Absolute grating ruler system

Abstract

The invention discloses an absolute grating ruler system, and belongs to the technical field of measuring instruments. The absolute grating ruler system comprises a scale grating, a light-emitting device, an image acquisition device and a control device, the scale grating is provided with a plurality of stripes which are arranged at equal intervals and are uneven in width, and the combination of the widths of any continuous P stripes has a unique value in the measuring range of the grating scale. A stripe image on the scale grating is acquired through an image acquisition device, and the absolute position of the grating scale is determined according to a preset stripe coding rule. Different from a traditional method depending on moire fringes, only one scale grating is needed, the fringe width value in the scale grating can be flexibly set according to actual requirements, high-precision measurement is guaranteed, meanwhile, the processing difficulty of grating scale fringes is effectively lowered, the anti-interference capacity of a system is improved, and the method is suitable for popularization and application. And large-scale production and wide application become possible.

Description

Technical Field

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

[0002] Traditional grating rulers usually consist of two parts: the scale grating and the indicator grating. The stripes on these two gratings overlap each other, forming a kind of alternating light and dark stripes in the overlapping area, which is called moiré fringes. 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 direction of movement. The measurement accuracy of traditional grating rulers based on the above principle is closely related to the width of their grating stripes. Generally speaking, when the stripe width is at the micron level, the grating ruler can achieve micron-level accuracy. However, as the grating stripes become thinner and thinner, its processing difficulty increases significantly, resulting in an increase in manufacturing costs and a decrease in production yield. The high manufacturing cost and low production yield of this high-precision grating ruler greatly limit its wide application and popularity, especially in applications that require high-precision displacement measurement.

[0003] In order to overcome the above problems, the market urgently needs a technical solution that can maintain high-precision measurement capabilities while reducing manufacturing complexity, improving production efficiency and reducing costs. Summary of the invention

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

[0005] To achieve the above-mentioned object, the present invention provides an absolute grating ruler system, including a scale grating, a light emitting device, an image acquisition device, and a control device; The scale grating is provided with a plurality of stripes arranged in a specific pattern, and the combination of the widths of any continuous P stripes has a unique value within the measuring range of the grating scale; 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 light path of the light emitting device, and the image acquisition device includes a calculation area located in the middle, the calculation area is directly opposite to 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 directly facing the light-emitting device based on the width of the stripe image captured 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, thereby obtaining the final absolute position value F=D+E.

[0006] In the absolute grating ruler system of the present invention, the method for generating the width of the stripes is: Generate a unique sequence of any combination of P consecutive values; Each value in the specific sequence is multiplied by a preset magnification factor to obtain the actual width value of each stripe. The magnification factor is set according to the required detection accuracy and the requirements of the manufacturing process.

[0007] In the absolute grating ruler system of the present invention, the specific sequence is the De Bruijn sequence.

[0008] In the absolute grating ruler system of the present invention, the absolute grating ruler system is used to measure linear displacement, and the ruler grating is in the shape of a straight bar.

[0009] In the absolute grating ruler system of the present invention, the absolute grating ruler system is used to measure the rotation angle, the ruler grating is a circular grating disk, and a circular grating scale area is arranged on the grating disk.

[0010] In the absolute grating ruler system of the present invention, the image acquisition device also includes auxiliary areas located 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 the recognition is incorrect, the width and center coordinates of the stripe image in the auxiliary area are corrected, and then the auxiliary area is used to assist in the calculation of the absolute position.

[0011] In the absolute grating ruler system of the present invention, the rotation angle calculation method is as follows: Determine the starting position; Determine the number of rotations; Determine the end position; Calculate the rotation angle: rotation angle = angle corresponding to the end position - angle corresponding to the starting position + 360*number of turns; There are two ways to calculate the angle corresponding to the end position minus the angle corresponding to the start position: 1. First, calculate the absolute positions corresponding to the starting position and the ending position 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, to obtain the angle value between the starting position and the ending position; Second, the angle corresponding to each stripe is calculated based on the number of stripes in the circular scale grating scale area, and the number of stripes passed is calculated based on the stripe positions at the starting position and the ending position to obtain the angle value between the starting position and the ending position.

