JP2010145149A - Electromagnetic induction type position detection device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic induction type position detection device and an electromagnetic induction type position detection method capable of stabilizing the position detection device by improving its S/N ratio even if noise having the same angular frequency as the angular frequency ω of an induced voltage V is contained in the voltage V. <P>SOLUTION: The following processing is performed. Exciting currents Ic and Is are caused to flow in first and second slider-side coils, The AD-conversion of the induced voltage V generated in a scale-side coil is performed, and the voltage is sampled by a sampling period T and the number N of sampling points. Based on the sampled data, the phase β of V is detected. By performing FFT processing on the basis of the sampled data, while representing the diffusion Fourier coefficient of the ω component of V as C, and expressing the phase Φ at C=¾C¾exp(jΦ) by Φ=tan<SP>-1</SP>(lm(C)/Re(C)), the amplitude ¾C¾ and the phase Φ of the signal component of ω are found. Based on ¾C¾, Φ, N, and β, an oblique image Vs in the direction of β of the amplitude is found. An excitation position α is adjusted so that Vs becomes equal to zero, and on the basis of α, Is and Ic are adjusted, and α at which Vs is equal to zero is determined as a detected position X. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electromagnetic induction position detector such as a linear scale and an electromagnetic induction position detection method.

  An inductive scale, which is an electromagnetic induction type position detector, is applied to position detection units of various machines such as machine tools, automobiles, and robots. Induct thin type scales include linear scales and rotary scales. Linear scales are applied to, for example, a linear movement axis of a machine tool to detect a movement position on the linear movement axis. Applied to a rotating shaft of a machine tool to detect a rotation angle of the rotating shaft.

  Both the linear type scale and the rotary type scale detect the position by electromagnetic induction of coil patterns arranged in parallel and face to face. This detection principle will be described based on the principle diagram of FIG. 4A is a perspective view showing a state in which the slider of the linear scale and the scale face each other in parallel, FIG. 4B shows the slider and the scale side by side, and FIG. 4C shows the slider. It is a figure which shows the electromagnetic coupling degree of the said scale. Although the principle diagram of the linear scale is shown in FIG. 4, the principle of the rotary scale is the same as this, and the stator and rotor of the rotary scale correspond to the slider and scale of the linear scale, respectively. ing.

  As shown in FIGS. 4A and 4B, the detection unit of the linear scale has a slider 1 as a primary side member and a scale 2 as a secondary side member. The slider 1 which is a movable part has a first slider side coil 3 as a first primary side coil and a second slider side coil 4 as a second primary side coil, and a scale 2 which is a fixed part. Has a scale side coil 5 as a secondary side coil. These coils 3, 4 and 5 are folded back in a zigzag shape (that is, formed in a comb pattern), and the whole is linear.

  As shown in FIG. 4A, the slider 1 (that is, the first slider-side coil 3 and the second slider-side coil 4) and the scale 2 (that is, the scale-side coil 5) are within a specified range. The inner gaps (gap) g are arranged in parallel and facing each other. Further, as shown in FIGS. 4A and 4B, the positional relationship between the first slider side coil 3 and the first slider side coil 4 and the scale side coil 5 is shifted by ¼ pitch.

Therefore, when an exciting current (alternating current) is passed through the first slider side coil 3 and the second slider side coil 4 and the slider 1 moves along the length direction of the scale 2 as indicated by an arrow A in FIG. As shown in FIG. 4C, the first slider-side coil 3 and the second slider-side coil 4 and the scale-side coil 5 change according to the change in the relative positional relationship between the slider-side coil 1 and the scale-side coil 5. Since the degree of electromagnetic coupling between the slider-side coil 3 and the second slider-side coil 4 and the scale-side coil 5 changes periodically, an induced voltage that periodically changes is generated in the scale-side coil 5.
Therefore, the position of the scale 2 (that is, the movement position of the slider 1 with respect to the scale 2) can be detected based on the induced voltage.

