Manipulability analysis of human thumb, index and middle fingers in cooperative 3D rotational movements of a small object

A five-bar mechanism to assist finger flexion-extension movement: system implementation

The lack of specialized personnel and assistive technology to assist in rehabilitation therapies is one of the challenges facing the health sector today, and it is projected to increase. For researchers and engineers, it represents an opportunity to innovate and develop devices that improve and optimize rehabilitation services for the benefit of society. Among the different types of injuries, hand injuries occur most frequently. These injuries require a rehabilitation process in order for the hand to regain its functionality. This article presents the fabrication and instrumentation of an end-effector prototype, based on a five-bar configuration, for finger rehabilitation that executes a natural flexion-extension movement. The dimensions were obtained through the gradient method optimization and evaluated through Matlab. Experimental tests were carried out to demonstrate the prototype’s functionality and the effectiveness of a five-bar mechanism acting in a vertical plane, where gravity influences the mechanism’s performance. Position control using fifth-order polynomials with via points was implemented in the joint space. The design of the end-effector was also evaluated by performing a theoretical comparison, calculated as a function of a real flexion-extension trajectory of the fingers and the angle of rotation obtained through an IMU. As a result, controlling the two degrees of freedom of the mechanism at several points of the trajectory assures the end-effector trajectory and therefore the fingers’ range of motion, which helps for full patient recovery.

On redundancy resolution of the human thumb, index and middle fingers in cooperative object translation

Redundancy in motion, and synergy in neuromuscular coordination provides significant versatility to the human fingers while performing coordinated grasping and manipulation tasks in several ways. This paper explores how humans may resolve the redundancy in their thumb, index and middle fingers when these digits flex to cooperatively translate a small object toward the palm. It is observed that humans actively employ a secondary subtask of maximizing instantaneous manipulability that helps determine all intermediate finger configurations when performing the primary subtask of following a tip trajectory. This behavior is accurately captured by an inverse kinematic model based on aredundancyparameter. The joint angles get determined unambiguously though the redundancy parameter is shown to depend on the instantaneous finger configurations and also, to attain negative values. Further, this parameter is noted to vary significantly across subjects performing the same kinematic task. The findings, that are based on the experimental finger motion data garnered from 12 subjects, are reckoned to be of significant importance, especially in reference to the challenges in design and control of finger exoskeletons for cooperative manipulation.

Application of robotic manipulability indices to evaluate thumb performance during smartphone touch operations

This study examined whether manipulability during smartphone thumb-based touch operations could be predicted by the following robotic manipulability indices: the volume and direction of the 'manipulability ellipsoid' (MEd), both of which evaluate the influence of kinematics on manipulability. Limits of the thumb's range of motion were considered in the MEd to improve predictability. Thumb postures at 25 key target locations were measured in 16 subjects. Though there was no correlation between subjective evaluation and the volume of the MEd, high correlation was obtained when motion range limits were taken into account. These limits changed the size of the MEd and improved the accuracy of the manipulability evaluation. Movement directions associated with higher performance could also be predicted. In conclusion, robotic manipulability indices with motion range limits were considered to be useful measures for quantitatively evaluating human hand operations.