Overview of Status of Analysis, Design, Fabrication, Tests, etc.
Committed to pursuing table design concept presented last week.
In process of ordering parts needed to assemble table
Completed additional repeatability tests to try to determine cause of positioning error
Accomplishments from Previous Week
Met with sponsors (17 Apr)
Discussion with sponsors led to joint conclusion that the positioning error growth is a nonissue in typical operation of the MRI scanner. Typical operating procedure is mounting the specimen to the tooling, sending it into the bore, taking a number of scan, moving it out of the bore, injecting dye into the specimen to highlight areas of interest, and sending it back into the bore for more scans. So in typical operation the scanner will make 2-3 complete back and forth movements. The positioning error remains within the desired error range (± 0.5 mm) for approximately twice this many positionings.
Completed additional repeatability tests to attempt to determine the cause of the positioning error
Load on the tooling plate does not noticeably affect the error growth of the system. Tests were performed with no load on the plate and with a 5 lbf load on the plate. In both cases the error's growth was approximately the same.
During testing it was noticed that the rubber belt began to oscillate up and down as the tooling plate moved forward or backward. These oscillations cause the tension in the belt to change during the plate's motion which affects the distance the belt moves during each motor step.
There is no effective way to solve this problem for us. It would require rework of the mechanical components of the positioning system which is outside the scope of our project. Sponsors are more than happy with how the existing system operates and do not want us to potentially 'break' the existing system. Further, we do not have much wiggle room with our budget as most of it is committed to the agreed upon work (in-room controller and stand/table). Rework/replacement of the belt system could potentially become very expensive.
Began completing ordering paperwork for unordered components
Goals for Next Week (list names after each item). Use specific and measurable objectives.
Hopefully pick up 80/20 order (Jake)
Begin Machining of Lifting Rod and Sleeve (Krishna)
Begin Machining of fastening hardware (Johnny)
Hit the Report and Website hard (ALL)
Sponsor Comments from Last Meeting and Actions Taken to Address these Comments (indicate date of comments and if via email or in person)
Sponsors expressed concern about the usability of the system. Concern revolved around determining the vertical position of the tooling relative to the bore while the operator was adjusting the wheel. Sponsor believed that this adjustment system would require the user to make a height adjustment, try running the sample into the bore, and readjusting as necessary. We pointed out that the sponsors had repeatedly stated their idea of having a measuring stick of some sort next to the table to indicate the appropriate height level for each tooling. This alleviated these concerns. (in person, 17 Apr)
Instructor Comments from Last Meeting and Actions Taken to Address these Comments (indicate date of comments and if via email or in person)
Concerns over rotation of the table top about y-axis (x-axis into bore, z-axis is vertical). Cross and side bracing will strengthen the table structure reducing the tendency to rotate due to applied moments. Also, the design for the sliding pieces were reversed allowing for internal and external bracing of the top (moving portion) of the table.
Comments from Other Students in the Class (indicate date of comments and if via email or in person)
See spreadsheet
Risks and Areas of Concern
Budget (as always)
Lead time on thrust bearings
Resources or Information Required but not Available
Where to buy the fasteners for everything that are non-magnetic
Schedule
Describe upcoming milestone
Update Gantt chart.
Budget (list amount spent and amount remaining)
$990/1500 spent with other expenses taken into account
Progress on Report and Webpage
Hitting it hard Thursday and Friday of this week and all next week