The movement of industrial robots not only requires reliable driving devices but also efficient transmission units to achieve precise control. These two are important parts of industrial robots besides the mechanical body. This article will introduce the driving devices and transmission units of industrial robots to help you gain a deeper understanding of these key components.
driving device
The driving device is the power source of the industrial robot arm, which enables various parts of the arm (including the body, arm, wrist, and hand) to move. Industrial robots typically use three basic types of driving methods: hydraulic drive, pneumatic drive, and electrical drive. Electrical drive is currently the most commonly used method for industrial robots, with AC servo motors being the most common choice. The arrangement of the driving device is usually one joint corresponding to one driver, which helps to achieve precise control and efficient movement.
At present, except for a few robots with low motion accuracy, heavy loads, or explosion-proof requirements that use hydraulic and pneumatic drives, most industrial robots use electrical drives, among which AC servo motors are the most widely used, and the driver layout mostly uses one joint, one driver.
Transmission unit
The transmission unit is an auxiliary component of the driving device, responsible for transmitting the motion of the driving device to various parts of the robotic arm to ensure that the end effector can accurately achieve the desired position and posture.
Industrial robots typically use reducers as their mechanical transmission units, which have specific requirements when compared to conventional reducers. The joint reducer of robots needs to have some characteristics, such as a short transmission chain, small size, high power, light weight, and easy control. These features help robots achieve efficient motion control.
working principle
When the wave generator is installed in the flexible wheel, it forces the profile of the flexible wheel to change from circular to elliptical. The teeth near the long axis end are fully engaged with the teeth of the rigid wheel (usually about 30% of the teeth are in a meshing state), while the teeth near the short axis end are completely disengaged from the rigid wheel. The teeth in other sections of the circumference are in a transitional state of meshing and disengagement. When the wave generator rotates continuously in a certain direction, the deformation of the flexible wheel constantly changes, causing the meshing state between the flexible wheel and the rigid wheel to alternate between meshing in, meshing out, disengaging, and re-meshing... This process repeats itself, and the number of external teeth of the flexible wheel is less than the number of internal teeth of the rigid wheel, thus achieving slow rotation of the flexible wheel relative to the rigid wheel in the opposite direction of the generator.
This device achieves motion control of the robot by changing the shape of the flexible wheel and the interaction between the teeth and the rigid wheel to achieve rotation. This process is repeated continuously to generate the required mechanical motion.
feature
(1) Simple structure, small size, and light weight. Compared with ordinary reducers with comparable transmission ratios, the volume and weight are reduced by about 1/3 or more.
(2) The transmission ratio range is large. The transmission ratio of the single-stage harmonic reducer is 50-300, with a preferred value of 75-250; The transmission ratio of the bipolar harmonic reducer is between 3000 and 60000.
(3) Simultaneously meshing with multiple teeth, high transmission accuracy, and large load-bearing capacity.
(4) Smooth movement, no impact, and low noise. The meshing and disengagement between the gears of the harmonic reducer gradually enter and exit between the rigid teeth as the flexible wheel deforms. During the meshing process, the teeth come into contact with each other, and the slip speed is small without sudden changes.
(5) High transmission efficiency, capable of achieving high-speed motion.
(6) Can achieve differential transmission. Suppose the wave generator and the rigid wheel are driven, and the flexible wheel is driven. In that case, a differential transmission mechanism can be formed to achieve the transition between fast and slow working conditions.
2. RV reducer
1) Structure
Compared with harmonic reducers, RV transmission not only has higher fatigue strength, stiffness, and longer lifespan, but also has stable hysteresis accuracy. Unlike a harmonic drive, as the usage time increases, the motion accuracy will significantly decrease. Therefore, RV reducers are often used in high-precision robot drives, and there is a trend of gradually replacing harmonic reducers. The schematic diagram of the RV reducer structure is shown in the figure below, which mainly consists of components such as the sun gear (center wheel), planetary gear, rotating arm (crank shaft), rotating arm bearing, cycloidal gear (RV gear), needle teeth, rigid disc, and output disc.
2) Working principle
① First stage deceleration: Firstly, the rotational motion of the motor is transmitted to two involute planetary gears through the gear shaft or sun gear. This process is like a large gear transmitting power to two small gears, achieving the first stage of deceleration.
② Second stage deceleration: Next, the planetary gears begin to rotate and drive the cycloidal gears 180 degrees apart through the crankshaft. This is like a pair of symmetrical cycloid gears interacting with each other, one starting to rotate around the other, thus completing the second stage of deceleration.
③ Rotation motion: During this process, the cycloid gear will be subjected to the force of the fixed needle teeth on the needle tooth housing during its revolution. This force will cause the cycloid wheel to undergo rotational motion, opposite to its orbital direction, just like spin.
④ Output mechanism: Finally, the rotation of the cycloidal gear is transmitted at a constant speed to the rigid disc and output disc through two crankshafts. This forms an equal angular velocity output mechanism of a parallelogram, transmitting motion to other parts of the robot.
The RV transmission device converts the rotational motion of the electric motor into the complex motion required by the robot through these complex interactions, thereby achieving efficient deceleration and precise control.
3) Characteristics
(1) The transmission ratio range is wide, and the transmission efficiency is high.
(2) The torsional stiffness is high, far greater than the output mechanism of a typical cycloidal pinwheel reducer.
(3) At rated torque, the elastic hysteresis is small.
(4) When transmitting the same torque and power, RV reducers are smaller in size compared to other reducers.
Understand the driving devices and transmission units of industrial robots
The movement of industrial robots not only requires reliable driving devices but also efficient transmission units to achieve precise control. This article will introduce the driving devices and transmission units of industrial robots to help you gain a deeper understanding of these key components.
The driving device and transmission unit of industrial robots are key components for achieving efficient and precise motion, and their selection and configuration play an important role in the performance and application of robots. Different types of driving and transmission methods are suitable for different industrial robots. Choosing appropriate components based on specific needs will help improve the efficiency and accuracy of the robot's work.