TW201602523A - Magnetic displacement sensor and method for detecting displacement - Google Patents

Abstract

A object of this invention is to reduce influences of ambient temperature on a magnetic displacement sensor. A magnetic displacement sensor of this invention includes a support, a shell that houses the support, and a fixing portion that fixes a center of the support to the shell along a longitudinal direction of a magnetic grating bar. In addition, the numbers of coils on both sides of the fixing portion are the same and the plurality of coils are supported by the support along the longitudinal direction of the magnetic grating bar.

Description

Magnetic displacement sensor and displacement detection method

The present invention relates to the detection of displacement using a magnetic displacement sensor, and more particularly to reducing errors due to temperature variations.

It is known to use a magnetic scale and a magnetic displacement sensor that alternately and periodically arrange a magnetic body and a non-magnetic body to detect a displacement. For example, a magnetic displacement sensor that extracts the output of sin(θ+ωt) using four primary coils and four secondary coils is disclosed in Japanese Laid-Open Patent Publication No. Hei 09-264758. Here, ω is the angular frequency of the alternating current for excitation, and θ is the electrical phase angle with respect to the magnetic scale. In the magnetic displacement sensor, the coil is annular, and the primary coil and the secondary coil are placed on the inner circumference side and the outer circumference side so as to overlap each other. Further, the magnetic displacement sensor causes the rod-shaped magnetic scale to pass through the hollow portion of the annular coil, and uses a magnetic mark provided at a fixed pitch on the magnetic scale to detect the displacement. Hereinafter, the magnetic displacement sensor is sometimes simply referred to as a sensor.

When the primary coil and the secondary coil are not used, the number of coils can be halved, for example, by using a coil that can be used as one or two times (Patent Document 2, JP-A-2013-024779). In this case, an alternating voltage is applied to the column of coils to detect the phase (θ + ωt) of the alternating current flowing through the coil. Further, if the directions in which the current flows are reversed and the rows of the coils are arranged in two rows, the error caused by the relative speed of the magnetic scale and the sensor can be reduced (Patent Document 2).

Proposal to compensate for thermal deformation to the machine tool by magnetic displacement sensor The influence of precision machinery (Patent Document 3 Japanese Patent Laid-Open No. 2011-093069). For example, if the distance between the spindle table and the tool table of the lathe changes due to thermal deformation of the lathe, the machining accuracy of the workpiece is lowered. Therefore, by measuring the position of the spindle head and the tool table, the interval therebetween can be determined, and the spindle head or the like can be moved without being affected by the ambient temperature, thereby compensating for the influence of thermal deformation. In Patent Document 3, the position of the spindle table and the tool table of the power tool is measured by a magnetic scale and a magnetic displacement sensor. Although not explicitly described in Patent Document 3, if the magnetic scale is formed of a material that does not substantially thermally expand, such as an invar alloy, it is a magnetic scale that is not affected by the ambient temperature.

The inventors focused on the fact that the magnetic displacement sensor itself is affected by thermal expansion. The sensor is, for example, a coil wound around a bobbin of a non-magnetic body. As the non-magnetic material, glass, ceramics, and the like having a very small coefficient of thermal expansion are known. However, if only these materials are used, it is difficult to process them into a correct shape. Further, when an invar alloy or the like having a small coefficient of thermal expansion is used for the bobbin, the invar alloy of the bobbin shaft blocks the influence of the magnetic scale. Therefore, it is difficult to solve the thermal expansion of the spool.

Further, in the position sensor of Patent Document 4 (Japanese Patent Laid-Open Publication No. 2003-269993), a film of Cu (copper) is provided on the surface of a cylinder composed of a material having a small thermal expansion coefficient such as ceramic or Invar. Coil. Further, a tube in which a film coil of Cu is introduced into and out of stainless steel is disclosed to measure the length of overlap between the stainless steel tube and the film coil. It is assumed that if the stainless steel tube can be changed to a tube such as Invar, and a precise magnetic mark is provided on the inner peripheral surface, the position can be measured without being affected by the ambient temperature. However, such processing is more difficult.

The subject of the present invention is to reduce the ambient temperature to the magnetic displacement sensor The impact.

The present invention is a magnetic displacement sensor for detecting displacement by interaction of a plurality of coils and a magnetic scale, the plurality of coils being supported by a support, the magnetic scale being disposed along a longitudinal direction A magnetic mark that changes periodically at a fixed pitch, and the magnetic displacement sensor is characterized by: a housing that houses the support; and a fixing portion that fixes the central portion of the support body to the outer casing along the longitudinal direction of the magnetic scale; and along the longitudinal direction of the magnetic scale, on both sides of the fixed portion The plurality of coils are each the same number and supported by the support.

