前馈控制(feed-forward control),是一个术语,描述控制系统中的一个元素或路径,它将控制信号从外部环境的來源传递到另一个外部环境中的负载。这通常是来自外部操作者的命令信号。

仅具有前馈行为的控制系统对其控制信号以预先定义的方式作出响应,而不对负载的响应方式作出响应;它与同样具有反馈的系统形成对比,反馈系统根据输出如何影响负载,以及负载本身如何不可预测地变化来调整输出;负载被认为属于系统的外部环境。

在前馈系统中,控制变量的调整不是以目標和回授之間的误差為基礎,它是以过程数学模型的知识和过程扰动的知识或测量为基础[1]

控制方案需要一些先决条件才能通过纯前馈而无反馈才能可靠:外部命令或控制信号必须可用,并且系统输出对负载的影响应该是已知的(这通常意味着负载必须与时间保持不变)。有时没有反馈的纯前馈控制称为“弹道”,因为一旦发出控制信号,就无法进一步调整;任何纠正调整必须通过新的控制信号。相比之下,“巡航控制”通过反馈机制调整输出以响应其遇到的负载。

概述编辑

前馈系统不是基于误差补偿,而是基于针对过程的知识,如过程的数学模型、过程的干扰的知识或度量[1]

纯前馈系统,通常要求负荷的行为是可预测的,这才能不需要负荷的输出的反馈。

对于前馈系统,过程的干扰在影响系统之前就被测量、应对。例如,居家环控系统检测到房门打开就会开启加热系统,以免室温下降。困难之处在于前馈控制系统必须对过程的干扰造成的效果有精确的预测。[2][3][4]

控制系统可分为3类:

  • 开环
  • 前馈
  • 反馈 (闭环)

开环控制系统的一个例子是纯手工无动力辅助的汽车转向系统。作为对比,动力转向英语power steering系统是个前馈系统,确保转向液压助力达到恒定压强。如果把驾驶员也包括在控制系统中,这形成了反馈路径,人在环中,通过转动方向盘来补偿汽车前进方向转变时的误差。

前馈控制不同于开环控制或遥控机器人英语teleoperator。前馈控制需要有过程的输入输出之间的数学模型。 [5][6]

计算机科学感知机网络是个前馈系统,因为每层神经元的输出只传给下一层,而不能传给上一层神经元,因此没有反馈

模型编辑

前馈控制系統(機器、程序或是生物體)的數學模型可以用控制工程的方式產生,也可以用控制系統自身學習而得到[7]。隨著微处理器運算速度的提昇,具有學習及調整數學模型能力的控制系統也就越來越接近實務應用。現代前馈控制的原理是因為微处理器的發明才有了實務發展的空間[8][6]

前馈控制需要將數學模型整合到控制演算法中,依照目前已知的系統狀態來決定控制動作。以重量輕、有可撓性的機械手臂而言,可能是在手臂有載重時加以補償,沒有載重時則不補償。目標的關節角度會以根據數學模型,載重造成系統的擾動,以及在理想位置下手臂的變形量調整。若是一系統決定命令,再由另一個系統執行命令,這不一定符合上述前馈控制的定義。只有系統有方式可以偵測擾動,或是有輸入信號,再將輸入信號送到數學模型中,以此來調整控制命令,這才稱為是真正的前馈控制[9][10][11]

開迴路系統编辑

系统科学中,開迴路系統(open system)是指沒有反馈可以控制其輸出的系統。相反的,閉迴路系統英语closed system (control theory)可以用回授迴路來控制系統運動。開迴路系統中,系統的輸出不會回授到系統,供控制或是運作使用。

应用编辑

生理前馈系統编辑

在生理学上,前馈控制的例子是在实际体力活动之前对心跳的正常预期调节。前馈控制可以比作对已知线索的预期反应。心跳的反馈调节为机体提供了进一步的对运动的适应性。

前馈系统也存在于人类和动物大脑的生物控制中。[12]即使在生物前馈系统的情况下,例如在人类大脑中,知识或植物(身体)的心理模型也可以被认为是数学模型,因为该模型具有极限、节奏、力学和模式的特征。[13][14]

