Harmonic drive reducers industry knowledge
Definition: It is mainly composed of four basic components: a wave generator, flexible gear, flexible bearing, and rigid gear. Harmonic drive reducer is a kind of flexible gear that is assembled with flexible bearing to make the flexible gear produce controllable elastic deformation. Gear transmission in which rigid gears mesh to transmit movement and power. Applied disciplines: mechanical engineering (first-level discipline); transmission (second-level discipline); gear transmission (third-level discipline) Harmonic gear transmission reducer is a new type of reducer developed using the principle of planetary gear transmission. Harmonic gear drive (referred to as harmonic drive).
Transmission principle
Figure 1
on the right shows the basic structure of the simplest harmonic drive reducer, and Figure 2 shows the working principle diagram of the harmonic drive.
It mainly consists of three basic components:
(1) Rigid gear (rigid wheel) with internal ring gear;
(2) Flexible gear (flexible gear) with outer ring gear;
(3) Wave generator H.
As a reducer, it usually adopts an active wave generator, a fixed rigid wheel, and an output form of a flexible wheel.
The wave generator H is a rod-shaped component, the two ends of which are equipped with rolling bearings to form rollers, and are pressed against the inner wall of the flex spline 1. The flex spline is a thin-walled gear that can produce greater elastic deformation, and its inner hole diameter is slightly smaller than the total length of the wave generator. The wave generator is a component that makes the flexible wheel produce controllable elastic deformation. When the wave generator is installed in the flex spline, the cross-section of the flex spline is forced to change from the original circular shape to an ellipse. The teeth near the two ends of its long axis are fully meshed with the teeth of the rigid wheel, while the teeth near the ends of the short axis are Completely separated from the Gang wheel. The teeth of other segments on the circumference are in a transitional state of meshing and disengaging. When the wave generator continuously rotates in the direction shown in the figure, the deformation of the flex spline is constantly changing, so that the meshing state of the flex spline and the rigid wheel is also constantly changed, from engagement, engagement, engagement, disengagement, re-engaging..., It goes back and forth, so as to realize the slow rotation of the flexible wheel relative to the rigid wheel in the opposite direction of the wave generator H. When working, the rigid wheel is fixed, the motor drives the wave generator to rotate, and the flexible wheel acts as a driven wheel to output rotation and drive the load to move. In the transmission process, the wave generator makes one revolution and the number of cycles of deformation at a certain point on the flex spline is called the wavenumber, which is represented by n. Commonly used are two waves and three waves. The flex spline of the double-wave transmission has less stress, simple structure, and easy to obtain a large transmission ratio. Therefore, it is the most widely used one.
The tooth pitch of the flexible wheel and rigid wheel of harmonic gear transmission is the same, but the number of teeth is not equal, usually, the difference between the number of teeth of rigid wheel and the flexible wheel is equal to the wavenumber, namely
z2－z1=n
In the formula, z2 and z1--respectively the number of teeth of rigid wheel and flexible wheel.
When the rigid wheel is fixed, the generator is active, and the flexible wheel is driven, the transmission ratio of the harmonic gear drive is
i=-z1/(z2-z1)
In double-wave transmission, z2-z1=2, there are many flex spline teeth. The minus sign in the above formula means that the steering of the flex spline is opposite to that of the wave generator. It can be seen that the harmonic reducer can obtain a large transmission ratio.
The wave generator elastically deforms the flex spline into an elliptical shape. For this reason, the long axis of the ellipse is completely meshed with the rigid wheel, while the teeth of the two wheels of the short axis are in a completely disengaged state.
The rigid wheel is fixed, the wave generator rotates clockwise, the flexible wheel is elastically deformed, and the parts meshing with the teeth of the rigid wheel move sequentially.
The wave generator rotates 180 degrees clockwise, and the steel wheel moves one tooth counterclockwise.
The wave generator rotates once (360 degrees). Since the number of teeth of the flexible wheel is two less than that of the rigid wheel, it moves two teeth counterclockwise. This movement is usually delivered as output.
1. High reduction ratio
Single-stage coaxial can obtain a high reduction ratio of 1/30～1/320. The structure and structure are simple, but it can realize a high reduction ratio device.
2. Small backlash
Harmonic Drive is different from ordinary gear meshing with extremely small backlash. This feature is an indispensable element in the field of controllers.
3. High precision
Multiple teeth mesh at the same time, and there are two 180-degree symmetrical gear meshes. Therefore, the gear pitch error and the accumulated pitch error have an even effect on the rotation accuracy, so that the position accuracy and rotation accuracy reach a very high level.
