A Research On MRF-damper-based Pneumatic Positioning Control Of Linear Actuator

Pneumatic systems have many obvious advantages and are widely used in the field of industrial automation.Pneumatic proportional control system has become one of the important researching subjects in the field of pneumatic servo technology because of its low cost,conciseness and contamination-free character.However,due to the intrinsic drawback of gas medium,nonlinearity of the system and the influence of the nonlinear friction of actuator, it is difficult to achieve a satisfactory positioning control result.To solve this problem, researchers have been trying to overcome the difficulties,and some achievements have been obtained.But most of them are not suitable to use in the practical production field because of their complexity and unstable performance.P.I.D is the core of classical control theory,and the knowledge about it has been well mastered by the control society.Due to the simplicity of its control strategy,easy tuning and high reliability,it is widely used in the control field,especially in the case where the system accurate transfer function can be obtained.However,it is sensitive to the change of system parameters and disturbance.The main cause of the sensitivity is as follows:the use of P.I.D in the field of nonlinear systems is based the theory of minute range linearization and the system parameters must keep their values within small range around the operation point.Accordingly, for the pneumatic positioning control system,the main parameters,such as mass flow rate and pressure of the actuator,must keep their values within small range around the set operation point.To solve the problems above,a P.I.D based DSDRV(different section different resistance of viscosity)control method is proposed.Namely,before the plant approach the target point to a certain distance,the positioning system is in the state of low viscous resistance,and the plant moves toward target point at full speed so as to shorten the running time.After it approach the target point to a certain distance,the control system turns to the state of suitable viscous resistance by means of switching on the excitation electric current of the magneto-rheological fluid(MRF)damper that mechanically connected to the cylinder slide to improve the dynamic properties of the system.The other role the MRF damper plays is to stabilize the system operation point and to keep the system varying parameters within a small range.Here,the operation premise of P.I.D is fulfilled,and the P.I.D's profit of simplicity, easy tuning and reliability could be taken to set up controller to curb pneumatic cylinder positioning control system.To solve friction-caused chattering around the target point,the friction compensation method is adopted.The compensation is based on the certain function about friction and velocity.Only coulomb friction is compensated and leaves the viscous friction to serve as a beneficial factor to the system dynamics.Simulation results show the method is efficient at any position of the cylinder stroke and a good result has been achieved in the pneumatic linear cylinder positioning control.