JP2016038228A - Displacement measurement device, signal processing device, and signal processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a displacement measurement device capable of generating as much accurate signal as possible and heightening measurement accuracy, and a signal processing device and a signal processing method that are used therein.SOLUTION: A displacement measurement device 100 includes an encoder unit 10 and a signal processing device 30. The signal processing device 30 is provided with an AD conversion unit 31, a standardization unit 33, an inverse trigonometric function calculation unit 35, a change amount calculation unit 37, and a displacement calculation unit 39. A sinusoidal signal generated by the encoder unit 10 is standardized by the standardization unit 33, and calculation pertaining to the amplitude value of the signal can thereby be simplified. Also, a triangular wave signal including a linear area can be obtained by the inverse trigonometric function calculation of the inverse trigonometric function calculation unit 35. Due to the fact that the change amount calculation unit 37 calculates a change amount per prescribed time of the signal in the linear area, the displacement measurement device 100 can generate an accurate signal and perform high-accuracy measurement.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a displacement measuring device that measures a displacement of a linear distance, a displacement of a rotation angle, and the like, a signal processing device used therefor, and a signal processing method thereof.

  A linear encoder or a rotary encoder is a device that generates a signal according to movement of a scale. For example, an optical dimension measuring apparatus described in Patent Document 1 uses a moving scale and two fixed scales having a phase difference of π / 2 and detects a two-phase sine wave signal having a phase difference of π / 2. . This dimension measuring device determines the relationship between the phase advance and delay of the two-phase signal and detects the moving direction of the moving scale. In addition, this dimension measuring apparatus counts the number of grids of the moving scale by the counter unit, and multiplies the distance for one pitch of the grid by the count number to measure the moving distance. This dimension measuring apparatus has a normalization processing unit that normalizes the amplitude of the two-phase signal to a sine wave signal of ± 1 (for example, paragraphs [0019] and [0021] in the specification of Patent Document 1). Etc.).

  The angle calculation device described in Patent Document 2 includes a three-phase optical encoder, a digital processing circuit (DSP), and the like. The angle calculation device obtains the angle information and rotation direction of the rotor by the DSP based on the three-phase sine wave signals obtained by the three-phase optical encoder and having phases different by 120 °. Specifically, the DSP performs calculation of an inverse trigonometric function in order to obtain angle information (see, for example, paragraph [0013] in the specification of Patent Document 2).

Japanese Patent Laid-Open No. 11-271026 JP 2009-063332 JP

  In measurement using an encoder, it is desired to reduce measurement errors as much as possible to increase measurement accuracy.

  An object of the present invention is to provide a displacement measuring device capable of generating a signal as accurate as possible to increase measurement accuracy, a signal processing device and a signal processing method used therefor.

In order to solve the above problems, a displacement measuring apparatus according to an aspect of the present invention includes an encoder unit, a normalization unit, an inverse trigonometric function calculation unit, and a change amount calculation unit.
The encoder unit includes a scale and a detector, and is configured to generate a periodic signal according to the relative displacement between the scale and the detector.
The normalization unit is configured to normalize the signal generated by the encoder unit.
The inverse trigonometric function calculation unit is configured to calculate an inverse trigonometric function of the signal normalized by the normalization unit.
The change amount calculation unit is configured to calculate a change amount per predetermined time of the signal calculated by the inverse trigonometric function calculation unit.
This displacement measuring apparatus simplifies the calculation related to the amplitude value of the signal by standardizing the signal, and can obtain a signal including a linear region by the inverse trigonometric function calculation. Then, by calculating the change amount of the signal in the linear region every predetermined time by the change amount calculation unit, the displacement measuring device can generate an accurate signal and perform highly accurate measurement.

The encoder unit may generate a plurality of signals having different phases.
Thereby, an appropriate signal can be selected from a plurality of analog signals, or information on the displacement direction can be obtained by quadrant division for each period as described later.

The displacement measuring device may further include an extraction unit. The extraction unit acquires the absolute values of the plurality of signals calculated by the change amount calculation unit, and among the acquired absolute values at the same time, is greater than a minimum value and includes a maximum value, It is configured to extract any one of the values from the minimum value to the maximum value.
Thereby, even if noise is included in the signal due to the influence of disturbance, the noise can be removed, and highly accurate measurement is possible. For example, the extraction unit may extract the maximum value.

