Displacement detection device

Abstract

To provide a displacement detector which, although a phase shift exists in a signal used for detecting displacement, is capable of obtaining the amplitude of the signal in short time.SOLUTION: A displacement detector 100 includes a scale 1, a sensor head 2, and a processing unit 3. In the scale 1, magnetic response parts 12 and non-magnetic response parts 11 are alternately arrayed. The sensor head 2 includes a secondary coil 22 outputting an output signal. The processing unit 3 calculates and outputs at least either relative displacement of the scale 1 relative to the sensor head 2, or a change speed of the relative displacement. The processing unit 3 obtains a first signal value at a first time, for a processing object signal, and a second signal value at a second time subjected to 1 / 4 cycle shifting relative to the first time, and calculates a square-root value of the sum of squares of the first signal value and the second signal value, as the amplitude of the processing object signal.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention mainly relates to a displacement detection device for detecting displacement information of a measurement object.

Background Art

[0002] The position detection device of Patent Document 1 includes a multi-pole magnet and two Hall elements (magnetic sensors). When the multi-pole magnet moves relative to the two Hall elements, the two Hall elements each output a signal based on the change in magnetic flux. The position detection device outputs a position signal based on the signals output by the two Hall elements. Further, in order to make the amplitudes of the two signals constant, the position detection device divides the two signals by the square root of the sum of the squares of the two signals.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a displacement detection device using electromagnetic induction phenomenon, in order to detect displacement, the amplitude of a signal may be required. Further, when the signal includes a phase shift, it is necessary to calculate the amplitude after specifying and correcting the amount of phase shift. However, it sometimes takes time to specify the amount of phase shift, and improvement has been demanded.

[0005] The present invention has been made in view of the above circumstances, and its main object is to provide a displacement detection device capable of obtaining the amplitude of a signal in a short time even when there is a phase shift in the signal used for detecting displacement. Means and Effects for Solving the Problems

[0006] The problems that this invention aims to solve are as described above, and next, the means for solving these problems and their effects will be explained.

[0007] In view of the present invention, a displacement detection device having the following configuration is provided. That is, the displacement detection device comprises a scale, a sensor head, and a processing device. The scale has magnetic response parts and non-magnetic response parts arranged alternately at a predetermined detection pitch in the displacement detection direction. The sensor head has at least four magnetic detection elements that output output signals expressed as a sine function, a cosine function, a negative sine function, and a negative cosine function, respectively. The processing device receives the output signals of the magnetic detection elements as input, and the processing device calculates and outputs displacement information which is at least one of the relative displacement of the scale with respect to the sensor head and the rate of change of the relative displacement. The processing device generates a first differential signal based on the difference between the cosine function and the negative cosine function, and a second differential signal based on the difference between the sine function and the negative sine function. The processing device calculates the amplitude by performing an amplitude calculation process on at least one of the output signals of the cosine function and the output signals of the negative cosine function, or on the first differential signal. The processing device calculates the amplitude by performing the amplitude calculation process on at least one of the output signal of the sine function and the output signal of the negative sine function, or on the second differential signal. After the amplitude calculation process, the processing device outputs the displacement information of the scale based on the first differential signal and the second differential signal. The amplitude calculation process performed by the processing device determines the first signal value at a first time and the second signal value at a second time, which is shifted by 1 / 4 period from the first time, for the signal to be processed, and takes the square root of the sum of the squares of the first signal value and the second signal value as the amplitude of the signal to be processed.

[0008] The square root of the sum of the squares of the signal values ​​of two signals with a phase difference of 1 / 4 period is equal to the amplitude. Therefore, even if a phase shift exists, the amplitude can be calculated in a short time without specifying the amount of phase shift.

[0009] In the displacement detection device described above, the following configuration is preferable. That is, the processing device calculates the amplitude by performing an amplitude calculation process on the first differential signal. The processing device calculates the amplitude by performing an amplitude calculation process on the second differential signal. The processing device outputs the displacement information of the scale based on the amplitude of the first differential signal and the amplitude of the second differential signal.

