In this paper, an attempt at summarizing the evolution and the state of the art in the field of robot hands is made. In such exposition, a critical evaluation of what in the author's view are the leading ideas and emerging trends is privileged with respect to exhaustiveness of citations. The survey is focused mainly on three types of functional requirements a machine hand can be assigned in an artificial system, namely, manipulative dexterity, grasp robustness, and human operability. A basic distinction is made between hands designed for mimicking the human anatomy and physiology,and hands designed to meet restricted, practical requirements. In the latter domain, arguments are presented in favor of a -minimalistic" attitude in the design of hands for practical applications, i.e., use the least number of actuators, the simplest set of sensors, etc., for a given task. To achieve this rather obvious engineering goal is a challenge to our community. The paper illustrates some of the new sometimes difficult, problems that are brought about by building and controlling simpler, more practical devices.

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Hands for dexterous manipulation and robust grasping: a difficult road toward simplicity

In this article we present two nonlinear force controllers based on the sliding mode control theory. For this purpose we use the detailed mathematical model of the pneumatic system developed in the first part of the paper. The first controller is based on the complete model, and exhibits superior performance both in the numerical simulation and experiments, but requires complex online computations for the control law. The second controller neglects the valve dynamics and the time delay due to connecting tubes. The performance of this controller exhibits slight degradation for configurations with relatively short tubes, and at frequencies up to 20 Hz. At higher frequencies or when long connecting tubes are used, however, the performance exhibits significant degradation compared to the one provided by the full order controller.@S0022-0434~00!00703-6#

A High Performance Pneumatic Force Actuator System: Part II—Nonlinear Controller Design

Many researchers have investigated pneumatic servo positioning systems due to their numerous advantages: inexpensive, clean, safe, and high ratio of power to weight. However, the compressibility of the working medium, air, and the inherent nonlinearity of the system continue to make achieving accurate position control a challenging problem. In this paper, two control algorithms are designed for the position tracking problem and their experimental performance is compared for a pneumatic cylinder actuator. The first algorithm is sliding-mode control based on a linearized plant model (SMCL) and the second is sliding-mode control based on a nonlinear plant model (SMCN). Extensive experiments using different payloads (1.9, 5.8, and 10.8 kg), vertical and horizontal movements, and move sizes from 3 to 250 mm were conducted. Averaged over 70 experiments with various operating conditions, the tracking error for SMCN was 18% less than with SMCL. For a 5.8-kg payload and a 0.5-Hz 70-mm amplitude, sine wave reference trajectory, the root-mean-square error with SMCN was less than 0.4 mm for both vertical and horizontal motions. This tracking control performance is better than those previously reported for similar systems.

Experimental Comparison of Position Tracking Control Algorithms for Pneumatic Cylinder Actuators

An apparatus for traversing obstacles having an elongated, round, flexible body that includes a plurality of articulating propulsion members. This plurality of propulsion members cooperate in a worm-like or alternating tripod gait to provide forward propulsion wherever a propulsion member is in contact with any feature of the environment, regardless of how many or which ones of the plurality of propulsion members make contact with such environmental feature.

Apparatus for obstacle traversion

This paper presents an active disturbance rejection position control scheme for a magnetic rodless cylinder in servo systems without pressure states. It is very hard to achieve precise position control of magnetic rodless cylinders due to nonlinearity from large friction force and hysteresis. In this paper, the overshoot, which has a negative influence on position control, is effectively reduced by using a tracking differentiator. Furthermore, the nonlinearity is estimated by a designed extended-state observer. In addition, the self-stable region theory is used to prove the convergence of the extended-state observer. Finally, both control precision and response speed are guaranteed via a nonlinear error feedback controller in the pneumatic system. Experimental results show that the steady-state error within 0.05 mm is achieved for a step signal.

