Magmites - wireless resonant magnetic microrobots

Abstract

Primary challenges in the building of untethered sub-millimeter sized robots include power supply, propulsion methods, and control. We present a novel type of microrobot termed Magmite that utilizes a new class of wireless magnetic actuator which accomplishes all three tasks. The device harvests magnetic energy from the environment and effectively transforms it into mechanical propulsion while being fully controllable. This microrobotic agent with dimensions less than 300 µm x 300 µm x 70 µm is capable of maneuvering with 3 degrees of freedom. A specially prepared substrate allows for adjustable speeds exceeding 12.5 mm/s or 42 times the robot's body length per second (see accompanying video). It is powered by oscillating fields in the kHz range and strengths as low as 2 mT -roughly 50 times the average earth magnetic field.

Control of many robots moving in the same direction with different speeds: A decoupling approach

“…As a case study in the control of microscale and nanoscale robotic systems, this paper considered the problem of controlling a group of microrobots that can move at different speeds but that must all move in the same direction [21], [22]. Since all robots must move in the same direction, the dynamic system is both nonlinear and coupled.…”

“…1, the value of ω does not have to be large-choosing ω = 5 (in other words, rotating the movement direction u(t) at a frequency of slightly less than 1 Hz) already significantly lowers the worst-case cost. Furthermore, for the robotic system of interest that we described in Section I [21], [22], ω = 5 is several orders of magnitude smaller than the resonant frequencies used to drive the microrobots.…”

“…As a case study, in this paper we consider a particular microscale robotic system, the "Magmite," that was developed recently by researchers at the Institute of Robotics and Intelligent Systems (ETH-Zurich) [21], [22]. It is controlled by an external magnetic field: rotating the field rotates the robot, while oscillating the field drives the robot to resonance and propels it forward.…”

“…In particular, it was a design compromise to restrict the movement of all robots to the same direction while allowing different speeds [21], [22]. We can say exactly what the expected cost would be if this constraint were lifted.…”

Modeling and analysis of wireless resonant magnetic microactuators

“…An additional electrostatic clamping force between the body and the ground allows arbitrary rectification of the oscillation by effectively controlling the friction between the robot and the ground. Such a device can be used for propelling microrobots-in particular the MagMites-a family of microrobotic agents based on the WRMMA, which were introduced in 2007, described in detail in [7], [8], [12] and demonstrated by video [13], [14]. Primary responses and driving behaviors have been experimentally characterized [12], and the overall performance was observed to be largely as intended by design: firstly, reliable turning behavior thanks to alignment with the external magnetic field; and secondly controlled forward and backward motion at near resonance thanks to rectification with a phaseshifted clamping potential in the substrate.…”