﻿ 倾转旋翼无人机最优过渡倾转角曲线<sup>*</sup>
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Optimal transition tilt angle curve of tiltrotor UAV
ZHOU Yu, LIU Li
School of Aerospace Engineering, Beijing Institute of Technology, Beijing 100081, China
Received: 2019-03-01; Accepted: 2019-05-27; Published online: 2019-06-13 14:50
Corresponding author. LIU Li, E-mail: liuli@bit.edu.cn
Abstract: A dynamic model of a typical tri-tiltrotor UAV was established. The optimal tilt angle curve in the transition process was studied to reduce the influence of lateral coupling on longitudinal motion, and energy consumption. Based on the analysis of the influence of the tilt angle curve on the transition process, a improved motion profile algorithm was proposed to parameterize the tilt angle curve. A two-phase optimization scheme was proposed to optimize parameters. In the first phase, the minimum coupling degree of lateral control and the minimum energy consumption of the transition process are considered. The optimal tilt angle problem model was constructed by using the curve parameters as the optimization variables.The optimal tilt angle problem was solved by genetic algorithm. In the second phase, a servo dynamics model was introduced for further optimization to reduce the overshoot in the end-stage considering transition time and system overshoot. The results of comparison with the three existing typical tilt angle curves show that, in given transition time, the proposed optimal tilt angle curve effectively reduces the lateral control coupling degree and the energy consumption during the transition process, and reduces the overshoot at the end of the transition.
Keywords: tiltrotor     transition process     tilt angle curve     genetic algorithm     coupling degree of lateral control

1 飞行器动力学模型

 图 1 飞行器动力布局 Fig. 1 Aircraft dynamic layout

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 参数 数值 巡航速度/(m·s-1) 33 巡航迎角/(°) 5 尾部电机平衡倾角/(°) 10 升降舵平衡舵偏角/(°) 6 飞行器质量/kg 5 单发最大推力/N 26 升力系数 0.178 8 阻力系数 0.044 1 机翼面积/m2 0.4 俯仰发动机力臂(前、后)/m 0.4 发动机横侧力臂 0.18 气动俯仰力矩系数 0.00 086 75 平均气动弦长/m 0.16

 图 2 飞行走廊曲线 Fig. 2 Curve of flight corridor
2 横侧控制耦合与能耗优化 2.1 优化模型

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2.2 遗传算法求解

Ta等[6-7]提出的运动剖面算法，在考虑执行机构动力学的基础上将倾转角度变化可以分成3个线性的任务段(如图 3所示)。

 图 3 运动剖面算法曲线[6-7] Fig. 3 Curves of motion profile algorithm[6-7]

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 图 4 改进运动剖面曲线 Fig. 4 Curves of improved motion profile

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 参数 μ1 μ2 数值 [0°, 90°] [μ1, 90°] [0, 9](°)/s

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 图 5 种群平均适应度曲线 Fig. 5 Curve of population's mean fitness

 参数 μ1/(°) μ2/(°) /((°)·s-1) 数值 45.15 90 9

 图 6 倾转角曲线 Fig. 6 Curve of tilt angle
 图 7 前飞速度曲线 Fig. 7 Curve of forward velocity
3 动态性能优化

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 图 8 无减速段舵机输出 Fig. 8 Servo output in non-deceleration section

 图 9 不同参数μ2下舵机输出 Fig. 9 Servo output with different μ2
 图 10 调节时间与参数μ2关系

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w′=1时，其结果如图 11所示。得到的参数μ2=76.9°。

 图 11 加权相交法 Fig. 11 Weighted intersection algorithm
4 对比分析

 图 12 Curve of optimal tilt angle
 图 13 最优速度曲线 Fig. 13 Curve of optimal velocity

 参数 匀速倾转 未优化“S”形曲线 本文结果 耦合大小 8.94 14.36 7.10 阻力做功 4 076.7 5 218.0 2 798.9 最大超调量 4.888 6 0.039 1 0.128 3

5 结论

1) 本文建立的考虑横侧耦合和能量损耗的优化模型得到了过渡过程中的最优倾转角曲线，进一步降低了过渡过程中横侧控制耦合的影响，提高了过渡过程的效率，减小了因横向耦合导致纵向运动参数的影响。

2) 本文在设计最优倾转角曲线时引入了舵机模型，通过不同倾转角曲线参数下的舵机动态响应，对倾转角曲线参数进一步进行优化，得到了兼顾减速时间和超调量的最优曲线参数。

3) 本文得到的最优倾转角曲线，对比分析后发现，该曲线能较好地兼顾耦合影响、能量损耗和过渡结束时的超调等多个指标，提高了倾转旋翼无人机过渡过程飞行品质。

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文章信息

ZHOU Yu, LIU Li

Optimal transition tilt angle curve of tiltrotor UAV

Journal of Beijing University of Aeronautics and Astronsutics, 2019, 45(11): 2277-2283
http://dx.doi.org/10.13700/j.bh.1001-5965.2019.0073