A method and system for calibrating a rotating double prism

Abstract

This invention relates to a method and system for calibrating a rotating biprism, belonging to the field of rotating biprism technology. By calibrating the relationship between various orientations in a spatial rectangular coordinate system and iterating using the characteristics of the rotating biprism, this invention achieves accurate calibration of the prism deflection angle and zero position, avoids large errors in the calibration process, ensures the beam steering effect of the rotating biprism, and improves the pointing accuracy of the rotating biprism.

Description

Technical Field

[0001] This invention belongs to the field of rotating biprism technology, specifically relating to a method and system for calibrating a rotating biprism. Background Technology

[0002] Rotating biprisms are small in size and possess excellent line-of-sight adjustment capabilities, enabling large-angle beam deflection. Therefore, they are suitable for space laser communication. Currently, research on the beam steering mechanism of rotating biprisms mainly revolves around the forward and reverse problems. The forward problem involves deriving the deflection and azimuth angles of the emitted beam from the rotation angles of the two prisms. Research on the forward problem is fundamental to applications such as beam scanning, imaging line-of-sight changes, and target tracking in rotating biprism systems. The reverse problem involves calculating the rotation angles of the two prisms from the deflection and azimuth angles of the emitted beam. The significance of the reverse problem lies in its focus on applications such as target tracking and target pointing. However, since a rotating biprism consists of two coaxial wedge prisms, the relationship between the emitted light and the rotation angle of the wedge prisms is not linear. Methods that calibrate the pointing of a rotating biprism by measuring the pointing of the emitted beam cannot isolate various factors affecting calibration accuracy, leading to significant errors in the calibration process and consequently affecting the beam steering effect of the rotating biprism. Summary of the Invention

[0003] In order to address the shortcomings of existing technologies and solve the aforementioned problems, a method and system for calibrating a rotating double prism is proposed.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for calibrating a rotating biprism includes the following steps:

[0006] A laser beam is emitted toward a reference surface, and the light spot on the reference surface is imaged at the center of the field of view of the image sensor;

[0007] Install and adjust the rotating double prism so that the azimuth angle of the laser beam emitted through the rotating double prism reaches the zero position of the rotating double prism, and record the rotation angle values ​​of the two prisms as the initial zero position value.

[0008] Place the tracking target on the reference plane, adjust the rotating biprism to image the tracking target onto the center of the field of view of the image sensor, obtain the displayed rotation angle value and the actual rotation angle value of the prism, and calculate the theoretical zero position value of the prism based on the initial zero position value, the displayed rotation angle value and the actual rotation angle value of the prism, and complete the deflection angle calibration of the rotating biprism.

[0009] Adjust the rotation angle of the prism to make the azimuth angle of the outgoing beam reach the zero position of the rotating double prism again. Based on the spot coordinates of the outgoing beam on the reference plane, calculate the difference between the theoretical zero position value and the standard zero position value, and complete the zero position calibration of the rotating double prism.

[0010] This technical solution is further configured such that, before emitting the laser beam to the reference plane, it also includes:

[0011] An optical platform is installed in front of the reference plane, and a total station is set up between the reference plane and the optical platform. The total station is used to determine the precise direction of the major axis of the optical platform and the normal vector of the reference plane.

[0012] This technical solution is further configured to place several marker points along the long axis of the optical platform, and use a total station to measure the position parameters of the marker points, including the azimuth angle, elevation angle, and slope distance between the marker point and the total station. The position parameters are then converted into rectangular coordinates in the total station's spatial rectangular coordinate system to determine the precise orientation of the long axis of the optical platform.

[0013] The technical solution is further configured to take three non-collinear measurement points on the reference plane, determine the coordinates of the measurement points, and obtain the normal vector of the reference plane in the total station's spatial rectangular coordinate system based on the coordinates of the measurement points.

[0014] The technical solution is further configured such that the laser emits laser light, the coordinates of the laser emission point are measured using a total station, the theoretical light spot coordinates on the reference plane are calculated based on the precise pointing of the long axis of the optical platform and the normal vector of the reference plane, the orientation of the laser is adjusted until the theoretical light spot coordinates coincide with the center of the actual light spot, and the actual light spot on the reference plane is imaged at the center of the field of view of the image sensor.