Moreover, the present invention is a method for detecting a displacement of a displacement detected by a support, a magnetic displacement sensor, and a magnetic scale, the magnetic displacement sensor having a plurality of coils supported by the support, the magnetic The scale has a magnetic mark that periodically changes at a fixed pitch along the longitudinal direction, wherein the magnetic displacement sensor is provided with: a casing that houses the support; and a fixing portion along the magnetic grid In the longitudinal direction of the ruler, the central portion of the support body is fixed to the outer casing; along the longitudinal direction of the magnetic scale, on the two sides of the fixed portion, the plurality of coils are each of the same number and supported by the support body, and are supported Each of the two sides of the fixed portion is between the same number of coils, offsetting the influence of thermal expansion of the support.

Regarding the fixing portion of the support body, that is, the position at which the support body is fixed to the outer casing, it is important to arrange the same number of coils on both sides of the fixed portion, and the coil is To offset the effect of thermal expansion of the support. The central portion is a fixed portion in order to arrange the coils on both sides thereof, and therefore the fixing portion is not limited to the center in the longitudinal direction. The arrangement of the coils is preferably symmetrical with respect to the central portion (fixed portion) of the support.

In the present invention, even if the position of the coil is changed by thermal expansion of the support, the same number of coils can be supported on both sides of the fixed portion to offset the influence of thermal expansion. If the arrangement of the coils is close to symmetry with respect to the fixed portion, the detection error of the displacement due to thermal expansion is reduced. However, even if it is not symmetrical, a considerable degree of error can be offset by arranging the same number of coils on both sides of the fixed portion.

For example, consider a coil of +sin phase and a coil of -sin phase, and a coil of +cos phase and a coil of -cos phase, and at least two coils of sin phase output and at least two coils of cos phase output are provided. In this case, if at least one sin phase output coil and one cos phase output coil are disposed on both sides of the fixed portion along the longitudinal direction of the magnetic scale, the coil of the +sin phase can be The offset error between the coils of the -sin phase can also be used to offset the error between the coil of the +cos phase and the coil of the -cos phase.

More preferably, the number of coils is set to 6 or 8. Further, 2π is used as the electrical phase angle of the magnetic mark between the magnetic scales, and two coils each having an electrical phase angle of θ are symmetrically arranged on both sides of the fixed portion, and will be oriented toward the magnetic scale. The electric phase angles are both two coils of θ + π, and one of them is arranged symmetrically on both sides of the fixed portion. A coil having an electrical phase angle of θ and θ+π, which may be a coil of a sin phase or a coil of a cos phase.

When the coil of the output of the +sin phase is symmetrically arranged with respect to the coil fixing portion of the output of the -sin phase, it is difficult to arrange one of the outputs of the ±cos phase symmetrically with respect to the coil. Further, if one of the outputs of the ±cos phase is symmetrically arranged with respect to the fixed portion, it is difficult to arrange one of the outputs of the ±sin phase symmetrically with respect to the coil. Again, the so-called sin Phase and cos phase are just the question of which position is set to 0 of the electrical phase angle. Therefore, for example, the coil of the output of the +sin phase and the coil of the output of the -sin phase are symmetrically arranged with respect to the fixed portion. One of the +cos phases may be symmetrically arranged with respect to the fixed portion, or one of the -cos phases may be symmetrically arranged with respect to the fixed portion. Therefore, if a pair of coils of the +cos phase and the coil of the -cos phase are arranged symmetrically on both sides of the fixed portion, the arrangement of the coils becomes symmetrical. Moreover, in this case, the error due to temperature fluctuation is almost zero.

It is preferable that the number of the plurality of coils is eight, and that two coils having an electrical phase angle toward the magnetic scale, for example, (θ + 1/2π), are arranged symmetrically on both sides of the fixed portion, and are oriented one by one. The electric phase angle of the magnetic scale is, for example, two coils of (θ-1/2π), and one of them is arranged symmetrically on both sides of the fixed portion. The phases of the remaining four coils are, for example, two in θ and two in θ + π. In this way, the coil of the +sin phase and the coil of the -sin phase, and the coil of the +cos phase and the coil of the -cos phase can be arranged symmetrically on both sides of the fixed portion located at the central portion of the support body. One. Moreover, since there are two coils of the same output phase, the drive circuit becomes simple.

