A Tendon-Driven Origami Hopper Triggered by Proprioceptive Contact Detection

We report on experiments with a laptop-sized (0.23m, 2.53kg), paper origami robot that exhibits highly dynamic and stable two degree-of-freedom (circular boom) hopping at speeds in excess of 1.5 bl/s (body-lengths per second) at a specific resistance O(1) while achieving aerial phase apex states 25% above the stance height over thousands of cycles. Three conventional brushless DC motors load energy into the folded paper springs through pulley-borne cables whose sudden loss of tension upon touchdown triggers the release of spring potential that accelerates the body back through liftoff to flight with a 20W powerstroke, whereupon the toe angle is adjusted to regulate fore-aft speed. We also demonstrate in the vertical hopping mode the transparency of this actuation scheme by using proprioceptive contact detection with only motor encoder sensing. The combination of actuation and sensing shows potential to lower system complexity for tendon-driven robots. For more information: Kod*lab (link to kodlab.seas.upenn.edu

Global results on reset-induced periodic trajectories of planar systems

We study the existence of asymptotically stable periodic trajectories induced by reset feedback. The analysis is developed for a planar system. Casting the problem into the hybrid setting, we show that a periodic orbit arises from the balance between the energy dissipated during flows and the energy restored by resets, at jumps. The stability of the periodic orbit is studied with hybrid Lyapunov tools. The satisfaction of the so-called hybrid basic conditions ensures the robustness of the asymptotic stability. Extensions of the approach to more general mechanical systems are discussed.Work supported in part by ANR under project LimICoS, contract number 12 BS03 005 01, by the iCODE institute, research project of the Idex ParisSaclay, and by the University of Trento, grant OptHySYS.This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by IEEE

A Robotic Torso Joint With Adjustable Linear Spring Mechanism for Natural Dynamic Motions in a Differential-Elastic Arrangement

To be operated in unknown or complex environments, modern robots have to fulfill various challenging criteria. Among them, one finds requirements such as a high level of robustness to withstand impacts and the capabilities to physically interact in a safe manner. One way to achieve that is to integrate variable-stiffness actuators into the systems, enabling compliant behavior through the elastic components and providing the additional adaptability of the impedance. Here, we introduce a novel adjustable linear stiffness joint mounted in a differential-elastic arrangement. The mechanism is integrated into the anthropomorphic upper body of the DLR David robot and responsible for the spinal rotation. Consequently, the actuator is crucial for the overall workspace of the robot and the realization of energy-efficient natural motions such as in dynamic running. The proposed hardware setup is experimentally validated in terms of the linearity in the spring characteristics, intrinsic damping, the excitation of resonance frequencies, and the ability to alter these resonance frequencies through stiffness adaptation during dynamic motions

Tele Running - Energy Efficient Locomotion for Elastic Joint Robots by Imitation Learning

This thesis presents an imitation learning approach to energy-efficient trajectory generation for elastic, legged robots. The trajectories are generated by teleoperation with force feedback. The presented framework allows an operator to achieve locomotion on an one-leg hopper by controlling its foot tip. The force feedback is designed to assist the operator to find gaits which exploit the natural harmonics of the hopper and thus improve energy efficiency. The resulting trajectory is approximated, parameterized, and replayed on the robot. The operator achieves a cost of transport of 0.25 at 0.63 m/s, considering the mechanical energy. Black-box optimization is used to keep this value with varying hardware parameters, such as different foot-tip stiffness. A reinforcement learning algorithm stabilizes lateral movement by active balance in simulation. Learning on hardware shows an improvement in stability. The concept is extended to multi-legged robots by teleoperating the two feet of the biped DLR C-Runner in simulation. The force feedback assists the operator to find stable gaits where the center of mass does not leave the support polygon of the feet. On both systems, the presented teleoperation framework utilizes the human's capability of estimating the properties of non-linear dynamics by designing appropriate haptic feedback

Simulation and Control of Running Models

This work focuses on the locomotion of one-legged robots, with focus on approaches that stabilize passive limit cycles. Locomotion based on the socalled passive gaits promises to greatly reduce the actuation effort required for legged robots to move. In this work, the passive gaits of robots of varying complexity are characterized and stabilizing controllers are reviewed from the literature and newly formulated. The robots are modelled as hybrid dynamical systems and numerically simulated, thereby allowing to validate the proposed control strategies. Firstly, the vertical control through energy regulation of a one-dimensional hopper is considered. Secondly, the SLIP model is reviewed and then extended to the “pitchingSLIP”, with the aim of characterizing its passive gaits with somersaults. Two controllers based on energy and angular momentum regulation are then formulated to stabilize passive gaits with somersaults, making the control effort converge to zero. A further extension of the SLIP template, denominated “bodySLIP”, is then used to test the control approach on a more realistic model. The controllers shall be later extended to more complex cases, in which the somersaults are not necessarily present in the passive gaits. Thirdly, the locomotion of a one-legged robot with a body link is studied. Raibert’s control approach based on the foot placement algorithm is reviewed and compared to the non-dissipative touchdown controller of Hyon and Emura. The latter is then extended to be used with continuous torque profiles and to perform velocity tracking. Moreover, damping is added to the joints in order to study its effect on the controller, which was then modified to achieve stable running even in such conditions. The results obtained shall lay the foundations for a later test on hardware on DLR’s quadruped Bert

Jumping Control for Compliantly Actuated Multilegged Robots

A feedback control to generate jumping motions for compliantly actuated multilegged robots is proposed. The method allows to specify the direction of the jumping motion. This is achieved by a constraint that defines a one-dimensional submanifold and a bang-bang control which generates a limit cycle on this submanifold. The approach is based on classical impedance control with the difference that the stiffness on the submanifold and the force to preserve a predefined nominal body configuration result from the intrinsic mechanical springs in the joints. Furthermore, we propose two controller implementations: the first implementation does not require to detect the contact state, while the second implementation requires contact state detection, but accounts in addition for Coulomb friction constraints. The controller is validated in simulation with a compliantly actuated quadruped