| In the servo control system,the friction characteristics of the cylinder is an important reason for the nonlinear generation of the system.Therefore,more and more scholars have been involved in the research of cylinder friction in recent years,and set up a variety of test platforms for cylinder friction.Based on the analysis and research of the test platform of cylinder friction built by predecessors,and summarizing the shortcomings,the test platform of friction between two cylinders is designed and built.In order to ensure that the pressure in the same chamber of the two relative mounted cylinders(the cylinder diameter is equal)is the target value,a pressure control system is designed.The theoretical analysis and experiment verify that when the test platform is used,the measurement value of the tension pressure sensor in the platform is only the sum of the friction force of the two relative mounted cylinders,which can effectively avoid the influence of pressure control or test error on the friction test accuracy.The valve control element used in pressure control system is proportional directional valve.The existence of dead zone of proportional directional valve is an important factor leading to the system nonlinearity.It can improve the response speed and control accuracy of the control system by identifying the dead zone of proportional directional valve and compensating it.Based on the research of the dead zone test method of proportional directional valve proposed by domestic and foreign scholars,a new method of identifying the dead zone of proportional directional valve is designed.The method can recognize the dead zone only by gas pressure sensor and some common equipment.According to the test results,the dead zone of the valve is compensated.Based on the common PID comparison of the pressure control system before and after the dead zone compensation,it is found that the control accuracy and response speed of the system are improved after the dead zone compensation of the proportional directional valve is carried out.Although the ordinary PID is simple and easy to grasp,it can not realize the self-tuning of parameters in the control process.In order to improve the flexibility of the pressure control system,the fuzzy PI control strategy is used to control the pressure of the gas tank.Through comparison with the ordinary PID control,it is found that the fuzzy PID control system has faster response speed and better flexibility.According to the experimental phenomena,the influence of air pressure,speed,cylinder installation and cylinder disassembly on friction test is analyzed,and the standard operation of friction test is put forward.Two cylinder banks with 32 mm and 50 mm diameter are selected.Based on both Single cylinder and double cylinder friction test platform,the influence of working pressure and pressure difference on the friction of cylinder is studied.The results show that the friction force of the cylinder under test increases with the increase of working pressure.The pressure difference has different influence on the friction force of the cylinder,among which the pressure difference has a small influence on the friction force of the cylinder(DSBC-32-150-PPVA-N3)produced by Festo company,and the friction force only increases with the increase of the pressure in the two chambers of the cylinder,and the friction force of the other cylinders measured decreases with the increase of the pressure difference on the value. |
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