Multi-target optical fiber positioning unit anti-collision method based on real-time control

Abstract

The invention discloses an anti-collision method for a multi-target optical fiber positioning unit based on real-time control. The method comprises the following steps: S1, predicting a track of the optical fiber positioning unit; s2, track collision detection is carried out on each optical fiber positioning unit; s3, when track collision is detected, executing S4, and when track collision is not detected, executing S5; s4, carrying out classification according to the positions of the collision points, executing a waiting, rollback or unfolding program according to the collision classification, forming a collision-free path, and executing S5; and S5, the units are controlled in real time according to the corresponding collision-free paths, so that all the optical fiber positioning units are converged to the precision required by the target position. According to the invention, the unit can be ensured to move along a planned path, and real-time collision detection can be carried out.

Description

Technical Field

[0001] The invention relates to the technical field of multi-target optical fiber, and in particular to an anti-collision method of a multi-target optical fiber positioning unit based on real-time control. Background Art

[0002] At present, the research of many major basic problems in astrophysics and cosmology relies on the statistical properties of a large number of samples. Therefore, it is becoming increasingly important to obtain spectral data of a large number of celestial bodies within a certain time frame, that is, large-scale spectroscopic surveys. Multi-object fiber spectral telescopes are an important part of large-scale spectroscopic survey projects. The development of fiber optic positioning technology enables scientists to observe thousands of celestial targets simultaneously in a short period of time. Due to the large number of celestial targets, in order to achieve the predetermined scientific goals, the survey efficiency is very important. The survey efficiency of large-scale spectroscopic survey projects depends on the utilization rate of fiber optic positioning units and the observation completeness rate of celestial targets, that is, it depends on the celestial target allocation method of the fiber optic positioning unit and the solution of the collision problem.

[0003] In order to ensure that there is no blind spot on the focal plane, the observation areas of adjacent fiber positioning units will overlap, which makes it possible for the units to collide. In order to solve the problem of collision between units, a variety of algorithms have been proposed. One idea is to solve the collision from the hardware aspect. By adding additional sensors to the units, the occurrence of collisions is detected by using changes in potential difference, waveform comparison, pulse count, etc., and the movement of the units is stopped in time. This method cannot avoid collisions, but can only stop the collision units in time to reduce damage to the units. The other is to plan the paths of the units from the software aspect. Makarem et al. proposed a decentralized navigation planning based on the artificial potential field method for the DESI project, that is, artificially constructing a natural potential field to guide the units to move from "high potential energy" to "low potential energy". However, this method will cause the units to lock and oscillate when the overlapping area of ​​the units increases. Tao et al. combined the priority-based finite state machine with this method for the MOONS project, which increased the probability of the units converging to the target position, but also increased the complexity of the algorithm.

[0004] In order to solve the collision problem more effectively, Zhang et al. proposed the concept of a safe zone. No matter how the unit moves in the safe zone, it will not collide with the adjacent unit. Therefore, a retract-rotate-expand method was proposed by Silber et al. The movement of the unit is divided into three steps. First, all the eccentric shafts of the units are retracted to ensure that all units are in the safe zone. Then the central axis of the unit is rotated to the target angle, and finally the eccentric shaft is expanded to the target position. This method can solve most collisions, but it increases the communication overhead, and in order to provide a margin for the anti-collision path, the accuracy of coarse positioning will be reduced. Zhang et al. also proposed a tangent walking method based on the safe zone. First, the unit moves to the tangent point of the target point to the safe zone, and then moves to the target point along the tangent. This method can be implemented in simulation, but in fact, due to the characteristics of the double rotation, the unit cannot run in a straight line. The above anti-collision methods are not real-time. That is to say, on the one hand, these methods cannot ensure that the unit moves along the planned path, and on the other hand, the unit movement cannot be stopped in time when the unit deviates from the planned path and collides. Summary of the invention

[0005] Based on the technical problems existing in the background technology, the present invention proposes an anti-collision method for a multi-target optical fiber positioning unit based on real-time control, which can ensure that the unit moves along the planned path and can perform real-time collision detection.

