JPH02150714A - Position detector - Google Patents

Abstract

PURPOSE:To highly accurately detect the position of a body to be detected irrespective of the position of the body by providing two sets of magneto- resistive elements, with each set being composed of two pieces of elements, and inputting different AC signals, and then, performing addition or subtraction on output signals. CONSTITUTION:Sine-wave voltages and cosine-wave voltages, between which a phase lag of 90 deg. exists, are applied across both ends of magneto-resistive elements 6-9 and signals are respectively outputted from intermediate sections between the elements 6 and 7 and between the elements 8 and 9. Moreover, permanent magnets 10 and 11 are arranged above the elements 6-9 and magnetic fluxes of the magnets 10 and 11 act on a rod 1 to be detected in the normal direction through the elements 6-9. The output signals from the intermediate sections of the above-mentioned elements 6-9 are subjected to addition or subtrac tion at an amplifier 12 which is an arithmetic means and the final output volt age is obtained. The final output becomes the same AC signal as the input signal and the phase difference can be detected with infinitesimal resolution, and thus, highly accurate position detection is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a position detection device that can detect the position of a detected object with high precision in a non-contact manner.

[Prior art and its problems]

2. Description of the Related Art Conventionally, there are position detection devices using magnetoresistive elements as shown in FIGS. 7 to 1O. The rod 20, which is the object to be detected, is made of a ferromagnetic material, and grooves 21 are formed at a constant pitch (P) on its circumferential surface. Therefore, high magnetic permeability portions 22 and low magnetic permeability portions 21 are provided alternately and at equal pitches on the circumferential surface of the rod 20 in the direction of movement thereof. A detection sensor 23 is arranged near the circumferential surface of the rod 20, and this detection sensor 23 has two magnetic resistance elements 24 and 25 arranged in a rod shape in the direction of movement of the rod 20. Magnetoresistive element 24,
25 is connected in a differential manner, and a constant voltage (2) is applied to both ends thereof, and the intermediate portion is taken out as an output terminal. A permanent magnet 26 is arranged above the magnetoresistive elements 24 and 25, and the magnetic flux is directed to the magnetoresistive element 24.
, 25 and act approximately perpendicularly to the rod 20.

Here, the operation of the position detection device will be explained.

First, in FIG. 7, the high magnetic permeability section 22 is located directly below the magnetoresistive element 24, and the low magnetic permeability section 21 is located directly below the magnetoresistive element 25, so the magnetic flux of the permanent magnet 26 is A magnetoresistive element 24, in which a large amount of magnetic flux flows through the resistance element 24, and a relatively small amount of magnetic flux flows through the magnetoresistive element 25,
As is well known, 25 has a characteristic that as the amount of magnetic flux passing through it increases, its resistance value increases in proportion to the amount of magnetic flux passing through it, so in the state shown in FIG. 7, the output voltage is ■. , t approaches 1, and becomes like point A in FIG.

Next, when the rod 20 (or the detection sensor 23) moves 174 pitches to the state shown in FIG.
, 25 are balanced. Therefore, since the resistance values of the remagnetoresistive elements 24 and 25 are the same, the output voltage V, ..., becomes the midpoint B, ie, Qv.

In this way, when moving 174 pitches to the 10th time in FIG. 9, the output voltage v0 and 0 points are respectively 0 points.

Changes to point D. In other words, the output voltage ■ within one pitch of the rod 20. , will change in a sinusoidal manner as shown in FIG.

In the case of the above-mentioned position detection device, since the displacement of the rod 20 is measured by detecting the magnitude of the output voltage V, which changes with the movement of the rod 20, the magnetoresistive element 24. When the approach distance between the rod 25 and the rod 20 changes, the magnitude of the output voltage V o a L also changes, resulting in a drawback that accurate position detection cannot be performed. Also, the output voltage ■. Since ulL changes in a sinusoidal manner, there is also the drawback that if only the voltage change is taken, a signal proportional to the moving distance cannot be obtained.

As a solution to the above-mentioned drawbacks, there is a method shown in FIG. 12. This position detection device uses two detection sensors similar to those shown in FIG. 7, and one detection sensor 30 is arranged to be shifted from the other detection sensor 31 by 1/4 pitch. As shown in FIG. 11, each detection sensor 30, 31 obtains an output voltage that changes sinusoidally as the detected object 20 moves, so the respective output voltages V+, V
If the waveform of * is shaped based on Ov, a rectangular wave as shown in FIG. 13 can be obtained.

