| Clearance is a typical multi-value nonlinear characteristic, which often leads to the accumulation of energy in the servo control system, and then causes instability or self-sustained oscillations of the system. During the development of the electro-hydraulic position servo control system, it found that a clearance is existed in the ball joint connection, which cited between the hydraulic cylinder piston rod earrings and load. This clearance will cause the steady-state error of unit step response increasing, overshoot increasing and turmoil intensifying, even induce limit cycle oscillation of system when clearance is larger, and seriously make the design of control system fail.For solving these problems, based on the analysis of the movement feature of the system from the active part across the clearance to the driven part, combining with a larger damping feature of system driven part, the electro-hydraulic position servo control system mathematical model containing the hysteresis clearance characteristic is established. With Matlab and AMEsim software, this paper simulated electro-hydraulic position servo control system with no clearance, and whose clearance size was respectively0.1mm,0.2mm,0.4mm,0.8mm and lmm, and analyzed the frequency response characteristics of the system containing the clearance, and its location response characteristics, speed response characteristics and force response characteristics in different clearance size. Based on the analysis of a variety of clearance compensation control method, for the clearance existed in the ball joint connection which cited between the hydraulic cylinder piston rod earrings and load, this paper proposed adding compensation cylinder at the load end, and then formed double cylinders linkage driven structure with the location system hydraulic cylinder. In the back and forth movement of load, compensation cylinder applied the force in the opposite direction of the location system hydraulic cylinder, which makes the load and the location system hydraulic cylinder always compress in a side of clearance, in order to achieve the approach of completely compensating system clearance. The modeling and simulation analyze using AMESim software showed that this method is fully compensating clearance system from structure.Finally, experimental study of the actual location of the electro-hydraulic servo control system whose largest clearance is1mm between a ball joint sleeve and the load shaft is carried out. Accordance with the specific parameters indicators of actual system, the hydraulic components and sensors required for the experimental system were selected; the monitoring section of experimental system was designed, and the combination of NI LabVIEW and Compact RIO slave computer to control electro-hydraulic position servo system was used. The results showed that with clearance increasing between the connection of ball joint shaft sleeve and load shaft, the unit step response oscillation intensifies, steady-state error increases and overshoot increase, even induce limit cycle oscillation phenomenon of system when clearance is about lmm. |
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