Displacement detection device

Abstract

The present application relates to a kind of displacement detection device.The displacement detection device (100) is equipped with detection signal processing device (3) and is equipped with the 1st differential amplifier (31), the 2nd differential amplifier (32) and operation processing part (35).The 1st differential amplifier (31) exports the 1st alternating current signal obtained by synthesizing cosine function and negative cosine function.The 2nd differential amplifier (32) exports the 2nd alternating current signal obtained by synthesizing sine function and negative sine function.Operation processing part (35) determines the value that substantially represents the phase shift amount of excitation signal and the 1st alternating current signal and the 2nd alternating current signal at least when displacement detection device (100) starts to use.In detection displacement, operation processing part (35) uses the value of the 1st alternating current signal and the value of the 2nd alternating current signal obtained at the timing based on the above-mentioned value determined to carry out arctan operation, and exports the relative displacement information of scale (1) relative to magnetic detection head (2).

Description

Technical Field

[0001] This invention relates to a displacement detection device for detecting and measuring the displacement of an object. Background Technology

[0002] Displacement detection devices that utilize electromagnetic induction to detect and measure the displacement of an object have been known for a long time. Patent Document 1 discloses a rotary decomposer as such a displacement detection device.

[0003] Patent Document 1 describes a rotation resolver used to obtain the rotation angle of a motor. This rotation resolver includes an analog-to-digital (A / D) converter and a correction unit. The A / D converter performs analog-to-digital conversion on multi-phase signal waves with different phases. The phase of the A / D converted signal wave is delayed relative to the phase of the excitation signal. An excitation signal having a reference phase position within the excitation cycle is input to the correction unit, along with multi-phase signal waves from the A / D converter. The correction unit detects the zero-crossing phase of the sum of the squares of the multi-phase signal waves and performs correction based on the position of the zero-crossing phase in the phase interval formed by equally dividing the excitation cycle and the correction direction of the phase shift, thereby delaying the phase of the excitation signal. The phase delay of the excitation signal is calculated by the phase difference between this phase and the phase of the aforementioned signal wave, i.e., the offset from the aforementioned reference phase position.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 5802588 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] In the configuration of Patent Document 1, the multiphase signal wave from the AD converter is ultimately converted into a signal whose phase changes according to the rotation angle of the motor. By determining the phase of this signal, the rotation angle of the motor can be obtained.

[0009] In the configuration of Patent Document 1, the phase of the signal needs to be accurately determined in order to accurately detect the rotation angle of the motor. Typically, the signal phase is detected by repeatedly counting from the reference timing of the excitation signal to the timing when a characteristic point (e.g., a zero-crossing) appears in the signal waveform using a counter. To detect the signal phase with high accuracy, the time resolution of the counter needs to be improved. However, since there are limits to improving the operating clock of the circuit, it is sometimes difficult to improve the time resolution of the counter.

[0010] Extending the excitation cycle can improve the resolution of the motor's rotation angle. However, if the excitation cycle becomes longer, the detection tracking performance will decrease when the motor's rotation angle changes rapidly. Thus, in the configuration of Patent Document 1, it is difficult to simultaneously achieve both high-speed response and high resolution, leaving room for improvement.

[0011] The present invention was made in view of the above circumstances, and its purpose is to provide a displacement detection device that can eliminate errors caused by changes due to external factors such as temperature on the spot through calculation, and can achieve high-speed response and high resolution.

[0012] The methods and effects used to solve problems

[0013] The problem to be solved by the present invention has been described above, and the means and effects of solving the problem will be described below.

[0014] According to the present invention, a displacement detection device with the following configuration is provided. That is, the displacement detection device detects the displacement of a measured object in the displacement detection direction. The displacement detection device includes a scale, a sensor head, and a signal processing unit. On the scale, magnetic response portions and non-magnetic response portions are alternately arranged at predetermined detection intervals in the displacement detection direction. The sensor head has an excitation element and at least four magnetic detection elements. An excitation signal is applied to the excitation element. The output signals of the four magnetic detection elements are sine functions, cosine functions, negative sine functions, and negative cosine functions, respectively. The output signals of the magnetic detection elements are input to the signal processing unit. The signal processing unit calculates and outputs the relative displacement information of the scale relative to the sensor head. The signal processing unit includes a first differential amplifier, a second differential amplifier, and a processing unit. The first differential amplifier outputs a first AC signal obtained by synthesizing the cosine function and the negative cosine function. The second differential amplifier outputs a second AC signal obtained by synthesizing the sine function and the negative sine function. The aforementioned processing unit determines, at least when the displacement detection device is first used, a value that substantially represents the phase offset between the excitation signal and the first and second AC signals. When detecting the displacement of the object being measured, the processing unit acquires the values ​​of the first and second AC signals at a timing based on the determined values, performs an arctan operation using the obtained values ​​of the first and second AC signals, and outputs the relative displacement information.

[0015] Therefore, the values ​​of each signal can be obtained at timings where the first and second AC signals are sufficiently deviated from zero. Consequently, a highly accurate tan value can be obtained through division of the signal values. Accurate displacement can be obtained by performing an arctan operation on this tan value. Furthermore, since the displacement is calculated using the arctan operation, the displacement can be calculated multiple times within each cycle of the excitation signal. Therefore, in addition to achieving high resolution, high-speed detection response can be easily achieved.

[0016] The displacement detection device preferably includes an amplitude adjustment unit that adjusts the amplitude of the first AC signal output by the first differential amplifier and the amplitude of the second AC signal output by the second differential amplifier.

[0017] Thus, for example, the amplitude can be changed in accordance with the change in the transformer ratio of the magnetic detection head. As a result, a waveform suitable for displacement detection can be stably obtained.

[0018] In the displacement detection device described above, the amplitude adjustment unit preferably adjusts the amplitude of the alternating current flowing in the excitation element.

[0019] Therefore, the gain setting process for the first and second differential amplifiers can be omitted, resulting in a simpler processing method.

[0020] Preferably, in the displacement detection device described above, the amplitude adjustment unit adjusts the amplification gain of the first differential amplifier and the second differential amplifier.

[0021] This allows for more direct adjustment of the amplitude of the waveforms output by the first and second differential amplifiers.

[0022] The displacement detection device described above is preferably configured as follows: At least at the start of use of the displacement detection device, multiple synchronous excitation signals are generated by applying different phase shifts from the excitation signals to the excitation element. As each of the synchronous excitation signals is applied to the excitation element, the arithmetic processing unit obtains the values ​​of the first AC signal and the second AC signal at a timing when the excitation signal becomes constant relative to the original excitation signal, and obtains the sum of the degrees to which the values ​​of the first AC signal and the second AC signal deviate from zero. The arithmetic processing unit determines the phase shift of the synchronous excitation signal with the largest sum among the multiple synchronous excitation signals, and calculates a value that substantially represents the phase shift based on this phase shift.

