Pneumatic Servo Research Articles

Identification of friction effects in a linear positioning servopneumatic system

Identification of friction effects in a linear positioning servopneumatic system

Globalized and bounded Nelder‐Mead algorithm with deterministic restarts for tuning controller parameters: Method and application

SummaryThis paper develops and examines an optimization algorithm for simulation‐based tuning of controller parameters. The proposed algorithm globalizes the Guin augmented variant of Nelder–Mead's nonlinear downhill simplex by deterministic restarts, linearly growing memory vector, and moving initial simplex. First, the effectiveness of the algorithm is tested using 10 complex and multimodal optimization benchmarks. The algorithm achieves global minima of all benchmarks and compares favorably against the evolutionary, swarm, and other globalized local‐search multimodal optimization algorithms in probability of finding global minimum and numerical cost. Next, the proposed algorithm is applied for tuning sliding mode controller parameters for a servo pneumatic position control application. The experimental results reveal that the system with sliding mode controller parameters tuned using the proposed algorithm targeting smooth position control with maximum possible accuracy, performs as desired and eliminates the need of manual online tuning for desired performance. The results are also compared with the performance of the same servo pneumatic system with parameters tuned using manual online tuning in an earlier published work. The system with controller parameters tuned using the proposed algorithm shows improvement in accuracy by 28.9% in sinusoidal and 42.2% in multiple step polynomials tracking.

Speed tracking control of pneumatic motor servo systems using observation-based adaptive dynamic sliding-mode control

This study aims to develop an adaptive high-precision control system for controlling the speed of a vane-type air motor (VAM) pneumatic servo system. In practice, the rotor speed of a VAM depends on the input mass air flow, which can be controlled by the effective orifice area (EOA) of an electronic throttle valve (ETV). As the control variable of a second-order pneumatic system is the integral of the EOA, an observation-based adaptive dynamic sliding-mode control (ADSMC) system is proposed to derive the differential of the control variable, namely, the EOA control signal. In the ADSMC system, a proportional–integral–derivative fuzzy neural network (PIDFNN) observer is used to achieve an ideal dynamic sliding-mode control (DSMC), and a supervisor compensator is designed to eliminate the approximation error. As a result, the ADSMC incorporates the robustness of a DSMC and the online learning ability of a PIDFNN. To ensure the convergence of the tracking error, a Lyapunov-based analytical method is employed to obtain the adaptive algorithms required to tune the control parameters of the online ADSMC system. Finally, our experimental results demonstrate the precision and robustness of the ADSMC system for highly nonlinear and time-varying VAM pneumatic servo systems.

Optimized linear active disturbance rejection control for pneumatic servo systems via least squares support vector machine

This paper presents an optimized linear active disturbance rejection controller to improve the response rapidity and anti-interference ability of a pneumatic servo system. Both a linear extended state observer and a least squares support vector machine are established to estimate and compensate total nonlinearity of the system. Moreover, a linear state error feedback controller is designed to ensure good performances of the closed-loop system. In addition, estimation error and tracking error are bounded and decrease with the increase of their respective eigenvalues. Lastly, simulation results show that the optimized controller has the better response rapidity and anti-interference ability than the traditional controller.

EXPERIMENTAL COMPARISON BETWEEN PROPORTIONAL AND PWM-SOLENOID VALVES CONTROLLED SERVOPNEUMATIC POSITIONING SYSTEMS

The performance of the Dynamical Adaptive Backstepping-Sliding Mode Control (DAB-SMC) scheme for positioning of a pneumatic cylinder regulated by two types of PWM-solenoid valves is experimentally investigated. The goal is to study the compromise in controller’s performance as the system moves from using a proportional valve to employing the low-cost PWM-solenoid valves. Sinusoidal and multiple-step inputs are used as the reference position trajectories. Experimental results show that the DAB-SMC scheme works best with the proportional valve. The performance, however, deteriorates by more than twofold, once the system utilizes PWM-solenoid valves of 3/2-way or 2/2-way configurations. From this study, trade-off between performances of different types of valves applied on a DAB-SMC scheme-controlled servo positioning system is successfully documented. This information helps to configure appropriate servo-pneumatic system for positioning applications.

