Among all the core components of the robot, the reducer is the most critical. The cost structure of industrial robots is roughly as follows: 22% for the body, 25% for the servo system, 38% for the reducer, 10% for the control system, and 5%. Simply split the cost of domestic 6-axis industrial robots (total cost 250,000 yuan), it can be seen that the cost of the reducer and servo motor is close to 130,000 yuan, mainly based on imports.
Today, we will synthesize the information of all parties and tell you about the RV reducer.
First, the mechanical principle of RV reducer
In 1926, the German Lorenz Brown proposed a planetary gear mechanism with a small tooth difference. It uses an external cycloid as the profile curve. This is the earliest pinion planetary transmission, due to the two meshing. One of the gears is in the form of a pin wheel, which is also referred to as a cycloidal pinion planetary gear.
RV transmission is a brand-new transmission method. It is developed on the basis of the traditional oscillating planetary transmission. It not only overcomes the shortcomings of the general swaying transmission, but also has a small size, light weight, large transmission ratio range and long service life. A series of advantages such as stable accuracy, high efficiency and smooth transmission.
Take the RV-E reducer as an example
First speed reduction unit – spur gear reduction mechanism
The rotation of the input shaft is transmitted from the input gear to the spur gear, and is decelerated by the gear ratio. This is the first speed reduction section.
Second speed reduction unit – differential gear speed reduction mechanism
The spur gear is connected to the crankshaft and becomes the input of the second reduction unit. In the eccentric portion of the crankshaft, the RV gear is mounted by a rolling bearing. In addition, the needle teeth on the inner side of the casing are only one more than the number of RV gears, and are arranged at the same pitch.
If the fixed housing rotates the spur gear, the RV gear also performs eccentric motion due to the eccentric motion of the crank shaft. At this time, if the crankshaft rotates one revolution, the RV gear will rotate one tooth in the opposite direction to the crankshaft. This rotation is output to the shaft of the second reduction unit. When the shaft is fixed, the casing side becomes the output side.
Second, the importance of RV reducer to robots
The RV reducer is used for the first joint to the fourth joint of the robot, and the fifth and sixth joints of the light load robot may use a harmonic reducer. RV reducers are required for all joints of heavy-duty robots. On average, each robot uses 4.5 RV reducers. In 2013, the world’s robot sales volume was 180,000 units, and 900,000 reduction gears were required.
The power source of an industrial robot is generally an AC servo motor. Because it is driven by a pulse signal, the servo motor itself can achieve speed regulation. Why do industrial robots also need a speed reducer? Industrial robots usually perform repetitive actions to complete the same process; in order to ensure that industrial robots can reliably perform process tasks in production and ensure process quality, the positioning accuracy and repeat positioning accuracy of industrial robots are very high. Therefore, to improve and ensure the accuracy of industrial robots requires the use of RV reducers or harmonic reducers. Another role of precision reducers in industrial robots is to deliver more torque. When the load is large, it is not cost-effective to increase the power of the servo motor. The output torque can be increased by the reducer in a suitable speed range. In addition, servo motors are prone to heat and low-frequency vibrations at low frequencies, which is not conducive to ensuring accurate and reliable operation for long-term and periodic industrial robots.
The presence of a precision reducer allows the servo motor to operate at a suitable speed and accurately reduce the speed to the speed required by various parts of the industrial robot, increasing the rigidity of the machine while outputting greater torque. Compared with universal reducers, robotic joint reducers require short drive chains, small size, high power, light weight and easy control.
There are two main types of reducers that are widely used on articulated robots: RV reducers and harmonic reducers. Compared to harmonic reducers, RV reducers have higher stiffness and rotational accuracy. Therefore, in the articulated robot, the RV reducer is generally placed at a heavy load such as the base, the boom, the shoulder, etc.; the harmonic reducer is placed on the arm, wrist or hand; the planetary reducer is generally used. On a Cartesian robot.
At the same time, the RV reducer has much higher fatigue strength, stiffness and life than the harmonic drive commonly used in robots, and the hysteresis accuracy is stable. Unlike the harmonic drive, the motion accuracy will be significantly reduced with the use of time. Many countries in the world use RV reducers for high-precision robot transmission. Therefore, this type of RV reducer has gradually replaced the development of harmonic reducers in advanced robot transmission.