A robot does not go to a particular point in space accurately relative to its coordinate frame. This is generally due to manufacturing tolerances for every robot unit, incorrect joint zero-mastering, mechanical flexibility, gear backlash, etc.
That problem is further compounded by the additional components forming the complete robot-cell. The end-effector attached at the end of the robot might have its own mechanical flexibility; furthermore, its actual built – and therefore its ‘point of interest’ (e.g. the tip of a drill) – probably differs from the design intent. The same holds true for the fixture located on the floor intended to hold the part. The situation gets even worse when involving one or more external axes along which the robot travels, and/or if the part is held on a one- or multi-axis positioner.
To achieve the highest possible Accuracy for a given robotic operation, it is therefore required to calibrate the entire robot-cell (robot plus end-effector, fixture, and external axes).
