Highly functional magnetic miniature robots with optimal six-DOF actuation

Abstract

Magnetic miniature robots (MMRs) are micro/millimeter-scale, mobile devices that are actuated by the magnetic field. As these small-scale machines can exploit their size and mobility to non-invasively access highly confined and enclosed spaces, they have great potential to revolutionize medical applications, such as targeted drug delivery and minimally invasive surgery. Furthermore, MMRs are proven to be powerful tools that can facilitate a wide range of fundamental studies in materials science and biology as well as enable critical manipulation tasks in lab-on-chip applications. One of the major advancements for this class of actuators is the creation of MMRs with six-degrees-of-freedom (six-DOF). While the six-DOF technology can potentially enhance the MMRs’ dexterity and manipulation capability significantly, existing six-DOF MMRs are not widely adopted due to two critical limitations; i) under precise orientation control, existing six-DOF MMRs have slow sixth-DOF angular velocities (4 degree/s), and it is challenging to apply desired magnetic forces on them; ii) existing six-DOF MMRs cannot perform soft-bodied functionalities. Here we propose a fabrication method that can construct optimal six-DOF MMRs, producing 51-297 folds larger sixth-DOF torque than existing six-DOF MMRs. We also present a universal six-DOF actuation strategy applicable for both rigid and soft MMRs. Under precise orientation control, our optimal six-DOF MMR could execute full six-DOF motions reliably and achieve sixth-DOF angular velocities of 173 degree/s. The proposed rigid optimal MMR and the soft jellyfish-like swimmer had demonstrated unprecedented dexterity by negotiating across barriers impassible by existing MMRs. In addition, we had created an optimal six-DOF gripper that could complete a complicated, small-scale assembly task within 4 minutes 54 seconds, 20 folds more efficient than its five-DOF predecessor. As it is highly desirable for MMRs to possess multimodal locomotion to enhance their adaptability in unstructured terrains, we also proposed a six-DOF, amphibious MMRs that could execute seven modes of soft-bodied locomotive gaits. The proposed MMR with six-DOF control capability exhibited significantly higher dexterity than existing MMRs with multimodal locomotion. It could jump through narrow slots to reach higher grounds; roll, two-anchor crawl, swim across tight openings with strict shape constraints; perform undulating crawling across three different planes in convoluted channels. We envision that this research will inspire future MMRs to become considerably more dexterous in navigating unstructured environments and more efficient for manipulation tasks.