Development of a robotic hand based on a palm with a metamorphic mechanism for extending the thumb’s functionality

The essential manipulation capabilities of the human hand are highly related to the flexion–extension, abduction–adduction, and opposition movements of the thumb. The thumb is considered the hand’s most mobile digit, and it is acknowledged that its loss corresponds to a 40% reduction in the hand’s function. In the development of robotic hands, efforts have been focused on replicating the thumb’s movements, but this is a complex task. As a possible solution, this article presents the development of a robotic hand that is capable of changing the orientation and position of the thumb finger, in order to replicate its movements as a human hand does through a metamorphic mechanism implemented in the palm design. The design of the proposed metamorphic mechanism was obtained from a morphological synthesis via constraint variation approach. Moreover, for fingers a trajectory tracking synthesis is developed using genetic algorithms to obtain the optimal solution of an underactuated mechanism. The kinematic and workspace analysis shows that changes in the metamorphic mechanism topology extends the thumb’s functionality. Experimental tests were carried out in order to demonstrate the hand’s ability to grasp objects with different shapes and sizes. In addition, applied grasping forces during tests were evaluated to know the minimum and maximum force ranges of the presented robotic hand design.