CN102809961B - Solution for time varying and time slag problems of telescope control system - Google Patents

Abstract

The solution to the time-varying delay problem of the telescope control system: design an absolute time calculation program; use the high-precision clock inside the UMAC; run in the background of the UMAC as a high-priority PLC program (even the highest priority PLC0 program); The initial value T ₀ of the absolute time is obtained from the GPS of the mobile phone, and the count value at this time is obtained from the high-precision clock at the same time; at any time in the future, the current count value obtained from sampling the high-precision clock is t, and the absolute time at this time can be obtained T; the functional characteristics are set by the parameter I variable; I10 sets the servo interruption time; the absolute time is obtained; the tracking data flow of the host computer is obtained during the tracking process, which contains the absolute time information of the tracked target; the UMAC motion program is based on the absolute time in the data flow Find the target and track it; thereby get rid of the dependence on the host computer clock and the influence of time lag in communication, and greatly improve the real-time performance and pointing and tracking accuracy of the telescope.

Description

The solution to the time-varying time-delay problem of the telescope control system

technical field

The invention relates to a solution to the time-varying time-delay problem of a control system, in particular to a solution to the time-varying time-delay problem of a large-aperture telescope control system. This invention is the research achievement of the National Natural Science Foundation of China project (11073034) "Research on Low-temperature Nonlinear Interference Compensation in Low-speed and High-precision Tracking of Antarctica Astronomical Optical Telescope" (Jiangsu Province "333" Project Co-funded Project).

Background technique

The time-lag problem is a problem in many control systems, and the time-lag will reduce the performance of the control system and even affect the stability of the system. There is also time lag in the telescope control system. The time lag problem is difficult to be solved by conventional control algorithms.

At present, the control system of several large astronomical telescopes in China (such as LAMOST) adopts the layered and distributed control method of "IPC + UMAC + independent high-performance servo drive + independent servo torque motor", which has proved to be very effective. Strong real-time tasks are completed by UMAC, and the host computer is only responsible for weak real-time tasks such as communication management, system maintenance and celestial trajectory calculation. The working methods of the directors of each department have been formed.

UMAC is the Universal Motion and Automation Controller (Universal Motion and Automation Controller), which is a multi-axis motion control product of Delta Tau Company in the United States. UMAC is a 3U architecture and integrated PMAC, which is easier to expand and more powerful. The UMAC motion controller has a PMAC programming language similar to BASIC, programming with this language can make the controller work independently. However, the disadvantage of UMAC is that the internal absolute time cannot participate in the operation. Its "DATE" and "TIME" are only for online command query and display, and the precision can only be down to the second. The tracking of celestial bodies by astronomical telescopes requires relatively high accuracy of time. If the azimuth axis tracking speed is 15″/s, the time error is 10 milliseconds, and the azimuth axis pointing error is 0.15″. The time lag in the data exchange process has brought great trouble to the control accuracy of the telescope. Since UMAC relies on the clock of the industrial computer and relies on the industrial computer to obtain the current pointing target, there is a time lag when sending the target from the industrial computer to the UMAC for tracking. The tracking error caused by the time lag varies with the speed of the tracking target. In addition, this time lag is affected by the communication medium, communication busyness, and real-time performance of the operating system during the communication process. The time lag itself also changes within a certain range, that is, a time-varying time lag.

As shown in Figure 1, this is azimuth axis tracking data for a telescope. It can be seen that as the speed changes, the tracking error of the azimuth axis gradually drifts from the range of -0.6" to -0.8" to the range of -1.2" to -1.4" within 19 minutes. It can be seen that the time-varying delay in data exchange has a huge impact on the tracking accuracy of the telescope.

The root of this time-varying time-lag problem is that the UMAC has no absolute time, so the telescope control system has to rely on the time of the upper industrial computer. At present, there is no good fundamental solution for the telescope control system, and it can only be alleviated by improving the real-time performance of communication and operating system.

Contents of the invention

The purpose of the present invention is to propose a solution to the time-varying time-lag problem of the telescope control system aiming at the deficiencies of the prior art. The method adopts the astronomical telescope tracking control system of the UMAC controller to obtain reliable absolute time, thereby solving the time-varying time-lag problem of the telescope control system, and can greatly improve the real-time performance and pointing tracking accuracy of the telescope.

