Grating encoder

Abstract

The invention discloses a grating encoder, and belongs to the technical field of photoelectric detection. The detector cover plate attached to the effective detection plane of the detector is manufactured on the surface of the detector, the detector cover plate distinguishes phases and then receives the phases through the corresponding detector, and compared with the detector, the detector cover plate can design sampling shapes and periodic intervals at will, so that the processing difficulty and the processing cost can be reduced; meanwhile, each cover plate element and the corresponding detector element form a small sampling structure, the cover plate elements form different phase structures in the first direction and the second direction, each detector element is matched with the corresponding cover plate element in phase, scattered sampling can be achieved through the simple structure, and the sampling efficiency is improved. Therefore, intensity distribution changes introduced in the first direction and the second direction due to the influence of harmonic waves can be homogenized, and the influence of the intensity distribution changes on signal and displacement calculation can be effectively eliminated.

Description

Technical Field

[0001] This application relates to the field of photoelectric detection technology, and in particular to a grating encoder. Background Technology

[0002] An optical encoder is a device capable of measuring optical position along a specific direction. A traditional optical encoder mainly consists of a readhead and a scale grating. The readhead includes a light source, a diffraction grating, and multiple detectors. The scale grating moves along the measurement direction. Light emitted from the light source, after passing through the diffraction grating and entering the scale grating, forms a periodic fringe distribution on the detector plane that moves with the scale grating. Each fringe period includes fringes of different phases. By adjusting the spacing between different detectors along the measurement direction, different phase fringes can be detected.

[0003] Meanwhile, during actual assembly and testing, the presence of secondary diffraction interference effects in the grating can generate harmonics that do not conform to the desired period, which will affect the uniformity of the intensity of the fringes received by the detector along the measurement direction. Detectors with specially designed shapes are usually used to reduce the harmonics introduced during movement.

[0004] However, as the resolution requirements for grating encoders become higher and higher, the stripe period received by the detector end also becomes smaller and smaller. Continuing to adjust the detector spacing and shape to match the phase distribution and filtering will significantly increase the difficulty and cost of detector manufacturing. Summary of the Invention

[0005] The purpose of this application is to provide a grating encoder that solves the problem of increased manufacturing difficulty and cost caused by the decrease in stripe period due to phase distribution matching and filtering by detectors.

[0006] To achieve the above objectives, this application provides a grating encoder, comprising: a reading head and a scale grating; the reading head includes a light source, a diffraction grating, a detector cover plate, and a detector;

[0007] The detector cover plate includes at least two cover plate element groups arranged sequentially along a first direction, and each cover plate element group includes at least two cover plate elements arranged sequentially along a second direction; different cover plate elements in each cover plate element group correspond to different phases, and the positions of cover plate elements corresponding to the same phase in different cover plate element groups are different; the second direction is perpendicular to the first direction.

[0008] The detector includes at least two detector element groups arranged sequentially along the first direction, and each detector element group includes at least two detector elements arranged sequentially along the second direction; the detector elements and the cover plate elements correspond one-to-one.

[0009] The light source emits divergent coherent light, which passes through the diffraction grating and is incident on the scale grating that moves along the first direction, resulting in diffraction interference and the generation of periodic fringes. Fringes of different phases in the periodic fringes pass through the cover plate element corresponding to the phase and are incident on the detector element corresponding to the phase, forming a scanning signal corresponding to the phase.

[0010] Optionally, the detector element includes a filter window; the profile of the filter window is determined by a window function.

[0011] Optionally, the window function may include a Blackman window function or a rectangular window function.

[0012] Optionally, the reading head further includes a circuit board; the light source and the detector are disposed on the same side surface of the circuit board.

[0013] Optionally, the diffraction grating is disposed on the light-emitting side of the light source, and the detector cover is disposed on the light-incident side of the detector, and the diffraction grating and the detector cover are disposed on the same height plane.

[0014] Optionally, the area and photoelectric conversion efficiency distributions of the different detector elements are all consistent.

[0015] Optionally, the detector elements corresponding to the same phase are connected to the same signal transmission line.

