The involute profile is involute, and the helical profile is involute. From the perspective of engineering, in order to understand the error characteristics of a surface, it is often realized by investigating the accuracy of the characteristic line network composed of two families of curves.
There are four families of characteristic lines on involute profile, namely: Involute family, helix family, straight generatrix family and contact trace family. For involute spur gears. The straight generatrix family and helix family coincide as one, and the contact trace family and involute family coincide as one. In principle, the feature line network composed of any two or two combinations of these four family feature lines can be used as the basis for investigating the accuracy characteristics of involute profile, which can be used for the formulation of involute gear tolerance alignment, the establishment of measurement principle The principle of gear machining configuration provides an important theoretical basis.
The end section of involute profile is involute, and its error is specified as tooth profile error in the national standard. The straight bus of spur gear and the helix of helical gear can be characterized as the tooth direction of gear. The error is characterized by the tooth direction error. It can be seen that the provisions of the national standard on the tolerance items of the profile of involute gears are based on the combination of involute family and helix family (straight bus family). For helical gears, the straight bus family on the profile is a meshing instantaneous contact line family, which is a family of inclined lines on the profile, tangent to the base cylinder, and clamped with the helix angle of the base circle with the axis, Then the most important significance of straight bus error is to directly characterize the contact accuracy of tooth surface, which is very important especially for large gears
The difference can be regarded as the compound of involute error and helix error. Therefore, in a certain sense, this error is a comprehensive reflection of tooth profile and tooth direction error.
If we adopt the combination of involute family and straight generatrix family in the measurement of large gears, it should also be completely feasible. Unfortunately, the straight generatrix error of involute profile is not specified in the national standard. For spur gears, the contact trace is the end involute. For helical gears, the contact trace is an inclined curve on its profile. Its error can be regarded as the comprehensive reflection of involute error and helix error. Its importance mainly lies in that when the overall error of worm single-sided meshing is measured comprehensively, the directly obtained error information is the contact trace error. Therefore, it is reasonable for some to call the contact trace the normal tooth profile of helical gear.
Using the combination of J contact trace family and helix family, I can also be used as the basis for the accuracy measurement of involute profile, in fact. At present, the widely used overall error measurement of worm gear is a typical application of this combination, but there is no tolerance standard for contact trace in the national standard.