Reducer – the core of mechanical equipment transmission, the joint of robot activity

The reducer is the core device that connects the power and the executive mechanism. It has a long history and many kinds

The input power source of mechanical equipment is usually small in size and large in speed, while the output actuator is usually heavy in load and small in speed, so it is necessary to use a reducer to achieve the purpose of reducing speed and increasing torque. Cylindrical tooth shape and worm gear reducer are more traditional structures. Epicycloid planetary gear was developed on the basis of involute planetary gear in the 1920s of last century, and then improved by Japanese enterprises for large-scale application; After the 1980s, cycloidal and involute planetary gears were combined to form RV and cycloidal pin wheel planetary gear reducer. The harmonic reducer was proposed and applied in the 1950s, and it also applied the principle of planetary gear transmission.

The application scenario of the reducer is very wide, and the deceleration ratio, transmission accuracy, output torque, transmission efficiency and service life are its core technical indicators. The industrial scenes with large load and low precision requirements mainly use cylindrical tooth shape, worm gear and cycloidal pin wheel reducer, and cycloidal pin wheel reducer can replace the first two kinds of reducer in most scenarios. Precision requirements of robots, CNC machine tools, aerospace and other fields mainly use precision planetary reducer, harmonic reducer and RV reducer.

Precision reducer detailed ratio: the principle is the same, the realization method has its own characteristics, can not be replaced

The harmonic reducer has small volume and large transmission ratio, and is suitable for robot forearm, hand, wrist and other parts. Structural features: mainly composed of flexible wheel, rigid wheel and wave generator; The flexible wheel is a thin-walled cylindrical outer gear, and the rigid wheel is a rigid annular inner gear. The wave generator is a thin-walled roller bearing mounted on an elliptical CAM with a long diameter slightly larger than the inner diameter of the flexwheel. Harmonic reducer structure is relatively simple, so the mass volume is small. Motion characteristics: Generally, the wave generator is used as the drive shaft, and its rotation drives the flexwheel to produce periodic elliptical elastic deformation, the long axis engages with the rigid wheel, and the short axis breaks off. Flexural deformation and misalignment motion during continuous rotation. The input rotates one circle, and the output end only rotates the Angle of the difference between the number of teeth of the flexwheel and the rigid wheel, so the deceleration ratio is large. Usage characteristics: Because the proportion of teeth engaged is 30% and 180° engaged, the average effect of meshing error makes the transmission accuracy higher; The relative sliding displacement of the meshing tooth surface is small, so the transmission efficiency is high and the wear is low. However, the flexural wheel is prone to fatigue fracture due to long time extrusion deformation.

PXI-8119

Robot industry: the form is changeable, the technology is upgraded, and the demand for reducer is large

The reducer is an important part of the movable joint of industrial robot. The precision reducer used by industrial robots is mainly harmonic and RV reducer, the former is used for the end of the actuator such as the wrist, hand and forearm because of its small size and low load, and the latter has larger volume and mass, strong stability and large load, and is usually used for the base, shoulder and big arm. The A1 to A3 joints of a six-axis robot generally use RV, and the end executive joints A4 and A5 mainly use harmonic wave retarders. Mobile robot wheel can use precision planetary reducer. The reducer accounts for a large proportion of the production cost of industrial robots, and the price drop is large after the local volume. Precision reducers account for 36% of the total cost of industrial robots. According to Green’s harmonic prospectus, from 2017 to 2019, its harmonic reducer production increased by 29%, the average price dropped from 1923 yuan to 1632 yuan, a decrease of 15%, and the subsequent cost is expected to further reduce with the production increase and achieve more widespread popularity.

The domestic precision reducer is gradually approaching the international frontier level, and there is still room for greater progress

Some parameters of domestic harmonic reducer and RV reducer have reached the international top level. In terms of harmonic reducer, the Japanese products represented by Hamanak have larger torque, higher transmission accuracy, smaller space and back backlash, and a life of up to 50,000 hours, and the domestic harmonic reducer is relatively superior in the deceleration ratio range, space and weight, of which Haozhi mechanical and electrical products transmission accuracy and life are basically equivalent to Hamanak products. In terms of RV reducer, the BX series products launched by China Power Germany are equivalent to Nabotsk’s RV-E series products in most indicators, but the accuracy performance is smaller. Overall, there is still a certain gap between the domestic reducer and the world’s advanced level, but some parameters have been comparable.

Because the harmonic reducer structure is relatively simple, compared with the RV reducer, domestic manufacturers are easier to approach the international frontier level. The main problems of harmonic reducer in China are: ① poor accuracy and retention ability; ② The carrying capacity is poor; ③ The design life is short. RV structure of high precision cycloidal gear quality and gear shape quality, tooth profile accuracy directly hook, at the same time, a variety of parts test assembly accuracy, for domestic production enterprises design end, process end and assembly end of the three links put forward a comprehensive challenge.