Position Control Of Pump-controlled Asymmetric Cylinder With Model Predictive Control Algorithm

Hydraulic systems are widely used in industries due to their high power density performance.Over the last decade,with the improvement of proportional pump technology,pump-controlled asymmetric cylinders have been used in more and more applications in various fields,such as injection molding machine,metal forming hydraulic press.Compared with traditional closed bidirectional pump-controlled asymmetric cylinders,opened unidirectional pump-controlled asymmetric cylinders have a simple structure and avoid flow balance issue.However,some control difficulties occur.On one hand,as unidirectional pumps fails to rotate in the opposite direction,the position of the direction valve must be changed and this will lead to a nonlinearity problem.On the other hand,it is very hard to realize and satisfy the demands of nonovershooting and pressure constraints by using conventional control methods.In this paper,researches about the position control of an opened unidirectional proportional pump-controlled asymmetric cylinder used in a powder forming hydraulic press have been made.A three-order state space model with constraints based on flow continuity equations and force balance equations is proposed in order to analyze the working principle of the powder forming hydraulic press.In addition,this paper proposes a design of a model predictive controller applicable to three-order systems based on model predictive control theory and Laguerre Function.This controller can effectively decrease the need of computer memory and improve the control performance.Experiments are carried out to validate the real-time performance of the unidirectional proportional pump-controlled asymmetric cylinder with the use of A/D and D/A converters and based on MATLAB xPC hardware-in-loop simulation platform.Research results indicate that a three-order linear model with input and output constraints can describe unidirectional proportional pump-controlled asymmetric cylinders' behavior and a model predictive control method with the use of the Laguerre Function can successfully resolve the overshooting problem.The model predictive controller based on the Laguerre Function provides a very good setpoint ramp tracking and an acceptable real-time performance.