On-machine multi-directional laser displacement sensor using scanning exposure method for high-precision measurement of metal-works

We propose a multi-directional triangulation optical system and scanning exposure method for precise height displacement measurement of metal-works. It is difficult to measure metal surfaces precisely with a conventional triangulation-laser displacement sensor due to machining traces. Because reflection characteristics vary by position on the workpiece, measurement errors occur even with positions of the same height. Our multi-directional triangulation optical system performs triangulation using a lens array consisting of four lenses located in a cross. Since our optical system can detect reflected light from four directions, we can achieve high-precision measurement even if the reflection characteristics vary. In addition, our scanning exposure method accumulates reflected light from many positions by scanning a projection beam onto a workpiece during the image sensor's exposure time. Because the shape of a spot image on an image sensor is the sum of the reflected light from many positions, measurement error due to measurement position is reduced. Our proposed methods can achieve on-machine deflection measurement of metal-works with a target accuracy of ±1 μm.