Arc line splicing grating ruler multi-reading head coordination data compensation method

Abstract

The application discloses an arc splicing grating ruler multi-reading head cooperative data compensation method. In view of the difficulty of matching a telescope super-large diameter rotary table for a traditional whole-circle grating ruler, the application adopts an absolute linear grating ruler splicing and cutting, and through cooperation of a mounting groove, tension and pre-tightening force, the linear grating ruler is attached to the arc surface of the rotary table, and the self-conversion of the linear ruler to the arc ruler is realized; four reading heads with a phase difference of 90 degrees are evenly installed on the circumference to realize closed-loop position feedback, the adjacent reading heads are cyclically replaced at the splicing joint, the mean value is calculated by a fixed number of effective data sources, and seamless switching of the position feedback is realized. The application realizes the self-controllable and flexible size adaptation of the linear grating ruler splicing scheme, and is suitable for azimuth and elevation angle measurement systems of different aperture ground-based optical telescopes.

Description

Technical Field

[0001] This invention relates to a measurement error compensation method for converting an absolute linear grating ruler to an arc splicing grating ruler, applicable to the circumference of the axis turntable of the azimuth and altitude axes of ground-based optical telescopes with increasingly larger apertures. Background Technology

[0002] High-precision pointing and tracking are crucial indicators for evaluating the overall performance of large-aperture ground-based optical telescopes. Modern large-aperture telescopes typically employ coordinated motion of the azimuth and altitude axes to achieve precise pointing and target tracking. The angular measurement accuracy of the axis system directly determines the telescope's pointing accuracy and tracking stability. As the core sensor for axis system angle measurement, the installation method, signal quality, and data processing reliability of the grating encoder are critical factors in ensuring the normal operation of the telescope's control system.

[0003] With the development of astronomy, the aperture of modern telescopes is getting larger and larger. The increase in the size of the shaft system makes traditional circular grating encoders no longer suitable. For example, the linear grating ruler of the azimuth axis of a 14.5-meter optical-infrared telescope is installed on a circle with a diameter of 4 meters, and the linear grating ruler of the altitude axis is installed on a circle with a diameter of 3.25 meters. The traditional circular grating rulers of 2.5-meter and 4.2-meter aperture telescopes are no longer applicable. In addition, due to the limitations of the manufacturing process, traditional circular grating encoders can usually only provide standard diameter specifications, which is difficult to match the differentiated size requirements of ultra-large diameter shaft turntables. Moreover, custom-made large-diameter circular grating rulers are expensive and time-consuming, and have gradually failed to meet the engineering needs of modern large-aperture telescopes.

[0004] To address the aforementioned issues, spliced ​​grating encoders, with their advantages of high precision, simple installation and adjustment, and flexible size adjustment, have become an important development direction for large telescope angle measurement systems. Spliced ​​grating encoders typically involve bending and mounting a linear grating ruler onto the circumferential surface of a turntable, forming a nearly complete circumferential angle measuring scale through splicing. Its size can be adapted to the turntable diameter on-site, offering excellent flexibility and expandability.

[0005] When linear grating rulers are cut and spliced ​​into arc grating rulers, the accuracy of the phase alignment of the engraving lines at the splicing point and the continuity and integrity of the moiré fringe signal are difficult to guarantee. At the same time, the beginning and end of the grating ruler cannot be completely closed, resulting in physical gaps, which can cause unpredictable measurement anomalies such as signal distortion or loss in the reading head in this area.

[0006] Currently, spliced ​​grating encoders have been reported in the field of large telescopes. Pan Nian, Huang Long, and others conducted a systematic study on incremental spliced ​​grating encoders. This study used Heidenhain ERA 8400C series incremental encoders for splicing, and developed a software subdivision angle measurement scheme with a 4-reading head and a phase difference of 90°. Harmonic analysis was used to compensate for the angle measurement data, achieving sub-arcsecond-level angle measurement accuracy. However, this scheme has the following inherent limitations:

[0007] (1) The encoder type is limited and relies on prefabrication by the manufacturer. Existing solutions mostly use incremental encoders (such as the ERA8400C series), whose splicing seam treatment technology is pre-completed by the manufacturer and equipped with special splicing seam fasteners. Users only need to install the finished product provided by the manufacturer, which is a "plug and play" solution. Users do not have the ability to independently design and modify the splicing solution. Once it is necessary to adapt to turntables of different diameters, it is necessary to re-customize splicing encoders of corresponding sizes from the manufacturer, which leads to extended development cycle, increased costs, and limited flexibility in telescope axis system design. At the same time, since the dimensions of customized products are usually discrete fixed specifications, the diameter of the telescope turntable often needs to be adapted to the size of the grating ruler, which brings unnecessary constraints to the overall axis system design of large-aperture telescopes.

