Development of a 4D Printed Variable Stiffness Gripper

The use of robots in various industrial applications keeps increasing every day. Such robots perform several tasks that require gripping objects while varying their stiffness values to adapt to the characteristics of the objects. So far, the use of soft materials in these variable stiffness grippers is limited. Four-dimensional (4D) printing allows creating complex structures that change their shape over time. This technique relies on the use of smart materials that change their shapes based on external stimuli. Therefore, this paper presents the use of 4D printed variable stiffness polylactic acid (PLA) actuators to create a variable stiffness gripper. The proposed actuators are 4D printed using four patterns, including grid, honeycomb, triangular, and rectilinear patterns. Combinations of these patterns are used to create 12 designs, where each design consists of two different patterns in its top and bottom parts. This combination allows each actuator to have a unique variable stiffness profile based on the pattern and the temperature used to activate the PLA. This also allowed the actuators to achieve different bending angles ranging from 1°to 12°. Then, selected actuators are used to develop a variable stiffness gripper that includes four fingers, where each finger consists of two joints and three segments. The segments are made from actuators that achieve different bending angles. The results show that the developed gripper is able to perform gripping when stimulated by temperature, making it suitable for various robotics applications.