KR101328996B1 - Absolute position measuring method, absolute position measuring apparatus, and binary scale - Google Patents

Abstract

In an absolute position measuring method prepared by the present invention, a data cell expressing one bit of an absolute position binary cord (APBC) includes a data section, a neutral section, and a clock section at a relatively fixed position. The method comprises as follows: a step where each section includes one or more segments, the data cell is subdivided by segments at regular intervals, and a binary scale composed of the APBC is provided; a step of acquiring the image of the binary scale; and a step of calculating an absolute position by processing the image. In the magnification of an optical system, the width of an image corresponding to one segment is integer times of a pixel width of a photo sensor array. [Reference numerals] (S102) Obtain binary scale intensity profile or image;(S112) Trace clock pixel;(S114) Set clock pixel index;(S122) Obtain absolute code pixel index;(S124) Determine binary sate of pixel sub-set by using the intensity of absolute code pixels corresponding to absolute code pixel index;(S126) Convert binary code of pixel sub-sets in which binary state is determined into absolute location through rockup table;(S130) Fine data pixel corresponding to the location of data section with maximum intensity in each pixel sub-set;(S142) Calculate relative phase of the data section by using pixel vales around the data pixels;(S144) Take -2� when the relative phase is over zero;(S150) Calculate absolute position by using absolute position code, absolute code pixel index and relative phase

Description

Absolute Position Measuring Method, Absolute Position Measuring Apparatus, and Binary Scale

The present invention relates to an absolute position measuring method, and more particularly, to a method for calculating an absolute position by optically reading a binary scale using an absolute position binary code (APBC).

In various precision systems and scientific instruments, precise position measurement is a fundamental component of monitoring and controlling actuating systems. Laser interferometers and optical encoders are typical position sensors. The laser interferometer counts and sub-divides the interference fringes to measure position with sub-nanometer resolution. The period of the interference fringe is determined by the wavelength of the laser light source.

Optical encoders use scale. The scale has a uniform and periodic pattern. The pattern has a pitch of several to tens of micrometers. The optical encoder processes the interference fringe or intensity profile to obtain position readouts.

The laser interferometer can achieve high precision. However, the laser interferometer requires well controlled environmental conditions and delicate alignment.

In incremental position measurement, the position value is obtained by accumulating relative displacements from the initial position. The incremental position measurement is applied in many applications such as precision stage and position monitoring.

However, the incremental position measurement only measures relative displacement and requires initialization with an additional sensor to measure the absolute position.

The absolute position measurement increases the efficiency and robustness of the precision system. Because absolute position measurement does not require initialization, it can handle various emergencies. The absolute position measurement also has advantages in applications where power consumption must be tightly controlled.

Since optical encoders can be implemented without increasing cost and complexity, optical encoders are widely used for absolute position measurements.

Absolute encoders require a specially designed scale. Absolute position binary code (APBC) is encoded at this scale. Initially, the APBC was encoded using multi-track code, and incremental tracks were added for high resolution. However, the complex configuration and alignment issues of the encoder head are inevitable due to the multi-track configuration of this scale.

Thus, there is a need for a new structure of encoder that provides absolute and accurate positions.

One technical problem to be solved of the present invention is to provide an absolute position encoder that can know the absolute position.

In an absolute position measuring method according to an embodiment of the present invention, a data cell representing one bit of an absolute position binary code (APBC) includes a data section, a neutral section, and a clock section of a relatively fixed position, wherein each section is Providing a binary scale comprising one or more segments, wherein the data cell is sub-divided into equal segments at equal intervals, the binary position consisting of the absolute position binary code; Acquiring the binary scale image through an optical system and an optical sensor array; And calculating the absolute position by processing the image. The magnification of the optical system is determined such that the width of the image corresponding to one segment is an integer multiple of the pixel width of the photosensor array.

In an embodiment of the present disclosure, the data section may move by an integer multiple of the segment width to represent a binary state inside the data cell.

