KR20150136570A

KR20150136570A - Magnetic displacement sensor and method for detecting displacement

Info

Publication number: KR20150136570A
Application number: KR1020150053121A
Authority: KR
Inventors: 테츠야 시미즈; 쇼고 테라다; 타쿠미 야마모토; 츠토무 오츠보
Original assignee: 무라다기카이가부시끼가이샤
Priority date: 2014-05-27
Filing date: 2015-04-15
Publication date: 2015-12-07
Also published as: KR101949176B1; JP2015224926A; TW201602523A; CN105300261B; JP6365824B2; TWI624645B; CN105300261A

Abstract

Provided is a magnetic displacement sensor to minimize the effect of an ambient temperature of the magnetic displacement sensor. The magnetic displacement sensor comprises: a support structure; a casing accommodating the support structure; and a fixing unit which fixates the center portion of the support structure to the casing along the lengthwise direction of a magnetic scale. A plurality of coils is supported by the support structure on the both sides of the fixing unit, with a same number of the coils on each sides, along the lengthwise direction of the magnetic scale.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a magnetic displacement sensor,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to detection of a displacement by a magnetic displacement sensor, and more particularly to reducing an error due to temperature fluctuation.

It is known to detect displacement using a magnetic scale and a magnetic displacement sensor in which a magnetic body and a non-magnetic body are arranged alternately and periodically. For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 09-264758) discloses a magnetic displacement sensor that draws output of sin (? +? T) using four primary coils and four secondary coils . Where? Is the angular frequency of the alternating current for excitation, and? Is the electrical phase angle relative to the magnetic scale. In this magnetic displacement sensor, the coil is ring-shaped, and the primary coil is disposed on the inner peripheral side and the secondary coil is disposed on the outer peripheral side. Then, the magnetic scale of the rod shape passes through the hollow portion of the ring-shaped coil, and the magnetic displacement sensor detects the displacement by using magnetic marks formed at a constant pitch on the magnetic scale. Hereinafter, the magnetic displacement sensor may be simply referred to as a sensor.

The number of coils can be reduced to half, for example, by using a coil serving as both a primary coil and a secondary coil instead of using a primary coil and a secondary coil (Patent Document 2: Japanese Patent Application Laid-Open No. 2013-024779). In this case, the phase (? +? T) of the AC current flowing through the coil is detected by applying an AC voltage to the row of the coils. In addition, by forming two rows of coils by reversing the direction of current flow, the error due to the magnetic scale and the relative speed of the sensor can be reduced (Patent Document 2).

It has been proposed to compensate for the influence of thermal deformation of a precision machine such as a machine tool by a magnetic displacement sensor (Patent Document 3: Japanese Patent Laid-Open Publication No. 2011-093069). For example, if the distance between the main shaft of the lathe and the tool rest is changed by the thermal deformation of the lathe, the work accuracy of the work is lowered. Therefore, by measuring the positions of the main shaft and the tool base, it is possible to compensate the influence of the thermal deformation by obtaining the interval therebetween and moving the main shaft or the like so as not to be influenced by the ambient temperature. In Patent Document 3, the position of the main shaft and the tool rest of the machine tool are measured by the magnetic scale and the magnetic displacement sensor. Although not described in Patent Document 3, if the magnetic scale is made of a material such as an invar alloy which does not substantially thermally expand, it becomes a magnetic scale free from the influence of ambient temperature.

The inventor has taken note of the fact that the magnetic displacement sensor itself is affected by thermal expansion. This sensor is, for example, a coil wound around a bobbin of a non-magnetic body. As a non-magnetic material, glass, ceramics or the like having a very small coefficient of thermal expansion is known, but it is difficult to process it into an accurate shape by using only such a material. In addition, when an invar alloy having a small coefficient of thermal expansion is used for the bobbin, the influence of the magnetic scale is blocked by the invar alloy of the bobbin. Therefore, it is difficult to eliminate the thermal expansion of the bobbin.

