Power-Scavenging MEMS Robots

This thesis includes the design, modeling, and testing of novel, power-scavenging, biologically inspired MEMS microrobots. Over one hundred 500-μm and 990-μm microrobots with two, four, and eight wings were designed, fabricated, characterized. These microrobots constitute the smallest documented attempt at powered flight. Each microrobot wing is comprised of downward-deflecting, laser-powered thermal actuators made of gold and polysilicon; the microrobots were fabricated in PolyMUMPs® (Polysilicon Multi-User MEMS Processes). Characterization results of the microrobots illustrate how wing-tip deflection can be maximized by optimizing the gold-topolysilicon ratio as well as the dimensions of the actuator-wings. From these results, an optimum actuator-wing configuration was identified. It also was determined that the actuator-wing configuration with maximum deflection and surface area yet minimum mass had the greatest lift-to-weight ratio. Powered testing results showed that the microrobots successfully scavenged power from a remote 660-nm laser. These microrobots also demonstrated rapid downward flapping, but none achieved flight. The results show that the microrobots were too heavy and lacked sufficient wing surface area. It was determined that a successfully flying microrobot can be achieved by adding a robust, light-weight material to the optimum actuator-wing configuration—similar to insect wings. The ultimate objective of the flying microrobot project is an autonomous, fully maneuverable flying microrobot that is capable of sensing and acting upon a target. Such a microrobot would be capable of precise lethality, accurate battle-damage assessment, and successful penetration of otherwise inaccessible targets

Methods Used to Evaluate the Hawkmoth (Manduca Sexta) as a Flapping-Wing Micro Air Vehicle

Examining a biological flapping-flight mechanism as a mechanical system provides valuable insight related to the development and construction of Flapping-Wing Micro Air Vehicles (FWMAVs). Insects provide excellent candidates for this reverse-engineering, and one species in particular, the hawkmoth Manduca sexta, stands out as an exceptional model. Engineers with FWMAV aspirations can benefit greatly from knowledge of M.sexta\u27s advanced yet deceptively simple flight mechanism. Avenues for investigating this mechanism include finite element modeling, nanoindentation for material properties, and mechanical power output calculations or measurement. This paper presents these concepts and reviews existing literature to provide a platform for ongoing FWMAV research and design

Challenges in flexible microsystem manufacturing : fabrication, robotic assembly, control, and packaging.

Microsystems have been investigated with renewed interest for the last three decades because of the emerging development of microelectromechanical system (MEMS) technology and the advancement of nanotechnology. The applications of microrobots and distributed sensors have the potential to revolutionize micro and nano manufacturing and have other important health applications for drug delivery and minimal invasive surgery. A class of microrobots studied in this thesis, such as the Solid Articulated Four Axis Microrobot (sAFAM) are driven by MEMS actuators, transmissions, and end-effectors realized by 3-Dimensional MEMS assembly. Another class of microrobots studied here, like those competing in the annual IEEE Mobile Microrobot Challenge event (MMC) are untethered and driven by external fields, such as magnetic fields generated by a focused permanent magnet. A third class of microsystems studied in this thesis includes distributed MEMS pressure sensors for robotic skin applications that are manufactured in the cleanroom and packaged in our lab. In this thesis, we discuss typical challenges associated with the fabrication, robotic assembly and packaging of these microsystems. For sAFAM we discuss challenges arising from pick and place manipulation under microscopic closed-loop control, as well as bonding and attachment of silicon MEMS microparts. For MMC, we discuss challenges arising from cooperative manipulation of microparts that advance the capabilities of magnetic micro-agents. Custom microrobotic hardware configured and demonstrated during this research (such as the NeXus microassembly station) include micro-positioners, microscopes, and controllers driven via LabVIEW. Finally, we also discuss challenges arising in distributed sensor manufacturing. We describe sensor fabrication steps using clean-room techniques on Kapton flexible substrates, and present results of lamination, interconnection and testing of such sensors are presented