In an embodiment of the present disclosure, processing the image to calculate an absolute position includes: finding a clock pixel that is most closely aligned with the clock section in a pixel subset corresponding to one data cell width; Assigning the order of the clock pixel as a clock pixel index in the pixel subset corresponding to one data cell width; Circularly shifting the clock pixel index in a direction of decreasing the clock pixel index to obtain an absolute code pixel index; Determining a binary state of a pixel subset using the intensity of absolute code pixels corresponding to the absolute code pixel index in each pixel subset; Converting the binary code of the pixel subsets whose binary state is determined into an absolute position code through a lookup table; Finding a data pixel corresponding to a position of the data section with a maximum intensity in each pixel subset; Calculating a relative phase of the data section using pixel values around the data pixel; Subtracting by -2π when the relative phase is zero or more; The method may further include calculating the absolute position using the absolute position code, the absolute code pixel index, and the relative phase.

In one embodiment of the present invention, there is provided a method comprising removing a length dependent error term using a linear regression technique; And correcting the nonlinear error of the sub-division process by a sinusoidal function according to the relative phase.

In one embodiment of the present invention, the data cell may represent one bit of a first absolute position binary code in a first direction and one bit of a second absolute position binary code in a second direction perpendicular to the first direction. have.

In an absolute position measuring apparatus according to an embodiment of the present invention, a data cell representing one bit of an absolute position binary code (APBC) includes a data section, a neutral section, and a clock section, wherein each section is one or more regular interval segments. Wherein the data cell comprises: a binary scale sub-divided into equal segments at said intervals, said binary position comprising said absolute position binary code; A light source for irradiating light to the scale; An optical system for focusing the light transmitted through the binary scale or reflected from the binary scale; And an optical sensor array for sensing the image of the binary scale. The magnification of the optical system is determined such that the width of the image corresponding to one segment is an integer multiple of the pixel width of the photosensor array.

In one embodiment of the present invention, the optical system comprises: an objective lens unit for irradiating the output light of the light source to the scale; And an image lens unit reflecting light reflected from the scale and passing through the objective lens unit to the optical sensor array.

In one embodiment of the present invention, a collimator lens for converting the light of the light source into parallel light; And a beam splitter configured to change the optical path of the parallel light to provide the objective lens unit and provide the light provided from the objective lens unit to the image lens unit.

A data cell representing one bit of an absolute position binary code (APBC) in a binary scale according to an embodiment of the present invention includes a data section, a neutral section, and a clock section, each section including one or more regular interval segments. And the data cell is sub-divided into equal segments at equal intervals and consists of the absolute position binary code.

In one embodiment of the present invention, the data section may move to indicate a binary state inside the data cell.

2 representing one bit of the first absolute position binary code in the first direction and two bits of the second absolute position binary code in the second direction perpendicular to the first direction in the two-dimensional binary scale according to an embodiment of the present invention. The dimensional data cell comprises a first data section, a first neutral section, and a first clock section in a relatively fixed position in a first direction, each section comprising one or more segments, wherein the two-dimensional data cell is described above. Sub-divided into equal intervals into segments. The two-dimensional data cell includes a second data section, a second neutral section, and a second clock section in a relatively fixed position in a second direction perpendicular to the first direction, each section comprising one or more segments. The two-dimensional data cell is subdivided into equal segments at equal intervals. The two-dimensional data cell displays a (0,0) state when a mark pattern is formed to fill an intersection area of the first data section and the second data section. When the mark pattern is formed by moving the two-dimensional data cell by the width of the first neutral region in the first direction, the two-dimensional data cell displays a (1,0) state. When the mark pattern is formed by moving the two-dimensional data cell by the width of the second neutral region in the second direction, the two-dimensional data cell displays a (0,1) state. The two-dimensional data cell moves in the first direction by the width of the first neutral region and in the second direction by the width of the second neutral region to form the mark pattern. Display. The two-dimensional data cells may be arranged in two dimensions to form a two-dimensional absolute position scale.

