A personal repository of random information in compensation for a fatigued biological computer
Mechanical Hardware, refer child sections below for details
Circuit boards commercial
Circuit boards custom made
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Base CNC X Y Z Router
Ebay CNC router package from .cn Approx US$1600, arrived... (eventually..., late shipping, poor communication..)
Large table
X, Y Z = Nema steppers, have 1.8deg step resolution.
Ball screws = 5mm pitch
Limit switches: unit comes with 6 microswitches in the box but no fittings/wiring
Steppers and leadscrews coupled with 8mm - 8mm (5/16) couplings)
Supplied as ready to run with PSU & Stepper controller PCB
Mechanical changes:
Pick Place Heads
Update 20110829: Conversion from DVD drive headsto Pneumatic is completed
I am using DVD drive head positioning units for pick place heads.
Each DVD drive provides a bipolar stepper driving a horizontal DVD pickup head via lead screw.
I remove the optical components from the DVD head and attach my own spring cushioned pickup head to the DVD head base.
Each head is a 5/32 tube with a industrial syringe tip attached. The tube is spring loaded via U type bracket so the downward stroke does not need to be accurate. This is particularly useful as the DVD drive heads have varying pitch on the leadscrews
Note to self re Motor setup in Mach 3 fot this z axiz
- The DVDs have differing pitch on their leadscrews.
- Mach3 Z axis is set up for 1 step per mm, speed 30,00 acceleration 500
- Heads in the spreadsheet have custom z value per head
USB cameras
On the Y gantry between the 2 rows of 4 Pick Place heads is a downward looking USB camera
On the main baseis an upward looking USB camera
Both cameras are used for calibrating Mach 3 offsets
Vacuum Pumps
Pumps are a hassle.
Tried multiple fish tank pumps, Chinese purpose built vacuum pumps but spit oil and overheat. Tried vacuum ejectors but they run my regular compressor too hard and it overheats
Currently using an old Thomas Industries dual head diaphram 'wobble' pump. Is the best yet but runs a bit hot as well
Stepper Driver PCB
Supplied with the router. Refer child page for additional details. Seems a quite nice PCB. Don't unplug a stepper whilst it's powered up or this PCB will go bang (my accidental empirical testing found that out)
Note on steps per mm calculation for Mach 3:
Steppers ar 1.8 degrees so without microstepping = 360/1.8 per rotation = 200 steps.
If pitch is 5mm, then steps per mm = 200 / 5 = 40
Setting micro stepping to 1/16 = 40 * 16 = 640 steps per mm
20110802: X axis has temporary 24" 10 acme lead screw. Pitch = 2.54mm
Steps per mm at 1/16 microstepping = ( (360/1.8) / 2.54 ) * 16 = 1259.8425...
ok, at 1/8 microstepping:
( (360/1.8) / 2.54 ) * 16 = 629.92126...
Feeders
Although this is a reasonably complicated project, mechanised feeders would make it much more so.
Do we actually really truly need mechanised feeders? Probably not at this time..
I have purchased multiple poor quality 8mm static feeders off ebay approx US$40 per unit (ouch). Each holds 5 x 8mm component tape reels. (Only 8mm tape width is available thus far). These are intended to be used for manual part placement and actually work quite well for that.
Our CNC router is wide enough to take 5 of these units across an end, so 25 x 8mm components are available at one end.
Before each PCB run we will feed the required component tape through and peel back the cover for the quantity of components required for that run.
The maximum no of components per feeder that can be exposed per run is 32 before the heads collide with the reels.
For other components (ie other than 8mm) the intention is to make our own static feeders along similar lines later.
Issues: Pulling the component tape through requires it to to be aligned correctly for pickup operation, I have pins at each end (cutoff syringes) but these are not accurate / repeatable enough. However longer term resolving the centering issue will negate the need for any more accuracy.
Counting components and sequential component offsets:
Of the up to 32 components available on each of the 8mm tape feeders above per run, the GCode increments a counter variable (Mach3 variable) for each feeder after a component is picked from that feeder. For the next pickup from that feeder it's counter is multipled by the component offset to determine the pickup point for that component. So nice and simple.
PCB Holder Array
With the larger boards now getting populated, no more arrays for now
Sounds fancy but is simply a piece of Board with holes drilled at regular intervals. With the use of pegs, allows multiple blank PCB's of the same design to be arrayed for inclusion in a single run.
Driling these holes manually and accurately was a pain. I wish I had a CNC router machine to do it. Hmmm.
As all my smt PCB designs utilise standard set of dimensions (y dimension mounting holes are spaced to a 10mm grid, and x dimension is either 41mm or 92 mm between mounting holes) this allows one peg board to accomodate almost all my SMT designs.
When set for a 0 degrees rotation, PCB must be oriented per its orientation in the PCB design package (So the PCB Pick Place export table is usable)
Parallel port breakout
Splits the Mach 3 parallel port output from the PC per the Mach 3 Parallel Port Mapping
Connects to:
Note that Limit switches and EStop switch are inputs are pulled high on this PCB and switch to ground when activated
Next revision:
8 x Stepper Driver PCB
20110908: now obsolete after heads converted to Pneumatic cylinders
Provides the ability to drive 8 x addressable Quad Half H bridge SN754410 IC's.
2 IO input ports:
Note that RefDes of the schematic and PCB image below dont align as added LEDs in the PCB package first as a quick&dirty(tm)..
Also made a mistake and second enable on all the 754410's (pin 7 maybe) is permanently high, so had to cut traces and hardwire the fix.. (Sch below is correct now but PCB isn't)
Next revision:
Head Vacuum Driver Board
4 x optoisolated Mosfet switches
20110908: Need of these currently, have made 3 of the design below and also one older stripboard version.
Inputs are pulled low. Mosfets switch high side to ground. Can directly drive a moderate DC load, or a mechanical relay or SSR.
Next revision:
Interface PCB
The secret sauce. General purpose PIC18F4610 or PIC18F4620. A PCB I designed / home made a few of back in 2007.
Senses signal changes on inputs B0-B7 and drives Pick Place Head driver board and Vacuum solenoid boards as appropriate.
Refer child page for additional details
Next revision:
Support hardware/components