Researcher: Adam Wahab
ANTS (Autonomous Nano-stepping Tool System) represents a paradigm shift in the design and implementation of precision scientific instruments. Conventional scientific apparatus intended for measurement and manipulation at micro/nano scales is often prohibitively expensive, imposing a limitation on accessibility. Furthermore, traditional micro/nano instrumentation platforms offer a restricted workspace, which limits specimen size and, potentially, system throughput. ANTS circumvents these shortcomings by combining low-cost fabrication techniques with a high-degree of subsystem integration, and by inverting the existing notion that specimens should be delivered to stationary bench-top instruments.
Each ANT (Autonomous Nano-stepping Tool) is a self-contained, miniature, mobile, robotic platform capable of untethered, holonomic positioning within an arbitrarily large planar workspace. ANTs may operate independently, allowing for large-scale parallel processing, or cooperatively for more elaborate tasks, such as fabrication or assembly. In volume, each ANT unit has a relatively low cost as compared to traditional precision positioning systems. An open-source, platform-independent browser-based user interface for control and monitoring further enhances accessibility and system flexibility.
Locomotion is achieved using three piezoelectric tubes, which serve as legs, each capable of three degree-of-freedom motion. The current implementation is capable of translational and rotational rates in excess of 3 mm/s and 6°/s, respectively, with step sizes ranging from hundreds of nanometers to greater than 1 μm. Compact, efficient high-voltage electronics were developed to individually drive each of the twelve leg electrodes.
The ANT subsystems have already undergone several major revisions. The first major revision, Mark II, involved integrating all of the electronic subsystems onto a fiber-resin composite reinforced flexible printed circuit board, or flex-PCB. The flex-PCB is then folded into a cube, thus serving as a stiff, yet light-weight chassis. Rechargeable lithium-polymer cells, which power the ANT, are contained inside of the body and provide more than 30 minutes of operation.
The most recent revision, Mark III, aims to provide the simplicity of the interconnect-free Mark II design, whilst allowing some degree of modularity, to facilitate subsystem prototyping and maintenance. Each subsystem (power management, core processing and control, wireless communication, locomotion, and instrumentation) is fabricated on a traditional rigid PCB module. The modules are then soldered to a generic flex-PCB backplane, much like surface mount components. This approach allows individual modules to be redesigned and/or replaced without necessitating modifications to the other subsystems.
For demonstration purposes, a miniature atomic force microscope (AFM) is being developed to serve as the first task-specific instrumentation module. The AFM utilizes active cantilevers, which include integrated thermal actuation and piezoresistive strain sensors. A small, low-power field programmable gate array (FPGA) controls the cantilever scanning and tapping motions, while data is acquired via a high-speed, high-resolution analog-to-digital converter. Acquired data will be transmitted wirelessly to a computer for processing and analysis.
An onboard vision system has been designed to allow each ANT to track its position during operation. Image data from a downward-facing miniature CMOS image sensor is be fed into a hardware accelerated, pipelined 2-D cross-correlation engine running on the aforementioned FPGA. The cross-correlation may be computed between subsequent images for relative position estimation, or with a stored template image of a patterned workspace surface for absolute positioning.