JPH04223218A - Magnetic sensor - Google Patents

Abstract

PURPOSE:To eliminate placement of a magnetic track and an MR element even at a saturation region of magnetic resistance in a magnetic sensor using the MR element consisting of a ferromagnetic resistance. CONSTITUTION:An MR element 7 consisting of a ferromagnetic resistance is placed opposing to at least two magnetized tracks 6A, 6B, 6C, and 6D around one periphery of a magnetic drum 1. A magnetization direction of the magnetic tracks 6A, 6B, 6C, and 6D is in axial direction over one periphery of the magnetic drum 1 and a magnetic strength is changed nearly in sinusoidal shape for the MR element 7 along with revolution of the magnetic drum 1. Also, at least two magnetic tracks 6A, 6B, 6C, and 6D are constituted so that the magnetic strength is nearly in 120-degree phase difference mutually.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an absolute type magnetic sensor widely used in robots, NC devices, etc.

0002

[Prior Art] An absolute encoder divides the circumference into multiple tracks of 2, 4, 8, 16, 32,...
This is an encoder that divides the image into 2n and detects its absolute position.

If this is done magnetically, a multi-stage magnetized track is required, which has the drawback of increasing the size and cost.

[0004] Therefore, the present inventor reduced the number of magnetized tracks and used tracks divided into 2, 16, 128, and 1024, for example, to generate sine wave and cosine wave signals from magnetic sensors facing each magnetic track. By the method of electric circuit processing, 2, 4, 8, 16, 32, 64, 128
, 256, 512, 1012, 2048, and 4096 divided signals, and filed a patent application for a low-frequency magnetic sensor such as 2,16, etc., with a rotation rate of 1 Hz to several tens of Hz.

The details are shown in FIG. 6, in which the shaft 2 is attached to the magnetic drum 1. shaft 2
A signal generator 3 is attached to generate a sine wave signal synchronized with the rotation as it rotates.

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

The magnetic tracks 6A, 6B, 6C, and 6D are magnetized so that the phase difference between them is 180 degrees for 6A and 6B, 180 degrees for 6C and 6D, and 90 degrees for 6A and 6C. For example, in the case of a signal of 1 Hz per rotation, magnetic heads A and B are installed at a mechanical angle of 180 degrees, C and D are 180 degrees, and 6A and 6C are installed at 90 degrees, and they are connected in series to generate the same current. Magnetize. Furthermore, 51A, 51B, 51C, 51D
The yoke openings of the magnetic heads 5A, 5B, 5C, and 5D coincide with the axial direction of the magnetic drum 1, and the magnetic tracks are provided with magnetic poles in the vertical direction.

Here, in the case of one rotation of 16 Hz, the angle of the magnetic heads 5A and 5B and 5C and 5D is 11.25.
degrees or equivalent 11.25 + n × 22.5 degrees (n≧1 integer), and 5A and 5C are 5,625 degrees or equivalent 5,
Install at 625+n×22.5 degrees (n≧1 integer).

Note that the magnetic tracks 6A, 6B, 6C, 6
Although the explanation has been given by simultaneously magnetizing the magnetic tracks D with the same current, the magnetic tracks 6A, 6B, 6C, and 6D may be provided with 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, there are ferromagnetic magnetoresistances MR1, MR2, MR3, M whose resistance value changes depending on the magnetic field.
Place R4. Magnetic resistance MR1, MR2, MR3, M
R4, MR5, MR6, MR7, and MR8 are arranged facing magnetic tracks 6A, 6B, 6C, and 6D, respectively, as shown in FIG.

These magnetic resistances MR1, MR2, MR3, M
R4, MR5, MR6, MR7, and MR8 were made simultaneously on the same board, and as shown in the equivalent circuit shown in Figure 8, M
R1 and MR2, MR3 and MR4, MR5 and MR6, and MR7 and MR8 are connected in series, respectively, and output signals Va,

[0013]

[Outside 1]

[0014] and Vb,

[0015]

[Outside 2]

[0016] respectively, and connect the other end to the power source E. A more specific relationship between the MR element and the magnetic track will be explained with reference to FIG.

Magnetoresistive MR1, MR2, MR3, MR4
, MR5, MR6, MR7, MR8 are NiFe or Ni
A resistor whose resistance changes depending on a magnetic field is made of a thin film of a ferromagnetic alloy such as Co. As shown in the figure, each resistor is made in the same shape on the same substrate. This ferromagnetic magnetoresistance has the largest resistance change in the direction of the magnetic field in the direction perpendicular to the direction of current flow on the same plane as the thin film. Magnetoresistive MR1 that senses the magnetic field so that the current flows at right angles to (from top to bottom)
, MR2, MR3, and MR4 are arranged.

[0018] Then, MR1 and MR2 are connected, and the output Va is output from the connection point, and MR3 and MR4 are connected, and the output Va is output from the connection point.

