Displacement detection device

Abstract

To provide a displacement detection device capable of suppressing an error caused by a difference in environmental characteristics of two A / D conversion parts.SOLUTION: A processor 3 of a displacement detection device 100 includes: an A / D conversion device 32; a switching circuit 31; and an arithmetic processing part 35. The A / D conversion device 32 includes a first A / D conversion part 33 and a second A / D conversion part 34. The switching circuit 31 periodically switches a first connection mode in which a first differential signal is A / D-converted by the first A / D conversion part 33 and a second differential signal is A / D-converted by the second A / D conversion part 34, and a second connection mode in which the first differential signal is A / D-converted by the second A / D conversion part 34 and the second differential signal is A / D-converted by the first A / D conversion part 33. The arithmetic processing part 35 outputs displacement information of a scale on the basis of an addition average value of the first differential signal outputted from each of the first A / D conversion part 33 and the second A / D conversion part 34 and an addition average value of the second differential signal outputted from each of the first A / D conversion part 33 and the second A / D conversion part 34.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] Conventionally, a displacement detection device that measures displacement information of a measurement object using the electromagnetic induction phenomenon has been known. Patent Documents 1 and 2 disclose this type of device.

[0003] The position detection device of Patent Document 1 is an induction sensor including an iron core and a winding portion. The position detection device is relatively movable with respect to a rail composed of a magnet. The position detection device detects the relative position with respect to the rail based on an output signal generated when moving with respect to the rail. Here, due to a change in the impedance of the winding portion, a phase fluctuation error may occur. In order to cope with the phase fluctuation error, the position detection device of Patent Document 1 includes a zero-cross detection circuit that detects the zero-cross of the output signal. The detection result of the zero-cross detection circuit is output to a latch circuit as a latch pulse. Since the data latched in the latch circuit corresponds to the phase shift of the output signal, the phase fluctuation error is calculated based on the average of those data.

[0004] The device of Patent Document 2 is an evaluation circuit for evaluating an induction sensor. This device includes an analog switch including two switch elements. The first switch element generates vibration by alternately connecting a resistor to ground and a reference voltage. The second switch element corresponds to an analog switch of a synchronous rectifier. Since the two switch elements are provided on the same chip, the phase positions of the vibrations generated by the two switch elements can be made the same.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] In a displacement detection device using the electromagnetic induction phenomenon, two AD conversion units for converting an electric signal based on an induced current from an analog signal to a digital signal may be provided. Since the AD conversion units have environmental characteristics, the characteristics change according to changes in the environment. As a result, an error may occur in the detected value of the displacement information due to the difference in the environmental characteristics of the two AD conversion units.

[0007] 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 suppressing an error caused by a difference in environmental characteristics between two AD conversion units. Means and effects for solving the problem

[0008] The problem to be solved by the present invention is as described above. Next, the means for solving this problem and its effects will be described.

[0009] According to an aspect of the present invention, a displacement detection device having the following configuration is provided. That is, the displacement detection device includes a scale, a sensor head, and a processing device. The scale has a magnetic response portion and a non-magnetic response portion alternately arranged at a predetermined detection pitch in the displacement detection direction. The sensor head has at least four magnetic detection elements that output respective output signals represented by a sine function, a cosine function, a minus sine function, and a minus cosine function. The processing device receives the output signals of the magnetic detection elements and calculates and outputs displacement information that is at least one of the relative displacement of the scale with respect to the sensor head and the change rate of the relative displacement. The processing device includes an AD conversion device, a switching circuit, and an arithmetic processing unit. The AD conversion device has a first AD conversion unit and a second AD conversion unit. The AD conversion device converts a first differential signal based on the difference between the cosine function and the minus cosine function and a second differential signal based on the difference between the sine function and the minus sine function into digital signals. The switching circuit periodically switches between a first connection mode in which the first differential signal is AD-converted by the first AD conversion unit and the second differential signal is AD-converted by the second AD conversion unit, and a second connection mode in which the first differential signal is AD-converted by the second AD conversion unit and the second differential signal is AD-converted by the first AD conversion unit. The arithmetic processing unit outputs the displacement information of the scale based on the additive average value of the first differential signal output from each of the first AD conversion unit and the second AD conversion unit and the additive average value of the second differential signal output from each of the first AD conversion unit and the second AD conversion unit.

