JPS6225969B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic flux-responsive multi-gap head for reading a reference scale based on a magnetic grating magnetically recorded on a coaxial magnetic scale.

Conventionally, when measuring length using a magnetic grating, the relative speed between the magnetic scale on which the magnetic grating is formed and the detection head is not constant, and reading in a stationary state is also necessary, so a magnetic response type is used. A head is used to read the reference scale made of a magnetic grid.
In this case, since the recording wavelength of the magnetic grating is constant, a magnetic flux responsive multi-gap head is used in which a plurality of gaps are arranged in parallel at gap intervals that have a constant relationship with the recording wavelength. By this, reading performance can be improved.

FIG. 1 shows an example of the basic configuration of a length measuring device that uses the magnetic flux responsive multi-gap head to read the magnetic grating of a band-shaped magnetic scale. That is, in FIG. 1, the magnetic flux responsive multi-gap head 10 has a spacer plate made of a non-magnetic material such as beryllium copper between a large number of thin plate cores 1 _a , 1 _b , . . . 1 _o made of a magnetic material such as permalloy. 2 _a , 2
A large number of magnetic gaps g _a , g with intervening _b , ...2 _n
A _detection coil 4 is wound around each of the magnetic legs 2 and 3 of the magnetic yoke 1 which is made up of magnetic yoke 1 arranged in parallel with each other, and a frame-shaped saturable magnetic core is installed between each _of the magnetic legs 2 and 3. 6
is inserted, and an excitation coil 7 is wound around this saturable magnetic core 6. The detection coil 4 is connected to a synchronous detection circuit 12 via a filter circuit 11. In addition, the excitation coil 7
is connected to the carrier wave oscillator 13. Magnetic flux responsive multi-gear head 10 with such a configuration
is arranged so as to be movable relative to a magnetic scale 5, which has a magnetic grating formed by recording a rectangular wave or a sine wave of a constant wavelength on a band-shaped magnetic medium as a reference scale, and constitutes a measuring device. .

The magnetic flux responsive multi-gap head 10 has the following features:
Supplied from the carrier wave oscillator 31 to the excitation coil 6
Excited by a carrier wave of about 5KHz to 10KHz,
From the magnetic scale 5, each magnetic gap g _a , g _b ,... g _n
By magnetically modulating the carrier wave according to the signal magnetic field applied to the magnetic head 10, a detection output signal of a balanced modulated wave as shown in FIG.
Output from. The detection output signal is a balanced modulated wave obtained by balanced modulating the carrier wave supplied to the excitation coil 7 with a signal magnetic field generated by a magnetic grating provided on the magnetic scale 5. Only a predetermined frequency component of the detection output signal is supplied to a synchronous detection circuit 12 via a filter circuit 11 having bandpass characteristics. This synchronous detection circuit 12 converts the carrier wave frequency from the carrier wave generator 13 into a multiplication circuit 14.
The detection output signal is synchronously detected using the synchronization signal multiplied by , and a sine wave detection output signal having a frequency corresponding to the wavelength of the magnetic grating provided on the magnetic scale 5 is output from the signal output terminal 18.

Magnetic flux responsive multi-gear head 1 as described above
In the measuring device using 0, wavelength selectivity is obtained by arranging the magnetic gaps g _a , g _b , ... g _n of the magnetic head 10 at predetermined intervals, so that the magnetic scale has a non-sinusoidal wave. Even when a magnetic grating is formed, a sinusoidal detection output signal can be obtained with high sensitivity.

In addition, when reading a reference scale using a coaxial magnetic scale in which a magnetic grating is formed on a round bar-shaped magnetic recording medium, a through hole is provided in the magnetic yoke through which the coaxial magnetic scale is inserted. A magnetic flux-responsive multi-gap head is used, which has a structure in which the signal magnetic field from the magnetic scale is detected through magnetic gaps arranged in parallel on the peripheral wall.

