55 research outputs found
Impedence Control for Variable Stiffness Mechanisms with Nonlinear Joint Coupling
The current discussion on physical human robot
interaction and the related safety aspects, but also the interest
of neuro-scientists to validate their hypotheses on human motor
skills with bio-mimetic robots, led to a recent revival of tendondriven
robots. In this paper, the modeling of tendon-driven
elastic systems with nonlinear couplings is recapitulated. A
control law is developed that takes the desired joint position
and stiffness as input. Therefore, desired motor positions are
determined that are commanded to an impedance controller.
We give a physical interpretation of the controller. More importantly,
a static decoupling of the joint motion and the stiffness
variation is given. The combination of active (controller) and
passive (mechanical) stiffness is investigated. The controller
stiffness is designed according to the desired overall stiffness.
A damping design of the impedance controller is included in
these considerations. The controller performance is evaluated
in simulation
Optimal control of quasi-1D Bose gases in optical box potentials
In this paper, we investigate the manipulation of quasi-1D Bose gases that
are trapped in a highly elongated potential by optimal control methods. The
effective meanfield dynamics of the gas can be described by a one-dimensional
non-polynomial Schr\"odinger equation. We extend the indirect optimal control
method for the Gross-Pitaevskii equation by Winckel and Borzi (2008) to obtain
necessary optimality conditions for state and energy cost functionals. This
approach is then applied to optimally compress a quasi-1D Bose gase in an
(optical) box potential, i.e., to find a so-called short-cut to adiabaticity,
by solving the optimality conditions numerically. The behavior of the proposed
method is finally analyzed and compared to simple direct optimization
strategies using reduced basis functions. Simulations results demonstrate the
feasibility of the proposed approach.Comment: 6 pages, 5 figures, 2 tables, accepted for IFAC World Congress 202
Sampling-Based Trajectory (re)planning for Differentially Flat Systems: Application to a 3D Gantry Crane
In this paper, a sampling-based trajectory planning algorithm for a
laboratory-scale 3D gantry crane in an environment with static obstacles and
subject to bounds on the velocity and acceleration of the gantry crane system
is presented. The focus is on developing a fast motion planning algorithm for
differentially flat systems, where intermediate results can be stored and
reused for further tasks, such as replanning. The proposed approach is based on
the informed optimal rapidly exploring random tree algorithm (informed RRT*),
which is utilized to build trajectory trees that are reused for replanning when
the start and/or target states change. In contrast to state-of-the-art
approaches, the proposed motion planning algorithm incorporates a linear
quadratic minimum time (LQTM) local planner. Thus, dynamic properties such as
time optimality and the smoothness of the trajectory are directly considered in
the proposed algorithm. Moreover, by integrating the branch-and-bound method to
perform the pruning process on the trajectory tree, the proposed algorithm can
eliminate points in the tree that do not contribute to finding better
solutions. This helps to curb memory consumption and reduce the computational
complexity during motion (re)planning. Simulation results for a validated
mathematical model of a 3D gantry crane show the feasibility of the proposed
approach.Comment: Published at IFAC-PapersOnLine (13th IFAC Symposium on Robot Control
Singularity Avoidance with Application to Online Trajectory Optimization for Serial Manipulators
This work proposes a novel singularity avoidance approach for real-time
trajectory optimization based on known singular configurations. The focus of
this work lies on analyzing kinematically singular configurations for three
robots with different kinematic structures, i.e., the Comau Racer 7-1.4, the
KUKA LBR iiwa R820, and the Franka Emika Panda, and exploiting these
configurations in form of tailored potential functions for singularity
avoidance. Monte Carlo simulations of the proposed method and the commonly used
manipulability maximization approach are performed for comparison. The
numerical results show that the average computing time can be reduced and
shorter trajectories in both time and path length are obtained with the
proposed approachComment: 8 pages, 2 figures, Accepted for publication at IFAC World Congress
202
Optimizing optical potentials with physics-inspired learning algorithms
We present our new experimental and theoretical framework which combines a
broadband superluminescent diode (SLED/SLD) with fast learning algorithms to
provide speed and accuracy improvements for the optimization of 1D optical
dipole potentials, here generated with a Digital Micromirror Device (DMD). To
characterize the setup and potential speckle patterns arising from coherence,
we compare the superluminescent diode to a single-mode laser by investigating
interference properties. We employ Machine Learning (ML) tools to train a
physics-inspired model acting as a digital twin of the optical system
predicting the behavior of the optical apparatus including all its
imperfections. Implementing an iterative algorithm based on Iterative Learning
Control (ILC) we optimize optical potentials an order of magnitude faster than
heuristic optimization methods. We compare iterative model-based offline
optimization and experimental feedback-based online optimization. Our methods
provide a new route to fast optimization of optical potentials which is
relevant for the dynamical manipulation of ultracold gases.Comment: 10 pages, 5 figure
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