The position detection process will be described in detail. A first excitation current Is shown in the following equation (1) is passed through the first slider-side coil 3, and a second equation shown in the following equation (2) is supplied to the second slider-side coil 4. 2 Excitation current Ic is supplied.
Is = I ・ cos (kα) ・ sin (ωt) (1)
Ic = -I · sin (kα) · sin (ωt) (2)
Where I: Excitation current magnitude
k: 2π / p
p: Length of 1 pitch of coil (angle on rotary scale)
ω: Angular frequency of excitation current (alternating current)
t: time
α: Excitation position

As a result, an induced voltage V expressed by the following equation (3) is generated in the scale side coil 5 by electromagnetic induction between the first slider side coil 3 and the second slider side coil 4 and the scale side coil 5. . Note that the phase β is a phase delay of the system, and occurs, for example, in a process in which a signal travels through a signal circuit.
V = Q · sin (kX) · [I · cos (kα) · sin (ωt + β)] + Q · cos (kX)
・ [−I ・ sin (kα) ・ sin (ωt ＋ β)]
= Q ・ I ・ sin (k (X−α)) ・ sin (ωt + β) (3)
Q: Coupling coefficient (coefficient related to the degree of electromagnetic coupling between the slider side coil and the scale side coil)
X: Scale position (position of slider relative to scale)
β: System phase delay

A linear scale computing unit (not shown) adjusts the excitation position α by PI control according to the amplitude K (ω) · I · sin (k (X−α)) of the induced voltage V, and this excitation position. The excitation current Is and the excitation current Ic are adjusted based on α so that the amplitude of the induced voltage V becomes 0, and the excitation position α when the amplitude of the induced voltage V becomes 0 (that is, α = X). Is obtained as a detection position X. Therefore, the position X can be obtained irrespective of Q · I.
That is, feedback control is performed so that α = X by following the excitation position α (excitation current Is and excitation current Ic) with respect to the displacement of the position X accompanying the movement of the slider 1 (see arrow A). Thus, the amplitude of the induced voltage V is set to 0, and the value of the excitation position α when the amplitude of the induced voltage V becomes 0 (that is, α = X) is set as the detection position X.

  When the detection position X is obtained by the above processing, if noise is added to the induced voltage V in the above equation (3), it is considered that the position X has changed. For this reason, conventionally, noise of an angular frequency higher than the angular frequency ω is cut from the induced voltage V by passing the induced voltage V through an analog filter.

In addition, there exist the following as a prior art document relevant to this application.
JP 2002-207563 A JP 2000-180208 A

As described above, conventionally, noise having an angular frequency higher than the angular frequency ω is cut by a filter.
However, noise is generally servo noise (noise due to the influence of a servo system such as a machine tool to which a linear scale is attached), and is harmonic noise having an angular frequency lower than the angular frequency ω as a fundamental wave. For this reason, noise having a component having the same angular frequency as the angular frequency ω of the induced voltage V is also added to the induced voltage V, and such noise cannot be cut by a filter.
When the resolution of the excitation position α is low, the fluctuation of the detection position X due to the noise is buried in the unit of resolution of the excitation position α. However, if the resolution of the excitation position α is increased, the fluctuation of the detection position X due to the noise is increased. There is a problem that appears.

  Therefore, in view of the above situation, the present invention can improve the S / N ratio and stabilize the position detector even when noise having the same angular frequency as the angular frequency ω of the induced voltage V is added to the induced voltage V. It is an object of the present invention to provide an electromagnetic induction type position detector and an electromagnetic induction type position detection method.