[0008] (2) Existing solutions are all prefabricated and spliced ​​by the manufacturer, and do not involve the independent design of the splicing method itself. The grating rulers used in the existing technology have their splicing seams professionally treated and calibrated at the factory. Users can directly install the finished product and use it without having to deal with the physical gaps and signal distortion at the splicing seams. In other words, the existing technology solves the problem of "how to make the readings of the pre-spliced ​​ruler more accurate", but does not solve the methodological problems of "how to autonomously convert the linear grating ruler into an arc spliced ​​grating ruler" and "how to deal with the unpredictable measurement anomalies introduced by on-site cutting and splicing". Since the existing solutions rely on the pre-treated splicing seams by the manufacturer, their angle measurement errors mainly come from the encoder's own engraving error and mechanical installation eccentricity, which are fundamentally different from the problems of physical breakage of absolute code values ​​and signal jump at the splicing seams caused by on-site cutting faced by this invention.

[0009] (3) Incremental encoders have an inherent defect of losing absolute position information after a power outage. Incremental encoders lose their absolute position memory function after a power outage, and a zeroing operation needs to be performed each time the power is restored to determine the current angular position of the axis system. For large-aperture telescopes, the rotational inertia of the axis system is large and the zeroing process takes a long time (usually several minutes). In emergency astronomical observation scenarios that require rapid response (such as observation of gravitational wave electromagnetic counterparts, tracking of fast radio bursts, etc.), the risk of missing critical observation windows due to zeroing after a power outage cannot be ignored. Although absolute encoders have the advantage of remembering absolute position after a power outage, since their code track contains a unique digital sequence, on-site trimming will destroy the continuity of the code value. At present, there is no mature technical solution to convert the on-site trimming and splicing of absolute linear grating rulers into curved grating rulers and solve the data anomalies at the splicing seams.

[0010] (4) There are differences in the data processing methods at the splicing seam. Although the multi-readhead scheme has been mentioned in the paper of the Chengdu Institute of Optics and Electronics, it is only used for error average elimination and does not involve the algorithm design for data switching compensation of readheads at the splicing seam. The multi-readhead switching scheme independently designed in this invention adopts the method of two adjacent readheads working alternately at the splicing seam. At the moment of switching, the invalid readhead participating in the average calculation will be replaced by the readhead adjacent in the rotation direction, which effectively solves the problem of step jump in the output value of the closed loop feedback position of the system and realizes the smooth continuity of the closed loop feedback in the entire circumference. Summary of the Invention

[0011] To address the shortcomings of existing technologies, this invention provides a method for autonomous splicing and multi-reading head collaborative data compensation based on an absolute linear grating ruler. By independently designing a cutting and splicing scheme and proposing a data compensation algorithm based on invalid interval identification and multi-reading head collaborative switching, the unpredictable measurement errors introduced by cutting and splicing are effectively eliminated. This allows the curved splicing grating ruler technology to be safely and reliably applied to future ground-based optical telescope axis measurement systems with larger apertures and more diverse dimensions. This invention aims to overcome the technical bottleneck of on-site cutting and splicing of absolute linear grating rulers, achieving a fully autonomous and controllable splicing scheme, flexible size adaptation, and a large-aperture telescope axis measurement solution that does not rely on pre-fabricated components from manufacturers.

[0012] To achieve the above objectives, the present invention provides the following technical solution:

[0013] A method for collaborative data compensation of multiple reading heads on an arc-stitched grating ruler includes the following steps:

[0014] Step 1: Based on the actual circumference of the telescope axis turntable, select an absolute linear grating ruler of approximately the corresponding length for cutting. Machine a mounting groove along the circumferential direction on the outer ring surface of the turntable. Utilize the tension force naturally generated after the grating ruler is bent and the preload applied by the mounting groove to make the grating ruler fit tightly against the arc surface of the turntable, thus realizing the conversion from an absolute linear grating ruler to an arc splicing grating ruler.

[0015] Step 2: Install four reading heads evenly on the circumference of the arc splicing grating ruler. The phase difference between adjacent reading heads is 90°. Each reading head collects the position feedback information of the absolute grating ruler in real time.

