Virtual Coupling Schemes for Position Coherency in Networked Haptic Virtual Environments

Sankaranarayanan, G. (2007) Virtual Coupling Schemes for Position Coherency in Networked Haptic Virtual Environments. Doctoral thesis, University of Washington.

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Abstract

In networked haptic virtual environments (NHVEs), multiple users remotely collaborate sharing the same virtual space. Maintaining position coherency between the copies of the virtual object in these environments is necessary to achieve consistency in collaboration, especially in the presence of time delays between users. To this end, three virtual coupling schemes are introduced in this thesis to maintain position coherency. Two of these utilize a peer-to-peer architecture and the third is a client-server. An experimental collaborative haptic system was built to objectively test the performance of the virtual coupling schemes. The schemes were first tested for constant time delays with virtual coupling parameters that resulted in stable operation. The experimental results demonstrate that one of the virtual coupling schemes has a comparable performance to the server-based method. Several globalscale haptic collaboration experiments were performed using the Internet to test the three three virtual coupling schemes under realistic network conditions and at three fixed packet transmission rates of 1000 Hz, 500 Hz and 100 Hz. Locally, the haptic update rate was maintained at 1000 Hz during all the experiments. The results show that the position error and the force rendered to the users increased with the reduction in the packet transmission rate. The results also demonstrated that a global-scale haptic collaboration is possible with a peer-to-peer architecture and maintaining position coherency at the same time. Two time-delay compensation techniques, wave variables and time-domain passivity controllers were used to stabilize the peer-to-peer scheme 1. The performance of these controllers was compared to a tuned PD controller in both stable and unstable regions of operation. The experimental results show that the tuned PD controller gave the best performance in terms of position error and wave variables in terms of force. In order to test the NHVE under repeatable network conditions, an emulator was implemented that can create realistic Internet-like characteristics in a laboratory setting. Experimental comparison of the performance of the virtual coupling schemes using the emulator and the Internet show that the emulator is best suited for testing NHVE under packet transmission rates below 1000 Hz.

Item Type: Thesis (Doctoral)
Subjects: B Teleoperation > BA Haptics for Teleoperation
D Haptics
Divisions: Department of Electrical Engineering
Depositing User: Tim Brown
Date Deposited: 28 Jul 2015 17:36
Last Modified: 28 Jul 2015 17:36
URI: http://brl.ee.washington.edu/eprints/id/eprint/122

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