Further, in the position sensor of Patent Document 4 (Japanese Patent Application Laid-Open No. 2003-269993), a thin film coil of Cu is provided on the surface of a cylinder made of a material having a small coefficient of thermal expansion such as ceramic, invar alloy or the like. Then, it is disclosed that the thin film coil of Cu is put in and out of the stainless steel pipe to measure the length of overlap of the stainless steel pipe and the thin film coil. For example, if a stainless pipe is changed to a pipe such as an invar alloy, and a precise magnetic mark can be formed on the inner circumferential surface thereof, the position can be measured without being influenced by the ambient temperature. However, such processing is difficult.

An object of the present invention is to reduce the influence of the ambient temperature on the magnetic displacement sensor.

The present invention relates to a magnetic displacement sensor for detecting a displacement by a plurality of coils supported on a support and magnetic scales in which a magnetic mark periodically changed at a predetermined pitch along a longitudinal direction is formed,

A casing for receiving the support,

And a fixing part for fixing the central part of the support to the casing along the longitudinal direction of the magnetic scale,

And a plurality of coils are supported on the supporting body on both sides of the fixing portion along the longitudinal direction of the magnetic scale.

The present invention also provides a method of detecting displacement by a magnetic scale having a support, a magnetic displacement sensor having a plurality of coils supported by a support, and magnetic marks periodically changing at a constant pitch along the length direction,

The magnetic displacement sensor

A casing for receiving the support,

A plurality of coils are supported on the support member on the both sides of the fixed portion along the longitudinal direction of the magnetic scale,

And the effect of thermal expansion of the support is canceled between the coils supported on the both sides of the fixed portion by the same number.

What is important in terms of the position at which the support member, that is, the support member is fixed to the casing, is that the same number of coils are arranged on both sides of the fixing member to cancel the influence of thermal expansion of the support member between the coils. The central portion is used as the stationary portion in order to dispose the coils on both sides thereof, and the stationary portion is not limited to the center in the longitudinal direction. It is preferable that the arrangement of the coils is symmetrical with respect to the central portion (fixed portion) of the support.

In the present invention, even if the position of the coil changes due to the thermal expansion of the support, the influence of the thermal expansion between the coils supported by the same number on both sides of the fixing portion can be canceled. When the arrangement of the coils becomes closer to the symmetry with respect to the fixed portion, the detection error of the displacement due to the thermal expansion becomes small. However, even if it is not symmetric, it is possible to offset a considerable error by arranging the same number of coils on both sides of the fixed portion.

Consider, for example, at least two coils of sinusoidal output and at least two coils of cosine output, such as a coil of + sin, a coil of -sin, a coil of + cos and a coil of -cos. In this case, if at least one coil of the sin phase output and at least one coil of the cos phase output are disposed on both sides of the fixed portion along the longitudinal direction of the magnetic scale, an error between the coil of + sin phase and the coil of- And the error between the coils on the + cos and the coils on the -cos can be canceled.

More preferably, the number of coils is six or eight. Then, two coils having an electric phase angle of all? Are arranged symmetrically on both sides of the fixed portion, one at an electric phase angle at which the pitch of the magnetic mark on the magnetic scale is 2?, And the electric phase angle to the magnetic scale Two coils of which all are + [theta] + are arranged symmetrically one by one on both sides of the fixed portion. The coil whose electric phase angle is? And? +? May be a coil of sin phase or a coil of cos phase.

If the coils of the output on + sin are arranged symmetrically with respect to the coil fixing part of the output on -sin, it is difficult to symmetrically arrange a pair of coils of the output on the cos. It is also difficult to arrange a pair of coils of an output of ± sin symmetrically if a pair of coils of an output of ± cos are arranged symmetrically with respect to the stationary portion. Further, the sin phase and the cos phase are only a matter of which position the electric phase angle is to be zero. Thus, for example, the coils of the output on + sin and the coils of the output on -sin are arranged symmetrically with respect to the fixed portion. a pair of coils of + cos can be arranged symmetrically with respect to the stationary portion, and a pair of coils on -cos can be arranged symmetrically with respect to the stationary portion. Therefore, when the coils on the + cos and the coils on the -cos are arranged symmetrically on both sides of the pair of fixing portions, the arrangement of the coils becomes symmetrical. In this case, the error caused by the temperature fluctuation becomes almost zero.

