In this article, a macro–mini aerial manipulator with elastic suspension is introduced. The mini is an omnidirectional aerial manipulator suspended from the macro by a spring. The macro is a Cartesian robot that moves the anchoring point of the spring. This design combines the advantages of the large workspace of the macrorobot with the high dynamics of aerial vehicles, while reducing energy consumption thanks to gravity compensation. A partitioned control scheme is first implemented to regulate the aerial manipulator and its carrier separately. The redundancy resolution strategy positions the macrorobot to minimize the energy consumption of the aerial manipulator at steady state. Then, a nonlinear model predictive controller replaces the partitioned controller to improve further the efficiency of the combined system, notably by anticipating the slow dynamics of the macrorobot. A sufficient condition for offset-free tracking has been investigated theoretically. Experiments with a cable-driven parallel robot as macro are carried out to assess the added value of the carrier. Both controllers are validated and compared experimentally.

Aerial Manipulators with Elastic Suspension (AMES) may be seen as a hybrid robot mixing properties of classical Aerial Manipulators (AMs) and Cable-Driven Parallel Robots (CDPRs). The optimal design and control of an AMES using unidirectional thrusters are considered in this paper. To maximize the workspace, an optimization algorithm is proposed. The position and orientation of the thrusters are optimized by adapting methods borrowed from both the AM and CDPR communities. The resulting design is used to build a prototype. Preliminary experimentations are carried out to validate the theoretical workspace and assess the trajectory tracking performance of this AMES. Experiments highlight the significant improvements with respect to a previous suboptimal prototype.

Aerial manipulation increases significantly the workspace size of robotic manipulators. However, aerial manipulation suffers from a lack of autonomy due to limited embedded energy. The Aerial Manipulator with Elastic Suspension (AMES) is designed to cope with this issue. It is an omnidirectional aerial vehicle equipped with a gripper and suspended under a robotic carrier by a spring for gravity compensation. In this paper, the AMES is controlled with a nonlinear model predictive controller (NMPC). To eliminate the steady-state errors, an observer based on a model of the AMES augmented with constant disturbances is implemented in conjunction with the NMPC controller. Experiments illustrate the efficiency of the NMPC by comparing it to a computed torque controller.

Since omnidirectional aerial vehicles can generate a six degrees of freedom wrench, they could be used for dexterous manipulation tasks without the need for an additional robotic arm. However, they suffer from a reduced efficiency and dynamics range due to the huge amount of energy lost in gravity compensation.In this work, we introduce an omnidirectional aerial manipulator suspended from a cable-driven parallel robot (CDPR) by a spring, combining the advantages of the CDPR large workspace with the high dynamics of aerial vehicles, while reducing energy consumption thanks to gravity compensation.A partitioned control scheme is implemented to regulate both systems separately. A preliminary control strategy is proposed for the CDPR motion that minimizes the total energy consumption. Experiments are carried out to assess the added value of the CDPR carrier.

This paper presents a preliminary study of an Aerial Manipulator suspended by a spring to a robotic carrier. The suspended aerial manipulator is actuated by six pairs of contra-rotating propellers generating a 6-DoF wrench. Simulations show path following results using a computed torque (feedback linearization) control strategy. Active vibration canceling is validated experimentally on a first prototype.

This work studies redundant actuation for both trajectory tracking and disturbance rejection on flexible cable-driven parallel robots (CDPR). High dynamics/bandwidth unidirectional force generators, like air propellers, are used in combination with conventional but slower cable winding winches. To optimally balance the action of the two types of actuation within their saturation constraints, a model predictive controller is used. Experiments show the added value of on-board propulsion units with respect to winch-only control in order to improve the overall CDPR dynamic behavior.

This work is a preliminary study assessing the feasibility of using cold-gas thrusters for active damping of flexible cable-driven parallel robots. The concept is validated experimentally on a planar robot embedding custom-built supersonic air thrusters operating at an industry-standard pressure level.