[0010] This allows for the rapid calculation of the amplitude of the output signal before generating the differential signal.

[0011] In the displacement detection device described above, the following configuration is preferable. That is, the processing device calculates a first amplitude by performing amplitude calculation processing on at least one of the output signal of the cosine function and the output signal of the negative cosine function. The processing device calculates a second amplitude by performing the amplitude calculation processing on at least one of the output signal of the sine function and the output signal of the negative sine function. The processing device calculates the amplitude of the first differential signal at the first time based on the first amplitude and the first differential signal. The processing device calculates the amplitude of the second differential signal at the first time based on the second amplitude and the second differential signal.

[0012] This allows for the rapid calculation of amplitude after generating a differential signal.

[0013] In the displacement detection device described above, it is preferable that the processing device calculates the displacement information of the scale by arctan calculation.

[0014] This allows displacement information to be obtained through simple calculations. [Brief explanation of the drawing]

[0015] [Figure 1] A block diagram showing the configuration of a displacement detection device according to one embodiment of the present invention. [Figure 2] This diagram illustrates the amplitude calculation process at time t when there is no phase shift in the signal being processed. [Figure 3] A diagram for explaining the amplitude calculation process at time t when there is a phase shift in the signal to be processed. [Figure 4] A block diagram showing the configuration of the displacement detection device according to the modification.

Embodiments for Carrying Out the Invention

[0016] Next, embodiments of the present invention will be described with reference to the drawings.

[0017] The displacement detection device 100 shown in FIG. 1 detects the displacement of a measurement object in a predetermined direction. In the following description, the direction in which the displacement (displacement information) of the measurement object is detected is referred to as the displacement detection direction.

[0018] Displacement is the amount of change in the current position with respect to the reference position. The reference position is, for example, the initial position. By defining the position information of the reference position, the position of the measurement object can be calculated based on the reference position and the displacement. Therefore, the displacement detection device 100 can be used as a position detection device.

[0019] The displacement detection device 100 mainly includes a scale 1, a sensor head 2, and a processing device 3. ]>[[ID=][

[0020] Either the scale 1 or the sensor head 2 is attached to the measurement object. For example, the scale 1 is attached to a movable member (not shown), and the sensor head 2 is attached to a fixed member (not shown) that is the measurement object. The movable member can move linearly along a path parallel to the displacement detection direction.

[0021] Alternatively, the scale 1 may be attached to the fixed member that is the measurement object, and the sensor head 2 may be attached to the movable member. Furthermore, both the scale 1 and the sensor head 2 may be attached to movable members that are relatively displaced from each other. In this case, the displacement detection device 100 detects the relative displacement of the measurement object (i.e., the scale 1 and the sensor head 2).

[0022] Scale 1 is used as a scale for detecting the displacement of the object to be measured in the longitudinal direction of the scale 1. The scale 1 is formed elongated in a direction parallel to the movement stroke so as to include the movement stroke of the sensor head 2 accompanying the movement of the movable member. The scale 1 may be formed in an elongated block shape or an elongated rod shape.

[0023] 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 having no remarkable magnetism or a material such as a plastic having no magnetism. The magnetic response portion 12 is made of, for example, a metal having ferromagnetism. The non-magnetic response portion 11 and the magnetic response portion 12 are alternately arranged in the longitudinal direction of the scale 1. The intervals between adjacent non-magnetic response portions 11 and the intervals between adjacent magnetic response portions 12 are a predetermined detection pitch C0. Therefore, in the longitudinal direction, the presence or absence or the strength of magnetic responsiveness alternately appears repeatedly every detection pitch C0 on the scale 1.

