Overview of Status of Analysis, Design, Fabrication, Tests, etc.
Stand design is close to being finalized and is on track for the scheduled Week 3 finish.
Accomplishments from Previous Week
Completed Individual Component Analyses (ICAs)
Cart caster ICA
Laboratory jack ICA
Table materials ICA
Wire harness ICA
Table materials
Settled upon using t-slotted aluminium framing (80/20) for the table's frame because they are very easy to work with, machinable, and allow for adjustments to the system as needed. Sponsors liked this decision.
For the table surface, the material we settled on is Trespa. Trespa is made out of compressed paper and resin. It is relatively cheap, a 6' x 2' x 0.5" rectangle costs ~$120, and is very rigid so the amount of supports and bracing needed is reduced. The material was suggested to us by the sponsors as it is widely used on laboratory surfaces, is easy to clean, and easy to machine. Since ultimately the sponsors would replace our table top choice with Trespa, it made sense to use it from the beginning.
Wire Harness
Settled upon wire harness system. Tom had an unused one lying around and donated it to us
Casters
Met with sponsors on Friday (03 Apr) and discussed ICA with them. They were very excited about the McMaster-Carr leveling caster option. While these casters use magnetic steel, since they will be securely mounted to the cart, it is a nonissue. Only concern is possibility of any kind of plating flaking off and possibly posing a hazard. However, there is an alternative design that can be implemented for a similar cost that fulfills the same functional requirements. Using the Shepherd MRI Series casters with a all plastic leveling mount would achieve the same functionality with zero magnetic components. Sponsors are happy with this solution too and ultimately left the decision to us.
Laboratory Jack
Further discussion with sponsors led to conclusion that current design solution would not be sufficient. The concern is the laboratory jack would not remain rigid during motion and the top plate would slide slightly relative to its initial position. This would reduce the precision greatly of the positioning system.
Risk reduction (RR) tests could be performed on the lab jack to indicate that the motion would have negligible effect. However, this would require a substantial investment of money ($300) to acquire a lab jack for testing. While we could borrow a lab jack from UCSD to test, those results would not necessarily reflect the performance of the one we would purchase. Additionally their concern is long term degradation of the lab jack's ability to remain rigid during motion which could be caused by fasteners loosening. Tests on a new lab jack would not target this concern.
Due to the financial and time expense of a RR effort, it was decided to rework the height adjustment system
Height Adjustment System
Due to concerns with the laboratory jack solution, it became necessary to rework the vertical height adjustment mechanism.
Currently generating concepts for the new system.
An early design idea used a timing belt to rotate four lead screws to raise and lower the equipment mounting plate. However, there are concerns with this design's complexity and durability.
The next iteration uses a metal (all steel or steel and aluminium combination) jack from Misumi to raise and lower the tabletop. While the jack is effectively solid steel, the sponsors indicated this is not an issue because they can build shielding around it and it is unlikely to become a projectile because it is securely mounted to the table. This solution would be relatively cost effective, the jack would cost ~$220. When accounting for the additional components necessary to install it, the cost should be comparable to the laboratory jack option which was estimated at a $350 minimum.
There are CAD files of the mock-ups attached below.
Established communication from in room controller to LabView
Conducted a preliminary test with a switch directly connected to the Arduino.
Set up LabView block diagram in current system to take input from switch.
Input was modeled as a button press on the front panel and controlled table movement.
Created preliminary bill of materials for the system
Created CAD mockups of design solutions
Completed positioning repeatability trials
Goals for Next Week (list names after each item). Use specific and measurable objectives.
Order casters and/or leveling mounts depending on which option we decide upon.
Order Trespa from supplier. Will need a minimum of 12 ft of 2 ft wide, 0.5 inch thick Trespa.
Finish 12 minute PowerPoint presentation for the Design Proposal presentations (All)
Create models in SolidWorks of:
Table design ideas including ideas mentioned in the Height Adjustment System section above. (Krishna)
The positioning of the equipment on the table top (including wire harness, MRI positioning system, associated controller boxes, and other equipment necessary) (Krishna)
Close-ups of any mechanical systems that need emphasizing (namely the timing belt and pulley system mentioned above) (Krishna)
Start on circuit design of in room controller (Jacob, Krishna).
Sponsor Comments from Last Meeting and Actions Taken to Address these Comments (indicate date of comments and if via email or in person)
Mostly summarized in last weeks accomplishments
Cannot use polycarbonate in design as it is likely to crack if cleaned with alcohol (03 Apr; in person)
Design uses no polycarbonate
Provided with samples of wire connectors used by the lab (03 Apr; in person)
Arranged trip to Fry's to see if parts are easily purchasable
Provided contact information of 80/20 Aluminum supplier (03 Apr; email)
Contacted supplier. Asked if they have designs for a vertically adjustable table. They do not but they have bearing options to reduce friction between moving parts.
Height from ground to centre of MRI bore is ~107 cm (42.1 in). (03 Apr; in person)
Table designed to reach this approximate height when height is raised to maximum. This will allow for the maximum range of tooling heights to fit into the bore
Concerns about strength of HDPE table top (03 Apr; in person)
Now using Trespa for the table top
Instructor Comments from Last Meeting and Actions Taken to Address these Comments (indicate date of comments and if via email or in person)
Suggested that we perform a RR test using a large sheet of aluminium near the scanner to see if there was any issues. (02 Apr; in person)
Since we have moved to a Trespa tabletop, this test is no longer necessary.
Comments from Other Students in the Class (indicate date of comments and if via email or in person)
N/A
Risks and Areas of Concern
Overall Budget
Resources or Information Required but not Available
80/20 price point on brackets/fasteners
Schedule
Describe upcoming milestone
Update Gantt chart.
Budget (list amount spent and amount remaining)
$0 spent
$1500.00 remaining
Progress on Report and Webpage