[0010] Thereby, the influence of the environmental characteristics of the first AD conversion unit and the environmental characteristics of the second AD conversion unit on the respective differential signals can be equalized. Therefore, an error in the displacement information when the environment changes can be suppressed.

[0011] In the above displacement detection device, it is preferable that the arithmetic processing unit calculates the displacement information of the scale by arctan operation.

[0012] As a result, displacement information can be obtained by simple calculations.

[0013] In the displacement detection device described above, it is preferable that the arithmetic processing unit performs even-stage moving average processing on the displacement information obtained by arctangent arithmetic.

[0014] As a result, by making the moving average processing even-stage, the number of detection values in the first connection mode and the number of detection values in the second connection mode can be made the same, and an addition average value can be calculated. Therefore, the error of the displacement information can be further suppressed.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

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] The displacement is the amount of change in the current position relative to a reference position. The reference position is, for example, an 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.

[0020] Either the scale 1 or the sensor head 2 is attached to an object to be measured. 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 object to be measured. The movable member is capable of moving linearly along a path parallel to the displacement detection direction.

[0021] Alternatively, the scale 1 may be attached to a fixed member that is the object to be measured, and the sensor head 2 may be attached to a movable member. Furthermore, both the scale 1 and the sensor head 2 may be attached to movable members that are 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 sensor head 2).

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

[0023] 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 significant 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 in 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 slender and rod-shaped, the sensor head 2 is cylindrical, 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 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 coils 22.

[0026] As shown in Fig. 1, the four secondary coils 22 are arranged side by side in a direction parallel to the longitudinal direction of the scale 1. The secondary coils 22 are arranged in the sensor head 2 at a portion closer to the scale 1 than the primary coil 21. An induced current generated by the magnetic field strengthened by the magnetic response unit 12 flows through the four secondary coils 22. The sensor head 2 detects and outputs an electrical signal (e.g., a voltage signal) based on this induced current.

[0027] As shown in Fig. 1, the four secondary coils 22 are arranged side by side at every predetermined unit pitch C1 in the displacement detection direction. The unit pitch C1 has the following relationship with the aforementioned detection pitch C0. Specifically, as shown by the following formula, 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 it is not limited to this.

[0028] In the following description, in order 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 the left side shown in Fig. 1.

[0029] Here, the signals (e.g., voltage signals) output by each secondary coil 22 will be briefly described. When an alternating current flows through the primary coil 21, a magnetic field whose direction and strength change periodically is generated in the primary coil 21. On the other hand, an induced current in a direction that hinders the change of the magnetic field of the coil is generated in the secondary coil 22. When a ferromagnetic material exists near the primary coil 21, this ferromagnetic material acts to strengthen the magnetic field generated by the primary coil 21. This effect becomes greater as the ferromagnetic material approaches the primary coil 21.

[0030] Focusing on the magnetic response unit 12, as the sensor head 2 moves relatively from one side to the other side in the longitudinal direction of the scale 1, 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 the minimum value, they gradually increase. The induced current generated in the secondary coil 22 is an alternating current, and the magnitude of its amplitude varies according to the positional relationship between the secondary coil 22 and the magnetic response unit 12.

[0031] Since the magnetic response units 12 are actually arranged side by side for each detection pitch C0, the change in the magnitude of the amplitude is repeated for each detection pitch C0. That is, when the position of the sensor head 2 is taken on the horizontal axis and the magnitude of the amplitude is taken on the vertical axis, the relationship between the amplitude and the position is a periodic curve with the detection pitch C0 as the period (specifically, a sine curve y = sinθ). If this θ can be obtained, it is possible to acquire the position of the scale 1 relative to the sensor head 2 within the detection pitch C0, which is the repeating unit.

