Robotic Arm Vertical Prismatic Joint

Photo of Susan Conover, Ross Davis, Chelsea Lawson, Austin Wheeler Students: Susan Conover, Ross Davis, Chelsea Lawson, Austin Wheeler

Sponsor: Los Alamos National Laboratory

Date: Fall 2012

Requirements:
LANL has specifically requested a joint that can interact with Motoman SIA5D robotic arms. The prismatic joint must move the robotic arms slowly and accurately (up to 1 mm) to access shelves from the ground level up to 9 feet high. The device must reach this maximum height but also collapse down to fit through eight-foot vault doors and travel stably through the vault. The joint must also move at a low speed to keep moments and torques acting within the support system to a minimum when stopping and starting the vertical motion. In addition, the joints need to fail safely, so the joint must have a braking system that works without power or computer communication. Due to the risk of the device being controlled by outside sources, the joint cannot use wireless communication. Also, the weight of the setup is constrained be less than 125 lbs. The last cost of the joint should not exceed $6,000-$10,000.

Problem:
Los Alamos National Laboratories must often move canisters of radioactive material within their vault in order to store this material in a safe and efficient manner. LANL employees currently enter the vault wearing hazardous material suits, which do not protect them from the high levels of radiation. LANL seeks a robotic method of handling the radioactive canisters inside the vault is desired to reduce the human interaction with radioactive material. The project focused on designing and analyzing an accurate, robust, vertical prismatic joint for robotic arms to handle radioactive material canisters safely and efficiently in the vault.

Solution:
The team chose a ball screw combined with linear rails as the best system to fit this application. The team worked directly with Olympus Controls to design and specify a dual ball screw assembly, with a four foot tall ball screw attached to a six foot tall ball screw, in order to reach the height requirements of the shelves and collapse down to fit through the eight foot vault doors. The team further researched external factors, such as cabling and sleeving, that affect the design's operation within the vault. The solution includes tightly controlling side-mounted cables, protecting ball screws with plastic bellows, and adapting the model to fit an Eagle E210 Flexcart platform.

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