An absolute grating scale system

Abstract

The present invention discloses an absolute grating scale system, belonging to the technical field of measuring instruments. The absolute grating scale system of this solution includes a scale grating, a light-emitting device, an image acquisition device, and a control device; multiple stripes with equal spacing but uneven widths are arranged on the scale grating, and the combination of the widths of any continuous P stripes has a unique value within the range of the grating scale. The stripe image on the scale grating is acquired through the image acquisition device, and the absolute position of the grating scale is determined according to a preset stripe coding rule. Different from the traditional method relying on Moiré fringes, the present invention only requires one scale grating, and the stripe width values in the scale grating can be flexibly set according to actual needs. While ensuring high-precision measurement, it effectively reduces the processing difficulty of the grating scale stripes, and also helps to improve the anti-interference ability of the system, making large-scale production and wide application possible.

Description

Technical Field

[0001] The present invention relates to the technical field of measuring instruments, and particularly to an absolute grating scale system. Background Art

[0002] Traditional grating scales usually consist of a scale grating and an indicator grating. The stripes on these two gratings overlap with each other, and an alternating pattern of light and dark stripes, called Moiré fringes, is formed in the overlapping area. When the scale grating and the indicator grating move relative to each other, the Moiré fringes will move accordingly. The photosensitive element detects the changes in these Moiré fringes and converts them into electrical signals. The signal processing circuit counts and subdivides these electrical signals to calculate the linear displacement or angular displacement and the moving direction. The measurement accuracy of traditional grating scales based on the above principle is closely related to the width of their grating stripes. Generally speaking, when the stripe width is in the micron level, the grating scale can achieve micron-level accuracy. However, as the grating stripes become thinner and thinner, the processing difficulty increases significantly, resulting in an increase in manufacturing cost and a decrease in production yield. The high manufacturing cost and low production yield of such high-precision grating scales greatly limit their wide application and popularity, especially in application fields that require high-precision displacement measurement.

[0003] To overcome the above problems, there is an urgent need in the market for a technical solution that can not only maintain high-precision measurement capabilities but also reduce manufacturing complexity, improve production efficiency, and reduce costs. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: in view of the above-mentioned defects of the prior art, to provide an absolute grating scale system.

[0005] To achieve the above object, the present invention provides an absolute grating scale system, including a scale grating, a light-emitting device, an image acquisition device, and a control device;

[0006] Multiple stripes arranged according to a specific rule are provided on the scale grating, and the combination of the widths of any continuous P stripes has a unique value within the range of the grating scale;

[0007] The light-emitting device and the image acquisition device are respectively located on both sides of the scale grating; the image acquisition device is arranged in a direction perpendicular to the optical path of the light-emitting device, and the image acquisition device includes a calculation area in the middle, and the calculation area faces the light-emitting device and is used to acquire images corresponding to at least P continuous stripes;

[0008] The control device determines the absolute position D of the stripe facing the light-emitting device based on the width of the stripe image collected by the image acquisition device and the preset scale grating stripe coding rule, and calculates the distance E between the center of the stripe and the center point of the image acquisition device, so as to obtain the final absolute position value F = D + E.

[0009] In the absolute grating scale system of the present invention, the method for generating the width of the stripe is as follows:

[0010] Generate a specific sequence with a unique combination of any continuous P values;

[0011] Multiply each value in the specific sequence by a preset magnification factor to obtain the actual width values of the respective stripes, and the magnification factor is set according to the required detection accuracy and the requirements of the manufacturing process.

[0012] In the absolute grating scale system of the present invention, the specific sequence is a De Bruijn sequence.

[0013] In the absolute grating scale system of the present invention, the absolute grating scale system is used to measure linear displacement, and the scale grating is straight.

[0014] In the absolute grating scale system of the present invention, the absolute grating scale system is used to measure the rotation angle, the scale grating is a circular grating disk, and an annular grating scale area is provided on the grating disk.

[0015] In the absolute grating scale system of the present invention, the image acquisition device further includes auxiliary areas at both ends of the calculation area, and the auxiliary areas are used to collect images of one or more stripes adjacent to at least P continuous stripes corresponding to the calculation area; if the number of stripe images in the calculation area of the image acquisition device is insufficient or the recognition is incorrect, the width and center coordinates of the stripe images in the auxiliary area are corrected, and then the auxiliary area is used to assist in calculating the absolute position.

