Circuit Board Ejector Mechanism
|from left to right: Jaime Ayala, Nikki Imanaka, Emily Chambers, Davis Hill|
|Sponsors||Schweitzer Engineering Laboratories|
|Duration||Fall 2018 - Spring 2019|
The goal of this project is to improve ergonomics for installation and removal of circuit boards in Schweitzer Engineering Laboratories (SEL) products.
- 1 Problem Definition
- 2 Project Learning
- 3 Design Selection
- 4 Selected Final Design
- 5 Validation
- 6 Team Members
- 7 Additional Documentation
SEL designs, manufactures, and supports products and services ranging from generator and transmission protection to distribution automation and control systems. In most of their products, circuit boards are connected by spring clips at the back of the case. These clips cause a large frictional force on the board, making it difficult to install and remove the boards. With the current clips the force required to remove and insert a board is around 40lbs (total).
The scope of this project is to design a mechanism or system that reduces the necessary force to install and remove circuit boards from SEL products.
- Research on existing mechanisms
- Any ejection system (not restrictive to tray ejectors)
- Decision Matrix
- Material selection and cost analysis
- Functional concepts, made using a variety of materials and methods
- Longevity analysis for chosen production material
- Fatigue testing
- Working prototype using production material
- Design validation testing results with various materials
- Insertion force
- Insertion cycles
- Thermal and Vibration
- Production implementation plan - proposed tooling method and supporting business case
- 3D prototype if feasible
- Mold and factor for plastic parts
- 3D prototype if feasible
- Final report containing full information listed above with detailed design info, analysis and test results
- Must pass SEL vibration testing
- Must reduce user force to <5 lbs
- Must be contained inside the chassis
- Must not contact the circuit board
|Over center latches used for wood work made from paint can lid clamps.|
|Idea #1: Rails||Currently in development. The pins on the long arms would sit in rails on the tray and would be able to push and pull the tray in and out of the chassis.|
|Idea #2: Over-Center Mechanism||Currently in development. One end of the mechanism is attached to the chassis, while the other end fits into a slot that can engage and disengage with the tray to push and pull the tray in and out.|
|Idea #3: Screw Rod||Currently in development. Threads would screw into nut at the back of the chassis, pulling the tray with it. The handle telescopes to give greater ease of access and clips into the bottom of the tray when collapsed.|
|Idea #4: Slot Arm||Currently in development. Arm would be attached to back of chassis. The arm would engage with the pin attached to the tray and pull it in. Future plans include adding spring return and movement stop to ensure the arm returns to an accepting position.|
|Idea #5: Y-lever||Not currently in development, but may be a viable option. The Y-lever would hook on the wall-mounted pin and push and pull the tray in by rotating a bar at the front of the tray; thumb operated.|
|Idea #6: Peg slot||Not currently in development; may not be a viable option, but could be worth exploring. The pin would slide in a track on the tray, the pin itself is attached to a arm that slides on a rail. Downside to this design is the pin does not apply force to the center of the tray, which could lead to tray jamming.|
|Idea #7: Gears||Not currently in development; may not be a viable option, but could be worth exploring. The pinion would engage with the rack on the chassis and would move the tray|
|Idea #8: rubber||Not currently in development; may not be a viable option, but could be worth exploring. The rubber engages with the chassis wall and transfers movement to the tray|
|Idea #9: L-Hole||Not currently in development; flawed design, not functional as designed. The tray would be moved by pushing on the edge of slot in tray by rotating arm. Interference with chassis causes non-function.|
|Idea #10: Puzzle Piece||Not currently in development; flawed design, not functional as designed. Interlocking pieces apply force on tray on both insertion and removal. Tolerance necessities in design are higher than feasible limits.|
|Idea #1: Lever and Rails||Design Summary:
This design consists of a basic lever arm to gain mechanical advantage. The design consists of two arms, one connected on the right side chassis wall and one on the left. This was intended to reduce any uneven movement of the tray that would result in unwanted friction. Each arm has a peg that is the contact point for the rails. The peg slides into the rails and outputs the force from the user into the tray. By summing the moments about the pivot point of the arm the mechanical advantage can be easily calculated assuming negligible friction.
This design was intending to reduce bulk in the chassis, but still deliver a substantial amount of mechanical advantage. The rails sit right up against the bottom side of the tray and all the way up to the front of the chassis. This ensures that the device is easily accessible. The design of the rails is meant to have a wide mouth area where the peg can slide into and then slide deeper into the parallel section of the rails where force will then be applied. The walls of the mouth were then designed to be smooth and curved to allow movement of the peg into the parallel section more effectively.
