GUANGZHOU HAOZHI INDUSTRIAL CO., LTD.

1. The Main Form of the Failure of the Harmonic Reducer

Fracture morphology of typical fatigue failure

The main failure forms of harmonic reducer are static strength failure and fatigue failure of flexible gear or flexible bearing, most of which are fatigue fracture or precision loss due to gear wear.

2. Pain Point of Harmonic Reducer Used by Kuka Robot Manufacturer

Harmonic reducer is the key component of the robot, and its quality directly determines the performance of the kuka robot, so strict control of its quality has become the top priority in the work of kuka robot enterprises.

Due to the lack of effective and fast evaluation methodology and evaluation system in the industry, most kuka robot manufacturers take installation test as the emphasis. After simple tests, they send them to the clients for verification, for which the period is long, thus the end-users bear great risks. In addition, the test cycle for the methods provided by the national standard and the industrial standard is long, which costs at least one year in short or even more. The enterprises need to invest a lot of manpower and material resources and waste a lot of time costs at the same time.

New Standards for Test of Harmonic Reducers

1. Overload test

1. The purpose of overload test is to solve the pain point of the kuka robot manufacturer in the test and reduce the difficulty of the kuka robot manufacturer in the test.

2. Improve the test efficiency, reduce the risk for conversion of core parts, and look for the harmonic reducer products which are more cost-effective and with better performance quickly;

3. Strengthen and perfect the test standard of the industry, establish and perfect the evaluation system for harmonic reducers.

2. Loading in overload test

In order to speed up the fatigue fracture and shorten the test period, the overload test uses a load close to the material's fatigue load that instantly allows the maximum torque to be the load.

Torque Table for CSG/ HSG Model Harmonic Reducer

3. Loading mode

In formula T=Jα,

T- fatigue torque of the harmonic reducer;

J－moment of inertia loaded by harmonic reducer;

α－angular acceleration of load

Under the action of fatigue load, the harmonic reducer continuously makes positive and negative rotations of acceleration → uniform velocity → deceleration.

4. Test content

1. Fatigue life evaluation

Under the overload load, the harmonic reducer makes positive and negative rotations of acceleration and deceleration until the fracture failure takes place and the test stops. The deformation times of the flexible gear are taken as the lateral evaluation basis for the life of the harmonic reducer.

2. Dynamic monitoring of transmission accuracy

Under the action of overload load, the harmonic reducer makes positive and negative rotations of acceleration and deceleration with rated speed, and observes and records the transmission precision every day. The variation of transmission accuracy can be used as a criterion in judging property retention and life. When the change of transmission accuracy is greater than the specified value of the manufacturer’s, the test is stopped and the life of the harmonic reducer is recorded.

3. Vibration spectrum analysis

Vibration spectrum monitoring can diagnose the early failure of reducer. By observing the variation trend of characteristic frequency of flexible bearing, circular spine and flexible gear, and the variation trend of mesh frequency of circular spine and flexible gear, the corresponding fault points can be predicted in advance. In addition, the lateral comparison can be used as a means to determine the quality of the reducer.

4. Lubricating grease test

During the overload test, the reducer is removed at every 24H to observe the state of lubricating grease. In the test process, temperature rise shall not exceed the manufacturer’s specified standard value. If phenomenon such as saponification and solidification appears in lubricating grease, it can be judged that the lubricating grease is abnormal. In addition, iron dust content can be detected to carry on the evaluation.

The life and the compression-resistance overloading ability shall be tested under the action of overload load to avoid the problems of precision and life of the products due to lubrication failure. In oil analysis, the content of iron dust in grease can be used as the standard for lateral evaluation of effect of lubrication. In addition, the change of transmission accuracy can be used as the auxiliary evaluation index of lubrication effect.

Note: Whether the lubricating grease fails or not cannot be determined by visual observation of grease color.

Color of lubricating grease after test

5. Sealability

Observe all joint positions of the reducer via visual observation, and no oil leakage and oil exudation are allowed. The leakage quantity shall be collected quantitatively with a measuring glass if necessary.

6. Monitoring of dynamic temperature rise

Under the overload load, the harmonic reducer makes positive and negative rotations of acceleration and deceleration with rated speed. When the system temperature is stable, the highest temperature shall be recorded. If the temperature fluctuates too much or the maximum temperature exceeds the manufacturer's specified value, there may be problems with installation the harmonic reducer.

Schematic Diagram of Temperature Monitoring

7. Noise test

Gear noise is caused by the periodic change of gear-mesh rigidity as well as the transmission error and installation error of gear. The quality of harmonic reducer is given a preliminary judgment by the size of noise.

The harmonic reducer continuously makes positive and negative rotations of acceleration and deceleration at the maximum speed under overloading load, the details for which can be seen in the GB/ T14623-93. The background noise level should be 6dBA lower than the measured sound pressure level at least, preferably lower than 12dBA.