Is there any Difference Between RV Reducer and Harmonic Drive?

As an important component of core components, precision reducers are an indispensable part of the reliable and precise operation of industrial robots. In fact, there are many categories of reducers, namely harmonic drive, cycloidal pinwheel planetary reducers, RV reducers, precision planetary reducers and filter gear reducers.

1.RV reducer and harmonic drive for industrial robot applications

As a precision reducer as the core component of industrial robots, compared with general reducers, robot reducers are required to have the characteristics of short transmission chain, small size, high power, light weight and easy control.

The precision reducer makes the robot servo motor run at a suitable speed, and accurately reduces the speed to the speed required by each part of the industrial robot, improving the rigidity of the mechanical body and outputting a larger torque.

There are two main types of reducers that are widely used in articulated robots: RV reducer and harmonic speed reducer.

Generally, the RV reducer is placed in the position of heavy load such as the machine base, arm, shoulder, etc., that is, it is mainly used for robot joints above 20 kg; while the harmonic drive is placed on the forearm, wrist or hand, that is Robot joints under 20 kg. In addition, planetary reducers are generally used in Cartesian coordinate robots.

Unlike harmonic drive, RV reducers do not experience a significant reduction in motion accuracy over time. Therefore, there is a popular saying in the industry that RV reducers have a tendency to gradually replace harmonic drive in advanced robot transmission. However, due to the more complex components and higher bearing strength of the RV reducer, it is not only more difficult to manufacture than the harmonic drive, but also the investment scale of its production line is much larger than that of the harmonic drive.

2.Principles and advantages and disadvantages of RV reducer and harmonic drive

The harmonic drive is composed of four basic components: "flexible wheel, wave generator, rigid wheel and bearing". The outer diameter of the flexible pulley is slightly smaller than the inner diameter of the rigid pulley, and usually the flexible pulley has 2 teeth less than the rigid pulley. The elliptical shape of the wave generator determines that the contact points of the teeth of the flexible and rigid gears are distributed on two opposite sides between the center of the ellipse. During the rotation of the wave generator, the contact parts of the flex wheel and the rigid wheel teeth begin to mesh. Every time the wave generator rotates 180° clockwise, the flexible wheel is equivalent to one tooth difference when the rigid wheel rotates counterclockwise. At the two places of 180° symmetry, more than 30% of the total number of teeth mesh at the same time, which also creates its high torque transmission.

Compared with harmonic drive, RV transmission is a new type of transmission. It is developed on the basis of traditional needle pendulum planetary transmission. It not only overcomes the shortcomings of general needle pendulum transmission, but also has the advantages of small size, light weight, It has a series of advantages such as large transmission ratio range, long life, stable precision, high efficiency and stable transmission.

From the perspective of the bearing capacity of the reducer, the casing and the cycloidal pinwheel of the RV reducer are driven by solid steel, so the bearing capacity is strong. The flexible wheel of the harmonic drive can continuously deform to transmit torque, which determines the limited ability of the harmonic drive to withstand large torque and impact load, so it is generally used in the front end.

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