观看无人机群飞过假森林而不会崩溃

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来自瑞士联邦理工学院洛桑或EPFL的数学工程师和机器人博士学生已经建立了一款计算机模型,用于模拟五个自主Quadcopters的轨迹,在不抵抗任何东西的情况下飞过密集的森林。但是一个错误的直升机不会用物理树生存一个tête-à-tête。“即使无人机撞到他们身上,”索里亚召回思考,“他们不会打破。”

但是,对控制无人机的“群”的公开和私人兴趣正在增长。五个Quadcopters跃入随机的起始位置,穿过假森林,并安全降落。

Enrica Soria需要柔软的树木。来自瑞士联邦理工学院洛桑或EPFL的数学工程师和机器人博士学生已经建立了一款计算机模型,用于模拟五个自主Quadcopters的轨迹,在不抵抗任何东西的情况下飞过密集的森林。但是一个错误的直升机不会用物理树生存一个tête-à-tête。

所以索里亚建造了一个卧室的虚假森林。运动捕获摄像机排列了悬挂在空间上方的轨道以跟踪Quadcopters的运动。对于“树木”,索里亚在宜家的八个绿色可折叠小孩的播放隧道网上定居,由柔软的织物制成。 “即使无人机撞到他们身上,”索里亚召回思考,“他们不会打破。”

她为无人机建造了软游乐场,以安全地测试一种新的自主控制形式:编程无人机根据他们期望他们的邻居如何移动,而不是依赖于无关的计算机来指导它们。一个自主群体通常是风险的 - 机器人可以粉碎进入不可预见的障碍物,例如树木或好奇的鸟类,或者彼此。碰撞可能具有扭曲效果,使整个植绒脱落。

但是,对控制无人机的“群”(如索里亚的假森林飞行员)的公开和私人兴趣正在增长。设计可靠的控制系统对现实世界任务承诺,群体必须一起飞行,例如在森林中的搜索和救出工作或在城市的协调交付中努力。一些群体目前由中央计算机或地面上的人控制,比如飞行的光明表明,取代烟火。 AG-Tech公司Rantizo去年赢得了批准,将三种无人机飞过农场的农作物喷洒服务,而且也从地面上的飞行员开始。但是,像研究人员想要用于监测空气质量或其他数据收集的研究人员一样,将受益于更全面的自主控制。

自主群通常被重新控制,意思是根据他们当前距离他们不应该击中的东西。如果无人机彼此漂移得太远,他们会越来越近;如果他们接近障碍,他们将减缓和距离自己。

此纠错是有道理的。 (“嘿无人机,不要打东西”)但要识别,计算和使这些调整所需的时间会减慢整个组。索里亚的系统避免了更好的规划速度。她的自动驾驶仪算法基于她所谓的“预测控制” - 无人机彼此通信,并解释实时运动捕获数据以预测其他附近的无人机将移动的地方。然后它们相应地调整自己。

一旦索里亚派出了旱地穿过她的织物森林,她很快就证实了障碍物的柔软性并不重要:无人机没有崩溃。五个Quadcopters跃入随机的起始位置,穿过假森林,并安全降落。 “他们能够及时看到未来,”索里亚说。 “他们可以预见到未来的邻居放缓,并实时降低飞行中的负面影响。”

基于计算机模拟和假林示范,索里亚的团队表明,他们的无人机通过障碍物拉链的障碍比不涉及预测的最先进的“反应性”控制。 5月份自然机器智能期刊出现了结果。

虽然索里亚的无人机依靠地面上的电脑来执行许多必要的计算,但她的系统是如何模仿无人机,如果计算完全分布。 “如果你想完全部署这些东西,我们应该真正削减与中央中心或电脑的沟通需求,”Carnegie Mellon的机械工程教授没有隶属于该研究。 “这是朝向这一目标的一步。”

对同时控制多种无人机的科学的许多灵感来自于自然界的华丽同步行为:鸟群,鱼类,以及蜜蜂的群。但蜜蜂群体比无人机群更好地导航意外的障碍,而索里亚说,“生物学家说没有中央计算机。”没有一只鸟或鱼或蜜蜂为其他人提供运动。相反,每个动物根据其邻居飞行计算自己的轨迹。他们避免彼此,以及令人惊讶的推动者。据报道,动物集体行为的奇妙同步依赖于预测计算。我们的大脑也被认为是通过不断比较预测的现实来运营。

