RASCAL 直升機設計與測試的控制律研究.doc

RASCAL設計與測試的控制律研究Abstract 設計了兩種獨特的控制律,在軍隊/NASA Rotorcraft Aircrew Systems Concepts Airborne Laboratory (RASCAL)的 JUH-60A黑鷹上測試,第一套控制系統(tǒng)使用簡單的速度反饋,來促進RASCAL的飛行控制系統(tǒng)的第一次和后來的飛行品質(zhì),第二套系統(tǒng)由更復雜的模型跟隨結構所組成,兩套系統(tǒng)都得以廣泛的發(fā)展和測試,采用臺式機到飛行”,分析,仿真工具,飛行測試與模型預測的響應很吻合,提供了證據(jù)與自信來發(fā)展未來RASCAL的飛行控制系統(tǒng)將是有效和精確的.Introduction本文描述了RASCAL的兩套控制系統(tǒng),一套的特征是響應反饋,一套是模型跟蹤,RASCAL是一種Sikorsky JUH-60A黑鷹直升機,改裝后用于研究,加裝了一套可編程,高帶寬, full-authority的研究飛行控制系統(tǒng),改裝內(nèi)容包括平行液壓作動器,高性能飛行控制計算機,通過傳遞系統(tǒng)使安全駕駛員把控制作用與有線飛行系統(tǒng)傳遞,右座副駕駛員的位置(周期變距駕駛桿,踏板等)得以移除,代之以側向三軸控制器,以及電子總距控制駕駛桿, RASCAL配置的主要細節(jié)可參考文獻1.RASCAL由軍方與 NASA共同研發(fā),是一種高度靈活的平臺,可用于探索寬范圍的飛行控制,戰(zhàn)場演示,相關系統(tǒng)配置,飛行控制的研究能力是由一系列桌面與地面仿真工具,所支持的,以確保新概念的高效,快速和安全飛行測試, RASCAL 還可以被當作一種變穩(wěn)定的飛行模擬器,文中所述模型跟蹤控制律很適合于此.飛行控制發(fā)展過程臺式電腦到飛行發(fā)展環(huán)境The Army/NASA Rotorcraft Division hasdeveloped a set of software tools enabling designers to take a flight control concept from inception to flight test in an efficient and reliable process.The first step in the process is the selection of a math model of the aircraft dynamics. In the case ofRASCAL, 6-degree-of-freedom (DOF) and 10-DOF linear models of the unaugmented UH-60 at a variety of flight conditions have been previously identified2 from flight test data using the Comprehensive Identification from Frequency Responses (CIFER?3) software. Inaddition, a validated non-linear real-time simulation code (GenHel) is available,4 enabling the robustness of a control system design to be subsequently evaluatedthroughout the entire flight envelope.軍隊/NASA Rotorcraft 分部發(fā)展了一系列工具軟件,來使得設計者的飛行控制構想可以從起初到飛行測試得以有效和可靠的實現(xiàn),第一步是選擇飛行器動力學的數(shù)學模型,在RASCAL, UH-60在各種飛行條件下的未放大的六自由度和10自由度的線化模型被預先辯識,使用頻率響應的綜合辯識軟件,來源于飛行測試數(shù)據(jù).另外一種已經(jīng)驗證過的非線性實時模擬程序被應用,使得控制系統(tǒng)設計的魯棒性能可以在整個飛行包線內(nèi)得以評估.Control loops are then designed around the linear math model using the MATLAB / Simulink? Control system modeling tools and the Control Designers Unified Interface (CONDUIT?) analysis/optimization environment.5 CONDUIT? is used to evaluate and optimize the control law gains to simultaneously meet a broad variety of stability, performance, and handlingquality specifications, as well as certain hardwarelimitations such as actuator rate capabilities.使用MATLAB / Simulink控制系統(tǒng)模型工具和控制設計統(tǒng)一分析優(yōu)化環(huán)境來設計控制回路, CONDUIT被使用于評估和優(yōu)化控制律增益,同時適合寬泛的穩(wěn)定性,性能要求,操縱能力,以及如作動器速率等硬件限制的變化,The resulting closed-loop models may be flown in aworkstation-based, real-time, piloted simulation (theReal-time Interactive Prototype TechnologyIntegration/Development Environment, RIPTIDE) toevaluate qualitative aspects such as control sensitivityand control mode transitions.6 The RIPTIDE facility atNASA Ames is equipped with a panoramic projectiondisplay system and an electromechanical backdrivencyclic controller to provide additional fidelity to thisotherwise low-cost fixed-base piloted simulation tool.