JP2000088607A - Flashing type dimension measuring apparatus using optical scale - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the measuring resolution fine by taking the sum of a travel distance equal to an integer multiple of a grating pitch detected by a grating moving counter and a travel distance less than a pitch detected by a grating stop position detector for the travel distance. SOLUTION: A flashing controller 13 blinks a light source 10 at fixed time intervals to intermittently illuminate a grating. A lighting pulse counter 15 detects and stores the light pulse number during moving of the grating by a pitch length in a specified section, and a lighting pulse counter 16 detects and stores a fist lighting pulse number from the grating stop position to a next grating reference position and a second lighting pulse number from a grating reference position just before stopping to a stop position. A grating stop position detector 17 compares both lighting pulse numbers to obtain a grating stop position and a travel distance less than one grating pitch length. A grating moving counter 19 counts up-/down of the moving unit number according to the moving direction to obtain the travel distance equal to an integer multiple of the grating pitch length, and, from the sum of both, the travel distance of a moving scale 11 is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a configuration of a stylus type dimension measuring apparatus using an optical scale for realizing a measuring resolution in a submicron region.

[0002]

2. Description of the Related Art In production lines for precision parts and the like, there is a strong need to measure the dimensions and shapes of workpieces on the spot with an accuracy in the micrometer range, and there is a strong demand for submicron (up to 0.1).
A measuring instrument having a resolution of (μm) is required. Conventionally, as a simple measuring device, a dimension measuring device of a system in which a linear grid (a fine linear grid pattern) is attached to a stylus and moved, and the movement of the stylus is optically read, is often used. This measuring device irradiates the grating with light, detects a light intensity signal that changes with the movement of the stylus, performs various kinds of signal processing, and measures dimensions from the moving distance of the grating. For this reason, the technology for realizing a submicron resolution becomes important for the above dimension measuring device.

FIG. 5 shows a configuration example of a conventional dimension measuring apparatus using an optical scale, and the measuring operation will be described. Light emitted from a light source 50 such as a white lamp or a light emitting diode (LED) illuminates a moving scale 52 via a collimating lens 51. The moving scale 52 is a stylus (not shown)
Moves in the directions A and B indicated by the arrows with the movement of the arrow, and measures the distance by detecting the movement distance. Moving scale 5
Reference numeral 2 denotes that a linear grating having a binary light transmission intensity distribution is formed on a glass substrate, and both the grating width of the black pattern portion that does not transmit light and the gap width of the white pattern portion that transmits light are a.
/ 2, one pitch length of the grating is a. A normal pitch length of one grating is about 10 μm, and the length a is a reference scale for dimension measurement.

[0004] Behind the movable scale 52, there are provided two fixed scales 53 and 54 which are fixed and do not move. The fixed scales 53 and 54 are individually formed at different positions on one glass substrate, each grid shape is equal to the grid shape of the moving grid 52, the grid width and the gap width are both a / 2, and the grid pitch length is one. Is also a. At this time, the positions of the gratings of the fixed scales 53 and 54 are shifted from each other by a / 4, and the grating positions are set so that the phase difference becomes π / 2. Two light receivers 535 and 545 are installed behind the fixed scales 53 and 54, and the light intensity transmitted through the moving grating 52 and the fixed gratings 53 and 54 are individually detected to generate two transmitted light signals 55 and 56. Output. In the above configuration, the light source 50 is continuously lit to illuminate the grid, and detects a temporally continuous light transmitted light signal.

Two transmitted light signals (two-phase signals) 55 and 56
Is a signal whose light intensity changes sinusoidally in accordance with the movement of the moving scale 52. Since the phases of the fixed scales 53 and 54 differ by π / 2, the phases of the signals 55 and 56 also differ by π / 2. ing. The signal processing unit 57 performs arithmetic processing on the two-phase signals having different phases, and detects a moving direction and a moving distance of the moving scale 52 to measure a dimension. The resolution of the dimension measurement is determined by the detection accuracy of the movement distance of one pitch length a or less of the grating. Therefore, for high-resolution measurement, it is important to finely divide one pitch of the grating to detect the stopping position of the grating. For example, when a = 10 μm, 0.1 μm
In order to achieve a resolution of m
It is necessary to detect the stop position of the grid by dividing it by zero.