[0016] In the absolute grating scale system of the present invention, the method for calculating the rotation angle is as follows:

[0017] Determine the starting position;

[0018] Determine the number of turns of rotation;

[0019] Determine the ending position;

[0020] Calculate the rotation angle: rotation angle = angle corresponding to the ending position - angle corresponding to the starting position + 360 * number of turns;

[0021] Wherein: there are two calculation methods for the angle corresponding to the ending position - the angle corresponding to the starting position:

[0022] 1. First, calculate the absolute positions corresponding to the starting position and the ending position, obtain the arc length between the starting position and the ending position, and then calculate the angle corresponding to the arc length, that is, obtain the angular value between the starting position and the ending position;

[0023] 2. Calculate the angle corresponding to each stripe according to the number of stripes in the scale grating scale area of the circular grating, and calculate the number of stripes passed according to the stripe positions at the starting position and the ending position, so as to obtain the angular value between the starting position and the ending position.

[0024] In the absolute grating scale system of the present invention, the control device is further configured to monitor in real time the number of pixels included in the image of a single stripe collected by the image acquisition device, and when the number of pixels is less than a preset threshold, increase the power of the light emitting device.

[0025] In the absolute grating scale system of the present invention, the scale grating is opaque, the stripes are hollow stripes, and the light emitted by the light emitting device passes through the stripes, and at least P light spots are formed in the calculation area of the image acquisition device.

[0026] In the absolute grating scale system of the present invention, the scale grating is light transmissive, the stripes are opaque stripes, and the light emitted by the light emitting device is blocked by the opaque stripes, and at least P shadows are formed in the calculation area of the image acquisition device.

[0027] The present invention has the following beneficial effects: The absolute grating scale system of the present invention includes a scale grating, a light emitting device, an image acquisition device, and a control device; a plurality of equidistant but uneven-width stripes are provided on the scale grating, and the combination of the widths of any continuous P stripes has a unique value within the range of the grating scale. The stripe image on the scale grating is obtained through the image acquisition device, and the absolute position of the grating scale is determined according to the preset stripe coding rule. Different from the traditional method relying on Moiré fringes, the present invention only requires one scale grating, and the stripe width value in the scale grating can be flexibly set according to actual needs. While ensuring high-precision measurement, the processing difficulty of the grating scale stripes is effectively reduced, and it is also helpful to improve the anti-interference ability of the system, making large-scale production and wide application possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings described herein are used to provide a further understanding of the present invention, and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention, and do not constitute an improper limitation to the present invention.

[0029] Figure 1 It is a schematic structural diagram of an absolute grating scale system provided by an embodiment of the present invention.

[0030] Figure 2 isFigure 1 Schematic diagram of the fringes of the scale grating.

[0031] Figure 3 Schematic diagram of the spot image provided by an embodiment of the present invention.

[0032] Figure 4 Schematic diagram of the structure of the absolute grating scale system provided by another embodiment of the present invention.

[0033] Figure 5 is Figure 3 Schematic diagram of the scale area of the scale grating in

[0034] Figure 6 Schematic diagram of the fringe width and the gap width.

[0035] In the drawings: 1, scale grating; 2, light-emitting device; 3, image acquisition device; 4, control device; 5, input / output device. Specific embodiments

[0036] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0037] The embodiments of the present invention provide an absolute grating scale system, including a scale grating, a light-emitting device, an image acquisition device, and a control device;

[0038] Multiple stripes arranged according to a specific rule are provided on the scale grating, and the combination of the widths of any continuous P stripes has a unique value within the range of the grating scale; the maximum value of the width value of the stripes is 500 times the detection accuracy of the grating scale.

[0039] In the embodiments of the present invention, there can be many situations for the arrangement rule of the stripes, that is, the width of the gap part between the stripes, such as the distance between the central positions of adjacent stripes or adjacent gaps is equal, the spacing between adjacent stripes or adjacent gaps is equal, the sum of the width of a stripe and the adjacent gap is a fixed value, etc. As long as it can be ensured that the width combination of adjacent P stripes has a unique value within the range of the grating scale, and the absolute displacement can be calculated based on its uniqueness. As Figure 6 shown, the white blocks represent the stripes, the black blocks represent the gaps between the stripes, the distance between the central positions of adjacent stripes is equal, but there are various different situations for the stripe and the adjacent gap beside it. It should be noted that Figure 6The numbers in it are only for illustration and not actual width values.

