Onur Ozcan

High speed locomotion for a quadrupedal microrobot

Research over the past several decades has elucidated some of the mechanisms behind high speed, highly efficient, and robust locomotion in insects such as cockroaches. Roboticists have used this information to create biologically inspired machines capable of running, jumping, and climbing robustly over a variety of terrains. To date, little work has been done to develop an at-scale insect-inspired robot capable of similar feats due to challenges in fabrication, actuation, and electronics integration for a centimeter-scale device. This paper addresses these challenges through the design, fabrication, and control of a 1.27 g walking robot, the Harvard Ambulatory MicroRobot (HAMR). The current design is manufactured using a method inspired by pop-up books that enables fast and repeatable assembly of the miniature walking robot. Methods to drive HAMR at low and high speeds are presented, resulting in speeds up to 0.44 m/s (10.1 body lengths per second) and the ability to maneuver and control the robot along desired trajectories.

Automated 2-D Nanoparticle Manipulation Using Atomic Force Microscopy

An automated manipulation procedure for spherical nanoparticles with an atomic force microscope (AFM) in 2-D is demonstrated. Robust particle-center and contact-loss detection algorithms are developed using force feedback to improve speed and reliability issues of AFM-based nanomanipulation. Unlike blind manipulation techniques, contact-loss detection enables better control over the success of manipulation. For pattern formation and assembly operations, a fully automated multiple-particle-manipulation method is developed, based on a commanding task planner. The task planner minimizes the obstacles to manipulation trajectories for better efficiency. Forces during AFM tip-particle-substrate contact are analyzed theoretically to determine the mode of manipulation as well as the effect of cantilever normal stiffness. The developed system is used to form patterns and assemblies of 100-nm-diameter gold nanoparticles on a flat substrate.

STRIDE II: A Water Strider-inspired Miniature Robot with Circular Footpads

Water strider insects have attracted the attention of many researchers due to their power-efficient and agile water surface locomotion. This study proposes a new water strider insect-inspired robot, called STRIDE II, which uses new circular footpads for high lift, stability and payload capability, and a new elliptical leg rotation mechanism for more efficient water surface propulsion. Using the advantage of scaling effects on surface tension versus buoyancy, similar to water strider insects, this robot uses the repulsive surface tension force on its footpads as the dominant lift principle instead of creating buoyancy by using very skinny (1 mm diameter) circular footpads coated with a superhydrophobic material. The robot and the insect propel quickly and power efficiently on the water surface by the sculling motion of their two side-legs, which never break the water surface completely. This paper proposes models for the lift, drag and propulsion forces and the energy efficiency of the proposed legged robot, and experiments are conducted to verify these models. After optimizing the robot design using the lift models, a maximum lift capacity of 55 grams is achieved using 12 footpads with a 4.2 cm outer diameter, while the robot itself weighs 21.75 grams. For this robot, a propulsion efficiency of 22.3% was measured. The maximum forward and turning speeds of the robot were measured as 71.5 mm/sec and 0.21 rad/sec, respectively. These water strider robots could be used in water surface monitoring, cleaning and analysis in lakes, dams, rivers and the sea.

Bio-inspired mechanisms for inclined locomotion in a legged insect-scale robot

Legged locomotion is an open problem in robotics, particularly for non-level surfaces. With decreasing robot size, different issues for climbing mechanisms and their attachment and detachment appear due to the physics of scaling. This paper describes micro-scale phenomena for different adhesion methods that can be employed in microrobots. These adhesion methods are applied to a sub-2 gram legged robot, the Harvard Ambulatory MicroRobot (HAMR), by leveraging recent advances in milli- and micrometer-scale manufacturing. The presented designs utilize different passively oriented adhesives on the legs of the robot to improve inclined locomotion performance. A 3DoF ankle joint is designed and implemented and the effects of a passive tail are studied. As a result, HAMRs climbing capability is increased from 3° inclines to 22° inclines and 45° declines. Finally, an analytical model of leg and foot force generation is presented and compared with experimental force data from the attachment mechanism on a single-leg experimental setup.

Powertrain selection for a biologically-inspired miniature quadruped robot.

Transmission and actuator selection are crucial for robot locomotion at any scale. This is especially true at small scales where actuation choices are limited and locomotion is energetically expensive. These components control the payload capacity and determine the height of the obstacles the robot can navigate over. In this study, we analyze the drivetrain of the new Harvard Ambulatory MicroRobot (HAMR-V) to improve its walking performance. We modeled several transmission and actuator design concepts and investigated their force and displacement outputs. The results led to the selection of improved actuator and transmission designs. Using these new insights, we constructed a miniature quadruped with a payload capacity of 63% of its weight that can be used for on-board electronics for sensing, control, and power.