2 representing one bit of the first absolute position binary code in the first direction and two bits of the second absolute position binary code in the second direction perpendicular to the first direction in the two-dimensional binary scale according to an embodiment of the present invention. The dimensional data cell comprises a first data section, a first neutral section, and a first clock section in a relatively fixed position in a first direction, each section comprising one or more segments, wherein the two-dimensional data cell is described above. Sub-divided into equal intervals into segments. The two-dimensional data cell includes a second data section, a second neutral section, and a second clock section in a relatively fixed position in a second direction perpendicular to the first direction, each section comprising one or more segments. The two-dimensional data cell is subdivided into equal segments at equal intervals. The two-dimensional data cell displays a (0,0) state when a first mark pattern is formed to fill an intersection area of the first data section and the second data section. The two-dimensional data cell displays a (1,0) state when the first mark pattern extends in the first direction by the width of the first neutral region to form the second mark pattern. The two-dimensional data cell displays a (0,1) state when the first mark pattern extends in the second direction by the width of the second neutral region to form the third mark pattern. In the two-dimensional data cell, when the first mark pattern extends in the first direction by the width of the first neutral region and in the second direction by the width of the second neutral region, a fourth mark mark pattern is formed. , (1,1) status is displayed. The two-dimensional data cells may be arranged in two dimensions to form a two-dimensional absolute position scale.

The present invention provides a new method of absolute position measurement. The absolute position measurement method uses a single track binary code, and the absolute position code is encoded by changing a phase of one binary state representation.

It can be efficiently decoded using the structural properties of the single track binary code. Sub-division of the single track binary code is possible by sensing the state position of the binary state representation used for absolute position encoding. Thus, the absolute position encoding does not interfere with the sub-division process. Thus, any pseudo-random sequence can be used as the absolute location code.

The method proposed in the present invention does not require an additional sensing unit for the sub-division. The proposed method can be realized with a simple configuration and efficient data processing.

In order to demonstrate and evaluate the proposed method, an absolute positioning device was installed using a binary code scale, a microscope imaging system, and a CCD camera. In comparison with the laser interferometer, the absolute position measuring device showed a resolution of less than 50 nm and a nonlinear error of less than ± 60 nm after compensation.

1 illustrates binary code encoding according to an embodiment of the present invention.
2 is a view illustrating an absolute position measuring apparatus according to an embodiment of the present invention.
3 shows the intensity intensity of the APBC in the image of the optical sensor array according to an embodiment of the present invention.
4 is a flowchart illustrating an absolute position measuring method according to an embodiment of the present invention.
5 illustrates an intensity profile of a 10-bit binary code according to an embodiment of the present invention.
6 is a view comparing the results of the absolute position measuring apparatus according to an embodiment of the present invention and the laser interferometer.
7 is a view comparing the measurement results of the absolute position measuring device and the laser interferometer according to an embodiment of the present invention.
8 shows nonlinear errors in the sub-division process before and after error compensation.
9 is a diagram illustrating a data cell of a two-dimensional binary scale according to an embodiment of the present invention.
10 is a diagram illustrating a two-dimensional absolute position scale using a data cell of a two-dimensional binary scale according to an embodiment of the present invention.
11 is a diagram illustrating a data cell of a two-dimensional binary scale according to an embodiment of the present invention.
12 illustrates a two-dimensional absolute position scale using a data cell of a two-dimensional binary scale according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Rather, the embodiments disclosed herein are being provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. In the drawings, the components have been exaggerated for clarity. Portions denoted by like reference numerals denote like elements throughout the specification.

In order to solve the above disadvantage, an absolute position encoder using a single track code has been developed. APBC was encoded using Manchester coding.

Since the absolute position encoder is not limited to the APBC representation, conventional pseudo-random binary sequences can be easily applied, and additional sensing units are required for sub-division based on the Moire principle. do.

An absolute position encoder has been proposed. The absolute position encoder uses binary scale. In the binary scale, the APBC is encoded by erasing one binary state representation on an incremental scale.

However, in order to maintain the incremental information for the sub-division process, the APBC expression is limited and complex APBC must be newly developed.

Also, although the single track scale has non-periodic patterns as a result of absolute position encoding, both methods rely on the sub-division algorithm used for the periodic incremental scale. The methods have error sources that are unavoidable in the sub-division process.

In the present invention, we propose a new absolute position measurement method using a single track binary code. The APBC is encoded by phase shifting the position of one binary state representation.

This absolute position encoding can represent any pseudo-random binary sequence without limitation and does not interfere with the sub-division process. By analyzing the intensity profile of the scale, decoding and sub-division of the APBC can be performed simultaneously without additional sensing methods and data acquisition.

