Circular Shell Gripper for Handling Food Products.

Pneumatically driven soft robotic grippers have been extensively studied in recent years. A majority of the grippers, especially those entirely composed of soft materials, can adapt to and handle various objects. However, there are limited studies regarding the realization of arbitrary grasping postures and twisting manipulation. Furthermore, the handling efficiency or the takt time of a handling task has not been investigated frequently. Therefore, this article proposes a circular shell gripper that consists of a rigid external shell and four soft internal air chambers. The soft chambers can be pneumatically inflated, thereby enabling it to grasp an object with a large contact area. The rigid shell allows the gripper to generate a large grasping force, while providing rigidity. This allows it to achieve arbitrary handling postures and twisting manipulations. A finite element model was constructed to simulate the chamber inflation, contact area upon grasping, lifting force, and twisting torque. An analytical model was formulated to quickly predict the lifting force and the twisting torque required to manipulate a known object. The models were validated via experimental tests on the lifting and twisting of a rigid cylinder. The experimental results indicate that the shell gripper can generate a maximum lifting force and twisting torque of 50.97 N and 0.73 Nm, respectively, with an input pressure of 10 kPa. Experimental tests on a variety of food and drink products revealed that the gripper could handle deformable, heavy, and irregularly shaped objects as well as realize arbitrary manipulation posture and twisting motion. The takt time for a pick-and-place task was found to be ∼2-5 s, using an SCARA robot; this time can be further optimized (less than 1 s) by using a parallel robot. However, the gripper was unable to handle low-profile objects, due to the downward pressing force; this was identified as a limitation of the proposed design.