[0012] In the absolute grating ruler system of the present invention, the control device is also used to monitor in real time the number of pixels contained in the image of a single stripe acquired by the image acquisition device, and when the number of pixels is less than a preset threshold, the power of the light-emitting device is increased.

[0013] In the absolute grating ruler 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 to form at least P light spots in the calculation area of ​​the image acquisition device.

[0014] In the absolute grating ruler system of the present invention, the scale grating is light-transmissive, the stripes are opaque stripes, 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.

[0015] The present invention has the following beneficial effects: the absolute grating ruler system of the present invention includes a scale grating, a light emitting device, an image acquisition device, and a control device; the scale grating is provided with a plurality of stripes with equal spacing but uneven width, and the combination of the widths of any continuous P stripes has a unique value within the range of the grating ruler. The stripe image on the scale grating is acquired by the image acquisition device, and the absolute position of the grating ruler is determined according to a preset stripe encoding rule. Unlike the traditional method that relies 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, it effectively reduces the processing difficulty of the grating ruler stripes, and also helps to improve the anti-interference ability of the system, making large-scale production and wide application possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings described herein are used to provide further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0017] Figure 1 A schematic structural diagram of an absolute grating ruler system provided for one embodiment of the present invention.

[0018] Figure 2 for Figure 1 Schematic diagram of the fringes of a medium-scale grating.

[0019] Figure 3 A schematic diagram of a light spot image provided by an embodiment of the present invention.

[0020] Figure 4 A schematic structural diagram of an absolute grating ruler system provided in another embodiment of the present invention.

[0021] Figure 5 for Figure 3Schematic diagram of the scale area of ​​the ruler grating in .

[0022] Figure 6 Schematic diagram of stripe width and gap width.

[0023] In the attached drawings: 1. scale grating; 2. light emitting device; 3. image acquisition device; 4. control device; 5. input and output device. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] The embodiment of the present invention provides an absolute grating ruler system, including a ruler grating, a light emitting device, an image acquisition device, and a control device; The scale grating is provided with a plurality of stripes arranged in a specific pattern, and the combination of the widths of any continuous P stripes has a unique value within the measuring range of the grating scale; the maximum value of the width of the stripes is 500 times the detection accuracy of the grating scale.

[0026] In the embodiment of the present invention, the arrangement rule of the stripes, that is, the width of the gaps between the stripes, can be in many cases, such as the distance between the center positions of adjacent stripes or adjacent gaps is equal, the spacing between adjacent stripes or adjacent gaps is equal, the sum of the widths of the stripes and the gaps next to them is a fixed value, etc., as long as it can be ensured that the width combination of P adjacent stripes has a unique value within the range of the grating ruler, and the absolute displacement can be calculated based on its uniqueness. Figure 6 As shown, white blocks represent stripes, black blocks represent gaps between stripes, and the distances between the centers of adjacent stripes are equal, but there are various situations between stripes and the gaps next to them. It should be noted that Figure 6 The numbers are for illustration only and are not the actual width values.

[0027] The embodiment of the present invention determines the absolute position by the uniqueness of the combination of widths of P adjacent stripes. It is understandable that, based on the same principle, the absolute position can also be determined by the uniqueness of the combination of widths of P adjacent gaps.

[0028] 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 located in the middle and auxiliary areas located at both ends of the calculation area, the calculation area is directly opposite to the light emitting device, and is used to acquire images corresponding to at least P continuous stripes, and the auxiliary area is used to acquire images of one or more stripes adjacent to the at least P continuous stripes corresponding to the calculation area. The image acquisition device can be an optical conversion unit, or it can include multiple optical conversion units arranged at predetermined intervals, such as a complementary metal oxide semiconductor image sensor, a charge coupled device image sensor, etc.