[0006] The anti-collision method of the multi-target optical fiber positioning unit based on real-time control proposed by the present invention comprises the following steps: S1: prediction of the trajectory of the fiber positioning unit; S2: Perform trajectory collision detection on each optical fiber positioning unit; S3: When a trajectory collision is detected, execute S4; when no trajectory collision is detected, execute S5; S4: classify according to the location of the collision point, and execute the waiting, backing off or expansion procedure according to the collision classification to form a collision-free path, and execute S5; S5: Control the units in real time according to the corresponding collision-free paths, so that all fiber positioning units converge to the target position within the required accuracy.

[0007] Preferably, the prediction method in S1 is: calculating the angles of rotation of the central axis and the eccentric axis according to the starting position and the target position of the optical fiber positioning unit, and the trajectory points obtained after equal division are the predicted unit trajectories.

[0008] Preferably, the starting position is obtained by lighting the optical fiber carried by the optical fiber positioning unit by back-illumination method, and taking a focal plane image with a camera system that has been calibrated in advance.

[0009] Preferably, the camera system adopts a telecentric lens, and calibrates the camera through an external calibration target to obtain fourth-order polynomial conversion parameters between world coordinates and pixel coordinates.

[0010] Preferably, the method of trajectory collision detection in S2 is: if the minimum value of the eccentric axis distance from a trajectory point of a certain optical fiber positioning unit to all trajectory points of a certain adjacent optical fiber positioning unit is less than the collision threshold, then the trajectory point of a certain optical fiber positioning unit is regarded as a collision point.

[0011] Preferably, the collision classification in S4 includes the following situations: the collision point does not coincide with the unit starting position and the target position, the collision point coincides with one of the unit starting positions, the collision point coincides with one of the unit target positions, the collision point coincides with two unit starting positions, the collision point coincides with one unit starting position and the other unit target position, the collision point coincides with two unit target positions, the collision point coincides with two unit starting positions and one unit target position, and the collision point coincides with two unit target positions and one unit starting position.

[0012] Preferably, when the collision point does not coincide with the unit starting position and the target position, the collision point coincides with one of the unit starting positions, the collision point coincides with one of the unit target positions, or the collision point coincides with one unit starting position and another unit target position, the unit behind the collision point is selected to execute the waiting procedure; when the collision point coincides with the starting positions of two units or the collision point coincides with the starting positions of two units and a unit target position, the unit behind the collision end point is selected to execute the back-off procedure; when the collision point coincides with the target positions of two units or the collision point coincides with the target positions of two units and a unit starting position, the unit in front of the collision point is selected to execute the expansion procedure.

[0013] Preferably, the real-time control method in S5 is: collecting the back-illuminated image of the optical fiber on the focal plane through the camera system, using the hardware acceleration platform on the FPGA development board to process the image to obtain the optical fiber position, and the control system performs real-time detection of the collision according to the optical fiber position; if the collision threshold is reached, the control unit stops moving, if the collision threshold is not reached, an adjustment command is sent to the unit, and the adjustment process is repeated until the unit reaches within the target accuracy.

[0014] Beneficial technical effects of the present invention: The present invention divides the rotation angles of the central axis and the eccentric axis of the optical fiber into equal parts and performs trajectory collision detection, then classifies the collision according to the starting point and the ending point of the collision unit pair, selects the corresponding waiting unit, the fallback unit or the expansion unit, and finally controls the unit in real time according to the corresponding collision-free path; on the basis of real-time control of the unit, this method can ensure that the unit moves along the planned collision-free path, and at the same time can perform real-time collision detection to avoid the unit deviating from the path or the unit collision in other unexpected situations. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A flow chart of the optical fiber positioning unit anti-collision method based on real-time control proposed by the present invention; Figure 2 A classification diagram of the collision of two unit trajectories proposed by the present invention; Figure 3 A schematic diagram of a collision-free path of a waiting unit proposed by the present invention; Figure 4 A schematic diagram of a collision-free path of the retraction unit proposed in the present invention; Figure 5 This is a schematic diagram of the collision-free path of the deployment unit proposed in the present invention. DETAILED DESCRIPTION

[0016] The present invention will be further explained below in conjunction with specific embodiments.

