Improved Haptic Two-Port Networks with use of Local Force Feedback and Passive Actuators

Haptic devices work with the operator to restrict or aid in the device's motion based on simulated environment, slave being teleoperated, or workspace restrictions so as to feedback tactile information to the user. Such devices are classified as either passive (use passive actuators) or active (use active actuators). Passive systems are inherently safer than active, but face fundamental limitations when trying to reflect arbitrary forces. Active systems pose safety concerns, but can lean on passivity theory to formulate control algorithms that theoretically guarantee stability when interfaced with passive environments. One such paradigm is the linear two-port haptic network proposed by Hannaford and Adams, analogous of two-port electrical networks, which utilizes Llewelyn's frequency based criterion for testing stability. In this proposal a modified version of the haptic two-port impedance network utilizing local force feedback to enhance the system's Z width is presented. First, several classifications of haptic devices and relevant research topics are discussed with special attention given to proposed hybrid active / passive systems and passivity control. The two-port paradigm is used to evaluate stability and performance benefits of the additional damper in a parallel active / passive combination. It is proposed that by measuring the simulated / interfaced environment's stiffness and choosing suited matched damping / virtual coupling pairs, or relationships that guarantee Llewelyn's two-port stability criterion, the total two-port system can be considered stable. Furthermore, it is suggested to extend the revised two-port haptic network designs to a slave robot two-port network for use in developing modular bilateral teleoperation components ii Table of Contents