Cutting error measurement of flexspline gears of harmonic speed reducers using laser probes

This paper presents a new system of measuring cutting errors of flexspline (FS) gears of harmonic speed reducers for quality control of the hobbing machine used to cut the gear. Two laser displacement probes are used to replace the conventional measurement method that employs a combination of Van Kuven wires and a micrometer. The two laser beams are projected onto different tooth surfaces with a certain spacing. When the tooth of the gear is over-cut/under-cut, the tooth thickness decreases/increases, resulting in variations in the outputs of the laser probes. The cutting error, which is caused by the error of the cutting depth of the hobbing machine and the wear of the cutting tool, can then be obtained from a differential output of the probes. The influence of the positioning error when aligning the relative position between the gear and the probes can be reduced greatly through rotating the gear and performing the measurement over the entire teeth. Experimental results indicated that the measurement uncertainty was on the less than ±2 μm (3σ), which meets the quality control requirement. It was also confirmed that the influence of cutting oil on the gear surface can be eliminated by blowing off the oil using compressed air.