Calibration and error compensation of a 4-DOF milling machine with parallel mechanism

Employing machine tools with more than three degrees of freedom, is one of the effective methods for increasing the flexibility and accuracy of the machining parts. The milling machines with parallel mechanisms and higher degrees of freedom, have great stiffness and flexibility and also have great capability in the machining of the complicated parts. The calibration of this type of device, allows for increasing the accuracy and repeatability of the produced parts. In this article, a 4DOF milling machine with a parallel mechanism is introduced and necessary tests are performed to detect the movement errors of its rails. Again, the movement errors of the device have been measured by means of a dial indicator on a fixed part of the device using a magnetic base for positioning and linear movement of the device, and the measurement of errors after calibration has shown that the errors of the device have been significantly reduced. And it has increased the accuracy of the movement axes of the milling machine. Furthermore, the straightness of the axes is measured using a dial indicator and the error compensations are done. It is shown that the straightness of each axis with the adjustment of limit switches are improved very well.