JPH06129808A - Magnetic sensor - Google Patents

Abstract

PURPOSE:To provide a magnetic sensor with high resolution and at low cost without increasing the number of gears of a rotary body and the number of magnetic resistance elements. CONSTITUTION:A first and a second magnetic resistance element bridge 18, 19 are arranged with the phase difference of 90 degrees. An output Va=Asinomegat, Vb=Asin(omegat pi/2) from the bridges 18, 19 is added to a reduction circuit 4 having an oscillation or amplitude control means R1-R9, an adding circuits 5, 6, 7 to output a voltage Vc=Asin(omega t-pi/4), Ve=Asin(omegat+pi/4). These voltages Vc, Ve have the phase difference of 45 degrees with respect to the voltages Va, Vb. The output waveform of four phases with the same amplitude is obtained accordingly from two pairs of bridges which provide the same resolution as four pairs of bridges. It is thus possible to have high resolution with the minimum number of magnetic resistance elements, and to thereby provide a low current consumption and low cost magnetic sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic sensor device for detecting a rotational speed or a rotational direction of a magnetic body using a magnetoresistive element.

[0002]

2. Description of the Related Art FIG. 7 is a schematic diagram showing a conventional general magnetic sensor device for detecting gear rotation. This magnetic sensor device is provided with a pair of magnetoresistive elements MR ₁ and MR ₂ connected in series above a magnetic bias magnet, and one end side of this series connection circuit is connected to a power supply V.
_The output voltage V _out is taken _out from the connection portion of the magnetoresistive elements MR ₁ and MR ₂ by connecting to the _dc and the other end side to the ground.

The magnetoresistive elements MR ₁ and MR ₂ are arranged opposite to a gear 16 made of a magnetic material as an object to be detected. When the crests of the gear 16 oppose to the magnetoresistive element MR ₁ , for example, the valleys of the gears become magnetic. By setting the arrangement pitch of the magnetoresistive elements MR ₁ and MR ₂ so as to pass through the resistive element MR ₂ , the rotation of the gear 16 is shown as a differential output of the magnetoresistive elements MR ₁ and MR ₂ as shown in FIG. Obtained with the output waveform. The rotation speed can be detected by discriminating the level of this output waveform with a reference voltage, converting it into a pulse signal, and counting the number of pulses per unit time.

Further, as described above, a pair of magnetoresistive elements M
The magnetic sensor device composed of R ₁ and MR ₂ can detect the rotation speed of the gear 16, but cannot detect the rotation direction. As shown in FIG. 5, as a magnetic sensor device, a pair of magnetoresistive elements M
A first magnetoresistive element bridge 18 in which R _a1 and MR _a2 are connected in series and a second magnetoresistive element bridge 19 in which another pair of magnetoresistive elements MR _b1 and MR _b2 are connected in series are provided. By electrically arranging the output phase difference, a two-phase output type rotary magnetic sensor can obtain an output waveform as shown in FIG. 6 and detect the rotation direction. That is,
It can be detected rotational direction by examining the phase advance relationship between the phase of the output voltage V _b of the output voltage V _a and the second magnetoresistive element bridges 19 from the first magnetoresistive element bridges 18.

[0005]

Recently, as the precision of equipment control is required to be high, the resolution of rotation detection is required to be improved. There are two possible ways to do this. Firstly, the inter-tooth pitch I of the gear 16 is reduced to increase the number of teeth, and secondly, the number of bridges of the magnetoresistive element is increased so as to have a subdivided phase difference (for example, the magnetoresistive element). If four pairs of bridges are prepared and each bridge has an electrical phase difference of 45 degrees, the resolution will be twice as high as that of two pairs of magnetoresistive element bridges).

However, in the first measure for improving the resolution, the inter-tooth pitch I becomes small, so that the induced magnetic field change amount decreases and the magnetoresistive element bridge output amplitude decreases. Therefore, the level discrimination reference potential at the time of pulse conversion must be lowered, or the magnetoresistive elements MR ₁ and MR ₂ must be arranged within a close range of the gear 16. If the level discrimination reference potential is lowered, noise may be output. On the other hand, if the magnetoresistive elements MR ₁ and MR ₂ and the gear 16 are placed close to each other, the element M is
There is a physical risk that R ₁ and MR ₂ will be destroyed by contact.

