Measurement and Calibration of Machine Tools in 6 DOFs in Large Workspace

The measurement and calibration of machine tools in the large workspace (for example 10x20x3m) and in all 6 DOFs (3 cartesian translations and 3 rotations) is not an easy task. A new device called RedCaM (Redundant Calibration and Measurement Machine) has been developed that enables simultaneously to measure all 6 DOFs in the workspace. The RedCaM machine was designed with redundant number of sensors and therefore as a parallel kinematical structure. Thus it profits from the fact that the sensor errors are not chaining. It is equipped only with the sensors and it is operated by the drives of the measured machine tool after the attachment of the platform into the machine tool spindle. The redundancy of sensors provides better accuracy, self-calibration property and very good ratio between the errors of particular sensors and the resulting error of the end effector position. This has been optimized and has proven the improved (minimized) transfer of the errors between the sensors and the position in space in 6 DOFs. In particular the used redundancy of sensors (9 sensors for 6 DOFs) enables the self-calibration (all kinematical parameters are calibrated during the first motions in the workspace) and the minimized transfer of errors between the sensors and the 6 DOFs of the platform that has been experimentally proven to be 1:1. The paper deals with the description of the modification of RedCaM for the usage in the large workspace of machine tools that are in principle unlimited.