Cubic Inch Robotic Arm (CIRA)

Abstract

This project investigates a robotic arm that is capable of performing the pick and place operation on objects as small as a grain of sand, while also having the ability to stow itself compactly inside of a cubic inch volume. The aim of this project is to come up with a design that is easy to manufacture, assemble and control. Design of the robotic arm was performed using CREO, a commercial computer-aided design software, and the skeleton of the arm was 3D printed using the Princeton University Mechanical and Aerospace Department 3D printers. All of the internal components of the robotic arm were purchased from outside vendors. The Cubic Inch Robotic Arm, or CIRA, contains four degrees of freedom, one base rotation and three arm segment rotations, and has a separate motor to control each joint. A free body analysis of CIRA was performed to determine the size and torque requirements of each of the four onboard motors. Throughout the design small safety factors were applied in order to make use of the smallest motors possible, thus reducing the overall size of the robotic arm. The gears that connect the motor shafts to each joint were chosen such that the smallest gear ratio possible was obtained given geometric constraints. Doing so increases CIRA’s precision by effectively reducing the step angle of each of the stepper motors. An initial design of the gripper to be mounted on CIRA has already been drafted. Early stages of assembly of the CIRA prototype have already been completed and tests of the stowing mechanism have been performed to ensure that the 3D printer has a high enough tolerance to produce such small parts. The final design of CIRA is able to pick and place objects within a 3.5 inch radius circular area. When stowed, CIRA assumes a vertical rectangular prism shape that has a volume of 1.75 cubic inches when the “first segment” motor is ignored.