Large-aperture telescope shafting angle detection method based on arc grating encoder

Abstract

The invention discloses a large-aperture telescope shafting angle detection method based on an arc grating encoder. The method comprises the following steps of: tensioning and mounting a linear grating ruler along the circumference of a shaft system turntable to form an arc grating body; n reading heads are uniformly arranged along the circumference of the rotation direction of the shaft system, the rotation position information of the shaft system is read, the effective range of the arc grating is calculated and converted into angle information, and the resolution of the arc grating is calculated; installing a full-circle grating, obtaining the detected shafting rotation position information, comparing the detected shafting rotation position information with the arc grating angle detection information, and verifying the correctness of the position information obtained by the arc grating. The arc grating is used for replacing an angle measurement grating, the measuring range and the resolution of the arc grating can be accurately obtained, the correctness of information obtained by the arc grating is verified through the concentric-shaft full-circle grating, the closed-loop effect does not exist, the machining difficulty is low, meanwhile, the length of the grating ruler can be selected according to the rotation range of a shaft system, and the measurement precision is high. And the installation and adjustment difficulty is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of driving control of large aperture telescope, in particular to an arc grating ruler for angle position detection of super-low speed and large inertia shaft system and a method for verifying the correctness of the position detection information. BACKGROUND

[0002] The scientific progress of astronomy and astrophysics highly depends on the observation of telescope. With the increasing demand for deep space exploration, the aperture of telescope is getting larger and larger, which puts forward higher requirements for the tracking accuracy of telescope shaft system. The position feedback encoder of telescope shaft system is one of the core components to ensure the high performance of the servo control system of telescope shaft system, and it requires extremely high. Circular grating encoder has the advantages of high precision and direct measurement, and has become the mainstream choice for the position feedback application of large astronomical telescope (including radio, optical and infrared telescope) shaft system.

[0003] The increase of the aperture of telescope inevitably leads to the increase of the size of shaft system, which requires the encoder at the shaft end to have a larger size. Taking the 14.5-meter optical infrared telescope developed by the Nanjing Institute of Astronomical Optics and Technology of the Chinese Academy of Sciences as an example, the angle position feedback grating of the azimuth shaft needs to be installed on a circle with a diameter D=4000mm. The processing difficulty and cost of circular grating increase geometrically with the increase of its diameter, therefore, the increase of the size of the shaft system of modern photoelectric telescope makes the traditional glass circular grating encoder no longer applicable. In addition, the M3 shaft system and the elevation shaft system do not need to rotate 360° during operation, and the use of circular grating will cause a certain degree of waste, and the larger the aperture of the telescope, the larger the size of the shaft system, and the more serious the waste.

[0004] Therefore, a new position feedback grating encoder for large diameter shaft system is urgently needed to provide protection for the development of large aperture astronomical telescope. SUMMARY

[0005] In view of the above problems existing in the prior art, the present application provides a large aperture telescope shaft system angle detection method based on arc grating encoder.

[0006] To achieve the above purpose, the present application provides the following technical scheme:

[0007] The large aperture telescope shaft system angle detection method based on arc grating encoder comprises the following steps:

[0008] Step 1: select a linear grating ruler with appropriate model according to the rotation range of telescope shaft system and the tracking technical index requirements;

[0009] Step 2: install the linear grating along the circumference of the shaft system turntable to form an arc grating body;

[0010] Step 3: evenly arrange n reading heads along the circumference of the shaft system rotation direction to read the shaft system rotation position information, calculate the effective range of the arc grating, and convert it into angle information, while calculating the resolution of the arc grating; specifically including: connecting the reading heads with the detector, reading the test signals of the n reading heads through the test software, and when the turntable reaches the blind area during forward rotation, the acquired position information is the left boundary, and when the turntable reaches the blind area during reverse rotation, the acquired position information is the right boundary, and the reading position data of the two ends of the grating corresponding to each reading head is recorded; taking the average value of the n reading heads as the left and right boundary values, calculating the effective range of the arc grating using the left and right boundary values, and converting it into angle through the quantity relationship, while calculating the angle resolution, so that each reading head can effectively acquire position information;

[0011] Step 4: install the whole circle grating to obtain the shaft system rotation position information detected by the whole circle grating, and compare it with the arc grating angle detection information to verify the correctness of the position information acquired by the arc grating.

