Direct-drive Robot Arm Research Articles

New energy-shaping based control plus an integral action for torque-driven robot manipulators using coordinate changes

This paper presents a robust energy shaping control for joint position tracking of torque-driven robot manipulators against disturbances. The controller design is based on an alternative energy shaping method, and an integral action is added to the theoretical framework as a novel strategy. Our contribution is to globally achieve joint position tracking of torque-driven robot manipulators, even in the presence of constant disturbances. The performance of the proposed controller is illustrated through experiments of a two degrees of freedom direct-drive robot arm.

Nonlinear PID global regulators with selftuned PD gains for robot manipulators: theory and experimentation

It is known that the Proportional Integral and Derivative (PID) regulator with constant and symmetric positive definite gain matrices (Kp, Kv and Ki), in closed loop with robotic manipulators, guarantees semiglobal asymptotic stability of the equilibrium point. In this paper, a fresh approach for control of robots manipulators based on a class of PID regulators with variable gain matrices Kp and Kv, which guarantee global asymptotic stability, is proposed. This PID control scheme, proposed with PD variable gains and fixed integral gains, improves the performance of the transient response and the handling of constraints, such as the limits of the actuator torques. Based on the authors experience, our proposal is the first scheme of a nonlinear PID regulator for robot manipulators whose PD gains are variable and its stability proof is global asymptotic in the sense of Lyapunov. The PD variable gains are directly dependent on the joint position errors and are fine tuned by fuzzy logic methodology. Good results were obtained on an experimental direct-drive robot arm of two degrees of freedom, when it was tested in order to verify the effectiveness of the new controller.

A GUAS Joint Position Tracking Controller of Torque-Driven Robot Manipulators Influenced by Dynamic Dahl Friction: Theory and Experiments

This article presents a controller for global joint position tracking control of torque-driven robot manipulators involving dynamic Dahl friction. The control law has been designed using a novel theoretical Hamiltonian inspired framework, which allows global uniform asymptotic stability (GUAS) of the nonautonomous nonlinear closed-loop system. An observer is provided to estimate the nonmeasurable state of internal friction of the Dahl model, preserving the GUAS attribute in the closed-loop system. The performance of the proposed control scheme is illustrated through experiments on a two-degree-of-freedom direct-drive robot arm.

Quasi-Minimum Time Trajectory Planning and Experiments for Prototype Direct-Drive Robot Arm Driven by Stepping Motors Using GA

In this paper, a quasi-minimum time trajectory planning of three-link direct-drive robot arm driven with stepping motors using a genetic algorithm (GA) was proposed. The prototype direct-drive robot arm was newly manufactured in this study. The trajectory for a semiconductor wafer transfer work consists of three trajectory portions: a straight line, a curved line, and a straight line. In the trajectory planning, three trajectory portions are expressed by polynomials of time. Using the boundary and continuous conditions concerning joint angle, joint angular velocity and joint angular acceleration, the whole trajectory is described by a chromosome consisting of five genes. Then, the fitness function of the genetic algorithm for the quasi-minimum time control was defined, under the constraint condition that the stepping motor torques should not exceed pull-out torques. Furthermore, the numerical calculations and experiments have been carried out, and it is confirmed that the quasi-minimum time trajectory planning can be executed successfully, and the trajectory tracking control can be well performed.

Fractional Fuzzy Adaptive Sliding-Mode Control of a 2-DOF Direct-Drive Robot Arm

This paper presents a novel parameter adjustment scheme to improve the robustness of fuzzy sliding-mode control achieved by the use of an adaptive neuro-fuzzy inference system (ANFIS) architecture. The proposed scheme utilizes fractional-order integration in the parameter tuning stage. The controller parameters are tuned such that the system under control is driven toward the sliding regime in the traditional sense. After a comparison with the classical integer-order counterpart, it is seen that the control system with the proposed adaptation scheme displays better tracking performance, and a very high degree of robustness and insensitivity to disturbances are observed. The claims are justified through some simulations utilizing the dynamic model of a 2-DOF direct-drive robot arm. Overall, the contribution of this paper is to demonstrate that the response of the system under control is significantly better for the fractional-order integration exploited in the parameter adaptation stage than that for the classical integer-order integration.

