1 Harmonic reducer bearing
1.1 Transmission principle of harmonic reducer bearing
The Harmonic Drive was invented by American inventor C. Musser Musser in the mid-1950s. It has features not found in other drives. The harmonic drive uses the original action principle of metal elasticity and three basic components (wave generator, flexible wheel and rigid wheel) to form a precision control reducer.
Harmonic drive is used as a reducer, usually in the form of wave generator initiative, rigid wheel fixed, flexible wheel output
When the wave generator is loaded into the inner circle of the flexible wheel, the flexible wheel is forced to produce elastic deformation and ellipse shape, and the teeth of the flexible wheel at the long axis are inserted into the tooth groove of the rigid wheel, which becomes a fully meshing state. And the short axis of the two wheels teeth do not contact at all, in the off state. The process from engagement to disengagement is in the state of snapping out or snapping in.
When the wave generator rotates continuously, the flexible wheel is forced to constantly deform, so that the teeth of the two wheels change their working states constantly in the process of biting in, meshing, snapping out and disconnecting, resulting in the so-called wrong tooth movement, so as to realize the motion transmission between the active wave generator and the flexible wheel.
1.2 Characteristics of harmonic reducer bearing
1) High precision.
Multi-tooth meshes simultaneously at two 180° symmetric positions, so the influence of gear pitch error and cumulative pitch error on rotation accuracy is relatively average, and high position accuracy and rotation accuracy can be obtained.
2) Large transmission ratio.
The transmission ratio of single stage harmonic gear transmission can reach 30-500, and the structure is simple. Three basic parts on the same axis can achieve high deceleration ratio.
3) Strong carrying capacity.
In harmonic transmission, the meshing between teeth is surface contact, and the number of teeth meshing at the same time is relatively large, so the load per unit area is small, and the bearing capacity is higher than other transmission forms.
4) Small size and light weight.
Compared with the common gear device, the volume and weight of the gear structure can be greatly reduced to achieve miniaturization and lightweight.
5) High transmission efficiency and long service life.
6) Smooth transmission, no impact, small noise.
1.3 Harmonic reducer bearing
Harmonic is out of the traditional involute gear design based on Willis theorem, and the new gear profile design theory is applied to design non-conjugate harmonic gear profile, which can improve the output efficiency and torque bearing capacity of harmonic reducer on the premise of greatly improving the service life of the reducer.
Compared WITH SIMILAR foreign PRODUCTS, THE new harmonic MEShing gear shape “P gear” overcomes the shortcomings of the previous harmonic meshing gear shape, and through a series of innovative improvement measures, can greatly improve the service life of flexible gear.
Advantages of “P-shaped teeth” include:
1) The tooth height is low, it does not need a deep meshing distance to obtain a large meshing amount, can withstand a large torque;
2) Larger tooth width and larger root radian can reduce the risk of fracture failure;
3) The required flexure deformation is small, so that the life of flexure can be greatly improved;
4) 20%-30% of the teeth are engaged, and the specific pressure of the teeth surface is small.
In terms of performance parameters, the advantages of harmonic reducer bearings include:
1) The load torque is greatly increased, which is more than twice that of similar domestic products, and the limit load is better than that of foreign famous brands;
2) Small size, light weight, the volume is less than half of the domestic similar products;
3) High efficiency, low backlash, can achieve zero error accurate transmission;
4) Long working life, the ultimate load life is more than 4 times that of foreign famous brands;
5) Ultra-stable low-frequency output characteristics can be obtained, which is of great significance for welding robots with precise point control requirements and stability.
2.1 Detailed Design
1) Strict axial positioning of the wave generator.
2) Harmonic reducer should pay attention to avoid interference
(1) Avoid interference between flexible wheel and matching parts when elastic deformation occurs.
(2) Pay attention to the length of the installation screw to prevent interference of the flexible wheel due to too long screw.
3) The screw on the harmonic reducer body cannot be removed.
4) Pay attention to the lubrication and sealing of harmonic reducer.
5) Pay attention to the shape and position tolerance of the matching parts of the harmonic reducer.
(1) The plane shape and position tolerance of the fixed installation of the reducer is: flatness 0.01mm, verticality 0.01mm, threaded hole or through hole position 0.1mm.
(2) Minimize the number of matching parts to prevent the cumulative error caused by too long size chain.
6) Confirm that the gear surface and the flexible bearing part of the reducer are always fully lubricated. It is not recommended that the tooth surface is always used upwards, which will affect the lubrication effect. If the tooth surface is always up, the oil level in the cavity must exceed the meshing tooth surface to ensure the effective lubrication of the tooth and the flexible bearing.
7) Sealing tolerance fit of transition flange.
2.2 Processing technology requirements
Harmonic reducer is very sensitive to the tilt of the axis of rotation, so it is necessary to consider the appropriate process plan, especially to ensure the corresponding shape and position tolerance.
2.3 Assembly process requirements
2.3.1 Assembly Environment Requirements
The harmonic reducer must be installed in a clean enough environment. No foreign matter can enter the reducer during the installation process, so as not to cause damage to the reducer during the use.
2.3.2 Assembling Tools
Including corresponding specifications of torque wrench, quantitative oiler, dust-free paper, thread glue, etc.
2.3.3 Assembly Points
Apply harmonic professional grease evenly on the inner wall of the flexible bearing and the flexible wheel, and then install. Start the electric machine at the speed of 100r/min, lock the transition flange of the motor in a cross way, and apply equal increasing force for 4-5 times until the screw is locked.
3 conclusion
Harmonic reducer as an open reducer, its application involves the whole process of product design, manufacturing and assembly. It not only to the designer, the manufacturer, but also to the assembler put forward many requirements. If any link fails to be effectively controlled, it will affect the application of harmonic reducer.
Harmonic reducer bearing as a kind of precision reducer inside the matching bearing, because of its small size, large speed ratio, large torque is widely used in SCARA robot. This PAPER DISCUSSES THE MEASURES TAKEN IN THE PROCESS OF DESIGN, MANUFACTURE and ASSEMBLY OF A TYPICAL SCARA ROBOT, AND shows the installation and use of harmonic reducer.
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