JP3198539B2 - Displacement detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement detecting device such as a magnetic scale used for a metal working machine or a precision measuring instrument.

[0002]

2. Description of the Related Art A conventional phase detecting type displacement detecting device used for a magnetic scale is as shown in FIG.
That is, in FIG. 8, reference numeral 1 denotes a scale portion, which is a scale 1 a on which a magnetic scale of a wavelength λ is recorded and two detection heads 1.
b, 1c. The scale section 1 of the detection head 1b, scale signal obtained from 1c is guided to the scale signal detection circuit 2, and outputs a signal e _PM which varies in phase in accordance with the displacement amount in the scale signal detection circuit 2. This phase modulation signal e _PM is

[0003]

(Equation 1)

[0004] However _{ω c = 2π × f c (} f c: carrier frequency), X represents a relative displacement (amount of movement). The phase modulation signal e _PM is supplied to the interpolation circuit 3 after being shaped. The interpolation circuit 3 by using a clock pulse having a nf _C comprising a frequency to the carrier frequency f _c,
A pulse signal (hereinafter referred to as UP) corresponding to the moving direction of the resolution λ / n
A signal or a Down signal).
The displacement amount is obtained by counting the UP signal or the Down signal with a counter.

In such a magnetic scale, various adjustment means as shown in FIG. 9 are provided in the scale signal detection circuit 2 in order to perform highly accurate detection. That is, the detection head 1b
And 1c cause a difference in DC bias,
This magnetizing phenomenon becomes a position error at the time of detection, and electrical compensation is required. Also, due to manufacturing variations of the detection heads 1b and 1c, differences in output levels and errors in the phase difference between the detection heads 1b and 1c. Then, it was necessary to adjust for each product.

In FIG. 9, one of the detection heads 1b
Is supplied to an addition amplifier 2f through a series circuit of a DC bias adjuster 2a for adjusting a DC bias due to magnetization of one of the detection heads 1b and a variable gain amplifier 2b for adjusting the level of the output signal. The phase of the output signal of the detection head 1c can be adjusted with a series circuit of a DC bias adjuster 2c for adjusting the DC bias due to the magnetization of the other detection head 1c and a variable gain amplifier 2d for adjusting the level of the output signal. ° Phase shifter 2e
To the summing amplifier 2f via the
f is output to the bandpass filter 2g and the amplifier 2h.
Is supplied to the interpolation circuit 3 as a phase modulation signal e _PM via the. The 2j In FIG 9 is energized amplifier supplies an exciting signal _{E X sin (ω C / 2} ) t a detection head 1b and 1c.

In FIG. 9, the DC bias adjusters 2 a and 2 c are used by the DC bias adjusters 2 a and 2 c so that the DC bias caused by the magnetization of one and the other detection heads 1 b and 1 c is reduced to zero during manufacturing. Adjust
The gains of the variable gain amplifiers 2b and 2d are adjusted by the variable gain amplifiers 2b and 2d so that the levels of the output signals of the detection heads 1b and 1c become the same, and the output signals of the detection heads 1b and 1c are adjusted. 90 ° phase difference
The phase of this 90 ° phase shifter was adjusted so that (λ / 4).

[0008]

However, this adjustment state may change subtly due to, for example, the passage of time or a change in the mounting state, and especially when high-precision detection is required, the adjustment state is periodically changed. Since adjustment is desired and this adjustment work is performed manually, there is a problem that the adjustment work requires skill, and that the adjustment varies. In view of the above, an object of the present invention is to make it possible to always perform stable adjustment without variation.

