Overview of Status of Analysis, Design, Fabrication, Tests, etc.
Unfortunately at this point in time we have not initiated the prototyping process. Understandably our sponsor wanted to touch base with us regarding the direction we are going in before we purchase any hardware. We have purchased the necessary parts as of (1/14/2019) for a prototype to test the feasibility of the 5 DoFs and are awaiting delivery which should be in the next day or two.
We are looking into the design of the supporting structure. There is a chance that the final design will not even be cantilevered and will be suspended from a bridge like support. This offers greater structural stability and greatly decreases the vibrations that would be seen with a cantilever design.
Quasi static analysis is being carried out to asses the counterbalancing mechanisms. Through this we will be able to approximate the required spring stiffness needed to properly counterbalance the microscope.
Accomplishments from Previous Week
Purchased necessary components for prototype (see first bullet of Overview)
The abstract of the report is being drafted and the project overview (chapter 1) of the report is nearly complete.
Review options/feasibility of linear rail.
Goals for Next Week (list names after each item). Use specific and measurable objectives.
Construct prototype, hopefully we can get a jump start by the end of this week. (everyone)
Determine counterbalancing specifics such as spring constants required and non-circular pulley geometry.
Sponsor Comments from Last Meeting and Actions Taken to Address these Comments (indicate date of comments and if via email or in person)
Meeting with sponsor (1/14/2019)
Consider a bridge design. The weight of the microscope + additional hardware is quite hefty. The bridge design would eliminate the cantilever altogether. Furthermore, it would lead to increased stability and vibrations would be less of a concern.
Response: This comment has been brought up in the past by a few different individuals. The above reasons are very compelling and are leading us to seriously consider this approach. Our main concerns are space restrictions as the bridge would take up space on both sides of the operating room table. Furthermore, this would require two vibration isolation supports instead of just one. Our sponsor has made it clear that it is not an issue if two legs are required in the final design, so long as it works. We are seriously considering this approach moving forward.
Linear rails: most rails act with the payload above the rail, our design will most likely require the payload to exist beneath the rail. Ensure the rail can support payloads attached from below. Furthermore ensure the carriage brake system can provide the necessary brake force as the force required will increase with increasing tilt angle of the microscope.
Response: This is a valid concern. We are going to reach out to a manufacturer for a more definitive answer regarding the feasibility of loading the carriage from below. Regarding the brakes: the 20° tilt in either direction needs to be taken into account and we will be carrying out static analyses to predict the maximum amount of brake force required. Additionally, if we can design the system in such a way that the linear rails are above the tilting mechanism we will eliminate this problem.
For the time being focus on the degrees of freedom & counterbalancing them properly. Specifically, the two rotary DoFs as those will generally be more complicated to properly implement compared to the translation DoFs. Furthermore, the operating room bed may be capable of vertical translation and horizontal translation along the length of the bed. It might be a waste of time to design those two DoFs when OR staff will just adjust the bed in those two directions.
Response: Agreed. This has basically been our design process from the start although we were not mainly focusing on the rotary DoFs. Special attention is currently being paid to counterbalancing the rotary DoFs. We hope to have a site visit soon or research the bed specifications to confirm bed travel.
Instructor Comments from Last Meeting and Actions Taken to Address these Comments (indicate date of comments and if via email or in person)
Meeting with instructor (1/10/2019)
Try to obtain a CAD model of the microscope from the sponsor. This is important for determining key information about the scope such as the center of gravity.
Response: This is true and accurately knowing the location of the center of gravity is crucial for static analysis. We requested a CAD from our sponsor during our last meeting.
Define precision needed when locking the degrees of freedom into place.
Response: The manual positioning is meant to serve as a coarse positioning. Internal to the microscope housing there are x,y translation stages with ~ 10 cm (4") of travel with micron resolution. Regarding the rotary motion, this is also coarse positioning which is to ensure that the microscope objective is for the most part normal to the patients head during imaging.
Comments from Other Students in the Class (indicate date of comments and if via email or in person)
None to report
Risks and Areas of Concern
None at this time.
Resources or Information Required but not Available
Bed specifications (will become clearer upon site visit/review of bed manufacturers specifications)
Schedule
Our next major task is to prototype our current design for the degrees of freedom to ensure feasibility of the design. Should this prototype not perform to our expectations we have an alternate design concept that we can fall back on.
Update Gantt chart.
Budget (list amount spent and amount remaining)
Spent: $129.50
Remaining: $1470.50
Progress on Report and Webpage
We are almost done writing up chapter 1 of the report and have started drafting the abstract which we can add to along the way.
We are staying up to date with the progress reports and are going to be uploading some static analyses in the "Docs" section in the coming days.