CN105910631B - Absolute grating scale and its measuring method - Google Patents

Abstract

The invention discloses an absolute grating ruler and a measuring method thereof. The absolute grating ruler includes a parallel light source module, a scale grating, a photodetector and a signal processing module. A basic track and a plurality of coding tracks are arranged on the scale grating. The basic track includes A grating stripe that is inclined to the measurement direction, each coding track includes a plurality of grating stripes that are evenly arranged periodically and are tilted to the measurement direction, and each coding track has a different period, and the parallel light beam emitted by the parallel light source module After passing through the scale grating, it is irradiated on the photodetector. The photodetector is used to collect the arriving optical signal and convert it into a measurement electrical signal and then send it to the signal processing module. The signal processing module is used to process the measurement electrical signal and analyze it to obtain multiple codes. The track measurements are then calculated to obtain absolute position measurements. The invention has low etching difficulty, reduces manufacturing cost, and has high measurement accuracy, and can be widely used in grating measurement industry.

Description

Absolute Grating Ruler and Its Measuring Method

technical field

The invention relates to the field of grating ruler measurement, in particular to an absolute grating ruler and a measuring method thereof.

Background technique

At present, the commonly used grating rulers can be divided into three types: incremental grating rulers, semi-absolute grating rulers and absolute grating rulers, which are widely used in the CNC machine tool manufacturing industry. The incremental grating scale is the most commonly used high-precision measuring device. It has an absolute zero mark, and the scale grating is equidistantly distributed thereafter. The reading head moves relative to the scale grating, and the Moiré fringes formed by the passing grid will pass through the electrical signal processing to get the distance relative to absolute zero. This measurement mode is simple and easy to implement, but in use, it is difficult to greatly improve the work efficiency because it must be recalibrated every time it returns to the vicinity of absolute zero. In order to meet the needs of upgrading CNC machine tools, semi-absolute grating scales have gradually been widely used. The semi-absolute grating is to set the absolute track on the incremental grating, and a series of zero gratings with different distances are designed on the absolute track. When using it, the absolute position is determined by detecting the distance between the adjacent zero gratings, which greatly reduces the The time to return to zero improves work efficiency. In addition, when this type of grating ruler fails, it can immediately send an alarm signal to the CNC machine tool to ensure the safety of processing. Recently, the appearance of the absolute grating scale has triggered a revolutionary progress in the equipment manufacturing industry. Compared with the semi-absolute grating scale, the absolute coded grating scale has more advantages. Since there is a corresponding absolute and unique code value at any point, there is no cumulative error , has the characteristics of high measurement resolution, strong anti-interference ability, high stability, etc., and can also perform nonlinear correction. In addition, the absolute encoding range is large, so the linear displacement of a large range can be measured. The structure of the absolute grating ruler is relatively simple, the key point is the realization of the absolute code, and each absolute code corresponds to an absolute position on the grating scale, the relative movement distance can be obtained by subtracting the absolute position from the starting point to the end point, The accumulated error is avoided, and the process of reading back the zero point is also eliminated. However, the main disadvantage of the absolute grating ruler is that it is slow in high-precision measurement, and the error rate is high when decoding. Moreover, the distance between the grid lines on the code track of the current absolute grating scale is very small, and the higher the precision required, the grid lines The smaller the spacing needs to be, the greater the production cost, and this method has limitations in the encoding range, which limits the expansion of the measurement range, and the slight manufacturing error of the grating code track will advance or delay individual code tracks. This will eventually cause measurement errors.

Contents of the invention

In order to solve the above technical problems, the object of the present invention is to provide an absolute grating ruler and a measuring method thereof.

The technical solution adopted by the present invention to solve its technical problems is:

An absolute grating scale, including a parallel light source module, a scale grating, a photodetector and a signal processing module. The scale grating is provided with a basic track and a plurality of coding tracks. The basic track includes a grating inclined to the measurement direction stripes, each of the coding tracks includes a plurality of grating stripes that are evenly arranged periodically and are inclined to the measurement direction, and each coding track has a different period, and the parallel light beam emitted by the parallel light source module passes through the scale grating and then irradiates On the photodetector, the photodetector is used to collect the arriving optical signal and convert it into a measurement electrical signal and then send it to the signal processing module. The signal processing module is used to process the measurement electrical signal and analyze to obtain multiple coded tracks The measured value is then calculated to obtain the absolute position measured value.

