Magnetic levitation in general is relevant to applications which require fine control of motion, vibration, force and torque. One common method for magnetic levitation is to use four iron core coils connected in pairs, two Hall effect sensors, and an outer ring of permanent magnets to levitate disk magnets from below. This method uses only two feedback control loops to stabilize rotation and translation of the magnet together in both horizontal directions, where vertical translation is passively stable and its vertical axis yaw rotation is left uncontrolled to rotate freely. The advantageous features of this levitation configuration is that only two sensors and actuators are needed to levitate a magnet above an array of coils.To investigate the characteristics of this magnetic levitation method, we have modeled the forces and torques produced on the levitated magnet from the fixed magnets and induced magnetization of the coil cores according to its position and orientation. This model will enable modification of the system design parameters to optimize performance in terms of levitated weight, height, stability or any other desired criteria of the levitation system. Our control implementation demonstrates that simple proportional-derivative (PD) control of the two feedback loops is sufficient to stabilize the motion of the levitated magnet.

This paper describes control system development for a large motion range Lorentz force magnetic levitation device designed as a haptic interface device to be grasped by the hand. Due to the 50 mm translation and 60 degree rotation motion ranges of the desktop-sized device, the transformation between the vector of coil currents and the actuation forces and torques generated on the levitated body varies significantly throughout its motion range. To improve the dynamic performance of the device, the current to force and torque transformation can be recalculated at each control update as the levitated body moves about its workspace, rather than using a constant transformation calculated from the unrotated and centered position of the levitated body. The design of the device is presented and the new methods used to calculate coil current to force and torque transformations for levitation are described. Long-range trajectory following feedback control motion results are shown.

We have formulated a method and implemented a device for magnetic levitation with a translation range which is at least twice as large as the dimensions of the levitated body in all directions. The motion range can be extended to any distance in the horizontal plane by adding more coils to the actuator array, and the rotation is potentially unlimited in all directions.

Lorentz force magnetic levitation devices have been used for fine positioning, compliant assembly, force- reflecting teleoperation, and haptic interaction. The advantages of Lorentz levitation devices compared to motorized linkage and/or cable devices include the lack of friction, hysteresis, and other nonlinearities in actuation dynamics, the simplicity and robustness of a single moving part, and the potential for high closed-loop control bandwidths, a large impedance range, and precise motion. The principal disadvantage of existing Lorentz levitation devices is their motion ranges of 25 mm or less in translation and 20 degrees or less in rotation, which limits their utility in application domains such as haptic interaction. In this paper a novel coil and magnet configuration is presented which extends the possible motion range of Lorentz force magnetic levitation devices to 50 mm and at least 60 degrees, twice the present maximum range in translation and three times the maximum rotation. The motion range of the device design is confirmed through computer-aided design models and the levitation feasibility is shown through magnetic finite element analysis.

Teleoperated robotic surgical systems have been commercially developed and shown to be effective yet their adoption into standard practice has been limited up to the present for reasons which may include size, complexity, and cost. In the Department of Mechanical Engineering at the University of Hawaii, we have developed a new prototype teleoperated robotic system for minimally invasive surgery (MIS) which is simple, compact, and easy to set up and use.

Minimally invasive surgery (MIS) has become an important technique in practical surgical procedures. Compared with manually operated MIS procedures, surgical robot systems provide more accuracy, enhance dexterity, and make more difficult surgical procedures feasible. In this paper, a prototype teleoperated robotic surgical system which is modular, compact and easy to use is tested with human operators. Two evaluation tasks were performed by participants using manual MIS instruments and this teleoperated robotic surgical system. The task data were analyzed and compared between the manual and robot instrument operation. The results show that compared with typical manual instrument operation, the teleoperated robotic system in this paper has advantages in ease of use, decreased task time, and better accuracy with smooth motions and less tremor.

Haptic interface devices and teleoperation masters are multiple degree of freedom devices manipulated by an operator to generate real-time motion commands to simulated environments or robot manipulators. In this work we examine the relationship between the simulated friction parameters of a particular spatial positioning master device and the completion times of planar positioning tasks by human operators. It is expected that increasing the Coulomb or viscous friction of the device would tend to increase the completion times of less difficult, quicker positioning tasks and decrease completion times for more difficult fine positioning tasks requiring higher precision from the operator. A common haptic interface device was used to perform continuous sequences of planar positioning tasks. Each trial required 10-12 minutes to complete and consisted of 15 positioning sequences which varied in the size of the target regions and the magnitude and type of simulated friction in the device. With a sample size of 10 test subjects, small effects were generally observed as expected, with the exception of the first 3 to 4 sequences of the trials which are concluded to be an adaptation or learning period for the users during each trial

We have developed a prototype teleoperated robotic surgical system which is modular, compact and easy to use. In this paper, the control software design of the prototype is introduced. The main function of the control software is to realize master-slave control. According to the functions, The control software consists of three layers: hardware drivers, master-slave control and human-machine interface. Each software layer includes several software modules which are easy to maintain and upgrade and are reliable. The preliminary motion control and experimental results are given in the end

Until recently, computer-aided medical interventions (CAMI) and medical robotics have focused on rigid and nondeformable anatomical structures. Nowadays, special attention is paid to soft tissues, raising complex issues due to their mobility and deformation. Mini-invasive digestive surgery was probably one of the first fields where soft tissues were handled through the development of simulators, tracking of anatomical structures and specific assistance robots. However, other clinical domains, for instance urology, are concerned. Indeed, laparoscopic surgery, new tumour destruction techniques (e.g., HIFU, radiofrequency, or cryoablation), increasingly early detection of cancer, and use of interventional and diagnostic imaging modalities, recently opened new challenges to the urologist and scientists involved in CAMI. This resulted in the last five years in a very significant increase of research and developments of computer-aided urology systems. In this paper, we propose a description of the main problems related to computer-aided diagnostic and therapy of soft tissues and give a survey of the different types of assistance offered to the urologist: robotization, image fusion, surgical navigation. Both research projects and operational industrial systems are discussed