FIG. 6 shows an example of a light intensity signal detected by the above method, and a conventional signal processing method will be described. The sine wave signals 60 and 61 whose phases have been shifted by π / 2 are two-phase signals obtained by passing through the moving scale 52 and the fixed scales 53 and 54, and are defined as A-phase signals and B-phase signals, respectively. Where A
The movement direction of the movement scale 52 indicated by the arrow is determined by detecting the relationship between the leading and lagging phases of the phase signal 60 and the B-phase signal 61. In the example of the figure, the phase of the A-phase signal 60 is advanced, and for example, it is determined that the moving scale 52 is moving in the A direction indicated by the arrow. If it moves in the opposite direction, A-phase signal 6
It is determined that the phase relationship between 0 and the B-phase signal 61 is inverted, and the signal is moving in the B direction indicated by the arrow. According to this moving direction,
The number of moving grids of the moving scale 52 is detected by an up / down type counter circuit. In this case, for example, if one pulse is generated in one cycle of the A-phase signal 60 and the number of movements of the grating is measured, a movement distance that is an integral multiple of the pitch length a of the grating can be detected from the number of movements.

A method of detecting the phase of a sine wave signal is used to divide one pitch length a of the grating. However, when viewed with a single sine wave signal, there are two phase states for a particular intensity, so that the phase cannot be directly detected from the intensity alone. It is necessary to detect the phase quadrants (1 to 4) in advance in order to detect the phases in a distinguished manner. Table 63 in FIG. 6 shows the relationship between the intensity code of the two-phase signal and the phase quadrant. A
When the phase of the phase signal 60 is ahead of the phase of the B-phase signal 61, for example, when the intensity of the A-phase signal 60 is positive and the intensity of the B-phase signal 61 is negative, the phase becomes the second quadrant (π / 2
π). When the phase quadrant is determined, the sine wave intensity directly corresponds to the phase. Therefore, the intensity of the A-phase signal 60 is normalized, and the phase is determined by referring to a trigonometric function table. In this way, the phase of the grating is calculated from the phase of the sine wave signal.
The distance between the pitches is finely divided to detect a moving distance of one pitch length or less of the grating, and the dimension is measured from the sum of the moving distance and an integral multiple of one grating pitch length.

[0008]

In dimensional measurement using an optical scale, the greatest factor that determines the measurement resolution is the accuracy with which one grating pitch is divided to detect the stop position of the grating. The more finely divided one pitch of the grating is detected, the more accurately the moving distance of one grating length or less can be measured and the resolution is improved. The conventional measuring device converts the intensity of the sine wave at the position where the grating is stopped into a phase and detects the moving distance of one pitch length or less of the grating, but the phase is directly calculated from the intensity of the sine wave signal. However, the following complicated processing was required because of no detection. In the case of a sine wave signal, since two different phases correspond to one intensity value, it is necessary to determine in advance which phase quadrant (1 to 4) the phase is in before detecting the phase. Was. For this purpose, the amplitudes of the two-phase sine wave signals having different phases are both normalized to ± 1, the sign of the intensity of the normalized signal at the grating stop position is determined, and the phase is detected after the phase quadrant is determined. In the phase detection, a trigonometric function table for reference is required when converting the normalized intensity into a phase, and there is a problem that hardware and software for determining the phase are complicated.

When one pitch length of the grating is 10 μm, the pitch is 0.1 mm.
To realize a resolution of 1 μm, the phase of the sine wave signal should be about 3
It is necessary to measure within a degree error, for which the intensity value of the sine wave must be detected with an error within 1%. That is, since the resolution of the dimension measurement depends on the detection accuracy of the signal intensity, the sine wave signal must be accurately detected using a high-resolution photodetector circuit. In addition, if the transmittance distribution at the time of forming the grating fluctuates, the light intensity transmitted through the grating fluctuates, causing an error in phase detection. Furthermore, if the detected light intensity signal is modulated from an ideal sine wave, an error occurs when converting to a phase,
There is also a problem that the dimension measurement accuracy is reduced. In order to solve the above-mentioned problems, the present invention detects a moving distance equal to or less than one pitch length of a grating from information on the number of time-discrete light intensity signals without detecting a phase from the light intensity information. It is intended to realize a measurement resolution of.