[0009]

According to the present invention, for example, as shown in FIG. 1, a pair of detection heads, a scale having a scale of period λ, and a relative movement between the detection head and the scale are provided. Generating a ripple component generated in the phase modulation signal in a displacement amount detection device having a scale signal detection circuit that outputs a changing phase modulation signal, and configured to detect a displacement amount by the phase modulation signal. A ripple component removing unit for identifying a factor, detecting the magnitude of the occurrence factor, and removing the ripple component is provided, and the ripple component removing unit detects the ripple component signal by detecting a waveform of the ripple component signal. The DC bias of the detection head, the difference in the output level between the detection heads, and the deviation of the phase difference between the output signals of the detection heads, which are the causes. Identify, calculate the deviation of the ripple component signal at two singular points where the extreme value of the ripple component signal occurs, detect the direction of the cause of the ripple component by the sign of the deviation, and calculate the direction of the ripple component by the magnitude of the deviation It is configured to detect the magnitude of the factor causing the ripple component.

[0010]

According to the present invention, a ripple component of a phase modulation signal is detected, an adjustment element such as a DC bias adjuster is specified by the ripple component, and the adjustment element is adjusted so that the ripple component is minimized. Therefore, stable adjustment can be performed without variation.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the displacement detecting apparatus according to the present invention will be described below with reference to FIGS. In FIGS. 1 and 2, parts corresponding to FIGS. 8 and 9 are denoted by the same reference numerals, and detailed description thereof will be omitted. Also in FIG. 1 of this example, the scale section 1 is composed of a scale 1a on which a magnetic scale of a wavelength λ is recorded and two detection heads 1b and 1c.
A scale signal obtained from the detection heads 1b and 1c of the scale section 1 is guided to a scale signal detection circuit 2, where the phase signal changes in accordance with the amount of displacement as shown in Equation 1 below. The signal e _PM is obtained. The phase modulation signal e _PM obtained at the output side of the scale signal detection circuit 2 is supplied to the interpolation circuit 3 after waveform shaping. This interpolation circuit 3 is nf for the carrier frequency f _C.
Using a clock pulse having a frequency of _C, the resolution λ /
A pulse signal corresponding to the moving direction of n is output, and the displacement amount is obtained by counting the UP signal or the Down signal with a counter. Where λ
= 200 μm and n = 200, an UP signal or Down signal for each 1 μm is obtained.

In this embodiment, the UP signal and the Down signal from the interpolation circuit 3 are supplied to a microcomputer 5 via a down-conversion circuit 4 for, for example, 1/5 (m = 5). 3 is supplied to the microcomputer 5. This step-down circuit 4 is a high-resolution UP
This is a circuit for reducing the signal or the Down signal, and is used for simplifying the processing of the microcomputer 5. That is, as a general requirement of the displacement amount detection circuit, a high resolution is required, but the order of the harmonic of the ripple component generated by the deviation of each parameter is second order, and from the sampling theorem, such a high resolution is not required. It depends.

In this embodiment, the phase modulation signal e _PM obtained at the output of the scale signal detection circuit 2 is supplied to a ripple detection circuit 6 for detecting the envelope component. The ripple detection circuit 6 can be constituted by, for example, a square detector. The ripple signal E _P of the phase modulation signal e _PM obtained at the output side of the ripple detection circuit 6 is output from the detection heads 1b and 1
c has a peculiar pattern corresponding to the deviation of the DC bias, the deviation of the output levels of the detection heads 1b and 1c, and the deviation between the output signals of the detection heads 1b and 1c from the phase of 90 °. That is, the pattern of the ripple signal when the DC bias of the detection heads 1b and 1c is shifted is such that the cycle of the ripple signal is one cycle with respect to the recording wavelength λ of the scale, and the output levels of the detection heads 1b and 1c are shifted. Of the ripple signal at the time and the detection head 1b
The pattern of the ripple signal when the output signal is shifted from the phase of 90 ° between the output signals 1c and 1c means that the cycle of the ripple signal is two cycles with respect to the recording wavelength λ. Is different from the ripple signal pattern when the phase is shifted from 90 ° by 90 ° in the ripple signal pattern.

[0014] Analog has a sample hold function ripple signal E _P obtained at the output side of the ripple detection circuit 6 - supplied to digital converter 7, the analog -
The microcomputer 5 in the digital converter 7
The microcomputer 5 supplies a ripple signal E _P (D) digitized for each sampling hold in accordance with the command from the microcomputer 5.

