I have zero experience with any serious mechanical design, but out of necessity and curiosity, I'm attempting to build a pick and place machine (for my hobby projects as well as low-volume PCB production) -- but a very basic version of it, customized to my own typical applications.
Specs: I'm trying to build the system with:
- Cost < US $100 (excluding the vacuum pickup, microscope, etc.)
- Board/panel area: Approx. one square foot (not important)
- Speed of about 1 part picked and placed within 5 seconds (not important).
- The "probe" (see figure below) is intended to be a vacuum pickup (as well as a miniature USB digital microscope attached)
- Resolution/step-size of 0.3 mm or less (my smallest part footprints are 1206 resistors and 3 mm QFNs).
- Accuracy and repeatability not too important since I have visual/magnified supervision of the process via the USB microscope.
My 1st draft of a very barebones structure, so far including 3 steppers, 3 rods threaded, a USB microscope, and a vacuum pickup:
- On my PC, for each part to be placed, I store (X, Y) coordinates for its corresponding tape reel as well as coordinates for target position on the PCB.
- Y-axis motor/rod/pickup moves to tape reel and picks up part, then moves along Y-axis to target position's Y-coordinate on PCB.
- X-axis motor/rod/PCB moves along X-axis so as to allow X-coordinate alignment too.
- Z-axis motor/rod/part descends to PCB to place part, then rises.
- Repeat until completion.
- I supervise any mis-alignments or part misses, etc. via the digital microscope viewed on my PC monitor.
- If any adjustments need to be made during any of this, I can just manually pause and adjust the position/action using the computer.
Here are my questions:
Is the mechanical setup drawn above too simple to accomplish the movement? Based on my reading of some literature and watching some videos of pick and places, the systems look much more intricate in build form, and also only either the PCB or the vacuum pickup moves, not both -- whereas in mine, I have one moving along the X-axis and the other along Y-axis (so as to simplify the stage/build).
What will be some key determinants you can think of that will make possible the resolution of 0.25 mm or better? I presume a good choice of stepper/motor (e.g., steps/revolution) is a start.
I see there is one laughably major flaw: Rotation of any of the three rods will cause the PCB or the vacuum pickup, or the picked-up part, respectively, to be rotated along with the rod! Any simple modification to solve this?