According to this method, it is possible to detect the moving distance up to 1/4 pitch using the rising and falling signals of each rectangular wave, and the detection sensor 30.31
Even if the approach distance between the rod 20 and the rod 20 changes, the detection accuracy is not affected. However, the resolution is only 1/4 pitch, making highly accurate position detection impossible.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly accurate position detection device that is not affected by changes in the proximity distance between a magnetoresistive element and an object to be detected, and can have infinitely small resolution.

[Structure of the invention]

In order to achieve the above object, the present invention provides a body to be detected in which portions having different magnetic permeabilities are provided alternately and at equal pitches, and two portions in which portions having different magnetic permeabilities are arranged close to each other so as to be relatively movable in the pitch direction with respect to the body to be detected. 2&[l magnetoresistive elements and a permanent magnet arranged so that magnetic flux passes through the magnetoresistive elements and acts on the object to be detected in a substantially perpendicular direction, and the relative movement of both sets of the magnetoresistive elements is provided. The directional distance is 1 for an integral multiple of the above pitch.
The magnetoresistive elements in each set are connected in series with each other, so that a signal is input to both ends of each set of magnetoresistive elements, and a signal is output from the center of each set of magnetoresistive elements. In this position detection device, alternating current signals with time phases different by 90 degrees are input to both ends of each set of magnetoresistive elements, and the signals output from the center of each set of magnetoresistive elements are added or subtracted from each other. It is characterized by having means.

〔Example〕

FIG. 1 shows an example in which the position detecting device according to the present invention is applied to detecting the displacement of a rod 1. As shown in FIG.

The rod l is made of a ferromagnetic material as in the past, and high magnetic permeability parts 2 and low magnetic permeability parts 3 are provided on its circumferential surface alternately and at equal pitches (P) in the direction of movement. , rod 1
Two detection sensors 4.5 are arranged close to each other near the circumferential surface of the sensor.
Magnetoresistive elements 6, 7 and 8, 9 are arranged in a line in the direction of movement of the rod 1. The magnetoresistive elements 6.7 and 8.9 are connected in series, and the distance P between the magnetoresistive elements 6.7 and 8.9 is set to 1/2 pitch, and the distance between the detection sensors 4.5 and 8.9 is set to 1/2 pitch. The distance m is shifted by 1/4 pitch from an integral multiple of the pitch P. That is, m=NP±1/4P (CN: positive integer). In the example shown in FIG. 1, the settings are as shown in the following equation.

m=2P-1/4P Note that the magnetoresistive elements 6 to 9 have the same sensitivity coefficient α.

A sine wave voltage (±a sinωL) and a cosine wave voltage (±a sin ωL) and a cosine wave voltage (
±acosωt) is applied, and the output voltage V,
, V4 has been taken out. Permanent magnets io and tt are arranged above the magnetoresistive elements 6 to 9, and the magnetic poles are oriented so that the magnetic flux passes through the magnetoresistive elements 6 to 9 and acts on the rod 1 in a direction substantially perpendicular to the magnetoresistive elements 6 to 9. It is set.

Note that the AC voltage signal (a sinωL+a cosω
t) can be easily generated using a known quadrature oscillation circuit or the like.

The output voltages Vt and V4 are respectively input to the positive and negative inputs of a differential amplifier 12 (gain K), which is an example of arithmetic means, and the differential amplifier 12 outputs a voltage Vs
, Va, and calculate the final output voltage V 611 L
I am getting .

Here, the operation of the position detection device having the above configuration will be explained.

If the high permeability part 2 or the low permeability part 3 of the rod l is in the center of the magnetoresistive element 6.7, then the re-magnetoresistive element 6.
Since the resistance values of the rods 1 and 7 are equal, the output voltage , taken out from the center of the magnetoresistive element 6.7, is Ov, and the
When the high magnetic permeability part 2 or the low magnetic permeability part 3 shifts from the center of the magnetoresistive element 6.7, the re-magnetoresistive element 6.7
The resistance value becomes unbalanced, and the output voltage
As explained in FIG. 0, it changes sinusoidally in accordance with the displacement amount X of the rod 1. That is, the voltage (3) is expressed by the following equation.

V, =a a sinωt - cos(2πx/P
) Similarly, for the magnetoresistive element 8.9, a voltage (4) corresponding to the amount of deviation of the high magnetic permeability portion 2 or the low i3 magnetic percent portion 3 is applied.
is obtained, but the magnetoresistive element 8.9 is the magnetoresistive element 6.9.
Since it is shifted by 1/4 pitch from 7, the voltage ■4
The displacement phase is shifted by 1/2π with respect to V as shown in the following equation.

V4 = a a cosωt 1 sin (2πX/
P) These voltages Vs and Va are input to the differential amplifier 12, so its output ■. □ is a simple trigonometric function as shown in the following equation.