[0012] Further, the step 1: calculate the length of the arc grating required according to the shaft system rotation range, and install the arc grating for the whole circle of the shaft system if the rotation range exceeds 360°, or flexibly select the grating length according to the rotation range if the shaft system is less than 360°.

[0013] Further, the step 2: combine the characteristics of the shaft system transmission structure and the specific size of the linear grating, and open a circumferential groove along the outer ring or inner ring of the shaft system turntable for installing the linear grating, the size of the circumferential groove being able to accommodate the grating body while providing the required friction, and using the tension of the linear grating after being radianized and the pre-tightening force provided by the installed groove to make the linear grating completely fit the curvature of the turntable, so that it is completely radianized to form a high-precision arc grating body for direct angle measurement.

[0014] Further, the step 5: install a standard whole circle grating on the concentric shaft of the arc grating installation turntable, and additionally install reading heads at the same radial position and axial layering of the arc grating reading heads to obtain the angle position information of the whole circle grating; by installing reading heads in layers, the same angle position of the shaft system rotation is obtained by using the whole circle grating and the arc grating of two different types of gratings, and the angle position information detected by the whole circle grating and the arc grating is compared to verify the correctness of the angle position information acquired by the arc grating; if they are consistent, it means that the arc grating is installed correctly and can effectively and correctly acquire the angle information of the shaft system rotation.

[0015] Further, the arc grating body does not have a closed loop effect, and its length can be selected according to the rotation range of the shaft system.

[0016] Further, the step 2: the tensioning installation of the linear grating ruler is realized by a mechanical tensioning device.

[0017] Further, a circumferential groove is arranged at the circumferential end surface of the shafting turntable, the linear grating ruler is installed in the circumferential groove, a tensioning groove is arranged at the shafting turntable end surface of the arc grating end, a fixed tensioning block and a floating tensioning block are arranged in the tensioning groove, the fixed tensioning block is fixed to the turntable, the floating tensioning block is connected to the fixed tensioning block through a tensioning force adjusting piece, and the spacing between the floating tensioning block and the fixed tensioning block can be adjusted through the tensioning force adjusting piece; when the length of the linear grating ruler is equal to the whole circumferential length of the turntable, one set of mechanical tensioning device is arranged, one end of the linear grating ruler is fixed to the floating tensioning block, and the other end is fixed to the fixed tensioning block; when the length of the linear grating ruler is less than the whole circumferential length of the turntable, two sets of mechanical tensioning devices are arranged, and two ends of the linear grating ruler are respectively fixed to the floating tensioning blocks at the two ends.

[0018] Compared with the prior art, the beneficial effects of the present application are:

[0019] The arc grating is used to replace the angle measurement grating, the range and resolution of the arc grating can be accurately obtained, the correctness of the information obtained by the arc grating is verified by using the concentric shaft whole circumferential grating, the processing difficulty is low due to the absence of closed loop effect, the cost is greatly reduced, in the case of the same budget, a grating with higher precision can be selected, meanwhile, the length of the grating ruler can be selected according to the rotation range of the shafting, a more flexible grating selection mode is provided, and the assembly and adjustment difficulty is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0020] The specific embodiments of the present application are further illustrated below in combination with the drawings.

[0021] Figure 1 is a top view structure diagram of the opened circumferential groove and the tensioning groove.

[0022] Figure 2 is a side view structure diagram of the opened circumferential groove and the tensioning groove.

[0023] Figure 3 is a top view installation diagram of the mechanical tensioning device.

[0024] Figure 4 is a side view installation diagram of the mechanical tensioning device.

[0025] Figure 5 is an enlarged structure diagram of the mechanical tensioning device.

[0026] Figure 6 is a side view of the mechanical tensioning device.

[0027] Figure 7 is a length and angle conversion principle diagram.

[0028] Figure 8 is a top view of the test installation principle.

[0029] Figure 9 is a sectional view along Figure 8 the A-A direction in the figure.

