42 research outputs found

    Design of a Haptic Interface for Medical Applications using Magneto-Rheological Fluid based Actuators

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    This thesis reports on the design, construction, and evaluation of a prototype two degrees-of-freedom (DOF) haptic interface, which takes advantage of Magneto-Rheological Fluid (MRF) based clutches for actuation. Haptic information provides important cues in teleoperated systems and enables the user to feel the interaction with a remote or virtual environment during teleoperation. The two main objectives in designing a haptic interface are stability and transparency. Indeed, deficiencies in these factors in haptics-enabled telerobotic systems has the introduction of haptics in medical environments where safety and reliability are prime considerations. An actuator with poor dynamics, high inertia, large size, and heavy weight can significantly undermine the stability and transparency of a teleoperated system. In this work, the potential benefits of MRF-based actuators to the field of haptics in medical applications are studied. Devices developed with such fluids are known to possess superior mechanical characteristics over conventional servo systems. These characteristics significantly contribute to improved stability and transparency of haptic devices. This idea is evaluated and verified through both theoretical and experimental points of view. The design of a small-scale MRF-based clutch, suitable for a multi-DOF haptic interface, is discussed and its performance is compared with conventional servo systems. This design is developed into four prototype clutches. In addition, a closed-loop torque control strategy is presented. The feedback signal used in this control scheme comes from the magnetic field acquired from embedded Hall sensors in the clutch. The controller uses this feedback signal to compensate for the nonlinear behavior using an estimated model, based on Artificial Neural Networks. Such a control strategy eliminates the need for torque sensors for providing feedback signals. The performance of the developed design and the effectiveness of the proposed modeling and control techniques are experimentally validated. Next, a 2-DOF haptic interface based on a distributed antagonistic configuration of MRF-based clutches is constructed for a class of medical applications. This device is incorporated in a master-slave teleoperation setup that is used for applications involving needle insertion and soft-tissue palpation. Phantom and in vitro animal tissue were used to assess the performance of the haptic interface. The results show a great potential of MRF-based actuators for integration in haptic devices for medical interventions that require reliable, safe, accurate, highly transparent, and stable force reflection

    Design and performance evaluation of a prototype MRF-based haptic interface for medical applications

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    This paper describes the construction and stability and transparency evaluation of a prototype two degrees-of-freedom (DoF) haptic interface, which takes ad-vantage of magneto-rheological fluid (MRF)-based clutches for actuation. These small-scale clutches were designed in our lab, and their evaluation were reported previously [1],[2]. MRF-based actuators exhibit superior characteristics,which can significantly contribute to transparency and stability of haptic devices. Based on these actuators, a distributed antagonistic configuration is used to develop the2-DoF haptic interface. This device is incorporated in a master–slave teleoperation setup intended for medical per-cutaneous interventions and soft-tissue palpation. Preliminary studies on the stability and transparency of the haptic interface in this setup using phantom and ex vivo samples show the great potential of MRF-based actuators for integr-tion in haptic devices that require reliable, safe, accurate,highly transparent, and stable force reflection

    Magneto-Rheological Actuators for Human-Safe Robots: Modeling, Control, and Implementation

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    In recent years, research on physical human-robot interaction has received considerable attention. Research on this subject has led to the study of new control and actuation mechanisms for robots in order to achieve intrinsic safety. Naturally, intrinsic safety is only achievable in kinematic structures that exhibit low output impedance. Existing solutions for reducing impedance are commonly obtained at the expense of reduced performance, or significant increase in mechanical complexity. Achieving high performance while guaranteeing safety seems to be a challenging goal that necessitates new actuation technologies in future generations of human-safe robots. In this study, a novel two degrees-of-freedom safe manipulator is presented. The manipulator uses magneto-rheological fluid-based actuators. Magneto-rheological actuators offer low inertia-to-torque and mass-to-torque ratios which support their applications in human-friendly actuation. As a key element in the design of the manipulator, bi-directional actuation is attained by antagonistically coupling MR actuators at the joints. Antagonistically coupled MR actuators at the joints allow using a single motor to drive multiple joints. The motor is located at the base of the manipulator in order to further reduce the overall weight of the robot. Due to the unique characteristic of MR actuators, intrinsically safe actuation is achieved without compromising high quality actuation. Despite these advantages, modeling and control of MR actuators present some challenges. The antagonistic configuration of MR actuators may result in limit cycles in some cases when the actuator operates in the position control loop. To study the possibility of limit cycles, describing function method is employed to obtain the conditions under which limit cycles may occur in the operation of the system. Moreover, a connection between the amplitude and the frequency of the potential limit cycles and the system parameters is established to provide an insight into the design of the actuator as well as the controller. MR actuators require magnetic fields to control their output torques. The application of magnetic field however introduces hysteresis in the behaviors of MR actuators. To this effect, an adaptive model is developed to estimate the hysteretic behavior of the actuator. The effectiveness of the model is evaluated by comparing its results with those obtained using the Preisach model. These results are then extended to an adaptive control scheme in order to compensate for the effect of hysteresis. In both modeling and control, stability of proposed schemes are evaluated using Lyapunov method, and the effectiveness of the proposed methods are validated with experimental results

    Analyse de performances des actionneurs à fluide magnétorhéologique pour les interfaces haptiques

