Craig D. McGray

The self-reconfiguring robotic molecule

We discuss a robotic module called a molecule. Molecules can be the basis for building self-reconfiguring robots. They support multiple modalities of locomotion and manipulation. We describe the design, functionality, and control of the molecule. We show how a set of molecules can aggregate as active three-dimensional structures that can move and change shape. Finally, we discuss our molecule experiments.

Power delivery and locomotion of untethered microactuators

The ability for a device to locomote freely on a surface requires the ability to deliver power in a way that does not restrain the devices motion. This paper presents a MEMS actuator that operates free of any physically restraining tethers. We show how a capacitive coupling can be used to deliver power to untethered MEMS devices, independently of the position and orientation of those devices. Then, we provide a simple mechanical release process for detaching these MEMS devices from the fabrication substrate once chemical processing is complete. To produce these untethered microactuators in a batch-compatible manner while leveraging existing MEMS infrastructure, we have devised a novel postprocessing sequence for a standard MEMS multiproject wafer process. Through the use of this sequence, we show how to add, post hoc , a layer of dielectric between two previously deposited polysilicon films. We have demonstrated the effectiveness of these techniques through the successful fabrication and operation of untethered scratch drive actuators. Locomotion of these actuators is controlled by frequency modulation, and the devices achieve maximum speeds of over 1.5 mm/s.

Power delivery and locomotion of untethered micro-actuators

This paper presents a micro-actuator that operates free of any physically restraining tethers. We show how capacitive coupling can be used to deliver power to MEMS devices, independently of the position and orientation of those devices. Then, we provide a simple mechanical release process for detaching MEMS devices from the fabrication substrate once chemical processing is complete. To produce these untethered micro-actuators in a batch-compatible manner while leveraging existing MEMS infrastructure, we have devised a novel post-processing sequence for the PolyMUMPS process. Through the use of this sequence, we show how to add, post hoc, a layer of dielectric between two previously-deposited polysilicon films. We have demonstrated the effectiveness of these techniques through the successful fabrication and operation of untethered scratch drive actuators. Locomotion of these actuators is controlled by frequency modulation, and the devices achieve speeds of over 1.5 mm/sec.

Self-reconfigurable molecule robots as 3D metamorphic robots

This paper describes a three-dimensional self-reconfiguring system that is capable of reconfiguration and the associated planning in polynomial time. The approach is to reduce a system composed of molecule robots to metamorphic robots. Having done so, we are able to apply polynomial-time planning algorithms that have previously been used only in two-dimensional systems.

MEMS Kinematics by Super-Resolution Fluorescence Microscopy

Super-resolution fluorescence microscopy is used for the first time to study the nanoscale kinematics of a MEMS device in motion across a surface. A device under test is labeled with fluorescent nanoparticles that form a microscale constellation of near-ideal point sources of light. The constellation is imaged by widefield epifluorescence microscopy, and the image of each nanoparticle is fit to a Gaussian distribution to calculate its position. Translations and rotations of the device are measured by computing the rigid transform that best maps the constellation from one image to the next. This technique is used to measure the stepwise motion of a scratch drive actuator across each of 500 duty cycles with 0.13-nm localization precision, 1.85-nm displacement uncertainty, and 100-μrad orientation uncertainty for a constellation diameter of 15 μm. This novel measurement reveals acute aperiodic variations in the step size of the actuator, which have been neither previously observed nor predicted by any of the published models of the operation of the device. These unexpected results highlight the importance of super-resolution fluorescence microscopy to the measurement of MEMS kinematics, which will have broad impact in fundamental investigations of surface forces, wear, and tribology in MEMS and related applications.

Untethered Micro-Actuators for Autonomous Micro-robot Locomotion: Design, Fabrication, Control, and Performance

This paper presents a micro-actuator that operates free of any physically restraining tethers. We show how capacitive coupling can be used to deliver power to untethered MEMS (micro-electromechanical systems) devices, independently of their position and orientation. Our novel power delivery and actuation mechanisms are designed for use in autonomous mobile robots whose dimensions can be measured in tens to hundreds of micrometers. Test devices utilizing these mechanisms have been fabricated at scale using MEMS technology, and have been shown capable of untethered locomotion at speeds exceeding 1.5 mm/sec. The corresponding speed, scaled to a car-sized robot would be over 100 km/hr. The possibility of autonomous (untethered) microactuators and microrobots less than 80 μm in length opens the door to novel applications in distributed and parallel robotics.

A Steerable, Untethered, 250 × 60 µm MEMS Mobile Micro-Robot

We present a steerable, electrostatic, untethered, MEMS micro-robot, with dimensions of 60 µm by 250 µm by 10 µm. This micro-robot is 1 to 2 orders of magnitude smaller in size than previous micro-robotic systems. The device consists of a curved, cantilevered steering arm, mounted on an untethered scratch drive actuator. These two components are fabricated monolithically from the same sheet of conductive polysilicon, and receive a common power and control signal through a capacitive coupling with an underlying electrical grid. All locations on the grid receive the same power and control signal, so that the devices can be operated without knowledge of their position on the substrate and without constraining rails or tethers. Control and power delivery waveforms are broadcast to the device through the capacitive power coupling, and are decoded by the electromechanical response of the device body. Individual control of the component actuators provides two distinct motion gaits (forward motion and turning), which together allow full coverage of a planar workspace (the robot is globally controllable). These MEMS micro-robots demonstrate turning error of less than 3.7 °/mm during forward motion, turn with radii as small as 176 µm, and achieve speeds of over 200 µm/sec, with an average step size of 12 nm. They have been shown to operate open-loop for distances exceeding 35 cm without failure, and can be controlled through teleoperation to navigate complex paths.