Design method for slit layout of reflective encoder

Abstract

The invention belongs to the technical field of photoelectric axial angle encoders, and particularly relates to a design method for a slit layout of a reflective encoder. The method comprises the following steps: S1, acquiring key parameters of the reflective encoder; s2, light emitted by the light source is modulated by a collimating lens to form parallel light, and the slit grating is uniformly illuminated by the parallel light; s3, taking an area between light spots formed by the first light and the second light in the slit code disc after the first light and the second light are reflected by the reflection code disc as a first blank area; s4, taking an area between respective incidence points of the third light and the fourth light on the slit code disc as a second blank area before the third light and the fourth light are reflected by the reflection code disc; s5, based on the circle center of the sector ring where the slit grating is located, a first sector ring and a second sector ring are drawn on the two radial sides of the slit grating respectively. The precision of the photoelectric axial angle encoder is improved.

Description

Technical Field

[0001] This invention belongs to the field of photoelectric shaft angle encoder technology, and particularly relates to a design method for a slit layout for a reflective encoder. Background Technology

[0002] An optoelectronic shaft angle encoder is a digital precision angle sensor integrating optical, mechanical, and electronic technologies. Using a high-precision measuring circular grating as the detection element, it converts angular position information into digital code through photoelectric conversion. It boasts advantages such as high accuracy, wide measurement range, small size, light weight, reliable operation, and ease of maintenance, and has been widely applied in radar, robotics, optoelectronic theodolites, and CNC machine tools. Compared to transmissive encoders, reflective encoders offer advantages such as compact structure, small size, large installation tolerance, and strong environmental adaptability. The output signal quality of a reflective encoder depends on many factors, the most fundamental being the contrast of the optical signal. Limited by the propagation principle of the reflective encoder's optical path, the current layout design of the code disk and slit in reflective encoders leads to redundant modulation of the light by the slit grating, and the contrast is significantly reduced due to the incident angle.

[0003] Furthermore, existing reflective encoders have an angle of incidence between the incident light and the code disk. The slit gratings used are typically made of glass of a certain thickness, and there is an air gap between the slit and the code disk. Under these assembly conditions, the light transmitted through the slit is reflected by the reflective code disk and then re-emerges from the back of the slit, undergoing redundant modulation by the slit. The light-blocking area on the back of the slit blocks some of the reflected light, resulting in a reduction in the total light intensity reaching the photodetector. This leads to a decrease in signal contrast and reduces the accuracy and overall resolution of the photoelectric shaft angle encoder. Summary of the Invention

[0004] In view of this, the present invention aims to provide a design method for a slit layout for a reflective encoder to solve the problems of redundant modulation of light and loss of reflected light intensity in existing reflective encoders. The present invention adopts a new slit grating design method, which not only solves the problem of redundant modulation of light by the slit, but also reduces the blocking effect of the back of the slit on the reflected light, increases the total light intensity received by the photoelectric receiver, increases the signal contrast, and improves the accuracy of the photoelectric shaft angle encoder.

[0005] To achieve the above objectives, the technical solution created by this invention is implemented as follows: A design method for a slit layout of a reflective encoder, the reflective encoder including a light source, a collimating lens, a slit code disk and a reflective code disk, wherein a slit grating is arranged on the slit code disk, and the design method specifically includes the following steps: S1: Obtain the key parameters of the reflective encoder; make the light emitted by the light source parallel light after being modulated by the collimating lens, and make the slit grating uniformly illuminated by the parallel light; S2: Establish a single-axis coordinate system along the radial direction of the slit encoder disk, obtain the coordinate values ​​of the two endpoints of the current grid bar along the same radial direction based on the single-axis coordinate system, and define the two endpoints as the front boundary point and the rear boundary point, respectively; S3: The first ray incident from the front boundary point is parallel to the second ray incident from the rear boundary point, so that the first ray is reflected by the reflective code disk and exits from the slit code disk through the rear boundary point, and the second ray is reflected by the reflective code disk and exits from the slit code disk. The radial length between the light spots formed by the first ray and the second ray on the slit code disk after being reflected by the reflective code disk is taken as the radial length of the first blank area. S4: The third ray emitted from the front boundary point is parallel to the fourth ray emitted from the rear boundary point. The third ray and the fourth ray are traced in reverse so that the third ray enters the slit code disk before being reflected by the reflective code disk, and the fourth ray enters the slit code disk through the front boundary point before being reflected by the reflective code disk. The radial length between the respective incident points of the third ray and the fourth ray on the slit code disk before being reflected by the reflective code disk is taken as the radial length of the second blank area. S5: Based on the center of the fan ring where the slit grating is located, draw the first fan ring and the second fan ring on the radial sides of the slit grating respectively. The radial length of the first fan ring is the radial length of the first blank area, and the radial length of the second fan ring is the radial length of the second blank area, thus completing the design of the slit pattern.

