A Telescope Tracking Control Strategy Based on Time Synchronization Method

Abstract

The present invention discloses a telescope tracking control strategy based on time synchronization method, including: a time server precisely synchronizes the time of the upper computer and the lower computer of the control system; the upper computer calculates the position of the target star and saves it to a document; the upper computer respectively assigns multiple position data to Group A and Group B; the data of Group A and Group B are alternately and cyclically sent to the lower computer; the lower computer selects different motion modes according to the target distance to achieve telescope tracking observation. The present invention aims to implement an astronomical telescope tracking strategy for packet transmission of target positions on the premise of the time synchronization method. The method of the present invention has a wide application prospect in the field of precise operation control of the same type of rotating platforms such as large telescopes. This method can reduce the interaction times between the upper computer and the lower computer during telescope tracking observation, and can ensure that the normal operation of the telescope is not affected in case of software / hardware crash of the upper computer of the control system within a certain period of time, with higher reliability and stronger fault tolerance.

Description

Technical Field

[0001] The present invention relates to a telescope tracking control strategy based on time synchronization method, specifically to a telescope tracking control strategy that uses a time server to synchronize and calibrate the time of the upper computer and the lower computer of the telescope control system, and realizes the packaged transmission of target positions. This method is particularly suitable for the precise tracking control of large-aperture astronomical telescopes. Background Art

[0002] An astronomical telescope is one of the ultra-high-precision instruments indispensable for the development of modern astronomy. In astronomical observations, a tiny error can lead to a huge deviation. Ensuring long-term and stable high-precision tracking performance is the key technology for the success or failure of a telescope.

[0003] The traditional tracking strategy is that the control computer first calculates the position of the target star and forms a star catalog, which includes time, azimuth position, altitude position, and derotation position, with a time interval of TimePeriod milliseconds. When the telescope conducts tracking observations on the target star, the control computer sends the positions in the star catalog to the controller one by one, and the controller then realizes tracking through the driver and the motor. In this tracking strategy, there are frequent interactive communication behaviors between the upper computer (control computer) and the lower computer (controller) because the upper computer needs to continuously send new target positions to the controller to achieve continuous tracking. Frequent interaction means that this behavior will increase the probability of errors. At the same time, it also means that if there are abnormal situations in the upper computer hardware or software (such as hardware crashes, software crashes, etc.), it will directly cause the telescope tracking to stop. Due to the time difference between the upper computer and the lower computer, it will also cause deviations in the telescope tracking. Therefore, it is necessary to frequently correct the tracking, which will also lead to the inability to guarantee the tracking accuracy and reliability.

[0004] Astronomical observation opportunities are fleeting, such as astronomical phenomena like fast radio bursts and supernova explosions. If the tracking strategy can avoid the telescope tracking stop caused by upper computer hardware or software abnormalities and at the same time reduce the probability of failures, then this technology is of great significance for astronomical observations. Therefore, improving the tracking reliability of telescopes is an issue that needs to be solved in astronomical technologies and methods. Summary of the Invention

[0005] The purpose of the present invention is to use a time server to provide a method for synchronizing and calibrating the time of the upper computer and the lower computer of the telescope control system, so as to realize a telescope tracking control strategy for packaged transmission of target positions based on the time synchronization method. This method and strategy can reduce the interaction frequency between the upper computer and the lower computer of the control system, thereby improving the fault tolerance of the telescope control system and at the same time improving the tracking accuracy.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A telescope tracking control strategy based on time synchronization method, including the following steps:

[0008] Step 1: The upper computer, lower computer of the telescope control system and the time server are connected through a gigabit industrial Ethernet via a switch, so that the three work under the same local area network;

[0009] Step 2: The upper computer calculates the position of the target star and generates a star catalog. The sampling interval is TimePeriod (ms). Each group of data includes time Time, azimuth position AZ_Position, altitude position ALT_Position, and derotation position Dero_Position;