Experiments on stabilizing receding horizon control of a direct drive manipulator

AbstractIn this paper, the application of receding horizon control to a two‐link direct drive robot arm is demonstrated. Instead of terminal constraints, a terminal cost on receding horizon control is used to guarantee stability, because of the computational demand. The key idea of this paper is to apply receding horizon control with a terminal cost derived from the energy function of the robot system. The energy function is defined as the control Lyapunov function by considering inverse optimality. In experimental results, stability and performance are compared with respect to the horizon length by applying receding horizon control and inverse optimal control to the robot arm. © 2008 Wiley Periodicals, Inc. Electron Comm Jpn, 91(5): 33–40, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10113

ADALINE based robust control in robotics: a Riemann-Liouville fractional differintegration based learning scheme

This paper presents an approach to improve the performance of intelligent sliding model control achieved by the use of a fundamental constituent of soft computing, named Adaptive Linear Element (ADALINE). The proposed scheme is based on the fractional calculus. A previously considered tuning scheme is revised according to the rules of fractional order differintegration. After a comparison with the integer order counterpart, it is seen that the control system with the proposed adaptation scheme provides (1) better tracking performance, (2) suppression of undesired drifts in parameter evolution and (3) a very high degree of robustness and insensitivity to disturbances. The claims are justified through some simulations utilizing the dynamic model of a two degrees of freedom (DOF) direct drive robot arm and overall, the contribution of the paper is to introduce the fractional order calculus into a robust and nonlinear control problem with some outperforming features that are absent when the integer order differintegration operators are adopted.

AN ESTIMATE OF THE DOMAIN OF ATTRACTION FOR THE PID REGULATOR OF MANIPULATORS

This paper deals with the problem of estimation of the domain of attraction for the linear Proportional Integral Derivative (PID) regulator of robot manipulators. We first recall a simple semiglobal asymptotic stability analysis, which is one of the simplest found in the literature; then, based on such analysis we obtain an estimate of the domain of attraction in terms of the PID controller gains, allowing to know, in an explicit way, the radius of such an estimate of the region of attraction. To the best of the authors' knowledge, for the classical linear PID regulator of robot manipulators, this is the first paper that explicitly parameterizes the range of attraction of the goal position in terms of the proportional, derivative and integral gain matrices. As a consequence, we also propose a tuning procedure which allows to ensure asymptotic stability for a given initial conditions. Finally, as a way of testing this tuning procedure in a real application, we accomplish some experiments in a direct-drive robot arm.

Experiments on Stabilizing Receding Horizon Control of a Direct Drive Manipulator

In this paper, the application of receding horizon control to a two-link direct drive robot arm is demonstrated. Instead of the terminal constraints, a terminal cost on receding horizon control is used to guarantee the stability, because of the computational demand. The key idea of this paper is to apply the receding horizon control with the terminal cost which is derived from the energy function of the robot system. The energy function is given as the control Lyapunov function by considering the inverse optimality. In the experimental results, the stability and the performance are compared with respect to the horizon length by applying the receding horizon control and the inverse optimal control to the robot arm.

Comparative experiments with a multiple model based adaptive controller for a SCARA type direct drive manipulator

In this paper, different adaptive control algorithms will be experimentally tested on a two axis SCARA type direct drive robot arm, and the performance of these algorithms will be compared. Being a direct drive system, the nonlinear effects, arising from the dynamics of the manipulator under high velocities, are directly reflected in the control of the manipulator. This makes the manipulator a more efficient test bed for testing the efficiency of the proposed adaptive schemes. In the experiments, we used fast trajectories rather than slow ones to observe how the proposed controllers compensate the dynamic nonlinear effects of manipulator dynamics. We will test some known adaptive control algorithms given in the literature along with our proposed adaptive control scheme which makes use of multiple models.

A novel global asymptotic stable set-point fuzzy controller with bounded torques for robot manipulators

This paper addresses the set-point control of robot manipulators with friction where avoiding saturation of the actuators is a major issue. The original contribution is a novel direct fuzzy control system dealing with both practical constraints in mechanical manipulators: saturation and friction. The control system is made by taking advantage of input-output properties of the so-called sectorial fuzzy controllers. When friction is considered, we prove, via Lyapunov theory, that the steady state position errors owing to static friction are inside of a global attractor, which can be arbitrarily reduced. In case of absence of friction, the closed-loop system becomes globally asymptotic stable. In both cases, the important theoretical and practical feature of maintaining the control actions always within prescribed limits according to the actuator torque capabilities is guaranteed. Experimental evaluation of the proposed direct fuzzy control system on a nonlinear direct-drive robot arm is presented to validate its effectiveness.

EXPERIMENTS ON STABILIZING RECEDING HORIZON CONTROL OF A DIRECT DRIVE MANIPULATOR

In this paper, the application of receding horizon control to a two-link direct drive robot arm is demonstrated. Instead of the terminal constraints, a terminal cost on receding horizon control is used to guarantee the stability, because of the computational demand. The key idea of this paper is to apply the receding horizon control with the terminal cost which is derived from the energy function of the robot system. The energy function is given as the control Lyapunov function by considering the inverse optimality. The experimental results are compared with respect to stability, performance by applying the receding horizon control and the inverse optimal control to the robot arm.