[0010]

In order to solve the above-mentioned problems, a flushing type dimension measuring apparatus using an optical scale according to the present invention has the following arrangement. From a moving scale on which a grid having a constant pitch and shape that moves with the stylus is formed, and a fixed scale fixed and installed near the moving scale with the same pitch and shape as the grid of the moving scale An optical scale comprising a light source that illuminates a grating of the optical scale, and a size using an optical scale that measures the size by detecting the intensity of transmitted light transmitted through the grating that changes with the movement of the stylus. In the measurement device, a light source capable of high-speed switching of lighting and non-lighting, a flashing control unit that repeatedly controls lighting and non-lighting of the light source at a constant frequency, and the light source is synchronized when the light source is turned on. An optical signal detector that detects transmitted light from the grating to generate a plurality of light intensity signals; and A moving direction determining unit that detects a direction in which the moving scale moves; a grid moving counting unit that counts the number of grid movements according to the moving direction of the grid from the light intensity signal; and The first lighting pulse number, which is the number of times the light source is turned on while the grating moves one pitch, is detected, and the lighting pulse number in a specific section near the movement start point and the movement stop point is stored. A first lighting pulse counting unit, and one pitch length of the grid for each of a moving period from the moving start point of the moving scale to the next grid position and a moving period from the grid position immediately before the moving stop point to the moving stop point. A second lighting pulse counting unit for detecting and storing a second lighting pulse number which is the number of times the light source is turned on while moving the following distance; and a first lighting pulse number and a second lighting pulse. Compare the numbers A grid stop position detection unit that measures a distance between a movement start point of the moving scale and a next grid position and a distance between a grid position immediately before the movement stop point and a movement stop point; The dimension is measured by detecting the moving distance of the moving scale from the sum of the moving distance that is an integral multiple of the pitch length of the grating detected by the counting unit and the moving distance that is equal to or less than the pitch length of the grid detected by the grid stop position detecting unit. I do.

Further, the lattice stop position detecting section is provided with the first stop.
Calculate the change in the number of the first lighting pulses detected and stored by the lighting pulse counting section to determine the moving speed of the moving scale in each of the vicinity where the moving scale starts moving and the vicinity where the moving scale stops moving. The grid is 1 in the two sections
While calculating the number of reference lighting pulses to be lighted during the period in which the pitch is moved, calculating the ratio between the number of second lighting pulses detected and stored by the second lighting pulse counter and the number of reference lighting pulses. The movement distance of the grating of one pitch length or less is measured. When the fixed scale is composed of two sets of fixed gratings having different phases, the fixed scale generated by the optical signal detection unit is used.
A difference intensity signal creating unit that creates a difference intensity signal that is an intensity difference between the light intensity signals of the phases is provided, and a peak intensity position of the difference intensity signal is used as a reference position of a lattice. The number of movements of an integral multiple of one pitch of the grid is counted, and the grid reference position is set to the first
Are the reference positions for detecting the number of lighting pulses and the second number of lighting pulses.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is directed to a method in which a pitch of one grating
It is divided into zero or more to detect the moving distance of less than one pitch length of the grating with high accuracy, and the measurement resolution in the submicron region (~
0.1 μm). For this purpose, a light intensity signal that changes with the movement of the grating is discretized on the time axis, and information on the number of discrete signals is detected to measure the movement distance of the grating. In order to obtain a discrete signal, a light emitting element such as a semiconductor laser or a light emitting diode, which can be turned on and off at a high speed (blinking) is used as an illumination light source of a grid, and the light source is turned on and off at a constant frequency (for example, 10 MHz). The grid is intermittently illuminated by repeated lighting.
This operation is referred to as grid illumination flushing. Transmitted light from the grating is received and photoelectrically converted in synchronization with the timing of turning on the light source, and a discrete light intensity signal is detected.

