Real-Time Control of Cycling in a High-Performance Leg With Series-Elastic Actuation

Bachelor of Science with DistinctionA high-performance, lightweight prototype robotic leg using series-elastic actuation was developed in previous work to study the effects of series-elastic actuation in vertical jumping. However, there was also a desire to perform other high-speed dynamic motions with the leg such as cycling. To this end, the thesis goals were focused on improving the existing embedded controller as well as implementing a high-speed cycling function. An analog potentiometer was used to replace a faulty sensor at the knee joint, which houses the compliant element of the series-elastic actuator. Changes were made to the previous controller hardware and software in order to utilize the data available from this new sensor. Using several new functions, a smooth cyclical trajectory was created and followed by the robotic leg at high speeds. The entire cycle was completed in less than 0.5 seconds with a stroke of more than 15cm. These functions will open the path for development of precise trajectory control in future robotic legs, as well as allow for the study of series-elastic actuation through a new dynamic motion. The design of the aforementioned changes and functions are discussed. The significance of the thesis results is discussed, as well as the expected course of future work.National Science Foundatio

Rapid inversion: running animals and robots swing like a pendulum under ledges.

Escaping from predators often demands that animals rapidly negotiate complex environments. The smallest animals attain relatively fast speeds with high frequency leg cycling, wing flapping or body undulations, but absolute speeds are slow compared to larger animals. Instead, small animals benefit from the advantages of enhanced maneuverability in part due to scaling. Here, we report a novel behavior in small, legged runners that may facilitate their escape by disappearance from predators. We video recorded cockroaches and geckos rapidly running up an incline toward a ledge, digitized their motion and created a simple model to generalize the behavior. Both species ran rapidly at 12-15 body lengths-per-second toward the ledge without braking, dove off the ledge, attached their feet by claws like a grappling hook, and used a pendulum-like motion that can exceed one meter-per-second to swing around to an inverted position under the ledge, out of sight. We discovered geckos in Southeast Asia can execute this escape behavior in the field. Quantification of these acrobatic behaviors provides biological inspiration toward the design of small, highly mobile search-and-rescue robots that can assist us during natural and human-made disasters. We report the first steps toward this new capability in a small, hexapedal robot

Hospital service areas – a new tool for health care planning in Switzerland

BACKGROUND: The description of patient travel patterns and variations in health care utilization may guide a sound health care planning process. In order to accurately describe these differences across regions with homogeneous populations, small area analysis (SAA) has proved as a valuable tool to create appropriate area models. This paper presents the methodology to create and characterize population-based hospital service areas (HSAs) for Switzerland. METHODS: We employed federal hospital discharge data to perform a patient origin study using small area analysis. Each of 605 residential regions was assigned to one of 215 hospital provider regions where the most frequent number of discharges took place. HSAs were characterized geographically, demographically, and through health utilization indices and rates that describe hospital use. We introduced novel planning variables extracted from the patient origin study and investigated relationships among health utilization indices and rates to understand patient travel patterns for hospital use. Results were visualized as maps in a geographic information system (GIS). RESULTS: We obtained 100 HSAs using a patient origin matrix containing over four million discharges. HSAs had diverse demographic and geographic characteristics. Urban HSAs had above average population sizes, while mountainous HSAs were scarcely populated but larger in size. We found higher localization of care in urban HSAs and in mountainous HSAs. Half of the Swiss population lives in service areas where 65% of hospital care is provided by local hospitals. CONCLUSION: Health utilization indices and rates demonstrated patient travel patterns that merit more detailed analyses in light of political, infrastructural and developmental determinants. HSAs and health utilization indices provide valuable information for health care planning. They will be used to study variation phenomena in Swiss health care

Minimally Actuated Dynamic Climbing in the Sagittal Plane

This thesis explores the design of systems that can climb vertical surfaces with non-negligible dynamics in the sagittal plane. The development of a low-dimensional model addresses a lack of understanding of sagittal plane dynamics during climbing in the space of reduced-order dynamic models of legged systems. Using a construction derived from the well-known and well-studied Spring-Loaded Inverted Pendulum (SLIP), we propose a two-legged system with both torsional and linear compliance driven by a position-controlled rotational actuator. Two simple foot models are considered to explore their effect on the dynamics and stability of the system. Results of the model indicate the existence of passively stable gaits during climbing as well as during inverted running and also suggest mechanical tuning parameters for physical climbing systems. A robotic platform capable of producing dynamic climbing behaviors is introduced. A reduced profile, sprawled posture, and improved internal mechanics allow the CLASH platform to be adapted to different climbing substrates. A passive claw engagement mechanism is proposed and tested with simulated steps to verify the design. With these mechanisms, CLASH becomes the first robotic platform capable of climbing loose cloth and climbs vertically at 15cm/s or 1.5 body-lengths per second. When climbing ferromagnetic surfaces, the system is capable of climbing at 1.8 body-lengths per second. To climb smooth, hard surfaces, a foot with a passively aligning ankle with a tendon-loaded gecko-inspired adhesive is designed and tested using simulated steps. With these engagement mechanisms, the system is able to climb at 1 body-length per second on acrylic with a 70-degree incline. A simple foot-impact model is created to explain the robot's inability to climb faster or up steeper inclines due to the sagittal plane reaction forces created during rapid running

Dynamic Climbing of Near-Vertical Smooth Surfaces

Abstract — A 10 cm hexapedal robot is adapted to dynamically climb near-vertical smooth surfaces. A gecko-inspired adhesive is mounted with an elastomer tendon and polymer loop to a remote-center-of-motion ankle that allows rapid engagement with the surface and minimizes peeling moments on the adhesive. The maximum velocity possible while climbing decreases as the incline gets closer to vertical, with the robot able to achieve speeds of 10 cm second −1 at a 70-degree incline. A model is implemented to describe the effect of incline angle on climbing speed and, together with high-speed video evidence, reveals that climbing velocity is limited by robot dynamics and adhesive properties and not by power. I

Systematic study of the performance of small robots on controlled laboratory substrates

Presented at Micro- and nanotechnology sensors, systems, and applications II 5-9 April 2010, Orlando, Florida, United States.DOI: 10.1117/12.851047©2010 SPIE--The International Society for Optical Engineering. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited. The electronic version of this article is the complete one and can be found online at: http://dx.doi.org/10.1117/12.851047The design of robots able to locomote effectively over a diversity of terrain requires detailed ground interaction models; unfortunately such models are lacking due to the complicated response of real world substrates which can yield and flow in response to loading. To advance our understanding of the relevant modeling and design issues, we conduct a comparative study of the performance of DASH and RoACH, two small, biologically inspired, six legged, lightweight (~ 10 cm, ~ 20 g) robots fabricated using the smart composite microstructure (SCM) process. We systematically examine performance of both robots on rigid and °owing substrates. Varying both ground properties and limb stride frequency, we investigate average speed, mean mechanical power and cost of transport, and stability. We find that robot performance and stability is sensitive to the physics of ground interaction: on hard ground kinetic energy must be managed to prevent yaw, pitch, and roll instability to maintain high performance, while on sand the fluidizing interaction leads to increased cost of transport and lower running speeds. We also observe that the characteristic limb morphology and kinematics of each robot result in distinct differences in their abilities to traverse different terrains. Our systematic studies are the first step toward developing models of interaction of limbs with complex terrain as well as developing improved limb morphologies and control strategies