JP4924825B2 - Electromagnetic induction type linear scale - Google Patents

Description

The present invention relates to a linear scale that measures the displacement of a measurement object in an absolute manner by an electromagnetic induction method.

A conventional electromagnetic induction type linear scale is generally composed of a plurality of coil elements and a coil array (detection head) extending in the detection axis direction, a magnet, and the like, and is disposed so as to be relatively displaceable with respect to the coil array. And a magnetic member (detection dog).

The coil array includes a predetermined number of coils arranged in parallel at equal intervals, for example, four coils as one coil set, and the plurality of coil sets are arranged in parallel. Each coil element is excited by a sine wave signal α = Asinωt.

When the magnetic member is positioned on the coil set in the coil array, a difference in self-inductance occurs between the four coil elements. Of the four coil elements, take the differential output between the first and third coil elements when counted from one end side, and the differential output between the second and fourth coil elements, and By combining and converting, a combined signal β = asin (ωt ± θ) is obtained. The electromagnetic induction linear scale can measure the relative displacement of the magnetic member with respect to the coil array in an absolute manner by detecting the phase difference between the combined signal β and the sine wave signal α.
JP 2001-141410 A

The electromagnetic induction linear scale as described above is configured such that the magnetic member is relatively displaced on the track along the detection axis of the coil array. However, inevitably, the magnetic member may deviate from its normal orbit and be relatively displaced. The self-inductance of the coil element also changes due to the relative displacement that deviates from the normal trajectory, and the measured value of the electromagnetic induction linear scale in this case includes an error. Conventional electromagnetic induction linear scales cannot detect the presence or absence of measurement errors due to the relative displacement of the magnetic member out of the normal trajectory.

The present invention has been made in view of the above circumstances, and an object of the present invention is to determine whether a magnetic member has deviated beyond a permissible range from a normal trajectory along the detection axis. It is to provide an inductive linear scale.

In order to solve the above problems, the present invention comprises a coil array composed of a predetermined number of coil elements arranged in parallel on the same axis, and a coil array excited by a first AC signal, and on the outside of the coil array. A magnetic member disposed and capable of being displaced relative to the coil array along the axis of the coil array, wherein the magnetism changes the amplitude of the output voltage of the coil element in accordance with the positional relationship with the coil element. And measuring the relative displacement based on the phase difference between the second AC signal obtained by synthesizing a plurality of differential outputs between the coil elements in the coil set and the first AC signal. An electromagnetic induction linear scale that is arranged along an axial direction of the coil array and outputs a detection value corresponding to a positional relationship with the magnetic member; and the magnetic sensor And a determination unit that determines whether an error included in the measurement value of the electromagnetic induction linear scale is within an allowable range based on whether the detected value is within a predetermined allowable range. An electromagnetic induction linear scale is provided.

The present invention also provides an electromagnetic induction linear scale characterized in that, in the above configuration, the magnetic member is composed of at least one magnet.

According to the present invention, there is provided an electromagnetic induction linear scale characterized in that, in the above-described configuration, the magnetic sensor is disposed in the vicinity of both ends of the coil array.

The present invention also provides an electromagnetic induction linear scale characterized in that, in the above configuration, the magnetic sensor is a Hall element.

According to the electromagnetic induction linear scale of the present invention configured as described above, based on the detection value of the magnetic sensor, whether the magnetic member has deviated beyond the allowable range from the normal trajectory along the detection axis. Whether it can be determined. That is, according to the electromagnetic induction linear scale of the present invention, it is possible to perform measurement while monitoring whether or not an error exceeding an allowable range is included in the obtained measurement value.

Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing the configuration of an electromagnetic induction linear scale according to the present embodiment, FIG. 2 is a diagram for illustrating a method for detecting displacement within the pitch of the electromagnetic induction linear scale according to the present embodiment, and FIG. FIG. 4 is a schematic perspective view showing a positional relationship between a magnetic member and a coil array, and FIG. 5 is a magnetic sensor according to the present embodiment. FIG. 6 is a diagram showing measurement error characteristics of the electromagnetic induction linear scale according to the present embodiment, FIG. 7 is a diagram for explaining a state when a magnetic member is brought close to the coil element, It is.
Hereinafter, depending on the case, the axial length of one coil set is expressed as “1 pitch”.