If the fixed scale is composed of two grating groups having different phases, two-phase discrete signals having different phases can be obtained by moving the moving scale. At this time, for example, one of the two-phase signals is used to detect the number of times the light source is flushed when the grating moves (the number of lighting pulses). Since the pitch length of the grating and the flushing frequency are constant, the number of lighting pulses detected during movement of the grating includes information on the moving distance and moving speed of the grating. However, since the number of lighting pulses changes according to the moving speed of the lattice, the detected number of lighting pulses cannot be used as a reference for the length. Therefore, the moving speed of the grating is determined from the detected change in the number of lighting pulses, and the reference number of lighting pulses when the grating moves by one pitch is calculated by calculation at the moving speed. The number of lighting pulses is converted into a distance using the estimated reference lighting pulse number as a length reference.

In the dimension measurement using the flashing method, the number of the following two types of lighting pulses are detected, and the moving speeds near the position where the grating starts moving and the position where the grating stops are determined, and the grating speed is equal to or less than one pitch length of the grating. Measure the distance traveled. The first detection is the detection of the number of lighting pulses flashed while the grating moves one pitch (referred to as the first number of lighting pulses). The first detection is performed in two sections near the movement start position and the movement stop position of the grating. The detected number of lighting pulses is stored in a memory circuit. Second
Is a detection when the grid moves one pitch length or less, and is a detection of a period from the position where the grid starts moving to the next grid position and a period between the grid position immediately before the grid stops and the stop position. For each of them, the number of flashing pulses (called the second number of lighting pulses) when the grating has moved a distance of one pitch length or less is detected, and the number of lighting pulses detected in both periods is stored in the memory circuit.

When the grid is moving at a constant speed, the first number of lighting pulses detected when the grid moves by one pitch serves as a reference for the distance. Therefore, a moving distance of one pitch length or less of the grating is detected from the proportional relationship between the first lighting pulse number and the second lighting pulse number. However, in general, the moving speed of the moving scale is not constant, and the first number of lighting pulses fluctuates in accordance with the movement of the grid, and cannot be a reference for the distance. In particular, since the grid moves at a low speed when it starts to move, a simple proportional relationship like when the grid moves at a constant speed does not hold, and it is necessary to determine and correct the moving speed of the grid. Therefore, when the grid starts moving, the moving speed immediately after the start of movement is determined from the change in the number of first lighting pulses detected and stored in a period of several cycles near the moving start position. Calculates the reference lighting pulse number when moves by one pitch. This reference pulse number is an estimated value obtained by calculation. Since the reference number of lighting pulses serves as a reference for the length of one pitch of the grating at the movement start position, the moving distance of less than the length of one grating pitch is determined from the proportional relationship with the second number of lighting pulses detected at the start of movement. To detect. The same applies to the case where the moving grid stops.

The above-described measurement is for detecting a moving distance equal to or less than one pitch length of the grating. However, the dimension measurement requires determination of the moving direction of the grating and counting of the number of movements of one grating pitch according to the moving direction. The moving direction is determined by comparing the leading and lagging phases of two-phase sinusoidal signals having different phases as in the conventional method. The number of movements of the grid is detected by a counter circuit using one of the two-phase sine wave signals in the same manner as the detection of the number of lighting pulses, and the movement distance is an integral multiple of one pitch length of the grid. Is detected. As another method, a difference signal which is the difference between the intensities of the two-phase sine wave signals may be created, and the number of movements of the grating may be counted using the peak intensity position of the difference signal as the reference position of the grating. The dimensions are measured from the sum of the moving distance of the integral multiple of one pitch of the grating and the moving distance of one pitch or less of the grating, obtained by the above means.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of a configuration of a dimension measuring apparatus using an optical scale according to the present invention. Light emitted from a light source 10 capable of high-speed switching between lighting and non-lighting by electric control such as a light emitting diode is transmitted to a collimating lens 1.
Irradiation is performed on the grating of the optical scale composed of the moving scale 11 and the fixed scale 12 through 05. That is, the light source 1
The grid is intermittently illuminated by blinking 0. The moving scale 11 is composed of a linear grating in which a white pattern that transmits light and a black pattern that does not transmit light are alternately formed on a glass substrate, and is attached to a stylus (not shown).
-Move in the B direction. Assuming that one pitch length of the lattice is a, the widths of the white and black patterns are both a / 2. Usually a
= 10 μm is used, and the length a is a reference scale for dimension measurement.