An electromagnetic induction type position detector according to a first aspect of the present invention that solves the above-described problem includes a primary member including a first primary coil and a second primary coil, a secondary coil, and the primary member. And a secondary side member arranged in parallel and facing each other, and the primary side member and the secondary side member are relatively movable, and this detection In an electromagnetic induction type position detector provided with a control unit for controlling the unit,
In the control unit,
By passing the exciting current Is represented by the following equation (4) through the first primary coil and the exciting current Ic represented by the following equation (5) through the second primary coil, the secondary side The induced voltage V represented by the following equation (6) is generated in the coil, and the induced voltage V is AD-converted and sampled at the sampling period T and the sampling number N, thereby obtaining the sampling data of the induced voltage V,
Is = I ・ cos (kα) ・ sin (ωt) (4)
Ic = -I · sin (kα) · sin (ωt) (5)
Where I: Excitation current magnitude
k: 2π / p
p: Value of one pitch of the coil
ω: Angular frequency of excitation current
t: time
α: Excitation position V = Q · I · sin (k (X−α)) · sin (ωt + β) (6)
Where Q: coupling coefficient
X: position of the detection unit
β: phase delay of the system phase β is detected based on the sampling data,
The diffusion Fourier coefficient of the angular frequency ω component of the induced voltage V is C, and the phase Φ = tan ⁻¹ (lm (C) / Re (C)) at C = | C | exp (jΦ) Based on the FFT processing, the amplitude | C | and the phase Φ of the signal component of the angular frequency ω are obtained,
Based on these amplitudes | C | and phase Φ, the number N of sampling points, and the phase β, a slope Vs in the β direction expressed by the following equation (7) is obtained, and this Vs is used as a signal component.
Vs = | C | / N · cos (Φ + π / 2−β) (7)
The excitation position α is adjusted so that the signal component Vs becomes 0, and the excitation current Is and the excitation current Ic are adjusted based on the excitation position α, so that the excitation position α where the signal component Vs becomes 0. Is a detection position X,
It is the structure which performs the process of.

In addition, the electromagnetic induction type position detection method of the second invention includes a primary side member having a first primary side coil and a second primary side coil, a secondary side coil, and a gap with respect to the primary side member. An electromagnetic induction type position using a detection unit that has a secondary side member that is disposed in parallel and that faces each other and that is relatively movable between the primary side member and the secondary side member In the detection method,
By passing an excitation current Is represented by the following equation (8) through the first primary coil and an excitation current Ic represented by the following equation (9) through the second primary coil, the secondary side The induced voltage V represented by the following equation (10) is generated in the coil, and the induced voltage V is AD converted and sampled at the sampling period T and the sampling number N, thereby obtaining the sampling data of the induced voltage V,
Is = I ・ cos (kα) ・ sin (ωt) (8)
Ic = -I · sin (kα) · sin (ωt) (9)
Where I: Excitation current magnitude
k: 2π / p
p: Value of one pitch of the coil
ω: Angular frequency of excitation current
t: time
α: Excitation position V = Q · I · sin (k (X−α)) · sin (ωt + β) (10)
Where Q: coupling coefficient
X: position of the detection unit
β: phase delay of the system phase β is detected based on the sampling data,
The diffusion Fourier coefficient of the angular frequency ω component of the induced voltage V is C, and the phase Φ = tan ⁻¹ (lm (C) / Re (C)) at C = | C | exp (jΦ) Based on the FFT processing, the amplitude | C | and the phase Φ of the signal component of the angular frequency ω are obtained,
Based on these amplitudes | C | and phase Φ, the number N of sampling points, and the phase β, a slope Vs in the β direction expressed by the following equation (11) is obtained, and this Vs is used as a signal component.
Vs = | C | / N · cos (Φ + π / 2−β) (11)
The excitation position α is adjusted so that the signal component Vs becomes 0, and the excitation current Is and the excitation current Ic are adjusted based on the excitation position α, so that the excitation position α where the signal component Vs becomes 0. Is a detection position X,
It is characterized by performing the process.

According to the electromagnetic induction type position detector of the first invention, the electromagnetic induction type position detector of the first invention includes a primary side member including a first primary side coil and a second primary side coil, and a secondary side. A secondary side member that includes a side coil and that is disposed in parallel and facing the primary side member with a gap therebetween, and the primary side member and the secondary side member are relatively In the electromagnetic induction type position detector including a movable detection unit and a control unit for controlling the detection unit, the control unit includes an excitation current represented by the above formula (4) in the first primary coil. By causing Is to flow and flowing the exciting current Ic expressed by the above equation (5) to the second primary coil, an induced voltage V expressed by the above equation (6) is generated in the secondary coil, Sampling period T, sampling by AD conversion of induced voltage V By sampling at a number N, the sampling data of the induced voltage V is obtained, the phase β is detected based on the sampling data, the diffusion Fourier coefficient of the angular frequency ω component of the induced voltage V is set as C, and C = | C | exp (jΦ) has a phase Φ = tan ⁻¹ (lm (C) / Re (C)), and by performing FFT processing based on the sampling data, the amplitude | C | And the phase Φ, and based on the amplitude | C | and the phase Φ, the sampling point number N, and the phase β, the slope Vs in the β direction expressed by the above equation (7) is obtained. Using Vs as a signal component, the excitation position α is adjusted so that the signal component Vs becomes 0, and the excitation current Is and the excitation current Ic are adjusted based on the excitation position α. The excitation position α that becomes 0 is the detection position X. Therefore, even when noise having the same angular frequency as the angular frequency ω of the induced voltage V is added to the induced voltage V, the information on the phase β of the induced voltage V is used. Thus, only the signal component Vs can be extracted, and the detection position X can be obtained by adjusting the excitation position α so that the signal component Vs becomes zero. Therefore, the SN ratio is improved and the position detector can be stabilized.