[0016] Optionally, the cover element includes at least two light-transmitting areas arranged periodically along the first direction, the period of the light-transmitting areas being equal to the period of the periodic stripes and less than the width of the detector element in the first direction.

[0017] The starting positions of the light-transmitting areas in the cover plate elements corresponding to different phases are different;

[0018] The misalignment distance between the starting positions of the light-transmitting areas in the cover element corresponding to adjacent phases is equal to the ratio of the period of the periodic stripes to the number of phases.

[0019] Optionally, the outline of the light-transmitting area is determined by a constructor that matches the period of the periodic stripes.

[0020] Optionally, the outline of the light-transmitting area includes a first line segment and a second line segment, with the two ends of the first line segment and the two ends of the second line segment connected one by one;

[0021] The first line segment is determined by a first function, and the second line segment is determined by a second function; the first function is:

[0022] ;

[0023] The second function is:

[0024] ;

[0025] In the formula, This indicates the position of the first line segment in the first direction. This indicates the position of the first line segment in the second direction; This indicates the position of the second line segment in the first direction. This indicates the position of the second line segment in the second direction; Indicates the tilt coefficient; , This indicates the period of the periodic stripes; Indicates the harmonic filtering coefficient; This represents the median adjustment coefficient.

[0026] Obviously, the grating encoder provided in this application has a detector cover plate that fits the effective detection plane of the detector on the detector surface. After the phase is distinguished by the detector cover plate, the corresponding detector receives the signal. Compared with the detector, the detector cover plate can be arbitrarily designed with sampling shape and period spacing, which can reduce the processing difficulty and processing cost. At the same time, each cover plate element and the corresponding detector element constitute a small sampling structure. By making the cover plate element form different phase structures in the first and second directions, and making each detector element phase matched with its corresponding cover plate element, distributed sampling can be achieved through a simple structure. This can homogenize the intensity distribution changes introduced by harmonics in the first and second directions, and thus effectively eliminate the influence of intensity distribution changes on signal and displacement calculation. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the structure of a grating encoder provided in an embodiment of this application;

[0029] Figure 2 This is a schematic diagram of the structure of a detector cover provided in an embodiment of this application;

[0030] Figure 3 This is a schematic diagram of the structure of a detector provided in an embodiment of this application;

[0031] Figure 4 A partial schematic diagram of a cover plate element provided in an embodiment of this application;

[0032] Figure 5 This is a schematic diagram of the structure of a detector element provided in an embodiment of this application.

[0033] The annotations in the attached figures are explained as follows:

[0034] 1-Reading head; 10-Circuit board; 11-Light source; 12-Diffraction grating; 13-Detector cover plate; 131-Cover plate element group; 1311-Cover plate element; 13111-Transmitting area; 14-Detector; 141-Detector element group; 1411-Detector element; 14111-Filter window;

[0035] 2-Scale grating. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0037] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of a grating encoder provided in an embodiment of the present application. The grating encoder may include: a reading head 1 and a scale grating 2; the reading head 1 includes a light source 11, a diffraction grating 12, a detector cover plate 13 and a detector 14.

[0038] The detector cover 13 includes at least two cover element groups 131 arranged sequentially along a first direction, and each cover element group 131 includes at least two cover elements 1311 arranged sequentially along a second direction; the phases corresponding to different cover elements 1311 in each cover element group 131 are different, and the positions of the cover elements 1311 corresponding to the same phase in different cover element groups 131 are different; the second direction is perpendicular to the first direction.

[0039] The detector 14 includes at least two detector element groups 141 arranged sequentially along a first direction, and each detector element group 141 includes at least two detector elements 1411 arranged sequentially along a second direction; the detector elements 1411 and the cover plate elements 1311 correspond one-to-one.

[0040] The light source 11 emits divergent coherent light, which passes through the diffraction grating 12 and is incident on the scale grating 2 that moves along the first direction. Diffraction interference is performed to generate periodic fringes. Fringes of different phases in the periodic fringes pass through the cover plate element 1311 corresponding to the phase and are incident on the detector element 1411 corresponding to the phase, forming a scanning signal corresponding to the phase.

