JP2022132769A - Displacement detection device - Google Patents

Abstract

To provide a displacement detection device capable of achieving both high accuracy and good trackability.SOLUTION: A displacement detection device 100 includes a scale 1, a magnetic detection head 2, and a detection signal processing device 3. The detection signal processing device 3 includes an arithmetic processing unit 35 and a filter processing unit 36. The arithmetic processing unit 35 arithmetically processes digital values and outputs a relative displacement of the scale 1. The filter processing unit 36 determines whether the speed of the scale 1 relative to the magnetic detection head 2 is high or low. If the relative speed is determined to be low, the filter processing unit 36 outputs a first filter processed displacement obtained by processing the relative displacement output from the arithmetic processing unit 35 with the first filter. If the relative speed is determined to be high, the filter processing unit 36 outputs a second filter processed displacement obtained by processing the relative displacement output from the arithmetic processing unit 35 with the second filter. The second filter is of lower order than the first filter.SELECTED DRAWING: Figure 1

Description

The present invention relates to a displacement detection device that detects displacement of an object to be measured.

Conventionally, there has been known a displacement detection device that measures the displacement of an object to be measured using an electromagnetic induction phenomenon. Patent Literature 1 discloses a position detection device that is a displacement detection device of this type.

The position detection device of Patent Document 1 includes a magnetic scale, a pair of magnetic sensors that output two-phase sine waves having a phase difference of 90° corresponding to the pitch of the magnetic scale, and resolution switching means. . In this position detection device, a rough position is obtained by performing calculation based on the center value for each pitch calculated from each sensor output peak value for each pitch of the magnetic scale and the comparison result of the sensor output. In addition, a precise position can be obtained by inverse trigonometric function calculation using two-phase corrected normalized signals. The position detection device outputs a digital position signal by summing the coarse position and the fine position. The digital position signal is switched to the digital position signal with the set resolution by shifting the data of each bit of the position signal to the lower bits according to the resolution set by the switch, and is output.

Japanese Patent No. 3317410

In the configuration of Patent Document 1, the resolution is artificially set by a switch or the like. Therefore, if the resolution is set to a low resolution, the detection accuracy will decrease, while if the resolution is set to a high resolution, the followability of detection will be insufficient when the relative speed between the magnetic scale and the magnetic sensor is high. There was room for improvement.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a displacement detection device capable of achieving both high accuracy and good followability.

Means and Effects for Solving Problems

The problems to be solved by the present invention are as described above. Next, the means for solving the problems and the effects thereof will be described.

According to the aspect of the present invention, a displacement detection device having the following configuration is provided. That is, this displacement detection device detects the displacement of the object to be measured in the displacement detection direction. A displacement detection device includes a scale, a sensor head, and a signal processing arithmetic device. On the scale, magnetically responsive portions and non-magnetically responsive portions are alternately arranged at a predetermined detection pitch in the displacement detection direction. The sensor head has at least four magnetic sensing elements that output respective output signals represented by a sine function, a cosine function, a minus sine function and a minus cosine function. An output signal of the magnetic detection element is input to the signal processing operation device. The signal processing arithmetic device calculates and outputs at least one of a relative displacement of the scale with respect to the sensor head and a rate of change of the relative displacement. The signal processing arithmetic device includes a first differential amplifier, a second differential amplifier, an AD converter, an arithmetic processing section, and a filter processing section. The first differential amplifier outputs a first AC signal obtained by synthesizing the cosine function and the minus cosine function. The second differential amplifier outputs a second AC signal obtained by synthesizing the sine function and the minus sine function. The AD converter converts the first AC signal and the second AC signal into digital values. The arithmetic processing unit arithmetically processes the digital value and outputs the relative displacement of the scale. The filter processor determines whether the speed of the scale relative to the sensor head is high or low. When it is determined that the relative velocity is low, the filter processing section processes the relative displacement output from the arithmetic processing section with a first filter, and converts the displacement after the first filter processing obtained by the relative displacement of the scale to the relative displacement of the scale. output as When it is determined that the relative velocity is high, the filter processing section processes the relative displacement output from the arithmetic processing section with a second filter, and converts the displacement after the second filter processing to the relative displacement of the scale. output as The second filter has a lower order than the first filter.

