In general a hydraulic system which uses a single rod hydraulic as an actuator is modeled as a nonlinear system. Especially it is well known that the system reveals uncertain parameter characteristics such as the density variation of hydraulic oil and is subjected to load variations and severe disturbances during operation. In order to cope with these undesirable internal and external problems, a nonlinear and time-varying control theory is needed and must be developed.
This paper is devoted to three main objectives eventually to accomplish a synchronizing position control of multiple hydraulic cylinders.
At first, a fuzzy PID control algorithm is thoroughly discussed which has nonlinear time-varying control parameters and is named a variable design-parameter fuzzy PID control. It is developed to control the systems whose mathematical dynamics are unknown and whose behaviors reveal nonlinear system characteristics. By way of computer simulations for several example systems, the effectiveness of the suggested algorithm is proved and the online time variation characteristics of the PID control parameters such as K_p,K_d and K_i are investigated.
At second, the discussed variable design-parameter fuzzy PID algorithm is applied to the position control of a single rod hydraulic cylinder system as a real control world of typical nonlinear systems. Computer simulation results reveal that the composed system is useful and effective in view of control performance and real time control possibility.
At last, a comprising method of position-synchronizing control of multiple hydraulic cylinders is suggested. The method is to comprise the control system using only electronic devices including synchronizing control algorithm. In order to prove the usefulness of the suggested method, computer simulations are executed for two cases. One is the case two cylinders have the same specifications except for different operating conditions. The other is the case two cylinders have different specifications as well as different operating conditions.
In the conclusion, according to the simulation results, the discussed variable design-parameter fuzzy PID control algorithm turned out adequate to control nonlinear systems and revealed very accurate PID control actions regardless of operating input ranges. The suggested position-synchronizing control method was proved so effective that it could be applied to the synchronizing control of multiple hydraulic cylinders with small position differences.