In cooperative networked haptic systems, some distributed distant users may decide to leave or join the cooperation while other users continue to manipulate the shared virtual object (SVO). Cooperative haptic systems that support interaction among a variable number of users, called scalable haptic cooperation systems herein, are the focus of this research. In this thesis, we develop distributed control strategies that provide stable and realistic force feedback to a varying number of users manipulating a SVO when connected across a computer network with imperfections (such as limited packet update rate, delay, jitter, and packet-loss).

We first propose the average position (AP) scheme to upper bound the effective stiffness of the SVO coordination and thus, to enhance the stability of the distributed multi-user haptic cooperation. For constant and small communication delays and over power-domain communications, the effectiveness of the proposed AP paradigm is compared with the traditional proportional-derivative (PD) scheme via multi-rate stability and performance analyses supported with experimental verif cations.

Next, in a passivity-based approach, the scalability is pursued by implementing the AP scheme over wave-domain communication channels along with passive simulation of the dynamics. By constructing a passive distributed SVO in closed-loop with passive human users and haptic devices, we guarantee the stability of the distributed haptic cooperation system. However, energy leak at joining/leaving instances may compromise the passivity of the SVO. We examine the preservation of passivity of the proposed SVO scheme for such situations. A switching algorithm is then introduced in order to improve the performance of the cooperative haptic system. Experiments in which three users take turn in leaving or joining the cooperation over a network with varying delay and packet-loss will support the theoretical results.