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極限工況下的無(wú)人駕駛路徑跟蹤 | 斯坦福大學(xué)團(tuán)隊(duì)最新研究成果

2018-09-26 23:56:49·  來(lái)源：集成與控制研究室 同濟(jì)智能汽車研究所  
　
5、試驗(yàn)結(jié)果
 
試驗(yàn)車輛安裝了普利司通的Potenza S-04輪胎來(lái)測(cè)試新的控制系統(tǒng)。斜坡轉(zhuǎn)角輸入的測(cè)試結(jié)果表明車輛的前后軸輪胎的等效側(cè)偏剛度分別為220kN/rad和240kN/rad，附著系數(shù)分別為0.99和1.04。直線制動(dòng)測(cè)試結(jié)果表明前后軸的有效縱向剛度為450kN?？刂破髦械膮?shù)XLA=10m，kp=1/s，kspeed=1000Ns/m。參考路徑設(shè)為一個(gè)半徑突變的逆時(shí)針圓周，從而驗(yàn)證車輛的路徑跟蹤性能。試驗(yàn)場(chǎng)地路面為向西傾斜2.5度的干凈柏油路面。
 圖8分別是路面附著系數(shù)的估計(jì)結(jié)果和輪胎側(cè)偏角跟蹤目標(biāo)值，圓周半徑在77.5s的時(shí)候從18m變?yōu)?0m?；诠烙?jì)的輪胎參數(shù)，峰值側(cè)偏角為7.4度。測(cè)量的側(cè)偏角比目標(biāo)值稍大，可能是由于側(cè)偏角控制器中轉(zhuǎn)向力矩的建模存在一定誤差，但是前軸的輪胎力也得到了充分的利用（如圖 6所示）。估計(jì)器的路面附著系數(shù)估計(jì)結(jié)果在1和1.1之間，與轉(zhuǎn)角斜坡輸入工況下的估計(jì)結(jié)果一致。
圖7是車輛跟蹤路徑時(shí)的車速目標(biāo)值和測(cè)量值。較小的kp和較大的kspeed參數(shù)對(duì)車速跟蹤控制效果更好。如圖 9所示，側(cè)向位移誤差在轉(zhuǎn)向半徑突變后逐漸收斂，并最終穩(wěn)定在1m左右，車輛在目標(biāo)軌跡的外側(cè)。而這部分偏差還需要更深入的研究。
圖8 路面附著系數(shù)估計(jì)結(jié)果（左）和路徑跟蹤的前軸側(cè)偏角的目標(biāo)值和測(cè)量值（右）
圖9 路徑跟蹤結(jié)果（俯視）
 
6、結(jié)論
試驗(yàn)數(shù)據(jù)表明在路徑跟蹤過(guò)程中的速度跟蹤控制和轉(zhuǎn)角控制需要路面附著系數(shù)的估計(jì)誤差在大約2%以內(nèi)。然而，基于輪胎側(cè)偏角設(shè)計(jì)的轉(zhuǎn)角控制能夠有效降低系統(tǒng)對(duì)于路面附著系數(shù)估計(jì)結(jié)果精度的依賴。采集到的專業(yè)賽車駕駛員數(shù)據(jù)指出通過(guò)側(cè)偏角控制能夠使得不足轉(zhuǎn)向的車輛更充分地利用輪胎的附著能力，并且可以通過(guò)速度反饋來(lái)實(shí)現(xiàn)路徑跟蹤。
為了驗(yàn)證這一理念，設(shè)計(jì)了根據(jù)虛擬橫擺角速度控制輸入得到的速度控制量來(lái)進(jìn)行路徑跟蹤。貝葉斯濾波在線估計(jì)器和試驗(yàn)數(shù)據(jù)表明，即使在路面附著系數(shù)不確定的條件下，控制器也能夠很好地跟蹤上圓周路徑。
不管是在賽道競(jìng)速或者公路上的緊急工況，文章設(shè)計(jì)的控制架構(gòu)在極限工況下的無(wú)人駕駛都能夠有很好地應(yīng)用前景。未來(lái)的研究將進(jìn)一步考慮縱向車速控制的建模、不同控制系統(tǒng)對(duì)附著系數(shù)的靈敏度、變曲率的路徑跟蹤、地形和輪胎的影響、以及路面附著系數(shù)不一致的情況。
 