Further, it is preferable that the support system is provided with a winding shaft in which the magnetic scale is inserted into a hollow shape, and a plurality of coils are wound around the bobbin. In this case, the central portion of the bobbin is fixed to the outer casing, and it is preferable that the coils are disposed on both sides of the central portion of the bobbin with the symmetry as high as possible, and it is preferable to arrange the coils symmetrically on the bobbin. On both sides of the central part. As a result, it is easy to offset the influence of thermal expansion between the coils. Further, in the magnetic scale, a relatively correct magnetic mark can be provided on the outer surface of the tube or the rod by plating or the like. Since the magnetic mark passes through the inside of the bobbin, the magnetic interaction between the coil and the magnetic mark can be enhanced.

Preferably, the outer casing and the support have different thermal expansion rates. Better to make the outer casing The thermal expansion rate is lower than the thermal expansion rate of the support. Further, in the present specification, the coefficient of thermal expansion is used as the coefficient of linear thermal expansion. When the support body is housed in the outer casing, it is common knowledge to make the thermal expansion rates of the two uniform. However, in the present invention, it is not necessary to make the thermal expansion rates of the two uniform. In particular, since the support body is stretched and contracted along the both sides of the fixing portion with respect to the outer casing, deformation due to the difference in thermal expansion rate does not occur. Since the outer casing has a wider range of materials than the support, it is preferred that the outer casing has a lower coefficient of thermal expansion than the support.

Preferably, the outer casing is a metal having a low thermal expansion rate such as Invar or Super Invar, and the support is an insulator of a mixture of a glass having a low thermal expansion rate and an organic binder. In the present specification, the low coefficient of thermal expansion means that the coefficient of thermal expansion at room temperature is 2 ppm or less, and that of wattage is 1.2 ppm. Further, the linear expansion ratio of the support is, for example, about 20 ppm. Since the support is fixed to the outer casing having a low thermal expansion rate, the influence of temperature fluctuation on the outer casing can be reduced. Moreover, since it is a metal case, the electric field from the outside can be blocked. In particular, Invar is magnetic, so it can also block the magnetic field from the outside. The support of the insulator does not interfere with the interaction of the magnetic scale with the coil, especially if it is a mixture of glass and plastic adhesive, it can be correctly processed into the desired shape.

2‧‧‧Magnetic scale

6‧‧‧Cu film

8‧‧‧Protective film

10‧‧‧Magnetic Displacement Sensor

12‧‧‧ Shell

14‧‧‧ tube

15‧‧‧Air bearing

16‧‧‧ inner shell

18‧‧‧ spool

20‧‧ ‧ sales

21‧‧‧ trench

22‧‧‧ coil

A1‧‧‧Differential Amplifier

A2‧‧‧Differential Amplifier

C‧‧‧ Center

C0‧‧‧ coil

C0'‧‧‧ coil

C1‧‧‧ coil

C1'‧‧‧ coil

C2‧‧‧ coil

C2'‧‧‧ coil

C3‧‧‧ coil

C3'‧‧‧ coil

PS‧‧‧AC power supply

R1‧‧‧ resistance

R2‧‧‧ resistance

R3‧‧‧ resistance

R4‧‧‧ resistance

Fig. 1 is a longitudinal sectional view of a magnetic displacement sensor of the embodiment.

Fig. 2 shows the arrangement of the coils, 1) shows the arrangement in the conventional example, 2) shows the arrangement in the embodiment, 3) shows the configuration in the modification 1, 4) shows the configuration in the preferred embodiment, 5) The arrangement in Modification 2 is shown, 6) shows the arrangement in Modification 3, and 7) shows the electrical phase angle (phase).

Fig. 3 is a circuit diagram of a driving circuit in the first embodiment.

Figure 4 is a circuit diagram of the drive circuit in the preferred embodiment.

Fig. 5 is a graph showing simulation results of errors caused by temperature dependence in the conventional examples, examples, and preferred embodiments.

Figure 6 is a graph showing measured values of errors in the embodiment and the preferred embodiment.

