JPH05300717A - Dc brushless motor - Google Patents

Abstract

PURPOSE:To reduce the peak value of a torque ripple generated in a DC brushless motor, by a cheap configuration. CONSTITUTION:In this axial-gap type DC brushless motor, three holes 21 arranged in a circumferential way are bored in a stator yoke 3 at angular spaces of 120 degrees, using a capstan axis 15 as a center. The rotational torque of the motor contains a very finely fluctuating torque ripple, and the rotational torque becomes maximum in some relative rotational positions occurring between a stator metallic board 11 and a rotor magnet 19. From this fact, magnetic fluxes are pulled partially out of the holes 21 provided in these relative rotational positions, and the magnetic flux densities thereof are made low instantaneously.

Description

Detailed Description of the Invention

[Object of the Invention]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC brushless motor for driving a capstan shaft such as a VTR (video tape recorder) or DAT (digital audio tape recorder).

[0003]

2. Description of the Related Art In recent years, as VTRs, DATs, and the like have been downsized, motors capable of highly accurate thinning and high efficiency have been desired as drive sources for capstan shafts. Therefore,
As a motor suitable for these conditions, the magnetic structure is simple,
Moreover, an axial gap type DC (direct current) brushless motor, which can make the commutation control mechanism small, is often used.

FIG. 4 is a sectional view showing an example of such a DC brushless motor. In the figure, 101 is a housing for supporting the motor. This housing 101
A flat plate-shaped stator yoke 103 is attached to one end of the stator substrate, and a stator substrate having a drive circuit (not shown), a coil 105 and a hall element (not shown) mounted on one surface of the stator yoke 103. 107 is attached.

A capstan shaft 111 is rotatably attached to the housing 101 via a bearing 109. At one end of the capstan shaft 111,
A disk-shaped rotor yoke 113 is fixed. A donut-shaped rotor magnet 115 having eight poles is mounted on the rotor yoke 113. The rotor magnet 115 has S-poles and N-poles alternately magnetized at equal angle divisions around the capstan shaft 111.
Further, the rotor magnet 115 and the coil 105 are arranged so as to face each other without contact.

FIG. 5 is a circuit diagram showing the structure of a drive circuit of this DC brushless motor.

In the figure, 105a to 105c are U-phase and V-phase, respectively, to which a driving current is supplied with a phase difference of 120 °
And W-phase coils. 201a to 201c are S poles,
It is a Hall element of each phase that detects the position of the N pole and outputs a detection signal corresponding to each detection. Reference numeral 203 denotes a forward / reverse signal (CW / CCW) from the outside and Hall elements 201a to 201a.
It is a three-phase logic circuit that outputs a switching signal having a phase difference by inputting the detection signal from 01c.
205 is six output transistors 207a-207c,
209a-209c and three diodes 211a-21
1c is a commutation circuit that performs phase switching of the drive current supplied from the power supply (Vs) by a switching signal or the like from the three-phase logic circuit 203.

In this drive circuit, the detection signals from the Hall elements 201a to 201c are input to the three-phase logic 203 together with the forward and reverse signals. As a result, the driving current is applied to two adjacent coils (two of 105a to 105c) by one.
It is switched sequentially while being supplied with a phase difference of 20 °. As a result, a rotating magnetic field is generated around the coils 105a to 105c, and the rotating magnetic field and the rotor magnet 115 magnetically act to rotate the motor.

By the way, in the case of a motor having such a drive circuit, even when the rotor magnet 115 is fully magnetized, at the moment when the phase is switched in the commutation circuit, the rotational torque between the phases is increased. Is not constant. This is because the magnetic action of the motor varies depending on the relative position of the rotor magnet 115 and the coil. For example, focusing on a certain coil, the rotation torque becomes maximum at the moment when the boundary between the N pole and the S pole of the rotor magnet 115 passes through the coil, and the rotation torque becomes minimum when one magnetic pole and the coil overlap. .. When this is counted as one torque ripple,
From the number of phases of the drive system and the number of magnetic poles attached to the rotor magnet 115, the torque ripple number for one rotation of the motor can be obtained. In a three-phase, eight-pole motor, a torque ripple is generated 24 times for one rotation of the motor, and in a mechanism such as VTR or DAT that requires low rotation and high-precision rotatability, this torque ripple has a large performance. affect.

Therefore, conventionally, auxiliary magnetization is added to the rotor magnet 115 in addition to the main magnetization, so that the rotating magnetic field is generated at the moment when the boundary between the north pole and the south pole of the rotor magnet 115 passes through one coil. Is used to reduce the ripple width.

However, according to this method, a step for auxiliary magnetization is added to the production of the rotor magnet 115, resulting in an increase in cost.

[0012]

As described above, the conventional DC is used.
The brushless motor has a problem that a torque ripple with a large wave height is generated as the phases are switched.

The present invention has been made to solve such a problem, and an object thereof is to provide a DC brushless motor which can reduce the wave height of torque ripple with an inexpensive structure.

[Constitution of the Invention]

[0015]

SUMMARY OF THE INVENTION A DC brushless motor of the present invention is an axial gap type DC brushless motor having a stator metal substrate on which a coil is mounted, the number of which corresponds to the number of phases of the drive system on the stator metal substrate. The holes are distributed at equal angles around the motor rotation axis.

