41,396 research outputs found
Reducing the Prediction Horizon in NMPC: An Algorithm Based Approach
In order to guarantee stability, known results for MPC without additional
terminal costs or endpoint constraints often require rather large prediction
horizons. Still, stable behavior of closed loop solutions can often be observed
even for shorter horizons. Here, we make use of the recent observation that
stability can be guaranteed for smaller prediction horizons via Lyapunov
arguments if more than only the first control is implemented. Since such a
procedure may be harmful in terms of robustness, we derive conditions which
allow to increase the rate at which state measurements are used for feedback
while maintaining stability and desired performance specifications. Our main
contribution consists in developing two algorithms based on the deduced
conditions and a corresponding stability theorem which ensures asymptotic
stability for the MPC closed loop for significantly shorter prediction
horizons.Comment: 6 pages, 3 figure
A New Contraction-Based NMPC Formulation Without Stability-Related terminal Constraints
Contraction-Based Nonlinear Model Predictive Control (NMPC) formulations are
attractive because of the generally short prediction horizons they require and
the needless use of terminal set computation that are commonly necessary to
guarantee stability. However, the inclusion of the contraction constraint in
the definition of the underlying optimization problem often leads to non
standard features such as the need for multi-step open-loop application of
control sequences or the use of multi-step memorization of the contraction
level that may induce unfeasibility in presence of unexpected disturbance. This
paper proposes a new formulation of contraction-based NMPC in which no
contraction constraint is explicitly involved. Convergence of the resulting
closed-loop behavior is proved under mild assumptions.Comment: accepted in short version IFAC Nolcos 2016. submitted to Automatica
as a technical communiqu
Stability analysis tool for tuning unconstrained decentralized model predicitive controllers
Some processes are naturally suitable to be controlled in a decentralized framework: centralized control solutions are often infeasible in dealing with large scale plants and they are technologically prohibitive when the processes are too fast for the available computational resources. In these cases, the resulting control problem is usually split in many smaller subproblems and the global requirements are guaranteed by means of a proper coordination. The unconstrained decentralized case is here considered and a coordination strategy is proposed for improving the global control performances. This paper present a tool for setting up and tuning a nominally stable decentralized Model Predictive Controller. Numerical examples are proposed for testing and validating the developed technique
Deep Haptic Model Predictive Control for Robot-Assisted Dressing
Robot-assisted dressing offers an opportunity to benefit the lives of many
people with disabilities, such as some older adults. However, robots currently
lack common sense about the physical implications of their actions on people.
The physical implications of dressing are complicated by non-rigid garments,
which can result in a robot indirectly applying high forces to a person's body.
We present a deep recurrent model that, when given a proposed action by the
robot, predicts the forces a garment will apply to a person's body. We also
show that a robot can provide better dressing assistance by using this model
with model predictive control. The predictions made by our model only use
haptic and kinematic observations from the robot's end effector, which are
readily attainable. Collecting training data from real world physical
human-robot interaction can be time consuming, costly, and put people at risk.
Instead, we train our predictive model using data collected in an entirely
self-supervised fashion from a physics-based simulation. We evaluated our
approach with a PR2 robot that attempted to pull a hospital gown onto the arms
of 10 human participants. With a 0.2s prediction horizon, our controller
succeeded at high rates and lowered applied force while navigating the garment
around a persons fist and elbow without getting caught. Shorter prediction
horizons resulted in significantly reduced performance with the sleeve catching
on the participants' fists and elbows, demonstrating the value of our model's
predictions. These behaviors of mitigating catches emerged from our deep
predictive model and the controller objective function, which primarily
penalizes high forces.Comment: 8 pages, 12 figures, 1 table, 2018 IEEE International Conference on
Robotics and Automation (ICRA
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