Haptic rendering from holonomic and nonholonomic constraints for interaction with virtual surfaces used in medical simulation

• Autores: José Daniel Castro Díaz
• Directores de la Tesis: Marco Arteaga Pérez (dir. tes.)
• Lectura: En la Universidad Nacional Autónoma de México ( México ) en 2021
• Idioma: inglés
• Enlaces
  • Tesis en acceso abierto en:  ru.dgb.unam.mx  tesiunamdocumentos.dgb.unam.mx (html) 
• Resumen

  • Virtual reality systems for medical training were inspired by teleoperation systems. In bothcases, robotic arms play a major role because they provide a force response to be transmit-ted to the human operator. Such force produces a tactile sensation that allow to feel someproperties of either the remote or virtual environment. However, in the last two decades, theresearch efforts in the area have been focused on visually simulating, as realistic as possible,the virtual environments present in surgical training. This entails the force response to begenerated by methods that cannot reproduce some characteristics of the virtual surfaces, asin the case of penetrable objects. To counteract such problem, in this work a virtual realitysystem with haptic feedback is studied using a teleoperation approach. By defining the inter-face manipulated by the operator as the master robot and the virtual environment as the slaverobot, the force response is obtained by approaching the virtual environment as a problem ofa robot in constrained motion.The main objective of this work is to reproduce the tactile properties of both a penetrableor non penetrable virtual surface by using virtual constraints. Additionally, a control algo-rithm based on a teleoperation system is implemented to feedback the corresponding forceto the operator. To achieve this objective, it was necessary to design a virtual environmentconsisting in a robot dynamic model in contact with either holonomic and nonholonomicconstraints. Furthermore, according with the functioning of a medical training simulator, be-fore the contact, there is always an stage of free motion. For this reason and specially in thecase of nonholonomic constraints, a collision detection algorithm was programmed using theimplicit equation of a sphere. This allows to have a tactile perception before and after contactto consequently make appropriate comparisons of the operation of the control algorithm,either in free or constrained motion.A set of experiments were carried out by considering the force feedback from a sensor atthe master side and reproducing computationally the virtual force by means of holonomicand nonholonomic constraints. Furthermore, a virtual environment was built in order to allow the operator to have visual feedback with the aim of heightening the realism of the appli-cation. Such environment needs forcefully a good performance of the control scheme since itis necessary an adequate tracking, both in force and position, to reproduce the virtual Carte-sian space and the sensation of being in contact with a surface.The experimental results shown some interesting differences between using holonomicand nonholonomic constraints. The principal of them is the modification of the controlscheme structure with respect to the force feedback. Furthermore, a good performance ofsuch scheme was obtained for both position and force. This means that the human opera-tor receives a visual image according to his/her movements and also a force response thatreproduces the tactile properties of the virtual surface. Since this haptic sensation is entirelysubjective, a discussion was carried out with special emphasis on the validity of the proposedapproach and how it can be used in the virtual simulation of a medical procedure.