Large-size angle dial error calibration device and calibration method

Abstract

The invention discloses a large-size angle dial error calibration device and calibration method. The system comprises a scribed line sighting device, a standard angle generating device, a concentric positioning device and a control system. According to the calibration device disclosed by the invention, the large-view and high-definition electron microscope with the display screen is adopted as the core of the scribed line sighting device, so that the reading error is reduced, and the accuracy and reliability of the measurement result are ensured. According to the calibration method disclosed by the invention, a traceability mode of transmitting angle measurement to angle is adopted, the actual use working condition of the measured angle dial can be completely simulated, and the measurement precision and the detection efficiency are improved.

Description

Technical Field

[0001] The invention belongs to the field of precision measurement, and in particular relates to a large-size angle scale error calibration device and a calibration method in the field. Background Art

[0002] An angle dial is a measuring instrument that indicates the plane angle of 0° to 360° by regularly engraving lines on the dial surface. It is made of metal or hard non-magnetic material, usually round or square, with a diameter (side length) ranging from 100mm to 1500mm. Through engraving, etching and other processing techniques, the required angle scale is engraved along the disk surface, and the common graduation values ​​are 1° and 0.5°. JJG628 "SLC9 Direct Reading Current Meter", JJG 876 "Ship Meteorological Instrument", JJG 1167 "Ocean Wind Measuring Instrument", JJG (Ocean) 01 "FZS2. FZS1 Ocean Data Buoy Sensor", HYT 270 "Ocean Wind Measuring Instrument Detection Method" and other standard documents all use the angle dial as one of the main standard instruments for the above-mentioned marine special measuring instruments, but there is no reliable calibration device and method that can meet the angle error traceability requirements of the angle dial.

[0003] The angle error of the angle dial is usually calibrated with reference to the standard GB / T3177-2009 "Product Geometry Technical Specification (GPS) Inspection of Smooth Workpiece Dimensions". The indirect traceability method of dimension measurement is adopted. In the process of dimension measurement, factors such as the positioning consistency of the measuring instrument, the measurement accuracy, and the selected measurement location will introduce a large measurement error, thereby affecting the angle measurement accuracy. Compared with the direct traceability method of angle measurement, the existing calibration method has the disadvantages of inaccurate measurement positioning, a large number of measurement data, unreliable data conversion results, and low calibration efficiency.

[0004] For small-sized angle dials with a diameter of φ≤300mm, an image measuring instrument is used for direct measurement. The scale is placed horizontally on the measuring platform of the image measuring instrument with the scale facing upward. The 0° (360°) scale line direction is adjusted to be parallel to the longitudinal movement direction of the measuring platform. The measuring software extracts multiple circles in sequence and automatically fits them into the scale outer end circle of the angle dial. The center of the circle is the rotation center of the angle dial by default. Take the nominal value α of the two measured angles, construct a straight line parallel to the scale line direction at the middle position of the measured angle scale width, construct the intersection of this straight line and the outer end circle, and connect this intersection with the center of the outer end circle as straight line L1. Use the same method to construct the straight line L2 of another measured angle. The angle value α′ between straight line L1 and straight line L2 is the actual value of the two measured angles, and the indication error δ is the difference between the nominal value and the actual value of the two measured angles (δ=α-α′). This method does not simulate working conditions when calibrating a small-angle dial, and the image measuring instrument cannot accurately locate its processing geometric center in a non-contact manner. The center positioning deviation directly affects the accuracy of the measurement results.

[0005] The large-size angle scale with a diameter of φ>300mm exceeds the measuring range of the general image measuring instrument. The angle error of the angle scale is calibrated by the chord length calculation method using a digital caliper and a steel ruler. The outer radius of the angle scale and the chord length connecting the two scale end points are measured, and the angle value is indirectly calculated using trigonometric functions. The difference between the angle value and the nominal value is the indication error δ. This method does not simulate the working conditions when calibrating the large-size angle scale. Due to the accuracy limitations of the measuring instrument, large-size measurement, and combined measurement, the measurement results are less accurate.