[0030] Figure 10 is an enlarged structural view of the A portion in the figure. Figure 9

[0031] Marked in the figure: 1-axis system turntable; 101-circumferential groove; 102-tensioning groove; 2-mechanical tensioning device; 201-floating tensioning block; 202-tensioning force adjusting screw; 203-grating fixing screw; 204-fixed tensioning block fixing screw; 205-fixed tensioning block; 3-arc grating; 4-limiting stop block; 5-supporting frame; 6-ECA reading head; 7-Hall sensor; 8-LIC reading head; 9-reading head support base; 10-LIC reading head platform; 11-reading head support arm; 12-ECA reading head platform. DETAILED DESCRIPTION

[0032] The application will be further described in detail below with reference to the accompanying drawings.

[0033] To solve the machining difficulty, high cost and long supply cycle of the current large aperture telescope shaft feedback angle measurement encoder, the application provides a large aperture telescope shaft angle detection method based on an arc grating encoder, which can be widely applied in a telescope angle measurement system as a new generation of angle encoder. The main feature is to install the linear grating in an arc shape, and to realize the conversion of linear position detection information to angle position detection information through a corresponding conversion method. The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the application.

[0034] The application scenario of the embodiment is a 14.5-meter optical infrared telescope, so the type of linear grating ruler is selected according to the tracking requirements of the 14.5-meter optical infrared telescope azimuth shaft system, and the experimental platform is transformed according to the rotation range and motion characteristics of the telescope azimuth shaft. The selected grating ruler is HEIDENHAIN LIC , with a grating pitch , which belongs to an absolute linear grating ruler. The shaft system turntable has a diameter of , and a circumference of about . To ensure the smooth progress of subsequent installation and testing, a certain margin is reserved, and the length of the linear grating ruler is selected as​ parts kit.

[0035] The main technical means upon which this invention is realized consist of two parts: the arcuate transformation of a linear grating ruler to form an arc grating body and the calculation of the measurement step distance of the arc grating, as well as the validity verification. The specific steps are as follows:

[0036] Step 1: The main implementation steps and required tooling components for the arc grating body are as follows: Figures 1-6 As shown. First, a circumferential groove 101 is made along the circumference of the rotary table 1, as follows. Figures 1-2 As shown, the slot is located at the radial center, and the slot diameter is... Width is The process requires removing all burrs and flash to precisely accommodate the selected linear grating; simultaneously, machining is performed on the disk. Tensioning groove 102 and deep The threaded holes are used for subsequent installation of mechanical tensioning mechanisms. Secondly, the design is as follows... Figures 3-6 The mechanical tensioning device 2 shown includes two floating tensioning blocks 201 and a fixed tensioning block 205. The fixed tensioning block 205 is fixed to the load turntable using a fixed tensioning block fixing screw 204, while the floating tensioning blocks 201 are not connected to the load turntable and are floated. When the length of the linear grating ruler is equal to the circumference of the turntable, one set of mechanical tensioning devices is sufficient. In this case, one end of the linear grating 3 is fixed to the floating tensioning block 201, and the other end is fixed to the fixed tensioning block 205. When the length of the linear grating 3 is less than the circumference of the turntable, two sets of mechanical tensioning devices are used. The two ends of the linear grating ruler are fixed to the floating tensioning blocks 201 at both ends by grating fixing screws 203. The two tensioning blocks are connected by tension adjustment screws 202 on the two side lugs. Adjusting the distance between the two tensioning blocks can adjust the tension. The mechanical tensioning device applies a constant tension perpendicular to the tape direction, tightly tauting the tape within the mounting surface of the grating groove. This keeps the tape straight and stable, counteracting the effects of thermal expansion and contraction. It ensures that the etched surface remains on an ideal optical plane throughout the entire stroke range, providing a stable and reliable signal source for the reading head. While ensuring effective tensioning of the grating scale, and considering that prolonged overstress could lead to deformation of the grating structure, this embodiment of the invention, based on actual testing, leaves a gap between the two tensioning mechanical structures. To prevent the mechanical structure from deforming due to gaps, tension shims are designed. Based on this, the linear grating is fully tensioned and installed within the grating groove, making the curvature of the linear grating and the turntable infinitely close, thus achieving the curvature of the linear grating ruler. The mechanical tensioning device and tension shims designed in this embodiment can be modified according to actual engineering conditions to meet the installation requirements of the curved grating ruler.