纯前馈系统不同于稳态控制系统,后者具有保持身体内部环境“稳定”或“长时间处于稳定状态”的功能。体内平衡控制系统主要依赖于反馈(尤其是负面反馈),以及系统的前馈元素。

基因调控与前馈编辑

基因的交叉调控可以用一个图来表示,其中基因是节点,如果一个节点是后者的转录因子,则一个节点与另一个节点相连。一个主要出现在所有已知网络(大肠杆菌,酵母,…)的基序是A激活B, A和B激活C。这种前馈控制在造血细胞谱系发育过程中很常见,在造血细胞谱系发育过程中会做出不可逆转的改变。

参见编辑

参考文献编辑

  1. ^ 1.0 1.1 Haugen, F. Basic Dynamics and Control. 2009. ISBN 978-82-91748-13-9. 
  2. ^ Fundamentals of Motion Control (PDF). ISA. [23 February 2013]. (原始内容 (PDF)存档于2011年9月27日). 
  3. ^ Book, W.J. and Cetinkunt, S. Optimum Control of Flexible Robot Arms OR Fixed Paths. IEEE Conference on Decision and Control. December 1985. 
  4. ^ Oosting, K.W. and Dickerson, S.L. Control of a Lightweight Robot Arm. IEEE International Conference on Industrial Automation. 1986. 
  5. ^ Learned Feed Forward - Innovations in Motion Control. Technology Association of Georgia. [24 February 2013]. 
  6. ^ 6.0 6.1 Alberts, T.E., Sangveraphunsiri, V. and Book, Wayne J., Optimal Control of a Flexible Manipulator Arm: Volume I, Dynamic Modeling, MHRC Technical Report, MHRC-TR-85-06, Georgia Inst, of Technology, 1985.
  7. ^ Learned Feed Forward - Innovations in Motion Control. Technology Association of Georgia. [24 February 2013]. 
  8. ^ Oosting, K.W., Simulation of Control Strategies for a Two Degree-of-Freedom Lightweight Flexible Robotic Arm, Thesis, Georgia Institute of Technology, Dept. of Mechanical Engineering, 1987.
  9. ^ Greene, P. H. (1969): "Seeking mathematical models of skilled actions". In: H. C. Muffley/D. Bootzin (Eds.), Biomechanics, Plenum, pp. 149–180
  10. ^ Book, W.J., Modeling, Design and Control of Flexible Manipulator Arms, PhD. Thesis, MIT, Dept. of Mech. Eng., April 1974.
  11. ^ Maizza-Neto, 0., Modal Analysis and Control of Flexible Manipulator Arms, PhD. Thesis-, MIT, Dept. of Mech. Eng., September 1974.
  12. ^ "Feedback Feedforward control". Psychology Encyclopedia. Retrieved 24 February 2013.
  13. ^ MacKay, D. M. (1966): "Cerebral organization and the conscious control of action". In: J. C. Eccles (Ed.), Brain and conscious experience, Springer, pp. 422–440
  14. ^ Greene, P. H. (1969): "Seeking mathematical models of skilled actions". In: H. C. Muffley/D. Bootzin (Eds.), Biomechanics, Plenum, pp. 149–180

