339 research outputs found
Cable-Driven Robots with Wireless Control Capability for Pedagogical Illustration in Science
Science teaching in secondary schools is often abstract for students. Even if
some experiments can be conducted in classrooms, mainly for chemistry or some
physics fields, mathematics is not an experimental science. Teachers have to
convince students that theorems have practical implications. We present
teachers an original and easy-to-use pedagogical tool: a cable-driven robot
with a Web-based remote control interface. The robot implements several
scientific concepts such as 3D-geometry and kinematics. The remote control
enables the teacher to move freely in the classroom.Comment: CAR - 8th National Conference on "Control Architecure of Robots"
(2013
Fast and Reliable Autonomous Surgical Debridement with Cable-Driven Robots Using a Two-Phase Calibration Procedure
Automating precision subtasks such as debridement (removing dead or diseased
tissue fragments) with Robotic Surgical Assistants (RSAs) such as the da Vinci
Research Kit (dVRK) is challenging due to inherent non-linearities in
cable-driven systems. We propose and evaluate a novel two-phase coarse-to-fine
calibration method. In Phase I (coarse), we place a red calibration marker on
the end effector and let it randomly move through a set of open-loop
trajectories to obtain a large sample set of camera pixels and internal robot
end-effector configurations. This coarse data is then used to train a Deep
Neural Network (DNN) to learn the coarse transformation bias. In Phase II
(fine), the bias from Phase I is applied to move the end-effector toward a
small set of specific target points on a printed sheet. For each target, a
human operator manually adjusts the end-effector position by direct contact
(not through teleoperation) and the residual compensation bias is recorded.
This fine data is then used to train a Random Forest (RF) to learn the fine
transformation bias. Subsequent experiments suggest that without calibration,
position errors average 4.55mm. Phase I can reduce average error to 2.14mm and
the combination of Phase I and Phase II can reduces average error to 1.08mm. We
apply these results to debridement of raisins and pumpkin seeds as fragment
phantoms. Using an endoscopic stereo camera with standard edge detection,
experiments with 120 trials achieved average success rates of 94.5%, exceeding
prior results with much larger fragments (89.4%) and achieving a speedup of
2.1x, decreasing time per fragment from 15.8 seconds to 7.3 seconds. Source
code, data, and videos are available at
https://sites.google.com/view/calib-icra/.Comment: Code, data, and videos are available at
https://sites.google.com/view/calib-icra/. Final version for ICRA 201
Cable Robot Performance Evaluation by Wrench Exertion Capability
Although cable driven robots are a type of parallel manipulators, the evaluation of their performances cannot be carried out using the performance indices already developed for parallel robots with rigid links. This is an obvious consequence of the peculiar features of flexible cables-a cable can only exert a tensile and limited force in the direction of the cable itself. A comprehensive performance evaluation can certainly be attained by computing the maximum force (or torque) that can be exerted by the cables on the moving platform along a specific (or any) direction within the whole workspace. This is the idea behind the index-called the Wrench Exertion Capability (WEC)-which can be employed to evaluate the performance of any cable robot topology and is characterized by an efficient and simple formulation based on linear programming. By significantly improving a preliminary computation method for the WEC, this paper proposes an ultimate formulation suitable for any cable robot topology. Several numerical investigations on planar and spatial cable robots are presented to give evidence of the WEC usefulness, comparisons with popular performance indices are also provided
Air vehicle simulator: an application for a cable array robot
The development of autonomous air vehicles can be an expensive research pursuit. To alleviate some of the financial burden of this process, we have constructed a system consisting of four winches each attached to a central pod (the simulated air vehicle) via cables - a cable-array robot. The system is capable of precisely controlling the three dimensional position of the pod allowing effective testing of sensing and control strategies before experimentation on a free-flying vehicle. In this paper, we present a brief overview of the system and provide a practical control strategy for such a system. ©2005 IEEE
Real2Sim2Real Transfer for Control of Cable-driven Robots via a Differentiable Physics Engine
Tensegrity robots, composed of rigid rods and flexible cables, exhibit high
strength-to-weight ratios and extreme deformations, enabling them to navigate
unstructured terrain and even survive harsh impacts. However, they are hard to
control due to their high dimensionality, complex dynamics, and coupled
architecture. Physics-based simulation is one avenue for developing locomotion
policies that can then be transferred to real robots, but modeling tensegrity
robots is a complex task, so simulations experience a substantial sim2real gap.
To address this issue, this paper describes a Real2Sim2Real strategy for
tensegrity robots. This strategy is based on a differential physics engine that
can be trained given limited data from a real robot (i.e. offline measurements
and one random trajectory) and achieve a high enough accuracy to discover
transferable locomotion policies. Beyond the overall pipeline, key
contributions of this work include computing non-zero gradients at contact
points, a loss function, and a trajectory segmentation technique that avoid
conflicts in gradient evaluation during training. The proposed pipeline is
demonstrated and evaluated on a real 3-bar tensegrity robot.Comment: Submitted to ICRA202
Redundant Hybrid Cable-Driven Robots: Modeling, Control, and Analysis
Serial and Cable-Driven Parallel Robots (CDPRs) are two types of robots that are widely used in industrial applications. Usually, the former offers high position accuracy at the cost of high motion inertia and small workspace envelope. The latter has a large workspace, low motion inertia, and high motion accelerations, but low accuracy. In this thesis, redundant Hybrid Cable-Driven Robots (HCDRs) are proposed to harness the strengths and benefits of serial and CDPRs. Although the study has been directed at warehousing applications, the developed techniques are general and can be applied to other applications.