[0032] However, considering one period of the sine curve y = sinθ, except for special cases, two values of θ corresponding to y can be considered and it is not determined uniquely to just one. Therefore, in this embodiment, four secondary coils 22 are arranged at intervals defined by the above-mentioned unit pitch C1 so that the positional relationship with the nearest magnetic response unit 12 is substantially shifted by 1 / 4 of the detection pitch C0.

[0033] As shown in FIG. 1, since each of the first coil 22a, the second coil 22b, the third coil 22c, and the fourth coil 22d is separated from each other by 1 / 4 of the detection pitch C0, they output voltage signals with a phase shift of 90° from each other. That is, when the voltage signal output by the first coil 22a is expressed as the cos+ phase, the second coil 22b outputs a voltage signal of the sin+ phase, the third coil 22c outputs a voltage signal of the cos - phase, and the fourth coil 22d outputs a voltage signal of the sin - phase.

[0034] The 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 scale 1 with respect to the sensor head 2.

[0035] For example, as shown in FIG. 1, the processing device 3 includes a switching circuit 31, an AD conversion device 32, an arithmetic processing unit 35, and a filter processing unit 36. The AD conversion device 32 includes a first AD conversion unit 33 and a second AD conversion unit 34.

[0036] In the present embodiment, the switching circuit 31 and the AD conversion device 32 are composed of an analog circuit and electronic components mounted on the circuit. The arithmetic processing unit 35 and the filter processing unit 36 are realized by an FPGA or the like constituting the processing device 3 executing a program. FPGA is an abbreviation for Field Programmable Gate Array.

[0037] The switching circuit 31 is disposed between the secondary coil 22 and the AD conversion device 32. The switching circuit 31 has a plurality of switch elements and switches the output destination of the voltage signal output from the secondary coil 22. Specifically, the switching circuit 31 can switch between a first connection mode shown in FIG. 2 and a second connection mode shown in FIG. 3 in response to a command from the FPGA.

[0038] In the first connection mode shown in FIG. 2, the cos+ phase voltage signal output by the first coil 22a and the cos- phase voltage signal output by the third coil 22c are input to the first AD conversion unit 33. Further, in the first connection mode, the sin+ phase voltage signal output by the second coil 22b and the sin- phase voltage signal output by the fourth coil 22d are input to the second AD conversion unit 34. In the second connection mode shown in FIG. 3, the sin+ phase voltage signal output by the second coil 22b and the sin- phase voltage signal output by the fourth coil 22d are input to the first AD conversion unit 33. Further, in the second connection mode, the cos+ phase voltage signal output by the first coil 22a and the cos- phase voltage signal output by the third coil 22c are input to the second AD conversion unit 34. The timing and effects of the FPGA switching between the first connection mode and the second connection mode will be described later.

[0039] The AD conversion device 32 is of a two-channel type and converts two systems of analog signals into digital signals. Hereinafter, the conversion from an analog signal to a digital signal is referred to as AD conversion. AD conversion by the first AD conversion unit 33 and AD conversion by the second AD conversion unit 34 can be performed. In the present embodiment, one AD conversion device 32 performs two-channel AD conversion, but instead, two AD conversion devices may be provided. The first AD conversion unit 33 and the second AD conversion unit 34 each include a differential amplifier. The differential amplifier amplifies the difference between the two input signals to generate a differential signal.

