What is needle winding technology of motor winding
Motor winding is to place the wire in the coil in the slot, which is usually wrapped in a coated flexible ferromagnetic core to form the magnetic pole. There are two basic pole configurations for motors, salient and non salient. The stator of two-phase induction motor has two pairs of coils, and each pair of coils corresponds to an AC two-phase. Each pair of coils is connected in series, corresponding to the relative magnetic pole of the electromagnet. One coil corresponds to an N pole, the other corresponds to an S pole, and the other pair of coils is 90 ° to the first pair of coils in space. If it is a two-phase motor, this pair of coils is connected with the AC coil with a time offset of 90 ° and the winding diagram of the motor is shown below.
Connection mode of winding
In the salient pole motor, the poles can be generated by the windings under the pole surface. In the non salient pole structure, the windings can be dispersed in the pole slot. A general shaded pole motor consists of a winding placed around the pole supporting the phase of the magnetic field. Some types of motors include conductors, which are made of thick sheet metal, usually made of copper or aluminum. According to the type of starting method used in the motor, the three-phase windings of the motor are connected by star or triangle. Motors like the squirrel cage can be connected to the delta stator by a star and run on the track frequently.
The insulation layer between the two-phase winding and the outer slot of the motor can be fixed between the stator winding and the outer slot. The winding is made of copper wire wound on the iron core to produce or obtain electromagnetic energy. The most commonly used winding material is enamelled paint wrapped copper or aluminum wire, including a group of coils in the slot and cogging in the edge area of the winding. In large motors, the pole windings are divided into several identical coils, which are inserted into smaller slots. This group is called phase band (see figure below). The distribution coil of the phase band counteracts some odd harmonics and produces sinusoidal magnetic field distribution on the magnetic pole. Because the phase bands can overlap, the number of turns of the slot at the edge of the pole may be less than that of other slots, and the edge slot may contain two-phase windings.
The rotating magnetic field is generated by two coils at right angles to each other and driven by 90 ° out of phase current. The three windings are placed in the space 120 ° apart and powered by the corresponding 120 ° phase current. The rotating magnetic field is also generated. When the 90 ° phase sine wave moves from point (a) to point (d), the magnetic field rotates counterclockwise (Fig. A-D).
The rotation speed of the stator rotating magnetic field is related to the number of poles in each phase. In the “full speed” diagram below, there are 6 or 3 pairs of poles and 3 phases, and each phase has only one pair of poles. The magnetic field rotates each sine wave cycle once. At 60Hz, the magnetic field rotates at 60 times per second or 3600 revolutions per minute (RPM), and at 50Hz, it rotates at 50 or 3000 revolutions per second. If the number of poles of the motor is doubled, the synchronous speed will be halved, because the magnetic field rotates 180 ° in space to produce a 360 ° sine wave.
In order to effectively wind the pole slots of multi pole three-phase motor with electronic commutation together, they will be coated with insulation layer and directly wound with needle winding method. The needle with the nozzle is at right angles to the direction of motion, moves in the way of lifting motion, passes through the slot between the two adjacent poles of the motor through the stator group, and drops the wire to the required position. Then, turn the reversal point of the stator on the winding head by one pitch so that the previous process can run again in reverse order. The disadvantage is that there must be a gap between two adjacent electrodes, the gap size is at least the nozzle diameter, and the nozzle diameter is about three times of the winding diameter. The space between two adjacent poles can not be completely filled. The figure below shows the right angle winding mode.
The advantage of needle winding technology is that the needle bracket carrying the guide wire nozzle is usually coupled with the numerical control coordinate system, so that the nozzle can move towards the stator through space. In this way, in addition to the normal lifting motion and the rotation of the stator, the laying motion can also be performed. Because the copper wire is pulled out from the copper wire guide nozzle at a 90 ° angle, the copper wire can only be placed in a limited range. Since the guide wire nozzle can move freely in the whole tooth slot, if equipped with additional rotating device, the nozzle can terminate the wire at the contact point. Like the traditional linear winding technology, the contact pin or hook contact can be in close contact with the moving surface, which is suitable for single pole interconnection in star connection or triangle connection. The following figure shows the winding mode with 45 ° angle.
The rotation motion and stroke motion need to be accurately synchronized, so that the needle will not contact the slot during the up and down motion. The variables that affect the maximum winding speed are: needle stroke, stator rotation angle (number of poles), wire diameter, slot width, helical angle of skewed slot stator. Due to the high acceleration of the wire guide and needle support, it will lead to unnecessary vibration and affect the quality of the winding. The improvement of motion quality is usually produced by the ball screw. In this moving process, the servo driver must be continuously reversed to meet the reverse direction movement of the wire guide.
Conclusion
With needle winding technology, finished components such as stator coils or connectors can be produced. In addition to the underutilized space between the magnetic poles, compared with the traditional pull in technology, the motor coil with good filling factor can also be wound on the lower height of the stator lamination (coiler head height).
Source: China Permanent Magnet Manufacturer www.rizinia.com
