Analysis of postures for handwriting on touch screens without using tools

The act of handwriting affected the evolutionary development of humans and still impacts the motor cognition of individuals. However, the ubiquitous use of digital technologies has drastically decreased the number of times we really need to pick a pen up and write on paper. Nonetheless, the positive cognitive impact of handwriting is widely recognized, and a possible way to merge the benefits of handwriting and digital writing is to use suitable tools to write over touchscreens or graphics tablets. In this manuscript, we focus on the possibility of using the hand itself as a writing tool. A novel hand posture named FingerPen is introduced, and can be seen as a grasp performed by the hand on the index finger. A comparison with the most common posture that people tend to assume (i.e. index finger-only exploitation) is carried out by means of a biomechanical model. A conducted user study shows that the FingerPen is appreciated by users and leads to accurate writing traits

Does torque minimization yield a stable human grasp

Abstract. In this paper, we present a study of the human grasp conducted with a mathematical formalism that has been developed in robotics during the last two decades. The main objective of this study is to assess the extent to which the structure of the hand is adapted to its grasping function by identify the conditions under which a model minimizing energy expenditure predicts a stable grasp. The idea is that the human hand, as the result of evolutionary pressure, must be designed in such a way that it can grasp objects with minimum effort. To test this hyptohesis, we defined a cost function minimizing the weighted norm of the joint torque vector of a simple biomechanical model of the hand. The contact forces predicted by the model are then compared to the ones observed in a experimental study of the human tripod grasp. The results indicate that this cost function can predict a stable grasp when the external force is zero. A possible interpretation of this result is that the external force represents an unknown that cannot be taken into account by an evolutionary process. “The coordination of a movement is the process of mastering redundant degrees of freedom of the moving organ, in other words its conversion to a controllable system ” (Bernstein, [6], p. 127).