The technical solution for realizing the above-mentioned purpose of the invention is: a solution to the time-varying time-lag problem of the telescope control system, characterized in that the steps are as follows:

⑴. Design an absolute time calculation program;

⑵. The absolute time calculation program uses the high-precision clock inside the UMAC (such as the servo cycle counter); the absolute time calculation program runs in the background of the UMAC as a high-priority PLC program (or PLC0 program);

⑶. The PLC program or PLC0 program obtains the initial value T ₀ of absolute time from the GPS of the upper computer, and at the same time obtains the count value t0 at this time from a high-precision clock (such as a servo cycle counter);

⑷. The functional characteristics of UMAC are set by the parameter I variable; among them, I10 sets the servo interruption time;

The relationship between the servo interruption time T _s and I10 is:

(1),

where 8388608 is 2 ²³ ;

The formula for calculating the absolute time at any time is:

(2),

In the formula (2), all time is calculated in seconds, so T is further converted into the form of year, month, day, hour, minute, and second to obtain the absolute time we need;

⑸. During the tracking process, UMAC obtains the tracking data stream from the host computer, which contains the absolute time information of the tracked target, and its information format is:

"Absolute Time Azimuth Axis Target altitude axis target derotation axis target";

Since the current absolute time has been obtained, the UMAC motion program finds the target according to the absolute time in the data stream to track; thus getting rid of the dependence on the host computer clock and the influence of time lag in communication.

Working principle of the present invention, and more specific and more optimized operation is:

There is a high-precision clock inside the UMAC, such as a servo cycle counter. The clock/counter is a 24-bit counter. Design an absolute time calculation program, using the servo cycle counter, the absolute time calculation program runs in the background of UMAC as a high-priority PLC program, and the initial value of its absolute time comes from the GPS of the host computer. The PLC program of PMAC can be executed repeatedly at a very fast speed. They are called PLC programs because these programs perform functions similar to hardware programmable logic controllers. The PLC control module is used for the logic control of the switching value of the system. While the motion program is running orderly in the foreground, UMAC can run up to 32 asynchronous PLC programs in the background. The PLC program can monitor analog input and digital input at a very high sampling rate, command motion stop/start, etc., and repeatedly scan the PLC program at a very high cycle speed. PLC0 is a more special PLC program, which is different from other PLC programs that execute in the background cycle. PLC0 is executed in the foreground together with the servo algorithm, and its priority is very high, so this program should not be too large, otherwise it will take up the time of the servo algorithm. PLC0 It is used to deal with high real-time requirements and urgent tasks. Here we use PLC0 to realize the calculation of absolute time to ensure the accuracy of time.

The PLC0 program obtains the initial value T ₀ of the absolute time from the GPS of the upper computer, and at the same time obtains the current count value t0 from the servo cycle counter, so that at any time in the future, the current count value obtained by sampling the servo cycle counter is t , the absolute time T at this time can be obtained (in the form of year, month, day, hour, minute, second), where the second has decimals and is accurate to 0.001 second.

The functional characteristics of the UMAC are set through the parameter I variable. Among them, I10 sets the servo interruption time.

The relationship between the servo interruption time T _s and I10 is:

(1)

where 8388608 is 2 ²³ .

The formula for calculating the absolute time at any time is:

(2)

In the formula (2), all times are calculated in seconds, so further convert T into the form of year, month, day, hour, minute, and second to obtain the absolute time we need. The reason why the GPS time is not taken from the host computer every time, but only read once when the initial value is assigned, and then accumulated by the PLC0 program is to avoid time-varying time lag in two-machine communication and data exchange.

During the tracking process, UMAC obtains the tracking data stream from the host computer, which contains the absolute time information of the tracked target, and its information format is:

"Absolute Time Azimuth Axis Target Altitude Axis Target Derotation Axis Target"

Since the current absolute time has been obtained, the UMAC motion program finds the target to track according to the absolute time in the data stream. Thus getting rid of the dependence on the host computer clock and the influence of time lag in communication.

The beneficial effect of the present invention is that the present invention obtains reliable absolute time for the astronomical telescope tracking control system using the UMAC controller, thereby solving the time-varying time-lag problem of the telescope control system, and greatly improving the real-time performance and pointing tracking of the telescope precision.

Description of drawings

Figure 1 is a graph of the variation of the tracking error of the azimuth axis with the speed;

Fig. 2 is an absolute time PLC program variable monitoring diagram;

Fig. 3 is the PLC program flowchart that obtains absolute time;

Figure 4 is a flow chart of the time calculation program.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Inside the UMAC there is a servo cycle counter, which is a high precision clock. Write the following code in UMAC:

#define ServoCounter M100 ; 24-bit servo cycle counter

ServoCounter->X:$000000,0,24,S

Make memory location M100 point to servo cycle counter X: $000000,0,24,S, this clock/counter is a 24-bit counter that increments by 1 every servo cycle. Its count starts when the UMAC is powered on, and it will roll over to a negative number when it reaches the maximum value. In the control system of the telescope of the embodiment, the crystal oscillator frequency of UMAC is 19.6608MHz, and the system parameter I10=4194560, the servo interruption time of obtaining UMAC is

(3)

That is, every increase of 1 in M100 represents an increase of 500 . This results in a resolution of 500 absolute clock.