The fixed scale 12 is composed of two grating groups 122 and 124 having different phases, each having the same pitch and shape as the grating of the moving scale 11. Behind the fixed scale 12, two light receivers 126 and 128 are provided.
Is provided, and the light transmitted through the grids of the movable scale 11 and the fixed scale 12 is individually detected. As in the conventional example, when the phases of the grating groups 122 and 124 are set to be shifted by a / 4, when the moving scale 11 moves, the phase becomes π /
Two different two-phase sine wave signals are obtained. Since the present invention does not detect the phase of the sine wave signal, the two-phase signal simply needs to be shifted in phase, and need not necessarily be shifted by a / 4 as described above. When the optical scale having the above configuration is used, it is important how to finely divide one pitch of the grating to detect a moving distance equal to or less than one pitch length of the grating. In the case of obtaining a resolution of 0.1 μm with a grating of a = 10 μm, it is necessary to divide one pitch of the grating into 100 or more for detection.

The flashing control unit 13 emits a signal 130 having a predetermined fixed frequency to perform a flashing control of repeating the lighting and non-lighting of the light source 10 at fixed time intervals. The grid is intermittently illuminated (flashing). The frequency of the signal 130 is determined based on the moving speed of the moving scale 11, the pitch length of one grating, and the required measurement resolution. For example, when the moving scale 11 moves at a speed of 1 m / sec, when detecting the distance between one pitch of a 10 μm grid by 100, it is 10
Flashing may be performed at a frequency of about MHz, and the light emitting diode can sufficiently perform such high-speed switching operation. The optical signal detection unit 14 synchronizes with the lighting timing of the flashing control unit 13 and
The transmitted light from the grating received at 28 is photoelectrically converted to create a two-phase light intensity signal. The light intensity signal created here is a discrete signal that is discontinuous in time. The present invention detects the number of times the light source 10 is turned on (the number of lighting pulses) while the grating is moving, converts the number information of the lighting pulses into length information, and determines the moving distance of one grating pitch or less. To detect. On the other hand, the conventional dimension measuring device detects the intensity value of a temporally continuous light intensity signal and converts it into a phase.

In order to detect the number of lighting pulses, one of the two-phase discrete signals detected by the optical signal detector 14 is used to count the number of times the light source 10 is turned on by the signal 130. Count in the circuit. At this time, the peak intensity position of one of the discretized sine wave signals may be used as a reference point of the grid as a trigger point of the counter operation, and the number of lighting pulses may be counted. Alternatively, binarization processing may be performed using the intermediate intensity of the sine wave signal as a slice level, and the rising or falling position of the binarized signal may be set as the reference position of the lattice. Furthermore, the difference intensity signal creation unit 145 may create a difference intensity signal which is an intensity difference between the two-phase signals, and set the position of the peak intensity as the reference position of the lattice. In the present invention, the following two types of lighting pulse numbers are counted.

The first lighting pulse counting unit 15 controls the light source 10 while moving one pitch length, which is the distance between the reference positions of the grating.
Detects the number of flashing lighting pulses and stores the number of lighting pulses in a specific section of movement in a memory circuit.
The first number of lighting pulses is detected over the entire period of movement of the grid, but is detected during a period of several cycles after the grid reference position immediately after the grid starts moving and before the grid reference position immediately before the grid stops. The number of lighting pulses in a period of several cycles is stored in a memory circuit. Since the flushing frequency and the length of one pitch of the grating are constant, the first lighting pulse number includes length information of one pitch of the grating, and is used as reference data when converting the number of signals into a length.

