What is a harmonic reducer
Harmonic drive reducer is a kind of gear transmission, which makes flexible gear produce controllable elastic deformation by wave generator, and transmits motion and power by meshing with rigid gear. It is mainly composed of wave generator, flexible gear and rigid gear.
Advantages of harmonic reducer:
(1) The transmission speed ratio is large. The speed ratio range of single-stage harmonic gear transmission is 70 ~ 320, which can reach 1000 in some devices, and the speed ratio of multi-stage harmonic gear transmission can reach more than 30000. It can be used not only for decelerating, but also for increasing speed.
(2) High bearing capacity. This is because the number of teeth in harmonic gear transmission is large, and the number of teeth in double wave transmission can reach more than 30% of the total number of teeth. Moreover, the flexspline adopts high-strength materials, and the teeth are in face contact.
(3) High transmission accuracy. This is because there are many teeth meshing at the same time in harmonic gear transmission, and the error is averaged, that is, the multi tooth meshing has mutual compensation effect on the error, so the transmission accuracy is high. In the case of the same gear accuracy level, the transmission error is only about 1 / 4 of the ordinary cylindrical gear transmission. At the same time, the radius of the wave generator can be slightly changed to increase the deformation of the flexspline, so that the backlash is very small, and even meshing without backlash can be achieved. Therefore, the harmonic gear reducer has small transmission clearance and is suitable for reverse rotation.
(4) High transmission efficiency and smooth movement. Due to the uniform radial movement of the flexspline gear teeth in the transmission process, the relative slip speed of the teeth is still very low even if the input speed is very high (so it is one percent of that of the ordinary involute gear transmission), so the tooth wear is small and the efficiency is high (up to 69% ~ 96%). Because both sides of the gear take part in the work when meshing in and out, there is no impact phenomenon and the movement is stable.
(5) The utility model has the advantages of simple structure, less parts and convenient installation. 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 light weight. Compared with the general reducer, when the output torque is the same, the volume and weight of harmonic gear reducer can be reduced by 2 / 3 and 1 / 2 respectively.
(7) It can transmit motion to the confined space. Using the flexible characteristics of flexspline, this valuable advantage of flexspline drive is incomparable with other existing drives.
Transmission principle of harmonic reducer
Figure 1 on the right shows the basic structure of the simplest harmonic drive reducer, and Figure 2 shows the working principle of harmonic drive.
Figure 1 basic structure
Figure 2 working principle diagram
It is mainly composed of three basic components: (1) rigid gear with inner ring gear, which is equivalent to the center gear in planetary system（ 2) The flexible gear with outer gear ring is equivalent to planetary gear（ 3) Wave generator h, which is equivalent to planet carrier. As a reducer, it usually adopts the form of wave generator driving, rigid wheel fixed and flexible wheel output. The wave generator h is a rod-shaped part with rolling bearings at both ends to form rollers, which are pressed against the inner wall of the flexspline 1. Flexspline is a thin-walled gear which can produce large elastic deformation, and its inner hole diameter is slightly less than the total length of the wave generator.
Wave generator is a component which can make flexible wheel produce controllable elastic deformation. When the wave generator is installed into the flexspline, the profile of the flexspline is forced to change from the original round to oval, and the teeth near the two ends of the long shaft are fully meshed with the teeth of the rigid pulley, while the teeth near the two ends of the short shaft are completely separated from the rigid pulley. The teeth of other sections on the circumference are in the transitional state of meshing and disengaging. When the wave generator rotates continuously along the direction shown in the figure, the deformation of the flexspline is constantly changing, so that the meshing state of the flexspline and the rigid pulley is also constantly changing, from meshing in, meshing out, meshing out, disengaging, meshing in again and again, so as to realize the slow rotation of the flexspline relative to the rigid pulley 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, as the driven wheel, outputs to rotate and drives the load to move. In the process of transmission, when the wave generator rotates for one cycle, the number of cycles of deformation at a certain point on the flexspline is called the wave number, expressed in n. Two wave and three wave are commonly used.
The flexspline of double wave transmission has the advantages of small stress, simple structure and easy to obtain large transmission ratio. So it is the most widely used one. The pitch of flexible gear and rigid gear in harmonic gear transmission is the same, but the number of teeth is different. Usually, the difference between the number of teeth of rigid gear and flexible gear is equal to the wave number, that is, z2-z1 = n, where Z2 and Z1 -- are the number of teeth of rigid gear and flexible gear respectively. When the rigid wheel is fixed, the generator is driving and the flexspline is driven, the transmission ratio of harmonic gear transmission is I = - Z1 / (z2-z1), and the flexspline is elastic deformed and elliptical by the wave generator. Therefore, the long axis part of the ellipse is fully meshed with the rigid wheel, while the teeth of the short axis part are completely disengaged.
When the rigid wheel is fixed and the wave generator rotates clockwise, the flexspline produces elastic deformation, and the meshing part of the rigid wheel teeth moves in turn. The wave generator rotates 180 degrees clockwise and the drum moves one tooth counterclockwise. When the wave generator rotates for one revolution (360 degrees), the flexspline has two fewer teeth than the rigid pulley, so it moves two teeth anticlockwise. This motion is usually passed as output.
Application scope of harmonic reducer
It is widely used in aviation, aerospace, energy, navigation, shipbuilding, bionic machinery, commonly used ordnance, machine tools, instruments, electronic equipment, mining metallurgy, transportation, lifting machinery, petrochemical machinery, textile machinery, agricultural machinery and medical equipment, especially in high dynamic performance servo system, The harmonic gear drive shows its superiority.
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