Motion Evaluation of Variable-Stiffness Link Based on Shape-Memory Alloy and Jamming Transition Phenomenon

In rapidly aging societies, the application of robots has spread from industry to nursing and social welfare. As the designs of industrial and non-industrial robots are different, numerous robot components with various shapes and stiffness are required for different tasks. In this study, we attached a variable-stiffness link based on a shape-memory alloy (SMA) and the jamming transition phenomenon to a robot arm and evaluated its pick-and-place motion for various objects with different shapes and weights. The link can be fixed in an arbitrary shape and then restored to its initial shape via the shape memory effect. The objects were picked up and moved by a prototype link, which consisted of four SMA wires inserted in the jamming mechanism. We compared two states of the link, namely with and without deformation of the link into a shape (the centerline and the cross section) to suit the target object using a mold. Experiments confirmed that changing and fixing the link shape to suit the target object increased both positioning accuracy and weight capacity.