JPH022086B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes a ferromagnetic thin film magnetoresistive system to transfer a magnetic signal recorded in the form of magnetization having equally spaced bit lengths to a disk attached to a rotating shaft and having a magnetic storage medium. The present invention relates to an angle detector that detects the rotation angle of the rotating shaft by reading it with a magnetic sensor comprising an effect element.

Conventionally, in this type of angle detector, the rotation angle of the rotating shaft is detected by directly reading the change in the signal magnetic field generated from the disk as the rotating shaft rotates as a change in the electrical resistance of the magnetoresistive element. This was done by Here, the amount of resistance change of the magnetoresistive element due to the signal magnetic field is about a few percent of its resistance value, and the angular position signal output is based on only this resistance change, regardless of the rotation speed of the rotating shaft. Accurate detection is required from the start to high-speed rotation. Therefore, the usual angular position detection method is to configure the magnetoresistive element in a bridge shape, amplify this differential output with a broadband DC amplification layer, and then shape it into a desired position signal. It is being In order to obtain stable operation in this angle detector, it is important to compare the DC offset voltage caused by variations in the resistance values of the magnetoresistive elements that make up the bridge and the offset voltage of the DC amplifier with the signal output voltage. The goal is to make it extremely small. However, in order to manufacture a magnetoresistive element so that the offset voltage of this bridge is extremely small, precise process control is required, and a DC amplifier with a low offset voltage is expensive, so in the conventional configuration, A high-performance, low-cost angle detector could not be obtained.

An object of the present invention is to provide a high-performance and inexpensive angle detector that solves the above-mentioned drawbacks. A feature of the present invention is that in an angle detector that combines a magnetic storage medium as a source of angular position information and a ferromagnetic magnetoresistive element as a magnetic sensor for this position information, in addition to the above-mentioned components, A completely new method of detecting and demodulating the angular position signal magnetic field in an amplitude-modulated form using the AC bias magnetic field as a carrier wave by installing a minute amplitude AC bias magnetic field applying means and an amplitude demodulation circuit, it is possible to detect and demodulate the angular position signal magnetic field in an AC manner using the AC bias magnetic field as a carrier wave. It can overcome the drawbacks caused by DC offset voltage, which was the biggest problem with magnetic field detection methods, and
As a result, a high-performance, low-cost angle detector can be realized.

That is, the configuration of the present invention includes a disk having a magnetic storage medium attached to the rotating shaft of a rotating body and in which magnetic signals are recorded in the form of magnetization having bit lengths at equal intervals along the circumference; A magnetic sensor consisting of a ferromagnetic thin film magnetoresistive element arranged so as to be able to sense changes in the magnetic field generated from the disk as a change in electrical resistance as the rotating shaft moves forward, and a minute alternating current bias magnetic field applied to the magnetic sensor. an application means, a drive circuit for the magnetic sensor, an amplification circuit for amplifying the output signal of the magnetic sensor, an amplitude demodulation circuit for rectifying and integrating the output waveform of the amplification circuit, and an amplitude demodulation circuit for rectifying and integrating the output signal of the amplitude demodulation circuit. It consists of a comparator that pulses.

A method for reproducing by applying an alternating current bias magnetic field to a magnetoresistive element, IEEETransacion on Audio,
It is shown in Vol Au-13 No. 2, March 1965, P41-43.

This applies an AC bias magnetic field with a larger amplitude than the signal magnetic field, detects the signal magnetic field, and reproduces as a signal the difference in the output amplitude envelope when the bias magnetic field is in the opposite direction. As an example based on the exact same principle, JP-A-53-
No. 57810, and U.S. Pat. No. 3,979,775 as an example of developing this method have been reported. but,
In principle, this method requires the strength of the AC bias magnetic field to be greater than that of the signal magnetic field, so it tends to cause various problems due to heat generation, and has drawbacks such as demagnetization of the signal magnetic field generation source.

According to the regeneration principle of the present invention, the above-mentioned drawbacks can be easily improved.

First, the principle of detecting a magnetic signal magnetic field by applying a minute amplitude AC bias magnetic field to a ferromagnetic magnetoresistive element, which is a feature of the present invention, will be explained with reference to FIG.
1 shows the relationship between the magnetic field H applied in the stripe width direction of the ferromagnetic magnetoresistive element and the resistance change amount ΔR of the magnetoresistive element. As is well known, the relationship between the two is approximately expressed as ΔR∝H ² . . . in a range where the magnitude of the applied magnetic field H does not exceed the saturation magnetic field Ho (|H|<Ho). Therefore, |∂ΔF/∂H|∝|H|... holds true. This shows that the amount of change in ΔR is proportional to the magnitude of the signal magnetic field H when an alternating current magnetic field of minute amplitude is applied to the magnetoresistive element, centering on the signal magnetic field H. For example, when detecting a signal magnetic field while applying a minute amplitude AC bias magnetic field 2 to the magnetoresistive element, the signal magnetic fields H ₁ , H ₂ and H ₃ each have a magnitude approximately proportional to the magnitude of the signal magnetic field. This produces alternating current ΔR changes 3, 4 and 5. By converting this change in ΔR into a change in voltage via a current flowing through the magnetoresistive element, the magnetoresistive element generates an AC output voltage proportional to the magnitude of the signal magnetic field as an output signal. arise.

