OPTIMIZATION OF WORKPIECE PLACEMENT IN SEALING OPERATION USING INDUSTRIAL ROBOT CONSIDERING MANIPULABILITY

Off-line teaching systems are becoming the mainstream method of making a robot program, as opposed to a teaching playback method that requires the technical skill of a worker. The off-line teaching system enables to make the robot program on a computer and allows the simulation of robot motion by checking the program. However, to make an optimal program with consideration to the prevention of sudden change in the robot’s motion, singularity should be avoided and workpiece placement should be optimized. In particular, to determine the workpiece placement, the operator must perform many trial and error operations. In this paper, we propose an optimization method for workpiece placement during a sealing operation by using an industrial robot. This method is based on manipulability, which is a measure of the robot’s manipulating ability. We confirmed the effectiveness of the proposed method by applying it to an actual sealing process. INTRODUCTION At a manufacturing production site, vertical articulated industrial robots are widely used to automate various operations, owing to their high versatility and operability. Typical examples of this application include the assembly, welding, painting, sealing, and handling of material. To operate an industrial robot, it is necessary to create a robot program that consists of end effector position/posture or joint angle sets. Typically, the operator makes the robot program by using the teaching playback method, which requires various operations through a special control device called the teaching pendant. Although the operator can make the robot program intuitively by using an actual robot, the teaching operation is time consuming. Moreover, the production cost may increase substantially because the production line must be stopped during the teaching operation. In recent years, an off-line teaching method, which can make a robot program by operating the robot in a virtual space, has been developed and is becoming a mainstream method of robot program creation. By using this method, the time for stopping the production line and the labor entailed in the operation of an actual robot may be reduced. Moreover, to conduct an optimal operation, the operator must determine the workpiece placement in order for the robot to perform the task safely, which requires many trial and error operations. Thus, some studies have proposed to optimize the robot program [1-3] and automate actual operations such as the polishing process [4-6]. However, it has been difficult to use these methods in practice. In this paper, we propose a method based on manipulability, which is a measure of the robot’s manipulating ability [7], with the objective of optimizing the workpiece placement. Moreover, we have confirmed the effectiveness of the proposed method by applying it to an actual sealing process. RELATIONSHIP BETWEEIN ROBOT POSTURE AND MANIPULABILITY This study focused on six degrees-of-freedom industrial robots. Robot motion can be represented in two ways: as a set of end effector positions/postures (r), or as a set of each joint angle (q). These approaches are represented by Eqs. (1) and (2), respectively, as follows: