Using a rigid gripper on objects of different compliance underwater

Underwater exploration and sample collection requires grasping techniques for a variety of objects. Soft-grippers are being developed for tasks that require a more delicate grasp, but these manipulators are often limited in versatility by grasping force. We sought to develop an algorithm for using an off-the-shelf rigid-gripper to grasp delicate objects without the need for additional tactile sensors. For this research, an interlocking finger gripper from Blueprint Lab was used. Preliminary force and electric current readings were obtained to understand how the current used drive the gripper related to the amount of force applied to an object. It was determined that while the two values had a rather linear relationship, using specified current values alone was not a reliable way to ensure a desired output force, especially for low values. Instead, the change in current was monitored to determine when contact was made with an object. A combination of position and current commands were used to drive the gripper. Once contact was detected, the gripper was held momentarily at that position. Depending on the compliance of the object, that current could then be held at a specified value or in some cases reversed. Tests were first performed on objects in air. Successful grasps in air were done on various objects, most notably a potato chip. Test were then performed on objects underwater and included objects such as grapes, kiwis, tomatoes, and a paper cup. All grasps on fruit were performed successfully, causing little to no damage to the skin. The grasp on the paper cup was unsuccessful and is being used now for further research.