[0029] In the embodiment of the present invention, the light emitting device is an LED or laser light source, which is usually in the shape of a hemisphere with a diameter of 1.6-2 mm, or a square with a length of 1.6-2.5 mm, or a rectangle with similar size.

[0030] The image of the stripes collected in the calculation area of ​​the image acquisition device may be a light spot or a shadow. In some embodiments of the present invention, the scale grating is opaque, and the stripes are hollow stripes, which are processed by photolithography, ion beam etching, electron beam processing, femtosecond laser processing and other methods. 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. In other embodiments of the present invention, the scale grating is translucent, and the stripes are opaque stripes. 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.

[0031] In the embodiment of the present invention, by adjusting the distances among the light emitting device 2, the scale grating 1, and the image acquisition device 3 and the width of the stripes on the scale grating 1, an 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.

[0032] The control device determines the absolute position D of the stripe directly facing the light-emitting device based on the width of the stripe image captured 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, thereby obtaining the final absolute position value F=D+E.

[0033] In the embodiment of the present invention, the method for generating the width of the stripes is: Generate a unique sequence of any combination of P consecutive values ​​to ensure that each group of P fringe width values ​​is unique within the entire scale grating range; Each value in the specific sequence is multiplied by a preset magnification factor to obtain the actual width value of each stripe. The magnification factor is set according to the required detection accuracy and the requirements of the manufacturing process.

[0034] In an embodiment 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 a traditional relative displacement detection method based on moiré fringes. Specifically, the present invention obtains a stripe image on a scale grating through an image acquisition device, and determines the absolute position of the grating ruler according to a preset stripe coding rule. The stripes on the scale grating have a specific width combination, and these width combinations are unique within the range of the grating ruler. By analyzing these width combinations, the absolute position of any point on the grating ruler can be accurately identified. Unlike the traditional method that relies on moiré fringes, the present invention only requires a scale grating, and the stripe width value 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 ruler, and can be set to a maximum of 500 times the detection accuracy of the grating ruler. For example, in some application scenarios, the spot width can be set to 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 for those application scenarios that are cost-sensitive but require high positioning accuracy. In addition, combined with the data collected in the auxiliary areas, the ability to adapt to complex working conditions is further enhanced.

[0035] In summary, the present invention uses innovative fringe coding and image processing technology to effectively reduce the difficulty of processing grating scale stripes while ensuring high-precision measurement, providing a more economical, efficient and reliable solution for high-precision displacement measurement.

[0036] The embodiments of the present invention are further described in detail below in conjunction with 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.

[0037] Embodiment 1 like Figure 1 As shown, the present invention provides an embodiment of an absolute grating ruler 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. The absolute grating ruler system in this embodiment is used to measure linear displacement, and the scale grating 1 is a straight strip. Figure 2 As shown, in this embodiment, the scale grating 1 can be made of opaque materials such as metal, ceramic, plastic, etc., and can also be formed by preparing an opaque film or coating on the surface of glass, plastic, metal, etc., and the stripes are hollow stripes.

[0038] The scale grating 1 is provided with a plurality of stripes with equal spacing but uneven width, and the combination of the widths of any continuous P stripes has a unique value within the measuring range of the grating scale; the width value of the stripes is 10 to 100 times the detection accuracy of the grating scale.

[0039] 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 predetermined intervals, 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 located in the middle and auxiliary areas located at both ends of the calculation area; the calculation area is directly opposite to the light emitting device 2 and is used to collect light spots corresponding to at least P continuous stripes, and the auxiliary area is used to collect images of one or more stripes adjacent to at least P continuous stripes corresponding to the calculation area. The calculation area is directly opposite to the light emitting device 2, so that the light from the light emitting device 2 received by the calculation area can basically be regarded as parallel light. Figure 1 In the figure, the calculation area is represented by a cross grid, and the auxiliary area is represented by a diagonal stripe.

[0040] In this embodiment, the light emitting device 2 is an LED or laser light source, which is usually in the shape of a hemisphere with a diameter of 1.6-2 mm, or a square with a length of 1.6-2.5 mm, or a rectangle with similar dimensions.