[0041] It should be noted that in this embodiment, the first direction is the measurement direction, and the second direction is perpendicular to the measurement direction. Harmonics not only affect the intensity uniformity of the stripes received by detector 14 along the measurement direction, but also affect the intensity uniformity perpendicular to the measurement direction. Traditional grating encoders can only solve the intensity uniformity problem in a single direction, and are limited by the stripe period, resulting in high manufacturing difficulty and cost. However, this embodiment, by designing the phase of detector cover plate 13 and ensuring phase matching between detector 14 and it, can not only solve the intensity uniformity problem in two directions simultaneously, but also has a simple structure and lower manufacturing difficulty and cost.

[0042] It should be noted that in this embodiment, the light source 11 emits divergent coherent light, which is incident on the diffraction grating 12 (which may include a transmissive diffraction grating 12). The diffraction grating 12 will generate reference optical modulation on the divergent coherent light (i.e., modulate the intensity distribution and diffraction order of the divergent coherent light). The optically modulated light will be incident on the scale grating 2, which will diffract and interfere with the optically modulated light to generate periodic fringes. When the scale grating 2 moves, the detector 14 receives the fringe movement caused by the movement of the scale grating 2. The different phases of the fringe movement are separated and detected by the detector cover plate 13 and the detector 14, and a sinusoidal signal with a fixed phase difference is output.

[0043] This embodiment does not limit the specific number of cover plate element group 131, the specific number of cover plate element 1311, the specific number of detector element group 141 and detector element 1411, which can be determined according to the actual required number of phases.

[0044] This embodiment does not limit the specific structure of the cover element 1311, as long as phase modulation can be performed. In one possible implementation, the cover element 1311 may include at least two light-transmitting regions 13111 arranged periodically along the first direction, the period of the light-transmitting regions 13111 being equal to the period of the periodic stripes and less than the width of the detector element 1411 in the first direction;

[0045] The starting position of the light-transmitting area 13111 in the cover element 1311 corresponding to different phases can be different;

[0046] The misalignment distance between the starting positions of the light-transmitting areas 13111 in the cover element 1311 corresponding to adjacent phases can be equal to the ratio of the period of the periodic stripe to the number of phases.

[0047] It should be noted that in this embodiment, all light-transmitting areas 13111 of each cover element 1311 can transmit stripes of the same phase, and light-transmitting areas 13111 of different cover elements 1311 transmit stripes of different phases. Different phase information is distinguished by periodic phase design of the detector cover 13. At the same time, the detector 14 is periodically phase designed to receive different phase information, and each cover element 1311 in the detector cover 13 is completely aligned with each detector element 1411 in the detector 14, so that each detector element 1411 can receive stripes of the same phase transmitted by all light-transmitting areas 13111 in its corresponding cover element 1311.

[0048] like Figure 2 A cover element 1311 and shown Figure 3 The detector 14 shown includes: a cover element 1311 comprising four cover element groups 131, each cover element group 131 comprising four cover elements 1311, the four cover elements 1311 being used to transmit stripes with phases of 0°, 90°, 180° and 270° respectively, each cover element 1311 comprising five light-transmitting regions 13111, the five light-transmitting regions 13111 transmitting stripes with the same phase, the light-transmitting regions 13111 in different cover elements 1311 along the first direction and the second direction being staggered; and a detector element 1411 comprising four detector element groups 141, each detector element group 141 comprising four detector elements 1411, the four detector elements 1411 being used to receive stripes with phases of 0°, 90°, 180° and 270° respectively, and the phase of the stripes transmitted by the cover element 1311 corresponding to its position being matched.

[0049] In one possible implementation, the outline of the light-transmitting region 13111 in this embodiment can be determined by a constructor that matches the period of the periodic stripes.

[0050] It should be noted that, by designing a filter for the contour of the light-transmitting area 13111, this embodiment can effectively filter out harmonics that deviate from the reference period (such as third, fifth, and seventh harmonics), enabling the detector 14 to receive the stripes of the reference period, which greatly improves the overall tolerance of the reading head 1 and steadily improves its performance.

[0051] This embodiment does not limit the specific type of constructor, as long as it can match the period of the stripes. In one possible implementation, such as Figure 4As shown, the outline of the light-transmitting area 13111 may include a first line segment and a second line segment, with the two ends of the first line segment and the two ends of the second line segment connected one by one.