In the microcomputer 5, depending on the pattern of the ripple signal E _P (D), whether an element to be adjusted, for example, the DC bias of the detection heads 1b and 1c is shifted, and the output of each of the detection heads 1b and 1c. It is determined whether the level of the signal is shifted or the phase between the output signals of the detection heads 1b and 1c is shifted by more than 90 °, and an adjustment signal is generated according to this determination.
In FIG. 1, reference numeral 5a denotes an adjustment command signal input terminal. When an adjustment command signal is supplied to the adjustment command signal input terminal 5a, the microcomputer 5 sends an adjustment signal from the microcomputer 5 via an electronic volume control circuit 8 to a scale signal detection circuit 2. Is supplied to the electronic volume for performing the predetermined adjustment of the above. The adjustment command signal is generated as needed, for example, each time the power is turned on.

The scale signal detection circuit 2 according to this embodiment is shown in FIG.
The configuration is as shown in FIG. A series circuit of a direct current bias regulator 2an and preamplifier 2bn output signal consists of the electronic volume ER ₁ for adjusting the DC bias due to magnetic susceptibility of the one detection head 1b in this figure at the 2 one detection head 1b And the other detection heads 1b and 1
Electronic volume ER ₃ for adjusting the level difference of the output signal of c
Consisting of the electronic regulator ER ₂ for adjusting the DC bias of the output signal of the other detector heads 1c by magnetic susceptibility of the other detection head 1c is supplied to one input terminal of the summing amplifier 2fn having a DC bias adjuster 2cn and before through a 90 ° phase shifter 2en capable phase adjustment is supplied to the other input terminal of the summing amplifier 2fn by the series circuit and the electronic regulator ER ₅ of preamplifier 2Dn, band-pass filter the output signal of the summing amplifier 2fn Amplifier 2 having 2 gn and electronic volume ER ₄ for adjusting the output level
hn to the interpolation circuit 3 as the phase modulation signal e _PM . The electronic regulators ER ₁ , ER ₂ , ER ₃ , E
As R ₄ and ER ₅ , known ones controlled by digital signals are used.

[0017] For example and as shown the amplifier 2hn in Figure 3A example configuration with electronic regulator ER _4. That is, the input terminal 10 is connected to the inverting input terminal-of the operational amplifier 11 via the resistor Ri, the non-inverting input terminal + of the operational amplifier 11 is grounded, and the inverting input terminal of the operational amplifier 11 is connected to the resistor Rf. via the electronic volume ER ₄ constituting connected to the output terminal 12. Resistors 16a of the resistance value R between the input end 14 and output end 15 as Examples of the electronic regulator ER ₄ shown in FIG. 3B, the resistor 16b of the resistance value 2R, resistor 16c of the resistance value 4R, resistance of the resistance value 8R A resistor 16d and a resistor 16e having a resistance value R are connected in series with each other, and switches 17a, 17b, 17c and 1 are respectively connected in parallel with the resistors 16a, 16b, 16c and 16d.
7d is provided, and the switches 17a, 17b, 17c and 17d are turned on / off by a 4-bit digital signal from the control digital signal input terminal 13. In this case, the resistance value can be obtained by switching the resistance value in 16 steps from the resistance value R to 16R.
hn can be varied in 16 steps.

[0018] excitation signal _{E X sin (ω C / 2} ) for supplying respectively a t the detection head 1b and 1c through the excitation amplifier 2Jn.

In this embodiment, when the adjustment command signal is supplied to the adjustment command signal input terminal 5a, the microcomputer 5 starts the automatic adjustment operation. When this adjustment command signal is supplied, the microcomputer 5 measures the pattern of the ripple signal within one wavelength with reference to the λ signal and stores it in an internal memory. By continuing this operation over several wavelengths, it is determined whether or not the component of the ripple signal satisfies the standard value, and the automatic adjustment operation is started if necessary. This automatic adjustment operation is performed according to the procedure of FIG. Note that the λ signal is a signal indicating the start point of the cycle λ, and is, for example, a pulse signal that generates a pulse for each cycle λ.