FIG. 3 is a schematic diagram showing the basic structure of a magnetic flux responsive multi-gap head 20 for a coaxial magnetic scale. That is, in FIG. 3, a magnetic yoke 21 formed by laminating a non-magnetic spacer plate and a thin plate core has a through hole 28 through which a coaxial magnetic scale 25 is inserted, and an excitation coil 27 is wound around the magnetic yoke 21. A frame-shaped saturable magnetic core 26 is mounted between the magnetic leg parts 22 and 23, and a detection coil 24 is further wound around the magnetic leg part 23. And this magnetic flux responsive multi-gear head 20
In this case, the saturable magnetic core 2 is
6 is excited, and the detection output signal obtained by magnetically modulating the carrier wave with the signal magnetic field from the coaxial magnetic scale 25 applied to the magnetic gap in the inner circumferential wall of the through hole 28 provided in the magnetic yoke 21 is sent to the detection coil 24. Output from. Note that the broken line arrows shown in FIG. 3 indicate the flow of magnetic flux for excitation, and the solid line arrows indicate the flow of magnetic flux due to the signal magnetic field.

By the way, in the magnetic flux responsive multi-gap head 20 for a coaxial magnetic scale having the above-described structure, the magnetic flux from the coaxial magnetic scale 25 given to the magnetic gap in the inner circumferential wall portion of the through hole 28 provided in the magnetic yoke 21 is Although the magnetic flux caused by the signal magnetic field flows through the magnetic circuit made up of the magnetic yoke 21 and the saturable magnetic core 26, the saturable magnetic flux of the inner circumferential wall of the through hole 28 flows as indicated by the dashed line arrow in FIG. Since the magnetic path flows through different lengths on the core 26 side and the opposite side, the detection sensitivity to the signal magnetic field applied to the magnetic gap in the inner circumferential wall portion on the saturable magnetic core 26 side, where the magnetic path length is short, is reduced. It gets expensive. In general, when the coaxial magnetic scale 25 is used, it is inserted into the through hole 28 provided in the magnetic yoke 21 to form the magnetic flux responsive multi-gap head 20.
However, due to installation errors, etc., the axes cannot be perfectly aligned, so the distance between the inner circumferential wall of the through hole 28 and the outer circumferential surface of the magnetic scale 25 may vary locally. It will be in a state where it is close to or in sliding contact with. Therefore, when reading the basic scale of the coaxial magnetic scale 25 using the magnetic flux responsive multi-gap head 20, there is a problem in that the detection sensitivity changes depending on the relative position thereof.

Further, the magnetic flux responsive multi-geap head 20 having the above-mentioned principle structure has been specifically assembled as shown in FIGS. 4 and 5 and has been used in the past. That is, the detection coil 24 is fitted onto the saturable magnetic core 26 around which the excitation coil 27 is wound, and the saturable magnetic core 26 is attached and fixed to the magnetic yoke 21 by a presser spring 29, thereby assembling.

However, in the conventional magnetic flux responsive multi-gear head 20 as described above, as shown in FIG.
7, the winding workability was not only poor, but also the amount of winding of the coil could not be increased very much.

SUMMARY OF THE INVENTION Therefore, the present invention is a novel system that improves the problems of the conventional magnetic flux responsive multi-gap head for coaxial magnetic scales, such as non-uniformity of detection sensitivity and poor winding workability of excitation coils. The present invention provides a magnetic flux responsive multi-gear head with a unique structure.

Hereinafter, the present invention will be described in detail with reference to the drawings showing one embodiment.

FIG. 6 is a schematic diagram showing the basic structure of the magnetic flux responsive multi-gap head according to the present invention.

That is, as shown in FIG. 6, the magnetic flux responsive multi-geap head 40 according to the present invention has protrusions formed at the center of each side edge of the first and second magnetic leg pieces 41 _o and 42 _o . A hole 46 _o into which the coaxial magnetic scale 45 is inserted is provided in the pieces 43 _o and 44 _o , and each protruding piece 4
3 _o and 44 _o so that the holes 46 _o communicate with each other.
and the second magnetic leg pieces 41 _o and 42 _o to each protruding piece 43
A magnetic yoke ₄₇ having a substantially H-shaped block shape and having a plurality of magnetic gaps arranged in parallel on the inner circumferential wall portion of a through hole 46 formed by the above-mentioned _hole in the center position, and an excitation coil A pair of magnetic cores 49A and 49B wound with magnetic cores 48A and 48B are provided, and a magnetic leg portion formed by the first magnetic leg piece _41o and a magnetic leg part formed by the second magnetic leg piece _42o . Legs 4
One magnetic core 49A is installed between one end of 1 and 42, and the other magnetic core 49B is installed between the other ends to create a closed magnetic path through which magnetic flux for excitation by carrier waves supplied to the excitation coils 48A and 48B flows. The detection coils 50A and 50B are wound around a part of the closed magnetic path.