Particularly preferably, there are eight coils, and two coils having, for example, all (? + 1/2?) Electric phase angles on the magnetic scale are symmetrically arranged one on each side of the fixed portion, Two coils having an electric phase angle to the magnetic scale of, for example, all ([theta] - 1/2 [pi] are symmetrically arranged on both sides of the fixed portion. The phases of the remaining four coils are, for example, two in theta and two in theta + n. Thus, a coil of + sin, a coil of -sin, a coil of + cos and a coil of -cos can be arranged symmetrically on both sides of the fixing part at the center of the supporting body. Since there are two coils having the same output phase, the driving circuit is simplified.

In addition, preferably, the support is a hollow bobbin through which a magnetic scale can be inserted, and a plurality of coils are wound around the bobbin. In this case, the central portion of the bobbin is fixed to the casing, and on both sides of the central portion of the bobbin, the coils are arranged symmetrically, preferably symmetrically, preferably as far as possible. This makes it easier to offset the effects of thermal expansion between the coils. In magnetic scale, an accurate magnetic mark can be formed on the outer peripheral surface of the pipe or 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 casing and the support have different thermal expansion rates. More preferably, the thermal expansion coefficient of the casing is made lower than the thermal expansion coefficient of the support. In the present specification, the coefficient of thermal expansion is used to mean the coefficient of linear thermal expansion. When the support is housed in the casing, it is a common sense to adjust the thermal expansion rate of both. However, in the present invention, it is not necessary to match the thermal expansion coefficients of both of them. Particularly, since the support member is stretched and expanded on both sides of the fixing portion with respect to the casing, deformation due to a difference in thermal expansion rate does not occur. Since the casing has a wider range of materials to be selected than the support, it is preferable to make the thermal expansion coefficient of the casing smaller than that of the support.

Preferably, the casing is a metal having a low thermal expansion coefficient such as an invar alloy or a super invar alloy, and the support is an insulator such as a mixture of a glass having a low thermal expansion coefficient and an organic binder. In the present specification, the low thermal expansion coefficient means that the linear thermal expansion coefficient at room temperature is 2 ppm or less and 1.2 ppm in Invar. The linear expansion coefficient of the support is, for example, about 20 ppm. Since the support is fixed to the casing having the low thermal expansion coefficient, the influence of the temperature variation on the casing can be reduced. In addition, since it is a metal casing, the electric field from outside can be cut off. In particular, the invar alloy is magnetic and can also block magnetic fields from the outside. The support of the insulator does not interfere with the interaction between the magnetic scale and the coil. In particular, when the mixture of glass and plastic binder is used, it can be precisely processed into a desired shape.

1 is a longitudinal sectional view of a magnetic displacement sensor of an embodiment.
Fig. 2 shows the arrangement of the coils, in which 1) shows the arrangement in the conventional example, 2) the arrangement in the embodiment, 3) the arrangement in the variant 1, and 4) , 5) shows the arrangement in the modified example 2, 6) shows the arrangement in the modified example 3, and 7) shows the electric phase angle (phase).
3 is a circuit diagram of the driving circuit in the first embodiment.
4 is a circuit diagram of a driving circuit in the optimum embodiment.
5 is a diagram showing simulation results of errors due to temperature dependency for the conventional example, the embodiment, and the optimum example.
Fig. 6 is a diagram showing measured values of errors in the embodiment and the optimum embodiment. Fig.

Figs. 1 to 6 show an embodiment and a modification thereof. Fig. 1 shows a structure of the magnetic displacement sensor 10. Fig. 2 is a magnetic scale and magnetic marks such as a ring-shaped Cu thin film 6 are formed at constant pitch on the surface of a round bar having a low thermal expansion coefficient such as an invar alloy or a super invar alloy. For example, . In order to form the Cu thin film 6, Cu plating and etching may be used. Instead of Cu, a non-magnetic metal film such as Al may be used.