[0016] Step 3: For the splicing seam of the arc splicing grating ruler, define the invalid interval of each reading head between the left and right boundaries of the splicing seam;

[0017] Step 4: When a reading head enters the invalid region, the position feedback information of that reading head is replaced in real time by the next adjacent reading head; when the reading head leaves the invalid region, its actual measurement value feedback is restored; thus, collaborative data compensation for measurement errors at the splicing seam is completed.

[0018] Furthermore, in step 1: the depth of the mounting groove is less than the thickness of the grating ruler, and the width of the groove is greater than the width of the grating ruler; after the grating ruler is embedded in the mounting groove, the rebound tension force generated by the bending of the ruler body and the elastic clamping pre-tightening force of the groove wall on the back of the ruler work together to make the surface of the grating ruler closely fit the arc surface of the turntable.

[0019] Furthermore, when the thickness of the grating ruler is 0.2mm, the depth of the mounting groove is 0.15mm~0.18mm, and the groove depth is 0.02mm~0.05mm smaller than the ruler thickness to provide a preload force of 0.5N~2N; the groove width is 0.1mm~0.2mm wider than the width of the grating ruler.

[0020] Furthermore, in step 2: a method of positioning using a combination of a full-circular grating ruler and an arc-shaped spliced ​​grating ruler is adopted. The test first uses the full-circular grating ruler for closed-loop control, and the grating ruler moves accurately to the command position. Then, the movement distance of the arc-shaped grating ruler is observed to correct and test the measurement error between the arc-shaped grating ruler and the command position.

[0021] Furthermore, in step 3: the left and right boundaries of the invalid interval are pre-calibrated in the following way: the circular turntable is rotated at a low and uniform speed, and the sequence of continuous measurement values ​​when each reading head passes through the splice seam is recorded. The starting point when the measurement value shows a continuous jump is recorded as the left boundary, and the point where the jump ends and returns to normal is recorded as the right boundary.

[0022] Furthermore, the specific data compensation logic for each reading head in step 4 is as follows:

[0023] The system monitors the position feedback value Pos1 of reading head #1 in real time. When Pos1 is greater than or equal to the preset left boundary value Pos1N and less than or equal to the preset right boundary value Pos1P, and reading head #1 is currently in an unswitched state, reading head #1 is marked as switched, and its position feedback value is replaced with the real-time measurement value of reading head #2. When Pos1 is less than Pos1N or greater than Pos1P, and reading head #1 is currently in a switched state, the switching state mark of reading head #1 is cleared, and its position feedback value is restored to its own real-time measurement value.

[0024] The system monitors the position feedback value Pos2 of reading head #2 in real time. When Pos2 is greater than or equal to the preset left boundary value Pos2N and less than or equal to the preset right boundary value Pos2P, and reading head #2 is currently in an unswitched state, reading head #2 is marked as switched, and its position feedback value is replaced with the real-time measurement value of reading head #3. When Pos2 is less than Pos2N or greater than Pos2P, and reading head #2 is currently in a switched state, the switching state mark of reading head #2 is cleared, and its position feedback value is restored to its own real-time measurement value.

[0025] The system monitors the position feedback value Pos3 of reading head #3 in real time. When Pos3 is greater than or equal to the preset left boundary value Pos3N and less than or equal to the preset right boundary value Pos3P, and reading head #3 is currently in an unswitched state, reading head #3 is marked as switched and its position feedback value is replaced with the real-time measurement value of reading head #4. When Pos3 is less than Pos3N or greater than Pos3P, and reading head #3 is currently in a switched state, the switching state mark of reading head #3 is cleared and its position feedback value is restored to its own real-time measurement value.

[0026] The system monitors the position feedback value Pos4 of reading head #4 in real time. When Pos4 is greater than or equal to the preset left boundary value Pos4N and less than or equal to the preset right boundary value Pos4P, and reading head #4 is currently in an unswitched state, reading head #4 is marked as switched and its position feedback value is replaced with the real-time measurement value of reading head #1. When Pos4 is less than Pos4N or greater than Pos4P, and reading head #4 is currently in a switched state, the switching state mark of reading head #4 is cleared and its position feedback value is restored to its own real-time measurement value.

[0027] Among them, Pos1, Pos2, Pos3, and Pos4 are the real-time position feedback values ​​of reading heads #1, #2, #3, and #4, respectively; Pos1N, Pos2N, Pos3N, and Pos4N are the left boundary values ​​of the invalid intervals corresponding to each reading head; Pos1P, Pos2P, Pos3P, and Pos4P are the right boundary values ​​of the invalid intervals corresponding to each reading head; the initial value of the switching status flag for each reading head is the unswitched state.

