Page - 46 - in Proceedings of the OAGM&ARW Joint Workshop - Vision, Automation and Robotics

The electronic screwdriver of the manual workplace is fitted with a push start mechanism, electronic control unit and a shut-off clutch and therefore starts rotating when pushed onto the screw and stops motion when retracted respectively when a predefined torque is reached. The working instruction of the workstation includes several additional process steps. An automatic screw tightening system is expected to provide assistance and to reduce the workload at the workstation for the human worker. A state-of-the-art collaborative robot system is equipped with the power tool (Fig. 1) and programmed to perform screw tightening operations in the required order and accuracy to meet a defined process quality (screw-in depth, torque,…). Fig. 1 - Usecase Combustion Engine Assembly – screw positions to be parameterized by the user. A. Robot A Robot A is a standard Universal Robot UR10 system with its teach pendant and the integrated programming and parameterization infrastructure. A basic script for the movement contains the pre-screwing process and can be called by the teach pendant program. The teach pendant program manages position variables (that have to be parameterized by the worker) and the execution of the global program to process the screws in the correct order. Fig. 2 - www.zacobria.com - UR10 programming B. Robot B To be able to provide smooth and precise one hand- guidability a FT-sensor was integrated in robot B. Shortkey buttons trigger alignment shortcuts (Fig. 3). Preconfigured TCP alignments can be triggered and cause the tool to rotate around the TCP to move the tool intuitively to an (e.g. perpendicular) orientation to maximize process stability and robustness towards inaccurate teach-in of process points. Fig. 3 - FT-sensor, shortcuts and DOF locks The GUI of the robot controller interface was replaced by XROB, a PC-based robot programming system, that covers both robotics and sensors and algorithms to assess sensor data. Benefits are on the one hand simplification of the interplay between robotics and machine vision and on the other hand simplification of the programming experience for the robot (that was perceived as confusing with robot A). XROB (Fig. 4) is capable to manage several sensors and evaluation algorithms. Program templates can be used to compose basic functionality to advanced and reusable subprograms. Prior to evaluation of robot B templates for a combined rough 3D position deviation compensation and a 2D position fine compensation were prepared for reuse by the workers. Fig. 4 - XROB framework 46