The main goal of this research is to develop integrated control systems to reduce vibrations and improve the position accuracy of HCDRs. For the proposed HCDRs, the research includes system modeling, redundancy resolution, optimization problem formulation, integrated control system development, and simulation and experimental validation.
In this thesis, first, a generalized HCDR is proposed for the step-by-step derivation of a generic model, and it can be easily extended to any HCDRs. Then, based on an in-plane configuration, three types of control architecture are proposed to reduce vibrations and improve the position accuracy of HCDR. Their performance is evaluated using several well-designed case studies. Furthermore, a stiffness optimization algorithm is developed to overcome the limitations of existing approaches.
Decoupled system modeling is studied to reduce the complexity of HCDRs. Control design, simulations, and experiments are developed to validate the models and control strategies. Additionally, state estimation algorithms are proposed to overcome the inaccurate limitation of Inertial Measurement Unit (IMU). Based on these state observers, experiments are conducted in different cases to evaluate the control performance.
An Underactuated Mobile Manipulator (UMM) is proposed to address the tracking and vibration- and balance-control problems. Out-of-plane system modeling, disturbance analysis, and model validation are also investigated. Besides, a simple but effective strategy is developed to solve the equilibrium point and balancing problem. Based on the dynamic model, two control architectures are proposed. Compared to other Model Predictive Control (MPC)-based control strategies, the proposed controllers require less effort to implement in practice. Simulations and experiments are also conducted to evaluate the model and control performance.
Finally, redundancy resolution and disturbance rejection via torque optimization in HCDRs are proposed: joint-space Torque Optimization for Actuated Joints (TOAJ) and joint-space Torque Optimization for Actuated and Unactuated Joints (TOAUJ). Compared to TOAJ, TOAUJ can solve the redundancy resolution problem as well as disturbance rejection. The algorithms are evaluated using a Three-Dimensional (3D) coupled HCDR and can also be extended to other HCDRs
Cable robot for non-standard architecture and construction: A dynamic positioning system
In the past few years, cable-driven robots have received some attention by the scientific community and the industry. They have special characteristics that made them very reliable to operate with the level of safeness that is required by different environments, such as, handling of hazardous materials in construction sites. This paper presents a cable-driven robot called SPIDERobot, that was developed for automated construction of architectural projects. This robot has a rotating claw and it is controlled by a set of 4 cables that allow 4 degrees of freedom. In addition to the robot, this paper introduces a Dynamic Control System (DCS) that controls the positioning of the robot and assures that the length of cables is always within a safe value. Results show that traditional force-feasible approaches are more influenced by the pulling forces or the geometric arrangement of all cables and their positioning is significantly less accurate than the DCS. Therefore, the architecture of the SPIDERobot is designed to enable an easily scaling up of the solution to higher dimensions for operating in realistic environments.This work is partly funded by the project PTDC/ATPAQI/
5124/2012 - Robotic Technologies for Non-Standard Design
and Construction in Architecture. This work is also
financed by the ERDF European Regional Development Fund
through the COMPETE Programme (operational programme
for competitiveness) and by National Funds through the FCT
Portuguese Foundation for Science and Technology within
project ”FCOMP - 01-0124-FEDER-022701”info:eu-repo/semantics/publishedVersio
An optimization approach for the inverse kinematics of a highly redundant robot
This paper describes a robot with 12 degrees of freedom for pick-and-place operations using bricks. In addition, an optimization approach is proposed, which determines the state of each joint (that establishes the pose for the robot) based on the target position while minimizing the effort of the servomotors avoiding the inverse kinematics problem, which is a hard task for a 12 DOF robot manipulator. Therefore, it is a multi-objective optimization problem that will be solved using two optimization methods: the Stretched Simulated Annealing method and the NSGA II method.
The experiments conducted in a simulation environment prove that the proposed approach is able to determine a solution for the inverse kinematics problem. A real robot formed by several servomotors and a gripper is also presented in this research for validating the solutions.info:eu-repo/semantics/publishedVersio
Design, Modeling, and Geometric Control on SE(3) of a Fully-Actuated Hexarotor for Aerial Interaction
In this work we present the optimization-based design and control of a
fully-actuated omnidirectional hexarotor. The tilt angles of the propellers are
designed by maximizing the control wrench applied by the propellers. This
maximizes (a) the agility of the UAV, (b) the maximum payload the UAV can hover
with at any orientation, and (c) the interaction wrench that the UAV can apply
to the environment in physical contact. It is shown that only axial tilting of
the propellers with respect to the UAV's body yields optimal results. Unlike
the conventional hexarotor, the proposed hexarotor can generate at least 1.9
times the maximum thrust of one rotor in any direction, in addition to the
higher control torque around the vehicle's upward axis. A geometric controller
on SE(3) is proposed for the trajectory tracking problem for the class of fully
actuated UAVs. The proposed controller avoids singularities and complexities
that arise when using local parametrizations, in addition to being invariant to
a change of inertial coordinate frame. The performance of the controller is
validated in simulation.Comment: 9 pages, 9 figures, ICRA201
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