Control of 4D Printed Actuators Twisting Behavior via Printing Direction

Controlling the shape memory behavior in four-dimensional (4D) printed actuators allows for great control and accuracy in performance, which can be achieved using the printing parameters or structural preferences. The use of these parameters eliminates the need for traditional programming of the printed materials to induce strain into these materials. This creates parameter-controlled actuators that are printed with pre-strain, allowing their use in applications right off the printer. In this study, 4D printing of strain-induced actuators is carried out by varying printing angles. This is done to assess the effect of this parameter on the twisting abilities of polylactic acid structures. The ability of actuators to twist allows them to perform non-linear movements that might offer advantages in applications of certain structures, such as the use of certain shapes or reaching cylindrical objects. The print angle is varied from 0° to 90° at intervals of 15°, as measured from the length of the actuators. The actuators are assessed based on their helix angle, with the highest angle of 22.63° achieved when printing at 45°. The 45° actuator is used to create a proof-of-concept gripper design that is made to grasp a cylindrical object. The gripper arms twist around and under the cylindrical object, providing a better grip that an arm that would only close on it because of its adapted shape. The full deformation of the gripper arms takes about 12 seconds to fully close. Moreover, this design offers different helix angles by changing the printing direction. The results show that the developed gripper is suitable for various robotics applications.