[0010] Step 3: The upper computer program reads the time of the first line of data in the star catalog, defined as Time_BaseLine1. At the same time, the position data of the 1st to Nth lines of the star catalog are sequentially assigned to group A variables P(StartAddressNum) to P(StartAddressNum+N-1). Then, the group A data is packed and sent to the lower computer of the control system;

[0011] Step 4: The upper computer program sequentially assigns the position data of the (N+1)th to (2*N)th lines of the star catalog to group B variables P(StartAddressNum+N) to P(StartAddressNum+2*N-1), a total of N target positions. Then, the group B data is packed and sent to the lower computer of the control system;

[0012] Step 5: While executing Step 4, start the lower computer motion program, obtain the current time of the lower computer system, defined as Time_Current, and calculate the time difference (ms) between the current time of the system and the calculated star catalog time, defined as Time_Difference. Then, Time_Difference = Time_Current - Time_BaseLine1, that is, the line number of the star catalog where the current position of the target star is located is PointLine = int(Time_Difference / TimePeriod);

[0013] Step 6: Calculate the current position of the target star, denoted as PointTarget, and the position of PointTarget can be known from the variable P(StartAddressNum + PointLine). Set the current position of the telescope as CurrentPosition, and since the position of CurrentPosition is known, the distance between the current telescope position and the target star can be obtained. When the distance between the telescope and the target star is greater than the critical value, the telescope executes motion mode 1: first accelerate to the maximum speed, then move at a constant speed, and finally decelerate; when the distance between the telescope and the target star is less than or equal to the critical value, the telescope executes motion mode 2: first accelerate and then decelerate, that is, there is no constant-speed motion process. Thus, the pointing motion time of the telescope can be obtained;

[0014] Step 7: Recalculate the line number in the star catalog where the telescope should point to the target star as PointLine = int(Time_Difference / TimePeriod) + int(Time_Pointing * 1000 / TimePeriod);

[0015] Step 8: Since the target star is not stationary and its speed is not uniform during the telescope pointing process, when the telescope points to the position of the target star calculated in Step 7, the target star is no longer at this position. Therefore, repeated iteration is required to calculate the exact position when the telescope and the target star meet, so repeat Steps 6 and 7;

[0016] Step 9: The controller drives the telescope to point to the target star, automatically switches to Group B data after completing the tracking of Group A data, updates Group A data while tracking Group B data, and thus realizes the alternating tracking of the two groups of data.

[0017] Furthermore, in Step 1: The purpose of the time server is to obtain an accurate time source and calibrate the time of the upper computer and the lower computer of the telescope control system at regular intervals, so that the time of the upper computer and the lower computer remains accurately synchronized.

[0018] Furthermore, in Step 2: When the star catalog sampling interval is TimePeriod (ms), the time accuracy should be accurate to the millisecond level, and the shorter the sampling interval, the higher the accuracy.

[0019] Furthermore, in Step 3: Where N > 1, StartAddressNum is the starting number of the controller variable, and the values of N and StartAddressNum are determined by the number of available registers of the controller.

[0020] Furthermore, in Step 4: The time interval between the first line of Group B data and the last line of Group A data is one sampling interval.

[0021] Further, in step 5, the current position of the target star is the value of variable P(StartAddressNum + PointLine).

[0022] Further, in step 6, the distance between the current position of the telescope and the current position of the target star is PositionDifference = PointTarget - CurrentPosition. If PositionDifference > S0, then execute motion mode 1, and obtain the time (s) required for pointing motion Time_Pointing = If PositionDifference ≤ S0, then execute motion mode 2, and obtain the time (s) required for pointing motion

[0023] Further, in step 7, the current position of the target star should be the value of the updated variable P(StartAddressNum + PointLine).

[0024] Further, in step 8, it is impossible to iterate infinitely in practical applications. Moreover, the telescope has a certain field of view, and the number of iterations usually depends on the specific situation.