[0040] In the embodiment of the present invention, the absolute position is determined by the uniqueness of the width combination of adjacent P stripes. It can be understood that, based on the same principle, the absolute position can also be determined by the uniqueness of the width combination of adjacent P gaps.

[0041] The light-emitting device and the image acquisition device are respectively located on both sides of the scale grating; the image acquisition device is arranged along the direction perpendicular to the optical path of the light-emitting device. The image acquisition device includes a calculation area in the middle and auxiliary areas at both ends of the calculation area. The calculation area faces the light-emitting device and is used to acquire images corresponding to at least P consecutive stripes. The auxiliary areas are used to acquire images of one or more stripes adjacent to the at least P consecutive stripes corresponding to the calculation area. The image acquisition device can be an optical conversion unit or can include a plurality of optical conversion units arranged at a predetermined interval, such as a complementary metal oxide semiconductor image sensor, a charge-coupled device image sensor, etc.

[0042] In the embodiment of the present invention, the light-emitting device is an LED or a laser light source, and this light source is usually a hemispherical shape with a diameter of 1.6 - 2 mm, or a square shape with a length of 1.6 - 2.5 mm or a rectangular shape with a similar size.

[0043] The images of the stripes acquired by the calculation area of the image acquisition device may be light spots or shadows. In some embodiments of the present invention, the scale grating is opaque, the stripes are hollowed-out stripes, and the hollowed-out stripes are processed by methods such as photolithography, ion beam etching, electron beam machining, femtosecond laser machining, etc. The light emitted by the light-emitting device passes through the stripes and forms at least P light spots in the calculation area of the image acquisition device. In other embodiments of the present invention, the scale grating is transparent, the stripes are opaque stripes, and the light emitted by the light-emitting device is blocked by the opaque stripes, forming at least P shadows in the calculation area of the image acquisition device.

[0044] In the embodiment of the present invention, by adjusting the distances between the light-emitting device 2, the scale grating 1, and the image acquisition device 3 and the width values of the stripes on the scale grating 1, the expected number of stripe images and good image quality are obtained on the image acquisition device. The clarity of the image needs to be high enough to ensure the accuracy of subsequent data analysis.

[0045] The control device determines the absolute position D of the stripe facing the light-emitting device based on the width of the stripe image acquired by the image acquisition device and the preset scale grating stripe coding rule, and calculates the distance E between the center of the stripe and the center point of the image acquisition device, so as to obtain the final absolute position value F = D + E.

[0046] In the embodiments of the present invention, the method for generating the width of the stripe is as follows:

[0047] Generate a specific sequence with unique combinations of any consecutive P values to ensure that each set of P stripe width values is unique within the entire range of the scale grating;

[0048] Multiply each value in the specific sequence by a preset magnification factor to obtain the actual width values of the respective stripes, where the magnification factor is set according to the required detection accuracy and manufacturing process requirements.

[0049] In the embodiments of the present invention, an absolute position recognition method based on an image acquisition device and a preset stripe coding rule is proposed, rather than the traditional relative displacement detection method based on Moiré fringes. Specifically, the present invention obtains the stripe image on the scale grating through the image acquisition device and determines the absolute position of the grating scale according to the preset stripe coding rule. The stripes on the scale grating have specific width combinations, and these width combinations are unique within the range of the grating scale. By analyzing these width combinations, the absolute position of any point on the grating scale can be accurately identified. Different from the traditional method relying on Moiré fringes, the present invention only requires one scale grating, and the stripe width values in the scale grating can be flexibly set according to actual needs, usually set to 10 to 100 times the detection accuracy of the grating scale, and can be set up to 500 times the detection accuracy of the grating scale at most. For example, in some application scenarios, the spot width can be set from 80 microns to 500 microns. This wider spot design not only helps to improve the anti-interference ability of the system, but also significantly reduces the requirements for the processing accuracy of the grating stripes, making large-scale production and wide application possible, especially suitable for those cost-sensitive application scenarios that require high positioning accuracy. In addition, combining the data collected from the auxiliary area further enhances the adaptability under complex working conditions.

[0050] In summary, through innovative stripe coding and image processing technologies, the present invention effectively reduces the processing difficulty of the grating scale stripes while ensuring high-precision measurement, providing a more economical, efficient and reliable solution for high-precision displacement measurement.

