Pratheev Sreetharan

Pop-up book MEMS

We present a design methodology and manufacturing process for the construction of articulated three-dimensional microstructures with features on the micron to centimeter scale. Flexure mechanisms and assembly folds result from the bulk machining and lamination of alternating rigid and compliant layers, similar to rigid-flex printed circuit board construction. Pop-up books and other forms of paper engineering inspire designs consisting of one complex part with a single assembly degree of freedom. Like an unopened pop-up book, mechanism links reside on multiple interconnected layers, reducing interference and allowing folding mechanisms of greater complexity than achievable with a single folding layer. Machined layers are aligned using dowel pins and bonded in parallel. Using mechanical alignment that persists during bonding allows device layers to be anisotropically pre-strained, a feature we exploit to create self-assembling structures. These methods and three example devices are presented.

Monolithic fabrication of millimeter-scale machines

Silicon-based MEMS techniques dominate sub-millimeter scale manufacturing, while a myriad of conventional methods exist to produce larger machines measured in centimeters and beyond. So-called mesoscale devices, existing between these length scales, remain difficult to manufacture. We present a versatile fabrication process, loosely based on printed circuit board manufacturing techniques, for creating monolithic, topologically complex, three-dimensional machines in parallel at the millimeter to centimeter scales. The fabrication of a 90?mg flapping wing robotic insect demonstrates the sophistication attainable by these techniques, which are expected to support device manufacturing on an industrial scale.

Progress on 'pico' air vehicles

As the characteristic size of a flying robot decreases, the challenges for successful flight revert to basic questions of fabrication, actuation, fluid mechanics, stabilization, and power, whereas such questions have in general been answered for larger aircraft. When developing a flying robot on the scale of a common housefly, all hardware must be developed from scratch as there is nothing ‘off-the-shelf’ which can be used for mechanisms, sensors, or computation that would satisfy the extreme mass and power limitations. This technology void also applies to techniques available for fabrication and assembly of the aeromechanical components: the scale and complexity of the mechanical features requires new ways to design and prototype at scales between macro and microeletromechanical systems, but with rich topologies and material choices one would expect when designing human-scale vehicles. With these challenges in mind, we present progress in the essential technologies for insect-scale robots, or ‘pico’ air vehicles.

Biologically-inspired locomotion of a 2g hexapod robot

Here we present the design, modeling, and fabrication of a 2g mobile robot. By applying principles from biology and existing meso-scale fabrication techniques, a 5.7cm hexapod robot with sprawled posture has been created, and is capable of locomotion up to 4 body-lengths per second using the alternating tripod gait at 20Hz actuation frequency. Furthermore, this work proves the viability of a new mechanical linkage design, fabricated using the smart composite microstructure process, to provide desirable leg trajectories for successful ambulation at the insect-scale.

Passive torque regulation in an underactuated flapping wing robotic insect

Recent developments in millimeter-scale fabrication processes have led to rapid progress towards creating airborne flapping wing robots based on Dipteran (two winged) insects. Previous work to regulate forces and torques generated by flapping wings has focused on controlling wing trajectory. An alternative approach uses underactuated mechanisms with tuned dynamics to passively regulate these forces and torques. The resulting ‘mechanically intelligent’ devices execute wing trajectory corrections to realize desired body forces and torques without the intervention of an active controller.This article describes an insect-scale flapping wing mechanism consisting of a single piezoelectric actuator, an underactuated transmission, and passively rotating wings. Wing stroke velocities are passively modulated to eliminate net airframe roll torque. A theoretical model predicts lift generating wing trajectories and quantifies the passive reduction in roll torque. An experimental structure provides an at-scale demonstration of passive torque regulation.