[0015] The technical solution is further configured to install a rotating double prism and rotate one of its prisms to change the relative angle difference between the two prisms, keep the relative angle difference constant, and rotate the two prisms synchronously so that the azimuth angle of the laser beam emitted through the rotating double prism reaches the zero position of the rotating double prism.

[0016] This technical solution is further configured such that the azimuth angle of the laser beam emitted from the rotating biprism reaches the zero position of the rotating biprism, specifically:

[0017] A rotating double prism spatial rectangular coordinate system is established with the right of the exit direction of the emitted beam as the positive X-axis, the top of the exit direction of the emitted beam as the positive Y-axis, and the exit direction of the emitted beam as the negative Z-axis.

[0018] When the deflection angle of the emitted beam reaches its maximum value, and the component of the emitted beam on the Y-axis is zero and the component in the positive X-axis direction reaches its maximum value, it is assumed that the azimuth angle of the emitted beam reaches the zero position of the rotating biprism. The azimuth angle of the emitted beam is obtained based on the spot miss distance on the image sensor.

[0019] This technical solution is further configured such that the calculated theoretical null value of the prism is specifically as follows:

[0020] Place the tracking target on the reference plane and adjust the rotating biprism to image the tracking target onto the center of the image sensor's field of view;

[0021] According to the first algorithm for reverse calculation of rotating double prisms, the relative rotation angle difference between the two prisms is calculated based on the deflection angle of the outgoing beam. The first actual rotation angle value of the two prisms is calculated based on the relative rotation angle difference, and the first displayed rotation angle value of the prism is recorded.

[0022] The second algorithm for reverse calculation based on rotating double prisms calculates the relative rotation angle difference between the two prisms based on the deflection angle of the outgoing beam, calculates the second actual rotation angle value of the two prisms based on the relative rotation angle difference, and records the second displayed rotation angle value of the prisms.

[0023] Based on the initial zero position value, the first displayed rotation angle value, the first actual rotation angle value, the second displayed rotation angle value, and the second actual rotation angle value, the theoretical zero position value and the actual relative rotation angle difference of the prism are calculated.

[0024] The technical solution is further configured such that the two prisms rotate synchronously, and the spot of the emitted beam on the reference plane forms a circular trajectory. By adjusting the rotation angle of the prisms, the azimuth angle of the emitted beam reaches the zero position of the rotating double prisms again.

[0025] The difference between the displayed rotation angle value and the actual rotation angle value of the two prisms is set to θ. When the displayed rotation angle value of both prisms is 0°, according to the center algorithm, θ1 = θ2 = θ. θ1 and θ2 represent the differences between the theoretical zero point and the standard zero point of the two prisms, respectively. θ3 represents the azimuth angle of the outgoing beam. θ3 is calculated based on the spot coordinates of the outgoing beam on the reference plane, and then θ is obtained. Subtracting θ from the theoretical zero point value of the prism yields the standard zero point value of the prism.

[0026] Furthermore, this invention also provides a rotating biprism calibration system, including an optical platform for mounting a rotating biprism. The optical platform also includes a laser and an image sensor. A reference surface is located in front of the optical platform. The laser emitted by the laser is transmitted to the reference surface via the rotating biprism to form a light spot. The image sensor is used to capture the light spot on the reference surface. A total station is positioned between the optical platform and the reference surface. The beneficial effects of this invention are:

[0027] 1. By calibrating the relationship between various orientations in the spatial rectangular coordinate system and iterating using the characteristics of the rotating biprism, the precise calibration of the prism deflection angle and zero position is achieved, avoiding large errors in the calibration process, ensuring the beam steering effect of the rotating biprism, and improving the pointing accuracy of the rotating biprism.

[0028] 2. No need for a lot of complex calculations, resulting in high calibration efficiency. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the rotating double prism calibration method in this invention;

[0030] Figure 2 It is a graph of the difference in relative rotation angle between the two prisms versus the deflection angle;

[0031] Figure 3 This is a schematic diagram showing the circular trajectory formed by the spot of the emitted light beam on the reference plane when the two prisms rotate synchronously.