[0028] Furthermore, before step 2, the experiment also includes: building a telescope axis experimental turntable that combines a full circular grating ruler and an arc-jointed grating ruler for positioning, using the full circular grating ruler as a closed-loop control reference, and correcting and testing the measurement error between the arc-jointed grating ruler and the command position.

[0029] Furthermore, the absolute linear encoder is a LIC 4005 series absolute linear encoder, and the reading head is an AK LIC 411 reading head.

[0030] Furthermore, the method is applicable to the installation of circumferential grating ruler encoders on the azimuth and / or height axes of large-aperture ground-based optical telescopes.

[0031] Furthermore, the aforementioned method for collaborative data compensation using multiple reading heads of the arc-jointed grating ruler is employed to compensate for the measurement error of the shaft-system circumferential grating ruler encoder.

[0032] Compared with the prior art, the present invention has the following significant effects:

[0033] (1) For the first time, the autonomous transformation of absolute linear grating ruler to arc splicing grating ruler was realized.

[0034] Existing spliced ​​linear encoder solutions all use pre-fabricated incremental encoders from manufacturers, with the splicing seams treated by the manufacturer before shipment. Users can only directly install and use the finished product, lacking the ability to design and modify it independently. Those skilled in the art generally believe that the code track of an absolute linear encoder has unique continuity; once cut, the code integrity is destroyed, making it unsuitable for high-precision angle measurement. This invention, through a technical approach of "mechanical structure fitting + software compensation algorithm mapping," achieves for the first time a high-precision arc application of an absolute linear encoder on a large turntable. Users can flexibly cut standard-sized absolute linear encoders according to the actual diameter of the turntable, without relying on manufacturer customization. This achieves complete autonomy and control over the splicing solution, effectively solving the engineering bottleneck of large-aperture telescopes being unable to match existing encoder specifications due to their diverse sizes.

[0035] (2) A multi-reading head cyclic replacement strategy with "constant mean" was proposed to achieve seamless switching of position feedback at the splicing seam.

[0036] Existing dual-readhead switching schemes suffer from a change in the number of data sources involved in averaging calculations during switching at the seam, leading to a step jump in the output value. This invention employs a cyclical substitution strategy of #1→#2→#3→#4→#1, ensuring that the system output is always averaged from a fixed number (4) of valid data sources before and after switching. This fundamentally avoids step jumps. Combined with pre-calibrated cross-calibration of each readhead, it ensures a smooth and continuous closed-loop feedback curve throughout the entire circumference, significantly improving the stability of the control system.

[0037] (3) No zero-finding operation is required during power outages, improving emergency observation efficiency.

[0038] This invention employs an absolute linear grating ruler, which can immediately output the current true absolute angle without performing a low-speed zero-finding operation when the system is powered on again after a power outage. This avoids missing the emergency observation window for transient celestial phenomena such as gravitational wave electromagnetic counterparts and fast radio bursts due to re-zeroing.

[0039] (4) Flexible size adaptation reduces development costs and cycle time.

[0040] This invention uses a standard shelf-grade absolute linear grating ruler, which can be freely cut according to the actual diameter of the telescope axis turntable. It is not limited by the fixed specifications of a whole circular grating ruler or a custom splicing ruler, which significantly reduces procurement costs and customization cycle. It is suitable for various ground-based optical telescopes of different apertures.

[0041] (5) Effective as verified by experiments

[0042] The invention was tested and verified on a telescope axis test turntable. The experimental results show that after applying the compensation algorithm of the invention, the closed-loop feedback value remains smooth and continuous without jumps or jitters in the four reading head switching intervals, which meets the requirements of the actual operation of the telescope for angle measurement accuracy. Attached Figure Description

[0043] Figure 1 This is a technical roadmap of the present invention;

[0044] Figure 2 This is a schematic diagram of the mechanical splicing and cutting method of the LIC 4005 absolute linear grating ruler;

[0045] Figure 3 These are comparison diagrams of the prior art solution and the solution proposed in this invention; wherein, (a) is a schematic diagram of the prior art solution, and (b) is a schematic diagram of the solution proposed in this invention;

[0046] Figure 4 This is a schematic diagram of the overall control principle of the telescope axis experimental turntable;

[0047] Figure 5 This is a schematic diagram illustrating the principle of measurement error data compensation method;

[0048] Figure 6 This is a closed-loop position feedback diagram without using the compensation algorithm;

[0049] Figure 7 It is a closed-loop position feedback diagram using a compensation algorithm. Detailed Implementation

[0050] The present invention will now be described in further detail with reference to the accompanying drawings.

