Today, the advanced level of industrial robots is astonishing, especially those intelligent 5-axis and 6-axis robots with so many joints. They can accurately transmit motion and commands, and all components work closely together to complete complex tasks. The reducer is the most critical component among all the core components of an industrial robot. (RV reducer principle and structure diagram?)
The cost structure of industrial robots is roughly as follows: robot body 22%, servo system 25%, reducer 38%, control system 10%, etc. 5%. A simple breakdown of the cost of a domestically produced six-axis industrial robot (total cost 250,000 yuan) shows that the reducer and servo motor cost close to 130,000 yuan, mainly due to imports.
1. Mechanical principle of RV reducer
In 1926, German scientist Lawrence Blanc creatively proposed a small-tooth-difference planetary transmission mechanism with an exocycloid gear curve, which was the earliest pin-cycloid planetary transmission. Because one of the two meshing gears uses a pinwheel, this transmission is also called a cycloidal pinwheel planetary gear transmission.
RV transmission is a new type of transmission developed based on traditional planetary pendulum transmission. It not only overcomes the shortcomings of ordinary pendulum transmission, but also has a series of advantages such as small size, light weight, wide transmission ratio range, long service life, stable precision, high efficiency, and smooth transmission.
2. The Importance of RV Reducers to Industrial Robots
RV harmonic reducers are used in the first to fourth joints of industrial robots, and can also be used in the fifth and sixth joints of light-duty industrial robots. All joints of heavy-duty industrial robots require RV reducers. On average, each industrial robot uses 4.5 RV reducers. In 2013, 180,000 industrial robots were sold globally, requiring 900,000 reducers.
Industrial robots are typically powered by AC servo motors. These servo motors are driven by pulse signals. Why then do industrial robots need reducers? Industrial robots often repeat the same processes; to ensure reliable completion of production tasks and maintain process quality, high positioning accuracy and repeatability are required. Therefore, it is necessary to improve and ensure the precision of RV reducers or harmonic reducers in industrial robots. Another function of precision reducers in industrial robots is to transmit greater torque. When the load is heavy, blindly increasing the power of the servo motor is not cost-effective; the reducer can increase the output torque within an appropriate speed range. Furthermore, servo motors are prone to heat and low-frequency vibration when operating at low frequencies, which is detrimental to the long-term cyclical operation of industrial robots and hinders their accurate and reliable operation.
The presence of a precision reducer enables the servo motor to operate at an appropriate speed and precisely reduce that speed to the required level for the industrial robot, thereby increasing the rigidity of the mechanical body and outputting greater torque. Compared to ordinary reducers, industrial robot joint reducers feature shorter transmission chains, smaller size, higher power, lighter weight, and easier control.
There are two types of reducers widely used in articulated industrial robots: RV reducers and harmonic reducers. Compared with harmonic reducers, RV reducers have higher rigidity and rotational accuracy. Therefore, in articulated industrial robots, RV reducers are usually placed in the seat, forearm, shoulder, and other heavy-duty positions, while harmonic reducers are placed in the forearm, wrist, or hand; planetary reducers are typically used in Cartesian coordinate industrial robots.
What is the principle and structure diagram of an RV reducer? Compared to harmonic drives commonly used in industrial robots, RV reducers offer higher fatigue strength, stiffness, and service life, as well as stable backlash accuracy. Unlike harmonic drives, whose motion accuracy significantly decreases with use, RV reducers are widely used in many countries worldwide for driving high-precision industrial robots. Therefore, in advanced industrial robot transmissions, reducers are gradually replacing harmonic reducers.