Magnetic flux-responsive multi-gear head 4 as described above
0, the excitation coil 48 from the carrier wave oscillator 51
The magnetic flux for excitation by the carrier waves supplied to A and 48B is applied to each magnetic leg portion 41 and 42 of the magnetic yoke 47 and each magnetic core 49, as shown by the broken line arrow in FIG.
The magnetic flux of the signal magnetic field generated by the coaxial magnetic scale 45 flowing through the closed magnetic path formed by A and 49B and inserted into the through hole 46 formed at the center of the magnetic yoke 47 is indicated by the solid arrow in FIG. As shown, a detection coil 50 is divided into two parts and flows through two magnetic paths passing through each magnetic core 49A, 49B, and is wound in two parts on one of the magnetic legs 42 forming the closed magnetic path.
From A and 50B, a detection output signal can be obtained by balanced modulating the carrier wave with a signal magnetic field according to the principle of magnetic modulation. The magnetic flux due to the signal magnetic field flows through symmetrical magnetic paths passing through the magnetic cores 49A and 49B which are arranged opposite to each other with the magnetic leg portions 41 and 42 of the magnetic yoke 47 in between. It is provided through a magnetic gap in the inner circumferential wall portion of the through hole 46 provided at the center of the magnetic yoke 47, which is a common portion. Therefore, in the magnetic flux responsive multi-gap head 40 having such a structure, the signal magnetic field from the coaxial magnetic scale 45 inserted into the through hole 46 of the magnetic yoke 47 is transmitted through the through hole 46.
It can be detected uniformly by the magnetic gap in the inner circumference of the sensor.

The magnetic flux-responsive multi-gap head 40 having the above-mentioned basic structure is specifically constructed as shown in FIGS. 7 to 11, for example. 7th
8 and 8 are an external perspective view and an exploded perspective view of a specific embodiment of the magnetic flux responsive multi-geap head 40 according to the present invention. In this embodiment, the present invention is applied to a multi-gap magnetic head 40 for reading a reference scale magnetically recorded on a coaxial linear magnetic scale 45, and has a through hole 46 through which the magnetic scale 45 is passed. Magnetic yoke 47 and excitation coils 48A and 48, respectively.
B and the respective saturated magnetic cores 49A, 49B around which the detection coils 50A, 50B are wound,
It has a configuration attached by 2. The magnetic yoke 47 has a substantially H-shaped block shape, and the saturable magnetic cores 49A, 4 are interposed between the magnetic leg portions 41, 42.
9B is placed and fixed.

The saturable magnetic core 49A is, for example, as shown in FIG. 9, a thin ferromagnetic plate 49 made of permalloy or the like.
A is attached to an insulating reinforcing plate 49b made of ceramic or the like, and after the excitation coil 48A is wound, the detection coil 50A is fitted.

Further, the other saturable magnetic core 49B is also formed in the same manner as the above-mentioned saturable magnetic core 49A, and after winding the excitation coil 48B, the detection coil 50B is formed.
is fitted. In this embodiment, the excitation coils 48A, 48B can be wound simply by winding the plate-shaped saturable magnetic cores 49A, 49B, and the frame shape can be changed as in the above-mentioned conventional example. Workability can be greatly improved compared to winding a saturated core. Furthermore, since the excitation coils 48A, 48B and the detection coils 50A, 50B are distributed and wound around each magnetic core 49A, 49B attached to the H-block magnetic yoke 47, a large space for winding is secured. By increasing the amount of winding, the detection coils 50A, 5 can be
The signal level of the detection output signal from 0B can be increased.