The absolute time calculation program runs in the background of UMAC as a high-priority PLC program. The initial value of its absolute time comes from GPS, and the computer assigns the value to UMAC through Ethernet communication.

The absolute time acquisition is done with PLC0 having the highest priority. The PLC0 program flow chart is shown in Figure 3, and the time calculation program flow chart is shown in Figure 4. It should be pointed out here that the time calculation program is not an independent subroutine, but a part of the program. In order to clearly illustrate the function of the program, it is especially independent.

Since the servo cycle counter is a 24-bit counter, there is a problem that it will flip when it counts to the maximum value, so the program specially judges this, and its flip constant value is 2 ²³ =8388608.

After obtaining the current time in seconds (that is, the total number of seconds), according to the needs of the telescope tracking control, the embodiment further converts the total number of seconds into the form of year, month, day, hour, minute, and second, which is completed by the time calculation program, such as Figure 4.

In flowcharts, seconds are integers, and total seconds have decimal places. The total seconds, total minutes, and total hours are the relative values from the zero point when the UMAC is powered on to the current count value plus the absolute time when the UMAC is powered on.

When calculating time, special consideration should be given to the calculation of ordinary years and leap years. Here the leap year is judged by the following conditions: divisible by 400; divisible by 4, but not divisible by 100.

Through the above method, the absolute time required by the astronomical telescope to track the celestial body is obtained. During the tracking process, the UMAC obtains the tracking data stream from the host computer. The information format is "absolute time Azimuth axis target Altitude axis target Race axis target", since the current absolute time has been obtained, the UMAC motion program finds the target according to the absolute time in the data stream for tracking.

Figure 2 is the monitoring diagram of the upper computer, which shows the absolute time change calculated by the PLC program in UMAC, which proves that the method is correct and reliable.

Claims (4)

1. a solution that becomes Time Delay when telescope control system, is characterized in that, step is as follows:

(1). design an absolute time calculation procedure;

(2). this absolute time calculation procedure utilizes the high-precision clock of UMAC inside; This absolute time calculation procedure is as the PLC program of a high priority, or PLC0 program, at UMAC running background;

(3). this PLC program or PLC0 program obtain the initial value T of absolute time from the GPS of host computer ₀, and the count value obtaining from high-precision clock is now t0 simultaneously; Random time afterwards, in the high-precision clock of sampling, obtaining current count value is t, can be in the hope of absolute time T now;

(4). the functional characteristic of UMAC is by parameter I variable set up; Wherein I10 arranges the servo interrupt time;

The servo interrupt time t _swith the relation of I10 be:

（1），

Wherein 8388608 is 2 ²³;

The absolute time computing formula of random time is like this:

（2），

In formula (2), institute all calculate in seconds if having time, further tturn to the form of date Hour Minute Second, obtained the absolute time needing;

(5). UMAC, in tracing process, obtains the streams of trace data from host computer, contains the absolute time information of tracked target in these data, and its information format is:

" absolute time azimuth axis object height axle target racemization axle target ";

Owing to obtaining current absolute time, UMAC motor program finds target to follow the tracks of according to absolute time in data stream; Thereby break away from the impact of time lag in dependence on host computer clock and communication;

Step is the high precision clock of described UMAC inside (1), is to adopt the servo period counter of 24.

2. the solution that becomes Time Delay when telescope control system according to claim 1, is characterized in that, (2) step writes following code in described UMAC:

#define ServoCounter M100 ; 24-bit servo cycle counter

ServoCounter->X:$000000,0,24,S

Make storage unit M100 point to servo period counter X:$ 000000,0,24, S.

3. the solution that becomes Time Delay when telescope control system according to claim 1, is characterized in that, (3) described " trying to achieve absolute time T now " of step, wherein second with decimal, is accurate to 0.001 second.

4. during according to telescope control system one of claim 1-3 Suo Shu, become the solution of Time Delay, it is characterized in that, in telescope control system, the crystal oscillator frequency of UMAC is 19.6608MHz, systematic parameter I10=4194560, the servo interrupt time of trying to achieve UMAC is

（3）。