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Bidirectional microscale rocker robots controlled via neutral position offset

A Correction to this article was published on 01 December 2021

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The recent advancements in nanoscale 3D printing and microfabrication techniques have reinvigorated research on microscale robots (microrobots). However, precise motion control of microrobots using compact actuation/control setups remains challenging to date. This work presents a novel motion direction control mechanism and contact design that enables bidirectional steering and object pushing. This is done via biasing the tilt position of the microrobot during stick–slip motion with an out-of-plane magnetic field generated by a single, compact coil. Equipped with rockers to contact the substrate, the microrobot—hence microrocker bot—is capable of well-controlled, selectable, forward, and backward movement given a set orientation. These 100 μm × 113 μm × 36 μm robots were 3D printed via two-photon lithography and subsequently deposited with a 300 nm layer of nickel, which determined their magnetization directions based on thin film magnetoelastic anisotropy. Under a static magnetic field, the bot tilts either forward or backward to align its magnetization vectors with the magnetic field lines. Combined with an oscillating magnetic field, the robot undergoes stick–slip motion in the predisposed direction, dictated by the tilt. Experimentally, the robot can travel up to 100 μm/s (1 body length per second) forward and backward and demonstrate micromanipulation capabilities. Finally, the robot dynamics is theoretically modeled and validated to analyze the present forces and the stick–slip motion.

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All data generated or analysed during this study are included in this published article (and its supplementary information files).

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This work is supported by Georgia Tech Institute for Electronics and Nanotechnology (IEN) and the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1650044. The device fabrication was performed at the Georgia Tech Institute for Electronics and Nanotechnology clean room facilities, a member of the National Nanotechnology Coordinated Infrastructure (NNCI), which is supported by the National Science Foundation (Grant ECCS-1542174). The authors acknowledge Prof. Saad Bhamla for the helpful discussions and insight and thank Prof. Martin Mourigal for magnetic characterization. Additionally, the authors thank Prof. Yuhang Hu for supplying polystyrene beads used for micromanipulation experiments and Dr. Chytra Pawashe for providing insights on simulation coding.

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Authors and Affiliations



T.W. and D.K. fabricated microrobots, designed experiments, and collected data under the guidance of A.A. Y.F. processed videos for motion tracking. C.H. helped generate images for figures.

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Correspondence to Azadeh Ansari.

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The original online version of this article was revised: the correct Supplementary Materials has been uploaded and replaces the incorrect materials.

Supplementary Information

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Movie S1: Microrocker Bot Bidirectional Travel. Under a magnetic sawtooth wave of amplitude 2.82mTpp and frequency 10Hz, the microrocker bot is able to move bidirectionally on a glass substrate at approximately 100μm/s for a total of 1.6mm. The static magnetic offsets for forward and backward motions are 307μT and -77μT respectively. A slight deviation in trajectory may be attributed to surface irregularities (MP4 1.21 MB).

Movie S2: Two Microrocker Bots Moving in Opposite Directions. Since the magnetic field is approximately out-of-plane to the microrobots, it serves more as a disruptive and restorative mechanism for generating oscillatory, stick-slip motion. As a result, two microrocker bots facing opposite to one another will move in opposite directions, demonstrating negligible influence from in-plane gradients. Here, the field amplitude is 2.82mTpp, the offset is -77μT, and the frequency is 2Hz (MP4 2.49 MB).

Movie S3: Micromanipulation of a 50μm Polystyrene Bead. Since the microrocker bot is restricted to bidirectional motion, the polystyrene bead is placed in its line of sight. The adhesive forces then allow the microrocker bot to pick up the bead and deliver it to a location, where a static magnetic field of amplitude ±5mT is alternatively switched. In response, the microrocker bot undergoes mechanical acceleration to remove the bead. Afterwards, the microrobot returns to close to its original position. The parameters found sufficient to push the bead were a field amplitude of 5.54mTpp, static magnetic offsets of 180/-90μT for forward/backward motion, and a frequency of 14Hz (MP4 1.24 MB).

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Wang, T., Kim, D., Shi, Y. et al. Bidirectional microscale rocker robots controlled via neutral position offset. J Micro-Bio Robot 17, 103–114 (2021).

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  • Microrobot
  • Magnetic Actuation
  • Steering
  • 3D Print