JPH0428218Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of application of the invention] The invention relates to a brushless motor suitable for VTRs, floppy disk drives, etc.
This invention relates to an improvement in a pick-up head for detecting the phase of a rotor.

[Background of the idea]

Conventionally, a brushless motor as shown in FIG. 6 has been widely used as a motor for rotating the head cylinder of a VTR.

In FIG. 6, 1 is a rotor section, and 2 is a stator section. The rotor portion 1 includes a circular rotor yoke 3, a ring-shaped rotor magnet 4 fixed inside the rotor yoke 3, and a rotor magnet 4 fixed to the center shaft of the rotor yoke 3. Furthermore, the stator portion 2 includes a stator yoke 6 and a drive coil 7 mounted on the stator yoke 6. 8,
9 is a pulse generating magnet (Puls) fixed to the outer peripheral surface of the rotor yoke 3 at 180 degree intervals.
One of the PG magnets 8 has its N pole exposed to the outside, and the other PG magnet 9 has its S pole exposed to the outside.
A pick up head (hereinafter referred to as PG head) 10 is attached to a predetermined position of the stator yoke 6 so as to face the stator yoke 9.

In the conventional brushless motor configured as described above, the rotor magnet 4 is magnetized in equal intervals along its circumferential direction, so that there is a gap between the rotor magnet 4 and the stator yoke 6. A field magnetic flux is generated in the drive coil 7, which causes a current to flow through the drive coil 7, generating torque and rotating the rotor magnet 4, that is, the rotor portion 1. Furthermore, when the rotor section 1 rotates, the PG magnets 8 and 9 also rotate, so the PG head 10
sequentially receives the magnetic fields from the two PG magnets 8 and 9 and outputs a predetermined PG pulse. The output waveform of such a PG pulse will be explained below.

FIG. 7 is a plan view showing the relationship between the above-mentioned PG head 10 and PG magnets 8 and 9. As shown in this figure, the PG head 10 has a C-shaped core 1.
1 and a coil 12 wound around the core 11, and the magnetic gap G is formed parallel to the end faces of the opposing PG magnets 8 and 9.

Further, FIG. 8 shows the magnetic flux distribution of the PG magnet 8 with the north pole exposed, where the solid line is the vector magnetic flux distribution in the Y direction, and the broken line is the vector magnetic flux distribution in the X direction. Although not shown, the magnetic flux distribution of the PG magnet 9 with its S pole exposed appears symmetrical to the PG magnet 8 with respect to the X axis.

Now, PG magnet 8 with such magnetic flux distribution
However, as the rotor section 1 rotates, the PG head 1
0, the PG head 10
The magnetic gap G is the opposite PG magnet 8.
Since the core 11 runs parallel to the end face of the
It will be affected by the vector magnetic flux distribution only in the X direction.

Therefore, when the vector magnetic flux distribution in the X direction shown in FIG. 8 is differentiated to obtain the rate of change of magnetic flux, the result is as shown in FIG. 9. At this time, the voltage e acting on the coil 12
is e=dΦ/dt, and it can be seen that it is directly affected by the amount of change in magnetic flux.

Therefore, the coil 12 has both polarities opposite to each other.
Corresponding to the magnetic flux change rate (only the vector magnetic flux distribution in the X direction) from the PG magnets 8 and 9, voltage waveforms having bouncing portions on both sides as shown in FIG. 10 are sequentially output.

In the voltage waveform obtained in this way, if thresholds are set at two predetermined points, positive and negative, for example at ±CV, when the output voltage of the coil 12 exceeds the threshold ±CV, the rotor section 1 phase can be detected. Therefore, if two video heads (both not shown) are attached to the rotating shaft 5 via an upper cylinder and the video heads and both PG magnets 8 and 9 are aligned respectively, the PG
The head 10 makes it possible to extract PG pulses synchronized with the rotation of both video heads.

However, in such a conventional phase detection device, variations in the surface Gaussian amount of the PG magnets 8 and 9 may cause variations in the output voltage of the coil 12. If is too small, the threshold ±
CV detection becomes impossible, and conversely, if the output voltage is too large, the threshold voltage ±CV
, and there is a risk of false detection.

[Purpose of invention]

An object of the present invention is to provide a brushless motor that can reliably detect the phase of the rotor section, regardless of the magnitude of the output voltage of the coil constituting the PG head, while eliminating the drawbacks of the prior art described above.

[Summary of the idea]

To achieve this objective, the present invention tilts the magnetic gap of the PG head with respect to the opposing end face of the PG magnet in a plane perpendicular to the axis of rotation, so that the core of the PG head The feature is that it is configured to be influenced by the vector magnetic flux distribution in the Y direction.

[Example of idea]

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

FIG. 1 is a cross-sectional view showing one embodiment of a brushless motor according to the present invention, and FIG. 2 is a plan view of the stator portion with the rotor portion removed, with the same reference numerals being used to designate parts corresponding to those in FIG.

In these figures, the stator yoke 6 is screwed to a wiring board 14 on which drive circuit components 13 and the like are mounted, and each drive coil 7 is attached to a coil holder 15 that is outsert molded on the stator yoke 6. Furthermore, an FG board 17 on which a comb-shaped FG coil 16 is printed is adhesively fixed onto each drive coil 7. Meanwhile, inside the rotor yoke 3, the FG
An FG magnet (Frequency Generator magnet) 18 is fixed to face the coil 16, and the FG magnet 18 is divided and magnetized at equal intervals along its circumferential direction to correspond to the FG coils 16. In addition, a plurality of magnetic sensors 19 consisting of Hall elements or the like are attached to the stator yoke 6 to face the magnetic pole faces of the rotor magnet 4.

