A Dynamics and Stability Framework for Avian Jumping Take-off

Jumping take-off in birds is an explosive behaviour with the goal of providing a rapid transition from ground to airborne locomotion. An effective jump is predicated on the need to maintain dynamic stability through the acceleration phase. The present study concerns understanding how birds retain control of body attitude and trajectory during take-off. Cursory observation suggests that stability is achieved with relatively little cost. However, analysis of the problem shows that the stability margins during jumping are actually very small and that stability considerations play a significant role in selection of appropriate jumping kinematics. We use theoretical models to understand stability in prehensile take-off (from a perch) and also in non-prehensile take-off (from the ground). The primary instability is tipping, defined as rotation of the centre of gravity about the ground contact point. Tipping occurs when the centre of pressure falls outside the functional foot. A contribution of the paper is the development of graphical tipping stability margins for both centre of gravity location and acceleration angle. We show that the nose-up angular acceleration extends stability bounds forward and is hence helpful in achieving shallow take-offs. The stability margins are used to interrogate simulated take-offs of real birds using published experimental kinematic data from a guinea fowl (ground take-off) and a diamond dove (perch take-off). For the guinea fowl the initial part of the jump is stable, however simulations exhibit a stuttering instability not observed experimentally that is probably due to absence of compliance in the idealised joints. The diamond dove model confirms that the foot provides an active torque reaction during take-off, extending the range of stable jump angles by around 45{\deg}.Comment: 21 pages, 11 figures; supplementary material: https://figshare.com/s/86b12868d64828db0d5d; DOI: 10.6084/m9.figshare.721056

The importance of muscle mechanics during movement: investigating power production and dynamic stability using a closed-loop system

Animals effectively move and negotiate a variety of environments exemplifying the neuromuscular system's ability to produce complex coordinated movements. Our central thesis is that the nonlinear dynamical properties of muscle play a critical role in power production and stability during such movements. We have developed a closed-loop system that couples an isolated muscle to a physical or computational load, facilitating the study of the interactions between intrinsic muscle properties and external forces. We used this system to determine how elastic elements in the frog semimembranosus can improve power production during a jumping task and how the contractile element automatically manages energy to maintain a stable bouncing gait. Our results reveal that, during ballistic movements (e.g. jumping), series elastic elements stretch and shorten to temporally concentrate energy transfer from the contractile element to the body, amplifying power production. We measured peak instantaneous power greater than twice the maximum power the contractile element could produce alone. Our results show how, during a bouncing gait, the contractile and elastic elements autonomously interact to produce, dissipate, and recycle energy and to maintain dynamic stability without sensory feedback. Our data suggest that muscles can recover over 75% of the kinematic energy from one step and apply it to the next. These results demonstrate the effects and importance of intrinsic muscle properties during movements. Ultimately, this research can guide the development of biomimetic robotic and prosthetic technologies capable of life-like mobility.Ph.D.Committee Chair: DeWeerth, Stephen P.; Committee Co-Chair: Ting, Lena H.; Committee Member: Burkholder, Thomas J.; Committee Member: Nichols, T. Richard; Committee Member: Tresch, Matthew C

Sensing, Design Optimization, and Motion Planning for Agile Pneumatic Artificial Muscle-Driven Robots

Mechanical compliance in robotic systems facilitates safe human-robot interaction and improves robot adaptation to environmental uncertainty. Several promising compliant actuator technologies have emerged from the field of soft robotics, in particular the pneumatic artificial muscle—a soft, lightweight actuator that contracts under pressure. The pneumatic muscle's passive compliance eliminates the need for precise high-bandwidth actuator control to simulate mechanical impedance. However, the pneumatic muscle is limited in practical robot applications—particularly, without sacrificing robot agility—due to several key challenges: development of compatible soft sensors, translation of conventional high-level control and planning techniques to pneumatic muscle-driven systems, and limitations in pneumatic muscle pressurization rate and force generation capabilities. This work seeks to address these challenges, via a threefold approach, to access the benefits of compliant robot actuation while maximizing the robot's dynamic capabilities. The first objective targets the development of a pneumatic muscle design with integrated sensing to enable kinematic and dynamic state estimation of muscle-actuated robots without hindering muscle compliance. The second objective focuses on the construction of a trajectory optimization framework for planning dynamic robot maneuvers using 'burst-inflation' muscle pressure control. Finally, the third objective explores a design optimization strategy utilizing biological joint mechanisms to compensate for pneumatic muscle limitations and maximize robot agility.Ph.D

Performance and manufacturing considerations for series elastic actuators

Robots are becoming an integral part of our lives. We are already physically connected with them through many robotic applications such as exoskeletons in military, orthosis devices in health care, collaborative robots in industry, etc. While the integration of robots improves the quality of human life, it still poses a safety concern during the physical human-robot interaction. Series Elastic Actuators (SEAs) play an important role in improving the safety of human-robot interaction and collaboration. Considering the fast expansion of robotic applications in our lives and the safety benefits of SEAs, it is conceivable that SEAs are going to play an important role in robotic applications in every aspect of human life. This dissertation focuses on reducing the cost, simplifying the use and improving the performance of SEAs. The first research focus in this dissertation is to reduce the cost of SEAs. Robots are successful in reducing production and service costs when used but the capital cost of robot installations are very high. As robotics research shifts to safe robotic applications, reducing the cost of SEAs will greatly help to deploy this technology in more robotic applications and to increase their accessibility to a broader range of researchers and educators. With this motivation, I present a case study on reducing the cost of a SEA while maintaining high force and position control performance and industrial grade service life. The second research focus in this dissertation is to simplify the laborious gain selection process of the cascaded controllers of SEAs. In order to simplify the gain selection process of the impedance controllers of SEAs, an optimal feedback gain selection methodology was developed. Using this method, the feedback gains of the cascaded PD-type impedance controllers of SEAs can easily be calibrated. The developed method allows the users to find the highest feedback gains for a desired phase-margin. Beyond the low-cost realization and simple controller tuning of SEAs, performance improvements on SEAs are possible utilizing the series elasticity in these actuators. As the third research focus in this dissertation, a sequential convex optimization-based motion planning technique is developed in order to improve the joint velocity capabilities of SEAs with nonlinearities. By using this method, higher joint velocities, that are not achievable with the rigid counterparts of SEAs can be achievedMechanical Engineerin

生物の二関節間筋腱複合体を規範とした脚ロボットの開発

電気通信大学201