[0006] Furthermore, in step S1, the key parameters include at least the radial length of the slit grating bars, the air gap between the slit code disk and the reflective code disk, and the incident angle of the light source onto the slit grating.

[0007] Furthermore, by adjusting the radial length of the grating strips of the slit grating and the air gap between the slit code disk and the reflecting code disk, the first ray is reflected by the reflecting code disk and exits from the slit code disk at the rear boundary point, while the second ray is reflected by the reflecting code disk and exits from the slit code disk; or, by adjusting the radial length of the grating strips of the slit grating and the air gap between the slit code disk and the reflecting code disk, the fourth ray is reflected by the reflecting code disk and enters the slit code disk at the front boundary point, while the third ray is reflected by the reflecting code disk and enters from the slit code disk. The formula used is: ; in, The angle of incidence for parallel light incident on the slit grating. The length of the grid bar along the radial direction. The air gap between the slit code disk and the reflective code disk.

[0008] Furthermore, the reflective encoder also includes a photoelectric receiver, the total width of the effective light received by the photoelectric receiver being twice the radial length of the grid strip.

[0009] Furthermore, the glass thickness of the slit grating is uniform, so that light only undergoes translation when passing through the slit glass, without changing its propagation direction.

[0010] Furthermore, the first and second sector rings are connected to the slit grating but do not overlap.

[0011] Compared with the prior art, the present invention can achieve the following beneficial effects: The slit layout design method for reflective encoders described in this invention can make greater use of the radial space of the slit grid compared to previous design methods. Furthermore, by allocating the slits reasonably, the signal contrast received by the photoelectric receiver can be significantly increased, thereby improving the encoder's resolution and accuracy. Attached Figure Description

[0012] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic flowchart illustrating the design method of a slit grating for a reflective encoder as described in an embodiment of the present invention; Figure 2 The positional layout diagram of the first sector ring and the second sector ring as described in the embodiment of the present invention; Figure 3 A radial cross-sectional view of the slit code disk layout of the reflective encoder described in the embodiment of the present invention; Figure 4 A radial cross-sectional view of the slit code disk layout of a conventional reflective encoder as described in an embodiment of the present invention.

[0013] Explanation of reference numerals in the attached figures: 1. Light source; 2. Slit code disk; 3. Reflective code disk; 4. Grid bar; 5. Photodetector; 6. First ray; 7. Second ray; 8. Third ray; 9. Fourth ray; 10. Front boundary point; 11. Back boundary point; 12. First blank area; 13. Second blank area; 14. First sector ring; 15. Second sector ring. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0015] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0016] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0017] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0018] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0019] like Figure 1 As shown, this invention proposes a design method for a slit layout of a reflective encoder. The reflective encoder includes a light source 1, a collimating lens, a slit code disk 2, and a reflective code disk 3. A slit grating is arranged on the slit code disk 2. The design method specifically includes the following steps: S1: Obtain the key parameters of the reflective encoder; make the light emitted by the light source 1 parallel light after being modulated by the collimating lens, and make the slit grating uniformly illuminated by the parallel light. S2: Establish a single-axis coordinate system along the radial direction of the slit encoder disk 2, obtain the coordinate values ​​of the two endpoints of the current grid bar 4 along the same radial direction based on the single-axis coordinate system, and define the two endpoints as the front boundary point 10 and the rear boundary point 11, respectively. S3: The first ray 6 incident from the front boundary point 10 is parallel to the second ray 7 incident from the rear boundary point 11, so that the first ray 6 is reflected by the reflective code disk 3 and then exits from the slit code disk 2 through the rear boundary point 11, and the second ray 7 is reflected by the reflective code disk 3 and then exits from the slit code disk 2. The radial length between the light spots formed by the first ray 6 and the second ray 7 after being reflected by the reflective code disk 3 in the slit code disk 2 is taken as the radial length of the first blank area 12. S4: The third ray 8 emitted from the front boundary point 10 is parallel to the fourth ray 9 emitted from the rear boundary point 11. The third ray 8 and the fourth ray 9 are traced in reverse so that the third ray 8 enters the slit code disk 2 before being reflected by the reflective code disk 3, and the fourth ray 9 enters the slit code disk 2 through the front boundary point 10 before being reflected by the reflective code disk 3. The radial length between the respective incident points of the third ray 8 and the fourth ray 9 on the slit code disk 2 before being reflected by the reflective code disk 3 is taken as the radial length of the second blank area 13. S5: Based on the center of the fan ring where the slit grating is located, draw the first fan ring 14 and the second fan ring 15 on the radial sides of the slit grating respectively. The radial length of the first fan ring 14 is the radial length of the first blank area 12, and the radial length of the second fan ring 15 is the radial length of the second blank area 13, thus completing the design of the slit pattern.