[0041] The control device 4 determines the absolute position D of the stripe directly facing the light-emitting device 2 based on the width of the light spot captured by the image acquisition device 3 and the preset scale grating stripe encoding rule, and calculates the distance E between the center of the stripe and the center point of the image acquisition device 3, thereby obtaining the final absolute position value F=D+E.

[0042] In practical applications, a guide rail is provided 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.

[0043] In this embodiment, the width value of the stripe is generated based on the De Bruijn sequence. The specific method for generating the stripe width value is described below by taking P=2 as an example: (1) Use the De Bruijn sequence generation algorithm to generate a unique decimal sequence for any combination of two consecutive values. The specific steps are as follows: a. Set the starting calculation base M and generate two calculation base values ​​with the value of M in succession; b. Generate a block structure. In each block structure, the calculation base N increases by 1. The block structure is generated according to the following rules: First, two calculation base values ​​of N are generated continuously; Generate N-1, and repeat once more for N; Generate N-2, and repeat once more for N; And so on, until M is inserted, at which time N is no longer inserted repeatedly and the current loop ends.

[0044] 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).

[0045] For example, assuming that the starting calculation base M = 11 and the calculation base N of the end block is 14, the generated decimal specific sequence is the De Bruijn sequence with an alphabet of {11, 12, 13, 14} and a subsequence length of 2: [11,11,12,12,11,13,13,12,13,11,14,14,13,14,12,14,11].

[0046] (2) Multiply each value in the specific sequence by a preset magnification factor to obtain the width value of each stripe.

[0047] In this embodiment, each value of the specific sequence is multiplied by the magnification factor 22 to obtain the width value of each stripe. The calculation base and the actual width of the stripe comparison table are shown in Table 1.

[0048] Table 1 Comparison table of specific sequences and stripe width

[0049] For ease of understanding, only some fragments of the scale grating 1 are listed above. In practical applications, the length of a specific sequence is determined according to the needs of the range. Among the stripe width values ​​generated by the above method, the combination of the width values ​​of any two consecutive stripes is unique within the full range, so the absolute position of any two stripes on the scale grating 1 can be determined by the width values ​​of the stripes. In other words, in theory, the absolute position of the corresponding stripes on the scale grating 1 can be determined by the two light spots collected by the calculation area at the center of the image acquisition device 3.

[0050] In addition to the De Bruijn sequence, the embodiment of the present invention may also use other specific sequences, as long as the combination of the width values ​​of a group of continuous stripes is unique within the full range.

[0051] In the embodiment of the present invention, the width between the stripes is usually more than 100um, so the impact of the diffraction of light between the stripes is small, and only burrs are formed on the edge of the light spot, which will not affect the center position of the light spot; in addition, because the embodiment of the present invention does not calculate the light intensity, but finds the center position of the light spot, even if there is diffraction, it will not affect the result.

[0052] like Figure 3 As shown, the light spot in this embodiment is relatively wide, usually covering more than 25 pixels on the photosensitive element. In order 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 at the center of 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 value of the light spot. The specific method is as follows: (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 five consecutive light spots are determined to be 13, 12, 13, 11, and 14, it can be obtained that N=13 and L=4. According to the block corresponding to the central light spot and its position in the block, the first absolute position D is obtained. Specifically: Assuming that the width corresponding to the starting calculation base M is m, let d = m / M, and assuming that the spacing between adjacent stripes is s, the first absolute position D can be calculated according to the following segmentation algorithm: (1.1) Initial part (corresponding stripes): The starting width is M, generated twice, each stripe width is m, and the distance between stripes is s.

[0053] The total length of this section is 2m+s.

[0054] (1.2) Calculate the total length T1 of all previous blocks (from M+1 to N-1): For each k (M+1≤k≤N-1) corresponding block, according to the rules: First, generate k twice, each stripe width is k*d, and the length of this part is 2k*d.

[0055] Then generate k-1, and repeat k again; generate k-2, and repeat k again; and so on, until M is inserted (k is no longer inserted repeatedly).