The embodiment and its modifications are shown in Figs. 1 to 6 . FIG. 1 shows the configuration of the magnetic displacement sensor 10. The component symbol 2 is a magnetic scale, and is a magnetic marker such as a surface of a round rod having a low thermal expansion rate such as an invar alloy or a super-invar alloy, and is provided with a ring-shaped Cu film 6 or the like at a fixed distance, for example, a surface. It is covered by the protective film 8. In order to provide the Cu thin film 6, Cu plating, etching, or the like can be used. Further, a non-magnetic metal film such as Al (aluminum) may be used instead of Cu.

The magnetic displacement sensor 10 (hereinafter simply referred to as the sensor 10) is provided with a casing 12 composed of a metal having a low thermal expansion rate such as Invar or Super Invar, and air is supplied from the pipe 14 and is supported by the air bearing 15 The magnetic scale 2 is supported in a non-contact manner. Further, the configuration in which the magnetic scale 2 is supported in a non-contact manner is arbitrary, and is not limited to the air bearing 15. The component symbol 16 is an inner casing of stainless steel or the like, and houses the bobbin 18. The bobbin 18 is composed of a glass frit and an adhesive, and is configured as an insulator. Further, the bobbin 18 is attached to one portion along the longitudinal direction, and is a central portion in the longitudinal direction, and is fixed to the outer casing 12 by, for example, the pin 20. For fixing, a fastening member such as a bolt, a screw, or a key may be used, or the outer casing 12 may be fitted or adhered to the bobbin 18. Hereinafter, the position fixed by the pin 20 along the longitudinal direction of the bobbin 18 (the axial direction of the magnetic scale 2) is referred to as the center C (of the bobbin 18). Further, the magnetic scale 2 can move freely inside the bobbin 18 along the longitudinal direction.

In the groove 21 provided at a predetermined position on the outer circumference of the bobbin 18, Preferably, a plurality of coils 22 are disposed in the grooves 21 that are symmetrically arranged with respect to the center of the bobbin 18. The configuration of the magnetic scale 2 and the arrangement of the coils 22 are shown enlarged in the chain line of FIG. Further, the coil 22 is not limited to a coiled wire, and may be a film coil of Cu or the like by plating, etching, or the like.

The arrangement of the coils is shown in 1) to 6) of Fig. 2, and 7) shows the electrical phase angle θ (phase θ) with respect to the center C of the winding bobbin 18, and the pitch of the Cu thin film 6 is set to 2π. The values of the phase and the pitch are obtained from the magnetic displacement sensor 10 and converted into displacements. C0~C3' is a coil wound around the groove 21 of the bobbin 18, such as the same as the C0 and C0' subscripts, but the difference between the "'" and the coil is the same phase coil, the electrical phase angle θ (phase θ) differs by only 2nπ (n is an integer other than 0). C1 is in phase with C1', C2 and C2' are also in phase, and C3 and C3' are also in phase. Further, the signal components included in the output of the coil are four types of +sin θ sin ωt, -sin θ sin ωt, + cos θ s sin ωt, and - cos θ s sin ωt. Further, the difference between the output including +sin θ ss ωt and the output including -sin θ sin ωt is amplified by a differential amplifier, and a signal of +sin θ sin ωt is extracted. Further, a differential amplifier is used to amplify the difference between the output including +cos θ ss ωt and the output including -cos θ sin ωt, and the signal of +cos θ sin ωt is extracted.

In the prior art, for example, both ends or one end of the bobbin 18 are fixed to the outer casing 12. In the conventional technique of 1), it is assumed that the position of the coil C0 of the +sin phase is fixed. Although there is temperature dependency in the impedance of the coil, if the output of the pair of coils is differentially amplified, the temperature dependence of the impedance can be almost eliminated. The problem is that the position of the coils C0 to C3 with respect to the center C of the bobbin shaft varies depending on the thermal expansion of the bobbin 18. In the prior art, since the countermeasure against thermal expansion of the bobbin 18 is not taken, the output of the sensor 10 is temperature dependent.

In the configuration of 2) (Embodiment 1), since 4 coils C0~C3 Since the same number is disposed on both sides of the center C, the error due to the temperature dependency becomes small. Although the arrangement of the four coils C0 to C3 is symmetrical, since the direction of expansion of the sin phase and the cos phase are opposite, an error due to temperature dependency remains.

In the arrangement of 3) (variation 1), the coils C2 and C3 of the cos phase are symmetrically arranged with respect to the center C, but since the coils C0 and C1 of the sin phase are not symmetrically arranged with respect to the center C, Some error will remain. Furthermore, the error in Modification 1 is smaller than the error in Embodiment 1.