[0032] Figure 4 This is a schematic diagram of the optical path of the rotating double prism calibration system in this invention. Detailed Implementation

[0033] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Based on the embodiments in this application, other similar embodiments obtained by those skilled in the art without creative effort should all fall within the scope of protection of this application. Furthermore, directional terms mentioned in the following embodiments, such as "up," "down," "left," and "right," are only for reference to the directions in the accompanying drawings; therefore, the directional terms used are for illustrative purposes and not for limiting the invention.

[0034] Example 1:

[0035] like Figure 1 As shown, a method for calibrating a rotating biprism includes the following steps:

[0036] S100: Emits a laser beam to the reference surface and images the light spot on the reference surface onto the center of the image sensor's field of view.

[0037] The reference plane can be any spatial reference plane, or a wall can be selected. An optical platform is installed in front of the reference plane, and a total station is set up between the reference plane and the optical platform. The total station is used to determine the precise direction of the major axis of the optical platform and the normal vector of the reference plane.

[0038] Specifically, several marker points are placed along the long axis of the optical platform, and the position parameters of the marker points are measured using a total station. The position parameters include azimuth, elevation, and slope distance between the marker point and the total station. The position parameters are then converted into rectangular coordinates in the total station's spatial rectangular coordinate system to determine the precise orientation of the long axis of the optical platform.

[0039] The following formula can be used to convert position parameters into rectangular coordinates in the total station's spatial rectangular coordinate system:

[0040] In the formula: x, y, and z represent the rectangular coordinates of the marker point in the total station's spatial rectangular coordinate system, in meters (m). l represents the slope distance of the marker point in the spatial polar coordinate system of the total station, in meters (m). θ represents the azimuth angle of the marker point in the spatial polar coordinate system of the total station, in rad. This represents the elevation angle of the marker point in the spatial polar coordinates of the total station's rectangular coordinate system, expressed in rad.

[0041] Specifically, three non-collinear measurement points are selected on the reference plane, the coordinates of the measurement points are determined, and the normal vector of the reference plane in the total station's rectangular coordinate system is obtained based on the coordinates of the measurement points.

[0042] The coordinates of the three measurement points are (x1, y1, z1), (x2, y2, z2), and (x3, y3, z3). The normal vector of the reference plane in the total station's rectangular coordinate system is:

[0043]

[0044] The laser emits laser light. Using a total station to measure the coordinates of the laser's emission point, and based on the precise orientation of the optical platform's major axis and the normal vector of the reference plane, the theoretical laser spot coordinates on the reference plane are calculated.

[0045]

[0046] Px, Py, Pz represent the coordinates of any point on the reference plane, px, py, pz represent the coordinates of the laser emission point, Nx, Ny, Nz represent the components of the reference plane normal vector on the x, y, z axes, and nx, ny, nz represent the components of the optical platform's major axis on the x, y, z axes.

[0047] Adjust the laser's orientation until the theoretical spot coordinates coincide with the actual spot center, and make the actual spot on the reference plane imaged at the center of the image sensor's field of view.

[0048] S200. Install and adjust the rotating double prism so that the azimuth angle of the laser beam exiting the rotating double prism reaches the zero position of the rotating double prism. Record the rotation angle values ​​of the two prisms as the initial zero position value θ. 10 θ 20 At this point, the zero position of the calibration is not accurate, but because the tracking uses relative positions, tracking can still be completed even if the calibration is inaccurate.

[0049] Specifically, a rotating double prism is installed and one of its prisms is rotated to change the relative angle difference between the two prisms. While keeping the relative angle difference constant, the two prisms are rotated synchronously so that the azimuth angle of the laser beam emitted through the rotating double prism reaches the zero position of the rotating double prism.

[0050] The azimuth angle of the laser beam emitted through the rotating biprism reaches the zero position of the rotating biprism, specifically:

[0051] A rotating biprism spatial rectangular coordinate system is established with the rightward direction of the emitted beam as the positive X-axis, the top of the emitted beam as the positive Y-axis, and the emitted beam direction as the negative Z-axis. The major axis of the optical platform is aligned with the negative z-axis in the rotating biprism spatial rectangular coordinate system.

[0052] The outgoing beam deflection angle reaches its maximum value, and the component of the outgoing beam on the Y-axis is zero, while the component in the positive X-axis direction reaches its maximum value. The default is that the azimuth angle of the outgoing beam reaches the zero position of the rotating biprism.

