A robot is generally capable of repeating the same move towards a specific point in space, over and over, within a high level of tolerance
(referred to as ‘unidirectional Repeatability’), generally well below 0.1mm. But this does not mean that that particular point in
space is well known relative some global coordinate frame (such as the robot base frame): the level of ‘Absolute Accuracy’ achieved
by an ‘off-the-shelf’ industrial robot is generally in the several millimeters and more. 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 Absolute Accuracy for a given robotic operation, it is therefore imperative to ‘close’
as much as possible the entire ‘metrological chain’ formed by the different components linking the point of interest on the robot’s
end-effector (the TCP), on one end, and the point on the part the robot is operating on, on the other end. Sometimes, the just described
general process is somewhat inversed, where the robot holds the part through a ‘gripper’ and the tool (TCP) is fixed on the floor. The
DynaCal™ robot calibration system allows not only robot calibration but the entire robot-cell calibration in one single step:
the robot, the end-effector’s TCP, the fixture’s location (alignment), and optionally the external axes and/or positioner are calibrated
altogether. This is achieved by moving the robot to a variety of positions in space, each time measuring the robot at (or at a point
in a known location relative to) the TCP, expressed in the part’s coordinate frame. This can be performed with the DynaCal proprietary
measurement hardware, or with any external (large-range) measurement equipment (such as a laser tracker). Full Absolute Accuracy robot
calibration as just described is used in virtually every kind of robotic application (except for very low-accuracy applications, such
as painting), e.g. in arc-welding, waterjet cutting, drilling and routing, assembly, spot-welding, gauging, etc. The purpose of robot
calibration is generally to reduce manual programming time, improve process quality, and/or to enable standard robots to achieve accuracies
of much more expensive equipment (i.e. CNC machines, CMMs, etc.). Robot calibration enables ‘Off-Line Programming’, ‘Cloning’ of existing
robot-cells, ‘Mirroring’ across production lines, ‘Swapping’ of robots, etc. (see “Off-Line Programming with No Touchup”, “Duplicate
Robot Programs with No Touchup”). Robot calibration, including calibration of its peripherals, for Absolute Accuracy with the
DynaCal system is generally done once at the installation of the robot-cell, but it can of course be repeated at any time throughout
production, for reasons such as robot maintenance, robot replacement, etc. However, during normal production operation, it is generally
recommended to use a dedicated in-line recovery tool instead – such as the AutoCal™ or the AccuBeam™ system – in order to automatically
detect and correct as promptly as possible any accuracy issue within the robot-cell, thus insuring that your robot-cell will maintain
throughout production the level of Absolute Accuracy achieved at installation with the DynaCal robot calibration system (see “Maintain
your Robot’s Accuracy throughout Production”).