In the preferred embodiment of 4), the six coils C0 to C3' are symmetrically arranged with respect to the center C, the coils C0, C0' are in phase (for example, -cos phase), and the coils C1, C1' are also in phase. (for example, +cos phase), the difference in output is almost free of temperature dependence. The coil C0 and the coil C1 have a phase difference of, for example, 3π (generally (2n+1)π, where n is an integer), and give an output of the +sin phase and an output of the -sin phase. Therefore, the difference between the output of the coil C0 and the coil C1 hardly includes temperature dependency.

In the preferred embodiment of 4), for example, the coils of the cos phase are four, and the coils of the sin phase are two, and the number is not uniform. Therefore, in the second modification of the fifth aspect, the coil of the sin phase is set to four of C0, C1, C0', and C1', and these are arranged symmetrically with respect to the center C. Further, the phases of the coils C0 and C0' are, for example, different by 2π, and the phases of the coils C1 and C1' are, for example, also different by 2π. Further, the phases of the coils C0 and C1' are, for example, different by π, and the phases of the coils C1 and C0' are, for example, also different by π. Similarly, the four coils C2 to C3' of the cos phase are arranged symmetrically with respect to the center C.

In the second modification of the fifth aspect, between the coils C1 and C1' of the same phase of the sin phase, there is a gap between the magnetic marks (2π in terms of phase). The modification 3 of 6) is a coil C2 and C3' in which the cos phase is arranged and the phases are different by π between the coils C1 and C1'. In the third embodiment of the preferred embodiment to 6), the temperature dependence of the sensor Almost 0.

3 shows an example of a driving circuit of the first embodiment and the first modification. The component symbol PS is an alternating current power supply, and outputs a voltage of A‧sin ωt, and R1 to R4 are fixed resistors, and the resistance values are, for example, the same. Furthermore, () is used in the case of the case of the preferred embodiment. If the output of the two coils of the sin phase is differentially amplified by the differential amplifier A1, the output of B‧sin θ sin ωt can be obtained, and if the output of the two coils of the cos phase is differentially amplified by the differential amplifier A2, The output of B‧cos θ sin ωt can be obtained. For example, if cotωt is multiplied by the signal of B‧sinθ‧sinωt and converted to B‧sinθ‧cosωt, the signal of sin(θ+ωt) can be obtained by the addition theorem, and according to the zero crossing point of the signal (θ+ωt =nπ) to find the phase θ.

In the case where the circuit of Fig. 3 is used to drive the preferred embodiment, the connection coil C1' is substituted for the resistor R1, and the connection coil C0' is substituted for the resistor R2. In this way, since four coils C0, C1', C1, and C0' are used in the sin phase, since two coils are used in the cos phase, the gain of the differential amplifier A1 is twice the gain of the differential amplifier A2. . In the bridge of the sin phase, if one end is in the order of (+sin, -sin), the other end is in the order of (-sin, +sin).

4 shows an example of a drive circuit according to Modifications 2 and 3. The component symbol PS is the above-described AC power supply, and A1 and A2 are the above-described differential amplifiers. Similarly to the preferred embodiment, for example, coils C3 and C2 are connected in series, coils C2' and C3' are connected in series to form a bridge, and the output of the bridge is amplified by a differential amplifier, and this is set to cos phase. Output. In this bridge, if one end is in the order of (+cos, -cos), the other end is also set to the order of (-cos, +cos). For example, the coils C1' and C0 are connected in series, and the coils C0' and C1 are connected in series to form a bridge, and the output of the bridge is amplified by a differential amplifier, and this is set as an output of the sin phase. For the bridge, if 1 is (+sin, -sin) In the order, the other end is also set to the order of (-sin, +sin).

Fig. 5 shows the performance of the conventional example and the first embodiment and the preferred embodiment, and the detection error of the displacement is obtained by simulation, and the length of the bobbin is thermally expanded by 0.1% to 0.3%. In the first embodiment, the absolute value of the error is reduced to about 40% of the conventional example, and the average value of the error is almost zero. On the other hand, in the conventional example, the sign of the error is fixed and does not become zero. Also in the preferred embodiment, the error is always approximately zero. Furthermore, in Modification 1 of FIG. 2, the error is smaller than that of Embodiment 1.