In the reproduction method of the present invention, the AC bias magnetic field strength is minute compared to the conventional AC bias magnetic field application method, so it does not affect the characteristics of the signal magnetic field generation source and the AC bias magnetic field application means can be easily configured. It has advantages such as:

Next, embodiments of the present invention will be described with reference to FIGS. 2, 3, and 4. FIG. 2 schematically shows an embodiment of the present invention focusing on basic functions. The bit length L is attached to the rotating shaft 6 of the rotating body, and the magnetic signals are distributed at equal intervals along the circumference.
a disk 10 having a magnetic storage medium 9 recorded in the form of magnetization 7; and a magnetic disk 10 arranged so that a change in a magnetic signal 8 caused by the rotation of the rotating shaft 6 can be detected as a change in electrical resistance. sensor 11 and
A minute alternating current bias magnetic field 1 is applied to this magnetic sensor 11.
6, and the magnetic sensor 11.
a drive circuit 18 such as a constant current circuit that supplies a constant current to the magnetoresistive element; an amplification circuit 24 that amplifies the output signals 19, 20, 21, and 22 of the magnetic sensor 11; and an amplification circuit output waveform. It includes an amplitude demodulation circuit 25 that cuts, rectifies, and integrates the DC offset voltage of , and a comparator 26 that extracts the output of the amplitude demodulation circuit as pulsed angular position signals 27, 28, and 17. Here, the magnetic sensor 11 includes four striped ferromagnetic magnetoresistive elements 12, 1 having uniaxial anisotropy in the longitudinal direction.
3, 14, and 15 are formed with a pitch of 1/4L, and are arranged substantially parallel to the disk 10 so that the horizontal component of the signal magnetic field 8 generated from the magnetic storage medium 9 can be detected. It is located. or,
Various methods are available as the AC bias magnetic field applying means 117 as described later, but in all of them, the AC bias magnetic field 16 with a frequency higher than the frequency of the signal magnetic field 8 is applied in the horizontal component direction of the signal magnetic field, that is, in the stripe of the magnetoresistive element. It is formed so as to be applied in the width direction. Further, the magnitude of the alternating current bias magnetic field is usually set to a magnitude of several to several tens of oersteds.

FIG. 3 shows the magnetoresistive element 12 in FIG.
FIG. 4 is a circuit diagram showing a specific example of the parts 13, 14, 15, the drive circuit 18, and the reproduction circuit 23, and is a diagram for explaining the detection process.

When the rotating shaft 6 rotates in the direction 45 of the arrow in FIG. 2, the magnetoresistive element 12 receives a magnetic signal as shown in FIG. 4b due to repeated magnetization 7 as shown in FIG. 4a. 8 horizontal components 46 are added as a signal magnetic field. When this signal magnetic field 46 is regenerated and AC amplified while applying a minute amplitude AC bias magnetic field with a frequency higher than the maximum frequency of the signal magnetic field, the AC bias magnetic field is used as a carrier wave as an amplification circuit output 33 as shown in FIG. 4c. , an output 47 similar to a waveform amplitude modulated by the signal magnetic field 46 is obtained. After cutting off the DC offset portion of this output with a capacitor 69, it is passed through an amplitude demodulation circuit 25 consisting of a diode 31 and an integrating circuit 32, as shown in Fig. 4e.
A demodulated output 49 shown in FIG. Similarly, a demodulated output 50 which is 180° out of phase with the demodulated output 49 is produced from the magnetoresistive element 14 which is separated from the magnetoresistive element 12 by 1/2L. By inputting both of them into the differential comparator 26, a pulse output 51 corresponding to the bit of the magnetic storage medium as shown in FIG. .

Similarly, the magnetoresistive elements 13 and 15 output a second signal (abbreviated as B-phase output) 5 as shown in FIG.
2. When the rotating shaft 6 rotates in the opposite direction, the phase of the B-phase output 52 advances by 1/4 cycle than the A-phase. Therefore,
The rotation angle of the rotating shaft 6 can be detected by counting the number of pulses of the A-phase output or B-phase output generated by the rotation, or the number of pulses of the output obtained by electrically combining both. The direction can be determined by the phase relationship between both phases.

