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