192 research outputs found
A Passivity-based Nonlinear Admittance Control with Application to Powered Upper-limb Control under Unknown Environmental Interactions
This paper presents an admittance controller based on the passivity theory
for a powered upper-limb exoskeleton robot which is governed by the nonlinear
equation of motion. Passivity allows us to include a human operator and
environmental interaction in the control loop. The robot interacts with the
human operator via F/T sensor and interacts with the environment mainly via
end-effectors. Although the environmental interaction cannot be detected by any
sensors (hence unknown), passivity allows us to have natural interaction. An
analysis shows that the behavior of the actual system mimics that of a nominal
model as the control gain goes to infinity, which implies that the proposed
approach is an admittance controller. However, because the control gain cannot
grow infinitely in practice, the performance limitation according to the
achievable control gain is also analyzed. The result of this analysis indicates
that the performance in the sense of infinite norm increases linearly with the
control gain. In the experiments, the proposed properties were verified using 1
degree-of-freedom testbench, and an actual powered upper-limb exoskeleton was
used to lift and maneuver the unknown payload.Comment: Accepted in IEEE/ASME Transactions on Mechatronics (T-MECH
Collision Detection and Reaction: A Contribution to Safe Physical Human-Robot Interaction
In the framework of physical Human-Robot Interaction
(pHRI), methodologies and experimental tests are
presented for the problem of detecting and reacting to collisions
between a robot manipulator and a human being. Using a
lightweight robot that was especially designed for interactive
and cooperative tasks, we show how reactive control strategies
can significantly contribute to ensuring safety to the human
during physical interaction. Several collision tests were carried
out, illustrating the feasibility and effectiveness of the proposed
approach. While a subjective “safety” feeling is experienced by
users when being able to naturally stop the robot in autonomous
motion, a quantitative analysis of different reaction strategies
was lacking. In order to compare these strategies on an objective
basis, a mechanical verification platform has been built. The
proposed collision detection and reactions methods prove to
work very reliably and are effective in reducing contact forces
far below any level which is dangerous to humans. Evaluations
of impacts between robot and human arm or chest up to a
maximum robot velocity of 2.7 m/s are presented
Nonlinear control of a seven degrees-of-freedom exoskeleton robot arm
Advances in the field of robotics have allowed increasingly integrating robotic devices for rehabilitation of physical disabilities. This research work is encompassed into the field of rehabilitation robotics; it presents the development of the robot ETS-MARSE, a seven degrees-of-freedom exoskeleton designed to be worn in the human arm. The developments include the study and implementation of a relatively novel nonlinear control approach, as well as different rehabilitation schemes.
One of the characteristics of a rehabilitation robot is that it deals with a wide number of patients that have different biomechanical and physiological conditions. The implementation of the nonlinear control technique known as Virtual Decomposition Control addresses this issue with its internal parameters’ adaptation that presents a robust behavior to different characteristics of the robot users. Besides, this technique simplifies the complexity of high degree-of-freedom robots by its innovative sub-systems decomposition. All of above, while ensuring the system asymptotic stability and excellent trajectory tracking.
Between the different rehabilitation schemes, we can mention: passive, active-assistive and active rehabilitation. The first one follows predefined trajectories and relies on the efficiency of the controller. The two other schemes require understanding the user’s intention of movement and take an action in order to guide, restrain, correct or follow it. For this purpose, we present an approach that utilizes a force sensor as the human-robot interface in order to transform, via an admittance function, the forces that the user exert to the robot end-effector (handle), and execute active-assisted or active rehabilitation. Finally among the main developments of this work, an approach is presented in which the need of a force sensor to perform some active rehabilitation tasks is removed. By means of a nonlinear observer, the interaction forces are estimated and the user’s intention of movement followed. Experimental results show the effectiveness of all the proposed approaches. All the tests involving humans were tested with healthy subjects.