[0023] Therefore, by using excitation signals with different phases to excite the excitation element, an investigation can be conducted to obtain the timing of the first AC signal and the second AC signal being sufficiently deviated from zero.

[0024] The displacement detection device described above is preferably configured as follows: At least at the start of use of the displacement detection device, the processing unit repeatedly acquires the values ​​of the first AC signal and the second AC signal at a sampling period shorter than the signal period. The processing unit acquires the sum of the degree to which the values ​​of the first AC signal and the second AC signal deviate from zero at multiple sampling times. The processing unit determines the sampling time at which the sum of the sums is largest among the multiple sampling times at which the sums are acquired, and calculates a value that substantially represents the phase offset based on that sampling time.

[0025] Therefore, it is possible to obtain the timing of the first AC signal and the second AC signal being sufficiently deviated from zero in a short period of time. Attached Figure Description

[0026] Figure 1 This is a block diagram illustrating the configuration of a displacement detection device according to one embodiment of the present invention.

[0027] Figure 2 It is a diagram showing the waveforms of the excitation signal, the first AC signal, and the second AC signal.

[0028] Figure 3 The diagram illustrates a constant excitation signal with the same phase as the original excitation signal in the first embodiment.

[0029] Figure 4 This diagram illustrates the generation of a constant excitation signal by delaying the phase of the original excitation signal by 40°.

[0030] Figure 5 This diagram illustrates the generation of a constant excitation signal by delaying the phase of the original excitation signal by 340°.

[0031] Figure 6 This is a diagram illustrating the acquisition of the values ​​of the first AC signal and the second AC signal in the second embodiment.

[0032] Figure 7 This is a diagram illustrating the acquisition of the values ​​of the first AC signal and the second AC signal in the third embodiment.

[0033] Figure 8 This is a flowchart illustrating the first example of the amplitude adjustment process in the fourth embodiment.

[0034] Figure 9 This is a flowchart illustrating the second example of the amplitude adjustment process in the fourth embodiment. Detailed Implementation

[0035] Next, embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a block diagram illustrating the configuration of a displacement detection device 100 according to one embodiment of the present invention. Figure 2 It is a diagram showing the waveforms of the excitation signal, the first AC signal y1, and the second AC signal y2.

[0036] Figure 1 The displacement detection device 100 shown is used to detect the displacement of an object in a specified direction. In the following description, the direction in which the displacement of the object is detected is sometimes referred to as the displacement detection direction.

[0037] Displacement refers to the degree to which the current position has changed compared to a reference position (e.g., an initial position). By defining the reference position using an appropriate method, the position of the object being measured can also be calculated from the displacement. Therefore, the displacement detection device 100 can be used as a position detection device.

[0038] The displacement detection device 100 mainly includes a scale 1, a magnetic detection head (sensor head) 2, and a detection signal processing device (signal processing and calculation device) 3.

[0039] One of the scale 1 and the magnetic detection head 2 is mounted on the object being measured. For example, the scale 1 is mounted on a movable part (not shown in the diagram), and the magnetic detection head 2 is mounted on a fixed part (not shown in the diagram), which is the object being measured. The movable part can move linearly along a path parallel to the displacement detection direction.

[0040] Alternatively, a scale 1 can be mounted on a fixed component that is the object to be measured, and a magnetic detection head 2 can be mounted on a movable component. Furthermore, the scale 1 and the magnetic detection head 2 can each be mounted on a movable component that is displaced relative to each other. In this case, the displacement detection device 100 detects the relative displacement of the object to be measured (i.e., the scale 1 and the magnetic detection head 2).

[0041] The scale 1 is used as a graduation for detecting the displacement of the object along its length. The scale 1 is elongated in a direction parallel to the travel of the magnetic detection head 2, so as to include the travel of the magnetic detection head 2 accompanying the movement of the movable part. The scale 1 can be formed as an elongated block or as an elongated rod.

[0042] The scale 1 includes a non-magnetic response portion 11 and a magnetic response portion 12. The non-magnetic response portion 11 is made of, for example, a metal or a non-magnetic plastic. The magnetic response portion 12 is made of, for example, a metal with strong magnetism. The non-magnetic response portion 11 and the magnetic response portion 12 are arranged alternately along the length of the scale 1.

[0043] The magnetic response units 12 are arranged along the length of the scale 1 at a predetermined detection interval C0. Because the magnetic response units 12 are arranged at predetermined intervals, a portion without (or with relatively weak) magnetism, i.e., a non-magnetic response portion, is formed between two adjacent magnetic response units 12. Therefore, in the magnetic response units 12, the presence or absence, or varying strength of magnetic responsiveness, alternates repeatedly along the length of the scale 1 at the detection interval C0.

[0044] like Figure 1 As shown, the magnetic detection head 2 and the magnetic response unit 12 are arranged at a predetermined interval. When the scale 1 is formed as an elongated rod, the magnetic detection head 2 can be formed as a cylinder, allowing the scale 1 to be inserted into its cylindrical hole. However, the shape of the magnetic detection head 2 is not limited. The magnetic detection head 2 includes a primary coil (excitation element) 21 and multiple secondary coils (magnetic detection elements) 22. In this embodiment, four secondary coils 22 are provided.

[0045] The primary coil 21 is used to generate an alternating magnetic field. For example... Figure 1 As shown, the primary coil 21 is disposed in the magnetic detection head 2 on the side further away from the scale 1 than the secondary coil 22.

[0046] When an alternating current of appropriate frequency flows in the primary coil 21, a magnetic field with periodically varying orientation and intensity is generated around the primary coil 21. In this embodiment, as... Figure 1 As shown, the primary coil 21 is subjected to an excitation signal (A·sinωt) obtained by performing a DA conversion on the excitation wave generated by the FPGA or similar device included in the detection signal processing device 3 described later. FPGA is short for Field Programmable Gate Array.

[0047] like Figure 1 As shown, four secondary coils 22 are arranged in a direction parallel to the length direction of the scale 1. The secondary coils 22 are positioned in the magnetic detection head 2 on the side closer to the scale 1 than the primary coil 21. An induced current flows through the four secondary coils 22, generated by the magnetic field amplified by the magnetic response unit 12. The magnetic detection head 2 detects and outputs an electrical signal (e.g., a voltage signal) based on this induced current.