ピンチ型空気圧サーボバルブの開発

Pneumatic servo valves are key components in pneumatic servo systems. In multi-degree-of-freedom systems such as robot systems, a lot of servo valves are installed. Nozzle flapper-type servo valves are not suitable for these systems because they release air all the time, so that air consumption is too large. Spool-type servo valves currently used allow leakage of air from a sliding portion of a spool. Therefore, in robot systems, vibration and noise of compressors are big problems. Reducing leakage of servo valves can solve these problems and save energy. In this study, we develop a 4-port pinch-type pneumatic servo valve controlling flow by pinching air tubes, aiming at a leak-less servo valve. Almost all existing pinch-type valves are 2 or 3 port and proportional valves, aiming to control flow of slurry and medicine. There are no 4-port pinch-type servo valves. Experimental results showed that the leakage was lower than 1.7% of the rated flow rate and dynamic characteristics was approximately 30 Hz. We conducted position control experiments of a pneumatic cylinder using the prototype valve and showed the effectiveness.

Nonlinear component-based modelling and hardware-in-the loop simulation of servo-pneumatic systems

Modelling and control of pneumatic systems are tedious and difficult because of the inherent nonlinearity associated with these systems. In this paper, a component-based modelling approach is proposed to create a nonlinear mathematical model of servo-pneumatic systems. According to the proposed modelling approach, the system is decomposed into the main components, the linkage nature between components is identified, and the model of each component is created separately. A generalised nonlinear model of pneumatic system is created by simply aggregating the model of the separate components. This model is then validated using a real pneumatic system available in De Montfort University labs. Experimental results show that real and simulated responses agreed well. Afterward, the developed model is used to design and tune PID-based controller using two different methods. Both controllers have been tested on the real system through hardware-in-the-loop (HIL). Experimental results show that both controllers succeeded to follow a reference speed profile. The proposed approach should lead to reduction in model complexity, faster model formulation, and high model accuracy and reliability.

Nonlinear component-based modelling and hardware-in-the loop simulation of servo-pneumatic systems

Nonlinear component-based modelling and hardware-in-the loop simulation of servo-pneumatic systems

Finite-time output feedback control for a pneumatic servo system

In this paper, the position tracking control problem of pneumatic servo systems is investigated. These systems usually have high nonlinearities and unmeasurable piston velocities. Firstly, by using adding a power integrator technique, a global finite-time state feedback controller is proposed. Secondly, based on homogeneous theory, a nonlinear observer is developed to estimate the piston velocity. Finally, the corresponding output feedback controller is derived, which local finite-time stabilizes the position tracking error system. Compared with the conventional backstepping output feedback control scheme, the developed nonsmooth output feedback control scheme offers a faster convergence rate and a better disturbance rejection property. Numerical simulations illustrate the effectiveness of the proposed control scheme.

Stability properties of a pneumatic-actuated rehabilitation system

Affected by discontinuous nature of the discrete controller and patients’ different characteristics, the stability analysis in servo pneumatic rehabilitation systems remains a challenge. Hence, the authors propose an approach to obtain stability boundaries of the admittance controller parameters so that a compliant interaction can be ensured. As the zero-order hold function adds nonlinear exponential terms to the continuous transfer function of the system, a discrete closed-loop root-locus analysis is presented describing how the changes in patients’ characteristics and system parameters shift the stability boundaries. The reasonable matches between the analytical and experimental stability boundaries demonstrate that the presented approach is reliable.

Cross-coupling integral adaptive robust posture control of a pneumatic parallel platform

A pneumatic parallel platform driven by an air cylinder and three circumambient pneumatic muscles was considered. Firstly, a mathematical model of the pneumatic servo system was developed for the MIMO nonlinear model-based controller designed. The pneumatic muscles were controlled by three proportional position valves, and the air cylinder was controlled by a proportional pressure valve. As the forward kinematics of this structure had no analytical solution, the control strategy should be designed in joint space. A cross-coupling integral adaptive robust controller (CCIARC) which combined cross-coupling control strategy and traditional adaptive robust control (ARC) theory was developed by back-stepping method to accomplish trajectory tracking control of the parallel platform. The cross-coupling part of the controller stabilized the length error in joint space as well as the synchronization error, and the adaptive robust control part attenuated the adverse effects of modelling error and disturbance. The force character of the pneumatic muscles was difficult to model precisely, so the on-line recursive least square estimation (RLSE) method was employed to modify the model compensation. The projector mapping method was used to condition the RLSE algorithm to bound the parameters estimated. An integral feedback part was added to the traditional robust function to reduce the negative influence of the slow time-varying characteristic of pneumatic muscles and enhance the ability of trajectory tracking. The stability of the controller designed was proved through Laypunov’s theory. Various contrast controllers were designed to testify the newly designed components of the CCIARC. Extensive experiments were conducted to illustrate the performance of the controller.