This makes it possible to output displacements obtained by processing with filters of different orders according to the relative speed between the sensor head and the scale. Therefore, both the followability and detection accuracy of the displacement detection device can be achieved.

Preferably, the displacement detection device described above has the following configuration. That is, the filter processing section of the displacement detection device obtains each of the first moving average, the second moving average, and the third moving average. The first moving average corresponds to the first filtered displacement. The second moving average corresponds to the displacement after the second filtering process. The third moving average corresponds to a post-third filtering displacement obtained by processing the relative displacement output from the arithmetic processing unit with a third filter. The third filter has a lower order than the first filter and a higher order than the second filter. The filtering unit uses at least one of a difference between the first moving average and the third moving average and a difference between the first moving average and the second moving average to determine the A determination is made as to whether the relative velocity of the scale is high or low.

This makes it possible to more accurately determine the relative velocity of the scale with respect to the sensor head.

It is preferable that the displacement detection device has the following configuration. That is, the filter processing section obtains each of the first moving average and the second moving average. The first moving average corresponds to the first filtered displacement. The second moving average corresponds to the displacement after the second filtering process. The filter processing section uses a difference between the first moving average and the second moving average to determine whether the speed of the scale relative to the sensor head is high or low.

This makes it possible to determine the relative speed of the scale with respect to the sensor head with simple processing.

In the displacement detection device, it is preferable that the arithmetic processing unit calculates the displacement of the scale by arctan calculation.

Thereby, the displacement can be obtained by a simple calculation.

1 is a block diagram showing the configuration of a displacement detection device according to an embodiment of the present invention; FIG. 4 is a block diagram showing an example of moving average; FIG. FIG. 10 is a diagram showing experimental results with different numbers of filter stages; FIG. 4 is an enlarged view of a portion of the experimental results of FIG. 3; FIG. 3 is a block diagram showing processing within the FPGA; 7A and 7B are graphs conceptually explaining the selection of the number of stages of the moving average filter according to the speed.

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a displacement detection device 100 according to one embodiment of the present invention. FIG. 2 is a block diagram illustrating an example of moving average. FIG. 3 is a diagram showing experimental results with different numbers of filter stages. FIG. 4 is an enlarged view of part of the experimental results of FIG. FIG. 5 is a block diagram showing processing within the FPGA. FIG. 6 is a graph conceptually explaining the selection of the number of stages of the moving average filter according to the speed.

A displacement detection device 100 shown in FIG. 1 is used to detect displacement in a predetermined direction of an object to be measured. In the following description, the direction in which the displacement of the object to be measured is detected may be called the displacement detection direction.

Displacement is a value that represents how much the current position has changed compared to a reference position (eg, initial position). By defining the reference position in an appropriate manner, the position of the measurement object itself can also be calculated from the displacement. Therefore, the displacement detection device 100 can be used as a position detection device.

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 operation device) 3 .

Either the scale 1 or the magnetic detection head 2 is attached to the object to be measured. For example, the scale 1 is attached to a movable member (not shown), and the magnetic detection head 2 is attached to a fixed member (not shown) which is the object to be measured. The movable member is linearly movable along a path parallel to the displacement detection direction.

Alternatively, the scale 1 may be attached to a fixed member, which is the object to be measured, and the magnetic detection head 2 may be attached to a movable member. Furthermore, both the scale 1 and the magnetic detection 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 (that is, the scale 1 and the magnetic detection head 2).

The 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 elongated in a direction parallel to the movement stroke so as to include the movement stroke of the magnetic detection head 2 accompanying the movement of the movable member. The scale 1 may be formed in the shape of an elongated block, or may be formed in the shape of an elongated rod.

