JPH04110725A - Magnetic sensor and its manufacturing method - Google Patents

Abstract

PURPOSE:To make a device compact by forming magnetic tracks, of which magnetic strength is changed on a sine-curve in relation with a magnetic resistance element having the strong magnetism with the rotation of a magnetic drum, and forming at least two magnetic tracks so that magnetic strength thereof is reverse to each other. CONSTITUTION:A signal generator 3 for generating the sine-curved wave signal synchronous with the rotation of a shaft 2 of a magnetic drum 1 is fitted to the shaft 2. The signal output from this generator 3 is amplified by an amplifier 4, and is magnetized as magnetic tracks 6 (6A - 6D) by magnetic heads 5 (5A - 5D). The strength of the magnetic field of the tracks 6 is synchronized with the sine-curve wave signal from the generator 3. A MR element 7 is located in the magnetized drum 6 in contactless to the tracks 6 with a certain gap (g). Magnetic resistances MR - MR for sensing the magnetic field are located, for example, so that the current is flowed transverse to the magnetic field direction of the tracks 6A, 6B. Consequently, resistance of the element 7, which is in the relation reverse to the relation of MR and MR, and MR and MR, is increased on a sine-curve and the output voltage, which is 1/2 of the voltage, can be take out.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an absolute type magnetic sensor widely used in robots, NC devices, etc., and a method for manufacturing the same.

Conventional technology Incremental magnetic encoders, as shown in FIG. 8, magnetize the outer periphery of a magnetic drum fixed to a soyaft 15, and apply the magnetic field to a magnetoresistive element (hereinafter referred to as an MR element).
A detection structure has been developed. As shown in FIG. 8, the magnetic drum 11 is magnetized on the outer periphery of two tracks, one of which is a multi-pole magnetized section 12, which magnetizes a predetermined magnetic pole. The other is the origin magnetization part 1 that magnetizes one pair of magnetic poles per rotation.
It becomes 3.

The magnetic drum 11 configured as described above will be explained below. The magnetic drum is constructed by applying magnetic powder to the outer periphery of a resin magnet or stainless steel heath. Two tracks of magnetization are performed on the outer periphery. In FIG. 8, the multi-pole magnetization section 12 performs magnetization of 1000 poles when an output of 1000 pulses per rotation is required. The outer diameter of the magnetic drum is 8
If On+m, the magnetization width is approximately 0.25 am+.The origin magnetized portion 13 is magnetized with approximately the same magnetization width, and serves as the origin magnetization portion 13 that indicates the origin of rotation. Signals are detected by an MR element 14 placed close to the magnetic drum 11. The signal is shown in FIG. Signal 16 is the origin magnetized section 13
Signals 17 and 18 are signals from the multi-pole magnetization section 12, and signals 1718 are two signals with a phase difference of 90 degrees. A method of obtaining rotational position information of the magnetic drum 11 using these three signals is called an incremental encoder.

Problems to be Solved by the Invention In the case of the above-mentioned incremental type encoder, when the power is turned off, the position information is lost, so it is always necessary to return to the origin. On the other hand, in the absolute type, the circumference is divided into multiple tracks, each with 2 tracks. 4. 8.16
．． An encoder that uses light as a medium divides the 32... This resulted in a larger size and higher price.By reducing the number of magnetized tracks, for example, 2, 16, 12
8. 4.8, 32 using 1024 divided tracks
．． If the 64.256512 and 2048.4096 divisions are created by electrical circuit processing, what would require 12 tracks can be created with 4 tracks. When dividing by electrical circuit processing like this, the original 2.16.128
．． It is said that the detection waveform of 1024 requires a sine wave with little distortion and a phase difference of 90 degrees. On the other hand, if it is a large magnetic drum with an outer diameter of 80 mm, it will be 128.1
Although it is possible to detect with a sine wave in 0.024 division,
2. In 16 division, the magnetization pitch is 125+on, 15.
7 mm, and in such a large pinch, a sinusoidal signal waveform could not be obtained with the conventional magnetization and MR element configuration that generates a magnetic field in the circumferential direction.

Means for Solving the Problems In order to solve the above problems, in the present invention, at least two magnetic tracks are created in which the magnetic field strength changes at a sin along the circumference, and the direction of the magnetic field is in the axial direction. The magnetic tracks are configured such that the magnetic field strength changes inversely to each other, and the magnetic tracks are detected as a sine wave signal by an MR element.

Effect: With this configuration, the MR element facing the magnetic drum, whose magnetic field strength varies sinically along the circumference, detects the magnetic field strength as a sine wave signal.