[0048] like Figure 1 As shown, the four secondary coils 22 are arranged in the displacement detection direction with a predetermined unit spacing C1. This unit spacing C1 is determined based on the detection spacing C0 in a manner that has a predetermined relationship with the aforementioned detection spacing C0. Specifically, as shown in the following formula, the unit spacing C1 is set to the sum of an integer multiple of the detection spacing C0 and one-quarter of the detection spacing C0.

[0049] C1 = (n + 1 / 4)·C0

[0050] Where n is an integer. In this embodiment, n = 0, but it is not limited to this.

[0051] In the following description, in order to identify these four secondary coils separately, sometimes from... Figure 1 The coils shown on the left are named 1st coil 22a, 2nd coil 22b, 3rd coil 22c, and 4th coil 22d respectively.

[0052] Here, the signals (e.g., voltage signals) output by each secondary coil 22 are briefly explained. When an alternating current of appropriate frequency flows in the primary coil 21, a magnetic field with a periodically changing orientation and intensity is generated in the primary coil 21. On the other hand, an induced current is generated in the secondary coil 22 in an orientation that opposes the change in the magnetic field of the coil. If a strong magnetic body is present near the primary coil 21, the strong magnetic body acts to enhance the magnetic field generated by the primary coil 21. The closer the strong magnetic body is to the primary coil 21, the greater this effect.

[0053] Focusing on the magnetic response unit 12, as the magnetic detection head 2 moves relative to each other from one side of the scale 1 along its length, the primary coil 21 and the secondary coil 22 approach the magnetic response unit 12, but then move away after reaching the closest point. The induced current generated in the secondary coil 22 is an alternating current, but its amplitude varies depending on the positional relationship between the secondary coil 22 and the magnetic response unit 12.

[0054] The magnetic response units 12 are actually arranged according to the detection interval C0, so the change in amplitude repeats according to the detection interval C0. That is, when the horizontal axis represents the position of the magnetic detection head 2 and the vertical axis represents the amplitude, the relationship between amplitude and position becomes a periodic curve with the detection interval C0 as the period (specifically, a sine curve y = sinθ). If this θ can be calculated, the position of the scale 1 relative to the magnetic detection head 2 in the detection interval C0, which is the unit of repetition, can be obtained.

[0055] However, when considering one period of the sine curve y = sinθ, except in special cases, two θ values ​​corresponding to y can be considered, not just one. Therefore, in this embodiment, four secondary coils 22 are arranged at intervals determined according to the unit spacing C1, so that the positional relationship between the secondary coils 22 and the nearest magnetic response unit 12 is substantially offset by 1 / 4 of the detection spacing C0.

[0056] like Figure 1As shown, coils 22a, 22b, 22c, and 22d are separated from each other by a detection distance C0 of 1 / 4, thus outputting voltage signals with phases offset by 90°. That is, when the voltage signal output by coil 22a is represented as a cos+ phase, coil 22b outputs a sin+ phase voltage signal, coil 22c outputs a cos- phase voltage signal, and coil 22d outputs a sin- phase voltage signal.

[0057] The detection signal processing device 3 processes the voltage signals output from the first coil 22a, the second coil 22b, the third coil 22c, and the fourth coil 22d, calculates and outputs the relative displacement of the scale 1 relative to the magnetic detection head 2.

[0058] For example, such as Figure 1 As shown, the detection signal processing device 3 includes a first differential amplifier 31, a second differential amplifier 32, and an arithmetic processing unit 35.

[0059] In this embodiment, the first differential amplifier 31 and the second differential amplifier 32 are composed of a portion of the analog circuitry (or electronic components) included in the detection signal processing device 3. The arithmetic processing unit 35 is implemented by executing a program such as an FPGA included in the detection signal processing device 3.

[0060] The first differential amplifier 31 is used to amplify the differential outputs of the first coil 22a and the third coil 22c. The first differential amplifier 31 amplifies the differential voltage signals output from the first coil 22a and the third coil 22c and outputs them as the first AC signal y1.

[0061] When the phase representing the displacement of the scale 1 relative to the magnetic detection head 2 is set as θ, the first AC signal y1 can be represented by the following formula.

[0062] y1=acosθ·sinωt

[0063] After being processed by a filter, the first AC signal y1 is converted from an analog signal to a digital signal by an AD converter and then input to the arithmetic processing unit 35.

[0064] The second differential amplifier 32 is used to amplify the differential outputs of the second coil 22b and the fourth coil 22d. The second differential amplifier 32 amplifies the differential voltage signals output from the second coil 22b and the fourth coil 22d and outputs them as the second AC signal y2.

[0065] When the phase representing the displacement of the scale 1 relative to the magnetic detection head 2 is set as θ, the second AC signal y2 can be represented by the following formula.

[0066] y2=asinθ·sinωt

[0067] Similar to the first AC signal y1 mentioned above, the second AC signal y2, after being processed by a filter, is converted from an analog signal to a digital signal by an AD converter and input to the arithmetic processing unit 35.

[0068] The arithmetic processing unit 35 performs an arctan operation on the first AC signal y1 and the second AC signal y2 of the digital signals. Specifically, the arithmetic processing unit 35 divides the second AC signal y2 of the digital signals by the first AC signal y1. The result is equivalent to the tanθ value. Then, the arithmetic processing unit 35 calculates the arctan value of the result. From this, the phase θ representing the displacement of the scale 1 relative to the magnetic detection head 2 can be obtained as the relative displacement information of the scale 1. Strictly speaking, θ is a phase, but in practice it represents the relative displacement of the scale 1 relative to the magnetic detection head 2. Therefore, θ will sometimes be referred to as displacement below.

[0069] The displacement θ calculated by the arithmetic processing unit 35 is input to a filter to remove high-frequency components. This removes noise and other noise. After undergoing subsequent processing such as linear correction, the filtered value is output as position information from the detection signal processing device 3.

[0070] Next, the phase shift generated between the primary coil 21 and the secondary coil 22 will be explained in detail.

[0071] As is known, such as Figure 2 As shown, a phase offset d is generated between the excitation signal applied to the primary coil 21 and the output (first AC signal y1 and second AC signal y2) of the secondary coil 22. Specifically, the phases of the first AC signal y1 and the second AC signal y2 are delayed by a phase offset d relative to the excitation signal. This phase offset d is generated based on different coil designs, the resistance factor of the wiring section (type, length, and routing of wiring), etc. The magnitude of the phase offset d varies depending on the surrounding environment such as temperature.

