Neural-network adaptive controller for nonlinear systems and its application in pneumatic servo systems

In this paper, a novel control law is presented, which uses neural-network techniques to approximate the affine class nonlinear system having unknown or uncertain dynamics and noise disturbances. It adopts an adaptive control law to adjust the network parameters online and adds another control component according to H-infinity control theory to attenuate the disturbance. This control law is applied to the position tracking control of pneumatic servo systems. Simulation and experimental results show that the tracking precision and convergence speed is obviously superior to the results by using the basic BP-network controller and self-tuning adaptive controller.

2D VARIABLE FACTOR LEARNING CONTROLLER AND ITS APPLICATION IN PNEUMATIC SERVO SYSTEM

A new learning control law is presented which can obtain learning gain matrices from a recursive identifier along the learning axis. The system convergence is proved when disturbances exist in the system. Finally it is applied to pneumatic servo control system, the experiment results show its validity.

Motion synchronization of dual-cylinder pneumatic servo systems with integration of adaptive robust control and cross-coupling approach

We investigate motion synchronization of dual-cylinder pneumatic servo systems and develop an adaptive robust synchronization controller. The proposed controller incorporates the cross-coupling technology into the integrated direct/indirect adaptive robust control(DIARC) architecture by feeding back the coupled position errors, which are formed by the trajectory tracking errors of two cylinders and the synchronization error between them. The controller employs an online recursive least squares estimation algorithm to obtain accurate estimates of model parameters for reducing the extent of parametric uncertainties, and uses a robust control law to attenuate the effects of parameter estimation errors, unmodeled dynamics, and disturbances. Therefore, asymptotic convergence to zero of both trajectory tracking and synchronization errors can be guaranteed. Experimental results verify the effectiveness of the proposed controller.

Control strategy for pneumatic rotary position servo systems based on feed forward compensation pole-placement self-tuning method

The pneumatic rotary position system, in which an electro-pneumatic proportional flow valve controled a rotary cylinder, was studied, and its mathematical model was built. The model indicated that the controlled pneumatic system had disadvantages such as inherent non-linearity and variations of system parameters with working points. In order to improve the dynamic performance of the system, feed forward compensation self-tuning pole-placement strategy was adopted to place the poles of the system in a desired position in real time, and a recursive least square method with fixed forgetting factors was also used in the parameter estimation. Experimental results show that the steady state error of the pneumatic rotary position system is within 3% and the identified system parameters can be converged in 5 s. Under different loads, the controlled system has an excellent tracking performance and robustness of anti-disturbance.

Pneumatic force servo system based on disturbance observer

In order to design a low-cost pneumatic force servo system with large output forces,a scheme of a booster cylinder controlled by high speed solenoid valves is proposed.A nonlinear model of the system is established,in which the hysteresis of high speed solenoid valve is considered.In order to deal with parameter uncertainty and disturbances of noise and friction,a feed-forward control method based on a disturbance observer is proposed.A practical pneumatic force servo system is used to testify the feasibility of the proposed controller.The experimental results show that pneumatic force servo system based on the proposed controller has high force tracking accuracy and quick response.

Adaptive Backstepping Slide Mode Control of Pneumatic Position Servo System

With the price decreasing of the pneumatic proportional valve and the high performance micro controller, the simple structure and high tracking performance pneumatic servo system demonstrates more application potential in many fields. However, most existing control methods with high tracking performance need to know the model information and to use pressure sensor. This limits the application of the pneumatic servo system. An adaptive backstepping slide mode control method is proposed for pneumatic position servo system. The proposed method designs adaptive slide mode controller using backstepping design technique. The controller parameter adaptive law is derived from Lyapunov analysis to guarantee the stability of the system. A theorem is testified to show that the state of closed-loop system is uniformly bounded, and the closed-loop system is stable. The advantages of the proposed method include that system dynamic model parameters are not required for the controller design, uncertain parameters bounds are not need, and the bulk and expensive pressure sensor is not needed as well. Experimental performance, as compared with some existing methods. results show that the designed controller can achieve better tracking

