As a precision speed reducer for the core components of industrial robots, compared with general-purpose speed reducers, the speed reducers used in robots have the characteristics of short drive chain, small size, large power, light weight, and easy control.
There are two main types of reducers that are used in joint-type robots: RV reducers and harmonic reducers.
1 Principle and advantages and disadvantages of RV reducer and harmonic reducer
RV reducer:
It is used for the robot with large torque and three joints at the waist and elbows. The industrial robot with large load uses RV on one or two or three axes. Compared to harmonic speed reducers, the key to RV speed reducers is the machining process and assembly process. RV reducer has a higher fatigue strength, stiffness and life, unlike the harmonic drive as the use of time increases, the movement accuracy will be significantly reduced, its disadvantage is heavy weight, large size.
â–² RV-E type reducer â–²
Harmonic reducer:
For a small load of industrial robots or several axes at the end of a large robot, a harmonic reducer is a type of harmonic transmission, and a harmonic transmission includes a harmonic accelerator and a harmonic reducer. Harmonic decelerators mainly include: rigid wheels, flexible wheels, bearings and wave generators, and four are indispensable. Among them, the number of teeth of the rigid wheel is slightly larger than the number of teeth of the flexspline. Harmonic gear reducer is used for small robots. Its characteristics are small size, light weight, large carrying capacity, high movement accuracy, and large single-stage transmission ratio.
â–² Harmonic Reducer â–²
Both are intermeshing with little teeth difference. The difference is that a key gear in the harmonics is flexible. It needs repeated high-speed deformation, so it is relatively fragile and has limited bearing capacity and life. RV is usually a cycloid wheel. Harmonic waves have previously used involute tooth shapes. Nowadays, some manufacturers use a double arc tooth profile, which is much more advanced than involute wire.
The two giants of the reducer are Nabtesco and Hamonica Drive. They almost monopolize the global robot reducer. Both of these reducers are micron-level machining precision, and it is difficult to achieve high reliability at the mass production stage, let alone high-speed operation of several thousand revolutions, and high life.
Harmonic reducer consists of four basic components: "flexible wheel, wave generator, rigid wheel, bearing".
The outer diameter of the flexspline is slightly smaller than the inner diameter of the rigid wheel, and usually the flexo wheel has 2 teeth less than the rigid wheel. The elliptical shape of the wave generator determines that the contact points of the teeth of the flexspline and the rigid wheel are distributed on two opposite sides of the center of the ellipse. During the rotation of the wave generator, the contact portion of the flex spline and the just-toothed tooth start to mesh. When the wave generator rotates by 180° every clockwise, the flexspline is equivalent to the one-tooth number difference of the counterclockwise rotation of the rigid wheel. In two places with 180° symmetry, more than 30% of all teeth are meshed at the same time, which also results in high torque transmission.
Compared to the harmonic reducer, the RV drive is a newly developed transmission. It is developed on the basis of the traditional pin-pendulum planetary transmission. It not only overcomes the disadvantages of the general pin-pendulum transmission, but also has a small size and light weight. Transmission ratio range, long life, stable accuracy, high efficiency, smooth transmission and a series of advantages.
The RV reducer is composed of a cycloidal pin wheel and a planetary carrier. It is widely used in industrial robots, machine tools, and medical care because of its small size, strong impact resistance, large torque, high positioning accuracy, low vibration, large reduction ratio, and many other advantages. Testing equipment, satellite receiving systems and other fields.
The housing of the RV reducer and the cycloidal pin wheel are driven by the solid steel, so the bearing capacity is strong. The flexspline of the harmonic reducer can be continuously deformed to transmit the torque, which determines the limited ability of the harmonic reducer to withstand large torque and impact loads, so it is generally used in the front end.
2 advantages and disadvantages of both RV reducer and harmonic reducer
The harmonic reducer has a simple and compact structure and is suitable for miniaturization, low and medium load applications.
The RV reducer has good rigidity, strong impact resistance, smooth transmission and high precision, and is suitable for medium and heavy load applications. However, the RV reducer needs to transmit a large amount of torque, withstands a large overload shock, and ensures an expected working life. Relatively complicated over-positioning structures are used in the design, making the manufacturing process and cost control more difficult. The RV reducer does not have an elastically deformable force element inside it, so it can withstand a certain amount of torque. The bearing of RV reducer is its weak link. When it is stressed, it is easy to break the limit of the bearing and cause the bearing to wear or break abnormally. This problem is even more pronounced at high speeds, so the rated torque of the RV reducer drops significantly with the input speed.
3 whether there is a replacement relationship between the reducer
proposition view:
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 transmission, the accuracy of movement will be significantly reduced with the use of time. Therefore, in many countries, high-precision robot drives use RV speed reducers. Therefore, RV speed reducers gradually replace the development trend of harmonic speed reducers in advanced robot drives.
There is indeed an alternative relationship between these products on some models, but these types of reducers can only achieve partial replacement. In most cases, various types of speed reducers are difficult to replace. For example, in terms of speed ratios, the speed ratio of harmonics and RV is much larger than that of the planets, so the area of ​​small speed ratios is the planet. Of course, the speed ratio of the planet can be made large, but it is difficult to replace harmonics and RV. In terms of rigidity, for example, the stiffness of planets and RVs is better than that of harmonics. Under conditions of rigid use, harmonics do not perform well.
Harmonic retarders are characterized by lightness and smallness. In this respect, planets and RVs are difficult to achieve. Therefore, all types of reducers can only be replaced in some cases, but it is not practical to replace one product with another.
Anti-party view:
Each type of reducer cannot replace each other, but a complementary relationship.
RV and harmonics are complementary to each other, but it does not rule out the structural design optimization and manufacturing process breakthrough, the formation of local competition in the low-load applications.
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