[0072] In the arithmetic processing unit 35 of this embodiment, in order to detect the displacement of the scale 1 relative to the magnetic detection head 2, the timing for acquiring the values ​​of the first AC signal y1 and the second AC signal y2 is predetermined while taking into account the aforementioned phase offset d, so that each signal is a value sufficiently deviated from zero. This timing is determined relative to the timing of the excitation signal.

[0073] As described above, tanθ is calculated by dividing the second AC signal y2 by the first AC signal y1. Therefore, if the values ​​of both signals are near zero, the accuracy of tanθ decreases. Considering this, the optimal timing for obtaining the values ​​of the first AC signal y1 and the second AC signal y2 is to coincide with the timing when the values ​​of the two signals reach their positive or negative peaks. However, as long as the values ​​of the two signals deviate from zero to a certain extent, the accuracy of tanθ can be sufficiently ensured; therefore, it is not necessary to obtain the signal values ​​at a timing strictly at the peaks.

[0074] When the excitation signal is expressed as A·sinωt, the first AC signal y1 and the second AC signal y2 are represented by the following formula.

[0075] y1 = a·cosθ·sin(ωt+d)

[0076] y2=a·sinθ·sin(ωt+d)

[0077] In this formula, d represents the aforementioned phase offset.

[0078] The timing of the positive or negative peak values ​​of the first AC signal y1 and the second AC signal y2 refers to the timing when the phase of ωt+d is 90° or 270°. On the other hand, when the phase of ωt+d is 0° or 180°, the values ​​of the first AC signal y1 and the second AC signal y2 are both near zero.

[0079] Therefore, in this embodiment, when measuring the displacement θ, the values ​​of the first AC signal y1 and the second AC signal y2 are obtained at timings that are sufficiently different from 0° or 180° relative to ωt+d. As long as the phase offset d can be calculated with a certain degree of accuracy, the timing for retrieving the values ​​of the first AC signal y1 and the second AC signal y2 used in the arctan operation can be appropriately generated.

[0080] For example, able to use Figures 3 to 5 The phase offset d is determined by the successive phase shift method of the excitation signal as shown.

[0081] The following is a detailed explanation. The arithmetic processing unit 35 generates multiple synchronous excitation signals based on the aforementioned excitation signal and sequentially applies these synchronous excitation signals to the primary coil 21. Multiple synchronous excitation signals are generated by shifting the phase of each signal by a different amount relative to the original excitation signal. Figures 3 to 5 An example of the same excitation signal is shown in .

[0082] Regarding the same excitation signal Figure 3 This shows the case where the phase shift D is 0°. Figure 4 This shows the case where the phase shift D is 40°. Figure 5 The case where the phase shift D is 340° is shown. Thus, among multiple identical excitation signals, there can also be signals without phase shift, that is, signals whose phase is the same as the original excitation signal.

[0083] The successive phase shift method is explained in detail. When the original excitation signal is set as A·sinωt, and the phase shift in the delay direction is set as D, the constant excitation signal can be expressed as A·sin(ωt+D). By successively changing the value of D such as 0°, 10°, 20°, ..., multiple constant excitation signals can be generated.

[0084] The arithmetic processing unit 35 applies the same-stress excitation signal to the primary coil 21 whenever a same-stress excitation signal is generated. Each same-stress excitation signal is applied to the primary coil 21 for a sufficient period of time, for example, more than one cycle of the excitation signal.

[0085] The arithmetic processing unit 35 acquires the values ​​of the first AC signal y1 and the second AC signal y2 at the timing when the original excitation signal A·sinωt reaches its amplitude peak position, whenever each constant excitation signal is applied to the primary coil 21. Regarding the amplitude peak position, the phase of ωt can be either 90° or 270°, but... Figures 3 to 5 The example shown illustrates an instance obtained at a time of 90°.

[0086] Thus, regardless of which synchronous excitation signal is applied, the timing for obtaining the values ​​of the first AC signal y1 and the second AC signal y2 remains constant. However, since the phase of the synchronous excitation signal changes at 10° intervals, correspondingly, the phases of the values ​​of the first AC signal y1 and the second AC signal y2 also change at 10° intervals. Therefore, as... Figures 3 to 5 As shown, if the excitation signals used are different, the values ​​of the first AC signal y1 and the second AC signal y2 obtained will also be different.

[0087] The arithmetic processing unit 35 calculates, each time a timing excitation signal is applied to the primary coil 21, a total value representing the degree to which the values ​​of the first AC signal y1 and the second AC signal y2 obtained at the aforementioned timing deviate from zero. Hereinafter, this value is sometimes referred to as the signal deviation total value. In this embodiment, the signal deviation total value is calculated as the square root of the sum of the squares of the first AC signal y1 and the second AC signal y2, as shown in the following formula.

[0088] Total signal deviation = √((first AC signal y1)^2 + (second AC signal y2)^2)

[0089] However, as shown in the following formula, the sum of the absolute values ​​of the first AC signal y1 and the second AC signal y2 can also be obtained as the total value of signal deviation.

[0090] Total signal deviation = |first AC signal y1| + |second AC signal y2|

[0091] In this case, the computational burden can be reduced compared to the square root of the sum of squares mentioned above.

[0092] After calculating the total signal deviation for each constant-stability excitation signal, the arithmetic processing unit 35 compares the total signal deviation values ​​with each other. From this, it can determine the phase shift D corresponding to the constant-stability excitation signal whose total signal deviation value is the maximum. In this example, the phase shift D is set to 340°. Figure 5 When the excitation signal is constant, the total deviation of the signal becomes the maximum. The arithmetic processing unit 35 subtracts 340°, which is the phase shift D, from 360° to obtain the estimated phase shift d. e In this example, the phase shift estimate d e Become 20° (d e =360° - 340° = 20°).

[0093] In this example, the phase shift D of the constant excitation signal varies according to a 10° scale, therefore the estimated phase shift d is... e The accuracy is not high. However, the phase shift estimation d e This becomes a value near the phase offset d. Therefore, the phase offset is estimated to be d. e This can be considered a value that substantially represents the phase offset d. When the determined phase offset is extrapolated to a value d... e The initial processing is complete when the data is stored in the appropriate storage unit.

[0094] In the subsequent measurement of displacement θ, the estimated value d was derived based on the obtained phase shift. e To determine the timing for acquiring the values ​​of the first AC signal y1 and the second AC signal y2. Specifically, in relation to ωt+d e The values ​​of the first AC signal y1 and the second AC signal y2 are obtained by timing that is sufficiently different, either at 0° or 180°, with the preferred timing being ωt+d. e This allows for timing at 90° or 270°. Based on the above, tanθ (and thus displacement θ) can be obtained with good accuracy.

