Mechanical design

Assignments:
            - design a machine (mechanism+automation), including the end effector
            - build the passive parts and operate it manually
            - document the group project and your individual contribution
          

Discussing with group members

- First idea: instead of making machine for some unique and arbitrary purposes, we decided to make PCB milling machine since 1) you can find other people's works (giving us good references and lower chance to fail):here, and 2) PCB cutting machine is really useful (as long as it actually works).
- We wanted to improve
,
but also wanted to include the broad bed from
(I forgot to take picture of bed)
so that it can stabilize the vibration from heavy spinning parts.
- None of us have firm background in mechanical design, so after talking about the basic structure, we decided to design on our own first and make it with 8mm cardboard to get some senses.
(At the beginning, we didn't stick to modular design.)
- I also wanted to try click joint. I saw

from here, and tried to draw on my own:

Two important thing to remember: align them properly. It worked fine with acryl board:

but cardboard caught fire while laser cutting (speed 10, power 80-85) for the joint test:

so I gave up using joint for the test design.
- This is my first design for machine:

- When I assembled these jointless cardboard

I used double sided tape or masking tape. The finished one was
and

Now let's get back to the original plan: each of us designs machine, and figure out which is good, which to improve, etc. Kurina made firm nice machine, and we decided to improve it.

In the middle, here are some comments to remember from Edu:
1) instead of having four shafts on one single line, have two by two (such as two distant colons: :) since this square distribution will be stronger. And maybe one leadscrew in the middle is enough.
2) shouldn't have any friction from touching the bed.
3) Nema17:stepping motor.
4) In case we put two plates together to make it thicker, use screw. In most cases, click joint is better than screw since screw can get loose from vibration, but in this case screw is better.
5) to have two (or more) shafts exactly parallel, we need some thin curves (such as (O)-->this. Even at the top and bottom) around all the holes for one of the shafts. It will make the positioning of the shaft a bit flexible.
6) make some extra space for the electronic parts and endmill box.

- After discussing to modify the design accordingly, we changed our minds for modular design due to the advantage of it.
It will be continued....

By the way, Kurina and Rodrigo did all the modular designing, and Tex did all the programming part. But I am sure that my presence was also very important especially when we use CNC machine (since no one is allowed to use CNC machine when he/she is alone :)


What I learned from the lecture and meeting:


- Important factors to consider: friction(for example, nylon+metal moves smoothly), backlash (by inertia+tilted end mill)
- ceramic:very nice for friction, but not for stress.
- can use cement-for big strong machine
- adhesive:not reversible. try not to use-use joint
- Fastener:

- not only friction, but pin can also strengthen the joint.
- involute gear:always contacting at one point with no discontinuity in the motion
- sprocket: larger forces, less smooth
- shaft:different roles:define axis,
- elastically loaded-not jiggle
- standard shaft coupling:enable a little mis-aligned shaft to be coupled:very small adjustment, but with tight tolerance
- joint coupling:add backlash, vibration, but a lot of freedom
- Thrust bearing: vertical-they are designed to support a predominately axial load. Really smooth, but weak at horizontal force.
- Sleeve bearing: slide on the precision rail
- Caster wheel:very heavy load
- Things get floppy in the machine after using for long: spring gives constraints on the freedom
- Hysteresis: 1. stress-strain relation, 2. Backlash for bolt and nut. Will not come back to the same position. Elastic loading(?) to lessen degree of freedom.
- Rubber, form:vibration damping, elastic property
- Force loop: the shorter, the better.
- more materials:Garolite - natural fiber
- Framing:metal-sensitive to temp, wood-sensitive to temp and humdity, plastic:good
- Cap type nuts:prevents rusting.
- Nylon insert lock-inside Heavy hex, there is nylon that prevents from unscrewing when vibrating
- Tee nuts insert. Coupling. Screwing from both sides.
- Slotted nuts, castle nuts: 2 or more nuts-really difficult to turn. Slotted and castle make it even harder.
- Cylindrical roller bearing needs warm up. Limited freedom in movements, but faster.(Rolland machine)




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