JPH02120615A - Displacement quantity detection circuit - Google Patents

Abstract

PURPOSE:To provide a displacement quantity detection circuit conserved in the current consumption of a magnetoresistance element and made easy to adjust by stabilizing the potential at the connection point of two fixed high resistor and control resistor not changed in their resistance values by a magnetic field. CONSTITUTION:This displacement quantity detection circuit is constituted so that mechanical displacement quantity is converted to quantity of electricity by utilizing a magnetoresistance element changed in its resistance value according to the direction of a magnetic field and a bridge circuit 13 having the first and second magnetoresistance elements 1, 2 changed in their resistance values according to the direction of a magnetic field as one side and a fixed resistor 3 not changed in its resistance value according to the direction of the magnetic field and a control resistor 4 as the other side is provided while the connection point (b) of the fixed resistor 3 and the control resistor 4 is connected to a buffer means 5. The potential of the connection point (a) of the magnetoresistance elements 1, 2 is amplified on the basis of the output of the buffer means 5 by an amplifying means 6. A judge level is set on the basis of the output of the buffer means 5, and said judge level and the output of the amplifying means 6 are compared with the change quantity of the current passed through a voltage/current converter circuit 9 to obtain an output waveform of a duty ratio of 1 : 1.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention uses a displacement detection circuit, more specifically, a magnetoresistive element whose resistance value changes depending on the direction of a magnetic field, to convert a mechanical displacement into an electrical quantity. This invention relates to a displacement detection circuit for converting.

[Prior Art] Conventionally, in order to detect the amount of displacement due to linear movement or rotation of an object, an encoder device that optically or electrically detects the amount of displacement is used, as is well known.

However, this encoder device does not have the ability to detect extremely minute amounts of displacement. Therefore, in recent years, detection devices that convert mechanical displacements such as rotation angles into electrical quantities are capable of detecting extremely minute displacements, and do not have a mechanical contact mechanism. There is a need for something that does not wear out or generate noise, and one way to meet these demands is to use four magnetoresistive elements with high detection sensitivity, whose resistance value changes depending on the magnetic field, and to increase detection sensitivity. A detection means using a detecting body connected in a bridge shape has been proposed.

That is, this detection means has four magnetoresistive elements connected in a bridge shape, and two opposite sides of the bridge, like the rotation angle detection device disclosed in Japanese Patent Publication No. 60-46641. An operating voltage is applied to the voltage application terminal between them, and a potential difference is output between the signal output terminals between the two opposite sides, depending on the resistance position of the magnetoresistive element and always having a gradient in the same direction. I'm trying to take it out.

Next, the operation of a conventional rotational displacement m detection circuit using a magnetoresistive element assembled in this bridge will be explained in more detail with reference to FIGS. 8 to 10. Usually, this magnetoresistive element has low sensitivity, so four magnetoresistive elements 41 to 44 are connected to a bridge as shown in Fig. 8, and the output signal taken out is waveform shaped. It is designed to be used.

FIG. 9 shows the arrangement of magnetoresistive elements 41 to 44 with respect to the magnetized rotor 20 for detecting the rotational position of the object to be detected. In the magnetized rotor 2o, adjacent magnetic poles have the same polarity. It is engraved like this.

The four magnetoresistive elements 41 to 44 face the magnetization pitch λ of the celadon rotor 20 at a pitch of 41.43, 4.
The magnetoresistive elements 41 and 42 are arranged at a pitch of λ/2 in the order of 4.42, and therefore the magnetoresistive elements 41 and 42 located at both ends are spaced apart by (3/2)λ.

In the magnetoresistive elements 41 to 44 arranged in this way, when the magnetized rotor 20 of the object to be detected rotates, the magnetic field vector thereof changes, so that the output voltage changes in a sinusoidal manner as shown in FIG. g1 is the magnetoresistive element 41 to 44
The signal is obtained between the signal output terminals x and y (see FIG. 8) of the bridge formed by.

One signal output terminal X, which is the connection point between the magnetoresistive elements 41 and 4.2,
to the non-inverting input terminal of the operational amplifier 48 through
are connected to the inverting input terminal of the operational amplifier 48 via a resistor 46, respectively. Note that the magnetoresistive elements 41 and 4
The connection point 3 is connected to the power supply, and the connection point between the magnetoresistive elements 42 and 44 is connected to GND.