[0006] In summary, the existing calibration schemes are not based on the actual working status of the angle dial, and also ignore the center positioning and zero aiming errors. The measurement accuracy is poor, especially for large-size angle dials. There is no good traceability device and calibration method, which cannot meet the customer's measurement traceability needs. Summary of the invention

[0007] The present invention aims to solve the following technical problems existing in the calibration of angle errors of angle scales of conventional instruments and equipment: (1) the calibration principles are inconsistent, and the angle measurement and transmission cannot be realized; (2) the calibration methods of large and small-sized angle scales are not universal; (3) the geometric center of the measured angle scale cannot be accurately located, and the manual alignment reading error is large, resulting in low measurement accuracy. Provided is a large-sized angle scale error calibration device and calibration method, which can realize the angle measurement and transmission angle traceability mode, has the technical characteristics of high precision and large range, and can simulate the use conditions to accurately calibrate the indication errors of angle scales of various sizes.

[0008] The present invention adopts the following technical solution: A large-size angle scale error calibration device, the improvement of which is that it includes a scale line aiming device, a standard angle generating device, a concentric positioning device and a control system; The scribed line aiming device comprises a base, a bracket is mounted on the base, and an electron microscope with a display screen is mounted on the bracket; The standard angle generating device is a circular grating and a reading head, and the reading head is fixedly mounted on a bracket parallel to the circular grating; The concentric positioning device comprises a servo turntable driven to rotate by a motor, a circular grating support frame is arranged on the top of the servo turntable, the circular grating is sleeved on the outside of the circular grating support frame, a marble platform is arranged on the top of the circular grating support frame, the circular grating support frame and the marble platform can rotate synchronously with the servo turntable, more than four track grooves extending from the center to the edge are arranged on the top of the marble platform, a clamping mechanism that can slide along the track groove is arranged in each track groove, and scales are arranged on four of the track grooves; The control system includes a controller and an input device electrically connected to the controller, a fine-tuning handwheel, a display device and a motor. The controller can control the motor to work according to the input of the input device or the fine-tuning handwheel, and the display device displays the input content of the input device; the reading head is electrically connected to the above-mentioned display device through a conversion module, and the conversion module can read the reading of the reading head and display it through the display device.

[0009] Furthermore, a track groove pointing to the center of the marble platform is provided on the base of the engraved line aiming device, a lead screw is installed in the track groove, one end of the lead screw is fixedly connected to a handle outside the track groove, the bracket is installed on the lead screw, and the bracket can slide along the lead screw by rotating the handle. A thread is provided on the outer wall of the bracket, and a turntable is screwed on the thread. One end of the support rod is inserted into the bracket and supported by the turntable, and an electron microscope is installed on the other end.

[0010] Furthermore, more than two locking mechanisms are provided at the bottom of the bracket.

[0011] Furthermore, the motor, servo turntable and circular grating support frame of the concentric positioning device are all installed in the shell, and the marble platform is arranged on the top of the shell.

[0012] Furthermore, the top of the servo turntable is a rotary worktable with a recessed platform, and the bottom of the circular grating support frame has a boss, which is embedded in the recessed platform; the rotary worktable and the circular grating support frame are matched with a base hole system, and are positioned with two cylindrical locating pins and fastened with ten hexagon socket screws.

[0013] Furthermore, the outer side of the circular grating support frame is a conical surface, and the circular grating is fastened to the outer conical surface of the circular grating support frame using more than three hexagon socket screws.

[0014] Furthermore, a hole is opened in the center of the marble platform, a boss is set at the top center of the circular grating support frame, the boss is inserted into the hole, and a dial center positioning device is installed in the boss. The marble platform and the circular grating support frame are fastened by more than three bolts.

[0015] Furthermore, eight track grooves extending from the center to the edge are arranged on the top of the marble platform, the eight track grooves are evenly distributed on the marble platform at equal intervals, and scales are arranged at intervals between the track grooves.