In the second measure, if the number of magnetoresistive element bridges is increased, the number of elements and the number of wirings are naturally increased, the assembly is not easy, the assembly cost is increased, and the magnetoresistive element has a low impedance. Therefore, current consumption increases in proportion to the number of elements. Further, when the inter-tooth pitch I is reduced, the area of the magnetoresistive element corresponding to the inter-tooth pitch I is reduced, the element sensitivity is weakened, the element impedance is also reduced, and the output voltage from the magnetoresistive element bridge is reduced. Since the amplitude is reduced, there is a problem that more current consumption is required.

The present invention has been made in order to solve the above-mentioned conventional problems, and an object thereof is to achieve low cost, low current consumption, high power consumption without increasing the number of magnetic resistance element bridges and the number of gear teeth. An object of the present invention is to provide a magnetic sensor capable of magnetic detection under the resolution.

[0009]

In order to achieve the above object, the present invention is constructed as follows. That is, in the magnetic sensor of the present invention, the first magnetoresistive element bridge and the second magnetoresistive element bridge formed by connecting magnetoresistive elements in series are electrically arranged with an output phase difference of 90 degrees. An adding circuit and a subtracting circuit for the output of the first magnetoresistive element bridge and the output of the second magnetoresistive element bridge are provided, and the output of the adding circuit and the output of the subtracting circuit and the outputs of the first and second magnetoresistive elements. It is characterized in that an amplitude adjusting means for equalizing is provided.

[0010]

In the present invention having the above-mentioned structure, the respective output voltages of the first magnetoresistive element bridge and the second magnetoresistive element bridge having an electrical output phase difference of 90 degrees are applied to the adding circuit and the subtracting circuit. The output voltage having a phase difference of 45 degrees with each of the output voltages obtained by the above calculation is obtained, that is, the same as when four pairs of magnetoresistive element bridges are provided by two pairs of magnetoresistive element bridges. The voltage waveform of the phase is obtained.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. In the description of the present embodiment, the same parts as those in the conventional example are designated by the same reference numerals, and the duplicate description thereof will be omitted. An embodiment of the magnetic sensor device according to this embodiment is shown in FIG. The magnetic sensor portion 26 is composed of two pairs of a first magnetoresistive element bridge 18 and a second magnetoresistive element bridge 19 as in the conventional case, and each of the bridges 18 and 19 has a phase difference of 90 degrees. A bias magnetic field is applied by a bias magnet (not shown) as in the conventional case.

The difference from the prior art is that the output voltage V _a = A sin ωt from the first magnetic resistance element bridge 18 and the output voltage V _b = A (sin ω) from the second magnetic resistance element bridge 19.
Conventionally, t + π / 2) was directly pulse-converted and output, but in the present embodiment, an arithmetic circuit such as a subtraction circuit and an addition circuit as shown in FIG. 1 is built in, and the output voltage is supplied to this arithmetic circuit. In addition, it is in pulse conversion.

The arithmetic circuit used in this embodiment shown in FIG. 1 is an operational amplifier 4 as a subtracting circuit, operational amplifiers 5, 6, 7 as an adding circuit, and resistors R _{1 to} R ₉ as amplitude adjusting means. And so on. This subtraction circuit 4
The voltage V _C output from V _C = V _a −V _b = A sin
ωt−Asin (ωt + π / 2) = √2Asin (ωt−π)
/ 4), and the voltage V _e output from the adding circuits 5, 6, 7 is V _e = V _a + V _b = √2A sin (ωt + π /
4) and both of these voltages V _c and V _e have output waveforms with an amplitude of √2 A, and therefore an amplitude adjusting means is provided in order to make them equal to the amplitude A of the voltages V _a and V _b . The resistance values of R _{1 to} R ₉ as the amplitude adjusting means are R ₁ = R ₂ and R ₃ = R.
₄ = R ₁ / √2, R ₅ = R ₆ , R ₇ = R ₅ / √2, R ₈
= R ₉ , the voltages V _c and V _e are equal to the voltage V _a
And the amplitude A of V _b is equalized and output.