The displacement measuring device may further include a displacement direction acquisition unit. The displacement direction acquisition unit is configured to determine the scale and the detector based on the change amounts of the plurality of signals calculated by the inverse trigonometric function calculation unit and the plurality of signals calculated by the change amount calculation unit. It is configured to obtain information on the direction of relative displacement of.
The displacement direction acquisition unit can perform quadrant division by calculation in the inverse trigonometric function calculation unit, and can obtain information on the displacement direction based on the polarity of the signal change amount in the quadrant.

The displacement measuring device may further include a storage unit that stores a maximum value and a minimum value of a signal generated by the encoder unit within a range in which relative movement between the scale and the detection unit is possible. The normalization unit may be configured to perform normalization using a maximum value and a minimum value stored in the storage unit.
Thereby, it is not necessary to obtain the maximum value and the minimum value for standardization for each measurement, the calculation by the standardization unit can be simplified, and the speed of the standardization process can be increased.

The displacement measuring device may further include an updating unit that updates the maximum value and the minimum value.
As a result, even if the amplitude value of the signal fluctuates due to a change with time (aging) of the displacement measuring device, the fluctuation can be absorbed and measurement errors can be suppressed.

  A signal processing device according to an aspect of the present invention is configured to process the signal output from an encoder unit that generates a periodic signal in accordance with a relative displacement between a scale and a detector. , A normalization unit, an inverse trigonometric function calculation unit, and a change amount calculation unit.

A signal processing method according to an aspect of the present invention is a signal processing method for processing the signal output from the encoder unit that generates a periodic signal according to the relative displacement between the scale and the detector. In this signal processing method, the following processing is executed.
A periodic signal is generated according to the relative displacement between the scale and the detector,
The generated signal is normalized,
An inverse trigonometric function of the normalized signal is calculated,
The amount of change of the calculated signal per predetermined time is calculated.

  As described above, according to the present invention, an accurate signal can be generated to improve measurement accuracy.

FIG. 1 is a block diagram showing a functional configuration of a displacement measuring apparatus according to the first embodiment of the present invention. FIG. 2 is a flowchart mainly showing processing by the signal processing device of the displacement measuring device according to the first embodiment. FIG. 3 is a simulation showing a three-phase sine wave signal output from the encoder unit. FIG. 4 shows a signal normalized by the normalization unit. FIG. 5 shows an inverse trigonometric function signal obtained by the inverse trigonometric function calculation unit. FIG. 6 shows an angle change signal for each predetermined time. FIG. 7 shows the absolute value of the change amount. FIG. 8 is a block diagram illustrating a functional configuration of the displacement measuring apparatus according to the second embodiment. FIG. 9 is a flowchart showing processing mainly by the signal processing device of the displacement measuring device according to the second embodiment. FIG. 10 shows a sine wave signal that is output by converting, for example, a three-phase sine wave signal generated by the encoder unit into a digital signal by the AD conversion unit. FIG. 11 shows a three-phase signal in which the standardization unit standardizes the signal output from the AD conversion unit. FIG. 12 shows a signal obtained by the inverse trigonometric function computation unit computing the inverse trigonometric function of the three-phase signal normalized by the normalization unit. FIG. 13 shows a signal obtained by the change amount calculation unit calculating the change amount of the three-phase signal calculated by the inverse trigonometric function calculation unit. FIG. 14 shows the amount of change using the maximum value extracted by the extraction unit. FIG. 15 is a graph showing the measurement accuracy when the present inventors use the displacement measurement device according to the second embodiment and expand the relative movement range of the scale and the detection unit to 1 mm. FIG. 16 is a block diagram showing a functional configuration of a displacement measuring apparatus according to the third embodiment of the present invention. FIG. 17 is a flowchart illustrating processing in the displacement direction acquisition unit. FIG. 18 shows a triangular wave signal obtained by the inverse trigonometric function operation unit, enlarged on the time axis.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
(Configuration of displacement measuring device)
FIG. 1 is a block diagram showing a functional configuration of a displacement measuring apparatus according to the first embodiment of the present invention. The displacement measuring device 100 includes an encoder unit 10 and a signal processing device 30. The signal processing device 30 includes an AD conversion unit 31, a normalization unit 33, an inverse trigonometric function calculation unit 35, a change amount calculation unit 37, and a displacement calculation unit 39.

  The encoder unit 10 is typically an optical encoder. As will be described later, the optical encoder unit includes an optical scale and a detector (not shown). In this case, for example, a diffraction grating is used as the scale. For example, a photodiode is used as the detector.

