Multi-link Robot Research Articles

Communication

In this article, issues in the design of passive controllers for a class of multilink manipulators with the last link flexible are discussed. It is well known that for the single flexible-link manipulator, the mapping from the input torques to the joint ve locities is passive, whereas the mapping from the input torques to the derivative of net-tip movements (the usual output chosen) is not. However, if an appropriate output variable is selected, the transfer function can be made passive, provided that the hub inertia seen by a flexible link is sufficiently small. Then, by the Passivity theorem, using any strictly passive controller with finite gain will result in an L2-stable system. However, for a multilink industrial robot, the effective hub inertia seen by the flexible link is usually large. In addition, the dynamic equations are highly nonlinear. Approaches are examined for extending these passivity results to multilink manipulators. Experimental results are presented for a five-bar-linkage manipulator with the last link being flexible.

産業用多関節形ロボットアームの相互位置同期制御を図った高精度輪郭制御法

A method for synchronous position control of mechatronic servo system of multiple axes was required to attain a high accuracy performance of contour control in sealing process, laser cutting and so on. Accurate contour control method for multi link robot arm was proposed by using synchronous position of mutual axes. The proposed method was evaluated by experiment of actual multi link robot arm and its simulation study under disturbed torque circumstance, and then showed satisfactory performance.

Trajectory control of multi-link elastic robot manipulators via a nonlinear feedback controller and a robust servo controller

This paper investigates the control problem for multi-link elastic robot manipulators tracking desired trajectories with suppressed vibrations due to the elasticity of links. By using the virtual rigid link coordinate system, the finite-dimensional model is obtained. Then the controller is constructed by the nonlinear feedback controller and the robust servo controller. The nonlinear feedback controller compensating for the nonlinear terms contains not only rigid modes but also elastic modes estimated on the basis of the asymptotic perturbation techniques. The robust servo controller is designed for the low-dimensional model as it suppresses the elastic vibrations and eliminates the control and observation spillover. Some results of numerical simulations are presented to show the effectiveness of the design procedure proposed in this paper. In particular, it is shown that the proposed controller is robust against the model errors with the linearization, the modal truncation, and the parameter uncertainties.

Linear robust trajectory control of flexible joint manipulators

SUMMARYThis paper presents a practical approach for the point-to-point control of elastic-jointed robot manipulators. With the proposed approach only position and velocity feedback are referenced, as opposed to most of the existing control schemes of elastic-jointed manipulators which require additional acceleration and/or jerk feedback. To guarantee the robustness of the controller, it is designed on extreme parameter uncertainties due to highly elastic joints of manipulators and energy motivated Lyapunov functions are used to derive the control law. Four pertinent controller gains are chosen in light of the on-line position and velocity feedback of the links and joint sensors. Through a simulated experimental verification, it is demonstrated that the designed simple position and velocity feedback controller, similar to that used for rigid-jointed robots, can globally stabilize the elastic-jointed robot for a bounded reference position. In addition, the tracking performance of the controller reveals that this simple control algorithm is robust in terms of joint flexibility. And the simplicity of the presented control algorithm, as compared to other model-based techniques for flexiblejoint robots, is particularly advantageous. Even though the simulated experiments are conducted on a single-link flexible joint robot, control law derived in this paper has general meaning for multi-link flexible joint robots.

Trajectory Motion Control and Coordination of Multi-Link Robots

The trajectory motion control problem for multi-link dexterous robots is analyzed on the basis of the Coordinating Control Principle. In addition to the trajectory description introducing the conventional coordinating relations of the endpoint coordinates, auxiliary holonomic relations of the robot variables are involved to define the configuration of the robot kinematic chain and overcome the problem redundancy. The resultant system is designed on the basis of standard nonlinear control techniques and includes a nonlinear converter and a set of linear controllers providing the execution of the local stabilization tasks.

A General Algorithm for Dynamic Control of Multilink Robots

One of the major tasks in the development of sophisticated methods for robot control is finding algorithms that are appli cable to a wide range of different robots. Another major task is to find algorithms that can be used for on-line control. Several attempts have been made to solve one or the other of these problems. This article presents a general method for solving both. It can be applied to any redundant or nonredundant robot with rigid subunits connected by revolute joints in a tree-like structure. The number of joints can be chosen arbitrarily large without singularity problems, in contrast to traditional inverse kinematics models. A system based on the presented method needs no modifications when changing from one specifrc robot to another structurally or kinematically completely different robot, only input parameters describing the robot are different. The method is founded on a very general algorithm for finding the Lagrangian equations of motion for a robot subject to a given set of artificial forces. The generality and power of the method are demonstrated by two examples. In the first example the method is used to simulate a 25-degrees-of-freedom (DOF) snake-like robot moving through a maze. In the second example the method is used to control an actual application: an 8-DOF industrial robot system welding a ship section.

A simplified finite element model of multilink robots with flexible links

In this paper the problem of modeling two-joint planar robots with a flexible forearm is considered. A simplified finite element approach is proposed in order to obtain simple and structured models which can easily take into account transient phenomena and external variable forces; gravity is also kept into account. The model can be easily generalised to robots with multiple elastic links. A comparison is made with the eigenfunction expansion model in stationary conditions by evaluating the eigenvalues of the elastic link. The remarkable structure of the model can be useful in control designing, owing to the fact that the usual properties of mechanical systems are still valid.

Lyapunov functions and the control of the Euler-Bernoulli beam

A controller for the Euler-Bernoulli beam is derived using the complete distributed model along with a Lyapunov function approach. Model structure is therefore preserved in the control law whose parameters can be used to balance two different types of behaviour: the gross motion of the beam and the vibration superimposed on it. In the limiting case of a rigid beam, these two types of behaviour become indistinguishable and so the controller reduces to a proportional feedback law. This approach also guarantees that the controller provides asymptotic trajectory tracking for smooth initial conditions. Also, since it is not constrained to linear systems it could, in principle, be used for multi-link flexible robot systems.

精密加工ロボットの制御系設計 放電改質加工への応用

Recently an industrial multi-link robot is expected to be applied to precision machining. However, the multi-link robot manipulators are highly coupled non-linear systems and their equations of motions are hardly identified. Therefore it has been thought that precision machining using a multi-link robot is impossible. In this paper, a new type of precision machining robot in proposed. This robot consists of a multi-link robot and the machining unit for micro-positioning. The control system of this robot is modelled as the singular perturbed system and is applied to the position control and electric discharge machining (EDM) control.

Learning control of robot manipulators

Abstract Recent interests in intelligent approaches to robotics and manufacturing have resulted in great promise for efficient use of robots in production processes. Although neural-driven robotic controllers are still some years away, expert systems have, on the other hand, proven to be an implementable approach for many off-line applications. In this paper, a rule-based expert learning controller is introduced to control a multi-link robot manipulator. The proposed control approach has a proven convergence through two-dimensional (2-D) systems theory and is very robust with respect to the variations of the robot's dynamic model. Simulation results for a 2-link robot show very promising results.

Decentralized control of nonlinear robot manipulators

Robot manipulators have highly nonlinear dynamics. Therefore the control of multi-link robot arms is a challenging and difficult problem. In this paper a nonlinear dynamic model is first presented for an x- axis robot arm. Then a linearized model is obtained for it. The linearized model is then considered as an n- controller large-scale system. The notion of decentralized stabilization has been introduced and applied to the robot arm. Controllers considered are pd, pid and pd plus a feedforward (inverse dynamics). Numerical simulation for decentralized control of a 3-axis puma arm will also be included.