156B Week 7

Overview of Status of Analysis, Design, Fabrication, Tests, etc.

    • Upon consulting with engineers from Thorlabs and Newport, we've come up with a couple of possible solutions to mitigate the instability issues using only two vibration isolators would present.

    • As of last week we have sent over the required parts to manufacture the bridge, and double rotisserie.

Accomplishments from Previous Week

    • Get some clarity regarding the vibration isolation legs.

    • Place main part orders through our sponsor.

    • Developed alternate safety mechanism.

Goals for Next Week (list names after each item). Use specific and measurable objectives.

    • Finish manufacturing the double rotisserie. (Everyone)

    • Order 80/20 and necessary fasteners for bridge. (Alex/Giovanni)

    • Continue information gathering about the isolation legs. (Giovanni/Ramzi)

    • Continue revising and updating the report.

      • Abstract - Chapter 1; appendices (Ramzi)

      • Chapter 2 (Alex)

      • Chapter 3 - 4 (Chase)

      • Chapter 5 - end (Giovanni)

      • Read through entire report. Sign off on each chapter & make suggestions for improvements (Everyone)

    • Put together an itemized list of the remaining odds and ends that still need to be purchased. (Giovanni)

    • Look into accelerometers for testing. Maybe there is a suitable one in the components room/available for check out. (Chase/Ramzi)

Sponsor Comments from Last Meeting and Actions Taken to Address these Comments (indicate date of comments and if via email or in person)

Sponsor meeting (2/20/2019)

    • Keep researching the legs and their feasibility. In the event that the isolation legs do not work out, perhaps springs could be implemented.

      • Response: we've been in contact with engineers from Thorlabs and Newport that have confirmed our suspicions that using only two legs could result in the structure oscillating. We have not gotten a definitive answer regarding if the center piston in the legs is capable of resisting a moment. We will also be in contact with Eugene Duval, a mechanical engineer that has experience with design for operating room application. Regarding the springs: while this is a solution, we're not sure if a system that uses springs and dampers would provide enough attenuation to meet the vibration criteria that this project calls for.

    • Regarding the base (the sub-assembly that is supposed to hold the isolation legs): it would be nice to have an adjustable size so that the base could accommodate isolation legs of different sizes. The jail post design could work. However, using 80/20 extrusions for this part seems unnecessary. Consider using aluminum bar stock, it would make machining easier. Additionally, try to avoid welding unless it is absolutely necessary. If mistakes are made, you wont have to scrap the whole part and start over.

      • Response: we agree that adjustability would be nice and we will work to implement something like this. We also agree that using bar stock would be a good choice compared to 80/20 for machining and cost. We had planned to weld the bottom base plate but the concerns about messing up and starting over are valid; additionally should the sponsor desire to disassemble everything, having a welded part would make this more challenging.

    • Use good quality, sizable casters. Large casters would make it easier to roll over obstacles. Also consider air tires, these could help with vibration attenuation. Northern Tool would be a good place to look. A simple wheel chair lock mechanism is a good idea.

    • Response: this is a very valid concern that none of us had given much thought. The device is useless if it gets stuck in the elevator or behind a cord laying on the floor. We're looking into air tire swivel casters. Some off the shelf models come with built in brakes, but we will also explore the possibility of a wheel chair lock as well.

    • It may be smart to have some kind of handle the operator can grab on to when positioning the x & y translation DoFs. Without one the operator would just grab wherever to position the microscope which could introduce high moment loads on the slides. Position the handle in a place where this would not happen.

      • Response: this is a good idea and we will implement it.

Instructor Comments from Last Meeting and Actions Taken to Address these Comments (indicate date of comments and if via email or in person)

Instructor meeting (2/14/2019)

    • Regarding the safety mechanism: when using a spring loaded pawl, two hands are simultaneously being used to to unlock the safety mechanism and manipulate the microscope. Consider something like a capacitive sensor that can unlock based on touch or a dead man's switch on a lawnmower. The current design may be acceptable, that is up to the requirements of the sponsor.

      • Response: The capacitive sensor is an interesting idea. We're currently looking into electromagnetic brakes to be used with a biased switch. Maybe we could use a capacitive sensor instead of a biased switch but we feel that using a simple push button switch would be easier to implement. Additionally, as mentioned in the "Accomplishments from Previous Week" section, we have come up with alternate safety mechanism which we believe to be truly fail safe (this was presented in the last instructor meeting.)

    • The information presented about the isolation legs is very concerning. Look further into this to better understand the problem and identify possible solutions.

      • Response: we've consulted engineers from Thorlabs and Newport and have made some progress in resolving the issue but we are not in the clear yet. As mentioned above we are going to continue to be in contact with the engineers and Eugene Duval as well. Additionally, our sponsor has an associate that works for Thorlabs that can help put us in touch with a mechanical engineer that is probably better fit to answer the types of technical questions that we are asking.

    • Performance testing: you are going to want to test the device on the OR floor while having someone walk around to simulate typical vibrations.

    • Response: agreed. It would be pointless to collect data and make claims on the functionality of the device if the data used to assert those claims is not at all similar to what would be experienced during regular use.

    • Regarding the report: no first person (avoid use of terms like we and us.) Also, past tense should be used throughout. The report is not up to date with the direction that the project is headed in. The first draft should be a fairly good representation of what the final report will look like, include CAD images and other figures to help with visualization.

      • Response: we appreciate the guidance and constructive comments. We are diligently working on making the necessary improvements.

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

    • Isolation legs (still). As previously mentioned we are still looking into this with the help of professionals in this field.

Resources or Information Required but not Available

    • Bed width (typically 50 - 60 cm, but we'll have to confirm to ensure we don't under size the bridge)

Schedule

    • Manufacturing and assembly of the double rotisserie.

    • Manufacturing and assembly of the bridge structure.

Budget (list amount spent and amount remaining)

    • Spent: $798.18

    • Remaining: $801.82

Progress on Report and Webpage

    • We are going to begin uploading CAD files in the near future and posting videos and images to the multimedia page. We've been cataloging the parts being used throughout the design process to upload to the parts page.

    • Currently revising the technical report per instructor's comments. We aim to achieve a much more refined report by February 22nd.