On the other hand, the operational amplifier 48 has resistors 46, 47 and N
The PN type 1-transistor 49 and tll are combined to form an amplifier, and the signal output terminal x of the bridge,
The human power signal obtained between y is amplified by a ratio determined by the ratio of the resistance value R4B''4□ of the resistor 46.47 with respect to the potential of the terminal X, and is supplied to one input terminal of the comparator 52 in the next stage. be done.

If the power supply voltage is VCC, the potential VZ of this input terminal is will be given.

The comparator 52 has a fixed resistor 5 at its other input terminal.
Since the judgment level V1 obtained by dividing the power supply voltage V by C and the adjustment resistor 51 is applied,
The adjustment resistor 51 is adjusted so that the potential change Vz of the one input terminal swings equally above and below the judgment level (1) as shown in FIG. Then, from the output terminal of the comparator 52, the rectangular wave output signal Ω2 shown in FIG.
You will be ignored.

[Problems to be Solved by the Invention] However, conventional methods amplify the signal obtained from the signal output terminal between such bridge-connected magnetoresistive elements and compare it with a judgment level to obtain a rectangular wave output. (1) Due to the nature of the magnetoresistive element itself, it is difficult to produce a high-resistance element, so if four magnetoresistive elements are used in a bridge connection in one detection circuit, the capacitance is limited. If there is only one power supply available, the current consumption will be large.

(2) In addition, to detect the direction of displacement of a displaced object, two identical detection circuits are used, and the magnetoresistive elements are placed relative to the magnetic body so that the phases of their output waveforms are shifted by 90 degrees. , the direction of displacement is detected from the phase advance of both output waveforms. However, in the case of the circuit shown in FIG. 8, the duty ratio of the output waveform changes depending on the judgment level of the comparator 52, so In order to make the phase difference of the output waveforms 90 degrees, it is necessary to adjust the adjustment resistor 51 of each circuit while observing both output waveforms so that the duty ratio of the output waveforms becomes exactly 1:1. ,
This is extremely difficult for workers.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, reduce current consumption in the magnetoresistive element, facilitate adjustment of the detection circuit, and provide a displacement detection circuit that is resistant to power supply noise.

[Means and effects for solving the problem] The displacement detection circuit of the present invention has a resistance value that changes depending on the direction of the magnetic field, and has first and second magnetoresistive elements connected in series as one side. a bridge circuit whose other side is a series connection of a fixed resistor and an adjustable resistor whose resistance value does not change depending on the direction; a buffer means connected to a connection point of the fixed resistor and the adjustable resistor; and the first and second magnetic resistors. An amplifying means for amplifying the potential at the connection point of the element by setting the output of the buffer means to 2;l, and a determination level based on the output of the buffer means, and comparing this determination level with the output of the amplifying means. The present invention is characterized by comprising a comparison means.

[Example] The present invention will be specifically described below with reference to the drawings. 1st
The figure is an electrical circuit diagram of a displacement amount detection circuit showing a first embodiment of the present invention.

In FIG. 1, a bridge circuit 13 is formed by a magnetoresistive element 1.2, a fixed high resistance 3 and an adjustment resistance 4, which are ordinary resistors whose resistance value does not change depending on the magnetic field and have the same temperature characteristics. A power supply voltage V is applied to the power supply terminal at the connection point between the resistance element 1 and the high resistance element 3, and the magnetoresistive element 2
The ground terminal at the connection point between and the adjustment resistor 4C is connected to the ground level. One signal output terminal a, which is the connection point between the magnetoresistive elements 1 and 2, is connected to an offset canceling resistor 12.
is connected to the non-inverting input terminal of amplification means 6 formed of a low offset type operational amplifier. The other signal output terminal, which is the connection point between the fixed high resistance 3 and the adjustment resistor 4, is connected to a non-inverting input terminal of a buffer means 5 formed of a low offset type operational amplifier. The potentials of the signal output terminals a and b are adjusted to be the same potential in the absence of a magnetic field. The buffer means 5 has its inverting input terminal connected to the output terminal C1 to form a unity gain amplifier. The output end C of the buffer means 5 is connected to the inverting input end of the amplifying means 6 via a resistor 7 having the same temperature characteristics whose resistance value does not change due to a magnetic field, and also connects the resistor 7 and its temperature characteristics to the inverting input end of the amplifying means 6. Resistor 8 whose resistance value does not change due to the magnetic field
It is connected to the output terminal d of the amplifying means 6 via the amplifying means 6. The output terminal of this amplifying means 6 is connected to one input terminal e of a voltage-current conversion circuit 9.