Further, the heights of the base track and each coding track are the same, each track has a different measurement resolution, and among adjacent tracks, the angle between the grating stripes on the track with a higher measurement resolution and the measurement direction The tangent value of is equal to n times of the tangent value of the angle between the grating stripes on the track with lower measurement resolution and the measurement direction, wherein n represents the number of photosensitive elements of the photodetector occupied by each track and n=h/ d, h represent the height of each track, and d represents the center-to-center distance between adjacent photosensitive elements.

Further, there are two encoding tracks, namely the first encoding track and the second encoding track, the first encoding track includes a plurality of uniformly arranged grating stripes at an angle α to the measurement direction, and the second The coding track includes a plurality of grating stripes that are evenly arranged and form an angle of β with the measurement direction. The angle is γ, α, β and γ satisfy the following relationship:

Wherein, n represents the number of photosensitive elements of the photodetector occupied by each track and n=h/d, and d represents the center-to-center distance between adjacent photosensitive elements.

Further, the photodetector adopts a linear array CMOS sensor or a linear array CCD sensor.

Another technical solution adopted by the present invention to solve its technical problems is:

The measuring method of the described absolute grating ruler comprises steps:

S1. Install the scale grating on the object to be measured, and drive the object to be measured to move;

S2. The parallel light beam emitted by the parallel light source is irradiated onto the photodetector after passing through the scale grating;

S3. The photodetector collects the arriving optical signal and converts it into an electrical signal for measurement, and then sends it to the signal processing module;

S4. The signal processing module analyzes and obtains the measurement values of the base track and multiple coded tracks after processing the measurement electrical signal, and then calculates and obtains absolute position measurement values.

Further, the step S4 specifically includes:

S41. After the signal processing module preprocesses the measurement electrical signal, it divides and obtains a plurality of measurement image blocks corresponding to the basic track and each coding track;

S42. After performing edge detection processing on a plurality of measurement image blocks respectively, obtain the distance between the code point collected in each measurement image block and the bottom of the corresponding code track;

S43. Combining the base track and the projected length of the grating stripes of each encoding track in the horizontal direction, calculate and obtain an absolute position measurement value.

Further, the step S43 is specifically:

Combined with the projection length of the grating stripes of the base track and each coded track in the horizontal direction, the absolute position measurement value is calculated according to the following formula:

d＝d ₀ ×(l ₀ /h)+d ₁ ×(l ₁ /h)+d ₂ ×(l ₂ /h)+…+d _n ×(l _n /h)

In the above formula, d represents the absolute position measurement value, d ₀ represents the distance between the code point in the measurement image block corresponding to the base track and the bottom of the code track, and d ₁ represents the distance between the code point in the measurement image block corresponding to the first code track The distance between the coded point and the bottom of the coded track, d ₂ represents the distance between the coded point in the measurement image block corresponding to the second coded track and the bottom of the coded track, d _n represents the measurement corresponding to the nth coded track The distance between the coding point in the image block and the bottom of the coded track, n is a natural number, l ₀ , l ₁ , l ₂ and l _n represent the base track, the first coded track, the second coded track and the nth coded track respectively The projection length of the grating stripes of the track in the horizontal direction, h represents the height of each track and l _n /h represents the cotangent value of the angle between the grating stripes of the corresponding code track and the horizontal direction.