[0053] S300. Place the tracking target on the reference plane, adjust the rotating biprism to image the tracking target onto the center of the field of view of the image sensor, obtain the displayed rotation angle value and the actual rotation angle value of the prism, and calculate the theoretical zero position value and the actual relative rotation angle difference of the prism based on the initial zero position value, the displayed rotation angle value and the actual rotation angle value of the prism, and complete the deflection angle calibration of the rotating biprism.

[0054] The relative rotation angle difference dθ between the two prisms is calculated based on the deflection angle of the outgoing beam, where the relationship between dθ and the deflection angle is as follows: Figure 2 As shown, the curve can be obtained by fitting it using a neural network.

[0055] After obtaining dθ, according to the first algorithm for reverse calculation of the rotating double prism, the first set of rotation angles of the two prisms can be expressed by the following formula:

[0056]

[0057] According to the second algorithm for reverse calculation of the rotating double prism, the second set of rotation angles of the two prisms can be expressed by the following formula:

[0058]

[0059] In the above formula, θ1 and θ2 represent the rotation angles of the two prisms, θ represents the azimuth angle of the emitted beam, the spot miss distance on the image sensor is obtained by forward calculation based on Snell's law, and f(θ) represents the nonlinear deviation of the prism, which can be calculated by a neural network.

[0060] S301. Place the tracking target on the reference plane and adjust the rotating biprism to image the tracking target onto the center of the image sensor's field of view.

[0061] S302. Based on the first algorithm of reverse calculation of the rotating double prism, calculate the relative rotation angle difference between the two prisms based on the deflection angle of the outgoing beam, calculate the first actual rotation angle value of the two prisms based on the relative rotation angle difference, and record the first displayed rotation angle value of the prism.

[0062] Specifically, let the deviations between the current zero position (i.e., the initial zero position) and the actual zero position be e1 and e2, respectively. The display angles of the two prisms are taken as the first display rotation angle values ​​and denoted as θ1 and θ2. The actual angles of the two prisms are taken as the first actual rotation angle values ​​and denoted as θ. 1t θ 2t The actual deflection angle and azimuth angle of the emitted beam are The actual azimuth angle of the emitted beam is θ. From their relative relationship, we can obtain the following equation:

[0063] θ1=θ 1t +θ 10 +e1, θ2=θ 2t +θ 20 +e2,

[0064] S303. According to the second algorithm of reverse calculation of the rotating double prism, calculate the relative rotation angle difference between the two prisms based on the deflection angle of the outgoing beam, calculate the second actual rotation angle value of the two prisms based on the relative rotation angle difference, and record the second displayed rotation angle value of the prism.

[0065] Specifically, the display angles of the two prisms are used as the second display rotation angle values, denoted as θ1′ and θ2′, and the actual angles of the two prisms are used as the second actual rotation angle values, denoted as θ. 1t ′、θ 2t Since the relative position information between the tracking target and the rotating biprism remains unchanged, the actual deflection angle and azimuth angle of the emitted beam will not change. Therefore, we can obtain the following relationship:

[0066] θ1′=θ 1t ′+θ 10 +e1, θ2′=θ 2t ′+θ 20 +e2,

[0067] S304. Based on the initial zero position value, the first displayed rotation angle value, the first actual rotation angle value, the second displayed rotation angle value, and the second actual rotation angle value, the theoretical zero position value and the actual relative rotation angle difference of the prism are calculated.

[0068] Specifically, from the above formula, we can obtain:

[0069]

[0070]

[0071]

[0072]

[0073] Solving the above four equations together, we can find the difference in the relative rotation angles of the two prisms.

[0074] as well as:

[0075] Therefore, we get:

[0076] The theoretical null values ​​of the two prisms are respectively

[0077] Replace the initial zero value with the theoretical zero value, and track the target again to ensure the miss distance is 0.

