1,556 research outputs found
A Sliding Mode Force and Position Controller Synthesis for Series Elastic Actuators
This paper deals with the robust force and position control problems of
Series Elastic Actuators. It is shown that a Series Elastic Actuator's force
control problem can be described by a second-order dynamic model which suffers
from only matched disturbances. However, the position control dynamics of a
Series Elastic Actuator is of fourth-order and includes matched and mismatched
disturbances. In other words, a Series Elastic Actuator's position control is
more complicated than its force control, particularly when disturbances are
considered. A novel robust motion controller is proposed for Series Elastic
Actuators by using Disturbance Observer and Sliding Mode Control. When the
proposed robust motion controller is implemented, a Series Elastic Actuator can
precisely track desired trajectories and safely contact with an unknown and
dynamic environment. The proposed motion controller does not require precise
dynamic models of the actuator and environment. Therefore, it can be applied to
many different advanced robotic systems such as compliant humanoids and
exoskeletons. The validity of the motion controller is experimentally verified.Comment: Accepted by Robotica in 201
AMC'24 "A Novel Stiffness Modulation Mechanism for Energy Efficient Variable Stiffness Actuators"
This paper presents a new stiffness modulation mechanism that enables
infinite-range stiffness modulation in a fast manner. The proposed stiffness
modulation mechanism can help improve many robot environment interaction
applications such as human-robot collaboration and robotic rehabilitation
Disturbance Observer-based Robust Control and Its Applications: 35th Anniversary Overview
Disturbance Observer has been one of the most widely used robust control
tools since it was proposed in 1983. This paper introduces the origins of
Disturbance Observer and presents a survey of the major results on Disturbance
Observer-based robust control in the last thirty-five years. Furthermore, it
explains the analysis and synthesis techniques of Disturbance Observer-based
robust control for linear and nonlinear systems by using a unified framework.
In the last section, this paper presents concluding remarks on Disturbance
Observer-based robust control and its engineering applications.Comment: 12 pages, 4 figure
Modelling and Control of a 2-DOF Robot Arm with Elastic Joints for Safe Human-Robot Interaction
Collaborative robots (or cobots) are robots that can safely work together or interact with humans in a common space. They gradually become noticeable nowadays. Compliant actuators are very relevant for the design of cobots. This type of actuation scheme mitigates the damage caused by unexpected collision. Therefore, elastic joints are considered to outperform rigid joints when operating in a dynamic environment. However, most of the available elastic robots are relatively costly or difficult to construct. To give researchers a solution that is inexpensive, easily customisable, and fast to fabricate, a newly-designed low-cost, and open-source design of an elastic joint is presented in this work. Based on the newly design elastic joint, a highly-compliant multi-purpose 2-DOF robot arm for safe human-robot interaction is also introduced. The mechanical design of the robot and a position control algorithm are presented. The mechanical prototype is 3D-printed. The control algorithm is a two loops control scheme. In particular, the inner control loop is designed as a model reference adaptive controller (MRAC) to deal with uncertainties in the system parameters, while the outer control loop utilises a fuzzy proportional-integral controller to reduce the effect of external disturbances on the load. The control algorithm is first validated in simulation. Then the effectiveness of the controller is also proven by experiments on the mechanical prototype.publishedVersio
Design and Control of Compliant Actuation Topologies for Energy-Efficient Articulated Robots
Considerable advances have been made in the field of robotic actuation in recent
years. At the heart of this has been increased use of compliance. Arguably the most
common approach is that of Series-Elastic Actuation (SEA), and SEAs have evolved
to become the core component of many articulated robots. Another approach is
integration of compliance in parallel to the main actuation, referred to as Parallel-
Elastic Actuation (PEA). A wide variety of such systems has been proposed. While
both approaches have demonstrated significant potential benefits, a number of key
challenges remain with regards to the design and control of such actuators.
This thesis addresses some of the challenges that exist in design and control of compliant
actuation systems. First, it investigates the design, dynamics, and control of
SEAs as the core components of next-generation robots. We consider the influence of
selected physical stiffness on torque controllability and backdrivability, and propose
an optimality criterion for impedance rendering. Furthermore, we consider disturbance
observers for robust torque control. Simulation studies and experimental data
validate the analyses. Secondly, this work investigates augmentation of articulated
robots with adjustable parallel compliance and multi-articulated actuation for increased
energy efficiency. Particularly, design optimisation of parallel compliance
topologies with adjustable pretension is proposed, including multi-articulated arrangements.
Novel control strategies are developed for such systems. To validate the
proposed concepts, novel hardware is designed, simulation studies are performed,
and experimental data of two platforms are provided, that show the benefits over
state-of-the-art SEA-only based actuatio
Evaluation and Comparison of SEA Torque Controllers in a Unified Framework
Series elastic actuators (SEA) with their inherent compliance offer a safe
torque source for robots that are interacting with various environments,
including humans. These applications have high requirements for the SEA torque
controllers, both in the torque response as well as interaction behavior with
its the environment. To differentiate state of the art torque controllers, this
work is introducing a unifying theoretical and experimental framework that
compares controllers based on their torque transfer behavior, their apparent
impedance behavior, and especially the passivity of the apparent impedance,
i.e. their interaction stability, as well as their sensitivity to sensor noise.
We compare classical SEA control approaches such as cascaded PID controllers
and full state feedback controllers with advanced controllers using disturbance
observers, acceleration feedback and adaptation rules. Simulations and
experiments demonstrate the trade-off between stable interactions, high
bandwidths and low noise levels. Based on these tradeoffs, an application
specific controller can be designed and tuned, based on desired interaction
with the respective environment
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