Evaluation of Linear Axis Motion Error of Machine Tools Using an R-test Device

The existing accuracy test standard for machining centers (ISO10791) is being revised in order to add a test method for five-axis machining centers. In the revised part of the standard (ISO10791-6), simultaneous three-axis interpolation motion accuracy tests for two linear axes and one rotary axis are proposed as an interpolation accuracy test for five-axis machining centers. These tests enable the measurement of the motion error in three directions, e.g., X, Y, and Z. Two devices can be used as the measurement instrument in these tests. One is a ball bar device, and the other is a combination of a ball and a displacement sensor. An R-test device that incorporates three displacement sensors has been designed for the latter. Using the ball bar device, measurement in three directions can be performed independently, and the radii of circular interpolations for each measurement are different. Using the R-test device, time is shortened by measuring three measurement directions at once, and the acquired data can be analyzed in various ways. The original goal of the measurement method using the R-test device was to measure the dynamic accuracy of the rotary axes. In the present study, the R-test device was actually prototyped and several machines were measured. In addition to the dynamic error of the rotary axes, incorrect pitch error compensation settings for the numerical controller, straightness, or squareness of the linear axes can be well detected.