the rt-32 radio telescope pointing system

ISSN 0020�4412, Instruments and Experimental Techniques, 2012, Vol. 55, No. 3, pp. 357–367. © Pleiades Publishing, Ltd., 2012.Original Russian Text © M.N. Kaidanovskiy, N.Y. Belousov, V.Y. Bykov, G.N. Ilin, I.G. Rubin, V.G. Stempkovskiy, A.M. Shishikin, 2012, published in Pribory i TekhnikaEksperimenta, 2012, No. 3, pp. 63–74.

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1. PURPOSE AND MAIN CHARACTERISTICS OF THE RADIO TELESCOPE ANTENNA

SYSTEM

The new�generation multiwave high�precisionradio telescope (RT) with a 32�m�diameter mirror wasdeveloped and manufactured within the framework ofthe project of creating the national Quasar�KVOradiointerferometric network [1–4]. To date, threeRTs have been built and actively operate at the Svetloe(Leningrad oblast), Zelenchuk (North Caucasus), andBadary (near lake Baikal) observatories. The RT of theBadary observatory is shown in Fig. 1.

The RT is intended for fundamental investigationsof celestial objects of different natures within wave�length ranges from 1.35 to 21.00 cm [5–8]. The mainelement of the RT is the reflector antenna system(AS). The AS was built according to the modified Cas�segrain scheme with a quasi�parabolic principal mir�ror and quasi�hyperbolic secondary mirror (conver�gent mirror) 4 m in diameter. An important feature ofthe focusing system is a slight deflection of the focalaxis of the secondary mirror from the rotation axis ofthe quasi�paraboloid of the principal mirror. Such anorientation scheme of the axes allows placement of theprimary feeds of the RT [9, 10] receivers on a circlewith a diameter of ~3 m and provides prompt switch�ing of the ranges of received signals via adjustment ofthe convergent�mirror position [3].

The rotary support of the AS provides azimuthaland elevation�angle rotations. The electrical drive of

the principal mirror provides azimuthal and elevation�angle displacements of the AS within angles of ±270°and 0°–90°, respectively.

The AS azimuthal movement is performed along a40�m�diameter circular rail track. The azimuthal driveconsists of four paired carriages, each of which isequipped with two pairs of dc motors with differentpowers.

The large weight of the RT�32 structure (>600 t)and the requirements imposed on the dynamic char�acteristics of the RT movement determine the param�eters of the AS electrical drive and control system.

The electrical drive provides high�speed displace�ments along the azimuthal (up to 1.5 deg/s) and eleva�tion�angle (up to 1 deg/s) coordinates with accelera�tions of up to 0.8 deg/s2 at the speed�up stage [3]. Inthis case, the AS control system must control the RTmovement dynamics so as to ensure the required accu�racy, absence of vibrations, and a dynamic but smoothacceleration and deceleration. Impact loads on the RTstructure must be excluded. When nonstandard situa�tions arise, the safe RT stoppage must be provided.

The electrical drive of the AS operates in twomodes. The AS is displaced to a specified region usingmore powerful high�speed motors for a maximallyrapid change in the orientation of the antenna princi�pal mirror upon a change to the next object underobservation. The source tracking mode is provided bylow�speed motors that are enabled after the ASreaches the rated vicinity of the radio�source coordi�

APPLICATION OF COMPUTERS IN EXPERIMENTS

The RT�32 Radio Telescope Pointing SystemM. N. Kaidanovskiy, N. Y. Belousov, V. Y. Bykov,

G. N. Ilin, I. G. Rubin, V. G. Stempkovskiy*, and A. M. ShishikinInstitute of Applied Astronomy, Russian Academy of Sciences, nab. Kutuzova 10, St. Petersburg, 191187 Russia

*e�mail: [email protected] July 20, 2011

Abstract—Quasar–KVO RT�32 radio telescopes of the radio interferometric complex of the Russian Acad�emy of Sciences are equipped with unique 32�m�diameter antennas. The telescopes provide radio astronomyobservations in the centimeter wavelength range within a network of radio telescopes, as well as in the singledish mode. The antenna system structure has a significant size and weight, thus determining the engineeringdifficulties in controlling the movement of the RT�32. The electrical drive of the antenna system must providetwo different operating modes: on the one hand, a rapid change in the antenna angular position, and on theother, precise tracking of a cosmic signal source. The high operational load and requirements for the serviceof radio telescopes as parts of radio interferometry networks impose stringent reliability requirements on theelectrical drive and control system. The pointing system consists of subsystems that include dc drives, powerequipment for controlling these drives, position sensors based on rotary transformers, and other items. Allsubsystems are integrated using switching devices of control signals and coordinate�transforming devices.The system is operated by a working monitoring and control station, which is based on an industrial computerand specially developed software.

