JPS63154903A - Linear scale - Google Patents

Abstract

PURPOSE:To minimize the effect of a leakage magnetic field, in a linear scale wherein a magnetic detector is arranged in a closed magnetic path in a movable manner, by forming the second magnetic path of the same direction outside the closed magnetic path. CONSTITUTION:Almost semicircular thin plates 115, 117 form an internal closed magnetic path 120 and a movable rod 125 having a magnetic resistance element 119 pierces the centers of magnets 111, 113 in an L-direction. Permanent magnets 143A(143B), 145A(145B) forming the second closed magnetic path are provided outside the magnetic path 120. A pair of thin plates 147A, 149A(147B, 149B) made of a magnetic material form the second closed path and the arrangement of the polarity of the permanent magnets 143A(143B), 145A(145B) is made inverse to that of the magnets 111, 113 of the magnetic path 120 so that the magnetic flux direction 151 of the thin plate 149A(149B) becomes the same to the magnetic flux direction 121 of the corresponding thin plate 115(117). By this constitution, magnetic fluxes 151 in the same direction are formed on both outsides of the magnetic path 120. By this method the effect of the leakage magnetic field due to the magnetic path 120 is prevented.

Description

[Detailed Description of the Invention] [Summary] In a linear scale in which a magnetic detector is movably disposed within a closed magnetic path, leakage magnetic fields can be reduced by forming a second magnetic path in the same direction outside the closed magnetic path. impact can be minimized.

[Industrial application field]

The present invention relates to a linear scale that measures the position and stroke of an object by detecting leakage magnetic fields from a closed magnetic path.

[Conventional technology]

4 and 5 show the structure of the conventional linear scale disclosed in the applicant's earlier application.

In Figures 4 and 5; 11, 13 is a permanent magnet, 15° 17 is a thin plate made of magnetic material (for example, an iron plate with a thickness of 0.4 mm), and 19 is a magnetic resistance (barber) made of, for example, a ferromagnetic metal (permalloy, etc.). This is a magnetic detector containing a pole-type magnetoresistive element.

A pair of strip-shaped thin plates 15 and 17 have permanent magnets 11 at both ends.
．． 13 to form a closed magnetic circuit 20, and a magnetic detector 19 is arranged inside the closed magnetic circuit 20. however,
The polarities of the permanent magnets 11 and 13 provided at the ends of the thin plates 15 and 17 are opposite, and the magnetic detector 19, which is movable in the length direction of the closed magnetic circuit 20, has a magnetic detection element accommodated in the thin plate 15. .17 (the thin plate 15 in the figure) and moves in opposition to it.

The detector 19 is mounted on a movable rod 25 extending through the magnet 11.13 to allow linear movement of the detector 19 in the L direction.

The detection output characteristic of the leakage magnetic flux 23 by the magnetic detector 19 in such a linear scale is as shown by the dashed line in FIG.

In the linear scale constructed in this way, the closed magnetic circuit 20 includes the N pole of the permanent magnet 11, the S pole of the permanent magnet 13, and the
The magnetic flux 21 passes from the N pole of No. 3 to the S pole of the permanent magnet 11, and leakage magnetic flux 23 flows inside the closed magnetic circuit 20, increasing as it moves away from the opposing center (L/2) of both permanent magnets. In FIG. 3, the vertical axis shows the amplified output voltage (1V) of the magnetic detector 19, and the horizontal axis shows the zero at the opposing center (intermediate center point) of the permanent magnets 11 and 13, and the magnetic detector output voltage from the zero position. Departure distance up to 19! l (nun)
shows.

[Problem that the invention seeks to solve]

As shown in FIG. 3, conventional linear scales have a problem in that their output and displacement (stroke) are not linearly proportional, impairing their characteristics as a linear scale.

This is because part of the magnetic flux leaks to the outside of the closed magnetic circuit. Conventionally, a shield case 27, 29 made of a magnetic material is provided outside the closed magnetic circuit. Although this shield case can prevent the influence of external magnetic fields to some extent, it prevents leakage magnetic flux 31 ( Figure 4) cannot be prevented. As a result, the magnetic flux of the closed magnetic circuit leaking through the shield case distorts the relationship between the stroke and the output, which should be linearly proportional.

An object of the present invention is to provide a highly reliable linear scale that shields disturbance magnetic fields and solves the above problems.