[0016] A calibration method, using the calibration device, wherein the improvement is as follows: fixing the measured angle scale dial upward on a marble platform, rotating a handle to adjust the position of the scale line aiming device bracket, so that the optical probe of the electron microscope is facing the measured angle scale dial, and the crosshairs displayed on the display screen of the electron microscope are illuminated on the scale of the measured angle scale dial, and adjusting the focal length so that the measured angle scale dial displayed on the display screen of the electron microscope is clear; Sending instructions to the controller through the input device or the fine-tuning hand wheel, the controller controls the motor to drive the servo turntable, the circular grating support frame, the marble platform and the angle scale to be measured on the marble platform to rotate synchronously, so that the center point of the cross mark displayed on the electron microscope display screen is aligned with the middle position of the 0° and 360° scale widths of the angle scale to be measured, the conversion module obtains the rotation angle of the circular grating through the reading head as the rotation angle displayed on the display device, and the rotation angle displayed on the display device is set to zero through the input device; A rotation angle instruction is sent to the controller through the input device, and the controller controls the motor to drive the servo turntable, the circular grating support frame, the marble platform and the measured angle dial on the marble platform to rotate synchronously. When the motor rotates to the instruction angle, it stops; a command is sent to the controller through the fine-tuning handwheel, and the controller controls the motor to drive the servo turntable, the circular grating support frame, the marble platform and the measured angle dial on the marble platform to rotate synchronously. When the center point of the cross mark displayed on the electron microscope display screen is aligned with the middle position of the α scale width of the measured angle dial, the controller controls the motor to stop. At this time, the rotation angle displayed on the display device is α', and the angle indication error δ of this measurement is α-α'; repeat this paragraph, select 6 to 12 scales along the circumference of the measured angle dial for measurement, and the δi obtained in sequence is the angle indication error of each measured angle of the measured angle dial, i=1, 2...n, n is a natural number.

[0017] Furthermore, when the angle dial to be measured is fixed on the marble platform, if the angle dial to be measured has a center hole, the center hole of the angle dial to be measured is sleeved on the dial center positioning device and clamped by a clamping mechanism; if the angle dial to be measured has no center hole, the dial center positioning device is removed, and the angle dial to be measured is placed on the marble platform so that its center falls in the central opening of the marble platform, and the distance from the outer edge to the center of the angle dial to be measured is calculated by the readings of its outer edge pressing on the four scales, and the angle dial to be measured is manually fine-tuned so that the readings of its outer edge pressing on the four scales are consistent, and then clamped by the clamping mechanism.

[0018] The beneficial effects of the present invention are: The calibration device disclosed in the present invention adopts a large-viewing-field, high-definition, high-display screen electron microscope as the core of a scribed line aiming device, thereby reducing reading errors and ensuring the accuracy and reliability of measurement results; adopts a large-size, high-precision circular grating as a standard angle generating device, thereby ensuring the consistency of inner and outer ring angles and measurement accuracy; adopts a large-size marble platform, thereby meeting the calibration requirements of angle dials of various specifications; a three-in-one concentric positioning device consisting of a servo turntable, a circular grating support frame and a marble platform ensures the synchronous rotation of the servo turntable, the circular grating support frame, the marble platform and the angle dial to be measured, thereby accurately simulating the actual use conditions of the angle dial to be measured and reducing the uncertainty of the calibration result; a track groove and a scale arranged on the top of the marble platform can accurately perform center positioning on angle dials of different external structures.

[0019] The calibration method disclosed in the present invention adopts a traceability method of angle measurement and angle transmission, which can completely simulate the actual use conditions of the angle dial being measured, improve the measurement accuracy and detection efficiency, can meet the angle error calibration of angle dials of various sizes and shapes, and can achieve autonomous calibration and traceability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of the calibration device disclosed in the present invention; Figure 2 It is a schematic diagram of the composition of the concentric positioning device; Figure 3 This is a schematic diagram of the distribution of the track grooves and scales on the top of the marble platform; Figure 4 is a schematic diagram of the outer cone surface of the circular grating support frame; Figure 5 It is a schematic diagram of the installation position of the dial center positioning device; Figure 6 This is a schematic diagram of the crosshairs being aligned with the 0° and 360° scales of the angle dial being measured.

