Overview of Status of Analysis, Design, Fabrication, Tests, etc.
We have decided on the tilt mechanism and we are in the process of ordering parts to begin manufacturing and assembly.
The linear slides for our device will be ordered within the week as we have received approval from our sponsor to proceed with this component.
One new obstacle has popped up due to conflicting information from two Thorlabs representatives (our planned vibration leg supplier). Engineers have advised us that our application is suitable for the product and it should work as advertised. However the table coordinator warned us that the freely floating piston could make contact with the base of the leg and significantly diminish isolating capabilities in the presence of lateral forces. Our sponsor has advised us to put this ordering on hold and do more research to confirm the discrepancy.
Accomplishments from Previous Week
Presented proof of concept of our project.
Finalized minor alterations on the "Double Rotisserie" concept and decided to move forward with it.
Came up with a rotation safety mechanism using ratcheting gears to prevent unwanted rotation.
Contacted the OR to get specifications regarding the bed dimensions and movements.
Began researching linear slides and ratcheting gear suppliers.
Completed a bare bones first draft of the report to be more thoroughly completed as we progress with the project.
Goals for Next Week (list names after each item). Use specific and measurable objectives.
Put in purchasing order with sponsor for the following components:
Linear slides: lightweight and compact; to be done this week. (Ramzi)
80/20 aluminum extrusions and fasteners for rotisserie; to be done this week. (Alex)
80/20 aluminum extrusions and fasteners for bridge (Giovanni)
Bearings: looking into specialty suppliers like SKF as opposed to McMaster (Alex/Giovanni)
Casters & sheet metal (Chase)
Get to the bottom of the isolation leg issue. (Everyone)
If they can be used: purchase stock for attachment (Giovanni)
If they cannot be used: draft alternate solutions. (Everyone)
3D print or laser cut ratchet gear and pawl (Everyone)
Begin manufacturing! (Everyone)
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 (2/11/2019)
Look into a better, more effective fastener to attach the load bearing 80/20 beams. A t-nut is probably not robust enough, look into the end fasteners for 80/20.
Response: will do, we agree that a strong and rigid fastener is crucial for structural integrity and for the transmission of vibrations so we will look into the 80/20 end fasteners and some alternatives.
Regarding the issues we encountered concerning the Thorlabs vibration isolation leg: talk to engineers specializing in the design of the legs. Sometimes at Thorlabs you deal with people that don’t really know what they’re talking about when advising you on a certain subject. Also talk to other companies such as Newport and TMC.
Response: we agree that we need to do some thorough investigating to get to the bottom of this issue. We are thankful that we did not pull the trigger on purchasing this component earlier and will be in contact with the appropriate professionals from the above companies. If we find out that we can indeed reliably utilize the isolation legs it will not be a problem since Thorlabs has this product available and ready to ship with no lead time. However, if we find that we cannot reliably use them we need to be able to come up with alternate solutions (we have been brainstorming a few already, just in case.)
Potential alternate approaches to help with the issues regarding the vibration legs could be to make a 3 legged bridge structure.
Response: this is an interesting approach as it would offer more stability and potentially help mitigate the issue (although we are unsure by how much) with the isolation legs. We are also considering using some sort of mini vibration isolation platform.
Regarding the linear slides: The Precision Alliance (TPA) seems to be a good vendor to purchase from. The 17.5 kN load rating seems to be a bit overkill but not an issue since the slides are not extremely expensive. However, the slides presented (SKU: HRC15MN-SZ-1-V0-N-160L - 20x20) are a bit bulky. Look into more low profile carriages to conserve space. Desired stroke length ~40 cm. Get the contact email for TPA so they can be added to the marketplace.
Response: we will look into a more appropriate rail for our application. Thankfully, TPA has a large variety of linear carriages and rail options. We will get the contact email for TPA as soon as possible so they may be added and subsequently purchased from.
Instructor Comments from Last Meeting and Actions Taken to Address these Comments (indicate date of comments and if via email or in person)
Comments made after proof of concept presentation (2/7/2019)
Consider making the pawl in the safety mechanism spring loaded or something similar. As it stands the safety mechanism is still easily defeated if the operator forgets to engage the pawl.
Response: this is a very valid concern, if we were assuming the operator could potentially forget to engage the main locking mechanism we should also assume that the operator would forget to engage the pawl with the ratchet. We would need to select a spring with appropriate stiffness to allow for rigid engagement while still allowing the user to easily raise the pawl when needed. We have also developed a method that allows for gravity to restore the pawl to its proper position, we'll need to settle on one of these in the near future.
With regard to testing the design: using an accelerometer in combination with a fast fourier transform would be good to determine the frequencies and magnitudes.
Response: this is a good suggestion as it takes care of our concerns with our previous testing set up and wouldn’t require any optical equipment that we are collectively not too familiar with. We have started to look into FFT algorithms as well as the fft command in MATLAB. As it stands we still need to figure out how to take the acceleration signal and use that to form a displacement signal via the FFT, but we imagine that shouldn’t be too difficult with some additional research.
Comments from Other Students in the Class (indicate date of comments and if via email or in person)
Comments made via online feedback forms
Keep the amount of words on the slides to a minimum. Highlight key ideas.
Response: we will keep this in mind when putting together future presentations.
A full concept photo or CAD would help the audience understand what we are trying to accomplish.
Response: we agree and we are in the process of integrating all the CAD sub assemblies together into a completed CAD project. Some variables are in the decision phase but we understand the value of clear and complete CAD figures.
Comments made after proof of concept presentation (2/7/2019)
Consider using a worm drive as opposed to the ratcheting mechanism. When the worm is rotating it would engage with the worm gear and cause the assembly to rotate in a given direction. When it is stationary the tendency for the worm gear to rotate backwards towards equilibrium would be inhibited.
Response: we will consider this as it would eliminate the need for the user to continuously engage and disengage the pawl from the ratchet mechanism.
Risks and Areas of Concern
As stated in the overview section, we have recently received conflicting information from two Thorlabs representatives and hope to clarify this information over the next few days. The information pertains to the isolator piston possibly hit the cylindrical shell if a non-axial load is applied. This may drive us to use another vibration leg supplier or another form of vibration isolation altogether.
The linear slides we currently plan to purchase are from a website that is not located on our sponsor’s “Marketplace” meaning this requires special approval from his work. It is a concern since the timeline for this process adds a few days, but it is not a high risk variable.
Resources or Information Required but not Available
Now that we are looking to purchase linear slides and bridge materials, we need to know the width and length of the OR bed to ensure that our bridge can span it’s width. Dr. Shtrahman hopes to get this information for us soon.
Operating Bed Z (vertical) movement: Our design no longer needs z-axis translation, but as we build the bridge we do need to know how high to place the laser, meaning we also need the various bed heights (highest and lowest vertical setting). Multiple bed models are used.
Schedule
Put in PO for slides and rotisserie components.
Start manufacturing/assembly once those components arrive.
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.
Upon receiving feedback, we will update/correct the final draft report, hopefully this coming weekend.
We will also begin adding the relevant CAD files to the website shortly.