Experimental Validation for Fuzzy Control of Servo Pneumatic Artificial Muscle Driven by Metal Hydride

This paper presents the servo control problem of pneumatic artificial muscle (PAM) powered by hydrogen-based metal hydride (MH) for mechanical servo actuation. Under various operations of a servo PAM actuator driven by hydrogen-based MH, the desired task of actuator is changed following those various operations. A fuzzy adaptive proportional-integral-derivative (PID) controller is proposed to improve the dynamic performance requirements in both transient and steady-state responses. The fuzzy logic part of the proposed controller is employed to be better than a conventional PID for automatic online tuning of the parameters of PID gain under different operating conditions. The nonlinear mathematical model of PAM actuated by hydrogen-based MH is determined as the desired characteristics of closed-loop control for a fuzzy rule base. Position control is examined to illustrate the performance of the proposed controller. The results show that the proposed technique is more suitable and effective in the case of servo actuation.

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 results show that the designed controller can achieve better tracking performance, as compared with some existing methods.

A continuous version of the LuGre friction model applied to the adaptive control of a pneumatic servo system

This work presents the application of a friction compensation scheme to the trajectory-tracking control of a pneumatic servo actuator. Such scheme is based on a continuous approximation of the LuGre friction model, developed so as to allow complete Lyapunov stability analyses without resorting to assumptions that are difficult to satisfy in practice due to their physical meaning. By using adaptive estimation, extensive identification procedures are also avoided for determining friction parameters. Experimental results illustrate the most significant advantages and potential limitations of the proposed scheme in real applications.

Fully Automatic Soup Machine

Accepted: 05.04.2016 Fully automatic soup machine project is made for meeting hunger needs of people in emergency situations without any request from anyone. Compared to systems that only cup soup, there is a system which suitable for Turkish society, meet bowl of soup and bread needs, at the same time self cleaning, report the lack of materials to system over web or mail with system to be installed. The system is controlled from PLC over and have visual support with a operator panel. Also, it transfers necessary information to central system with GSM mode and fiber lines. The system is characterized in that self cleaning. It is thought to take place near the municipality and police stations buildings, in parks and schools to serve the people. PLC programming is designed with twin cat. System software is designed in codesys ST language. Mechanical materials used is selected in accordance with food. Fingerprint application which prevent multiple use in the same day is developed. Mechanical design is prepared with Solid Works. Also remote monitoring module is developed. This module is designed two kinds. First designed is a cloud application. Remote access is designed making IP routing with cloud application in Beckoff PLC system. On the other system is designed to access codesys software via modemforwarding on port. The movement of mechanical equipment is designed on servo motor and pneumatic. Two servo motors and rotary pneumatic activators are used. Servo motors is designed for bread units and rotary activators for soup preparation mechanism.

Position control of a servo-pneumatic actuator with mis-matched uncertainty using multiple-surface sliding mode controller and high-gain observer

This research develops a multiple-surface sliding mode control (MSSC) approach for position control of a servo-pneumatic system in the presence of mismatched uncertainties due to the friction force of the cylinder sealing. Servo-pneumatic actuators have many applications such as industrial automation, haptic interfaces, rehabilitation robots and non-invasive surgeries. Non-linearities due to internal and external disturbances, such as the friction force between the piston seal and cylinder wall, make it difficult to achieve adequate performance from these actuators. Thus, modelling and identification of friction parameters is an essential part of the controller design procedure. A simple model for friction such as the Stribeck model may be used in order to reduce the complexity of the identification procedure. In addition, a bounded uncertainty owing to the unmodelled dynamics of friction is considered. The lack of direct measurement for systems velocity necessitates finding a solution to estimate this parameter. One answer to this problem is to employ a high-gain observer. Whereas mismatched uncertainties appear in the state space equation of the system before control input, control input cannot apply directly to them. In the proposed framework, an MSSC scheme has been used to cope with these types of uncertainties. Asymptotic stability of the closed-loop system is proven by using the Lyapunov method; experimental results show that the proposed controller can deliver a good tracking performance and is robust to uncertainties. Experimental results validate the controller performance.