The scale 1 includes a non-magnetic responsive portion 11 and a magnetic responsive portion 12 . The non-magnetic response section 11 is made of, for example, a metal that does not have significant magnetism, or a material that does not have magnetism, such as plastic. The magnetic response section 12 is made of, for example, metal having ferromagnetism. The non-magnetic responsive portions 11 and the magnetic responsive portions 12 are alternately arranged in the longitudinal direction of the scale 1 .

The magnetic response sections 12 are arranged in the longitudinal direction of the scale 1 at predetermined detection pitches C0. Since the magnetic response portions 12 are arranged side by side while forming a predetermined interval, there is a non-magnetic portion, which is a portion with no (or relatively weak) magnetism, between two magnetic response portions 12 adjacent to each other. A response part is formed. Therefore, in the magnetic response section 12, presence or absence or strength of the magnetic response appears alternately and repeatedly at each detection pitch C0 in the longitudinal direction of the scale 1. FIG.

As shown in FIG. 1, the magnetic detection head 2 is arranged with a predetermined distance from the magnetic response section 12 . When the scale 1 is shaped like an elongated bar, the magnetic detection head 2 can be shaped like a cylinder, and the scale 1 can be inserted into the cylinder hole. However, the shape of the magnetic detection head 2 is not limited. The magnetic detection head 2 includes a primary coil 21 and a plurality of secondary coils (magnetic detection elements) 22 . Four secondary coils 22 are provided in this embodiment. Note that the primary coil 21 can be omitted.

A primary coil 21 is used to generate an alternating magnetic field. When an alternating current of an appropriate frequency is passed through the primary coil 21, a magnetic field whose direction and strength periodically change is generated around it. As shown in FIG. 1, the primary coil 21 is arranged in a portion of the magnetic detection head 2 farther from the scale 1 than the secondary coil 22 is.

The four secondary coils 22 are arranged side by side in a direction parallel to the longitudinal direction of the scale 1, as shown in FIG. The secondary coil 22 is arranged in a portion of the magnetic detection head 2 closer to the scale 1 than the primary coil 21 is. An induced current induced by the magnetic field strengthened by the magnetic response section 12 flows through the four secondary coils 22 . The magnetic detection head 2 detects and outputs an electric signal (for example, a voltage signal) based on this induced current.

As shown in FIG. 1, the four secondary coils 22 are arranged side by side at predetermined unit pitches C1 in the displacement detection direction. The unit pitch C1 is determined based on the detected pitch C0 so as to have a predetermined relationship with the detected pitch C0. Specifically, as shown in the following formula, the unit pitch C1 is set to be the sum of an integral multiple of the detection pitch C0 and 1/4 of the detection pitch C0.
C1=(n+1/4)*C0
However, n is an integer. Although n=0 in this embodiment, the present invention is not limited to this.

In the following description, in order to specify each of the four secondary coils, they are referred to as a first coil 22a, a second coil 22b, a third coil 22c, and a fourth coil 22d in order from the left side shown in FIG. Sometimes.

Here, the signal (for example, voltage signal) output by each secondary coil 22 will be briefly described. When an alternating current of an appropriate frequency is passed through the primary coil 21, a magnetic field is generated in the primary coil 21, the direction and strength of which change periodically. On the other hand, an induced current is generated in the secondary coil 22 in a direction that hinders the change in the magnetic field of the coil. If a ferromagnetic material exists in the vicinity of the primary coil 21, this ferromagnetic material acts to strengthen the magnetic field generated by the primary coil 21. FIG. This effect increases as the ferromagnetic material approaches the primary coil 21 .

Focusing on the magnetic response section 12, the primary coil 21 and the secondary coil 22 approach the magnetic response section 12 as the magnetic detection head 2 relatively moves from one side of the scale 1 to the other side in the longitudinal direction. It moves away after coming closest. The induced current generated in the secondary coil 22 is an alternating current, and the magnitude of the amplitude varies depending on the positional relationship between the secondary coil 22 and the magnetic response section 12 .