EXAMPLE Hereinafter, an example of the present invention will be described based on the accompanying drawings. In FIG. 1, a shaft 2 is attached to a magnetic drum 1. A signal generator 3 is attached to the shaft 2 to generate a sine wave signal synchronized with the rotation as the shaft 2 rotates.

The signal output from the signal generator 3 is amplified by an amplifier 4 and magnetized by magnetic heads 5A, 5B, 5C, and 5D (not shown because they are shaded) as magnetic tracks 6A, 686C, and 6D. The magnetic field strength of the magnetic tracks 6A, 6B, 6C, and 6D is synchronized with the sinusoidal signal from the signal generator, and the magnetic field strength of the magnetic tracks 6A, 6 changes in a sinusoidal manner.
B.

They become 6C and 6D.

The phase relationship of magnetic tracks 6A, 6B, 6C, and 6D is 6A.
and 6B are 180 degrees, 6C and 6D are 180 degrees, 6A and 60
are magnetized to have a phase difference of 90 degrees.

For example, in the case of a signal of 1 rotation IH2, the mechanical angle between magnetic heads A and B is 180 degrees, and magnetic heads C and D are 180 degrees.
0 is 90 degrees, connected in series, and magnetized with the same current. Note that 51A, 51851C, and 51D are the yoke openings of the magnetic heads 5A, 5B, 5C, and 5D.
It coincides with the axial direction of the magnetic drum 1, and the magnetic track is provided with magnetic poles in the vertical direction.

Here, if one rotation is 16Hz, the angle for magnetic hands 5A and 5B and 5C and 5D is 11.25 degrees or equivalently 11.25 + n x 22.5 degrees (an integer of n≧1), and 5A and 50 are 5,625 degrees or equivalent 5,625
Install at 10n x 22.5 degrees (n≧1 integer).

Although the explanation was given by magnetizing the magnetic tracks 6A, 6B, 6C, and 6D at the same time with the same current, the magnetic tracks 6A
, 6B, 6C, and 6D may be separate magnetizing currents, and their phases may be set to have a predetermined phase difference.

The MR element 7 is placed close to the magnetic tracks 6A, 6B, 6C, and 6D with a constant gap g on the magnetic drum 1 magnetized in this manner.

Inside the MR element 7 are ferromagnetic magnetoresistances M R+ , MR2, and MR whose resistance value changes depending on the magnetic field.

Place MR. Magnetoresistive MR,,MR.

MR3, MRa, MRs, MRb, MRq, MR
e is 6A of each magnetic track as shown in Figure 2.
It is arranged facing 6B, 6C, and 6D.

These magnetic resistances MR1, MR2, MRi, MRaMRs
, MRb , MR? , MRs , were made simultaneously on the same substrate, and as shown in the equivalent circuit shown in Figure 3, M
R+ and MR2, MR3 and MR, MR5 and MR,
, MR, and MR are connected in series, and the output signals VA, VA and VB are taken out from the connection point, respectively, and the other end is connected to the power source.

A more specific relationship between the MR element and the magnetic track will be explained with reference to FIG.

Magnetoresistive MR,, MR2, MR3, MR.

MRs, MRb, MRv, and MRs are resistors whose resistances change depending on the magnetic field and are made of ferromagnetic alloy thin films such as NiFe or NiCo, and as shown in the figure, each resistor is made in the same shape on the same substrate. This ferromagnetic magnetoresistance has a maximum resistance change in the direction of the magnetic field in the direction perpendicular to the direction of current flow in the same plane as the thin film. (from top to bottom)
A magnetic resistance M that senses a magnetic field so that a current flows at right angles to
Arrange R,,MR,,MR,,MR,.

Then, MR3 and MR are connected, and the output VA is taken out from the connection point.MR3 and MR are connected, and the output VA is taken out from the connection point. On the other hand, the other terminal side of each
Connect to. At this time, as shown in the figure, MR and MR are connected to the power source E so that they have opposite polarities.

With this configuration, the resistance of the MR element 7 becomes the fifth
MR, and MR, and MR as shown in figure a.

and MR3 are inversely related to each other and increase or decrease with Sin.

Therefore, as shown in FIGS. 5b and 5C, the output voltage VA can be obtained as an output voltage centered around % of the power supply voltage. If only one side MR is operated, the output of VA will be 2 as shown by the dotted line in FIG. MR connected to a power supply with opposite polarity: 1. Similarly, from the MR4, an output voltage having the opposite phase to VA as indicated by the dotted line in FIG. 5C can be obtained. In this way, VA and VA output with a phase difference of 180 degrees centered on the power supply voltage 2,
Taking this difference (VA-VA) doubles the output voltage.