DOI: 10.1134/S0020441212020200

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KAIDANOVSKIY et al.

nates within ±2′.Using the motors, the RT reaches therequired trajectory and tracks the radio source.

The requirements for the tracking accuracy aredetermined as 1/20 of the RT directivity pattern widthat a half�power level θ0.5 = kλ/D, where k is a factor of~1 that depends on the mirror irradiation efficiency, λis the wavelength, and D is the antenna diameter. Forthe shortest wavelength λ = 1.35 cm, the value of θ0.5is 1.5′. Thus, the required tracking error must notexceed ±5″.

Both movement velocities (high and low) of the RTAS were implemented in the electrical drive using dcmotors of different types, which are connectedthrough reduction gears with appropriate transmissionratios. Speeds are changed with a system of planetaryclutches and disk brakes.

The electrical drive of the convergent mirror is builtaccording to the single�speed scheme and allows dis�placements of the secondary mirror by distances of±75 mm along three linear coordinates and its rota�tions about the axis by 360°. The requirements for theconvergent�mirror setting accuracy are also ratherhigh and are equal to ±0.01 mm along the X, Y, and Zlinear coordinates and ±1′ for the γ angular coordi�nate, respectively.

Figure 2 shows the structure of the control systemof the AS electrical drive. The RT electrical drive iscontrolled in the following order. Instructions fromthe workstation of the RT [11–13] are transmitted tothe working monitoring and control station (WMCS)and then to the pointing�system automation equip�ment, which ensures control of the power devices ofthe electrical drive. The pointing�system automation

equipment includes switching units of the control sig�nals, motor�driving units (MDUs) and thyristor con�verters (TCs) for powering the armature circuits of themotors of the RT AS electrical drive. The switchingdevices of the pointing system automatics are placed inthe corresponding switching–control units SCU�PMof the principal mirror electrical drive, and SCU�CMfor the RT convergent mirror.

The WMCS control computer forms a sequence ofinstructions that is transmitted to the pointing�systemequipment [14] and calculates the difference betweenthe specified and current positions of the RT AS,which are obtained from sensors and the coordinate�transforming device (CTD). The calculation resultsare used to specify the required RT AS movementdynamics and form an appropriate control voltage thatdetermines the AS movement speed.

Having received an instruction from the WMCS,the SCU�PM switching unit enables the necessaryactuating devices in accordance with a specified algo�rithm and switches control voltages depending on thespeed range and the antenna position. The actuatingdevices in turn supply voltages to the AS motors andbraking devices and report data on their correct oper�ation and the fact of the instruction fulfillment to theswitching unit.

2. COMPOSITION AND PURPOSE OF THE ELECTRICAL DRIVE COMPONENTS

The equipment of the RT AS electrical drive ismounted in seven standard racks and placed in the

Fig. 1. Antenna system of the RT�32 radio telescope of the Quasar�KVO complex.


THE RT�32 RADIO TELESCOPE POINTING SYSTEM 359

room for the cable loop in the base of the rotary sup�port of the RT�32 antenna.

2.1. Electrical Drive of the Principal Mirror

The structure of the electrical�drive equipment ofthe RT AS principal mirror is largely determined bythe type of used electrical motors.

The high�speed drive uses eight ДПМ�42 dcmotors for the azimuthal coordinate and four analo�gous motors for the elevation�angle coordinate. In thelow�speed drive, ДПМ�11 dc motors (eight for theazimuth and two for the elevation angle) are used.

The armatures of the electrical drives are poweredusing thyristor converters of two types (with differentpowers). Automatic switches are included in the arma�ture circuits for protecting electrical drives againstoverloads. The drive windings of the electrical motorsare powered from the MDU driving units, which alsoprovide the control of the planetary clutches and thelow�speed brakes.

2.2. Electrical Drive of the Convergent Mirror

The RT convergent mirror is displaced along fourcoordinates for focusing the AS in different wave�length ranges. All four electrical drives are builtaccording to a similar scheme and consist of a motorwith a reduction gear, a rotation angle sensor that

determines the position of the converging mirror, anda sensor of limiting displacements that determines themaximum range of the converging mirror displace�ments along the linear coordinate.

The power circuit of the electrical�drive connec�tion is as a whole analogous to the circuit of the prin�cipal�mirror drive connection: the armature circuits ofthe motors are powered from the TC units, and thedriving circuits, from the special driving unit MDU�CM. The automatic operation of the power compo�nents is controlled by a switching unit SCU�CM.

2.3. Thyristor Converters

The circuit of the power part of the TC consists oftwo groups of thyristor�based bridge circuits. Boththyristor groups are controlled from a common pulse�phase control system. The rectifiers that provide rever�sal of the TC output voltage are switched by signalsfrom a logical device and a switch of the characteris�tics. In addition to the mentioned functional units, theTC includes a current�limiting device, a nonlinearelement (which linearizes the TC static characteristicin the mode of operation with intermittent currents),a protection unit, a speed regulator, and other devices[15].