An alternative approach to standard computed torque with feedback linearization is proposed in this paper to control cable-driven parallel robots (CDPRs) with highly flexible cables. Exteroceptive feedback is used to measure the end-effector Cartesian position at a high sampling rate. Stability is demonstrated using singular perturbation theory. The proposed control scheme is experimentally validated on a planar 3-degree-of-freedom CDPR and its efficiency is assessed by comparison with a simple kinematic control law.

Cable-Driven Parallel Robots (CDPRs) can execute fast motions across a large workspace. However, these performances are reached at the cost of a relatively low stiffness which often yields parasitic vibrations at the CDPR mobile platform. In this paper, vibration damping of CDPRs is addressed by means of an original active stabilizer consisting of actuated rotating arms installed on-board the CDPR mobile platform. A control strategy for the whole system, which consists of the CDPR and the stabilizer, and with one purpose for each-position control for the platform and vibration damping for the stabilizer-is designed. The system being controlled at two different time scales, the singular perturbation theory can be used to prove the stability of the corresponding closed-loop system. The efficiency of the proposed device and control strategy is tested in simulations in the case of a planar 3-DOF CDPR equipped with a three-arm stabilizer.

Compared to other parallel robots, cable-driven parallel robots can achieve bigger workspace, higher dynamics with lighter parts and fewer energy while being economically competitive. However, such robots with big workspaces are affected either by cable sagging or by a very low end-effector stiffness, both causing positioning errors. With lightweight cables, the very low stiffness yields disturbing vibrations. In this paper, we address the problem of decoupled active canceling of those vibrations in the modal space. In modal space, vibrations are decomposed in orthogonal signals which allows to use simple SISO control methods to build an active vibration canceling algorithm for the end-effector. As the modal space depends on the end-effector position, better performances are achieved if the controller is tuned for the current robot position. The proposed method is tested both on a realistic simulation and on a 8-cables and 6-degrees of freedom robot.

Cable-driven parallel robots allow for fast motions and huge workspaces, using relatively lightweight moving masses and low-power actuation. This kind of structure yields usually very cost-effective solutions. However, the wider the workspace, the lower the equivalent stiffness of the end-effector yielding inaccuracies due mainly to unwanted vibrations. In this paper, we propose a new approach to compensate for these vibrations. Reaction wheels are used to cancel rotational oscillations of the platform. A planar cable-driven robot built with cheap and lightweight Lego Mindstorms parts is used to validate the concept.

We present herein an original solution to actively stabilize the epicardium in the context of beating-heart coronary artery bypass grafting. Our solution uses a control moment gyroscope to generate the compensation torque and an accelerometer for sensing. This approach makes the designed system completely independent from the stabilizing instrument, as well as independent from any external measurement. We compare two control approaches in a simulation: The first one uses a Kalman filter with a harmonic disturbance model, and the second one uses an adaptive algorithm. Results highlight the superiority of the adaptive control for our application. The first in vivo assessments are presented, showing the efficiency of the principle under real conditions. Using only accelerometric measurements, targeted cardiac motion harmonics are reduced on the order of 68%. With an optical sensor, the reduction exceeds 90%. This constitutes an improvement compared with prior solutions, despite the presence of nonnegligible uncertainties and distant sensing.

Active heart stabilization can help the development of less invasive surgical techniques in the cardiac field. The GyroLock device we propose insures this function using Control Moment Gyro (CMG) actuation, which avoids linkage to the environment. This system is completely independent and pluggable on commercial instruments. For control we use an adaptive algorithm featuring harmonic disturbance cancellation. The first in vivo experiments of the GyroLock using the adaptive control are presented and the results based on two sensor technologies are compared. They exhibit a displacement reduction of more than 90% for cardiac harmonics.

