Showing papers by "Septimiu E. Salcudean published in 2002"

Transparency in time-delayed systems and the effect of local force feedback for transparent teleoperation

Abstract: This paper first investigates the issue of transparency in time-delayed teleoperation. It then studies the advantages of employing local force feedback for enhanced stability and performance. In addition, two classes of three-channel control architectures, that are perfectly transparent under ideal conditions are introduced. The stability robustness of the proposed architectures to delays is rigorously analyzed, leading to certain bounds on force feedforward control parameters. Experimental results are included in support of the theoretical work.

Image-guided control of a robot for medical ultrasound

Abstract: A robot-assisted system for medical diagnostic ultrasound has been developed by the authors. The paper presents the visual servo controller used in this system. While the ultrasound transducer is positioned by a robot, the operator, the robot controller, and an ultrasound image processor have shared control over its motion. Ultrasound image features that can be selected by the operator are recognized and tracked by a variety of techniques. Based on feature tracking, ultrasound image servoing in three axes has been incorporated in the interface and can be enabled to automatically compensate, through robot motions, unwanted motions in the plane of the ultrasound beam. The accuracy of the system is illustrated through a 3-D reconstruction of an ultrasound phantom. An Internet-based robot-assisted teleultrasound system has also been demonstrated.

Bilateral parallel force/position teleoperation control

Abstract: The extension of parallel force/position control to teleoperation systems is considered in this article. In the proposed four-channel bilateral controller, higher priority is granted to position control at the master side and to force control at the slave side. The primary goal of this control architecture is the enhancement of force and position tracking performance in the presence of uncertainties in the system and environment. The stability and performance of the proposed controller is investigated by analyzing the three decoupled single-degree-of-freedom systems obtained from decoupling and projecting the closed-loop system dynamics onto the slave task-space orthogonal directions. Experimental results demonstrate significant improvement in transparency. © 2002 Wiley Periodicals, Inc.

Needle insertion modelling and simulation

Abstract: A methodology for estimating the force distribution that occurs along a needle shaft during insertion is described. To validate the approach, an experimental system for measuring planar tissue deformation during needle insertions has been developed and is presented. The planar motion of a soft tissue phantom is measured during needle penetration and used in conjunction with a two dimensional linear elastostatic material model, discretised using the finite element method, to derive contact force information that is not directly measurable. This approach provides a method for quantifying the needle forces and soft tissue deformations that occur during general needle trajectories in multiple dimensions. A simulation algorithm that is based upon these results is also described.

Impedance control of a teleoperated excavator

Abstract: Earth-moving machines such as hydraulic excavators are usually used for carrying out contact tasks. Impedance control can be employed as an approach for achieving compliant motion in such tasks. This paper describes a position-based impedance controller that has been developed in our laboratory for excavator-type manipulators, and presents the supporting experimental results. First, the problem of impedance control for a single hydraulic cylinder is addressed and a method is presented to analyze the system stability. The steady-state position and force tracking accuracy of the closed-loop system is also studied. Next, the problem of impedance control for a multi-link hydraulic excavator is addressed and the arm Jacobian and accurate estimates of the arm inertial terms are employed to map the desired impedance of the end-effector (bucket of the excavator) onto the hydraulic cylinders. Various contact experiments carried out using an instrumented mini-excavator demonstrate that the proposed impedance controller has very good performance for both single-link and multilink cases.

Simulated interactive needle insertion

Abstract: A novel interactive virtual needle insertion simulation is presented. The simulation models are based on planar tissue deformations and forces measured during needle insertion experiments. Users are able to control a three degree-of-freedom virtual needle as it penetrates a linear elastostatic tissue model, while experiencing steering torques and lateral needle forces through a planar haptic interface. Efficient numerical computation techniques permit fast simulation of relatively complex two-dimensional and three-dimensional environments at haptic control rates.

Needle Insertion Modelling for the Interactive Simulation of Percutaneous Procedures

Abstract: A novel interactive virtual needle insertion simulation is presented. The insertion model simulates three-degree-of-freedom needle motion, physically-based needle forces, linear elastostatic tissue deformation and needle flexibility for the planning and training of percutaneous therapies and procedures. To validate the approach, an experimental system for measuring planar tissue deformation during needle insertions has been developed and is presented. A real-time simulation algorithm allows users to manipulate the virtual needle as it penetrates a tissue model, while experiencing steering torques and lateral needle forces through a planar haptic interface. Efficient numerical computation techniques permit fast simulation of relatively complex two-dimensional and three-dimensional environments at haptic control rates.