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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 - PowerPoint PPT Presentation
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P14311: PCB Isolation Routing System
Subsystems Review
Agenda
1. Review of Systems Level Design2. Determination of Subsystems3. Critical Subsystems Review
a. Vacuum Table Assemblyb. Transverse Feed Assemblyc. Vertical Spindle Feed Assemblyd. Electrical Architecture
4. Risk Management Update5. Schedule Update
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
o Long lead times
o Expensive
o Limits circuit refinement
o Students not involved in process
Selected Concept
Selected Concept
Subsystems Definition
Priority Level Subsystem # Subsystems Name Description
31
Debris Management SystemRemoves, isolates, and contains copper/substrate debris
1.1 Pressurized Air System Delivers pressurized air to the system
92
Vacuum Clamp AssemblyUses vacuum force to secure/align PCB copper bare board to mill base plate
2.1Registration Subsystem
Makes sure board is aligned with a zero zero reference point in place
93
Transverse Feed AssemblyEnergizes and Controls motion in the X-Y axis in defined increments
94
Vertical Spindle Feed AssemblyEnergizes and Controls motion in the Z axis in defined increments
Priority Level Subsystem # Subsystems Name Description
35
Enclosure AssemblyCreates a physical barrier between the operator and the milling/debris subsystems
3
5.1
Safety SystemInterlock circuitry to shut off machine if physical barrier is disrupted (the saftey electrical circuit becomes open)
96
Control System/Controller SystemTakes commands from the computer and output signals to control the various motors.
6.1
Feedback Sensor System Monitors key elements of the process and provides feedback to the user
6.2Control Display System Displays feedback and information to operator
37
Support Assembly Foundation for entire machine consisting of base, column, and headstock
38
Milling Head or Spindle Assembly Spindle, Mounts, Collets, Bits, etc
99
Power System Conditioning and distributing across assemblies
310
Software Interface system Mach3, G code, optimization code\
1 10.1 Optimization
Critical SubsystemsPriority Level Subsystem # Subsystems Name Description
9 2 Vacuum Clamp Assembly
Uses vacuum force to secure/align PCB copper bare board to mill base plate
9 3 Transverse Feed Assembly
Energizes and Controls motion in the X-Y axis in defined increments
9 4 Vertical Spindle Feed Assembly
Energizes and Controls motion in the Z axis in defined increments
9 6Control
System/Controller System
Takes commands from the computer and output signals to control the various motors.
9 9 Power System Conditioning and distributing across assemblies
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
Vacuum Clamp- Shopvac vs PumpShopvac
+ 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
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
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.
Shop Vac Vacuum Clamp Demo
Registration System on Vacuum Clamp Assembly
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
● 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
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
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 systemso Technical suggestions for our project from a Engineer Support
Representativeo Gave a cost estimate for their system
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.
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
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
Gantry System Cost Estimates
• DIY CNC Gantry Kits for as low as $350o This handles motion
in the X and Y while also including the structural support for Z motion and Spindle.
Zen Toolworks CNC DIY Kit
Gantry supports are manufactured from PVCModulus of Elasticity 370 – 409 ksi
Easily replaced with Aluminum plateModulus of Elasticity 10,000 ksiRefine gantry height
Stepper Motor Calculations
Equations from Shigley’s Mechanical Engineering Design (8-1) and (8-2)
Spindle Motor Considerations
• Feasibilityo Air motors
- Infrastructure (air dryer, supply regulator, etc.)
- Rare and Expensive (All supplier quotes over budget)
+ Easily reach speeds of 100,000+ RPM
o DC motors + Simple implementation (voltage or PWM speed control)
- Low speed (12,000 RPM unless specialty and over budget)
o 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)
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
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
Control Software and Breakout Board Selection
● Considered Software Options● Software Breakdown● Hardware Breakdown● Concept Scoring● FInal Selection
Software Breakdown (Top Three)
* Software and Hardware included in one price
Hardware Breakdown (Top Three)
* Software and Hardware included in one price
Concept Scoring
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 Controller MK2/4CNC USB Software
120V,60 Hz
System Architecture - Power Distribution
Breakout Board
Main Logic Board
DC Power Supply
X Motor Driver
Y Motor Driver
Z Motor Driver
Wall Outlet
120V,60 Hz 12-36V, DC
6V
Wall Outlet
Palm Router
System Architecture - Controls
Breakout Board
Main Logic Board
Computer
X Motor Driver
Y Motor Driver
Z Motor Driver
Router Motor Driver
USB
Vacuum System
Interlock System
Breakout Board - Processes design file, converts file to motor control signals
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
Main logic Board - Monitors all systems (ie halts operation if vacuum table is off, interlock open)
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:o Modifying router circuitryo Microcontroller: Using a microcontroller with
PWM channel and H-bridge configuration.
Preliminary Family Tree Diagram
PCB Isolation Routing System
Supply / Interconnect System
Milling Machine Assembly
Shop Vacuum PC
Zen Toolwork
s CNC DIY Kit
Safety Enclosu
re
Control Architectur
e
Router Assembl
y
120 VAC
Power
Vacuum
Piping
USB / Serial Cable
Pressurized Air Line
Updated DMC Estimate
Risk Analysis Update
Schedule Update
Next Steps