As a crucial component of core parts, precision reducers are indispensable for the reliable and accurate operation of industrial robots. In fact, there are many types of reducers, including harmonic gear reducers, cycloidal pinwheel planetary reducers, RV reducers, precision planetary reducers, and filter gear reducers.
As a core component of industrial robots, precision reducers, compared to general-purpose reducers, require characteristics such as short transmission chains, small size, high power, light weight, and ease of control. Precision reducers enable robot servo motors to operate at appropriate speeds and precisely reduce the rotational speed to the speeds required by various parts of the industrial robot, improving the rigidity of the mechanical body while outputting greater torque.
There are two main types of speed reducers widely used in articulated robots: RV speed reducers and harmonic speed reducers. RV speed reducers are generally placed in heavy-load positions such as the base, upper arm, and shoulder, mainly for robot joints weighing over 20 kg; while harmonic speed reducers are placed in the forearm, wrist, or hand, for robot joints weighing less than 20 kg. In addition, planetary speed reducers are generally used in Cartesian coordinate robots.
RV-E type reducer
So, what are the principles, advantages, and disadvantages of these two types of speed reducers?
Zhang Jie of Zhejiang Laifu Harmonic Drive Co., Ltd. explained that a harmonic reducer consists of four basic components: a flexible wheel, a wave generator, a rigid wheel, and bearings. The outer diameter of the flexible wheel is slightly smaller than the inner diameter of the rigid wheel, and the flexible wheel typically has two fewer teeth than the rigid wheel. The elliptical shape of the wave generator determines that the tooth contact points of the flexible wheel and the rigid wheel are distributed on two opposite planes located at the center of the ellipse. During the rotation of the wave generator, the tooth contact points of the flexible wheel and the rigid wheel begin to mesh. For every 180° clockwise rotation of the wave generator, the flexible wheel rotates by the equivalent of one tooth difference counterclockwise on the rigid wheel. At two symmetrical points within 180°, more than 30% of the total number of teeth are engaged simultaneously, which results in its high torque transmission.
Harmonic reducer
Zhang Jie believes that compared with harmonic reducers, RV transmission is a newly emerging type of transmission. It was developed on the basis of traditional pinwheel planetary transmission. It not only overcomes the shortcomings of general pinwheel transmission, but also has a series of advantages such as small size, light weight, large transmission ratio range, long service life, stable accuracy, high efficiency, and smooth transmission.
The key to RV reducers lies in their manufacturing and assembly processes. RV reducers have higher fatigue strength, rigidity, and lifespan, unlike harmonic drives which experience a significant decrease in motion accuracy over time. Their disadvantages are heavy weight and larger dimensions.
It is understood that the RV reducer is composed of a cycloidal pinwheel and a planetary support. With its many advantages such as small size, strong impact resistance, large torque, high positioning accuracy, low vibration, and large reduction ratio, it is widely used in industrial robots, machine tools, medical testing equipment, satellite receiving systems and other fields, and is increasingly attracting widespread attention at home and abroad.
Dr. Zhang Jing from Zhejiang Shuanghuan Transmission Machinery Co., Ltd. further analyzed the advantages and disadvantages of RV reducers and harmonic reducers. He believes that harmonic reducers have a simple and compact structure, making them suitable for miniaturized, low- to medium-load applications. RV reducers have good rigidity, strong impact resistance, smooth transmission, and high precision, making them suitable for medium- to heavy-load applications. However, RV reducers need to transmit large torques and withstand significant overload impacts to ensure their expected service life. Therefore, they employ relatively complex over-positioning structures in their design, making manufacturing processes and cost control more challenging.
In conclusion, what appears to be a simple speed reducer is actually a challenge to my country's industrial infrastructure. Without a thorough understanding of the relevant materials, heat treatment, and processes, it is entirely expected that it will be difficult to produce a precision speed reducer that fully meets the requirements of robots.
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