V. ,, -Ka α(sinωt -cos(2π
X/P)cosωt-5in(2πx/P)1=K
a a sin ((L)t -2πx/P) Figure 2 shows the input voltage a sin ωt and the output voltage ■. .

and the time phase shift T (=2
πx/P), it is possible to detect the absolute displacement X of the rod l within the range of one pitch. In other words, the resolution becomes infinitesimal. It goes without saying that if the number of pitches exceeds one, the linear displacement of the rod 1 can be measured incrementally by counting the number of pitches.

In addition, in the above embodiment, the voltages ■3 and ■4 are generated by the differential amplifier 12.
However, the same is true even if the sum of these voltages is calculated, and the only difference is whether the phase advances or lags by 2πIT/P. Moreover, ±acosω is applied to both ends of the magnetoresistive element 6.7.
t and ±a sinωt may be input to both ends of the magnetoresistive elements 8 and 9, respectively. In this case, the differential amplifier 12
The output of is the cosine function.

The object to be detected used in the present invention is not limited to a rod having a groove on its circumferential surface. For example, as shown in FIG. 3 and FIG. A low magnetic permeability material 15 such as copper foil may be embedded in the groove 14. In this case, the circumferential surface of the rod 13 can be made smooth, making it suitable as a rod for pneumatic or hydraulic cylinders. Moreover, since a large difference in magnetic permeability can be obtained, there is an advantage that sensitivity is improved.

In addition, FIGS. 5 and 6 use a disk 16 as the object to be detected, and thin films 17 made of a low magnetic permeability material are coated at 5 regular pitches on the upper surface of the outer circumference of the disk 16 made of a high magnetic permeability material. The rotational displacement of the disk 16 is detected. In this case, as shown in FIG.
All you have to do is place the .

Furthermore, in addition to forming high magnetic permeability parts and low magnetic permeability parts using materials with different magnetic permeability, it is also possible to form high permeability parts on the same material by locally treating the surface of the metal material with a laser or the like. A magnetic permeability portion and a low magnetic permeability portion may be formed.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, AC signals having a time phase different by 90 degrees are input to both ends of two sets of magnetoresistive elements connected in a differential type, and each set of magnetoresistive Since the signals output from the center of the element are added or subtracted by the calculation means, the output obtained by the calculation means is a simple AC signal similar to the AC signal that is the input signal. Therefore, by detecting the phase difference between these output signals, the relative displacement of the detected object can be detected with infinitesimal resolution, and a highly accurate position detection device can be realized.

Furthermore, even if the approach distance between the magnetoresistive element and the object to be detected varies, the errors can be canceled out by both sets of magnetoresistive elements, so even if the approach distance changes, the detection accuracy is not affected at all.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an example in which the position detection device according to the present invention is used to detect displacement of a rod, Fig. 2 is a waveform diagram of the input terminal and output voltage, and Fig. 3 is a perspective view of another example of the detected object. 4 is a partial sectional view thereof, FIG. 5 is a perspective view of still another example of the detected object, FIG. 6 is a sectional view showing the detection method, FIG. 7 to 10 are cross-sectional views showing the operation of a conventional position detection device, and FIG. 11 is an output signal waveform diagram thereof.
FIG. 12 is a sectional view of another conventional example, and FIG. 13 is an output signal waveform diagram thereof. 1... Rod (detected object), 2... High magnetic permeability part, 3
...Low permeability part, 4.5...Detection sensor, 6-9.
... Magnetoresistive element, 10.11 ... Permanent magnet, 12.
...Differential amplifier. Figure 1 Patent applicant Sankyo Boeki Co., Ltd. Agent Hidetaka Tsutsui Figure 3 Figure 7 Figure 4 Figure 6 Figure 8

Claims (1)

[Claims] A detected object in which portions with different magnetic permeabilities are provided alternately and at equal pitches, and two sets of magnetic resistors arranged close to each other so as to be movable relative to the detected object in the pitch direction. and a permanent magnet arranged so that a magnetic flux passes through the magnetoresistive element and acts on the object to be detected in a substantially perpendicular direction, and the distance in the relative movement direction of both sets of the magnetoresistive elements is equal to the pitch. The magnetoresistive elements in each set are connected in series with each other, and the signals are input to both ends of the magnetoresistive elements in each set. In a position detection device configured to output a signal, AC signals having a time phase different by 90 degrees are input to both ends of each set of magnetoresistive elements, and the signal output from the center of each set of magnetoresistive elements is input to both ends of each set of magnetoresistive elements. A position detection device characterized by comprising calculation means that add or subtract from each other.