22,237 research outputs found
Stiffness Change for Reconfiguration of Inflated Beam Robots
Active control of the shape of soft robots is challenging. Despite having an
infinite number of passive degrees of freedom (DOFs), soft robots typically
only have a few actively controllable DOFs, limited by the number of degrees of
actuation (DOAs). The complexity of actuators restricts the number of DOAs that
can be incorporated into soft robots. Active shape control is further
complicated by the buckling of soft robots under compressive forces; this is
particularly challenging for compliant continuum robots due to their long
aspect ratios. In this work, we show how variable stiffness can enable shape
control of soft robots by addressing these challenges. Dynamically changing the
stiffness of sections along a compliant continuum robot can selectively
"activate" discrete joints. By changing which joints are activated, the output
of a single actuator can be reconfigured to actively control many different
joints, thus decoupling the number of controllable DOFs from the number of
DOAs. We demonstrate embedded positive pressure layer jamming as a simple
method for stiffness change in inflated beam robots, its compatibility with
growing robots, and its use as an "activating" technology. We experimentally
characterize the stiffness change in a growing inflated beam robot and present
finite element models which serve as guides for robot design and fabrication.
We fabricate a multi-segment everting inflated beam robot and demonstrate how
stiffness change is compatible with growth through tip eversion, enables an
increase in workspace, and achieves new actuation patterns not possible without
stiffening
Energy Efficient Actuation with Variable Stiffness Actuators
Research effort in the field of variable stiffness actuators is steadily increasing, due to their wide range of possible applications and their advantages. In literature, var- ious control methods have been proposed, solving particular problems in human-robot and robot-environment interaction applications, in which the mechanical compliance introduced by variable stiffness actuators has been shown to be beneficial. In this work, we focus on achieving energy efficient actuation of robotic systems using variable stiffness actuators. In particular, we aim to exploit the energy storing properties of the internal elastic elements
Investigation on energetic optimization problems of stochastic thermodynamics with iterative dynamic programming
The energetic optimization problem, e.g., searching for the optimal switch-
ing protocol of certain system parameters to minimize the input work, has been
extensively studied by stochastic thermodynamics. In current work, we study
this problem numerically with iterative dynamic programming. The model systems
under investigation are toy actuators consisting of spring-linked beads with
loading force imposed on both ending beads. For the simplest case, i.e., a
one-spring actuator driven by tuning the stiffness of the spring, we compare
the optimal control protocol of the stiffness for both the overdamped and the
underdamped situations, and discuss how inertial effects alter the
irreversibility of the driven process and thus modify the optimal protocol.
Then, we study the systems with multiple degrees of freedom by constructing
oligomer actuators, in which the harmonic interaction between the two ending
beads is tuned externally. With the same rated output work, actuators of
different constructions demand different minimal input work, reflecting the
influence of the internal degrees of freedom on the performance of the
actuators.Comment: 14 pages, 7 figures, communications in computational physics, in
pres
Multi-physic system simplification method applied to a helicopter flight axis active control
A helicopter flight axis control, which is a complex multi-physic system, is modelled using an energetic based graphical tool: the Energetic Macroscopic Representation. Elements of the system are mainly composed of passive technologies and their number tends to increase year after year to improve the pilots comfort by adding new functions. A new methodology is proposed to transform the system into a new active one by replacing some hydro-mechanical elements by a new controllable active mechanical source. The challenge is to simplify the flight control architecture while preserving the global behaviour of the system
Parameters Identification for a Composite Piezoelectric Actuator Dynamics
This work presents an approach for identifying the model of a composite piezoelectric (PZT) bimorph actuator dynamics, with the objective of creating a robust model that can be used under various operating conditions. This actuator exhibits nonlinear behavior that can be described using backlash and hysteresis. A linear dynamic model with a damping matrix that incorporates the BoucâWen hysteresis model and the backlash operators is developed. This work proposes identifying the actuatorâs model parameters using the hybrid master-slave genetic algorithm neural network (HGANN). In this algorithm, the neural network exploits the ability of the genetic algorithm to search globally to optimize its structure, weights, biases and transfer functions to perform time series analysis efficiently. A total of nine datasets (cases) representing three different voltage amplitudes excited at three different frequencies are used to train and validate the model. Four cases are considered for training the NN architecture, connection weights, bias weights and learning rules. The remaining five cases are used to validate the model, which produced results that closely match the experimental ones. The analysis shows that damping parameters are inversely proportional to the excitation frequency. This indicates that the suggested hysteresis model is too general for the PZT model in this work. It also suggests that backlash appears only when dynamic forces become dominant
Control Augmented Structural Synthesis
A methodology for control augmented structural synthesis is proposed for a class of structures which can be modeled as an assemblage of frame and/or truss elements. It is assumed that both the plant (structure) and the active control system dynamics can be adequately represented with a linear model. The structural sizing variables, active control system feedback gains and nonstructural lumped masses are treated simultaneously as independent design variables. Design constraints are imposed on static and dynamic displacements, static stresses, actuator forces and natural frequencies to ensure acceptable system behavior. Multiple static and dynamic loading conditions are considered. Side constraints imposed on the design variables protect against the generation of unrealizable designs. While the proposed approach is fundamentally more general, here the methodology is developed and demonstrated for the case where: (1) the dynamic loading is harmonic and thus the steady state response is of primary interest; (2) direct output feedback is used for the control system model; and (3) the actuators and sensors are collocated
Electromechanical Simulation of Actively Controlled Rotordynamic Systems with Piezoelectric Actuators
Theories and tests for incorporating piezoelectric pushers as actuator devices for active vibration control are discussed. It started from a simple model with the assumption of ideal pusher characteristics and progressed to electromechanical models with nonideal pushers. Effects on system stability due to the nonideal characteristics of piezoelectric pushers and other elements in the control loop were investigated
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