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Assembly!
Presentation Video
Safety Sander
A sander that is able to detect potential injuries before they occur and stop rotation to prevent them.
Product Contract
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Storyboard
CAD Images
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Contributors
Melody Yu: (Communications Subteam, Storyboard Subsystem Lead) organized meetings, Storyboard owner and presenter, presentation preparation and template, graphic design
Weixuan Li: (Communication Subteam, Presentation Lead) organized meetings, presentation owner
Sophia Chen: (Communication Subteam, Storyboard Subsystem) Storyboard outline, user persona research, presentation preparation
Hannah Gazdus: (Design Subteam Lead) CAD Lead/Main assembly Owner, organized meetings, set cad standards and documentation, main correspondent between subteams, subsystems, produced CAD Images and Additional Files deliverable, worked on assembly
Andrew Johnson: (Design Subteam, Structures Subsystem) Motor and Motor Housing CAD, Brush CAD, Electronics Housing CAD
Christopher Perrino: (Design Subteam, Structures Subsystem) Base/Support CAD
Rishi Kommalapati: (Design Subteam, Structures Subsystem Lead) organized meetings, structures assembly, Table CAD, Housing CAD, Electronics Housing CAD
Paul Portman: (Design Subteam, Braking Subsystem Lead) organized meetings, Brake CAD and Brake Research
Benjamin Owen-Block: (Design Subteam, Braking Subsystem) Brake CAD, Brake Research
Luke Woodcock: (Design Subteam, Braking Subsystem) Brake CAD, Main Brake Research, Brake Analysis and Calculations, Helped with overall assembly
Magnus-Tryggvi Kosoko-Thoroddsen: (Communication Subteam, Design Subteam, Decoupling Subsystem) Spring Linkage and Lever CAD, presentation preparation, presenter, electronics research
Dylan Ryan: (Design Subteam, Decoupling Subsystem Lead) Spring CAD and animation, Linkage coupling CAD, General Subsystem Assembly
Devin McCabe: (Design Subteam, Decoupling Subsystem) Inertial Disk Assembly CAD and Linkage Coupling CAD
Josh Noguera: (Design Subteam, Decoupling Subsystem, Electronics Subsystem) Inertial and Sanding Disc CAD, Coupling Research, Electronics Sourcing
Rihn: (Design Subteam, Electronics Subsystem Lead) organized meetings, Electronics Schematic and Part sourcing
May Huang: (Communications Subteam, Design Subteam, Electronics Subsystem) Electronics integration and cross team communication, presentation preparation, presenter
Reviewer Feedback
Aditya Ghodgaonkar
Feedback
I'm curious how 150 rel. cap. as the threshold was picked, and if the user load could possibly trigger it during safe operation?
Rebecca Thorndike-Breeze
Feedback
Decoupling system gets at my intuitive concern about this sander -- the inertial consequences of trying to stop the sander so fast. I’m still wondering what kind of recoil would occur and what the consequences would be. Would the machine lurch in any direction? What else could break? This can be dangerous, for user or the machine. Glad to see this is being worked on. / The capacitive sensing works once you touch it, so some contact is inevitable. So the user isn’t perfectly protected. What’s an acceptable amount of friction/burning/injury for a user? (I recall Talon, a safe utility knife that used capacitive sensing. The goal there was major injury -- a user could still get nicked, but wouldn’t lose a finger/thumb.)
Charlotte Folinus
Feedback
Use case: of the 1500 injuries per year, how do they occur? What’s the breakdown of abrasion vs. part getting jammed/sucked in? Product contract: what about reliability? How often should your device catch true positives (can also consider different false/true positive/negative combinations). Does footprint on the counter matter? Your model looks a bit deeper than some disk sanders — will your target users have space for this? CAD/design: your assembly looks to have many pinned joints. A sanding disk rotates and vibrates significantly. Do you have concerns about the device shaking itself apart? Over time, will dust/grit /grease gum up the pinned joints? If either of these is a concern (vibration, gunk) is a concern, perhaps a compliant element could perform the same job with higher reliability/moving parts. It wasn’t clear to me how the user interacts with the device to reset it after it engages. Braking: there wasn’t a discussion of what the decoupling is (this seemed rather abstracted, and I would have appreciated more discussion of how the decoupling happens and how each portion of the device gets stopped).
