24 research outputs found
FootTile: a Rugged Foot Sensor for Force and Center of Pressure Sensing in Soft Terrain
In this paper we present FootTile, a foot sensor for reaction force and
center of pressure sensing in challenging terrain. We compare our sensor design
to standard biomechanical devices, force plates and pressure plates. We show
that FootTile can accurately estimate force and pressure distribution during
legged locomotion. FootTile weighs 0.9g, has a sampling rate of 330Hz, a
footprint of 10 by 10mm and can easily be adapted in sensor range to the
required load case. In three experiments we validate: first the performance of
the individual sensor, second an array of FootTiles for center of pressure
sensing and third the ground reaction force estimation during locomotion in
granular substrate. We then go on to show the accurate sensing capabilities of
the waterproof sensor in liquid mud, as a showcase for real world rough terrain
use
Trunk Pitch Oscillations for Energy Trade-offs in Bipedal Running Birds and Robots
Bipedal animals have diverse morphologies and advanced locomotion abilities.
Terrestrial birds, in particular, display agile, efficient, and robust running
motion, in which they exploit the interplay between the body segment masses and
moment of inertias. On the other hand, most legged robots are not able to
generate such versatile and energy-efficient motion and often disregard trunk
movements as a means to enhance their locomotion capabilities. Recent research
investigated how trunk motions affect the gait characteristics of humans, but
there is a lack of analysis across different bipedal morphologies. To address
this issue, we analyze avian running based on a spring-loaded inverted pendulum
model with a pronograde (horizontal) trunk. We use a virtual point based
control scheme and modify the alignment of the ground reaction forces to assess
how our control strategy influences the trunk pitch oscillations and energetics
of the locomotion. We derive three potential key strategies to leverage trunk
pitch motions that minimize either the energy fluctuations of the center of
mass or the work performed by the hip and leg. We suggest how these strategies
could be used in legged robotics.Comment: 16 pages, 18 figures, accepted manuscript, online since 12 February
2020, published by IOP Publishing Lt
Towards Pitch-Free Control of an Underactuated and Compliant Bipedal Robot
The 11th International Symposium on Adaptive Motion of Animals and Machines. Kobe University, Japan. 2023-06-06/09. Adaptive Motion of Animals and Machines Organizing Committee.Poster Session P7
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
Multi-segmented Adaptive Feet for Versatile Legged Locomotion in Natural Terrain
Most legged robots are built with leg structures from serially mounted links
and actuators and are controlled through complex controllers and sensor
feedback. In comparison, animals developed multi-segment legs, mechanical
coupling between joints, and multi-segmented feet. They run agile over all
terrains, arguably with simpler locomotion control. Here we focus on developing
foot mechanisms that resist slipping and sinking also in natural terrain. We
present first results of multi-segment feet mounted to a bird-inspired robot
leg with multi-joint mechanical tendon coupling. Our one- and two-segment,
mechanically adaptive feet show increased viable horizontal forces on multiple
soft and hard substrates before starting to slip. We also observe that
segmented feet reduce sinking on soft substrates compared to ball-feet and
cylinder-feet. We report how multi-segmented feet provide a large range of
viable centre of pressure points well suited for bipedal robots, but also for
quadruped robots on slopes and natural terrain. Our results also offer a
functional understanding of segmented feet in animals like ratite birds
Slack tendon enables tunable damping for legged locomotion
The 11th International Symposium on Adaptive Motion of Animals and Machines. Kobe University, Japan. 2023-06-06/09. Adaptive Motion of Animals and Machines Organizing Committee.Poster Session P