JP3282269B2 - Rotation detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotation detecting device suitable for use in a capstan motor of a VTR, a tape recorder or the like.

[0002]

2. Description of the Related Art In a VTR (video tape recorder) or a tape recorder, a capstan motor 1 as shown in FIG. 4 is used for transporting a magnetic tape.
The capstan motor 1 is a surface-facing motor, and includes a rotor unit 10, a stator unit 20, and a rotation detection unit 30.

As shown in FIG. 5, a cover 12 for covering the outer peripheral side and the upper side of a rotor magnet 11 is attached to a rotor section 10, and an FG (rotation detecting FG) is further provided on the outer peripheral side. Frequency Generator) A magnet 13 is attached. Rotor magnet 11
A rotary shaft 14 is attached to the center of the rotor unit 10, and the rotary shaft 14 is rotatably supported by a bearing 22 fixed to the bottom plate 21 of the rotor unit 10. Thereby, the rotor unit 1
0 smoothly rotates without rattling. As shown in FIG. 6, a plurality of magnetic poles are magnetized over the entire circumference of the rotor magnet 11 and the FG magnet 13.

In the stator section 20, FIGS.
As shown in FIG. 2, a plurality of exciting coils 23 arranged opposite to the lower surface of the rotor magnet 11 are fixed to the bottom plate 21. A magnetic field is generated by sequentially supplying an exciting current to the exciting coil 23, and the magnetic field causes the rotor magnet 11 to rotate.

In the rotation detecting section 30, the rotor section 10
The magnetic sensitive element 31 is arranged to face the outer peripheral surface of the FG magnet 13. The magnetic sensing element 31 detects a change in a magnetic field caused by the rotation of the FG magnet 13, and for example, a conductive material is elongated on a substrate 32 formed of an insulating material such as a glass plate or a ceramic plate as shown in FIG. It is formed by printing in a U-shape.

In this embodiment, the magnetic pole width λ of the FG magnet 13 is
Four magnetic sensing elements 31 are provided at an interval of 1/2 of the above, and these are connected in series to form a rotation detecting circuit 38.
The equivalent circuit of the rotation detection circuit 38 is a bridge circuit as shown in FIG. The power supply VCC and the ground GND are connected to two terminals 34 and 35 on one diagonal line of the bridge circuit, and outputs for outputting two signals P1 and P2 having different phases to two terminals of the other diagonal line. Terminals 36 and 37 are connected.

The resistance of the magneto-sensitive element 31 changes with the change of the magnetic field. Therefore, when the FG magnet 13 rotates, the resistance value of the bridge circuit changes, and as a result, sine wave signals P1 and P2 whose phases are shifted by 180 degrees are output from the output terminals 36 and 37 as shown in FIG. By counting the zero-cross points of the signals P1 and P2 or these difference signals, it is possible to detect the rotation speed of the FG magnet 13, that is, the rotation speed of the rotor unit 10. If the difference signal between the signals P1 and P2 is used, the S / N ratio is improved.

In FIG. 5, a substrate 32 holding a magnetic sensitive element 31 is attached to a predetermined position of a bottom plate 21 by a support portion 33. Thereby, the magnetic sensitive element 31
The distance between the FG magnet 13 and the FG magnet 13 has a predetermined size.
A change in the magnetic field of the G magnet 13 can be reliably detected by the magnetic sensitive element 31.

[0009]

By the way, in the conventional capstan motor 1, the support portion 33 of the rotation detecting portion 30 is usually formed of a non-magnetic material such as PBT or zinc die cast. . Therefore, as shown in FIG. 10, the magnetically sensitive element 31 forms a magnetic path, through which the leakage magnetic flux of the rotor magnet 11 passes. Due to this influence, the magnetic sensitive element 31 cannot accurately detect the magnetic field of the FG magnet 13, and the signal P1,
The output of P2 may decrease or noise may occur. In some cases, it was impossible to accurately detect the number of revolutions.

In order to reduce the size and increase the torque of the capstan motor 1, when samarium cobalt or neodymium having a high residual magnetic flux density is used as the material of the rotor magnet 11, the leakage flux of the rotor magnet 11 increases. However, there is a problem that the rotation detection is further adversely affected.

Accordingly, the present invention has been made to solve the above-mentioned problem, and proposes a rotation detecting device capable of preventing the influence of the leakage magnetic flux of the rotor magnet and accurately detecting the rotation speed of the motor. Things.

[0012]

In order to solve the above-mentioned problems, according to the present invention, an FG for rotation detection which is attached to the outer peripheral side of a rotor magnet of a surface facing motor and has a plurality of magnetic poles along the outer peripheral surface. A magnet, a magnetic-sensitive element for detecting a change in a magnetic field generated by rotation of the FG magnet, a substrate holding the magnetic-sensitive element,
A rotation detecting device having a support for attaching the substrate to a stator of the surface-facing motor, wherein a rotation path for forming a magnetic path of a leakage magnetic flux of the rotor magnet is provided ;
A magnetic plate made of a soft magnetic material having a higher magnetic permeability than the magnetic sensitive element is disposed behind the substrate .

[0013]

In FIG. 1, a magnetic sensitive element 31 for detecting a change in the magnetic field of the FG magnet 13 is printed on a substrate 32 made of an insulating material, and this substrate 32 is supported by a support portion 33 made of a magnetic material. It is attached to the bottom plate 21.
The support part 33 is formed of a material having a higher magnetic permeability than the magnetic sensitive element 31.