In this paper a bilateral teleoperation scheme is proposed to compensate force perturbations due to repetitive motions of the environment. Based on a Repetitive-Generalized Predictive Controller (R-GPC), it allows to reject periodical disturbances as those generated by respiration motion under breathing apparatus while in contact with the environment. The proposed method is detailed and experimental results are presented for the first time, using a 1-DOF teleoperation testbed.

In this paper, control strategies for an active stabilizer dedicated to beating heart coronary artery bypass grafting are investigated. The active stabilizer, which consists of a piezoactuated compliant mechanism, has to be controlled to compensate for the displacements induced by the beating heart in order to provide the surgeon with a locally motionless myocardium surface. Three controllers, including different levels of prior knowledge about the heart motion, are presented. Their performance with respect to modeling uncertainties, arising unknown interactions of the stabilizer with its positioning mechanism, and the heart, is studied through simulations, as well as laboratory and in vivo experiments. Finally, the selection of the most adequate control scheme and the performance of the device from a clinical point of view are discussed.

In this paper, we study a class of one degree-of-freedom mechanisms in order to design linear haptic interfaces. They allow to perform straight line motions with only revolute joints, thus limiting the friction that characterizes linear bearings. We particularly describe the characteristics of these systems and their good properties to design haptic displays: parallel architecture, very good linearity, good use of the actuator torque. The Hoeken's mechanism which has the best characteristics to build a direct drive general purpose haptic display is selected. We present the fabricated prototype and its evaluation in terms of bandwidth, Coulomb friction and apparent mass.

In this paper, the design of a new active cardiac stabilizer, Cardiolock2, is presented. Following the proof of concept Cardiolock [7], this device allows an active stabilization of the surface of a beating heart in two directions, which is considered sufficient for a complete stabilization. Piezoelectric actuation is combined with a compliant architecture to obtain high dynamics and accuracy. A remote center of motion is obtained with a serial architecture, and parallel mechanisms in configurations close to singularity are used to increase the workspace. A kinematic analysis is first presented, before detailing the main properties of the device and the current development of the prototype.

Flexible endoscopes are used in many surgical procedures and diagnostic exams, like in gastroscopy or coloscopy. They have also been used recently for new surgical procedures using natural orifices called NOTES. While these procedures are very promising for the patients, they are quite awkward for the surgeons. The flexible endoscope allows the access to operating areas which are not easily reachable, with small or no incisions; but the manipulation of the system is complex. In order to help the practicians during NOTES or classical interventions with flexible endoscopes, we propose to motorize the system so as to partially robotize the movements. This paper presents the problems in the use of the flexible endoscope and explains how the system can be used to stabilize the endoscope on an area of interest despite physiological motions and therefore to improve the manipulation of the system.

The development of new medical therapies often require experiments on small animals. In order to improve the medical protocol during treatments with needles, we propose a new robotic needle insertion system using CT-scan imaging and visual servoing. The biologist defines the skin entry point and the target to be reached in the CT-image. The needle target is then expressed in the robot frame thanks to a 3D registration between the 3D structured light reconstruction of the animal bed and the 3D model obtained from the CT-scan data. Finally the needle pointing is performed thanks to a 2D visual servoing. This approach is independent of the needle model and allows a high positioning accuracy: less than 0.5 pixel for the tip of the needle and less than 10-3rad for the direction. Experiments show promising results: a needle with a diameter of 0.72 mm can be inserted through two holes with diameters of 2 mm.

The commercial development of haptic devices is very promising. Existing systems are often 6-degree-of-freedom mechanisms equipped with a stylus that acts as a tool. They exhibit force feedback for 3 or 6 degrees of freedom of their end-effector, depending on whether only forces or both forces and torques are rendered. Some planar devices are also used but oddly, one-degree-of-freedom linear haptic devices are quite rare. This lack can probably be explained by the necessary mechanical transformations that are required to achieve linear motions with rotary motors. In this paper, we review several possible structures and present the design of a new one-degree-of-freedom linear haptic device with a limited number of joints and a compact design, compatible with rotary actuation. We evaluate this device in the telemanipulation context.