[0056] There are kM numbers from k-1 to M, so the length of this part is d*(k-1+M)*(kM) / 2.

[0057] The distance between stripes in each block is k-M+1 intervals between the stripes calculated above, with a length of (k-M+1)*s, and there is a distance s between the end of each block and the beginning of the next block.

[0058] In summary, the total length of each corresponding block is 2k*d+s+d*(k-1+M)*(kM) / 2+(k-M+1)*s+s.

[0059] The total length of all blocks from M+1 to N-1 is .

[0060] (1.3) Calculate the length of the first L stripes in the block corresponding to N: First generate N twice, each stripe width is N*d.

[0061] If L=1, the length of this part is N*d, and the total length of all previous parts plus the interval s between this stripe and the previous one, then the main displacement D=2m+s+T1+s+N*d.

[0062] If L=2, the length of this part is 2N*d, and there is a gap s. At this time, the main displacement D=2m+s+T1+s+2N*d+s.

[0063] If L>2: The first two stripes have length 2N*d and are separated by a gap s.

[0064] Starting from the 3rd stripe, it is generated according to the rule of N-1, then repeat N; N-2, then repeat N; and so on.

[0065] Assume p=L-2, the length of the stripe from N-1 to Nq (q satisfies 2q≥L-2), this part has Groups (one decreasing number and one N per group) of length T2= .

[0066] this There are -1 interval, plus 1 interval between the first two N, for a total of intervals, the interval length is *s.

[0067] If p is even, there are no remaining stripes; if p is odd, add the width of the remaining decreasing number (N- -1) *d, and the interval s between this part and the previous one.

[0068] Therefore, the first absolute position D = 2m + s + T1 + s + 2N * d + s + T2 + *s+(p mod 2)*(N- -1)*d+s.

[0069] (2) Then, the distance E between the central light spot and the center point of the image acquisition device 3 is calculated. Any of the following methods can be selected: (2.1) Centroid method: First, preprocess the image collected by the image acquisition device, such as denoising, grayscale, etc. Then separate the light spot from the background by threshold segmentation and other methods to obtain a binary image. Finally, calculate the center coordinates of the light spot according to the centroid calculation formula. For a binary light spot image, assuming that the pixel coordinates of the light spot area in the image are (xi), and its corresponding weight is mi, then the centroid is (xc), where xc= The weight here is usually a pixel value (1 represents a spot pixel, 0 represents a non-spot pixel), or it can be other meaningful physical quantities.

[0070] (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.

[0071] Assuming that the stripe width is 100um, there are 21 pixels in a stripe, and the pixel pitch is 5 microns, according to the principle of sub-pixel subdivision, the accuracy that can be achieved through the centroid method or fitting algorithm is 1um, that is, the accuracy of 1um can be achieved through a 100um stripe.

[0072] (3) The absolute position F = D + E is calculated, which is the final result.

[0073] It should be noted that if there is an offset G at the beginning of the measurement, the offset value should be subtracted, F=D+EG. The offset G of the zero point can be entered by the input and output device before measurement. After the absolute position calculation is completed, the reading is output through the input and output device.

[0074] In practical applications, the control device is programmed with information such as the starting calculation base M, the ending calculation base N, the adjacent stripe spacing s, the magnification factor, the number of stripes, the relative position of the calculation area, etc. When using the grating ruler 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, and then determine the direction of displacement according to the change of the absolute position in two adjacent time intervals and the arrangement of the stripes.

[0075] In practical applications, if the light spot size formed by the stripes is too small or unclear due to insufficient brightness of the light emitting device 2, and it is inconvenient to calculate the absolute position value, a threshold value of the number of pixels in the light 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 stripe collected by the image acquisition device, and when the number of pixels is less than the preset threshold value, the power of the light emitting device is increased.

[0076] Embodiment 2 3, 3, 1, 3, 4, 1, 4, 2, 1, 4, 3, 1, 4, 4, 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, 4, 3, 3, 3, 4, 4, 4, 4, 3, 4, 4, 4, 4, 4, 3, 3, 3, 4, 4, 4, 4, 4, 3, 4, 4, 4, 4, 4, 4, 3, 3, 3, 4, 4, 4, 4, 4.

