Force Control of a 3D Printed Soft Gripper with Built-In Pneumatic Touch Sensing Chambers

This work reports on a soft gripper with three-dimensional (3D) printed soft monolithic fingers that seamlessly incorporate pneumatic touch sensing chambers (pTSCs) for real-time pressure/force control to grasp objects with varying stiffness (i.e., soft, compliant, and rigid objects). The fingers of the soft gripper were 3D printed simultaneously along with the pTSC, without requiring support materials, using an inexpensive fused deposition modeling 3D printer. The pTSCs embedded in the fingers have numerous advantages, including fast response, repeatability, reliability, negligible hysteresis, stability over time, durability, and very low power consumption. Finite element modeling is used to predict the behavior of the pTSCs under different body contacts and to design their topology. Real-time pressure/force control was performed experimentally based on the feedback data provided by the pTSCs to grasp various objects with different weights, shapes, sizes, textures, and stiffnesses using an experimentally tuned proportional-integral-derivative (PID) controller with the same gains for all the objects grasped. In other words, the gripper can self-adapt to different environments with different stiffnesses and provide stable contact and grasping. These results are validated theoretically by modeling the soft gripper in contact with the objects with varying stiffness to show that the stability of the contact motion is not affected by the stiffness of the environment (i.e., the grasped object) when constant PID control gains are used.