  The encoder unit 10 has a function of outputting a three-phase periodic signal, for example, an analog three-phase sine wave signal from the detector in accordance with the relative displacement between the scale and the detector. These three-phase signals are sinusoidal signals whose phases are shifted from each other by 120 degrees. There is a linear optical scale as means for realizing generation of a three-phase sine wave signal. As the linear optical scale, for example, a linear optical scale having a diffraction grating having three grating pattern regions having the same pitch and shifted from each other by 1/3 pitch is used. The means for realizing the generation of the three-phase signal is not limited to this, and other known means can be used.

The AD conversion unit 31 has a function of sampling the analog signal output from the encoder unit 10 and generating a digital signal.
The normalization unit 33 has a function of normalizing (normalizing) the signal output from the AD conversion unit 31.
The inverse trigonometric function calculation unit 35 has a function of calculating the inverse trigonometric function of the signal normalized by the normalization unit 33.
The change amount calculation unit 37 has a function of calculating a change amount of the signal calculated by the inverse trigonometric function calculation unit 35 for each predetermined time, for example, a change amount for each sampling value of the digital signal.
The displacement calculation unit 39 has a function of calculating the relative displacement of the scale and the detection unit based on the change amount calculated by the change amount calculation unit 37.

  For example, the signal processing device 30 includes a central processing unit (CPU), a micro processing unit (MPU), a random access memory (RAM), a read only memory (ROM), and the like. In place of or in addition to the CPU, a DSP (Digital Signal Processor), a PLD (Programmable Logic Device), or the like may be used.

(Processing by signal processor)
A signal processing method mainly performed by the signal processing device 30 of the displacement measuring device 100 configured as described above will be described. FIG. 2 is a flowchart showing the processing.

  The encoder unit 10 generates a three-phase sine wave voltage signal according to the relative displacement between the scale and the detection unit (step 101). FIG. 3 is a simulation showing a three-phase sine wave signal output from the encoder unit 10. In other words, this represents an ideal sine wave signal. The three-phase waves shifted by 120 deg are U (0 deg), V (120 deg), and W (240 deg). For example, the minimum value of the amplitude of these signals is about 1.1V, and the maximum value is about 2.3V. These voltage values are merely examples of output voltage values by a detector (for example, a photodiode as described above).

  The sine wave signal output from the encoder unit 10 is converted into a digital signal at a predetermined sampling interval by the AD conversion unit 31 (step 102). The AD-converted signal is normalized by the normalization unit 33 (step 103). FIG. 4 shows a signal normalized by the normalization unit 33. The amplitude value is standardized at ± 1.0. Each plot is a voltage value at the sampling time.

Here, the voltage value of the three-phase signal at an arbitrary time (an arbitrary sampling time) is assumed to be (Vu ₀ , Vv ₀ , Vw ₀ ). The maximum value of the voltage within an arbitrary period is (Vu ₀ _max, Vv ₀ _max, Vw ₀ _max), and the minimum value is (Vu ₀ _min, Vv ₀ _min, Vw ₀ _min). The normalization unit 33 normalizes the amplitude by the following arithmetic expressions (1a), (1b), and (1c), and the normalized signal V ₁ (Vu ₁ , Vv ₁ , Vw ₁ ) shown in FIG. Is output.

Vu ₁ = [(Vu ₀ -Vu ₀ _min) / Vu ₀ _max -0.5] * 2 Equation (1a)
_{Vv 1 = [(Vv 0 -Vv} 0 _min) / Vv 0 _max -0.5] * 2 ··· formula (1b)
_{Vw 1 = [(Vw 0 -Vw} 0 _min) / Vw 0 _max -0.5] * 2 ··· formula (1c)
("*" Represents multiplication. The same applies hereinafter.)

When the normalized signal V ₁ is generated, the inverse trigonometric function computing unit 35 computes the inverse trigonometric function of the normalized signal V ₁ (step 104). The inverse trigonometric function signal V ₂ (Vu ₂ , Vv ₂ , Vw ₂ ) is calculated by the following arithmetic expressions (2a), (2b), (2c). Figure 5 shows an inverse trigonometric function signal V ₂ calculated.

Vu ₂ = 180 / π * arcsin (Vu ₁ ) Equation (2a)
Vv ₂ = 180 / π * arcsin (Vv ₁ ) Equation (2b)
Vw ₂ = 180 / π * arcsin (Vw ₁ ) Equation (2c)

In general, when the sine wave is V ₁ = sin (θπ / 180) (the unit of θ (= V ₂ ) is deg), the inverse trigonometric function signal V ₂ can be derived. The voltage value on the vertical axis shown in FIG. 5 indicates the angle deg. That is, the voltage value representing the amplitude of the sine wave signal is converted into the voltage value representing the angle by the inverse trigonometric function calculation.