Since the magnetic response units 12 are actually arranged side by side for each detection pitch C0, the change in amplitude is repeated for each detection pitch C0. That is, if the horizontal axis represents the position of the magnetic detection head 2 and the vertical axis represents the magnitude of the amplitude, the relationship between the amplitude and the position is a periodic curve (specifically, a sine curve y=sin θ). If this θ can be obtained, it is possible to obtain the position of the scale 1 with respect to the magnetic detection head 2 within the detection pitch C0, which is the repeating unit.

However, considering one period of the sine curve y=sin θ, there are two possible values of θ corresponding to y except for special cases, and only one value is not determined. Therefore, in this embodiment, the secondary coils 22 are spaced apart by the unit pitch C1 so that the positional relationship with the nearest magnetic response section 12 is substantially shifted by 1/4 of the detection pitch C0. There are four

As shown in FIG. 1, since the first coil 22a, the second coil 22b, the third coil 22c, and the fourth coil 22d are separated from each other by 1/4 of the detection pitch C0, they are out of phase with each other by 90°. outputs a voltage signal That is, when 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 22c outputs a voltage signal of cos− phase. The coil 22d outputs a sin-phase voltage signal.

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, and calculates the relative displacement of the scale 1 with respect to the magnetic detection head 2. Output.

The detection signal processing device 3, for example, as shown in FIG. and a filtering unit 36 .

In the present embodiment, the first differential amplifier 31, the second differential amplifier 32, the first AD converter 33, and the second AD converter 34 are part of the circuits (or electronic parts). The arithmetic processing unit 35 and the filter processing unit 36 are realized by executing a program by an FPGA or the like that constitutes the detection signal processing device 3 . FPGA is an abbreviation for Field Programmable Gate Array.

The first differential amplifier 31 is used to amplify the difference between the outputs of the first coil 22a and the third coil 22c. The first differential amplifier 31 amplifies the difference between the voltage signals output from the first coil 22a and the third coil 22c, and outputs it as the first AC signal y1.

Assuming that the phase representing the displacement of the scale 1 with respect to the magnetic detection head 2 is θ, the first AC signal y1 can be expressed by the following equation.
y1=a cos θ·sin ωt

The second differential amplifier 32 is used to amplify the difference between the outputs of the second coil 22b and the fourth coil 22d. The second differential amplifier 32 amplifies the difference between the voltage signals output from the second coil 22b and the fourth coil 22d and outputs it as a second AC signal y2.

Assuming that the phase representing the displacement of the scale 1 with respect to the magnetic detection head 2 is .theta., the second AC signal y2 can be expressed by the following equation.
y2=asinθ·sinωt

The first AD converter 33 and the second AD converter 34 respectively convert the analog signals (the first AC signal y1 and the second AC signal y2) from the first differential amplifier 31 and the second differential amplifier 32 into digital signals. used to convert to The first AD converter 33 and the second AD converter 34 are electrically connected to the arithmetic processing section 35 and output converted digital signals to the arithmetic processing section 35 .

The arithmetic processing unit 35 divides the second AC signal y2 by the first AC signal y1. This result corresponds to the value of tan θ. After that, 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 magnetic detection head 2 can be obtained. Strictly speaking, θ is the phase, but substantially indicates the relative displacement of the scale 1 with respect to the magnetic detection head 2 . Therefore, θ may be referred to as displacement below.

The filter processing unit 36 filters the displacement θ(t) obtained by the arithmetic processing unit 35 . The filter processing unit 36 is configured as, for example, a moving average filter. High frequency components contained in the displacement θ(t) are removed from the displacement θ(t) by filtering. Accordingly, noise and the like can be removed.

The filter processing unit 36 can be configured using a shift register, as shown in FIG. 2, for example. This shift register has a configuration in which a plurality of registers are cascaded. Each time a common shift clock is input to each register, data representing the displacement θ(t) is sequentially transferred to the next-stage register.