Similarly, according to the electromagnetic induction type position detection method of the second invention, a primary side member provided with a first primary side coil and a second primary side coil, a secondary side coil, and the primary side member And a secondary side member arranged in parallel and facing each other, and using a detection unit in which the primary side member and the secondary side member are relatively movable In the inductive position detection method, the excitation current Is expressed by the above equation (8) is supplied to the first primary coil, and the excitation current Ic expressed by the above equation (9) is supplied to the second primary coil. As a result, the induced voltage V represented by the above equation (10) is generated in the secondary side coil, and this induced voltage V is AD-converted and sampled at the sampling period T and the sampling point number N. Sampling sampling Get the data, to detect the phase β on the basis of the sampling data, a spreading Fourier coefficient of the angular frequency ω component of the induced voltage V and C, C = | C | exp phase [Phi = tan ^-1 in (j.phi) (lm (C) / Re (C)), the amplitude | C | and the phase Φ of the signal component of the angular frequency ω are obtained by performing FFT processing based on the sampling data, and the amplitude | C | Based on Φ, the number of sampling points N, and the phase β, a slope Vs in the β direction expressed by the above equation (11) is obtained, and this Vs is used as a signal component, and the signal component Vs becomes zero. The excitation position α is adjusted as described above, the excitation current Is and the excitation current Ic are adjusted based on the excitation position α, and the excitation position α at which the signal component Vs becomes 0 is set as the detection position X. Since it is characterized by processing, the angle of the induced voltage V Even when noise having the same angular frequency as the frequency ω is added to the induced voltage V, only the signal component Vs can be extracted using the information of the phase β of the induced voltage V, and this signal component Vs becomes zero. Thus, the detection position X can be obtained by adjusting the excitation position α. Therefore, the SN ratio can be improved and the position detection can be stabilized.

  Embodiments of the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a block diagram showing the function of a linear scale according to an embodiment of the present invention, FIG. 2 is a flowchart showing the function of a signal extraction unit in the arithmetic circuit of the linear scale, and FIG. 3 is before and after correction. It is a graph which shows S / N ratio of.

  As shown in FIG. 1, the linear scale that is an electromagnetic induction type position detector includes a detection unit (scale unit) 11 and a control unit 12 for controlling the detection unit 11.

  The linear scale detection unit 11 has the same configuration as that of the conventional linear scale detection unit (see FIGS. 4A to 4C). That is, the detection unit 11 of the linear scale has a slider 1 as a primary side member and a scale 2 as a secondary side member. The slider 1 which is a movable part has a first slider side coil 3 as a first primary side coil and a second slider side coil 4 as a second primary side coil, and a scale 2 which is a fixed part. Has a scale side coil 5 as a secondary side coil. These coils 3, 4 and 5 are folded back in a zigzag shape (that is, formed in a comb pattern), and the whole is linear. The slider 1 (that is, the first slider-side coil 3 and the second slider-side coil 4) and the scale 2 (that is, the scale-side coil 5) hold a gap (gap) g within a specified range therebetween. In a state, they are arranged facing each other in parallel. Further, the positional relationship between the first slider side coil 3 and the first slider side coil 4 and the scale side coil 5 is shifted by ¼ pitch.