[Means for solving problems]

In order to achieve the above object, according to the present invention, a second magnetic path is provided outside the closed magnetic path to provide magnetic flux in the same direction by a magnet.

[For production]

If the magnetic field leaking to the outside from the internal closed magnetic circuit is complemented by the leakage magnetic field created by the second magnetic path provided outside, the leakage magnetic fluxes cancel each other out, and as a result, the influence of the leakage magnetic field to the outside is eliminated. Ru.

〔Example〕

FIG. 1.2 shows a longitudinal section and a cross section, respectively, of a linear scale according to an embodiment of the invention. Parts corresponding to FIGS. 4-5 are numbered by adding 100 to the respective part number. In Figure 1.2, 115 and 117 are, for example, 2mrr
A substantially semicircular thin plate 111, 113 forming an internal closed magnetic path 120 made of magnetic stainless steel or permalloy with a thickness of I is a ferrite or alnico magnet, and a movable rod 125 having a magnetic resistance element 119 at its center penetrates in the L direction. .

According to the present invention, the second closed magnetic path 1 is provided outside the closed magnetic path 120.
Permanent magnet 143A (143B) forming 40,
145A (145B) is provided. Second closed magnetic path 140
A pair of thin plates made of magnetic material (for example, a thickness of 2
mm) 147A, 149A (1478, 149B
) corresponds to the conventional shield case, but the magnetic flux direction 151 in the thin plate 149A (149B) is the 1st f.
The magnets 143A (143B) and 145 are arranged so that the direction of magnetic flux is the same as the magnetic flux direction 121 of the corresponding thin plate 115 (117) of the li path.
The polarity arrangement of A (145B) is opposite to the polarity of the magnets 111 and 113 of the first closed magnetic path 120. Thus the first
Magnets 143A (143B
) N pole - magnet 145A (145B) S pole - magnetic pole 1
45A (145B) N pole - magnet 143A (143
A magnetic flux 151 directed toward the S pole of B) is formed.

Preferably, the strength of the magnetic field in the first closed magnetic path is equal to that in the second closed magnetic path.

In Figure 1.2, the shapes of the thin plates, magnets, etc. are as shown in Figure 4.
Although it is different from that shown in Fig. 5, its shape and size are not limited in any way; for example, the thin plates 115°, 117, 1478, 147B, 149A, and 149B are made into a flat plate shape as in Fig. 4, and an arcuate magnet is used. 113.143A, 143
B, 145A, and 145B may be rectangular.

Note that 150 is a non-magnetic spacer, but it is not necessarily necessary (spacer 150 is not shown in Figure 1).
.

By configuring as described above, the magnetic flux leaking to the outside from the first closed magnetic path 120 is complemented by the magnetic flux leaking to the outside (inside the first closed magnetic path) from the second closed magnetic path 140, and the magnetic flux is almost canceled out. Impact is prevented.

In FIG. 3, the output characteristics of the magnetic detector 119 in the present invention are shown by a solid line. According to this, it can be seen that in the present invention, the output of the linear scale and the stroke (displacement) are almost linearly proportional.

In the above embodiment, a permanent magnet is used as a means for applying magnetic flux, but it goes without saying that the same effect can be obtained by using an electromagnet.

Also, the second magnetic path does not necessarily have to be a "closed" magnetic path, thus, for example, the outermost lamina 147A.

147B may not be provided.

〔Effect of the invention〕

According to the present invention, characteristic deterioration due to external leakage magnetic fields can be prevented, and a linear scale with high reliability and detection accuracy can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention, FIG. 2 is a sectional view taken along the line ■-■ in FIG. 1, FIG. 3 is a diagram showing the characteristics of a linear scale, and FIG. A longitudinal sectional view of the scale, and FIG. 5 is a sectional view taken along the line V-V in FIG. 4. 111.113... Permanent magnet, 119... Magnetic field detector, 120... First closed magnetic path, 140... Second closed magnetic path, 143A, 143B, 145A, 145B.
··magnet.

Claims (1)

[Claims] A linear magnet having a closed magnetic path (120) made of a magnetic material, magnets (111, 113) that apply magnetic flux to the magnetic path, and a linearly movable detection means (119) that detects a leakage magnetic field of the magnetic path. The scale has magnets (143A, 143B, 145A, 145B) outside the closed magnetic circuit that passes magnetic flux.
a second magnetic path (140) that is given magnetic flux in the same direction by
A linear scale that is characterized by being attached.