結果的閉環(huán)模型放入一個基于工作站的實時,用模擬駕駛(實時交互技術,集成/研發(fā)的環(huán)境)來評估性能,比如控制敏度,控制模式轉換, RIPTIDE設施裝備有全景的目標展示系統(tǒng)和機械電子的變距控制器,來提供更多的仿真度給這個低費用,固定駕駛模擬器.Final checkout and pilot familiarization with thecontrol laws is accomplished using the RASCALDevelopment Facilitys hardware-in-the-loopsimulator,7 which includes the flight control computer,evaluation pilot interface, and high-fidelity real-timenon-linear simulations of the RASCAL research flightcontrol actuators, sensors, and UH-60 dynamics.最終的檢查和駕駛員熟悉控制律已經(jīng)完成,使用RASCAL的人在回路設備,包括飛行控制計算機,評估駕駛界面, RASCAL研究的飛行控制作動器,傳感器和UH-60動力學的高仿真度,實時非線性模擬.Prior to approval of the flight control software forrelease to the aircraft, it undergoes a controlled test andevaluation sequence in the Development Facility (DF),after which it is loaded into the aircrafts flight controlcomputer. Once the basic functionality of the softwarehas been checked in flight, the flight control laws arevalidated by recording closed-loop piloted doubletsand/or frequency sweeps. These flight test data are thenanalyzed using CIFER? to extract frequency responses.The flight test time histories and frequency responsescan then be compared to the responses predicted by thesimulation model.預先批準把飛行控制軟件準用于飛行器,在Development Facility (DF),經(jīng)歷了一個控制測試和評估順序,然后才安裝入飛機的飛行控制計算機,一旦軟件的基本功能在飛行中得到檢查,飛行控制律得以 驗證通過記錄的閉環(huán)或掃頻,然后用CIFER軟件來分析這些數(shù)據(jù),提取出頻率響應,然后可以把飛行測試中的時間歷程和頻率響應和之前模擬模型的作比較.RASCAL is the first in-house Army/NASAprogram to utilize the full suite of desktop-to-flighttools. However, the preceding description of thedesktop-to-flight process has been proven out in severalrecent flight vehicle development activities conductedwith industry partners, including the Kaman AerospaceBroad-area Unmanned Responsive ResupplyOperations (BURRO) 6000-lb unmanned helicopter,8the Northrop-Grumman/Schweitzer Fire Scout VerticalTake-off Unmanned Aerial Vehicle (VTUAV),9 and theMicrocraft iStar 9-inch diameter unmanned vehicle.10RASCAL是首個軍隊/ NASA的室內(nèi)項目,利用整套桌面到飛行的工具,然而, 前述桌面到飛行過程,最近已經(jīng)由工業(yè)伙伴所承擔的的幾個飛行器發(fā)展活動所證明是合適的,包括BURRO 6000-lb無人直升機,諾斯-格魯曼垂直起飛無人飛行器,微航-9英寸,無人機.RASCAL Flight Control ComputerThe RASCAL Research Flight Control ComputerAssembly (RFCCA) is divided into two physicallysegregated elements: a Flight Control Computer (FCC)and a Servo Control Unit (SCU). This architectureallows a great deal of freedom in the development andtesting of new flight control laws, while protecting theaircraft and systems from any unforeseen anomalies inthose control laws, or in system operation. A summaryof the RFCCA is provided here, while greater detail isavailable in Ref. 1.RASCAL 飛行控制計算機RASCAL 研究飛行控制計算機組合(RFCCA)包括兩個隔離的物理單元:飛行控制計算機(FCC),伺服控制單元(SCU).