Therefore, when an exciting current (alternating current) is passed through the first slider side coil 3 and the second slider side coil 4 and the slider 1 moves along the length direction of the scale 2, the first slider is moved by the movement of the slider 1. In accordance with the change in the relative positional relationship between the side coil 3 and the second slider side coil 4 and the scale side coil 5, the electromagnetic force between the first slider side coil 3, the second slider side coil 4 and the scale side coil 5 Since the degree of coupling periodically changes (see FIG. 4C), an induced voltage that periodically changes is generated in the scale side coil 5.
Therefore, the position of the scale 2 (that is, the moving position of the slider 1 with respect to the scale 2) can be detected based on the induced voltage.

Such detection processing is performed by the control unit 12 of the linear scale. The control unit 12 includes a low-pass amplifier circuit 21, an AD converter 22, an arithmetic circuit 23, and a DA converter 24.
The arithmetic circuit 23 includes a signal extraction unit 31, a position change amount calculation unit 32, and an excitation current waveform formation unit 33. Although any arithmetic circuit 24 can be used, for example, an FPGA (Field Programmable Gate Array) may be used.
The DA converter 28 has a first excitation power supply 41 and an excitation current 42. The first excitation power source 41 is connected to the first slider side coil 3, and the second excitation power source 42 is connected in series to the second slider side coil 4.
The scale side coil 5 is connected to the arithmetic circuit 23 via the low-pass amplifier circuit 21 and the AD converter 22.

  Hereinafter, the principle of the position detection process performed by the control unit 12 will be described first, and then the processing contents of each functional unit of the control unit 12 will be described.

  In order to detect the position, an excitation current Is expressed by the following equation (12) is passed through the first slider side coil 3 as in the prior art, and an excitation current expressed by the following equation (13) is supplied to the second slider side coil 4. When Ic flows, the induced voltage V shown in the following equation (14) is generated in the scale side coil 5 by electromagnetic induction between the first slider side coil 3 and the second slider side coil 4 and the scale side coil 5. To do. Note that the phase β is a phase delay of the system, and occurs, for example, in a process in which a signal travels through a signal circuit.

Is = I ・ cos (kα) ・ sin (ωt) (12)
Ic = −I · sin (kα) · sin (ωt) (13)
Where I: Excitation current magnitude
k: 2π / p
p: Length of 1 pitch of coil (angle on rotary scale)
ω: Angular frequency of excitation current (alternating current)
t: time
α: Excitation position

V = Q · sin (kX) · [I · cos (kα) · sin (ωt + β)] + Q · cos (kX)
・ [−I ・ sin (kα) ・ sin (ωt ＋ β)]
= Q ・ I ・ sin (k (X−α)) ・ sin (ωt + β) (14)
Q: Coupling coefficient (coefficient related to the degree of electromagnetic coupling between the slider side coil and the scale side coil)
X: Scale position (position of slider relative to scale)
β: System phase delay

The diffusion Fourier coefficient C of the angular frequency ω component of the induced voltage V is expressed by the following equation (15).
C = ΣV (nT) exp (−j2πm · n / N) (15)
However, n = 0 to N−1
T: Sampling cycle
N: Number of sampling points
m = NTω / (2π)
j: Imaginary unit

Here, if C = | C | exp (jΦ) (where phase Φ = tan ⁻¹ (lm (C) / Re (C))), the inverse Fourier transform of this component is expressed by the following (16) It becomes an expression.
Vf (nT) = C / N ・ exp (j2πmn / N)
＝ | C | / N ・ exp (jΦ) exp (j2πmn / N)
= | C | / N · cos (2πmn / N + Φ)
= | C | / N · cos (ωnT + Φ)
= | C | / N · sin (ωnT + Φ + π / 2) (16)

Therefore, by comparing this equation (16) with the above equation (14), the component of the phase β of Vf is a signal component, so the β direction of the amplitude | C | / N as shown in the following equation (17): The excitation position α is adjusted so that the signal component Vs becomes zero.
Vs = | C | / N · cos (Φ + π / 2−β) (17)

  That is, in a general filter, the target frequency component is extracted by paying attention only to the amplitude, but in the present invention, only the component whose signal frequency and phase match is extracted. The induced voltage V has a system phase lag β, and this phase β can be known when the linear scale is started. Therefore, only the signal component can be extracted using the information of the phase β.

  Next, the processing content of each function part of the control part 12 is demonstrated based on FIG.

