This study investigates natural single-arm interaction with kinematic constraints. Smooth, frictionless, kinematic constraints reduce the degrees-of-freedom of motion at the hand, but add force freedoms. These force freedoms allow the hand to push and pull against the constraints with no effect on the task. Understanding how subjects take advantage of kinematic constraints will be useful in designing constraint surfaces for assisted manipulation. This paper reports the results of an experiment studying how subjects make use of the presence of a kinematic constraint in a static planar single-arm task. Subjects are asked to hold a handle that is free to slide on a linear rail, and to apply a force tangent to the rail to resist a pulling force. Thus the goal of the task is to hold the handle stationary. Subjects are also free to apply any force normal to the rail, as these forces have no effect on the task. This freedom does not exist without a kinematic constraint. We find that subjects make use of the force freedom by applying significant forces against the constraint in a consistent and constraint-configuration-dependent fashion. We show that the constraint forces can be predicted by a convex, scale-invariant objective function on the hand force space. The level curves of this objective function can be found directly from the experimental data without any biomechanical modeling.

We describe a one-joint planar arm which repeatedly throws and catches parts on its surface, and we demonstrate that proper choice of the throw velocity and arm geometry guarantees that the part will enter a unique recurrent motion pattern from a large set of initial configurations. The resulting system resembles an open-loop stable juggler of polygonal parts. Combined with a simple 1-bit sensor, the system can be used as a parts feeder.

We describe a one-joint planar arm which repeatedly throws and catches parts on its surface, and we demonstrate that proper choice of the throw velocity and arm geometry guarantees that the part will enter a unique recurrent motion pattern from a large set of initial configurations. The resulting system resembles an open-loop stable juggler of polygonal parts.