Visual servoing refers to the closed-loop position control of the robot end-effector (Hutchinson et al., 1996) using visual feedback and should be distinguished from vision-based expert systems (Corke and Good, 1996). In this work, we focus our interest on high performance visual servoing. Our goal is to maximize the bandwidth of the visual loop. This means usually, considering the average dynamics of robots, that the use of a high speed camera is necessary. To achieve this goal, the model of the visual loop must be known with a good accuracy. This includes the dynamics of the robot and the dynamics of the vision system. The main objective of this work is to propose a new dynamic model for the vision sensor. The proposed model is validated by experiments. Ultrasonic motors are used in the experiments since they exhibit a very short response time and can be modeled by a simple transfer function, thus simplifying the decoupling between vision and actuation.

Off-pump coronary artery bypass grafting (CABG) is probably an important milestone in the cardiac surgery history. This technique is currently made possible thanks to the use of mechanical stabilizers. Nevertheless, the available stabilizers are not fully satisfying. Indeed, they have been demonstrated to exhibit significant residual motion. In this paper we propose a novel piezo-actuated compliant stabilizer, whose architecture is compatible with a minimally invasive surgery context. This active stabilizer is controlled using high speed visual feedback in order to compensate in real time for the residual cardiac motion. In vivo experimental results using the developed prototype are given to demonstrate the efficiency of the adopted approach.

Medical robotics is a field where dedicated mechanisms have an increasing importance. The strong operating room constraints, both medical and practical, lead to heavily customized solutions. In this paper, we consider the practical problems that must be solved to build a robotic system dedicated to medical interventions under CT-scan guidance. This compact robotic assistant is placed on the patient what raises new generic robotic design problems. Practical solutions together with the evaluation of a prototype are presented in this paper

Robotic technologies provide new ways to compensate quasi-periodic biological motion, enabling higher surgical accuracy without invasive measures such as cardiopulmonary bypass. This paper describes current research in robotic compensation of hand tremor, respiratory motion, and heartbeat during surgical procedures. An analysis of each physiological motion pattern is provided, as well as a description of novel compensation techniques

In this paper is considered fast visual servoing of a two-links arm including flexibilities for compensation of heart movements in surgery. The flexibilities are globally identified with no additional sensor than the external-500 Hz camera used in the visual servoing loop. The obtained model is valid around the working position of the arm and can be easily modified for new positions of the camera. Two control strategies to handle flexibilities and achieve high bandwidth are implemented: Generalized Predictive Control (GPC) and H∞ control. Simulation and experimental results are given allowing to compare their efficiencies.

In this paper, we present a robot positioning task with respect to a static target using visual servoing and optimization techniques. The vision system is uncalibrated. The displacements of the robot are generated in real time in order to minimize an objective function using a simplex method and a Newton-like method. Our method allows for the inclusion of constraints in the image as well as in joint space. On-line image Jacobian estimation runs at the same time, and is used to accelerate convergence near the target. We successfully validate this method with simulations under the graphic library OpenGL, and practical experiment with industrial manipulators.

This work presents a predictive-control approach to active mechanical filtering of complex, periodic motions of organs induced by respiration or heart beating in robotized surgery. Two different predictive-control schemes are proposed for the compensation of respiratory motions or cardiac motions. For respiratory motions, the periodic property of the disturbance has been included into the input-output model of the controlled system so as to have the robotic system learn and anticipate perturbation motions. A new cost function is proposed for the unconstrained generalized predictive controller (GPC), where reference tracking is decoupled from the rejection of predictable periodic motions. Cardiac motions are more complex, since they are the combination of two periodic nonharmonic components. An adaptive disturbance predictor is proposed which outputs future predicted disturbance values. These predicted values are used to anticipate the disturbance by using the predictive feature of a regular GPC. Experimental results are presented on a laboratory testbed and in vivo on pigs. They demonstrate the effectiveness of the two proposed methods to compensate complex physiological motion.

