A Novel Variable Stiffness Robotic Gripper Based on Layer Jamming
A soft robotic gripper design which incorporates layer jamming as a means for creating tunable stiffness control and higher load capacities.
Automation using robotics has taken many forms including, but not limited to, automotive manufacturing, transportation of good in shipping warehouses, and the delicate handling of wafers in semiconductor plants. In many of these applications grippers and end-of-arm-tools (EOAT’s) are incorporated to allow robotic arms to complete specific tasks. Largely due to these considerations, Mckinsey & Company recently reported that grippers and EOAT’s will grow from a $2.4 billion USD market in 2017 at a rate of 13-14% per annum to become a $5.1 billion USD market in 2023. Traditional rigid-body robotic grippers, however, consist of inflexible arms actuated by a large, unrestrained force. In this regard, damage to the product as well as danger to operators pose potential unwanted risks. Moreover, the rigid body nature of these grippers makes them less capable to handle items of unusual shapes, thereby limiting their applications. To address these concerns, some researchers have begun to develop soft robotic grippers which utilize a compliant structure and an actuating mechanism. Although much better suited for handling delicate and irregular objects, these soft grippers suffer from a limited loading capacity. In addition, many of these robotic grippers utilize complex designs and require expensive materials, thus reducing their feasibility as suitable alternatives. There is, therefore, a need for an easily implemented robotic gripper with tunable stiffness control for interacting with a wide variety of object geometries and materials.
To address this need, researchers at The Ohio State University have developed a variable stiffness robotic gripper capable of reaching 30-40 times the load capacity of traditional soft/compliant robotic grippers. A main innovation of this design is the incorporation of a novel, compliant backbone to a vacuum layer-jamming system within the fingers of the gripper design. The compliant backbone possesses a series of branches which take-on a semi-elliptical shape and provide additional support to the vacuum-sealing bag that surrounds each finger. At their narrow end, these branches are attached to an elongated beam and at their wide end, these branches come in contact with a series of thin-layered sheets. Having the flexible beam located on the opposite side of the layered sheets enables a greater range of bending in the gripper’s fingers. Tension cables run through the middle of the backbone branches and a servo-motor provides the rotational energy required to induce flexion and shape restoration in the gripper fingers. Alternative actuation method for shape flexion is via pneumatic network channels which are activated by pressured air.
The layer-jamming system consists of a series of thin-layered sheets sealed within an airtight bag. When negative pressure is applied to the bag via a vacuum pump, the sheets are compressed together, creating a large friction force. This friction force restricts the motion of the sheets and holds the current shape of the system. By incorporating a vacuum layer-jamming technique into a compliant backbone, this novel gripper can adjust its stiffness for both stiff and soft materials. The final gripper design makes use of the stiffness control associated with vacuum layer jamming and a novel, easy-to-integrate backbone structure that minimizes stress concentrations and maximizes range of bending.