The harmonic reducer is the knee of the robot. Where is the performance gap between domestic and foreign products?

 The so-called harmonic reducer is a reducer made of the principle of harmonics. Compared with other reducers, it has the characteristics of compact structure, large reduction ratio, high precision and low noise. The harmonic reducer is very suitable for the joints of various robots to adjust the movement speed and output torque of each arm of the robot.

Advantages of harmonic reducers

1. High bearing capacity In harmonic transmission, the meshing of teeth and teeth is surface contact, and the number of meshing teeth (overlap coefficient) is relatively large at the same time, so the load per unit area is small, and the bearing capacity is higher than other transmission forms.

2. Large transmission ratio The transmission ratio of single-stage harmonic gear transmission can reach i=70～500.

3. Small size and light weight.

4. High transmission efficiency and long service life.

5. Smooth transmission, no impact, no noise, and high movement precision.

Harmonic reducers, especially high-precision harmonic reducers, have always been a type of product that our country has been developing. It is a revolutionary product.

The harmonic reducer has a simple and compact structure and is mainly composed of three basic components: a flexible wheel, a rigid wheel and a wave generator. The failure of the harmonic reducer is largely caused by the fatigue fracture of the flexible wheel, which affects the service life. What causes the fatigue fracture of the flex wheel of the harmonic reducer, and what can be done to better solve this problem?

1. The main reason for the fatigue fracture of the flexible wheel

The fatigue fracture of the flex wheel of the harmonic reducer mainly goes through three stages: nucleation, expansion and fracture, and the cracks are generally formed on the surface and then expand to the inside. The rate is the lowest, and the final fracture occurs when the crack expands to a larger extent.

2. Solutions to Fatigue Fracture of Flexible Wheels

1. Select high-strength and high-impact toughness materials to increase the material strength and reduce the impact toughness.

2. Strengthen the flexible wheel through material surface treatment, reduce surface defects and improve surface stress state, and prevent fatigue cracks from nucleating on the surface.

3. Make the core of the part have a good combination of strength and impact toughness, and reduce the expansion rate of fatigue cracks.

Fatigue fracture of the flex wheel is one of the main reasons for the failure of the harmonic reducer. The quality of the flex wheel directly determines the service life of the harmonic reducer. Therefore, the choice of the material of the flex wheel is very important, and the surface treatment process of the flex wheel is also very important.

my country is a big manufacturing country and is currently developing towards a manufacturing power. According to relevant statistics, in 2014, the sales volume of robots in my country was 57,000 units, of which the number of domestic robots was about 18,000 units; The sales volume has reached 248,000 units, an increase of 12% over 2014, while the consumption of industrial robots in China is 67,000 units, making it the largest market in the world.

In order to keep up with the pace of global manufacturing upgrading, my country has successively released "Made in China 2025" and the robot industry development plan, proposing that by 2020, the annual output of self-owned brand industrial robots will reach 100,000 units, and the annual output of six-axis and above industrial robots will reach 100,000 units. More than 50,000 units, cultivate more than 3 leading enterprises with international competitiveness, and create more than 5 robot supporting industrial clusters. It can be seen from this that the development potential and market prospects of robots and even harmonic reducers.

However, at present, most of the high-end robots in industrial robots are imported robots. The harmonic reducers installed in these high-end robots basically come from the products produced by Japanese HD company. In today's world market, the harmonic reducers produced by the company Almost monopolized the entire industry, so the medium and high-grade harmonic reducer has also become a bottleneck restricting the development of my country's robots and related industries.

Comprehensive analysis, if the tooth shape can be reasonably designed according to the working principle of harmonics, so that the working life of the harmonic reducer can reach the level of Japanese HD company, and at the same time, it can maintain a good running accuracy, it can be applied to medium and high-grade robots. So as to open up domestic and foreign markets.

Break through the domestic robot industry development bottle

A complete robot mainly consists of a reducer, a controller and a servo motor. As one of the three core components, the harmonic reducer has particularly high requirements for technical content. However, at present, there are very few domestic manufacturers of harmonic reducers, and even fewer can mass-produce them, which is less than 5.

The products are not only used in industrial robots, but also in aerospace, ordnance, machine tools, medical equipment and other fields. Up to now, the company's annual production capacity has reached 20,000 sets, and it has 6 national invention patents and 20 utility model technology patents. There are five series of harmonic reducer products produced by the company, with a total of more than 100 specifications, and can also be developed and customized according to customer needs.

According to reports, the entire R&D process of this project is divided into the preliminary test stage and the pilot test stage. The preliminary test stage is centered on improving product quality, and the pilot test stage is centered on improving product quality stability.

The preliminary test stage includes the research and development of tooth profile, the research and development of materials and the research and development of lubricating grease. According to the introduction of scientific researchers, according to the working principle of harmonics, a suitable tooth profile is developed, which can better conform to the conjugate principle and has better anti-load capability; During the working process, it is constantly under the action of alternating stress, and at the same time it has to transmit the load. Therefore, the flexible wheel material should have good strength; during the working process of the harmonic reducer, its working cavity is a closed container. The requirements for the lubricating grease are very strict, and the grease is required to have good lubrication, extreme pressure and thermal conductivity. For this reason, it is necessary to start from the actual working conditions of the harmonic reducer. Lubricating grease.

The pilot test stage is based on the preliminary test stage to further stabilize and improve product quality by exploring the manufacturing process, mainly including exploring and stabilizing the manufacturing process and assembly process of key parts of the harmonic reducer, as well as the performance requirements for key parts, Explore a set of effective material heat treatment process. In addition, necessary post-processing should be performed on the key parts of the harmonic reducer to further improve the performance of the parts.

Comparison of performance indicators of domestic harmonic reducers VS foreign harmonic reducers

The harmonic reducer market has always been dominated by Japanese brands. The domestic harmonic reducer has gradually occupied the market share in recent years. However, in terms of performance indicators, the domestic harmonic reducer is compared with foreign harmonic reducers. There is still a big gap in the reducer. The important performance indicators for measuring the harmonic reducer mainly include: transmission accuracy, free travel, backlash, transmission efficiency, torsional stiffness, starting torque, service life, overload performance and so on. Where is the main gap between domestic harmonic reducers and foreign harmonic reducers?

1. Gap in the form of failure

The failure mode of domestic harmonic reducer is mainly the decrease of transmission accuracy caused by gear wear; the main failure mode of foreign harmonic reducer is the damage of flexible bearing.

2. Repeated positioning accuracy stability gap

The repeated positioning accuracy of the domestic harmonic reducer can be compared with that of foreign harmonic reducers in the initial stage of use, but with the passage of time, the increased wear and tear will cause the harmonic reducer to fail, thus affecting its repeatable positioning accuracy. .

3. Differences in materials used

The harmonic reducer relies on the elastic deformation of the flexible wheel for power transmission, which has high requirements on the wear resistance and fatigue resistance of the material.

4. Differences in processing technology

The processing technology of foreign harmonic reducer manufacturers has long been able to produce 2 steel parts per minute, while domestic harmonic reducer manufacturers still use traditional slow wire walking, gear hobbing and gear shaping processes.

At present, the domestic harmonic reducer has greatly improved in terms of transmission accuracy, transmission efficiency, service life, batch consistency and other important performance indicators, and has been rapidly approaching or even surpassing foreign harmonic reducers.