EPFL的索里亚的团队没有发明对无人机的预测控制的想法。科学家们已经模仿它来导航在预定义轨迹上行驶的两辆车辆的无障碍区域和系统。但是,她说,这不是规范,因为预测控制依赖于大量的实时计算,可以最大限度地符合小型无人机的计算能力,这重量比智能手机少10倍。

预测控制是关于发现与类似变量相互帧间距离和速度的问题的最佳答案 - 这应该将所有悬停在所需值附近。模拟预测控制,索里亚编程的数学数学方程代表最重要的约束。无人机不应该互相抨击,所以她的模型限制了他们可以飞到另一个人的近距离。无人机不应该通过障碍试图翱翔,所以她的模型可以保留在其脑海背部的“无飞区域”列表。与此同时,每个无人机都应该达到并保持优选的速度朝着其目标。因此,索里亚编程了每个无人机的自动驾驶仪,以便根据其当前状态和这些约束来想象最好的轨迹。重要的是,每个无人机也可以根据其对其位置和运动的知识来想其最近邻居的这种轨迹。

这就像一个夫妇网球专业专业公司,制定了最佳的球员抨击球。 “他们不仅反应球在给定时间的地方,”索里娅说。 “他们还规划了接下来将发生的事情,例如基于他们看到对手正在移动的方向。”

当然,数学变得凌乱。一个无人机的轨迹影响其余的,反之亦然 - 一种类型的系统被称为“非线性”。解决非线性的缠结的网是一个漫步。但现实本身就是非线性的。使索里亚的计算昂贵的方法值得。

索里亚的团队在用五种无人机和八个障碍物的模拟上测试了新方法,并确认了他们的亨希。在一种情况下,反应群在34.1秒内完成了他们的使命 - 预测成绩于21.5。

接下来是真正的演示。索里亚的团队聚集了研究人员使用的小疯狂Quadcopters。每个人都足够微小,以适应她的手掌,并重量小于高尔夫球,而是携带加速度计,陀螺仪,压力传感器,无线电发射器和小运动捕获球,间隔几英寸在四个刀片之间。传感器的读数和房间的运动捕捉相机,其跟踪球,流到运行每个无人机模型的计算机作为地面控制站。 (小型无人机无法携带在板上运行预测控制计算所需的硬件。)

索里亚将无人机放在地板上,在第一棵树的障碍物附近的“开始”区域。当她推出实验时,五个无人机洒起来,快速移动到起飞区域上方的3D空间中的随机位置。然后,转台开始移动。它们通过空气,柔软的绿色障碍物之间,在柔软的绿色障碍物之间,在彼此之间,朝向终点线,在那里他们落在温柔的反弹。没有碰撞。只需在实时更新数学计算的障碍,就可以平稳不变蜂拥而至。

“NMPC [非线性模型预测控制]模型的结果非常有前途,”EötvösLoránd大学的机器人GáborVásárhelyi在布达佩斯,匈牙利,匈牙利,在一封电子邮件中,匈牙利·埃达塔斯·洛拉姆大学(Vásárhelyi的团队创造了使用的反应模型索里亚,但他没有参与工作。)

然而,Vásárhelyi注意事项,该研究并未解决实施预测控制的重要障碍:计算需要一个中央计算机。远距离的外包控制可以留下整个群体易受通信延误或错误的影响。更简单的分散控制系统可能找不到最好的飞行轨迹,但“他们可以在非常小的船上设备上运行(如蚊子,女士虫子或小无人机),并使用群体规模更好,”他写道。人工和天然无人机群不能有庞大的船上电脑。

“这是一种质量或数量问题,”Vásárhelyi继续。 “然而,自然有这两者。”