[0037] Step 1: Select the model and length of the linear grating ruler according to the technical specifications and characteristics of the shaft transmission system, design a special mechanical tensioning mechanism, install the selected linear grating ruler in the high-precision mounting slot, and use the tension force of the bending of the linear grating and the friction between the mounting slot and the grating to form an arc grating body, converting the linear position feedback into angular position feedback.

[0038] Step 2: After completing the curvature conversion of the linear grating ruler, the measurement step distance of the curved grating needs to be calculated to verify whether it meets the usage requirements. The measurement step distance, i.e., the resolution of the grating ruler, is the smallest positional change that the grating encoder can detect and report. It determines the minimum detectable displacement and achievable control accuracy of the system, and is a key parameter that must be defined first when selecting and predicting the matching of the controller-drive-motor system. For the servo control system of a large-aperture telescope axis, the signal output by the grating encoder is directly received by the controller. The controller needs to know how much displacement each pulse represents in order to perform correct calculations and control, and achieve high-precision tracking of celestial targets. Figure 7 As shown, the linear grating ruler (left side of the figure) is based on the radius of the mounting disk. After being bent into an arc-shaped grating (right side of the image), when the disk rotates by a tiny angle... (in radians) linear displacement in the tangential direction With angle The relationship is: The linear measurement step distance (i.e., the resolution of the linear grating ruler) corresponds to a tiny linear displacement; therefore, the corresponding angle measurement step distance... for: .

[0039] This shows that when using an arc grating to measure circumferential angles, the angle measurement step size (i.e., the resolution of the arc grating) depends only on the linear measurement step size of the linear grating ruler and the radius of the disk, and is independent of the effective length of the grating ruler (i.e., the measurement range). The larger the telescope aperture, the greater the axis driving torque and the larger the axis size; this conclusion is advantageous for the application of arc gratings in large-aperture telescopes. Based on the above, the 1nm measurement step size of the selected linear grating ruler is converted to the angle measurement step size of the arc grating ruler as follows: ,but The number of steps in the entire circle is: It fully meets the usage requirements.

[0040] After the installation of the arcuate grating and the calculation of the angle measurement step, the reading head needs to be installed for position detection to ensure that the arcuate grating can effectively detect the angle position information. Since the first-order harmonic and the second-order harmonic have a large proportion in the encoder angle measurement error, four reading heads are uniformly arranged on the circumference of 360°, the first-order harmonic error is eliminated by using the radial reading head angle measurement scheme, the second-order harmonic error is eliminated by using the two-by-two perpendicular reading head angle measurement scheme, and the four reading heads are used to obtain the arcuate grating angle position detection information, and the average value of the readings of the four reading heads is taken as the measurement value to eliminate the harmonic error in the angle measurement error and improve the angle measurement accuracy. The position feedback information of the arcuate grating is measured in all directions. The modified rotary table assembly is shown in Figures 8-10 The shaft system rotary table 1 is rotatably installed on the support frame 5, wherein the limit stop 4 is used as the last safety measure to prevent overtravel; four LIC reading heads 8 are installed on the corresponding LIC reading head platforms 10, and at the same time, two ECA reading head platforms 12 are reprocessed at the same radial position of the two diagonally distributed LIC reading head platforms for subsequent installation of the ECA reading head 6 to obtain the angle position detection information of the whole circle grating. The angle position information obtained by the arcuate grating is compared and verified.

[0041] In the arcuate grating angle position information detection process, first, the four LIC reading heads are numbered, and it is specified that when the disc rotates forward to the blind area, the position information obtained is the left boundary, and when the disc reverses to the blind area, the position information obtained is the right boundary; second, the reading head is connected with the PWM21 detector, and the ATS test software is used to obtain the angle position detection information of each reading head, and the reading position data of the grating scale at both ends corresponding to each reading head is recorded, a total of two groups, which are the left boundary group data and the right boundary group data, each group has four values; finally, the detection data of all reading heads are counted, the average value of the four values in each group is taken as the left and right boundary values respectively, the difference value is calculated, the effective detection range of the arcuate grating is tested, and the arc length formula is applied to convert it into an angle, that is wherein L is the left and right boundary difference, is the arcuate grating range, and R is the radius of the arcuate grating.

