JPS63157652A - Brushless motor - Google Patents

Abstract

PURPOSE:To obtain a brushless motor with less rotation irregularity, by a method wherein gear-shaped teeth are formed on the outer periphery of a rotor yoke and magnets, fixed so as to correspond to the teeth, are provided on the outer periphery of the teeth. CONSTITUTION:Gear-shaped teeth 15 are provided along the whole outer periphery of a rotor yoke 14. Three pieces of the teeth are provided with respect to one pole of a multi-pole magnet, provided on the side of a rotor. Accordingly, the number of teeth is 24 and a pitch angle is 15 deg. when the number of pole is eight. Magnets 16 are fixed at positions opposing to the teeth 15 of the toothed rotor yoke 14. Upon the provision of the magnets 16, the position of the magnets 16 is set so that a loss torque, corresponding to a torque ripple generated in a motor, is generated. In a motor, constituted in such a manner, the flux changes into waveform between a position, whereat the teeth 15 are opposed to the fixed magnets 16, and another position, whereat the groove or the trough 17 between the teeth 15 is opposed to the fixed magnet 16, whereby torque ripple may be restrained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a brushless motor, and more specifically, a stator yoke is provided with a plurality of spiral coils, and a permanent magnet is located on the rotor side facing the coils. The present invention relates to a flat type brushless motor in which rotational driving force is obtained by detecting the rotational phase of the rotor with a detection element and sequentially switching and supplying current to the coils at predetermined timing.

[Conventional technology]

FIG. 8 shows an example of a capstan motor used in a magnetic recording/reproducing device, etc., as an example of a conventional flat type brushless motor of this type. Here, 1 is a stator yoke attached to a housing 2, and a plurality of spiral coils 3 are arranged in the circumferential direction of the stator yoke 1. Also,
The rotor yoke 4 is held on the rotating shaft 5 via a bush 6, and a spiral coil 3 is mounted on the rotor yoke 4.
A corresponding multipolar magnet 7 is attached at a position opposite to . Furthermore, FG magnets 8 magnetized at a fine pitch are provided around the outer periphery of the rotor yoke 4.
The magnetic sensing element 9 attached to the stator yoke 1 is generally a semiconductor magnetic resistance element that detects changes in magnetic resistance.
The rotational state of the rotating shaft 5 is detected through the fluctuation of the magnetic field caused by the magnetic field.

IO is a Hall element fixed to the stator yoke 1, and the phase of the multipolar magnet 7 when the rotor yoke 4 rotates around the axis 5 can be detected by this Hall element 10.

11 is a ball bearing, 12 is a metal bearing, and the rotating shaft 5 is supported by the housing 2 by these bearings.

Therefore, in the brushless motor configured as described above, a current is switched and supplied to the coil 3 at a predetermined timing by the output from the Hall element 1O, thereby generating rotational torque and driving the rotor yoke 4 to rotate by degrees. However, let us now discuss the case where such a motor has three phases. In this case, a composite torque is generated in the form shown in FIG. 9.

That is, assuming that the number of magnetic poles of the multi-pole magnet 7 is n, the coils 3 of each phase are arranged on the stator yoke 1 with an electrical angle of 120° shifted from these poles. In the coil 3 of each phase, the magnetic flux density distribution is as shown in FIG. 9 (A), the first phase of (A),
The second phase (b) and the third phase (c) change in a sine wave state that is shifted from each other. Note that current is sequentially supplied to the coils 3 of each phase in the positive and negative directions at the timings shown by (a) to (c) in FIG. 9(B), respectively, according to the output from the Hall element 10. Due to the phase, torque is generated as shown in (d) of FIG. 9(C), and the combined torque of these has a waveform form as shown in (e), and a torque ripple occurs.

Therefore, rotational unevenness occurs due to such torque ripple, but if the magnitude of the torque ripple is T1, the rotational speed of the rotating shaft 5 is N1, the inertial force is J1, and the rotational unevenness is ΔN, then the relationship in equation (1) holds true. Therefore, especially in the case of a capstan with a low rotational speed N, rotational unevenness ΔN due to torque ripple T
As a result, the magnetic recording and reproducing device M suffers from low-frequency wow and flutter in the audio signal and jitter in the video signal. Conventionally, this problem has been solved by increasing the inertial force. Doing this would go against the desire to reduce the weight of the device.

[Problem that the invention seeks to solve]

In view of the above-mentioned conventional problems, the purpose of the invention is to provide a brushless motor that can suppress the occurrence of torque ripple, improve rotational performance, contribute to weight reduction, and is suitable for magnetic recording and reproducing devices. Our goal is to share our ideas.

[Means for solving problems]

In order to achieve such an object, the present invention includes a stator yoke having a plurality of coils arranged in the circumferential direction, and a rotor yoke having a multi-pole permanent magnet at a position facing the plurality of coils. In a brushless system that rotates the rotor yoke by supplying current to multiple coils at predetermined timing, the rotor yoke is provided with gear-shaped teeth around its outer periphery, and the teeth are placed opposite the tips of the teeth. A magnet with a shape corresponding to the rotor yoke is installed, and when the rotor yoke rotates, loss torque ripples are generated in the motor due to fluctuations in the relative position of the magnet and tooth profile, and the loss torque ripples eliminate the torque ripples generated in the motor. It is characterized by what it did.

