Daisuke Kushida

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.

Flexible motion realized by force free control: pull-out-work by articulated robot arm

Flexible motion of an industrial articulated robot arm, i.e., the passive motion of the robot arm for an external force, is realized by the proposed method of force-free control. The force-free control enables the motion of an industrial articulated robot arm as if it were in a circumstance of non-gravity and non-friction condition. The effectiveness of the force-free control was assured by applying the approach to a pull-out-work with a two degree-of-freedom articulated 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.

Flexible motion of pull-out-work by articulated robot arm based on forcefree control

Flexible motion of an industrial articulated robot arm is realized by using force-free control, in which the flexible motion means that the robot arm is actuated by external force passively. Force-free control enables the natural motion of the industrial articulated robot arm as if the robot arm exists in a circumstance of non-gravity and non-friction condition. The effectiveness of the force-free control was assured by the application of pull-out-work on a 2-degree-of-freedom articulated robot arm.

Analysis of Contouring Error for Articulated Robot Arm and Determination of Operational Condition.

Mechanism of locus error for contour following control of industrial articulated robot arms was analyzed and the locus error was derived theoretically. Main causes of locus error were found in the nonlinear transformation between kinematics and the inverse kinematics, and the delay of dynamics. The derived equation of the locus error was assured by simulation and experimental studies. Besides, the relationship between locus error and objective velocity was obtained by using the analyzed equation. As a result, objective velocity can be decided based on the maximum locus error and position loop gain of the servo controller. Moreover, optimal ratio of length of links was obtained by use of the derived relationship.