[0051] The angular measurement accuracy of a telescope's axis system is a crucial indicator of the performance of its mechanical and electrical control systems. Grating encoders are commonly used angle measurement instruments in position control. In the field of astronomical telescopes, the requirements for position control accuracy are extremely high; therefore, accurately positioned grating encoders are essential for achieving high-precision tracking in telescopes. This invention is applicable to the installation of grating encoders on the circumference of different sized axis systems in large-aperture ground-based optical telescopes and is scalable.

[0052] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0053] The principle of the design technology method of this invention is as follows: Figure 1 As shown, it includes the following steps:

[0054] Step 1: Calculate the total length of the required absolute linear grating ruler based on the actual circumference of the experimental rotary table, and select a suitable absolute linear grating ruler accordingly. Cut and splice the ends of the linear grating ruler, ensuring continuous spacing and consistent phase of the engraving lines during splicing to avoid breaks or overlaps. Machine a precision mounting groove circumferentially on the outer ring surface of the rotary table. The groove is typically rectangular in cross-section, with a width slightly larger than the width of the grating ruler to provide lateral positioning; the groove depth is designed to be slightly smaller than the thickness of the grating ruler. In a preferred embodiment, when the grating ruler thickness is 0.2 mm, the mounting groove depth is 0.15 mm to 0.18 mm, the groove depth is 0.02 mm to 0.05 mm less than the ruler thickness, and the groove width is 0.1 mm to 0.2 mm wider than the grating ruler width. However, this parameter range does not constitute a limitation of the invention; in practical applications, it can be optimized and adjusted according to the grating ruler model, rotary table material, and diameter. When the ruler is pressed into the groove, the groove wall forms a uniform elastic clamping force on the back of the ruler, generating moderate frictional constraint. During installation, the linear grating ruler is bent circumferentially and embedded into the groove. The ruler's own bending generates a springback tension force, attempting to restore its straightness. This force compels the ruler to adhere tightly to the curved surface of the groove bottom. Simultaneously, the preload introduced because the groove depth is less than the ruler thickness further presses the grating ruler firmly against the curved surface of the groove bottom. The combined effect of the tension and preload forces ensures that the linear grating ruler perfectly conforms to the radius of curvature of the turntable, eliminating local warping or gaps, thus achieving complete curvature of the grating ruler. Figure 2 and Figure 3As shown in (b), this is a schematic diagram of the transformation from a linear grating ruler to an arc-jointed grating ruler. The solution adopted in this invention is similar to... Figure 3 (a) is different from existing technology.

[0055] Step 2: Construct an experimental turntable for the telescope axis system, combining a full-circle grating ruler (ECA 4402) with a spliced ​​linear grating ruler (LIC4005). Because some areas of the curved spliced ​​grating ruler are invalid, it cannot accurately provide 360° position information. Initially, the information from the full-circle grating ruler is used to correct and measure the error between the curved grating ruler and the commanded position. Figure 4 As shown; then, the reading head mounting bracket is machined, the full-circle grating ruler is equipped with 2 reading heads, and the arc splicing grating ruler is equipped with 4 reading heads. The sensor uses the Power UMAC Acc-84E series board to collect and feedback position information data.

[0056] Step 3: Analyze and determine the main sources of measurement error for the spliced ​​grating ruler. The main sources of measurement error for the curved grating ruler include: systematic errors, machining and installation errors, and other errors. Systematic errors mainly consist of grating ruler scale line errors and irregular deformation of the grating ruler caused by temperature changes. Currently used grating rulers can guarantee a scale line error of less than 5 mm per meter. Generally, the thermal stability of the grating ruler material is excellent. Mathematical analysis shows that irregular deformation of the grating ruler caused by temperature changes has little impact on the angle measurement error. Machining and installation errors mainly include installation eccentricity between the grating ruler and the turntable, machining and installation errors of the grating ruler's reading head bracket, and wobbling errors of the turntable's shaft system. Actual measurements confirm that the measurement error primarily originates from the splicing parts of the grating ruler, as well as errors caused by machining and reading head bracket installation. Other errors, including signal acquisition errors and signal subdivision errors, are not considered here.