[0052] The first line segment can be determined by the first function, and the second line segment can be determined by the second function; the first function can be:

[0053] ;

[0054] The second function can be:

[0055] ;

[0056] In the formula, This indicates the position of the first line segment in the first direction. Indicates the position of the first line segment in the second direction; This indicates the position of the second line segment in the first direction. Indicates the position of the second line segment in the second direction; Indicates the tilt coefficient; , Indicates the period of the periodic stripes; Indicates the harmonic filtering coefficient; This represents the median adjustment coefficient.

[0057] It should be noted that in this embodiment... , and All are constants, among which and None of them are equal to 0, k, and The specific value can be determined based on the actual situation.

[0058] In one possible implementation, such as Figure 5 As shown, the detector element 1411 may include a filter window 14111; the outline of the filter window 14111 is determined by a window function. The filter window 14111 is a hollowed-out area constructed within the detector element 1411.

[0059] It should be noted that in actual use, due to the internal assembly and adjustment tolerances of the reading head 1, the fringe period received by the detector 14 may deviate from the reference period, thus introducing subdivision error. Position measurement under these circumstances will cause spectral leakage, resulting in the leakage of second harmonics, thereby affecting the accuracy of position measurement. This embodiment constructs a filter window 14111 in the detector element 1411 using a window function, which can reduce the period mismatch problem caused by assembly and adjustment tolerances, thereby reducing spectral leakage and harmonic leakage, and ultimately reducing position detection error.

[0060] It should be noted that in this embodiment, the two methods of filtering the contour of the light-transmitting area 13111 and adding a filter window 14111 to the detector element 1411 can be used individually or simultaneously, depending on the actual situation.

[0061] This embodiment does not limit the specific type of window function, which can be determined based on the type of leakage spectrum. In one possible implementation, the window function may include a Blackman window function or a rectangular window function, etc.

[0062] This embodiment does not limit the specific arrangement of the components in the reading head 1, as long as the light source 11, diffraction grating 12, scale grating 2, detector cover plate 13, and detector 14 are on the same light transmission path. In one possible implementation, the reading head 1 may further include a circuit board 10; the light source 11 and detector 14 may be disposed on the same side surface of the circuit board 10. It should be noted that in this embodiment, the light source 11 and detector 14 are on the same height plane and are fixed together on the circuit board 10, and the light-emitting side of the light source 11 and the light-incident side of the detector 14 are located on the same side of the circuit board 10. Preferably, the light-emitting side of the light source 11 and the light-incident side of the detector 14 are on the same height plane. In one possible implementation, the diffraction grating 12 may be disposed on the light-emitting side of the light source 11, and the detector cover plate 13 may be disposed on the light-incident side of the detector 14, and the diffraction grating 12 and detector cover plate 13 may be disposed on the same height plane. It should be noted that in this embodiment, the diffraction grating 12 and the detector cover plate 13 are both located on the same side of the circuit board 10 and at the same height plane, synchronously and closely attached to the front end of the light source 11 and the detector 14. In one possible implementation, the scale grating 2 can be located on the same side of the circuit board 10 as the diffraction grating 12 and the detector cover plate 13.

[0063] In one possible implementation, the area and photoelectric conversion efficiency distribution of different detector elements 1411 can be consistent. It should be noted that this embodiment improves the position measurement accuracy by ensuring the consistency of the area and photoelectric conversion efficiency distribution of each detector element 1411.

[0064] In one possible implementation, detector elements 1411 with the same phase are connected to the same signal transmission line. It should be noted that this embodiment can aggregate the same-phase signals generated by detector elements 1411 with the same phase distributed at different locations onto the same signal transmission line for output.