Improvement of Dynamic and Steady Characteristics of Pneumatic Position Servo with Fuzzy-PI Control

This paper provided a fuzzy-PI control. It makes use of the advantages of fuzzy controller for dynamic characteristics, and the advantages of PI control for steady characteristics of pneumatic position servo. Experimental results show that positioning accuracy meets the conventional industrial needs, and prove that the fuzzy-PI controller to be correct and more effective than the usual PID controller. The control method improve the dynamic and steady characteristics of the system.

Performance analysis of a pneumatic to servo converted system for electrode actuation in resistance spot welding using 304L austenitic stainless steel

A high current, AC waveform controller with C-type body frame of spot welder(75 k VA), was examined for the electrode actuating system whose pneumatically driven system has been redesigned and refitted for the servo based system without any vertical spring assistance in the 50 mm movable distance. Moreover, the pressing mechanism was carefully handled during the entire pressing tasks as to ensure that no catastrophic reaction happens for the electrodes' caps, electrodes' holders as well as the other part of mechanical assembly. With the mechanically originated-pneumatic and also the converted-servo systems, the stainless steels are welded for both systems to characterize the improvements. While the welding processes were carried out, the electrical signals have been captured to compute the signals' representation of entire sequences. Later, the welded samples were underwent the tensile shear test, metallurgical observation and hardness test. The analytical results show distinct changes in the force profiles which has led to profound changes in mechanical properties of welded specimens.

Adaptive Robust Tracking Control of Pressure Trajectory Based on Kalman Filter

When adaptive robust control（ARC） strategy based on backstepping design is applied in pneumatic servo control, accurate pressure tracking in motion is especially necessary for both force and position trajectories tracking ofrodless pneumatic cylinders, and therefore an adaptive robust pressure controller is developed in this paper to improve the tracking accuracy of pressure trajectory in the chamber when the pneumatic cylinder is moving. In the proposed adaptive robust pressure controller, off-line fitting of the orifice area and on-line parameter estimation of the flow coefficient are utilized to have improved model compensation, and meanwhile robust feedback and Kalman filter are used to have strong robustness against uncertain nonlinearities, parameter fluctuations and noise. Research results demonstrate that the adaptive robust pressure controller could not only track various pressure trajectories accurately even when the pneumatic cylinder is moving, but also obtain very smooth control input, which indicates the effectiveness of adaptive model compensation. Especially when a step pressure trajectory is tracked under the condition of the movement of a rodless pneumatic cylinder, maximum tracking error of ARC is 4.46 kPa and average tracking error is 0.99 kPa, and steady-state error of ARC could achieve 0.84 kPa, which is very close to the measurement accuracy of pressure transducer.

Research on the dynamic characteristics of pneumatic proportional regulator in pneumatic-loading system and design of fuzzy adaptive controller

Pneumatic proportional control servo regulator is the core component of a pneumatic-loading experimental system,which is very important in solving the overcharging problem.However,previous research on control of pneumatic proportional regulator in a pneumatic-loading experimental system led to failure in analysis of the influence of opening error of the switch regulator because it did not analyze the regulator basic working principle and process.The traditional control method cannot fully solve the overcharging problem nor ensure adequate control performance of the regulator.After seriously studying the working principle and key mechanical parameters of the valve,a fuzzy parameter-adaptive controller is designed by introducing a linear mixture of the pressure and opening errors of the switch regulator to reduce pressure overshoot and optimize its control performance.According to the fuzzy-control strategy based on the working characteristics and mechanical parameters of the valve,the overshoot phenomenon of the pneumatic-loading system is solved,and the pressure overshoot is eliminated.The error of the output air pressure of the regulator is 1.24%,which is small.The adjustable pressure range of the regulator is 0.2–0.6 MPa.The maximum deviation is 0.012 MPa.The linearity of the case is 1.34%F.S.