[0024] As shown in FIG. 1, the sensor head 2 is arranged at a predetermined interval from the magnetic response portion 12. For example, the scale 1 is in an elongated rod shape, the sensor head 2 is in a cylindrical shape, and the scale 1 is inserted into the sensor head 2. However, the shape of the sensor head 2 is not limited to this example. The sensor head 2 includes a primary coil 21 and a plurality of secondary coils (magnetic detection elements) 22. In this embodiment, four secondary coils 22 are provided. Note that the primary coil 21 can be omitted.

[0025] The primary coil 21 is used to generate an alternating magnetic field. When an alternating current flows through the primary coil 21, a magnetic field whose direction and strength change periodically is generated around it. The periodic excitation signal (A·sinωt) obtained by DA-converting the excitation wave generated by the processing device 3 is applied to the primary coil 21. The period of the excitation signal is referred to as the excitation period. As shown in FIG. 1, the primary coil 21 is arranged in the sensor head 2 at a portion farther from the scale 1 than the secondary coil 22.

[0026] The four secondary coils 22 are arranged in a direction parallel to the longitudinal direction of scale 1, as shown in Figure 1. The secondary coils 22 are located in the sensor head 2 on the side closer to scale 1 than the primary coil 21. Induced currents generated by the magnetic field strengthened by the magnetic response unit 12 flow through the four secondary coils 22. The sensor head 2 detects and outputs an electrical signal (e.g., a voltage signal) based on these induced currents.

[0027] As shown in Figure 1, the four secondary coils 22 are arranged in a row at predetermined unit pitches C1 in the displacement detection direction. The unit pitch C1 has the following relationship with the detection pitch C0. Specifically, as shown in the following equation, the unit pitch C1 is set to be the sum of an integer multiple of the detection pitch C0 and 1 / 4 of the detection pitch C0. C1 = (n + 1 / 4) * C0 However, n is an integer. In this embodiment, n=0, but is not limited to this.

[0028] In the following explanation, to identify each of the four secondary coils, they may be referred to as the first coil 22a, the second coil 22b, the third coil 22c, and the fourth coil 22d, in order from left to right as shown in Figure 1.

[0029] Here, we will briefly explain the signals (for example, voltage signals) output by each secondary coil 22. When an alternating current is passed through the primary coil 21, a magnetic field is generated in the primary coil 21 whose direction and strength change periodically. On the other hand, an induced current is generated in the secondary coil 22 in a direction that opposes the change in the coil's magnetic field. If a ferromagnetic material is present near the primary coil 21, this ferromagnetic material acts to strengthen the magnetic field generated by the primary coil 21. This effect becomes stronger as the ferromagnetic material approaches the primary coil 21.

[0030] Focusing on the magnetic response unit 12, as the sensor head 2 moves relative to the scale 1 from one side to the other in the longitudinal direction, the distance from the primary coil 21 to the magnetic response unit 12, and the distance from the secondary coil 22 to the magnetic response unit 12, change. Specifically, these distances gradually decrease as the sensor head 2 moves, and after exceeding a minimum value, they gradually increase. The induced current generated in the secondary coil 22 is an alternating current, but the magnitude of its amplitude differs depending on the positional relationship between the secondary coil 22 and the magnetic response unit 12.

[0031] Since the magnetic response units 12 are actually arranged in a line at each detection pitch C0, the change in amplitude is repeated at each detection pitch C0. That is, if the horizontal axis is the position of the sensor head 2 and the vertical axis is the amplitude, the relationship between amplitude and position becomes a periodic curve (specifically, a sine curve y=sinθ) with the detection pitch C0 as its period. If this θ can be determined, it is possible to obtain the position of scale 1 relative to the sensor head 2 within the detection pitch C0, which is the unit of repetition.

[0032] However, when considering one period of the sine curve y=sinθ, except in special cases, there are two possible values ​​for θ corresponding to y, and it is not uniquely determined. Therefore, in this embodiment, four secondary coils 22 are arranged at intervals determined by the unit pitch C1 described above, such that the positional relationship with the nearest magnetic response unit 12 is substantially shifted by 1 / 4 of the detection pitch C0 each time.

