Magnetically actuated gearbox for the wireless control of millimeter-scale robots

The limited force or torque outputs of miniature magnetic actuators constrain the locomotion performances and functionalities of magnetic millimeter-scale robots. Here, we present a magnetically actuated gearbox with a maximum size of 3 millimeters for driving wireless millirobots. The gearbox is assembled using microgears that have reference diameters down to 270 micrometers and are made of aluminum-filled epoxy resins through casting. With a magnetic disk attached to the input shaft, the gearbox can be driven by a rotating external magnetic field, which is not more than 6.8 millitesla, to produce torque of up to 0.182 millinewton meters at 40 hertz. The corresponding torque and power densities are 12.15 micronewton meters per cubic millimeter and 8.93 microwatt per cubic millimeter, respectively. The transmission efficiency of the gearbox in the air is between 25.1 and 29.2% at actuation frequencies ranging from 1 to 40 hertz, and it lowers when the gearbox is actuated in viscous liquids. This miniature gearbox can be accessed wirelessly and integrated with various functional modules to repeatedly generate large actuation forces, strains, and speeds; store energy in elastic components; and lock up mechanical linkages. These characteristics enable us to achieve a peristaltic robot that can crawl on a flat substrate or inside a tube, a jumping robot with a tunable jumping height, a clamping robot that can sample solid objects by grasping, a needle-puncture robot that can take samples from the inside of the target, and a syringe robot that can collect or release liquids.

微型磁致动器（miniature magnetic actuators）有限的出力与转矩输出，限制了磁性毫米尺度机器人的运动性能与功能。本文提出一款最大尺寸为3毫米的磁驱动齿轮箱（magnetically actuated gearbox），用于驱动无线式毫米机器人。该齿轮箱由参考直径低至270微米的微型齿轮（microgears）组装而成，这些齿轮采用填铝环氧树脂（aluminum-filled epoxy resins）通过浇铸工艺（casting）制备。在输入轴（input shaft）上加装磁盘（magnetic disk）后，该齿轮箱可由强度不超过6.8毫特斯拉（millitesla）的旋转外部磁场驱动，在40赫兹工况下可产生最高达0.182毫牛·米（millinewton meters）的转矩。其对应转矩密度与功率密度分别为12.15微牛·米每立方毫米与8.93微瓦每立方毫米。该齿轮箱在空气中的传动效率在1至40赫兹的驱动频率下介于25.1%至29.2%之间，在粘性液体中驱动时传动效率会有所降低。这款微型齿轮箱可实现无线操控，并可与各类功能模块集成，以反复输出大驱动力、应变与速度；可在弹性组件中储存能量；还可锁定机械连杆机构。这些特性使我们得以开发出多种实用机器人：可在平坦基底或管道内爬行的蠕动式机器人、跳跃高度可调的跳跃式机器人、可通过抓取对固体物体进行采样的夹持式机器人、可从目标内部获取样本的穿刺针机器人，以及可收集或释放液体的注射器式机器人。