An aluminum plate with a thickness of several mm and a diameter of several tens of centimeters is used as the disk 10 which is a source of magnetic information, and several to several magnetic media 9 with a saturation magnetization of 5000 to 10000 Gauss and a coercive force of 200 Oersted or more are placed on the end face of this aluminum plate. It is formed to a thickness of several tens of microns. This magnetic medium is
Metal ferromagnetic materials such as Co-Ni and γ-Fe ₂ O ₃ are used. Magnetoresistive elements 12, 13, 14, 1
15, a metal ferromagnetic alloy containing permalloy, cobalt, etc. as the main component is formed into a shape several hundred angstroms thick, several tens of microns wide, and several millimeters long on a substrate with a smooth surface such as silicon single crystal or glass. As can be seen, the magnetic sensor section 11 is formed by using the electrical terminals at both ends, which are fabricated by thin film fabrication technology.

The magnetic sensor section 11 is located at a position where it can sufficiently detect the horizontal component of the signal magnetic field 8 of several to several hundred degrees generated from the magnetic medium 9 that changes with the rotation of the rotating shaft 6, for example, several tens of degrees from the end surface of the magnetic medium 9. ~
They are placed horizontally several hundred microns apart. The size of the disk 10 and the number and pitch of the magnetoresistive elements are appropriately selected depending on the desired rotational angle detection accuracy.

Next, a specific example of the minute amplitude AC bias magnetic field applying means 17 will be explained.

FIG. 5 shows a first example of the AC bias magnetic field applying means in the present invention, in which the insulating layer (the fifth
A conductor layer 53 formed in parallel to the magnetoresistive elements 12, 13, 14, and 15 via magnetoresistive elements (omitted in the figure), and an oscillator 54 that flows an AC bias signal current i to the conductor layer 53. Consists of. An AC bias magnetic field in the stripe width direction is applied to the magnetoresistive elements 12, 13, 14, and 15 by the AC bias current i flowing through the conductor layer 53. The magnitude of the AC bias magnetic field is determined by the magnetoresistive element 12,
It is appropriately set depending on the thickness of the insulator layer formed between the conductor layer 53 and the conductor layer 13, 14, 15 and the AC bias current value. The conductive layer 53 is made of gold, copper, aluminum, etc. with a thickness of several thousand to several tens of microns, and the conductive layer is made of SiO, SiO ₂ , Al ₂ O ₃ , etc. with a thickness of several thousand angstroms to several microns. A thin film is suitable.

FIG. 6 shows a second example of the AC bias magnetic field applying means according to the present invention, in which a core 55 made of a highly permeable material has a winding 56 and a gap 63.
and an oscillator 54 that flows an alternating current bias current i to the winding 56.
3, 14, and 15 are installed in the gap 63. A leakage magnetic field generated in the gap 63 of the core 55 due to the AC bias current i flowing through the winding 56 is used as an AC bias magnetic field in the magnetoresistive element 12,
It is applied in the width direction of stripes 13, 14, and 15. The magnitude of the AC bias magnetic field is appropriately set depending on the size of the gap 63 of the core 55 and the value of the AC bias current. As the core 55, a material obtained by processing a high permeability magnetic material such as permalloy or ferrite into an appropriate size is suitable.

FIG. 7 shows a third example of the minute amplitude alternating current bias applying means according to the present invention, in which the magnetization 58 rotates at a constant speed and the magnetic signal has a bit length L ₂ equally spaced along the circumference. recorded in the form.
It consists of a cylinder 60 with a magnetic storage medium 59 and a bias magnetic field 64 generated from this magnetic storage medium 59.
is applied in the stripe width direction of the magnetoresistive elements 12, 13, 14, and 15. The magnitude and frequency of the AC bias magnetic field are determined by the diameter of the cylinder 60, the thickness of the magnetic storage body 59, the bit length L ₂ , the magnetoresistive element 12 of the cylinder 60,
Installation position and rotation axis 5 for 13, 14, 15
The desired value is set by adjusting the rotation speed of 7. The material and structure of this alternating current bias magnetic field generation source are suitably similar to those of the magnetic signal generation source described above.

FIG. 8 shows a fourth example of the minute amplitude alternating current bias applying means according to the present invention, in which magnetization 66 which travels at a constant speed and has a magnetic signal having equally spaced bit lengths L ₃ along the traveling direction is shown in FIG. It consists of a magnetic tape 62 having a magnetic storage medium 65 recorded in the form of
The voltage is applied in the width direction of stripes 4 and 15. The magnitude and frequency of the AC bias magnetic field, the thickness of the magnetic storage medium 65, the bit length L ₃ ,
The magnetic tape 62 has magnetoresistive elements 12, 13,
Installation position for 14, 15 and magnetic tape 62
It is set to a desired value by adjusting the strike speed of . An ordinary magnetic tape is suitable as a source of this AC bias magnetic field.

