264 research outputs found
Optimizing plane-to-plane positioning tasks by image-based visual servoing and structured light
This paper considers the problem of positioning an eye-in-hand system so that it gets parallel to a planar object. Our approach to this problem is based on linking to the camera a structured light emitter designed to produce a suitable set of visual features. The aim of using structured light is not only for simplifying the image processing and allowing lowtextured objects to be considered, but also for producing a control scheme with nice properties like decoupling, convergence and adequate camera trajectory. This paper focuses on an imagebased approach that achieves decoupling in all the workspace and for which the global convergence is ensured in perfect conditions. The behavior of the image-based approach is shown to be partially equivalent to a 3D visual servoing scheme but with a better robustness with respect to image noise. Concerning the robustness of the approach against calibration errors, it is demonstrated both analytically and experimentally
Improving detection of surface discontinuities in visual-force control systms
In this paper, a new approach to detect surface discontinuities in a visualâforce control task is described. A task which consists in tracking a surface using visualâforce information is shown. In this task, in order to reposition the robot tool with respect to the surface it is necessary to determine the surface discontinuities. This paper describes a new method to detect surface discontinuities employing sensorial information obtained from a force sensor, a camera and structured light. This method has proved to be more robust than previous systems even in situations where high frictions occur
Boosting Performance of Visual Servoing Using Deep Reinforcement Learning From Multiple Demonstrations
In this study, knowledge of multiple controllers was used and combined with deep reinforcement learning (RL) to train a visual servoing (VS) technique. Deep RL algorithms were successful in solving complicated control problems, however they generally require a large amount of data before they achieve an acceptable performance. We developed a method that generates online hyper-volume action bounds from demonstrations of multiple controllers (experts) to address the issue of insufficient data in RL. The agent then continues to explore the created bounds to find more optimized solutions and gain more rewards. By doing this, we cut out pointless agent explorations, which results in a reduction in training time as well as an improvement in performance of the trained policy. During the training process, we used domain randomization and domain adaptation to make the VS approach robust in the real world. As a result, we showed a 51% decrease in training time to achieve the desired level of performance, compared to the case when RL was used solely. The findings showed that the developed method outperformed other baseline VS methods (image-based VS, position-based VS, and hybrid-decoupled VS) in terms of VS error convergence speed and maintained higher manipulability
Robot Visual Servoing Using Discontinuous Control
This work presents different proposals to deal with common problems in robot visual servoing based on the application of discontinuous control methods. The feasibility and effectiveness of the proposed approaches are substantiated by simulation results and real experiments using a 6R industrial manipulator. The main contributions are:
- Geometric invariance using sliding mode control (Chapter 3): the defined higher-order invariance is used by the proposed approaches to tackle problems in visual servoing. Proofs of invariance condition are presented.
- Fulfillment of constraints in visual servoing (Chapter 4): the proposal uses sliding mode methods to satisfy mechanical and visual constraints in visual servoing, while a secondary task is considered to properly track the target object. The main advantages of the proposed approach are: low computational cost, robustness and fully utilization of the allowed space for the constraints.
- Robust auto tool change for industrial robots using visual servoing (Chapter 4): visual servoing and the proposed method for constraints fulfillment are applied to an automated solution for tool changing in industrial robots. The robustness of the proposed method is due to the control law of the visual servoing, which uses the information acquired by the vision system to close a feedback control loop. Furthermore, sliding mode control is simultaneously used in a prioritized level to satisfy the aforementioned constraints. Thus, the global control accurately places the tool in the warehouse, but satisfying the robot constraints.
- Sliding mode controller for reference tracking (Chapter 5): an approach based on sliding mode control is proposed for reference tracking in robot visual servoing using industrial robot manipulators. The novelty of the proposal is the introduction of a sliding mode controller that uses a high-order discontinuous control signal, i.e., joint accelerations or joint jerks, in order to obtain a smoother behavior and ensure the robot system stability, which is demonstrated with a theoretical proof.
- PWM and PFM for visual servoing in fully decoupled approaches (Chapter 6): discontinuous control based on pulse width and pulse frequency modulation is proposed for fully decoupled position based visual servoing approaches, in order to get the same convergence time for camera translation and rotation.
Moreover, other results obtained in visual servoing applications are also described.Este trabajo presenta diferentes propuestas para tratar problemas habituales en el control de robots por realimentación visual, basadas en la aplicación de métodos de control discontinuos. La viabilidad y eficacia de las propuestas se fundamenta con resultados en simulación y con experimentos reales utilizando un robot manipulador industrial 6R. Las principales contribuciones son:
- Invariancia geomĂ©trica utilizando control en modo deslizante (CapĂtulo 3): la invariancia de alto orden definida aquĂ es utilizada despuĂ©s por los mĂ©todos propuestos, para tratar problemas en control por realimentaciĂłn visual. Se apuertan pruebas teĂłricas de la condiciĂłn de invariancia.