To the non-inverting input terminal of the operational amplifier 4 as a subtraction circuit, the voltage V _a = Asin ωt from the first magnetoresistive element bridge 18 via the resistor R ₁ and the resistor R ₃ are applied. The reference voltage F from the power source 3 is applied, and the second magnetoresistive element bridge is connected to the inverting input terminal via the resistor R _2.
The voltage V _b = A sin (ωt + π / 2) from 19 is applied.
Voltage from the output of the operational amplifier _{4 V c = V a -V b} = Asi
n ωt−Asin (ωt + π / 2) = √2Asin (ωt−
V _c = A sin (ωt−π / 4) in which the amplitude of (π / 4) is adjusted
Is output.

A reference voltage F is applied to a non-inverting input terminal of an operational amplifier 5 as an inverting type addition circuit, and a voltage V _a via a resistor R ₆ and a voltage V via a resistor R ₅ are applied to an inverting input terminal. _b is added, and the output voltage of the inverting addition circuit from the output side is V _d = − (V _a + V _b ) = − √2A sin (ωt + π /
4) outputs the V _d = -Asin that amplitude adjustment (ωt + π / 4), the voltage V _d is applied to the non-inverting input terminal of the operational amplifier 6. At the inverting input terminal of this operational amplifier 6,
The output voltage from the operational amplifier 6 is negatively fed back and serves as a buffer (buffer amplifier). The output voltage from the buffer 6 is applied to the inverting input terminal side of the operational amplifier 7 as an inverting circuit via the resistor R ₈ , and the reference voltage F is applied to the non-inverting input terminal of the operational amplifier 7. Voltage output of the operational amplifier 7 inverts the voltage V _d V _e = Asin
(Ωt + π / 4) is output.

Therefore, according to this embodiment, the voltage V _a
And V _b have a phase difference of 90 degrees, and the voltages V _c and V _e have a phase difference of 45 degrees with respect to the voltages V _a and V _b , and have the same amplitude as shown in FIG. A four-phase output waveform can be obtained, and a four-phase output type rotary magnetic sensor can be obtained. Similar output waveforms can be obtained from two pairs of magnetoresistive element bridges 18 and 19. . That is, the minimum two pairs of magnetoresistive element bridges required to detect the direction of the rotating body without increasing the number of gear teeth.
By using only 18 and 19, the resolution can be doubled compared to the conventional one. Moreover, since the number of magnetoresistive elements is also kept to the required minimum, current consumption can be kept to a minimum, assembly is easy, assembly cost is reduced, and a low-cost magnetic sensor can be obtained.

Further, since the amplitude adjusting means for setting the resistance values of the resistors R _{1 to} R ₉ as described above is provided, the voltage V _a ,
The amplitudes of V _b , V _c , and V _e are all equal, and the number of reference voltage settings used for pulse conversion may be one, which simplifies the circuit configuration.

As described above, the voltage V _a output in FIG.
V _b, V _c, V _e is applied to the pulse conversion circuit and a logic circuit shown in FIG. A power supply 15 for applying a reference voltage E is connected to all the inverting input terminals of the comparators 8 to 11, the voltage V _a of the comparator 8, the voltage V _b of the comparator 9, and the voltage V _c of the comparator. The voltage V _{e of} 10 is connected to the non-inverting input terminal side of the comparator 11, and the respective voltages V _a , V _b , V _c ,
V _e is compared with the reference voltage E. The voltage V _{ap of the} pulse waveform output from the comparator 8 and the voltage V _{bp of the} pulse waveform output from the comparator 9 are applied to the input terminal side of the EXOR gate 12 which is an exclusive OR operator. The voltage V _f is output from the output side. As shown in FIG. 4, this voltage V _f has a resolution twice that of the voltages V _a and V _b . Voltage V _{cp of} pulse waveform output from comparator 10
And the voltage V _{ep of the} pulse waveform output from the comparator 11 are applied to the input terminal side of the EXOR gate 13, and the voltage V _g is output from the output side. Further, the voltage V _g and the voltage V _f
Are applied to the input terminal side of the EXOR gate 14, and the voltage V _h is taken out from the output side. This voltage V _h has twice the resolution of the above voltages V _g and V _f ,
Further, it has four times the resolution for the voltages V _a and V _b .