A speed feedback signal arrives at the TC from fourTG�102 tachometer generators, which are connectedin series (through the armature circuits). Power

. . . . . .

WMCS

CSU�CMCSU�MCTD

MPC

Electromechanical drive Electromechanical driveof the convergent mirrorof the principal mirror

Ind

icat

ors

PS PS

5 T

DU

MotorMotor

MDU�CMTC�CM

XY

Zr

MDUrack

TC EA

rack

TC AZrack№2

TC AZrack№1

Fig. 2. Functional diagram of the monitoring and control system of the electrical drive of the RT�32 RT AS: (WMCS) workingmonitoring and control system, (CTD) coordinate transformation device, (CSU�M) modernized control and switching unit,(CSU�CM) convergent�mirror control and switching unit, (TC) thyristor converters, (MDU) motor driving units, (AZ) azimuth,(EA) elevation angle, (MPC) motor protection cabinet, and (PS) position sensors.

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optothyristor modules and pellet thyristors with atransformer�based control system are used in the low�speed and high�speed TCs, respectively. The TCs arepower�supplied from a 380�V three�phase network at afrequency of 50 Hz.

2.4. Motor Driving Rack

The RT�32 electrical drive includes three MDUsthat are placed in a common rack. The case of eachunit contains power�supplying transformers, modulesfor enabling magnetic starters, and subunits of threetypes: SCU�2, SCU�1, and CSU. The first two are dccurrent sources for powering the drive windings of thehigh� and low�speed motors, respectively, and low�speed disk brakes. The CSU subunit is the switch ofthe three�phase supply voltage and is intended forcontrolling the planetary clutches via hydropushers,which are actuated by asynchronous motors.

The subunits were initially built on the basis ofoptothyristors, which were connected according to thecircuit of three�phase half�wave rectifiers (SCU�1 andSCU�2), and switches of the power circuits (CSU).

Because the thyristors operate into inductive loads(the drive windings of the motors), when a thyristor isenabled, significant pulse voltage surges (up to severalkilovolts) arise, which lead to the gradual thyristordegradation and failure. Therefore, during the MDUmodernization, new motor�driving and brake�con�trolling subunits were developed using state�of�the�artthree�phase power optical relays with control of thevoltage�phase transition through zero. Thus, we man�aged to solve the problem of the reliability of the MDUowing to both the longer service life (50000–100000 h) of the optical relays and the installation ofadditional varistor�based protective devices.

All the subunits included in the MDU are built onthe basis of the basic motor�driving module(BMDM), whose appearance is shown in Fig. 3. Thissolution was possible because the subunits perform the

functions according to similar algorithms and havesimilar parameters.

The BMDM consists of an ac optical relay, a recti�fier, a module�protecting circuit, and an indicationand feedback�acknowledgment circuit.

The required configuration of the subunit isachieved by mounting the required electronic compo�nents and switching the components of the BMDM.The module is installed in the existing structure of thesubunit directly in observatories and is immediatelyready for operation as a component of the MDU. Thisapproach allowed us to upgrade the equipment of theMDU racks within short terms (at most a week) with�out stopping regular observations.

3. SWITCHING EQUIPMENT OF THE POINTING SYSTEM

In accordance with the design, the equipment ofthe RT AS pointing system was placed in the ACH�02rack in the form of several units. Each of them per�formed an individual set of functions. Binary�logicsmicrocircuits with a low integration level and manyelectromagnetic relays served as the circuitry elementsof these units. This caused awkward circuitry solu�tions, and, as a result, the system’s reliability andmaintainability were comparatively low.

An increase in the amount and intensity of radio�astronomical observations imposed increased require�ments on the reliability to the pointing system. As aresult, it was decided to develop a new control andswitching unit SCU�PM, whose functional diagram isshown in Fig. 4. The basic elements of this unit areATmega microcontrollers that perform the controlalgorithms and new�generation solid�state opticalrelays (КР293КП, Russia) serving the actuatingdevices of the switching units.

The modernized switching�control unit is built in a19�inch case, on whose front panel controls and indi�cators are placed. Its external view is shown in Fig. 5.

The equipment of this unit receives executiveinstructions from the WMCS, processes them, andsequentially sends to the devices and facilities of theelectrical drive. As these devices operate, receipts ofthe fulfillment of the instructions are delivered, and adecision on the continuation of the electrical�driveturning�on procedure is made on this basis. The turn�ing�on algorithms are included in the program of themicrocontrollers, which are included in the azimuthal(AZCB) and elevation�angle (EACB) control boardsof the electrical drive. The control and indicationboard (CIB) serves for switching control signals fromthe WMCS, receiving and indicating receipts of theantenna positions, and monitoring the safety blockageand end limitations.

