Visualization of multidigit manipulation mechanics: manipulation mechanics

The purpose of this paper is to develop a visualization tool for the investigation of the contact mechanics at the object-digit interface and force coordination among multiple digits during manipulation tasks. Five miniature six-component force/torque transducers, mounted on a custom-made instrumented handle, were used to record force/torque data at the tips of individual digits during five-digit manipulation tasks. A digitizing device was used to obtain three-dimensional (3-D) coordinates of anatomical landmarks of the hand for the construction of a hand geometric model. The 3-D hand model and force data from transducers were transformed to a common handle coordinate frame so that force vectors were superimposed on digit-tips. One subject performed three static manipulation tasks (grasping, rotating, and lifting) with maximum voluntary contraction on the stabilized instrumented handle. The magnitude and orientation of the force vectors of individual digits were dependent on the tasks, and the subject tended to maximize task efficiency by utilizing different force coordination strategies for different tasks. The visualization methods developed in this paper could potentially provide an effective tool for the examination of object-digit interaction mechanics and interdigit force coordination.