[0033] As shown in Figure 1, the first coil 22a, second coil 22b, third coil 22c, and fourth coil 22d are each separated from each other by 1 / 4 of the detection pitch C0, so they output voltage signals (output signals) that are 90° out of phase with each other. That is, if the voltage signal output by the first coil 22a is expressed as cos+ phase, the second coil 22b outputs a sin+ phase voltage signal, the third coil 22c outputs a cos- phase voltage signal, and the fourth coil 22d outputs a sin- phase voltage signal. These signals correspond to the output signals of the cosine function, the sine function, the negative cosine function, and the negative sine function, respectively.

[0034] The processing unit 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 the relative displacement of the scale 1 with respect to the sensor head 2, and outputs it. As shown in Figure 1, the processing unit 3 comprises an analog circuit unit 31 and an FPGA 32. FPGA is an abbreviation for Field Programmable Gate Array.

[0035] The analog circuit section 31 consists of analog circuits and electronic components. The electronic components that perform the aforementioned DA conversion are mounted in the analog circuit section 31. The analog circuit section 31 is equipped with two differential amplifiers and two AD converters. Hereinafter, these will be referred to as the first differential amplifier, the second differential amplifier, the first AD converter, and the second AD converter in order to distinguish them.

[0036] The first differential amplifier is used to amplify the difference between the outputs of the first coil 22a and the third coil 22c. The first differential amplifier amplifies the difference between the voltage signals output from the first coil 22a and the third coil 22c and outputs it as the first differential signal y1.

[0037] When θ is the phase representing the displacement of scale 1 relative to sensor head 2, the first differential signal y1 can be expressed by the following equation. y1 = acosθ·sinωt

[0038] The first differential signal y1 is processed by a filter (not shown in the diagram), then converted from an analog signal to a digital signal by a first AD converter, and input to FPGA32.

[0039] The second differential amplifier is used to amplify the difference between the outputs of the second coil 22b and the fourth coil 22d. The second differential amplifier amplifies the difference between the voltage signals output from the second coil 22b and the fourth coil 22d and outputs it as the second differential signal y2.

[0040] When θ is the phase representing the displacement of scale 1 relative to sensor head 2, the second differential signal y2 can be expressed by the following equation. y² = asinθ·sinωt

[0041] The second differential signal y2 is processed by a filter (not shown in the diagram) in the same way as the first differential signal y1, then converted from an analog signal to a digital signal by a second AD converter and input to FPGA32.

[0042] Figure 1 shows functional blocks such as amplitude calculation, arctan operation, and filtering within the FPGA32 block. These functional blocks represent the functions that are realized when the FPGA executes a program and performs signal processing.

[0043] FPGA32 performs amplitude calculation processing on the first differential signal y1 input from the first AD converter to calculate the amplitude of the first differential signal y1. Similarly, FPGA32 performs amplitude calculation processing on the second differential signal y2 input from the second AD converter to calculate the amplitude of the second differential signal y2. Details of the amplitude calculation processing will be described later.

[0044] Next, FPGA32 performs an arctan operation on the first differential signal y1 and the second differential signal y2, whose amplitudes have been calculated through amplitude calculation processing. Specifically, FPGA32 divides the second differential signal y2 of the digital signals by the first differential signal y1. This result corresponds to the value of tanθ. Subsequently, FPGA32 calculates the value of the arctan of the calculated result. This allows us to obtain the phase θ, which represents the displacement of scale 1 with respect to sensor head 2, as relative displacement information of scale 1. Strictly speaking, θ is the phase, but in practice it represents the relative displacement of scale 1 with respect to sensor head 2. Therefore, θ may be referred to as displacement below.

[0045] The displacement θ obtained by FPGA32 is input to a filter to remove high-frequency components. This removes noise and other unwanted signals. After filtering, the value undergoes post-processing such as linearity calibration and is output as position information from processing unit 3.