Active Disturbance Rejection Position Control for a Magnetic Rodless Pneumatic Cylinder

Pneumatic robot manipulators are characterized by high-order, time-variant actuator dynamics, nonlinearities due to compressibility of air, external disturbances such as static and Coulomb friction, and wide range of payload variations. Conventional PID controllers suffer from problems of gain tuning under these conditions. In this paper, a new control algorithm is proposed for the position and trajectory control of pneumatic actuators based on the sliding mode control approach. The stability of motion is proved for the case of a linear, time-invariant switching surface. A disadvantage of using sliding mode control for third- and higher-order mechanical systems is the need for acceleration feedback. In this paper, to overcome this difficulty we propose the use of differential pressure. The proposed controller is simple, easy to implement, and robust to payload and parametric variations. The effectiveness of the new scheme for position and trajectory control is illustrated by experiments on an industrial piston-driven cylindrical actuator with proportional valves.

Practical Design of a Sliding Mode Controller for Pneumatic Actuators

Recent research has shown that robust and precise high-speed control of pneumatic actuators is practicable, by application of advanced control techniques such as model-based adaptive and sliding-mode control. However, the resulting need for full state-based feedback and feedforward control-in particular, the measurement of air pressures-increases both the cost and complexity of the overall system. In this paper, we consider the problem of design of observers to estimate the chamber pressure variables in a cylinder actuator. Since the cylinder pressures are not simultaneously observable because of the nature of cylinder dynamics, we first propose a continuous gain observer in which the pressure on one side of the cylinder is measured and the pressure on the other side is estimated. Next, we propose a sliding-mode observer where numerically estimated acceleration is used in order to observe both pressures, with ultimate bounded stability. A sliding-mode controller is proposed, whose sensitivity to errors under the sliding-mode observer is studied. The proposed observers are simple, effective and easy to implement. Results of experimental implementation illustrate the practical effectiveness of the new observers.

Pressure observer-controller design for pneumatic cylinder actuators

Pneumatic actuators are among a variety of actuators under active study by the robotics community, for the advantages they offer over conventional electric actuators widely used in present-day robots. So far, however, only pneumatic cylinders which provide linear actuation have been mainly studied in literature. Air motors are the pneumatic counterparts of electric motors, providing rotary actuation. They have several advantages over electric motors, especially high power-to-weight and power-to-size ratios, good compliance, and resistance to environmental hazards. We consider the model-based control of vane-type air motors which are the most commonly used class of air motors. Various control problems are considered namely, position control, trajectory control, adaptive control, and force control. Results of experimental implementation on an industrial vane-type air motor illustrate the effectiveness of the air motor as a high-performance rotary actuator.

Control performance of an air motor-can air motors replace electric motors?

Pneumatic motors have many advantages over electric motors, conventionally used for robotics and automation applications. However, the control performance of pneumatic motors is quite unsatisfactory, mainly due to the compressibility of air. We have recently proposed the development of hybrid pneumatic/electric motors where a small electric motor is used in conjunction with vane-type pneumatic motors, so that the hybrid actuator has better damping and ease of control than the pneumatic motor. In the present work, we consider the switching control of the hybrid actuator system, and, propose control algorithms for position, and trajectory control of the system. The performance improvement of the new actuator is illustrated by results of experimental implementation.

Control of a hybrid pneumatic/electric motor

A grinder pressing device, wherein either the bottom part of a cylinder main body (10) of an air cylinder (1) in a vertical posture or a piston rod (11) is fixed to a fixed plate (2) and the other one is fixed to a movable plate (3) disposed under the fixed plate (2), either a guide table (G2) or a guide (G1) is mounted on the movable plate (3) and the other one is mounted on the outer peripheral surface of the cylinder main body (20) and the guide table (G2) is guided on the guide (G1) in a vertical direction under the rolling frictional condition through balls and, in the air cylinder (1), a coefficient of friction between the outer peripheral walls of a piston (12) and the piston rod (11) and the structural wall of the cylinder main body (10) is set lower by a metal seal so as to support the piston rod (11) by a ball bush movably in forward and backward directions over an extensive distance, a grinder (G) being mounted on the movable plate (3) and air pressures in upper and lower cylinder chambers (13 and 14) divided by the piston (12) being controlled so as to adjust the pressing force of the grinder (G) to a work to be ground.

Yasuhiro Hayakawa

Papers

Practical Design of a Sliding Mode Controller for Pneumatic Actuators

Pressure observer-controller design for pneumatic cylinder actuators

Control performance of an air motor-can air motors replace electric motors?

Control of a hybrid pneumatic/electric motor

Grinder pressing device