To use this design to eject a tray, the user grabs on to both arms and pulls outward. This ejects the tray from the connectors and when the tray is pulled the rest of the way out the pegs slide out of the rails easily avoiding any obstruction. To insert the tray back into the chassis, a little more thought is needed. The lever arms must be at a minimum angle to the tray in order for the pegs to slide correctly into the rails. Once positioned, the user then slides the tray all the way in until the tray hits the connectors. Then, the user grabs both arms and pushes inward to insert all the way. The arms should then be parallel to the front of the tray and mostly hidden from sight.
|Idea #2: Over-Center||Design Summary:
This design utilizes mechanical advantage generated by an over-center mechanism. Current models utilize two levers mirrored about the central axis parallel to the side of the tray. Double levers allow for balanced forces from left to right.
The user can use both hands to either push (to close) or pull (to open) the lever arms simultaneously. These arms interact with the linkages to create a mechanical advantage, either pulling or pushing the tray with user input.
|Idea #3: Gears||No refinement since preliminary design. This system uses a gear and rack connected to a simple lever to provide the mechanical advantage to eject the trays. As there is one gear/rack on each side, the user is able to modulate the input force to counteract the unsymmetrical forces on the tray. Alignment of the gears is an issue and tolerances may be an issue.|
|Idea #4: Rubber||No refinement since preliminary design. This system uses a rubber "foot" connected to a simple lever to provide the mechanical advantage to eject the trays. As there is one "foot" on each side the user is able to modulate the input force to counteract the unsymmetrical forces on the tray. The main concern with using rubber is that rubber is very unpredictable and will most likely dry out over time and shrink.|
|Idea #5: Y-Rod||No refinement since preliminary design. This mechanism utilizes a lever to eject and insert the tray. Two "Y" pieces apply force on a peg on the side of the chassis to eject the tray. Geometry has a 1:1 mechanical advantage and therefore does not assist the user.|
|Idea #6: L-Hole||No refinement since preliminary design. This system uses a simple lever to push on the edges of a slot in the tray. The geometry of the lever can be easily adjusted to create the force required for removal of the tray, but the current geometry does not allow for full removal of the tray.|
|Idea #7: Slotted Arm||This system uses a simple lever to push on a pin attached to the tray, the lever in its current format creates the necessary force to eject/ insert the tray, and the design can be easily modified to have spring loaded return for positioning. Because there is only one lever per tray canting is a large concern due to the unsymmetrical friction on the tray.|
|Idea #8: Peg Slide||No Refinement since preliminary design. This system uses a pin that pushes on a ramped channel to insert/ eject the tray from the chassis. The ramp can be increased or decreased to output the force necessary to supply the proper amount of force. The pin is attached to an arm that slides on a track. Placement and fit of the track is an issue as the track may interfere with removal of other trays.|
|Idea #9: Threaded Rod||This system uses a screw to apply the necessary for insertion/removal of the tray. The handle itself telescopes for easier access and collapses when not in use. The pitch of the threads can be adjusted for the needs of the client. Because there is only one rod per tray canting is a large concern due to the unsymmetrical friction on the tray.|
|Idea #10: Linkage System||No refinement since preliminary design. This system is an alternate design using a over-center mechanism. At current state the linkage is permanently attached to tray, not allowing the card to be removed from chassis. Two linkages would be installed on each side of the tray and would allow the user to modulate force to overcome any unsymmetrical friction forces.|
|Idea #11: Cleat and Claw||This system utilizes a simple lever. It uses a claw and the edge of the card as a cleat to provide insertion and ejection. Current model did not meet space requirements. Two levers on the side of the chassis allows for user modulation of input force to overcome unsymmetrical friction force. Preliminary idea worked well using wood model but did show some signs of uncomfortable using the model.
A decision matrix was used to narrow down the list of eleven refined ideas to one final idea. Through the use of the online priority tool the team was able to come up with the following weights for each category of the decision matrix shown below. The weightings represent percentages and all the category weightings should add up to 100 with higher values signifying greater importance.
