147 research outputs found
Neuromorphic Control using Input-Weighted Threshold Adaptation
Neuromorphic processing promises high energy efficiency and rapid response
rates, making it an ideal candidate for achieving autonomous flight of
resource-constrained robots. It will be especially beneficial for complex
neural networks as are involved in high-level visual perception. However, fully
neuromorphic solutions will also need to tackle low-level control tasks.
Remarkably, it is currently still challenging to replicate even basic low-level
controllers such as proportional-integral-derivative (PID) controllers.
Specifically, it is difficult to incorporate the integral and derivative parts.
To address this problem, we propose a neuromorphic controller that incorporates
proportional, integral, and derivative pathways during learning. Our approach
includes a novel input threshold adaptation mechanism for the integral pathway.
This Input-Weighted Threshold Adaptation (IWTA) introduces an additional weight
per synaptic connection, which is used to adapt the threshold of the
post-synaptic neuron. We tackle the derivative term by employing neurons with
different time constants. We first analyze the performance and limits of the
proposed mechanisms and then put our controller to the test by implementing it
on a microcontroller connected to the open-source tiny Crazyflie quadrotor,
replacing the innermost rate controller. We demonstrate the stability of our
bio-inspired algorithm with flights in the presence of disturbances. The
current work represents a substantial step towards controlling highly dynamic
systems with neuromorphic algorithms, thus advancing neuromorphic processing
and robotics. In addition, integration is an important part of any temporal
task, so the proposed Input-Weighted Threshold Adaptation (IWTA) mechanism may
have implications well beyond control tasks
An Adaptive Control Strategy for Neural Network based Optimal Quadcopter Controllers
Developing optimal controllers for aggressive high-speed quadcopter flight is
a major challenge in the field of robotics. Recent work has shown that neural
networks trained with supervised learning can achieve real-time optimal control
in some specific scenarios. In these methods, the networks (termed G&CNets) are
trained to learn the optimal state feedback from a dataset of optimal
trajectories. An important problem with these methods is the reality gap
encountered in the sim-to-real transfer. In this work, we trained G&CNets for
energy-optimal end-to-end control on the Bebop drone and identified the
unmodeled pitch moment as the main contributor to the reality gap. To mitigate
this, we propose an adaptive control strategy that works by learning from
optimal trajectories of a system affected by constant external pitch, roll and
yaw moments. In real test flights, this model mismatch is estimated onboard and
fed to the network to obtain the optimal rpm command. We demonstrate the
effectiveness of our method by performing energy-optimal hover-to-hover flights
with and without moment feedback. Finally, we compare the adaptive controller
to a state-of-the-art differential-flatness-based controller in a consecutive
waypoint flight and demonstrate the advantages of our method in terms of energy
optimality and robustness.Comment: 7 pages, 11 figure
Costlets: A Generalized Approach to Cost Functions for Automated Optimization of IMRT Treatment Plans
We present the creation and use of a generalized cost function methodology based on costlets for automated optimization for conformal and intensity modulated radiotherapy treatment plans. In our approach, cost functions are created by combining clinically relevant “costlets”. Each costlet is created by the user, using an “evaluator” of the plan or dose distribution which is incorporated into a function or “modifier” to create an individual costlet. Dose statistics, dose-volume points, biological model results, non-dosimetric parameters, and any other information can be converted into a costlet. A wide variety of different types of costlets can be used concurrently. Individual costlet changes affect not only the results for that structure, but also all the other structures in the plan (e.g., a change in a normal tissue costlet can have large effects on target volume results as well as the normal tissue). Effective cost functions can be created from combinations of dose-based costlets, dose-volume costlets, biological model costlets, and other parameters. Generalized cost functions based on costlets have been demonstrated, and show potential for allowing input of numerous clinical issues into the optimization process, thereby helping to achieve clinically useful optimized plans. In this paper, we describe and illustrate the use of the costlets in an automated planning system developed and used clinically at the University of Michigan Medical Center. We place particular emphasis on the flexibility of the system, and its ability to discover a variety of plans making various trade-offs between clinical goals of the treatment that may be difficult to meet simultaneously.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47484/1/11081_2005_Article_2066.pd
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