As shown in FIG. 1, the electromagnetic induction linear scale 1 according to the present embodiment includes a predetermined number of coil elements, in the present embodiment, four coil elements, as one coil set, and coil elements L _{11 to} L _14.・ ・ ・ L _{n1 to} L _n4 n sets of coils L ₁ ... L _n are coaxially arranged in parallel and the coil array 3 is arranged outside the coil array 3 and the axis of the coil array 3 And a magnetic member 2 that can be relatively displaced along.

Four coil elements (first to fourth coil elements) L _{11 to} L ₁₄ constituting the coil set L ₁ are arranged in parallel at a predetermined interval on the same axis, and a sinusoidal signal (first wave) generated by the AC generation source 11. 1 AC signal) α = Asin ωt, respectively.
Further, the output signal _{V o1} from the first coil element _{L 11} and the output signal _{V o3} from third coil element _{L 13} is input to the differential amplifier 41, the output from the second coil element _{L 12} The signal V _o2 and the output signal V _o4 from the fourth coil element L ₁₄ are input to the differential amplifier 42.

The magnetic member 2 is composed of a member having magnetism, and in the present embodiment, is composed of several magnets. When close to the excited coil element, the magnetic member 2 increases the self-inductance of the coil and increases the amplitude of the inter-terminal voltage of the coil. On the contrary, when the magnetic member 2 moves away from the coil, the self-inductance of the coil is reduced and the amplitude of the voltage between the terminals of the coil is reduced (see FIG. 7).

Magnetic member 2, relative to the coil set _{L 1,} that is within one pitch, the displacement x when only the relative displacement (hereinafter, referred to as the pitch in the displacement x), from the differential amplifier 41, the differential output C = kcos · sinωt is output, and the differential amplifier 42 outputs the differential output S = asinθ · sinωt (see FIG. 2A).
Here, θ = 2π / P · x (P: length of 1 pitch).
The differential outputs S and C are input to the differential output combining unit 5.

The differential output S = asin θ · sin ωt input to the differential output combining unit 5 is phase-shifted by 90 ° through the conversion circuit and converted into S ′ = asin θ · cos ωt. The differential output combining unit 5 combines the converted differential output S ′ and the differential output C. The composite signal β is obtained from the addition theorem.
Composite signal β = asin θ · cos ωt ± acos θ · sin ωt
= Asin (ωt ± θ)
It becomes. The differential output combining unit 5 outputs the combined signal beta to the in-pitch displacement detecting unit 6.

The in-pitch displacement detector 6 receives the input of the composite signal β = asin (ωt ± θ) from the differential output combiner 5 and the input of the sine wave signal α = Asinωt from the AC generation source 11. The in-pitch displacement detector 6 detects the phase difference between the sine wave signal α = Asin ωt and the combined signal β = asin (ωt ± θ).

As shown in FIG. 2B, the phase difference is detected by counting the time from the zero cross point of the Asin ωt graph to the zero cross point of the asin (ωt ± θ) graph.

And the in-pitch displacement detector 6 has the following two formulas:
θ = 2π / P · x
θ = 2π / T × (phase difference) (T: period of sine wave signal α)
Thus, the in-pitch displacement x of the magnetic member 2 is calculated and output to the in-scale displacement detector 8 as an in-pitch displacement output.

The other coil sets L ₂ ... L _n are configured in the same manner as the coil set L 1. Therefore, when the magnetic member 2 is displaced with respect to the other coil sets L ₂ ... L _n , that is, within each pitch, the in-pitch displacement x in each coil set (each pitch) is detected in the same way. The displacement output is output to the in-scale displacement detector 8.

The electromagnetic induction linear scale 1 further includes a pitch detector 7 as shown in FIG. A signal from an element (not shown) that can detect the magnetic member 2, which is the hall switch 12 in this embodiment, is input to the pitch detection unit 7. The hall switch 12 is arranged in the vicinity of each coil set L ₁ ... L _n in the coil array 3, and outputs an ON signal when the proximity of the magnetic member 2 is detected, and outputs an OFF signal when not detected. The pitch detection unit 7 detects on which pitch the magnetic member 2 is positioned based on the ON / OFF detection signal from the hall switch 12 and outputs the detected pitch to the in-scale displacement detection unit 8.

