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P14311: PCB Isolation Routing System

P14311: PCB Isolation Routing System. Subsystems Review. Agenda. Review of Systems Level Design Determination of Subsystems Critical Subsystems Review Vacuum Table Assembly Transverse Feed Assembly Vertical Spindle Feed Assembly Electrical Architecture Risk Management Update

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P14311: PCB Isolation Routing System

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  1. P14311: PCB Isolation Routing System Subsystems Review

  2. Agenda • Review of Systems Level Design • Determination of Subsystems • Critical Subsystems Review • Vacuum Table Assembly • Transverse Feed Assembly • Vertical Spindle Feed Assembly • Electrical Architecture • Risk Management Update • Schedule Update

  3. Problem Statement • RIT students need rapid prototyping for creation of unique circuit boards • Requires multiple revisions to perfect each circuit board • Currently each iteration must be created off campus • Long lead times • Expensive • Limits circuit refinement • Students not involved in process

  4. Selected Concept

  5. Selected Concept

  6. Subsystems Definition

  7. Critical Subsystems

  8. Vacuum Clamp Assembly • A system that creates negative pressure to hold down work pieces during machining • Will allow for easy set up by user • Work pieces will be held down after being cut • Collect debris being cut from board • Corrects for board warpage

  9. Vacuum Clamp- Shopvac vs Pump Vacuum Pump + Quieter than shopvac - Can be expensive - Very low flow rate(~10 cfm) - Could not have any leaks in system - Could not allow debris to reach vacuum pump Shopvac + More affordable + Very high flow rate(150+ cfm) + Could share vacuum with debris management system. + Allows for leaks in system + Also acts as a debris management system - High noise level

  10. Vacuum clamp calculations About 2.5 lbf is supplied from each hole. In a feasibility test, our prototype had 16 holes. A total of 40 lbf was applied to the PCB.

  11. Shop Vac Vacuum Clamp Demo

  12. Registration System on Vacuum Clamp Assembly • Particularly important for zeroing a double sided PCB board • Ability to hold the board more securely and flip the board halfway through • Pins help restrict translational degrees of freedom and z-axis rotation and allow for realignment when flipping the board over • Pin holes can be incorporated into the PCB design • At least 2 pins needed, possibly up to 4 Process 1.PCB is secured to vacuum table 2.A number 57 bit (42 mil) is inserted into the mill and can drill holes the size of a push pin 3.Drill alignment holes for reference pins 4.Stop the mill and insert pins through holes into sacrificial layer 5.Mill one side, flip the board over, and re-pin

  13. Transverse Feed Assembly Motion in the X and Y direction was initially planned to occur exclusively in the base plate of the mill • Mount the vacuum table on two linear slides perpendicular to each other • Wire Management will be more manageable than with a gantry system • With less movement of the spindle head, likely to be more accurate

  14. Analysis of XY Base Plate motion • Initial Vacuum Table Weight Estimate- 40 lbs max • Contacted Isel USA, a linear slide company to get more information about their rail and table systems • Technical suggestions for our project from a Engineer Support Representative • Gave a cost estimate for their system

  15. Transverse Feed Cost Estimates • Isel USA systems cost upwards of $3000- way over our budget • Other sources- these types of systems are more expensive than expected- $350 for just the slides, around $700 for entire structure.

  16. Mobile Bed vs. Mobile Gantry Mobile Bed Design +Typically found on smaller CNCs (PCB, engraving, etc.) +Sturdy, will not flex under load +Better wire management - Requires a larger footprint - Must Consider moving the weight of the table - Hard to support router/spindle

  17. Mobile Bed vs. Mobile Gantry Mobile Gantry Design +Can be designed to be as sturdy as a fixed gantry +Most popular for DIY CNC routers +Can be arbitrarily large- Must consider weight and size of the gantry - Must account for deflection and vibration

  18. Gantry System Cost Estimates • DIY CNC Gantry Kits for as low as $350 • This handles motion in the X and Y while also including the structural support for Z motion and Spindle.