The magnetic displacement sensor 10 (hereinafter simply referred to as the sensor 10) is provided with a casing 12 made of a metal having a low thermal expansion coefficient such as an invar alloy or a super invar alloy and supplies air from the pipe 14, And the magnetic scale 2 is held in a noncontact manner by the magnetic force sensor 15. The structure for supporting the magnetic scale 2 in a noncontact manner is optional and is not limited to the air bearing 15. [ Reference numeral 16 denotes an inner case made of stainless steel or the like, which houses the bobbin 18. The bobbin 18 is made of a glass powder and a binder, and is formed as an insulator. The bobbin 18 is located at one position along the longitudinal direction, and is fixed to the casing 12 by, for example, a pin 20 at the center in the longitudinal direction. A fastening member such as a bolt, a screw, or a key may be used for fixing, or the casing 12 and the bobbin 18 may be fitted or bonded. Hereinafter, the position fixed by the pin 20 along the longitudinal direction of the bobbin 18 (axial direction of the magnetic scale 2) is referred to as the center C of the bobbin 18 (of the bobbin 18). The magnetic scale 2 is movable along the longitudinal direction inside the bobbin 18.

A plurality of coils 22 are arranged in a groove 21 formed at a predetermined position on the outer circumference of the bobbin 18 and preferably in a groove 21 arranged symmetrically with respect to the center of the bobbin 18. The structure of the magnetic scale 2 and the arrangement of the coils 22 are shown in an enlarged scale in the chain line of Fig. The coil 22 is not limited to a coil, and may be a thin film coil made of Cu or the like by plating, etching, or the like.

2 shows the arrangement of the coils in 1) to 6) in Fig. 2, 7) shows the electric phase angle? (Phase?) With respect to the center C of the bobbin 18, 1 pitch is set to 2 pi. The number of phases and pitches is obtained from the magnetic displacement sensor 10 and converted into displacement. C0 to C3 'are coils wound around the groove 21 of the bobbin 18, and a pair of coils having the same subscripts such as C0 and C0' and having different "" "s are coils of the same phase, ) (Phase?) Is different by 2n? (N is an integer other than 0). C1 and C1 'are in phase, C2 and C2' are in phase, and C3 and C3 'are in phase. In addition, the signal components included in the output of the coil are + sin? Sin? T, -sin? Sin? T, + cos? Sin? T and -cos? Sin? T. The differential amplifier amplifies the difference between the output including + sin? Sin? T and the output including -sin? Sin? T to extract a signal of + sin? Sin? T. Further, the difference between the output including + cos? Sin? T and the output including -cos? Sin? T is amplified by the differential amplifier to extract a signal of + cos? Sin? T.

In the prior art, for example, both ends or one end of the bobbin 18 are fixed to the casing 12. [ 1), it is supposed to be fixed at the position of the coil C0 on the + sin. The impedance of the coil is temperature-dependent. Differential amplification of the output of the pair of coils can substantially eliminate the temperature dependency of the impedance. The problem is that the position of the coils C0 to C3 with respect to the center C of the bobbin varies according to the thermal expansion of the bobbin 18. [ In the prior art, since the countermeasure against the thermal expansion of the bobbin 18 is not implemented, temperature dependency occurs in the output of the sensor 10.

2) (Example 1), the same number of coils C0 to C3 are arranged on both sides of the center C, so that the error due to temperature dependency is reduced. The arrangement of the four coils (C0 to C3) is symmetric, but since the expansion direction is opposite to that of the sin phase and the cosine phase, errors due to temperature dependency remain.

The coils C0 and C1 in the sin phase are arranged symmetrically with respect to the center C while the coils C2 and C3 in the cosine phase are arranged symmetrically with respect to the center C in the arrangement Some errors remain because there is not. In addition, the error in Modification 1 is smaller than the error in Embodiment 1.