Using these weightings, each of the 11 designs were ranked on a scale of 1-10 with 10 being the perfect design and 1 being the worst. Descriptions of each category at the high end of the spectrum are as follows: • Ergonomic – Comfortable, causes no pain, repetition causes no harm
• Operation Time – Minimizes time to complete task, very fast
• Ease of Access – Up front, no reaching or squeezing into small spaces needed
• Simplicity – Easy to understand without prior instruction
• Low Profile – Takes up minimal available space within chassis
• Cost – Relative price of materials needed, higher volume= higher price, metals>plastics
• Repairability – Minimal cost and time to repair parts
• Complexity of Design – No complex parts (gears, threads, high tolerances)
• Tooling Cost –cheaper tooling/fabrication and minimal set up time
• Modification Complexity – Simple, low cost, and minimal modifications needed on existing components
The decision matrix assumed that all designs being considered had met all SEL requirements. Some ideas scored high but through preliminary prototyping failed to meet the main requirements of the project. These ideas are highlighted in red in the table below and were not considered moving forward. From the remaining ideas, the top idea came out to be the Rails design followed closely by the Over-Center Mechanism and the Threaded Rod designs.
Selected Final Design
The Rails idea was decided on for the final design, it showed the most benefits, namely, ease of use, simple individual parts, and is available for multiple manufacturing processes. The next step of the design process is to select the manufacturing process for the parts, while keeping in mind the clients needs. The processes available that suited the needs of the project and client are sheet metal fabrication and injection molding.
The project sponsors at SEL are proponents of injection molding, because of their ability to make these parts on-site, which lowers the overall cost of manufacturing. Modifications were made to the parts to factor in limitations with the process, particularly, draft angle and wall thickness, and filleted corners.
Shown above is the final iteration of the injection molded parts. The main Arm adopted a I-Beam structure for torsional rigidity and bending stress resistance, the Connector hinge piece became an enclosed box for structure, and the Rail block was hollowed out with webbing to satisfy wall thickness restraints and strength requirements.
Sheet Metal Fabrication
SEL is also a proponent of sheet metal fabrication as the company already has a contractor for sheet metal fabrication.
Shown above is the final iteration of the sheet metal parts. The main Arm has a folded finger tab and a tab running the length the arm for rigidity, the Connector hinge piece has a stop folded to position the arm in the correct position for insertion, and the Rail block is laser cut easily.
|Jaime Ayala||Mechanical Engineeringemail@example.com||Twin Falls, Idaho||Meetings/ Organization|
Jaime is 23-year-old Mechanical Engineering Student at the University of Idaho. He is originally from Southern Idaho where his family works on a farm. He plans on graduating from the University of Idaho with a Bachelor’s of Science in Mechanical Engineering. After graduation, he plans on working out in industry for a few years and work towards attaining his professional engineering license. Some of his hobbies are Motorcycle riding and anything else that goes fast. He is 100% reckless when it comes to riding his motorcycle and enjoys it a great deal.
|Emily Chambers||Mechanical Engineering||Emily@chambersohana.com||Meridian, Idaho||Budget/ Meeting Minutes|
Emily Chambers is a senior in the mechanical engineering department, graduating in the spring of 2019. She grew up in Meridian, ID, often working with her father in the garage rebuilding a 1972 Chevelle. She enjoys working with solid modeling software to prove concepts before implementing them in the physical world. After graduation Emily plans to join industry, working towards an MBA and PE license. She is a member of the Vandal Marching Band, and in her spare time loves playing the piano and flute.
|Davis Hill||Mechanical Engineeringfirstname.lastname@example.org||Coeur D'Alene, Idaho||Client Communications/ Wikipage|
Davis Hill is a senior mechanical engineering student graduating with a B.S.M.E in May 2019. His academic interests include computer simulation and vehicle testing. After graduation he plans to work in an industrial environment, hopefully in a process manufacturing company. He also plans to receive an MBA and PE certification within 4 years of graduation. His hobbies include playing guitar, dabbling in analog circuits, fixing his ever-broken truck and spending time outdoors.
|Nikki Imanaka||Mechanical Engineeringemail@example.com||Kaneohe, Hawaii||Team Leader|
Nikki Imanaka was born and raised in Hawai'i on the Island of O'ahu. Nikki is a Mechanical Engineering student at the University of Idaho and a member of the Women's Swimming and Diving Team as a spring-board diver. She hopes to gain designing and possibly quality assurance experience in the work force upon graduating in May 2019 with her B.S.M.E. Nikki considers herself adventurous and loves trying new things. Some of her hobbies include surfing, hiking, hunting, art, diving, piano, and more. She is a visual learner and loves working with her hands to create physically real ideas. Through her passion to learn, she is excited to be working on her CSWP-Adv certificates, gaining shop experience, and to be taking a beginning welding class next semester!