[0040] In the first connection mode, the first AD conversion unit 33 generates a first differential signal based on the cos+ phase voltage signal and the cos- phase voltage signal. In the first connection mode, the second AD conversion unit 34 generates a second differential signal based on the sin+ phase voltage signal and the sin- phase voltage signal. When the phase representing the displacement of scale 1 with respect to the sensor head 2 is θ, the first differential signal y1 and the second differential signal y2 can be expressed by the following equations. y1 = acosθ·sinωt y2 = asinθ·sinωt The first AD conversion unit 33 AD-converts the first differential signal and outputs it to the arithmetic processing unit 35. The second AD conversion unit 34 AD-converts the second differential signal and outputs it to the arithmetic processing unit 35.

[0041] In the second connection mode, the first AD conversion unit 33 generates the second differential signal, AD-converts the second differential signal, and outputs it to the arithmetic processing unit 35. In the second connection mode, the second AD conversion unit 34 generates the first differential signal, AD-converts the first differential signal, and outputs it to the arithmetic processing unit 35.

[0042] In this embodiment, a differential amplifier is built in the AD conversion device 32. Instead of this configuration, a differential amplifier may be provided separately from the AD conversion device 32. In this case, a switching circuit 31 may be arranged between the differential amplifier and the AD conversion device 32. The switching circuit 31 receives the first differential signal and the second differential signal, and switches between a first connection mode in which the first differential signal is output to the first AD conversion unit 33 and the second differential signal is output to the second AD conversion unit 34, and a second connection mode in which the first differential signal is output to the second AD conversion unit 34 and the second differential signal is output to the first AD conversion unit 33.

[0043] The arithmetic processing unit 35 divides the second differential signal by the first differential signal. This result corresponds to the value of tanθ. Then, the arithmetic processing unit 35 obtains the arctan value of the calculation result. Thereby, the phase θ representing the displacement of the scale 1 with respect to the sensor head 2 can be obtained. Although θ is strictly a phase, substantially, it indicates the relative displacement of the scale 1 with respect to the sensor head 2. Therefore, hereinafter, θ may be referred to as displacement.

[0044] The filter processing unit 36 performs filter processing on the displacement θ obtained by the arithmetic processing unit 35. The filter processing unit 36 is, for example, a moving average filter that calculates the countable average value of the signal values. The filter processing unit 36 performs processing to calculate the countable average value of the displacement θ. This processing is substantially the same as the processing of calculating the countable average value of the cosine phase detection value and the countable average value of the sine phase detection value and calculating the displacement θ using these addition average values. That is, even if the object for which the filter processing unit 36 calculates the addition average value is the displacement θ, the filter processing unit 36 performs processing to calculate the final displacement θ based on the countable average value of the cosine phase detection value and the countable average value of the sine phase detection value.

[0045] The filter processing unit 36 can be configured using, for example, a shift register. This shift register has a configuration in which a plurality of registers are cascade-connected. Each time a common shift clock is input to each register, the data indicating the displacement θ(t) is sequentially transferred to the next-stage register. If the number of stages of the register is N stages, the filter processing unit 36 can perform a moving average process of up to N stages (N is a positive integer). The N-stage moving average process is a process of calculating the countable average value for N detection values arranged in time series and repeating this according to the time. By the filter processing of the filter processing unit 36, the high-frequency components included in the displacement θ(t) are removed. Thereby, noise and the like can be removed. Note that, instead of the displacement θ, filter processing may be performed on, for example, the first differential signal and the second differential signal.

[0046] The displacement after filter processing output by the filter processing unit 36 is output as position information after undergoing post-processing such as linearity calibration and high-speed prediction calculation, as shown in FIG. 1.

[0047] Next, with reference to FIGS. 4 and 5, the influence of environmental changes on the displacement θ and the method for eliminating it will be described.

[0048] First, consider the situation where the environment changes from Environment 1 to Environment 2 in a displacement detection device that does not have the switching circuit 31. Environment 1 and Environment 2 have different temperatures, for example. The AD conversion device 32 has environmental characteristics, and gain fluctuations occur due to environmental changes. Let the gain fluctuation of the first AD conversion unit 33 when changing from Environment 1 to Environment 2 be d, and the gain fluctuation of the second AD conversion unit 34 be e. Since there are individual differences in environmental characteristics, generally d and e are different.

