| When the position feedback of the electro-hydraulic position servo system adopt the external feedback sensors, the clearance would exist in transmission chain between the piston rod and the position sensors because of the installation, abrasion, impact and other reasons. This would cause backlash nonlinearity of the feedback path, impact the control accuracy and stability of the system, make the system work unstable.For feedback channel clearance exists, according to the system input-output and low damping characteristics, the hysteretic clearance model is selected, the model of electro-hydraulic position servo system with feedback channel clearance is established. The different dimension clearance value of electro-hydraulic position servo system is simulated by Matlab/Simulink, the results of simulation indicates:(1) the greater clearance between the channel feedback, the unit step response of system adjustment time is longer and the oscillation more intense;(2) when the value of the feedback channel clearance increased to 0.08 mm, the system occurs limit cycle oscillations and cannot work stable;(3) when the feedback channel clearance value is increased to 0.1mm, the overshoot of the system from 37.08% to 43.85%.The clearance of nonlinear compensation algorithm is designed: The control process is divided into four states(ascent stage, clearance stage, initial steady state stage and steady state stage) According to the two samples displacement difference valueand displacement rate; on this basis, the electro-hydraulic position servo system feedback channel clearance state is distinguished,the PID control parameters of the electro-hydraulic position servo systems in clearance state are obtained by experimental cut-and-trial method, then, the clearance compensation is achieved.To validate the simulation results and the compensation algorithm, run the different clearance value of electro-hydraulic position servo system step response experiments, experimental the results of experimental indicates: when the feedback channel does not exist clearance, step response electro-hydraulic position servo system is almost non-existent the steady-state error and limit cycle oscillations; when the feedback channel clearance increases from 1mm to 3mm, the overshoot of step response of electro-hydraulic position servo system increased obviously and limit cycle oscillation occurs, and as the clearance increases, the frequency of limit cycle oscillations reduced; when experiment with the clearance of nonlinear compensation algorithm, the overshoot of step response of electro-hydraulic position servo system decreased obviously or even disappeared, substantially inhibited the phenomenon of limit cycle oscillations. Sothecompensationalgorithm for the clearance is efficiency.The experiment researching project of the clearance influence on the electro- hydraulic position servo system is designed, The possibility of using PLC as the controller is verified from the cycling scanning time and the realize of the complex algorithm, selecting the PLC as the controller, the control algorithm and compensation control algorithm is written by ladder diagram, the man-machine interface is designed by Labview, the serial communication of host compute and Omron CP1H-XA is achieved based on the Hostlink, the adjusting device and measuring devices of feedback channel clearance is designed. |
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