[0057] Step 4: Theoretically, the more reading heads installed, the smaller the error. Considering experimental costs and minimizing error, a software subdivision scheme was designed with four AK LIC 411 reading heads evenly distributed with a phase difference of 90°, as shown below. Figure 4 As shown. When installing a telescope grating ruler encoder, using the average of the readings from multiple reading heads as the encoder's measurement value is a method of error elimination. Especially in high-precision angle measurement applications in astronomical observations, multi-reading head measurement is the most common and effective method to improve angle measurement accuracy, and it also has real-time compensation capabilities. In this scheme, the circular grating ruler uses two reading heads installed radially to eliminate angle measurement errors caused by mechanical installation eccentricity; the arc-jointed grating ruler uses four reading heads with a 90° phase difference, evenly distributed to correct errors caused by machining and installation, thereby improving angle measurement accuracy. Furthermore, the software performs real-time average calculation of the measurements from the four reading heads.

[0058] Step 5: Defining the compensation intervals for the telescope axis experiment turntable in both clockwise and counterclockwise directions. Taking the clockwise rotation of the curved spliced ​​grating ruler as an example, the mean value gradually increases with clockwise rotation. The reading heads are defined as #1, #2, #3, and #4. When reading head #1 passes the left boundary of the splice seam of the curved grating ruler, the measured value is recorded as Pos1N. Similarly, when reading head #1 passes the right boundary of the splice seam, the measured value is recorded as Pos1P. The left and right boundaries are defined as invalid intervals. The same applies to the others; the measured values ​​at the left and right boundaries of reading heads #2, #3, and #4 are recorded as Pos2N, Pos2P, Pos3N, Pos3P, Pos4N, and Pos4P, respectively. The counterclockwise rotation is similar and will not be elaborated further here. Figure 5 As shown, the corresponding reading head information is detected and judged within the interval. When the seam is detected, the designed data compensation method is activated; otherwise, no action is taken.

[0059] It should be noted that in actual engineering installation, the four reading heads are distributed at approximately 90° intervals on the circumference, and the software configuration is set according to a 90° phase difference. Since there is only one physical gap in the splicing seam on the entire circumference, only one reading head will fall into its corresponding invalid interval. There will be no situation where multiple reading heads enter the invalid interval at the same time. Therefore, there is no need to design complex priority arbitration logic.

[0060] Step 6: The error reading head compensation method is designed so that when the seam of the grating ruler enters the invalid range of a certain reading head, its position feedback information will be replaced by the information from the next corresponding reading head. Outside the invalid range, the actual measured value of that reading head will be used as feedback, thus completing the measurement error compensation. The data compensation method design is as follows: Figure 5 As shown, the specific implementation regulations are as follows:

[0061] When a reading head is determined to be in an invalid range ( When the original measurement value exhibits abnormal fluctuations and becomes unacceptable, it must be replaced by an adjacent valid reading. This invention adopts the compensation principle of "adjacent replacement, constant mean". Let the final output position feedback value of the system be... Under normal circumstances, One reading head ( When all are valid: When the first Number of reading heads ( When it enters the invalid interval, its measured value Consistent successive reading heads Instead, the system output is: Among them, when hour, =Pos1.

[0062] In practical systems, an even number of reading heads are usually arranged at equal intervals. Considering engineering constraints such as limited installation space, hardware cost, and the number of signal acquisition channels, this invention adopts a scheme with 4 reading heads distributed at equal intervals.

[0063] A specific implementation example is the data compensation method for measurement error of reading head #1:

[0064] The system monitors the position feedback value Pos1 of the #1 reading head in real time.

[0065] First, determine whether Pos1 falls within the preset invalid interval [Pos1N, Pos1P]:

[0066] If Pos1 has entered the interval and has not yet performed a switching action, immediately mark the #1 reading head as "invalid" and forcibly replace its current feedback value with the real-time measurement value of the #2 reading head to complete the data handover;

[0067] If Pos1 leaves the interval and has previously been marked as "invalid", its "invalid" mark will be immediately cleared, and the feedback value of the #1 reading head will be restored to its own measurement value, returning to normal participation in the mean calculation.

[0068] #2 Reading Head Measurement Error Compensation Method:

[0069] The system monitors whether Pos2 falls within the interval [Pos2N, Pos2P]:

[0070] If Pos2 enters the interval and has not yet switched, mark #2 as "invalid" and replace its value with the real-time measurement value of the #3 reading head;

[0071] If Pos2 leaves the interval and has been marked, then clear the mark and restore the measurement value of #2.

[0072] #3 Reading Head Measurement Error Compensation Method:

[0073] The system monitors whether Pos3 falls within the interval [Pos3N, Pos3P]:

[0074] If Pos3 enters the interval and has not yet switched, mark #3 as "invalid" and replace its value with the real-time measurement value of the #4 reading head;

[0075] If Pos3 leaves the interval and has been marked, then clear the mark and restore the original measurement value of #3.

