A Variable Stiffness Anthropomorphic Finger Through Embodied Intelligence Design

Most existing anthropomorphic robotic fingers are either too stiff to offer compliance, or too soft to provide postural stability. Yet human subjects tend to stiffen their finger when producing fingertip forces and lower their joint stiffness when grasping objects. Variable joint stiffness is therefore required to offer compliance and postural stability to the finger when interacting with its environment. We therefore propose the novel design of a robotic anthropomorphic finger capable of variable stiffness by making use of the embodied intelligence design principle through multifunctionality of the hardware parts. The ligaments of the finger are not only used to connect the phalanges together, but also to provide local variable stiffness at the finger joints through the use of miniature McKibben pneumatic artificial muscles. This novel design can therefore offer compliance at lower stiffness levels and postural stability and a higher applied force at higher stiffness levels while keeping the finger look and movement anthropomorphic and its control quite basic. The developed anthropomorphic finger with variable stiffness was tested by interacting with a flat surface. The finger presented a significantly higher stiffness (6.710(-3) +/- 310(-3) Nm/rad) when the stiffening system was used than when the finger was purely used in compliance mode, without stiffness adaptation (4.810(-3) +/- 0.710(-3) Nm/rad).