LER is a compact surgical assistant robot for positioning of an endoscope and camera during minimally invasive surgery. In contrast to typical endoscope manipulators, LER is particularly compact and lightweight at 625 g and 110 mm in diameter, so that it is simple to set up and use, occupies no floor space, and does not limit access to the patient in any way. Our current prototype is fully sterilizeable by autoclave and is ready for clinical trials. It features a full motion range of 360/spl deg/ in rotation and inclination to 10/spl deg/ from the horizontal plane and is backdriveable for manual positioning. Actuation forces are limited for safety. LER may be held in place on the abdomen by adhesive strips or sutures, or attached to the sides of the table with elastic straps or clamps. We have implemented a variety of different user command interfaces for LER, including a miniature keypad, automatic optical instrument motion tracking, and voice command recognition. Experimental trajectory following results and performance parameters are given.

This paper reports the development of a new miniature force sensor designed to measure contact forces at the tip of a microsurgical instrument in three dimensions, and its application to scaled force feedback using a cooperatively manipulated microsurgical assistant robot. The principal features of the sensor are its small size of 12.5 mm in diameter and 15 mm in height, a novel configuration of flexure beams and strain gauges in order to measure forces isotropically at the instrument tip 40 mm from the sensor body, and sub-mN three-axis force-sensing resolution.

We have developed a cable-driven manipulator using pneumatic artificial muscle actuators to control the orientation and insertion depth of an endoscope during abdominal surgery. This manipulator enables a single surgeon to manipulate surgical instruments with both hands while the endoscope position is controlled to view an area of interest inside the abdomen. The surgeon may then control the endoscope by alternate methods such as voice commands, pedals, a joystick, or head movements. The advantages of our newly developed endoscope manipulator over those of commercially available robotic laparoscopic surgical systems are its low cost, simplicity, ease of setup and use, compliance, nonintrusiveness, and very small size and light weight, with the disadvantage of somewhat reduced absolute positioning accuracy. Multiple instruments may be manipulated simultaneously by the manipulators set close together. Experimental performance results of open-loop and feedback control methods are presented.

We describe an experimental arrangement for comparison of user performance during a real and a virtual 3D peg-in-hole task. Tasks are performed using a unique six-degree-of-freedom (6-DOF) magnetic levitation haptic device. The arrangement allows a user to exert and experience real and virtual forces using the same 6-DOF device. During the virtual task, a peg and hole are rendered haptically, and visual feedback is provided through a graphical display. During the real task, a physical peg is attached to the underside of the haptic device. Using only real forces/torques, the peg is inserted into a hole in a plate attached to a force/torque sensor, while positions/orientations are measured by the haptic device. positions/orientations and forces/torques are recorded for both modes. Preliminary results indicate increased task time, larger total forces and more failures occur with the virtual task. Recorded data reveal user strategies that are similar for both tasks. Quantitative analysis of the strategies employed should lead to identification of significant factors in haptic interface design and haptic rendering techniques.

Reports preliminary experiments with a robot system designed to cooperatively extend a human's ability to perform fine manipulation tasks requiring human judgement, sensory integration and hand-eye coordination. A completed steady-hand robot is reported. A stable force control law is reviewed. Preliminary experiments validate theoretical predictions of stable one-dimensional control of tool-tip forces in contact with both linearly and nonlinearly compliant objects. Preliminary feasibility experiments demonstrate stable one-dimensional robotic augmentation and "force scaling" of a human operator's tactile input.

A high performance six degree-of-freedom magnetic levitation haptic interface device has been integrated with a physically-based dynamic rigid-body simulation to enable realistic user interaction in real time with a 3-D dynamic virtual environment. The user grasps the levitated handle of the device to manipulate a virtual tool in the simulated environment and feels its force and motion response as it contacts and interacts with other objects in the simulation. The physical simulation and the magnetic levitation controller execute independently on separate processors. The position and orientation of the virtual tool in the simulation and the levitated handle of the maglev device are exchanged at each update of the simulation. The position and orientation data from each system act as impedance control setpoints for the other, with position error and velocity feedback on each system acting as virtual coupling between the two systems. The setpoints from the simulation are interpolated by the controller at the faster device control rate so that the user feels smooth sliding contacts without chattering due to the slower updates of the simulation. The simple feedback coupling between the two systems enables the overall stiffness and stability of the combined system to be tuned easily and provides realistic haptic user interaction. Sample task simulation environments have been programmed to demonstrate the effectiveness of the haptic interaction system.

A high-performance magnetic levitation haptic interface has been developed to enable the user to interact dynamically with simulated environments by holding a levitated structure and directly feeling its computed force and motion responses. The haptic device consists of a levitated body with six degrees of freedom and motion ranges of /spl plusmn/5 mm and /spl plusmn/3.5 degrees in all directions. The current device can support weights of up to 20 N and can generate a torque of 1.7 Nm. Control bandwidths of up to 50 Hz and stiffnesses from 0.01 to 23 N/mm have been achieved by the device using a digital velocity estimator and 1 KHz control on each axis. The response of the levitated device has been made successfully to emulate virtual devices such as gimbals and bearings as well as different dynamic interactions such as hard solid contacts, dry and viscous friction, and textured surfaces.