Towards Reactive Control of Transitional Legged Robot Maneuvers

We propose the idea of a discrete navigation problem – consisting of controlling the state of a discrete-time control system to reach a goal set while in the interim avoiding a set of obstacle states – to approximate a simplified class of transitional legged robotic tasks such as leaping which have no well established mathematical description that lends itself to synthesis. The control relation given in Theorem 1 is (assuming a task solution exists) necessary and sufficient to solve a discrete navigation problem in a minimum number of steps, and is well suited to computation when a legged system’s continuous-time within-stride controller anchors sufficiently simple stance mechanics. We demonstrate the efficacy of this control technique on a physical hopping robot affixed to a boom to reactively leap over an obstacle with a running start, controlling in continuous time during stance to exhibit a linear stance map

The Role of ΑV integrins in Human Skin Tissue Homeostasis, Wound Healing and Squamous Cell Carcinoma

Integrins play crucial roles in epithelial adhesion, proliferation, wound healing and cancer. In the epidermis, the roles of many integrin subunits are incompletely defined and mechanistic details regarding their functions are lacking. We performed a multiplexed shRNA screen to define roles for each subunit in human organotypic skin. This screen identified the integrin αv class of heterodimers as essential for generation of human skin tissue. We demonstrate that integrin αv loss drives a keratinocyte G1-S cell cycle checkpoint block. Surprisingly, αv integrins are not localized within keratinocyte focal adhesions and instead maintain proliferation by controlling c-myc translation through FAK, p38 and p90RSK signaling pathways. These phenotypes depend only on αv’s binding partners β5 and β6, but not β1 or β8. Utilizing inducible genetic depletion of integrin αv, or blocking antibodies targeting αv heterodimers, we show that αv integrins are required for de novo tissue generation, but dispensable for epidermal maintenance. In an in vivo human xenograft skin model, we use blocking antibodies to show that integrin αv is required for epidermal proliferation during wound healing, but is dispensable for normal epidermal homeostasis. In organotypic human neoplasias driven by Cdk4 R24C and oncogenic H-Ras G12V, we show that integrin αv is necessary for neoplastic tissue thickness and invasion through the basement membrane. This is dependent on expression of both binding partners β5 and β6. Blocking antibodies targeting αv heterodimers reduce tumor burden and proliferation in an inducible, orthotopic xenograft cutaneous squamous cell carcinoma tumor model. In conclusion, we demonstrate, for the first time, essential roles for αv integrins in human cutaneous wound re-epithelialization and tumorigenesis. We further determine a novel focal adhesion-independent signaling mechanism for αv’s involvement in cell cycle progression

Empirical validation of a spined sagittal-plane quadrupedal model

We document empirically stable bounding using an actively powered spine on the Inu quadrupedal robot, and propose a reduced-order model to capture the dynamics associated with this additional, actuated spine degree of freedom. This model is sufficiently accurate as to roughly describe the robots mass center trajectory during a bounding limit cycle, thus making it a potential option for low dimensional representations of spine actuation in steady-state legged locomotion

An Empirical Investigation of Legged Transitional Maneuvers Leveraging Raibert’s Scissor Algorithm

We empirically investigate the implications of applying Raibert’s Scissor algorithm to the Spring Loaded Inverted Pendulum (SLIP) model in combination with other controllers to achieve transitional maneuvers. Specifically, we are interested in how the conjectured neutral stability of Raibert’s algorithm allows combined controllers to push the system’s operating point around the state space without needing to expend limited control affordance in overcoming its stability or compensating for its instability. We demonstrate 2 cases where this facilitates the construction of interesting transitional controllers on a physical robot. In the first we use the motors in stance to maximize the rate of change of the body energy; in the second we take advantage of the local environmental energy landscape to push the robot’s operating point to a higher or lower energy level without expending valuable motor affordance. We present data bearing on the energetic performance of these approaches in executing an accelerate-and-leap maneuver on a monopedal hopping robot affixed to a boom in comparison to the cost of anchoring the robot to the SLIP template. For more information: Kod*la

Technical Report on: Towards Reactive Control of Simplified Legged Robotics Maneuvers

This technical report provides proofs and calculations for the paper Towards Reactive Control of Simplified Legged Robotics Maneuvers, as well as implementation notes and a discussion on robustness

Affordances And Control Of A Spine Morphology For Robotic Quadrupedal Locomotion

How does a robot\u27s body affect what it can do? This thesis explores the question with respect to a body morphology common to biology but rare in contemporary robotics: the presence of a bendable back. In this document, we introduce the Canid and Inu quadrupedal robots designed to test hypotheses related to the presence of a robotic sagittal-plane bending back (which we refer to as a ``spine morphology\u27\u27). The thesis then describes and quantifies several advantages afforded by this morphological design choice that can be evaluated against its added weight and complexity, and proposes control strategies to both deal with the increase in degrees-of-freedom from the spine morphology and to leverage an increase in agility to reactively navigate irregular terrain. Specifically, we show using the metric of ``specific agility\u27\u27 that a spine can provides a reservoir of elastic energy storage that can be rapidly converted to kinetic energy, that a spine can augment the effective workspace of the legs without diminishing their force generation capability, and that -- in cases of direct-drive or nearly direct-drive leg actuation -- the spine motors can contribute more work in stance than the same actuator weight used in the legs, but can do so without diminishing the platform\u27s proprioceptive capabilities. To put to use the agility provided by a suitably designed robotic platform, we introduce a formalism to approximate a set of transitional navigational tasks over irregular terrain such as leaping over a gap that lend itself to doubly reactive control synthesis. We also directly address the increased complexity introduced by the spine joint with a modular compositional control framework with nice stability properties that begins to offer insight into the role of spines for steady-state running. A central theme to both the reactive navigation and the modular control frameworks is that analytical tractability is achieved by approximating the modes driving the environmental interactions with constant-acceleration dynamics

Core Actuation Promotes Self-Manipulability on a Direct-Drive Quadrupedal Robot

For direct-drive legged robots operating in unstructured environments, workspace volume and force generation are competing, scarce resources. In this paper we demonstrate that introducing geared core actuation (i.e., proximal to rather than distal from the mass center) increases workspace volume and can provide a disproportionate amount of work-producing force to the mass center without affecting leg linkage transparency. These effects are analytically quantifiable up to modest assumptions, and are demonstrated empirically on a spined quadruped performing a leap both on level ground and from an isolated foothold (an archetypal feature of unstructured terrain)

Towards a Comparative Measure for Legged Agility

We introduce an agility measure enabling the comparison of two very different leaping-from-rest transitions by two comparably powered but morphologically different legged robots. We use the measure to show that a flexible spine outperforms a rigid back in the leaping- from-rest task. The agility measure also sheds light on the source of this benefit: core actuation through a sufficiently powerful parallel elastic actuated spine outperforms a similar power budget applied either only to preload the spine or only to actuate the spine during the leap, as well as a rigid backed configuration of the identical machine