JPH03262920A - Contactless displacement sensor - Google Patents

Abstract

PURPOSE:To detect the quantity of position displacement and the quantity of angular displacement at the same time by one sensor by modulating magnetic fields which are produced by two magnets with different frequencies, and detecting the resistance variation of a magneto-resistance element as voltage variation. CONSTITUTION:The leak generated when pieces of main magnetic flux from a couple of fixed magnets 51 and 52 pass magnetic metal pieces 53 and 54 intersects a sense current is flowing in an MR element 61 at right angles, and its extent is maximum nearby the magnets 51 and 52 and minimum almost in the middle between the magnets 51 and 52. When a sensor part 55 is moved toward the magnet 51, a 1st magnetic field B51 operating on the element 61 increases, so the resistance value of the element 61 varies. Consequently, the quantity of variation in the relative position between a magnetic circuit 50 and the sensor part 55 is detected as variation in resistance value. When a frequency-modulated exciting current is supplied to electromagnets 57 and 58 on the sensor part 55, the electromagnets 57 and 58 are changed in polarity alternately every second and pieces of magnetic flux which change in direction with frequency are produced from those magnetic poles.

Description

[Detailed Description of the Invention] [Summary] Regarding a non-contact displacement sensor, the purpose is to simultaneously detect the amount of positional displacement and the amount of angular displacement with one sensor. 2 magnets and
a first magnetic field modulating means that alternately inverts the polarity of the first magnet at a first frequency;
a second magnetic field modulating means that alternatingly inverts at a second frequency different from the frequency of the first magnet and the second magnetic field generated from the first magnet and the second magnet; a magnetoresistive element that captures a change in resistance value as a change in resistance value; a conversion means that converts the change in resistance value of the magnetoresistive element into an electrical signal; and extracting means for extracting and outputting each as a first extracted signal and a second extracted signal.

[Industrial application field]

The present invention relates to a non-contact displacement sensor, and particularly to a ferromagnetic metal resistance element (MR element).
The present invention relates to a non-contact displacement sensor using a magnetoresistive element such as a semiconductor magnetoresistive element or a Hall element.

In recent years, with the development of the information society, industrial equipment, office equipment,
Demand for various sensors that can input data directly into computers is increasing in various fields such as automobiles. For example, a non-contact displacement sensor using a magnetoresistive element has excellent interfacing with a computer because it does not cause problems such as wear or electrical noise. In particular, devices using MR elements have temperature characteristics that are more than an order of magnitude better than those using InSb elements, and have high magnetic field sensitivity at low magnetic fields. It also has the advantage of being able to adopt a manufacturing process and be miniaturized.

As shown in FIG. 8, in the MR element, when a magnetic flux B crossing the current i is applied to a ferromagnetic thin film 10 through which a unidirectional current (sense current i) is passed, the resistance between the terminals of the ferromagnetic thin film 10 increases. The so-called magnetoresistance effect (magnetoresistance effect) whose value changes
sistance effect).
An example of its application is shown below.

[Conventional technology]

That is, FIG. 9 shows a conventional example of a displacement sensor using the MR element 16, which detects the amount of positional displacement. In this sensor, a pair of magnets 11 and 12 with opposite polarities (N, S) are placed facing each other. Furthermore, these magnets 11 and 12 are coupled with magnetic metal 13 and 14 to form a magnetic circuit 15, and an M
The R element 16 is arranged movably.

In such a configuration, the main magnetic flux 17.18 generated from the magnet 1112 passes through the inside of the magnetic metal 13.14, but at this time, a leakage magnetic field (schematically indicated by four arrows 19) is generated in the closed space of the magnetic opening 1115. ~22) is generated, and the leakage magnetic field 19-22 is maximum in the vicinity of the magnet 11.12 and minimum between the pair of magnets 11.12. Now, when the MR element I6 is moved, the resistance value of the MR element 16 changes as the strength of the magnetic field acting on the MR element 16 changes, and the amount of positional displacement can be detected from this change.

By the way, the amount of angular displacement can be detected by applying this configuration. For example, in FIG. 10, a magnetic circuit 3 having a configuration similar to that of FIG. 9 rotates integrally with the rotating shaft 30.
If the MR element 33 fixed to the case 32 is placed in the closed space of 1, the relative rotational displacement (angular displacement) between the case 32 and the rotating shaft 30 can be detected as a change in the resistance value of the MR element 33.

[Problem to be solved by the invention]

However, since such conventional non-contact displacement sensors detect either the amount of positional displacement or the amount of angular displacement, it is necessary to prepare two types of sensors for each application. If the positions are detected together, there are problems such as a cost disadvantage and a complicated mechanism.