In the control unit 12, first, the excitation current waveform forming unit 33 forms the waveform of the excitation current Is of the above expression (12) and the waveform of the excitation current Ic of the above expression (13). Note that the value of the initial excitation position α may be an arbitrary value such as an initial set value or a value adjusted last in the previous position detection process.
The excitation current Is of the above expression (12) formed by the excitation current waveform forming unit 33 is converted from digital to analog (DA conversion) by the DA converter 24 and then from the first excitation power supply 41 to the first slider side coil 3. Shed. The excitation current Ic of the above formula (13) formed by the excitation current waveform forming unit 33 is DA-converted by the DA converter 24 and then flows from the second excitation power source 42 to the first slider-side coil 3.

  As a result, the induced voltage V of the above equation (14) is generated in the scale side coil 5, and this induced voltage V is amplified by the low-pass amplifier circuit 21 after the noise having the angular frequency higher than the angular frequency ω is cut and amplified. The signal is converted from analog to digital (AD conversion) by the AD converter 22 and input to the arithmetic circuit 23.

  Then, although details will be described later (see FIG. 2), the signal extraction unit 31 samples the induced voltage V by sampling the induced voltage V AD-converted by the AD converter 22 at the sampling period T and the sampling number N. Data is acquired, the phase β is obtained based on the sampling data, and the signal component Vs as shown in the above equation (17) is extracted using the information of the phase β.

The position change amount calculation unit 32 performs PI (proportional integration) control according to the signal component Vs so that the signal component Vs becomes 0 (that is, the signal component Vs multiplied by a proportional gain). The excitation position α is obtained (adjusted) by adding the signal component Vs multiplied by the integral gain and integrating it).
The excitation current waveform forming unit 33 forms the waveform of the excitation current Is of the above expression (12) and the waveform of the excitation current Ic of the above expression (13) based on the excitation position α obtained by the position change amount calculation unit 32. (adjust).

  The excitation current Is and the excitation current Ic whose waveforms are formed (adjusted) by the excitation current waveform forming unit 33 are DA-converted by the DA converter 24, and then from the first excitation power supply 41 and the second magnetic power supply 43 to the first slider. The current flows through the side coil 3 and the second slider side coil 4. By such feedback control, the signal component Vs finally becomes zero. That is, an excitation position α where the signal component Vs becomes 0 is obtained. Then, the position change amount calculation unit 32 outputs the excitation position α where the signal component Vs becomes 0 as the detection position X.

  Next, the processing content of the signal extraction part 31 is demonstrated based on FIG.

In the signal extraction unit 31, first, in step S 1, as described above, the induced voltage V AD-converted by the AD converter 22 is sampled at a predetermined sampling period T and sampling number N, thereby sampling data of the induced voltage V. To get. This sampling data is sent to steps S2 and S5.
In step S2, the phase β is detected based on the sampling data by a technique such as synchronous detection.
In step S3, when the detection of phase β is completed in step S2, this detected phase β is sent to step S6, and a phase detection completion signal (for example, flag 1 is set) is sent to step S4.
In step S4, it is determined whether or not the detection of the phase β is completed. That is, when the phase detection completion signal is not sent from step S3 to step S4, it is determined that the phase detection is not completed and the process returns to step S2, while the phase detection completion signal is sent from step S3 to step S4. If YES, it is determined that the phase detection is completed, and the process proceeds to step S5.

  Since the phase β does not change according to the scale position X, the phase β is detected only when the signal extraction unit 31 starts signal processing. Specifically, the phase β is detected only when the linear scale is started (that is, before the power of the linear scale is turned on and the slider 1 starts moving).

  In step S5, the FFT process is performed based on the sampling data sent from step S1, thereby obtaining the amplitude | C | and the phase Φ of the signal component of the angular frequency ω, and the amplitude | C | Information and information on the number N of sampling points of the sampling data are sent to step S6. Note that FFT is a fast Fourier transform that performs discrete Fourier transform and inverse Fourier transform at high speed.

  In step S6, the amplitude as shown in the above equation (17) is based on the phase β sent from step S3, the amplitude | C |, the phase Φ sent from step S5, and the number N of sampling points. A slope Vs in the β direction is obtained, and this is output to the position change amount calculation unit 32 as a signal component Vs.