Further, as shown in FIGS. 10 and 11, the magnetic yoke 47 has a plurality of H-shaped plate-shaped non-magnetic spacer members 53 _a , 53 _b , . . . , 53 _n that form different magnetic poles. Magnetic leg pieces 41 _a , 42 _a ,
41 _b , 42 _b . . . 41 _o , 42 _o are laminated in order, and each magnetic gap g _a , g _b , . . . g _n are formed by the respective spacer members 53 _a , 53 _b , . . . 53 _n .
Each of the magnetic leg pieces _41a , _42a ,... _41o , _42o is as follows:
The odd-numbered pieces form one magnetic leg part 41, and the even-numbered pieces form the other magnetic leg part 42, and each protruding piece _43a formed at the center of each side edge
_44a ,... _43o , _44o are laminated, and the first
H-block shaped magnetic yoke 47 as shown in Figure 1
form. Each of the laminated magnetic leg pieces 41 _a , 4
Reinforcing plates 56 _and 57 are attached to the outermost sides of 2 _{a ,} . Each of these members has holes 46 _a , 46 _b , . . . , 46 _z forming the through hole 42 through which the magnetic scale 45 passes.

The embodiment of the structure described above has the following effects compared to the conventional example shown in FIG. 4 described above.

That is, in this embodiment, the magnetic flux of the carrier wave is magnetically modulated by the magnetic flux of the signal magnetic field applied through the magnetic gap in the inner circumferential wall of the through hole provided at the center position of the H-shaped block. With a detection sensitivity that is the average of the detection sensitivities in the circumferential direction, it is possible to always obtain a detection output signal with a constant sensitivity as shown by the solid line in FIG. On the other hand, in the conventional example, the detection sensitivity in the circumferential direction of the through hole changes depending on the length of the magnetic path through which the magnetic flux due to the signal magnetic field flows, and as shown by the broken line in Fig. 12, the detection sensitivity changes in the direction of the detection surface. Therefore, the signal level of the detection output signal changes. In Fig. 12, the horizontal axis indicates the direction of the detection surface with the inner peripheral wall of the through hole in the conventional example, that is, the detection surface located on the saturable core side, as 0°, and the vertical axis indicates the signal level of the detection output signal. It shows the ratio. As described above, in the magnetic flux responsive multi-gap head according to the present invention, a uniform detection sensitivity distribution can be obtained in the circumferential direction of the detection surface.

Therefore, for example, when a coaxial magnetic scale with a spiral magnetization unevenness moves while unevenly touching the same location on the inner circumferential wall of a through hole, in the conventional example, as shown by the broken line in FIG. As shown in FIG. 13, the level fluctuation of the detection output signal due to the spiral magnetization unevenness becomes large, whereas in the above embodiment, the level fluctuation is reduced as shown by the solid line in FIG. I can do it. In addition,
In this case, in an ideal state where there is no clearance between the coaxial magnetic scale and the inner circumferential wall of the through hole, the level fluctuation can be reduced to zero, as shown by the dashed line in FIG.

In general, in a measuring device using a magnetic scale, two detection heads are arranged at an interval of nλ±1/4λ with respect to the recording wavelength λ of the magnetic grating of the magnetic scale, and the detection output from each detection head is A phase detection type detection circuit that calculates a measured value based on a change in the phase of a signal is used, and the resolution is further improved by interpolation processing. In this embodiment, the detection sensitivity distribution is uniform as described above, so if the magnetic flux responsive multi-gap head of the embodiment described above is used as each detection head, the envelope waveform of the composite wave of each detection output signal is stabilized. Errors in the above interpolation process can be reduced.

Furthermore, when reading a reference scale using a coaxial magnetic scale having azimuth and magnetization unevenness and detecting it with a phase detection type detection circuit, in the conventional example, a large phase error caused by the above-mentioned azimuth and magnetization unevenness occurs. As shown by the broken line in FIG. 14, this occurs between each detection output signal. On the other hand, in the embodiment described above, since the detection sensitivity is uniform as described above, the phase error can be reduced as shown by the solid line in FIG.

Furthermore, in this embodiment, errors due to changes in the relative angular position between the scale and the head that occur when reading a reference scale using a coaxial magnetic scale that is uniformly magnetized and whose azimuth is out of alignment are also eliminated. As shown by the solid line in the figure, it can be made smaller than the conventional example (shown by the broken line).

As described above, in the magnetic flux responsive multi-gap head according to the present invention, when a phase detection type detection circuit is used, fluctuations in the envelope waveform of the composite wave of each detection output signal are reduced, and interpolation errors are reduced. Moreover, errors caused by fluctuations in the relative positional relationship between the scale and the head can also be reduced.