“那是我说'是的,我可以,'”亚利桑那州立大学的系统工程师丹布里斯说。 Bliss不参与索里亚团队,导致DARPA项目为无人机和消费技术提供更高效的移动处理。即使是小型无人机也会随着时间的推移而变得更加计算。 “我采取了一百瓦的电脑问题,并尝试将其放在消耗1瓦特的处理器上,”他说。 Bliss补充说,创建一个自主驱动器群不仅仅是一个控制问题,也是一种传感问题。地板工具映射周围世界,如计算机愿景,需要大量的处理能力。


英文译文:

Enrica Soria needed soft trees. The mathematical engineer and robotics PhD student from the Swiss Federal Institute of Technology Lausanne, or EPFL, had already built a computer model to simulate the trajectories of five autonomous quadcopters flying through a dense forest without hitting anything. But an errant copter wouldn’t survive a tête-à-tête with a physical tree.

So Soria built a fake forest the size of a bedroom. Motion-capture cameras lined a rail hanging above the space to track the movement of the quadcopters. And for “trees,” Soria settled on a grid of eight green collapsible kids’ play tunnels from Ikea, made of a soft fabric. “Even if the drones crash into them,” Soria recalls thinking, “they won't break.”

She built the soft playground for the drones to safely test a new form of autonomous control: programming drones to adjust their trajectory based on how they expect their neighbors to move—rather than relying on an omniscient computer to direct them. An autonomous swarm is generally risky—the robots could smash into unforeseen obstacles, such as trees or curious birds, or each other. And a collision could have a ripple effect that derails the whole flock.

But public and private interest in controlling “swarms” of drones (like Soria’s fake forest fliers) is growing. Designing a reliable control system has promise for real-world missions in which a swarm has to fly together, such as search and rescue efforts in forests or coordinated deliveries in cities. Some swarms are currently controlled by a central computer or person on the ground, like flying light shows that replace fireworks. The ag-tech company Rantizo earned approval last year to fly three drones over farms for its crop-spraying services, and those take direction from a pilot on the ground too. But large swarms, like the ones researchers want to use for monitoring air quality or other data collection, would benefit from more fully autonomous controls.

Autonomous swarms are usually controlled reactively, meaning based on their current distance from stuff they shouldn’t hit. If drones drift too far from each other, they'll pull in closer; if they approach an obstacle, they'll slow down and distance themselves.

This error correction makes sense. ("Hey drones, don't hit stuff.") But the time it takes to recognize, compute, and make those adjustments slows down the whole group. Soria's system avoids slowdowns with better planning. Her autopilot algorithm is based on what she calls "predictive control"—the drones communicate with each other and interpret real-time motion-capture data to predict where other nearby drones will move. Then they adjust themselves accordingly.

Once Soria sent the drones flying through her fabric forest, she soon confirmed that the softness of the obstacles didn’t really matter: The drones didn’t crash. The five quadcopters sprang up into randomized starting positions, coasted through the fake forest, and landed safely. “They are able to see ahead in time,” says Soria. “They can foresee a future slowdown of their neighbors and reduce the negative effect of this on the flight in real time.”

Based on the computer simulation and the fake-forest demonstration, Soria’s team showed that their drones zipped through the obstacles 57 percent faster than state-of-the-art “reactive” controls that don’t involve prediction. The results appeared in the journal Nature Machine Intelligence in May.

Although Soria’s drones rely on a computer on the ground to perform the many necessary calculations, her system imitates how drones would communicate with each other if the computation were entirely distributed. “If you want to fully deploy these things, we should really cut the need for communication with a central hub or computer,” says ‪Amir Barati Farimani, a mechanical engineering professor at Carnegie Mellon who is not affiliated with the study. “This is one step toward that goal.”

A lot of inspiration for the science of simultaneously controlling multiple drones comes from gorgeously synchronized behavior in nature: flocks of birds, schools of fish, and swarms of bees. But bee swarms navigate unexpected obstacles better than drone swarms, and, Soria says, “biologists say that there's no central computer.” No one bird or fish or bee directs movement for the rest. Instead, each animal computes its own trajectory based on its neighbors’ flight. They avoid each other, as well as surprise interlopers. The wondrous synchrony of animal collective behavior reportedly relies on predictive computations. Our brains are also thought to operate by constantly comparing reality to predictions.

