  Although the multi-jointed underactuated manipulator is highly dexterous, its
grasping capacity does not match that of the parallel jaw gripper. This work
introduces a fractal gripper to enhance the grasping capacity of multi-joint
underactuated manipulators, preserving their passive clamping features. We
describe in detail the working principle and manufacturing process of the
fractal gripper. This work, inspired by the 'Fractal Vise' structure, resulted
in the invention of a fractal gripper with mode switching capabilities. The
fractal gripper inherits the inherent adaptive properties of the fractal
structure and realizes the self-resetting function by integrating spring into
the original design, thereby enhancing the efficiency of object grasping tasks.
The fractal gripper prevents object damage by distributing pressure evenly and
applying it at multiple points through its fractal structure during closure.
Objects of various shapes are effectively grasped by the fractal gripper, which
ensures a safe and secure grasp. The superior performance was provided by the
force distribution characteristics of the fractal gripper. By applying the
flexible polymer PDMS, which possesses superior elasticity, to the fractal
structure's wrapping surface, potential scratching during grasping is
effectively prevented, thus protecting the object's geometric surface. Grab
experiments with objects of diverse shapes and sizes confirm fractal gripper
multi-scale adaptability and superior grasping stability.
