Generalized predictive control approach for a modified single acting pneumatic cylinder

Abstract

Pneumatic actuator is a device that converts air pressure to possible motions such as linear and rotary motion. Although the pneumatic actuator offers many advantages it is difficult to control. This is due to the nonlinearities involved such as friction and air compressibility. The equipment used in this research is the Intelligent Pneumatic Actuator (IPA). Previously, Proportional-Integral (PI) has been used as the controller for the IPA. Based on the previous result, a controller called generalized predictive controller (GPC) is proposed. Compared to PI, this controller has the capability to take into account the nonlinearity factor which is very important in this research. There are two types of GPC proposed in this research which are GPC with First Order Time Delay (GPC-FOTD) and GPC with Higher Order (GPC-HO). This research starts with the implementation of PI, GPC-FOTD and GPC-HO controllers for position and force control in simulations. Then, the simulation result is validated with the real-time experiments. There are two experiments for position control, which are position control with and without loads and one experiment for force control. Then, a Haptic Pneumatic Device (HPD) is developed in order to emulate a spring by combining the position and force control. By implementing the spring characteristic to the pneumatic device, a human machine interaction concept is applied to the device. In summary, GPC-FOTD shows better performance compared to GPC-HO and PI in terms of stability and better response for position control. For force control the GPC-HO shows better performance compared to other controllers in terms of tracking and accuracy. Then for the spring characteristic implementation, response of force versus displacement is presented where the results show stiffness coefficient (Ks ) is directly proportional to the output force generated. This device together with GPC controller are capable of giving better results in terms of spring characteristic emulation control compared to the previous research on IPA. These results and application hopefully can be used to help people such as in rehabilitation sector, as exercise equipment and entertainment tools as well as comparison data for other controller development.