這種結構在發(fā)展和測試新飛行控制律時,允許許多空間自由,從而在控制律或者系統(tǒng)操作發(fā)生未料的異常情況下可以保護飛行器和系統(tǒng), RFCCA的總結提供于此,其它細節(jié)可參考文獻1.The SCU is a dualized system that comprises theRFCCAs interface to the aircraft and is responsible formonitoring the RFCS for safe operation. The SCUoperates with the assumption that a hardware failure,sensor failure or flight control law failure could occur atany time, and continuously monitors a wide variety ofparameters. The SCUs monitoring software detectsand captures failures that would generate unacceptablylarge flight control transients, and in such an eventreverts the aircraft to safety pilot control in less than100ms. The design criteria for the monitors wereestablished through piloted simulation researchconducted at Ames using the Vertical MotionSimulator; details may be found in Ref. 11. Functionaltesting, fine-tuning, and validation of the monitors wasaccomplished in the RASCAL DF as well as on theaircraft.SCU是一種雙核系統(tǒng),把RFCCA的界面整合入飛機,負責監(jiān)控RFCS的安全操作, SCU的操作假定硬件失效,傳感器失效,或者飛行控制律失效,會在任何時間發(fā)生,持續(xù)監(jiān)控大量的參數(shù). SCU的監(jiān)控軟件察覺和捕獲失效,將產(chǎn)生不可接受的大的飛行控制瞬變,在這樣的事件中.不到100毫秒內(nèi),恢復到安全的駕駛控制狀態(tài),監(jiān)控的設計標準是通過駕駛模擬研究建立的, 在Ames使用豎向機動模擬,細節(jié)可參考文獻11,功能測試,以及監(jiān)控的批準都是在RASCAL DF與飛機上完成的.The FCC hosts the flight control law code. TheFCC is a single-channel system. A basic set of softwareelements provides a standardized interface to sensordata, pilot inputs and aircraft actuator outputs forimplementation of flight control laws. This allows theflight control law development to take place at a highlevel, without requiring knowledge of theimplementation details of each system interface. Forexample, commands generated by the FCC are in “pilotaxes”, i.e. inches of equivalent UH-60 inceptordisplacement, which the SCU translates through asoftware representation of the Black Hawksmechanical mixing box into “servo axes”, i.e. inches ofdisplacement of the forward, aft and lateral researchservos driving the UH-60 primary servos (and in turnthe swash plate) as well as the tail research servo thatdrives the tail rotor primary servo. Because thetranslation from pilot axes to servo axes is handled inthe SCU, it is transparent to the flight controldeveloper, who needs only to be concerned withproducing control law commands in “pilot axes”.FCC是飛行控制律程序的主機,是一個單通道的系統(tǒng),基本的軟件單元提供傳感數(shù)據(jù)標準的界面,駕駛輸入和飛機輸出來實現(xiàn)飛行控制律,這就使得飛行控制律可以發(fā)展到一個很高的階,不需要每個系統(tǒng)界面的實現(xiàn)所需要的細節(jié)知識.比如,由FCC產(chǎn)生的命令在駕駛軸,也就是,離初始位移幾英寸的距離, SCU通過表示飛機機械特性的軟件把駕駛軸轉換為伺服軸,也就是,朝前幾英寸,尾部和側向的研究伺服駕駛UH-60主要的伺服機構,與尾部研究伺服駕駛尾旋轉主要伺服一樣,因為把駕駛軸轉換為伺服軸是需要提交SCU完成,很顯然,對于飛行控制的發(fā)展,只需要考慮駕駛軸中的過程控制律,Baseline Control Law DevelopmentAn initial set of control laws was designed expresslyfor the first flight and system qualification phase of theRASCAL RFCS. These “baseline” control laws wereintentionally simple, consisting of only the minimumelements needed to provide basic stability augmentationin a manner compatible with the RASCAL sidestickinceptor. The rationale for using simple control lawsfor the earliest work on the aircraft was that anyanomalous behavior of the overall RFCS would beeasier to identify, and comparison of the aircraftresponse to that of the simulation model would be morestraightforward.基線控制律研究.