[0049] The displacement calculated in Environment 1 is θ as described above (see (1) in FIG. 4). On the other hand, when changing from Environment 1 to Environment 2, since the first differential signal is being converted by the first AD conversion unit 33, the coefficient of the cosine phase detection value changes from a to d·a. Since the second differential signal is being converted by the second AD conversion unit 34, the coefficient of the sine phase detection value changes from a to e·a. As a result, the calculated displacement is tan -1 (e / d·tanθ), as shown in (2) of FIG. 4. That is, an error corresponding to the ratio of e to d occurs in the displacement calculated in Environment 2. As shown by this formula, the error is due to the difference between the temperature characteristics of the first AD conversion unit 33 and the temperature characteristics of the second AD conversion unit 34.

[0050] Next, the calculation of the displacement performed by the displacement detection device 100 having the switching circuit 31 will be described. As shown in (1) of FIG. 5, the switching circuit 31 switches between the first connection mode and the second connection mode for each switching period. The switching period coincides with the excitation period, but as will be described later, the switching period may be different from the excitation period.

[0051] The cos-phase detection value includes the detection value in the first connection mode and the detection value in the second connection mode. Similarly, the sin-phase detection value also includes the detection value in the first connection mode and the detection value in the second connection mode. The filter processing unit 36 calculates the displacement considering both the detection value in the first connection mode and the detection value in the second connection mode by performing a moving average process. Specifically, the filter processing unit 36 calculates the displacement based on the arithmetic mean of the displacement θ based on the detection value in the first connection mode and the displacement θ based on the detection value in the second connection mode. In this embodiment, the filter processing unit 36 performs a moving average process on the calculated displacement θ. However, in FIG. 5(2), for the sake of clearly showing the handling of the detection values in the first connection mode and the second connection mode, the arithmetic mean value of the cos-phase detection value and the arithmetic mean value of the sin-phase detection value are described.

[0052] In environment 1, the coefficient of the detection value of the differential signal AD-converted by the first AD conversion unit 33 is set as a, and the coefficient of the detection value of the differential signal AD-converted by the second AD conversion unit 34 is also set as a. That is, there is no difference in the detection value regardless of which AD conversion unit performs the conversion. Therefore, the displacement calculated by the displacement detection device 100 in environment 1 is the same as θ, which is the displacement calculated by the displacement detection device without the switching circuit 31 (see FIG. 5(3)).

[0053] In environment 2, the coefficient of the detection value of the differential signal AD-converted by the first AD conversion unit 33 is d·a, and the coefficient of the detection value of the differential signal AD-converted by the second AD conversion unit 34 is e·a. However, since the switching circuit 31 evenly performs the AD conversion by the first AD conversion unit 33 and the AD conversion by the second AD conversion unit 34, the coefficients of the respective detection values are both the arithmetic mean value of d·a and e·a. That is, even when the environment changes, the coefficients of the cos-phase detection value and the sin-phase detection value maintain an equal state. As a result, since the coefficients cancel each other out during the displacement calculation, the displacement calculated by the displacement detection device 100 in environment 2 is also θ (see FIG. 5(4)). As described above, by providing the switching circuit 31, it is possible to suppress the error caused by the environmental characteristics of the AD conversion device 32 even when the environment changes.

[0054] In order to further reduce the error caused by the difference in temperature characteristics between the first AD conversion unit 33 and the second AD conversion unit 34, it is preferable to set the moving average processing to an even number of stages so that the detection values in the first connection mode and the second connection mode are included substantially evenly.