The design of the SCU provides an easy access toelectronic modules, thus substantially facilitating therequired repair and maintenance works. The optoelec�

Fig. 3. Basic motor driving module.



tronic elements and microcontrollers are mounted onDIP boards in order to simplify and accelerate theirreplacement.

4. DEVICE FOR PICKING�UP THE ANGULAR COORDINATES

The device for picking�up the angular coordinates(DPAC) together with the sensors of the AS angular�coordinate position largely determines the accuracycharacteristics of the RT pointing to a cosmic�radia�tion source and its subsequent tracking. The DPAC isa combination of sensors of the AS angular positionand a device that transforms signals from the azi�muthal and elevation�angle sensors into a digital code(coordinate transformation device, CTD). In order totrack a source with an accuracy of 5′′, the informationfrom the AS position sensors must be transformed witha resolution no worse than 1′′ (arc) or 20 bits in thebinary code.

In order to measure the RT AS coordinates with a1′′ angular resolution, the reading devices are designedaccording to a two�channel scheme that consists ofrough and precise reading sensors. Rough and precisereading sensors are used to form 8 high�order and 12low�order bits of the antenna position code.

A multipole (256 poles) rotary transformer with flatwindings, viz., a so�called inductosyn, serves as thesensor of precise readings of the RT�32 RT AS posi�tion. The operating principle of the rough and precisereading sensors is the same. As a result, to form thedigital code of the angular positions of the sensors, it

was possible to use single�type microcircuits for pro�cessing analog signals from the sensors, which consid�erably simplified the development of the CTD [16]and simultaneously allowed unification of the CTDcircuitry components for these sensors. In the devel�oped CTDs, the modern circuitry components (Ana�log Devices) with small dimensions and an optimalcost�to�quality ratio are used. A number of additionalfeatures were imparted to the DPAC owing to the useof these circuitry components and the built�in facili�ties for digital signal processing.

The developed DPAC performs the following func�tions:

(i) Transforms signals from the sensors of the angu�lar position of the principal mirror over the azimuthaland elevation�angle coordinates into a 20�bit digitalcode;

(ii) Calculates the velocities along both coordi�nates;

(iii) Measures the temperatures of units;

(iv) Provides data transmission through an RS�485two�wire interface with galvanic decoupling;

(v) Provides entering of the angular coordinates tothe WMCS, to the PIO�D96 board in a 20�bit parallelcode;

(vi) Displays coordinates in the binary and decimalforms on character�display liquid�crystal and LEDindicators;

(vii) Displays the speed and temperature on the liq�uid�crystal indicator.

CIB

PSU

AZCB

EACB

Crossboard

WMCS instructions

MC instructions

Status receipts

Indication

+5 V

+5, +12,–12, +24 V

AZ controlinstructions

and receipts

EA control instructionsand receipts

AZ error voltage

Instruction

to AZ AD

Receipts

from AZ AD

ЕА error voltage

Instruction

to EA AD

Receipts

from EA AD

Fig. 4. Functional diagram of the CSU�M unit: (AZCB, EACB) azimuthal and elevation�angle electrical�drive control boards,(CIB) control and indication board, (MC) manual control, (AD) actuating devices, and (PSU) power supply unit.

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The device is easy to manufacture and has a highreliability, small dimensions, and low energy con�sumption. The period of updating data on the coordi�nates is 28 ms.

5. ANTENNA CONTROL SYSTEM

The RT control system includes several subsystemsfor providing the combined agreed functioning of thecomplex measuring tool. The antenna control system(ACS) provides the purposeful movement of theantenna in accordance with the problems to be solvedduring preparation and in the course of observations.The AS movement control subsystem is a three�levelsystem for generating, transmitting, and receivingcontrol information. The workstation is at the upperlevel, and the next levels are occupied by the ACS andthe actuating part of the AS electrical drive.

The workstation performs stringently time�lockedtargeting for the ACS by specifying both the coordi�nates of a radio�signal source, to which the antenna isrepointed, and a piecewise�linear approximation ofthe tracked source trajectory. The most complexrequirements for RT pointing are imposed when theRT operates as a component of national or interna�tional networks of very�long�baseline radiointerfer�ometers [17]. In such networks, a large number of RTs(up to 30) separated by distances of several thousandkilometers simultaneously observe the same sources.Observations last several days and consist of continu�ous cycles of pointing to a source, its tracking, and achange to the next source. The average number of suchcycles is 400 per day of observations.

