This project aims to develop a novel large stroke asymmetric pneumatic servo system of a hardware-in-the-loop for path tracking control under variable loads based on the MATLAB Simulink real-time system. High pressure compressed air provided by the air compressor is utilized for the pneumatic proportional servo valve to drive the large stroke asymmetric rod-less pneumatic actuator. Due to the pressure differences between two chambers, the pneumatic actuator will operate. The highly nonlinear mathematical models of the large stroke asymmetric pneumatic system were analyzed and developed.
The functional approximation technique based on the sliding mode controller (FASC) is developed as a controller to solve the uncertain time-varying nonlinear system. The MATLAB Simulink real-time system was a main control unit of a hardware-in-the-loop system proposed to establish driver blocks for analog and digital I/O, a linear encoder, a CPU and a large stroke asymmetric pneumatic rod-less system. By the position sensor, the position signals of the cylinder will be measured immediately. The measured signals will be viewed as the feedback signals of the pneumatic servo system for the study of real-time positioning control and path tracking control.
Finally, real-time control of a large stroke asymmetric pneumatic servo system with measuring system, a large stroke asymmetric pneumatic servo system, data acquisition system and the control strategy software will be implemented. Thus, upgrading the high position precision and the trajectory tracking performance of the large stroke asymmetric pneumatic servo system will be realized to promote the high position precision and path tracking capability. Experimental results show that fifth order paths in various strokes and the sine wave path are successfully implemented in the test rig. Also, results of variable loads under the different angle were implemented experimentally.
THE SENSOR-INTEGRATED HARDWARE-IN-THE-LOOP OF A LARGE-STROKE ASYMMETRIC PNEUMATIC SERVO SYSTEM
Figure 2 presents the system architecture of the proposed sensor-integrated hardware-in-the-loop of a large-stroke asymmetric pneumatic servo system. In the PC-based control unit, a main computer unit (MCU) is responsible for processing the integrated digital/analogue processing system (DAPS) and a large-stroke asymmetric pneumatic servo system. The DAQ cards are installed and used to output the control signals and receive the input signal data from the optical encoder sensor.
ESTABLISHMENT OF DYNAMIC MODELS FOR THE PNEUMATIC SYSTEM
Figure 4 shows an architecture of a large stroke pneumatic system. In this study, the pneumatic system mainly consisted of a large rod-less pneumatic cylinder and a pneumatic proportional valve. The nonlinear dynamic models in the mathematic forms can be described in four parts: models of a pneumatic valve, mass flow rates of pneumatic cylinder, continuous equations and loading motion equations.
The designed controller was used to solve the problems of system non-linearity and time variation and thereby to control the large-stroke trajectory of the proposed system. The function approximation technique was the foundation of the mathematical models for the proposed system because such models are generally complex and accurate models can be difficult to obtain. Therefore, the functional approximation technique based on the sliding mode controller (FASC) is developed as a controller to solve the uncertain time-varying nonlinear system. The block diagram of a large stroke asymmetric rod-less pneumatic system is shown in Figure 5.
Figure 6 shows the hardware-in-the loop of a large-stroke asymmetric pneumatic servo system which consists of MCU, DAPS, a rod-less pneumatic cylinder, a proportional pneumatic valve and an air reservoir. The nonlinear controller, FASC, runs on PC via MATLAB Simulink real-time environment that can support reliable real-time control by digital I/O and analogy I/O for high precision and synchronization.
In this study, a hardware-in-the-loop of a large-stroke asymmetric pneumatic servo system by incorporating sensing components was developed and implemented for real-time path tracking control. A rod-less pneumatic actuator, a large stroke cylinder, was assigned in a vertical direction, where gravity effects render asymmetric motions. The mathematical models of a large-stroke asymmetric pneumatic system were analyzed in analytical forms. In order to implement the real-time control for a large-stroke asymmetric pneumatic servo system, the FASC was applied in the test rig based on MATLAB Simulink real-time environment.
Afterwards, the experimental system was fully designed and established; the fifth path and the sine wave path are proposed to perform real-time control by analyzing data collected from sensor components to realize accurate positioning tracking performance for the large-stroke asymmetric pneumatic servo system. Also, different loading experiments under 45 degrees are verified experimentally. Compared with the relevant nonlinear controllers, the proposed FASC offers a better performance, with maximum errors of 0.222%, for the real-time path tracking servo system.
Source: Feng Chia University
Author: Hao-Ting Lin