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    Les interfaces haptiques sont des dispositifs permettant un retour en force, qui est généralement fait par l’entremise de moteurs électriques. Les interfaces haptiques peuvent être utilisées en formation pour simuler des environnements virtuels, par exemple, des organes virtuels pour la formation de chirurgien. Cependant, les moteurs électriques font face à un dilemme technique entre la densité de couple et une réponse dynamique, limitant ainsi les performances des interfaces haptiques. Les actionneurs magnétorhéologiques, composé d’une source de puissance et d’embrayages à fluide magnétorhéologique, ont démontré leur potentiel face à ce dilemme technique. En effet, une multitude d’embrayages magnétorhéologique peuvent se partager une seule source de puissance. Les actionneurs magnétorhéologiques ont donc une excellente densité de couple tout en ayant de bonnes performances dynamiques. Ce projet de recherche présente une analyse de performances des actionneurs magnétorhéologique pour les interfaces haptique. Les performances des actionneurs magnétorhéologique ont été comparées avec les moteurs électriques présentement utilisés dans la plupart des interfaces haptiques. Des critères de performances ont été établis à l’aide de la littérature scientifique. Un modèle dynamique d’une interface haptique a été développé et utilisé pour faire une analyse sur les performances des actionneurs magnétorhéologiques et des moteurs électriques. Un banc de test a été développé pour valider le modèle et les résultats obtenus en simulation. Les résultats démontrent que les actionneurs magnétorhéologiques permettent une meilleure génération d’environnement virtuel. L’amortissement des actionneurs magnétorhéologiques doit être adressé pour augmenter la variété d’environnements virtuels pouvant être générés

    Shape Localization and Recognition using a Magnetorheological-fluid Haptic Display

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    Smart materials such as magnetorheological fluids (MRF) offer an interesting technology for use in haptic displays as changes in the magnetic field are rapid, reversible, and controllable. These interfaces have been evaluated in a number of medical and surgical simulators where they can provide cues regarding the viscoelastic properties of tissues. The objective of the present set of experiments was first to determine whether a shape embedded in the MRF could be precisely localized and second whether 10 shapes rendered in a MRF haptic display could be accurately identified. It was also of interest to determine how the information transfer associated with this type of haptic display compares to that achieved using other haptic channels of communication. The overall performance of participants at identifying the shapes rendered in the MRF was good with a mean score of 73 percent correct and an Information Transfer (IT) of 2.2 bits. Participants could also localize a rigid object in the display accurately. These findings indicate that this technology has potential for use in training manual palpation skills and in exploring haptic shape perception in dynamic environments

    Hybrid Magneto-Rheological Actuators for Human Friendly Robotic Manipulators

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    In recent years, many developments in the field of the physical human robot interaction (pHRI) have been witnessed and significant attentions have been given to the subject of safety within the interactive environments. Ensuring the safety has led to the design of the robots that are physically unable to hurt humans. However, Such systems commonly suffer from the safety-performance trade-off. Magneto-Rheological (MR) fluids are a special class of fluids that exhibit variable yield stress with respect to an applied magnetic field. Devices developed with such fluids are known to provide the prerequisite requirements of intrinsic safe actuation while maintaining the dynamical performance of the actuator. In this study, a new concept for generating magnetic field in Magneto-Rheological (MR) clutches is presented. The main rationale behind this concept is to divide the magnetic field generation into two parts using an electromagnetic coil and a permanent magnet. The main rationale behind this concept is to utilize a hybrid combination of electromagnetic coil and a permanent magnet. The combination of permanent magnets and electromagnetic coils in Hybrid Magneto-Rheological (HMR) clutches allows to distribute the magnetic field inside an MR clutch more uniformly. Moreover, The use of a permanent magnet dramatically reduces the mass of MR clutches for a given value of the nominal torque that results in developing higher torque-to-mass ratio. High torque-to-mass and torque-to-inertia ratios in HMR clutches promotes the use of these devices in human-friendly actuation

    Integration of the hybrid-structure haptic interface: HIPHAD v1.0

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    Design, manufacturing, integration and initial test results of the 6-DoF haptic interface, HIPHAD v1.0, are presented in this paper. The hybrid haptic robot mechanism is composed of a 3-DoF parallel platform manipulator, R-Cube, for translational motions and a 3-DoF serial wrist mechanism for monitoring the rotational motions of the handle. The device is capable of displaying point-type of contact since only the R-Cube mechanism is actuated. The dimensions and the orientation of the R-Cube mechanism are reconfigured to comply with the requirements of the haptic system design criteria. The system has several advantages such as relatively trivial kinematical analysis, compactness and high stiffness. The integration of the system along with its mechanism, data acquisition card (DAQ), motor drivers, motors, position sensors, and computer control interface are outlined.Marie Curie International Reintegration Grant within the 7th European Community Framework Programm

    Dual Response of Materials under Electric and Magnetic Fields

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    The electrorheological (ER) effect is known as the change in the rheological behaviors of ER fluids under applied electric field E. When an E is imposed, ER fluids show phase transition from a liquid to a solid-like state due to the interactions of polarized particles. This solid-like behavior of particles is due to the increasing viscosity of suspensions. ER materials belong to a family of controllable fluids. ER fluids are dispersions of solid particles in a hydrophobic insulating dispersion medium. These solid particles play a very important role in the ER activity of dispersions. As the dispersed phase, diverse materials such as polymer blends, gels, biodegradable materials, clays, graphene oxide, hybrid nanocomposites, copolymers, ionic liquids, and conducting polymers have been proposed. In the magnetorheological fluids, this control is provided with magnetic field. Various magnetic particles such as carbonyl iron and iron oxides have been suggested as MR material. The combined effect of magnetic and electric field produces intensified rheological changes in the suspensions. This synergic effect is termed as electromagnetorheological effect (EMR). The EMR effect provides a new strategy to control the rheological properties of dispersions
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