[0021] Figure numerals: 1—marked line aiming device, 11—screw, 12—handle, 13—turntable, 14—display device, 15—cross mark, 16—fine-tuning hand wheel, 2—concentric positioning device, 21—servo turntable, 22—circular grating support frame, 23—circular grating, 24—marble platform, 25—cylindrical locating pin, 26—dial center positioning device, 27—track groove, 28—clamping mechanism, 29—scale ruler. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] Embodiment 1, this embodiment discloses a large-size angle scale error calibration device, such as Figure 1 As shown, it includes a scribed line aiming device 1, a standard angle generating device, a concentric positioning device 2 and a control system (not shown in the figure); The scribed line aiming device comprises a base, a bracket is mounted on the base, and a large-viewing-field electron microscope with a display screen is mounted on the bracket; The standard angle generating device is the core, mainly using circular grating and reading head; the circular grating is composed of a large number of high-precision grating lines engraved on the stainless steel cylindrical surface, with a engraving accuracy of ±0.5″, a period error of less than ±40nm, and a repeatability of 0.02 seconds. The matching reading head is a high-precision reading head with an advanced optical filtering system, excellent signal stability and very low electronic subdivision error. The reading head is fixedly installed on a bracket parallel to the circular grating; like Figure 2 As shown, the concentric positioning device 2 comprises a servo turntable 21 driven to rotate by a motor, a circular grating support frame 22 is arranged on the top of the servo turntable, the circular grating 23 is sleeved on the outside of the circular grating support frame, and a marble platform 24 is arranged on the top of the circular grating support frame. The circular grating support frame and the marble platform can rotate synchronously with the servo turntable, as shown in FIG. Figure 3 As shown, eight track grooves 27 extending from the center to the edge are arranged on the top of the marble platform, and the eight track grooves are evenly spaced on the marble platform. A clamping mechanism 28 capable of sliding along the track groove is arranged in each track groove, and scales 29 are arranged on four of the track grooves, and scales are arranged at intervals between the track grooves for positioning the angle dial to be measured; The control system includes a controller (PLC programmable controller) and an input device electrically connected to the controller, a fine-tuning hand wheel 16, a display device 14 and a motor. The controller can control the motor to work according to the input of the input device or the fine-tuning hand wheel. Specifically, the controller converts the rotation angle instruction into a signal recognizable by the motor driver, which receives and amplifies the signal and then drives the motor to rotate the instruction angle. The display device displays the input content of the input device, and the display device can be a touch screen integrated with the input device; the high-precision reading head is electrically connected to the above-mentioned display device through a conversion module, and the high-precision reading head automatically reads the rotation angle of the circular grating. The conversion module can read the reading of the high-precision reading head and display it through the display device.

[0024] A track groove pointing to the center of the marble platform is arranged on the base of the engraved line aiming device, a lead screw 11 is installed in the track groove, one end of the lead screw is fixedly connected to a handle 12 outside the track groove, the bracket is installed on the lead screw, and the bracket can slide along the lead screw by rotating the handle, a thread is arranged on the outer wall of the bracket, a turntable 13 is screwed on the thread, one end of the support rod is inserted into the bracket and supported by the turntable, and an electron microscope is installed at the other end, and the support rod and the electron microscope can be raised and lowered by rotating the turntable. This liftable design can meet the angle scale line aiming in the size range of 100mm to 1500mm. Two or more locking mechanisms are arranged at the bottom of the bracket to lock and fix the bracket.

[0025] The motor, servo turntable and circular grating support frame of the concentric positioning device are all installed in the shell, and the marble platform is arranged on the top of the shell.

[0026] To ensure that the rotation centers of all components of the concentric positioning device are consistent, all components use the same design datum. The top of the servo turntable is a rotary table with a concave platform, and the bottom of the circular grating support frame has a boss, which is embedded in the concave platform; the rotary table and the circular grating support frame are matched with a base hole system, and two cylindrical positioning pins 25 are used for positioning. The boss and the positioning pin are matched to form a complete positioning between the servo turntable and the circular grating support frame, and ten hexagon socket screws are used to fasten them.

[0027] like Figure 4 As shown in the figure, the outer side of the circular grating support frame is a conical surface, which is convenient for concentric alignment when installing the circular grating. The circular grating is fastened to the outer conical surface of the circular grating support frame using more than three hexagonal screws, which can not only compensate for eccentricity, but also have excellent mechanical stability and can withstand thermal cycles, shocks and vibrations.

[0028] like Figure 5 As shown, a hole is opened in the center of the marble platform, a boss is set at the top center of the circular grating support frame, the boss is inserted into the hole, and a dial center positioning device 26 is installed in the boss. The marble platform and the circular grating support frame are fastened by more than three bolts to ensure synchronous rotation and concentric alignment of the servo turntable, the circular grating support frame, the circular grating and the marble platform.

