248 research outputs found
Inclined Surface Locomotion Strategies for Spherical Tensegrity Robots
This paper presents a new teleoperated spherical tensegrity robot capable of
performing locomotion on steep inclined surfaces. With a novel control scheme
centered around the simultaneous actuation of multiple cables, the robot
demonstrates robust climbing on inclined surfaces in hardware experiments and
speeds significantly faster than previous spherical tensegrity models. This
robot is an improvement over other iterations in the TT-series and the first
tensegrity to achieve reliable locomotion on inclined surfaces of up to
24\degree. We analyze locomotion in simulation and hardware under single and
multi-cable actuation, and introduce two novel multi-cable actuation policies,
suited for steep incline climbing and speed, respectively. We propose
compelling justifications for the increased dynamic ability of the robot and
motivate development of optimization algorithms able to take advantage of the
robot's increased control authority.Comment: 6 pages, 11 figures, IROS 201
Legged Robot Using Hydro-Muscles
Multiple hydraulically actuated muscles (HAM) can be recruited in parallel to exert a greater force than a single muscle is capable of producing. Many of these âmuscle groupsâ can be used to equip a system for high force output applications. The hopping biped system uses four muscle groups attached to the legs of the biped apparatus to perform a single jumping action actuated. Two muscle groups are attached to the lower section of the apparatus to act similarly to Gastrocnemius muscles, while the other two muscle groups are attached to the upper section of the apparatus to act similarly to Quadriceps muscles. The height reached by the biped system demonstrates the high force output capabilities of HAM and the apparatus will serve as a test-bed for future studies of legged hopping dynamics
Reachability and Real-Time Actuation Strategies for the Active SLIP Model
Running and hopping follow similar patterns for different animals, independent of the number of legs employed. An aerial phase alternates with a ground contact phase, during which the center of mass moves as if a spring were compressed and then extended to recover stored elastic energy. Hence, consisting of a point mass mounted on a massless spring leg, the Spring Loaded Inverted Pendulum (SLIP) is a prevalent model for analyzing running and hopping. In this work we consider an actuated version of the SLIP model, with a series elastic actuator added to the leg, serving the purposes of adding/removing energy to/from the system and of modifying dynamics during stance, toward achieving non-steady locomotion on varying terrain. While the SLIP model has been a topic of research in legged locomotion for several decades, studies on the effect of actuation on the system's behavior are still not complete.The goal of this thesis is to explore how a series elastic actuator applied to the SLIP model's leg can change the system's dynamics. This, in turn, enables a variety of long-term planning strategies for using limited footholds and design non-steady gaits while simultaneously recovering from unexpected perturbations, both sensorial and due to a limited knowledge of the terrain profile.We principally investigate how, through actuation, we can solve partially or completely the system's equations of motion, to enforce a desired trajectory and reach a desired state. We also determine the reachable state space of the model using several different actuation strategies, investigating the variation of the reachable set with respect to particular actuator motions and providing relationships between local actuator displacements throughout stance and location of the reached apex state. We then propose a control strategy based on graphical and numerical studies of the reachability space to drive the system to a desired state, with the ability to reduce the effects of sensing errors and disturbances happening at landing as well as during ground contact
Cable-Driven Actuation for Highly Dynamic Robotic Systems
This paper presents design and experimental evaluations of an articulated
robotic limb called Capler-Leg. The key element of Capler-Leg is its
single-stage cable-pulley transmission combined with a high-gap radius motor.