Inverse trigonometric function signal V ₂ is a sawtooth wave having a linear region as shown in FIG. 5 (a triangular wave). Thus, the displacement measurement apparatus 100, by measuring the amount of change using the inverse trigonometric function signal V _2, can be obtained measurement result error is suppressed. Specifically, the change amount is calculated as follows.

Change amount calculation unit 37, the inverse trigonometric function signal V ₂ calculated by the inverse trigonometric function calculating section 35 calculates the amount of change per predetermined time (for example, the sampling interval) (step 105). The change amount of the angle is calculated by the following arithmetic expressions (3a), (3b), and (3c). FIG. 6 shows a signal (ΔVu ₂ , ΔVv ₂ , ΔVw ₂ ) of the change amount of the angle. This amount of change in angle is a unit angle change amount and corresponds to resolution.

ΔVu ₂ = Vu _{2 (m)} -Vu _{2 (m-1)}・ ・ ・ Formula (3a)
ΔVv ₂ = Vv _{2 (m)} -Vv _{2 (m-1)}・ ・ ・ Formula (3b)
ΔVw ₂ = Vw _{2 (m)} -Vw _{2 (m-1)}・ ・ ・ Formula (3c)
(N is a natural number and indicates the number of samplings.)

The amount of change obtained by the above arithmetic expressions (3a), (3b), and (3c) is a difference between the current angular coordinate and the angular coordinate calculated immediately before. In FIG. 6, since it is an ideal signal in increments of 10 degrees, the difference in angular coordinates is divided into values of 10 degrees or −10 degrees. When absolute values abs (ΔVu ₂ ), abs (ΔVv ₂ ), and abs (ΔVw ₂ ) are taken with respect to these changes, as shown in FIG. 7, the plots of all three phases are constant values. (For example, 10 deg) is obtained.

  The computer, such as the CPU or DSP, issues a command for obtaining the current voltage value, obtains data, and sequentially compares the amount of change with the voltage value at the time of issuing the previous command. What is necessary is just to calculate.

  Such a unit angle change amount (for example, 10 deg) can be converted into a distance change amount (unit distance displacement) according to the design of the scale. For example, when the displacement measuring apparatus 100 is designed or manufactured, a lookup table for the conversion is stored in the memory.

  The displacement calculation unit 39 uses the number of plots of the unit angle variation obtained as shown in FIG. 7 as a count, and by multiplying them, the position from the position where the scale and the detection unit start to move relative to each other is obtained. The displacement can be output (step 106). In other words, the displacement measuring device 100 is an incremental measuring device.

  In the case of the present embodiment, as will be described later, it is only necessary to count the plot values of only one of the three-phase change amounts (absolute values) shown in FIG.

(Summary)
As described above, the displacement measuring apparatus 100 can simplify the calculation related to the amplitude value of the signal by normalizing the sine wave signal. Further, a triangular wave signal including a linear region is obtained by inverse trigonometric function calculation. The change amount calculation unit 37 calculates the change amount of the signal in the linear region every predetermined time, so that the displacement measuring apparatus 100 can generate an accurate signal and perform highly accurate measurement.

  In addition, individual differences in measurement accuracy due to product manufacturing variations can be absorbed by the normalization process.

  In the present embodiment, the encoder unit 10 has been described as obtaining an ideal three-phase sine wave signal of U, V, and W. Therefore, in FIGS. 4-7, three values are obtained at the same sampling time, and equations (1a)-(1c), (2a)-(2c), (3a)-(3c) The same calculation is performed. In the present embodiment, it is only necessary to obtain a sine wave signal of at least one phase among the three phases, and the encoder unit 10 can be used in any structure as long as it can generate a sine wave signal of at least one phase. . When handling a one-phase sine wave signal, the displacement calculator 39 may count the value obtained as the absolute value shown in FIG. 7 as described above. The reason described as the three phases is to make it possible to efficiently understand the description of the second embodiment to be described later.

  In the above, a computer such as a CPU or a DSP is taken as an example of hardware that implements the processing from the normalization unit 33 to the displacement calculation unit 39. However, the analog circuit may perform processing from the normalization unit 33 to at least one unit including processing by the normalization unit 33, for example. In that case, the output signal of the analog circuit is AD converted, and the subsequent processing is processed with a digital signal. The same applies to the embodiments described below.