[0046] Next, we will briefly explain the phase shift that occurs between the primary coil 21 and the secondary coil 22. As shown in Figure 3, a phase shift amount d occurs between the excitation signal applied to the primary coil 21 and the output of the secondary coil 22 (first differential signal y1 and second differential signal y2). Specifically, the phases of the first differential signal y1 and the second differential signal y2 lag behind the excitation signal by a phase shift amount d. This phase shift amount d is caused by differences in coil design, resistance factors in the wiring section (type of wiring, length, routing), etc. The magnitude of the phase shift amount d varies depending on the surrounding environment such as temperature.

[0047] As described above, tanθ is calculated by dividing the second differential signal y2 by the first differential signal y1. In this case, if the two signal values ​​are near zero, the accuracy of tanθ decreases. Considering this, it is preferable to obtain the peak signal value of the first differential signal y1 and the peak signal value of the second differential signal y2, and perform the arctan operation using these values. In other words, the peak signal value corresponds to the amplitude of the signal waveform.

[0048] When the excitation signal is represented as A·sinωt, the first differential signal y1 and the second differential signal y2 are expressed by the following equations. y1 = a·cosθ·sin(ωt+d) y² = a·sinθ·sin(ωt+d) In this equation, d represents the phase shift amount mentioned above.

[0049] If the phase shift amount d can be determined by some method, the peak signal values ​​of the first differential signal y1 and the second differential signal y2 can be obtained by acquiring the signal value at the timing when the phase of ωt+d is 90° or 270°. However, in order to determine the phase shift amount d, it is necessary to acquire and analyze the signal values ​​of the first differential signal y1 and the second differential signal y2 multiple times. Therefore, it takes a certain amount of time until the calculation of the phase shift amount d is completed. As a result, the displacement detection device 100 cannot output displacement information until the calculation of the phase shift amount d is completed.

[0050] In contrast, the FPGA32 of this embodiment obtains the peak signal values ​​(amplitudes) of the first differential signal y1 and the second differential signal y2 without determining the phase shift amount d by performing amplitude calculation processing. The amplitude calculation processing will be described below.

[0051] First, we will explain the situation where there is no phase shift. Figure 2 shows the waveforms of the excitation signal and the signal to be processed in the situation where there is no phase shift. The signal to be processed is the signal to which amplitude calculation processing is performed. In this embodiment, the first differential signal y1 and the second differential signal y2 correspond to the signals to be processed. The signal to be processed is represented as B·sinωt. B is the amplitude, and when the signal to be processed is the first differential signal y1, B=a·cosθ, and when the signal to be processed is the second differential signal y2, B=a·sinθ. The signal value of the signal to be processed at time t is represented as D(t) as a function of time t.

[0052] The amplitude calculation process calculates the amplitude (peak signal value) at time t using equation (1) shown in Figure 2. That is, the amplitude at time t is calculated as the square root of the sum of the squares of the signal value at time t-1 and the signal value at time t. Note that time t-1 corresponds to the first time, D(t-1) to the first signal value, time t to the second time, and D(t) to the second signal value. Time t-1 is the time shifted 1 / 4 period in the past direction relative to time t. If there is no phase shift, the phase at time t corresponds to 90°, so the value of the square root of the sum of squares is B, as shown in the equation in Figure 2. Also, when calculating the amplitude every 1 / 4 period, one of the two signal values ​​is the peak and the other is 0, so the calculation is the same.

[0053] Furthermore, since equation (1) includes the square root of the sum of squares, the amplitude at time t calculated by equation (1) is strictly an absolute value. Therefore, it may be necessary to determine the sign. In this embodiment, since the amplitude is calculated every 1 / 4 period, four values ​​are treated as one set, and the sign of the first signal value in each set is applied. For example, from time t to time t+4, the sign of D(t) at time t is applied, and from time t+4 to time t+7, the sign of D(t4) at time t4 is applied. When applying a sign to the amplitude in this way, it is preferable that the phase shift amount is known to be 180° or less in advance in order to apply an appropriate sign. Note that the method of applying the sign is just one example and may differ from that of this embodiment.