Chuck Xia
Feedback
The system works together with a combination of decoupling system and the brake. When the skin contact is sensed, the decoupling mechanism triggers, pulls the inertial disk away from the lighter sanding disk. The brake, directly connected to the shaft, starts braking. If I understand this correctly, it is equally if not more important for the decoupling to happen before the brake in order for the brake to effectively stop the sanding disk. From the cad design I am not sure how the bistable decoupling system is triggered and how everything is connected electronically. This length of the shaft from the motor to sanding disk is concerning. Everything is currently attached to the housing which is a cylindrical shell. With the most of the weight (brake & motor) at the end of the housing, the base feels off center. Is the leg and the shell properly supporting the weight. For a longer shaft, you really need the all the component centered. All the little deviation will adds up. The shaft and shell feels like is going to bend at the middle. The motor and the brake should be mount to the base as stiff as possible, not through the cylindrical shell. You want to reduce the distance from the motor to the sanding disk as much as possible. This will also add stiffness to the system avoid vibration. Longer shaft might cause issue. Can the decouple system be shorter? Try brainstorm some way to reduce the distance between the motor to the sanding disk. As the inertial break disengage, there will be friction that rubs away the angle interface. The equal important topics (but something you started to explore in previous model) the reliability of conductivity sensor. The challenges are what if the user is sanding metal? Can the conductive piece (black electronic box) wear out? What if dust get stuck between the conductive piece and the edge of the disk?
Lauren Futami
Feedback
Is the Safety Sander meant to act as a part to retrofit current disc sanders to have this capacitive sensing/decoupling mechanism, or is it an entirely new sander? I was a bit confused about the difference between the heavy flywheel and the light sandpaper disc. A fair amount of disc sanders use sandpaper discs with adhesive backing that's attached to a heftier rotational wheel (the wheel that keeps spinning after turning the sander off, which the user then needs to stop with the hand brake). How much lighter will the sandpaper disc wheel be and will the entire system be able to maintain the sanding fidelity of a current sander? By including an additional decoupling system, will it all be able to rotate accurately and withstand the vibrational disturbances? These questions mostly come from looking at existing disc sanders and seeing the relatively thin profile give to the rotational wheel, I'm just unsure how much is being restrained currently to keep it spinning accurately at its high speeds and how this might get more difficult as you widen this dimension. What was the method to stop the lighter disc wheel after decoupling? After decoupling, how much damage do you anticipate the disc sander to face in the best case and worst case scenario? Do you intend to have the user be able to re-rig the decoupling mechanism and start it up again or would this be a major repair? Great work with the CAD, it looked like a lot of thought went into the design!
Rob Podoloff
Feedback
I'd really like to get more detail on the 1500 injuries per year that are reported for disc sanders to gauge whether your solution would actually help those situations. 500 degrees of rotation before stopping seems like a lot. I would assume that the majority of serious injuries occur not from just abrasion from the disc but from a finger or hand getting pinched between the disk and the bridge. Do your solutions help this scenario?
Josh Wiesman
Feedback
When thinking about the response time of the sander vs human response time to injury it is clear you are confident in stopping the sander "faster" than the human can react, but some damage will be done. How many sander accidents are "jams" vs abrasion type injury. How will you reset the product after trigger? What does that process look like given you have manual and e-type brakes that will all require re-set. Accessories to bench sanders are very popular with hobbyists. Will your product be compatible - what are the most popular accessories? How about compatibility with sand paper discs? Overall: Would like to see a cost of features vs value add. Does the consumer value the safety features enough to pay-up? Great consumer survey question. Will the COGS create a margin / pricing issue? Ability to perform maintenance – how does this perform after extended use? Does the user need to test it? How will the user know it is armed and ready to work? Thinking about failure mode analysis, what are the key concerns that came up in DFMEA and AFMEA review - how will you mitigate these risks of failure?
Micki Dupnik
Feedback
It seemed like a lot of the questions in lecture were based around how the mechanism worked. It would've been beneficial to have a CAD animation or even an animation in PPT to show how things move out of the way or retract. I think you have a lot to think about when it comes to calculations of how much power is required move your parts, how heavy the parts are and what the system reaction physically will be. It would be good to start prototyping with things of similar weight and see how things react. Or try to run a simulation to see how the entire system reacts when the decoupling is activated. Perhaps you'll need an additional attachment to the table to account for any movement. I really liked your CAD images you uploaded and that it wasn't just CAD but with an explanation.