As shown in FIG. 2, the filter processing unit 36 of this embodiment is composed of 4096 stages of shift registers. Therefore, the filter processing unit 36 can perform moving average processing from 1 to 4096 steps.

The value after 4096 stages of moving average filtering can be expressed by the following equation. However, s is the shift period of the shift register.
θ1(t)=(θ(t)+θ(t−1·s)+θ(t−2·s)+ . . . +θ(t−4095·s))/4096
In the present embodiment, this 4096-stage moving average filter process corresponds to the process of the first filter. Hereinafter, the value of θ1(t) may be referred to as a first moving average (displacement after first filtering).

The value after 16-stage moving average filtering can be expressed by the following equation.
θ2(t)=(θ(t)+θ(t−1·s)+θ(t−2·s)+ . . . +θ(t−15·s))/16
In the present embodiment, this 16-stage moving average filter process corresponds to the process of the second filter. Hereinafter, the value of θ2(t) may be referred to as a second moving average (displacement after second filtering).

As is known, the SN ratio (SNR: signal-to-noise ratio) of an AD converter is generally represented by the following mathematical model. where N is the resolution.
SNR = 6.02 N + 1.76 [dB]
Therefore, theoretically speaking, the resolution is improved by n bits by performing the moving average processing of 4 to the nth power. For example, with a moving average of 16 stages (=4 squared), the effective resolution is improved by 2 bits compared to no filter. With a moving average of 4096 steps (=4 to the 6th power), the effective resolution is improved by 6 bits compared to the unfiltered value.

3 and 4 show the effect of filter processing when the scale 1 moves from position P1 to position P3 and then stops relative to the magnetic detection head 2, and further moves from position P3 to position P2 and stops. It is shown. The graph of FIG. 3 was obtained by experiment, and a part of the graph is enlarged and shown in FIG. In FIG. 4, large-amplitude fluctuation occurs in the sensor output without the filter.

FIG. 4 intuitively shows that the shake can be effectively suppressed by filtering. That is, the larger the number of steps of the moving average, the smaller the deviation of the value of the moving average, so that a good value of the SN ratio can be obtained.

On the other hand, as shown in the lower part of FIG. 3, when the scale 1 moves, the greater the number of steps of the moving average, the greater the time lag of the obtained moving average. For example, when the shift cycle (sampling cycle) s is 16 μs, a time delay of 128 μs occurs in the second moving average θ2(t) obtained by performing 16 stages of moving average processing. A time delay of 32.768 ms occurs in the first moving average θ1(t) obtained by performing 4096 stages of moving average processing.

As described above, the larger the number of stages of the filter, the better the accuracy of the obtained moving average (displacement after filtering), but the greater the time delay, the lower the followability. A position detection error due to a time delay becomes particularly large when the scale 1 is displaced at high speed.

Regarding this point, in the displacement detection device 100 of the present embodiment, the number of stages of the moving average filter to be output is selected according to whether the scale 1 is substantially moving or stationary with respect to the magnetic detection head 2. . That is, the displacement detection device 100 outputs moving averages processed with different numbers of filter stages according to the relative moving speed of the scale 1 .

Specifically, as shown in FIG. 5, each of the first AC signal y1 and the second AC signal y2 is input to the arithmetic processing unit 35 after undergoing processes such as offset correction amount addition and gain correction amount multiplication. be. The calculation processing unit 35 obtains the displacement θ(t) by performing an arctan calculation using the first AC signal y1 and the second AC signal y2. The obtained displacement θ(t) is input to the filter processing section 36 after undergoing processing such as pitch synthesis.

The filter processing unit 36 of the present embodiment performs the moving average processing with each of the first filter, the second filter, and the third filter described later, and based on the post-filter processing displacement obtained, the magnetic detection head 2 It is determined whether or not the scale 1 is moving.

