Research status and development of transmission accuracy of RV Reducer

As a classic Mechatronics digital equipment, industrial robot has a wide range of applications. The reducer accounts for about 35% of the cost of a single complete industrial robot system. It can be seen that the reducer is the main factor affecting the development of industrial robot. Although the application of robots has developed rapidly in China, the main suppliers of industrial robots are still from Japan and Europe. Therefore, the localization of the core component reducer is the primary task to reduce the cost and break the foreign monopoly.

1. RV Reducer principle

RV (rotate vector) reducer is a two-stage closed planetary transmission mechanism with low tooth difference developed on the basis of cycloidal pin gear. It is a new planetary transmission mechanism used in the field of mechanical and electrical engineering such as CNC machine tools and industrial robot joints. Because it has the advantages of high motion precision, large transmission ratio, large torsional stiffness and high transmission efficiency, many scholars and research institutions take it as the focus of research.

Fig. 1 is a schematic diagram of RV Reducer transmission. The first stage involute cylindrical gear planetary transmission mechanism and the second stage cycloidal needle gear planetary gear reduction mechanism are composed. The input shaft and sun gear form the input part of RV Reducer. The input of cycloid pin gear is completed by planetary gear and crank shaft. When the mechanism starts to drive, if the sun gear rotates clockwise, the planetary gear enters the coexistence of revolution and counterclockwise rotation. At this time, the cycloid gear is driven by the crank shaft for eccentric movement. In this case, the cycloid wheel will be impacted by the meshing needle wheel, and its axis revolves around the axle and rotates in the opposite direction. At this time, it will push the planet carrier output mechanism to rotate clockwise through the crank shaft.

2. Research status of error of two-stage cycloidal pinwheel transmission mechanism

The main indicators of transmission accuracy of RV Reducer are return error and transmission error. The main influencing factors are: the error of primary involute cylindrical gear planetary transmission mechanism, the error of secondary cycloidal pinwheel transmission mechanism and the error of output mechanism.

Because the error of the secondary cycloidal pinwheel transmission mechanism does not need to be transmitted to the output mechanism through a series of transmission, on the contrary, the error of the primary reduction mechanism of RV Reducer needs to be divided by the total transmission ratio of the system. Therefore, the correlation error of involute gear in the primary gear transmission has little impact on the transmission accuracy of RV Reducer, while the transmission accuracy weighting coefficient of cycloidal pin gear planetary mechanism is large, which has a great impact on the transmission error. When designing and producing RV Reducer, the error factors in the two-stage cycloidal pinwheel transmission mechanism should be carefully considered. The main factors that change the error of the two-stage cycloidal pinwheel transmission mechanism are the modification of the Cycloidal Tooth profile, the eccentricity error of the crank shaft, the clearance of the crank shaft bearing and so on.

2.1 modification of cycloid tooth profile

The study of cycloidal profile modification is of great significance to the influence of load distribution and side clearance, and has great engineering application value to improve the transmission accuracy of RV Reducer.

2.2 meshing clearance error between needle tooth and needle wheel (needle tooth shell)

Meshing clearance is one of the main factors affecting the transmission accuracy of RV Reducer. There are a series of studies on the meshing clearance of cycloidal needle wheel.

2.3 crankshaft eccentricity error and crankshaft bearing clearance

Transmission error and backlash are important factors affecting transmission accuracy. Crankshaft eccentricity error and crankshaft bearing clearance are one of the main factors affecting transmission error and backlash.

2.4 other influencing factors

In addition, the speed and load of RV Reducer and the center circle of needle wheel also affect the transmission accuracy, and some progress has been made in this field.

3. Existing problems in the study of transmission accuracy of RV Reducer

Due to the high complexity of RV Reducer system, domestic researchers have used many simplified methods to model RV Reducer when studying the influencing factors of transmission accuracy, which makes it easier for researchers to study RV Reducer. However, the research on the transmission accuracy of complex gear system will be subject to certain constraints.

(1) When studying the transmission accuracy model of RV Reducer, researchers ignore the effects of specific components, bending deformation and bearing stiffness on the transmission accuracy of RV Reducer. At the same time, the effects of temperature and friction are ignored; It is also one of the existing problems to use fixed value to deal with the equivalent error of the meshing line between planetary gear and cycloidal needle gear.

(2) When studying the comprehensive influence of multiple errors on the transmission accuracy of RV Reducer, there is insufficient research on the correlation of various errors. When various errors are simply superimposed together, once multiple errors change together, the coupling of transmission accuracy change law and multiple errors affects the transmission accuracy of RV Reducer is very key.

(3) RV Reducer has the characteristics of high precision and complex structure. As a new type of high-precision transmission mechanism, the design of transmission accuracy detection platform and the research of transmission accuracy detection principle are urgent problems to be solved.

4. Summary and Prospect

With the proposal of China intelligent manufacturing 2025, RV Reducer has a very important application because of its high precision and performance. It is the main application area of industrial robots, CNC machine tools and so on. At present, the research of RV Reducer mainly focuses on the improvement of efficiency and accuracy. By improving its efficiency and accuracy, it can better meet the needs of intelligent upgrading of China's manufacturing industry. Its transmission accuracy and operation safety are the problems that must be solved in the core components of industrial robot.

RV Reducer system has very complex characteristics. Scholars have omitted a lot in the research on its transmission accuracy, especially in the modeling process, the phenomenon of simplification is more extensive, which limits the research on the transmission accuracy of complex gear system to a certain extent. In the future, the research related to RV Reducer can be carried out according to the time change, so as to integrate the influence of the correlation of deformation, friction, temperature and each part error on the transmission accuracy as the condition for calculating the instantaneous equivalent error of each error on the meshing line, so as to improve the transmission accuracy of the model.

With the launch of China's intelligent manufacturing 2025 policy and the high and new technologies such as CAE technology, the research on the transmission accuracy of RV Reducer system can also provide more favorable technical support. Through the detailed research on the transmission accuracy mechanism of RV Reducer, it can not only improve the transmission accuracy and operation safety, but also play a key role in improving the service life.