This paper presents a new type of pneumatic motor, a pneumatic step motor (PneuStep). Directional rotary motion of discrete displacement is achieved by sequentially pressurizing the three ports of the motor. Pulsed pressure waves are generated by a remote pneumatic distributor. The motor assembly includes a motor, gearhead, and incremental position encoder in a compact, central bore construction. A special electronic driver is used to control the new motor with electric stepper indexers and standard motion control cards. The motor accepts open-loop step operation as well as closed-loop control with position feedback from the enclosed sensor. A special control feature is implemented to adapt classic control algorithms to the new motor, and is experimentally validated. The speed performance of the motor degrades with the length of the pneumatic hoses between the distributor and motor. Experimental results are presented to reveal this behavior and set the expectation level. Nevertheless, the stepper achieves easily controllable precise motion unlike other pneumatic motors. The motor was designed to be compatible with magnetic resonance medical imaging equipment, for actuating an image-guided intervention robot, for medical applications. For this reason, the motors were entirely made of nonmagnetic and dielectric materials such as plastics, ceramics, and rubbers. Encoding was performed with fiber optics, so that the motors are electricity free, exclusively using pressure and light. PneuStep is readily applicable to other pneumatic or hydraulic precision-motion applications

A New Type of Motor: Pneumatic Step Motor

This paper studies the identification and the real-time control of an electrohydraulic servo system. The control strategy is based on the nonlinear backstepping approach. Emphasis is essentially on the tuning parameters effect and on how it influences the dynamic behavior of the errors. While the backstepping control ensures the global asymptotic stability of the system, the tuning parameters of the controller, nonetheless, do greatly affect the saturation and chattering in the control signal, and consequently, the dynamic errors. In fact, electrohydraulic systems are known to be highly nonlinear and non-differentiable due to many factors, such as leakage, friction, and especially, the fluid flow expression through the servo valve. These nonlinear terms appear in the closed loop dynamic errors. Their values are so large that in the presence of a poor design, they can easily overwhelm the effect of the controller parameters. Backstepping is used here because it is a powerful and robust nonlinear strategy. The experimental results are compared to those obtained with a real-time proportional-integral-derivative (PID) controller, to prove that classic linear controllers fail to achieve a good tracking of the desired output, especially, when the hydraulic actuator operates at the maximum load. Before going through the controller design, the system parameters are identified. Despite the nonlinearity of the system, identification is based on the recursive least squares method. This is done by rewriting the mathematical model of the system in a linear in parameters (LP) form. Finally, the experimental results will show the effectiveness of the proposed approach in terms of guaranteed stability and zero tracking error

Identification and Real-Time Control of an Electrohydraulic Servo System Based on Nonlinear Backstepping

A digital signal processor (DSP)-based cross-coupled intelligent complementary sliding mode control (ICSMC) system is proposed in this paper for the synchronous control of a dual linear motor servo system. The dual linear motor servo system with two parallel permanent magnet linear synchronous motors is installed in a gantry position stage. The dynamic model of single-axis motion control system with a lumped uncertainty, which comprises parameter variations, external disturbances, and nonlinear friction force, is introduced first. Then, to achieve an accurate trajectory tracking performance with robustness, a cross-coupled ICSMC is developed. In this approach, a Takagi-Sugeno-Kang-type fuzzy neural network estimator with accurate approximation capability is implemented to estimate the lumped uncertainty. Moreover, since a cross-coupled technology is incorporated into the proposed intelligent control scheme for the gantry position stage, both the position tracking and synchronous errors of the dual linear motors will simultaneously converge to zero. Furthermore, to effectively demonstrate the control performance of the proposed intelligent control approach, a 32-b floating-point DSP-based control computer is developed for the implementation of the proposed cross-coupled ICSMC system. Finally, some experimental results are illustrated to show the validity of the proposed control approach.