The beneficial effects of the present invention are: the absolute grating ruler of the present invention includes a parallel light source module, a scale grating, a photodetector and a signal processing module, a basic track and a plurality of coding tracks are arranged on the scale grating, and the basic track includes a Grating stripes with inclined directions, each coding track includes a plurality of grating stripes that are evenly arranged periodically and inclined to the measurement direction, and each coding track has a different period, and the parallel light beam emitted by the parallel light source module passes through the scale grating After irradiating on the photodetector, the photodetector is used to collect the arriving optical signal and convert it into a measurement electrical signal and then send it to the signal processing module. The signal processing module is used to process the measurement electrical signal and analyze it to obtain the measurement of multiple coded tracks. The value is then calculated to obtain an absolute position measurement. The absolute grating ruler has lower requirements for grating stripes, reduces the difficulty of grating etching, reduces the production cost, can effectively reduce the error rate of the grating, reduces the manufacturing cost, and has high measurement accuracy.

Another beneficial effect of the present invention is: the measuring method of the absolute grating ruler of the present invention includes steps: S1, installing the scale grating on the object to be measured, and driving the object to be measured to move; S2, the parallel light emitted by the parallel light source The light beam passes through the scale grating and irradiates the photodetector; S3, the photodetector collects the incoming optical signal and converts it into a measurement electrical signal, and then sends it to the signal processing module; S4, the signal processing module processes the measurement electrical signal and then analyzes it to obtain the basis The measurements of the track and the multiple coded tracks are then calculated to obtain absolute position measurements. The measurement method is simple to operate, can quickly obtain measurement results, and has high measurement accuracy.

Description of drawings

The present invention will be further described below in conjunction with drawings and embodiments.

Fig. 1 is the structural representation of absolute grating ruler of the present invention;

Fig. 2 is a schematic structural view of the scale grating of Embodiment 1 of the absolute grating scale of the present invention;

Fig. 3 is the measurement image obtained by collecting the basic track in the first embodiment of the absolute grating ruler of the present invention;

Fig. 4 is the measurement image collected from the first code track in Embodiment 1 of the absolute grating ruler of the present invention;

Fig. 5 is a measurement image collected from the second code track in Embodiment 1 of the absolute grating ruler of the present invention.

Detailed ways

Referring to Fig. 1 and Fig. 2, the present invention provides an absolute grating ruler, including a parallel light source module 1, a scale grating 2, a photodetector 3 and a signal processing module 4, and the scale grating 2 is provided with a basic track 10 and A plurality of coding tracks, the basic track 10 includes a grating stripe that is inclined to the measurement direction, and each of the coding tracks includes a plurality of grating stripes that are evenly arranged periodically and are inclined to the measurement direction, and each coding The tracks have different periods respectively. The parallel light beam emitted by the parallel light source module 1 passes through the scale grating 2 and then irradiates the photodetector 3. The photodetector 3 is used to collect the arriving optical signal and convert it into a measurement electrical signal before sending To the signal processing module 4, the signal processing module 4 is used to analyze and obtain the measured values of multiple coded tracks after processing the measured electrical signals, and then calculate and obtain the absolute position measured values.

Further as a preferred embodiment, the heights of the base track 10 and each coding track are the same, each track has a different measurement resolution, and among adjacent tracks, the grating stripes on the track with a higher measurement resolution The tangent of the angle with the measurement direction is equal to n times the tangent of the angle between the grating stripes on the track with a lower measurement resolution and the measurement direction, where n represents the photosensitive elements of the photodetector 3 occupied by each track number and n=h/d, h represents the height of each track, and d represents the center-to-center distance between adjacent photosensitive elements.

Further as a preferred embodiment, the number of the encoding track is two, respectively the first encoding track 11 and the second encoding track 12, the first encoding track 11 includes a plurality of evenly arranged and at an angle α with the measurement direction The grating stripes of the second coding track 12 include a plurality of grating stripes that are evenly arranged and form an angle of β with the measurement direction, and the heights of the basic track 10, the first coding track 11 and the second coding track 12 are all h, The included angle between the grating stripes of the basic track 10 and the measuring direction is γ, and α, β and γ satisfy the following relationship:

Wherein, n represents the number of photosensitive elements of the photodetector 3 occupied by each track and n=h/d, and d represents the center-to-center distance between adjacent photosensitive elements.

As a further preferred embodiment, the photodetector 3 adopts a linear array CMOS sensor or a linear array CCD sensor.