[0017] Reference Figure 1 The anti-collision method of the multi-target optical fiber positioning unit based on real-time control proposed by the present invention has the following steps: S1: Based on the starting position and target position of the unit, the angles of rotation of the central axis and the eccentric axis can be calculated. Both angles are divided into 2000 equal parts to obtain 2000 trajectory points, which are the predicted unit trajectory.

[0018] S2: When unit a is at trajectory point a i (i=1, 2…2000), calculate ai to the adjacent unit b at trajectory point b j (j=1, 2…2000) eccentric axis distance. Each ai traverses all b j Get the minimum distance s ai (i=1, 2…2000), if s ai If i is less than the collision threshold, the trajectory point is marked as a collision point. The collision point with the smallest i is the collision start point, and the collision point with the largest i is the collision end point. Similarly, trajectory collision detection is performed on each unit.

[0019] S3: When a trajectory collision is detected, Figure 2 As shown in FIG. 1 , the collision starting point S of the collision unit pair1、 S2 and end point E 1、 E2, classify the collision. When the collision point does not coincide with the unit start position and target position, the collision is marked as M; when the collision point coincides with one of the unit start positions, it is marked as H; when the collision point coincides with one of the unit target positions, it is marked as T. Similarly, the remaining HH, HT, TT, HHT, and HTT can be obtained. When no trajectory collision is detected, the real-time control process is directly entered.

[0020] S4: Obtain the corresponding collision-free path according to the collision classification: When the collision type is M, H, T, or HT, select the unit after the collision point as the waiting unit, such as Figure 3 As shown, the other unit moves first until it passes the collision end point E1, and then the waiting unit moves again, and finally both units can reach the target position; when the collision type is HH or HHT, the unit behind the collision end point is selected as the fallback unit, such as Figure 4 As shown in the figure, the retracting unit first retracts the eccentric shaft to allow the other unit to move. After the other unit moves through the collision end point E2, the retracting unit then unfolds the eccentric shaft to the initial position, and then moves to the target position. Finally, both units can reach the target position. When the collision type is TT or HTT, the unit with the collision point in front is selected as the unfolding unit, as shown in the figure. Figure 5 As shown, the unfolding unit first moves to the target position which is also the collision end point E2, then retracts the eccentric shaft, and then another unit moves to the target position, and finally the unfolding unit unfolds the eccentric shaft back to the target position.

[0021] S5: The unit is controlled in real time according to the corresponding collision-free path. The photogrammetry device collects the back-illuminated image of the optical fiber on the focal plane. The hardware acceleration platform on the FPGA development board is used to process the image to obtain the optical fiber position. The control system detects the collision in real time according to the optical fiber position. If the collision threshold is reached, the unit stops moving. Otherwise, an adjustment command is sent to the unit. The adjustment process is repeated until the unit reaches the target accuracy.

[0022] The photogrammetry device in this embodiment uses a double telecentric lens with a magnification of 0.355, a CCD camera with a resolution of 2048x2448, and the fiber positioning unit is at the optimal imaging distance from the photogrammetry device. The FPGA development board uses the ZynqUltra+ MPSoC ZU3EG, and the image processing speed can reach 17ms for the resolution image used.

[0023] The above scheme of the embodiment of the present invention does not involve complicated devices and structures, and the experimental cost required to implement the entire scheme is relatively low. On the basis of real-time control of the unit, it can be ensured that the unit moves along the planned collision-free path, and real-time collision detection can be performed to avoid the unit deviating from the path or the unit collision in other unexpected situations.