初始的控制律設計明確是為RASCAL RFCS首次飛行和系統(tǒng)限制階段,這些基線控制律是有意簡化,由最小單元組成,需要提供基本穩(wěn)定放大,采用一種和RASCAL邊初始兼容的方式,使用簡單控制律進行飛行器的早期工作的基本原理是RFCS任何異常行為能夠容易被識別,比較飛機的響應和模擬模型也會更直接簡單.The baseline control laws therefore included onlyrate feedbacks to pitch, roll and yaw; collective was“direct-drive” from the RASCAL inceptor. Low-gainintegrators in pitch, roll and yaw provided trim followup,which slowly trimmed the sidestick to centerposition as the aircraft trim state varied with flightcondition. Synchronization of the control law outputwith the safety pilot controls was provided to preventtransient behavior at the instant of RFCS engagement.Figure 2 illustrates the architecture of the pitch channel,which is representative of the roll and yaw axes. which is representative of the roll and yaw axes基線控制律因此僅包括俯仰,滾轉,偏航的速度反饋,總距是從RASCAL inceptor開始的”直接駕駛”,采用低增益積分器對俯仰,滾轉,偏航,提供剪裁,慢慢的從邊到中間位置,當飛機裁剪狀態(tài)隨著飛行條件而變化,安全駕駛控制與控制律輸出的同步性, 在RFCS的瞬間,提供了瞬態(tài)行為的阻止,圖2說明了俯仰通道的組成,同樣代表了滾轉,偏航通道.The control laws included limiters on authority,rate, and the trim integration; the rate limits, as well asmost system gains, were manually adjustable in-flightvia the RASCAL cockpits Control/Display Unit(CDU).控制律包括權限,速率,和微調(diào)積分, 速率限制和其他大部分系統(tǒng)增益一樣,在飛行中手動可調(diào),通過RASCAL駕駛員座艙的控制/展示單元.To accurately represent the dynamics of the totalsystem, it is essential to include the high frequencyelements. In the case of helicopters, the delayintroduced by these elements (in particular, the mainrotor) is a key limiting factor for the achievablebandwidth of the flight control system. 12 Thecontributing elements in the RASCAL RFCS are listedin Table 1.為了精確表現(xiàn)全部系統(tǒng)的動力學,有必要包括高頻單元,在直升機中,這些單元(特別地,主軸)所產(chǎn)生的延時,是飛行控制系統(tǒng)可達到帶寬關鍵的限制因素,表1列出了主要貢獻的單元.The initial values of the control system gains weredesigned using total system models of the aircraft at thehover, 80 knot and 130 knot flight conditions. Thesystem models included 6-DOF linear models of theUH-60 rigid-body dynamics, with second-ordernonlinear models of the RASCAL RFCS actuators andUH-60 primary actuators, and Pad approximations ofthe sensor and computational delays. Models of thesensor filters to be used in the aircraft were alsoincluded. CONDUIT was used to analyze the brokenloop,on-axis frequency responses for each of the threeflight conditions to select the rate feedback gains.Modest crossover frequencies in the range of 2 3rad/sec were selected to avoid excitation of unmodeledrotor and structural modes, while attempting tomaintain the MIL-HDBK-1797 stability marginguidelines of 45 deg phase margin and 6 dB gain margin.13 A single set of gains was selected to cover all flight conditions.使用飛機的完全系統(tǒng)模型來設計控制系統(tǒng)增益的初始值,盤旋狀態(tài),80130 海里/小時,系統(tǒng)模型包括6自由度UH-60剛體動力學線性模型, RASCAL RFCS作動器和UH-60主作動器采用二階非線性模型, Pad近似傳感器與計算延遲,還包括飛機的傳感器濾波, CONDUIT被使用于分析三種飛行條件下的破環(huán),在軸的頻率響應,來選擇速度反饋增益, 2 3rad/sec范圍內(nèi)的交叉頻率選擇來避免非建模旋轉和結構模態(tài)的激勵,當試圖維護MIL-HDBK-1797的穩(wěn)定裕度,45度相位裕度和6 dB幅值裕度,一個簡單的增益被用于覆蓋所有的飛行條件.Control authority limits were set to approximate thecontrol throws of the UH-60s mechanical flightcontrols, although in practice the SCU control limitmonitors were reached first. The trim integrators werelimited to prevent wind-up; the limits were chosen tomaintain 20% control margin, at the expense of reducedtrim authority. The resulting gains were, incidentally, agood approximation of the responses of the ratefeedbackportion of the UH-60 stability augmentationsystem.