[0055] In the above-described example, the switching period during which the switching circuit 31 switches between the first connection mode and the second connection mode coincides with the excitation period. However, the switching period may be an integral multiple of the excitation period. Specifically, in the detection values used for the moving average processing, it is preferable that the detection values in the first connection mode and the second connection mode have a substantially equal ratio. Therefore, when performing N-stage moving average processing, the switching period is preferably shorter than half of the time during which N detection values are detected. Further, when the AD conversion device 32 is of the ΣΔ type, since the AD conversion device 32 calculates the error based on the previous detection value and the linearity may be higher when the period is longer, it is preferable to set the switching period to a multiple of the excitation period rather than making it coincide with the excitation period.

[0056] FIG. 6 shows the results of an experiment confirming that the change in the detection value when the environment changes is suppressed by having the switching circuit 31. In this experiment, the sensor head 2 is placed in a normal temperature environment, the processing device 3 is placed in the environment 1 at the first temperature, and the detection value when the sensor head 2 is moved is recorded. Next, with the sensor head 2 placed at normal temperature, the processing device 3 is placed in the environment 2 at the second temperature, and the detection value when the sensor head 2 is moved is recorded. The horizontal axis of the graph in FIG. 6 represents the position of the sensor head 2, and the vertical axis of the graph in FIG. 6 represents the change amount of the detection value in environment 2 with respect to the detection value in environment 1.

[0057] The detection value of the displacement detection device without the switching circuit 31 changes significantly as the environment changes. In contrast, the detection value of the displacement detection device 100 having the switching circuit 31 changes little even when the environment changes. Therefore, it was confirmed that having the switching circuit 31 makes it less likely for an error caused by a change in the environment to occur.

[0058] As described above, the displacement detection device 100 includes a scale 1, a sensor head 2, and a processing device 3. The scale 1 has a magnetic response portion 12 and a non-magnetic response portion 11 alternately arranged at a predetermined detection pitch in the displacement detection direction. The sensor head 2 has at least four magnetic detection elements (a first coil 22a, a second coil 22b, a third coil 22c, and a fourth coil 22d) that output respective output signals represented by a sine function, a cosine function, a minus sine function, and a minus cosine function. The processing device 3 receives the output signals of the magnetic detection elements and calculates and outputs displacement information that is at least one of the relative displacement of the scale 1 with respect to the sensor head 2 and the change rate of the relative displacement. The processing device 3 includes an AD conversion device 32, a switching circuit 31, and an arithmetic processing unit 35. The AD conversion device 32 has a first AD conversion unit 33 and a second AD conversion unit 34, and converts a first differential signal based on the difference between the cosine function and the minus cosine function and a second differential signal based on the difference between the sine function and the minus sine function into digital signals. The switching circuit 31 periodically switches between a first connection mode in which the first differential signal is AD-converted by the first AD conversion unit 33 and the second differential signal is AD-converted by the second AD conversion unit 34, and a second connection mode in which the first differential signal is AD-converted by the second AD conversion unit 34 and the second differential signal is AD-converted by the first AD conversion unit 33. The arithmetic processing unit 35 outputs displacement information of the scale based on the additive average value of the first differential signals respectively output from the first AD conversion unit 33 and the second AD conversion unit 34 and the additive average value of the second differential signals respectively output from the first AD conversion unit 33 and the second AD conversion unit 34.

[0059] Thereby, the influence of the environmental characteristics of the first AD conversion unit 33 and the environmental characteristics of the second AD conversion unit 34 on the respective differential signals can be equalized. Therefore, the error of the displacement information when the environment changes can be suppressed.

[0060] In the displacement detection device 100 of the present embodiment, the arithmetic processing unit 35 calculates the displacement information of the scale 1 by arctan operation.

[0061] Thereby, displacement information can be obtained by a simple operation.

[0062] In the displacement detection device 100 of the present embodiment, the arithmetic processing unit 35 performs a moving average process with an even number of stages on the displacement information obtained by the arctangent operation.

[0063] By making the moving average process have an even number of stages, the number of detection values in the first connection mode and the second connection mode can be made the same, and an addition average value can be calculated. Therefore, the error of the displacement information can be further suppressed.