The third filter is similar to the first and second filters except that the moving average is 2048 stages. It can be said that 2048 stages is an intermediate number of stages between the first filter and the second filter. The value after 2048 stages of moving average filtering can be expressed by the following equation.
θ3(t)=(θ(t)+θ(t−1·s)+θ(t−2·s)+ . . . +θ(t−2047·s))/2048
In the present embodiment, this 2048-stage moving average filter process corresponds to the process of the third filter. Hereinafter, the value of θ3(t) may be referred to as a third moving average (displacement after third filtering).

In this embodiment, whether the scale 1 is moving or stationary with respect to the magnetic detection head 2 is determined by the filter processing unit 36 based on appropriate calculations based on whether the relative speed of the scale 1 is relatively high or low. Based on determined results. Therefore, the stationary state includes a completely stationary state in which the relative speed is zero, and a slow moving state in which the relative speed is slight although the relative speed is not completely stationary.

When the filter processing unit 36 determines that the scale 1 is stationary with respect to the magnetic detection head 2, the first moving average obtained by performing the moving average processing with the first filter (displacement after first filtering) to select and output.

On the other hand, when the filter processing unit 36 determines that the scale 1 is moving with respect to the magnetic detection head 2, the second moving average (after the second filter processing) obtained by performing the moving average processing with the second filter displacement) to output.

Whether or not the scale 1 is moving with respect to the magnetic detection head 2 is determined, for example, as shown in FIG. Specifically, the filter processing unit 36 calculates a first difference that is the difference between the first moving average and the third moving average, and a second difference that is the difference between the first moving average and the second moving average. Compare with a predetermined threshold. The filtering unit 36 determines that the scale 1 is stationary when both the first difference and the second difference are smaller than the threshold. On the other hand, the filter processor 36 determines that the magnetic detection head 2 is moving when at least one of the first difference and the second difference is equal to or greater than the threshold.

When the displacement θ(t) changes, the second moving average reacts most sensitively among the three moving averages, and the reaction slows down in the order of the third moving average and the first moving average. The first difference and the second difference are moving average differences due to the time lag being different according to the number of moving average stages. When the moving speed of the scale 1 is close to zero, the displacement θ(t) hardly changes, so both the first difference and the second difference are small. On the other hand, when the moving speed of the scale 1 is considerably high, the displacement θ(t) changes greatly, so both the first difference and the second difference become large. Therefore, it can be said that the filter processing section 36 substantially determines whether the speed of the scale 1 relative to the magnetic detection head 2 is high or low.

The method for determining whether the relative speed of the magnetic detection head 2 is high or low is not limited to the above. For example, determination may be made based on only one of the first difference and the second difference. The determination may be made simply by comparing the difference between the first moving average and the second moving average with a predetermined threshold value. The difference between the current value of an appropriate moving average (for example, the second moving average) and the value a predetermined time ago is obtained, and the difference can be determined by comparing the difference with a predetermined threshold value.

As shown in FIG. 5 and the like, the post-filtering displacement output by the filtering unit 36 is output as position information after undergoing post-processing such as linearity calibration and prediction calculation.

As described above, the displacement detection device 100 of this embodiment, as shown in FIG. is output as the detected value, and when the relative speed of the scale 1 is relatively large, the value obtained by the 16-step moving average process is output as the detected value. Although FIG. 6 shows that the relative velocity itself is directly compared with the threshold value, this is a conceptual explanation for convenience and differs from actual processing.

Thus, the displacement detection device 100 of the present embodiment can achieve both good followability and accuracy, which are usually in a trade-off relationship.