As a result, as shown in FIG. 2, most of the leakage magnetic flux of the rotor magnet 11 passes through the support portion 33 as a magnetic path, and the magnetic sensitive element 31 is hardly affected by the leakage magnetic flux. Therefore, the rotation detection device of the present invention can accurately detect the rotation speed of the capstan motor 1.

[0015]

Next, an embodiment in which the rotation detecting device according to the present invention is applied to a capstan motor will be described in detail with reference to the drawings. The same portions as those described above are denoted by the same reference numerals, and detailed description is omitted.

FIG. 1 shows a configuration of a capstan motor 1 to which a rotation detecting device according to the present invention is applied. The capstan motor 1 is a surface-facing motor, and its configuration is almost the same as the conventional capstan motor 1 (FIGS. 4 and 5). However, here, the substrate 3 on which the magnetic sensitive element 31 is printed is used.
The support part 33 for fixing 2 to the bottom plate 21 is formed of a magnetic material. The support portion 33 is formed of a material having a higher magnetic permeability than the magnetically sensitive element 31.

Therefore, as shown in FIG. 2, most of the leakage magnetic flux of the rotor magnet 11 passes through the support portion 33 as a magnetic path. As a result, the leakage magnetic flux passing through the magnetic sensitive element 31 is almost eliminated, so that the magnetic sensitive element 31 can accurately detect a change in the magnetic field generated by the rotation of the FG magnet 13.

The magnetic material forming the support portion 33 is as follows.
Resins mixed with magnetic powders such as soft ferrite and permalloy in addition to ordinary soft magnetic materials can be used. If such a resin is used, the support portion 33 can be easily formed into an arbitrary shape.

FIG. 3 shows another embodiment of the rotation detecting section 30. FIG. 5A shows a case where the support portion 33 made of a magnetic material is projected from the substrate 32. This makes it easier for the leakage magnetic flux of the rotor magnet 11 to flow into the inside from the protruding portion of the support portion 33. Therefore, it is possible to prevent the magnetic sensitive element 31 from being affected by the leakage magnetic flux and further improve the accuracy of rotation detection. .

FIG. 2B shows a case where a magnetic path forming portion 39 made of a magnetic material is attached or deposited on the back side of the substrate 32. In this case, the support portion 33 is formed of a non-magnetic material. As a result, most of the leakage magnetic flux of the rotor magnet 11 passes through the magnetic path forming portion 39.
The influence of the leakage magnetic flux on the magnetic sensitive element 31 is almost eliminated, and the rotation speed of the FG magnet 13 can be accurately detected.

[0021]

As described above, the present invention relates to a rotation detecting device for detecting the rotation speed of a surface-facing motor,
A magnetic plate made of a soft magnetic material having a higher magnetic permeability than the magnetic element for forming a magnetic path of the leakage magnetic flux from the rotor magnet is formed on the back side of the magnetic element for detecting a change in the magnetic field of the FG magnet. It is arranged.

Therefore, according to the present invention, almost all of the leakage magnetic flux of the rotor magnet passes through the magnetic plate, so that it is possible to prevent the magnetic sensitive element from being affected by the leakage magnetic flux. Thus, the magnetic sensitive element can accurately detect a change in the magnetic field of the FG magnet, and thus can accurately detect the rotation speed of the motor. In addition, there is an effect that the rotation detecting device can be easily configured.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a capstan motor to which a rotation detection device according to the present invention is applied.

FIG. 2 is a diagram illustrating a flow of a leakage magnetic flux of a rotor magnet 11;

FIG. 3 is a diagram for explaining another embodiment of the rotation detecting device according to the present invention.

FIG. 4 is a configuration diagram of a general capstan motor 1.

FIG. 5 is a sectional view of a conventional capstan motor 1.

FIG. 6 shows a rotor magnet 11 and an FG magnet 13
FIG.

FIG. 7 is a diagram illustrating an example of a magnetic sensitive element.

8 is a diagram illustrating an equivalent circuit of the rotation detection circuit 38. FIG.

FIG. 9 is a waveform diagram of output signals P1 and P2 of the rotation detection circuit 38.

FIG. 10 is a diagram illustrating a flow of a leakage magnetic flux of a rotor magnet 11 in a conventional capstan motor 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Capstan motor 11 Rotor magnet 13 FG magnet 14 Rotating shaft 21 Bottom plate 22 Bearing 23 Excitation coil 31 Magnetic sensitive element 32 Substrate 33 Supporting part 38 Rotation detecting circuit 39 Magnetic path forming part

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) H02K 29/00 G01D 5/245 G01P 3/487 H02K 11/00 H02K 21/00

Claims (4)

(57) [Claims] An FG magnet for rotation detection, which is attached to an outer peripheral side of a rotor magnet of a surface facing motor and has a plurality of magnetic poles along the outer peripheral surface, and detects a change in a magnetic field generated by rotation of the FG magnet. A magnetic sensing element, a substrate for holding the magnetic sensitive element, and a support for attaching the substrate to the stator of the surface-facing motor. A rotation detecting device, wherein a magnetic plate to be formed and made of a soft magnetic material having a higher magnetic permeability than the magnetically sensitive element is disposed behind the substrate . 2. The rotation detecting device according to claim 1, wherein the magnetic plate is the support. 3. The rotation detecting device according to claim 1, wherein the magnetic plate is attached or vapor-deposited on the back side of the substrate. 4. The rotation detecting device according to claim 1, wherein the magnetic plate protrudes from the substrate.