[0077] In this embodiment, any combination of width values ​​of three consecutive stripes is unique within the full range. As in the first embodiment, the absolute position can be determined theoretically by the positions of the three light spots.

[0078] It is understandable that the length of the subsequence in the De Bruijn sequence may also be 4, 5, or other values.

[0079] Embodiment 3 The difference between this embodiment and the first embodiment is that the scale grating 1 is made of a light-transmitting material, and the stripes are opaque stripes, which are formed by methods such as plating or coating. The light emitted by the light-emitting device 2 is blocked by the opaque stripes, forming multiple shadows on the image acquisition device 3, and the absolute position is determined by the shadows collected by the image acquisition device 3.

[0080] Embodiment 4 In this embodiment, 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 center coordinates of the stripe image in the auxiliary area are corrected, and then the auxiliary area is used to assist in calculating the absolute position. Because of the angle of light, the width of the stripe image in the auxiliary area is usually larger than the actual stripe width value, and needs to be corrected. The center position of the stripe image is also offset and needs to be corrected. Assuming 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, and the center of the image acquisition device is taken as the origin. The correction amount of the stripe image width is δ*tan (m / △), and the center coordinates of the stripe image in the auxiliary area after correction are (xc= ,yc= ±δ*tan(m / △))), if the ordinate of the center of the fringe image is less than 0, the sign before the correction amount in yc is -; if the ordinate of the center of the fringe image is greater than 0, the sign before the correction amount in yc is +.

[0081] Embodiment 5 like Figure 4As shown, the present invention provides an embodiment of an absolute grating ruler system, including a ruler grating 1, a light emitting device 2, an image acquisition device 3, a control device 4 and an input-output device 5.

[0082] The difference between this embodiment and the first embodiment is that the absolute grating ruler system in this embodiment is used to measure the rotation angle, the scale grating 1 is a circular grating disk, and the grating disk is provided with a circular grating scale area, and the distance between the center positions of adjacent stripes is equal, or the sum of the widths of the stripes and the gaps next to them 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, and 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 irrelevant to the focus of the present invention and will not be repeated here.

[0083] In this embodiment, the scale grating 1 is opaque and the stripes are hollow stripes. Figure 5 As shown, the white part is a stripe, and a plurality of stripes with equal spacing are arranged in the annular scale area of ​​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 scale area of ​​the scale grating 1 in this embodiment is equivalent to converting the linear scale area of ​​the first embodiment into a ring. The stripes present a radial 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.

[0084] The rotation angle calculation method of this embodiment is as follows: (1) Determine the starting position: Determine the position of the central light spot captured by the image acquisition device when starting measurement according to the method of Embodiment 1.

[0085] (2) Determine the number of rotations: Each time the imaging device captures the starting position, the number of rotations increases by 1.

[0086] (3) Determine the end position: Determine the position of the central light spot captured by the image acquisition device at the end of the measurement according to the method of the first embodiment.

[0087] (4) Calculate the rotation angle: rotation angle = angle corresponding to the end position - angle corresponding to the starting position + 360*number of turns.

[0088] There are two ways to calculate the angle corresponding to the end position - the angle corresponding to the start position: (4.1) First, the absolute positions at the starting position and the ending position are calculated according to the method of Example 1 to obtain the arc length between the starting position and the ending position, and then the angle corresponding to the arc length is calculated to obtain the angle value between the starting position and the ending position.

[0089] (4.2) Calculate the angle corresponding to each stripe according to the number of stripes in the circular scale grating scale area, calculate the number of stripes passed according to the stripe positions at the starting and ending positions, and obtain the angle value between the starting and ending positions. Assuming there are 16 stripes in total, 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 and ending positions, then the angle value between the starting and ending positions is 22.5°*8=180°.