The second lighting pulse counting section 16 calculates a period from the position where the grid is stopped to the next grid reference position that starts moving, and a period between the grid reference position immediately before the grid is stopped and the position where the grid is stopped. For the two times, the number of second lighting pulses that flush the light source 10 in each period is detected,
Store in the memory circuit. Therefore, the detection of the second lighting pulse number is a special case of the detection of the first lighting pulse number, and is detected when the grating is moved by one pitch length or less. The stop position of the lattice described above includes not only the state where the stylus is physically stopped but also the moment when the stylus hits the object to be measured. When the stylus hits the object under test and the stylus recoils, the light intensity signal changes in the direction in which the intensity reverses, so detecting the inversion of the intensity stops the movement at the moment the stylus hits the object under test. The position can be detected. In the above-described detection of the number of lighting pulses, the number of lighting pulses includes information on the moving distance, but the number changes according to the moving speed of the lattice.

The grating stop position detecting section 17 detects the stop position of the grating by comparing the first lighting pulse number and the second lighting pulse number, and measures the moving distance of one grating pitch or less.
If the moving scale 11 is moving at a constant speed, the first
Since the number of lighting pulses is the reference for the length, a moving distance of one pitch length or less of the grating is obtained from a simple proportional relationship between the first lighting pulse number and the second lighting pulse number. But,
In an actual operation, since the moving speed of the moving scale 11 is not constant, the first lighting pulse number does not serve as a reference for the distance, and it is necessary to determine and correct the moving speed. In general,
When the grid starts to move, it moves at a low speed, then moves at a constant speed, and comes into contact with the object and stops. When the lattice starts to move, the moving speed at the start of the movement is estimated from the change in the first lighting pulse number detected and stored during the period of several cycles at the beginning of the movement. When the grid linearly increases the moving speed, the change in the number of first lighting pulses is applied to a regression line to determine the moving speed. In the case of non-linear movement, the moving is performed from a regression equation of a higher-order function. Determine the speed. The same applies when the grid stops.

From the movement speeds near the movement start and movement stop positions determined as described above, a reference lighting pulse number to be lighted during a period in which the grating moves one pitch length at the movement speed is calculated. This value is an estimated value calculated. Since the length of one pitch of the lattice is constant, the reference lighting pulse number obtained during the period in which the lattice moves one pitch at the moving speed serves as a reference for the distance. Therefore, the moving distance of the grating by one pitch or less is measured from the proportional relationship between the reference lighting pulse number and the second lighting pulse number. The detection of the movement distance is performed twice when the movement of the lattice starts and when the movement stops. One pitch of grid is 10μ
m, the flushing frequency is 10 MHz, and the moving speed of the grating is 1 m / sec. Since one lighting pulse corresponds to 0.1 μm, submicron resolution is possible. In the above intermittent illumination method, the measurement resolution is determined by the frequency at which the light source is flushed, so that the higher the flushing frequency, the higher the measurement resolution.

In the dimensional measurement, it is necessary to detect not only the above-described movement distance equal to or less than the grating one pitch length, but also the movement distance that is an integral multiple of the grating one pitch length and the grating movement direction. The moving direction determining unit 18 detects the direction in which the moving scale 11 moves based on the leading and lagging of the mutual phases of the two-phase discrete sine wave signals detected by the optical signal detecting unit 14. The grid movement counting section 19 performs an up / down type counting operation according to the moving direction of the grid, and counts the number of grid movements.
Here, a moving distance that is an integral multiple of one pitch length of the grating is detected. This counting operation is performed simultaneously with the detection of the number of lighting pulses. The distance that the moving scale 11 has moved, that is, the dimension, is measured from the sum of the detected moving distance equal to or less than the grating one pitch length and the moving distance that is an integral multiple of the grating one pitch length.

FIG. 2 shows an example of detection of the number of lighting pulses by showing an example of a discrete signal. The signal 20 is a differential intensity signal generator 1
In the difference signal waveform which is the intensity difference between the two-phase signals detected at 45, black points indicate light intensity detected when the light source 10 is turned on, and positions 201, 202, and 203 at which positive peak intensity is obtained.
Are reference positions of the grating (one period corresponds to one pitch length of the grating). Using the position as a trigger point of the counter operation, the number of lighting pulses, which is the number of times the light source 10 is turned on, is detected. The position 21 is the position where the grating starts to move, and the second number of lighting pulses is detected during a period in which the grating moves by a distance equal to or less than one pitch length of the grating between the positions 21 and 201, and the number of lighting pulses is Ps. Suppose.

