JPH10185507A - Position detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove harmonic components contained in the positional information of a scale. SOLUTION: A magnetic sensor head 14 reads in positional information varying periodically with a basic wavelength λ written in a scale 10. The magnetic sensor head 14 comprises two reluctance element groups 22, 24 including first, second and third magnetoresistive elements 16, 18, 20 delivering the positional information in the form of a specified signal. The second and third magnetoresistive elements 18, 20 are arranged on the opposite sides of the first magnetoresistive element 16 at an interval of δwhile being connected in series. N-order harmonic can be removed when a condition represented by a following expression r+2cos(2nπδ/λ)=0 (n is an odd number of 3 or above) where, r is the output ratio between the first reluctance element 16 and the second and third magnetoresistive elements 18, 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position measuring instrument for measuring a position by calculating a relative movement amount with respect to a scale on which position information that periodically changes in a length direction is written.

[0002]

2. Description of the Related Art A detecting element for detecting position information is relatively moved with respect to a scale on which position information that changes periodically in the length direction is written, and a relative movement between the scale and the detecting element is performed based on a change in the detected value. Position measuring devices that calculate an amount and measure a position are known. For example, such a measuring device includes a magnetic scale magnetized at a predetermined interval and a magnetic position measuring device that detects a change in a magnetic field based on the magnetization by a magnetoresistive element.

[0003]

In a position measuring instrument using a scale as described above, the periodic change of the position information often includes not only a fundamental wavelength component but also a harmonic component. There is a problem that high detection accuracy cannot be obtained due to the harmonic components.

The present invention has been made to solve the above-mentioned problem, and has as its object to provide a position measuring instrument capable of detecting position information from which harmonic components have been removed.

[0005]

In order to achieve the above-mentioned object, a position measuring device according to the present invention detects a scale on which position information periodically changing at a fundamental wavelength λ is written, and the position information, A detection element group including first, second, and third detection elements that output a predetermined signal, wherein the second and third detection elements are arranged at both sides of the first detection element with an interval δ; A detection element group that outputs a sum of outputs of the second and third detection elements, and a relative movement amount calculation unit that calculates a relative movement amount with respect to the scale based on an output of the detection element group, The output of the first detecting element and the second
And when the output ratio of the third detection element is r,

R + 2 cos (2nπδ / λ) = 0 (n is 3
(Odd number).

When this condition is satisfied, it is possible to remove the n-th harmonic.

Further, a detection element bridge can be formed by using two of the detection element groups, and two detection element bridges can be arranged with a phase difference of λ / 4. By forming the detection element bridge, a detection signal having a large SN ratio can be obtained. Further, by arranging the two detection bridges with a phase difference of λ / 4, it is possible to obtain a resolution of a wavelength λ or less.

When removing the third harmonic, the interval δ can be set to λ / 8 and the output ratio r can be set to √2.

[0009]

Embodiments of the present invention (hereinafter, referred to as embodiments) will be described below with reference to the drawings. FIG. 1 shows a main configuration of a magnetic position measuring device according to the present embodiment. The scale 10 has a magnetic pole 1 with a period λ in the longitudinal direction.
2 are arranged. A magnetic sensor head 14 for detecting a magnetic field formed by the magnetic poles 12 is arranged to face the scale 10. The magnetic sensor head 14 has a first magnetoresistive bridge 26 composed of two magnetoresistive element groups 22, 24 having three magnetoresistive elements 16, 18, 20, respectively. It has the same configuration, and has a second magnetoresistive bridge 28 that is arranged at a λ / 4 offset from the first magnetoresistive bridge 26 in the length direction. The first and second magnetoresistive bridges 26 and 28 differ only in the position where they are arranged. In the following description, only the first magnetoresistive bridge 26 will be referred to, and the second magnetoresistive bridge 28 will be described. Description is omitted.

The first magnetoresistive bridge 26 has a first
And the second magnetoresistive element groups 22 and 2 have the same configuration and are arranged at an interval of λ / 2. For the description of the individual configurations of the two magnetoresistive element groups 22 and 24, the first magnetoresistive element group 22 will be referred to, and the other will be omitted. The first magnetoresistive element group 22 has a length L1
First magnetoresistive element 16 and the first magnetoresistive element 16
And the second and third magnetoresistive elements 18 and 20 having a length L2 arranged at an interval .delta. The widths of the three magnetoresistive elements 16, 18, 20 are the same. And these three magnetoresistive elements 16, 18, and 20 are connected in series.