[0016]

In the DC brushless motor of the present invention, the stator metal substrate is provided with the holes of the number corresponding to the number of phases of the drive system, which are distributed at equal angles about the motor rotation shaft, thereby generating the maximum torque. The wave height of the torque ripple can be reduced by releasing the magnetic flux at the relative rotational position of the metal substrate and the rotor magnet from this hole.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is an exploded perspective view showing an axial gap type three-phase eight-pole full-wave drive capstan motor according to one embodiment of the present invention.

In the figure, 1 is a housing for supporting the motor. A metal stator yoke 3 is attached to one end of the housing 1, and a drive circuit (not shown), six coils 5a to 5f and three holes are attached to one surface of the stator yoke 3. A stator substrate 9 on which the elements 7a to 7c are mounted is attached. The stator yoke 3 and the stator substrate 9 form a stator metal substrate 11.

A capstan shaft 15 is rotatably attached to the housing 1 via a bearing (not shown). A disk-shaped rotor yoke 17 is fixed to the capstan shaft 15. Further, a doughnut-shaped rotor magnet 19 having 8 poles is mounted on the rotor yoke 17. This rotor magnet 1
Reference numeral 9 has S-poles and N-poles alternately magnetized with a uniform angle division around the capstan shaft 15. Further, the rotor magnet 19 and the coils 5a to 5f are arranged so as to face each other without contact.

FIG. 2 is a plan view showing the above-mentioned stator metal substrates 11 collectively on a plane. In the figure, the stator metal substrate 11 is a diagram in which the stator yoke 3 and a stator substrate (not shown) are seen through from the stator yoke 3 side, and all are shown by solid lines.

In the figure, the coils 5a to 5f are mounted on the lower surface of a stator substrate (not shown) facing the rotor magnet 19. Here, the coils 5a and 5d are in the U phase and the coils 5b and 5e are in the V phase.
The coils of c and 5f correspond to the W phase. The coils of each pair are arranged so as to face each other around the capstan shaft 15. Hall elements 7a, 7b, 7c are arranged at positions inside the coils 5a, 5b, 5c representing the U-phase, V-phase, and W-phase, respectively, on the stator substrate 9.

On the other hand, the stator yoke 3 is provided with holes 21, for example, three holes 21 selected according to the number of phases of the driving method. The holes 21 are provided at equal angles (for example, 120 °) distributed around the capstan shaft 15, and in this embodiment, the coils 5 of each phase on the stator substrate 9 are provided.
It is provided by selecting positions within a, 5e, and 5f.

The size and shape of the hole 21 and the positional relationship with the coils 5a to 5f are preferably selected by experiments so that the wave height of the torque ripple becomes small. FIG. 3 is a diagram showing the relationship between the rotation angle of the motor and each phase drive current, and the rotation angle and the rotation torque. In the figure, the waveforms of A, B, and C are U depending on the rotation angle of the motor.
The drive currents supplied to the phase, V phase, and W phase coils are shown.
Since this motor is a three-phase full-wave drive system, the supplied drive current has a phase of 120 ° between each phase and the direction of flow is switched. The drive current having the waveforms of A, B, and C is supplied to each phase, so that the motor rotates.

Further, D is shown by a solid line with a waveform before the hole 21 is provided in the stator yoke 3. E is a waveform when the hole 21 is provided in the stator yoke 3, and is indicated by a dotted line. As described in the conventional example, the portion where the torque ripple is high is the moment when the boundary between the S pole and the N pole of the rotor magnet 19 overlaps with any of the six coils 5a to 5f, and the magnetic flux density is the maximum. It is also a part that has become.

As is apparent from this figure, the maximum value of the torque ripple in this embodiment is smaller than the maximum value of the torque ripple generated in the prior art, and it is possible to reduce the wave height t1 of the torque ripple. It was

This is because the magnetic flux at the relative rotational position between the stator substrate 9 and the rotor magnet 19 where the maximum torque is generated is partially released from the hole 21 provided in the stator substrate 9, so that the magnetic flux density is instantaneously increased. Due to lowering.

In this way, fluctuations in the rotational torque of the motor are reduced, and the torque ripple is reduced as shown by the wave height t2 of the torque ripple shown in FIG.

[0029]

As described above, according to the DC brushless motor of the present invention, the wave height of the torque ripple can be reduced only by providing the holes in the stator metal substrate.

[Brief description of drawings]

FIG. 1 is an exploded perspective view for explaining the configuration of a DC brushless motor according to an embodiment of the present invention.

FIG. 2 is a plan view collectively showing a stator metal substrate in this embodiment on a plane.

FIG. 3 is a diagram showing a relationship between a coil drive current and a rotating torque in this embodiment.

FIG. 4 is a cross-sectional view illustrating a configuration of a conventional DC brushless motor.

FIG. 5 is a circuit diagram for explaining a drive circuit in this conventional example.

[Explanation of symbols]

3 ... Stator yoke, 5a-5f ... Coil, 11 ... Stator metal substrate, 15 ... Capstan shaft, 17 ... Rotor yoke, 19 ... Rotor magnet, 21 ... Hole.

Claims (1)

[Claims] 1. A DC brushless motor of an axial gap type having a stator metal substrate on which a coil is mounted, wherein the stator metal substrate has holes of a number corresponding to the number of phases of a drive system at an equal angle with respect to a motor rotation shaft. A DC brushless motor characterized by being dispersed.