[0051] The following further describes the embodiments of the present invention in detail with reference to the accompanying drawings of the specification. It should be understood that the embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0052] Embodiment 1

[0053] As Figure 1As shown in the figure, the present invention provides an embodiment of an absolute grating scale system, which includes a scale grating 1, a light emitting device 2, an image acquisition device 3, a control device 4, and an input / output device 5. The absolute grating scale system in this embodiment is used to measure linear displacement, and the scale grating 1 is straight bar-shaped. As Figure 2 shown, in this embodiment, the scale grating 1 can be made of opaque materials such as metal, ceramic, and plastic, or can be formed by preparing an opaque film or coating on the surface of materials such as glass, plastic, and metal. The stripes are hollow stripes.

[0054] Multiple stripes with equal spacing but uneven widths are provided on the scale grating 1, and the combination of the widths of any continuous P stripes has a unique value within the range of the grating scale; the width value of the stripes is 10 to 100 times the detection accuracy of the grating scale.

[0055] The light emitting device 2 and the image acquisition device 3 are respectively located on both sides of the scale grating 1; the image acquisition device 3 includes a plurality of optical conversion units arranged at a predetermined interval, and the plurality of optical conversion units are arranged in a direction perpendicular to the optical path of the light emitting device 2. The image acquisition device 3 includes a calculation area in the middle and auxiliary areas at both ends of the calculation area. The calculation area faces the light emitting device 2 and is used to collect the light spots corresponding to at least P continuous stripes, and the auxiliary areas are used to collect the images of one or more stripes adjacent to the at least P continuous stripes corresponding to the calculation area. The calculation area faces the light emitting device 2 so that the light received by the calculation area from the light emitting device 2 can basically be regarded as parallel light. Figure 1 In the figure, the calculation area is represented by a cross grid, and the auxiliary areas are represented by diagonal stripes.

[0056] In this embodiment, the light emitting device 2 is an LED or a laser light source, and this light source is usually a hemispherical shape with a diameter of 1.6~2mm, or a square shape with a length of 1.6~2.5mm or a rectangular shape with a similar size.

[0057] The control device 4 determines the absolute position D of the stripe facing the light emitting device 2 based on the width of the light spots collected by the image acquisition device 3 and the preset stripe coding rule of the scale grating, and calculates the distance E between the center of the stripe and the center point of the image acquisition device 3, so as to obtain the final absolute position value F = D + E.

[0058] In practical applications, a guide rail is arranged along the length direction of the scale grating 1, and the light emitting device 2, the image acquisition device 3, the control device 4, and the input / output device 5 are encapsulated in a housing to form a reading head that can slide along the guide rail.

[0059] In this embodiment, the width values of the stripes are generated based on the De Bruijn sequence. Taking P = 2 as an example, the specific generation method of the stripe width values is described as follows:

[0060] (1) Use the De Bruijn sequence generation algorithm to generate a decimal specific sequence with unique combinations of any consecutive 2 values; the specific steps are as follows:

[0061] a. Set the starting calculation base M, and continuously generate calculation base values with a value of M twice;

[0062] b. Generate block structures. In each block structure, the calculation base N increases by 1 in turn. The block structures are generated according to the following rules:

[0063] First, continuously generate two calculation base values with a value of N;

[0064] Generate N - 1, and then repeat N once;

[0065] Generate N - 2, and then repeat N once;

[0066] And so on until M is inserted. At this time, N is no longer repeated and inserted, and the current loop ends.

[0067] The block length corresponding to each calculation base N is 2 + 2×(N - (M + 1)) + 1, that is, 2N - 2M + 1 (applicable to N ≥ M + 1).

[0068] For example, assuming the starting calculation base M = 11 and the calculation base N = 14 of the last block, the generated decimal specific sequence is a De Bruijn sequence with an alphabet of {11, 12, 13, 14} and a subsequence length of 2:

[0069] [11, 11, 12, 12, 11, 13, 13, 12, 13, 11, 14, 14, 13, 14, 12, 14, 11].

[0070] (2) Multiply each value in the specific sequence by a preset amplification factor to obtain the width values of each stripe.

[0071] In this embodiment, each value of the specific sequence is multiplied by the amplification factor 22 to obtain the width values of each stripe. The comparison table of the calculation base and the actual stripe width is shown in Table 1.

