RASCAL 直升机设计与测试的控制律研究.doc

RASCAL设计与测试的控制律研究Abstract 设计了两种独特的控制律,在军队/NASA Rotorcraft Aircrew Systems Concepts Airborne Laboratory (RASCAL)的 JUH-60A黑鹰上测试,第一套控制系统使用简单的速度反馈,来促进RASCAL的飞行控制系统的第一次和后来的飞行品质,第二套系统由更复杂的模型跟随结构所组成,两套系统都得以广泛的发展和测试,采用台式机到飞行”,分析,仿真工具,飞行测试与模型预测的响应很吻合,提供了证据与自信来发展未来RASCAL的飞行控制系统将是有效和精确的.Introduction本文描述了RASCAL的两套控制系统,一套的特征是响应反馈,一套是模型跟踪,RASCAL是一种Sikorsky JUH-60A黑鹰直升机,改装后用于研究,加装了一套可编程,高带宽, full-authority的研究飞行控制系统,改装内容包括平行液压作动器,高性能飞行控制计算机,通过传递系统使安全驾驶员把控制作用与有线飞行系统传递,右座副驾驶员的位置(周期变距驾驶杆,踏板等)得以移除,代之以侧向三轴控制器,以及电子总距控制驾驶杆, RASCAL配置的主要细节可参考文献1.RASCAL由军方与 NASA共同研发,是一种高度灵活的平台,可用于探索宽范围的飞行控制,战场演示,相关系统配置,飞行控制的研究能力是由一系列桌面与地面仿真工具,所支持的,以确保新概念的高效,快速和安全飞行测试, RASCAL 还可以被当作一种变稳定的飞行模拟器,文中所述模型跟踪控制律很适合于此.飞行控制发展过程台式电脑到飞行发展环境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.军队/NASA Rotorcraft 分部发展了一系列工具软件,来使得设计者的飞行控制构想可以从起初到飞行测试得以有效和可靠的实现,第一步是选择飞行器动力学的数学模型,在RASCAL, UH-60在各种飞行条件下的未放大的六自由度和10自由度的线化模型被预先辩识,使用频率响应的综合辩识软件,来源于飞行测试数据.另外一种已经验证过的非线性实时模拟程序被应用,使得控制系统设计的鲁棒性能可以在整个飞行包线内得以评估.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控制系统模型工具和控制设计统一分析优化环境来设计控制回路, CONDUIT被使用于评估和优化控制律增益,同时适合宽泛的稳定性,性能要求,操纵能力,以及如作动器速率等硬件限制的变化,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.结果的闭环模型放入一个基于工作站的实时,用模拟驾驶(实时交互技术,集成/研发的环境)来评估性能,比如控制敏度,控制模式转换, RIPTIDE设施装备有全景的目标展示系统和机械电子的变距控制器,来提供更多的仿真度给这个低费用,固定驾驶模拟器.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.最终的检查和驾驶员熟悉控制律已经完成,使用RASCAL的人在回路设备,包括飞行控制计算机,评估驾驶界面, RASCAL研究的飞行控制作动器,传感器和UH-60动力学的高仿真度,实时非线性模拟.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.预先批准把飞行控制软件准用于飞行器,在Development Facility (DF),经历了一个控制测试和评估顺序,然后才安装入飞机的飞行控制计算机,一旦软件的基本功能在飞行中得到检查,飞行控制律得以 验证通过记录的闭环或扫频,然后用CIFER软件来分析这些数据,提取出频率响应,然后可以把飞行测试中的时间历程和频率响应和之前模拟模型的作比较.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是首个军队/ NASA的室内项目,利用整套桌面到飞行的工具,然而, 前述桌面到飞行过程,最近已经由工业伙伴所承担的的几个飞行器发展活动所证明是合适的,包括BURRO 6000-lb无人直升机,诺斯-格鲁曼垂直起飞无人飞行器,微航-9英寸,无人机.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 飞行控制计算机RASCAL 研究飞行控制计算机组合(RFCCA)包括两个隔离的物理单元:飞行控制计算机(FCC),伺服控制单元(SCU).这种结构在发展和测试新飞行控制律时,允许许多空间自由,从而在控制律或者系统操作发生未料的异常情况下可以保护飞行器和系统, RFCCA的总结提供于此,其它细节可参考文献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是一种双核系统,把RFCCA的界面整合入飞机,负责监控RFCS的安全操作, SCU的操作假定硬件失效,传感器失效,或者飞行控制律失效,会在任何时间发生,持续监控大量的参数. SCU的监控软件察觉和捕获失效,将产生不可接受的大的飞行控制瞬变,在这样的事件中.不到100毫秒内,恢复到安全的驾驶控制状态,监控的设计标准是通过驾驶模拟研究建立的, 在Ames使用竖向机动模拟,细节可参考文献11,功能测试,以及监控的批准都是在RASCAL DF与飞机上完成的.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是飞行控制律程序的主机,是一个单通道的系统,基本的软件单元提供传感数据标准的界面,驾驶输入和飞机输出来实现飞行控制律,这就使得飞行控制律可以发展到一个很高的阶,不需要每个系统界面的实现所需要的细节知识.比如,由FCC产生的命令在驾驶轴,也就是,离初始位移几英寸的距离, SCU通过表示飞机机械特性的软件把驾驶轴转换为伺服轴,也就是,朝前几英寸,尾部和侧向的研究伺服驾驶UH-60主要的伺服机构,与尾部研究伺服驾驶尾旋转主要伺服一样,因为把驾驶轴转换为伺服轴是需要提交SCU完成,很显然,对于飞行控制的发展,只需要考虑驾驶轴中的过程控制律,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.