Soria's team at EPFL didn't invent the idea of predictive control for drones. Scientists have modeled it to navigate obstacle-free areas and systems for two vehicles traveling on predefined trajectories. But it’s not the norm, she says, because predictive control relies on a flood of real-time calculations that can max out whatever computational power fits on small drones, which weigh 10 times less than a smartphone.

Predictive control is all about finding the optimal answer to a problem with a ton of variables—like inter-drone distance and speed—that should all hover near desired values. To simulate predictive control, Soria programmed math equations representing the most important constraints. Drones shouldn’t slam into each other, so her model limits how close they can fly to another. Drones shouldn’t try to soar through an obstacle, so her model can keep a list of “no-fly zones” logged in the back of its mind. At the same time, each drone should reach and maintain a preferred speed toward its goal. So Soria programmed each drone’s autopilot to imagine a best trajectory based on its current state and these constraints. Importantly, each drone also imagines this trajectory for its nearest neighbors, based on its knowledge of their position and motion.

It’s like a couple tennis pros working out the best way to slam the ball back. “They are not only reacting to where the ball is at a given time,” Soria says. “They are also planning what's going to happen next, for instance based on the direction they see that the opponent is moving.”

The math, of course, gets messy. One drone’s trajectory influences the rest, and vice versa—a type of system referred to as being “nonlinear.” Solving the tangled web of nonlinearity is a slog. But reality is itself nonlinear. That makes Soria's computationally expensive approach worth it.

Soria’s team tested the new approach against a state-of-the-art reactive model on a simulation with five drones and eight obstacles, and confirmed their hunch. In one scenario, reactive swarms finished their mission in 34.1 seconds—the predictive one finished in 21.5.

Next came the real demonstration. Soria’s team gathered small Crazyflie quadcopters used by researchers. Each one was tiny enough to fit in the palm of her hand and weighed less than a golf ball, but carried an accelerometer, a gyroscope, a pressure sensor, a radio transmitter, and small motion-capture balls, spaced a couple of inches apart and between the four blades. Readings from the sensors and the room’s motion-capture camera, which tracked the balls, flowed to a computer running each drone’s model as a ground control station. (The small drones can’t carry the hardware needed to run predictive control computations onboard.)

Soria placed the drones on the floor in a “start” region near the first tree-like obstacles. As she launched the experiment, five drones sprang up and quickly moved to random positions in the 3D space above the takeoff area. Then the copters started moving. They slipped through the air, between the soft green obstacles, over, under, and around each other, and toward the finish line where they landed with a gentle bounce. No collisions. Just smooth uneventful swarming made possible by a barrage of mathematical computations updating in real time.

“The results of the NMPC [nonlinear model predictive control] model are quite promising,” writes Gábor Vásárhelyi, a roboticist at Eötvös Loránd University in Budapest, Hungary, in an email to WIRED. (Vásárhelyi’s team created the reactive model Soria used, but he was not involved in the work.)

However, Vásárhelyi notes, the study doesn’t address a crucial barrier to implementing predictive control: the computation requires a central computer. Outsourcing controls over long distances could leave the entire swarm susceptible to communication delays or errors. Simpler decentralized control systems may not find the best possible flight trajectory, but “they can run on very small onboard devices (such as mosquitoes, lady bugs or small drones) and scale much, much better with swarm size,” he writes. Artificial—and natural—drone swarms can’t have bulky onboard computers.

“It is a bit of a question of quality or quantity,” Vásárhelyi continues. “However, nature kind of has it both.”

“That's where I say ‘Yes, I can,’” says Dan Bliss, a systems engineer at Arizona State University. Bliss, who is not involved with Soria’s team, leads a Darpa project to make mobile processing more efficient for drones and consumer tech. Even small drones are expected to become more computationally powerful with time. “I take a couple-hundred-watt computer problem and try to put it on a processor that consumes 1 watt,” he says. Bliss adds that creating an autonomous drone swarm isn’t just a control problem, it’s also a sensing problem. Onboard tools that map the surrounding world, such as computer vision, require a lot of processing power.


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