Senior Design Presentation

bendembarrassElectronics - Devices

Nov 2, 2013 (4 years and 5 days ago)

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A CNC Machine that can be used not only by manufacturers but also
by small scale hobbyists at costs much less than competitors.


Three forms of communication either through serial port, Ethernet,
or USB jump drive


Controllable through a specially designed hand pendant


Multiple tool heads for different applications including milling, paste
dispensing, and air brushing


Able to move at high speeds with longer working life compared to
other relative machines



Other machines perform only one specific task


Loading different programs by current methods result in longer
machine down times and loss in revenue.

Base

Y Axis

X Axis

Z Axis

Base

Table Specifications:


Table Work Area: 1160 in
2


Maximum Part Weight: +18 lbs


Table Supported by Rail: 0.375 in x 1 in


Y
-
Axis Rail Design:


Length: 38 in


Weight Supported: 40 lbs


Length and Weight was significant


Guide system selected: Supported rail

Y Axis

X Axis

Designed Considerations:


5.5 lb cutting force


10 lb tool head


100
lb.in

moment due to weight


75
lb.in

moment due to cutting force


Design Specifications:


X
-
Rod Diameter: 1.18 in (30mm)


Rod Spacing: 4 in


Supports 37.8 lbs/rod


Maximum deflection: 0.001 in


System Loads:


26.70 lbs, 15.63 lbs, 22.53 lbs


Alternative Design:


4 Rods with 15.63 lbs/rod


Rod Diameter : 1 in


Cost increases

x

Rod

1:
26.70

Rod 2:
15.63


y



Rod

3:
22.53

Z Axis

Z
-
Axis Design Considerations:


Minimize moment about x
-
axis
ballscrew


Guide system selected: Versa rails


Moves tool head closer to center of x
-
axis


Alternative Design:


2 Guide Rods


Increases moment

Ballscrew

Drive Specifications:


Lead: 0.2 in/rev


Diameter: 5/8 in


Supports: Ball bearing & Thrust bearing
block assembly


Thrust Forces:


Acceleration 28.9 lbs


-
Static friction and acceleration force


Constant Velocity 18.8 lbs


-
Only kinetic friction




Tool Head Options:


Spindle


Paste dispenser


Motor Drive Assembly


Purpose: Power Motors to drive
ballscrews
,
providing motion in 3 dimensions

Motor Design Requirements


Provide a minimum 20oz.in of torque at a
speed of 4 in/sec. Required to move each
axis.


Be cable of providing a minimum torque
safety factor of 100%.

Motor Specifications

Motor sizes:


276
oz.in

(X
-
axis & Y
-
axis)


166
oz.in

(Z
-
axis)

Motor Requirements:


2.8 amps/phase


Voltage of approx. 48 volts for a torque of
80oz.in at 4in/sec.


Motor Driver Considerations

Requirements:


step and direction inputs to move
motors


Cable of driving motors at a
minimum of 2.8 amps.


Surface mount chips to save
space.


Selected:


Allegro A3986 [micro
-
stepping
sequencer]

Motor Driver Considerations

Other design requirements


Low power dissipation:
Mosfet

H
-
Bridge
with very low on resistance. (.050 ohm)


Current sense resistor: very low
resistance (.043 ohms)



Traces :
2 oz vs. 1 oz copper.


To Provide low trace inductance to
reduce high voltage spikes from
destroying chips. Provide low power
dissipation for motor traces.



Power Transformer selection:

provide
power to motors that would fit into small
cabinet with minimum stray magnet
fields.



System monitoring and fault
identification:
fuses and LEDs added to
aid trouble shooting and protect circuit

Features


Pulse width modulation, MOSFET H
-
Bridge


Motor size from 2 to 4.7 amps


Optical Isolation for all inputs


Full, Half, 1/4, 1/16 step resolution


Over Current Protection


Over temperature and under voltage protection


Fuse Blown Indicators (3 LED’s)


5 V supply Good LED


Outputs to Controller


Drive Board Ready Signal


Drive Board Fault Signal


Motor Power Supply Ready Signal



Ethernet Microprocessor


ENC624J600 (Microchip Technology)


Communication Controller


PIC24FJ256GB110 (Microchip Technology)


Motion Controller


PIC24HJ256GP610 (Microchip Technology)


PIC24HJ256GP610 PIC24FJ256GB110 ENC624J600

24 bit 100 pin micro
-
processor is used to control the communications for the CNC.