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. A 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 sections 12 and non-magnetic response sections 11 are alternately arranged at a predetermined detection pitch in the displacement detection direction. The magnetic detection head 2 has at least four secondary coils 22 that output respective output signals represented by a sine function, a cosine function, a minus sine function and a minus cosine function. The output signal of the secondary coil 22 is input to the detection signal processing device 3, and the detection signal processing device 3 calculates the relative displacement of the scale 1 with respect to the magnetic detection head 2 and outputs it. The detection signal processing device 3 includes a first differential amplifier 31, a second differential amplifier 32, AD converters (first AD converter 33 and second AD converter 34), an arithmetic processing unit 35, and a filter processing unit. 36 and. The first differential amplifier 31 outputs a first AC signal y1 obtained by synthesizing the cosine function and the minus cosine function. The second differential amplifier 32 outputs a second AC signal y2 obtained by synthesizing the sine function and the minus sine function. The AD converter converts the first AC signal y1 and the second AC signal y2 into digital values. The arithmetic processing unit 35 arithmetically processes the digital values and outputs the relative displacement of the scale 1 . The filtering unit 36 determines whether the speed of the scale 1 relative to the magnetic detection head 2 is high or low. When the filter processing unit 36 determines that the relative velocity is low, the displacement after the first filter processing obtained by processing the relative displacement output from the arithmetic processing unit 35 with the first filter is used as the relative displacement of the scale 1. Output. When the filter processing unit 36 determines that the relative velocity is high, the filter processing unit 36 outputs the second filtered displacement obtained by processing the relative displacement output from the arithmetic processing unit 35 with the second filter as the relative displacement of the scale 1. do. The second filter is of lower order than the first filter.

This makes it possible to output the displacement obtained by processing with filters of different orders according to the relative speed between the magnetic detection head 2 and the scale 1 . Therefore, both the followability and detection accuracy of the displacement detection device 100 can be achieved.

Moreover, in the displacement detection device 100 of the present embodiment, the filtering unit 36 obtains each of the first moving average, the second moving average, and the third moving average. The first moving average corresponds to the first filtered displacement. The second moving average corresponds to the second filtered displacement. The third moving average corresponds to the post-third filtering displacement obtained by processing the relative displacement output from the arithmetic processing unit 35 with the third filter. The third filter has a lower order than the first filter and a higher order than the second filter. The filtering unit 36 uses the first difference, which is the difference between the first moving average and the third moving average, and the second difference, which is the difference between the first moving average and the second moving average. A determination is made as to whether the speed of scale 1 relative to scale 2 is high or low.

As a result, the relative speed of the scale 1 with respect to the magnetic detection head 2 can be accurately determined.

However, in the displacement detection device 100 of the present embodiment, the filter processing unit 36 determines whether the speed of the scale 1 relative to the magnetic detection head 2 is high or low based on the difference between the first moving average and the second moving average. can also be configured to

In this case, the relative speed of the scale 1 with respect to the magnetic detection head 2 can be determined by simple processing.

Further, in the displacement detection device 100 of the present embodiment, the arithmetic processing unit 35 calculates the displacement of the scale 1 by arctan arithmetic.

Thereby, the displacement can be obtained by a simple calculation.

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

The scale 1 is not limited to the configuration described above, and may have an appropriate configuration 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 alternately arranging a ferromagnetic material and a weakly magnetic material/non-magnetic material in the longitudinal direction of the scale 1 . By arranging the north and south poles of magnets, repetition of changes in magnetic properties may be realized.

Instead of the secondary coil 22, the magnetic detection element may be composed of a conductive pattern on a printed circuit board, a Hall element, or the like.

If the secondary coil 22 can detect the change according to the displacement from the scale 1 (the magnetic response section 12), the primary coil 21 is arranged on the side closer to the scale 1, and the secondary coil 22 is positioned closer to the scale 1. may be arranged on the far side from the

The arithmetic processing unit 35 can also obtain θ by a method other than calculating tan θ. Specifically, the phase of the second AC signal y2 is shifted by 90° by a known shift circuit and added to the first AC signal y1. The signal after the addition can be represented 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 AC signal asinωt (specifically, the difference in the timing at which each signal crosses zero). Further, the arithmetic processing unit 35 can also obtain θ by PD (Phase-Digital) conversion.