This feature allows us to implement an absolute positioning system with simple configuration and efficient data processing.

Hereinafter, the operation principle of the present invention will be described.

1 illustrates binary code encoding according to an embodiment of the present invention.

[Single track binary code]

A data cell representing one data bit of the APBC consists of three sections. One data cell includes a data section (D), a clock section (C), and a neutral section (N). Each section contains one or more segments. Thus, each data cell consists of three or more segments.

In order to indicate a "0" state (first binary state), the data section and the clock section may have different binary states, and the neutral section may have the same state as the clock section.

The clock section is repeated in a periodic position, which provides us with an alignment key pattern for data processing.

The location of the data section is shifted to indicate another second binary state of each data cell in the APBC. The movement is possible at other sites except for the clock section. The shift magnitude is an integer multiple of one segment width. The neutral section is segments that do not belong to the data section and the clock section.

Specifically, each data cell consists of six segments and each section consists of two segments. The data section has been moved by one segment to indicate the "1" state (second binary state).

Sub-division of the APBC is required to obtain high resolution. Sub-divided absolute position is calculated by sensing the positions of the data sections.

The sub-division process is performed using data obtained for absolute position decoding without additional sensing or data acquisition. The position measuring method according to the present invention does not remove the information about the sub-division to encode the APBC.

Thus, we can apply any pseudo-random code that represents absolute position in the sub-division process without sacrificing accuracy.

[Data Acquisition]

2 is a view illustrating an absolute position measuring apparatus according to an embodiment of the present invention.

The measurement principle is described assuming that a single track binary code is made of a reflective chrome mask and the absolute position is calculated by analyzing the reflected intensity profile of the single track binary code.

Therefore, we need to obtain intensity profiles for data processing. The absolute position measuring apparatus 100 for obtaining the intensity profile may include a binary scale 110, an optical system 120, a light source 160, and a photo-sensor array 140. The photosensor array 140 may be a CCD or a photodiode array. The optical system 120 may include an objective lens unit 122 and an imaging lens unit 124.

The light provided by the light source 160 is changed into parallel light through the collimation lens 162. The parallel light is provided to the beam separator 164 and provided to the objective lens unit 122. The light passing through the objective lens unit 122 is reflected by the binary scale 110 and passes through the objective lens unit 122 and the beam separator 164 to be provided to the imaging lens unit 124. Light passing through the imaging lens unit 124 provides an image of the scale to the optical sensor array 140. The image acquired by the photosensor array 140 is provided to the processor 150 to process data.

The data processing depends on the structural nature of the binary code that must be maintained in the intensity profile. Thus, to precisely decode the APBC, the width of the image of one segment is equal to an integer multiple of the pixel width of detector array of the photosensor array 140. Should match. Therefore, magnification of the optical system 120 should be adjusted to satisfy the above condition.

For sub-division of the APBC, the relative position of the data sections in the intensity profile should be calculated with sub-pixel resolution.

Several algorithms, such as the center of gravity algorithm and zero-crossing algorithm, are widely used for peak detection. However, because the algorithms require the intensity profile to represent the park shape of the data section with many pixels to obtain sufficient precision, the algorithms require a lot of resources and computation time for data acquisition and processing.

In order to efficiently obtain the relative position, we have adopted the phase calculation algorithm used in the phase-shifting interferometery. The phase calculation algorithm can calculate the phase of a sinusoidal intensity profile precisely with a small number of equally spaced pixel data.

However, the fully-resolved image of the binary code is not a sinusoidal shape but a rectangular shape.

The FFT spectrum of the image has odd order high harmonic terms except for a first order term representing a single frequency sinusoidal function. Thus, we can use the objective lens portion 122 with a low numerical aperture (NA) to reduce the odd order high frequency terms and obtain the intensity intensity of the data section similar to the sinusoidal function.

[Data processing]

3 shows the intensity intensity of the APBC in the image of the optical sensor array according to an embodiment of the present invention.

4 is a flowchart illustrating an absolute position measuring method according to an embodiment of the present invention.