[0072] Table 1 Comparison table of specific sequence and stripe width

[0073]

[0074] For ease of understanding, only a partial segment of the scale grating 1 is listed above. In actual applications, the length of a specific sequence is determined according to the requirements of the measurement range. Among the stripe width values generated according to the above method, the combination of the width values of any two consecutive stripes is unique within the full measurement range. Therefore, the absolute position on the scale grating 1 can be determined by the width values of any two stripes. That is to say, in theory, the absolute position of the corresponding stripe on the scale grating 1 can be determined by the two light spots collected in the calculation area centered on the image acquisition device 3.

[0075] In addition to the De Bruijn sequence, other specific sequences can also be adopted in the embodiments of the present invention, as long as the combination of the width values of a continuous group of stripes is unique within the full measurement range.

[0076] In the embodiments of the present invention, the width between the stripes is usually more than 100 μm. Therefore, the influence caused by the diffraction of light between the stripes is small, and only burrs are formed at the edge of the light spot, which does not affect the center position of the light spot. In addition, since the embodiments of the present invention do not calculate the light intensity but find the center position of the light spot, even if there is diffraction, it will not affect the result.

[0077] As Figure 3 shown, the light spots in this embodiment are relatively wide and usually cover more than 25 pixel points on the photosensitive element. To prevent misjudgment, by adjusting the distances between the scale grating 1, the light emitting device 2, and the image acquisition device 3 and the width of the stripes on the scale grating 1, at least 5 light spots can be clearly presented in the calculation area centered on the image acquisition device 3. Then, the absolute position of the central light spot among the 5 light spots is jointly determined by the width values of the light spots. The specific method is as follows:

[0078] (1) First, according to the size of the light spot and the value of the starting calculation base M, determine the calculation base N of the block corresponding to the central light spot and the position L in the block. For example, when the widths of 5 consecutive light spots are determined to be 13, 12, 13, 11, and 14, then N = 13 and L = 4 can be obtained. According to the block corresponding to the central light spot and the position in the block, the first absolute position D is obtained. Specifically:

[0079] Assume that the width corresponding to the starting calculation base M is m, let d = m / M, and assume that the distance between adjacent stripes is s. Then, the first absolute position D can be calculated according to the following piecewise algorithm:

[0080] (1.1) Starting part (corresponding stripes):

[0081] The starting width is M, generated twice, the width of each stripe is m, and the distance between the stripes is s.

[0082] The total length of this part is 2m + s.

[0083] (1.2) Calculate the total length T1 of all the blocks before the calculation (from M + 1 to N - 1):

[0084] For each block corresponding to k (M + 1 ≤ k ≤ N - 1), according to the rule:

[0085] First, generate k twice, with each stripe width being k*d, and the length of this part is 2k*d.

[0086] Then generate k - 1 and repeat k once; generate k - 2 and repeat k once; and so on until M is inserted (no longer repeat inserting k).

[0087] There are k - M numbers from k - 1 to M, so the length of this part is d*(k - 1 + M)*(k - M) / 2.

[0088] The distance between the stripes within each block, among the stripes calculated above, there are k - M + 1 intervals, with a length of (k - M + 1)*s, and there is a distance s between the end of each block and the start of the next block.

[0089] In summary, the total length for each corresponding block is 2k*d + s + d*(k - 1 + M)*(k - M) / 2 + (k - M + 1)*s + s.

[0090] The total length of all the blocks from M + 1 to N - 1 is .

[0091] (1.3)Calculate the length of the first L stripes in the block corresponding to N:

[0092] First, generate N twice, with each stripe width being N*d.

[0093] If L = 1, the length of this part is N*d, and adding the distance s between this stripe and the previous part to the total length of all the previous parts, at this time the main displacement D = 2m + s + T1 + s + N*d.

[0094] If L = 2, the length of this part is 2N*d, with one interval s, and at this time the main displacement D = 2m + s + T1 + s + 2N*d + s.

[0095] If L > 2:

[0096] The length of the first two stripes is 2N*d, with one interval s.

[0097] Starting from the 3rd stripe, it is generated according to the rule of N - 1 and repeat N once; N - 2 and repeat N once; and so on.

[0098] Let p = L - 2, for the stripes from N - 1 to N - q (q satisfies 2q ≥ L - 2), the length of this part is Group (each group has a decreasing number and an N), with a length of T2 = .

[0099] This There are -1 intervals between these groups, plus 1 interval between the first two Ns, for a total of intervals, with an interval length of *s.

[0100] If p is even, there are no remaining stripes; if p is odd, add the width of the remaining decreasing numbers (N - -1)*d, and the interval s between this part and the previous one.

