API’s approach to the volumetric calibration of large 5 axis machine tools comprises a 6 DoF RADIAN Laser Tracker with interferometry capability and its Active Target motorized SMR. The interferometer feature of the API laser tracker is the identical technology traditional laser interferometry systems have used for decades to successfully calibrate machine tools. Coupling the interferometry technology with a laser tracker offers the added capability to track the machine’s tool-tip location through extensive axial movements and throughout the entire volume of large machines. The motorized Active Target locks onto the API laser tracker and automatically positions itself so as to never lose the tracker laser beam.
Using the laser tracker and API’s Active Target, the Volumetric Error Compensation (VEC) technique used measures all 21 error parameters for as many as 400 points within the machine’s working volume with all possible machine poses, even with the rotary head. Each point becomes an accurate reflection of the machine’s kinematic errors. A complex algorithm is used to decouple error sources and build an extremely accurate volumetric machine error map. Error compensation is completed by adding the compensation from the entire measured axis to achieve optimum tool-tip position.
The API calibration solution also includes proprietary calibration software that uses a polynomial equation-based, kinematic model of the machine to map errors throughout the volume. To compensate the machine in real time, the software resides on the machine’s controller or on a separate PC that directly interfaces with the machine tool controller.
In summary, the software uses the measurements from the API Radian Laser Tracker and Active Target to develop compensation values to drastically reduce machine errors. Once the machine is put back in production, the software runs in the background, monitors the programmed tool path, and applies for real-time compensations automatically to the tool tip.