1, 3, and 4, we used the binary code configuration shown in FIG. Gray and white colors represent reflective and non-reflective areas, respectively. An n-bit linear shift feedback register (LSFR) was used for the APBC generation. The APBC has a combination of 2n-1 numbers except when all n bits are zero-state. The magnification of the optical system 120 is adjusted so that the width of one pixel of the photosensor array corresponds to the width of one segment. The photosensor array acquires an intensity profile or an image of a binary scale (S102).

Thus, an intensity profile of 6 X n pixels is required for data processing of n-bit APBC. In the computer simulated intensity profile of the scale, the 4-bit binary code was shifted with respect to a 24-pixel light sensor array by about one fifth of the pixel width to show a general situation. From this intensity profile, the absolute position with the sub-divided resolution can be obtained through the following procedure.

[Step S110 of finding clock pixels C _p ]

We find the clock pixels C _p most closely aligned with the clock section (S112). The clock pixels may be detected by checking an intensity sum S _m of pixels having a 6-pixel interval.

Where I _j represents the intensity of the j th pixel. Since the clock sections are periodic non-reflective areas, the sum of the intensities of Cp has a minimum value. One data cell width corresponds to one pixel subset. The order of C _p (order of C _p) is assigned as a pixel clock index _{(C pi = 1, ...,} 6) (S114).

[Step for finding absolute location code (S120)]

In order to decode the APBC, the absolute code pixel index A _pi is obtained by circularly shifting in a direction of decreasing the clock pixel index by 2 (S122). In this example, the absolute code pixel index A _pi is three.

Binary states of the subset are determined using the intensities of the absolute code pixels A _p corresponding to the absolute code pixel index A _pi in each pixel subset (S124). If the pixel has an intensity greater than the average intensity of all the absolute code pixels A _ps , then the subset containing the pixel is determined to be in a "1" state (second binary state). In the opposite case, the subset represents a " 0 " state (first binary state). The obtained binary code is converted into an absolute position code p _LUT using a lookup table (LUT) (S126).

The subdivision of the APBC is processed in two steps. First of all, we use A _pi The relative position between the photo sensor array and the scale having a resolution of one pixel is obtained. In the next step, using a phase calculation algorithm, the relative position of the data section is calculated with high resolution.

Finding the data pixels (S130)

From the absolute code pixel index A _pi obtained in the above step, we locate the data pixels D _p , which are the position of the data section and are expected to have the maximum intensity in each subset of the subset (S130). ).

If the subset to have its "0" state, the second pixel from the previous pixels A _p is assigned to D _p. The subset to have its "1" state, the previous pixel one pixel from A _p is assigned to D _p.

[Phase calculation step (S140)]

The precise relative position of the data section is calculated using pixel values around D _p (S142). The intensity distribution of the three pixels around the D _p may be the same for all pixel subsets. Averages of the pixel values of the same order are used to calculate the precise relative position. Thus, we can avoid iterative calculation of the relative position of each D _p . In this example, three pixel value sets were used in the calculation except subset 1 was an incomplete set.

Each pixel position has a π / 2 phase difference in the sinusoidal intensity profile of the data section. Thus, we can use a phase calculation algorithm to obtain a phase φ representing the relative position of the data section. The phase calculation algorithm is given by

Here, Ii represents the i-th pixel intensity of the detector array. The phase φ has a value ranging from -π / 2 to -π.

However, if D _p and another adjacent pixel have similar intensity values, then the sum of these adjacent pixels can be greater than the sum of D _p , and the phase has a value in the range of -π / 2 to -π. Do not. Because of the discontinuity of the arctangent function, the phase value shows a sharp change near -π. To compensate for the discontinuity, we subtract 2 [pi] from the calculated phase if the phase has a positive value (S144).

[Step Calculate Absolute Position Value (S150)]

The absolute position value p _abs is given by

The first term on the right side is the decoded absolute position with the resolution of one cell. The second term represents a particular pixel. 6 is the number of pixels per cell. The third term is the relative phase of D _P in one pixel. Here, the conversion factor is 2/3. The pitch of the sinusoidal profile of D _p is 4 pixels and the pitch of one cell is 6 pixels. To obtain the absolute position value p _{abs in the} longitudinal direction, the sum of the three terms is multiplied by the pitch of the data cell (p).