- Cumplimiento de restricciones en control por realimentaciĂłn visual (CapĂtulo 4): esta propuesta utiliza mĂ©todos de control en modo deslizante para satisfacer restricciones mecĂĄnicas y visuales en control por realimentaciĂłn visual, mientras una tarea secundaria se encarga del seguimiento del objeto. Las principales ventajas de la propuesta son: bajo coste computacional, robustez y plena utilizaciĂłn del espacio disponible para las restricciones.
- Cambio de herramienta robusto para un robot industrial mediante control por realimentaciĂłn visual (CapĂtulo 4): el control por realimentaciĂłn visual y el mĂ©todo propuesto para el cumplimiento de las restricciones se aplican a una soluciĂłn automatizada para el cambio de herramienta en robots industriales. La robustez de la propuesta radica en el uso del control por realimentaciĂłn visual, que utiliza informaciĂłn del sistema de visiĂłn para cerrar el lazo de control. AdemĂĄs, el control en modo deslizante se utiliza simultĂĄneamente en un nivel de prioridad superior para satisfacer las restricciones. AsĂ pues, el control es capaz de dejar la herramienta en el intercambiador de herramientas de forma precisa, a la par que satisface las restricciones del robot.
- Controlador en modo deslizante para seguimiento de referencia (CapĂtulo 5): se propone un enfoque basado en el control en modo deslizante para seguimiento de referencia en robots manipuladores industriales controlados por realimentaciĂłn visual. La novedad de la propuesta radica en la introducciĂłn de un controlador en modo deslizante que utiliza la señal de control discontinua de alto orden, i.e. aceleraciones o jerks de las articulaciones, para obtener un comportamiento mĂĄs suave y asegurar la estabilidad del sistema robĂłtico, lo que se demuestra con una prueba teĂłrica.
- Control por realimentaciĂłn visual mediante PWM y PFM en mĂ©todos completamente desacoplados (CapĂtulo 6): se propone un control discontinuo basado en modulaciĂłn del ancho y frecuencia del pulso para mĂ©todos completamente desacoplados de control por realimentaciĂłn visual basados en posiciĂłn, con el objetivo de conseguir el mismo tiempo de convergencia para los movimientos de rotaciĂłn y traslaciĂłn de la cĂĄmara .
Ademås, se presentan también otros resultados obtenidos en aplicaciones de control por realimentación visual.Aquest treball presenta diferents propostes per a tractar problemes habituals en el control de robots per realimentació visual, basades en l'aplicació de mÚtodes de control discontinus. La viabilitat i eficà cia de les propostes es fonamenta amb resultats en simulació i amb experiments reals utilitzant un robot manipulador industrial 6R. Les principals contribucions són:
- InvariĂ ncia geomĂštrica utilitzant control en mode lliscant (CapĂtol 3): la invariĂ ncia d'alt ordre definida acĂ Ă©s utilitzada desprĂ©s pels mĂštodes proposats, per a tractar problemes en control per realimentaciĂł visual. S'aporten proves teĂČriques de la condiciĂł d'invariĂ ncia.
- Compliment de restriccions en control per realimentaciĂł visual (CapĂtol 4): aquesta proposta utilitza mĂštodes de control en mode lliscant per a satisfer restriccions mecĂ niques i visuals en control per realimentaciĂł visual, mentre una tasca secundĂ ria s'encarrega del seguiment de l'objecte. Els principals avantatges de la proposta sĂłn: baix cost computacional, robustesa i plena utilitzaciĂł de l'espai disponible per a les restriccions.
- Canvi de ferramenta robust per a un robot industrial mitjançant control per realimentaciĂł visual (CapĂtol 4): el control per realimentaciĂł visual i el mĂštode proposat per al compliment de les restriccions s'apliquen a una soluciĂł automatitzada per al canvi de ferramenta en robots industrials.
La robustesa de la proposta radica en l'Ășs del control per realimentaciĂł visual, que utilitza informaciĂł del sistema de visiĂł per a tancar el llaç de control. A mĂ©s, el control en mode lliscant s'utilitza simultĂ niament en un nivell de prioritat superior per a satisfer les restriccions. AixĂ doncs, el control Ă©s capaç de deixar la ferramenta en l'intercanviador de ferramentes de forma precisa, a la vegada que satisfĂ les restriccions del robot.
- Controlador en mode lliscant per a seguiment de referĂšncia (CapĂtol 5): es proposa un enfocament basat en el control en mode lliscant per a seguiment de referĂšncia en robots manipuladors industrials controlats per realimentaciĂł visual. La novetat de la proposta radica en la introducciĂł d'un controlador en mode lliscant que utilitza senyal de control discontĂnua d'alt ordre, i.e. acceleracions o jerks de les articulacions, per a obtindre un comportament mĂ©s suau i assegurar l'estabilitat del sistema robĂČtic, la qual cosa es demostra amb una prova teĂČrica.
- Control per realimentaciĂł visual mitjançant PWM i PFM en mĂštodes completament desacoblats (CapĂtol 6): es proposa un control discontinu basat en modulaciĂł de l'ample i la freqĂŒĂšncia del pols per a mĂštodes completament desacoblats de control per realimentaciĂł visual basats en posiciĂł, amb l'objectiu d'aconseguir el mateix temps de convergĂšncia per als moviments de rotaciĂł i translaciĂł de la cĂ mera.