The maximum value (Vu ₀ _max, Vv ₀ _max, Vw ₀ _max within the movable range of the scale (or the detection unit) when executing the arithmetic expressions (1a), (1b), (1c) by the above standard part ), Minimum values (Vu ₀ _min, Vv ₀ _min, Vw ₀ _min) may be stored in the memory (storage unit) at the time of product design, manufacture, factory shipment, or the like. The movable range is a range of a scale that can be measured by the displacement measuring apparatus 200 substantially. When the user uses the displacement measuring apparatus 100 (at the time of arbitrary measurement), the normalization unit 33 calculates the arithmetic expressions (1a) and (1) based on the maximum value and the minimum value stored in the storage unit. Normalization may be performed according to 1b) and (1c). Thereby, it is not necessary to obtain the maximum value and the minimum value for standardization for each measurement, the calculation by the standardization unit 33 can be simplified, and the speed of the standardization process can be increased.

  Further, the displacement measuring apparatus 100 may further include an update unit that updates the maximum value and the minimum value. Thereby, even if the amplitude value of the signal fluctuates due to a change with time (aging) of the displacement measuring apparatus 100, the fluctuation can be absorbed and a measurement error can be suppressed. In other words, the updating unit has a function of rewriting the data of the maximum value and the minimum value at a predetermined timing and storing it in the memory. The predetermined timing is a timing desired by the user or a timing at which the displacement measuring apparatus 100 automatically updates under a predetermined condition. Further, the displacement measuring apparatus 100 may have a function of determining the life of the product from the maximum value and minimum value data obtained by the updating unit.

  In addition, storing the maximum value and the minimum value is advantageous in that it is not necessary to use a compensation value for the measurement error for each position with respect to the absolute position of the movable range of the scale (or detection unit). There is also. That is, storing the maximum value and the minimum value eliminates the effort of creating a database of compensation values at the time of product design, manufacture, and the like.

[Second Embodiment]
Next, a displacement measuring apparatus according to the second embodiment of the present invention will be described. In the following description, elements that are substantially the same with respect to members, functions, and the like included in the displacement measuring apparatus 100 according to the first embodiment will be denoted by the same reference numerals, the description thereof being simplified or omitted, and different points. The explanation will be focused on.

  FIG. 8 is a block diagram showing a functional configuration of the displacement measuring apparatus 200 according to the second embodiment. The signal processing device 40 provided in the displacement measuring device 200 is configured to extract a maximum value from, for example, three-phase signals output from the change amount calculation unit 37 and output the maximum value. Is provided. As described above, the hardware of the signal processing device 40 including the extraction unit 32 is realized by a CPU (including RAM and ROM), a PLD, and / or a DSP.

  FIG. 9 is a flowchart showing a signal processing method mainly performed by the signal processing device 40 of the displacement measuring device 200. In FIG. 9, steps 201 to 205 and 207 are substantially the same processing as steps 101 to 106.

  FIG. 10 shows a sine that is output by converting a three-phase sine wave signal (U (0 deg), V (120 deg), W (240 deg)) generated by the encoder unit 10 into a digital signal by the AD conversion unit 31, for example. Wave signal is shown. In this example, based on actual measurement, a diffraction grating having a pattern region with a grating pitch of 3.6 μm was used as a scale. Further, using a stepping motor, the scale (or detection unit) was mechanically moved by a distance of 50 μm in steps of 0.1 μm (= 100 nm).

  Since the three-phase sine wave signal shown in FIG. 10 includes disturbances such as noise and circuit noise due to higher-order interference light of the diffraction grating, the amplitude value and symmetry of each signal are disturbed.

  FIG. 11 shows a three-phase signal in which the normalization unit 33 standardizes the signal from the AD conversion unit by the arithmetic expressions (1a), (1b), and (1c). As shown in the figure, since the original sine wave signal is disturbed as described above, the three-phase amplitude value does not become ± 1.0 even if normalized, and accurate standardization cannot be performed.

  FIG. 12 shows a signal obtained by the inverse trigonometric function computation unit 35 computing the inverse trigonometric function of the three-phase signal normalized by the normalization unit 33 using the arithmetic expressions (2a), (2b), and (2c). Since these signals are also affected by the disturbance, an accurate triangular wave cannot be obtained. Each signal includes a region where linearity is not ensured.

FIG. 13 shows a signal obtained by the change amount calculation unit 37 calculating the change amount of the three-phase signal calculated by the inverse trigonometric function calculation unit 35 using the calculation formulas (3a), (3b), and (3c). In FIG. 13, the angle change amount is converted into a distance change amount (ΔVu ₂ ′, ΔVv ₂ ′, ΔVw ₂ ′). As described above, since the three-phase signal is affected by disturbance, the amount of change is different compared to the case shown in FIG. 7 even though the scale is moved in a predetermined step (0.1 μm). Value.