A new variable structure PID-controller design for robot manipulators

In this brief, a new variable structure proportional-integral-derivative (PID) controller design approach is considered for the tracking stabilization of robot motion. The work corroborates the utility of a certain PID sliding mode controller with PID sliding surface for tracking control of a robotic manipulator. Different from the general approach, the conventional equivalent control term is not used in this controller because that needs to use the matching conditions and exact full robot dynamics knowledge, which involves unavailable parameter uncertainties. Though the sliding surface includes also the integral error term, which makes the robot tracking control problem complicated, the existence of a sliding mode and gain selection guideline are clearly investigated. Moreover, different from uniformly ultimately boundedness, the global asymptotic stability of the robot system with proposed controller is analyzed. The sliding and global stability conditions are formulated in terms of Lyapunov full quadratic form and upper and lower matrix norm inequalities. Reduced design is also discussed. The proposed control algorithm is applied to a two-link direct drive robot arm through simulations. The simulation results indicate that the control performance of the robot system is satisfactory. The chattering phenomenon is handled by the use of a saturation function replaced with a pure signum function in the control law. The saturation function results in a smooth transient performance. The proposed approach is compared with the existing alternative sliding mode controllers for robot manipulators in terms of advantages and control performances. A comparative analysis with a plenty of simulation results soundly confirmed that the performance of developed variable structure PID controller is better under than those of both classical PID controller and an existing variable structure controller with PID-sliding surface.

Modeling and Identification for High-Performance Robot Control: An RRR-Robotic Arm Case Study

This paper explains a procedure for getting models of robot kinematics and dynamics that are appropriate for robot control design. The procedure consists of the following steps: 1) derivation of robot kinematic and dynamic models and establishing correctness of their structures; 2) experimental estimation of the model parameters; 3) model validation; and 4) identification of the remaining robot dynamics, not covered with the derived model. We give particular attention to the design of identification experiments and to online reconstruction of state coordinates, as these strongly influence the quality of the estimation process. The importance of correct friction modeling and the estimation of friction parameters are illuminated. The models of robot kinematics and dynamics can be used in model-based nonlinear control. The remaining dynamics cannot be ignored if high-performance robot operation with adequate robustness is required. The complete procedure is demonstrated for a direct-drive robotic arm with three rotational joints.

Precise slow motion control of a direct-drive robot arm with velocity estimation and friction compensation

Precise low speed motion control of a robot manipulator calls for precise position and velocity measurement and joint friction compensation, as well as robustness and adaptability of the control scheme. However, precise velocity measurement and friction compensation remain challenging research tasks, especially for very slow motions. In the present work, a simple and efficient method is proposed to estimate velocity from a sampled incremental encoder pulse train, which is then utilized in the experimental investigation on a proposed robust decomposition-based friction compensation method. The experimental results on a direct drive robot arm have demonstrated precise motion control at very slow speeds and in the presence of significant joint friction.

Real-time process manager and its application in robotics

The Real Time Process Manager consists of a graphic user interface that enables the user to generate programs for real time applications based on programs written in standard C, assigns priority and execution period to each program, and also interchanges data among them. The functionality of this Process Manager was tested in computer control system of direct drive robot arm of CICESE research center.

Experimental evaluation of model-based controllers on a direct-drive robot arm

This paper describes the experimental comparison among four model-based control algorithms on a direct-drive robotic arm. We present experimental results of the following controllers: Computed-Torque control, PD+ control, PD control with computed feedforward and PD control. All controllers include Coulomb and viscous friction compensation as well as cancellation of gravitational torques. They are tested under common trajectory specification and performance index.

An Attempt to Raise the Level of Software Abstraction in Assembly Robotics through an Apposite Choice of Underlying Mechatronics

Robot manipulators were meant to be the production engineer"s flexible friend. Assembly robots, however, have failed to fulfill their promise. The problem that has continuously plagued robotic assembly is that of spatial uncertainty. It is our thesis that the ubiquitous problem of spatial uncertainty is an artefact of the fact that current industrial manipulators are designed for an operational paradigm that assumes position control is of primary importance. In this paper we propound an alternative approach based on sliding as the primary motion primitive. We first present a model that uses sliding to allow us to raise the level of abstraction of robot programming tasks. We then describe an inherently accommodating, (planar) three degree of freedom, direct-drive robot arm that was constructed to test our approach. Finally, we present data collected from representative (planar) manipulation tasks that substantiate our claims.

Evaluation of Real-Time Motion Controllers on a Direct-Drive Robot Arm

Motion control of robot manipulators offers inter-esting practical and theoretical challenges to control researchers. This paper describes experimental comparison among four model-based control algorithms on a direct-drive robotic arm. All controllers include Coulomb and viscous friction compensation as well as cancellation of gravity torques, they are tested under common trajectory specification and performance index.

Point-to-point robot control under actuator constraints

This paper provides a solution to the point-to-point control of robot manipulators, taking into account that the actuators deliver torques in a limited operating zone. A smooth controller, proposed in this paper, yields a globally asymptotically stable closed loop system while the torques remain within specified limits. The performance of the proposed controller is illustrated via experiments on a two degrees-of-freedom direct-drive robot arm.