Servomechanism for steering of antenna One of the earliest e arliest applicaons of radar tracking was for an-aircra an-aircra re control, rst with guns and later with missiles. Today many civilian applicaons eist as well, such as satellite tracking radars, navigaonaiding radars etc. The radar scene include the radar itself, itself, a target, and the transmi!ed wave wave form that travels to the target and "ack, informaon a"out the target#s spaal posion is rst o"tained "y measuring the changes in the "ack sca!ered wave-form relave to the transmi!ed waveform. waveform. The me shi provides informaon a"out the target#s range, the fre$uency shi provides informaon a"out the target radial#s radial#s velocity, and the received voltage magnitude and phase provide informaon a"out the target#s angle %n the typical radar applicaon, it is necessary to point the radar antenna toward the target and follow its movements. The radars sensor detects the error "etween the antenna ais and the target, and directs the antenna to follow the target. The servomechanism for steering the antenna in response to commands from radar sensor is considered here. The antenna is designed for two independent angular moons, one a"out the vercal ais in which the a&imuth angle is varied, and the other a"out the hori&ontal hori&ontal ais in which the elevaon angle is varied. The servomechanism for steering the antenna is descri"ed "y two controlled controlled varia"les-the a&imuth angle angle ' and the elevaon angle angle (, of the target. The feed"ack control pro"lem involves involves error self-nulling under condions of distur"ances "eyond our control )such as wind power* The control system for steering of antenna can "e treated as two independent system-the a&imuth-angle Servomechanism and the elevaon-angle servo mechanism. This is "ecause the interacon e+ect are usually small. The operaonal diagram of the a&imuth-angle servomechanism is shown in g... the steering command from the radar sensor which corresponds to the target a&imuth angle is compared with the a&imuth angle of the antenna ais. The occurrence of the a&imuth angle error causes an error signal to pass through the amplier, which increases the angular velocity of the servomotor in a direcon towards an error reducon. %n the scheme of g .. the measurement and processing of signals )calculaon of control signal* is digital in nature and is "ased on proporonal control logic. igure ./a gives the funcon diagram of the control system. system. 0 simple model of the load )antenna* on the motor is shown in g ./". the moment moment of inera 1 and the viscous rcon coe2cient coe2cient ' are the parameters parameters of the assumed model. The nominal load is included the plant model of the control design. The main distur"ance input is the deviaon of the load from the nominal esmated value as the result of uncertainty in our esmate, e+ect of wind power, etc. %n the tracking system of g ./a, the occurrence of error causes the motor to the rotate in a direcon favouring favouring the dissoluon of error. error. 3ote that the components of our system system cannot respond instantancously instantancously since any real world system cannot go from one energy level to another in &ero me. Thus, in any real world system there is some kind of dynamic lagging "ehavior "etween the input and the output. %n the servo system of g ./a, the control acon on the occurrence of the deviaon of the controlled output from the desired desired value )occurrence of error * will "e delayed "y cumulave dynamic lags of the sha angle encoder, encoder, digital computer and digital to analog converter, converter, power amplier and the
servomotor with load. 4ventually, however, the trend of the controlled varia"le deviaon from the desired value will "e reserved "y the acon of the amplier output on the rotaon of the motor, returning the controlled varia"le towards the desired value. 3ow, if a strong correcon )high amplier gain* is applied )which is desira"le from the point of view of control system performance ,e.g, strong correcon improves the speed of response. The controlled varia"le overshoots the desired value )the 5run-out6 of the motor towards an error with the opposite rotaon*, causing a reversal in the alge"raic sign of the system error. 7nfortunately, "ecause of system dynamic lags, a reversal of correcon does not occur immediately and the amplier output )acng on 5old6 informaon* is now actually driving the controlled varia"le in the same direcon as it is already going, rather than opposing its ecursions, leading to the a larger deviaon. 4ventually, the reversed does cause a reversed correcon "ut the controlled varia"le overshoots the desire value in the opposite direcon and the correcon is again in the wrong direcon. The controlled varia"le is thus driven alternavely in the opposite direcon "efore it se!les to an e$uili"rium condion. This oscillatory state is unaccepta"le as the "ehaviour of the antenna steering servomechanism. The considera"le amplier gain, which is necessary if the high accuracies are to "e o"tained, aggravates the descri"ed unfavoura"le phenomenon. The occurrence of these oscillatory e+ects can "e controlled "y the applicaon of special compensaon feed"ack. 8hen a signal proporonal to motor#s angular velocity )called the rate signal* is su"tracted from the error signal )g ./c* the "raking process starts sooner "efore the error reaches a &ero value. The 5loop within a loop6)velocity feed"ack system em"edded within a posion feed"ack system* conguraon uli&ed in this applicaon is a classical scheme called cascade control in the process eld and minor-loop feedback ( or state variable feedback ) in servomechanisms.