The in-scale displacement detection unit 8 detects the in-scale displacement X in response to the in-pitch displacement output from the in-pitch displacement detection unit 6 and the pitch output from the pitch detection unit 7. Here, the in-scale displacement X means the total displacement of the magnetic member 2 with respect to the electromagnetic induction linear scale 1 and is expressed as follows using the in-pitch displacement x of the magnetic member 2.
X = (p−1) × P + x (p: pitch at which the magnetic member 2 is located, P: length of 1 pitch)
For example, when the magnetic member 2 is positioned on the third pitch (coil set L ₃ ), the in-scale displacement detector 8 is based on the pitch output p = 3 and the in-pitch displacement output x,
X = (3-1) × P + x
Thus, the in-scale displacement X is detected (see FIG. 3).

This in-scale displacement X becomes a measured value of the electromagnetic induction linear scale 1 and is output to a monitor (not shown) or the like.

As shown in FIG. 1, the electromagnetic induction linear scale 1 further includes magnetic sensors 9 that can detect the magnetic member 2 in the vicinity of both ends of the coil array 3. The magnetic sensor 9 linearly outputs a detection value corresponding to the positional relationship with the magnetic member 2, and is a Hall element in this embodiment. The magnetic sensor 9 outputs a detection value when the magnetic member 2 passes through the vicinity thereof. The detection value of the magnetic sensor 9 is input to the determination unit 10.

Here, when the magnetic member 2 is ideally displaced on the normal trajectory (X axis in FIG. 4) along the detection axis, the detection value of the magnetic sensor 9 is always constant. However, in reality, the magnetic member 2 may be displaced in the Y-axis / Z-axis direction of FIG. In this case, the magnetic sensor 9 outputs a detection value corresponding to the displacement of the magnetic member 2.

Information relating to the allowable range of the detection value of the magnetic sensor 9, for example, an upper limit value and a lower limit value are input to the determination unit 10 in advance. This allowable range can be determined based on the detection characteristics of the magnetic sensor 9 with respect to the magnetic member 2 and the measurement error characteristics of the electromagnetic induction linear scale 1 when the magnetic member 2 deviates from the normal orbit. .

The detection characteristics of the magnetic sensor 9 with respect to the magnetic member 2 are obtained by acquiring in advance the detection value of the magnetic sensor 9 when the magnetic member 2 is variously shifted from the reference position in a direction other than the detection axis direction with respect to the magnetic sensor 9. It can be obtained by placing it. The reference position here means a position when the center of the magnetic member 2 corresponds to the center of the magnetic sensor 9 when the magnetic member 2 is ideally displaced only in the detection axis direction.

In one example, the detection characteristic for the magnetic member 2 of the magnetic sensor 9 as shown in FIG. 5 is obtained. Note that the Y axis and the Z axis in FIG. 5 correspond to the Y axis and the Z axis in FIG. 4. Also, the output difference on the vertical axis in FIG. 5 means a value obtained by subtracting the detection value obtained at the reference position from the detection value obtained at each shift position.

On the other hand, the measurement error characteristic of the electromagnetic induction linear scale 1 is obtained in advance as a measurement value of the electromagnetic induction linear scale 1 when the magnetic member 2 is variously shifted from the reference position in a direction other than the detection axis direction. Can be obtained. Here, the reference position means a predetermined position on a normal orbit.

For example, the electromagnetic induction linear scale 1 has a measurement error characteristic as shown in FIG. Note that the Y axis and the Z axis in FIG. 6 correspond to the Y axis and the Z axis in FIG. 4.

That is, the allowable range of the detection value of the magnetic sensor 9 can be determined as follows.
First, an allowable measurement error range is set for a measurement object to which the electromagnetic induction linear scale 1 is applied. Next, the deviation range (allowable range) of the magnetic member 2 when the measured value falls within the allowable measurement error range is based on the measurement error characteristics of the electromagnetic induction linear scale 1 obtained in advance. obtain. Then, by obtaining the detection value range (allowable range) of the magnetic sensor 9 when the deviation of the magnetic member 2 falls within the allowable range based on the detection characteristics of the magnetic sensor 9 obtained in advance, the magnetic sensor 9 An acceptable range of nine detected values can be determined.

The determination unit 10 determines whether or not the input detection value of the magnetic sensor 9 is determined as described above and falls within the allowable range of the detection value of the magnetic sensor 9 input in advance, and the result is not illustrated. Output to the monitor.

According to the electromagnetic induction linear scale 1 configured as described above, the relative displacement of the magnetic member 2 with respect to the coil array 3 over each pitch can be measured in an absolute manner.