[0025] Furthermore, the astronomical telescope tracking strategy that realizes the packaged transmission of the target position based on time synchronization is particularly suitable for the precise tracking control of large-aperture astronomical telescopes.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] The present invention utilizes the astronomical telescope tracking strategy that realizes the packaged transmission of the target position based on the time synchronization method. Compared with the existing methods, the method of the present invention has a wide application prospect in the field of precise operation control of the same type of rotating platforms such as large telescopes. This method can reduce the number of interactions between the upper computer and the lower computer during the telescope tracking observation, and can ensure that the telescope operates normally without being affected in the case of software / hardware crashes of the upper computer of the control system within a certain period of time, with higher reliability and stronger fault tolerance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic diagram of the telescope tracking a star;

[0029] Figure 2 is two pointing motion modes of the telescope;

[0030] Figure 3 is a schematic diagram of the control strategy principle.

[0031] Markings in the figure: 1 - Telescope position; 2 - Target star position; 3 - Position where the telescope catches up with the target star. Detailed Implementation Modes

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

[0033] Currently, most of the tracking methods for large-aperture telescopes adopt a mode in which the upper computer calculates the position of the target star first, and then sends the position of the target star to the lower computer one by one to drive the actuator for tracking. This method results in frequent interactions between the upper computer and the lower computer, and at the same time means the risks of low efficiency and poor reliability. That is, when the upper computer hardware or software crashes, it will affect the telescope tracking and observation. Therefore, the present invention provides an astronomical telescope tracking strategy for realizing the packaged transmission of the target position based on the time synchronization method. This method can reduce the interaction frequency between the upper computer and the lower computer of the control system, thereby improving the fault tolerance of the telescope control system and at the same time improving the tracking accuracy. The present invention is applicable to the control system platform of large-aperture astronomical telescopes to achieve stable tracking and observation.

[0034] The present invention is funded by the National Natural Science Foundation of China projects "Research on the evolution and evaluation method of unexpected states of the direct drive system of extremely large telescopes in extreme environments" (11973065), "Research on the intelligence of the control system of large astronomical optical telescopes" (U1931207), and the Jiangsu Excellent Postdoctoral Program (2022ZB449). It is funded by the China Scholarship Council (CSC201904910254) and the Overseas Scholarship Fund of the Chinese Academy of Sciences (Xu Lingzhe).

[0035] The present invention will be further described below with reference to the accompanying drawings and implementation cases.

[0036] The telescope tracking control strategy based on the time synchronization method includes the following steps:

[0037] The time server provides timing time calibration services for both the upper computer and the lower computer of the telescope control system simultaneously, and the calibration accuracy reaches the millisecond level, so that the time error between the upper computer and the lower computer is controlled within the millisecond level.

[0038] The upper computer of the control system calculates the azimuth, altitude, and derotation positions of the target star within a fixed time period according to the right ascension and declination in the astronomical coordinate system, and generates a star catalog and saves it to the local computer. The sampling time interval is TimePeriod (ms). The star catalog can be regarded as an N×4-order matrix, where N is the number of target star position samples, and 4 is the number of parameters to be saved, namely time, azimuth position, altitude position, and derotation position, denoted as Time, AZ_Position, ALT_Position, Dero_Position.

[0039] The telescope starts to execute the tracking instruction. The host computer reads the time of the first line of the star catalog, converts it into a timestamp and records it as Time_BaseLine1, with the unit of ms. At the same time, the 1st to Nth lines are cyclically assigned to variables P(StartAddressNum) to P(StartAddressNum+N-1). These N lines of data are recorded as Group A tracking data, where N>1, StartAddressNum is the starting value of the target register, and the values of N and StartAddressNum are determined by the available register quantity of the controller P variable. Then, the N target positions from P(StartAddressNum) to P(StartAddressNum+N-1) are packed and sent to the lower computer. The above operations are all completed in the host computer program.