[0076] #4 Reading Head Measurement Error Compensation Method:

[0077] The system monitors whether Pos4 falls within the interval [Pos4N, Pos4P]:

[0078] If Pos4 enters the interval and has not yet switched, mark #4 as "invalid" and replace its value with the real-time measurement value of the #1 reading head (forming a cyclic substitution closed loop).

[0079] If Pos4 leaves the interval and has been marked, then clear the mark and restore the original measurement value of #4.

[0080] Among them, Pos1, Pos2, Pos3, and Pos4 are the real-time location information feedback for #1, #2, #3, and #4, respectively. Figure 6 As can be seen from the original curve, when the #1 reading head enters and leaves the splice seam of the gap section, its position measurement value Pos1 shows a significant jump, causing Pos2~Pos4 and the final closed-loop feedback value to change. All exhibit significant jitter. This sudden change directly causes motor torque fluctuations and abnormal vibrations in the spindle turntable due to closed-loop feedback. Without a compensation algorithm, the performance at the splicing seam is very poor, failing to meet the telescope tracking accuracy requirements in actual engineering. Figure 7 Demonstrates high-speed motor ( The performance of the rotating spindle in reverse rotation within a 360° range, and the compensation effect when the four reading heads sequentially pass through the seam. The rotating spindle sequentially switches compensation algorithms for reading heads #4, #3, #2, and #1, with Pos4, Pos3, Pos2, and Pos1 exhibiting jitter within their respective switching intervals. From... Figure 7 Four switching intervals can be clearly seen in the image, and the final closed-loop feedback value is shown. The output curves remain smooth within each interval, indicating that the algorithm can work reliably at the switching points of the four reading heads, which meets the actual operational requirements of the telescope project.

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for collaborative data compensation of multiple reading heads in an arc-stitched grating ruler, characterized in that, Includes the following steps: Step 1: Based on the actual circumference of the telescope axis turntable, select an absolute linear grating ruler of the corresponding length for cutting. Machine a mounting groove along the circumferential direction on the outer ring surface of the turntable. Utilize the tension force naturally generated after the grating ruler is bent and the preload applied by the mounting groove to make the grating ruler fit tightly against the arc surface of the turntable, thus realizing the conversion from an absolute linear grating ruler to an arc splicing grating ruler. Step 2: Install four reading heads evenly on the circumference of the arc-spliced ​​grating ruler, with a 90° phase difference between adjacent reading heads. Each reading head collects the position feedback information of the absolute grating ruler in real time. Then, using the ECA 4402 full-circle grating ruler as a reference, analyze and determine the main sources of measurement error of the arc-spliced ​​grating ruler. Step 3: For the splicing seam of the curved splicing grating ruler, define the invalid interval of each reading head between the left and right boundaries of the splicing seam; Step 4: When a reading head enters the invalid region, the position feedback information of that reading head is replaced in real time by the next adjacent reading head; when the reading head leaves the invalid region, its actual measurement value feedback is restored; thus, collaborative data compensation for measurement errors at the splicing seam is completed.

2. The method for collaborative data compensation of multiple reading heads in an arc-stitched grating ruler according to claim 1, characterized in that, In step 1: the depth of the mounting groove is less than the thickness of the grating ruler, and the width of the groove is greater than the width of the grating ruler; after the grating ruler is embedded in the mounting groove, the rebound tension force generated by the bending of the ruler body and the elastic clamping pre-tightening force of the groove wall on the back of the ruler work together to make the surface of the grating ruler fit tightly against the arc surface of the turntable.

3. The method for collaborative data compensation of multiple reading heads in an arc-stitched grating ruler according to claim 2, characterized in that, When the thickness of the grating ruler is 0.2mm, the depth of the mounting groove is 0.15mm~0.18mm, and the groove depth is 0.02mm~0.05mm smaller than the ruler thickness to provide a preload force of 0.5N~2N; the groove width is 0.1mm~0.2mm wider than the width of the grating ruler.

4. The method for collaborative data compensation of multiple reading heads in an arc-stitched grating ruler according to claim 1, characterized in that, In step 2: a method of positioning using a combination of a full-circular grating ruler and an arc-shaped spliced ​​grating ruler is adopted. The test first uses the full-circular grating ruler for closed-loop control. The grating ruler moves accurately to the command position. Then, the movement distance of the arc-shaped grating ruler is observed to correct and test the measurement error between the arc-shaped grating ruler and the command position.