6, the six coils C0 to C3 'are arranged symmetrically with respect to the center C, the coils C0 and C0' are in the same phase (for example, -cos phase) C1 and C1 'are also in phase (for example, + cos phase), and the difference in their outputs hardly includes the temperature dependency. The coil C0 and the coil C1 are different in phase from each other, for example, 3? (Generally, (2n + 1)? And n is an integer) and give an output on + sin and an output on -sin. Therefore, the difference between the output of the coil C0 and the output of the coil C1 hardly includes the temperature dependency.

4), for example, there are four coils in the cos phase and two coils in the sin phase, so that the number does not match. Thus, in Modification Example 2 of 5), the sin-phase coil is made of four coils C0, C1, C0 'and C1', and these coils are arranged symmetrically with respect to the center C. The phases of the coils C0 and C0 'are different, for example, by 2π, and the phases of the coils C1 and C1' are also different by, for example, 2π. Further, the coils C0 and C1 'have different phases, for example,?, And the coils C1 and C0' also have different phases, for example,?. Similarly, the four coils C2 to C3 'on the cosine phase are arranged symmetrically with respect to the center C. [

5), there is an interval (2π in phase) of magnetic mark by one pitch between coils C1 and C1 'in sin phase. And a coil C2 and C3 'having phases different from each other by π on cos between the coils C1 and C1'. 4) In Modification 3 of the embodiment 6), the temperature dependency of the sensor is almost zero.

Fig. 3 shows an example of a driving circuit according to the first embodiment and the first variation. PS is an AC power source and outputs a voltage of A 占 ω ω t. R1 to R4 are fixed resistors and the resistance value is, for example, the same. Further, () is the arrangement when used in the optimum embodiment. sin &thetas; &thetas; t is obtained by differentially amplifying the outputs of the two coils on the sine by the differential amplifier A1, and when the outputs of the two coils are differentially amplified by the differential amplifier A2, The output of sin ωt is obtained. For example, the signal of B · sin θ · sin ωt is multiplied by cot ωt to convert it to B · sin θ · cos ωt, and the signal of sin (θ + ωt) is obtained by summation theorem and the zero crossing (θ + ωt = ) From the phase difference?

When the optimum embodiment is driven in the circuit of Fig. 3, the coil C1 'is connected instead of the resistor R1, and the coil C0' is connected instead of the resistor R2. Then, since two coils are used for cos in comparison with the use of four coils (C0, C1 ', C1, and CO') in the sin phase, the gain of the differential amplifier A1 is made twice the gain of the differential amplifier A2 . In a sinusoidal bridge, one side is in the order of (+ sin, -sin) and the other side is in the order of (-sin, + sin).

Fig. 4 shows an example of a drive circuit according to Modifications 2 and 3, wherein PS is an electric AC power source, and A1 and A2 are the differential amplifiers. As in the case of the optimum embodiment, for example, coils C3 and C2 are connected in series and coils C2 'and C3' are connected in series to sandwich a bridge. The output of the bridge is amplified by a differential amplifier, do. In this bridge, one is in the order of (+ cos, -cos) and the other is in the order of (-cos, + cos). For example, the coils C 1 'and C 0 are connected in series, the coils C 0' and C 1 are connected in series, the bridge is sandwiched, and the output of the bridge is amplified by the differential amplifier to obtain sin output.

In this bridge, one side is (+ sin, -sin) order and the other side is (-sin, + sin) order.

Fig. 5 shows the performance of the conventional example, the first embodiment and the best embodiment, and the error of detection of the displacement was obtained by simulating that the bobbin was thermally expanded by 0.1% to 0.3% in length. In Embodiment 1, 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. In contrast, in the conventional example, the error is constant in sign and does not become zero. And, in the optimal embodiment, the error is almost always zero. In Modification 1 of Fig. 2, the error is smaller than that of Embodiment 1. Fig.

