Modeling and Control of Formations of Nonholonomic Mobile Robots

This paper addresses the control of a team of nonholonomic mobile robots navigating in a terrain with obstacles while maintaining a desired formation and changing formations when required, using graph theory.We model the team as a triple, (g, r, H), consisting of a group element that describes the gross position of the lead robot, a set of shape variables g that describe the relative positions of robots, and a control graph H that describes the behaviors of the robots in the formation. Our framework enables the representation and enumeration of possible control graphs and the coordination of transitions between any two formations

On Controlling Aircraft Formations

We describe a framework for controlling a group of unmanned aerial vehicles (UAVs) flying in close formation. We first present a nonlinear dynamical model which includes the induced rolling moment by the lead aircraft on the wing of the following aircraft. Then, we outline two methods for trajectory generation of the leading aircraft, based on interpolation techniques on the Euclidean group, SE(3). Two formation controllers that allow each aircraft to maintain its position and orientation with respect to neighboring UAVs are derived using input-output feedback linearization. Numerical simulations illustrate the application of these ideas and demonstrate the validity of the proposed framework

DESIGN & DEVELOPMENT OF A 2-DOF MINIATURE FORCE SENSOR FOR SURGICAL PROCEDURES

ABSTRACT Force sensing is an important component for a number of surgical procedures as it can help to prevent undesirable damage to the tissue and at the same time provides the surgeons with a better "feel" of the tool-tissue interaction. However, most of the current commercially available multi-DOF force sensors are relatively large in size and it is a challenge to incorporate them into the surgical tool. Hence, a multi-DOF miniature force sensor is desired and this paper presents the design and development of a miniature 2-DOF force sensor. In order to achieve a miniature force sensor, microfabrication technique is used and the proposed force sensor is a capacitive-based sensor. The proposed force sensor can be used in a number of percutaneous procedures as well as catheter-based procedures. This paper presents the design and microfabrication process of the proposed miniature force sensor

3D and 2D finite element analysis in soft tissue cutting for haptic display

Paper presented at the 2005 International Conference on Advanced Robotics, ICAR '05, Seattle, WA.Real-time medical simulation for robotic surgery planning and surgery training requires realistic yet computationally fast models of the mechanical behavior of soft tissue. This paper presents a study to develop such a model to enable fast haptics display in simulation of softtissue cutting. An apparatus was developed and experiments were conducted to generate force-displacement data for cutting of soft tissue such as pig liver. The forcedisplacement curve of cutting pig liver revealed a characteristic pattern: the overall curve is formed by repeating units consisting of a local deformation segment followed by a local crack-growth segment. The modeling effort reported here focused on characterizing the tissue in the local deformation segment in a way suitable for fast haptic display. The deformation resistance of the tissue was quantified in terms of the local effective modulus (LEM) consistent with experimental force-displacement data. An algorithm was developed to determine LEM by solving an inverse problem with iterative finite element models. To enable faster simulation of cutting of a three-dimensional (3D) liver specimen of naturally varying thickness, three levels of model order reduction were studied. Firstly, a 3D quadratic-element model reduced to uniform thickness but otherwise haptics-equivalent (have identical forcedisplacement feedback) to a 3D model with varying thickness matching that of the liver was used. Next, hapticsequivalent 2D quadratic-element models were used. Finally, haptics-equivalent 2D linear-element models were used. These three models had a model reduction in the ratio of 1.0:0.3:0.04 but all preserved the same input-output (displacement, force) behavior measured in the experiments. The values of the LEM determined using the three levels of model reduction are close to one another. Additionally, the variation of the LEM with cutting speed was determined. The values of LEM decreased as the cutting speed increased