[0064] Although the preferred embodiments of the present invention have been described above, the above configuration can be changed as follows, for example.

[0065] The scale 1 is not limited to the above-described configuration. As long as different magnetic properties (such as the strength of magnetism and the direction of the generated magnetic field) are repeated, an appropriate configuration can be adopted. For example, the magnetic response unit 12 may be configured by alternately arranging a ferromagnetic material and a paramagnetic / diamagnetic material in the longitudinal direction of the scale 1. By arranging the N pole and S pole of the magnet, the repetition of the change in magnetic properties may be realized.

[0066] The magnetic detection element may be composed of a conductive pattern on a printed circuit board, a Hall element, etc. instead of the secondary coil 22.

[0067] If the secondary coil 22 can capture the change corresponding to the displacement from the scale 1 (magnetic response unit 12), the primary coil 21 may be arranged on the side closer to the scale 1, and the secondary coil 22 may be arranged on the side farther from the scale 1.

[0068] The arithmetic processing unit 35 can also obtain θ by a method other than calculating tanθ. Specifically, the phase of the second differential signal y2 is shifted by 90° by a known shift circuit and added to the first differential signal y1. The signal after addition can be expressed as asin(ωt + θ) by the well-known addition theorem of trigonometric functions. The arithmetic processing unit 35 obtains θ by measuring the phase difference between this signal and the reference differential signal asinωt (specifically, the difference in the timing at which each signal crosses zero). Also, the arithmetic processing unit 35 can obtain θ by PD (Phase-Digital) conversion.

[0069] The discrimination of the relative speed of scale 1 in the filter processing unit 36 does not have to be performed in real time. For example, the discrimination may be performed at a preset fixed time interval, or at a time interval that changes according to the relative speed of scale 1.

[0070] The displacement detection device can also output the change rate of the relative displacement (displacement information) instead of or in addition to the relative displacement of scale 1. The change rate of the relative displacement substantially means the relative speed of scale 1. The change rate of the relative displacement can be easily obtained by calculating the difference between the current relative displacement of scale 1 and the relative displacement before a predetermined time.

Explanation of Signs

[0071] 1 Scale 2 Sensor head 3 Processing device 31 Switching circuit 32 AD conversion device 33 First AD conversion unit 34 Second AD conversion unit 35 Arithmetic processing unit 36 Filter processing unit

Claims

1. A scale in which a magnetic response part and a non-magnetic response part are alternately arranged at a predetermined detection pitch in a displacement detection direction, A sensor head having at least four magnetic detection elements that output respective output signals represented by a sine function, a cosine function, a minus sine function, and a minus cosine function, A processing device into which the output signals of the magnetic detection elements are input, and which calculates and outputs displacement information that is at least one of the relative displacement of the scale with respect to the sensor head and the change rate of the relative displacement, Comprising: The processing device: Has a first AD conversion unit and a second AD conversion unit, and an AD conversion device that converts a first differential signal based on the difference between the cosine function and the minus cosine function and a second differential signal based on the difference between the sine function and the minus sine function into digital signals, A switching circuit that periodically switches between a first connection mode in which the first differential signal is AD-converted by the first AD conversion unit and the second differential signal is AD-converted by the second AD conversion unit, and a second connection mode in which the first differential signal is AD-converted by the second AD conversion unit and the second differential signal is AD-converted by the first AD conversion unit, An arithmetic processing unit that outputs the displacement information of the scale based on the additive average value of the first differential signal output from each of the first AD conversion unit and the second AD conversion unit and the additive average value of the second differential signal output from each of the first AD conversion unit and the second AD conversion unit, A displacement detection device characterized by comprising.

2. The displacement detection device according to Claim 1, The arithmetic processing unit calculates the displacement information of the scale by arctan operation. A displacement detection device characterized by this.

3. The displacement detection device according to Claim 2, The arithmetic processing unit performs even-stage moving average processing on the displacement information obtained by arctan operation. A displacement detection device characterized by this.

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