quick release mechanism

Mission

Design and implement an emergency quick release solution on a medical device for removal of the therapy.

Elements

(1) Push/Pull Toggle Clamp

(2) Precision Linear Shafts

(3) Oil Embedded Bronze Sleeve Bearings

(4) CNC Machined Aluminum Components

(5) Clevis Pin (pivot)

(6) Single Piece Motor Bracket

Details

This project to design, develop, and implement a release mechanism was a critical step towards finishing the design of a much larger electro-mechanical system. While developing the rest of the system in parallel, the team was made aware of a requirement to have a "quick release" system that would override the entire system in the case of an emergency. The design had to fulfill a few requirements:

The mechanism must be purely mechanical in the event of a power outage
The quick release must deploy/activate in under 5 seconds
All motions must be user friendly, intuitive, and relatively low force
No tools or accessories would be required
The completed design would be low cost

To begin the process of designing a solution, I first held a relatively large brainstorm to gather as many ideas as possible. Concepts ranged from incredibly vague to detailed, extremely complex to straightforward, and expensive to dirt cheap. Sketches were gathered, grouped, and then the top categories and concepts were discussed in further detail with the group to provide more insight to better understand.

Once I had organized, grouped, and reviewed the top concepts produced in the brainstorm activity, I down-selected to two concepts with respect to the following criteria:

Development Effort
Usability
Complexity
Material Cost
Robustness
Speed

A toggle clamp design and a drawer pull design were the two winners to be further developed into physical prototypes. Initial crude prototypes were created to get an early read on whether or not the ideas were truly feasible. The "drawer pull" concept involved a single ramp on either one side or both sides of the device drawer and a pivoting triangle. The triangle would be on a pivot and would catch on the drawer as it was pulled out. Due to the location of the pivot point, the triangle would cause the clamping piece to raise up high enough to clear the contents of the device as the user pulled the drawer out manually. An initial prototype was created on a FDM 3D printer that could be retrofitted to the existing prototype. The design was iterated upon to include "teeth" for biting, which acted almost like a clutch mechanism. The large benefit of this design is that there was only a single motion required from the user...just grab the drawer and pull it out! However, there were some drawbacks such as the large amount of force required and that it might not be very intuitive based on the device's overall design. In parallel to the "drawer pull" mechanism, I was also developing a "toggle clamp" design. The toggle clamp design effectively took an off-the-shelf Destaco-style push/pull toggle clamp and utilizing the motion to pull a linkage backwards, which causes the clamping mechanism to raise up and allow the user to open the drawer to easily retrieve the contents. For the first pass, I simply made some modifications to the existing prototype on our manual Bridgeport mill to allow for assembly of the toggle clamp. The design seemed to work very well, so I went ahead and optimized it for ease of access, intuitiveness, and cost reduction. While updating the toggle clamp quick release design, I was able to actually reduce the part count of this subsystem by 10 components and make assembly much easier and quicker. After lots of side by side testing with requirements of lift height, I needed to compare the two with a Pugh matrix to provide documentation and direction on which design to fully integrate into the device for production.

Using the same requirements from the initial brainstorm down-selection, I created a simple Pugh matrix to compare the two concepts to the current design (used as a control). Weighting of each category was reviewed with the team as well as the client to ensure that I was placing importance in the right places. After comparing the two, it was clear that the Toggle Clamp mechanism design was a better solution to implement into production.

Once all initial prototyping, testing, and final comparisons were complete, the next step was to design for alpha prototypes and low volume production. Before building the mechanism into the full CAD database, I first started with a search of push/pull toggle clamps to ensure that I had the best option with respect to throw distance, overall size, and cost. I needed to ensure that I could account for all sizes of contents that the mechanism would be acting on by means of sufficient throw distance, find a small enough package to fit inside the overall device, and select a cost effective off-the-shelf option. With this in mind, I moved towards a panel mounted push/pull toggle clamp from a well known supplier so that I knew it would be readily available, and I was able to check drawings to ensure fit and function before even purchasing the toggle clamps. In addition to this research, I also created a simple dynamic 2D sketch mechanism within Solidworks so that I could guarantee that the quick release mechanism would be able to pull the clamping portion of the device high enough to allow the user to retrieve the contents for all package sizes that the contents were available in. This was a great gut check and verification prior to all the work to fully implement the design into the full product. Many of the components used in the initial prototype testing were able to be moved into the production design since the oil embedded sleeve bearings worked very well on the stainless steel shafts for smooth motion in order to reduce binding or sticking. While most of the design revolved around functionality, I always try to keep an eye on the usability and user-centric part of the design. With this in mind, I added some features into components to aid in the intuitiveness of what state the clamp was in. First, I designed a cover that would allow for an instruction label to be placed on in the event of an emergency. This provided space for instructions, an aesthetic cover, protection of the mechanism, and finally ensured that the device would be properly set up if the cover was on. Once the cover was removed, the user would simply rotate the lever until it hit a hard stop. Rather than allowing a full 180 degrees of rotation, I designed in hard stops so that the handle of the quick release would be sticking out at a funky angle if the device was not set up for normal function. This provided a visual cue for the user to help understand whether something is in its normal resting state, or if the quick release was activated and needed to be re-set. Once everything was designed in, fully prototyped in production materials, and tested on a number of Alpha prototypes, I knew the design was robust and received great feedback from the internal team, the client, and potential users. Next step...full production!