Joystick Teaching System for Industrial Robots Using Fuzzy Compliance Control

Industrial robots have been applied to several tasks, such as handling, assembling, painting, deburring and so on (Ferretti et al., 2000), (Her & Kazerooni, 1991), (Liu, 1995), (Takeuchi et al., 1993), so that they have been spread to various fields of manufacturing industries. However, as for the user interface of the robots, conventional teaching systems using a teaching pendant are only provided. For example, in the manufacturing industry of wooden furniture, the operator has to manually input a large mount of teaching points in the case where a workpiece with curved surface is sanded by a robot sander. This task is complicated and time-consuming. To efficiently obtain a desired trajectory along curved surface, we have already considered a novel teaching method assisted by a joystick (Nagata et al., 2000), (Nagata et al., 2001). In teaching mode, the operator can directly control the orientation of the sanding tool attached to the tip of the robot arm by using the joystick. In this case, since the contact force and translational trajectory are controlled automatically, the operator has only to instruct the orientation with no anxiety about overload and noncontact state. However, it is not practical to acquire sequential teaching points with normal directions, adjusting the tool's orientation only with operator's eyes. When handy air-driven tools are used in robotic sanding, keeping contact with the curved surface of the workpiece along the normal direction is very important to obtain a good surface quality. If the orientation of the sanding tool largely deviates from normal direction, then the kinetic friction force tends to become unstable. Consequently, smooth and uniform surface quality can’t be achieved. That is the reason why a novel teaching system that assists the operator is now being expected in the manufacturing field of furniture. In this paper, an impedance model following force control is first proposed for an industrial robot with an open architecture servo controller. The control law allows the robot to follow a desired contact force through an impedance model in Cartesian space. And, a fuzzy compliance control is also presented for an advanced joystick teaching system, which can provide the friction force acting