1,346 research outputs found
Model based methods for the control and planning of running robots
Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Sciences of Bilkent University, 2009.Thesis (Master's) -- Bilkent University, 2009.Includes bibliographical references leaves 115-122.The Spring-Loaded Inverted Pendulum (SLIP) model has long been established
as an effective and accurate descriptive model for running animals of widely
differing sizes and morphologies. Not surprisingly, the ability of such a simple
spring-mass model to capture the essence of running motivated several hopping
robot designs as well as the use of the SLIP model as a control target for more
complex legged robot morphologies. Further research on the SLIP model led to
the discovery of several analytic approximations to its normally nonintegrable
dynamics. However, these approximations mostly focus on steady-state running
with symmetric trajectories due to their linearization of gravitational effects,
an assumption that is quickly violated for locomotion on more complex terrain
wherein transient, non-symmetric trajectories dominate. In the first part of the
thesis , we introduce a novel gravity correction scheme that extends on one of the
more recent analytic approximations to the SLIP dynamics and achieves good
accuracy even for highly non-symmetric trajectories. Our approach is based on
incorporating the total effect of gravity on the angular momentum throughout
a single stance phase and allows us to preserve the analytic simplicity of the
approximation to support research on reactive footstep planning for dynamiclegged locomotion. We compare the performance of our method with two other
existing analytic approximations by simulation and show that it outperforms
them for most physically realistic non-symmetric SLIP trajectories while maintaining
the same accuracy for symmetric trajectories. Additionally, this part of
the thesis continues with analytical approximations for tunable stiffness control
of the SLIP model and their motion prediction performance analysis. Similarly,
we show performance improvement for the variable stiffness approximation with
gravity correction method. Besides this, we illustrate a possible usage of approximate
stance maps for the controlling of the SLIP model.
Furthermore, the main driving force behind research on legged robots has always
been their potential for high performance locomotion on rough terrain and the
outdoors. Nevertheless, most existing control algorithms for such robots either
make rigid assumptions about their environments (e.g flat ground), or rely on
kinematic planning with very low speeds. Moreover, the traditional separation of
planning from control often has negative impact on the robustness of the system
against model uncertainty and environment noise. In the second part of the
thesis, we introduce a new method for dynamic, fully reactive footstep planning
for a simplified planar spring-mass hopper, a frequently used dynamic model for
running behaviors. Our approach is based on a careful characterization of the
model dynamics and an associated deadbeat controller, used within a sequential
composition framework. This yields a purely reactive controller with a very
large, nearly global domain of attraction that requires no explicit replanning
during execution. Finally, we use a simplified hopper in simulation to illustrate
the performance of the planner under different rough terrain scenarios and show
that it is robust to both model uncertainty and measurement noise.Arslan, ÖmürM.S
Beyond Basins of Attraction: Quantifying Robustness of Natural Dynamics
Properly designing a system to exhibit favorable natural dynamics can greatly
simplify designing or learning the control policy. However, it is still unclear
what constitutes favorable natural dynamics and how to quantify its effect.
Most studies of simple walking and running models have focused on the basins of
attraction of passive limit-cycles and the notion of self-stability. We instead
emphasize the importance of stepping beyond basins of attraction. We show an
approach based on viability theory to quantify robust sets in state-action
space. These sets are valid for the family of all robust control policies,
which allows us to quantify the robustness inherent to the natural dynamics
before designing the control policy or specifying a control objective. We
illustrate our formulation using spring-mass models, simple low dimensional
models of running systems. We then show an example application by optimizing
robustness of a simulated planar monoped, using a gradient-free optimization
scheme. Both case studies result in a nonlinear effective stiffness providing
more robustness.Comment: 15 pages. This work has been accepted to IEEE Transactions on
Robotics (2019
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
The Penn Jerboa: A Platform for Exploring Parallel Composition of Templates
We have built a 12DOF, passive-compliant legged, tailed biped actuated by
four brushless DC motors. We anticipate that this machine will achieve varied
modes of quasistatic and dynamic balance, enabling a broad range of locomotion
tasks including sitting, standing, walking, hopping, running, turning, leaping,
and more. Achieving this diversity of behavior with a single under-actuated
body, requires a correspondingly diverse array of controllers, motivating our
interest in compositional techniques that promote mixing and reuse of a
relatively few base constituents to achieve a combinatorially growing array of
available choices. Here we report on the development of one important example
of such a behavioral programming method, the construction of a novel monopedal
sagittal plane hopping gait through parallel composition of four decoupled 1DOF
base controllers.
For this example behavior, the legs are locked in phase and the body is
fastened to a boom to restrict motion to the sagittal plane. The platform's
locomotion is powered by the hip motor that adjusts leg touchdown angle in
flight and balance in stance, along with a tail motor that adjusts body shape
in flight and drives energy into the passive leg shank spring during stance.
The motor control signals arise from the application in parallel of four
simple, completely decoupled 1DOF feedback laws that provably stabilize in
isolation four corresponding 1DOF abstract reference plants. Each of these
abstract 1DOF closed loop dynamics represents some simple but crucial specific
component of the locomotion task at hand. We present a partial proof of
correctness for this parallel composition of template reference systems along
with data from the physical platform suggesting these templates are anchored as
evidenced by the correspondence of their characteristic motions with a suitably
transformed image of traces from the physical platform.Comment: Technical Report to Accompany: A. De and D. Koditschek, "Parallel
composition of templates for tail-energized planar hopping," in 2015 IEEE
International Conference on Robotics and Automation (ICRA), May 2015. v2:
Used plain latex article, correct gap radius and specific force/torque
number
Development, Control, and Empirical Evaluation of the Six-Legged Robot SpaceClimber Designed for Extraterrestrial Crater Exploration
In the recent past, mobile robots played an important role in the field of extraterrestrial surface exploration. Unfortunately, the currently available space exploration rovers do not provide the necessary mobility to reach scientifically interesting places in rough and steep terrain like boulder fields and craters. Multi-legged robots have proven to be a good solution to provide high mobility in unstructured environments. However, space missions place high demands on the system design, control, and performance which are hard to fulfill with such kinematically complex systems. This thesis focuses on the development, control, and evaluation of a six-legged robot for the purpose of lunar crater exploration considering the requirements arising from the envisaged mission scenario. The performance of the developed system is evaluated and optimized based on empirical data acquired in significant and reproducible experiments performed in a laboratory environment in order to show thecapability of the system to perform such a task and to provide a basis for the comparability with other mobile robotic solutions
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