2. Concept Exploration and Dynamic Sketches
Concepts and Sketches
2016
In this assignment, I explored different concepts to create SteinBot. Two weeks ago, I came to the conclusion that only a lay-down (not vertical) open or closed bridge concept would work. I also concluded I would have to lower the bridge to be 2" from the stage. I started this assignment by confirming these numbers using Dr. Slocum's spreadsheet.
Next I thought of different ways to create linear actuators and attach them to SteinBot. I concluded that I would probably need a leadscrew for the X-axis open bridge actuator, but could use leadscrews or belts for the other X and Y actuators. I also thought about what linear guides I would need. I concluded that I would need internal circular rails for the open bridge, but could use external square rails for the closed bridge X actuators.
Next I appropriated different geometric., thermal, and load-induced errors to the structures and bearings of both designs. The closed design started to look better because of its resistance to loads and symmetric thermal properties.
I made a FRDPAARC chart to compare both concepts and create design paramters for the next level of the design process. I also did some writing speed tests and concluded that my machine must be able to move 6mm/s on one axis to satisfy the "write as fast as a human" requirement.
Then I created dynamic sketches of my concepts out of cardboard. The open bridge turned out to be bulky while the closed bridge was nice and slid well. I'm starting to lean to the closed bridge, but open is so cool!
Next I looked at the geometric errors caused by rotations along each axis at each center of stiffness. I concluded that the bearing error needed for an open and closed design were similar in magnitude.
Finally, I compared the open and closed bridge from a risk and countermeasure point of view. The closed bridge won on almost every practical characteristic. The open bridge won more style points because it looks harder to do.
In conclusion, I'm leaning toward a closed bridge. I really want to do an open bridge if the error appropriation is manageable. The open bridge is just so much cooler! When I become more familair with errors I will eliminate one or the other.