A wirelessly powered, biologically inspired ambulatory microrobot

Onboard power remains a major challenge for miniature robotic platforms. Locomotion at small scales demands high power densities from all system components, while limited payload capacities place severe restrictions on the size of the energy source, resulting in integration challenges and short operating times when using conventional batteries. Wireless power delivery has the potential to allow microrobotic platforms to operate autonomously for extended periods when near a transmitter. This paper describes the first demonstration of RF wireless power transfer in an insect-scale ambulatory robot. A wireless power transmission system based on magnetically coupled resonance is designed for the latest iteration of the Harvard Ambulatory MicroRobot (HAMR), a piezoelectrically driven quadruped that had previously received power through a tether. Custom power and control electronics are designed and implemented on lightweight printed circuit boards that form a part of the mechanical structure of the robot. The integration of the onboard receiver, power and control electronics, and mechanical structure yields a 4cm, 2.1g robot that can operate autonomously in two wireless power transmission scenarios.

Automated 2-D nanoparticle manipulation with an atomic force microscope

Atomic force microscope (AFM) based nanomanipulation systems are generally slow, not repeatable and imprecise due to a lack of control on the success of limited attempts in the literature. To improve the amount of control, reliability and precision of such systems, this work proposes an automated nanomanipulation method. Spherical gold nanoparticles with 100 nm diameter are positioned mechanically on a flat mica substrate by contact manipulation by the AFM probe tip to a desired position autonomously. The most significant issue of the manipulation operation is the lack of real-time visual feedback. This issue is solved by developing a robust algorithm for particle center detection and using the AFM cantilever deflection (force) signals to detect contact losses in real-time and to repeat the manipulation again until the target location is reached. Using these solutions, an automated AFM manipulation system is developed and a statistical study is made, where gold nanoparticles are positioned for 50 times to random target positions in different directions and pushing distances. 86% of all the particles could be successfully positioned to the target positions with an accuracy less than 100 nm. Unsuccessful positioning operations are due to the particle sticking to either the tip (8%) or the substrate (6%). Additionally, performance of the successful manipulations are investigated on 60 manipulation operations in 12 different directions and 5 different distances. The metrics used to quantify performance are the final particle position error and the average manipulation speed.

Feedback control of a legged microrobot with on-board sensing

Full autonomy remains a challenge for miniature robotic platforms due to mass and size requirements of on-board power and control electronics. This paper presents a solution to these challenges with a 2.3g autonomous legged robot. An off-the-shelf optical mouse sensor is adapted for use on the Harvard Ambulatory Microrobot (HAMR) by reducing the sensor weight by 36% and achieving a position error below 11% when suspended 3mm above a cardstock surface. The position data is combined with data from a gyroscope for feedback control of both position and orientation. A microcontroller processes the sensor data and commands a controlled gait to HAMR that is powered by a battery, a boost converter and high voltage drive electronics. Solar cells are used as an alternative source providing enough power for autonomous operation of the robot. The resulting deviation for a controlled straight-line walk using both sensors to minimize lateral deviation and angular error is only 4.6%, compared to an error of 31% in an uncontrolled, straight-line walk.

Planar fabrication of a mesoscale voice coil actuator

Mesoscale robots are devices with characteristic dimensions in the centimeter to millimeter scale, with feature sizes ranging from millimeters to micrometers. Due to the physics involved in scaling down conventional motors, such robots frequently require novel approaches to actuation. Actuation can have a very significant effect on robot performance, particularly at small scales where locomotion becomes energetically expensive; however, existing options for small-scale actuation are quite limited. We present a mesoscale voice coil actuator (VCA) with favorable scaling characteristics and a design that minimizes costly frictional effects at small scales while allowing fast, linear, high-displacement motion. The VCA is fabricated using planar manufacturing techniques, making it well-suited for integration into a number of mesoscale robotic platforms and for mass production. The designed VCA has a mass of 310mg, maximum force of 11.8mN, bandwidth of 51Hz, and a stroke of 4mm.

Design and feedback control of a biologically-inspired miniature quadruped

Insect-scale legged robots have the potential to locomote on rough terrain, crawl through confined spaces, and scale vertical and inverted surfaces. However, small scale implies that such robots are unable to carry large payloads. Limited payload capacity forces miniature robots to utilize simple control methods that can be implemented on a simple onboard microprocessor. In this study, the design of a new version of the biologically-inspired Harvard Ambulatory MicroRobot (HAMR) is presented. In order to find the most suitable control inputs for HAMR, maneuverability experiments are conducted for several drive parameters. Ideal input candidates for orientation and lateral velocity control are identified as a result of the maneuverability experiments. Using these control inputs, two simple feedback controllers are implemented to control the orientation and the lateral velocity of the robot. The controllers are used to force the robot to track trajectories with a minimum turning radius of 55 mm and a maximum lateral to normal velocity ratio of 0.8. Due to their simplicity, the controllers presented in this work are ideal for implementation with on-board computation for future HAMR prototypes.