The main functions of the ACS during the sourcetracking are as follows: the interpolation of a specified

trajectory, the analysis of the difference between thespecified and actual AS positions, and the minimiza�tion of this difference through a change in the ASmovement speed. The feedback in the workstation–ACS loop is ensured by regular reports on the state ofthe AS and the ACS actions, which are formed in thecourse of the fulfillment of instructions of the worksta�tion. The feedback from the electrical drive to the ACSis ensured by the regular interrogation of the AS posi�tion sensors and sensors of the states of the electricaldrive’s individual elements (notice). The AS controlsubsystem operates mainly in an automatic mode butalso admits human intervention at all levels.

5.1. Software–Hardware Interpretation of ACS Instructions

The lower level of the AS control system is the elec�trical drive of the AS, which has a hardware interfacewith the WMCS and performs its own WMCS–elec�trical drive system of instructions. The software of theWMCS translates the instructions arriving from theconsole of a pointing operator (CPO) and enters thecontrol data to the data input–output devices of theindustrial computer. The digital input and output areused for obtaining data from the receipt sensors andissuing the instructions for enabling/disabling individ�ual elements of the electrical drive, respectively. Thedigital input is also used for obtaining data from thesensors of the positions of the principal and conver�gent mirrors and inputting the time code. The analogoutput allows the formation of control voltages for theactuating units of the electrical drive.

БУК�М

+5 В +24 ВСеть

Защита поскорости

БлокировкаОПУ

Сброс

Угол местаСкорость

Азимут

МС БС

Общий

Секция 1

Секция 2

УправлениеА3

ЭПА А3Готов

УправлениеУМ

ЭПА УМГотов

Положение антенныПоложение антенны

Возвратноеограничение

Ограничениескорости

Слевана улитке

Справана улитке







АЗ УМ

Fig. 5. Front panel of the CSU�M unit with indicators of the electrical�drive status: (ЭП, ED) electrical drive, (ОПУ, RSD) rotarysupport device, and (MC, LS; БС, HS) low and high speeds.



5.2. Fulfillment of Tasks

After a task from the workstation is received, theWMCS processes it and formulates it in the form ofinstructions that are required for the actuating gears ofthe electrical drive and ensure the fulfillment of thistask. The actuating mechanism confirms the fulfill�ment of an instruction by an appropriate receipt. TheWMCS interrogates the actuating mechanisms anddevices for measuring and transforming the RT coor�dinates with a frequency of up to 1000 Hz. On the basisof the obtained receipts and coordinates, the WMCScontrol computer forms the antenna and convergent�mirror status words, which are sent via a communica�tion line to the CPO and then to the workstation.

The WMCS forms and generates analog controlvoltages, which, using the data input–output boardsare fed directly to the actuating devices of the electri�cal drive through the unit of matching modules. Theinteraction of the WMCS with the electrical drive isshown in Fig. 6.

5.3. Hardware Solutions in the ACS

Instructions and target designations are coded inaccordance with the workstation–WMCS communi�cations protocol and are transmitted through theobservatory’s local Ethernet network to the CPO usingthe TCP/IP protocol.

The computer of the CPO retranslates the obtaineddata to the COM port, to which the CPO–WMCScommunication line is connected. To reliably transmitsignals to long distances, standard ADAM 4520 inter�face modules are used, which transform RS�232 pro�tocol signals to RS�422 and provide the galvanicdecoupling of the signal transmission line.

Time signals to which the ACS operation is lockedarrive at the WMCS from the hydrogen standard of thefrequency and time service (FTS) through the timecode transformation module (TCTM). The module isintended for the hardware transformation of a serialpulsed time code, which arrives from the FTS, into aparallel digital code. A parallel code at the TCTM out�put is formed once a second and coincides with a sec�ond mark, which is generated in the universal time sys�tem of the observatory.

The data on the coordinates of the main and sec�ondary mirrors of the RT�32 radiotelescope in theform of a parallel code are generated by the coordi�nate�transforming devices [16] and are then enteredinto the WMCS together with receipt signals throughthe unit of matching modules. In the latter unit, thecommunication lines though which control signals aretransmitted from the WMCS to the actuating devicesof the electrical drive are electrically switched.

A single�board Rocky 6161E/EG (Intel945GV+ICH6 chipset) industrial computer with aPICMG (PCI/ISA) combined bus is used as the con�trol computer in the WMCS. The computer is assem�

bled on a passive cross�board with 14 slots (5 ISA, 7PCI, and 2 ISA/PCI). The system board includes aPentium�IV processor with a 3.2�GHz clock fre�quency, RAM with a capacity of 2 GB, an Intel 945Gvideo card, and controllers of peripheral devices, towhich a 160�GB SATA hard disk is connected, aSATA DVD�ROM optical�disk readout device, a1.44�MB floppy disk drive, and other accessories.