[0019]

[Outer 3]

Take out [0020]. On the other hand, each other terminal side is connected to a power source E. At this time, as shown in the figure, MR1 and M
MR3 and MR4 are connected to power supply E so as to have opposite polarity to R2.

With this configuration, the MR element 7
The resistances are MR1, MR2 and M as shown in Figure 10(a).
R4 and MR3 are inversely related to each other and increase and decrease with a sin ratio. Therefore, the output voltage Va is
), approximately 1/2 of the power supply voltage can be extracted as an output voltage such as Va. If only MR1 operates on one side, 1/1 of Va as shown by the dotted line in Fig. 10(b).
The output will be 2. MR3, MR connected to a power supply with opposite polarity
From 4 onwards, it is similarly shown by the dotted line in Fig. 10(c).

[0022]

[Outside 4]

It can be obtained as an output voltage having a phase opposite to Va as shown in the following. In this way, Va and around 1/2 of the power supply voltage

[0024]

[Outer 5]

0025 is an output whose phase is shifted by 180 degrees, and this difference

[0026]

[Math 1]

By taking ##EQU1##, the output voltage doubles. Also, if the output voltage is amplified by a differential amplifier as shown in Figure 11, M
The noise entering R1, MR2, MR3, and MR4 can be significantly reduced by common mode rejection of the differential amplifier.
Significantly improves noise resistance.

Similarly, magnetic tracks 6C, 6D and MR5, MR6, MR7, MR with a phase difference of 90 degrees
From 8, Va,

[0029]

[Outside 6]

Vb with a 90 degree phase difference with respect to

00
31]

[Outside 7]

##EQU1## is obtained. Note that the resistance of ferromagnetic magnetoresistance changes symmetrically with respect to both the N and S magnetic poles, so in order to obtain 1 Hz per revolution, as shown in Figure 12, magnetization is performed using a magnetizing current with superimposed direct current, and the magnetic track is (If the polarity is reversed, the output signal will be 2Hz per rotation.)

[0033] When the frequency per revolution is 2 Hz or more, direct current may or may not be superimposed.

[0034]

[Problems to be Solved by the Invention] In the conventional example with the above configuration, as shown in FIG. 13, when the gap between the magnetic sensor using an MR element and the magnetic drum is wide, the output voltage is large with respect to the gap. Change. Also, when the magnetic drum and sensor are placed close to each other, the output voltage is large and almost constant, but the waveform of the output voltage is distorted due to the saturation phenomenon occurring in the change in magnetic resistance, so the high output voltage cannot be applied over a wide range of gaps. Moreover, a distortion-free waveform could not be obtained.

[0035]

[Means for Solving the Problems] In order to solve the above problems, in the present invention, a ferromagnetic magnetoresistive element is disposed facing at least two magnetic tracks magnetized around one circumference of a magnetic drum, and The magnetic track is a magnetic track whose magnetization direction is the axial direction over one circumference of the magnetic drum, and whose magnetic field strength changes approximately sinusoidally with respect to the ferromagnetic magnetoresistive element as the magnetic drum rotates, and at least The two magnetic tracks are constructed so that their magnetic field strengths are approximately 120 degrees out of phase with each other.

Further, in the present invention, two ferromagnetic magnetoresistances are arranged at right angles to the magnetization direction of the two magnetic tracks, and the two ferromagnetic magnetoresistances are connected in series to form a ferromagnetic magnet. A configuration in which the serially connected terminals of a magnetoresistive element are used as signal detection terminals and the other end is connected to a power supply;
A configuration in which at least two sets of ferromagnetic magnetoresistive elements are used as one set, and each set of ferromagnetic magnetoresistive elements is set in opposite phase to each other, or a configuration in which two magnetic tracks and two ferromagnetic magnetoresistive elements are used. Two sets of the magnetic tracks are provided on the magnetic drum with a phase difference of 90 degrees from each other, and two sets of the ferromagnetic magnetoresistances are provided so as to obtain outputs with a phase difference of 90 degrees from each other. may be configured.

[0037]

[Operation] With this configuration, the third harmonic is removed from the two magnetic resistances with a phase difference of 120 degrees, and the second harmonic is further removed by the combination with the magnetic resistance with the opposite phase.
It can be detected as an in-wave signal. The other set of magnetic tracks is set at an electrical angle of 90 degrees with respect to the magnetic tracks, and can be detected as a cosine wave signal with higher precision than the four magnetic resistors facing each magnetic track.

[0038]

[Embodiment] An embodiment of the magnetic sensor of the present invention will be described below.

First, the magnetic sensor according to the present invention has basically the same structure as the sensor shown in FIGS.
It is configured to have a phase difference of degrees.