[0054] Furthermore, in this embodiment, signal values ​​acquired prior to time t, which serves as the reference time for calculating the amplitude, are used. Alternatively, signal values ​​acquired 1 / 4 of a period in the future from time t, which serves as the reference time for calculating the amplitude, may be used. In this case, the amplitude at time t will be calculated after time t+1 has arrived.

[0055] Furthermore, in this embodiment, the amplitude is calculated every 1 / 4 period, but the frequency of amplitude calculation is not limited to this. For example, the amplitude may be calculated every 1 / 2 period.

[0056] Next, we will explain the situation in which a phase shift exists. Figure 3 shows the waveform of the excitation signal and the waveform of the signal to be processed in which a phase shift amount d has occurred. As shown in Figure 3, because a phase shift has occurred, the signal value D(t) obtained at 1 / 4 of a period is off-peak. However, by using equation (1) described above, the amplitude of the signal to be processed can be calculated. That is, by substituting the waveform equation into equation (1) in Figure 3, equation (2) is obtained. Furthermore, by using the fact that the function obtained by shifting a sine function by 1 / 4 period is a cosine function, equation (3) can be derived from equation (2). In addition, by using the fact that the sum of the squares of the sine function and the cosine function in phase is 1, the amplitude of the signal to be processed can be calculated from equation (3).

[0057] In other words, by using the amplitude calculation process of this embodiment, it is possible to calculate the amplitude (peak signal value) at each time point without calculating the phase shift amount d, even when a phase shift exists. Therefore, displacement information can be output in a shorter time compared to when the phase shift amount d is calculated.

[0058] Next, a modified example of the above embodiment will be described with reference to Figure 4. In this description of the modified example, the same or similar components as those in the previously described embodiment will be denoted by the same reference numerals in the drawings, and their descriptions may be omitted.

[0059] The above embodiment and this modified example differ in that the signals to be processed for amplitude calculation are different. In the above embodiment, the signals to be processed are the first differential signal y1 and the second differential signal y2. In contrast, the signals to be processed in this modified example are the output signals of the first coil 22a, the second coil 22b, the third coil 22c, and the fourth coil 22d. In other words, in the above embodiment, the amplitude is calculated after the first differential signal y1 and the second differential signal y2 are generated, whereas in this modified example, the amplitude is calculated before the first differential signal y1 and the second differential signal y2 are generated.

[0060] In detail, as shown in Figure 4, the output signals of the first coil 22a, the second coil 22b, the third coil 22c, and the fourth coil 22d are each individually converted using AD conversion and input to the FPGA 32. Next, the FPGA 32 performs amplitude calculation processing on all the output signals of the first coil 22a, the second coil 22b, the third coil 22c, and the fourth coil 22d. Then, similar to the embodiment described above, the FPGA 32 generates a first differential signal y1 and a second differential signal y2.

[0061] The first differential signal y1 is generated by performing a known operation based on the output signals of the cosine function and the output signals of the negative cosine function. Therefore, FPGA32 can calculate the amplitude of the first differential signal y1 based on the amplitude of the output signal of the cosine function (first amplitude) and the amplitude of the output signal of the negative cosine function (first amplitude). FPGA32 performs a similar process on the output signals of the sine function and the output signals of the negative sine function to calculate the second amplitude and then calculates the amplitude of the second differential signal y2. Subsequent processing is the same as in the above embodiment.

[0062] In this modified example, FPGA32 performs amplitude calculation processing on all of the output signals of the cosine function, the negative cosine function, the sine function, and the negative sine function. Alternatively, FPGA32 may perform amplitude calculation processing on only one of the output signals of the cosine function or the negative cosine function. In this case, FPGA32 calculates the ratio of the signal value D(t) at time t to the amplitude B calculated in the amplitude calculation processing for the output signal of the cosine function. Next, FPGA32 calculates the amplitude of the first differential signal y1 by applying the previously calculated ratio to the signal value D(t) of the first differential signal y1 at time t. FPGA32 performs the same processing for the second differential signal y2 to calculate the amplitude of the second differential signal y2.