First, the microcomputer 5 starts adjustment from the DC bias of the output signal of the detection head 1b (step 100). This DC bias adjustment is shown in FIG.
First, it is determined whether or not the output signal of the detection head 1b has a DC bias shift as shown in the flowchart of FIG.
The pattern of the ripple signal resulting from the deviation of the DC bias is a sinusoidal waveform having one cycle component with respect to the wavelength λ. If there is a deviation in the DC bias of the output signal of the detection head 1b, a maximum point or a minimum point appears at a position near the wavelengths λ / 4 and 3λ / 4 within one cycle. Although the distance between the maximum point and the minimum point is λ / 2, the position where the extreme value appears is not always exactly the position of the wavelengths λ / 4 and 3λ / 4, but changes depending on circuit conditions. The amplitude of the ripple signal indicates the magnitude of the deviation of the DC bias, and the order in which the maximum and the minimum appear, that is, the waveform indicates the direction of the DC bias, that is, the direction of magnetization. For example, when a local maximum point appears at a position near the wavelength λ / 4 of the ripple signal and a local minimum point appears at a position near the wavelength 3λ / 4, the direction of the DC bias is on the positive side, and the wavelength λ / 4 of the ripple signal. A minimum point appears at a position near the wavelength 3λ
When the maximum point appears at a position near / 4, the direction of the DC bias is on the minus side. The order in which the local maximum and the local minimum appear, that is, the relationship between the waveform and the direction of the DC bias varies depending on circuit conditions, and may be opposite to the example described here. If there is no deviation in the DC bias of the output signal of the detection head 1b and it is a standard value, this adjustment ends.

A position near the wavelength λ / 4 where the maximum or minimum point in the ripple signal appears is defined as a first singular point B11, and a position near the wavelength 3λ / 4 is defined as a second singular point B12. If there is a deviation in the DC bias, the two singularities B11,
Difference ΔE between voltage values E (B11) and E (B11) of B12
(B) is obtained. ΔE (B) = E (B11) −E (B11) The magnitude of the voltage difference ΔE (B) indicates the magnitude of the DC bias, and the sign indicates the direction of the DC bias. For example, when ΔE (B) ≧ 0, the DC bias is magnetized on the plus side, and when ΔE (B) <0, the DC bias is magnetized on the minus side. As described above, ΔE (B)
And the direction of the DC bias direction depend on circuit conditions. For example, the relationship between the sign of ΔE (B) and the direction of the DC bias may be opposite to the example described here. Therefore, the microcomputer 5 adjusts the electronic regulator ER1 according to the magnitude and sign of the voltage difference ΔE (B) until the value of the ΔE (B) becomes a standard value (minimum). This adjustment is terminated when the value of ()) reaches the standard value.

Next, the microcomputer 5 adjusts the DC bias of the output signal of the detection head 1c (step S).
101). The adjustment of the DC bias of the output signal of the detection head 1c is performed in the same manner as the adjustment of the DC bias of the output signal of the detection head 1b in FIG. Point B1
1, the difference Δ between the voltage values E (B11) and E (B11) of B12
This adjustment is terminated when E (B) becomes the standard value (minimum).

Next, the microcomputer 5 adjusts the level difference between the output signals of the detection heads 1b and 1c (step S102). The adjustment of the output level difference between the respective output signals of the detection heads 1b and 1c first determines whether there is an output level difference between the output signals as shown in the flowchart of FIG. If there is no level difference between the output signals, this adjustment ends.

