed by use of VC + + and LabVIEW. Experimental results show that compensation is obtained by adding dither signals to the control signal to keep the spool vibrating persistently, the proportional valve friction is obviously reduced, the system crawl disappears, and the time delay is shortened. The proposed friction compensation method is shown to be valuable in engineering.