As explained above, according to the present invention, in an angle detector that combines a magnetic storage medium as an angular position information generation source and a ferromagnetic magnetoresistive element as a magnetic sensor for this position information, the above-mentioned components are combined. In addition, means for applying a minute amplitude AC bias magnetic field to the magnetic sensor and an amplitude demodulation circuit are provided,
By detecting and demodulating the angular position signal magnetic field in an AC manner in an amplitude-modulated form using the minute amplitude AC bias magnetic field as a carrier wave, it is possible to eliminate DC offset, which has been the biggest problem with conventional DC signal magnetic field detection methods. This has the effect of overcoming various drawbacks caused by voltage.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the reproduction principle of the present invention, FIG. 2 is a diagram schematically showing the basic configuration of an embodiment of the present invention, and FIG. 3 is a diagram for explaining the reproduction principle of the present invention. FIG. 4 is a circuit diagram showing a specific example of a resistive effect element, a drive circuit, and a reproducing circuit, and FIG. 4 is a diagram showing the detection process of the present invention. A diagram showing the signal magnetic field applied to the magnetoresistive element from the storage medium, c is a diagram showing the amplifier output waveform, d is a diagram showing the rectifier circuit output waveform, e
is a diagram showing an amplitude demodulation circuit output waveform, f is a diagram showing an A-phase output waveform, and g is a diagram showing a B-phase output waveform. 5, 6, 7, and 8 are schematic perspective views showing examples of alternating current bias magnetic field applying means in the present invention, respectively. 1... Static characteristic curve of ferromagnetic magnetoresistive element,
2...Minute amplitude AC bias magnetic field, 3, 4, 5...
...Change in AC-like ΔR, 6,57,68...Rotation axis, 7,58,66...Magnetization, 8,64,67...
...Signal magnetic field and bias magnetic field generated from magnetic medium, 9,59,65...Magnetic storage medium, 10...
Disc, 11... Magnetic sensor, 12, 13, 1
4, 15...Ferromagnetic magnetoresistive element, 16...
Minute alternating current bias magnetic field, 17...Minute alternating current bias magnetic field applying means, 18... Drive circuit, 19,2
0, 21, 22...Output terminal of magnetoresistive element, 23...Reproduction circuit, 24...AC amplifier circuit,
25...amplitude demodulation circuit, 26...comparator,
27...A phase output terminal, 28...B phase output terminal,
29...Capacitor, 30...Amplifier, 31...
Diode, 32...Integrator circuit, 33, 34, 3
5, 36... AC amplifier circuit output terminal, 37, 3
8, 39, 40... Rectifier circuit output terminal, 41, 4
2, 43, 44...amplitude demodulation circuit output terminal, 45
...Rotation direction of the rotating shaft, 46...Signal magnetic field, 47
... Amplifier circuit output waveform, 48 ... Rectifier circuit output waveform, 49, 50 ... Amplitude demodulation circuit output waveform, 51
...A phase output waveform, 52...B phase output waveform, 53
... Conductor layer, 54 ... Oscillator, 55 ... Core,
56...Winding, 61...Motor, 62...Magnetic tape, 63...Core gap, 69...Capacitor.

[Claims]

1. A rotatable rotor is placed in the measurement chamber, and blades are placed on the rotor to face each other across the rotor shaft, and cutouts are provided at the top and bottom of the retracted end of the blades to form external jaws and An inner jaw is formed that protrudes beyond this, and a roller shaft with a rotatably held roller is placed in the inner and outer jaw, while a plate cam is fixed at the center of the inner side of the lower lid above the measurement chamber. In a sliding blade flowmeter, in which cam storage holes for storing the plate cam are provided on both sides of the rotor, and rollers at the upper and lower parts of the blade are arranged to rotate along the cam surface of the plate cam, The upper and lower parts of the opposing blades are connected at a predetermined interval by connecting rods that pass through the rotor shaft, and the rollers on the upper and lower parts of the blades are brought into contact with the cam surface of the plate cam. Sliding blade flow meter.

Claims (1)

4. A patent claim in which the alternating current bias magnetic field applying means consists of a disk or cylinder having a magnetic storage medium that rotates at a constant speed and in which magnetic signals are recorded in the form of magnetization with equally spaced bit lengths along the circumference. An angle detector according to range 1. 5. The alternating current bias magnetic field applying means comprises a magnetic tape having a magnetic storage medium running at a constant speed and in which magnetic signals are recorded in the form of magnetization having bit lengths equally spaced along the running direction. Angle detector according to item 1.