A més, es presenten també altres resultats obtinguts en aplicacions de control per realimentació visual.Muñoz Benavent, P. (2017). Robot Visual Servoing Using Discontinuous Control [Tesis doctoral no publicada]. Universitat PolitÚcnica de ValÚncia. https://doi.org/10.4995/Thesis/10251/90430TESI
3D Spectral Domain Registration-Based Visual Servoing
This paper presents a spectral domain registration-based visual servoing
scheme that works on 3D point clouds. Specifically, we propose a 3D model/point
cloud alignment method, which works by finding a global transformation between
reference and target point clouds using spectral analysis. A 3D Fast Fourier
Transform (FFT) in R3 is used for the translation estimation, and the real
spherical harmonics in SO(3) are used for the rotations estimation. Such an
approach allows us to derive a decoupled 6 degrees of freedom (DoF) controller,
where we use gradient ascent optimisation to minimise translation and
rotational costs. We then show how this methodology can be used to regulate a
robot arm to perform a positioning task. In contrast to the existing
state-of-the-art depth-based visual servoing methods that either require dense
depth maps or dense point clouds, our method works well with partial point
clouds and can effectively handle larger transformations between the reference
and the target positions. Furthermore, the use of spectral data (instead of
spatial data) for transformation estimation makes our method robust to
sensor-induced noise and partial occlusions. We validate our approach by
performing experiments using point clouds acquired by a robot-mounted depth
camera. Obtained results demonstrate the effectiveness of our visual servoing
approach.Comment: Accepted to 2023 IEEE International Conference on Robotics and
Automation (ICRA'23
Uncalibrated visual servo for unmanned aerial manipulation
© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper addresses the problem of autonomous servoing an unmanned redundant aerial manipulator using computer vision. The overactuation of the system is exploited by means of a hierarchical control law, which allows to prioritize several tasks during flight. We propose a safety-related primary task to avoid possible collisions. As a secondary task, we present an uncalibrated image-based visual servo strategy to drive the arm end-effector to a desired position and orientation by using a camera attached to it. In contrast to the previous visual servo approaches, a known value of camera focal length is not strictly required. To further improve flight behavior, we hierarchically add one task to reduce dynamic effects by vertically aligning the arm center of gravity to the multirotor gravitational vector, and another one that keeps the arm close to a desired configuration of high manipulability and avoiding arm joint limits. The performance of the hierarchical control law, with and without activation of each of the tasks, is shown in simulations and in real experiments confirming the viability of such prioritized control scheme for aerial manipulation.Peer ReviewedPostprint (author's final draft
Survey of Visual and Force/Tactile Control of Robots for Physical Interaction in Spain
Sensors provide robotic systems with the information required to perceive the changes that happen in unstructured environments and modify their actions accordingly. The robotic controllers which process and analyze this sensory information are usually based on three types of sensors (visual, force/torque and tactile) which identify the most widespread robotic control strategies: visual servoing control, force control and tactile control. This paper presents a detailed review on the sensor architectures, algorithmic techniques and applications which have been developed by Spanish researchers in order to implement these mono-sensor and multi-sensor controllers which combine several sensors
Modelling the Xbox 360 Kinect for visual servo control applications
A research report submitted to the faculty of Engineering and the built environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering.
Johannesburg, August 2016There has been much interest in using the Microsoft Xbox 360 Kinect
cameras for visual servo control applications. It is a relatively cheap
device with expected shortcomings. This work contributes to the practical
considerations of using the Kinect for visual servo control applications.
A comprehensive characterisation of the Kinect is synthesised
from existing literature and results from a nonlinear calibration procedure.
The Kinect reduces computational overhead on image processing
stages, such as pose estimation or depth estimation. It is limited
by its 0.8m to 3.5m practical depth range and quadratic depth resolution
of 1.8mm to 35mm, respectively. Since the Kinect uses an
infra-red (IR) projector, a class one laser, it should not be used outdoors,
due to IR saturation, and objects belonging to classes of non-
IR-friendly surfaces should be avoided, due to IR refraction, absorption,
or specular reflection. Problems of task stability due to invalid
depth measurements in Kinect depth maps and practical depth range
limitations can be reduced by using depth map preprocessing and
activating classical visual servoing techniques when Kinect-based approaches
are near task failure.MT201
Hierarchical task control for aerial inspection
Trabajo presentado al Workshop and Summer School on Field Robotics (euRathlon/ARCAS), celebrado en Sevilla (España) del 15 al 18 de junio de 2014.This paper presents a task oriented control strategy for aerial vehicles equipped with a robotic arm and a camera attached to its end-effector. With this setting the camera can reach a new set of orientations previously not feasible for the quadrotor. The over-actuation of the whole system is exploited with a hierarchical control law to achieve a primary task consisting on a visual servoing control, whilst secondary tasks can also be attained to minimize gravitational effects or undesired arm configurations. Results are shown in a Robot Operating System (ROS) simulation.This work has been partially funded by the EU project ARCAS FP7-287617.Peer Reviewe
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