基线控制律研究.初始的控制律设计明确是为RASCAL RFCS首次飞行和系统限制阶段,这些基线控制律是有意简化,由最小单元组成,需要提供基本稳定放大,采用一种和RASCAL边初始兼容的方式,使用简单控制律进行飞行器的早期工作的基本原理是RFCS任何异常行为能够容易被识别,比较飞机的响应和模拟模型也会更直接简单.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基线控制律因此仅包括俯仰,滚转,偏航的速度反馈,总距是从RASCAL inceptor开始的”直接驾驶”,采用低增益积分器对俯仰,滚转,偏航,提供剪裁,慢慢的从边到中间位置,当飞机裁剪状态随着飞行条件而变化,安全驾驶控制与控制律输出的同步性, 在RFCS的瞬间,提供了瞬态行为的阻止,图2说明了俯仰通道的组成,同样代表了滚转,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).控制律包括权限,速率,和微调积分, 速率限制和其他大部分系统增益一样,在飞行中手动可调,通过RASCAL驾驶员座舱的控制/展示单元.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.为了精确表现全部系统的动力学,有必要包括高频单元,在直升机中,这些单元(特别地,主轴)所产生的延时,是飞行控制系统可达到带宽关键的限制因素,表1列出了主要贡献的单元.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.使用飞机的完全系统模型来设计控制系统增益的初始值,盘旋状态,80130 海里/小时,系统模型包括6自由度UH-60刚体动力学线性模型, RASCAL RFCS作动器和UH-60主作动器采用二阶非线性模型, Pad近似传感器与计算延迟,还包括飞机的传感器滤波, CONDUIT被使用于分析三种飞行条件下的破环,在轴的频率响应,来选择速度反馈增益, 2 3rad/sec范围内的交叉频率选择来避免非建模旋转和结构模态的激励,当试图维护MIL-HDBK-1797的稳定裕度,45度相位裕度和6 dB幅值裕度,一个简单的增益被用于覆盖所有的飞行条件.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.控制权限被用于近似UH-60的飞行控制,虽然实际上, SCU的控制限制监控器已经首先到达,修剪积分器被限制来阻止wind-up;限制被选择于维持20%的控制裕度,为此造成减小修剪权限的损失,结果增益是,偶然的, UH-60稳定放大系统的速度反馈部分的响应的一个很好近似.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.在飞行测试过程中,在前向飞行中,一个轻微-阻尼的有过载因素的6.5 Hz气动伺服弹性模型可以观察到,比如说在转弯和起飞, 当达到模型频率时,俯仰率传感器滤波随后得以调整到一个更低的截止频率来增加衰减,这样就消除了共振.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.在测试任务的早期,使用CIFER得到并分析记录下的piloted doublet(双座?)机动,用于检查预先模型的精确性,如图3所示,模拟的响应和飞行中辩识的响应相信是匹配的,尽管限制频率是双控制输入,遥控扫频同样得到,辩识的频率响应与预先模型一般很好地匹配,一旦基本系统的性能得到确认,项目的重点将是把更先进的控制律置于飞机上.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.先进控制律开发.RASCAL的先进控制律是由波音直升机公司开发的,有先进的数字光学控制系统, (ADOCS) 和 RAH-66科曼奇血统,控制律软件是由波音公司的图像到代码算法所产生的,那些代码被用于RASCAL飞行控制计算机,到期了,但是控制律被转入Simulink,从而可以平行使用项目的”台式机到飞行”工具, 这些控制律对于系统批准是趋向于稳健和稳定的基础,并为将来的开发提供弹性,他们是一个明确的模型-跟踪架构.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-跟踪概念这里是模型-跟踪控制系统特性一个简短的介绍,以帮助不熟悉此概念的理解以下的讨论,更多彻底的处理方式在文献17,18.模型-跟踪控制系统主要的是由反馈补偿H(s)来稳定飞机和阻止干扰,前馈单元F(s)由飞机动力学的反转模型P-1(s)和反馈补偿H(s),指令模型M(s) 所组成,这些单元在图4中得到概念性阐述.为了分析,图4A可以被重新组合变为图4B,通过组合,稳定和前馈部分产生了一个一致传递函数.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.假定一个完整而可实现的反转模型P-1(s)是可以利用的,飞行器的响应q将完全跟踪模型的响应qm,实际上,取消高频动态比如与转轴和作动器有关的,并不可行,同时,低频特性比如气动力剪裁效果或者重力或质心,没有被完全取消,能够容易的被稳定回路所抑制,因此,简单的第一或者第二阶表现通常就可以满足翻转模型的需要了.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.因为飞机的主要的固有模态被取消,需要的动态响应可以被介绍做为指令模型M(s),从图4可见,显然,模型跟踪架构提供了高水平的模块,并且给他自己能够继续演化与发展,改变一个指令模型并不需要改变前馈模型或者反馈稳定单元增加反馈回路或者控制结构是直接的方法,这些属性使得此架构需要如RASCAL一样的空中实验室,在里面飞行控制需求不断随着任务的改变而变化, RASCAL的飞行中模拟特性将主要的依靠这个模型跟踪控制律结构.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