控制權限被用于近似UH-60的飛行控制,雖然實際上, SCU的控制限制監(jiān)控器已經(jīng)首先到達,修剪積分器被限制來阻止wind-up;限制被選擇于維持20%的控制裕度,為此造成減小修剪權限的損失,結果增益是,偶然的, UH-60穩(wěn)定放大系統(tǒng)的速度反饋部分的響應的一個很好近似.During the course of flight testing, a lightly-dampedaeroservoelastic mode at about 6.5 Hz was observed inforward flight with sustained load factor, such as duringturns and pull-ups. The pitch rate sensor filter wassubsequently adjusted to a lower cutoff frequency (3Hz) to increase attenuation at the modal frequency.This eliminated the resonance.在飛行測試過程中,在前向飛行中,一個輕微-阻尼的有過載因素的6.5 Hz氣動伺服彈性模型可以觀察到,比如說在轉彎和起飛, 當達到模型頻率時,俯仰率傳感器濾波隨后得以調(diào)整到一個更低的截止頻率來增加衰減,這樣就消除了共振.Early in the test program, records of piloted doubletmaneuvers were obtained and analyzed using CIFERto check the accuracy of the model predictions. Asseen in Figure 3, the modeled response is a reasonablematch to the flight-identified response, despite thelimited frequency content of the doublet control input.Piloted frequency sweeps were also obtained and theidentified frequency responses generally matched themodel predictions well. Once the basic systemperformance was validated, the focus of the project wasplaced on bringing the more advanced set of controllaws onto the aircraft.在測試任務的早期,使用CIFER得到并分析記錄下的piloted doublet(雙座?)機動,用于檢查預先模型的精確性,如圖3所示,模擬的響應和飛行中辯識的響應相信是匹配的,盡管限制頻率是雙控制輸入,遙控掃頻同樣得到,辯識的頻率響應與預先模型一般很好地匹配,一旦基本系統(tǒng)的性能得到確認,項目的重點將是把更先進的控制律置于飛機上.Advanced Control Law DevelopmentRASCALs advanced control laws were developedby Boeing Helicopter, and have Advanced Digital-Optical Control System (ADOCS) and RAH-66Comanche heritage.14,15,16 The control law softwarewas generated using Boeing-proprietary pictures-tocodealgorithms. That code has, to date, been utilizedin the RASCAL flight control computer, but the controllaws have also been ported to Simulink? for parallel usein the projects desktop-to-flight tools.These control laws were intended to be a robust andstable foundation for system validation, and to provideflexibility for future development;1 they are of anexplicit model-following architecture.先進控制律開發(fā).RASCAL的先進控制律是由波音直升機公司開發(fā)的,有先進的數(shù)字光學控制系統(tǒng), (ADOCS) 和 RAH-66科曼奇血統(tǒng),控制律軟件是由波音公司的圖像到代碼算法所產(chǎn)生的,那些代碼被用于RASCAL飛行控制計算機,到期了,但是控制律被轉入Simulink,從而可以平行使用項目的”臺式機到飛行”工具, 這些控制律對于系統(tǒng)批準是趨向于穩(wěn)健和穩(wěn)定的基礎,并為將來的開發(fā)提供彈性,他們是一個明確的模型-跟蹤架構.Model-Following ConceptA brief overview of the characteristics of a model followingcontrol system is provided here to help thoseunfamiliar with the concepts understand the discussionthat follows; much more thorough treatments may befound in References 17 and 18. Model-followingcontrol systems are typically comprised of feedbackcompensation H(s) to stabilize the vehicle and rejectdisturbances, a feedforward element F(s) consisting ofan inverse model of the aircraft dynamics P-1(s)together with a model of the feedback compensationH(s), and a command model M(s). These elements areillustrated conceptually in Figure 4. For purposes ofanalysis, the architecture of Figure 4A can be reorganizedas shown in Figure 4B. Combined, thestabilization and feedforward portions produce atransfer function of unity:模型-跟蹤概念這里是模型-跟蹤控制系統(tǒng)特性一個簡短的介紹,以幫助不熟悉此概念的理解以下的討論,更多徹底的處理方式在文獻17,18.