[0090] If you want to calculate the average rotation speed, then ω=φ / (2π*t), where φ is the rotation angle mentioned above and t is the time from start to end. If you want to calculate the instantaneous rotation speed, then ω'=360° / (Q*2π*t'), where Q is the total number of stripes and t' is the time from the center of one shadow to the center of the next shadow. Based on the position changes of the stripes at adjacent times and the arrangement of the stripes, it can be determined whether it is rotating clockwise or counterclockwise.

[0091] Embodiment 6 The difference between this embodiment and the fifth embodiment is that the scale grating 1 is made of a light-transmitting material, and the stripes are opaque stripes, which are formed by methods such as plating or coating. The light emitted by the light-emitting device 2 is blocked by the opaque stripes, forming multiple shadows on the image acquisition device 3, and the absolute position is determined by the shadows collected by the image acquisition device 3.

[0092] The above are only specific implementations of the present invention, which cannot be used to limit the scope of the present invention. Equivalent changes made by ordinary technicians in this technical field based on this creation, as well as changes known to technicians in this field, should still fall within the scope of the present invention.

Claims

1. An absolute grating ruler system, characterized in that: It includes a scale grating, a light emitting device, an image acquisition device, and a control device; The scale grating is provided with a plurality of stripes arranged in a specific pattern, and the combination of the widths of any continuous P stripes has a unique value within the measuring range of the grating scale; 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 light path of the light emitting device, and the image acquisition device includes a calculation area located in the middle, the calculation area is directly opposite to 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 directly facing the light-emitting device based on the width of the stripe image captured 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, thereby obtaining the final absolute position value F=D+E.

2. The absolute grating ruler system according to claim 1, characterized in that: The width of the stripes is generated by: Generate a unique sequence of any combination of P consecutive values; Each value in the specific sequence is multiplied by a preset magnification factor to obtain the actual width value of each stripe. The magnification factor is set according to the required detection accuracy and the requirements of the manufacturing process.

3. The absolute grating ruler system according to claim 2, characterized in that: The specific sequence is the De Bruijn sequence.

4. The absolute grating ruler system according to claim 1, characterized in that: The absolute grating ruler system is used to measure linear displacement, and the ruler grating is in the shape of a straight bar.

5. The absolute grating ruler system according to claim 1, characterized in that: The absolute grating ruler system is used to measure the rotation angle, and the ruler grating is a circular grating disk, and a circular grating scale area is arranged on the grating disk.

6. The absolute grating ruler system according to claim 4, characterized in that: The image acquisition device further includes auxiliary areas located at both ends of the calculation area, the auxiliary areas being 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 fringe images in the calculation area of ​​the image acquisition device is insufficient or the recognition is incorrect, the width and center coordinates of the fringe images in the auxiliary area are corrected, and then the auxiliary area is used to assist in calculating the absolute position.

7. The absolute grating ruler system according to claim 5, characterized in that: The rotation angle is calculated as follows: Determine the starting position; Determine the number of rotations; Determine the end position; Calculate the rotation angle: rotation angle = angle corresponding to the end position - angle corresponding to the starting position + 360*number of turns; There are two ways to calculate the angle corresponding to the end position minus the angle corresponding to the start position:

1. First, calculate the absolute positions corresponding to the starting position and the ending position 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, to obtain the angle value between the starting position and the ending position; Second, the angle corresponding to each stripe is calculated based on the number of stripes in the circular scale grating scale area, and the number of stripes passed is calculated based on the stripe positions at the starting position and the ending position to obtain the angle value between the starting position and the ending position.

8. The absolute grating ruler system according to claim 1, characterized in that: The control device is also used to monitor in real time the number of pixels contained in the image of a single stripe acquired 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.

9. The absolute grating ruler system according to claim 1, characterized in that: The scale grating is opaque, the stripes are hollow stripes, and the light emitted by the light emitting device passes through the stripes to form at least P light spots in the calculation area of ​​the image acquisition device.

10. The absolute grating ruler system according to claim 1, characterized in that: The scale grating is light-transmissive, the stripes are opaque stripes, 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.

Images