[0101] Therefore, the first absolute position D = 2m + s + T1 + s + 2N*d + s + T2 + *s + (p mod 2)*(N - -1)*d + s.

[0102] (2) Then calculate the distance E corresponding to the center of the central spot and the center point of the image acquisition device 3. Any of the following methods can be selected:

[0103] (2.1) Centroid method: First, preprocess the image collected by the image acquisition device, such as denoising, grayscale conversion, etc. Then, separate the spot from the background through methods such as threshold segmentation to obtain a binary image. Finally, calculate the center coordinates of the spot according to the centroid calculation formula. For a binary spot image, assuming the pixel coordinates of the spot area in the image are (xi) and their corresponding weights are mi, the centroid is (xc), where xc = . Here, the weight is usually the pixel value (1 represents the spot pixel, 0 represents the non-spot pixel), and it can also be other meaningful physical quantities.

[0104] (2.2) Fitting algorithm: After preprocessing the spot image, extract the boundary points or feature points of the spot. Then use the fitting algorithm to fit these points to obtain the parameters of the fitting model, thereby determining the center coordinates of the spot. Usually, ellipse fitting, Gaussian function fitting, etc. are used.

[0105] Assume the stripe width is 100um, there are 21 pixels in one stripe, and the pixel pitch is 5 microns. According to the principle of sub-pixel subdivision, the accuracy that can be achieved through the calculation of the centroid method or the fitting algorithm is 1um, that is, an accuracy of 1um can be achieved through a 100um stripe.

[0106] (3) Calculate the absolute position F = D + E, which is the final result.

[0107] It should be noted that if there is an offset G at the zero point when the measurement starts, the offset value should be subtracted, i.e., F = D + E - G. The offset G of the zero point can be input by the input / output device before the measurement. After the absolute position calculation is completed, the reading is output through the input / output device.

[0108] In practical applications, information such as the starting calculation base M, the ending calculation base N, the adjacent fringe spacing s, the magnification factor, the number of fringes, and the relative position of the calculation area is programmed into the control device. When using the grating scale system for measurement, the control device can quickly lock the position of the calculation area, extract the corresponding spot image, and quickly calculate the absolute position according to the preset parameters. Then, based on the change in the absolute position within two adjacent time intervals and the arrangement pattern of the fringes, the direction of displacement can be determined.

[0109] In practical applications, if the spot size formed by the fringes is too small or unclear due to insufficient brightness of the light-emitting device 2, making it inconvenient to calculate the absolute position value, a threshold for the number of pixels within a spot can be set. The control device is also used to monitor in real time the number of pixels contained in the image of a single fringe collected by the image acquisition device. When the number of pixels is less than the preset threshold, the power of the light-emitting device is increased.

[0110] Embodiment 2

[0111] The difference between this embodiment and Embodiment 1 is that when generating the fringe width in this embodiment, a De Bruijn sequence with an alphabet of {1, 2, 3, 4} and a subsequence length of 3 is generated: [1, 1, 1, 2, 1, 1, 3, 1, 1, 4, 1, 2, 2, 1, 2, 3, 1, 2, 4, 1, 3, 2, 1, 3, 3, 1, 3, 4, 1, 4, 2, 1, 4, 3, 1, 4, 4, 2, 2, 2, 3, 2, 2, 4, 2, 3, 3, 2, 3, 4, 2, 4, 3, 2, 4, 4, 3, 3, 3, 4, 3, 4, 4, 4].

[0112] In this embodiment, the combination of the width values of any three consecutive fringes is unique within the full range. Similar to Embodiment 1, theoretically, the absolute position can be determined through the positions of three spots.

[0113] It can be understood that the length of the subsequence in the De Bruijn sequence can also be values such as 4 or 5.

[0114] Embodiment 3

[0115] The difference between this embodiment and the first embodiment is as follows: The scale grating 1 is made of a light-transmitting material, and the stripes are light-blocking stripes, which are formed by methods such as coating or plating. The light emitted by the light-emitting device 2 is blocked by the light-blocking stripes, forming multiple shadows on the image acquisition device 3, and the absolute position is determined by the shadows collected on the image acquisition device 3.