[0095] In this embodiment, the displacement θ is obtained by calculating the arctan of the value obtained by dividing the second AC signal y2 by the first AC signal y1. Therefore, for the first AC signal y1 and the second AC signal y2 of one cycle, the displacement θ can be obtained at any timing as long as the timing avoids the signal value being close to zero. The frequency of obtaining the displacement θ can be once or more in each cycle of the excitation signal. If the displacement θ is obtained multiple times in each cycle of the excitation signal, the displacement can be detected at high speed even when the scale 1 moves at high speed relative to the magnetic detection head 2.

[0096] As described above, the displacement detection device 100 of this embodiment detects the displacement of the object to be measured in the displacement detection direction. The displacement detection device 100 includes a scale 1, a magnetic detection head 2, and a detection signal processing device 3. On the scale 1, magnetic response units 12 and non-magnetic response units 11 are alternately arranged at a predetermined detection interval in the displacement detection direction. The magnetic detection head 2 has a primary coil 21 to which an excitation signal is applied, and at least four secondary coils 22 whose output signals are sine, cosine, negative sine, and negative cosine functions, respectively. The output signals of the secondary coils 22 are input to the detection signal processing device 3. The detection signal processing device 3 calculates and outputs the relative displacement information of the scale 1 relative to the magnetic detection head 2. The detection signal processing device 3 includes a first differential amplifier 31, a second differential amplifier 32, and an arithmetic processing unit 35. The first differential amplifier 31 outputs a first AC signal y1 obtained by synthesizing the cosine function and the negative cosine function. The second differential amplifier 32 outputs a second AC signal y2 obtained by synthesizing a sine function and a negative sine function. The arithmetic processing unit 35, at least when the displacement detection device 100 is first used, determines the value of (phase offset estimate d) that substantially represents the phase offset d between the excitation signal and the first AC signal y1 and the second AC signal y2. e When detecting the displacement of the scale 1 relative to the magnetic detection head 2, the arithmetic processing unit 35 estimates the quantity d based on the determined phase shift. e The timing unit acquires the values ​​of the first AC signal y1 and the second AC signal y2. The arithmetic processing unit 35 uses the obtained values ​​of the first AC signal y1 and the second AC signal y2 to perform an arctan operation and outputs relative displacement information.

[0097] Therefore, the values ​​of each signal can be obtained at a timing when the first AC signal y1 and the second AC signal y2 are sufficiently deviated from zero. Thus, a highly accurate tanθ value can be obtained through division of the signal values. By performing an arctan operation on this tanθ value, an accurate displacement θ can be obtained. Furthermore, since the displacement is calculated using the arctan operation, the displacement can be calculated multiple times within each cycle of the excitation signal, avoiding the timing when the signal values ​​are close to zero. Therefore, in addition to achieving high resolution, high-speed detection response can be easily achieved.

[0098] Furthermore, in the displacement detection device 100 of this embodiment, multiple synchronous excitation signals based on the excitation signal are applied to the primary coil 21. Multiple synchronous excitation signals are generated by shifting their phases by different amounts D relative to the original excitation signal. As each synchronous excitation signal is applied to the primary coil 21, the arithmetic processing unit 35 obtains the values ​​of the first AC signal y1 and the second AC signal y2 at a constant timing relative to the original excitation signal, and obtains the sum of the degree to which the values ​​of the two signals deviate from zero (signal deviation sum). The arithmetic processing unit 35 calculates the phase shift D of the synchronous excitation signal with the largest sum among the multiple synchronous excitation signals. Based on this phase shift D, the arithmetic processing unit 35 calculates the phase shift estimation d. e .

[0099] Therefore, by energizing the primary coil 21 with different phase excitation signals, it is possible to obtain the timing when the values ​​of the first AC signal y1 and the second AC signal y2 are sufficiently deviated from zero.

[0100] Next, the second embodiment will be described. Furthermore, in the description of this embodiment, components that are the same or similar to those in the above embodiments are marked with the same symbols in the drawings, and sometimes the description is omitted.

[0101] In this embodiment, the arithmetic processing unit 35 uses a waveform tracking method of the output signals (i.e., the first AC signal y1 and the second AC signal y2) output from the secondary coil 22 instead of the successive phase shift method of the excitation signal to perform the phase offset determination processing described above and determine the phase offset used in the phase shifting process.

[0102] In detail, the arithmetic processing unit 35 acquires the values ​​of the first AC signal y1 and the second AC signal y2 with a sampling period sufficiently short than the signal period during initial processing, so as to reproduce the waveforms of the acquired first AC signal y1 and the second AC signal y2. At this time, the normal excitation signal A·sinωt is applied to the primary coil 21 instead of the aforementioned constant excitation signal. In order to shorten the sampling period, it is preferable to perform the AD conversion of the AD converter at high speed.

[0103] The arithmetic processing unit 35 calculates the total signal deviation value for each sampling timing, specifically for the first AC signal y1 and the second AC signal y2. Similar to the above, the total signal deviation value can be the square root of the sum of the squares of the two signal values, or it can be the sum of their absolute values. After calculating the total signal deviation value for each sampling timing, the arithmetic processing unit 35 compares the total signal deviation values ​​with each other. Therefore, it is possible to determine the sampling timing at which the total signal deviation value reaches its maximum value. Figure 6 As shown, the phase shift estimate d can be easily obtained based on the sampling timing when the signal deviation from the total value reaches its maximum. e The subsequent process for determining the displacement θ of the object being measured is essentially the same as in the first embodiment, therefore the explanation is omitted.

[0104] As explained above, in the displacement detection device 100 of this embodiment, the arithmetic processing unit 35 repeatedly acquires the values ​​of the first AC signal y1 and the second AC signal y2 with a sampling period shorter than the signal period. The arithmetic processing unit 35 acquires the sum of the degree to which the signal values ​​deviate from zero for each of the multiple sampling times. The arithmetic processing unit 35 determines the sampling time with the largest sum among the multiple sampling times for which the above sum has been acquired. Based on the sampling time with the largest sum, the arithmetic processing unit 35 calculates the phase offset estimation d. e .

[0105] Therefore, by investigating the waveform of a short period of time, such as one cycle of the excitation signal, it is possible to obtain the timing at which the values ​​of the first AC signal y1 and the second AC signal y2 are sufficiently deviated from zero.

