Comparison of Characteristics of Harmonic, Planetary, and RV Reducers

Comparison of Characteristics of Harmonic, Planetary, and RV Reducers
Concept of reducer

The reducer is an intermediate mechanism that connects the power source and the actuator, and has the function of matching speed and transmitting torque. According to control accuracy, reducers can be divided into general transmission reducers and precision reducers. The control accuracy of general transmission reducers is low, which can meet the basic power transmission requirements of mechanical equipment. Precision reducers have small backlash, high precision, long service life, and are more reliable and stable, and are applied in high-end fields such as robots and CNC machine tools. There are many types of precision reducers, including harmonic reducers, RV reducers, cycloidal pin wheel planetary reducers, precision planetary reducers, etc.

in short

The reducer reduces speed and increases torque.

Transmission ratio i=input shaft speed/output shaft speed;

Output torque=Input torque x Transmission ratio x Efficiency;

Planetary gearbox

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

Harmonic reducer:

Harmonic gear reducer is a type of transmission structure composed of a fixed internal toothed rigid wheel, flexible wheel, and a wave generator that causes radial deformation of the flexible wheel. Harmonic gear reducer is a new type of transmission structure in gear reducers, which uses flexible gears to generate controllable elastic deformation waves, causing relative misalignment between the teeth of the rigid wheel and flexible wheel to transmit power and motion. This type of transmission is fundamentally different from general gear transmission, and has special characteristics in meshing theory, ensemble calculation, and structural design. Harmonic gear reducers have advantages such as high precision and high load-bearing capacity. Compared with ordinary reducers, due to the use of 50% less materials, their volume and weight are reduced by at least one-third.

RV reducer:

The RV reducer consists of a front stage of a planetary gear reducer and a rear stage of a cycloidal pinwheel reducer. The RV reducer has a compact structure, a large transmission ratio, and a self-locking function under certain conditions. It is one of the commonly used reducers with low vibration, low noise, and low energy consumption.

Moreover, the hysteresis accuracy is stable, unlike harmonic drives where the motion accuracy significantly decreases over time. Therefore, many countries in the world use RV reducers for high-precision robot transmissions. Therefore, this type of RV reducer has a trend of gradually replacing harmonic reducers in advanced robot transmissions

Its disadvantages are heavy weight and large external dimensions.

Transmission efficiency:

Planets are superior to harmonics;

Transmission accuracy:

Harmonics are superior to planets;

Production and manufacturing costs:

The cost of harmonics is higher than that of planets;

Under the same output torque, harmonics have small mass, small volume, and small transmission inertia;

Harmonic single-stage transmission has a large ratio, the manufacturing cost of harmonic reducers is relatively high, and they are prone to elastic deformation and wear. Their lifespan is not as good as planets, and the input speed cannot be too high

The harmonic transmission of harmonic reducers mainly utilizes the controllable elastic deformation of flexible components to transmit motion and power. It has a small volume and high accuracy, but its disadvantage is that the service life of flexible components - flexible wheels - is limited and not resistant to impact. Its rigidity is relatively poor compared to metal components. Another disadvantage of harmonic reducers is that their input speed cannot be too high, which has certain limitations.