Adaptive robust trajectory tracking control of a parallel manipulator driven by pneumatic cylinders

Due to the compressibility of air, non-linear characteristics, and parameter uncertainties of pneumatic elements, the position control of a pneumatic cylinder or parallel platform is still very difficult while comparing with the systems driven by electric or hydraulic power. In this article, based on the basic dynamic model and descriptions of thermal processes, a controller integrated with online parameter estimation is proposed to improve the performance of a pneumatic cylinder controlled by a proportional valve. The trajectory tracking error is significantly decreased by applying this method. Moreover, the algorithm is expanded to the problem of posture trajectory tracking for the three-revolute prismatic spherical pneumatic parallel manipulator. Lyapunov’s method is used to give the proof of stability of the controller. Using NI-CompactRio, NI-PXI, and Veristand platform as the realistic controller hardware and data interactive environment, the adaptive robust control algorithm is applied to the physical system successfully. Experimental results and data analysis showed that the posture error of the platform could be about 0.5%–0.7% of the desired trajectory amplitude. By integrating this method to the mechatronic system, the pneumatic servo solutions can be much more competitive in the industrial market of position and posture control.

Identification of time‐varying OE models in presence of non‐Gaussian noise: Application to pneumatic servo drives

SummaryIntensive research in the field of mathematical modeling of pneumatic servo drives has shown that their mathematical models are nonlinear in which many important details cannot be included in the model. Owing the influence of the combination of heat coefficient, unknown discharge coefficient, and change of temperature, it was supposed that parameters of the pneumatic cylinder are random (stochastic parameters). On the other side, it has been well known that the nonlinear model can be approximated by a linear model with time‐varying parameters. Due to the aforementioned reasons, it can be assumed that the pneumatic cylinder model is a linear stochastic model with variable parameters. In practical conditions, in measurements, there are rare, inconsistent observations with the largest part of population of observations (outliers). Therefore, synthesis of robust algorithms is of primary interest. In this paper, the robust recursive algorithm for output error models with time‐varying parameters is proposed. The convergence property of the proposed robust algorithm is analyzed using the methodology of an associated ordinary differential equation system. Because ad hoc selection of model orders leads to overparameterization or parsimony problem, the robust Akaike's criterion is proposed to overcome these problems. By determining the least favorable probability density for a given class of probability distribution represents a base for design of the robust version of Akaike's criterion. The behavior of the proposed robust identification algorithm is considered through intensive simulations that demonstrate the superiority of the robust algorithm in relation to the linear algorithms (derived under an assumption that the stochastic disturbance has a Gaussian distribution). The good practical values of the proposed robust algorithm to identification of the pneumatic cylinder are illustrated by experimental results. Copyright © 2016 John Wiley & Sons, Ltd.

Finite-Time Composite Position Control for a Disturbed Pneumatic Servo System

This paper investigates the finite-time position tracking control problem of pneumatic servo systems subject to hard nonlinearities and various disturbances. A finite-time disturbance observer is firstly designed, which guarantees that the disturbances can be accurately estimated in a finite time. Then, by combining disturbances compensation and state feedback controller together, a nonsmooth composite controller is developed based on sliding mode control approach and homogeneous theory. It is proved that the tracking errors under the proposed composite control approach can be stabilized to zero in finite time. Moreover, compared with pure state feedback control, the proposed composite control scheme offers a faster convergence rate and a better disturbance rejection property. Finally, numerical simulations illustrate the effectiveness of the proposed control scheme.

A Harvest Vehicle with Pneumatic Servo System for Gathering a Harvest and its Control

Abstract: A series of works such as harvesting and transporting in a farm is one of such works with so care as not to damage the harvest in order to maintain the value of harvests. We are developing an autonomous cart for gathering a harvest with the bed to be controlled to keep in horizontal level, in order to avoid harvests gathered article in front of particular area of the bed and avoid to be damaged in harvests. It is proposed a method of control of maintaining the horizontal level of the bed of the cart with air cylinder suspension systems.