模型-跟蹤控制系統(tǒng)主要的是由反饋補償H(s)來穩(wěn)定飛機和阻止干擾,前饋單元F(s)由飛機動力學的反轉模型P-1(s)和反饋補償H(s),指令模型M(s) 所組成,這些單元在圖4中得到概念性闡述.為了分析,圖4A可以被重新組合變?yōu)閳D4B,通過組合,穩(wěn)定和前饋部分產(chǎn)生了一個一致傳遞函數(shù).Assuming a perfect and realizable inverse model of theaircraft P-1(s) is available, the vehicle response q willexactly track the model response qm. In practice, it isnot feasible to attempt to cancel the high-frequencydynamics such as those associated with the rotor andactuators. At the same time, low-frequencycharacteristics such as aerodynamic trim effects orweight or center of gravity effects that are notcompletely cancelled can be easily suppressed by thestabilization loop. Therefore, simple first- or second orderrepresentations usually suffice for the inversemodel.假定一個完整而可實現(xiàn)的反轉模型P-1(s)是可以利用的,飛行器的響應q將完全跟蹤模型的響應qm,實際上,取消高頻動態(tài)比如與轉軸和作動器有關的,并不可行,同時,低頻特性比如氣動力剪裁效果或者重力或質(zhì)心,沒有被完全取消,能夠容易的被穩(wěn)定回路所抑制,因此,簡單的第一或者第二階表現(xiàn)通常就可以滿足翻轉模型的需要了.Because the aircrafts principal inherent modes arecancelled, the desired dynamic response may beintroduced as the command model M(s). From Figure 4,it is evident that the model-following architectureprovides a high level of modularity and lends itself toincremental evolution and development. Changing acommand model does not necessitate changing thefeed-forward shaping, or the feedback stabilizationelements; adding feedback loops or control structures isstraightforward. These attributes make this architecturedesirable for a flying laboratory such as RASCAL, inwhich the flight control requirements are expected toevolve and change from project to project. The inflightsimulation features of RASCAL would mainlyrely on this model-following control law structure.因為飛機的主要的固有模態(tài)被取消,需要的動態(tài)響應可以被介紹做為指令模型M(s),從圖4可見,顯然,模型跟蹤架構提供了高水平的模塊,并且給他自己能夠繼續(xù)演化與發(fā)展,改變一個指令模型并不需要改變前饋模型或者反饋穩(wěn)定單元增加反饋回路或者控制結構是直接的方法,這些屬性使得此架構需要如RASCAL一樣的空中實驗室,在里面飛行控制需求不斷隨著任務的改變而變化, RASCAL的飛行中模擬特性將主要的依靠這個模型跟蹤控制律結構.Figure 5 illustrates the basic implementation of themodel-following concepts shown in Figure 4 into theRFCS pitch channel.The current RASCAL model-following control laws(MFCL) reflect standard features developed forrotorcraft over the past decade. They providehover/low-speed control modes of pitch and rollattitude-command, attitude-hold stabilization (ACAH),together with heading rate command, direction(heading) hold stabilization (RCDH). These controlcharacteristics are implemented as simple first- andsecond-order linear command models. The commandmodels produce first-order angular rate responses andsecond-order attitude responses to pilot inputs. Theresulting rate and attitude commands drive t