7、參考文獻(xiàn)
[1] K. Kritayakirana, “Autonomous vehiclecontrol at the limits of handling,” Ph.D. dissertation, Stanford University,2012.
[2] C. E. Beal and J. C. Gerdes, “Modelpredictive control for vehicle stabilization at the limits of handling,” IEEETransactions on Control Systems Technology, vol. 21, no. 4, pp. 1258–1269,2013.
[3] Y.-H. J. Hsu, S. M. Laws, and J. C.Gerdes, “Estimation of tire slip angle and friction limits using steeringtorque,” IEEE Transactions on Control Systems Technology, vol. 18, no. 4, pp.896–907, 2010.
[4] J.-O. Hahn, R. Rajamani, and L.Alexander, “GPS-based real-time identification of tire-road frictioncoefficient,” IEEE Transactions on Control Systems Technology, vol. 10, no. 3,pp. 331–343, 2002.
[5] L. R. Ray, “Nonlinear estimation ofvehicle state and tire forces,” in American Control Conference, 1992. IEEE,1992, pp. 526–530.
[6] L. R. Ray, “Real time determination ofroad coefficient of friction for IVHS and advanced vehicle control,” inAmerican Control Conference, Proceedings of the 1995, vol. 3. IEEE, 1995, pp.2133–2137.
[7] L. R. Ray, “Nonlinear state and tireforce estimation for advanced vehicle control,” Control Systems Technology,IEEE Transactions on, vol. 3, no. 1, pp. 117–124, 1995.
[8] L. R. Ray, “Nonlinear tire forceestimation and road friction identification: Simulation and experiments,”Automatica, vol. 33, no. 10, pp. 1819–1833, 1997.
[9] L. R. Ray, “Experimental determinationof tire forces and road friction,” in American Control Conference, 1998.Proceedings of the 1998, vol. 3. IEEE, 1998, pp. 1843–1847.
[10] J. Subosits and J. C. Gerdes, “Asynthetic input approach to slip angle based steering control for autonomousvehicles,” in 2017 American Control Conference (ACC). IEEE, 2017 (in press).
[11] N. R. Kapania and J. C. Gerdes,“Design of a feedback-feedforward steering controller for accurate pathtracking and stability at the limits of handling,” Vehicle System Dynamics,vol. 53, no. 12, pp. 1687– 1704, 2015.
[12] H. Pacejka, Tyre and Vehicle Dynamics,3rd ed. Butterworth- Heinemann, 2012.
[13] R. Y. Hindiyeh, “Dynamics and controlof drifting in automobiles,” Ph.D. dissertation, Stanford University, 2013.
[14] C. Voser, R. Y. Hindiyeh, and J. C.Gerdes, “Analysis and control of high sideslip manoeuvres,” Vehicle SystemDynamics, vol. 48, no. S1, pp. 317–336, 2010.
[15] P. A. Theodosis and J. C. Gerdes,“Nonlinear optimization of a racing line for an autonomous racecar usingprofessional driving techniques,” in ASME 2012 5th Annual Dynamic Systems andControl Conference joint with the JSME 2012 11th Motion and VibrationConference. American Society of Mechanical Engineers, 2012, pp. 235–241.
[16] J. Subosits and J. C. Gerdes,“Autonomous vehicle control for emergency maneuvers: The effect of topography,”in 2015 American Control Conference (ACC). IEEE, 2015, pp. 1405–1410.
[17] N. R. Kapania, J. Subosits, and J. C.Gerdes, “A sequential two-step algorithm for fast generation of vehicle racingtrajectories,” Journal of Dynamic Systems, Measurement, and Control, vol. 138,no. 9, p. 091005, 2016.
[18] J. Y. Goh and J. C. Gerdes,“Simultaneous stabilization and tracking of basic automobile driftingtrajectories,” in 2016 IEEE Intelligent Vehicles Symposium (IV). IEEE, 2016,pp. 597–602.
 
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