When there is a level difference between the output signals of the two detection heads 1b and 1c, the pattern of the ripple signal is a sine wave having a component of two periods with respect to the wavelength λ. 2
If there is a level difference between the output signals of the two detection heads 1b and 1c, the wavelengths λ / 8, 3λ / 8, 5λ / 8 and 7
A maximum point or a minimum point appears at a position near λ / 8. The amplitude of the ripple signal indicates the magnitude of the level difference between the two output signals, and the order or waveform in which the maximum and the minimum appear indicates the direction of the level difference, that is, which detection head has a higher output signal level. For example, the wavelength λ / 8 of the ripple signal
When a maximum point appears at a position near 5λ / 8 and a minimum point appears at a position near 3λ / 8 and 7λ / 8, the first
Is higher than the level of the output signal of the second detection head 1c. When a minimum point appears at a position near the wavelength λ / 8 and 5λ / 8 of the ripple signal and a maximum point appears at a position near the wavelength 3λ / 8 and 7λ / 8, the level of the output signal of the first detection head 1b Is smaller than the level of the output signal of the second detection head 1c. The extreme value appears every λ / 4, but the position where the extreme value appears is not always exactly nλ / 8 (n is an integer) and varies depending on circuit conditions. A position near the wavelength λ / 8 where the maximum or minimum point in the ripple signal appears is defined as a first singular point G1, and a position near the wavelength 3λ / 8 is defined as a singular point G2.
The position near 8 is the third singular point G3, and the position near the wavelength 7λ / 8 is the fourth singular point G4. When there is a difference between the levels of the output signals of the two detection heads, the voltage values E (G1) and E (G1) of the first and second singularities G1 and G2 are obtained.
2) Find the difference ΔE (G). Third and fourth singularities G
3, the difference ΔE between the voltage values E (G3) and E (G4) of G4
(G) may be obtained. The microcomputer 5 controls the electronic volume E according to the magnitude and sign of the voltage difference ΔE (G).
R3 is adjusted, and this voltage difference ΔE (G) becomes a specified value (minimum).
This adjustment ends when has been reached.

Subsequently, the microcomputer 5 adjusts the output level (step S103). This detects the average value of the output voltage including the ripple signal, and adjusts the electronic volume E so that the average value of the output voltage reaches a specified output level.
To adjust the R _4.

Next, the shift of the phase difference (λ / 4) between the respective output signals of the detection heads 1b and 1c is adjusted (step S104). The adjustment of the phase difference (λ / 4) between the respective output signals of the detection heads 1b and 1c, that is, the deviation from 90 °, is as shown in the flowchart of FIG. ) Is determined. This adjustment ends when the phase difference between these output signals is 90 ° and there is no shift.

When the phase difference between the output signals of the two detection heads 1b and 1c is shifted by more than 90 degrees, the pattern of the ripple signal is a cosine wave having a component of two periods with respect to the wavelength λ. When the phase difference between the output signals of the two detection heads 1b and 1c deviates from 90 degrees, the local maximum point or the local minimum is located at a position near wavelengths 0, λ / 4, λ / 2, 3λ / 4 and λ within one cycle. A point appears. The amplitude of the ripple signal indicates the magnitude of the deviation of the phase difference between the two output signals from 90 degrees, and the order in which the local maximum and the local minimum appear, that is, the waveform is the phase difference of 90 degrees.
The direction of deviation from the degree, that is, whether the deviation is positive or negative.
For example, when a maximum point appears at a position near the wavelengths 0, λ / 2 and λ of the ripple signal and a minimum point appears at a position near the wavelengths λ / 4 and 3λ / 4, the phase difference deviates from 90 degrees. Positive. When a minimum point appears at a position near wavelengths 0, λ / 2 and λ of the ripple signal and a maximum point appears at positions near wavelengths λ / 4 and 3λ / 4, the deviation of the phase difference from 90 degrees is negative. is there. The extreme value appears every λ / 4, but the position where the extreme value appears is not always exactly 2nλ / 8 (n is an integer) and varies depending on circuit conditions. A position near the wavelength 0 where the maximum or minimum point appears in the ripple signal is defined as a first singular point P1, a position near the wavelength λ / 4 is defined as a second singular point P2, and a position near the wavelength λ / 2 is defined as the first singular point P2. 3, a position near the wavelength 3λ / 4 is set as the fourth singular point P4, and the wavelength λ
A nearby position is defined as a fifth singular point P5. If the phase difference between the output signals of the two detection heads deviates from 90 degrees, the voltage value E (P) of the first and second singular points P1 and P2
1) Find the difference ΔE (P) between E (P2). Voltage values E (P3), E (P4) of the third and fourth singular points P3, P4
The difference ΔE (P) may be obtained. The microcomputer 5 adjusts the electronic regulator ER5 according to the magnitude and sign of the voltage difference ΔE (P), and ends the adjustment when the voltage difference ΔE (P) reaches a specified value (minimum).