[0029] This embodiment also discloses a calibration method, using the calibration device, fixing the measured angle scale on a marble platform with the scale upward, ensuring that the center of the measured angle scale is accurately positioned before measuring. Rotating the handle to adjust the position of the bracket of the scale aiming device, so that the optical probe of the electron microscope is facing the measured angle scale, and the crosshairs displayed on the display screen of the electron microscope are reflected on the scale of the measured angle scale, and adjusting the focal length so that the scale of the measured angle scale displayed on the display screen of the electron microscope is clear; The controller is given a command through the input device or the fine-tuning hand wheel, and the controller controls the motor to drive the servo turntable, the circular grating support frame, the marble platform and the measured angle dial on the marble platform to rotate synchronously, such as Figure 6 As shown, the center point of the crosshairs 15 displayed on the electron microscope display screen is aligned with the middle position of the 0° (360°, the 0° and 360° scales on the angle scale are overlapped) scale width of the angle scale to be measured, the conversion module obtains the rotation angle of the circular grating as the rotation angle displayed on the display device through the high-precision reading head, and the rotation angle displayed on the display device is set to zero through the input device; A rotation angle instruction is sent to the controller through the input device, and the controller controls the motor to drive the servo turntable, the circular grating support frame, the marble platform and the measured angle dial on the marble platform to rotate synchronously. When the motor rotates to the instruction angle, it stops; a command is sent to the controller through the fine-tuning handwheel, and the controller controls the motor to drive the servo turntable, the circular grating support frame, the marble platform and the measured angle dial on the marble platform to rotate synchronously. When the center point of the cross mark displayed on the electron microscope display screen is aligned with the middle position of the α scale width of the measured angle dial, the controller controls the motor to stop. At this time, the rotation angle displayed on the display device is α', and the angle indication error δ of this measurement is α-α'; for example, if the target α scale is 30°, the rotation angle instruction sent to the controller through the input device is a value close to 30°, such as 29.9°. It is not directly set to 30° because there is an error in the measured angle dial, and the actual rotation degree is inconsistent with the scale of the cross mark on the measured angle dial. The instruction value is slightly smaller than 30° to avoid backstroke. After rotating 29.9°, use the fine-tuning handwheel to control the rotation until the center point of the cross mark is aligned with the middle position of the 30° scale width of the measured angle dial. At this time, the actual rotation angle displayed on the display device is α'. Subtracting α' from 30° is the angle indication error δ of this measurement. The pulse transmitter is used as a fine-tuning means. The fine-tuning handwheel is equipped with a knob switch, a main knob, and a magnification adjustment knob. The magnification adjustment knobs are ×1 (fine-tuning), ×10, and ×100 (fast magnification adjustment). Repeat this paragraph, select 6 to 12 scales along the circumference of the measured angle dial for measurement, until the circumference of the measured angle dial is measured, and the δi obtained in sequence is the angle indication error of each measured angle of the measured angle dial (unit: °), i=1, 2…n, n is a natural number.

[0030] When the angle dial to be measured is fixed on the marble platform, if the angle dial to be measured has a center hole, the center hole of the angle dial to be measured is sleeved on the dial center positioning device and clamped by a clamping mechanism; if the angle dial to be measured has no center hole, the dial center positioning device is removed, the angle dial to be measured is placed on the marble platform so that its center falls in the central opening of the marble platform, the distance from the outer edge to the center of the angle dial to be measured is calculated by the readings of the outer edge of the angle dial pressed on the four scales, the angle dial to be measured is manually fine-tuned so that the readings of the outer edge of the angle dial pressed on the four scales are consistent, and then it is clamped by the clamping mechanism.

Claims

1. A large-size angle scale error calibration device, characterized in that: It includes a marking line aiming device, a standard angle generating device, a concentric positioning device and a control system; The scribed line aiming device comprises a base, a bracket is mounted on the base, and an electron microscope with a display screen is mounted on the bracket; The standard angle generating device is a circular grating and a reading head, and the reading head is fixedly mounted on a bracket parallel to the circular grating; The concentric positioning device comprises a servo turntable driven to rotate by a motor, a circular grating support frame is arranged on the top of the servo turntable, the circular grating is sleeved on the outside of the circular grating support frame, a marble platform is arranged on the top of the circular grating support frame, the circular grating support frame and the marble platform can rotate synchronously with the servo turntable, more than four track grooves extending from the center to the edge are arranged on the top of the marble platform, a clamping mechanism that can slide along the track groove is arranged in each track groove, and scales are arranged on four of the track grooves; The control system includes a controller and an input device electrically connected to the controller, a fine-tuning handwheel, a display device and a motor. The controller can control the motor to work according to the input of the input device or the fine-tuning handwheel, and the display device displays the input content of the input device; the reading head is electrically connected to the above-mentioned display device through a conversion module, and the conversion module can read the reading of the reading head and display it through the display device.

