A Soft Electromagnetically Controlled Robotic Gripper to Manipulate Delicate Food Products

This study addresses the design and testing of a novel soft robotic gripper actuated by an electromagnet with which to handle of unpackaged delicate fruits in the food industry. Traditional rigid mechanical grippers are not applicable to manipulate delicate food products because their gripping action can easily bruise or damage fragile food products during handling due to hard contacts. In addition, the size, shape and weight of individual food items can vary widely. Because of this statistical variation and the need for delicate handling, the system integration and control requirements for a soft gripper are sufficiently complex that conventional rigid mechanical grippers are not a practical solution when handling delicate food products. To overcome the disadvantages of rigid mechanical grippers, a soft robotic gripper, which can softly and gently hold fragile objects by inflating flexible compliant elastomeric fingers, have been recently developed. The compliance of the soft grippers can be controlled by adjusting a pressure level of air and safe grasping of sensitive objects can be achieved because excessive gripping force is intrinsically avoided. In addition, when using pressurized air as an actuating source, hygienic risks during handling of food products is minimized. But, soft pneumatic grippers require a bulky and noisy compressor to supply pressurized air to the soft elastomeric fingers. In this study, the design of a soft robotic gripper, operated by an electromagnet, is proposed and its feasibility for soft gripping action were validated experimentally. A soft gripper configured as two opposing fingers, was designed in this study to achieve compactness, lightness, simple design, and to reduce system complexity. The flexible two-finger appendages were 3D printed via fused filament fabrication (FFF) method using soft elastic thermoplastic polyurethane (TPU) filament material. Thus, the manufacturing process was simple and quick, and production cost was low. The soft electromagnetic gripper was constructed by mounting the flexible two-finger appendage atop an electromagnet. A permanent magnet was attached to the bottom center of the two-finger part. When the electromagnet is activated by applied current input, the attractive electromagnetic force pulls the magnet attached to the two-finger part toward the electromagnet. As a result, the two opposing fingers are closer against each other and a pinch grasp occurs when an object is placed between these two fingers. In the absence of current input, these two fingers act like passive flexible elastomeric fingers, thus releasing the object. If the polarity of the electromagnet is reversed by changing the direction of current input, the repulsive force pushes the magnet against the electromagnet, thereby letting the two fingers opened wider so as to accommodate larger object. In this study, the gripping displacement and the holding force of the soft gripper will be experimentally evaluated by different initial gaps between the magnet and the electromagnet. In addition, feasibility of the soft electromagnetic gripper will be demonstrated by grasping a population of different sizes, shapes and weights of delicate fruit items.