Industrial robots are extremely good at repetitive tasks. They exhibit excellent repeatability, making them ideal candidates for many tasks. However, increasing use of CAD based offline programming highlights the fact that industrial robots are generally not accurate devices. Several approaches have been used to compensate for this deficiency. Robot calibration is well established and factory calibrated robots are available from most industrial robot manufacturers. This can improve the spatial accuracy of robots to figures better than 1mm which is adequate for most robot processes in use today. Improvements in accuracy beyond this point can be achieved if the working range of the robot is constrained in some way. For example, limiting a robot to working in a single plane or restricting the robot to a reduced work volume can contribute to significant improvements in accuracy. However, for applications requiring high accuracy without these constraints some additional control is needed. Systems have existed for several years that integrate metrology systems with robots to provide closed loop positional feedback to the robot controller. These systems have generally been limited to static processes and also introduce significant delays into the process while measurements are taken.
The paper proposes a solution to improve robot path accuracy by implementing real-time closed loop positional control of the robot end effector using a high speed, high accuracy metrology device. It has been shown that using this method it is possible to correct robot paths such that accuracies of better than 0.2mm are achievable at speeds of 50mm/s.
