JPS61189412A - Magnetic flux density change detector - Google Patents

Abstract

PURPOSE:To obtain a required detecting signal (displacement to be detected) without using a permanent magnet for the bias of a magnetoelectric element by arranging the element in a fixed magnetic flux affecting area to be affected from a subject to be detected. CONSTITUTION:A rotor 6 of a stepping motor 2 is obtained by fixing soft magnetic plates 9a, 9b on a shaft 10 through a permanent magnet 7 and pole teeth 8a, 8b on the outer peripheries of the plates 9a, 9b are shifted by a half pitch (signal wavelength lambda). Two pairs of magneto-resistance elements 11a, 11b are arranged on the surface of a substrate 12 and made to correspond to the pole tooth 8a between poles 4 of a stator 3. The elements 11a, 11b are positioned on the center of the thickness of the pole plate 9a to change their resistance only to a magnetic field turned in an axial direction. A bridge is formed by the elements 11a, 11b and resistors 15 and an output from the bridge is inputted to a differential amplifier 18 through resistors 19 to obtain an amplitude difference signal S0. The amplitude difference signal S0 is obtained from the other pair of elements through a similar course and the turning direction of the rotor 6 is discriminated from the two signals S0. Since the magnetic field in the fixed bias direction can be obtained in said constitution even if a bias magnet is not embedded in the substrate, a prescribed output signal is obtained also by the magneto-resistance elements.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an apparatus for electrically detecting displacement of a detection target using a magneto-electric element such as a magnetoresistive element or a Hall element.

BACKGROUND OF THE INVENTION This type of magnetoelectric element, such as a magnetoresistive element (MR element), is a semiconductor element that converts changes in magnetic flux into changes in resistance in a magnetic field, and is used as a non-contact displacement sensor.

As shown in the characteristic graph in Figure 1, the rate of change in resistance R is close to the square characteristic in the range of low magnetic flux density, regardless of the characteristics of the magnetic field strength H, and as the magnetic flux density increases,
Shows linear characteristics with a certain slope.

Therefore, when the magnetic flux B of the rotor of a detection target, such as a magnetic encoder or a small motor, alternates around the neutral point of the magnetic field, the output signal S is greatly distorted and becomes a full-wave rectified waveform with a low peak value, and is sinusoidal. It doesn't become a wave.

Such inconveniences in characteristics can be solved by embedding a permanent magnet for bias in the substrate of the magnetoresistive element and applying a direct current bias magnetic field of this permanent magnet to the magnetoresistive element. However, according to the solution,
Manufacturing of the magnetoresistive element becomes complicated and the product becomes expensive.

OBJECTS OF THE INVENTION AND SOLUTION THEREOF The object of the invention is therefore to make it possible to obtain the necessary detection signals without using permanent magnets for biasing.

Therefore, the present invention focuses on the fact that, for example, in a hybrid stepping motor, a constant magnetic flux acts in a certain direction even when the magnetic flux changes in the displacement direction, and this constant magnetic flux is used to bias the magnetoelectric element. It is used as a magnetic field.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of an embodiment of the present invention will be specifically described below with reference to the drawings.

First, FIGS. 2 and 3 show an example in which the magnetic flux density change detection device 1 of the present invention is incorporated into a hybrid stepping motor 2. As shown in FIG. The stator 3 of this stepping motor 2 includes, for example, four poles 4, and an excitation coil 5 is provided at the poles. Further, the rotor 6 of the stepping motor 2 is provided with a permanent magnet 7 and a pair of soft magnetic materials 9a and 9b relative to the shaft 10. The pair of soft magnetic materials 9a, 9b are both disk-shaped, and are fixed to the shaft 10 in a manner that sandwiches the permanent magnet 7 between them, and the pole teeth 8a, 8b are formed on the outer peripheral surface of the shaft 10. It is fixed in a state shifted by a half pitch (signal wavelength λ) of 8b. and,
Since the permanent magnet 7 is magnetized to the north pole and the south pole in the axial direction, the pole teeth 8a are magnetized to the north pole, and the pole teeth 8b are magnetized to the south pole, for example. Then, the magnetoelectric elements, for example, a pair of magnetoresistive elements 11a and llb are connected to the substrate 1.
Two sets are formed on the surface of the rotor 6, and the space between the balls 4 corresponds to, for example, one pole tooth 8a of the rotor 6.