The present invention was made in view of these problems, and
The purpose is to simultaneously detect the amount of positional displacement and the amount of angular displacement with one sensor.

[Means to solve the problem]

In order to achieve the above object, the present invention, as shown in FIG. .4
a first magnetic field modulating means 44 that alternately inverts the polarity (N, S) of 1 at a first frequency f1, and the second magnet 42.43.
a second frequency f2 whose polarity is different from the first frequency f;
a second magnetic field modulating means 45 which is alternately inverted, and a first magnetic field B4°, B41 and a second magnetic field B4□, generated from the first magnet 40.41 and the second magnet 42.43.
A magnetoresistive element 46 that is interposed within B43 and captures changes in these magnetic fields as changes in resistance value, and the magnetoresistive element 4
converting means 47 for converting the change in resistance value of 6 into an electric signal; extracting the first frequency f and the second frequency f2 from the electric signal E; S
, and an extraction means 4 outputting it as a second extraction signal S2.
9.

Here, the first magnetic field B4°, Bo and the second magnetic field B4
The modulation frequencies (f,, rz) of □ may be different from each other. For example, if fl is xHz, f2 is x
y) lz other than Hz. One of x and y may be zero.

[Effect]

FIG. 2 is a diagram showing the state of the magnetic field acting on the magnetoresistive element 46. In this figure, when the magnetoresistive element 46 is located approximately in the middle of the first magnet 40.41 (as shown by the solid line), the first magnet 40.4
1 (magnetic flux is expressed as a magnetic field for convenience) B4 B41 and the magnetic field from the second magnet 42.43 B4□, B,
3 is working. If the sense current inside the magnetoresistive element 46 flows in the longitudinal direction, B
Only 4°, B41 is orthogonal, but 84°, B at this position
41 are in opposite directions and cancel each other out, so the resistance value of the magnetoresistive element 46 does not change.

Now, if the magnetoresistive element 46 moves by Δl, 84° in the moving direction increases, and as a result, B4, which has f1 strength,
A change corresponding to ° appears in the resistance value. Further, if the magnetoresistive element 46 rotates by Δθ, the sense current becomes B4
□, B with rztc as a result of slightly intersecting with BI3
, 2, a change corresponding to BI3 appears in the resistance value.

On the other hand, considering the case where these moving displacements and rotational displacements occur in combination, if f,>f, then the magnetoresistive element 4
6 resistance value has f, component B. and B4 with f2 configuration
□, changes corresponding to BI3, and f.

=0, fl=zlz, Bo changes with frequency f2, 84! , BI3 changes by twice fz (2zHz). Therefore, by converting the change in the resistance value of the magnetoresistive element 46 into an electrical signal and then separating and extracting the two frequency components, f2, the amount of positional displacement and the amount of angular displacement can be detected simultaneously.

〔Example〕

Hereinafter, the present invention will be explained based on the drawings.

3 to 7 are diagrams showing an embodiment of the non-contact displacement sensor according to the present invention, in which an MR element (magnetic resistance element) is attached to a magnetoresistive element.
This is an example using a torsistive eiement.

To explain the configuration, in FIG. 3, 50 is a magnetic circuit. The magnetic circuit 50 combines a pair of fixed magnets (first magnet, first magnetic field modulating means) 51.52 that are spaced apart with opposite polarities (N, S) and a pair of fixed magnets 51.52. The sensor part 55 is housed inside the closed space, and the sensor part 55 is shown in the direction of arrow A.
Hold it so that it can be moved in the direction shown.

As shown in FIG. 4, the sensor unit 55 includes a pair of electromagnets (second magnets) on a first substrate 56 that is only allowed to move.
57 and 58, a shaft 59 that moves and is allowed to rotate integrally with the first substrate 56, and a second substrate 60 attached to the shaft 59. It is configured by placing an MR element (magnetoresistive element) 61 thereon. A pair of electromagnets 57 and 58 are spaced apart with their polarities facing the same direction, and their polarities are alternately reversed in accordance with the frequency of an excitation current iz (described later). Note that N and S in parentheses after the polarities N and S represent alternating changes.

In FIG. 4, 62 indicates a sense current is applied to the MR element 61.
A first current source 63 supplies a pair of electromagnets 57.5
8 is a second current source (second magnetic field modulation means) that supplies an excitation current iz modulated at a predetermined frequency fo (however, fo > 0 Hz); A detection circuit (conversion means) 65 detects a component (Sa) of frequency fo from the detected electrical signal EiO.
and a filter circuit (extraction means) for extracting components (Sb) other than f'o.