[0106] Next, the third embodiment will be described. Furthermore, in the description of this embodiment, components that are the same or similar to those in the above embodiments are marked with the same symbols in the drawings, and sometimes the description is omitted.

[0107] This embodiment is suitable for situations where, due to limitations in the processing power of the AD converter, it is impossible to increase the number of samples per cycle when sampling the waveform as in the second embodiment. The waveform being sampled refers to the output signals output from the secondary coil 22, namely the first AC signal y1 and the second AC signal y2.

[0108] The following explanation will specifically focus on the case where the excitation signal can be sampled three times per cycle. In the initial processing, the arithmetic processing unit 35 uses a sampling waveform of two cycles instead of one cycle's worth to obtain the AC signal value. In the measurement of the first cycle (first measurement), as... Figure 7As shown on the upper side, the values ​​of the first AC signal y1 and the second AC signal y2 are obtained at timings where the phase relative to the waveform of the excitation signal is 0°, 120°, and 240°. In the second cycle (second measurement), as... Figure 7 As shown on the lower side, the values ​​of the first AC signal y1 and the second AC signal y2 are obtained at timings when the phase relative to the waveform of the excitation signal is 60°, 180°, and 300°.

[0109] Then, similar to the second embodiment, the total signal deviation value for each sampling timing is calculated. The arithmetic processing unit 35 calculates the sampling timing in which the total signal deviation value reaches its maximum value among the sampling timings of two cycles (a total of 6 times).

[0110] Thus, by making the sampling timing phase different in each cycle, it becomes possible to sample the first AC signal y1 and the second AC signal y2 with a shorter period than the actual time and determine the estimated phase shift d. e The situation is the same. Figure 7 In the example, the estimated phase shift d can be obtained by performing 6 samples in each cycle. e The same effect as in the case of [the previous situation].

[0111] In this embodiment, the waveform of two cycles is sampled, but it is also possible to sample the waveform of three or more cycles while slightly shifting the phase each time.

[0112] Next, the fourth embodiment will be described. Furthermore, in the description of this embodiment, components that are the same or similar to those in the above embodiments are marked with the same symbols in the drawings, and sometimes the description is omitted.

[0113] The detection signal processing device 3 of this embodiment can adjust the amplitude 'a' of the waveform (a·cosθ·sinωt) input to the AD converter from the first differential amplifier 31 and the amplitude 'a' of the waveform (a·sinθ·sinωt) input to the AD converter from the second differential amplifier 32. This embodiment can be combined with any of the first to third embodiments described above.

[0114] As described above, in the configurations of the first to third embodiments, the values ​​of each signal are obtained at a timing when the first AC signal y1 and the second AC signal y2 are sufficiently deviated from zero, and an arctan operation is performed. However, it is also possible that the amplitude of the waveforms output by the first differential amplifier 31 and the second differential amplifier 32 is not suitable relative to the input voltage range of the AD converter.

[0115] The following describes specific examples of waveform amplitudes that are too large or too small. The permissible physical size of the magnetic detection head 2 varies depending on the object being measured, the size of the surrounding space, etc. Considering such factors, in order to improve the versatility of the displacement detection device 100, it is sometimes configured to allow selection of one magnetic detection head 2 from various sizes depending on the situation. The transformation ratio of the primary coil 21 and the secondary coil 22 varies depending on the type of head. If the transformation ratio of the magnetic detection head 2 differs from the transformation ratio assumed in the detection signal processing device 3, the amplitude of the waveform output from the first differential amplifier 31 and the second differential amplifier 32 will become too large or too small.

[0116] An analog-to-digital converter (ADC) is positioned downstream of the first differential amplifier 31 and the second differential amplifier 32 in the direction of signal flow. If the amplitude of the output signals of the first differential amplifier 31 and the second differential amplifier 32 is too large relative to the signal input range of the ADC, waveform saturation occurs in the ADC, resulting in false detection of displacement θ. On the other hand, if the amplitude of the output signals of the first differential amplifier 31 and the second differential amplifier 32 is too small, the signal-to-noise ratio (SN ratio) deteriorates, leading to a decrease in the detection accuracy of displacement θ.

[0117] Therefore, in this embodiment, the amplitude A of the excitation signal (A·sinωt) output by the arithmetic processing unit 35 is configured to be changeable. After estimating the phase shift as described in the above embodiment, the arithmetic processing unit 35 investigates whether the peak values ​​of the waveforms of the first AC signal y1 and the second AC signal y2 fall within a predetermined range. The values ​​(including peak values) of the first AC signal y1 and the second AC signal y2 can be obtained from the two AD converters respectively.

[0118] When using the successive phase shift method of the first embodiment, it is possible to estimate the d based on the determined phase shift. e The values ​​of the first AC signal y1 and the second AC signal y2, obtained during timing, are considered as the peak values ​​of each waveform. When using the waveform tracking method of the second embodiment, the peak values ​​of the first AC signal y1 and the second AC signal y2 can be easily determined.

[0119] In this embodiment, based on the values ​​of the first AC signal y1 and the second AC signal y2, which are obtained substantially at the timing of the peak values ​​of the waveforms, a signal deviation total value, defined as the square root of the sum of squares, is calculated as described above. This signal deviation total value substantially represents the magnitude of the amplitude 'a' of the first AC signal y1 and the second AC signal y2. The signal deviation total value can also be defined as the sum of absolute values, as described above. In this case, the signal deviation total value also substantially represents the magnitude of the amplitude 'a' of the first AC signal y1 and the second AC signal y2.

[0120] If the calculated total deviation of the signal exceeds a specified range, the arithmetic processing unit 35 changes the amplitude of the excitation wave output (the amplitude A mentioned above) to, for example, half. As a result, the amplitude a of the waveform (a·cosθ·sinωt) output by the first differential amplifier 31 becomes half, and the amplitude a of the waveform (a·sinθ·sinωt) output by the second differential amplifier 32 becomes half.

[0121] If the calculated total deviation of the signal is less than a specified range, the arithmetic processing unit 35 changes the amplitude of the excitation wave output (the amplitude A mentioned above) to, for example, twice. As a result, the amplitude a of the waveform (a·cosθ·sinωt) output by the first differential amplifier 31 becomes twice, and the amplitude a of the waveform (a·sinθ·sinωt) output by the second differential amplifier 32 becomes twice.

[0122] By making the above adjustments, a signal with an appropriate amplitude is input to the AD converter, thus enabling high-precision detection of displacement θ.

[0123] The following is for reference Figure 8 The flowchart illustrates specific processing examples.

[0124] when Figure 8 When the automatic amplitude adjustment process shown begins, firstly, the detection signal processing device 3 initializes the value of the amplitude A of the excitation signal to the maximum value (step S101).

