1. Empty back and the factors that produce empty back
The so-called air return is a phenomenon that the driven wheel lags behind when the main wheel reverses its rotation. The hysteresis angle is the error angle of the idle back. The main reason for idle back is due to the presence of side clearance in a pair of gears. Theoretically, a pair of meshing gears can be without side clearance. However, in some cases, the side clearance is necessary for the proper operation of the transmission. The presence of the side clearance prevents the gear teeth from jamming due to machining errors in the parts; in addition, it provides space for storing lubricant, as well as taking into account factors such as changes in the dimensions of the parts due to temperature changes. However, the air return error caused by the side clearance in the reverse transmission will directly affect the transmission accuracy.
The main factors that produce the empty back are: for the gear itself, there are the center distance becomes larger, tooth thickness deviation, base circle eccentricity and tooth shape error, etc.. In addition, the eccentricity of the gear when mounted on the shaft, the radial eccentricity of the rotating seat ring of the rolling bearing and the mating clearance between the fixed seat ring and the housing will also have an impact on the air return.
In the reduction chain, the air return error of the last level (or the last few levels) of the gear has the greatest impact on the air return error of the whole transmission chain. Therefore, it is important to improve the manufacturing accuracy of the last level (or the last few levels) of gears to reduce the air return error of the whole transmission chain. At the same time, it is reasonable to arrange the transmission ratio at all levels according to the smallest and then the largest.
2. Eliminate or reduce the method of empty return
①Use of spring force
② Fixed double piece gear
③ Utilization of the contact spring
④ Adjustment of center distance method