As a core component of industrial robots, precision reducers used in robotics require features such as a short transmission chain, small size, high power, light weight, and ease of control compared to general-purpose reducers.
There are two main types of reducers widely used in articulated robots: RV reducers and harmonic reducers.
RV Reducer
Used in the legs, waist, and elbows of large robots with high torque, all three axes of heavy-duty industrial robots use RV reducers. Compared to harmonic reducers, the key to RV reducers is in their manufacturing and assembly processes. RV reducers have higher fatigue strength, rigidity, and lifespan. Unlike harmonic drives, where motion precision significantly decreases with increased usage time, RV reducers do not have this issue. However, their drawbacks are heavier weight and larger size.
Harmonic Reducer
Used in smaller industrial robots or the end axes of large robots, harmonic reducers are a type of harmonic drive device, which includes harmonic accelerators and harmonic reducers. Harmonic reducers primarily consist of: a rigid wheel, a flexible wheel, bearings, and a wave generator – all of which are indispensable. The tooth count of the rigid wheel is slightly more than that of the flexible wheel. Harmonic reducers feature compact size, light weight, large load capacity, high motion precision, and large single-stage transmission ratio, which makes them suitable for smaller robots.
Both employ differential tooth engagement, but a key gear in harmonic reducers is flexible, requiring repetitive high-speed deformation, which makes it more fragile with limited load capacity and lifespan. RV reducers typically use cycloidal pinwheels, whereas harmonic drives historically used involute gear profiles; nowadays, some manufacturers have adopted double-arc profiles, which are more advanced than involute profiles.
Harmonic reducers are composed of four basic components: the flexible wheel, wave generator, rigid wheel, and bearings. The outer diameter of the flexible wheel is slightly smaller than the inner diameter of the rigid wheel, usually with the flexible wheel having 2 fewer teeth than the rigid wheel. The elliptical shape of the wave generator determines that the contact points of the teeth on the flexible and rigid wheels are distributed on two opposing sides of the ellipse center. During the rotation of the wave generator, the contact points of the flexible and rigid wheel teeth begin to engage. For every 180° clockwise rotation of the wave generator, the flexible wheel is equivalent to a 1 tooth difference counterclockwise rotation relative to the rigid wheel. At the two 180° symmetrical points, over 30% of the teeth are simultaneously engaged, resulting in high torque transmission. The simple and compact structure of harmonic reducers makes them suitable for miniaturized, low, and medium-load applications.
