Control of A High Performance Bipedal Robot using Viscoelastic Liquid Cooled Actuators

This paper describes the control, and evaluation of a new human-scaled biped robot with liquid cooled viscoelastic actuators (VLCA). Based on the lessons learned from previous work from our team on VLCA [1], we present a new system design embodying a Reaction Force Sensing Series Elastic Actuator (RFSEA) and a Force Sensing Series Elastic Actuator (FSEA). These designs are aimed at reducing the size and weight of the robot's actuation system while inheriting the advantages of our designs such as energy efficiency, torque density, impact resistance and position/force controllability. The system design takes into consideration human-inspired kinematics and range-of-motion (ROM), while relying on foot placement to balance. In terms of actuator control, we perform a stability analysis on a Disturbance Observer (DOB) designed for force control. We then evaluate various position control algorithms both in the time and frequency domains for our VLCA actuators. Having the low level baseline established, we first perform a controller evaluation on the legs using Operational Space Control (OSC) [2]. Finally, we move on to evaluating the full bipedal robot by accomplishing unsupported dynamic walking by means of the algorithms to appear in [3].Comment: 8 pages, 8 figure

Towards versatile, high-performing and interactive humanoids

While studies on humanoid robots have matured in recent years, deploying a practical and versatile humanoid in real life remains a challenge. This challenge comes from the multidisciplinary nature of the field; indeed, elaborate actuation technologies, robust whole-body planning and control frameworks, and intelligent high-level decision-making policies are all necessary for a versatile and high-performing humanoid. To this end, this dissertation presents my research to bring these technologies to the next level and achieve intelligent and practical humanoids. First, I studied an actuation technology that is designed for energy efficiency, torque density, impact resistance, joint position, and force controllability. I implemented a disturbance observer-based force controller to achieve a wide range of impedance behaviors. I performed experiments on mechanical robustness by studying the response of the actuator to external impacts. I further evaluated the performance of the actuation technology by testing a variety of robotics platforms such as a single-leg testbed and a DRACO biped. Second, I investigated versatile planning and control solutions to various problem setups for humanoids. For long-horizon locomotion planning problems such as maze navigation, I proposed a sampling-based kinodynamic planning framework by combining an inverted pendulum model and rapidly-exploring random tree. For the problems that require a more descriptive yet still computationally efficient model and decisions on how to interact with the environment in addition to motion trajectories, I formulated a trajectory optimization framework based on a phase-based parameterization and a learned centroidal model. For a reactive footstep planning problem, I incorporated hierarchical reinforcement learning into a model-based footstep planner to improve robustness. Lastly, I studied the machine learning of system dynamics and safety that can be utilized for humanoid planning and control. In particular, I studied a neural network structure that can represent and learn hybrid systems efficiently using a mixture of experts. I demonstrated that this network structure can optimize the bias-variance problem in dynamical system representation and enable data-efficient learning of dynamics. For safety learning, I proposed a probabilistic verification framework that verifies the safety of planned trajectories by learning an assessment function from trajectories collected from a closed-loop system.Mechanical Engineerin

Collective behaviors of second-order nonlinear consensus models with a bonding force

We study the collective behaviors of two second-order nonlinear consensus models with a bonding force, namely the Kuramoto model and the Cucker-Smale model with inter-particle bonding force. The proposed models contain feedback control terms which induce collision avoidance and emergent consensus dynamics in a suitable framework. Through the cooperative interplays between feedback controls, initial state configuration tends to an ordered configuration asymptotically under suitable frameworks which are formulated in terms of system parameters and initial configurations. For a two-particle system on the real line, we show that the relative state tends to the preassigned value asymptotically, and we also provide several numerical examples to analyze the possible nonlinear dynamics of the proposed models, and compare them with analytical results.Comment: 37 pages, 5 figure

Floatable photocatalytic hydrogel nanocomposites for large-scale solar hydrogen production

Storing solar energy in chemical bonds aided by heterogeneous photocatalysis is desirable for sustainable energy conversion. Despite recent progress in designing highly active photocatalysts, inefficient solar energy and mass transfer, the instability of catalysts and reverse reactions impede their practical large-scale applications. Here we tackle these challenges by designing a floatable photocatalytic platform constructed from porous elastomer-hydrogel nanocomposites. The nanocomposites at the air-water interface feature efficient light delivery, facile supply of water and instantaneous gas separation. Consequently, a high hydrogen evolution rate of 163 mmol h(-1) m(-2) can be achieved using Pt/TiO2 cryoaerogel, even without forced convection. When fabricated in an area of 1 m(2) and incorporated with economically feasible single-atom Cu/TiO2 photocatalysts, the nanocomposites produce 79.2 ml of hydrogen per day under natural sunlight. Furthermore, long-term stable hydrogen production in seawater and highly turbid water and photoreforming of polyethylene terephthalate demonstrate the potential of the nanocomposites as a commercially viable photocatalytic system. Floatable hydrogel nanocomposites, with facile intercalation of various photocatalysts, effectively produce hydrogen. The easily scalable nature of the nanocomposites demonstrates the practical application of this new type of photocatalytic platform.N