  Therefore, in the present embodiment, the extraction unit 32 extracts the maximum value of the change amount (absolute value) sampled at the same time from the value calculated by the change amount calculation unit 37 (step 206 in FIG. 9). That is, the maximum value among the values at the same time of the three-phase signal shown in FIG. 13 is output. Thereby, a result as shown in FIG. 14 is obtained. FIG. 14 shows that the stepping motor moving step (0.1 μm) is regularly measured. An error of 0.1 μm ± 23.8 nm was obtained, confirming that high-precision measurement was possible.

  The displacement calculator 39 calculates and outputs the displacement using the extracted maximum value (step 207).

  The extraction target of the extraction unit 32 according to the present embodiment is not limited to the maximum value. The extraction target may be any one of the values from the minimum value to the maximum value that are larger than the minimum value and include the maximum value. For example, the next largest value after the maximum value may be extracted. According to such an extraction unit 32, the encoder unit 10 has a great merit for a displacement measuring device that outputs a plurality of sine wave signals of, for example, four phases or more. The four-phase signal is, for example, a sine wave signal whose phases are shifted by 45 degrees from each other. As the number of signals out of phase increases, the measurement accuracy improves according to the present embodiment.

  For example, as a merit to extract one of the values from the minimum value to the maximum value that is larger than the minimum value and includes the maximum value, if there is high output spike noise as the maximum value, the maximum value is The point which can be excluded is mentioned. Such spike noise can be removed by using a separate filter. However, according to this extraction unit, such a separate filter is not required.

  FIG. 15 shows measurement accuracy when the present inventors use the displacement measuring device 200 to expand the relative movement range of the scale and the detection unit to 1 mm, which is 20 times 50 μm. The amount of movement of one step of the stepping motor was 140 nm.

  As shown in FIG. 15, when the movement range (that is, the measurement range) is widened, the above-described disturbance appears to be emphasized, and the mechanical production accuracy seems to be reduced. Specifically, the amplitude fluctuation of the three-phase sine wave signal of U, V, and W is large. However, even in the case where there is an amplitude variation as described above, in the present embodiment, the maximum value is extracted by the extraction unit 32 as described above. The extracted maximum value is stable. The accuracy of ± 20.2 nm was obtained, and it was confirmed that the compensation function by the extraction unit 32 worked satisfactorily without decreasing the accuracy even when the movement range was widened.

[Third Embodiment]
FIG. 16 is a block diagram showing a functional configuration of a displacement measuring apparatus according to the third embodiment of the present invention. The signal processing device 50 provided in the displacement measuring device 300 further includes a displacement direction acquisition unit 34 in addition to the components of the signal processing device 50 according to the second embodiment.

  The displacement direction acquisition unit 34 calculates the relative displacement of the scale and the detector based on the change amounts of the three-phase signal calculated by the inverse trigonometric function calculation unit 35 and the three-phase signal calculated by the change amount calculation unit 37. It has a function of acquiring direction information and outputting it. The direction of relative displacement means the direction of movement of the other when, for example, one of the scale and the detector is fixed. Specifically, the direction of relative displacement is acquired as follows.

FIG. 17 is a flowchart showing processing in the displacement direction acquisition unit 34. FIG. 18 shows a triangular wave signal obtained by the inverse trigonometric function calculator 35 in an enlarged manner on the time axis. As shown in FIG. 18, the 360 deg phase region can be divided into first to sixth quadrants based on the magnitude relationship of the three-phase signals. The displacement direction acquisition unit 34 includes the inverse trigonometric function signal V ₂ (Vu ₂ , Vv ₂ , Vw ₂ ) obtained by the calculation according to the calculation expressions (2a), (2b), (2c), and the calculation expressions (3a), Based on the change amount signals (ΔVu ₂ , ΔVv ₂ , ΔVw ₂ ) obtained by the calculations of (3b) and (3c), the displacement direction is acquired using the algorithm shown below.