Furthermore, according to the electromagnetic induction linear scale 1, the determination unit 10 determines whether the magnetic member 2 has deviated beyond the allowable range from the normal trajectory along the detection axis based on the detection value of the magnetic sensor 9. Can be determined. Therefore, according to the electromagnetic induction linear scale 1, it is possible to perform measurement while monitoring whether or not an error exceeding the allowable range is included in the obtained measurement value.

When the determination unit 10 determines that the allowable range is exceeded, the measurement by the electromagnetic induction linear scale 1 is stopped, or the trajectory of the relative displacement of the magnetic member 2 with respect to the coil array 3 is corrected. Some kind of response can be taken.

As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to these.
In the above embodiment, the description has been made based on the configuration in which the magnetic member is relatively displaced with respect to the fixed coil array. However, the coil array may be relatively displaced with respect to the fixed magnetic member. .

In the above embodiment, the magnetic sensors are arranged at both ends of the coil array. However, a large number of magnetic sensors may be arranged at predetermined intervals along the coil array.

The magnetic sensor only needs to output a detection value corresponding to the positional relationship with the magnetic member, and a magnetoresistive element (MR element), a magnetic impedance element (MI element), or the like may be used.

In the above embodiment, the number of coil elements constituting one coil set is four. However, the present invention is not limited to this. For example, the first to third three coil elements may be sequentially arranged in parallel to constitute one coil set. In this case, by taking differential outputs between the first and second coil elements and between the second and third coil elements, respectively, the differential output C = a ′ cos θ ′ · sin ωt, By obtaining the differential output S = a′sin θ ′ · sin ωt, the combined signal β = a′sin (ωt ± θ ′) can be obtained. Then, by detecting the phase difference between the synthesized signal β and the sine wave signal α = Asinωt, the displacement within the pitch and the displacement within the scale can be obtained in the same manner as in the above embodiment (for details, see Japanese Patent Application Laid-Open No. 2004-2004). No. 233311). In other words, if the configuration can obtain a sine wave signal showing the cosine phase amplitude function characteristic and a sine wave signal showing the amplitude function characteristic of the sine phase by taking the differential output between the coil elements, 1 Any number of coil elements may be included in one coil set.

It is the schematic which shows the structure of the electromagnetic induction type linear scale concerning this embodiment. It is a figure for demonstrating the detection method of the displacement in the pitch of the electromagnetic induction type linear scale concerning this embodiment. It is a figure for demonstrating the detection method of the displacement in the scale of the electromagnetic induction type linear scale concerning this embodiment. It is a schematic perspective view which shows the positional relationship of a magnetic member and a coil array. It is a figure which shows the detection characteristic of the magnetic sensor concerning this embodiment. It is a figure which shows the measurement error characteristic of the electromagnetic induction type linear scale concerning this embodiment. It is a figure for demonstrating a state when a magnetic member is made to adjoin to a coil.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electromagnetic induction type linear scale 2 Magnetic member 3 Coil array 41, 42 Differential amplifier 5 Differential output synthetic | combination part 6 In-pitch displacement detection part 7 Pitch detection part 8 In-scale displacement detection part 9 Magnetic sensor 10 Determination part 11 AC generation source L Coil element

Claims (4)

A coil array comprising a predetermined number of coil elements arranged coaxially in parallel, and a coil array excited by a first AC signal;
A magnetic member disposed outside the coil array and capable of relative displacement with respect to the coil array along an axis of the coil array, wherein the output of the coil element depends on the positional relationship with the coil element. A magnetic member that changes the amplitude of the voltage,
An electromagnetic induction linear scale that measures the relative displacement based on a phase difference between a second AC signal obtained by combining a plurality of differential outputs between coil elements in the coil set and the first AC signal. Because
At least one magnetic sensor disposed along the axial direction of the coil array and outputting a detection value corresponding to a positional relationship with the magnetic member;
A determination unit that determines whether an error included in the measured value of the electromagnetic induction linear scale is within an allowable range based on whether the detection value of the magnetic sensor is within a predetermined allowable range;
An electromagnetic induction linear scale characterized by further comprising: The electromagnetic induction linear scale according to claim 1, wherein the magnetic member is made of at least one magnet. 3. The electromagnetic induction linear scale according to claim 1, wherein the magnetic sensors are respectively disposed in the vicinity of both end portions of the coil array. The electromagnetic induction linear scale according to claim 1, wherein the magnetic sensor is a Hall element.