5.4. Software Solutions in the ACS

The control software for the antenna electricaldrive includes the WMCS software and the CPO soft�ware.

5.4.1. Organization of the quasi�real time mode.The WMCS controls the AS in the quasi�real timemode. All components of the WMCS software are ini�tiated by a program timer that operates 1000 times/s.Some operations of the timer can be blocked by high�priority interrupts, but this does not interfere with theoperation of the control algorithms, since the genera�tion of a control action follows changes in the state ofthe control object without delays.

5.4.2. Operational environment for the WMCS andCPO software. The Linux operational system with the2.6.18 kernel, which was assembled from the ScientificLinux 5.2 distribution disk (http://www.scientifi�clinux.org) was chosen as the target operational sys�tem of the CPO and WMCS. As the computer aids fordeveloping application software, the GCC (CNUCompiler Collection) compiler family for high�levellanguages (http://gcc.gnu.org) and the Qt3 library ofthe C++ classes for developing applications with adeveloped user interface [http://www.trolltech.com]were used.

5.4.3. Software development and debugging tech�nology. The development and initial refinement of theRT�32 pointing system as a component of the controlsystem were performed using a mathematical model ofthe controlled object, viz., the AS, which includes mod�els of the principal and convergent mirror drives [18].

The multiple�machine complex at the develop�ment and debugging stage was also simulated usingfacilities for virtualization of computational resources.For this purpose, we applied the technology for debug�ging the multiple�machine control system of theRT�32 RT that includes three computers: the main(workstation), CPO, and WMCS computers. Thedebugging technology is based on the use of VMwareWorkstation (VMware Inc.) aids for virtualization ofcomputational resources (http://www.vmware.com)[19]. The VMware Workstation virtualization aidsallow emulation of the intermachine data exchangeusing the TCP/IP protocol and serial interface, leav�ing the necessity of developing a software emulationonly for special equipment, such as the PIO�seriesinput–output boards that are produced by the ICPDAS Co. (http://www.icpdas.com) and used for com�munication with the electrical drive.

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5.4.4. Organization of the user interface. The userinterface management aids provide a set of C++classes that are used to create the frame part of the usergraphic interface and to provide the reference service,protocol maintenance service, and call for the auxil�iary service, whose functionality is regulated onlywhen organizing a dialogue with a user. The frame partof the user graphic interface yields information on thecurrent data and time and introduces the concept of asession as the period between the software applicationstart and its termination.

When the aforementioned aids are used, the onlytask is to complement the reference service with anhtml file that contains a user manual.

The software for organizing the user interface waswritten according to the application developmentstandard using the Qt class library, which implies thatall texts are written in English and the application isequipped with a dictionary file. Using this file, theapplication internationalization system provides auser interface in the language that corresponds to thesettings of the operational system.

5.5. WMCS Software Functionality

When developing the ACS software, an RT ASmodel was developed, in which several dynamic char�acteristics of the AS and the actual control�loop struc�ture were taken into account. Such an approach wasapplied in order to minimize the possibility of appear�ance of nonstandard situations in software tests on thecontrolled object and completely justified itself duringdebugging.

The AS model abstracts from details of the imple�mentation of the AS itself and its electrical drive to adegree to which it is convenient to perform the AScontrol, i.e., to produce control discrete signals andvoltages. The principal and secondary mirrors are con�

sidered as integral inelastic objects; thus, deformationsare disregarded. It is assumed that the speed of azi�muthal or elevation�angle displacements is propor�tional to the control voltage fed to the motors.

Such external factors as the wind load and temper�ature effects on the electrical�drive elements (freez�ing) are also disregarded.

However, it is undesirable to fully reject the accountfor the AS mass because, in the case of an emergencyAS stoppage, the engagement of brakes immediatelyafter the control voltage is zeroed may lead to undesir�able impact loads because of the object inertia. Inorder to avoid such consequences, an experimentallyselected pause is held between the moments of thecontrol voltage removal and enabling of the brakes.Moreover, for the high�speed mode, a smooth increaseand decrease in the movement speed, when impactloads do not arise, are provided as well. No limitationsare provided for the low�speed mode.

The main operating mode of the WMCS software isautomatic without participation of an operator. How�ever, the AS preparation stages for observations areequally obligatory as the observations themselves.When maintenance works are prepared and per�formed, it is more convenient to locally control thesystem directly from the WMCS console. This oppor�tunity is afforded owing to the developed user interfaceof the WMCS. It helps to perform all AS movements.The WMCS allows independent movements alongindependent coordinates of both the principal andconvergent mirrors. The WMCS software providesthree operating modes: manual, automatic, and withexternal control.

