Overview
Both 3-axis and 6-axis robot arms use AC servo motors equipped with brakes. Encoders are typically absolute. Motors without absolute encoders require a homing operation after each shutdown.
1. Reducers Used in Robot Arms
Early imported ABB robot arms generally used gear reduction mechanisms manufactured by ABB. On 6-axis industrial robots, axes 1, 2, and 3 typically use RV reducers, which are cycloidal pin-wheel structures. Axes 4, 5, and 6 generally use harmonic reducers. Because the bearings are specialized, the axial length of these cycloidal RV reducers is very short. A commonly used RV reducer is the model from Japan's Teijin. Short-axial servo motors include Japan's FANUC; China's Guangzhou CNC also produces servo motors matched to its industrial robots with much shorter axial dimensions than their traditional servo motors.
2. What Is an RV Reducer
The RV reducer is a common type of worm gear reducer. It consists of a worm and a worm wheel, featuring a compact structure, a large transmission ratio, and, under certain conditions, a self-locking function. It is one of the most commonly used reducers and offers low vibration, low noise, and low energy consumption.
RV reducers are generally used for low-speed, high-torque transmission equipment. They reduce the high rotational speed of a motor, internal combustion engine, or other high-speed power source by meshing a small-number-of-teeth gear on the reducer input shaft with a larger gear on the output shaft. Ordinary reducers may have several pairs of gears based on the same principle to achieve the desired reduction. The ratio of the numbers of teeth on the large and small gears is the transmission ratio. A reducer is a power transmission mechanism that uses gear speed conversion to reduce motor RPM to the required speed while providing higher torque.
RV reducer input forms include: hollow input, shaft input, and extended worm-shaft types. Output forms include: hollow output, single-direction shaft output, and double-direction shaft output.
3. What Is a Harmonic Reducer
A harmonic drive consists mainly of four basic components: the wave generator, the flexible gear, the flexible bearing, and the rigid gear. The harmonic reducer is a gear transmission that relies on the wave generator to mount a flexible bearing so that the flexible gear undergoes controllable elastic deformation and meshes with the rigid gear to transmit motion and power. It evolved from planetary gear transmission principles and is commonly used with the wave generator as the active component, the rigid gear fixed, and the flexible gear as the output.
Key Characteristics of Harmonic Reducers
1. High load capacity: Meshing in harmonic drives is face contact and multiple teeth mesh simultaneously (high overlap), so the unit-area load is low and load capacity is higher than many other transmission forms.
2. Large reduction ratio: A single-stage harmonic drive can achieve ratios of i = 70 to 500.
3. Compact size and light weight.
4. High transmission efficiency and long service life.
5. Smooth transmission with no impact, low noise, and high motion accuracy.
6. Because the flexible gear endures significant alternating loads, its material fatigue strength as well as processing and heat-treatment requirements are demanding, making manufacturing processes relatively complex.
Harmonic reducers began development in China in the 1960s and 1970s; many manufacturers now produce them in series. They are widely applied in electronics, aerospace, and robotics, and their use in the chemical industry is increasing due to their advantages.