[0020] The high signal contrast reflective encoder layout design method proposed in this invention is as follows: Step 1: Based on the design scheme of the reflective encoder, determine the relevant key parameters, mainly including the grating pitch of the slit grating and the code disk grating, the circumferential width of the slit grating, the radial length of the grating strips 4 of the slit grating (each grating strip 4 has the same length) and the glass thickness, the air gap between the slit grating and the code disk grating, and the incident angle of the light source 1, etc. Typically, the code disk grating is arranged around the entire circumference, especially for incremental code disks, where the grating strips 4 are evenly distributed across the entire circumference. Step 2: Draw the overall optical path propagation diagram. Since the light emitted from the light source 1 can be considered nearly parallel after being modulated by the collimating lens, and its range basically covers all areas that need to be considered, the slit area can be considered uniformly illuminated. Step 3: Based on the above optical path diagram, establish a coordinate system radially distributed along the grating direction. According to predetermined parameters, calculate the coordinates of each key point where the light passes through each blank area and the two sides of the slit grating, as well as the corresponding reflection position on the reflective code disk 3. Key locations include the area of ​​the slit grating illuminated by the incident light, the exit area after the light is refracted by the slit grating, the area illuminated after the light reaches the reflective code disk 3, the area on the back of the slit grating reached by the reflected light, and the area where the returning light exits the slit grating after refraction through the slit glass. Step 4: Analyze the incident light, focusing on the two rays illuminating the front and rear boundaries of the slit grating area and the illuminated area between them. Tracee the area where the light re-arrives on the upper surface of the slit after refraction, reflection, and refraction, and record this area. Of particular concern is that if this area coincides with the slit grating itself, it indicates that the encoder design parameters are unreasonable. Adjust the radial length of the slit grating 4 or the air gap between the slit code disk 2 and the reflective code disk 3 so that this area connects with the slit grating without coinciding. Step 5: Analyze the reflected light rays, focusing on the two rays at the front and rear boundaries of the area illuminated by the reflected light rays in the slit grating, as well as the illuminated area contained between the two rays. Traverse the light rays to find the corresponding incident light ray, and record the area on the upper surface of the slit illuminated by this incident light ray emitted from light source 1. If the parameters in the previous step are set reasonably, this area and the slit grating also satisfy the positional relationship of being adjacent but not overlapping, requiring no readjustment of parameters. Step 6: After recording the two areas from the above steps, keep the original grating strip 4 layout unchanged during the slit grating design process, while designing the above two areas as blank areas, i.e., a fully transparent state without grating strip 4. Conduct a sample fabrication experiment according to the newly designed slit layout. Compare the design with the original slit layout scheme using the same reflective code disk 3 and keeping the structure of the other components unchanged. It can be seen that the signal contrast received by the encoder receiver is significantly improved.

[0021] Additionally, it should be noted that the overall design of this invention is completed in the radial sectional view of the slit encoder 2, and the incident angle of each ray is typically chosen to be 45 degrees.