[0063] As described above, the displacement detection device 100 of the above embodiment comprises a scale 1, a sensor head 2, and a processing device 3. The scale 1 has magnetic response units 12 and non-magnetic response units 11 arranged alternately at a predetermined detection pitch C0 in the displacement detection direction. The sensor head 2 has at least four secondary coils 22 that output output signals expressed as a sine function, a cosine function, a negative sine function, and a negative cosine function, respectively. The processing device 3 receives the output signals from the secondary coils 22 as input, and the processing device 3 calculates and outputs displacement information which is at least one of the relative displacement of the scale 1 with respect to the sensor head 2 and the rate of change of the relative displacement. The processing device 3 generates a first differential signal y1 based on the difference between the cosine function and the negative cosine function, and a second differential signal y2 based on the difference between the sine function and the negative sine function. The processing device 3 calculates the amplitude by performing an amplitude calculation process on at least one of the output signals of the cosine function and the output signals of the negative cosine function, or on the first differential signal y1. The processing unit 3 calculates the amplitude by performing an amplitude calculation process on at least one of the output signals of the sine function and the negative sine function, or on the second differential signal y2. After the amplitude calculation process, the processing unit 3 outputs displacement information of scale 1 based on the first differential signal y1 and the second differential signal y2. The amplitude calculation process performed by the processing unit 3 determines the first signal value at the first time and the second signal value at the second time, which is shifted by 1 / 4 period from the first time, for the signal to be processed, and takes the square root of the sum of the squares of the first signal value and the second signal value as the amplitude of the signal to be processed.

[0064] The square root of the sum of the squares of the signal values ​​of two signals with a phase difference of 1 / 4 period is equal to the amplitude. Therefore, even if a phase shift exists, the amplitude can be calculated in a short time without specifying the amount of phase shift.

[0065] In the displacement detection device 100 of the above embodiment, the processing device 3 calculates the amplitude by performing amplitude calculation processing on the first differential signal y1. The processing device 3 calculates the amplitude by performing amplitude calculation processing on the second differential signal y2. Based on the amplitude of the first differential signal y1 and the amplitude of the second differential signal y2, displacement information of scale 1 is output.

[0066] This allows for the rapid calculation of amplitude after generating a differential signal.

[0067] In the displacement detection device 100 of the above modified example, the processing device 3 calculates a first amplitude by performing amplitude calculation processing on at least one of the output signal of the cosine function and the output signal of the negative cosine function. The processing device 3 calculates a second amplitude by performing amplitude calculation processing on at least one of the output signal of the sine function and the output signal of the negative sine function. The processing device 3 calculates the amplitude of the first differential signal y1 at the first time based on the first amplitude and the first differential signal y1. The processing device 3 calculates the amplitude of the second differential signal y2 at the first time based on the second amplitude and the second differential signal y2.

[0068] This allows for the rapid calculation of the amplitude of the output signal before generating the differential signal.

[0069] In the displacement detection device 100 of the above embodiment, the processing device 3 calculates displacement information of scale 1 by arctan calculation. This feature is not limited to the above embodiment and is also applied to the above modified example.

[0070] This allows displacement information to be obtained through simple calculations.

[0071] Preferred embodiments and modifications of the present invention have been described above, but the above configuration can be modified as follows, for example.

[0072] Scale 1 is not limited to the above configuration, and can be configured as appropriate as long as different magnetic properties (strength of magnetism, direction of generated magnetic field, etc.) are repeated. For example, the magnetic response section 12 may be configured by arranging ferromagnetic materials and weakly magnetic / non-magnetic materials alternately in the longitudinal direction of Scale 1. The repetition of changes in magnetic properties may also be achieved by arranging the north and south poles of a magnet.

