JPS63287388A - Brushless motor - Google Patents

Abstract

PURPOSE:To reduce the unevenness of rotation of a motor by magnetizing an FG magnet through causing the pitch of magnetization of said FG magnet to correspond to the displacement of a torque ripple. CONSTITUTION:A control system for a brushless motor 19 is composed of an FG magnet 10 with a magnetoresistance element 11, an amplifier 14, a comparator 16, a compensating filter 17 and a driver 18, and magnetizes said FG magnet through causing the pitch of magnetization of the FG magnet 10 to correspond to the displacement of a torque ripple. Thus, an FG pulse as information about the number of revolutions outputted from said magnetoresistance element 11 is outputted as such information as to show said number of revolutions 'slower- faster-slower' than the target number of revolutions in the manner of corresponding to the 'low-high-low' state of a torque ripple. Therefore, said torque ripple in the voltage output of said comparator 16 is decreased, since an electric current is supplied so as to offset a torque variation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application J] The present invention relates to a brushless motor, and more particularly to a device for appropriately controlling its output torque.

[Prior Art] FIG. 4 is a sectional view showing an example of the configuration of a brushless motor. The figure shows a capstan motor as an example, in which a rotating shaft 1 is supported by a metal bearing 3 and a ball bearing 4. 2 is a bearing housing, 6 is a thinly wound coil, and a plurality of them are arranged on the stator yoke 5, and a multipolar magnet 7 is arranged on the rotor yoke 9 so as to face this.

The multipolar magnet 7 is connected to the rotating shaft 1 via a bush 8 and a rotor yoke 9, and rotates accordingly. 10 is FG
It is a magnet, and is formed by subjecting the outer periphery of the rotor yoke 9 to ultra-multipole magnetization with a narrow pitch. lj is a magnetoresistive element as a magnetic sensing element, and F
In combination with the G magnet 10, FG pulses are output according to the rotational state of the rotating shaft 1. That is, the faster the rotation speed, the shorter the pulse width, and the slower the rotation speed, the longer the pulse width. Reference numeral 12 denotes a Hall element, which serves as one end of a mechanism that detects the phase of the multipolar magnet 7 and switches the current supply to the coil 6. 19 is a brushless motor as a controlled object.

FIG. 5 is a diagram showing torque fluctuations generated by the brushless motor. Generally, in a three-phase brushless motor, the magnetic flux distribution in the coil becomes a sine wave as shown in FIG. When the number of magnetic poles is n, the coils of each phase are mutually (2/
They are fixed on the stator yoke 5 with a phase shift of 3·360/n ) degrees, thereby producing a three-phase magnetic flux change.

Based on this and the output of each Hall element 12, the same figure (B
) The current flows through the coil 6 of each phase at the timing shown in
As the torque flows through the cylinder, the generated torque takes the form shown in the same figure (C), and torque ripple occurs. This causes uneven rotation of the rotating shaft 1.

[Problems to be Solved by the Invention] By the way, the rotational unevenness ΔN and the torque ripple T are in a relationship via the inertia J of the rotation-related part and the rotational speed N, so especially in a capstan motor with a slow rotational speed, , rotational unevenness due to this torque ripple is large,
Therefore, in magnetic recording and reproducing apparatuses using such brushless motors, problems arise such as wow and flutter in audio signals and jitter in video signals. For this reason, this problem has been dealt with by increasing the inertia J, which has been a major obstacle to reducing the weight of the motor and, by extension, the weight of equipment to which such a motor is applied.

Therefore, in view of the above-mentioned conventional problems, the present invention improves the rotational performance of a motor by reducing or almost eliminating torque ripple, which is a cause of uneven rotation, and provides great possibilities for reducing the weight of such a motor. The purpose is to

[Means for Solving the Problems] Therefore, the present invention includes a speed detecting means that is disposed at a predetermined part of the rotating body and detects the speed of the rotating body in a non-linear manner, and a predetermined rotation speed that is set in advance. Comparing means for comparing the speed detected by the speed detecting means and converting the speed difference obtained by the comparison into a voltage value corresponding to the speed difference and outputting it, and supplying the voltage to the rotating body based on the voltage value from the comparing means. and a drive control means for controlling the current value.

[Function] According to the above configuration, by magnetizing the FG magnet so that the pitch of magnetization corresponds to the displacement of the torque ripple, the detected speed corresponds to the torque ripple, and the torque ripple of the motor is reduced.・It is possible to reduce

[Example] Hereinafter, the present invention will be described in detail based on the example shown in the drawings.

FIG. 1 is a block diagram showing an embodiment of a control system including a device to which the present invention is applied.