In this embodiment, the ripple of the phase modulation signal is detected as described above, and the DC bias of each output signal of the detection heads 1b and 1c is adjusted by the pattern of the ripple signal, and the level difference between the output signals is detected. Adjustment and adjustment of the phase difference (λ / 4) deviation between output signals are performed automatically until the ripple signal pattern reaches the standard value (minimum), so it is always stable and stable. Can be
There is an advantage that the displacement amount can always be detected with high accuracy.

In the above embodiment, the microcomputer 5 determines the maximum point and the minimum point of the ripple signal pattern of the phase modulation signal e _PM by the microcomputer 5. In this case, the electronic regulators ER ₁ , ER ₁ , If ER ₂ , ER ₃ and ER ₅ are changed from minimum to maximum respectively to detect the maximum point and the minimum point, and then the above adjustment is performed, it is easy to detect the maximum point and the minimum point. There are benefits.

The maximum point and the minimum point of the ripple signal pattern of the phase modulation signal e _PM are based on the wavelength λ, and if this λ is determined, the positions where the maximum point and the minimum point are generated in advance according to the adjustment item. If the maximum and minimum points are stored in the memory of the microcomputer 5 in advance, and the maximum and minimum points are determined by signals from the memory according to the adjustment items, There is an advantage that the above adjustment can be accelerated by the time required for determining the maximum point and the minimum point.

The present invention is not limited to the above-described embodiment, but may adopt various other configurations without departing from the gist of the present invention.

[0032]

According to the present invention, even when a plurality of errors are included in the phase modulation signal in a superimposed manner, the error factors can be individually specified, so that the errors can be removed according to the error factors. There are advantages that can be done. According to the present invention, even when a plurality of errors are included in the phase modulation signal in a superimposed manner, the errors can be individually removed only by supplying the adjustment signal to the scale signal detection circuit that outputs the phase modulation signal. There are advantages that can be done from.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a displacement amount detection device of the present invention.

FIG. 2 is a configuration diagram illustrating an example of a scale signal detection circuit in FIG. 1;

FIG. 3 is a connection diagram illustrating an example of an electronic regulator.

FIG. 4 is a diagram for describing the present invention.

FIG. 5 is a diagram for describing the present invention.

FIG. 6 is a diagram for describing the present invention.

FIG. 7 is a diagram for describing the present invention.

FIG. 8 is a configuration diagram illustrating an example of a conventional displacement amount detection device.

FIG. 9 is a configuration diagram illustrating an example of a conventional scale signal detection circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Scale part 2 Scale signal detection circuit 2an, 2cn DC bias adjuster 2en 90 degree phase shifter 2fn Addition amplifier 2hn amplifier 3 Interpolation circuit 5 Microcomputer 6 Ripple detection circuit 8 Electronic volume control circuit

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01B 7/00 G01D 5/245

Claims (4)

