An Improved Measuring Device for Autonomous Form Measurement of Free Form Surfaces on Machining Centers

Abstract

The paper presents research on the improvements over an autonomous non-contact device with a vertical spindle for free form measurement which the authors developed previously. The fundamental ideas in the previous work include combining two displacement sensors with a servo motor, keeping the position of the sensor to directly measure the surface at the central value of the sensor's measuring range by controlling the motor rotation and performing scanning motions with NC functions of a MC. The inspection is entirely independent of the NC apparatus of the MC. Taking into account both the measurement accuracy and efficiency, three major improvements have been made retaining the advantages of the device. These improvements include 1) introducing a new sensing method for reference position along a scanning line to separate the reference position detection from the contour profile measurement, 2) accepting an AC servo motor controlled by a speed rule to raise the capability of autonomous movement following the contour profile to be measured, and 3) adopting a new laser displacement detector to widen the applicable range for both the shape and material of the surface to be measured. To assess the performance of the improved device, verification experiments are carried out on a machining center with several samples made of different materials. The experiment results demonstrate the effectiveness of the improvements made on the device.