Furthermore, when the output voltage is amplified by a differential amplifier as shown in Figure 6, the noise entering MR+, MR2, MR3, and MR4 can be significantly reduced by the common mode rejection of the differential amplifier, resulting in significant noise resistance. Improves sex.

Similarly, magnetic track 6C2 with a 90 degree phase difference
6D and MRs, MR-, MRl, MRs from V
VBVB with a 90 degree phase difference with respect to A and VA is obtained.

Note that the magnetic resistance of ferromagnetism changes symmetrically with respect to both the N and S magnetic poles, so when obtaining 1) 1z per rotation, the 7th
As shown in the figure, the magnetic track is magnetized by the M1 current superimposed with a direct current to prevent the polarity of the magnetic track from being reversed. (If the polarity is reversed, the output signal will be 2Hz per revolution).

] If the rotation is 2Hz or more, direct current may or may not be superimposed.

Effects of the Invention With this configuration, low-frequency sine wave detection such as IHz per revolution or 16H2 per revolution can be detected as a high-output, low-noise signal, and even with an absolute type, it is possible to detect a low-frequency sine wave with a small number of magnetic tracks. The encoder can be constructed with a small number of MR elements, and a small and inexpensive encoder can be manufactured.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the relationship between the magnetic drum and the magnetized head in an embodiment of the present invention, FIG. 2 is a schematic diagram showing the relationship between the magnetic drum and the MR element of the present invention, and FIG. 3 is a schematic diagram showing the relationship between the magnetic drum and the MR element of the present invention. M of
An equivalent circuit diagram showing the connection of the R element, FIG. 4 is a schematic diagram showing the relationship between the magnetic track of the present invention and the magnetic resistance of the MR element,
Figures 5a-c are waveform diagrams showing changes in the magnetic resistance of the MR element in Figure 4 and changes in output voltage in the example, and Figure 6 is a circuit diagram showing the connection of the amplifier circuit in the example in Figure 4. , Fig. 7 is a waveform diagram showing the magnetizing current during one revolution at IHz, Fig. 8 is a schematic diagram showing the αb relationship between the magnetic track and the MR element in the conventional example, and Fig. 9 shows the output voltage in the conventional example. FIG. 1...magnetic drum, 2...shaft,
3...signal generator, 4...amplifier, 5
A, 5B, 5C, 5D...Magnetic head, 51A
51B 51C, 51D...Magnetic yoke opening, 6A, 6B, 6C16D...Magnetic track, 7...MR element, MR, MR. MR3MR, MR5MR, MR, MR. ...Ferromagnetic magnetic resistance. Name of agent: Patent attorney Akira Odaji and 2 others 1 Figure 2 Figure 47 Rede Figure 6 Figure 7 Turning Aya Figure Figure Figure 1

Claims (5)

[Claims] (1) A ferromagnetic magnetoresistance element is arranged opposite to at least two magnetic tracks that are magnetized around one circumference of the magnetic drum, and the magnetic tracks are magnetized in the axial direction around one circumference of the magnetic drum. At the same time, the magnetic track is such that the magnetic field strength changes in a sinusoidal manner with respect to the ferromagnetic magnetoresistive element as the magnetic drum rotates, and the magnetic field strength of at least two magnetic tracks changes in the opposite direction. The configured magnetic sensor. (2) arranging two ferromagnetic magnetoresistances at right angles to the magnetization direction of the two magnetic tracks, and connecting the two ferromagnetic magnetoresistances in series to form a ferromagnetic magnetoresistive element;
2. The magnetic sensor according to claim 1, wherein the terminals connected in series are used as signal detection ends, and the other end is connected to a power source. (3) The magnetic sensor according to claim 1, wherein at least two sets of two ferromagnetic magnetoresistive elements are used, and the ferromagnetic magnetoresistive elements of each set have phases opposite to each other. (4) Each set includes two magnetic tracks and two ferromagnetic magnetoresistances, and the magnetic tracks are provided in two sets with a phase difference of 90 degrees from each other on the magnetic drum, and the ferromagnetic magnetoresistive 2. The magnetic sensor according to claim 1, wherein two sets are provided so as to obtain outputs with a phase difference of 90 degrees from each other. (5) When creating four magnetic tracks with a predetermined phase difference from each other on the magnetic drum, four magnetic heads for magnetization facing the magnetic drum are provided at positions separated by a predetermined angle from each other, and 2. The method of manufacturing a magnetic sensor according to claim 1, wherein a magnetizing current synchronized with the rotation of the magnetic drum is simultaneously applied to the four magnetizing magnetic heads.