The determination of the relative velocity of the scale 1 in the filter processing section 36 may not be performed in real time. For example, determination may be performed at predetermined time intervals, or may be performed at time intervals that vary according to the relative speed of the scale 1 .

In the above embodiment, the first to sixteenth stage shift registers are shared by the first filter, the second filter and the third register. The first to 2048th shift registers are shared by the first and third filters. However, a shift register may be provided independently for each filter.

Filters other than the moving average filter may be used as the first and second filters as long as the second filter satisfies the condition that the order of the second filter is lower than that of the first filter. A filter other than the moving average filter may be used as the third filter as long as the third filter has a lower order than the first filter and a higher order than the second filter.

Instead of or in addition to the relative displacement of the scale 1, the displacement detection device can also output the rate of change of the relative displacement. The change speed of 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 the scale 1 and the relative displacement a predetermined time ago.

In FIGS. 1 and 5, the unmarked processing (for example, processing such as offset correction amount addition, gain correction amount multiplication, pitch count generation, pitch synthesis, linearity calibration, prediction calculation, etc.) in FIG. It may be omitted as appropriate depending on the conditions.

1 scale 2 magnetic detection head (sensor head)
3 Detection signal processing device (signal processing arithmetic device)
11 non-magnetic response section 12 magnetic response section 22 secondary coil (magnetic detection element)
31 first differential amplifier 32 second differential amplifier 33 first AD converter 34 second AD converter 100 displacement detector

Claims (4)

A displacement detection device for detecting displacement of an object to be measured in a displacement detection direction,
a scale in which magnetic response portions and non-magnetic response portions are alternately arranged at a predetermined detection pitch in a displacement detection direction;
a sensor head having at least four magnetic sensing elements that output respective output signals expressed by a sine function, a cosine function, a minus sine function and a minus cosine function;
a signal processing arithmetic unit that receives an output signal from the magnetic detection element and calculates and outputs at least one of a relative displacement of the scale with respect to the sensor head and a rate of change of the relative displacement;
with
The signal processing arithmetic device is
a first differential amplifier that outputs a first AC signal obtained by synthesizing the cosine function and the minus cosine function;
a second differential amplifier that outputs a second AC signal obtained by synthesizing the sine function and the minus sine function;
an AD converter that converts the first AC signal and the second AC signal into digital values;
an arithmetic processing unit that arithmetically processes the digital value and outputs the relative displacement of the scale;
A determination is made as to whether the relative velocity of the scale with respect to the sensor head is high or low, and when it is determined that the relative velocity is low, a first The filtered displacement is output as the relative displacement of the scale, and when it is determined that the relative velocity is high, the relative displacement output from the arithmetic processing unit is processed by a second filter having a lower order than the first filter. a filter processing unit that outputs the displacement after the second filter processing obtained by the above as the relative displacement of the scale;
A displacement detection device comprising: The displacement detection device according to claim 1,
The filter processing unit is
a first moving average corresponding to the displacement after the first filtering;
a second moving average corresponding to the displacement after the second filtering;
Corresponds to displacement after third filter processing obtained by processing the relative displacement output from the arithmetic processing unit with a third filter having a lower order than the first filter and a higher order than the second filter. a third moving average;
find each of
Using at least one of the difference between the first moving average and the third moving average and the difference between the first moving average and the second moving average, the relative velocity of the scale with respect to the sensor head increases or decreases. A displacement detection device characterized in that it discriminates with respect to. The displacement detection device according to claim 1,
The filter processing unit is
a first moving average corresponding to the displacement after the first filtering;
a second moving average corresponding to the displacement after the second filtering;
find each of
A displacement detection device, wherein a difference between the first moving average and the second moving average is used to determine whether the relative velocity of the scale with respect to the sensor head is high or low. The displacement detection device according to any one of claims 1 to 3,
The displacement detection device, wherein the arithmetic processing unit calculates the displacement of the scale by arctan arithmetic.

Images