FIG. 2 is a diagram showing output signals when the magnetic drum 1 and the MR element 7 are brought close to each other.
Magnetic saturation occurs, the resistance value changes as shown in FIG. 2, and the output signal with respect to the signal magnetic field becomes distorted. At this time, the resistance values of the magnetoresistances MR1 and MR2 and MR3 and MR4 change at an angle of 120 degrees from each other as shown in FIG.

According to FIG. 3, due to this 120 degree phase difference, 3
Explain that harmonics are removed. In FIG. 3, the thick solid line shows the signal from MR1, the thin solid line shows the third harmonic included therein, and the thick dotted line shows the signal from MR2,
The thin dotted line indicates the third harmonic included therein. In this way, the third harmonics included in the signals of MR1 and MR2 are in phase, and as shown in FIG. 8, the series connection results in a differential output, so the third harmonics are removed.

Next, the signals Va and M from MR1 and MR2
Signals from R3 and MR4

[0043]

[Outside 8]

FIG. 4 shows how to remove the second harmonic from
This is explained by: The thick solid line indicates the signal Va, and the thin solid line indicates the second harmonic included therein. Also, the thick dotted line is the signal

[0045]

[Outer 9]

The thin dotted line indicates the second harmonic contained therein. By inputting this signal to a differential amplifier as shown in FIG. 11, the second harmonic is removed because it is in phase. In this way, the output signal VA is a highly accurate sin
wave signal is obtained. Also magnetic tracks 6A, 6B and 90
Output signals V from MR5, MR6, MR7, and MR8 facing magnetic tracks 6C and 6D with a phase difference of
Similarly, a highly accurate cosine wave signal can be obtained in case b.

[0047]

As described above, according to the present invention, a constant high output can be obtained over a wide gap range between the magnetic drum and the MR element as shown in FIG.
By obtaining wave and cosine wave signals, even an absolute type encoder can be constructed with fewer magnetic tracks and fewer MR elements, making it possible to create a small, highly accurate, and inexpensive encoder.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the resistance change of magnetic resistance with respect to the rotation of the magnetic drum in the magnetic sensor of the present invention.

[Figure 2] Waveform diagram also showing the relationship between the signal magnetic field and the output signal

[Figure 3] 12
Conceptual diagram explaining the state of the third harmonic due to magnetic resistance with a phase difference of 0 degrees

[Fig. 4] Conceptual diagram explaining the state of second harmonics in the output of an MR element with negative phase

FIG. 5 is a characteristic diagram showing the relationship between output voltage and harmonic components with respect to the gap between the magnetic drum and MR element in the present invention.

[
FIG. 6 is a schematic diagram showing the relationship between the magnetic drum and the magnetizing head in the present invention.

[Figure 7] Schematic diagram showing the relationship between the magnetic drum and the MR element

[Figure 8] Equivalent circuit diagram showing the connection of MR elements

[Figure 9] Schematic diagram showing the relationship between the magnetic track and the magnetic resistance of the MR element

[Figure 10] (a) to (c) are waveform diagrams showing changes in magnetic resistance and output voltage of a conventional MR element.

[Figure 11] Electrical circuit diagram of magnetic sensor

[Figure 12] 1
Waveform diagram showing magnetizing current at 1Hz rotation

[Fig. 13] Characteristic diagram showing the relationship between output voltage and harmonic components with respect to the gap between the conventional magnetic drum and MR element.

[Explanation of symbols]

1 Magnetic drum 5A, 5B, 5C, 5D Magnetic head 6A, 6B, 6
C, 6D Magnetic track 7 MR element MR1, MR2, MR3, MR4, MR5, MR6, M
R7, MR8 Ferromagnetic magnetoresistance

Claims (4)

[Claims] 1. A ferromagnetic magnetoresistive element is disposed opposite to at least two magnetic tracks magnetized around one circumference of a magnetic drum, and the magnetic tracks have a magnetized direction axially extending around one circumference of the magnetic drum. a magnetic track in which the magnetic field strength changes approximately sin-like with respect to the ferromagnetic magnetoresistive element as the magnetic drum rotates;
The magnetic tracks of the book are magnetic sensors configured so that the magnetic field strengths are approximately 120 degrees out of phase with each other. 2. A ferromagnetic magnetoresistive element is constructed by arranging two ferromagnetic magnetoresistances perpendicular to the magnetization direction of the two magnetic tracks and connecting the two ferromagnetic magnetoresistances in series. 2. The magnetic sensor according to claim 1, wherein the terminals connected in series are used as a signal detection end, 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 opposite phases to each other. 4. Each set includes two magnetic tracks and two ferromagnetic magnetic resistors, and the magnetic tracks are provided in two sets on a magnetic drum with a phase difference of 90 degrees, and the ferromagnetic magnetic 2. The magnetic sensor according to claim 1, wherein two sets of resistors are provided to obtain outputs with a phase difference of 90 degrees.