This work presents first in-vivo results of beating heart tracking with a surgical robot arm in off-pump cardiac surgery. The tracking is performed in a 2D visual servoing scheme using a 500 frame per second video camera. Heart motion is measured by means of active optical markers that are put onto the heart surface. Amplitude of the motion is evaluated along the two axis of the image reference frame. This is a complex and fast motion that mainly reflects the influence of both the respiratory motion and the electro-mechanical activity of the myocardium. A model predictive controller is setup to track the two degrees of freedom of the observed motion by computing velocities for two of the robot joints. The servoing scheme takes advantage of the ability of predictive control to anticipate over future references provided they are known or they can be predicted. An adaptive observer is defined along with a simple cardiac model to estimate the two components of the heart motion. The predictions are then fed into the controller references and it is shown that the tracking behaviour is greatly improved.

Periodic deformations of organs and soft tissues are complex, repetitive disturbances for surgeons manipulating robotic interfaces in computer-assisted surgery. They are due to respiratory movements or heart beats, and they have to be manually compensated for by the surgeon whenever accurate gestures are needed, as it is the case in cardiac or robotized laparoscopic surgery. This work presents a repetitive model predictive control scheme for the cancellation of fast periodic motions by a robot arm, which is controlled by visual servoing at 500 Hz by means of a high-speed camera. The problem we address is to keep a constant distance in the camera images from a surgical tool's tip to the organ surface. Contributions of the control input to reference tracking and to the fast-disturbance rejection are split and computed separately to ensure that the surgeon's interaction on the robot bas no influence on the cancellation performance. The system is tested in a laboratory experiment with an experimental surgical arm and in in vivo conditions on a living pig with a standard surgical robot. Results show the effectiveness and the potential of the proposed control scheme.

This paper presents a robotic vision system that automatically retrieves and positions surgical instruments during robotized laparoscopic surgical operations. The instrument is mounted on the end-effector of a surgical robot which is controlled by visual servoing. The goal of the automated task is to safely bring the instrument at a desired three-dimensional location from an unknown or hidden position. Light-emitting diodes are attached on the tip of the instrument, and a specific instrument holder fitted with optical fibers is used to project laser dots on the surface of the organs. These optical markers are detected in the endoscopic image and allow localizing the instrument with respect to the scene. The instrument is recovered and centered in the image plane by means of a visual servoing algorithm using feature errors in the image. With this system, the surgeon can specify a desired relative position between the instrument and the pointed organ. The relationship between the velocity screw of the surgical instrument and the velocity of the markers in the image is estimated online and, for safety reasons, a multistages servoing scheme is proposed. Our approach has been successfully validated in a real surgical environment by performing experiments on living tissues in the surgical training room of the Institut de Recherche sur les Cancers de l'Appareil Digestif (IRCAD), Strasbourg, France.

This paper presents a robotic vision system that automatically retrieves and positions surgical instruments in robotized laparoscopic surgery. The surgical instrument is mounted on the end-effector of a surgical robot which can be controlled by automatic visual feedback. The goal of the automated task is to bring the instrument at a desired location from an unknown or hidden position. To achieve this task, a special instrument-holder is designed with optical fibers and collimators. This instrument-holder projects laser dot patterns onto the organ surface which are seen in the endoscopic images. Then, the instrument is retrieved and centered in the image plane using a visual servoing algorithm. With this system, the surgeon can also specify a desired position for the instrument in the image. Our approach is successfully validated in a real surgical environment by performing experiments on living animals in the surgical training room of IRCAD.

In this paper, we address the problem of controlling the motion of a surgical instrument close to an unknown organ surface by visual servoing in the context of robotized laparoscopic surgery. To achieve this goal, a visual servoing algorithm is developed that combines feature errors in the image and errors in depth measurements. The relationship between the velocity screw of the surgical instrument, the depth and the motion field is defined and a two-stage servoing scheme is proposed. In order to measure the orientation and the depth of the instrument with respect to the organ, a laser dot pattern is projected on the organ surface and optical markers are stuck on the instrument. Our work has been successfully validated with a surgical robot by performing experiments on living tissues in the surgical training room of IRCAD.