The present invention also provides a method for measuring an absolute grating ruler, comprising the steps of:

S1. Install the scale grating 2 on the object to be measured, and drive the object to be measured to move;

S2. The parallel light beam emitted by the parallel light source passes through the scale grating 2 and then irradiates on the photodetector 3;

S3. The photodetector 3 collects the arriving optical signal and converts it into a measurement electrical signal and sends it to the signal processing module 4;

S4. The signal processing module 4 processes the measurement electrical signal, analyzes and obtains the measurement values of the base track 10 and a plurality of coded tracks, and then calculates and obtains absolute position measurement values.

Further as a preferred implementation manner, the step S4 specifically includes:

S41. After the signal processing module 4 preprocesses the measurement electrical signal, it divides and obtains a plurality of measurement image blocks corresponding to the basic track 10 and each coding track;

S42. After performing edge detection processing on a plurality of measurement image blocks respectively, obtain the distance between the code point collected in each measurement image block and the bottom of the corresponding code track;

S43. Combining the base track 10 and the projected length of the grating stripes of each coded track in the horizontal direction, calculate and obtain an absolute position measurement value.

Further as a preferred implementation manner, the step S43 is specifically:

Combining the projected length of the grating stripes of the basic track 10 and each coded track in the horizontal direction, the absolute position measurement value is obtained according to the following formula:

d＝d ₀ ×(l ₀ /h)+d ₁ ×(l ₁ /h)+d ₂ ×(l ₂ /h)+…+d _n ×(l _n /h)

In the above formula, d represents the absolute position measurement value, d ₀ represents the distance between the code point in the measurement image block corresponding to the base track 10 and the bottom of the code track, and d ₁ represents the measurement image block corresponding to the first code track 11 The distance between the coding point in the coded track and the bottom of the coded track, d ₂ represents the distance between the coded point in the measurement image block corresponding to the second coded track 12 and the bottom of the coded track, and d _n represents the nth coded track Correspondingly measure the distance between the coded point in the image block and the bottom of the coded track, n is a natural number, l ₀ , l ₁ , l ₂ and l _n respectively represent the basic track 10, the first coded track 11, the second coded track The projection length of the grating stripes of the track 12 and the nth coded track in the horizontal direction, h represents the height of each track and l _n /h represents the cotangent value of the angle between the grating stripes of the corresponding code track and the horizontal direction.

The present invention will be described in detail below in conjunction with specific embodiments.

Embodiment 1 Referring to Fig. 1 and Fig. 2, an absolute grating ruler includes a parallel light source module 1, a scale grating 2, a photodetector 3 and a signal processing module 4, and a basic track 10 and a plurality of codes are arranged on the scale grating 2 track, the basic track 10 includes a grating stripe that is inclined to the measurement direction, and each coded track includes a plurality of grating stripes that are evenly arranged periodically and are inclined to the measurement direction, and each coded track has a different period respectively, parallel The parallel light beam emitted by the light source module 1 passes through the scale grating 2 and then irradiates on the photodetector 3. The photodetector 3 is used to collect the arriving optical signal and convert it into a measurement electrical signal before sending it to the signal processing module 4. The signal processing module 4 uses After processing the measurement electrical signal, the measurement values of multiple coded tracks are analyzed and obtained, and then the absolute position measurement values are calculated and obtained.

The heights of the base track 10 and each coding track are the same, each track has a different measurement resolution, and among the adjacent tracks, the tangent of the angle between the grating stripes on the track with a higher measurement resolution and the measurement direction is equal to the measured n times of the tangent of the angle between the grating stripes on the track with lower resolution and the measurement direction, wherein n represents the number of photosensitive elements of the photodetector 3 occupied by each track and n=h/d, h represents The height of each track, d represents the center-to-center distance between adjacent photosensitive elements.