[0042] Step 3: In order to verify the engineering usability of the above-mentioned arcuate grating, it is further verified that the position information detected by the arcuate grating is correct. First, install a whole circle grating scale concentric with the arcuate grating, and in Figure 8Two ECA reading head platforms 12 are installed in axial layering at the same radial position of the diagonal distribution of the LIC reading head platform shown in the middle of the figure, and 2 ECA reading heads 6 are installed thereon to obtain corresponding whole-circle grating angle position detection information at the same position.

[0043] The linear grating selected by the embodiment of the application is an absolute value grating, and the evolution into an arc grating does not change its category. In the testing process, a mark is made at the rotary table corresponding to the No. 1 reading head, the serial data (count value) at this position is directly read by the reading head using ATS software, and the absolute angle position of the shaft system is converted through the formula: The disc is then rotated forward, and the mark is made to traverse the 4 LIC reading heads, and the absolute angle position conversion process is repeated for each reading head information and recorded. Then, the disc is reversed, and the foregoing process is repeated. The average value of the 8 angle position information obtained by the 4 reading heads during forward rotation and reverse rotation is taken as the absolute angle information of the mark position obtained by the arc grating. At the same time, the average value of the angle position information of the mark position passing through the circular grating reading head in the process is taken as the absolute angle information of the mark position obtained by the whole-circle grating. Finally, the arc grating angle detection information is compared with the arc grating angle detection information, and if they are the same or the difference is less than a micro-angle second, it is considered that the arc grating angle detection information is correct and unique.

[0044] Steps 2 and 3: The reading heads are uniformly arranged in the circumferential direction to obtain effective angle position feedback information, and the angle resolution and effective range of the arc grating ruler are further calculated, and the correctness of the arc grating angle position detection information is verified by comparing the angle position detection information obtained by the whole-circle grating and the arc grating.

[0045] The arc grating is used to replace the angle measurement grating in the application, and the processing difficulty is low and the cost is greatly reduced due to the absence of closed loop effect. In the case of the same budget, a higher precision grating can be selected. At the same time, the length of the grating ruler can be selected according to the rotation range of the shaft system. For example, for a ground-based telescope, the rotation range of the azimuth axis is generally greater than 360°, and the whole-circle installation circumference can be calculated according to the diameter of the shaft system, and a linear grating of corresponding length is selected. The rotation range of the height axis is generally 0~90°, and only 1 / 4 of the circle is taken as the installation circumference, and a linear grating of corresponding length is selected. This method provides a more flexible grating selection method, which can greatly avoid waste and reduce the difficulty of installation and adjustment.

[0046] In summary, the present application provides a method for large aperture telescope shaft system angle detection based on arc grating encoder, including the tooling set required for installation and testing of arc grating: mechanical tensioning structure, reading head support, and the method for testing and verifying the correctness of arc grating reading data. The main steps are: on the basis of mastering the position detection requirements of shaft system servo control system, selecting the type of linear grating ruler, according to the size of grating ruler, opening a steel belt groove along the circumference of shaft system turntable, designing a mechanical tensioning device to install the linear grating in the steel belt groove, realizing the arcing of linear grating ruler through this step; then, installing a certain number of reading heads on the specially designed reading head support, preferably evenly installed along the rotation circumferential angle, to eliminate installation errors and collect position detection signals as accurately as possible; finally, using the conversion method provided by the present application to convert the position information of linear grating into the angle information of arc grating, and calculating the angle resolution of arc grating, laying the foundation for the next step of control system hardware selection; finally, using the whole circle grating comparison test method provided by the present application to detect and verify whether the angle detection information of arc grating is correct.