The other input terminal f of the conversion circuit 9 is connected to the output terminal C of the buffer means 5, and the output terminal g is connected to the input terminal of a comparison means 10 consisting of a current discrimination type comparator with hysteresis. The output terminal i of the comparison means 10 is connected to the input terminal of a delay circuit 11 having a certain output response delay, and an output signal is obtained from the output terminal 0 of the delay circuit 11. Further, another output terminal g of the delay circuit 11 is connected to another input terminal m of the comparison means 10, thereby forming a hysteresis changeover switch.

Note that the conversion circuit 9. The specific circuit configurations of each of the comparison means 10 and the delay circuit 11 are shown in FIG. 2, for example.

FIG. 3 shows the magnetic rotor 2 shown in a flat unfolded state.
FIG. 2 is a diagram showing the arrangement of the magnetoresistive element 1.2 with respect to FIG.

In the figure, the magnetized rotor 20 is made up of a plurality of magnets, arranged so that adjacent magnetic poles have the same polarity, and when the magnetized pitch is λ and an arbitrary integer is n, the magnetoresistive element The magnetoresistive cable 1 is connected to the magnetized rotor 20 so that the interval of 1°2 is −(n+1)λ.
．． 2 are arranged.

In the displacement detection circuit of the first embodiment configured as described above, first, the signal output terminal 'r-a (
1) and the potential Va of the fixed resistor 3. Potential vb of signal output terminal b (see Figure 1), which is the connection point of adjustment resistor 4
The first adjustment resistor 4 is varied so that the potentials are the same. When the magnetized rotor 20 rotates in this state, the magnetic vector due to the movement of the rotor 20 changes accordingly. In response to this change in the magnetic vector, the resistance value of the magnetoresistive element 1.2 changes, so the potential Va at the terminal a of the element 1.2 changes as shown in FIG. It changes in the form of a 17 sinusoidal wave with respect to the magnetic pitch λ (hereinafter, this will be referred to as iiJ variable potential Va). On the other hand, fixed high resistance 3. As shown in the figure, the potential vb of the terminal of the adjustment resistor 4 is at a constant level regardless of the rotation angle of the six-magnetic rotor 20 (hereinafter referred to as fixed potential vb), and this constant level of fixed potential vb The variable potential Va is distributed above and below with equal amplitude. Then, a variable potential V is applied sinusoidally with equal amplitude above and below a fixed potential V b at a certain level.
The relationship in which a is distributed is independent of the number of IC circuits in the subsequent stage; It is determined only by the bridge circuit consisting of the adjustment resistor 4. That is, as long as the adjustment resistor 4 is accurately adjusted, a variable potential Va that is distributed with equal amplitude above and below the fixed potential Vb can be obtained. The above-mentioned fixed high resistance 3 and adjustment resistance 4 can have a high resistance value by setting their resistance ratio equal to the resistance ratio of the magnetoresistive element 1.2 in the forced magnetic field, so this bridge circuit It is possible to reduce the current consumed.

The fixed potential Vb at a constant level generated at the signal output terminal is applied to the non-inverting input terminal of the buffer means 5 to undergo impedance conversion, and the stabilized fixed potential (hereinafter referred to as stabilized potential) is applied to the output terminal C. ) is output as Vc. Since the buffer means 5 constitutes a unity gain amplifier, the following formula holds true.

