Browsing by Author "Gupta, Abhishek"
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Item Design and control of a haptic arm exoskeleton(2004) Gupta, Abhishek; O'Malley, Marcia K.Robot-assisted physical therapy has been shown to aid in the rehabilitation process following neurological injuries. As a therapeutic or training tool, the robot provides a means to implement and evaluate assistance cues to the operator's arm in addition to displaying the forces arising from the dynamics of the virtual environment. Furthermore, training in virtual environments also provides increased repeatability, scalability, safety and a greater control on the experimental setup over training in natural environments. This thesis presents the analysis of various design constraints that apply to the design of such devices. In this context, the author also presents the design of a five degree-of-freedom haptic arm exoskeleton designed for training and rehabilitation in virtual environments. The device has high structural stiffness, minimal backlash, low friction and absence of mechanical singularities in the workspace, which are some of the properties that characterize high quality haptic interfaces. A scheme for the force control of the robot, using a novel joint-based methodology is also presented.Item Disturbance observer based closed loop control of haptic interfaces(2008) Gupta, Abhishek; O'Malley, Marcia K.Traditionally, control of haptic interfaces is achieved using open-loop impedance or admittance control. During open-loop control, the quality of haptic feedback is limited by the dynamics of the haptic device. Further improvements in quality of the haptic feedback require the use of closed-loop control techniques. Closed loop control of haptic interfaces is limited due to stability and cost considerations associated with closed loop force control. In this work, a non-linear disturbance observer for estimating human-machine contact forces during haptic interactions is presented. These estimated forces are then used for closed loop impedance control of the haptic interface. Globally exponential stability of the disturbance observer under the assumption of slowly varying disturbances is demonstrated. Finally, simulation and experimental results corresponding to disturbance observer based closed-loop control of a haptic interface are provided. Qualitative as well as quantitative comparison of the performance of disturbance observer-based control with traditional open and closed loop controllers is presented. In addition to control of haptic interfaces, the disturbance observer can be employed for contact force estimation between the slave and environment during teleoperation.