Optodyne's SD-500
A new method for the measurement of volumetric errors of a CNC machine tool or a coordinate measuring machine is described here. As compared with conventional laser interferometer measurement, the "VECTOR" method measures the vector errors, namely, the displacement error, vertical straightness error and horizontal straightness error, rather than the displacement error only. It can also measure the angular errors and the non rigid-body errors. Once the volumetric errors are measured, they can be used to compensate the repeatable errors of the machine.
The linear displacement errors, straightness errors, squareness errors, angular errors and non-rigid body errors determine the performance or accuracy of a CNC machine tool or a coordinate measuring machine (CMM).
The characterization of a machine movement is very complex. For each axis of motion, there are 6 errors, linear, vertical straightness, horizontal straightness, pitch, yaw and roll angles. For a 3-axis machine, there are 18 errors plus 3 for squareness, a total of 21 errors. The machine accuracy can be improved by measuring all these errors and then to compensate these errors, providing that the machine is repeatable. The key is how to measure these errors accurately and quickly. There are many methods to measure these errors however; all of these methods are very complex and time consuming. The body diagonal measurements have been recommended by machine tool standards such as ASME B5.54 for a quick check of the volumetric accuracy. This is because it is sensitive to all the error components.
However, if the measured errors are large, there is not enough information to identify the error sources.
Described here is a vector method. It can measure all these errors, using the simple and portable MCV-500 Linear Calibration System, in 4 settings and within a few hours.
Optodyne Incorporated, 1180 Mahalo Place, Compton, CA 90220. Tel: 310-635-7481; Fax: 310-635-6301.