Furthermore, in the embodiment of the structure described above, the saturable core around which the excitation coil is wound is divided into two parts and attached to the magnetic yoke, so that the dimensions and shape of the saturable core are the same as in the conventional example. It can be freely set without being limited to the frame shape. By selecting the shape and dimensions of the saturable core, third-order distortion of the carrier wave can be reduced. FIG. 16 shows actual measurement results of the occurrence of third-order distortion in the conventional example and the embodiment. This actual measurement result was obtained by measuring third-order distortion using a dummy signal converted into a scale input, and the solid line in FIG. 16 indicates the example.
A broken line is also shown. As is clear from FIG. 16, this embodiment has a greater effect of reducing third-order distortion over the entire signal range than the conventional example, and was able to significantly reduce third-order distortion particularly for large input signals.

Further, in this embodiment, as described above, the work of winding the excitation coil is simple, and by increasing the amount of winding of the detection coil, it is possible to obtain a detection output signal with a large signal level.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the basic structure of a measuring device in which a reference scale based on a band-shaped magnetic scale is read by a magnetic flux responsive multi-gap head. FIG. 2 is a waveform diagram of a detection output signal obtained from the magnetic flux responsive multi-gap head. FIG. 3 is a schematic diagram showing the structure of a conventional magnetic flux responsive multi-gap head for a coaxial magnetic scale. FIG. 4 is an external perspective view showing a specific example of the structure of the conventional magnetic flux responsive multi-gap head. FIG. 5 is an enlarged exploded perspective view of the saturable core portion in the conventional example. FIG. 6 is a schematic diagram showing the basic structure of the magnetic flux responsive multi-gap head according to the present invention. 7 to 11 show specific embodiments of the magnetic flux responsive multi-geap head according to the present invention, FIG. 7 is a perspective view of the overall appearance, FIG. 8 is an exploded perspective view of the main parts, FIG. 9 is an enlarged exploded perspective view of the saturable magnetic core portion, FIG. 10 is an exploded perspective view of the magnetic yoke, and FIG. 11 is an external perspective view of the magnetic yoke. Figures 12 to 16
The figures are characteristic diagrams that compare and show the respective performances of the conventional example and the example, Fig. 12 shows the distribution of detection sensitivity, and Fig. 13 shows the output level due to uneven magnetization of the magnetic scale. Fig. 14 shows the phase error due to magnetization unevenness and azimuth of the magnetic scale, Fig. 15 shows the occurrence of error due to changes in the relative angular position between the head and the scale, and , FIG. 16 shows the occurrence of third-order distortion of the carrier wave. 40...Magnetic flux responsive multi-gear head, 41
_a to 41 _o ...first magnetic leg piece, 42 _a to 42 _o ...second magnetic leg piece, 41, 42...magnetic leg part, 43 _o to 43 _o ...protruding piece of first magnetic leg piece, 44 _a to 44 _o ... Protruding piece of second magnetic leg piece, 45... Coaxial magnetic scale, 46 _o ... Hole provided in protruding piece, 46... Through hole of magnetic yoke, 47
...Magnetic yoke, 48A, 48B...Excitation coil, 4
9A, 49B...Saturable magnetic core, 50A, 50B
...Detection coil.

Claims (1)

[Claims] 1. A hole through which a coaxial magnetic scale is inserted is provided in each protruding piece formed at the center of one side edge of the first and second magnetic leg pieces, and the first and second magnetic leg pieces are arranged so that the holes in each protruding piece communicate with each other. Laminating the second magnetic leg piece at each protruding piece part,
A magnetic yoke having a substantially H-shaped block shape and having a plurality of magnetic gaps arranged in parallel on the inner circumferential wall portion of the through hole formed by the above-mentioned hole at the center position, and a pair of magnetic cores around which an excitation coil is wound. one magnetic core is installed between one end of the magnetic leg part formed by the first magnetic leg piece and the magnetic leg part formed by the second magnetic leg piece, and the other magnetic core is installed between the other ends. for a coaxial magnetic scale, characterized in that a closed magnetic path is formed through which magnetic flux for excitation by a carrier wave supplied to the excitation coil flows, and a detection coil is wound around a part of the closed magnetic path. Magnetic flux responsive multi gear head.