1) First quadrant a) When Vv ₂ ≧ Vu ₂ and Vu ₂ > Vw _2, it is determined as the first quadrant, and when ΔVu ₂ > 0, it is determined as the positive direction. B) Vv ₂ ≧ If Vu ₂ , and Vu ₂ > Vw _2, it is determined as the first quadrant, and if ΔVu ₂ <0, it is determined as a negative direction. Judgment

2) Second quadrant a) When Vu ₂ > Vv ₂ and Vv ₂ ≧ Vw ₂ , it is determined as the second quadrant, and when ΔVv ₂ <0, it is determined as the positive direction. B) Vu ₂ > Vv ₂ , and Vv ₂ ≧ Vw ₂ , it is determined as the second quadrant, and if ΔVv ₂ > 0, it is determined as the negative direction. Determined

3) Third quadrant a) When Vu ₂ ≧ Vw ₂ and Vw ₂ > Vv ₂ , it is determined as the third quadrant, and when ΔVw ₂ > 0, it is determined as the positive direction. B) Vu ₂ If ≧ Vw ₂ , and Vw ₂ > Vv ₂ , it is determined as the third quadrant, and if ΔVw ₂ <0, it is determined as the negative direction. Determined

4) Fourth quadrant a) If Vw ₂ > Vu ₂ and Vu ₂ ≧ Vv ₂ , determine the fourth quadrant, and if ΔVv ₂ <0, then determine positive direction b) Vw ₂ > Vu ₂ , and Vu ₂ ≧ Vv ₂ , it is determined as the fourth quadrant, and if ΔVv ₂ > 0, it is determined as the negative direction. Determined

5) 5th quadrant a) When Vw ₂ ≧ Vv ₂ and Vv ₂ > Vu ₂ , it is determined as the 5th quadrant, and when ΔVu ₂ > 0, it is determined as the positive direction. B) Vw ₂ If ≧ Vv ₂ and Vv ₂ > Vu ₂ , it is determined as the fifth quadrant, and if ΔVu ₂ <0, it is determined as the negative direction. Determined

6) Sixth quadrant a) When Vv ₂ > Vw ₂ and Vw ₂ ≧ Vw ₂ , it is determined as the sixth quadrant, and further, when ΔVw ₂ <0, it is determined as the positive direction. B) Vv ₂ > Vw ₂ , and Vw ₂ ≧ Vw ₂ , it is judged as the 6th quadrant, and if ΔVw ₂ > 0, it is judged as negative direction. Determined

  That is, as shown in FIG. 17, the displacement direction acquisition unit 34 specifies the current quadrant (phase region) based on the inverse trigonometric function signal (step 301). And the displacement direction acquisition part 34 specifies a displacement direction based on the specified quadrant and the variation | change_quantity calculated by the variation | change_quantity calculation part 37 (step 302). These steps 301 and 302 are executed after step 206 shown in FIG. 9, for example.

In the method of determining the positive / negative polarity in the above (ΔVu ₂ , ΔVv ₂ , ΔVw ₂ ), the amount of change in the signal other than the above may be used. For example, in the above case of the first quadrant, the positive direction in the case of ΔVu _2> 0, but is determined to negative direction in the case of ΔVu ₂ <0, the forward direction in the case of ΔVv ₂ <0, ΔVv _A negative direction may be determined when ₂ > 0.

  For example, the apparatus of Patent Document 2 uses a method in which the phase region is divided into 12 quadrants, and the current angular position and moving direction of the encoder are directly calculated by inverse trigonometric function calculation. Therefore, it is necessary to perform a complicated calculation as described in paragraph [0019] of the specification. On the other hand, the signal processing method according to the present embodiment specifies the polarity in the movement direction based on the amount of change, and thus does not require complicated calculation as in Patent Document 2.

  The paragraph [0023] of Patent Document 2 states that “the method of the present invention has a periodic error of only ± 0.6% due to harmonics, which is lower than the harmonic error in the prior art method. It has ". On the other hand, in the second embodiment and the third embodiment, errors due to harmonics can be suppressed in this way.

[Encoder section]
As an example of the encoder unit 10, a known encoder including, for example, International Publication No. 2011/043354, Japanese Patent Application Laid-Open No. 2014-102260, Japanese Patent Application Laid-Open No. 2014-102260, or the like can be employed. Known encoders cited as these documents are applicable to the above-described embodiments of the present invention. Of the pair of diffraction gratings disclosed in these documents, a diffraction grating that moves integrally with the light source corresponds to a “scale”, and a PD (Photo Detector) corresponds to a “detector”.

  In each of the above known documents, an example in which a pair of diffraction gratings move in a direction in which they are separated from each other is disclosed, but even if the diffraction gratings move relative to each other along the arrangement direction of the grating patterns (grid lines), the same applies. The displacement can be measured. Such a form is also applicable to the first to third embodiments of the present invention.

[Other Embodiments]
The present invention is not limited to the embodiment described above, and other various embodiments can be realized.