In this embodiment, there are two encoding tracks, which are respectively the first encoding track 11 and the second encoding track 12. The first encoding track 11 includes a plurality of grating stripes that are uniformly arranged and form an angle α with the measurement direction. The coded track 12 includes a plurality of grating stripes arranged uniformly and at an angle of β to the measurement direction. The heights of the basic track 10, the first coded track 11 and the second coded track 12 are all h, and the height of the grating stripes of the basic track 10 and the measurement direction is The included angle is γ, and α, β and γ satisfy the following relationship:

Wherein, n represents the number of photosensitive elements of the photodetector 3 occupied by each track and n=h/d, and d represents the center-to-center distance between adjacent photosensitive elements.

By analogy, when the number of encoding tracks is three or more, the relationship between the tangent of the angle between the grating stripes of adjacent tracks and the measurement direction is also n times, and the present invention will not list them one by one.

In this embodiment, the photodetector 3 adopts a linear array CMOS sensor or a linear array CCD sensor. The acquisition direction of the linear array is perpendicular to the movement direction of the absolute grating ruler. The line array images captured by the photodetector 3 are a series of images perpendicular to the relative movement direction of the absolute grating scale. Assuming that a linear array CCD sensor with a total number of pixels of 2048 is used as an example, the total number of pixels is 2048, and the maximum number of pixels that can be resolved in each of the basic track and the two encoding tracks is 2048/3. It should be noted that the height in the present invention refers to the measurement in the vertical direction in FIG. 2 . In fact, when the scale grating 2 is laid flat, this direction can also be called the width direction.

In more detail, in this embodiment, the pixel center distance of the linear CCD sensor is 14 μm, the number of pixels is 2048, and the pixels occupied by each track on the linear CCD sensor are 680 pixels. The first coding track 11 is an oblique line with an angle of α=45 degrees, the width of the grid line is 10 μm, and this oblique line is repeated continuously throughout the entire coding length of the code track. The second coded track 12 is a plurality of grating stripes that are evenly arranged and have an angle β with the measurement direction, and the first complete oblique line (that is, the grating stripe) of the second coded track 12 corresponds to the n cycles of the first coded track 11 All grating stripes, similarly, the second complete oblique line (ie grating stripe) of the second code track 12 corresponds to all grating stripes within n periods of the first code track 11, and so on according to this law. The base track 10 has only one grating stripe with an inclination angle of γ, which corresponds to all the grating stripes in the n periods of the second code track 12 . The above n is the number of pixels occupied by each track on the line array CCD sensor, and its value is 680. Therefore, after adopting the present invention, the marking distance between the grating stripes of the first coding track 11 and the second coding track 12 is relatively large, thereby greatly reducing the difficulty of marking, reducing the production cost, and improving the accuracy of measurement and the resolution of measurement. Rate.

The distance from the target point of each segment in Figure 3, Figure 4, and Figure 5 to the starting point a1, a2 or a3 of the segment is between 0 and 680 pixels, and the arrangement and combination of the target point information of the three tracks contains There are 680 ³ pieces of absolute position information. By calculating the collected distances d ₁ , d ₂ , and d ₃ , specific absolute position measurement values can be obtained. The calculation method is relatively simple, which is conducive to improving the processing speed of the absolute position measurement value.

When the position collected by the linear CCD sensor is at the leftmost end of the scale grating 2, the grating lines of the three tracks are at the starting points a1, a2 and a3 of the linear CCD sensor respectively, that is: the code zero point corresponding to the absolute grating scale Code (d ₁ , d ₂ , d ₃ ) is (0,0,0). When the scale grating moves, the linear array CCD collects the grating images of the three code tracks, and the grating images are transmitted to the signal processing module to obtain d ₁ , d ₂ and d ₃ after processing.

By calculating the collected distances d ₁ , d ₂ , and d ₃ , specific absolute position values can be obtained. The calculation method is relatively simple, which is conducive to improving the processing speed of the absolute position value. The mathematical calculation formula of the absolute position value d is:

d＝d ₀ ×(l ₀ /h)+d ₁ ×(l ₁ /h)+d ₂ ×(l ₂ /h)

In the present invention, the absolute position code corresponding to the maximum absolute position in the three code tracks is (680, 680, 680). The total encoding period is 680 ³ , and the encoding length is (680×680×680)×10 μm, which is 314.4m.

