Abstract: According to the characteristic that there are three families of curves, that is, involute family, helix family and straight generatrix family on the involute helicoid, the measurement principle based on the error of straight generatrix family is put forward. Taking the straight-line-rack as the tool, the error of straight generatrix is measured, and by error analysis, the tooth profile error and tooth orientation error can be obtained. This kind of measuring method takes the benchmark of the machine tool as the measuring one, and overcomes the problem that the weight and the inertia of the large gear are big and the control of its motion is difficult, so there are the advantages of high measuring accuracy and convenient operation. At last, the experiment has been done, which indicate that the principle is correct and the technology is practicable.

Key words: Large gear, Measurement on-line, Spiral line total deviation, Straight generatrix error, Tooth profile total deviation