[0078] At this moment, the displayed rotation angle value of the other prism is... Based on the first algorithm for reverse calculation of the rotating double prism, the first actual rotation angle value (θ) of the two prisms is calculated. 1t With θ 2t ), and record the first displayed rotation angle value of the prism, then:

[0079]

[0080]

[0081] At this point, the difference between the displayed angle values ​​actually used in the calculation is:

[0082] This demonstrates that the above calibration process ensures the consistency between the displayed angle difference of the prism and the actual angle difference. Since the deflection angle of the rotating biprism is determined only by the angle difference between the two prisms, it further ensures the consistency between the deflection angle of the rotating biprism and the true value, indicating that the deflection angle calibration of the rotating biprism has been completed. Furthermore, steps S301 to S304 can be iterated multiple times to obtain a more accurate theoretical zero-point value.

[0083] S400. Adjust the rotation angle of the prism to make the azimuth angle of the outgoing beam reach the zero position of the rotating double prism again. Based on the spot coordinates of the outgoing beam on the reference plane, calculate the difference between the theoretical zero position value and the standard zero position value, and complete the zero position calibration of the rotating double prism.

[0084] Specifically, the rotation angle difference between the two prisms is controlled to be 180°. Since the displayed rotation angle difference is consistent with the actual rotation angle difference and is both 180°, the azimuth angle of the emitted beam reaches the zero position of the rotating double prism. Due to the refraction relationship between the two prisms, the position of the emitted beam at the exit point of the prism is different. Even if the emitted beam is parallel to the optical axis, its position will still deviate from the optical axis to some extent. Simultaneously, the two prisms are controlled to rotate at the same speed. At this time, the relative rotation angle difference between the two prisms remains unchanged, and the spot of the emitted beam on the reference plane forms a circular trajectory, such as... Figure 3 As shown, the two coordinate axes δx and δy represent the deflection angles of the light beam in the X and Y axis directions.

[0085] The difference between the displayed rotation angle value and the actual rotation angle value of the two prisms is set to θ. When the displayed rotation angle value of both prisms is 0°, according to the center algorithm, θ1 = θ2 = θ. θ1 and θ2 represent the differences between the theoretical zero point and the standard zero point of the two prisms, respectively. θ3 represents the azimuth angle of the outgoing beam. θ3 is calculated based on the spot coordinates of the outgoing beam on the reference plane, and then θ is obtained. Subtracting θ from the theoretical zero point value of the prism yields the standard zero point value of the prism.

[0086] like Figure 4 As shown, the present invention also provides a rotating biprism calibration system, including an optical platform for mounting a rotating biprism, a laser and an image sensor on the optical platform, a reference surface in front of the optical platform (the reference surface can also be a wall), the laser emitted by the laser is transmitted to the reference surface through the rotating biprism to form a light spot, the image sensor is used to collect the light spot on the reference surface, and a total station is provided between the optical platform and the reference surface.

[0087] The present invention has been described in detail above. The above description is only a preferred embodiment of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of this application should still fall within the scope of the present invention.

Claims

1. A method for calibrating a rotating biprism, characterized in that, Includes the following steps: A laser beam is emitted toward a reference surface, and the light spot on the reference surface is imaged at the center of the field of view of the image sensor; Install a rotating double prism and rotate one of its prisms to change the relative angle difference between the two prisms. Keep the relative angle difference constant and rotate the two prisms synchronously so that the azimuth angle of the laser beam emitted through the rotating double prism reaches the zero position of the rotating double prism. Record the angle values ​​of the two prisms as the initial zero position value. Place the tracking target on the reference plane, adjust the rotating biprism to image the tracking target onto the center of the field of view of the image sensor, obtain the displayed rotation angle value and the actual rotation angle value of the prism, and calculate the theoretical zero position value of the prism based on the initial zero position value, the displayed rotation angle value and the actual rotation angle value of the prism, and complete the deflection angle calibration of the rotating biprism. Adjust the rotation angle of the prism to make the azimuth angle of the outgoing beam reach the zero position of the rotating double prism again. Based on the spot coordinates of the outgoing beam on the reference plane, calculate the difference between the theoretical zero position value and the standard zero position value, and complete the zero position calibration of the rotating double prism.

2. The method for calibrating a rotating biprism according to claim 1, characterized in that, Before emitting the laser towards the reference plane, the process also includes: An optical platform is installed in front of the reference plane, and a total station is set up between the reference plane and the optical platform. The total station is used to determine the precise direction of the major axis of the optical platform and the normal vector of the reference plane.