The first number of lighting pulses is detected during a period in which the grating moves one pitch length between the positions 201 and 202,
It is assumed that the number of pulses at that time is P1. Next position 2
The number of pulses detected when moving between the periods 02 and 203 is P2. For example, the first lighting pulse numbers P1, P2, P3, and P4 detected in the period of four cycles after the position 201 are stored. When the moving scale 11 starts moving,
The moving speed is not constant, but changes so that the speed increases with the movement. Since the flashing cycle of the light source 10 is constant, the number of detected lighting pulses is not constant, and P1
>P2>P3> P4. On the other hand,
Since the pitch length is constant, the detected first number of lighting pulses includes information on the distance. However, the fact that the number is not constant does not serve as a reference for the distance. For this purpose, the moving speed of the moving scale 11 is determined, and the number of lighting pulses serving as a reference for the moving distance is calculated.

FIG. 3 shows an example of calculating the reference lighting pulse number as a reference of the moving distance by showing the change of the first lighting pulse number after the grid starts moving. The horizontal axis in the figure is the moving section, and the vertical axis is the number of lighting pulses. The figure shows an example in which the moving speed increases with the movement of the lattice and moves at a constant speed, but what is important is a change in speed near the movement start position. When the moving speed linearly increases up to the fourth period near the movement start position, the data of P1 to P4 are approximated by a linear regression equation, and the reference lighting pulse number P0 immediately after the start of the movement is detected. This P0 is the number of lighting pulses at which the grid moves one pitch length when the grid starts moving, and is a reference when converting the number of lighting pulses into distance. Therefore, based on the second lighting pulse number Ps, the moving distance of the grid 1 pitch length or less at the position where the grid starts moving is aPs / P0. The same is true when the grid stops moving.

FIG. 4 shows another example of the discrete signal similar to FIG. The waveform 40 in FIG. 4 shows a case where the intensity level of the discrete signal fluctuates in accordance with the movement of the grating. If there is a change in the transmittance at the time of creating the grating, the intensity level changes. In the present invention, for example, a positive peak intensity position of the light intensity signal is detected and used as a reference position for detecting the number of lighting pulses. However, the peak intensity position is not affected by a change in the intensity level. Therefore, in the present invention, stable dimensional measurement can be performed even when the intensity level varies.
As described above, according to the present invention, a submicron measurement resolution can be realized by converting the number of times the light source is turned on by intermittent grating illumination into a moving distance. Although the present invention has been described as an operation as a dimension measuring device, it can be applied to a precise positioning device and the like.

[0030]

As described above, the dimension measuring apparatus according to the present invention intermittently illuminates the moving scale and fixed scale gratings, detects a signal that has been discretized in time, and detects the number of times the light source is flushed. This is a configuration for detecting a moving distance of one pitch length or less. The conventional analog method of continuously illuminating the light source and detecting the phase from the intensity of the continuous signal is a problem in that the resolution is determined by the detection accuracy of the intensity of the sine wave signal, and fluctuations in the signal intensity level result in measurement errors. There is.
Since the present invention is a digital method for measuring the number of pulses of a signal for turning on a light source, the number of lighting pulses is not affected even if the intensity level of the signal fluctuates, and the measurement is highly reliable. Further, since the measurement resolution in the present invention depends on the flashing frequency, the measurement resolution can be easily improved by increasing the flushing frequency.

Conventionally, when the phase is detected from the light intensity signal, there has been a problem that the calculation processing of the phase detection becomes complicated, such as the necessity of a light intensity standardization process and a conversion table of a trigonometric function. Since the present invention only needs to detect the number of lighting pulses, the above-described complicated arithmetic processing is not required, and hardware and software can be simplified. Also,
The conventional method requires two-phase sinusoidal signals whose phases are exactly π / 2 different from each other, and it is necessary to accurately shift the phases of two sets of fixed-scale gratings by a / 4. In the present invention, the two-phase signal is used only for determining the moving direction of the lattice, and the number of lighting pulses is detected using either one of the two-phase signals or only the differential signal. The phase simply needs to be shifted. Therefore, it is only necessary to roughly set the phase relation of the grating, and there is an advantage that the setting is simplified.