Further, the first and second magnetoresistive element groups 2
2, 24 are connected in series, and a power supply voltage −V,
+ V is applied to the two magnetoresistive element groups 2
A bridge from which the output voltage Va is taken out between 2 and 24 is formed. By forming a bridge, S
An output signal Va having a high N ratio is obtained.

The output V of a bridge formed by two magnetoresistive elements having a length L2 arranged at an interval of λ / 2 is
Assuming that the movement amount of the bridge with respect to the scale 10 is x,

(Equation 3) It is expressed as If we ignore the third harmonic, we have (1)
The expression is

(Equation 4) It can be simplified. Equation (2) is

(Equation 5) It can be simplified.

Here, the two magnetoresistive element groups 22, 24
, And the output V2 of the two second magnetoresistive elements 18 and 18, respectively.
And the output V3 of the two third magnetoresistive elements 20, 20
Is

(Equation 6) It is expressed as The output Va to which the outputs V1, V2 and V3 are added is

(Equation 7) It is represented by The condition that the third-order harmonic component is 0 is only required to be 0 in the parentheses in the second term.

(Equation 8) Becomes There are countless combinations of r (= L1 / L2) and δ satisfying the expression (8), for example, r = √2
δ = λ / 8 satisfies this condition. At this time, the voltage value V1,
FIG. 2 shows V2, V3, (V2 + V3), and Va.

On the other hand, the output V of the second magnetoresistive bridge 28
b also removes the third harmonic component,

(Equation 9) Get. X satisfying the expression (9) is the position of the magnetic sensor head 14 between the arrangement pitches of the magnetic poles. Therefore, in the movement amount calculation unit, the scale 10 and the magnetic sensor head 1
4 is calculated from the number N of cycles of the output Va or Vb and the value x.

X = Nλ + x (10)

Equation (8) is a condition obtained for removing the third harmonic. To remove the n-th harmonic,

It suffices that r + 2 cos (2nπδ / λ) = 0 (11) be satisfied.

In the above description of the embodiment, λ is
The ratio of the length of the first magnetoresistive element 16 to the lengths of the second and third magnetoresistive elements 18 and 20 can be considered as the ratio of the output to a certain magnetic field. Therefore, the ratio of the sensitivities of the three magnetoresistive elements may be set to r. For example, in addition to the above-described length ratio, the width ratio may be 1 / r, and the film thickness ratio may be 1 / r.

Further, in the above-described embodiment, three magneto-resistive elements are arranged in series. However, it is also possible to individually apply voltages and add individually output voltage values later. In this case, assuming that the three magneto-resistive elements are equivalent, the ratio of the voltage applied to the magneto-resistive element disposed at the center to the voltage applied to the other magneto-resistive elements is represented by r.
The output ratio of each magnetic resistance element is r. Similar results can be obtained by applying a common voltage and amplifying the output voltage of the centrally arranged magnetoresistive element at a ratio r.

In addition to the magnetic type position detector, the relative movement amount is calculated based on a scale on which periodic position information is written, such as a capacitance type or a photoelectric type, and an output of a sensor which reads this position information. It can be applied to any position detector.

[0019]

According to the present invention, it is possible to remove the n-th harmonic component of the position information written on the scale, and it is possible to detect the position with high accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a main part of a position detector according to an embodiment.

FIG. 2 is an example of an output voltage of the magnetoresistive element of the present embodiment.

[Explanation of symbols]

10 scale, 12 magnetic poles, 14 magnetic sensor heads, 16 first magnetic resistance element, 18 second magnetic resistance element, 20 third magnetic resistance element, 22 first magnetic resistance element group, 24 second magnetic resistance element group, 26 1 MR bridge, 28 2 MR bridge.

Claims (3)

[Claims] 1. A scale on which position information that changes periodically at a fundamental wavelength λ is written, and a first, which detects the position information and outputs the position information as a predetermined signal.
A detection element group including second and third detection elements, wherein the second and third detection elements are arranged on both sides of the first detection element with an interval δ, and the outputs of the first, second, and third detection elements A detection element group that outputs a total sum of, and a relative movement amount calculation unit that calculates a relative movement amount with respect to the scale based on an output of the detection element group;
When the ratio of the output of the detecting element to the output of the second and third detecting elements is r, the following equation is obtained: r + 2 cos (2nπδ / λ) = 0 (n is 3
A position detector that satisfies the above condition (odd number). 2. The position detector according to claim 1, wherein
A position detector comprising first and second detection element bridges each comprising two of said detection element groups and arranged with a phase difference of λ / 4. 3. The position detector according to claim 1, wherein n is 3, the interval δ is λ / 8, and the output ratio r is √2.