In this paper, we present a robot positioning task with respect to a static target using visual servoing and optimization techniques. The vision system is uncalibrated and the kinematic model of the robot may be totally unknown. The displacements of the robot are generated in real time in order to minimize an objective function. The objective function includes the quadratic error between the current target image and the desired target image. A simplex method is used to minimize the objective function. Our method allows the system to include constraints in the image as well as in joint-space. We successfully validate this method, with simulations under the graphic library QpenGL and with experiments on a 6-DOF industrial manipulator.

This paper presents the visual servoing of a six degrees of freedom (6-DOF) manipulator for unknown three-dimensional profile following. The profile has an unknown curvature, but its cross section is known. The visual servoing keeps the transformation between a cross section of the profile and the camera constant with respect to 6 DOE The position of the profile with respect to only five degrees of freedom can be measured with the camera since the image does not provide position information along the profile. The kinematic model of the robot is used to reconstruct the displacement along the profile, i.e., the sixth degree of freedom, and allows to control the profile-following velocity. Experiments show good accuracy for positioning at a sampling rate of 50 Hz. Two control strategies are tested: proportional-integral control and generalized predictive control (GPC). The visual servoing exhibits better accuracy with the GPC in simulations and in real experiments on a 6-DOF manipulator due to the predictive property of the algorithm.

This paper presents a novel approach to model and control high speed 6 DOF visual servo loops. The modelling and control strategy takes into account the dynamics of a velocity controlled 6 DOF manipulator as well as a simplified model of the camera and acquisition system in order to increase the bandwidth of the servo loop. multi-input multi-output (MIMO) generalized predictive control (GPC) is used to optimally control the visual loop with respect to the proposed dynamic model. The visual sensor used in the experiments is a high speed camera that allows to acquire 120 noninterlaced images per second. With this camera, we achieve a sampling frequency of 120 Hz for the visual loop. Experimental results on a 6 DOF industrial robot are presented that validate the proposed model. They show drastic improvement of the loop performance with respect to more classical control strategies like PID type control.

This paper presents the visual servoing of a 6-DOF manipulator for profile following. The profile has an unknown curvature, but its cross-section is known. The visual servoing keeps the transformation constant between a cross-section of the profile and the camera with respect to 6 degrees of freedom. The position of the profile with respect to only five of these degrees of freedom can be measured with the camera, since the image gives no position information along the profile. The kinematic model of the robot is used to reconstruct the displacement along the profile and allow us to control the profile following velocity. Experiments show good accuracy for positioning at a sampling rate of 20 ms. Two control strategies are tested: PI control and generalized predictive control (GPC). The visual servoing exhibits better accuracy with the GPC in simulations and in real experiments.

Presents a way to model visual servoing in the case of a 6 DOF industrial manipulator. The manipulator with its actuators (DC motors), their current feedback loops and their velocity control loops, are modeled as a "virtual Cartesian device". The system with its visual feedback loop is decoupled to form 6 independent loops. Then, 6 generalized predictive controllers (GPC) are implemented online to take into account the dynamics of the manipulator. Simulations and experimental results show a drastic improvement in performance for a 6 DOF industrial manipulator in an eye-in-hand configuration compared to standard approaches neglecting these dynamics.

In this paper, the design of a position tracking control scheme for an industrial robot manipulator is considered. The design is based on the normalized left coprime factors robust stabilization approach. By coupling this H/sub /spl infin// synthesis to a sequential quadratic programming optimization procedure, a systematic design method is developed optimizing the performance of the controller. Further, the role of the nominal model for the design is explored. The control scheme is successfully implemented and tested on a real industrial robot manipulator. The computed controller worked immediately in the first experiment without any further tuning and showed excellent robust performance.