The automatic WMCS mode allows an operator tonot have to control the entire displacement processand ensures a smoother movement of the AS and moreaccurate displacement procedure. In this mode, thetask is specified using macroinstructions for displacing

POC

RS�422/485RS�232ADAM 4520 ADAM 4520

TCCM

RS�232

FTSS

Workstation

Matching modules unit

Principal�mirrordrive

Convergent�mirrordrive

Position sensors

CoordinatesReceipts ReceiptsInstructionsInstructions

Fig. 6. Scheme of interaction of the WMCS with the AS electrical drive in the RT�32 RT movement control system: (POC) point�ing operator console, (TCCM) time�to�code conversion module, and (FTSS) frequency and time service standard.



the AS to a specified point and setting the convergentmirror in an assigned position.

The external control mode is the main WMCSoperational mode. In this control mode, all target des�ignations arrive to the WMCS from the workstationthrough the CPO. An operator can visually control theAS operation and, if necessary, scan files of the proto�col that belong to the completed and current sessionsof the WMCS operation. In the external controlmode, all instructions from the workstation are dis�played on the screen (Fig. 7).

5.6. Algorithmic Provision of the Automatic AS Control

The WMCS software realizes three movementalgorithms of the main and secondary AS mirrors: dis�placement (repointing), tracking, and installing theconvergent mirror. The fulfillments of all algorithmshave specific features that distinguish them from thoseused previously.

The displacement algorithm provides smoothacceleration and smooth stoppage of the AS. Thesmoothness is regulated by two parameters—the max�imum rated azimuthal and elevation�angle speeds.

The algorithm of pointing to a source and trackingit provides smoothing of the trajectory that is specifiedby the workstation. The smoothing leads to a subdivi�sion of the initial piecewise�linear approximation ofthe source trajectory and a decrease in the jumps of therated speed values of the movement on adjacent sec�tions of the trajectory. This reduces the loads appliedto the electrical drive and softens possible jerks duringthe antenna motion.

The convergent�mirror control algorithm uses thefeedback with respect to the adjusted coordinate of theconvergent mirror; the latter is set independently in allfour coordinates. The algorithm is based on the sameprinciples as the azimuthal and elevation�angle dis�placement algorithm, and the presence of the feed�back allows positioning of the convergent mirrorwithin the limits of the position sensor error (0.01 mmfor the linear coordinates and 1′–2′ for the angularcoordinate).

5.6.1. AS displacement algorithm. The displace�ment is determined by the initial point, target point,maximum movement velocity, and the time of theantenna stoppage after zeroing the control voltage. Inorder to ensure the smooth acceleration and decelera�tion, the entire trajectory is divided into three seg�ments: acceleration, uniform motion, and decelera�tion. Azimuthal and elevation�angle displacementsare performed simultaneously and asynchronously.

The segment of the uniform AS movement may beabsent if the distance between the initial and targetpoints is insufficient for acceleration to the maximumspeed in view of the provision of a smooth decelera�tion.

5.6.2. Trajectory smoothing algorithm. The neces�sity of trajectory smoothing arises in special cases ofantenna movement, when a sharp change in the move�ment speed is required during displacements alongone or two coordinates and during scanning [20]. Thenecessity of smoothing is determined by the calcula�tion of the rated movement speeds on adjacent linearsegments of the trajectory. If the speed change exceedsa specified threshold, two trajectory segments aretransformed into three.

5.6.3. Source tracking algorithm. The mode ofsource tracking by the AS is provided by using a mod�ification of a well�known proportionally integral (PI)algorithm. This algorithm utilizes the feedback on thebasis of the position of the controlled object for gener�ating a control action. The control action for the elec�trical drive of the AS is the control voltage fed to theelements of the drive.

When a source is tracked, the control system has atask to hold the AS on the required trajectory, which isspecified by a piecewise�linear approximation, withina fixed value of the tracking error. Let us consider the[P0(A0, H0, T0), P1(A1, H1, T1)] segment of the trajec�tory, where P0 and P1 and neighboring points of thetrajectory with the coordinates А (azimuth), H (eleva�tion angle), and Т (time).

The rated movement speed is calculated for theentire time interval T0 < t < T1:

and .

At the moment t, the antenna is at the point P0(A0,H0) but must be at the point Pc(Ac, Hc), where Ac =A0 + CVA (t – T0) and Hc = H0 + CVH (t – T0). Thetracking error is defined as the difference EA = A0 – Acand EH = H0 – Hc and is used for determining the con�trol voltage so as to eliminate the appearing error. Theazimuthal (A) and elevation�angle (H) controls areperformed independently.