3. The method for calibrating a rotating biprism according to claim 2, characterized in that, Several marker points are placed along the long axis of the optical platform. The position parameters of the marker points are measured using a total station. The position parameters include azimuth, elevation, and slope distance between the marker point and the total station. The position parameters are converted into rectangular coordinates in the total station's spatial rectangular coordinate system to determine the precise orientation of the long axis of the optical platform.

4. The method for calibrating a rotating biprism according to claim 2, characterized in that, Take three non-collinear measurement points on the reference plane, determine the coordinates of the measurement points, and obtain the normal vector of the reference plane in the total station's rectangular coordinate system based on the coordinates of the measurement points.

5. A method for calibrating a rotating biprism according to any one of claims 2-4, characterized in that, The laser emits a laser beam. The coordinates of the laser emission point are measured using a total station. Based on the precise pointing of the long axis of the optical platform and the normal vector of the reference plane, the theoretical beam coordinates on the reference plane are calculated. The orientation of the laser is adjusted until the theoretical beam coordinates coincide with the center of the actual beam, and the actual beam on the reference plane is imaged at the center of the field of view of the image sensor.

6. The method for calibrating a rotating biprism according to claim 1, characterized in that, The azimuth angle of the laser beam emitted through the rotating biprism reaches the zero position of the rotating biprism, specifically: A rotating double prism spatial rectangular coordinate system is established with the right of the exit direction of the emitted beam as the positive X-axis, the top of the exit direction of the emitted beam as the positive Y-axis, and the exit direction of the emitted beam as the negative Z-axis. When the deflection angle of the emitted beam reaches its maximum value, and the component of the emitted beam on the Y-axis is zero and the component in the positive X-axis direction reaches its maximum value, it is assumed that the azimuth angle of the emitted beam reaches the zero position of the rotating biprism. The azimuth angle of the emitted beam is obtained based on the spot miss distance on the image sensor.

7. The method for calibrating a rotating biprism according to claim 6, characterized in that, The calculation yields the theoretical null value of the prism, specifically as follows: Place the tracking target on the reference plane and adjust the rotating biprism to image the tracking target onto the center of the image sensor's field of view; According to the first algorithm for reverse calculation using a rotating double prism, the relative rotation angle difference between the two prisms is calculated based on the deflection angle of the outgoing beam. The first actual rotation angle value of the two prisms is then calculated based on this relative rotation angle difference, and the first displayed rotation angle value of the prisms is recorded. This first actual rotation angle value of the two prisms is denoted as θ. 1t θ 2t , , θ represents the azimuth angle of the emitted beam, which is obtained by forward calculation based on the spot miss distance on the image sensor using Snell's law. The nonlinear deviation of the prism is calculated using a neural network. This represents the difference in the relative rotation angles of the two prisms; The second algorithm, based on the reverse calculation of the rotating double prism, calculates the relative rotation angle difference between the two prisms based on the deflection angle of the outgoing beam. Then, it calculates the second actual rotation angle value of the two prisms based on this relative rotation angle difference and records the second displayed rotation angle value. The second actual rotation angle value of the two prisms is denoted as... , , , ; Based on the initial zero position value, the first displayed rotation angle value, the first actual rotation angle value, the second displayed rotation angle value, and the second actual rotation angle value, the theoretical zero position value and the actual relative rotation angle difference of the prism are calculated.

8. The method for calibrating a rotating biprism according to claim 7, characterized in that, Set the difference between the displayed rotation angle value and the actual rotation angle value of both prisms to θ. When the displayed rotation angle value of both prisms is 0°, we obtain... , , as well as These represent the differences between the theoretical null position and the standard null position of the two prisms, respectively. The azimuth angle of the emitted beam is calculated based on the beam spot coordinates on the reference plane. Then, θ is obtained, and the theoretical zero point value of the prism is subtracted from θ to obtain the standard zero point value of the prism.

9. A system for implementing the rotating biprism calibration method as described in any one of claims 1-8, characterized in that, The system includes an optical platform for mounting a rotating biprism, a laser and an image sensor, and a reference surface in front of the optical platform. The laser emitted by the laser is transmitted to the reference surface through the rotating biprism to form a light spot. The image sensor is used to collect the light spot on the reference surface. A total station is installed between the optical platform and the reference surface.

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