Vc-Vb The reason for using such a buffer means 5 is as follows. That is, in order to reduce the current consumed by the bridge circuit, high resistance is selected for the fixed high resistance 3 and the adjustment resistance 4 that constitute the other side of the bridge circuit, so that, for example, except for the buffer means 5, the Terminal and output terminal C in figure 1
This is to prevent a change in the current flowing through the resistor 7 from flowing into the adjustment resistor 4, resulting in a large effect on the potential change at the terminal, and preventing the fixed potential vb from being established.

The variable potential Va is the offset canceling resistor 12.
The stabilizing potential Vc is input to each of the amplifying means 6 via a resistor 7.

The variable potential Va is non-invertingly amplified based on the potential Vc. Therefore, the relationship between the amplified signal Vd output from the amplification means 6 and the variable potential Va is as shown in the following equation.

FIG. 5 is a waveform diagram showing the relationship among the variable potential Va applied to the non-inverting input terminal of the amplifying means 6, the stabilizing potential Vc applied to the inverting input terminal, and the amplified signal Vd output from the output terminal d. It is. In the figure, if the amplitude of the variable potential Va is Aa and the amplitude of the amplified signal Vd is Ad, the following formula holds true.

The amplified signal Vd thus obtained and the stabilized potential Vc are input to the input terminal e of the voltage-current conversion circuit 9 in the next stage.
When applied to f, the conversion circuit converts the voltage change of the amplified signal Vd with respect to the stabilized potential Vc into a current change IA.
Converted to Ig. This converted current 1g is calculated by comparing means 1 consisting of a current discrimination type comparator with hysteresis.
0, and the comparison means 10 compares two reference currents Ir
l''r2 and a shaped square wave signal Vi is output from the output terminal i.

FIG. 6 is a waveform diagram illustrating the comparison operation in the comparison means 10, in which the vertical axis shows the amplified signal V with respect to the time T on the horizontal axis.
d and a converted current of 1 g for the blower l-L. In the figure, Igr is the instantaneous value of the converted current 1g at the time when the instantaneous value of the amplified signal Vd becomes equal to the above-mentioned stabilizing potential Vc, whose potential does not change even if the magnetic field vector changes, and the instantaneous value of the converted current 1g is Igr. The converted current 1g at the time when the potential (Vc+u) and (Vc-u) shifted by mu are (Igr+u) and (Igr-w)
Then, Irl−Igr+u! Let's set it as r2-1gr-w. Then, since the amplified signal Vd should have equal amplitude above and below the stabilizing potential Vc, the determination level in the comparing means 10 is set to the above-mentioned reference current 'rl''r2. The shaped output signal Vi obtained from the output terminal i of 10 is
With respect to the waveform change of the amplified signal Vd, the ratio of the "H" level time T1 to the "L" level time T2, that is, the duty ratio becomes a signal of 1=1.

The above-mentioned shaped output signal Vi is supplied to the input terminal j of the delay circuit 11 at the next stage. The delay circuit 11 uses a time constant circuit in which a resistor and a capacitor are connected in series to convert the input shaped output signal Vi from the 1H" level to the "L" level or from the "L" level to the "H" level. This delay circuit is configured so that an output signal is output after a certain time delay in response to a change.The delay circuit 11 also includes a reference current Irl''r2 that provides the judgment level of the comparison means 10. It also has a function of sending a signal for switching from the other output terminal g to the input terminal m of the comparison means 10 in synchronization with the change in the output terminal.

In the first embodiment described above, a comparison means 10 with hysteresis and a delay circuit 11 are used, and a time constant circuit having a resistor and a capacitor connected in series is used to obtain the delay time. Therefore, even if there is power line noise generated from a drive means such as a motor, the noise will be more resistant to the hysteresis compared to the case where the comparator judgment level is simply set by dividing the resistance, and the time constant circuit Since it is absorbed by the circuit, there is no risk of it having an adverse effect on the normal operation of the circuit. Further, it is possible to set the duty ratio of the shaped output signal to 1:1 without adjusting the circuit equally.

Note that when the power supply line noise is negligibly small, it is not necessary to provide the comparison means 10 consisting of a current discrimination type comparator with hysteresis characteristics, and the reference current Irl"r2 that provides two judgment levels is I rl -1r2- 1 gr, and the delay circuit 11 can be omitted.