[0116] Embodiment Four

[0117] In this embodiment, if the number of stripe images in the calculation area of the image acquisition device 3 is insufficient or the recognition is incorrect, the width and central coordinates of the stripe images in the auxiliary area are corrected, and then the auxiliary area is used to assist in calculating the absolute position. Due to the light angle problem, the width of the stripe images in the auxiliary area is usually larger than the actual stripe width value and needs to be corrected, and the central position of the stripe images also shifts and needs to be corrected. Assume that the distance from the light-emitting device to the scale grating is △, the distance from the scale grating to the image acquisition device is δ, m is the width value of the first stripe, with the center of the image acquisition device as the origin, the correction amount of the stripe image width is δ * tan(m / △), and the central coordinates of the stripe images in the auxiliary area after correction are (xc = , yc = ±δ * tan(m / △)). If the ordinate of the center of the stripe image is less than 0, the sign before the correction amount in yc is taken as -; if the ordinate of the center of the stripe image is greater than 0, the sign before the correction amount in yc is taken as +.

[0118] Embodiment Five

[0119] As Figure 4 shown, the present invention provides an embodiment of an absolute grating scale system, including a scale grating 1, a light-emitting device 2, an image acquisition device 3, a control device 4, and an input / output device 5.

[0120] The difference between this embodiment and the first embodiment is as follows: The absolute grating scale system in this embodiment is used to measure the rotation angle. The scale grating 1 is a circular grating disk, and an annular grating scale area is provided on the grating disk. The distance between the central positions of adjacent stripes is equal, or the sum of the width of a stripe and the gap beside it is a fixed value. The light-emitting device 2, the image acquisition device 3, the control device 4, and the input / output device 5 are encapsulated in a housing. During the measurement process, the housing remains stationary, and the scale grating 1 can rotate around its center. The circular angle grating is also provided with other mechanical structures, which are not relevant to the focus of the present invention and will not be elaborated here.

[0121] In this embodiment, the scale grating 1 is light-blocking, and the stripes are hollow stripes. As Figure 5As shown, the white part is the stripe. Multiple equally spaced stripes are provided in the circular scale area of the scale grating 1, and the combination of the widths of any continuous P stripes has a unique value within the measuring range of the grating scale. In this embodiment, the scale area of the scale grating 1 is equivalent to changing the linear scale area in the first embodiment into a circular shape. The stripes present a radiation stripe effect starting from the center of the scale grating 1, and the extension line of the long side of the stripe passes through the center of the circle.

[0122] The method for calculating the rotation angle in this embodiment is as follows:

[0123] (1) Determine the starting position: Determine the position of the central light spot collected by the image acquisition device at the start of measurement according to the method in the first embodiment.

[0124] (2) Determine the number of rotations: Each time the imaging device collects the starting position, the number of rotations +1.

[0125] (3) Determine the ending position: Determine the position of the central light spot collected by the image acquisition device at the end of measurement according to the method in the first embodiment.

[0126] (4) Calculate the rotation angle: Rotation angle = Angle corresponding to the ending position - Angle corresponding to the starting position + 360 * Number of rotations.

[0127] Among them, there are two calculation methods for the angle corresponding to the ending position - the angle corresponding to the starting position:

[0128] (4.1) First, calculate the absolute positions at the starting position and the ending position according to the method in the first embodiment to obtain the arc length between the starting position and the ending position, and then calculate the angle corresponding to the arc length, that is, obtain the angle value between the starting position and the ending position.

[0129] (4.2) Calculate the angle corresponding to each stripe according to the number of stripes in the circular scale area of the scale grating. Calculate the number of stripes passed according to the stripe positions at the starting position and the ending position to obtain the angle value between the starting position and the ending position. Suppose there are a total of 16 stripes. Since the spacing between adjacent stripes is the same, the angle corresponding to each stripe is 360° / 16 = 22.5°. If there are 8 stripes between the starting position and the ending position, then the angle value between the starting position and the ending position is 22.5° * 8 = 180°.

[0130] If the average rotational speed is to be calculated, then ω = φ / (2π * t), where φ is the rotational angle in the above text and t is the time from the start to the end. If the instantaneous rotational speed is to be calculated, then ω’ = 360° / (Q * 2π * t’), where Q is the total number of fringes and t’ is the time from the center position of one shadow to the center position of the next shadow. It can be determined whether it is rotating clockwise or counterclockwise based on the position change of adjacent time fringes and the arrangement pattern of the fringes.