The control action in the PI algorithm is deter�mined on the basis of two parameters: the trackingerror (EA and EH) and the integral tracking error (IEAand IEH), where IEA = EA[1] + EA[2] + … + EA[n] andIEH = EH[1] + EH[2] + … EH[n]. The rules of accumu�lation of the integral error and the moments of itszeroing have a very strong effect on the algorithm effi�ciency. In the used realization of the algorithm, theintegral error is zeroed when the instantaneous errorEA or EH exceeds a specified threshold, i.e., for thetime moment k:

if EA[k] < EA max, then IEA[k] = IEA[k – 1] + EA[k], otherwise IEA[k] = 0,

if EH[k] < EH max, then IEH[k] = IEH[k – 1] + EA[k], otherwise IEH[k] = 0,

where IEA[k] and IEH[k] are the integral errors by themoment k.

1 0

1 0A

A ACV

T T

−

=

−

1 0

1 0H

H HCV

T T

−

=

−

366


KAIDANOVSKIY et al.

The integral�error zeroing threshold is generally anadjustable parameter, but it is fixed in an individualobservation session.

UA = –KpAEA – KiAIEA, UH = –KpHEH – KiHIEH.The resulting voltages UA and UH are checked for

the acceptability for the existing electrical drive of theAS and, if necessary, decrease in magnitude to themaximum (minimum) possible value.

The presented tracking algorithm provides the ser�viceability of the control system within the entirerange of changes in the AS coordinates with a requiredspeed of pointing to the tracked source. Figure 8 showsthe plot of the AS movement when tracking a cosmicsource. The horizontal and vertical axes are the timescale in seconds and the current value of the trackingerror in angular seconds, respectively. The plot pre�sents a 25�s history of errors beginning with themoment of the start of tracking of a radio signalsource; i.e., the pointing to the source lasted approxi�mately 3 s, and then tracking was performed. As isseen, the random errors are within 2′′.

5.6.4. Convergent�mirror setting algorithm. Theconvergent�mirror setting algorithm generally corre�sponds to the displacement algorithm. The differenceis that the convergent�mirror drive does not use theprinciple of the hardware speed limitation near thereturn end limiters. A more significant difference isthat, when a displacement (along any coordinate) ter�

minates, the convergent�mirror position is checkedand, if the difference between the actual and calcu�lated positions exceeds the specified value, the ASmoves in the direction of a decrease in the positioningerror. The movement is executed via supplying a startvoltage, which is determined and fixed for each coor�dinate of the convergent mirror. Because of the limiteddigit capacity of the position sensor, the AS displace�ment may exceed that corresponding to the targetposition. For the oscillatory process around the targetposition not to be infinite, the number of iterations islimited.

5.7. Provision of Safe Operation

The measures for safe operation of the AS at theSKUA level are based on the analysis of readings of theposition sensors.

When the return end limiters of the principal andsecondary mirrors are reached, the correspondingreceipts arrive at the WMCS. The arrival of such areceipt blocks the further movement in the directionbehind the return limiter to the nonreturn limiter ofmovement.

The most dangerous situation is observed whenposition sensors fail to operate. A malfunction maymanifest itself as a generation of a value that is impos�sible for a current AS position, e.g., a change by several

Fig. 7. The main window of the WMCS application in the external control mode.



degrees within a fraction of a second. Such readingsare filtered out and are not accepted for generating acontrol voltage.

Another malfunction variant is that the values stopchanging within a time interval that is much longerthan the interval within which a parallel code isformed in the angle�to�code converter. This situationis diagnosed by using the coordinate history. All read�ings of the position sensors are saved within a certaintime interval (in the current realization, it is 1 s). Newreadings are compared to those that were obtained inthe previous session. If the readings coincide, then acomparison with the entire coordinate history is per�formed. The presence of identical readings in theentire history at a control voltage that exceeds a spec�ified threshold (3.5 V in the current realization) indi�cates that the position sensor has failed, and an emer�gency stoppage is executed with a delivery of a noticefor an operator to the WMCS, CPO, and workstation.

6. CONCLUSIONS

In order to solve problems of automatic pointing ofthe AS of an RT, new automatics and control equip�ment manufactured using multiple optoelectronicswitching devices and microcontrollers were devel�oped and fundamentally new software, built accordingto the modular principle, was created. As a result of theperformed work, the reliability of the AS has signifi�cantly increased, and its dynamic characteristics andoperational safety have improved.

The hardware–software complex was built in amanner that easily allows its further upgrading. Thenumerous facilities for visualization, recording, andbuilt�in monitoring ensure the high performancecharacteristics of the system.

This system can be widely used at other operatingradio telescopes and those being under development

owing to its versatility and adaptability to new tasksand techniques.

ACKNOWLEDGMENTS

This work was supported by the Ministry of Educa�tion and Science of the Russian Federation (state con�tract no. 16.518.11.7098).

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20

0

25

–2

–4

–6

6

4

2

15 10 5 0

Error, ang. s

Time, s

Fig. 8. Azimuthal tracking of a radio�signal source.

the rt-32 radio telescope pointing system

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