32 research outputs found
Free Energy Principle for the Noise Smoothness Estimation of Linear Systems with Colored Noise
The free energy principle (FEP) from neuroscience provides a framework called
active inference for the joint estimation and control of state space systems,
subjected to colored noise. However, the active inference community has been
challenged with the critical task of manually tuning the noise smoothness
parameter. To solve this problem, we introduce a novel online noise smoothness
estimator based on the idea of free energy principle. We mathematically show
that our estimator can converge to the free energy optimum during smoothness
estimation. Using this formulation, we introduce a joint state and noise
smoothness observer design called DEMs. Through rigorous simulations, we show
that DEMs outperforms state-of-the-art state observers with least state
estimation error. Finally, we provide a proof of concept for DEMs by applying
it on a real life robotics problem - state estimation of a quadrotor hovering
in wind, demonstrating its practical use.Comment: 6 pages, 8 figure
Active Inference and Behavior Trees for Reactive Action Planning and Execution in Robotics
We propose a hybrid combination of active inference and behavior trees (BTs)
for reactive action planning and execution in dynamic environments, showing how
robotic tasks can be formulated as a free-energy minimization problem. The
proposed approach allows to handle partially observable initial states and
improves the robustness of classical BTs against unexpected contingencies while
at the same time reducing the number of nodes in a tree. In this work, the
general nominal behavior is specified offline through BTs, where a new type of
leaf node, the prior node, is introduced to specify the desired state to be
achieved rather than an action to be executed as typically done in BTs. The
decision of which action to execute to reach the desired state is performed
online through active inference. This results in the combination of continual
online planning and hierarchical deliberation, that is an agent is able to
follow a predefined offline plan while still being able to locally adapt and
take autonomous decisions at runtime. The properties of our algorithm, such as
convergence and robustness, are thoroughly analyzed, and the theoretical
results are validated in two different mobile manipulators performing similar
tasks, both in a simulated and real retail environment
The effects of swing-leg retraction on running performance: analysis, simulation, and experiment
Using simple running models, researchers have argued that swing-leg retraction can improve running robot performance. In this paper, we investigate whether this holds for a more realistic simulation model validated against a physical running robot. We find that swing-leg retraction can improve stability and disturbance rejection. Alternatively, swing-leg retraction can simultaneously reduce touchdown forces, slipping likelihood, and impact energy losses. Surprisingly, swing-leg retraction barely affected net energetic efficiency. The retraction rates at which these effects are the greatest are strongly model-dependent, suggesting that robot designers cannot always rely on simplified models to accurately predict such complex behaviors
Unwieldy Object Delivery with Nonholonomic Mobile Base: A Stable Pushing Approach
This paper addresses the problem of pushing manipulation with nonholonomic
mobile robots. Pushing is a fundamental skill that enables robots to move
unwieldy objects that cannot be grasped. We propose a stable pushing method
that maintains stiff contact between the robot and the object to avoid
consuming repositioning actions. We prove that a line contact, rather than a
single point contact, is necessary for nonholonomic robots to achieve stable
pushing. We also show that the stable pushing constraint and the nonholonomic
constraint of the robot can be simplified as a concise linear motion
constraint. Then the pushing planning problem can be formulated as a
constrained optimization problem using nonlinear model predictive control
(NMPC). According to the experiments, our NMPC-based planner outperforms a
reactive pushing strategy in terms of efficiency, reducing the robot's traveled
distance by 23.8\% and time by 77.4\%. Furthermore, our method requires four
fewer hyperparameters and decision variables than the Linear Time-Varying (LTV)
MPC approach, making it easier to implement. Real-world experiments are carried
out to validate the proposed method with two differential-drive robots, Husky
and Boxer, under different friction conditions.Comment: The short version of the paper is accepted by RA
Pharmacological treatment of Lambert-Eaton Myasthenic Syndrome
Lambert-Eaton myasthenic syndrome (LEMS) is a very rare antibody-mediated autoimmune disease of the neuromuscular junction. Therapy can be divided in symptomatic treatment and immunosuppressive treatment. Symptomatic treatment with amifampridine is the only therapy currently authorized for use in LEMS patients. In the Netherlands the first choice drug is amifampridine base in an extended release formulation instead of the currently authorized amifampridine phosphate. This formulation has lower costs and is possibly safer due to lower peak concentrations. Other therapy used in LEMS patients is prescribed off-label and is based on experience in patients with myasthenia gravis. In many cases pyridostigmine is added as symptomatic treatment. In almost half of patients immunosuppressive therapy is started, mostly corticosteroids with or without azathioprine. Intravenous immunoglobulins and plasma exchange are used as emergency treatment.
Currently no randomized clinical trials with new therapies are ongoing or announced in patients with LEMS, although multiple new therapies for myasthenia gravis are being investigated. These future therapies can be differentiated in symptomatic and immunomodulating drugs. The immunomodulating drugs can be further differentiated in early stage drugs which target the B-cell, later stage drugs which target the circulating antibodies and targeted therapy which have a disease-specific target. Some early and later stage immunomodulating drugs show promising results in myasthenia gravis although high cost and uncertain long term safety may be limiting for incorporating these drugs in LEMS treatment guidelines.
Clinical trials in LEMS patients are lacking due to the rarity of the disease and we suggest the following requirements for future trials of potential new treatments: Sufficient power by performing multicenter or n-of-1 trials when appropriate, a cross-over design to reduce the number of patients and using a LEMS-specific quantitative primary outcome measure like the 3TUG score