  19. Zen Toolworks CNC DIY Kit • Gantry supports are manufactured from PVC • Modulus of Elasticity 370 – 409 ksi • Easily replaced with Aluminum plate • Modulus of Elasticity 10,000 ksi • Refine gantry height

  20. Stepper Motor Calculations Equations from Shigley’s Mechanical Engineering Design (8-1) and (8-2)

  21. Spindle Motor Considerations • Feasibility • Air motors - Infrastructure (air dryer, supply regulator, etc.) - Rare and Expensive (All supplier quotes over budget) + Easily reach speeds of 100,000+ RPM • DC motors + Simple implementation (voltage or PWM speed control) - Low speed (12,000 RPM unless specialty and over budget) • AC motors +/- Inexpensive and common (many vendors, but little documentation, no warranty) - High complexity (VFD speed control, could be purchased) + Acceptable speeds (24,000 to 48,000 RPM)

  22. Reconsideration of Commercial Routers + Affordable at around $200 + Available at any home improvement store + Speed of 16,000 to 35,000 RPM + Mounting documentation available from gantry manufacturer + Aftermarket collets with published TIR < 0.0004” + Can control speed with PWM or built in dial Bosch PR20EVSNK Colt and aftermarket collet from precisebits.com

  23. Spindle Speed and Feed Rate • Low Feed Rate and High Spindle Speed for small mill bits (< ~0.020”/0.5mm) • High Feed Rate and Lower Spindle Speed for larger mill bits ( up to 0.125”/3.175mm) • For a 0.015”/0.38mm mill bit on .5 to 1 oz Copper: 10 to 40 in/min @ 24,000 to 60,000 RPM • For a 0.625”/1.6mm mill bit on .5 to 1 oz Copper: 60 in/min @ 24,000 to 40,000 RPM

  24. Control Software and Breakout Board Selection • Considered Software Options • Software Breakdown • Hardware Breakdown • Concept Scoring • FInal Selection

  25. Software Breakdown (Top Three) * Software and Hardware included in one price

  26. Hardware Breakdown (Top Three) * Software and Hardware included in one price

  27. Concept Scoring

  28. Final Selection It was a difficult and arduous process, but with aid from the Concept Scoring exercise, we ultimately chose to go with the CNC USB Controller Package CNC USB Software CNC USB Controller MK2/4

  29. System Architecture - Power Distribution Wall Outlet DC Power Supply 12-36V, DC 120V,60 Hz X Motor Driver Y Motor Driver Z Motor Driver Wall Outlet Main Logic Board 120V,60 Hz Breakout Board 6V Palm Router

  30. System Architecture - Controls Breakout Board - Processes design file, converts file to motor control signals Main logic Board - Monitors all systems (ie halts operation if vacuum table is off, interlock open) Vacuum System Main Logic Board Computer USB Breakout Board Interlock System Motor Drivers - Takes motor control signals and amplifies to usable form to drive motors Router Motor Driver - Takes signal and modifies it for variable speed Router Motor Driver X Motor Driver Y Motor Driver Z Motor Driver

  31. Router Speed Control • Radial motion in our machine will accomplished using a palm router. Different speeds are required for drilling and milling. Here are some options being considered: • Modifying router circuitry • Microcontroller: Using a microcontroller with PWM channel and H-bridge configuration.

  32. Preliminary Family Tree Diagram PCB Isolation Routing System PC Shop Vacuum Milling Machine Assembly Supply / Interconnect System Zen ToolworksCNC DIY Kit USB / Serial Cable Router Assembly Safety Enclosure Control Architecture Pressurized Air Line 120 VAC Power Vacuum Piping

  33. Updated DMC Estimate

  34. Risk Analysis Update

  35. Schedule Update

  36. Next Steps

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