Networked haptic cooperation using remote dynamic proxies Zhi Li Department of Mechanical Engineering University of Victoria Victoria, BC, Canada zhil@me.uvic.ca Daniela Constantinescu Department of Mechanical Engineering University of Victoria Victoria, BC, Canada Danielac@me.uvic.ca Abstract Networked haptic cooperation entails direct interaction among users as well as joint manipulation of virtual ob- jects. To increase the realism of both types of interactions, this paper introduces remote dynamic proxies. Remote dy- namic proxies are second order dynamic representations of users at the remote peer sites. They are generated accord- ing to dynamics laws and are controlled by the user whom they represent through a virtual coupler. Hence, they move in a physically intuitive manner and do not suffer from posi- tion discontinuities due to network packet transmission lim- itations. The remote dynamic proxies are integrated into a distributed control architecture for networked haptic coop- eration. An experimental comparison of the new controller to two recently proposed controllers demonstrates smoother rendering of contact between users, as well as stable coop- eration for larger network delays. 1. Introduction Networked haptic cooperation finds its applications in a variety of areas, including surgical training [9], telerehabil- itation [15], and computer games. Multiple users haptically present in a virtual environment at the same time want: (1) to manipulate virtual objects together; and (2) to touch and feel each other. For example, an experienced surgeon and a remote resident may want to interact with a virtual organ si- multaneously during surgical teletraining. A therapist may want to guide the hand of a remote patient during telereha- bilitation. Cooperative manipulation of virtual objects by multiple remote users has been the primary focus of existing haptics research. Both centralized (client-server) [6, 13] and dis- tributed (peer-to-peer) [1, 3, 8, 7, 13, 14] controllers have been proposed. Distributed controllers have been shown to render higher contact stiffness [6] and maintain better position coherency among copies of the shared virtual ob- ject [13] than centralized controllers. Several distributed control architectures have been de- veloped to combat the destabilizing effect of network de- lay on cooperative haptic interaction. In [14], three peer-to- peer haptic cooperation approaches have been compared. In those approaches, users manipulate their local copies of the shared virtual object and the controller coordinates among object copies at all peer sites. Stability and position co- herency via virtual coupling [4], time domain passivity [12] and wave variables [10] coordination have been studied. The investigation in [14] has shown that: virtual coupling control is most sensitive to network delay; time domain pas- sivity control may not be able to prevent distracting oscil- lations; wave variable control renders much smaller forces and results in much larger position errors between shared object copies than the other controllers. In [6], kinematic representations of the remote users have been provided at all peer sites. This has alleviated the effect of the communi- cation delay on users’ perception of their peers’ interaction with the shared virtual object. Coherency among all copies of the shared object has been maintained via virtual cou- plers. Although not developed for this purpose specifically, the architecture in [6] can render both cooperative manipu- lations and direct user-to-user interaction. Direct haptic interaction among multiple users has mo- tivated the introduction of massless proxies with first or- der dynamics in [9]. Compared to the conventional, purely kinematic proxies [16, 11], the motion of the dynamic prox- ies can be better controlled during collisions with fixed vir- tual objects and among multiple proxies. The performance of proxies with first order dynamics during networked hap- tic cooperation has not been investigated. Proxies with sec- ond order dynamics have been proposed in [5]. For single user interaction with a slow virtual environment, the second order dynamic proxies have mitigated the effect of compu- tational delay on the stability of the interaction and on user’s perception of rigid contact. This paper introduces a distributed control architec-