进一步阅读编辑

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  • Meckl, P.H. and Seering, W.P., "Feedforward Control Techniques Achieve Fast Settling Time in Robots", Automatic Control Conference Proceedings. 1986, pp 58–64.
  • Sakawa, Y., Matsuno, F. and Fukushima, S., "Modeling and Feedback Control of a Flexible Arm", Journal of Robotic Systems. August 1985, pp 453–472.
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  • Leu, M.C., Dukovski, V. and Wang, K.K., "An Analytical and Experimental Study of the Stiffness of Robot Manipulators with Parallel Mechanisms", 1985 ASME Winter Annual Meeting PRD-Vol. 15 Robotics and Manufacturing Automation, pp. 137–144
  • Asada, H., Youcef-Toumi, K. and Ramirez, R.B., "Designing of the MIT Direct Drive Arm", Int. Symp. on Design and Synthesis, Japan, July 1984.
  • Rameriz, R.B., Design of a High Speed Graphite Composite Robot Arm, M.S. Thesis, M.E. Dept., MIT, Feb. 1984.
  • Balas, M.J., "Feedback Control of Flexible Systems", IEEE Trans. on Automatic Control, Vol.AC-23, No.4, Aug. 1978, pp. 673–679.
  • Balas, M.J., "Active Control of Flexible Systems", J. of Optim. Th. and App., Vol.25, No.3, July 1978,
  • Book, W.J., Maizzo Neto, 0. and Whitney, D.E., "Feedback Control of Two Beam, Two Joint Systems With Distributed Flexibility", Journal of Dynamic Systems, Measurement and Control, Vol.97, No.4, December 1975, pp. 424–430.
  • Book, W.J., "Analysis of Massless Elastic Chains With Servo Controlled Joints", Journal of Dynamic Systems, Measurement and Control, Vol.101, September 1979, pp. 187–192.
  • Book, W.J., "Recursive Lagrangian Dynamics of Flexible Manipulator Arms Via Transformation Matrices", Carnegie-Mellon University Robotics Institute Technical Report, CMU-RI-TR-8323, Dec. 1983.
  • Hughes, P.C., "Dynamics of a Flexible Manipulator Arm for the Space Shuttle", AAS/AIAA Astrodynamics Conference, September 1977, Jackson Lake Lodge, Wyoming.
  • Hughes, P.C., "Dynamics of a Chain of Flexible Bodies", Journal of Astronautical Sciences, 27,4, Oct.-Dec. 1979, pp. 359–380.
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  • Schmitz, E., "Experiments on the End-point Position Control of a Very Flexible One Link.Manipulator", Ph.D. Dissertation,-Stanford Univ., Dept. of Aero & Astro., June 1985.
  • Martin, G.D., On the Control of Flexible Mechanical Systems, Ph.D. Dissertation, Stanford Univ., Dept. of E.E., May 1978.
  • Zalucky, A. and Hardt, D.E., "Active Control of Robot Structure Deflections", J. of Dynamic Systems, Measurement and Control, Vol. 106, March 1984, pp. 63–69.
  • Sangveraphunsiri, V., The Optimal Control and Design of a Flexible Manipulator Arm, Ph.D Dissertation, Dept. of Mech. Eng., Georgia Inst, of Tech., 1984. 1985.
  • Nemir, D. C, Koivo, A. J., and Kashyap, R. L., "Pseudolinks and the Self-Tuning Control of a Nonrigid Link Mechanism", Purdue University, Advance copy submitted for publication, 1987.
  • Widmann, G. R. and Ahmad, S., "Control of Industrial Robots with Flexible Joints", Purdue University, Advance copy submitted for publication, 1987.
  • Hollars, M. G., Uhlik, C. R., and Cannon, R. H., "Comparison of Decoupled and Exact Computed Torque Control for Robots with Elastic Joints", Advance copy submitted for publication, 1987.
  • Cannon, R. H. and Schmitz, E., "Initial Experiments on the End- Point Control of a Flexible One Link Robot", International Journal of Robotics Research, November 1983.
  • Oosting, K.W. and Dickerson, S.L., "Low-Cost, High Speed Automated Inspection", 1991, Industry Report
  • Oosting, K.W. and Dickerson, S.L., "Feed Forward Control for Stabilization", 1987, ASME
  • Oosting, K.W. and Dickerson, S.L., "Control of a Lightweight Robot Arm", 1986, IEEE International Conference on Industrial Automation
  • Oosting, K.W., "Actuated Feedforward Controlled Solar Tracking System", 2009, Patent Pending
  • Oosting, K.W., "Feedforward Control System for a Solar Tracker", 2009, Patent Pending
  • Oosting, K.W., "Smart Solar Tracking", July, 2010, InterSolar NA Presentation