24 research outputs found
On Time Optimization of Centroidal Momentum Dynamics
Recently, the centroidal momentum dynamics has received substantial attention
to plan dynamically consistent motions for robots with arms and legs in
multi-contact scenarios. However, it is also non convex which renders any
optimization approach difficult and timing is usually kept fixed in most
trajectory optimization techniques to not introduce additional non convexities
to the problem. But this can limit the versatility of the algorithms. In our
previous work, we proposed a convex relaxation of the problem that allowed to
efficiently compute momentum trajectories and contact forces. However, our
approach could not minimize a desired angular momentum objective which
seriously limited its applicability. Noticing that the non-convexity introduced
by the time variables is of similar nature as the centroidal dynamics one, we
propose two convex relaxations to the problem based on trust regions and soft
constraints. The resulting approaches can compute time-optimized dynamically
consistent trajectories sufficiently fast to make the approach realtime
capable. The performance of the algorithm is demonstrated in several
multi-contact scenarios for a humanoid robot. In particular, we show that the
proposed convex relaxation of the original problem finds solutions that are
consistent with the original non-convex problem and illustrate how timing
optimization allows to find motion plans that would be difficult to plan with
fixed timing.Comment: 7 pages, 4 figures, ICRA 201
Humanoid Momentum Estimation Using Sensed Contact Wrenches
This work presents approaches for the estimation of quantities important for
the control of the momentum of a humanoid robot. In contrast to previous
approaches which use simplified models such as the Linear Inverted Pendulum
Model, we present estimators based on the momentum dynamics of the robot. By
using this simple yet dynamically-consistent model, we avoid the issues of
using simplified models for estimation. We develop an estimator for the center
of mass and full momentum which can be reformulated to estimate center of mass
offsets as well as external wrenches applied to the robot. The observability of
these estimators is investigated and their performance is evaluated in
comparison to previous approaches.Comment: Submitted to the 15th IEEE RAS Humanoids Conference, to be held in
Seoul, Korea on November 3 - 5, 201
Automatic Gain Tuning of a Momentum Based Balancing Controller for Humanoid Robots
This paper proposes a technique for automatic gain tuning of a momentum based
balancing controller for humanoid robots. The controller ensures the
stabilization of the centroidal dynamics and the associated zero dynamics.
Then, the closed-loop, constrained joint space dynamics is linearized and the
controller's gains are chosen so as to obtain desired properties of the
linearized system. Symmetry and positive definiteness constraints of gain
matrices are enforced by proposing a tracker for symmetric positive definite
matrices. Simulation results are carried out on the humanoid robot iCub.Comment: Accepted at IEEE-RAS International Conference on Humanoid Robots
(HUMANOIDS). 201
Optimal Reduced-order Modeling of Bipedal Locomotion
State-of-the-art approaches to legged locomotion are widely dependent on the
use of models like the linear inverted pendulum (LIP) and the spring-loaded
inverted pendulum (SLIP), popular because their simplicity enables a wide array
of tools for planning, control, and analysis. However, they inevitably limit
the ability to execute complex tasks or agile maneuvers. In this work, we aim
to automatically synthesize models that remain low-dimensional but retain the
capabilities of the high-dimensional system. For example, if one were to
restore a small degree of complexity to LIP, SLIP, or a similar model, our
approach discovers the form of that additional complexity which optimizes
performance. In this paper, we define a class of reduced-order models and
provide an algorithm for optimization within this class. To demonstrate our
method, we optimize models for walking at a range of speeds and ground
inclines, for both a five-link model and the Cassie bipedal robot.Comment: Submitted to ICRA 202
Sequential Motion Planning for Bipedal Somersault via Flywheel SLIP and Momentum Transmission with Task Space Control
In this paper, we present a sequential motion planning and control method for generating somersaults on bipedal robots. The somersault (backflip or frontflip) is considered as a coupling between an axile hopping motion and a rotational motion about the center of mass of the robot; these are encoded by a hopping Spring-loaded Inverted Pendulum (SLIP) model and the rotation of a Flywheel, respectively. We thus present the Flywheel SLIP model for generating the desired motion on the ground phase. In the flight phase, we present a momentum transmission method to adjust the orientation of the lower body based on the conservation of the centroidal momentum. The generated motion plans are realized on the full-dimensional robot via momentum-included task space control. Finally, the proposed method is implemented on a modified version of the bipedal robot Cassie in simulation wherein multiple somersault motions are generated