Nobuhiro Kyura

Accurate contour control of mechatronic servo systems using Gaussian networks

This paper presents a method of contour control of mechatronic servo systems by using neural networks. The neural network learns the inverse dynamics of the mechatronic servo system. The input data for the mechatronic servo systems are modified from objective trajectories by using the neural network. The Gaussian network is adopted to construct the inverse dynamics of the mechatronic servo system because the Gaussian function is well defined, and its structure and initial parameters can be systematically selected such that the initial network approximates the inverse dynamics of the mechatronic servo system. The actual input/output data of the mechatronic servo system are used for the learning of the Gaussian network. Effectiveness of the proposed method is assured by experimental results of contour control of an X-Y table.

Human direct teaching of industrial articulated robot arms based on force-free control

Force-free control produces motion in a robot arm as if it were under conditions with no gravity and no friction. In this study, a method of force-free control is proposed for industrial articulated robot arms. The force-free control proposed was applied to the direct teaching of industrial articulated robot arms in that the robot arm was moved by direct human force. Generally, the teaching of industrial articulated robot arms is carried out using operational equipment called a teach-pendant. Smooth teaching can be achieved if direct teaching is applicable. The force-free control proposed enables humans to teach industrial articulated robot arms directly. The effectiveness of force-free control was confirmed by experimental work on an articulated robot arm with two degrees of freedom.

Enhanced contour control of SCARA robot under torque saturation constraint

Contour control of a robot arm is an act of the end-effector tip being moved along a reference Cartesian path, with an assigned velocity. When torque saturation occurs, and lasts for some time, contour deteriorations result. In addition, system delay dynamics also causes contour deteriorations. In this paper, an offline trajectory generation algorithm is described, which achieves both optimum avoidance of torque saturation and delay dynamics compensation.

Optimum contouring of industrial robot arms under assigned velocity and torque constraints

Presents a general solution to the contouring problem of industrial robot arms, under the constraints of assigned Cartesian velocity and joint torque/acceleration. The proposed solution is an off-line trajectory generation algorithm and, therefore, it possesses significant industrial implications, as no hardware changes are needed for its implementation. According to the proposed method, the maximum utility of joint torque/acceleration is guaranteed to be bound to the assigned velocity constraint. In the proposed method, a realizable trajectory is generated from the objective trajectory and its delay dynamics are compensated for by using a forward compensator. The proposed method has been experimented with using a Performer MK-3s (PMK-3s) industrial robot arm, and optimum contouring has been realized.

High speed precise control of robot arms with assigned speed under torque constraint by trajectory generation in joint co-ordinates

This paper presents a methodology for off-line trajectory generation that guarantees high-speed and precise end-effector point-to-point (positioning) control of industrial robot arms, within the bounds of the most relevant constraints. The constraints being addressed are the saturation of joint torque and the limit of Cartesian velocity. In the proposed methodology, shortest path of travel and maximum-joint torque/acceleration utility is guaranteed so that the true minimum-time trajectory is generated. The minimum-time trajectory is then compensated for the delay dynamics using a feedforward compensator. An illustrative implementation is presented using the Performer MK-3s robot arm, with which attractive results have been obtained. Being an off-line algorithm, the proposed method can be conveniently introduced into existing servo control systems of industrial robot arms, and to enhance their performance.

Highly accurate contour control of an articulated robot manipulator using a Gaussian neural network

Purpose – Aims to realize the high accurate contour control with high‐speed motion of articulated robot manipulator (ARM) with interference.Design/methodology/approach – Proposes a new contour control method by using Gaussian neural network (GNN) to solve the problem of the deterioration of the contour control performance due to the interference between robot links. The construction of the GNN controller and the approximation of the interference are based on the Euler‐Lagrange model of ARM. The actual input/out data about the motion of ARM are used for training the GNN to accurately represent the inverse dynamics of ARM with interference. With the Lyapunov function, the stability and the robustness of the GNN controller are discussed. Through the simulation and experiment, it verified that the precision of the contour control has been improved, and illustrated the good features of the proposed method.Findings – Finds that the actual data about the motion of ARM, which is easily obtained from the working f...

Precise control of industrial robot arms considering trajectory allowance under torque and speed constraints

Presents a control algorithm for industrial robot arms. This algorithm is based on off-line trajectory generation with compensation of statics and dynamics. Using the proposed method, the Performer MK-3s industrial robot arm was controlled and improved performance has been realized. The proposed algorithm appears as a feedforward, off-line block in the robot arm control system. Therefore, it could be conveniently incorporated with the industrial robot arms without significant hardware alterations.

Pole selection of feedforward compensators considering bounded control input of industrial mechatronic systems

A new pole selection method for feedforward compensators of mechatronic servo systems is presented in this paper. It is necessary to have the system poles located at desirable positions on the s-plane in order to realize better servoing performance. However, selection of new poles is not a straightforward problem and in most industrial mechatronic systems, it has been a mere cut-and-dry procedure. In this research, feedforward compensator poles are related to the control input, and a criterion was developed to determine the desirable poles that improve the control input within its limits. This method was developed for the second-order model and it was simulated and experiments were performed with the Performer MK3s articulated industrial robot manipulator. Some attractive results have been obtained with the new method.

Property of force-free control with independent compensation for inertia, friction and gravity of industrial articulated robot arm

Force-free control can realize the flexible motion of industrial articulated robot arms without any change of the built-in controller. In this paper, the force-free control was extended to realize the motion as if it were under the circumstance of any inertia, any friction and any gravity through the independent compensation of inertia, friction and gravity. The property of the force-free control with independent compensation was also investigated by the experimental study of an actual industrial articulated robot arm, where the external force was measured by the force sensor which was attached to the tip of the robot arm.

Force-free control of articulated robot arm considering velocity along assigned locus

Force-free control with velocity consideration under the assigned locus is proposed for an articulated robot arm. The tip of the robot arm is moved on an objective locus according to the tip velocity. Then, the direction of the tip velocity, which corresponds to the exerted force, is modified to the tangential direction of the assigned locus. The contouring work of an articulated robot arm is, therefore, carried out with a force-free control. The effectiveness of the proposed force-free control is assured by simulation and experimental work on a two-degree-of-freedom articulated robot arm. Applications of the force-free control with an assigned locus are also discussed.