Embodiment 2, a method of measuring an absolute grating ruler, comprising steps:

S1. Install the scale grating 2 on the object to be measured, and drive the object to be measured to move;

S2. The parallel light beam emitted by the parallel light source passes through the scale grating 2 and then irradiates on the photodetector 3;

S3. The photodetector 3 collects the arriving optical signal and converts it into a measurement electrical signal and sends it to the signal processing module 4;

S4. The signal processing module 4 analyzes and obtains the measured values of the base track 10 and multiple encoded tracks after processing the measured electrical signals, and then calculates and obtains the absolute position measured values, specifically including steps S41 to S43:

S41. After the signal processing module 4 preprocesses the measurement electrical signal, it divides and obtains a plurality of measurement image blocks corresponding to the basic track 10 and each coding track;

S42. After performing edge detection processing on a plurality of measurement image blocks respectively, obtain the distance between the code point collected in each measurement image block and the bottom of the corresponding code track;

S43. Combining the projected length of the grating stripes of the basic track 10 and each coded track in the horizontal direction, calculate and obtain the absolute position measurement value. Step S43 is specifically:

Combining the projected length of the grating stripes of the basic track 10 and each coded track in the horizontal direction, the absolute position measurement value is obtained according to the following formula:

d＝d ₀ ×(l ₀ /h)+d ₁ ×(l ₁ /h)+d ₂ ×(l ₂ /h)+…+d _n ×(l _n /h)

In the above formula, d represents the absolute position measurement value, d ₀ represents the distance between the code point in the measurement image block corresponding to the base track 10 and the bottom of the code track, and d ₁ represents the measurement image block corresponding to the first code track 11 The distance between the coding point in the coded track and the bottom of the coded track, d ₂ represents the distance between the coded point in the measurement image block corresponding to the second coded track 12 and the bottom of the coded track, and d _n represents the nth coded track Correspondingly measure the distance between the coded point in the image block and the bottom of the coded track, n is a natural number, l ₀ , l ₁ , l ₂ and l _n respectively represent the basic track 10, the first coded track 11, the second coded track The projection length of the grating stripes of track 12 and the nth coded track in the horizontal direction, h represents the height of each track and l _n /h represents the cotangent value of the angle between the grating stripes of the corresponding code track and the horizontal direction, such as l ₀ /h represents the cotangent value of the angle between the grating stripes of the basic code track and the horizontal direction, and l ₂ /h represents the cotangent value of the angle between the grating stripes of the second code track 12 and the horizontal direction.

The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments, and those skilled in the art can also make various equivalent deformations or replacements without violating the spirit of the present invention. Equivalent modifications or replacements are all included within the scope defined by the claims of the present application.

Claims (7)

1. absolute grating scale, it is characterised in that including source of parallel light module, scale grating, photodetector and signal transacting Module, the scale grating are provided with a basal orbit and multiple encoded tracks, and the basal orbit includes one and measurement The inclined grating fringe in direction, it is in equably periodic arrangement and and measurement direction that each encoded tracks, which include multiple, Inclined grating fringe, and each encoded tracks have different cycles respectively, the source of parallel light module sends parallel By being irradiated to after scale grating on photodetector, the photodetector is used to collect the optical signal reached and conversion light beam To be sent to signal processing module after measurement electric signal, the signal processing module is used to after handling measurement electric signal solve Analysis, which obtains the measured value of multiple encoded tracks and then calculated, obtains Absolute position measurement value.

2. absolute grating scale according to claim 1, it is characterised in that the basal orbit and the height of each encoded tracks All same is spent, each encoded tracks have different Measurement Resolutions, and in adjacent track, the higher rail of Measurement Resolution The tangent value of the angle of grating fringe and measurement direction on road be equal to grating fringe on the relatively low track of Measurement Resolution with N times of the tangent value of the angle of measurement direction, wherein n represent the photosensitive first number and n of the photodetector shared by each track =h/d, h represent the height of each track, and d represents the centre-to-centre spacing between neighboring photosensitive member.