[0040] Start the lower computer motion program, obtain the current time of the lower computer system, convert it into a millisecond timestamp and record it as Time_Current, with the unit of ms. Calculate the time difference between the current time and the time of the first line of the calculated star catalog and record it as Time_Difference, that is, Time_Difference = Time_Current - Time_BaseLine1. Then the line number of the star catalog where the current position of the target star is located is PonitLine = int(Time_Difference / TimePeriod), that is, the value of the position variable P(StartAddressNum+PonitLine).

[0041] Since it takes a certain amount of time for the telescope to move from the current position to the current target position of the star, and during the pointing movement, the target position of the star will also change. Therefore, it is necessary to recalculate the time required for the telescope to point and move to the latest target position of the star. Since the telescope tracks the star movement mode as first high-speed pointing and then low-speed tracking, and the high-speed pointing movement mode is first accelerating, then uniform motion, and then decelerating. Therefore, according to the critical value of the distance between the telescope and the target star, the high-speed pointing movement mode can be divided into two cases: Movement mode 1: When the distance between the telescope and the target star is greater than the critical value, the telescope first accelerates to the maximum speed, then moves at a uniform speed, and finally decelerates; Movement mode 2: When the distance between the telescope and the target star is less than or equal to the critical value, the telescope first accelerates and then decelerates, that is, there is no uniform motion process. The critical distance is when the telescope pointing movement accelerates to the maximum speed and then starts to decelerate, without a uniform motion process. From the above two cases, the time required for the telescope's high-speed pointing movement is solved according to the distance. The two movement modes are as Figure 2As shown in the figure. The time taken for the telescope pointing movement is recorded as Time_Pointing. Then, the row number of the star catalog where the current position of the target star is located is recalculated as PonitLine = int(Time_Difference / TimePeriod) + int(Time_Pointing * 1000 / TimePeriod).

[0042] To achieve continuous tracking and observation of the telescope, when executing Group A tracking data, the upper computer program sequentially assigns the position data of the (N + 1)th to (2 * N)th rows of the star catalog to the variables P(StartAddressNum + N) to P(StartAddressNum + 2 * N - 1) in Group B, a total of N target positions. Then, the data in Group B is packed and sent to the lower computer of the control system. The alternating tracking between Group A and Group B is achieved by means of a flag bit.

[0043] The astronomical telescope tracking strategy for realizing the packing and sending of target positions based on the time synchronization method is particularly suitable for large-aperture astronomical telescopes to achieve precise tracking control with high reliability and high fault tolerance.

[0044] From Figure 1 As can be seen from the schematic diagram of the telescope tracking the star, the telescope is currently at the first position (i.e., Telescope Position 1), and the target star is currently at the second position (i.e., Target Star Position 2). At the third position (i.e., Telescope Catching up with the Target Star Position 3), the telescope catches up with the target star, that is, the time taken for the telescope to move from the first position to the third position is the same as the time taken for the target star to move from the second position to the third position.

[0045] During the telescope chasing the star movement process, the two movement modes are as Figure 2 shown. Let the maximum pointing running speed of the telescope be Vmax, and the running acceleration be a. That is, the time taken for the telescope to accelerate from rest to the maximum speed The distance traveled The telescope pointing running mode is to accelerate first and then decelerate. Therefore, the critical distance between the telescope and the target star

[0046] Movement mode one is as Figure 2 shown in (a) below. In this mode, the initial distance between the telescope and the target star is less than or equal to the critical distance S0, that is, the telescope only has the processes of acceleration and acceleration, and no uniform speed process; Movement mode two is as Figure 2 shown in (b) below. In this mode, the initial distance between the telescope and the target star is greater than the critical distance S0, that is, the telescope accelerates first, then moves at a uniform speed, and then decelerates.

[0047] The implementation principle of the technical method involved in the present invention is as Figure 3 shown, and includes the following steps:

[0048] Step 1: The upper computer, lower computer of the telescope control system and the time server are connected through a gigabit industrial Ethernet switch and work under the same local area network. The signal receiver is installed in an outdoor open environment to receive time signals such as GPS, Beidou or satellites. The purpose of the time server is to obtain an accurate time source and calibrate the time of the upper computer and lower computer of the telescope control system regularly, so that the time of the upper computer and lower computer remains accurately synchronized.