As shown in FIG. 4, the pair of magnetoresistive elements 11a and llb are formed of a thin film of magnetoresistive semiconductor on the surface of the substrate 12 in relation to the signal wavelength λ, and the respective electrodes 13a and 13b and a common electrode 14. These magnetoresistive elements 11a and llb are
For example, it is located approximately at the center in the thickness direction of the soft magnetic material 9a, exhibits a resistance change with respect to a magnetic field in the Y direction, that is, the axial direction of the shaft 10, and is not sensitive to the X direction. Note that the pattern is formed long in either direction, as shown in FIG. 5 or 6.

As shown in FIG. 7, these magnetoresistive elements 11a and llb are connected together with two resistors 15 between a power supply 16 and a ground 17 to form a bridge circuit. And the midpoint of this bridge circuit is
It is connected to the differential amplifier 18 via a resistor 19. At this time, the output signal S0 from the input signals s, , 52 of the differential amplifier 18 is as shown in FIG. Here, the output signal S0 is composed of two differential input signals S8, S
This is the difference in the amplitude of z. The reason why two pairs of magnetoresistive elements 11a and llb are provided is to determine the rotational direction of the rotor 6 to be detected, and the other magnetoresistive elements 11a and 11b are also provided in the same manner as described above. The rotation direction of the rotor 6 is determined from the two output signals S0.

Function of the embodiment Next, with reference to FIG. 9, the above magnetic flux density detection device 1
Explain the effect of

FIG. 9 shows the changes in the magnetic field components in the X and Y directions and the resistance values of the pair of magnetoresistive elements 11a and 11b in relation to the direction of the magnetic flux when the rotor 6 is expanded in the X direction. ing.

As already mentioned, the pole teeth 8a, 8b of the rotor 6 are λ/
They are combined with a difference of 2. Therefore, the magnetic flux B of the permanent magnet 7 is formed in an oblique direction from one pole tooth 8a to the other pole tooth 8b.

First, (1) shows the magnetic field components Hax and Hay in the X direction when the magnetic field component is decomposed into the X direction and the Y direction. Here, the change in the magnetic field component I (ay) is influenced by the permanent magnet 7 of the rotor 6, and becomes as high as the DC bias magnetic field.Moreover, the DC bias magnetic field also changes when the rotor 6 rotates. It does not change and is always constant.This (1
) corresponds to the detection position of one magnetoresistive element 11a.

Next, (2) shows the magnetic field components) (bx, Hb) F at a position λ/2 distance away from the detection position in (1), that is, at a detection position corresponding to the magnetoresistive element 11b. ing. The magnetic field component Hbx at this point is completely inverted with respect to the magnetic field component Hax.

Next, (3) is the magnetic field component of (1) above) (aX, Hay
The resistance value Rax, Ra of the magnetoresistive element 11a against
In addition, (4) shows the change in the resistance values Rbx and Rby of the magnetoresistive element 11b due to the magnetic field components Hbx and Hby in (2). The magnetoresistive elements 11a and 11b respond to changes in the magnetic field in the X direction.
Since it does not show any change in resistance, it remains unchanged at the reference value R0.The waveforms shown by broken lines in parts (3) and (4) show that the resistance value does not change with respect to changes in the magnetic field in the X direction. This shows the case where the change is made.

Next, (5) shows the waveform of the differential output signal due to the difference in resistance values (Rax-Rbx) and the difference in resistance values (Ray-Rby). In the former output waveform, no output is obtained despite the rotation of the rotor 6, whereas in the present invention, a waveform close to a sine wave is obtained. Moreover, the amplitude of the waveform corresponds to twice the signal level obtained by changing the resistance values Ray and Rby.