[0131] Embodiment Six

[0132] The difference between this embodiment and Embodiment Five is that the scale grating 1 is made of a light-transmitting material, the fringes are light-impermeable fringes, and the fringes are formed by methods such as coating or plating. The light emitted by the light-emitting device 2 is blocked by the light-impermeable fringes, and multiple shadows are formed on the image acquisition device 3, and the absolute position is determined by the shadows collected on the image acquisition device 3.

[0133] The above are only specific embodiments of the present invention and cannot be used to limit the scope of the present invention. Equivalent changes made by those of ordinary skill in the art based on this creation, as well as changes well-known to those skilled in the art, should still fall within the scope covered by the present invention.

Claims

1. An absolute grating scale system, characterized in that, It includes a scale grating, a light-emitting device, an image acquisition device, and a control device; Multiple stripes arranged according to a specific rule are provided on the scale grating, and the combination of the widths of any continuous P stripes has a unique value within the range of the grating scale; The arrangement rule of the P stripes and the gaps between the P stripes includes: the distance between the central positions of adjacent stripes or adjacent gaps is equal, the spacing between adjacent stripes or adjacent gaps is equal, and the sum of the width of a stripe and the width of the adjacent gap is a fixed value; The light-emitting device and the image acquisition device are respectively located on both sides of the scale grating; the image acquisition device is arranged in a direction perpendicular to the optical path of the light-emitting device, and the image acquisition device includes a calculation area in the middle, and the calculation area faces the light-emitting device and is used to acquire images corresponding to at least P continuous stripes; The control device determines the absolute position D of the stripe facing the light-emitting device based on the width of the stripe image acquired by the image acquisition device and the preset stripe encoding rule of the scale grating, and calculates the distance E between the center of the stripe and the center point of the image acquisition device by using the centroid method or the fitting algorithm, so as to obtain the final absolute position value F = D + E; The method for generating the width of the stripe is as follows: Generate a specific sequence with a unique combination of any continuous P values; Multiply each value in the specific sequence by a preset magnification factor to obtain the actual width values of the respective stripes, and the magnification factor is set according to the required detection accuracy and the requirements of the manufacturing process; The specific sequence includes a De Bruijn sequence.

2. The absolute grating scale system according to claim 1, characterized in that The absolute grating scale system is used to measure linear displacement, and the scale grating is straight.

3. The absolute grating scale system according to claim 1, wherein The absolute grating scale system is used to measure the rotation angle, the scale grating is a circular grating disc, and an annular grating scale area is provided on the grating disc.

4. The absolute grating scale system according to claim 2, characterized in that, The image acquisition device further includes auxiliary areas at both ends of the calculation area, and the auxiliary areas are used to acquire images of one or more stripes adjacent to at least P continuous stripes corresponding to the calculation area; If the number of stripe images in the calculation area of the image acquisition device is insufficient or misidentified, correct the width and center coordinates of the stripe images in the auxiliary area, and then use the auxiliary area to assist in calculating the absolute position.

5. The absolute grating scale system according to claim 3, characterized in that, For measuring the rotation angle, the rotation angle calculation method is as follows: Determine the starting position; Determine the number of turns of rotation; Determine the ending position; Calculate the rotation angle: rotation angle = the angle corresponding to the ending position - the angle corresponding to the starting position + 360 * the number of turns; Wherein: there are two calculation methods for the angle corresponding to the ending position - the angle corresponding to the starting position: One, first calculate the absolute positions corresponding to the starting position and the ending position, obtain the arc length between the starting position and the ending position, and then calculate the angle corresponding to the arc length, that is, obtain the angle value between the starting position and the ending position; Or: Two, calculate the angle corresponding to each stripe according to the number of stripes in the annular scale grating scale area, calculate the number of stripes passed according to the stripe positions at the starting position and the ending position, and obtain the angle value between the starting position and the ending position.

6. The absolute grating scale system according to claim 1, wherein The control device is further configured to monitor in real time the number of pixels included in the image of a single stripe collected by the image acquisition device, and when the number of pixels is less than a preset threshold, increase the power of the light-emitting device.

7. The absolute grating scale system according to claim 1, wherein The scale grating is opaque, the stripe is a hollow stripe, and the light emitted by the light-emitting device passes through the stripe, forming at least P light spots in the calculation area of the image acquisition device.

8. The absolute grating scale system according to claim 1, wherein The scale grating is transparent, the stripe is an opaque stripe, and the light emitted by the light-emitting device is blocked by the opaque stripe, forming at least P shadows in the calculation area of the image acquisition device.

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