[0125] Next, the detection signal processing device 3 calculates the phase offset, for example, by a successive phase shift method (step S102).

[0126] Next, the detection signal processing device 3 estimates the phase offset d based on the phase offset calculated in step S102. e The values ​​of the first AC signal y1 and the second AC signal y2 are acquired at regular intervals. The detection signal processing device 3 calculates the total deviation of the above signals based on the two values ​​and investigates whether the total deviation of the signals is below a predetermined threshold (step S103).

[0127] In step S103, if the total deviation of the above signals is below the specified threshold, the adjustment process ends, and the amplitude A of the currently set excitation signal is used in subsequent processes.

[0128] In step S103, if the total deviation of the above signals exceeds a predetermined threshold, the detection signal processing device 3 changes the amplitude A of the excitation signal to, for example, half of the current set value (step S104). After that, the processing returns to step S102.

[0129] Through the above processing, the amplitude A of the excitation signal can be adjusted so that the amplitude a of the first AC signal y1 and the second AC signal y2 is greater than 1 / 2 of the threshold and below the threshold.

[0130] Instead of changing the amplitude A of the excitation signal, or based on that, the amplification gain of the first differential amplifier 31 and the second differential amplifier 32 can also be changed. According to this method, the amplitude a of the waveform (a·cosθ·sinωt) input from the first differential amplifier 31 to the AD converter and the amplitude a of the waveform (a·sinθ·sinωt) input from the second differential amplifier 32 to the AD converter can also be changed.

[0131] The order in which the process of determining the value that essentially represents the phase shift is determined can also be reversed compared to the order in which the amplitude is adjusted. See below for reference. Figure 9 The flowchart illustrates an example of the process of first adjusting the amplitude.

[0132] when Figure 9 When the automatic amplitude adjustment process shown begins, firstly, the signal processing device 3 detects the phase shift estimation d, which represents the phase shift. e And set an appropriate value (step S201). The value set in step S201 is arbitrary, for example, it can be set to a random value. The phase offset is estimated by d. e The setting is temporary and will later be changed to the actual estimated value.

[0133] Next, the detection signal processing device 3 initializes the amplitude A of the excitation signal to the maximum value (step S202).

[0134] Subsequently, the detection signal processing device 3 estimates the phase shift d based on the phase shift value temporarily set in step S201. e The values ​​of the first AC signal y1 and the second AC signal y2 are obtained at a certain time. The detection signal processing device 3 calculates the total signal deviation value (in other words, the amplitude a of the first AC signal y1 and the second AC signal y2) based on the two values, and investigates whether the total signal deviation value is below a predetermined threshold (step S203).

[0135] In the determination of step S203, if the above signal deviates from the total value below the specified threshold, the process proceeds to step S205 as described later.

[0136] In step S203, if the total deviation of the above signals exceeds a predetermined threshold, the detection signal processing device 3 changes the amplitude A of the excitation signal to, for example, half of the current set value (step S204). After that, the processing returns to step S203.

[0137] Through the processing of steps S202 to S204, the phase offset d is estimated based on the phase offset set in step S201. e The values ​​of the first AC signal y1 and the second AC signal y2 obtained at the time are used as a reference to change the amplitude A of the excitation signal so that the values ​​of the first AC signal y1 and the second AC signal y2 are within a specified range.

[0138] Next, the detection signal processing device 3 generates an excitation signal based on the amplitude A determined by the processing in steps S202 to S204, for example, by calculating the phase shift estimation d using a successive phase shift method. e (Step S205).

[0139] Next, the detection signal processing device 3 estimates the phase offset d based on the phase offset calculated in step S205. e The values ​​of the first AC signal y1 and the second AC signal y2 are acquired at regular intervals. The detection signal processing device 3 calculates the total signal deviation value based on the two signal values ​​and investigates whether the total signal deviation value is within a specified range (step S206). The specified range is equivalent to the range that is greater than 1 / 2 of the threshold value in step S203 and is below the threshold value.

[0140] In step S206, if the total deviation of the above signals is within the specified range, the adjustment process ends, and subsequent processing uses the currently set amplitude A of the excitation signal and the estimated phase offset d. e .

[0141] In the determination of step S206, if the above signal deviates from the total value and falls outside the specified range, the phase offset estimation d temporarily set in step S201 can be considered invalid. e Inappropriate. Therefore, the process returns to step S202 to readjust the amplitude A of the excitation signal. During the readjustment of amplitude A, in step S203, the phase shift estimate d obtained in step S205 is used. e (In other words, to estimate the d value for the most recently obtained phase shift) e The values ​​of the first AC signal y1 and the second AC signal y2 are obtained at a specific time. As a result, through the processing in steps S202 to S204, a more appropriate value for the amplitude A can be obtained.

[0142] If steps S202 to S206 are repeated, the amplitude A and phase shift d of the excitation signal that satisfy the condition in step S206 can eventually be obtained. e The combination of . At that moment, Figure 9 The series of processes shown has ended.

[0143] As explained above, the displacement detection device 100 of this embodiment includes an amplitude adjustment unit that adjusts the amplitude of the first AC signal y1 output by the first differential amplifier 31 and the amplitude a of the second AC signal y2 output by the second differential amplifier 32.

[0144] Therefore, for example, the amplitudes 'a' of the first AC signal y1 and the second AC signal y2 can be automatically changed in response to changes in the transformer ratio of the magnetic detection head 2. As a result, a waveform suitable for displacement detection can be stably obtained.

[0145] The amplitude a can be adjusted by adjusting the amplitude A of the alternating current flowing in the primary coil 21 through the "excitation wave output" block of the detection signal processing device 3. In this configuration, the part that realizes the "excitation wave output" is equivalent to the amplitude adjustment unit.

[0146] In this case, the gain setting process for the first differential amplifier 31 and the second differential amplifier 32 can be omitted. Therefore, a simpler process can be achieved.

[0147] The amplitude 'a' can also be adjusted by adjusting the amplification gain of the first differential amplifier 31 and the second differential amplifier 32. In this configuration, the "gain change" block (not shown) included in the detection signal processing device 3 corresponds to the amplitude adjustment unit.

[0148] In this case, the amplitude 'a' of the waveform can be adjusted more directly.

[0149] The preferred embodiments of the present invention have been described above, but the above configuration can be modified, for example, as follows.