4. Few parts and easy installation
The three basic components achieve high reduction ratios, and they are all on the same axis, so the kit is easy to install and simple in shape.
5. Small size and lightweight
Compared with the conventional gear unit, the volume is 1/3 and the weight is 1/2, but it can obtain the same torque capacity and reduction ratio, realizing small and lightweight.
6. High torque capacity
The material of the flexible wheel uses special steel with high fatigue strength. Unlike ordinary transmissions, the number of teeth meshed at the same time accounts for about 30% of the total number of teeth, and it is in surface contact, so the pressure on each gear is reduced, and high torque capacity can be obtained.
7. High efficiency
The sliding of the gear tooth meshing part is very small, reducing the power loss caused by friction, so while obtaining a high reduction ratio, it is possible to maintain high efficiency and realize the miniaturization of the drive motor.
8. Low noise
The meshing speed of the gear teeth is low, and the transmission force is balanced, so it runs quietly and has very little vibration.
Basic Features
1. High load-carrying capacity In harmonic transmission, the tooth-to-tooth meshing is in surface contact, and the number of simultaneously meshing teeth (overlap coefficient) is relatively large, so the load per unit area is small and the load-bearing capacity is higher than other transmission forms.
2. Large transmission ratio The transmission ratio of single-stage harmonic gear transmission can reach i=70～500.
3. Small size and lightweight.
4. High transmission efficiency and long life.
5. Smooth transmission, no impact, no noise, and high movement precision.
6. Because the flex spline bears a large alternating load, the fatigue strength, processing and heat treatment requirements of the flex spline material are high, and the process is complicated.
Harmonic speed reducer only began to be developed in China in the 1960s and 1970s, and many manufacturers have specialized in production and formed serialization. It is widely used in electronics, aerospace, robotics, and other industries. Due to its unique advantages, its applications in the chemical industry are gradually increasing.
Model series
Cup type series harmonic drive reducer
Cap type series harmonic drive reducer
Ultra-thin series harmonic drive reducer
High torque type series harmonic drive reducer
Main advantage
(1) The transmission speed ratio is large. The single-stage harmonic gear transmission speed ratio ranges from 70 to 320, in some devices it can reach 1000, and the multi-stage transmission speed ratio can reach more than 30,000. It can be used not only for speed reduction but also for speed increase occasions.
(2) High carrying capacity. This is because the number of teeth meshed at the same time in the harmonic gear drive is large, and the number of teeth meshed at the same time in the double-wave drive can reach more than 30% of the total number of teeth. Moreover, the flex spline uses high-strength materials, and the teeth and teeth are in surface contact.
(3) High transmission accuracy. This is because the number of teeth meshed at the same time in the harmonic gear transmission is large, and the error is averaged, that is, multi-tooth meshing has a mutual compensation effect on the error, so the transmission accuracy is high. In the case of the same gear accuracy grade, the transmission error is only about 1/4 of that of ordinary cylindrical gear transmission. At the same time, the radius of the wave generator can be slightly changed to increase the deformation of the flex spline, so that the backlash is small, and even the backlash-free meshing can be achieved. Therefore, the transmission of the harmonic gear reducer is small and suitable for reverse rotation.
(4) High transmission efficiency and smooth movement. Due to the uniform radial movement of the flex spline gear teeth during the transmission process, even if the input speed is high, the relative slip speed of the gear teeth is still extremely low (so it is one percent of the ordinary involute gear transmission) Therefore, the gear teeth are less worn and the efficiency is high (up to 69%~96%). In addition, both sides of the gear participate in the work when engaging in and out, so there is no impact phenomenon and the movement is stable.
(5) The structure is simple, the number of parts is small, and the installation is convenient. There are only three basic components, and the input and output shafts are coaxial, so the structure is simple and the installation is convenient.
(6) Small size and lightweight. Compared with general reducers, when the output torque is the same, the volume of the harmonic gear reducer can be reduced by 2/3, and the weight can be reduced by 1/2.
(7) can transmit motion to confined spaces. Utilizing the flexibility of the flex spline, this valuable advantage of the wheel drive is unmatched by other existing drives.
Scope of application
Harmonic gear reducers are used in aviation, aerospace, energy, navigation, shipbuilding, bionic machinery, common ordnance, machine tools, instruments, electronic equipment, mining and metallurgy, transportation, lifting machinery, petrochemical machinery, textile machinery, agricultural machinery and medical treatment Equipment and other aspects are increasingly widely used, especially in the servo system with high dynamic performance, the use of harmonic gear transmission shows its superiority. It transmits power from tens of watts to tens of kilowatts, but high-power harmonic gear drives are mostly used in short-term workplaces
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