[Experiment]

Single track binary code scales are fabricated from quartz through a photo-mask fabrication process. The chrome pattern forms reflective areas that give high intensity values in the scale image. The width of one segment is 5 μm and the width of one cell is 30 μm. The binary code sequence was generated using LSFR.

The microscope imaging system includes an objective lens portion having a predetermined numerical aperture (NA = 0.07) and a predetermined magnification (M = 3), a zoom lens portion, a 2D CCD camera, and an LED light source. The pixel size of the 2D camera is 7.4 μm × 7.4 μm.

We adjust the magnification of the zoom lens part. Thus, the 6-pixel width is filled with the image of one cell.

A one-dimensional intensity profile is obtained by averaging the 2D images in the vertical direction.

Reflective mirrors for binary scales and laser interferometers were fixed to the moving parts of the moving stage. The laser interferometer provides a basis for performance evaluation.

The computer captures the 2D image of the code scale using an image grabber, processes and captures the captured image within 1 ms.

5 illustrates an intensity profile of a 10-bit binary code according to an embodiment of the present invention.

6 is a view comparing the results of the absolute position measuring apparatus according to an embodiment of the present invention and the laser interferometer.

The intensity profile is obtained by averaging partial images (60 pixels by 40 pixels). The 10-bit binary code using LSFR represents the 1023 case and corresponds to the 30 mm range when the pitch of the data cell is 30 μm. The dotted line shows the average intensity of the pixels for the calculation of the relative phase.

The binary scale is moved in the 25 mm range by a DC motor driven stage. Displacement is simultaneously measured by the absolute positioning system and the laser interferometer.

Comparison results show no abnormal deviations and are consistent within ± 0.5 μm. The deviation is calculated as residuals in linear regression to eliminate the effects of cosine error and scale factor error.

Since the length dependent error terms are eliminated through the linear regression, the deviation is due to an error term that is not proportional to the measured length. The error term results from the nonlinearity in the binary code scale and the sub-division process.

7 is a view comparing the measurement results of the absolute position measuring device and the laser interferometer according to an embodiment of the present invention.

To evaluate the resolution in the absolute position measurement, the binary scale was shifted in 50 nm steps using a PZT actuator. The stepwise displacement of 50 nm is measurable and the repeatability is less than 15 nm. The nonlinear error in the sub-division process is obtained as a deviation from the laser interferometer measurement.

8 shows nonlinear errors in the sub-division process before and after error compensation. The nonlinear error is plotted relative to the relative phase φ. The nonlinear error is of periodic nature and appears to be a sinusoidal signal having six periods within the pitch of the data cell. This kind of error is due to the intensity profile not being a perfect sinusoidal function. This kind of error has high harmonic terms. The harmonic term may in particular be a third-order harmonic term.

Although the objective lens portion has removed the harmonic terms of the intensity profile, some of the harmonic terms still remain and cause nonlinear errors in the sub-division process.

This periodic nonlinear error can be expressed as a sinusoidal function of phase φ. Thus, the amplitude A _ne of the error can be calibrated by fitting the error value to the sinusoidal function. Using a correction term expressed as A _ne x sin (4φ + π), we can reduce the nonlinear error below ± 0.06 μm.

9 is a diagram illustrating a data cell of a 2D binary scale according to an embodiment of the present invention.

9, a two-dimensional binary scale is two-dimensional data representing one bit of a first absolute position binary code in a first direction and one bit of a second absolute position binary code in a second direction perpendicular to the first direction. The cell comprises a first data section (3/8), a first neutral section (2/8), and a first clock section (3/8) in a relatively fixed position in a first direction, each section being one And two-dimensional data cells are sub-divided into equal segments at equal intervals.

The two-dimensional data cell includes a second data section, a second neutral section, and a second clock section in a relatively fixed position in a second direction perpendicular to the first direction, each section comprising one or more segments. The two-dimensional data cell is subdivided into equal segments at equal intervals.

The two-dimensional data cell displays a (0,0) state when a mark pattern is formed to fill an intersection area of the first data section and the second data section.