[0150] The scale 1 is not limited to the above configuration; any combination of different magnetic properties (magnetic strength, direction of the generated magnetic field, etc.) can be used to create a suitable configuration. For example, the magnetic response section 12 can be constructed by alternately arranging strongly magnetic and weakly magnetic / non-magnetic materials along the length of the scale 1. The repetition of magnetic property variations can also be achieved by arranging the N and S poles of a magnet.

[0151] As long as the change in displacement corresponding to the secondary coil 22 relative to the scale 1 (magnetic response unit 12) can be controlled, the primary coil 21 can be arranged on the side close to the scale 1, and the secondary coil 22 can be arranged on the side far away from the scale 1.

[0152] The magnetic detection element can also be made of conductive patterns on a printed circuit board, Hall elements, etc., instead of the secondary coil 22.

[0153] Phase offset estimation d in the arithmetic processing unit 35 eThe decision can be made not only at the start of use of the displacement detection device 100, but also at other appropriate times that do not affect the use of the displacement detection device 100.

[0154] In the first embodiment, the interval at which the phase shift D of the same excitation signal is different is not limited to 10°, and can be set to 20°, 45°, etc. for example.

[0155] In the first embodiment, as the phase shift D of the constant excitation signal increases, the calculated total signal deviation tends to decrease after increasing. If it is determined that the possibility of updating the maximum value of the total signal deviation is small, the process can be stopped. Similarly, in the second embodiment, if the total signal deviation calculated by repeated sampling tends to decrease after increasing, the process can also be stopped.

[0156] Figure 1 The linear correction and high-speed prediction operations shown can be omitted as appropriate, depending on the conditions used.

[0157] In the fourth embodiment, the amplitude A of the excitation signal is changed by multiplying by 1 / 2, but it can also be multiplied by any other number less than 1. Alternatively, the amplitude can be changed arithmetically instead of proportionally. Figure 8 as well as Figure 9 As shown, the amplitude can be changed multiple times, or it can be changed only once. Similarly, the amplification gain of differential amplifiers 31 and 32 can also be changed by various methods.

[0158] exist Figure 8 as well as Figure 9 In the example, a maximum value is set as the initial value of the excitation signal amplitude A, and then changed to decrease it as needed. Alternatively, a minimum value can be set as the initial value of the excitation signal amplitude A, and then changed to increase it as needed. In this case, the amplitude of the excitation signal can be changed, for example, by multiplying by any number greater than 1 (e.g., 2). Similarly, the amplification gain of the differential amplifiers 31 and 32 can also be changed by various methods.

[0159] Explanation of symbols

[0160] 1: Scale; 2: Magnetic detection head (sensor head); 3: Detection signal processing device (signal processing and computing device); 11: Non-magnetic response unit; 12: Magnetic response unit; 22: Secondary coil (magnetic detection element); 31: First differential amplifier; 32: Second differential amplifier; 100: Displacement detection device.

Claims

1. A displacement detection device for detecting the displacement of an object in the displacement detection direction, characterized in that, have: The scale has magnetic and non-magnetic response parts arranged alternately at a specified detection interval in the displacement detection direction; The sensor head has an excitation element to which an excitation signal is applied, and at least four magnetic detection elements whose output signals are sine functions, cosine functions, negative sine functions, and negative cosine functions, respectively. as well as The signal processing unit receives the output signal from the magnetic detection element, processes it, and outputs the relative displacement information of the scale relative to the sensor head. The aforementioned signal processing and computing device includes: The first differential amplifier outputs the first AC signal obtained by combining the above cosine function and negative cosine function; The second differential amplifier outputs a second AC signal obtained by combining the above sine function and the above negative sine function; The processing unit, at least when the displacement detection device is first used, determines a value that substantially represents the phase offset between the excitation signal and the first and second AC signals. When detecting the displacement of the object being measured, it acquires the values ​​of the first and second AC signals at a timing based on the determined values, performs an arctan operation using the acquired values ​​of the first and second AC signals, and outputs the relative displacement information. At least at the start of use of the displacement detection device, multiple constant excitation signals are generated by applying different phase shifts to the excitation element. As each of the aforementioned constant excitation signals is applied to the excitation element, the arithmetic processing unit acquires the values ​​of the first AC signal and the second AC signal at a timing when the excitation signal becomes constant relative to the original excitation signal, and acquires the sum of the degree to which the values ​​of the first AC signal and the second AC signal deviate from zero. The aforementioned processing unit calculates the phase shift of the aforementioned co-current excitation signal with the largest total value among the multiple co-current excitation signals, and calculates a value that substantially represents the aforementioned phase offset based on the phase shift.

2. A displacement detection device for detecting the displacement of an object in the displacement detection direction, characterized in that, have: The scale has magnetic and non-magnetic response parts arranged alternately at a specified detection interval in the displacement detection direction; The sensor head has an excitation element to which an excitation signal is applied, and at least four magnetic detection elements whose output signals are sine functions, cosine functions, negative sine functions, and negative cosine functions, respectively. as well as The signal processing unit receives the output signal from the magnetic detection element, processes it, and outputs the relative displacement information of the scale relative to the sensor head. The aforementioned signal processing and computing device includes: The first differential amplifier outputs the first AC signal obtained by combining the above cosine function and negative cosine function; The second differential amplifier outputs a second AC signal obtained by combining the above sine function and the above negative sine function; The processing unit, at least when the displacement detection device is first used, determines a value that substantially represents the phase offset between the excitation signal and the first and second AC signals. When detecting the displacement of the object being measured, it acquires the values ​​of the first and second AC signals at a timing based on the determined values, performs an arctan operation using the acquired values ​​of the first and second AC signals, and outputs the relative displacement information. At least at the start of use of the displacement detection device, the aforementioned processing unit repeatedly acquires the values ​​of the first AC signal and the second AC signal at a sampling period shorter than the signal period, and acquires the sum of the degree to which the values ​​of the first AC signal and the second AC signal deviate from zero at multiple sampling times. The aforementioned processing unit calculates the sampling time with the largest total value among the multiple sampling times that have obtained the aforementioned total value, and calculates the value that substantially represents the aforementioned phase offset based on the sampling time.

3. The displacement detection device according to claim 1 or 2, characterized in that, It includes an amplitude adjustment unit that adjusts the amplitude of the first AC signal output by the first differential amplifier and the amplitude of the second AC signal output by the second differential amplifier.

4. The displacement detection device according to claim 3, characterized in that, The amplitude adjustment unit adjusts the amplitude of the alternating current flowing in the excitation element.

5. The displacement detection device according to claim 3, characterized in that, The amplitude adjustment unit adjusts the amplification gain of the first differential amplifier and the second differential amplifier.

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