[0049] Step 2: The upper computer of the telescope control system calculates the position of the target star and generates a star catalog, which is saved in a document. The position sampling time interval in the star catalog is TimePeriod (ms), and each group of data contains Time, azimuth position AZ_Position, altitude position ALT_Position, and derotation position Dero_Position.

[0050] Step 3: The upper computer program reads the time of the first line of data in the star catalog, defined as Time_BaseLine1. At the same time, it assigns the position data of the 1st to Nth lines in the star catalog to the variables of group A, P(StartAddressNum) to P(StartAddressNum+N-1) in sequence, where N>1, and the specific size is determined by the number of available registers of the controller. Then it packs and sends the data of group A to the lower computer of the control system. The data of group A contains N target positions in total.

[0051] Step 4: The upper computer program assigns the position data of the (N+1)th to (2*N)th lines in the star catalog to the variables of group B, P(StartAddressNum+N) to P(StartAddressNum+2*N-1) in sequence, which are N target positions in total. Then it packs and sends the data of group B to the lower computer of the control system.

[0052] Step 5: While step 4 is being executed, start the lower computer motion program, obtain the current time of the lower computer system, defined as Time_Current, calculate the time difference (ms) between the current time of the system and the calculated time of the star catalog, defined as Time_Difference, and Time_Difference = Time_Current - Time_BaseLine1. Then the line number of the star catalog where the current position of the target star is located is PointLine = int(Time_Difference / TimePeriod), that is, the value of the variable P(StartAddressNum+PointLine).

[0053] Step 6: Calculate the current position of the target star, denoted as PointTarget, and the position of PointTarget can be known from the variable P(StartAddressNum + PointLine). Set the current position of the telescope as CurrentPosition, and the position of CurrentPosition is known. Thus, the distance between the current position of the telescope and the current position of the target star can be obtained as PositionDifference = PointTarget - CurrentPosition. If PositionDifference > S0, then execute Motion Mode 2 to obtain the time required for the pointing motion (s). If PositionDifference ≤ S0, then execute Motion Mode 1 to obtain the time required for the pointing motion (s).

[0054] Step 7: Recalculate the star catalog row number where the telescope should point to the target star as PointLine = int(Time_Difference / TimePeriod) + int(Time_Pointing * 1000 / TimePeriod), that is, the value of the variable P(StartAddressNum + PointLine).

[0055] Step 8: Since the target star is not stationary and its speed is non-uniform during the pointing process of the telescope, when the telescope points to the position of the target star calculated in Step 7, the target star is no longer at this position. Therefore, repeated iteration is required to calculate the exact position when the telescope and the target star meet. Hence, repeat Steps 6 and 7. However, in practical applications, infinite iteration is impossible, and considering the telescope has a certain field of view, the number of iterations usually depends on the specific situation.

[0056] Step 9: From the above steps, the position where the telescope should point to the target can be calculated. The controller drives the telescope to point to the target star, automatically switches to Group B data after completing the tracking of Group A data, updates Group A data while tracking Group B data, and thus realizes the alternating tracking of the two groups of data.

[0057] In summary, the present invention is an astronomical telescope tracking strategy for realizing the packet transmission of the target position based on the time synchronization method. The present invention not only includes the above basic technical route and implementation method, but also includes the relevant software design scheme, and programs are written according to the above design principle. The present invention realizes the astronomical telescope tracking strategy for realizing the packet transmission of the target position based on the time synchronization method.

