Michael J. Smith

Design and manufacturing rules for maximizing the performance of polycrystalline piezoelectric bending actuators

Increasing the energy and power density of piezoelectric actuators is very important for any weight-sensitive application, and is especially crucial for enabling autonomy in micro/milli-scale robots and devices utilizing this technology. This is achieved by maximizing the mechanical flexural strength and electrical dielectric strength through the use of laser-induced melting or polishing, insulating edge coating, and crack-arresting features, combined with features for rigid ground attachments to maximize force output. Manufacturing techniques have also been developed to enable mass customization, in which sheets of material are pre-stacked to form a laminate from which nearly arbitrary planar actuator designs can be fabricated using only laser cutting. These techniques have led to a 70% increase in energy density and an increase in mean lifetime of at least 15× compared to prior manufacturing methods. In addition, measurements have revealed a doubling of the piezoelectric coefficient when operating at the high fields necessary to achieve maximal energy densities, along with an increase in the Youngs modulus at the high compressive strains encountered—these two effects help to explain the higher performance of our actuators as compared to that predicted by linear models.

Electronic image stabilization using optical flow with inertial fusion

When a camera is affixed on a dynamic mobile robot, image stabilization is the first step towards more complex analysis on the video feed. This paper presents a novel electronic image stabilization (EIS) algorithm for highly dynamic mobile robotic platforms. The algorithm combines optical flow motion parameter estimation with angular rate data provided by a strapdown inertial measurement unit (IMU). A discrete Kalman filter in feedforward configuration is used for optimal fusion of the two data sources. Performance evaluations are conducted using a simulated video truth model (capturing the effects of image translation, rotation, blurring, and moving objects), and live test data. Live data was collected from a camera and IMU affixed to the DAGSI Whegs mobile robotic platform as it navigated through a hallway. Template matching, feature detection, optical flow, and inertial measurement techniques are compared and analyzed to determine the most suitable algorithm for this specific type of image stabilization. Pyramidal Lucas-Kanade optical flow using Shi-Tomasi good features in combination with inertial measurement is the EIS algorithm found to be superior. In the presence of moving objects, fusion of inertial measurement reduces optical flow root-mean-squared (RMS) error in motion parameter estimates by 40%.

Aerodynamic evaluation of four butterfly species for the design of flapping-gliding robotic insects

Alternating gliding and active propulsion is a potentially energy saving strategy for small-scale flight. With the goal of finding optimal wing shapes for flapping-gliding robots we evaluate the quasi-steady aerodynamic performance of four butterfly species (Monarch (Danaus plexippus), the Orange Aeroplane (Pantoporia consimilis), the Glasswing (Acraea andromacha) and the Four-barred Swordtail (Protographium Ieosthenes)). We fabricate at-scale wing models based on measured wing shapes and vary the forewing angle in nine steps to account for the ability of the butterfly to change the relative orientation of its forewing and hindwing during flight. For comparison we include twelve non-biological planforms as performance benchmarks for the butterfly wing shapes. We then test these 48 wing models at 2m/s, 3.5m/s and 5m/s (Reynolds number between 2597 and 12632) in a low speed wind tunnel which allows lift and drag force measurements of centimeter-size wings. The results indicate that the forewing orientation which maximizes the wing span offers the best gliding performance and that overall the gliding ratios are highest at 3.5m/s. The wing shapes with the best gliding ratio are found in the Glasswing butterfly with a maximum of 6.26 which is very high compared to the gliding performance of similarly sized flying robots. The results from this study are important for the development of novel biologically-inspired flying micro robots as well as for biomechanics studies in biology.

Estimating surgical needle deflection with printed strain gauges.

The ability to track surgical needle deflection during procedures such as therapeutic drug delivery, biopsies, and medical device implantation allows clinicians to minimize positioning errors and procedural complications due to instrument deviations. We describe the use of a novel strain gauge printing method to sensorize surgical needles for the purpose of sensing needle shape and deflection during surgical procedures. The additive vapor-deposition based sensor fabrication method used here is capable of applying strain gauges (and resistive circuit elements) with micron-scale features onto surgical instruments of varying curvature and material composition without the need for mechanical machining. This fabrication method is used to apply several strain gauges onto an 18 gauge core biopsy needle to sense deflections. Validation experiments demonstrate a gauge factor of 1.16 for the printed strain gauges and nominal needle deflection measurement resolution of 500 microns.

A Cryogenic Stabilization Scheme for Radio Astronomy Applications

We report on a scheme to stabilize short term cryogenic temperature variations in equipment used for high frequency radio telescope receivers. A 45.9 cm3 copper helium pot is affixed to a Sumitomo/Daikin 308, GM/JT cold head. 5.7×103 cm3 of helium gas is introduced at the end of the cooling cycle and condensation until zero kPaa is reached. Short term temperature stabilization is achieved through the specific heat of the liquefied helium diminishing thermal deviations up to 46%.© 2009 ASME

Cryogenic Temperature Stabilization of the Daikin 308 Cryocooler

We report on a scheme developed at the Harvard-Smithsonian Center for Astrophysics to stabilize longer term cryogenic temperature variations in equipment used for high frequency radio telescope receivers. Cryogenic temperature variations of the 30 minute time scale are reduced an average of 55 percent by controlling the helium pressure flowing through the cryostat. Applications in the field of cryogenic radio astronomy will benefit from this resulting reduction of power fluctuations and corresponding reductions in observation time on source. An Equilibar® back pressure regulator was used to allow helium from the compressor to bypass the cryostat, thereby providing a very stable pressure control system. Manually set reference port pressure regulates the helium bypass and deviates less than 6.2 × 10^−4 MPa for the 30 minute time period while power output deviations of the heterodyne receiver are reduced as a result of the increase in pressure stability an average of 46%.Copyright