3. absolute grating scale according to claim 1, it is characterised in that the quantity of the encoded tracks totally two, point Not Wei the first encoded tracks and the second encoded tracks, first encoded tracks include multiple evenly distributed and with measurement direction are in The grating fringe at α angles, second encoded tracks include grating fringe multiple evenly distributed and with measurement direction in β angles, institute The height for stating basal orbit, the first encoded tracks and the second encoded tracks is h, the grating fringe of the basal orbit and measurement The angle in direction is γ, and α, β and γ meet following relation：

<mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mi>t</mi> <mi>a</mi> <mi>n</mi> <mi>&amp;beta;</mi> <mo>=</mo> <mi>n</mi> <mi> </mi> <mi>t</mi> <mi>a</mi> <mi>n</mi> <mi>&amp;gamma;</mi> </mtd> </mtr> <mtr> <mtd> <mi>t</mi> <mi>a</mi> <mi>n</mi> <mi>&amp;alpha;</mi> <mo>=</mo> <mi>n</mi> <mi> </mi> <mi>t</mi> <mi>a</mi> <mi>n</mi> <mi>&amp;beta;</mi> <mo>=</mo> <msup> <mi>n</mi> <mn>2</mn> </msup> <mi>t</mi> <mi>a</mi> <mi>n</mi> <mi>&amp;gamma;</mi> </mtd> </mtr> </mtable> </mfenced>

Wherein, n represents photosensitive first number of the photodetector shared by each track and n=h/d, d represent neighboring photosensitive member Between centre-to-centre spacing.

4. absolute grating scale according to claim 1, it is characterised in that the photodetector is passed using linear array CMOS Sensor or linear CCD sensor.

5. the measuring method of the absolute grating scale described in claim 1, it is characterised in that including step：

S1, scale grating is arranged on object under test, and drives object under test to move；

The collimated light beam that S2, source of parallel light are sent after scale grating by being irradiated on photodetector；

S3, photodetector collect the optical signal reached and are sent to signal processing module after being converted to measurement electric signal；

Parsing obtains the measurement of basal orbit and multiple encoded tracks after S4, signal processing module are handled measurement electric signal It is worth and then calculates and obtains Absolute position measurement value.

6. the measuring method of absolute grating scale according to claim 5, it is characterised in that the step S4, specific bag Include：

After S41, signal processing module pre-process to measurement electric signal, segmentation obtains and basal orbit and each encoded tracks pair The multiple measurement image blocks answered；

S42, after carrying out edge detection process to multiple measurement image blocks respectively, obtain the volume collected in each measurement image block The distance between code-point and bottom of corresponding encoded tracks；

S43, the projected length with reference to basal orbit and the grating fringe of each encoded tracks in the horizontal direction, calculate and obtain definitely Position measurements.

7. the measuring method of absolute grating scale according to claim 6, it is characterised in that the step S43, its is specific For：

With reference to the projected length of basal orbit and the grating fringe of each encoded tracks in the horizontal direction, calculated and obtained according to following formula Absolute position measurement value：

D=d₀×(l₀/h)+d₁×(l₁/h)+d₂×(l₂/h)+…+d_n×(l_n/h)

In above formula, d represents Absolute position measurement value, d₀Represent the encoded point and the volume in measurement image block corresponding to basal orbit The distance between bottom of code track, d₁Represent the encoded point and the coding rail in measurement image block corresponding to the first encoded tracks The distance between the bottom in road, d₂Represent the encoded point and the encoded tracks in measurement image block corresponding to the second encoded tracks The distance between bottom, d_nRepresent the encoded point in measurement image block corresponding to the n-th encoded tracks and the bottom of the encoded tracks The distance between, n is natural number, l₀、l₁、l₂And l_nRespectively represent basal orbit, the first encoded tracks, the second encoded tracks and The projected length of the grating fringe of n-th encoded tracks in the horizontal direction, h represent the height and l of each track_n/ h represents corresponding Code channel grating fringe and horizontal direction angle cotangent value.