592 research outputs found
Asymptotically Stable Walking of a Five-Link Underactuated 3D Bipedal Robot
This paper presents three feedback controllers that achieve an asymptotically
stable, periodic, and fast walking gait for a 3D (spatial) bipedal robot
consisting of a torso, two legs, and passive (unactuated) point feet. The
contact between the robot and the walking surface is assumed to inhibit yaw
rotation. The studied robot has 8 DOF in the single support phase and 6
actuators. The interest of studying robots with point feet is that the robot's
natural dynamics must be explicitly taken into account to achieve balance while
walking. We use an extension of the method of virtual constraints and hybrid
zero dynamics, in order to simultaneously compute a periodic orbit and an
autonomous feedback controller that realizes the orbit. This method allows the
computations to be carried out on a 2-DOF subsystem of the 8-DOF robot model.
The stability of the walking gait under closed-loop control is evaluated with
the linearization of the restricted Poincar\'e map of the hybrid zero dynamics.
Three strategies are explored. The first strategy consists of imposing a
stability condition during the search of a periodic gait by optimization. The
second strategy uses an event-based controller. In the third approach, the
effect of output selection is discussed and a pertinent choice of outputs is
proposed, leading to stabilization without the use of a supplemental
event-based controller
Virtual Constraints and Hybrid Zero Dynamics for Realizing Underactuated Bipedal Locomotion
Underactuation is ubiquitous in human locomotion and should be ubiquitous in
bipedal robotic locomotion as well. This chapter presents a coherent theory for
the design of feedback controllers that achieve stable walking gaits in
underactuated bipedal robots. Two fundamental tools are introduced, virtual
constraints and hybrid zero dynamics. Virtual constraints are relations on the
state variables of a mechanical model that are imposed through a time-invariant
feedback controller. One of their roles is to synchronize the robot's joints to
an internal gait phasing variable. A second role is to induce a low dimensional
system, the zero dynamics, that captures the underactuated aspects of a robot's
model, without any approximations. To enhance intuition, the relation between
physical constraints and virtual constraints is first established. From here,
the hybrid zero dynamics of an underactuated bipedal model is developed, and
its fundamental role in the design of asymptotically stable walking motions is
established. The chapter includes numerous references to robots on which the
highlighted techniques have been implemented.Comment: 17 pages, 4 figures, bookchapte
Developmental acquisition of entrainment skills in robot swinging using van der Pol oscillators
In this study we investigated the effects of different
morphological configurations on a robot swinging
task using van der Pol oscillators. The task was
examined using two separate degrees of freedom
(DoF), both in the presence and absence of neural
entrainment. Neural entrainment stabilises the
system, reduces time-to-steady state and relaxes the
requirement for a strong coupling with the
environment in order to achieve mechanical
entrainment. It was found that staged release of the
distal DoF does not have any benefits over using both
DoF from the onset of the experimentation. On the
contrary, it is less efficient, both with respect to the
time needed to reach a stable oscillatory regime and
the maximum amplitude it can achieve. The same
neural architecture is successful in achieving
neuromechanical entrainment for a robotic walking
task
Hierarchical and Safe Motion Control for Cooperative Locomotion of Robotic Guide Dogs and Humans: A Hybrid Systems Approach
This paper presents a hierarchical control strategy based on hybrid systems
theory, nonlinear control, and safety-critical systems to enable cooperative
locomotion of robotic guide dogs and visually impaired people. We address
high-dimensional and complex hybrid dynamical models that represent
collaborative locomotion. At the high level of the control scheme, local and
nonlinear baseline controllers, based on the virtual constraints approach, are
designed to induce exponentially stable dynamic gaits. The baseline controller
for the leash is assumed to be a nonlinear controller that keeps the human in a
safe distance from the dog while following it. At the lower level, a real-time
quadratic programming (QP) is solved for modifying the baseline controllers of
the robot as well as the leash to avoid obstacles. In particular, the QP
framework is set up based on control barrier functions (CBFs) to compute
optimal control inputs that guarantee safety while being close to the baseline
controllers. The stability of the complex periodic gaits is investigated
through the Poincare return map. To demonstrate the power of the analytical
foundation, the control algorithms are transferred into an extensive numerical
simulation of a complex model that represents cooperative locomotion of a
quadrupedal robot, referred to as Vision 60, and a human model. The complex
model has 16 continuous-time domains with 60 state variables and 20 control
inputs
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