How is the positioning accuracy of the rotary axis measured on a cradle-type five-axis machining center?

Precision Measurement of the Rotary Axis in a Cradle-Type Five-Axis Machining Center

Release time:

2021-12-02

Traditionally, calibration of a machine tool’s rotary axis requires mounting an automatic precision rotary table at the axis’ center of rotation to perform the calibration. In cradle-type five-axis machining centers, the rotary axis’ center of rotation (C.O.R.) is constrained by the absence of a coupling joint, necessitating more complex support and alignment procedures for axis calibration—thereby potentially increasing the difficulty of calibrating the machine tool.

Solution:

Measurement configuration: SJ6000 laser interferometer main unit + angle mirror assembly + WR50 automatic precision rotary table + eccentric shaft accessory + eccentric shaft measurement software.

Mount the WR50 automatic precision rotary table on the A-axis of a cradle-type five-axis machining center—installation does not need to be centered on the axis of rotation—and perform the test. The eccentric shaft measurement software synchronizes linear and rotary motions while maintaining laser beam collimation throughout the entire test, which significantly simplifies the hardware setup requirements.

Working principle:

The operating principle of eccentric shaft measurement relies on the synchronized motion of the machine tool’s linear axes and rotary axes. As illustrated in the figure, each movement of a rotary axis is matched by a corresponding movement of a linear axis. It is important to note that, even for identical angular-axis movements, the linear-axis travel intervals will vary to ensure collimation between the laser interferometer and the automated precision rotary table.

Precautions:

Since one of the optical lens assemblies is fixed to the moving linear axis, the measured angular-axis data will also include errors attributable to the linear axis—for example, the angular error shown below. For this reason, an additional, independent angular measurement should be performed along the linear axis at the same stop position used during the initial synchronous movement. The two error files can then be combined to eliminate the influence of linear-axis angular error, thereby accurately reflecting the rotational accuracy of the rotary axis.