Volumetric Measurement of CNC Machines

The goal of volumetric measurement is to assess the overall accuracy of a machine as it moves through space, enabling a better understanding of the CNC machine’s overall performance. This contributes to resolving accuracy issues, improving manufacturing quality, and preventing potential errors in production.

Typically, volumetric measurements of CNC machines are performed on Fanuc and Heidenhain controllers. Full volumetric compensation can be provided for modern controllers such as Heidenhain TNC640. On other controllers that do not support the necessary options, we perform standard laser calibration using the same measuring equipment. This approach always provides a complete picture of the machine’s geometric condition, but we can only correct the errors that the machine's controller supports for compensation.

After a thorough geometric analysis using state-of-the-art high-tech measuring technology and equipment, we identify and evaluate individual errors across the entire machine volume. For 5-axis machines, we also simultaneously adjust the machine’s kinematics (rotary axis positions).

We conduct measurements with the most advanced diagnostic equipment. Essential devices for volumetric measurements include the Renishaw laser calibrator and the HEXAGON ETALON calibrator. For backlash detection, axis misalignment, and vibration analysis, the circular test with the Renishaw BallBar diagnostic device remains the best method, as it measures deviations in the circular motion of the machine.

Volumetric Compensation Corrects All Errors

Volumetric compensation corrects all 21 errors on a 3-axis machine and all 43 errors on a 5-axis machine.

ISO Definition:

• 6 errors in the movement of the linear X-axis
• 11 errors in the movement of the rotary C-axis
• A total of 21 linear movement errors fully define the accuracy and precision of the 3D workspace of a 3-axis machine

Understanding the actual deviation of the tool tip from the expected movement accuracy is complex, as individual errors interact and influence one another.

Existing conventional standards, such as ISO 230-1, ISO 10791, and JIS B 6190-1, which manufacturers use to evaluate the accuracy and precision of CNC machines, only describe:

• Distance errors
• Repeatability of positioning along a linear axis between specific measurement points

However, these standards do not account for:

• Transverse misalignments
• Angular errors

Due to the interaction of different errors, significant deviations can occur at various positions and with different tool lengths. As a result, conventional standards do not provide a complete and clear picture of a machine’s accuracy.