What is a speed reducer?
The speed reducer is an important component for improving the running accuracy and torque of the robotic arm joints. It mainly consists of transmission parts (gears or worm gears), shafts, bearings, housings and accessories.
Generally, speed reducers can be divided into three basic structures: ① gear, shaft and bearing assembly; ② housing; ③ speed reducer accessories.
What is the function of a speed reducer?
When the power output of an engine cannot directly meet the low-speed operating requirements, a speed reducer can match the speed and transmit torque between the prime mover and the driven machine or actuator, thereby reducing the speed and increasing the torque. Taking robot applications as an example, a speed reducer enables the servo motor to operate at an appropriate speed, precisely reducing the speed to the speed required by various parts of the robot, improving the robot's rigidity while outputting greater torque.
Six-axis robots typically use 2 RVs + 4 harmonics:
Gear reducers also come in different types. Commonly used gear reducer types include: RV gear reducers, harmonic gear reducers, planetary gear reducers, cycloidal pinwheel gear reducers, etc. The following is a brief introduction.
Harmonic reducer
Harmonic reducers consist of three basic components: a wave generator, a flexible gear, and a rigid gear. They are gear drives that transmit motion and power by using a wave generator fitted with a flexible bearing to induce controllable elastic deformation in the flexible gear, which then meshes with the rigid gear. They are increasingly widely used in energy electronics , mining and metallurgy, transportation, hoisting machinery, petrochemical machinery, and medical devices. Harmonic gear drives are particularly advantageous in high-dynamic-performance servo systems. The advantages of harmonic reducers include a large transmission ratio, high load capacity, high transmission accuracy, high transmission efficiency, simple structure, small size, light weight, and the ability to transmit motion into confined spaces. Disadvantages include susceptibility to fatigue damage in the flexible gear, high rotational inertia and starting torque, and complex manufacturing processes.
Figure 1 Harmonic reducer
RV reducer
The RV reducer consists of a planetary gear reducer (front stage) and a cycloidal pinwheel reducer (rear stage), featuring a compact structure and a large transmission ratio. Under certain conditions, the RV reducer can possess a self-locking function and is one of the most commonly used reducers. The advantages of the RV reducer include low noise, low energy consumption, the ability to withstand large loads, and a high reduction ratio, which is beneficial for achieving high precision . However, the RV reducer is significantly affected by manufacturing processes and assembly, requiring high wear resistance and rigidity of the gears, and necessitating specialized component machining and precision assembly techniques.
Figure 2. RV reducer structure diagram
Planetary gear reducer
Planetary gear reducers consist of planetary gears, a sun gear, an internal gear ring, and a planet carrier. The planetary gears rotate around the sun gear. See Figure 3 for a detailed structure. Planetary gear reducers offer power splitting and feature multi-tooth meshing. They are small, lightweight, yet have high load-bearing capacity. Furthermore, they boast a long service life and smooth operation, making them commonly used in industries such as lifting, excavation, and construction.
Figure 3. Structure diagram of planetary gear reducer
Cycloidal pinwheel reducer
Cycloidal pinwheel reducers utilize cycloidal pin-tooth meshing and planetary transmission principles, hence they are also commonly called planetary cycloidal reducers. The external gear tooth profile is a modified cycloidal shape, while the internal gear teeth are round pins; the two mesh internally. The structure of the cycloidal pinwheel reducer is shown in Figure 4. The advantages of cycloidal pinwheel reducers are their small size and light weight; wide transmission ratio range; relatively smooth transmission; and good efficiency and accuracy. However, their disadvantages include an inability to withstand large loads; relatively complicated disassembly and assembly; and potentially high maintenance costs.
Figure 4 Animation of cycloidal pinwheel reducer
