Key words: how the positioning ring and bushing of the DC motor rotor (armature) limit the position of the commutator
The positioning rings are all made of bar turning, and the armature has been assembled on the center shaft before spraying glue. The thickness of the positioning ring can provide a blocking thrust in the axial direction. It is mainly used for working in situations with vibration or impact. in the motor below. In addition, in this type of motor, a bushing is added between the commutator and the chip to increase the thrust of the commutator insertion. It is mainly made of copper material, and its fixing force is the friction provided by the interference between the inner diameter of the positioning ring and the outer diameter of the shaft. When the positioning ring is assembled, if there is a flat position on the shaft, there may be a flat position. The copper material on the inner diameter of the positioning ring is shoveled off. When the thickness is the same, the fixing force that can be obtained by the shaft with the flat position is slightly smaller than that of the shaft without the flat position. The positioning ring to achieve the same fixing force requirements.
The main function of the positioning ring and the shaft sleeve is to match the position of the commutator to limit the total length of the rotor (armature), so as to ensure that after adding a certain number of oil-proof rings and gaskets, the two bearings of the magnetic bottom and the rubber cover are installed. There can be a certain virtual position between them to ensure the normal operation of the motor. When installing the positioning ring, if the distance between the positioning ring and the patent leather wire is very close, in order to prevent the entire motor from being short-circuited due to the damage of the patent leather wire when installing the positioning ring, a protection ring should also be placed between the positioning ring and the patent leather wire. After the assembly is completed, check and control the verticality of the end of the positioning ring and the shaft center, which is generally controlled within 0.03 mm, otherwise it may produce defective core jumps.
The working principle of the shaft sleeve is different from that of the positioning ring. There are two ways to cooperate with the shaft depending on the material. Metal materials are generally clearance fit or small interference fit. During clearance fit, in order not to shift or fall off during the manufacturing process, knurling is often used to fix the shaft. The shape of non-metallic materials (mostly injection molded parts) adopts transition fit. When designing the shaft sleeve, it is not considered to fix its position by friction, but to consider its supporting role. The end of the rotor is close to the chip (or other insulating material), and the other end is in contact with the end face of the bearing through the meson to achieve the position of the fixed rotor (armature) between the front and rear bearings.
If it is a metal material, its inner diameter generally has a clearance fit with the shaft, and knurling is used to fix it on the shaft during assembly. If it is a plastic part, its inner diameter is generally a transition fit with the shaft. Mainly considering the mechanical strength of the plastic parts, if an interference fit is used, the plastic parts may be deformed or damaged due to excessive assembly force during assembly. When the transition fit is assembled, due to the slight out-of-roundness or straightness of the plastic part, there will be enough force to fix it on the shaft without losing or shifting.
For the positioning ring, the value of its outer diameter is mainly determined according to the size of the elastic deformation area of the material inside the positioning ring after the inner diameter of the positioning ring is stressed. The material of copper has poor plasticity. If the elastic deformation area is larger than the entire Section, and reaching plastic deformation may cause the positioning ring to burst and lose its function. The specific value should vary according to the different copper materials used. It is recommended that the maximum area of elastic deformation should not exceed the cross-sectional area of the positioning ring.
For the shaft sleeve, its outer diameter mainly depends on the thickness of the positioning ring required by the structure, and depends on the required fixing force of the positioning ring. If the required fixing force is large, the thickness is large. When the fixing force is small, the thickness is small, and the structure of the positioning ring is required to be large, and when the required positioning force is small, the method of stepping the inner diameter can be used to solve the problem. The length of the shaft sleeve is also mainly determined by the needs of the structure.
On the side of the positioning ring close to the positioning ring, it is required that there should be no burrs, so as to prevent the burrs from deflecting the positioning ring and causing the motor to produce defective core jumps. If the burr is only controlled on one side during production and assembly, it must be marked and be careful not to flip it. When designing the positioning ring, the burrs at both ends must be considered, and the perpendicularity between the positioning ring surface and the inner hole is generally required to be at most 0.03 mm.
in conclusion
Use these high performance retaining rings and bushings to reduce rotational speed friction due to side load drag between the rotor and commutator. Any motor must have shims to properly uniform the rotor so that it "floats" in the magnetic field. The DC motor can adjust the axial gap between the adjacent laminations and the commutator through the positioning ring and the shaft sleeve, and can also adjust the ventilation volume in the rotor body. The structure is simple, the installation is convenient, and the service life of the bearing and the performance of the motor can be improved.
