Overview of Status of Analysis, Design, Fabrication, Tests, etc.
In accordance with our Gantt Chart, we began fabrication. This process included testing the materials load capacities with a factor of safety of greater than or equal to 1.5.
We have also conducted more research in our exact requirements for our design. Some of these answers are still pending but this may lead to a much more simplified design, which would save us time and cost. One example is the Z-axis (vertical movement) may no longer be required from us as the OR bed supplies a certain amount of displacement in this axis.
Accomplishments from Previous Week
Construct and test two prototype concepts.
Began CAD modeling of refined design based on prototype performance.
Not entirely completed at this point in time as we are waiting on some key specifications from our sponsor. We are holding a second meeting with our sponsor this Friday to iron out these details and press forward with the CAD process.
Preliminary FEA of isolation leg "cup holder" sub-assembly to asses feasibility of material.
Determined apt source of compressed air and simple means of storage.
Reviewed several sources of engineering standards relevant to our design such as OSHA, OSHPD, ISO, and CBC.
Goals for Next Week (list names after each item). Use specific and measurable objectives.
Determine logistics of welding. (Everyone)
FEA and optimization of:
Bridge & compressed air storage unit (Ramzi)
Double rotisserie mechanism (Alex)
Connection of microscope to double rotisserie (Alex)
Isolation leg "cup holder" (Chase/Giovanni)
Top connection of isolation leg (Giovanni)
Linear rail for lifting & counterweight (Chase)
Determine material to be used and source viscoelastic pad for patient to lie on (Chase)
Make some purchases
Thorlabs vibration isolation legs
ID tube clamp
Possibly the bearings and square tubing for the double rotisserie mechanism.
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 (1/28/2019)
Dr. Shtrahman wants to plan an additional meeting later this week with demonstrations of our two prototypes. His concerns with the ball joint design are maneuverability and counter balancing it. His main concern with the “double rotisserie” design is the space requirement and it being potentially difficult to motorize in the future.
Response: We are going to demo both prototypes for him on Friday the 31st. We understand his concerns but we feel that it may be fairly straightforward to motorize the double rotisserie in the future.
The precision slides are mounted to the outside of the microscope.
Response: This clarification was very helpful and made us realize that more care should be taken when mounting the microscope to the double rotisserie. We are considering an open box that these slides could be mounted to, and subsequently mounting said box to the double rotisserie.
Will get us some sort of information on the OR bed manufacturer (a name, a phone number, model #, etc).
Response: Given this info we will do some research to inquire about bed movement and dimensions. This will give us an idea of how much vertical translation (if any) is required from our device.
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 (1/24/2019)
Regarding the cross bar, a few potential issues could arise with this concept. Clearance issues between the crossbar and operating room table. Also, the potential for the cross bar to rise and lower non-uniformly will result in misalignment that could decrease the life of the hardware. Perhaps raise & lower the double rotisserie assembly as opposed to the entire cross bar.
Response: we acknowledged this fact and we are trying to incorporate the z-axis movement into the double rotisserie assembly. However, it has been difficult due to the x and y movements. In addition, z-axis may not even be needed if the operating bed can be raised and lowered.
Consider a cranking mechanism instead of using two counterweights for z translation.
Response: This would be a more compact solution and add less mass to the entire system than two counterweights on either side of the bridge. The advantages to the counterweighted solution are that it would take less time to achieve the desired position and that there is virtually zero maintenance required. We will consider the cranking solution moving forward.
Consider a modular setup where the legs of the bridge have notches or hooks that the cross bar can be placed onto, and the microscope can subsequently be mounted to the cross bar.
Response: while this would help with storage, portability, and ease of assembly this is not a feasible approach in this project due to the weight of the microscope and additional hardware. It would require too much effort to lift the 25 kg microscope (plus additional hardware) on and off of the cross bar every time a change in vertical position is needed.
Locking mechanism for the double rotisserie: friction locking should be easy to implement and provide sufficient braking force.
Response: We completely agree since this design should be nearly counterbalanced at all times. However, with the micro-positioning sliders within this design, the center of mass will shift. We hope to perform analysis soon to determine a secure amount of force needed given the center of mass shifts to the worst case scenario.
Crucial pieces of information needed moving forward: operating room specs, looking like an OR visit is not going to happen. Bed specs may be enough. Also, CAD model to determine COM of microscope.
Response: We wholeheartedly agree that these are key parameters in our design. We plan to meet with Dr. Shtrahman later in the week so he can give us a definite answer on the bed manufacturer. We have requested the CAD files of the microscope previously but we will ask again for good measure at our next meeting.
Comments from Other Students in the Class (indicate date of comments and if via email or in person)
In person comment, post design proposal (1/17/2019)
Look into the constant force spring to eliminate the need of the non circular pulley.
Response: This design works well in theory but our current model does not need a counter-balance mechanism for our tilts as the rotations goes through the center of mass. However, we will keep this in consideration if we need a Z-axis counter-balance.
Risks and Areas of Concern
Attachment to the ThorLabs vibration isolation leg.
Spoke to an engineer and said that the top cap is sealed and the screws are loctite.
May need to attach to .5 in deep cylindrical hole on end-cap.
Locking mechanism.
Shifting COM due to precision slides.
Possible misalignment caused by non-uniform movements of the linear sliders on the two bridge posts.
Resources or Information Required but not Available
Operating Bed Z (vertical) movement: We are going to reach out to the OR bed manufacturer to get the bed’s vertical displacement abilities as this may be enough to eliminate the need for our mechanism to have a Z DoF. Therefore, we are focusing on other design aspects until it is confirmed how much (if any) vertical movement we must supply.
CAD of microscope: This CAD is needed to determine the center of mass for attachment purposes.
Schedule
Our next major task is to demo our prototypes to Shtrahman later this week and address his concerns. From this meeting, we hope to finalize our 2 DoF tilt design.
Update Gantt chart and website.
Budget (list amount spent and amount remaining)
Spent: $151.74
Remaining: $1448.26
Progress on Report and Webpage
We are up to date on the Project Report by using the guidelines from the website.
We are staying up to date with the progress reports (seen above) and are going to be uploading some static analyses in the "Docs" section in the coming days. We are also starting to complete the auxiliary pages of the website such as announcements.