[0047] Although embodiments of the present application have been shown and described above, it is to be understood that the above-described embodiments are merely illustrative of the principles and spirit of the present application, and that various modifications, changes, substitutions and variations can be made by those skilled in the art without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A large aperture telescope shaft angle detection method based on an arc grating encoder, characterized in that, The method comprises the following steps: Step 1: selecting a linear grating ruler with a proper type according to the rotation range of the telescope shaft system and the tracking technical index requirements; Step 2: installing the linear grating ruler along the circumference of the shaft system turntable to form an arc grating body; Step 3: arranging n reading heads along the circumferential direction of the shaft system rotation to read the shaft system rotation position information, calculate the effective range of the arc grating, convert the effective range into angle information, and calculate the resolution of the arc grating; specifically, connecting the reading heads with a detector, reading the test signals of the n reading heads through a test software, and setting that the position information obtained when the turntable reaches the blind area in the forward rotation as the left boundary, the position information obtained when the turntable reaches the blind area in the reverse rotation as the right boundary, and recording the reading position data of the two ends of the grating ruler corresponding to each reading head; taking the average value of the n reading heads as the left and right boundary values, calculating the effective range of the arc grating by using the left and right boundary values, converting the effective range into angle through a quantitative relationship, and calculating the angle resolution, so that each reading head can effectively obtain the position information; Step 4: installing a whole-circle grating to obtain the shaft system rotation position information detected by the whole-circle grating, comparing the information with the angle detection information of the arc grating, and verifying the correctness of the position information obtained by the arc grating.

2. The large aperture telescope shaft angle detection method based on arcuate grating encoder according to claim 1, characterized in that, In the step 1, the length of the arc grating is calculated according to the rotation range of the shaft system, and the arc grating is installed in the whole circle of the shaft system if the rotation range exceeds 360°, or the length of the arc grating is flexibly selected according to the rotation range if the rotation range is less than 360°.

3. The large aperture telescope shaft angle detection method based on arcuate grating encoder of claim 1, wherein, In the step 2, a circumferential groove is opened on the outer ring or the inner ring of the shaft system turntable according to the characteristics of the shaft system transmission structure and the specific size of the linear grating ruler, the linear grating ruler is installed in the circumferential groove, the size of the circumferential groove is designed to accommodate the grating body and provide the required friction force, the linear grating is completely fitted to the curvature of the turntable by using the tension of the linear grating after being radianized and the pre-tightening force provided by the installation groove, so that the linear grating is completely radianized to form a high-precision arc grating body for direct angle measurement.

4. The large aperture telescope shaft angle detection method based on arcuate grating encoder of claim 1, wherein, In the step 5, a standard whole-circle grating is installed on the concentric shaft of the arc grating installation turntable, and reading heads are additionally installed at the same radial position and the axial layering position of the arc grating to obtain the angle position information of the whole-circle grating; the same angle position of the shaft system rotation is obtained by using the whole-circle grating and the arc grating through the layering installation of the reading heads, and the angle position information detected by the whole-circle grating and the arc grating is compared to verify the correctness of the angle position information obtained by the arc grating; if the two are consistent, it indicates that the arc grating is installed correctly and can effectively and correctly obtain the angle information of the shaft system rotation.

5. The large aperture telescope shaft angle detection method based on arcuate grating encoder of claim 1, wherein, The arc grating body does not have a closed loop effect, and the length of the arc grating body is selected according to the rotation range of the shaft system.

6. The large aperture telescope shaft angle detection method based on arcuate grating encoder of claim 3, wherein, In the step 2, the linear grating ruler is installed by a mechanical tensioning device.

7. The large aperture telescope shaft angle detection method based on arcuate grating encoder of claim 6, wherein, The shafting turntable is provided with a circumferential groove at the circumferential end face, the linear grating ruler is installed in the circumferential groove, a tensioning groove is arranged at the shafting turntable end face of the arc linear grating end, the tensioning groove is provided with a fixed tensioning block and a floating tensioning block, the fixed tensioning block is fixed to the turntable, the floating tensioning block is connected with the fixed tensioning block through a tensioning force adjusting member, and the distance between the floating tensioning block and the fixed tensioning block can be adjusted through the tensioning force adjusting member; when the length of the linear grating ruler is equal to the whole circumference of the turntable, one set of mechanical tensioning device is arranged, one end of the linear grating ruler is fixed to the floating tensioning block, and the other end is fixed to the fixed tensioning block; when the length of the linear grating ruler is less than the whole circumference of the turntable, two sets of mechanical tensioning devices are arranged, and two ends of the linear grating ruler are respectively fixed to the floating tensioning blocks at the two ends.

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