[Brief description of the drawings]

FIG. 1 is a system block diagram illustrating a configuration example of a dimension measuring device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of detecting the number of lighting pulses from a discrete signal according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating detection of a moving speed of a grating according to the embodiment of the present invention.

FIG. 4 is a diagram illustrating another example of a discrete signal according to the embodiment of the present invention.

FIG. 5 is a diagram showing a configuration example of a conventional dimension measuring device.

FIG. 6 is a waveform chart showing an example of detecting a phase by a conventional dimension measuring device.

[Explanation of symbols]

 Reference Signs List 10 light source 11 moving scale 12 fixed scale 13 flashing control unit 14 optical signal detecting unit 15 first lighting pulse counting unit 16 second lighting pulse counting unit 17 grid stop position detecting unit 18 moving direction determining unit 19 grid moving counting unit

Claims (3)

[Claims] 1. A moving scale on which a grating having a constant pitch and shape that moves with a stylus is formed, and is fixedly installed near the moving scale with the same pitch and shape as the grating of the moving scale. An optical scale consisting of a fixed scale and a light source for illuminating the grating of the optical scale, and measuring the size by detecting the intensity of transmitted light transmitted through the grating that changes with the movement of the stylus. In a dimension measuring device using an optical scale, a light source capable of high-speed switching of lighting and non-lighting, a flashing control unit for repeatedly controlling the lighting and non-lighting of the light source at a constant frequency, and the light source being lit Sometimes an optical signal detector that detects transmitted light from the grating in synchronization and generates a plurality of optical intensity signals, and the phase advance of the optical intensity signal created by the optical signal detector The moving direction judgment unit in which the movable scale is detected the direction of movement of Les relationship,
A grating movement counting unit that counts the number of movements of the grating according to the movement direction of the grating from the light intensity signal, and the light source is turned on while the grating moves one pitch while the movement scale is moving. A first lighting pulse counting unit that detects a first lighting pulse number that is a number and stores the lighting pulse number in a specific section near a movement start point and a movement stop point; The number of times the light source was turned on while moving a distance equal to or less than one pitch length of the grid for each of the movement period from the point to the next lattice position and the movement period from the lattice position immediately before the movement stop point to the movement stop point. A second lighting pulse counting unit for detecting and storing a certain second lighting pulse number; comparing the first lighting pulse number with the second lighting pulse number to compare the first lighting pulse number and the second lighting pulse number with the movement start point of the moving scale and the next Distance to grid position A grid stop position detector for measuring the distance between the grid position immediately before the movement stop point and the movement stop point; a movement distance of an integral multiple of the grid 1 pitch length detected by the grid movement counting unit; A flushing type dimension measuring device using an optical scale, wherein a dimension is measured by detecting a moving distance of the moving scale from a sum of a moving distance equal to or less than one pitch length of a grating detected by a grating stop position detecting unit. 2. A grid stop position detecting section calculates a change in the number of first lighting pulses detected and stored by the first lighting pulse counting section to determine the vicinity of the movement scale starting movement and the movement. The moving speed of the moving scale is determined for each of the vicinity of the stop, and a reference lighting pulse number to be turned on during a period in which the grid moves by one pitch in the two sections is calculated. 2. The optical scale according to claim 1, wherein a ratio between the detected and stored second lighting pulse number and the reference lighting pulse number is calculated to measure a moving distance of one grating length or less of the grating. The flushing type dimension measuring device used. 3. A differential intensity signal generating unit for generating a differential intensity signal which is an intensity difference between the two-phase light intensity signals generated by the optical signal detecting unit, wherein the fixed scale includes two sets of fixed gratings having different phases. Is provided, the peak intensity position of the differential intensity signal is used as the reference position of the lattice, and the lattice movement counting unit counts the number of movements of the lattice reference position by an integral multiple of one pitch of the lattice, and sets the lattice reference position to the The flushing type dimension measuring device using an optical scale according to claim 1, wherein the reference positions are used as detection positions of the first lighting pulse number and the second lighting pulse number.