Circuit Board Ejector Mechanism

The goal of this project is to improve ergonomics for installation and removal of circuit boards in Schweitzer Engineering Laboratories (SEL) products.

=Problem Definition=

Background
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).

Deliverables
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.

Specifically:
 * 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
 * Final report containing full information listed above with detailed design info, analysis and test results

Value Proposition
Project Value Proposition

Specifications
=Project Learning=
 * Must pass SEL vibration testing
 * Must reduce user force to <5 lbs
 * Must be contained inside the chassis
 * Must not contact the circuit board

Refined Designs
=Design Selection= 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.



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.

=Validation=

Design Validation Plan

=Team Members=

=Additional Documentation=

Project Schedule

Gantt Chart

Meeting Minutes

Meeting Minutes Presentations

Informal Design Review Formal Design Review Detailed Design Review

Client Interview