In the figure, IO and 11 are the aforementioned FG magnet and magnetoresistive element, and 19 is a brushless motor as a controlled object. Reference numeral 15 is a pulse reference signal having target rotation speed information for the motor 19, and this information is set in advance and output from a predetermined device. A comparator 16 compares the reference signal 15 with the FG pulse from the magnetoresistive element 11 via the amplifier 14, and outputs the difference in rotation speed as a voltage value based on a predetermined relationship. here,
The FG pulse functions as a detector for negative feedback. 17 is a compensation filter that determines the responsiveness of the loop. A driver 18 changes the current supplied to the motor 19 according to the input voltage.

FIG. 2 is a top view schematically showing a multipolar magnet and an FG magnet according to an embodiment of the present invention. In this example, as shown in the figure, the multipolar magnet 7 has six poles, and the FG magnet IO has 360 poles.

In this case, the number of torque ripples is 6 per rotation of rotating shaft 1.
(Pole) x 3 (Phase) = 18, so one period of torque ripple is t = a, b as shown in Fig. 5.

C1... is divided into 18 time points and shown.

Here, as shown in FIG. 2, when t=a, the positions of the multipolar magnet 7 and the FG magnet IO with respect to, for example, the first phase coil are indicated by the broken lines in the same figure, and this position is designated as ao, as follows. When t-b, position b°.

..., t.'', the position is r°. Therefore, during the period when one torque ripple occurs, ab and b in Fig. 5(C)
c.

"', qr are the sections a'b', b'c', - in FIG.
, q'r'.

By the way, in the FG magnet 10, since there are 360 poles with 18 ripples, there are 20 poles each between ab, bc, ..."+Qr, and the magnetization pitch of these 20 poles is shown in Figure 5 (C ) Magnetization is performed in accordance with the torque ripple waveform shown in ().

This magnetization mode and the F-V output from the comparator 16 are shown in FIG. Figure (B) is a horizontally expanded view of the FG magnet IO, and Figure (A) is a diagram with the horizontal axis representing the length in the expanded direction and the vertical axis representing the magnetization density. .

As can be understood from these figures and Fig. 5 (C), magnetization is performed in the order of coarse-fine-coarse J, corresponding to the torque ripple that generates the magnetization density.In other words, the areas with high torque are and magnetize it so that the lower parts are coarser.

As a result, the FG pulse as the rotation speed information output from the magnetoresistive element 11 is output as "low - speed one slow" than the target rotation speed, corresponding to the torque ripple r low - high one low. be done. Therefore, the voltage output of the comparator 16 is "high-low-high" as shown in FIG.

This provides a current supply that offsets torque fluctuations, thereby reducing torque ripple.

[Effects of the Invention] As is clear from the above explanation, by magnetizing the FG magnet so that its pitch corresponds to the displacement of the torque ripple, the detected speed corresponds to the torque ripple, and the motor speed increases. It becomes possible to reduce torque ripple. This has the effect that uneven rotation of the motor can be improved, and furthermore, the rotational inertia can be reduced, thereby providing a great possibility of reducing the weight of the motor device.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an apparatus according to an embodiment of the present invention, FIG. 2 is a top view schematically showing a multipolar magnet and an FG magnet according to an embodiment of the present invention, and FIG. ＞～(
C) is an explanatory diagram for explaining the mode of magnetization of the FG divided by the magnet shown in Figure 2 and its effects. Figure 4 is a sectional view showing the configuration of a flat brushless motor. Figure 5 is the magnetic flux of the brushless motor. , is a waveform diagram showing an example of output of current and torque. DESCRIPTION OF SYMBOLS 1... Rotating shaft, 2... Bearing housing, 3... Metal bearing, 4... Ball bearing, 5... Stator yoke, 6... Spiral coil, 7... Multipolar magnet, 8... Bush, 9... Rotor yoke, 10... FG magnet, 11... Magnetoresistive element, 12... Hall element, 14... Amplifier, 15... Reference signal, 16... Comparator, 17... Roof compensation filter, 18... Driver, 19... Brushless motor. Block diagram of IQ FG Mac-dot firing gloss Ida V device IFiM tooth r'rI of brushless motor configuration! Figure 0 Ward Wall, ■ Drop

Claims (1)

[Scope of Claims] 1) a speed detection means disposed at a predetermined portion of the rotating body to nonlinearly detect the speed of the rotating body; and a predetermined rotation speed detected by the speed detection means set in advance. a comparison means for comparing the speed and converting the speed difference obtained by the comparison into a voltage value corresponding to the speed difference and outputting the voltage value, and a current value to be supplied to the rotating body based on the voltage value from the comparison means. A brushless motor characterized by comprising a drive control means for controlling the brushless motor. 2) In the brushless motor according to claim 1, the speed detection means is a plurality of magnetic poles magnetized around a rotating body and a magnetoresistive element that detects the magnetic field of the magnetic poles, and A brushless motor characterized by a non-uniform magnetic pattern.