Open loop-Servomechanism untuk kemudi antena Salah satu aplikasi awal pelacakan radar adalah untuk pengendalian ke"akaran an-pesawat, pertama dengan sen1ata dan kemudian dengan rudal. Saat ini "anyak aplikasi sipil ada 1uga, seper radar pelacakan satelit, navigasi mem"antu radar dll 0degan radar termasuk radar itu sendiri, target, dan "entuk gelom"ang yang ditransmisikan melalui per1alanan ke target dan kem"ali dengan informasi tentang posisi spasial target pertama diperoleh dengan mengukur peru"ahan dalam "entuk gelom"ang yang kem"ali terse"ar secara relaf terhadap gelom"ang yang ditransmisikan. 8aktu pergeseran menyediakan informasi tentang "er"agai target, pergeseran frekuensi mem"erikan informasi tentang kecepatan radial target, dan "esarnya tegangan yang diterima dan fase mem"erikan informasi tentang sudut target . 9alam aplikasi radar yang khas, maka perlu untuk menun1ukkan antena radar ke arah target dan mengiku gerakannya. :adar sensor mendeteksi kesalahan antara sum"u antena dan target, dan mengarahkan antena untuk mengiku target. Servomechanism "erfungsi untuk mengarahkan antena dalam menanggapi perintah dari sensor radar. 0ntena yang dirancang untuk dua gerakan sudut "e"as , satu tentang sum"u verkal di mana sudut a&imuth "ervariasi, dan yang lainnya tentang sum"u horisontal di mana sudut elevasi "ervariasi. Servomechanism 1uga "erfungsi untuk mengarahkan antenna yang digam"arkan oleh dua varia"le control sudut a&imuth ' dan sudut elevasi ( dari target. ;asalah kontrol umpan "alik meli"atkan kesalahan diri nulling dalam kondisi gangguan di luar kendali kita )seper tenaga angin* Sistem kontrol kemudi untuk antena dapat diperlakukan se"agai dua sistem "e"as. Servomechanism a&imuth-angle dan mekanisme elevasi sudut servo.
e"an nominal termasuk model tanaman desain kontrol. %nput gangguan utama adalah deviasi dari "e"an dari esmasi nilai nominal se"agai hasil dari kedakpasan dalam perkiraan kami, pengaruh tenaga angin, dll 9alam sistem pelacakan ara ./a, ter1adinya kesalahan sehingga menye"a"kan motor untuk memutar
dalam arah dapat mendukung pem"u"aran kesalahan. ?erhakan "ahwa komponen dari sistem kami dak "isa menanggapi secara instant karena dalam sistem dunia nyata energi dak "isa pergi dari satu ngkat ke ngkat yang lain dalam waktu nol. 9engan demikian, dalam sistem dunia nyata ada "e"erapa 1enis perilaku lagging dinamis antara input dan output. 9alam sistem servo ara ./a, aksi kontrol pada ter1adinya penyimpangan output dikendalikan dari nilai yang diinginkan )ter1adinya error* akan ditunda oleh kelam"anan dinamis kumulaf encoder sudut poros, komputer digital dan digital ke analog converter, power amplier dan servomotor dengan "e"an. 0khirnya, "agaimanapun 1uga tren deviasi varia"el dikendalikan dari nilai yang diinginkan akan disediakan oleh aksi keluaran penguat pada putaran motor,di kem"alikan oleh controlled varia"le terhadap nilai yang diinginkan. Sekarang, 1ika koreksi yang kuat )gain amplier yang nggi* diterapkan )yang diinginkan dari sudut pandang kiner1a sistem kontrol, misalnya, koreksi yang kuat meningkatkan kecepatan respon. @aria"el kendali lampaui nilai yang diinginkan )yang Arun-out Amotor terhadap kesalahan dengan rotasi "erlawanan*, menye"a"kan pem"alikan dalam tanda al1a"ar dari kesalahan sistem. Sayangnya, karena sistem kelam"atan dinamis, pem"alikan koreksi dak ter1adi segera dan output amplier )"erndak lama atas %nformasi* kini "enar"enar mengemudikan controlled varia"le dalam arah yang sama seper yang sudah ter1adi, daripada menentang kun1ungan nya, yang mengarah ke penyimpangan yang le"ih "esar. 0khirnya, varia"le kendali ter"alik sehingga dak menye"a"kan koreksi ter"alik tetapi varia"el yang dikontrol sehingga dapat melampaui nilai keinginan dalam arah yang "erlawanan dan koreksi lagi ke arah yang salah. 9engan demikian dorongan alternaf dalam arah yang "erlawanan se"elum mengendap ke kondisi ekuili"rium ini dak dapat diterima se"agai perilaku servomechanism antena kemudi. ?enguat yang cukup menguntungkan diperlukan 1ika akurasi nggi tetapi akan memper"uruk fenomena yang dak menguntungkan. Ter1adinya efek osilasi dapat dikontrol oleh aplikasi umpan "alik yang "erkompensasi khusus. Beka sinyal se"anding dengan kecepatan sudut motor )dise"ut sinyal rate* dikurangi dari sinyal kesalahan )gam"ar ./c* proses pengereman dimulai le"ih cepat se"elum kesalahan mencapai nilai nol. The Aloop dalam loopA )sistem umpan "alik kecepatan tertanam dalam sistem umpan "alik posisi* kongurasi yang digunakan dalam aplikasi ini adalah skema klasik dise"ut kontrol cascade di "idang proses kecil-umpan "alik )atau negara umpan "alik varia"el* dalam ser vomechanisms.
The system to "e controlled has C inputs )steering and acceleraonD"raking* and C controlled outputs )heading and speed*. The two command inputs are the direcon of highway and speed limits with tra2c signal. 0 "lock diagram of this inputs, two outputs is shown in g .E System with more than one controlled outputs and command inputs are called mulvaria"le or mul input , mul output );%;O* System. On the other hand, in single input, single output )S%SO* system, are single output are controlled "y single input. %n mulvaria"le system, an input that is meant to control a parcular output, also a+ects the other controlled outputs. This conpling is called interacon. The automo"ile driving system is a ;%;O system. 8e can decouple the system into C system for the purpose of design "ecause the interacon is negligi"le. Steering control a+ect the heading and not speed and accelerator control a+ect the speed and not the heading.
