JPH022072Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is a pulse signal generator for an electric motor, particularly for detecting the specific position of a field magnet that forms the rotor of an electric motor that drives a rotating magnetic head for, for example, a VTR. The present invention relates to a pulse signal generator for the purpose of the present invention.

[Prior art]

In a conventional electric motor having a pulse signal generator, a thin ring-shaped PG (pulse signal generator) magnet 2 made of plastic magnet material is attached to the outer periphery of the main magnet 2, as shown in FIGS. 1a to 1c.
0 are fitted, and these are located inside the rotor yoke 1 of the electric motor. In addition, small magnets 21, 21 for PG are integrally formed with the magnet 20 at positions 180 degrees apart from each other and protrude to the outside of the yoke through a groove provided on the outer periphery of the yoke 1. The magnetic field detector 10 is PG
It is arranged on plate 9.

The polarity of the small magnet 21 matches the polarity of the main magnet 2 on which it is installed.

3 is the rotor hub of the electric motor, 4 is the rotor shaft, and 5 is the rotor hub of the electric motor.
6 is a bearing bracket, 6 is a bearing, and 8 is a stator winding of a motor attached to P and C plates 9.

The plastic magnet that forms the PG magnet 20 has a lower magnetic flux density than sintered ferrite magnets, etc., so in order to obtain the same output, the volume of the small PG magnets 21, 21 must be increased. It is necessary to increase the width W in the moving direction,
As a result, the output voltage waveform of the conventional pulse signal generator shown in FIGS. 1a to 1c does not become a sharp pulse voltage as shown in FIG. 2a, but becomes a blunt waveform as shown in FIG. There was a problem that sufficient output could not be obtained from the detector 10.

[Purpose of invention]

The purpose of this invention is to solve the problems in the conventional technology as described above, and to provide P.O.
Magnetic field detector 10 with improved magnetization method of small magnet for G
An object of the present invention is to provide a pulse signal generator for an electric motor, which can obtain a sufficient output voltage for a motor.

[Summary of the idea]

The pulse signal generator for an electric motor of the present invention includes a main magnet with N and S poles alternately magnetized along its outer periphery, a PG magnet fitted on the outer periphery of the main magnet,
It consists of a small signal generating magnet formed at a 180° different position on the outer circumference of this PG magnet, and a magnetic field detector arranged to face this signal generating magnet with an air gap in between. One side is magnetized adjacent to the N-pole, S-pole, and N-pole in the magnetic pole arrangement direction of the main magnet, and the other is similarly magnetized with the S-pole, N-pole, and S-pole.
The signal generating magnet is magnetized adjacent to the pole, and one S pole of the signal generating magnet is located at a position corresponding to the S pole of the main magnet, and the other N pole is located at a position corresponding to the N pole of the main magnet. It is characterized by

[Example of idea]

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

In this invention, plastic magnet material
PG provided protruding from the outside of the PG magnet 20
As shown in FIG. 3a, the width W of the small magnet 21 facing the detector 10 is determined by W ₁ , W ₂ ,
Divide into approximately 3 parts W ₃ and from the end, each part of W ₁ , W ₂ , W ₃ can be set as S pole, N pole, S pole, or vice versa.
The small magnet 21 is magnetized to have S pole and N pole, and the N pole part in the center matches the N pole position of the main magnet 2. As mentioned above, the N pole, S pole,
The small magnet 21 magnetized to the north pole is formed so that its central south pole portion coincides with the south pole position of the main magnet 2, which is 180 degrees different from the north pole.

By magnetizing in this way, the state of the residual magnetic flux of the small PG magnet 21 becomes P as shown in FIG. 3b.
The amount of change in magnetic flux near the center of the G small magnet 21 is large, and the amount of change on both sides thereof is small. As a result, the rate of change dΦ/ of the magnetic flux interlinking with the magnetic field detector 10
As shown in Fig. 3c, dt has a shape in which the width a at the center is narrower and the height h is higher than the conventional example shown in Fig. 2b, and the magnetic flux change rate in the opposite direction on both sides is wider as shown in b. As the height r decreases widely, the effective component V _p of the output of the magnetic field detector 10 becomes high and the harmful component V _r decreases, as shown in FIG. 3d, and the pulse signal has a sharp waveform.

[Effect of idea]

As described above, according to the present invention, the change in magnetic flux at the center of the small magnet for generating pulse signals formed by a plastic magnet becomes sharp, thereby making the waveform of the pulse signal voltage generated in the magnetic field detector sharp and high. There is a great benefit in that the output voltage can be obtained.

[Brief explanation of the drawing]

FIG. 1a is a longitudinal sectional view of a motor having a conventional pulse signal generator, FIG. 1b is an explanatory plan view of a small magnet for signal generation, and FIG. 1c is a longitudinal sectional view thereof.
Figure 2a is a diagram showing the change in magnetic flux of a small magnet for generating pulse signals in the conventional device, Figure 2b is a diagram showing the rate of change of the magnetic flux, and Figure 2c is a diagram showing the output waveform of the magnetic field detector. FIG. 3a is an explanatory diagram of the magnetized state of a small magnet for generating pulse signals in the device of the present invention, and FIGS. 3b to 3d are diagrams corresponding to FIGS. 2a to c, respectively. 1...Rotating yoke, 2...Main magnet, 3...Rotor hub, 4...Rotor shaft, 5...Bearing bracket, 6...Bearing, 8...Stator winding, 9...P ，
C plate, 10...Magnetic field detector, 20...Magnet, 21
...Small magnet for signal generation.

Claims (1)

[Scope of utility model registration request] A main magnet 2 with N and S poles alternately magnetized along its outer periphery, and a PG fitted on the outer periphery of this main magnet 2.
PG magnet 20 and a small signal generating magnet 21 formed at 180° different positions on the outer circumference of this PG magnet 20.
and a magnetic field detector 10 arranged to face this signal generating magnet 21 with an air gap in between, one of the signal generating magnets 21 having an N pole and an S pole in the magnetic pole arrangement direction of the main magnet 2. , are magnetized adjacent to the N pole, and the other are similarly magnetized adjacent to the S pole, N pole, and S pole, and the S pole of one of the signal generating magnets 21 is adjacent to the main magnet 2. A pulse signal generator for a motor, characterized in that the other N pole is located at a position corresponding to the S pole of the main magnet 2, and the other N pole is located at a position corresponding to the N pole of the main magnet 2.