  This study presents the design and the kinematic optimization of a novel,
underactuated, linkage-based robotic hand exoskeleton to assist users in
performing grasping tasks. The device has been designed to apply only normal
forces to the finger phalanges during flexion/extension of the fingers, while
providing automatic adaptability for different finger sizes. Thus, the easiness
of the attachment to the user's fingers and better comfort have been ensured.
The analyses of the device kinematic pose, statics, and stability of grasp have
been performed. These analyses have been used to optimize the link lengths of
the mechanism, ensuring that a reasonable range of motion is satisfied while
maximizing the force transmission on the finger joints. Finally, the usability
of a prototype with multiple fingers has been tested during grasping tasks with
different objects.
