Shahram Payandeh

On application of virtual fixtures as an aid for telemanipulation and training

This paper presents a study on the application of virtual fixtures as a control aid for performing telemanipulation or in the training environment. The implementation features both manual and supervisory control modes. It also studies approaches for using virtual fixtures in generating visual and force clues and/or for restricting the motion of the slave using the definition of virtual fixtures. In this preliminary study it was found that the virtual fixtures could: improve the speed and precision of the operator, and reduce the operators workload and the duration of the training phase for the novice operator.

Design of spherical parallel mechanisms for application to laparoscopic surgery

This paper addresses an optimal study of workspace for spherical parallel mechanism for laparoscopic surgery. The spherical parallel manipulator has been selected because of its characteristics. Two designs have been studied for maximizing their workspaces; a haptic device, as part of training system, and a laparoscope holding mechanism. The laparoscope holding mechanism has to satisfy additional constraints by minimizing the occupied space above the patient. The objective is to solve design problem to offer the maximal workspace for such mechanisms. The design of a haptic interface and the laparoscope holding mechanism based on the optimal parameters are presented. This paper presents a Genetic Algorithm (GA) approach for selecting optimal design parameters for maximizing workspace of spherical parallel mechanism.

Application of visual tracking for robot-assisted laparoscopic surgery

With the increasing popularity of laparoscopic surgery, the demand for better modes of laparoscopic surgery also increases. The current laparoscopic surgery mode requires an assistant to hold and manipulate the endoscope through commands from the surgeon. However, during lengthy surgery procedures, accurate and on-time adjustment of the camera cannot be guaranteed due to the fatigue and hand trembling of the camera assistant. This article proposes a practical visual tracking method to achieve automated instrument localization and endoscope maneuvering in robot-assisted laparoscopic surgery. Solutions concerning this approach, such as, endoscope calibration, marker design, distortion correction, and endoscope manipulator design are described in detail. Experimental results are presented to show the feasibility of the proposed method.

Assembling virtual fixtures for guidance in training environments

We set up a library of virtual fixtures with both haptic and graphic properties and behaviors. For a given task, Virtual Fixture Assembly Language (VFAL) could be used to construct various virtual fixture series, with graphic and force guidance rules, making the low-level haptic and graphic rendering details transparent to the developers. An experiment evaluated the application of virtual fixtures as an aid for guiding a user in a path navigation task. The task was performed with or without force field guidance of virtual fixtures, and then transferred to the condition with no virtual fixtures. Results showed significant learning and transfer effects measured by performance time and path length. However, training using virtual fixtures with force guidance had comparable results to training with graphic only fixtures representing the path. Results are discussed in terms of motor learning theory, future work and applications for the design of better VR training environments.

A delay prediction approach for teleoperation over the Internet

Based on the notion of wave variables and the idea of wave-integral transmission, a new method is suggested to match the system parameters with changes in the delay. An autoregressive model is used as a predictor to forecast the future values of the delay. The predictions are used with a lookup table to tune the gain with which the wave integrals are to be fed to the system. This gain scheduling and tuning improves the system performance and decreases the mismatch between forces and velocities at the master and slave sides.

A Robotic Case Study: Optimal Design for Laparoscopic Positioning Stands

A positioning stand can help a surgeon with positioning and locking endoscopic tools, thereby avoiding the need foran assistant surgeon. The kinematic configuration of the positioning stand is comprised of two main parts: the arm (forpositioning), and the wrist (for orienting the tool). The main requirement of the wrist is to perform spherical movements around the incision point. A concentric multilink spher ical joint design has been developed for the wrist mechanism. The size synthesis is performed to minimize the overall size of the wrist, and also to maximize its range of angular movements. The type synthesis of the positioning arm has led to the use of a SCARA con figuration as a balanced and easily moved arm configuration. The size synthesis of the arm is carried out with the goal of minimizing its overall dimensions, based on the arms reachable workspace and manipulability. The integration of the wrist and arm is performed by optimizing the orientation of the wrist in such a way that the in terference between the wrist and the workspace of the surgeon is minimized.

Control strategies for rodotic contact tasks: An experimental study

In this article, we study the contact instability problem encountered in robotic manipulators while trying to make contact with an environment, such as grasping or pushing against objects, and propose a unified control strategy capable of achieving a stable contact against both stiff and compliant environments. The problem has three distinct stages of the contact task. In the first stage, free-space motion, the robot is approaching the environment; in the second stage, post-contact force regulation; in the third, impact stage, the transition from the first stage to the second. We make an experimental comparison of the control schemes that may be used for the three stages. For example, during impact, the manipulator should not lose contact with the environment, nor exert high impulsive forces on the environment, and in the post-impact phase, the robot should have a fast force trajectory tracking. The best strategies for the above stages are experimentally determined and then combined into a single unified controller that can achieve stable contact as well as a fast force trajectory tracking response for surfaces of variable stiffnesses. This control scheme does not require a priori knowledge of the stiffness of the environment, and is able to estimate the environmental stiffness and tune gains accordingly so as to achieve the best response. Also experimentally compared is the use of such a scheme with impedance control, another method proposed in the literature for robotic contact task control.

Haptic subdivision: an approach to defining level-of-detail in haptic rendering

Soft objects are often desired in applications such as virtual surgery training. Soft object simulations are computationally intensive because object deformation involves numerically solving a large number of differential equations. However, realistic force feedback requires deformation be computed fast and graphic feedback requires deformation be highly detailed. In this paper, we propose an approach that balances these requirements by subdividing the area of interest on a relatively coarse mesh model. Thus we keep the number of nodes of the model under control so that the simulation can be run at a sufficiently high rate for force feedback. The model we use is based on a mass-spring model. When a portion of the surface is subdivided, new values of mass and spring constants are determined such that computed force feedback offers the user the same reaction force as before subdivision.

On cutting and dissection of virtual deformable objects

Tissue dissection is an important procedure in surgical simulation systems. Dissection involves cutting through and separating the tissue after a cut. In this paper, we use a surface mass-spring model to simulate virtual dissection by progressive subdivision and re-meshing. We introduce novel algorithms to generate interior structures that show the cutting result generated by the interaction between instrument and model. In addition, a novel data structure for object representation after the cutting action is proposed which allows the original soft object to be divided and a portion manipulated away. The dissection environment can support a number of user interface devices which can manipulate different representation of virtual instruments. These techniques are being integrated into a training environment for both open and minimally invasive surgery.

Motion Planning of Multiple Agents in Virtual Environments using Coordination Graphs

Motion planning of multiple mobile agents in virtual environments is a very challenging problem, especially if one wants to plan the motions of these agents in real-time. We propose a two layered approach to plan motions of multiple mobile agents in real-time. The mobile agents are moving in a 2-dimensional static environment with open spaces connected to each other by narrow corridors. The global path of each agent is computed by a decoupled planner during the preprocessing process with minimum delay. Each agent’s local path is generated in real-time by combining steering behaviors and a new, principled and efficient AI technique for decision making and planning cooperative multi-agent dynamic systems, Coordination Graph (CG). With CG, we can not only avoid deadlocks in narrow corridors, but also achieve more complicated behavior such as leader-and-followers behavior. We show, via some preliminary examples, real-time performance of our approach, for instance, several robots avoiding deadlocks and successfully navigating a corridor.