Browsing by Author "Chawda, Vinay"
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Item Evaluation of Velocity Estimation Methods Based on Their Effect on Haptic Device Performance(IEEE, 2018) Chawda, Vinay; Celik, Ozkan; O’Malley, Marcia K.This paper comparatively evaluates the effect of real-time velocity estimation methods on the passivity and fidelity of virtual walls implemented using haptic interfaces. Impedance width or Z-width is a fundamental measure of performance in haptic devices. Limited accuracy of velocity estimates from position encoder data is an impediment in improving the Z-width in haptic interfaces. We study the efficacy of Levant's differentiator as a velocity estimator to allow passive implementation of higher stiffness virtual walls as compared to some of the commonly used velocity estimators in the field of haptics. We first experimentally demonstrate feasibility of Levant's differentiator as a velocity estimator for haptics applications by comparing Z-width performance achieved with Levant's differentiator and commonly used finite difference method (FDM) cascaded with a low-pass filter. A novel Z-width plotting technique combining the passivity and fidelity of haptic rendering is proposed, and used to compare the haptic device performance obtained with Levant's differentiator, FDM+low-pass filter, first-order adaptive windowing (FOAW), and Kalman-filter-based velocity estimation methods. Simulations and experiments conducted on a custom single degree-of-freedom haptic device demonstrate that the stiffest virtual walls are rendered with velocity estimated using Levant's differentiator, and the highest wall rendering fidelity is achieved by FOAW-based velocity estimation scheme.Item Method and device for real-time differentiation of analog and digital signals(2018-03-06) Celik, Ozkan; Chawda, Vinay; O'malley, Marcia K.; Rice University; United States Patent and Trademark OfficeThe controller includes a differentiating engine configured to receive an input signal value (ISV), wherein the ISV corresponds to state information for one selected from a group consisting of a controlled process and a user interface. The differentiating engine is further configured to determine an error between the ISV and an estimated input signal (EIS), estimate a frequency of the IS, select a plurality of pre-determined gains using the frequency, wherein at least one plurality of pre-determined gains is a suction control gain, determine a first estimated derivative of the input signal (EDIS) using the plurality of pre-determined gains and the error, and to output the first EDIS.Item On stability and performance characteristics in control of haptic interfaces and bilateral teleoperation systems(2013-11-27) Chawda, Vinay; O'Malley, Marcia K.; Dick, Andrew J.; Clark, John W., Jr.Stability and performance are the two conflicting goals in control of force reflecting robotic systems, such as haptic interfaces and bilateral teleoperation systems. Both the uncertainty attributed to inclusion of a human user in the control loop, and stringent robust stability requirements typically result in very conservative performance. Furthermore, time-varying delays inherent in commercial communication lines compound the already difficult nonlinear control problem of stabilizing bilateral teleoperation systems, and subsequently affect performance. In the first part of this thesis, factors affecting the range of achievable performance in haptic interfaces are analyzed, and accurate real-time velocity estimation from position encoder data is identified as a limiting factor. The efficacy of Levant's differentiator as a velocity estimator, to allow passive implementation of higher stiffness virtual walls, as compared to some of the commonly used velocity estimators in the field of haptics, is studied. A novel performance descriptor, combining passivity and fidelity of haptic rendering, is proposed and used to compare the haptic device performance obtained with Levant's differentiator, to other methods using simulations and experiments. In the second part of this thesis, the effect of time-varying delays on the stability and performance of bilateral teleoperation systems is considered. A framework for increasing performance in Time Domain Passivity Approach (TDPA) based bilateral teleoperation is developed, while preserving robust stability characteristics against time-varying communication delays and remote environment conditions. Several performance compensation schemes are developed within the proposed framework that ensure position tracking between master and slave robot trajectories, and improve force reflection during hard contact interactions. The proposed performance compensation schemes are compared experimentally for their effectiveness in position tracking and force reflection capabilities. In addition, a feedback passivity control based scheme to achieve position synchronization in bilateral teleoperation with power-based TDPA is developed and implemented in simulations and experiments. The proposed method encodes position information with velocity to construct a composite signal, which is transmitted across the communication channel to attain position tracking. Results demonstrate robust position tracking performance with the proposed approach under variable communication delays and remote environment conditions. Combined, these analyses, simulations, and experiments extend the limits of performance in haptic interfaces and bilateral teleoperation systems, while preserving robust stability characteristics.