Force-Based Pick-and-Place Along Curved Surfaces Exploiting Robot Repeatability

Abstract:
Monotonous pick-and-place applications in manufacturing are often automated using robots. Depending on the quantity of units, the geometry of the construction, the know-how of the collaborating workers, and the possibility to use external sensors, different approaches are generally implemented. To achieve high accuracy, the in general teached or pose controlled systems must be calibrated or measured at great expense, which limits their flexibility. In this contribution, the placing of bushings or bolts that need to be welded along a curved surface is considered. An approach exploiting the robot’s repeatability to achieve high precision without the need for interference-prone external sensors for pose control is introduced, guaranteeing low setup costs. The introduced robot-assisted automation includes autonomous surface scanning, force-based sensing for surface unevenness, and pose adjustment to ensure that a relative alignment of the bushings or bolts to each other is fulfilled so that further components can be mounted to them. Since the robot performs both the detection and the setting by evaluating its direct kinematics at the same poses, the robot’s repeatability can be exploited, which is significantly more accurate than the absolute accuracy of robots that would have to be utilized if the poses were specified externally by the underlying CAD drawing, as it is usually done in the conventional approaches. The evaluation of the precise setting procedure is performed by using a standard industrial robot Stäubli TX2-90 with UNIVAL DRIVE combined with a force-torque sensor in a real experimental setup.