156B Week 3

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

• • We have prototypes of two designs as of 1/23/2019. The first being of proposed design #1 (see slide #6 of the design proposal presentation) and an alternate being similar to proposed design #2 (slide #9) but with both axes of rotation passing through the center of mass of the test mass. We realized that although prototype #1 combines both rotational DoFs into a single sub-assembly, our alternate prototype performs more reliably and intuitively for the end user when compared to prototype #1.

  • We have made the decision to forego the cantilever and adopt a bridge design to support the microscope instead. This increases structural stability and decreases the level of vibration that would be encountered with a cantilevered 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 and the counter weight needed to properly counterbalance the microscope.

Accomplishments from Previous Week

• • Came up with 2 alternate design approaches as backups in case our initial design prototype does not perform to our expectations.

  • Presented our design proposal to instructor and colleagues.

  • Outline our method of prototyping including what criteria we should be assessed.

  • Updated our report and completed necessary sections for the current week.

  • Review options & feasibility of linear rails.

Goals for Next Week

• • Make final decision regarding rotary DoFs based on prototype performance. (Everyone)

  • CAD file(s) for refined design & begin sourcing parts for final product.

    • Bridge, compressed air storage unit (Ramzi)

    • Double rotation mechanism (Alex)

    • Isolation leg "cup holder" (Chase/Giovanni)

    • Top connection of isolation leg (Giovanni)

    • Linear rail for lifting & counterweight (Chase)

  • Work with our sponsor to at least set a date in which we will be visiting the OR. (Everyone)

  • Specifics regarding compressed air supply (pressure, size of tank, etc.) and means of storage. (Giovanni & Ramzi)

  • Determine material to be used and find a source for the viscoelastic pad which the patient will lie on. (Chase)

  • Determine appropriate mass of counterweight. (Alex)

  • Review OSHA standards regarding lifting loads and reaching overhead. (Ramzi)

Sponsor Comments from Last Meeting and Actions Taken to Address these Comments

• • Due to the holiday on Monday we were unable to meet with our sponsor. Regularly scheduled meetings resume next week.

Instructor Comments from Last Meeting and Actions Taken to Address these Comments

Comments made in person following design proposal presentation (1/17/2019)

• • Consider a constant force spring to counterbalance the rotary degrees of freedom.

  • Response: We initially thought this approach would not be feasible due to the loading. However, considering the desired rotation is 20° in either direction the component of weight that induces a moment would only be roughly 8.5 kg (~19 lbs). Keep in mind this value is only considering the weight of the microscope. Furthermore it would eliminate the need to design our own non circular pulley. We will consider this approach moving forward.

  • Regarding proposed design #2 (see slide 9 of the design proposal presentation): have both axes of rotation going through the center of mass.

    • Response: Although this seems obvious, none of us had even considered it when coming up with this concept! Our alternate prototype concept takes advantage of this and upon conducting initial testing we are pleased with the concept and its performance.

  • Regarding static analysis in design proposal: implementing a numerical method for a more rigorous solution should not be too difficult to carry out.

    • Response: Agreed. We had already been planning to carry this out and the simplified static analysis was meant to serve as an intermediate step to validate our intuition (stronger spring force requires shorter moment arm.) However, as per the response to the first comment this may not be a necessary task to carry out if we choose to utilize a constant force spring.

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

• • Means of rigidly attaching vibration isolation leg to the rest of our structure.

    • Spoke with Thorlabs engineer, the top cap is sealed. Screws held in place using Loctite.

  • Locking mechanism.

Resources or Information Required but not Available

• • Microscope and operating room specifications.

    • We will be following up with our sponsor regarding the microscope CAD file(s) and operating room field trip.

Schedule

• • Once both of the prototypes have been assessed we hope to kick off the manufacturing phase of the project.

Budget (list amount spent and amount remaining)

• • Spent: $154.97

  • Remaining: $1445.03

Progress on Report and Webpage

• • We are working hard to keep the webpage up to date. We are up to date with the report writing and have already completed the "impact on society" section. You can find all of our completed sections here Special care is being taken to document the source of photos taken from our sponsor or alternate internet sources to ensure every person/entity requiring credit receives it.