Fig. 6 is a graph showing the measured value of the displacement error (change in the indication value when the ambient temperature is changed from 20 ° C to 28 ° C). ○ indicates the result of Example 1, △ indicates the result of the preferred embodiment, and Example 1 indicates the interpolation between the measured values by the sin wave. The error of the preferred embodiment is small, and this small error is supposed to be caused by the temperature dependence of the differential amplifier and the poor configuration of the coils C0 to C3'.

Since the magnetic displacement sensor 10 having a small temperature dependency can be obtained in the embodiment, the machining position of the machine tool such as a lathe, a drill, a grinder, and the like can be accurately measured, thereby improving the machining accuracy.

Moreover, the gap between the dies can be accurately measured in a mold clamping device such as a press machine, an injection molding machine, or a die-casting machine. In addition, the displacement can be accurately measured in an environment where the temperature changes and it is difficult to perform optical measurement.

In the embodiment, the magnetic scale 2 passes through the bobbin 18, but a planar magnetic scale may be opposed to a planar thin film coil or the like. Further, a dummy coil may be disposed on both sides of the row of coils constituted by the coils C0 to C3'.

The driving circuit is not limited to those shown in FIG. 3 and FIG. 4. For example, the average value of the outputs of the coils C0 and C0' of the same phase and the outputs of the coils C1 and C1' of the same phase may be used. The difference between the average values is amplified. Similarly, the difference between the average value of the outputs of the coils C2 and C2' of the same phase and the average of the outputs of the coils C3 and C3' of the same phase can be amplified. Further, the primary coil and the secondary coil may be laminated, or a secondary coil may be disposed between the primary coil and the primary coil. In this case, each coil 22 of the embodiment corresponds to a secondary coil.

C‧‧‧ Center

C0‧‧‧ coil

C0'‧‧‧ coil

C1‧‧‧ coil

C1'‧‧‧ coil

C2‧‧‧ coil

C2'‧‧‧ coil

C3‧‧‧ coil

C3'‧‧‧ coil

Claims (8)

A magnetic displacement sensor that detects displacement by interaction of a plurality of coils and a magnetic scale, the plurality of coils being supported by a support, the magnetic scale being disposed along a longitudinal direction a magnetic mark that changes periodically with a fixed pitch; and is characterized in that: a housing that houses the support; and a fixing portion that fixes a central portion of the support along a longitudinal direction of the magnetic scale And the plurality of coils are each of the same number and supported by the support body on both sides of the fixing portion along the longitudinal direction of the magnetic scale. The magnetic displacement sensor of claim 1, wherein the magnetic displacement sensor is provided with at least two coils having a sin phase output and two coils of a cos phase output as the plurality of coils, along the magnetic In the longitudinal direction of the scale, at least one coil of the sin phase output and at least one coil of the cos phase output are supported on both sides of the fixed portion. The magnetic displacement sensor of claim 1, wherein the plurality of coils are six or eight, and the pitch of the magnetic scale is taken as an electrical phase angle of 2π, which is toward the magnetic scale. Two coils each having an electrical phase angle of θ are symmetrically arranged on each side of the fixed portion, and two coils having electrical phase angles toward the magnetic scale are θ+π, symmetrically One of the configurations is provided on both sides of the fixed portion. The magnetic displacement sensor of claim 3, wherein the plurality of the plurality of coils are eight. Two coils having an electrical phase angle of θ+π/2 toward the magnetic scale are arranged symmetrically on each side of the fixed portion, and the electrical phase angles toward the magnetic scale are all Two coils of θ-π/2 are arranged symmetrically on each side of the fixed portion. The magnetic displacement sensor according to claim 1, wherein the support system is a bobbin having a hollow shape in which the magnetic scale is inserted, and a plurality of coils are wound around the bobbin. The magnetic displacement sensor according to any one of claims 1 to 5, wherein the outer casing and the support have different thermal expansion rates. The magnetic displacement sensor of claim 6, wherein the outer casing is a metal having a low thermal expansion coefficient, and the support is an insulator. A displacement detecting method for detecting displacement by a support body, a magnetic displacement sensor, and a magnetic scale sensor having a plurality of coils supported by a support body, the magnetic scale system having a magnetic mark that changes periodically along a longitudinal direction at a fixed pitch; wherein the magnetic displacement sensor is provided with: a casing that houses the support; and a fixing portion along the magnetic scale a longitudinal direction of the support body fixed to the outer casing; along the longitudinal direction of the magnetic scale, on the two sides of the fixed portion, the plurality of coils are each the same number and supported by the support body The effects of thermal expansion of the support are offset between the same number of coils supported on both sides of the fixed portion.