LINEAR DRIVE GRIPPER
GETTING A GRIP ON MECHANISM DESIGN
The purpose of this project was to create a lightweight mechanical gripper capable of securing a five-pound hammer and swinging it without the object falling. Working with a team of four other engineering students, we spent two months modeling, fabricating, and testing designs. In the end, our gripper successfully completed the task of swinging the hammer while remaining among the lightest grippers in the class.
PROJECT OBJECTIVE
For the successful completion of the gripping task, the gripper had to "grab" the hammer using some kind of power transmission mechanism supplied from a motor in the robot wrist then keep the hammer securely in place as the arm swings from a 90-degree angle with respect to the centerline. In addition, the gripper had to be able to reliably grip as well as un-grip the object when the motor was switched backwards and forwards without causing harm to the gripping mechanism.
EARLY ITERATIONS
After taking carful calculations for the power transmission elements in order to optimize the amount of force in the grippers, we modeled all elements on Solidworks to create a completed preliminary assembly, then cut and fit each part using machine tools including the lathe, drill press, and milling machines.
In this early design, power is transmitted to the grippers using a pulley system that ultimately turns a dual-thrust lead screw that has been threaded into the sides of the grippers using custom bearings. With this dual-thrust lead screw, the two 3D-printed gripper faces are able to close symmetrically around the hammer while staying equidistant from the hammer's long axis. The force of the two grippers pushing inward on the hammer, in addition to friction tape on the inside faces, were enough to successfully grab and swing the hammer.
Though this early design was very successful, the gripper itself was vastly overbuilt and heavy. While we liked the power transmission elements, our team then worked to minimize mass in the grippers and mounting block.
FINAL DESIGN
After running stress and displacement studies on Solidworks for the assembly and each individual component, we were able to see which parts of the original design were weakest and which parts may have been overbuilt. While our final design is visually very similar to that of the first, we dropped significant amounts of weight by using smaller alignment rods, making the grippers thinner, and 3D printing the mounting components instead of machining them from aluminum.