As described above, according to the linear scale of the present embodiment, the slider 1 including the first slider side coil 3 and the second slider side coil 4, the scale side coil 5, and the slider 1 A detecting unit 11 having a scale 2 arranged in parallel and facing each other while maintaining a gap, and the slider 1 and the scale 2 being relatively movable (in this case, the slider 1 is movable); In the linear scale including the control unit 12 for controlling the detection unit 11, the control unit 12 causes the exciting current Is represented by the above expression (12) to flow through the first slider side coil 3, and the second slider side. By causing the exciting current Ic represented by the above equation (13) to flow through the coil 4, an induced voltage V represented by the above equation (14) is generated in the scale side coil 5, and this induced voltage V is AD converted. The sampling data of the induced voltage V is obtained by sampling at the sampling period T and the number of sampling points N, the phase β is detected based on the sampling data, and the diffusion Fourier coefficient of the angular frequency ω component of the induced voltage V And C = | C | exp (jΦ), the phase Φ = tan ⁻¹ (lm (C) / Re (C)), and the signal of the angular frequency ω is obtained by performing FFT processing based on the sampling data. The amplitude | C | and the phase Φ of the component are obtained. Based on the amplitude | C | and the phase Φ, the number N of sampling points, and the phase β, the shadow Vs in the β direction expressed by the above equation (17). The excitation position α is adjusted so that the signal component Vs becomes 0, and the excitation current Is and the excitation current Ic are adjusted based on the excitation position α. , The signal generation The present invention is characterized in that the processing is such that the excitation position α at which the minute Vs becomes 0 is set as the detection position X.
Therefore, even when noise having the same angular frequency as the angular frequency ω of the induced voltage V is added to the induced voltage V, only the signal component Vs can be extracted using the information of the phase β of the induced voltage V. The detection position X can be obtained by adjusting the excitation position α so that the signal component Vs becomes zero. Therefore, the SN ratio is improved and the position detector can be stabilized.
FIG. 1 shows the effect when the amplitude of the signal is 1, the amplitude of the noise is 1, and the frequency of the signal and the noise is the same, and before the correction indicated by the dotted line (that is, the above processing is not performed). The S / N ratio is improved after the correction indicated by the solid line (that is, when the above-described processing is performed), particularly when the phase β is close to 90 degrees. The S / N ratio is greatly improved.

The present invention is particularly useful when applied to a linear scale, but is not necessarily limited to this, and can also be applied to a rotary scale.
Although not shown, the outline of the rotary scale will be described. The rotary scale includes a detection unit and a control unit that controls the detection unit. The detection unit of the rotary scale has the same configuration as the detection unit of the conventional rotary scale, and includes a stator as a primary side member and a rotor as a secondary side member.
The stator which is a fixed part has a first stator side coil as a first primary side coil and a second stator side coil as a second primary side coil. The rotor which is a rotating part has a rotor side coil as a secondary side coil. These coils are folded back in a zigzag shape and formed in an annular shape as a whole. The stator (that is, the first stator side coil and the second stator side coil) and the rotor (that is, the rotor side coil) are arranged in parallel and facing each other with a gap between them, and move relative to each other. It is possible (in this case, the rotor can rotate). In addition, the positional relationship between the first stator side coil and the second stator side coil and the rotor side coil is shifted by ¼ pitch.
The control unit controls the detection unit in the same manner as the control unit 12 of the linear scale.

  The present invention relates to an electromagnetic induction type position detector and an electromagnetic induction type position detection method, and is particularly useful when applied to gap adjustment of a linear scale, but is also applied to gap adjustment of a rotary scale. Can do.

It is a block diagram showing the function of the linear scale which concerns on the embodiment of this invention. It is a flowchart which shows the function of the signal extraction part in the arithmetic circuit of the said linear scale. It is a graph which shows S / N ratio before correction | amendment and after correction | amendment. (A) is a perspective view showing a state in which a slider of a linear scale and the scale face each other in parallel, (b) is a view showing the slider and the scale side by side, and (c) is an electromagnetic coupling of the slider and the scale. It is a figure which shows a degree.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Slider 2 Scale 3 1st slider side coil 4 2nd slider side coil 5 Scale side coil 11 Detection part (scale part)
DESCRIPTION OF SYMBOLS 12 Control part 21 Low pass amplifier circuit 22 AD converter 23 Operation circuit 24 DA converter 31 Signal extraction part 32 Position variation calculation part 33 Excitation current waveform formation part 41 1st excitation power supply 42 2nd excitation power supply