Here, the MR element 61 is formed into a single element by laminating a permalloy magnetic layer, an adhesion layer, a conductive layer, and a protective film on a silicon wafer substrate whose surface is oxidized, as shown in FIG. It is constructed by connecting four single elements 61a to 61d in a bridge shape. A pair of opposing single elements 61a and 61C, which are blacked out in the figure, have positive output characteristics with respect to the magnetic field, and the remaining two single elements 61b and 61d have negative output characteristics. In this way, magnetic field sensitivity can be improved approximately four times as compared to an MR element composed of one single element. Note that unbalanced voltage due to variations in resistance values of each single element that is a bridge element may be adjusted by pattern trimming using a laser.

Next, the effect will be explained.

The main magnetic flux from a pair of fixed magnets 5L 52 is a magnetic metal 53
．． 54 (hereinafter referred to as the first
The magnetic field (B, expressed as BSt) is perpendicular to the sense current is flowing in the MR element 61, and its magnitude is maximum near the fixed magnet 51.52, and the magnitude is maximum near the fixed magnet 51.5.
The minimum value is approximately halfway between 2 and 2.

Now, when the sensor unit 55 is moved closer to one of the fixed magnets 51, the first magnetic field BS+ acting on the MR element 61
changes in the increasing direction, and the resistance value of the MR element 61 changes with this change. Thereby, the amount of displacement in the relative position between the magnetic circuit 50 and the sensor section 55 is detected as a change in resistance value.

Here, the frequency f is applied to the electromagnets 57 and 58 on the sensor section 55.
When an excitation current iz modulated by o is given, the electromagnet 57.5
8 is alternately reversed at a rate of re times per second, and a magnetic flux (hereinafter referred to as a second magnetic field and expressed as BSt and Bse) whose direction changes at a frequency fO is generated from this magnetic pole.

FIG. 6 is a diagram showing the state of the first magnetic field and the second magnetic field Els+, 8%g, BSt, B, ll acting on the MR element 61. In this figure, a first magnetic field BSI, B5□ from a pair of fixed magnets 51.52 is orthogonal to the sense current is, and a second magnetic field BSI, B5 from a pair of electromagnets 57.58
S? , 13sa are parallel to the sense current is.

When the MR element 61 is located approximately in the middle of the fixed magnets 51 and 52 (the position shown in the figure), the first magnetic fields BSI, BS
Since Z cancel each other, the second magnetic field BS
? , E3ss is parallel to the sense current is, so M
No change in resistance value occurs in the R element 61.

Now, move the MR element 61 and, for example, move the MR element 61 to one fixed magnet 51.
When the MR element 61 approaches , BSt of the first magnetic field perpendicular to the sense current is becomes stronger, so that the MR element 61 changes its resistance value according to its own movement amount.

Alternatively, when the MR element 61 is rotated, the second magnetic field B
Since S'l and E3sa have a cross relationship with the sense current is, the MR element 61 changes its resistance value according to its own rotational displacement amount.

Here, while the direction of the magnetic flux of the first magnetic field B, Bsg is always in one direction (that is, zero frequency modulation),
Second magnetic field BS? , BS8, the direction of the magnetic flux is at the frequency f
It is alternately inverted at O (that is, frequency fO modulation),
As a result, the internal magnetization direction of the MR element 61 also changes to the frequency fO.
The change is reversed.

Therefore, while the resistance value change due to positional displacement changes at frequency fO, the resistance value change due to angular displacement changes at frequency 2r.
It will change at O.

Therefore, if the resistance change of the MR element 61 is converted into an electrical signal Ei by the detection circuit 64, and the frequency fO acid component and the frequency 2fO component are separated and extracted from the electrical signal EiO by the filter circuit 65, each frequency component The amount of positional displacement and the amount of angular displacement can be detected simultaneously from the magnitude of .

As described above, in this embodiment, the first magnetic field 13s generated from the fixed magnet 51.52 and the electromagnet 57.53, respectively.
+, BSZ, second magnetic field BS? , 13sa, an MR element 61 that enables positional displacement and angular displacement is arranged, and the excitation current iz of the electromagnet 57.58 is set at a frequency fo.
The resistance value of the MR element 61, which changes according to changes in the magnetic field, is converted into an electrical signal Ei, and frequency #! is generated from this electrical signal EiO. 1. Since the fO precept and the number of components 2fO precept are separated and extracted, the positional displacement can be detected using the first magnetic field BS+, E3sz, and the second magnetic field BS? , Else can detect angular displacement. Therefore, it is possible to simultaneously reproduce two pieces of displacement information from the extraction results corresponding to the modulation frequency of each magnetic field.