[0022] In some embodiments, in step S1, the key parameters include at least the grating pitch of the slit grating, the circumferential width of the slit grating, the radial length of the grating strips 4 of the slit grating, the glass thickness of the slit grating, the grating pitch of the code disk grating, the air gap between the slit grating and the code disk grating, and the incident angle of the light source 1.

[0023] In some embodiments, the radial length of the grating strip 4 of the slit grating and the air gap between the slit code disk 2 and the reflective code disk 3 are adjusted so that the first light ray 6 is reflected by the reflective code disk 3 and exits from the slit code disk 2 through the rear boundary point 11, and the second light ray 7 is reflected by the reflective code disk 3 and exits from the slit code disk 2; or, the radial length of the grating strip 4 of the slit grating and the air gap between the slit code disk 2 and the reflective code disk 3 are adjusted so that the fourth light ray 9 is reflected by the reflective code disk 3 and enters the slit code disk 2 through the front boundary point 10, and the third light ray 8 is reflected by the reflective code disk 3 and enters from the slit code disk 2, based on the following formula: ; in, The angle of incidence for parallel light incident on the slit grating. The length of bar 4 along the radial direction. The air gap between the slit code disk 2 and the reflective code disk 3.

[0024] In some embodiments, the reflective encoder further includes a photodetector 5, the total width of the effective light received by the photodetector 5 being twice the radial length of the grid 4.

[0025] In some embodiments, the glass thickness of the slit grating is uniform, and light only undergoes translation when passing through the slit glass without changing its propagation direction.

[0026] In some embodiments, such as Figure 2 As shown, the first sector ring 14 and the second sector ring 15 are connected to the slit grating but do not overlap.

[0027] Example 1 First, we set the variable parameters, and then perform the relevant derivations. We define the air gap between the slit code disk 2 and the reflective code disk 3 as D, the radial length of the slit grid 4 as L, and the incident angle of the light emitted from the light source 1 onto the slit grid 4 after passing through the collimating lens as θ. Assuming that the thickness uniformity of the slit code disk 2 is good, the refraction of the light through the slit grid 4 (made of glass) will only cause the light to be translated by the same distance, without changing the direction of light propagation. Therefore, the refraction effect of the slit glass can be ignored in the design process.

[0028] First, focus on the area where slit bar 4 is located, by Figure 3 As can be seen from the geometric relationships, the following relationships should be satisfied between the angle of incidence of light, the air gap between the two code disks (slit code disk 2 and reflective code disk 3), and the radial span of the slit grid 4: ; Under this relationship, light rays incident on the front end of the slit can be reflected and exited from the rear end of the slit without passing through the slit region a second time.

[0029] Next, we focus on the first blank area 12. The light in the first blank area 12 is formed by the reflection of the light incident on the slit grating, while the light in the second blank area 13 passes through the grating strip 4 region of the slit grating after reflection. From the light received at the photodetector 5, it can be seen that the light from both locations is modulated by the slit grating only once, and their effects are equivalent. Therefore, the total effective light width received at the photodetector 5 is twice the radial length of the slit grating strip 4, which is 2L.

[0030] The sample design experiment was carried out according to the newly designed slit pattern. Under the condition of using the same reflective code disk 3 and keeping the structure of the other components unchanged, it was compared with the original slit pattern design scheme. Finally, the scheme of the present invention was adopted, and the signal contrast received by the photoelectric receiver 5 was greatly improved.

[0031] A specific comparison is made using a typical reflective encoder structure as an example to analyze the above design method. Generally, the incident angle of the incident light emitted by the light source 1 of a reflective encoder is 45°. First, the original encoder slit design method is considered, such as... Figure 4 As shown, there are no blank areas on either side of the radial direction of the slit grid 4. The radial length of the slit grid 4 is designed to be 1 mm, and the air gap between the slit and the reflective code disk 3 is 0.2 mm. The overall optical path is as follows. Figure 4 As shown. By Figure 4 It is evident that the incident light is not only subject to redundant modulation by the slit, but the effective light intensity actually received at photodetector 5 is only 1 - 0.2 × 2 = 0.6 mm, and it decreases as the air gap D increases.

