如果你已经设计了一个软体机器人，再往里塞一个刚性电机，那基本上就违背了初衷。这就是瑞士科学家创造一种细而柔的纤维形态电机的原因。这种装置叫FiberMotor，由瑞士洛桑联邦理工学院的一组研究人员开发。它建立在EPFL之前的一项创新之上，那项创新把泵送液体的管状纤维集成到服装里。
If you've already designed a soft-bodied robot, it kind of defeats the purpose if you just go and stick a rigid motor inside of it. That's why Swiss scientists have created a motor that takes the form of a thin, flexible fiber. Known as the FiberMotor, the device was developed by a team of researchers at the EPFL university in Switzerland. It builds upon a previous EPFL innovation, which incorporates liquid-pumping tubular fibers into clothing.
每根FiberMotor的直径在1到3毫米之间，实际上由两根同心的中空聚合物纤维组成，外面一根更宽，里面嵌套一根更窄的。细铜线紧密缠绕在每根纤维上，作为每根纤维的电极。当电流施加到这些电极上时，静电力反复把纤维拉向彼此对齐，导致内层纤维在外层纤维内滑动。在实验室测试中，利用这种拉力，单根FiberMotor能够支撑约75克的静止负载，而四根电机捆在一起可以举起一根46克的巧克力棒，并弯曲一根肌腱驱动的机器人手指。
Ranging in diameter from 1 to 3 millimeters, each FiberMotor is in fact composed of two concentric hollow polymer fibers—a wider one on the outside, with a narrower one nested inside of it. Thin copper wire is tightly wound around each of the fibers, serving as an electrode on each fiber. When an electrical current is applied to these electrodes, electrostatic forces repeatedly pull the fibers into alignment with one another, causing the inner fiber to slide within the outer one. Utilizing that pulling force in lab tests, individual FiberMotors were able to support stationary loads equivalent to about 75 g, while four of the motors bundled together could lift a 46-g chocolate bar and flex a tendon-driven robotic finger.
重要的是，因为没有齿轮或传动装置，FiberMotor是可以反向驱动的。这意味着如果它被外部相反的力推动，它不会锁死。科学家们现在正通过衍生公司Elecsyor提高这项技术的耐久性和性能，并希望把FiberMotor集成到移动辅助服装、VR触觉反馈系统和轻量假肢设备等物品中。EPFL软换能器实验室负责人Herbert Shea说：“我们的FiberMotor是第一根纤维形态的滑动电机。它产生的力足以驱动软体机器人应用的设备，同时保持安静、柔性和双向性。”这项研究的论文最近发表在《Advanced Materials》杂志上。
And importantly, because there are no gears or transmissions, the FiberMotor is back-driveable. This means that if it's pushed by an external opposing force, it won't lock up. The scientists are now working on boosting the durability and performance of the technology via spinoff company Elecsyor, and hope to integrate the FiberMotors into items such as mobility-assisting clothing, VR haptic feedback systems, and lightweight prosthetic devices. "Our FiberMotor is the first fiber-format, sliding motor," says Herbert Shea, head of EPFL's Soft Transducers Lab. "It produces enough force to actuate devices for soft robotic applications, while remaining silent, flexible, and bidirectional." A paper on the research was recently published in the journal Advanced Materials.
这个电机的技术路线值得单独说清楚。它用的是静电驱动，不是传统的电磁驱动。静电驱动的原理是，两个带电体之间会产生吸引力，电压越高，吸引力越大。FiberMotor把两根纤维做成同心结构，铜线缠绕形成电极，加电压后内外纤维之间产生静电力，内层纤维被拉着滑动。这个结构的优势是，它把电机做成了纤维形态，可以织进布料、嵌进软体结构里，而不需要一个硬邦邦的圆柱形外壳。缺点是静电驱动通常需要较高的电压，产生的力相对有限。单根75克的负载能力，四根捆起来能举46克巧克力棒，这个力量水平说明它适合驱动手指、辅助衣物这类轻负载应用，不是用来做重载机器人的。
The motor's technical route deserves clarity. It uses electrostatic actuation, not conventional electromagnetic drive. Electrostatic actuation works on the principle that two charged bodies attract each other, with higher voltage producing greater attraction. FiberMotor makes two fibers into a concentric structure, with copper wire wound to form electrodes. When voltage is applied, electrostatic force arises between inner and outer fibers, pulling the inner fiber to slide. The advantage of this structure is that it turns the motor into a fiber form, which can be woven into fabric or embedded in soft structures without a rigid cylindrical housing. The downside is that electrostatic actuation typically requires higher voltages and produces relatively limited force. A single unit's 75-gram load capacity, and four bundled units lifting a 46-gram chocolate bar, indicate this force level suits light-load applications like driving fingers or assistive clothing, not heavy-duty robots.
把这项技术和前面讨论的触觉传感器、软体机器人放在一起看，指向的是同一个方向：机器人的身体正在被重新设计，不再是把传统刚性部件塞进一个软壳子里，而是从材料层面就做成柔性的。墨现科技的柔性触觉传感器是把感知做成薄膜，EPFL的FiberMotor是把驱动做成纤维。这两个方向加在一起，是软体机器人从概念走向实用的两块拼图。感知和驱动都柔性化了，软体机器人才能真正做到全身柔软，而不是只有外壳柔软、里面全是硬零件。Elecsyor这家衍生公司的进展，会决定FiberMotor能不能从实验室走向实际应用。
Placing this technology alongside the tactile sensors and soft robots discussed earlier points to the same direction: robot bodies are being redesigned, no longer stuffing traditional rigid components into a soft shell, but making them flexible at the material level. Moxian Technology's flexible tactile sensors make sensing into thin films; EPFL's FiberMotor makes actuation into fibers. Together, these two directions are two pieces of the puzzle for soft robots moving from concept to practicality. When both sensing and actuation are flexible, soft robots can truly be soft throughout, rather than having only a soft shell with rigid parts inside. The progress of spinoff company Elecsyor will determine whether FiberMotor can move from laboratory to practical application.