  The present invention can be applied to any type of encoder unit such as an electromagnetic induction type, a magnetic type, and a capacitance type in addition to an optical type as long as it has an encoder unit capable of obtaining a sine wave as an electric signal. Applicable. Moreover, it is not restricted to a linear encoder, A rotary encoder may be sufficient. In the case of a rotary encoder, “displacement” is measured as a displacement of a rotation angle.

  The scale of the optical encoder is not limited to the one that obtains interference light using a diffraction grating as described above. A scale having a plurality of slits that transmit light from the light source (a scale in which light transmission regions and blocking regions are alternately arranged) may be used.

  Although the encoder unit 10 according to each of the above embodiments outputs an analog signal, the encoder unit may include an AD conversion unit and have a function of outputting a digital signal. In this case, the first stage AD conversion unit is not required in the signal processing apparatus.

  The change amount calculation unit 37 according to each of the above embodiments calculates the change amount at the sampling interval as the change amount every predetermined time. However, the change amount calculation unit 37 may have a longer interval. That is, the predetermined time may be an interval for each of a plurality of samplings.

It is also possible to combine at least two feature portions among the feature portions of each embodiment described above. For example, the displacement measuring apparatus 100 according to the first embodiment may include the displacement direction acquisition unit according to the third embodiment (without the extraction unit as in the second embodiment).
Alternatively, the storage and updating of the maximum value and the minimum value described in the first embodiment can be applied to the second and third embodiments.

DESCRIPTION OF SYMBOLS 10 ... Encoder part 30, 40, 50 ... Signal processing apparatus 30 ... Signal processing part 31 ... AD conversion part 32 ... Extraction part 33 ... Normalization part 34 ... Displacement direction acquisition part 35 ... Inverse trigonometric function calculation part 37 ... Change amount calculation 39: Displacement calculation unit 100, 200, 300 ... Displacement measuring device

Claims (9)

An encoder unit having a scale and a detector and generating a periodic signal according to the relative displacement between the scale and the detector;
A normalization unit that normalizes the signal generated by the encoder unit;
An inverse trigonometric function calculation unit for calculating an inverse trigonometric function of the signal normalized by the normalization unit;
A displacement measuring device comprising: a change amount calculation unit that calculates a change amount of the signal calculated by the inverse trigonometric function calculation unit every predetermined time. The displacement measuring apparatus according to claim 1,
The encoder unit generates a plurality of signals having different phases. The displacement measuring device according to claim 2,
Each of the absolute values of the plurality of signals calculated by the change amount calculation unit is acquired, and among the acquired absolute values at the same time, the minimum value is greater than the minimum value, and includes the maximum value, and the maximum value to the maximum The displacement measuring device which further comprises the extraction part which extracts any one among the values to a value. The displacement measuring apparatus according to claim 3,
The extraction unit is a displacement measuring device that extracts the maximum value. The displacement measuring device according to any one of claims 2 to 4,
Information on the direction of relative displacement of the scale and the detector based on the change amounts of the plurality of signals calculated by the inverse trigonometric function calculation unit and the plurality of signals calculated by the change amount calculation unit. A displacement measuring device further comprising a displacement direction obtaining unit for obtaining The displacement measuring device according to any one of claims 2 to 5,
A storage unit for storing a maximum value and a minimum value of the signal generated by the encoder unit within a range in which relative movement between the scale and the detection unit is possible;
The said normalization part performs the normalization using the maximum value and minimum value which were memorize | stored in the said memory | storage part. Displacement measuring device. The displacement measuring device according to claim 6,
A displacement measuring device further comprising an updating unit for updating the maximum value and the minimum value. A signal processing device that processes the signal output from the encoder unit that generates a periodic signal according to the relative displacement between the scale and the detector,
An encoder unit that generates a periodic signal according to the relative displacement between the scale and the detector;
A normalization unit that normalizes the signal generated by the encoder unit;
An inverse trigonometric function computing unit that computes a signal normalized by the normalization unit into an inverse trigonometric function;
A signal processing device comprising: a change amount calculation unit that calculates a change amount of the signal calculated by the inverse trigonometric function calculation unit every predetermined time. A signal processing method for processing the signal output from the encoder unit that generates a periodic signal according to the relative displacement between the scale and the detector,
Generating a periodic signal according to the relative displacement between the scale and the detector;
Normalize the generated signal,
Calculate the inverse trigonometric function of the normalized signal,
A signal processing method for calculating a change amount of the calculated signal per predetermined time.