[0032] According to the invention design parameters, the radial length of the slit grid 4 is 0.5mm, the air gap between the slit and the code disk is 0.25mm, and the optical path is as follows: Figure 3 As shown in the figure. Analysis shows that all light rays pass through the slit grating 4 only once, and the effective light intensity received by the photodetector 5 is 0.5 × 2 = 1 mm. The contrast ratio of the two methods is 0.6:1. Furthermore, experimental verification shows that the contrast ratio before and after the experiment is 0.9:1.5, which is close to the theoretical value of 0.6:1.

[0033] The slit pattern design method proposed in this invention, compared with the original pattern design, not only solves the problem of redundant modulation of light by the slit grating, but also greatly increases the contrast of the light intensity signal received by the photoelectric receiver 5, thereby improving the resolution and accuracy of the encoder.

[0034] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0035] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for designing a slit layout for a reflective encoder, the reflective encoder comprising a light source, a collimating lens, a slit code disk, and a reflective code disk, wherein a slit grating is arranged on the slit code disk, characterized in that: The design methodology specifically includes the following steps: S1: Obtain the key parameters of the reflective encoder; make the light emitted by the light source parallel light after being modulated by the collimating lens, and make the slit grating uniformly illuminated by the parallel light; S2: Establish a single-axis coordinate system along the radial direction of the slit encoder disk, obtain the coordinate values ​​of the two endpoints of the current grid bar along the same radial direction based on the single-axis coordinate system, and define the two endpoints as the front boundary point and the rear boundary point, respectively; S3: The first ray incident from the front boundary point is parallel to the second ray incident from the rear boundary point, so that the first ray is reflected by the reflective code disk and exits from the slit code disk through the rear boundary point, and the second ray is reflected by the reflective code disk and exits from the slit code disk. The radial length between the light spots formed by the first ray and the second ray on the slit code disk after being reflected by the reflective code disk is taken as the radial length of the first blank area. S4: The third ray emitted from the front boundary point is parallel to the fourth ray emitted from the rear boundary point. The third ray and the fourth ray are traced in reverse so that the third ray enters the slit code disk before being reflected by the reflective code disk, and the fourth ray enters the slit code disk through the front boundary point before being reflected by the reflective code disk. The radial length between the respective incident points of the third ray and the fourth ray on the slit code disk before being reflected by the reflective code disk is taken as the radial length of the second blank area. S5: Based on the center of the fan ring where the slit grating is located, draw the first fan ring and the second fan ring on the radial sides of the slit grating respectively. The radial length of the first fan ring is the radial length of the first blank area, and the radial length of the second fan ring is the radial length of the second blank area, thus completing the design of the slit pattern.

2. The design method of the slit grating for a reflective encoder according to claim 1, characterized in that: In step S1, the key parameters include at least the radial length of the slit grating bars, the air gap between the slit code disk and the reflective code disk, and the incident angle of the light source onto the slit grating.

3. The design method of the slit grating for a reflective encoder according to claim 1, characterized in that: Adjust the radial length of the grating strips of the slit grating and the air gap between the slit code disk and the reflective code disk so that the first light ray is reflected by the reflective code disk and then exits from the slit code disk through the rear boundary point, and the second light ray is reflected by the reflective code disk and then exits from the slit code disk. Alternatively, adjust the radial length of the grating bars of the slit grating and the air gap between the slit code disk and the reflecting code disk so that the fourth ray enters the slit code disk through the front boundary point before being reflected by the reflecting code disk, and the third ray enters the slit code disk from the slit code disk before being reflected by the reflecting code disk. The formula used is: ； in, The angle of incidence for parallel light incident on the slit grating. The length of the grid bar along the radial direction. The air gap between the slit code disk and the reflective code disk.

4. The design method of the slit grating for a reflective encoder according to claim 1, characterized in that: The reflective encoder also includes a photodetector, the total width of the effective light received by the photodetector being twice the radial length of the grid.

5. The design method of the slit grating for a reflective encoder according to claim 1, characterized in that: The glass of the slit grating has a uniform thickness, and when light passes through the slit glass, it only undergoes translation and does not change its propagation direction.

6. The design method of the slit grating for a reflective encoder according to claim 1, characterized in that: The first and second sector rings are connected to the slit grating but do not overlap.

Images