Improving a Gripper End Effector

Rendering of the redesigned gripper
end effector and the grip fixture.

Battelle was tasked with providing a gripper end effector (GEE) for a new robotic arm (Grey Pilgrim's EMMA) for retrieval of nuclear materials processing wastes from two large storage silos. The GEE had two primary functions. It was required to grasp debris such as pipe, wire, small containers, tools, and the like and place them into a cutting device or a retrieval basket. It was also required to grasp a waterjet retrieval end effector (WREE), a jet pump and a large umbilical with special grip fixtures along its length.

The debris retrieval function required a strong grip over the full range of jaw opening (~15 cm). Some textured mating areas for general-purpose grasping are machined on the jaws. The end effector grasping function required high grip force only at a partially closed jaw position, where the jaws engage the grip fixture.

The analysis of the linkage was a straightforward 2-D kinematics problem. The base design and a new concept configuration were modeled in a simplified form and run through a kinematic analysis with DesignWorks™, an add-in package for SolidWorks™. It became apparent that fine-tuning could be accomplished much faster with a simple spreadsheet. A spreadsheet was prepared and validated the output against the DesignWorks™ results and baseline model test results, then used the spreadsheet to examine a number of other cases.

Test were also conducted to measure the jaw force using a simple compression load cell and spacers inserted between the jaws to obtain grip force at a range of jaw displacements.

In summary, a reasonably brief and inexpensive analysis effort yielded a significant improvement in the performance of the gripping end effector and the mating grip fixture for the end effector and other payloads.

Project Contact: O.D. Mullen