When the mark pattern is formed by moving the two-dimensional data cell by the width of the first neutral region in the first direction, the two-dimensional data cell displays a (1,0) state.

When the mark pattern is formed by moving the two-dimensional data cell by the width of the second neutral region in the second direction, the two-dimensional data cell displays a (0,1) state.

The two-dimensional data cell moves in the first direction by the width of the first neutral region and in the second direction by the width of the second neutral region to form the mark pattern. Display.

Referring to FIG. 10, the two-dimensional data cells may be arranged in two dimensions to form a two-dimensional absolute position scale, and one-dimensional absolute position information in each direction may be recorded.

The method of obtaining the first absolute position in the first direction and the method of obtaining the second absolute position in the second direction are the same as described in the one-dimensional binary scale.

 11 is a diagram illustrating a data cell of a 2D binary scale according to another embodiment of the present invention.

Referring to FIG. 11, a two-dimensional binary scale is two-dimensional data representing one bit of a first absolute position binary code in a first direction and one bit of a second absolute position binary code in a second direction perpendicular to the first direction. The cell comprises a first data section (3/8), a first neutral section (2/8), and a first clock section (3/8) in a relatively fixed position in a first direction, each section being one And two-dimensional data cells are sub-divided into equal segments at equal intervals.

The two-dimensional data cell includes a second data section, a second neutral section, and a second clock section in a relatively fixed position in a second direction perpendicular to the first direction, each section comprising one or more segments. The two-dimensional data cell is subdivided into equal segments at equal intervals.

The two-dimensional data cell displays a (0,0) state when a first mark pattern is formed to fill an intersection area of the first data section and the second data section.

The two-dimensional data cell displays a (1,0) state when the first mark pattern extends in the first direction by the width of the first neutral region to form the second mark pattern.

The two-dimensional data cell displays a (0,1) state when the first mark pattern extends in the second direction by the width of the second neutral region to form the third mark pattern.

In the two-dimensional data cell, when the first mark pattern extends in the first direction by the width of the first neutral region and in the second direction by the width of the second neutral region, a fourth mark pattern is formed. Displays the (1,1) state.

Referring to FIG. 12, the two-dimensional data cells may be arranged in two dimensions to form a two-dimensional absolute position scale, and one-dimensional absolute position information in each direction may be recorded.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, And all of the various forms of embodiments that can be practiced without departing from the technical spirit.

100: absolute position measuring device
110: scale
120: Optical system
160: Light source
140: optical sensor array
150:

Claims (12)