In addition, in this embodiment, fixed magnets 51 and 52 are used as the first magnet.
is used, but it is not limited to this, and an electromagnet may also be used.

In short, it is sufficient to generate a magnetic field modulated at a frequency different from the frequency (fo in this embodiment) that modulates the magnetic field of the second magnet (electromagnets 57 and 58 in the embodiment). Incidentally, when a fixed magnet is used as in this embodiment, the magnetic field is modulated at zero frequency, so the first magnetic field modulation means is included in the fixed magnets 51 and 52.

Further, the positions of the electromagnets 57 and 58 as the second magnets are not limited to the above embodiments. For example, as shown in FIG. 7, electromagnets 57a and 58a may be positioned between a pair of fixed magnets 51 and 52 and the MR element 61.

In this case, the pair of electromagnets 57a, 58a are arranged so that the polarities of the opposing surfaces of the electromagnets 57a, 58a are opposite.

That is, they are arranged so that their polarities are the same in the arrangement direction. Alternatively, the electromagnets 57 and 58 may be arranged so that the direction of the magnetic field and the direction of the sense current is are orthogonal (orthogonal here means non-parallel). For example, an arrangement where a magnetic field Ba of frequency fa (assumed to be a magnetic field that provides positional information) and a magnetic field Bb of frequency fb (fa≠fb) (assumed to be a magnetic field that provides angular information) are applied to the MR element in parallel. When this is adopted, since the magnetization direction of the MR element is constant, the positional information is outputted as fa and the angular information is outputted as fb, so that positional displacement and angular displacement can be detected simultaneously.

Furthermore, in the above embodiment, an MR element (ferromagnetic metal resistance element) 61 is used as the magnetoresistive element 46, but even if
It may also be a Hall element or a semiconductor magnetoresistive element. In short, any device that can sense changes in the magnetic field is sufficient.

〔Effect of the invention〕

According to the present invention, each magnetic field generated from two sets of magnets is modulated at a different frequency, the resistance change of a magnetoresistive element placed within each magnetic field is detected as a voltage change, and the modulation frequency is determined from the voltage change. Since the corresponding frequency components are extracted, the amount of positional displacement and the amount of angular displacement can be detected simultaneously with one sensor.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle configuration of the present invention, FIG. 2 is a diagram explaining the principle of the present invention, FIGS. 3 to 7 are diagrams showing an embodiment of the non-contact displacement sensor according to the present invention, and FIG. A configuration diagram including the magnetic circuit and the sensor section, FIG. 4; a configuration diagram of the main part including the other sensor section, FIG. 5 a configuration diagram of the MR element, and FIG. 6 showing the magnetic field acting on the MR element. 7 are diagrams showing other examples of arrangement of electromagnets. Figures 8 to 10 are diagrams showing conventional examples, and Figure 8 is the M
FIG. 9 is a diagram illustrating the principle of the R element, FIG. 9 is a configuration diagram of its position displacement sensor, and FIG. 10 is a configuration diagram of its angular displacement sensor. 48-- Extraction means, 51.52... Fixed magnet (first magnet, first magnetic field modulation means), 57.58... Electromagnet (second magnet), 61・・・
...MR element (magnetoresistive element), 63...
Second current source (second magnetic field modulation means), 64...
- Detection circuit (conversion means), 65... Filter circuit (extraction means). 40.41--First magnet, 42.43--Second magnet, 44--First magnetic field modulation means, 45...
・Second magnetic field modulation means, 46... Magnetoresistive element, 47... Conversion means, Fig. 2 Fig. 4 Fig. λS - Configuration diagram of the MR element of the embodiment Fig. 5 shows another example of the arrangement of electromagnets Fig. 7 is an explanatory diagram of the principle of a conventional MR element Fig. 8 Fig. 10 shows the configuration of a conventional angular displacement sensor

Claims (1)

[Scope of Claims] a) two pairs of first and second magnets that are spaced apart and facing each other, and b) a first magnetic field modulation means that alternately inverts the polarity of the first magnet at a first frequency. c) a second magnetic field modulating means for alternating the polarity of the second magnet at a second frequency different from the first frequency; and d) generated from the first magnet and the second magnet. 1st
and a second magnetic field, and captures changes in these magnetic fields as changes in resistance; e) conversion means for converting changes in resistance of the magnetoresistive element into electrical signals; ) Extract the first frequency and second frequency components from the electrical signal, and separate them into the first extracted signal and the second frequency component, respectively.
A non-contact displacement sensor comprising: an extraction means for outputting an extraction signal as an extraction signal.