5. The method for collaborative data compensation of multiple reading heads in an arc-stitched grating ruler according to claim 1, characterized in that, In step 3: the left and right boundaries of the invalid interval are pre-calibrated in the following way: the circular turntable is rotated at a low speed and the continuous measurement value sequence of each reading head when passing through the splice seam is recorded. The starting point when the measurement value jumps continuously is recorded as the left boundary, and the point where the jump ends and returns to normal is recorded as the right boundary.

6. The method for collaborative data compensation of multiple reading heads in an arc-stitched grating ruler according to claim 1, characterized in that, The specific data compensation logic for each reading head in step 4 is as follows: The system monitors the position feedback value Pos1 of reading head #1 in real time. When Pos1 is greater than or equal to the preset left boundary value Pos1N and less than or equal to the preset right boundary value Pos1P, and reading head #1 is currently in an unswitched state, reading head #1 is marked as switched, and its position feedback value is replaced with the real-time measurement value of reading head #2. When Pos1 is less than Pos1N or greater than Pos1P, and reading head #1 is currently in a switched state, the switching state mark of reading head #1 is cleared, and its position feedback value is restored to its own real-time measurement value. The system monitors the position feedback value Pos2 of reading head #2 in real time. When Pos2 is greater than or equal to the preset left boundary value Pos2N and less than or equal to the preset right boundary value Pos2P, and reading head #2 is currently in an unswitched state, reading head #2 is marked as switched, and its position feedback value is replaced with the real-time measurement value of reading head #3. When Pos2 is less than Pos2N or greater than Pos2P, and reading head #2 is currently in a switched state, the switching state mark of reading head #2 is cleared, and its position feedback value is restored to its own real-time measurement value. The system monitors the position feedback value Pos3 of reading head #3 in real time. When Pos3 is greater than or equal to the preset left boundary value Pos3N and less than or equal to the preset right boundary value Pos3P, and reading head #3 is currently in an unswitched state, reading head #3 is marked as switched and its position feedback value is replaced with the real-time measurement value of reading head #4. When Pos3 is less than Pos3N or greater than Pos3P, and reading head #3 is currently in a switched state, the switching state mark of reading head #3 is cleared and its position feedback value is restored to its own real-time measurement value. The system monitors the position feedback value Pos4 of reading head #4 in real time. When Pos4 is greater than or equal to the preset left boundary value Pos4N and less than or equal to the preset right boundary value Pos4P, and reading head #4 is currently in an unswitched state, reading head #4 is marked as switched and its position feedback value is replaced with the real-time measurement value of reading head #1. When Pos4 is less than Pos4N or greater than Pos4P, and reading head #4 is currently in a switched state, the switching state mark of reading head #4 is cleared and its position feedback value is restored to its own real-time measurement value. Among them, Pos1, Pos2, Pos3, and Pos4 are the real-time position feedback values ​​of reading heads #1, #2, #3, and #4, respectively; Pos1N, Pos2N, Pos3N, and Pos4N are the left boundary values ​​of the invalid intervals corresponding to each reading head; Pos1P, Pos2P, Pos3P, and Pos4P are the right boundary values ​​of the invalid intervals corresponding to each reading head; the initial value of the switching status flag for each reading head is the unswitched state.

7. The method for collaborative data compensation of multiple reading heads in an arc-stitched grating ruler according to claim 1, characterized in that, Before step 2, the method further includes: constructing a telescope axis experimental turntable that combines a full-circular grating ruler with an arc-shaped spliced ​​grating ruler for positioning, using the full-circular grating ruler as a closed-loop control reference, and correcting and testing the measurement error between the arc-shaped spliced ​​grating ruler and the command position.

8. The method for collaborative data compensation of multiple reading heads in an arc-stitched grating ruler according to claim 1, characterized in that, The absolute linear encoder is a LIC 4005 series absolute linear encoder, and the reading head is an AK LIC 411 reading head.

9. The method for collaborative data compensation of multiple reading heads in an arc-stitched grating ruler according to claim 1, characterized in that, The method is applicable to the installation of circumferential grating ruler encoders on the azimuth and / or height axes of large-aperture ground-based optical telescopes.

10. The method for collaborative data compensation of multiple reading heads in an arc-stitched grating ruler according to claim 1, characterized in that, The measurement error compensation of the shaft system circumferential grating ruler encoder is performed using the multi-reading head collaborative data compensation method of the arc splicing grating ruler as described in any one of claims 1 to 9.

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