By passing each output signal through the exclusive OR calculator in this way, the resolution can be doubled.

The present invention is not limited to the above-mentioned embodiment, and various embodiments can be adopted. For example, a circuit such as a comparator (comparator) may be used instead of the operational amplifiers 4 to 7, and a circuit such as an operational amplifier may be used instead of the comparators 8 to 11. Further, in the above embodiment,
Although the gear 16 has been described as the object to be detected, the object to be detected may be formed by, for example, a magnetic linear scale or the like to detect linear movement of the linear scale, and the type thereof is limited. Not done.

Further, the magnetoresistive elements MR _a1 , MR _a2 , M
A magnetoelectric conversion element such as a Hall element may be used instead of R _b1 and MR _b2 .

[0022]

According to the magnetic sensor of the present invention, the respective outputs from the first and second magnetoresistive element bridges are added to the subtraction circuit and the addition circuit, so that the waveforms output from these circuits are applied to the respective bridges. 45 degrees out of phase from the waveform output from. Further, since the amplitude adjusting means is provided, the amplitude of the output voltage that has passed through the subtraction circuit and the addition circuit becomes the same amplitude as the output voltage from the bridge.

Therefore, without increasing the number of teeth of the rotating body, and even if the number of bridges of the magnetoresistive element is 2 pairs, an output waveform of the same amplitude of 4 phases is obtained as in the case where 4 pairs of bridges are installed. And becomes a four-phase output type rotary magnetic sensor. Therefore, the number of magnetoresistive elements is the minimum, the current consumption is low, the assembling is easy, and the assembling cost is low. Therefore, a magnetic sensor with high resolution and low cost can be obtained.

Further, since the amplitude adjusting means is provided, the amplitude of the output voltage from each of the bridges becomes equal to the amplitude of the output voltage from the subtracting circuit or the adding circuit, and the reference voltage used for pulse conversion is 1 or the like. The circuit configuration is easy because the number of types is sufficient.

[Brief description of drawings]

FIG. 1 is an arithmetic circuit diagram of an embodiment of a magnetic sensor of the present invention.

FIG. 2 is a circuit configuration diagram showing a pulse conversion circuit and a logic circuit used in one embodiment of the magnetic sensor of the present invention.

FIG. 3 is a waveform chart output from the arithmetic circuit of FIG.

4 is a pulse waveform diagram output from the pulse conversion circuit and the logic circuit of FIG.

FIG. 5 is a schematic configuration diagram of a magnetic sensor device using two pairs of magnetoresistive element bridges.

FIG. 6 is a voltage waveform diagram output from the magnetic sensor device of FIG.

FIG. 7 is a schematic configuration diagram of a conventional magnetic sensor device using a pair of magnetoresistive element bridges.

FIG. 8 is a voltage waveform diagram output from the magnetic sensor device of FIG. 7.

[Explanation of symbols]

4 Subtraction circuit (operational amplifier) 5, 6, 7 Addition circuit (operational amplifier) 18 First magnetoresistive element bridge 19 Second magnetoresistive element bridge MR _a1 , MR _a2 , MR _b1 , MR _b2 magnetoresistive element R ₁ ~ R ₉ resistor (amplitude adjusting means)

Claims (1)

[Claims] 1. A first magnetoresistive element bridge formed by connecting magnetoresistive elements in series and a second magnetoresistive element bridge are electrically arranged with an output phase difference of 90 degrees to form a first magnetoresistive element. An amplitude circuit for providing an output of the element bridge and an output of the second magnetoresistive element bridge with an addition circuit and a subtraction circuit for equalizing the output of the addition circuit and the output of the subtraction circuit with the outputs of the first and second magnetoresistive elements A magnetic sensor provided with adjusting means.