Our cable-pulley system is designed to be as light-weight as possible and to
additionally serve as the primary cooling element, thus significantly
increasing the power density and efficiency of the overall system. The total
weight of active elements on the leg, i.e. the stators and the rotors,
contribute more than 60% of the total leg weight, which is an order of
magnitude higher than most existing robots. The resulting robotic leg has low
inertia, high torque transparency, low manufacturing cost, no backlash, and a
low number of parts. Capler-Leg system itself, serves as an experimental setup
for evaluating the proposed cable- pulley design in terms of robustness and
efficiency. A continuous jump experiment shows a remarkable 96.5 % recuperation
rate, measured at the battery output. This means that almost all the mechanical
energy output used during push-off returned back to the battery during
touch-down
An Overview on Principles for Energy Efficient Robot Locomotion
Despite enhancements in the development of robotic systems, the energy economy of today's robots lags far behind that of biological systems. This is in particular critical for untethered legged robot locomotion. To elucidate the current stage of energy efficiency in legged robotic systems, this paper provides an overview on recent advancements in development of such platforms. The covered different perspectives include actuation, leg structure, control and locomotion principles. We review various robotic actuators exploiting compliance in series and in parallel with the drive-train to permit energy recycling during locomotion. We discuss the importance of limb segmentation under efficiency aspects and with respect to design, dynamics analysis and control of legged robots. This paper also reviews a number of control approaches allowing for energy efficient locomotion of robots by exploiting the natural dynamics of the system, and by utilizing optimal control approaches targeting locomotion expenditure. To this end, a set of locomotion principles elaborating on models for energetics, dynamics, and of the systems is studied
Effective Viscous Damping Enables Morphological Computation in Legged Locomotion
Muscle models and animal observations suggest that physical damping is
beneficial for stabilization. Still, only a few implementations of mechanical
damping exist in compliant robotic legged locomotion. It remains unclear how
physical damping can be exploited for locomotion tasks, while its advantages as
sensor-free, adaptive force- and negative work-producing actuators are
promising. In a simplified numerical leg model, we studied the energy
dissipation from viscous and Coulomb damping during vertical drops with
ground-level perturbations. A parallel spring-damper is engaged between
touch-down and mid-stance, and its damper auto-disengages during mid-stance and
takeoff. Our simulations indicate that an adjustable and viscous damper is
desired. In hardware we explored effective viscous damping and adjustability
and quantified the dissipated energy. We tested two mechanical, leg-mounted
damping mechanisms; a commercial hydraulic damper, and a custom-made pneumatic
damper. The pneumatic damper exploits a rolling diaphragm with an adjustable
orifice, minimizing Coulomb damping effects while permitting adjustable
resistance. Experimental results show that the leg-mounted, hydraulic damper
exhibits the most effective viscous damping. Adjusting the orifice setting did
not result in substantial changes of dissipated energy per drop, unlike
adjusting damping parameters in the numerical model. Consequently, we also
emphasize the importance of characterizing physical dampers during real legged
impacts to evaluate their effectiveness for compliant legged locomotion
Spacecraft/Rover Hybrids for the Exploration of Small Solar System Bodies
This study investigated a mission architecture that allows the systematic and affordable in-situ exploration of small solar system bodies, such as asteroids, comets, and Martian moons (Figure 1). The architecture relies on the novel concept of spacecraft/rover hybrids,which are surface mobility platforms capable of achieving large surface coverage (by attitude controlled hops, akin to spacecraft flight), fine mobility (by tumbling), and coarse instrument pointing (by changing orientation relative to the ground) in the low-gravity environments(micro-g to milli-g) of small bodies. The actuation of the hybrids relies on spinning three internal flywheels. Using a combination of torques, the three flywheel motors can produce a reaction torque in any orientation without additional moving parts. This mobility concept allows all subsystems to be packaged in one sealed enclosure and enables the platforms to be minimalistic. The hybrids would be deployed from a mother spacecraft, which would act as a communication relay to Earth and would aid the in-situ assets with tasks such as localization and navigation (Figure 1). The hybrids are expected to be more capable and affordable than wheeled or legged rovers, due to their multiple modes of mobility (both hopping and tumbling), and have simpler environmental sealing and thermal management (since all components are sealed in one enclosure, assuming non-deployable science instruments). In summary, this NIAC Phase II study has significantly increased the TRL (Technology Readiness Level) of the mobility and autonomy subsystems of spacecraft/rover hybrids, and characterized system engineering aspects in the context of a reference mission to Phobos. Future studies should focus on improving the robustness of the autonomy module and further refine system engineering aspects, in view of opportunities for technology infusion
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