Correct selection, installation and maintenance of precision planetary gear reducer

Update:16 Sep 2020

Precision planetary gear reducer is widely used in the drive system of servo, stepper, DC brushless control motor (also known as drive motor) because of its small size (basically the same diameter as the matching motor), high transmission efficiency (90% ~ 96), wide range of reduction ratio (single stage: 3 ~ 100), high precision (small side clearance). On the premise of ensuring the precision transmission, it can reduce the speed, increase the torque and reduce the moment of inertia ratio between the load and the driving motor.
However, in practical use, there are often faults caused by improper installation. One of the main types of faults is the broken shaft of reducer and drive motor. The analysis of shaft breaking mechanism is helpful for customers to understand how to correctly install the precision planetary gear reducer and better play the role of driving motor.

1、 The problem of broken shaft caused by too small output of precision planetary gear reducer
If the drive motor shaft is not broken, but the output shaft of the reducer is broken, in addition to the causes of poor assembly concentricity of the reducer output end, there will be the following possible reasons.
First of all, the wrong type selection results in insufficient output of the reducer.
Some users mistakenly think that as long as the rated output torque of the selected reducer meets the working requirements, it is not. One is that the rated output torque of the drive motor multiplied by the speed ratio, the value obtained should be less than the rated output torque provided by the reducer product sample in principle; the other is to consider the overload capacity of the drive motor and the maximum working torque required in practical application. In theory, the maximum working torque required by the user must be less than the rated output torque of the reducer (proportion: the coefficient of uniform load is 1.5 times, the coefficient of medium impact is 2 times, and the coefficient of impact load is more than 3 times). In particular, some applications must strictly abide by this criterion, which is not only to protect the internal gear and shafting of the reducer, but also to avoid the output shaft of the reducer from being twisted. If these factors are not taken into account, once there is a problem in the installation of the equipment, the output shaft of the reducer will be stuck by the load. At this time, the overload capacity of the drive motor will make it continuously increase the output, until the force of the output shaft of the reducer exceeds its maximum output torque, the shaft will be broken.
Secondly, in the process of acceleration and deceleration, if the instantaneous impact torque of the reducer output shaft is more than twice of its rated output torque, and the acceleration and deceleration are too frequent, the reducer shaft will eventually be broken. If this happens, it should be carefully calculated and considered to increase the torque margin.

2、 Correct installation of precision planetary gear reducer
The correct installation, use and maintenance of the drive motor is an important link to ensure the normal operation of mechanical equipment. Therefore, when installing the precision planetary gear reducer, please strictly follow the following installation sequence and correctly install and cooperate.
Step 1: before installation, confirm whether the motor and reducer are in good condition, and strictly check whether the sizes of the parts connecting the drive motor and the reducer match. This refers to the size and fit tolerance between the positioning boss and shaft diameter of the drive motor flange and the positioning groove and hole diameter of the reducer flange; wipe and treat the dirt and burr on the fitting surface.
Step 2: screw off the screw plug on the process hole on the side of the reducer flange, rotate the input end of the reducer to make the locking hexagon screw cap align with the process hole, insert the hexagon socket tool to loosen and tighten the hexagon socket screw.
Step 3: hold the drive motor so that the keyway on the shaft is perpendicular to the screw holding the input end hole of the reducer, and insert the drive motor shaft into the input end hole of the reducer. When inserting, the concentricity of the two must be consistent and the two side flange should be parallel. If the concentricity is inconsistent or the two side flange is not parallel, the cause must be found out. In addition, it is strictly forbidden to use hammering during installation, which can prevent the axial force or radial force of hammering from damaging the bearings of both sides, and the fitting of the two can be judged by the feeling of assembly. The method to judge the matching centrality and flange parallelism is as follows: after the two are inserted into each other, the flanges of the two are basically close and the gap is consistent.

Step 4: in order to ensure that the flange connection stress is uniform, first screw on the fastening screws of the drive motor arbitrarily, but do not tighten them; then gradually tighten the four fastening screws according to the diagonal position; finally, tighten the locking screws of the input end hole of the reducer. Be sure to tighten the fastening screw of the drive motor first, and then tighten the locking screw of the input end hole of the reducer.
Remarks: the correct installation of precision planetary gear reducer and mechanical equipment is similar to that between reducer and drive motor. The key is to ensure that the concentricity of the reducer output shaft and the driven part of the input shaft is consistent.

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