FIG. 7 is an electrical circuit diagram of a displacement detection circuit showing a second embodiment of the present invention. This second embodiment differs greatly from the first embodiment in that a voltage comparison type is used instead of a current comparison type for the comparator as a comparison means, which allows the current required in the first embodiment to be -Voltage conversion circuit 9
becomes unnecessary.

Note that the same constituent members in the second embodiment shown in FIG. 7 as those in the first embodiment are designated by the same reference numerals, and a description thereof will be omitted.

In FIG. 7, reference numeral 21 is a low offset type operational amplifier, and 22 is a comparison means consisting of a voltage comparison type comparator with hysteresis.

23 is a delay circuit having a certain output response delay; 24
．． 25 is a constant current source, 26.27 is an analog switch, 2
8 is a resistor whose resistance value does not change even if the magnetic field changes.

The signal output terminal, which is the connection point between the fixed high resistance 3 and the adjustment resistor 4 that constitute the other side of the bridge circuit, is also connected to the non-inverting input terminal of the operational amplifier 21 that generates the hysteresis voltage of the comparison means 22. .

The inverting input terminal of the operational amplifier 21 is connected to its output terminal t via a resistor 28, and is also connected to one input terminal 0 of the comparing means 22. A constant current source 24 is connected to the inverting input terminal of the operational amplifier 21 via an analog switch 26 to a power supply terminal, and a constant current source 25 is connected to a ground terminal via an analog switch 27.

The output terminal t of the operational amplifier 21 and the output terminal d of the amplification means 6
are connected to the input terminals o and n of a voltage comparison type comparison means 22 with hysteresis, respectively. The output terminal p of the comparison means 22 is connected to the input terminal q of a delay circuit 23 having a certain output response delay, and one output terminal S of the delay circuit 23 is connected to the low active control input terminal of the analog switch 26. and the high active control input terminal of the analog switch 27. Therefore, when the output terminal S of the delay circuit 23 is at the "L" level, the analog switch 26 is turned on, and when the output terminal S is at the H" level, the analog switch 27 is turned on. A shaped output signal is output.

In the displacement detection circuit of the second embodiment configured in this way, the bridge circuit 13 has a fixed potential Va of the signal output terminal a of the magnetoresistive element 1.2 and a fixed high resistance 3.2, as described above. The variable potential vb of the terminal of the adjusting resistor 4 is adjusted to the same potential by 1'72 in the absence of a magnetic field. Therefore,
When arranged at intervals as in the first embodiment, a variable potential Va and a fixed potential Vb as shown in FIG. 4 are obtained in response to changes in the magnetic field vector.

In this way, the fixed potential (b) and the variable potential Va are each buffered by the buffer means 5. It will be input to the amplification means 6. The fixed potential vb is input to the buffer means 5 and stabilized potential Vc
get. At this stabilized potential rate, an amplified signal Vd is obtained by the amplifying means 6 having a non-inverting amplifying amplifier configuration (see FIG. 5).

The above relationship is expressed by the following formula.

Further, the fixed potential vb is also applied to the non-inverting input terminal of the operational amplifier 21. Since a resistor 28 is connected to 181 between the inverting input terminal and the output terminal t of the operational amplifier 21, the resistance value of the resistor 28 is R28, and the current value of the constant current source 24 is
1. Assuming that the current value of the constant current source 25 is 12, the following relational expression is established between the hysteresis voltage Vt at the output terminal t and the fixed potential vb due to the deafness of the analog switches 26 and 27.

That is, when the output terminal S of the delay circuit 23 is at "L" level, the analog switch 26 is on, and the analog switch 27 is off, Vt1-Vb-R,, 8·Il. “At H° level,
Turn off analog switch 26 and turn off analog switch 27.
When is on, V t2 - V b + R28' I 2 This vtl
'Vt2 becomes the determination level of the comparison means 22, which will be described later.

here,! , -12-■, the lower judgment level Vt
1 and the upper judgment level "12" are potentials shifted by the same width level R28·I with respect to the fixed potential vb.The amplified signal Vd mentioned above also becomes an output having an equal amplitude with the fixed potential vb (-Vc) as a reference. Therefore, if the judgment level V11VL2 in the case of I i -12 is taken as the judgment level of the comparison means 22, the output waveform Vp obtained from the output terminal p of the comparison means 22 has a duty ratio of 1 with respect to the waveform change of the amplified signal Vd. :1 is obtained as a shaped output signal.

