Enhancement of finger motion range with compliant anthropomorphic joint design

Abstract

Robotic researchers have been greatly inspired by the human hand in the search to design and build adaptive robotic hands. Especially, joints have received a lot of attention upon their role in maintaining the passive compliance that gives the fingers flexibility and extendible motion ranges. Passive compliance, which is the tendency to be employed in motion under the influence of an external force, is the result of the stiffness and the geometrical constraints of the joints that define the direction of the motion. Based on its building elements, human finger joints have multi-directional passive compliance which means that they can move in multiple axis of motion under external force. However, due to their complex anatomy, only simplified biomechanical designs based on physiological analysis are preferred in present day robotics. To imitate the human joints, these designs either use fixed degree of freedom mechanisms which substantially limit the motion axes of compliance, or soft materials that can deform in many directions but hinder the fingers' force exertion capacities. In order to find a solution that lies between these two design approaches, we are using anatomically correct finger bones, elastic ligaments and antagonistic tendons to build anthropomorphic joints with multi-directional passive compliance and strong force exertion capabilities. We use interactions between an index finger and a thumb to show that our joints allow the extension of the range of motion of the fingers up to 245% and gripping size to 63% which can be beneficial for mechanical adaptation in gripping larger objects.

Soft Robotic Grippers

“…Mimicking the structure of the human hand by using rigid and elastic parts to resemble bones and tissues respectively, anthropomorphic design was used to build tendon‐driven grippers . The concept aimed to achieve the high dexterity provided by the biomechanics of the human hand.…”

Soft Manipulators and Grippers: A Review

“…There are also "limb" based multi-finger soft manipulators, such as the MIT hand (Homberg et al, 2015), which introduce a finger-based morphology, drawing inspiration from human hands, and an example of such design can be found at Culha and Iida (2016). The large joint deformations of this design extend the range of motion and ultimately seek to replicate the high dexterity of manipulation which is seen in the human hand.…”

Artificial-Hand Technology—Current State of Knowledge in Designing and Forecasting Changes

“…Alternative designs are ellipsoidal or saddle joints that are inspired by the human skeletal system. Both [93,100,103] devices were based on biocorrect bone models, thereby replicating a natural-link strategy. Contrary to previously described constructions, these were not equipped with a mechanism that keeps parts of the structure together.…”