(Function) According to the brushless motor of the present invention, a gear-shaped tooth profile is provided around the outer periphery of the rotor yoke, and a magnet is provided at a position facing the tooth profile of the stator yoke, so that a magnetic field is generated between the magnet and the gear-shaped tooth profile. Cogging torque is generated by changes in magnetic flux, and the ripple of this cogging loss torque can eliminate the torque ripple that occurs in the motor. Ripples can be significantly suppressed by combining with.

(Examples) Examples of the present invention will be described below in detail and specifically based on the drawings.

FIG. 1 shows an embodiment of the invention. In this example, a gear-shaped tooth portion 15 is provided on the outer circumference of the rotor yoke 14 over the entire circumference. Therefore, the angle occupied by the pitch of the tooth profile on which this gear 15 is provided (hereinafter referred to as pitch angle) θX
is determined by the number n of poles of the multi-pole magnet 7 provided on the rotor side, and the number N of teeth is assumed to be three per pole n. Therefore, in this example, since the number of poles n is 8 balls, the number of teeth is 24, and the pitch angle θX is 15@.

Reference numeral 16 denotes a magnet fixed to the rotor yoke 14, which is provided with a tooth profile as described above, at a position opposite to the tooth portion 15 of the rotor yoke 14. In providing this magnet 16, its position is set so that a loss torque ripple corresponding to the torque ripple generated in the motor occurs, as will be described later.

Therefore, in the motor configured in this way, the tooth portion 1
5 is in a position facing the fixed magnet 16, and when the tooth portion 1
The magnetic flux changes into a waveform when the groove between the teeth, that is, the trough 17 is in a position facing the fixed magnet 16, and as a result, cogging loss torque as shown in FIG. 2 occurs. Therefore, the number of ripples in this case is 24 per rotation of the rotor yoke. In Fig. 3, (A) shows the loss torque shown in Fig. 2, and (B) shows the loss torque shown in Fig. 9 first.
This is the combined generated torque of the type shown as (e) in C).

Therefore, the generated torque (B) and loss torque (A
) and the peaks and troughs of the ripples match, in the motor, the torque is subtracted and synthesized as shown in (C) in Figure 3, making it possible to suppress the torque ripple significantly. Become.

FIG. 4 shows another embodiment of the invention. In this example, the teeth 25 and the valleys 27 are both U-shaped and comb-like, and the other configurations are the same as in FIG. 1. Furthermore, FIGS. 5 to 7 each show still other embodiments of the present invention, in which two magnets 26^ and 26B are arranged in the tooth 15 and the valley 17 adjacent thereto. FIG. 6 shows one in which one magnet 36 is provided across three adjacent teeth 15, and FIG. 7 shows a high magnetic permeability metal body having the same shape as the magnet 36 shown in FIG. 6. For example, the iron member 36
A magnet 46 is provided on A, and the same effect can be achieved in either case.

In addition, in the above explanation, an example was described in which the number of poles of the multi-pole magnet provided on the rotor yoke is 8 balls, but the number of poles is not limited to this, and may be, for example, 4 balls or 12 balls. It goes without saying that the shape of the tooth profile constituting the tooth portion is not particularly limited to the shape as in the above-mentioned example.

〔Effect of the invention〕

As explained above, according to the present invention, a gear-shaped tooth profile is formed on the outer periphery of the rotor yoke, and a magnet having a sharp shape corresponding to the tooth profile is fixedly provided on the outside of the tooth profile, so that the rotor yoke rotates. The loss torque ripple that occurs due to fluctuations in the relative position between the magnet and the tooth profile of the yoke is made to match the torque ripple that occurs in the motor, so the motor's torque ripple can be canceled out by the loss torque ripple. Therefore, it has become possible to provide a brushless motor that has less uneven rotation and is suitable for magnetic recording/reproducing devices and the like.

[Brief explanation of the drawing]

Fig. 1 is an exploded perspective view showing an example of the configuration of the brushless motor of the present invention, Fig. 2 is a waveform diagram showing one form of loss torque obtained by the brushless motor of the invention, and Fig. 3 is a torque generated by the motor due to the loss torque. A series of waveform diagrams for explaining that ripple disappearance can be obtained, FIG. 4 is an exploded perspective view showing the configuration of another embodiment of the present invention, and FIGS. Furthermore, FIG. 8 is a cross-sectional view showing an example of the configuration of a conventional brushless motor, and FIG. 9 is a diagram showing changes in magnetic flux generated in each coil in the conventional brushless motor and the coils. FIG. 3 is an explanatory diagram showing the relationship between the timing of current supplied to the motor and the shape of torque ripple generated in the motor. DESCRIPTION OF SYMBOLS 1... Stator yoke, 3... Spiral coil, 4.14... Rotor yoke, 5... Rotating shaft, 7... Multipolar magnet, 10... Hall element, 15, 25- ... Teeth, 18, 26A, 26B, 36.46... Magnet, 36^... Iron member. Figure 7

Claims (1)

[Claims] A stator yoke in which a plurality of coils are arranged in the circumferential direction;
A brushless motor comprising a rotor yoke having a permanent magnet magnetized with multiple poles at a position facing the plurality of coils, and rotating the rotor yoke by supplying current to the plurality of coils at a predetermined timing. A gear-shaped tooth profile is provided around the outer periphery of the rotor yoke, a magnet having a shape corresponding to the tooth profile is provided at a position opposite to the tip of the tooth profile, and when the rotor yoke is rotated, the magnet and the tooth profile are disposed. A brushless motor, characterized in that loss torque ripples are generated in the motor by fluctuations in relative position with respect to the motor, and the torque ripples generated in the motor are canceled by the loss torque ripples.