The output signal Vp obtained in this way is supplied to the input terminal q of the next-stage delay circuit 23, and the delayed outputs Vr and Vs, which are delayed for a certain period of time, are output to the output terminal r of the delay circuit 23,
Obtained from s. Of these, Vs is used as a signal for switching the analog switches 26 and 27.

As described above, if this circuit is used, power line noise generated by a driving body such as a motor can be removed by hysteresis and delay as in the first embodiment, and the duty ratio of the shaped waveform can be set to 1=1. This provides a displacement amount detection circuit that can perform

Note that, similarly to the first embodiment, when power supply noise etc. are negligibly small, the operational amplifier 21, resistor 28, constant current #, 2, which determines the determination level of the comparing means 22,
4, 25, the analog switches 26, 27, and the delay circuit 23 may be omitted, and in this case, the input terminal O of the comparison means 22 may be connected to the output terminal C of the buffer means 5.

In each of the above embodiments, at least one buffer means is provided to stabilize the potential at the connection point of two resistors, the fixed high resistance whose resistance value does not change due to the magnetic field and the adjustable resistance,
Comparison means for non-inverting amplifying the connection point potential of the magnetoresistive element using the output of the buffer means as a base, and comparing this amplified output and the reference output of the buffer means with a judgment level having a certain width of hysteresis. The output of this comparison means is connected to a delay circuit which uses human power and has a delay in response to changes in the input. Therefore, the duty ratio of the shaped output becomes 1:1 by simply making the connection point potential of the magnetoresistive element equal to the connection point potential of the fixed high resistance and the adjustment resistor in the absence of a magnetic field, and the above circuit can be used in two phases. In addition, the hysteresis and duty ratio can also serve as noise countermeasures.

[Effects of the Invention] As described above, the present invention has the remarkable effect of realizing a displacement detection circuit that can reduce the current consumed by the magnetoresistive element and is extremely easy to adjust. be done.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram of a displacement detection circuit showing a first embodiment of the present invention, and FIG. 2 is a voltage-current conversion circuit shown in FIG. 1. Specific electric circuit diagrams of the comparator and the delay circuit, FIG. 3 is a diagram showing the arrangement of the magnetic resistance elements with respect to the magnetic pole positions of the magnetic rotor developed and drawn in a plane, and FIG. FIG. 5 is a waveform diagram depicting the variable potential Va at one connection point of the bridge circuit and the fixed potential Vb at the other connection point in relation to the magnetic pole arrangement of the magnetized rotor in the example displacement detection circuit. , a waveform diagram showing the relationship between the input and output signals of the amplification means in the displacement detection circuit of the first embodiment, and FIG. 6 explains the operation of the comparison means in the displacement detection circuit of the first embodiment. 7 is an electric circuit diagram of a displacement detection circuit showing a second embodiment of the present invention, FIG. 8 is an electric circuit diagram showing an example of a conventional displacement detection circuit, and FIG. 9 is a waveform diagram. FIG. 10 is a diagram showing the arrangement of the bridge-connected magnetoresistive elements in the detection circuit of FIG. 8 above with respect to the magnetic pole positions of the magnetized rotor developed and drawn on the bottom surface. FIG. 3 is a waveform diagram showing the relationship between the signal obtained between the opposing points X and y of the bridge circuit and the comparator output signal and the magnetic pole position of the magnetized rotor, which is developed and drawn in a plane.

Claims (1)

[Claims] (1) The resistance value changes depending on the direction of the magnetic field, and one side is the first and second magnetoresistive elements connected in series, and the other is a series connection of a fixed resistor and an adjustable resistor whose resistance value does not change depending on the direction of the magnetic field. a bridge circuit as a side; a buffer means connected to a connection point between the fixed resistor and the adjustment resistor; and a potential at a connection point between the first and second magnetoresistive elements, with the output of the buffer means as a reference. A displacement detection circuit comprising: amplification means for setting a determination level based on the output of the buffer means, and comparison means for comparing the determination level with the output of the amplification means.