What is the difference between RV reducer and harmonic reducer?

It is understood that there are currently two main types of reducers used in articulated robots: RV reducers and harmonic reducers
The principle of RV reducer and harmonic reducer
RV reducer:
It is used for the three joints of the waist and elbow of the leg of the robot with large torque, and the industrial robot with large load uses RV for one, two and three axes. Compared with the harmonic reducer, the key to the RV reducer lies in the processing technology and assembly process. RV reducer has higher fatigue strength, stiffness and life. Unlike harmonic drive, as the use time increases, the motion accuracy will be significantly reduced. Its disadvantage is that it is heavy in weight and large in size.
Harmonic reducer:

For industrial robots with small loads or several shafts at the end of large robots, the harmonic reducer is a kind of harmonic transmission device. The harmonic transmission device includes a harmonic accelerator and a harmonic reducer. Harmonic reducer mainly includes: rigid wheel, flexible wheel, bearing and wave generator, all of which are indispensable. Among them, the number of teeth of the rigid wheel is slightly larger than that of the flexible wheel. The harmonic reducer used in small robots is characterized by small size, light weight, large carrying capacity, high motion accuracy, and large single-stage transmission ratio.
Both are meshes with small tooth difference. The difference is that one of the key gears in the harmonics is flexible. It needs repeated high-speed deformation, so it is relatively fragile and has limited bearing capacity and life. RV usually uses a cycloidal pinwheel. Harmonics used to use an involute tooth profile. Now some manufacturers use a double arc tooth profile, which is much more advanced than the involute tooth profile.
Compared with the harmonic reducer, the RV drive is a new type of transmission. It is developed on the basis of the traditional pin pendulum planetary drive. It not only overcomes the shortcomings of the general pin pendulum drive, but also has small size, light weight, and A series of advantages such as large transmission ratio range, long life, stable accuracy, high efficiency and smooth transmission.
The RV reducer is composed of a cycloidal pin wheel and a planetary support. It is widely used in industrial robots, machine tools, and medical applications due to its small size, strong impact resistance, large torque, high positioning accuracy, low vibration, and large reduction ratio. Detection equipment, satellite receiving system and other fields.
The housing and cycloidal pin wheel of the RV reducer are driven by solid steel, so the load capacity is strong. The flexible wheel of the harmonic reducer can continuously deform to transmit torque. This determines that the harmonic reducer has a limited ability to withstand large torque and impact loads, so it is generally used in the front end.
The advantages and disadvantages of RV reducer and harmonic reducer
The harmonic reducer has a simple and compact structure and is suitable for miniaturized, low and medium load applications.
The RV reducer has good rigidity, strong impact resistance, smooth transmission, and high precision. It is suitable for medium and heavy load applications. However, the RV reducer needs to transmit a large torque, bear a large overload impact, and ensure the expected working life. In the design, a relatively complicated over-positioning structure is used, and the manufacturing process and cost control are difficult. The RV reducer has no elastically deformed force components inside, so it can withstand a certain torque. The bearing of the RV reducer is its weak link. It is easy to break through the bearing force limit and cause abnormal wear or breakage of the bearing. This problem is more prominent during high-speed operation, so the rated torque of the RV reducer decreases significantly with the input speed.

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