Trajectory tracking of the robot is executed in joint space; some trajectories are given in Cartesian space and transformed to joint space by means of the pseudoinverse of the Jacobian technique. However this option is limited; a mandatory next step to improve many functionalities of the robot is to solve its inverse kinematics. Between other progresses that are in development, is an approach to process electromyographic signals in order to obtain information from the robot’s users. First results on this methodology are presented. Teleoperation and haptic capabilities are also in the initial stage of development
Design and Control of Robotic Systems for Lower Limb Stroke Rehabilitation
Lower extremity stroke rehabilitation exhausts considerable health care resources, is labor intensive, and provides mostly qualitative metrics of patient recovery. To overcome these issues, robots can assist patients in physically manipulating their affected limb and measure the output motion. The robots that have been currently designed, however, provide assistance over a limited set of training motions, are not portable for in-home and in-clinic use, have high cost and may not provide sufficient safety or performance. This thesis proposes the idea of incorporating a mobile drive base into lower extremity rehabilitation robots to create a portable, inherently safe system that provides assistance over a wide range of training motions. A set of rehabilitative motion tasks were established and a six-degree-of-freedom (DOF) motion and force-sensing system was designed to meet high-power, large workspace, and affordability requirements. An admittance controller was implemented, and the feasibility of using this portable, low-cost system for movement assistance was shown through tests on a healthy individual. An improved version of the robot was then developed that added torque sensing and known joint elasticity for use in future clinical testing with a flexible-joint impedance controller
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
Accomplishing task-invariant assembly strategies by means of an inherently accommodating robot arm
Despite the fact that the main advantage of robot manipulators was always meant to
be their flexibility, they have not been applied widely to the assembly of industrial
components in situations other than those where hard automation might be used. We
identify the two main reasons for this as the 'fragility' of robot operation during tasks
that involve contact, and the lack of an appropriate user interface. This thesis describes
an attempt to address these problems.We survey the techniques that have been proposed to bring the performance of cur¬
rent industrial robot manipulators in line with expectations, and conclude that the
main obstacle in realising a flexible assembly robot that exhibits robust and reliable
behaviour is the problem of spatial uncertainty.Based on observations of the performance of position-controlled robot manipulators and
what is involved during rigid-body part mating, we propose a model of assembly tasks
that exploits the shape invariance of the part geometry across instances of a task. This
allows us to escape from the problem of spatial uncertainty because we are 110 longer
working in spatial terms. In addition, because the descriptions of assembly tasks that
we derive are task-invariant, i.e. they are not dependent on part size or location, they
lend themselves naturally to a task-level programming interface, thereby simplifying
the process of programming an assembly robot.the process of programming an assembly robot.
However, to test this approach empirically requires a manipulator that is able to control
the force that it applies, as well as being sensitive to environmental constraints. The
inertial properties of standard industrial manipulators preclude them from exhibiting
this kind of behaviour. In order to solve this problem we designed and constructed a
three degree of freedom, planar, direct-drive arm that is open-loop force-controllable
(with respect to its end-point), and inherently accommodating during contact.In order to demonstrate the forgiving nature of operation of our robot arm we imple¬
mented a generic crank turning program that is independent of the geometry of the
crank involved, i.e. no knowledge is required of the location or length of the crank.
I11 order to demonstrate the viability of our proposed approach to assembly we pro¬
grammed our robot system to perform some representative tasks; the insertion of a peg
into a hole, and the rotation of a block into a corner. These programs were tested on
parts of various size and material, and in various locations in order to illustrate their
invariant nature.We conclude that the problem of spatial uncertainty is in fact an artefact of the fact
that current industrial manipulators are designed to be position controlled. The work
described in this thesis shows that assembly robots, when appropriately designed,
controlled and programmed, can be the reliable and flexible devices they were always
meant to be
Improving Automated Operations of Heavy-Duty Manipulators with Modular Model-Based Control Design
The rapid development of robotization and automation in mobile working machines aims to increase productivity and safety in many industrial sectors. In heavy-duty applications, hydraulically actuated manipulators are the common solution due to their large power-to-weight ratio. As hydraulic systems can exhibit nonlinear dynamic behavior, automated operations with closed-loop control become challenging. In industrial applications, the dexterity of operations for manipulators is ensured by providing interfaces to equip product variants with different tool attachments. By considering these domain-specific tool attachments for heavy-duty hydraulic manipulators (HHMs), the autonomous robotic operating development for all product variants might be a time-consuming process.
This thesis aims to develop a modular nonlinear model-based (NMB) control method for HHMs to enable systematic NMB model reuse and control system modularity across different HHM product variants with actuators and tool attachments. Equally importantly, the properties of NMB control are used to improve the high-performance control for multi degrees-of-freedom robotic HHMs, as rigorously stability-guaranteed control systems have been shown to provide superior performance. To achieve these objectives, four research problems (RPs) on HHM controls are addressed. The RPs are focused on damping control methods in underactuated tool attachments, compensating for static actuator nonlinearities, and, equally significantly, improving overall control performance. The fourth RP is introduced for hydraulic series elastic actuators (HSEAs) in HHM applications, which can be regarded as supplementing NMB control with the aim of improving force controllability.
Six publications are presented to investigate the RPs in this thesis. The control development focus was on modular NMB control design for HHMs equipped with different actuators and tool attachments consisting of passive and actuated joints. The designed control methods were demonstrated on a full-size HHM and a novel HSEA concept in a heavy-duty experimental setup. The results verified that modular control design for HHM systems can be used to decrease the modifications required to use the manipulator with different tool attachments and floating-base environments
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