Claims (2)

A primary side member having a first primary side coil and a second primary side coil, and a secondary side having a secondary side coil and arranged in parallel facing each other while maintaining a gap with respect to the primary side member In an electromagnetic induction type position detector comprising a detection unit having a side member, the primary side member and the secondary side member being relatively movable, and a control unit for controlling the detection unit ,
In the control unit,
By passing an excitation current Is represented by the following equation (1) through the first primary coil and an excitation current Ic represented by the following equation (2) through the second primary coil, the secondary side The induced voltage V represented by the following equation (3) is generated in the coil, and the induced voltage V is AD-converted and sampled at the sampling period T and the sampling number N, thereby obtaining the sampling data of the induced voltage V,
Is = I ・ cos (kα) ・ sin (ωt) (1)
Ic = -I · sin (kα) · sin (ωt) (2)
Where I: Excitation current magnitude
k: 2π / p
p: Value of one pitch of the coil
ω: Angular frequency of excitation current
t: time
α: Excitation position V = Q · I · sin (k (X−α)) · sin (ωt + β) (3)
Where Q: coupling coefficient
X: position of the detection unit
β: phase delay of the system phase β is detected based on the sampling data,
The diffusion Fourier coefficient of the angular frequency ω component of the induced voltage V is C, and the phase Φ = tan ⁻¹ (lm (C) / Re (C)) at C = | C | exp (jΦ) Based on the FFT processing, the amplitude | C | and the phase Φ of the signal component of the angular frequency ω are obtained,
Based on the amplitude | C | and the phase Φ, the number N of sampling points, and the phase β, a slope Vs in the β direction expressed by the following equation (4) is obtained, and this Vs is used as a signal component.
Vs = | C | / N · cos (Φ + π / 2−β) (4)
The excitation position α is adjusted so that the signal component Vs becomes 0, and the excitation current Is and the excitation current Ic are adjusted based on the excitation position α, so that the excitation position α where the signal component Vs becomes 0. Is a detection position X,
An electromagnetic induction type position detector characterized in that the processing is performed. A primary side member having a first primary side coil and a second primary side coil, and a secondary side having a secondary side coil and arranged in parallel facing each other while maintaining a gap with respect to the primary side member In an electromagnetic induction type position detection method using a detection unit that has a side member and the primary side member and the secondary side member are relatively movable,
By passing an excitation current Is represented by the following equation (5) through the first primary coil and an excitation current Ic represented by the following equation (6) through the second primary coil, the secondary side The induced voltage V represented by the following formula (7) is generated in the coil, and the induced voltage V is AD converted and sampled at the sampling period T and the sampling number N, thereby obtaining the sampling data of the induced voltage V,
Is = I ・ cos (kα) ・ sin (ωt) (5)
Ic = -I · sin (kα) · sin (ωt) (6)
Where I: Excitation current magnitude
k: 2π / p
p: Value of one pitch of the coil
ω: Angular frequency of excitation current
t: time
α: Excitation position V = Q · I · sin (k (X−α)) · sin (ωt + β) (7)
Where Q: coupling coefficient
X: position of the detection unit
β: phase delay of the system phase β is detected based on the sampling data,
The diffusion Fourier coefficient of the angular frequency ω component of the induced voltage V is C, and the phase Φ = tan ⁻¹ (lm (C) / Re (C)) at C = | C | exp (jΦ) Based on the FFT processing, the amplitude | C | and the phase Φ of the signal component of the angular frequency ω are obtained,
Based on these amplitudes | C | and phase Φ, the number N of sampling points, and the phase β, a slope Vs in the β direction expressed by the following equation (8) is obtained, and this Vs is used as a signal component.
Vs = | C | / N · cos (Φ + π / 2−β) (8)
The excitation position α is adjusted so that the signal component Vs becomes 0, and the excitation current Is and the excitation current Ic are adjusted based on the excitation position α, so that the excitation position α where the signal component Vs becomes 0. Is a detection position X,
The electromagnetic induction type position detection method characterized by performing the process.

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