A data cell representing one bit of absolute position binary code (APBC) comprises a data section, a neutral section, and a clock section of relatively fixed position, each section comprising one or more segments, wherein the data cell comprises the segment Providing a binary scale sub-divided into equal intervals into the plurality and consisting of the absolute position binary code;
Acquiring the binary scale image through an optical system and an optical sensor array; And
Processing the image to calculate an absolute position,
The magnification of the optical system is an absolute position measuring method, characterized in that the width of the image corresponding to one segment is an integer multiple of the pixel width of the optical sensor array. The method of claim 1,
And said data section moves in an integer multiple of said segment width to represent a binary state within said data cell. The method of claim 1,
Processing the image to yield an absolute position is:
Finding a clock pixel most closely aligned with the clock section in the pixel subset corresponding to one data cell width;
Assigning the order of the clock pixel as a clock pixel index in the pixel subset corresponding to one data cell width;
Circularly shifting the clock pixel index in a direction of decreasing the clock pixel index to obtain an absolute code pixel index;
Determining a binary state of a pixel subset using the intensity of absolute code pixels corresponding to the absolute code pixel index in each pixel subset;
Converting the binary code of the pixel subsets whose binary state is determined into an absolute position code through a lookup table;
Finding a data pixel corresponding to a position of the data section with a maximum intensity in each pixel subset;
Calculating a relative phase of the data section using pixel values around the data pixel;
Subtracting by -2π when the relative phase is zero or more;
Calculating the absolute position using the absolute position code, the absolute code pixel index, and the relative phase; and at least one of the absolute position code. The method of claim 1,
Removing the length dependent error term using a linear regression technique; And
And correcting the nonlinear error of the sub-division process by a sinusoidal function according to the relative phase. The method of claim 1,
And wherein said data cell represents one bit of a first absolute position binary code in a first direction and one bit of a second absolute position binary code in a second direction perpendicular to said first direction. A data cell representing one bit of an absolute position binary code (APBC) comprises a data section, a neutral section, and a clock section, each section comprising one or more regularly spaced segments, the data cell into the segments, and the like. A binary scale sub-divided at intervals and composed of the absolute position binary code;
A light source for irradiating light to the scale;
An optical system for focusing the light transmitted through the binary scale or reflected from the binary scale; And
An array of photosensors for sensing the image of the binary scale,
The magnification of the optical system is an absolute position measuring device, characterized in that the width of the image corresponding to one segment is an integer multiple of the pixel width of the optical sensor array. The method of claim 6,
The optical system comprising:
An objective lens unit for irradiating output light of the light source to the scale; And
And an image lens unit for focusing the light reflected from the scale and passing through the objective lens unit to the optical sensor array. The method of claim 7, wherein
A collimator lens for converting light of the light source into parallel light; And
And a beam splitter configured to change the optical path of the parallel light to provide the objective lens unit and provide the light provided from the objective lens unit to the image lens unit. A data cell representing one bit of an absolute position binary code (APBC) comprises a data section, a neutral section, and a clock section, each section comprising one or more regularly spaced segments, the data cell into the segments, and the like. A binary scale sub-divided into intervals and consisting of said absolute position binary code. 10. The method of claim 9,
And said data section is moved within said data cell to indicate a binary state. A two-dimensional data cell representing one bit of the first absolute position binary code in the first direction and one bit of the second absolute position binary code in the second direction perpendicular to the first direction is a first data section in the first direction, A first neutral section and one bit of a first absolute position binary code in a first first direction of a relatively fixed position and one bit of a second absolute position binary code in a second direction perpendicular to the first direction The two-dimensional data cell comprises a first data section, a first neutral section, and a first clock section in a relatively fixed position in a first direction, each section comprising one or more segments, wherein the two-dimensional data cell comprises Sub-divided into equal segments at equal intervals,
The two-dimensional data cell includes a second data section, a second neutral section, and a second clock section in a relatively fixed position in a second direction perpendicular to the first direction, each section comprising one or more segments. The two-dimensional data cell is sub-divided into equal segments at equal intervals,
The two-dimensional data cell displays a (0,0) state when a mark pattern is formed to fill an intersection area of the first data section and the second data section.
When the mark pattern is formed by moving the two-dimensional data cell by the width of the first neutral region in the first direction, the two-dimensional data cell displays a (1,0) state,
If the mark pattern is formed by moving the two-dimensional data cell by the width of the second neutral region in the second direction, and displays the (0,1) state,
The two-dimensional data cell moves in the first direction by the width of the first neutral region and in the second direction by the width of the second neutral region to form the mark pattern. Displaying a two-dimensional binary scale. A two-dimensional data cell representing one bit of the first absolute position binary code in the first direction and one bit of the second absolute position binary code in the second direction perpendicular to the first direction is a first data section in the first direction, A first neutral section, and a first clock section in a relatively fixed position, each section comprising one or more segments, the two-dimensional data cell sub-divided into equal segments at equal intervals,
The two-dimensional data cell includes a second data section, a second neutral section, and a second clock section in a relatively fixed position in a second direction perpendicular to the first direction, each section comprising one or more segments. The two-dimensional data cell is sub-divided into equal segments at equal intervals,
The two-dimensional data cell indicates a (0,0) state when a first mark pattern is formed to fill an intersection region of the first data section and the second data section,
The two-dimensional data cell displays the (1,0) state when the first mark pattern extends in the first direction by the width of the first neutral region to form the second mark pattern.
The two-dimensional data cell displays a (0, 1) state when the first mark pattern extends in the second direction by the width of the second neutral region to form the third mark pattern.
In the two-dimensional data cell, when the first mark pattern extends in the first direction by the width of the first neutral region and in the second direction by the width of the second neutral region, a fourth mark mark pattern is formed. , (1,1) two-dimensional binary scale characterized by displaying the state.

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