(57) [Claims] 1. A pair of detection heads, a scale having a scale of a period λ, a scale signal detection circuit for outputting a phase modulation signal whose phase is changed by a relative displacement between the detection head and the scale, An interpolation circuit that receives the phase modulation signal and outputs a pulse signal corresponding to the amount of change in the phase of the phase modulation signal using a predetermined clock pulse. In a displacement amount detection device configured to detect displacement, a ripple detection circuit that inputs the phase modulation signal and generates a ripple signal that is an envelope thereof, and converts an analog signal output from the ripple detection circuit into a digital signal An A / D converter for conversion; a pulse signal corresponding to a relative displacement between the detection head and the scale output from the interpolation circuit; A λ signal indicating a point and the output of the AD converter are input, and the DC bias of the detection head, a difference in output level between the detection heads, which is a factor of an error superimposed on the phase modulation signal, and Calculating means for detecting a deviation of a phase difference between output signals of the detecting head, wherein the calculating means has a maximum of a sine wave component having a period and a phase unique to each of the error factors in the ripple signal. The magnitude and polarity of the error are determined by determining the amplitude deviation between two singular points indicating a point and a minimum point, and the position of the two singular points in the ripple signal is detected using the λ signal. The displacement amount detecting device is configured as described above. 2. The displacement amount detection device according to claim 1, wherein the scale signal detection circuit has an electronic volume for removing the error, and the electronic volume is a magnitude of the deviation supplied from the arithmetic unit. And a displacement detection device configured to be adjusted by an adjustment signal indicating the polarity. 3. A pair of detection heads, a scale having a scale of a period λ, a scale signal detection circuit for outputting a phase modulation signal whose phase changes by a relative displacement between the detection head and the scale, An interpolation circuit that receives the phase modulation signal and outputs a pulse signal corresponding to the amount of change in the phase of the phase modulation signal using a predetermined clock pulse. A displacement amount detection device configured to detect a displacement, comprising: a ripple detection circuit that receives the phase modulation signal and generates a ripple signal that is an envelope thereof; and converts an analog signal output from the ripple detection circuit into a digital signal. DC bias of the detection head, which is a factor of an error included in the AD converter and the phase modulation signal in a superimposed manner, and an output level between the detection heads Calculating means for detecting the deviation of the phase difference between the detection signal and the output signal of the detection head,
The scale signal detection circuit has a plurality of electronic regulators for removing the error, and the arithmetic means includes a DC bias of one of the pair of detection heads of the plurality of electronic regulators based on an external adjustment command signal. An adjustment signal is supplied to an electronic volume for removing an error caused by the ripple signal so that the amplitude of the ripple signal changes to a maximum, and one of the maximum change points of the ripple signal is used as a reference point to adjust the ripple signal. In the configuration, the deviation and the polarity of the amplitude between two singular points unique to each of the factors of the error are obtained, and the electronic volume is sequentially adjusted based on the magnitude and the polarity of the deviation. Characteristic displacement detector. 4. A pair of detection heads, a scale having a scale of a period λ, a scale signal detection circuit for outputting a phase modulation signal whose phase is changed by a relative displacement between the detection head and the scale, An interpolation circuit that receives the phase modulation signal and outputs a pulse signal corresponding to the amount of change in the phase of the phase modulation signal using a predetermined clock pulse. A displacement amount detection device configured to detect a displacement, comprising: a ripple detection circuit that receives the phase modulation signal and generates a ripple signal that is an envelope thereof; and converts an analog signal output from the ripple detection circuit into a digital signal. DC bias of the detection head, which is a factor of an error included in the AD converter and the phase modulation signal in a superimposed manner, and an output level between the detection heads Calculating means for detecting the deviation of the phase difference between the detection signal and the output signal of the detection head,
The scale signal detection circuit has a plurality of electronic regulators for removing the error, and the arithmetic means sequentially changes the amplitude of the ripple signal to the plurality of electronic regulators to the maximum by an external adjustment command signal. And the two maximum change points of the ripple signal are detected as singular points unique to each of the errors, and the deviation and polarity of the position and amplitude of the two singular points in the ripple signal are calculated. A displacement amount feedback device configured to sequentially adjust the plurality of electronic volumes so as to reduce the amplitude of the ripple signal.