A pair of window holes 3a and 3b are bored in the outer peripheral surface of the rotor yoke 3 at an interval of 180 degrees.
One PG magnet 8 is fixed to the outer peripheral surface of the rotor magnet 4 through the window hole 3a so that its S pole contacts the N pole of the rotor magnet 4.
The other PG magnet 9 is fixed to the outer circumferential surface of the rotor magnet 4 through the window hole 3b so that its north pole contacts the south pole of the rotor magnet 4. As a result, the N pole appears on the surface of the PG magnet 8, and the S pole appears on the surface.
The magnetic flux density of each of the PG magnets 9 can be increased using the magnetic flux density of the rotor magnet 4.

A PG head 20 is attached to a predetermined position of the stator yoke 6 so as to face the end surfaces of the PG magnets 8 and 9 with a slight gap therebetween. this
As shown in FIG. 3, the PG head 20 includes an L-shaped core 21 and a coil 1 wound around the core 21.
2, and compared to the conventional C-shaped core, the core 21 has a shape in which the portion indicated by the two-dot chain line is cut off. Therefore, the magnetic gap G of the PG head 20 is formed to be inclined with respect to the end faces of the opposing PG magnets 8 and 9 in a plane perpendicular to the rotation axis.

In the brushless motor configured in this way, when current is supplied from the drive circuit component 13 to the drive coil 7, torque is generated and the rotor portion 1 rotates, as described above. Each magnetic sensor 1
Numeral 9 generates pulses due to changes in the magnetic field as the rotor magnet 4 rotates, and the pulses control the currents of each phase supplied to the drive coil 7, so that the rotor portion 1 continues to rotate. Also, FG
The coil 16 also generates pulses due to changes in the magnetic field as the FG magnet 18 rotates, and the rotor section 1 is controlled at a constant speed based on the pulses.

When the rotor section 1 is driven to rotate at a constant speed in this way, the coil 12 of the PG head 20
A PG pulse is output by receiving the magnetic flux of PG magnets 8 and 9 that rotate in conjunction with the PG magnet. Below, such PG
The pulse output waveform will be explained.

FIG. 4 shows the magnetic flux distribution affected by the core 21 of the PG head 20. Since the magnetic gap G of the PG head 20 is inclined with respect to the end faces of the PG magnets 8 and 9, the core 21 teeth,
Under the influence of the vector magnetic flux distribution in both the X and Y directions in FIG. 8 described above, the magnetic flux distribution becomes such that the solid line and the broken line shown in FIG. 8 are superimposed.

Figure 5 shows the rate of change in magnetic flux by differentiating the magnetic flux distribution shown in Figure 4.
From the figure, it can be seen that the coil 12 sequentially outputs a voltage waveform with no bouncing portion on one side.

The voltage waveform obtained in this way is due to the fact that the magnetic gap G is wider than that of the conventional PG head.
Although the output itself is small, by setting the threshold value to OV and detecting the current direction at the threshold value OV, the phase of the rotor section 1 can be detected, so a so-called zero-cross method becomes possible. Therefore,
What was conventionally detected using two threshold values of ±CV can now be detected using one threshold value of OV, and the detection circuit and servo system can be simplified.

In the above embodiment, the brushless motor phase detection device according to the present invention was applied to drive the head cylinder of a VTR.
It can also be applied to floppy disk drives, cube drives, etc.

Further, in the above embodiment, two PG magnets 8 and 9 were provided on the rotor portion 1 side with an interval of 180 degrees, but the number of PG magnets is not limited to two, and may be used as necessary. It can be selected as appropriate.

[Effect of idea]

As explained above, according to the present invention, PG pulses can be detected using the zero-crossing method, so the phase of the rotor section can be reliably determined regardless of the magnitude of the output voltage from the PG head (pickup head). It becomes possible to detect

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of the brushless motor according to the present invention, FIG. 2 is a plan view of the stator section of the brushless motor shown in FIG.
Figure 4 is an explanatory diagram showing the magnetic flux distribution affected by the PG head in Figure 3. Figure 5 is a plan view of the PG head in Figure 3.
The figure is an explanatory diagram showing the rate of change in magnetic flux obtained by differentiating the magnetic flux distribution in Fig. 4, Fig. 6 is a sectional view showing an example of a conventional brushless motor phase detection device, and Fig. 7 is a
Figure 8 is an explanatory diagram showing the magnetic flux distribution of the PG magnet in Figure 6. Figure 9 is the magnetic flux obtained by differentiating the X-direction vector magnetic flux distribution in Figure 8. FIG. 10 is an explanatory diagram showing the voltage waveform output from the PG head of FIG. 7. DESCRIPTION OF SYMBOLS 1... Rotor part, 2... Stator part, 3... Rotor yoke, 3a, 3b... Window hole, 4... Rotor magnet, 5... Rotating shaft, 6... Stator yoke, 7... Drive coil, 8, 9...PG magnet (pulse generation magnet), 12...Coil, 20
...PG head (pick up head), 21...
core.

Claims (1)

[Scope of utility model registration request] Pulse generating magnets 8 and 9 are provided on the rotor 1 side which is rotatable with respect to the stator 2, a pick-up head 20 is provided on the stator 2 side opposite to the magnets 8 and 9, and a magnetic gap G of the pick-up head 20 is provided. In a brushless motor in which the phase of the rotating rotor 1 is detected by changes in the magnetic flux of the magnets 8 and 9 that traverse the rotor 1, the magnetic gap G is aligned with the end face of the magnets 8 and 9 facing the pickup head 20. A brushless motor is tilted in a plane perpendicular to a rotation axis 5.