Claims

1. An anti-collision method for a multi-target optical fiber positioning unit based on real-time control, characterized in that: The steps are as follows: S1: prediction of the trajectory of the fiber positioning unit; S2: Perform trajectory collision detection on each optical fiber positioning unit; S3: When a trajectory collision is detected, execute S4; when no trajectory collision is detected, execute S5; S4: classify according to the location of the collision point, and execute the waiting, backing off or expansion procedure according to the collision classification to form a collision-free path, and execute S5; S5: Control the units in real time according to the corresponding collision-free paths, so that all fiber positioning units converge to the target position within the required accuracy.

2. The anti-collision method of a multi-target optical fiber positioning unit based on real-time control according to claim 1, characterized in that: The prediction method in S1 is: according to the starting position and the target position of the optical fiber positioning unit, the angles to be rotated by the central axis and the eccentric axis are calculated, and the trajectory points obtained after equal division are the predicted unit trajectories.

3. The anti-collision method of a multi-target optical fiber positioning unit based on real-time control according to claim 2, characterized in that: The starting position is obtained by lighting the optical fiber carried by the optical fiber positioning unit by back-illumination method, and taking the focal plane image by using a camera system that has been calibrated in advance.

4. The anti-collision method of a multi-target optical fiber positioning unit based on real-time control according to claim 3, characterized in that: The camera system adopts a telecentric lens, and calibrates the camera through an external calibration target to obtain fourth-order polynomial conversion parameters of world coordinates and pixel coordinates.

5. The anti-collision method of a multi-target optical fiber positioning unit based on real-time control according to claim 1, characterized in that: The method of trajectory collision detection in S2 is: if the minimum value of the eccentric axis distance from a trajectory point of a certain optical fiber positioning unit to all trajectory points of a certain adjacent optical fiber positioning unit is less than the collision threshold, then the trajectory point of a certain optical fiber positioning unit is regarded as a collision point.

6. The anti-collision method of a multi-target optical fiber positioning unit based on real-time control according to claim 1, characterized in that: The collision classification in S4 includes the following situations: the collision point does not coincide with the unit starting position and the target position, the collision point coincides with one of the unit starting positions, the collision point coincides with one of the unit target positions, the collision point coincides with two unit starting positions, the collision point coincides with one unit starting position and the other unit target position, the collision point coincides with two unit target positions, the collision point coincides with two unit starting positions and one unit target position, and the collision point coincides with two unit target positions and one unit starting position.

7. The anti-collision method of a multi-target optical fiber positioning unit based on real-time control according to claim 6, characterized in that: When the collision point does not coincide with the starting position and target position of the unit, the collision point coincides with the starting position of one of the units, the collision point coincides with the target position of one of the units, or the collision point coincides with the starting position of one unit and the target position of another unit, the unit behind the collision point is selected to execute the waiting procedure; when the collision point coincides with the starting positions of two units or the collision point coincides with the starting positions of two units and the target position of one unit, the unit behind the collision end point is selected to execute the back-off procedure; when the collision point coincides with the target positions of two units or the collision point coincides with the target positions of two units and the starting position of one unit, the unit in front of the collision point is selected to execute the expansion procedure.

8. The anti-collision method of a multi-target optical fiber positioning unit based on real-time control according to claim 1, characterized in that: The real-time control method in S5 is as follows: the camera system is used to collect the back-illuminated image of the optical fiber on the focal plane, the hardware acceleration platform on the FPGA development board is used to process the image to obtain the optical fiber position, and the control system performs real-time detection of the collision according to the optical fiber position; if the collision threshold is reached, the control unit stops moving; if the collision threshold is not reached, an adjustment command is sent to the unit, and the adjustment process is repeated until the unit reaches within the target accuracy.

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