[0058] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A telescope tracking control strategy based on time synchronization method, characterized in that It includes the following steps: Step 1: The upper computer, lower computer of the telescope control system and the time server are connected through a gigabit industrial Ethernet via a switch, so that the three work under the same local area network; Step 2: The upper computer calculates the position of the target star and generates a star catalog. The sampling interval is TimePeriod (ms). Each group of data includes time Time, azimuth position AZ_Position, altitude position ALT_Position, and derotation position Dero_Position; Step 3: The upper computer program reads the time of the first line of data in the star catalog, defined as Time_BaseLine1. At the same time, the position data of the 1st to Nth lines of the star catalog are sequentially assigned to the variables P(StartAddressNum) to P(StartAddressNum+N-1) in group A. Then, the data in group A are packed and sent to the lower computer of the control system; Step 4: The upper computer program sequentially assigns the position data of the (N+1)th to (2*N)th lines of the star catalog to the variables P(StartAddressNum+N) to P(StartAddressNum+2*N-1) in group B, with a total of N target positions. Then, the data in group B are packed and sent to the lower computer of the control system; Step 5: While step 4 is being executed, start the lower computer motion program. Take the current time of the lower computer system, defined as Time_Current, and obtain the time difference between the current system time and the calculated star catalog time, defined as Time_Difference. Then, Time_Difference = Time_Current - Time_BaseLine1, that is, the line number of the star catalog where the current position of the target star is located is PointLine = int(Time_Difference / TimePeriod); Step 6: Calculate the current position of the target star, set as PointTarget, and the position of PointTarget can be known from the variable P(StartAddressNum+PointLine); the current position of the telescope is set as CurrentPosition, and the position of CurrentPosition is known, so the distance between the current telescope position and the target star can be obtained; when the distance between the telescope and the target star is greater than the critical value, the telescope executes motion mode 1: first accelerate to the maximum speed, then move at a constant speed, and finally decelerate; when the distance between the telescope and the target star is less than or equal to the critical value, the telescope executes motion mode 2: first accelerate and then decelerate, that is, there is no constant speed motion process; thus, the telescope pointing motion time can be obtained; Step 7: Recalculate the line number of the star catalog where the telescope should point to the target star as PointLine = int(Time_Difference / TimePeriod) + int(Time_Pointing*1000 / TimePeriod); Step 8: Repeat step 6 and step 7; Step 9: The controller drives the telescope to point at the target star. After completing the tracking of Group A data, it automatically switches to Group B data, updates Group A data while tracking Group B data, and thus realizes the alternating tracking of the two groups of data.

2. The telescope tracking control strategy based on the time synchronization method according to claim 1, wherein, The said Step 1: The time server is used to obtain an accurate time source and calibrate the time of the upper computer and the lower computer of the telescope control system regularly, so that the time of the upper computer and the lower computer remains accurately synchronized.

3. A telescope tracking control strategy based on the time synchronization method according to claim 1, characterized in that, The said Step 2: When the star catalog sampling interval is TimePeriod (ms), the time accuracy should be accurate to the millisecond level, and the shorter the sampling interval, the higher the accuracy should be.

4. A telescope tracking control strategy based on the time synchronization method according to claim 1, characterized in that The said Step 3: Where N > 1, StartAddressNum is the starting number of the controller variable, and the values of N and StartAddressNum are determined by the number of available registers of the controller.

5. A telescope tracking control strategy based on the time synchronization method according to claim 1, characterized in that The said Step 4: The time interval between the first line of Group B data and the last line of Group A data is one sampling interval.

6. A telescope tracking control strategy based on the time synchronization method according to claim 1, characterized in that, The said Step 5: The current position of the target star is the value of the variable P(StartAddressNum + PointLine).

7. A telescope tracking control strategy based on the time synchronization method according to claim 1, characterized in that, Step 6: The distance between the current position of the telescope and the current position of the target star, PositionDifference = PointTarget - CurrentPosition; if PositionDifference > S0, then execute Motion Mode 1 to obtain the time required for the pointing motion If PositionDifference ≤ S0, then execute Motion Mode 2 to obtain the time required for the pointing motion 8. A telescope tracking control strategy based on the time synchronization method according to claim 1, characterized in that, The said Step 7: The current position of the target star should be the value of the updated variable P(StartAddressNum + PointLine).

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