Fig. 6 shows measured values of the detection error of displacement (change of the indication value when the ambient temperature is changed from 20 캜 to 28 캜). ? Indicates the results of the first embodiment,? Indicates the results of the optimum embodiment, and Example 1 indicates interpolation of the measured values between the sin wave. The error of the optimum embodiment is small, and this slight error is thought to be due to the temperature dependency of the differential amplifier, disarrangement of the coils C0 to C3 ', and the like.

In the embodiment, since the magnetic displacement sensor 10 having a small temperature dependency is obtained, it is possible to accurately measure the machining position in a machine tool such as a lathe, a drill, and a grinding machine, thereby improving the machining accuracy.

Further, the mold clamping device such as a press, an injection molding machine, or a die casting molding machine can accurately measure the distance between the molds. It is possible to accurately measure the displacement in an environment where the temperature is otherwise changed and optical measurement is difficult.

In the embodiment, the magnetic scale 2 passes through the inside of the bobbin 18, but the magnetic scale on the plane and the thin film coil on the plane may be opposed to each other. Further, dummy coils may be disposed on both sides of the row of coils made up of the coils C0 to C3 '.

The drive circuit is not limited to the one shown in Figs. 3 and 4, and for example, the difference between the average value of the outputs of the in-phase coils C0 and C0 'and the average value of the outputs of the coils C1 and C1' . Similarly, the difference between the average value of the outputs of the in-phase coils C2 and C2 'and the average value of the outputs of the in-phase coils C3 and C3' may be amplified. Further, the primary coil and the secondary coil may be laminated, or the secondary coil may be disposed between the primary coil and the primary coil. In that case, each coil 22 in the embodiment corresponds to a secondary coil.

Claims

There is provided a magnetic displacement sensor for detecting displacement by a plurality of coils supported on a support and a magnetic scale formed with a magnetic mark periodically changing at a predetermined pitch along a longitudinal direction,
A casing for accommodating the support,
And a fixing portion for fixing a central portion of the support to the casing along the longitudinal direction of the magnetic scale,
And the plurality of coils are supported on the support member on the both sides of the fixed portion along the longitudinal direction of the magnetic scale by the same number.

The method according to claim 1,
The magnetic displacement sensor has at least two coils of a sin phase output and a cos phase output as the plurality of coils,
Wherein at least one coil of sin phase output and at least one coil of cos phase output are supported on both sides of the fixed portion along the longitudinal direction of the magnetic scale.

The method according to claim 1,
The number of the plurality of coils is six or eight,
Wherein two coils each having an electric phase angle of &thetas; to the magnetic scale are arranged symmetrically on both sides of the fixed portion, and the electric phase angle is 2 &
Wherein two coils having an electric phase angle of? +? Are arranged symmetrically with respect to one another on both sides of the fixed portion.

The method of claim 3,
The number of the plurality of coils is eight,
Two coils having an electric phase angle of? +? / 2 on the magnetic scale are symmetrically arranged one by one on both sides of the fixed portion,
Wherein two coils having an electric phase angle of? -? / 2 on the magnetic scale are symmetrically arranged one on each side of the fixed portion.

The method according to claim 1,
Wherein the support is a hollow bobbin through which the magnetic scale can be inserted, and a plurality of coils are wound on the bobbin.

6. The method according to any one of claims 1 to 5,
Wherein the casing and the support have different thermal expansion coefficients.

The method according to claim 6,
Wherein the casing is a metal having a low thermal expansion coefficient, and the support is an insulator.

1. A method of detecting a displacement by a magnetic scale having a support, a magnetic displacement sensor having a plurality of coils supported by a support, and a magnetic scale periodically changing at a predetermined pitch along the longitudinal direction,
The magnetic displacement sensor
A casing for accommodating the support,
And a fixing portion for fixing a central portion of the support to the casing along the longitudinal direction of the magnetic scale,
Wherein the plurality of coils are supported on the support member on the same side of the fixed portion along the longitudinal direction of the magnetic scale,
Wherein the influence of the thermal expansion of the support is canceled between the coils supported by the same number on both sides of the fixed portion.