This paper investigates the effect of environmental factors on user performance in a dual-user haptic guidance system. The system under study allows for interaction between both users, the trainee and the trainer, to collaboratively perform a common task in a shared virtual environment. User studies are carried out to experimentally evaluate the users' performance while following square and circular trajectories with two viewpoints of the environment (top view and front view), while the virtual manipulator tool moves in free motion or against forbidden-region virtual fixtures. The performance is measured and statistically evaluated against task completion time, tracking accuracy, and user energy exchange. The studies revealed that changing the environment geometry from a square to a circle results in reduced task completion time and tracking error. Changing the environment viewpoint from top to front decreases the task completion time in both geometries. Forbidden-region virtual fixtures increase energy exchange by both users and decrease task completion time while compromising the tracking performance in the square-following task. However, when visual feedback is removed in the presence of the fixtures, the square tracking performance improves. The results also indicate a strong relationship between user dominance and tracking error only when the experiment is time-limited.

The dynamics of a PHANToM Premium 1.5A haptic device from SensAble Technologies, Inc. is experimentally identified and analyzed for different installations of the device and its accessories, such as the typical upright, upside down, with gimbal and counterbalance weight, and with force sensor. 1 An earlier formulation of the robot dynamic model is augmented with a friction model, linearly parameterized, and experimentally identified using least squares. The identified dynamics are experimentally evaluated with an inverse dynamics controller and verified by comparing user hand force estimates with the measured values. The contribution of different dynamic terms such as inertial, Coriolis and centrifugal, gravitational, and Coulomb and viscous friction are demonstrated and discussed. The identified model can be used for a variety of haptic applications, such as hand force estimation, accurate active gravity compensation and counterbalance weight determination for various installation conditions, and model-based control for haptic simulation and teleoperation.