Determining fracture characteristics in scalpel cutting of soft tissue

Paper presented at the First IEEE/RAS-EMBS International Conference on Biomedical Robotics and Biomechatronics, BioRob 2006, Pisa, Italy.This paper addresses the characteristic response of soft tissue to the growth of a cut (cracking) with a scalpel blade. We present our experimental equipment, experiments, and the results for scalpel cutting of soft tissue. The experimentally measured cut-force versus cut-length data was used to determine the soft tissue’s resistance to fracture (resistance to crack extension) in scalpel cutting. The resistance to fracture (the toughness) of the soft tissue is quantified by the measure R defined as the amount of mechanical work needed to cause a cut (crack) to extend for a unit length in a soft-tissue sample of unit thickness. The equipment, method, and model are applicable for all soft tissue. We used pig liver as soft-tissue samples for our experiments

Evaluating the role of force feedback for biomanipulation tasks

Paper presented at the IEEE Virtual Reality, Haptics Symposium and Symposium on 3D User Interface, Alexandria, VA.Conventional cell manipulation techniques do not have the ability to provide force feedback to an operator. Poor control of cell injection force is one of the primary reasons for low success rates in cell injection and transgenesis in particular. Therefore, there exists a need to incorporate force feedback into a cell injection system. We have developed an automated cell injection system, which has the capability of measuring forces in the range of μN. We tested our system with 40 human subjects to evaluate the role of force feedback in cell injection task. Our experimental results indicate that the subjects were able to feel the cell injection force and confirmed our research hypothesis that the use of combined vision and force feedback leads to higher success rate in cell injection task compared to using vision feedback alone

Motion planning and control of cooperative robotic systems

I would like to express my gratitude to the people who made an important difference and played a vital role in the successful completion of my Doctoral studies at the University of Pennsylvania. I am grateful to my advisor Professor Vijay Kumar without whose competence, dedication, generosity, and vision this dissertation would not have been possible. Professor Kumar has been my mentor and an inspiring role model. His energy and relentless support encouraged me towards the completion of my Masters in Mathematics. Professor James Ostrowski, my co-advisor since 1996, provided valuable advice and insight towards my work. I am very thankful for his opinion and guidance during the course of my dissertation. I am very thankful to Professor Joel Burdick (Caltech), Chairman of the committee, Professor G. K. Ananthasuresh, Professor Ruzena Bajcsy, Professor Vijay Kumar and Professor James Ostrowski for agreeing to be the members of my dissertation committee and for taking the time to read my thesis and provide valuable suggestions. This dissertation has allowed me to work with people who are both competent and compassionate. I have been fortunate to receive constant guidance and support from Professo

Medical Robotics

The evolution of robotics in surgery is a new and exciting development. Surgical robotics brings together many disparate areas of research such as: design, development and modeling of robotic systems, nonlinear control, safety in medical robotics, ergonomics in minimally invasive procedures, and last but not the least, surgery. Over the past decade there have been significant advances in basic research and technology that have made it possible for the development of robots for surgery. One of the main advantages of robots is the increased precision and repeatability in carrying out surgical procedures, which were not possible in the past by a human surgeon. Robots and computers in conjunction can perform complex computations at much higher speeds compared to humans. On the other hand, humans are more adept in integrating diverse sources of information and making decisions based on their past experience of working in that field. They are also dexterous on the “human’ ’ scale, have very strong hand-eye coordination and an excellent sense of touch. Robots on the other hand have very good accuracy in carrying out pre-specified tasks, are not prone to fatigue or boredom, can carry out fast computations for surgical planning based on 3-D imaging data and other sensory feedback, and can also be designed for a wide range of operating conditions and scales. There are however severe limitations of robots and humans. One of the main disadvantages of robots is that they have poor judgment capability, limited dexterity and poor hand-eye coordination. Humans on the other hand cannot operate beyond their physical capability (their natural scale of operation) and are prone to tremor and fatigue [Taylor96]. Robots are thus seen more as augmenting human capabilities rather than replacing surgeons. The strengths and weaknesses of humans and robots are summarized in Table 1. Several robotic systems have been developed for surgical procedures. Some of the key areas where robotics has made a significant impact are orthopaedics, neurosurgery, laparoscopic procedures, opthalmic surgery, and cardiac surgery