Toward a Flying MEMS Robot

The work in this thesis includes the design, modeling, and testing of motors and rotor blades to be used on a millimeter-scale helicopter style flying micro air vehicle (MAV). Three different types of motor designs were developed and tested, which included circular scratch drives, electrostatic motors, and comb drive resonators. Six different rotor designs were tested; five used residual stress while one design used photoresist to act as a hinge to achieve rotor blade deflection. Two key parameters of performance were used to evaluate the motor and rotor blade designs: the frequency of motor rotation and the angle of deflection achieved in the rotor blades. One successful design utilized a scratch drive motor with four attached rotor blades to try to achieve lift. While the device rotated successfully, the rotational frequency was insufficient to achieve lift-off. The electrostatic motor designs proved to be a challenge, only briefly moving before shorting out; nonetheless, lessons were learned. Comb drive designs operated over a wide range of high frequencies, lending them to be a promising method of turning a rotary MAV. None of the fabricated devices were able to achieve lift, due to insufficient rotational rates and low angles of attack on the rotor blades. With slight modifications to the current designs, the required rotational rates and rotor blade deflections would yield a viable MAV. The ultimate objective of this effort was to create an autonomous MAV on the millimeter scale, able to sense and act upon targets in its environment. Such a craft would be virtually undetectable, stealthily maneuvering and capable of precision engagement

Untethered Microrobots of the Rolling, Jumping & Flying kinds

In this dissertation we study microrobot design for three modes of locomotion, namely rolling, jumping, and flying. This work covers power electronics, actuator and mechanical transmission design for these types of microrobots along with power source selection. Though interesting, we do not cover the sensors, controllers/computers, communications and useful payloads for these bots. This remains a topic for future work. Piezoelectric and electrostatic actuators generally have been the actuators of choice for researchers working in microrobotics, since conventional electromagnetic motor designs don't scale down well. Here we design an electromagnetic actuator in a way that significantly reduces its scaling down disadvantages, while still retaining its original advantages. This has enabled us to achieve untethered operation for our bots, which is one of the coveted goals for researchers working in this domain. Though untethered rolling and jumping is demonstrated, the untethered flying bot reported in this dissertation remains underpowered and doesn't take flight yet. First a micro-ratcheting mechanism is developed as a means to convert small periodic motions of actuators to continuous rotational motion. A supercapacitor, a fixed frequency H-bridge, and a low-voltage electromagnetic actuator is then used to drive this micro-ratchet to achieve untethered rolling motion for 8 seconds at 27mm/s. At 130mg mass, this is the lightest and fastest untethered rolling microrobot reported yet. The same continuous rotation mechanism developed for the rolling bot is then used to load a spring in an energy storage mechanism that can then release the stored energy rapidly and passively, via use of magnets, after the stored energy crosses a certain threshold. In this case, the continuous rotation mechanism is driven using laser-powered photovoltaic cells and untethered jumping up to heights of 8mm is demonstrated. At 75mg mass, it is the lightest untethered jumping microrobot with onboard power source. Next, a highly efficient resonant low-voltage electromagnetic actuator is developed to generate insect-like flapping wing motion. It is demonstrated to produce 90% of its weight in lift. Further light-weight and power-efficient power electronics are developed to power this actuator using laser-powered photovoltaic cells. The designed power electronics are an order of magnitude lighter and two orders of magnitude more efficient than all other power electronics units reported yet for flying microrobots. While sufficient lift for flight is not achieved, due to the actuator being underpowered because of power source overheating, untethered flapping wing motion is demonstrated. To provide inspiration to future generations of microroboticists, a fruit fly scale flapping winged robot is developed. At 0.7mg mass, even though tethered, it is the lightest and smallest bot to demonstrate flapping wing kinematics

Conceptual Study of Rotary-Wing Microrobotics

This thesis presents a novel rotary-wing micro-electro-mechanical systems (MEMS) robot design. Two MEMS wing designs were designed, fabricated and tested including one that possesses features conducive to insect level aerodynamics. Two methods for fabricating an angled wing were also attempted with photoresist and CrystalBond™ to create an angle of attack. One particular design consisted of the wing designs mounted on a gear which are driven by MEMS actuators. MEMS comb drive actuators were analyzed, simulated and tested as a feasible drive system. The comb drive resonators were also designed orthogonally which successfully rotated a gear without wings. With wings attached to the gear, orthogonal MEMS thermal actuators demonstrated wing rotation with limited success. Multi-disciplinary theoretical expressions were formulated to account for necessary mechanical force, allowable mass for lift, and electrical power requirements. The robot design did not achieve flight, but the small pieces presented in this research with minor modifications are promising for a potential complete robot design under 1 cm2 wingspan. The complete robot design would work best in a symmetrical quad-rotor configuration for simpler maneuverability and control. The military’s method to gather surveillance, reconnaissance and intelligence could be transformed given a MEMS rotary-wing robot’s diminutive size and multi-role capabilities