Any data that comes into the
the

Controller board goes thorough the Communication
micro controller.

Specific requirements:

1


SPI

2


UART

8


Data Pins

16


Address Pins



Connections to the Com controller:



RS232


Serial


USB to Go


Ethernet


VGA(Output)


64 pin micro
-
controller specifically for Ethernet implementation.


No programming was needed for this chip. It comes pre
-
configured to take Ethernet
data. This micro chip connects directly to the Com Controller


Specific Requirements:


1


SPI


External Connections:




RJ45 Connector



24 bit micro
-
controller used to take the data from the communication micro chip and
distribute Data to the motor driver board.


Specific Requirements:


2


SPI (to communication)

1


UART (to Pendent)

8


Data Input Pins

4


External Interrupts



Case

Screen


Requirements


LCD Screen


Four buttons for accessing different function
screens, accepting a command, canceling a
command, and switching the axis between y and z
on up and down directional buttons


Four buttons to change direction on x, y, or z axes


Feed pot dial to increase or decrease feed/speed
rates


Casing


Upper section will have a width of
5 inches and a length of around 2.5
inches


Placement for LCD Screen, Function
button, Accept Button, Cancel Button,
Axis Switch Button, and Feed Pot
Override


Lower section will have a width 3
inches and a length of 3.5 inches


Placement for X, Y, and Z directional
buttons



System Diagram


LCD Screen


PIC 24 Microcontroller


DB9 and MAX32


Receive and transmit information
from main controller system to
pendant system


Voltage Regulator


Input of 5 volts to make controlled
output of 3.3 volts


Feed pot/Potentiometer


Control of feed/speed rate


Clock chip


Steady, constant flow of
information


Switch buttons



PCB Layout


Top Layer


LCD Screen


Top four buttons are function,
accept, cancel, and axis switch


Bottom four buttons are four axis
direction movement


Left and right control x axis


Top and bottom control y or z axes


Bottom Layer


Remaining Components


Tightly packed to prevent losses


Connector at bottom to attach to
main controller system



Screens


Main Screen


Upper left box contains current x, y, z,
and acceleration axes


Lower left box contains circles for limit
switches which will either be red/green
to show on/off


Upper right box contains current
adjustment of feed pot ranging from +
-
50 % of the rated value


Lower right box displays the current
state of the machine which can be jog,
idle, or run


Other Screens


All Sub Screens


Offsets Screens
-

Home, Park, Work
Offset 1, Work Offset 2


Soft Limits Screens
-

Upper and Lower


Parameters Screens
-

Machine
Parameters, TCP/IP Configuration,
Communications Port


Flash Drive Screen



Mechanical Total

$ 2,406.89

Electrical Total

$ 779.76

Grand Total

$ 3,186.65

The Mechanical Total comprises of:


Frame


Bolts


Ballscrews


Rods


Shafts
The Electrical Total comprises of:


Circuit Chips


Driver Boards


Controller Boards


Pendent

Step

#

Step

Description

Hours

1

Place

parts

on

boards

4

2

Table

Assembly

20

3

Gantry

Assembly

15

4

Tapping

and

Drilling

13

5

Electric

Box

Assembly

8

6

Assemble

Systems

4

7

Testing

5

Total

Hours

69

Each component requires different time
frames to finish each subassembly. The
construction is simple once all subassemblies
are finished, and the machine can be fully
assembled in a 4 hour period with a three man
team. The machine is ready for operation after
testing is complete.
Dr.
Haibo

Wang
-

Faculty Technical Advisor

Mr. Mark Hopkins
-

Technician/ Field Engineer for Allegro Micro
-
devices

Mr. Howard Everton
-

President of
Norva

Plastics

Barb
Saathoff
-

Representative from
Dytronix

Tim
Attig
-

Mechanical Shop Machinist