3. Error Budgets and Bearings
Errors and Bearings
2016
This week I thought about my machine dimensions, error budgets, bearings, and structure. Click on the first notebook photo for a link to download a pdf with the whole assignment. Keep going through the slideshow for links to my spreadsheets (made by Alex Slocum and adapted for my use).
I made rough sketches with dimensions for my open and closed design and went along making the geometric and load-induced error budgets. I received OK numbers for my load-induced errors, but terribly wrong answers for my geometric errors.
I know I need to go back and redo these spreadsheets. I know a lot of mistakes I can fix like the servo positioning and attachment points. I didn't totally understand some of the things on the spreadsheet at first, but I got some help and I will redo it soon.
Afterwards I began to design my bearing system. I chose to go with twin rails because they were cheap to get. I thought using a press-fit to apply a preload was a good idea, but it turned out to have a huge frictional force. I need to revisit this. I can maybe use a flexure or allow some clearance in the twin rails and use magnetic preload. I also did some calculations to see how long the bearing would last for the press-fit and it was over 4000 pages!
Finally, I went over the risks and countermeasures for my designs. In the end, I think they will both look great after I put on my finishing touches. What really matters is the two designs differ in error budgets. I need to get that right first before I decide.
-Max