DSP-Based Cross-Coupled Synchronous Control for Dual Linear Motors via Intelligent Complementary Sliding Mode Control

In this study, a new sliding mode control with varying boundary layers is proposed to improve the tracking performance of a nonlinear electro-hydraulic position servo system, which can be found in many manufacturing devices The key feature of the proposed control scheme is the use of varying boundary layers instead of fixed boundary layers, which are usually employed in conventional sliding mode control The validity of the proposed control scheme is verified through practical testing on an experimental electro-hydraulic positioning device In the cases of step and sinusoidal command inputs, the experimental results strongly suggest that the proposed control scheme is capable of improving the tracking precision without causing any chattering In addition, the new control scheme seems to be very robust against various set point conditions 

Sliding mode control with varying boundary layers for an electro-hydraulic position servo system

An innovative approach to adaptive fuzzy sliding mode control for a class of SISO continuous nonlinear systems with unknown dynamics and bounded disturbances is introduced in this paper. The main idea of the presented method consists in the introduction of the fuzzy self-tuning mechanism for adaptation of the sliding mode control parameters - extended feedback and switching gains. Such modification reduces the well-known chattering problem in classical sliding mode control. In comparison with the other algorithms eliminating this problem the proposed method results in faster convergence and more transparent and interpretable design of self-tuning mechanism. Moreover, the proposed method guaranteing the asymptotic reference signal tracking with bounded system signals can be easily implemented to high order systems. The performance of the presented control design is demonstrated on control of a nonlinear electro-hydraulic servo mechanism.

Adaptive fuzzy sliding mode control for electro-hydraulic servo mechanism

Experimental and CFD study on the mass flow-rate characteristic of gas through orifice-type restrictor in aerostatic bearings

In this study, an unconventional electro-hydraulic proportional flow control valve based on a switching solenoid and a fuzzy-logic controller is proposed for application to hydraulic presses. The main purpose of this study is the attempt to develop an electro-hydraulic proportional flow control valve with lowest cost. Since the switching solenoid possesses quite nonlinear force/stroke characteristics, it is basically not suitable for the development of hydraulic proportional valves. Therefore, the fuzzy-logic controller is employed to linearize the force/stroke characteristics. The basic idea is the utilization of the numerically estimated pseudo-force as the feedback signal. Finally, this newly developed electro-hydraulic proportional flow control valve is installed in a hydraulic press. Experimental results show that the control of the ram velocity of the press cylinder using the proposed electro-hydraulic proportional flow control valve is quite successful.

Development of an unconventional electro-hydraulic proportional valve with fuzzy-logic controller for hydraulic presses

In this study, the performance of the rotational speed control of a proportional-valve-controlled pneumatic motor is investigated The main application field of the proposed prototype is the pneumatic tools, which are currently very important manufacturing devices Generally speaking, it is usually quite difficult to obtain a satisfactory and precise speed control of a servo-pneumatic motor at a low rotational speed because of the nonlinear deadband and stick-slip friction inside the proportional valve Therefore, the fuzzy-sliding mode controller is proposed Experiment results show that the fuzzy-sliding mode controller is superior to the traditional PID controller, especially when the command input is set at a low rotational speed This newly designed prototype may be utilised to develop advanced pneumatic tools

A study on the speed control performance of a servo-pneumatic motor and the application to pneumatic tools

In this study, the sensorless control algorithm is applied to improve the position control accuracy of the output plunger of a switching solenoid. The main purpose of this study is the attempt to develop a fluid-technical proportional valve with simplest construction and lowest cost. Since the switching solenoid is not equipped with a position sensor and consequently no closed-loop control theory can be applied, the accuracy of the position control of the output plunger becomes a most critical question. Therefore, a modified open-loop controller using the sensorless control algorithm is proposed. The basic idea is the utilization of the sensorless control algorithm to estimate the steady-state position of the plunger. Then, this estimated position is fedback to the controller and the input current during the steady-state response is real-time adjusted according to the error signal. Finally, a series of experiments are carried out and the results show that the proposed modified open-loop controller improves significantly the steady-state accuracy of the plunger position and provides an alternative approach to design unconventional proportional valves.

https://www.jstage.jst.go.jp/article/jsmec/47/2/47_2_637/_pdf

Jyh-Chyang Renn

Papers

Sliding mode control with varying boundary layers for an electro-hydraulic position servo system

Experimental and CFD study on the mass flow-rate characteristic of gas through orifice-type restrictor in aerostatic bearings

Development of an unconventional electro-hydraulic proportional valve with fuzzy-logic controller for hydraulic presses

A study on the speed control performance of a servo-pneumatic motor and the application to pneumatic tools

Sensorless Plunger Position Control for a Switching Solenoid