[0073] The magnetic detection element may be composed of a conductive pattern on a printed circuit board, a Hall element, or the like, instead of the secondary coil 22.

[0074] If the secondary coil 22 can capture changes corresponding to the displacement from scale 1 (magnetic response section 12), the primary coil 21 may be positioned closer to scale 1 and the secondary coil 22 may be positioned further away from scale 1.

[0075] FPGA32 can also obtain θ in ways other than calculating tanθ. Specifically, the phase of the second differential signal y2 is shifted by 90° using a known shift circuit and added to the first differential signal y1. The resulting signal can be expressed as asin(ωt+θ) using the well-known trigonometric addition formula. FPGA32 obtains θ by measuring the phase difference (specifically, the difference in the timing at which each signal crosses zero) between this signal and the reference differential signal asinωt. FPGA32 can also obtain θ by PD (Phase-Digital) conversion.

[0076] The determination of the relative velocity of scale 1 in the filtering process does not have to be performed in real time. For example, the determination may be performed at a predetermined fixed time interval, or at a time interval that changes according to the relative velocity of scale 1.

[0077] The displacement detection device can also output the rate of change of relative displacement (displacement information) in addition to, or instead of, the relative displacement of scale 1. The rate of change of relative displacement essentially means the relative velocity of scale 1. The rate of change of relative displacement can be easily obtained by calculating the difference between the current relative displacement of scale 1 and the relative displacement from a predetermined time ago. [Explanation of Symbols]

[0078] 1 Scale 2 Sensor heads 3 Processing Unit 100 Displacement detection device

Claims

1. A scale in which magnetic response parts and non-magnetic response parts are alternately arranged at a predetermined detection pitch in the displacement detection direction, A sensor head having at least four magnetic detection elements that output output signals represented by a sine function, a cosine function, a negative sine function, and a negative cosine function, A processing device that receives the output signal of the magnetic detection element and calculates and outputs displacement information which is at least one of the relative displacement of the scale with respect to the sensor head and the rate of change of the relative displacement, Equipped with, The aforementioned processing apparatus is A first differential signal is generated based on the difference between the cosine function and the negative cosine function, and a second differential signal is generated based on the difference between the sine function and the negative sine function. The amplitude is calculated by performing an amplitude calculation process on at least one of the output signal of the cosine function and the output signal of the negative cosine function, or on the first differential signal. The amplitude is calculated by performing the amplitude calculation process on at least one of the output signal of the sine function and the output signal of the negative sine function, or on the second differential signal. After the amplitude calculation process, the displacement information of the scale is output based on the first differential signal and the second differential signal. Displacement detection device characterized in that the amplitude calculation process performed by the processing device determines a first signal value at a first time and a second signal value at a second time that is shifted by 1 / 4 period from the first time, and takes the square root of the sum of the squares of the first signal value and the second signal value as the amplitude of the signal to be processed.

2. A displacement detection device according to claim 1, The aforementioned processing apparatus is The amplitude is calculated by performing an amplitude calculation process on the first differential signal, The amplitude is calculated by performing an amplitude calculation process on the second differential signal. A displacement detection device characterized by outputting the displacement information of the scale based on the amplitude of the first differential signal and the amplitude of the second differential signal.

3. A displacement detection device according to claim 1, The aforementioned processing apparatus is An amplitude calculation process is performed on at least one of the output signal of the cosine function and the output signal of the negative cosine function to calculate a first amplitude. The amplitude calculation process is performed on at least one of the output signal of the sine function and the output signal of the negative sine function to calculate the second amplitude. Based on the first amplitude and the first differential signal, the amplitude of the first differential signal at the first time is calculated. A displacement detection device characterized by calculating the amplitude of the second differential signal at a first time based on the second amplitude and the second differential signal.

4. A displacement detection device according to claim 1, The processing device is a displacement detection device characterized by calculating the displacement information of the scale by arctan calculation.

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