How to choose harmonic, planetary, and RV reducers? Comprehensive analysis of features and differences

What is a reducer?

A reducer is an intermediate device that connects the power source and the actuator, mainly used to match the speed and transmit torque. According to the control accuracy, reducers can be divided into general transmission reducers and precision reducers.
The control accuracy of general transmission reducers is low, which meets the basic power transmission needs.
Precision reducers have small return clearance, high precision, and long service life. They are often used in high-end equipment such as robots and CNC machine tools.
There are many types of precision reducers, and common types include: harmonic reducers, RV reducers, cycloidal pinwheel planetary reducers, precision planetary reducers, etc.
In short, the basic function of the reducer is to reduce speed and increase torque.
Transmission ratio i = input shaft speed ÷ output shaft speed
Output torque = input torque × transmission ratio × efficiency

Planetary Gear Reducer

The cylindrical gears evenly distributed around the planetary gear reducer move around a concentric circle between the inner gear and the outer gear. The circular motion of the cylinder and gears is similar to the orbit of the planets in the solar system. Therefore, planetary gear reducers are also called planetary reducers.

Main features of planetary gear reducers

High transmission efficiency: usually above 95%, with low energy loss.
Compact structure: Since multiple planetary gears share the load, planetary reducers have high power density, small size and light weight.
High precision: multi-point meshing design, high transmission accuracy.
Strong load-bearing capacity: can withstand large radial and axial loads.
Long service life: the uniform force of the gears and the high-quality manufacturing process make the planetary reducer have a long service life.

harmonic reducers

Harmonic gear reducers are composed of a fixed internal gear rigid wheel, a flexible wheel, and a wave generator that causes radial deformation of the flexible wheel. Harmonic gear reducers are a new type of transmission structure in gear reducers. It uses flexible gears to generate controllable elastic deformation waves, causing the teeth of the rigid wheel and the flexible wheel to be relatively staggered to transmit power and motion.
This transmission is essentially different from general gear transmission, and has particularities in meshing theory, set calculation and structural design.
Harmonic gear reducers have the advantages of high precision and high load-bearing capacity. Compared with ordinary reducers, the material used is 50% less, and its volume and weight are reduced by at least 1/3.

Main features of harmonic reducers

Small and light: small size and light weight. Compared with general gear reducers, the volume of harmonic reducers can be reduced by 2/3 and the weight can be reduced by 1/2 when the output torque is the same.
High transmission accuracy: because there are many teeth meshing at the same time in harmonic transmission, the error is averaged, that is, multi-tooth meshing has a mutual compensation effect on the error, so the transmission accuracy is high. Under the same gear accuracy level, the transmission error is only about 1/4 of that of ordinary cylindrical gear transmission. At the same time, the radius of the wave generator can be slightly changed to increase the deformation of the flexible wheel to make the tooth gap very small, and even to achieve side clearance-free meshing, so the transmission idle stroke is small, which is suitable for reverse rotation.
Large transmission ratio: The speed ratio range of single-stage harmonic transmission is 70-320, which can reach 1000 in some devices, and the speed ratio of multi-stage transmission can reach more than 30,000. It can be used not only for deceleration but also for speed increase.
Simple and compact structure: It consists of only three main components, and the input and output are the same, so the structure is simple and compact, and it is easy to install.
High load-bearing capacity: This is because there are many teeth meshing at the same time in harmonic transmission, and the number of teeth meshing at the same time in double-wave transmission can reach more than 30% of the total number of teeth, and the flexible wheel uses high-strength materials, and the teeth are in surface contact.
Suitable for confined spaces: The flexible characteristics of the flexible wheel can be used in special environments.
Smooth movement: Both sides of the gear mesh at the same time, without impact.

RV reducer

RV reducer consists of planetary gears and cycloidal pinwheels, and is often used in high-precision robots.

Main features of RV reducers

Large transmission ratio: Suitable for high reduction ratio requirements.
Stable accuracy: The hysteresis accuracy is stable and not easy to decrease over time.
Strong impact resistance: More impact-resistant than harmonics.

How to choose harmonic, planetary, and RV reducers?

Transmission efficiency: Planetary is better than harmonic.
Transmission accuracy: Harmonic is better than planetary.
Production cost: Harmonic is higher than planetary.
Volume and weight: Harmonic is smaller and lighter.
Durability: Planetary and RV reducers are better, and harmonic flexible wheels have a limited life.

When choosing a reducer, you should choose according to the specific application requirements. If you focus on accuracy and have limited space, you can give priority to harmonic reducers; if you need higher durability and load capacity, RV and planetary reducers are more suitable.
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