As described above, the magnetoresistive element is placed in the direction in which the magnetic field component in the direction perpendicular to the displacement direction of the rotor 6, that is, the rotation direction, is detected, in other words, in the direction in which a constant magnetic flux from the permanent magnets 7 acts. By arranging 11a and llb, a predetermined output signal S0 can be obtained even without a large bias magnet.

Here, two-phase signals with a phase difference of λ/4 are obtained with the pitch of the rotor 6, that is, the signal wavelength λ, as a period, so the rotation direction can be determined and can be used as a position detection signal for the rotor 6. , whereby the stepping motor 2 can be driven in a closed loop.

Modification of the invention Note that the pair of magnetoresistive elements 11a and llb are
As shown in FIG. 0, it can also be arranged in the axial direction of the shaft 10. In this case, a pair of magnetoresistive elements 11a, llb
Even if they are on the same straight line, a shift of λ/2 can be ensured due to the phase shift between the pole teeth 8a and 8b.

Moreover, the magnetoresistive effect element 1 is
By changing the distances d, , d2 to 1a, llb, the bias magnetic field by the rotor 6 changes. Therefore, in the characteristics of the magnetoresistive elements 11a and 11b, the distance d,
, this can be easily done by setting the dt dimension.

Here, if the distance d and the distance d2 are set not to be equal, the detection signal S0 can be waveform-shaped and detected as a waveform that facilitates closed-loop control, for example, an accurate sine wave.

Furthermore, since the magnetoresistive elements 11a and llb are themselves made of ferromagnetic material, the electrodes 13a and 13b and the common electrode 14a are made wide as shown in FIG. , 9b, in the process of the magnetic flux passing from one soft magnetic material 9a to the other magnetic material 9b, the magnetic flux flows through those electrodes 13a, 13b, 14.
Since the magnetic field passes through the area intensively, changes in the magnetic field can be detected efficiently.

Further, this stepping motor 2 may be of a flat type.

In the flat rotor 6, a soft magnetic material 9a, a permanent magnet 7, and a soft magnetic material 9b are arranged concentrically on a plane. Therefore, in that case, the pair of magnetoresistive elements 11a and Ilb
are arranged in the radial direction of the rotor 6.

Effects of the Invention In the present invention, even if there is not a very large bias magnet inside the magneto-electric element, a magnetic flux in an oblique direction, in other words, a magnetic field in a constant bias direction from a permanent magnet can be obtained. A predetermined output signal can also be obtained with a magnetoresistive element.

[Brief explanation of drawings]

Fig. 1 is a graph showing the characteristics of the magnetoresistive element, Fig. 2 is a plan view of the magnetic flux density sensing device according to the present invention, Fig. 3 is a cross-sectional view thereof, and Fig. 4 is a front view showing the arrangement of the magnetoresistive element. Figures 5 and 6 are plan views showing the pattern of the magnetoresistive element, Figure 7 is a circuit diagram of the detection circuit, Figure 8 is a waveform diagram of the detection circuit, and Figure 9 is a change in the magnetic field relative to the rotor. 10 and 11 are front views showing the arrangement of magnetoresistive elements in other embodiments. 19. Magnetic flux density detection device, 2... hybrid stepping motor, 3... stator, 4... ball,
5. Excitation coil, 6. Rotor, 7. Permanent magnet, 8
a, 8b...Pole tooth, 9a, 9b...Soft magnetic material, 10.
・Axis, lla, llb...Magnetoelectric element, 12...Substrate, 1
8...Differential amplifier. Figure 1 Figure 10 Figure 77 Figure 8 Figure 7 Figure 6

Claims (1)

[Claims] In a magnetic flux density change detection device that uses a magnetoelectric element to detect changes in the magnetic flux density of a subject whose magnetic flux changes with respect to the displacement direction and which always applies a constant magnetic flux to the outside, A magnetic flux density change detection device characterized in that it is arranged in a magnetic flux action area.