[0065] Based on the above embodiments, this application fabricates a detector cover plate 13 on the surface of the detector 14 that fits the effective detection plane of the detector 14. After the phase is distinguished by the detector cover plate 13, it is received by the corresponding detector 14. Compared with the detector 14, the detector cover plate 13 can be arbitrarily designed with sampling shape and period spacing, which can reduce the processing difficulty and processing cost. At the same time, each cover plate element 1311 and the corresponding detector element 1411 constitute a small sampling structure. By making the cover plate element 1311 form different phase structures in the first direction and the second direction, and making each detector element 1411 phase matched with its corresponding cover plate element 1311, dispersed sampling can be achieved through a simple structure. This can homogenize the intensity distribution changes introduced by harmonics in the first and second directions, and effectively eliminate the influence of intensity distribution changes on signal and displacement calculation.

[0066] This document uses specific examples to illustrate the principles and implementation methods of this application. The various embodiments are progressive, with each embodiment focusing on its differences from others. Similar or identical parts between embodiments can be referred to interchangeably. The descriptions of the above embodiments are merely for the purpose of helping to understand the method and core ideas of this application. For those skilled in the art, various improvements and modifications can be made to this application without departing from its principles, and these improvements and modifications also fall within the protection scope of this application.

[0067] It should also be noted that, in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

Claims

1. A grating encoder characterized by, The application relates to a reading head and a scale grating; the reading head comprises a light source, a diffraction grating, a detector cover plate and a detector; the detector cover plate comprises at least two cover plate element groups arranged in sequence along a first direction, each cover plate element group comprises at least two cover plate elements arranged in sequence along a second direction; different cover plate elements in each cover plate element group correspond to different phases, and the positions of the cover plate elements corresponding to the same phase are different between different cover plate element groups; the second direction is perpendicular to the first direction; the detector comprises at least two detector element groups arranged in sequence along the first direction, each detector element group comprises at least two detector elements arranged in sequence along the second direction; the detector elements and the cover plate elements correspond to each other in one-to-one mode; the light source emits divergent coherent light, the light passes through the diffraction grating, is incident on the scale grating moving along the first direction, and is diffracted and interfered to generate periodic fringes; the fringes corresponding to different phases pass through the cover plate elements corresponding to the phases, are incident on the detector elements corresponding to the phases, and form scanning signals corresponding to the phases. The detector elements comprise filter windows; the profiles of the filter windows are determined by window functions. The window functions comprise Blackman window functions or rectangular window functions. The reading head further comprises a circuit board; the light source and the detector are arranged on the same side surface of the circuit board. The diffraction grating is arranged on the light-emitting side of the light source, the detector cover plate is arranged on the light-incident side of the detector, and the diffraction grating and the detector cover plate are arranged on the same height plane.

2. The optical encoder of claim 1, wherein, The areas and photoelectric conversion efficiencies of different detector elements are uniformly distributed.

3. The optical encoder of claim 2, wherein, The detector elements corresponding to the same phase are connected to the same signal transmission line.

4. The optical encoder of claim 1, wherein, The cover plate elements comprise at least two light-transmitting regions arranged in a periodic mode along the first direction; the period of the light-transmitting regions is equal to the period of the periodic fringes and is smaller than the width of the detector elements in the first direction; 5. The optical encoder of claim 4, wherein, The starting positions of the light-transmitting regions in the cover plate elements corresponding to different phases are different; 6. The optical encoder of claim 1, wherein, The distance of misalignment between the starting positions of the light-transmitting regions in the cover plate elements corresponding to adjacent phases is equal to the ratio of the period of the periodic fringes to the number of phases.

7. The optical encoder of claim 1, wherein, The profiles of the light-transmitting regions are determined by a construction function matched with the period of the periodic fringes.

8. The optical encoder of any one of claims 1 to 7, wherein, The profile of the light-transmitting region comprises a first line segment and a second line segment, and the two ends of the first line segment and the two ends of the second line segment are connected in one-to-one mode; The first line segment is determined by a first function, and the second line segment is determined by a second function; the first function is: The second function is:

9. The optical encoder of claim 8, wherein, ​ 10. The optical encoder of claim 9, wherein, ​ ​ ； ​ ； wherein denotes a position of the first line segment in the first direction, denotes a position of the first line segment in the second direction; denotes a position of the second line segment in the first direction, denotes a position of the second line segment in the second direction; denotes a tilt coefficient; , denotes a period of the periodic fringe; denotes a harmonic filter coefficient; denotes a median line adjustment coefficient.

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