2. The large-size angle scale error calibration device according to claim 1 is characterized in that: A track groove pointing to the center of the marble platform is arranged on the base of the engraved line aiming device, a lead screw is installed in the track groove, one end of the lead screw is fixedly connected to a handle outside the track groove, the bracket is installed on the lead screw, and the bracket can slide along the lead screw by rotating the handle, a thread is arranged on the outer wall of the bracket, a turntable is screwed on the thread, one end of the support rod is inserted into the bracket and supported by the turntable, and an electron microscope is installed on the other end.

3. The large-size angle scale error calibration device according to claim 2 is characterized in that: More than two locking mechanisms are arranged at the bottom of the bracket.

4. The large-size angle scale error calibration device according to claim 1 is characterized in that: The motor, servo turntable and circular grating support frame of the concentric positioning device are all installed in the shell, and the marble platform is arranged on the top of the shell.

5. The large-size angle scale error calibration device according to claim 1 is characterized in that: The top of the servo turntable is a rotary table with a recessed platform, and the bottom of the circular grating support frame has a boss, which is embedded in the recessed platform. The rotary table and the circular grating support frame are matched with a base hole system, and are positioned with two cylindrical locating pins and fastened with ten hexagon socket screws.

6. The large-size angle scale error calibration device according to claim 1 is characterized in that: The outer side of the circular grating support frame is a conical surface, and the circular grating is fastened to the outer conical surface of the circular grating support frame using more than three hexagon socket screws.

7. The large-size angle scale error calibration device according to claim 2 is characterized in that: A hole is opened in the center of the marble platform, a boss is set at the top center of the circular grating support frame, the boss is inserted into the hole, and a dial center positioning device is installed in the boss. The marble platform and the circular grating support frame are fastened by more than three bolts.

8. The large-size angle scale error calibration device according to claim 1, characterized in that: Eight track grooves extending from the center to the edge are arranged on the top of the marble platform. The eight track grooves are evenly distributed on the marble platform at equal intervals, and scales are arranged at intervals between the track grooves.

9. A calibration method, using the calibration device according to claim 7, characterized in that: Fix the angle dial to be measured on the marble platform with the scale upward, rotate the handle to adjust the position of the bracket of the scale line aiming device, so that the optical probe of the electron microscope is facing the angle dial to be measured, and the crosshairs displayed on the electron microscope display screen are reflected on the scale of the angle dial to be measured, and adjust the focal length so that the scale of the angle dial to be measured displayed on the electron microscope display screen is clear; Sending instructions to the controller through the input device or the fine-tuning hand wheel, the controller controls the motor to drive the servo turntable, the circular grating support frame, the marble platform and the angle scale to be measured on the marble platform to rotate synchronously, so that the center point of the cross mark displayed on the electron microscope display screen is aligned with the middle position of the 0° and 360° scale widths of the angle scale to be measured, the conversion module obtains the rotation angle of the circular grating through the reading head as the rotation angle displayed on the display device, and the rotation angle displayed on the display device is set to zero through the input device; A rotation angle instruction is sent to the controller through the input device, and the controller controls the motor to drive the servo turntable, the circular grating support frame, the marble platform and the measured angle dial on the marble platform to rotate synchronously. When the motor rotates to the instruction angle, it stops; a command is sent to the controller through the fine-tuning handwheel, and the controller controls the motor to drive the servo turntable, the circular grating support frame, the marble platform and the measured angle dial on the marble platform to rotate synchronously. When the center point of the cross mark displayed on the electron microscope display screen is aligned with the middle position of the α scale width of the measured angle dial, the controller controls the motor to stop. At this time, the rotation angle displayed on the display device is α', and the angle indication error δ of this measurement is α-α'; repeat this paragraph, select 6 to 12 scales along the circumference of the measured angle dial for measurement, and the δi obtained in sequence is the angle indication error of each measured angle of the measured angle dial, i=1, 2...n, n is a natural number.

10. The calibration method according to claim 9, characterized in that: When the angle dial to be measured is fixed on the marble platform, if the angle dial to be measured has a center hole, the center hole of the angle dial to be measured is sleeved on the dial center positioning device and clamped by a clamping mechanism; if the angle dial to be measured has no center hole, the dial center positioning device is removed, the angle dial to be measured is placed on the marble platform so that its center falls in the central opening of the marble platform, the distance from the outer edge to the center of the angle dial to be measured is calculated by the readings of the outer edge of the angle dial pressed on the four scales, the angle dial to be measured is manually fine-tuned so that the readings of the outer edge of the angle dial pressed on the four scales are consistent, and then it is clamped by the clamping mechanism.

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