Vacuum pick and place head for 3-axis machine v0.0
by Drmn4ea, published
This is a vacuum pick-and-place head design for automated electronic assembly. It features a stepper-driven rotary head with Luer-Lock port for interchangeable needles, and a feature for attachment of an \"eyeball\" style Webcam for optical placement (you can modify to support your own favorite camera). Vacuum is provided to the head via flex (fishpump) tubing.
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The .cb files can be opened with the freeware version of CamBam, available from http://www.cambam.co.uk/
First, make any desired modifications to the plates, such as changing the camera mount for a specific camera, and adding a mounting mechanism for your 3-axis machine (e.g. angle brackets, or a dovetail, etc.). Machine the top and bottom plate.
The order of assembly is not critical, but it\'s probably best to do a test-fit before gluing anything down. Press-fit the ball bearing into the pocket on the top side of the bottom plate. The sleeve bearing screws onto the corresponding hole in the top plate using #4-40 bolts, and can be placed on either the top or bottom. The stepper motor mounts to the bottom side of the bottom plate using #4-40 bolts. The smaller of the two pulleys slides onto the motor shaft.
Next assemble the structure by bolting the standoffs onto the top of the bottom plate, #8-32 bolts entering from the bottom. Secure the top plate to these standoffs using 4 more #8-32s. If you will use a camera, mount it too.
Finally, assemble the rotating frame by passing the length of 1/4\" steel tubing through the sleeve bearing, followed by the larger pulley and timing belt, then the ball bearing. Slip the barbed end of the Luer-lock adapter into the bottom end of the tubing (screw on a needle if you like) and test the \"fit\" with your machine setup and camera. Determine the desired height of the steel tubing/needle, and cut the tubing to the desired length.
Making it permanent: Secure the large and small pulleys and Luer adapter with a bit of adhesive. These should not see any significant load, so a dab will do. Likewise, take the plastic right-angle hose barb and glue it into the top of the steel tube. For the Luer adapter and hose barb, be careful not to clog the air path with adhesive! Finally, loosen the bolts holding the motor, loop the timing belt onto the motor pulley (moving the motor as necessary), then move the motor out to take up any slack in the belt and re-tighten the motor bolts.
OPTICAL USER TIP: To determine the needle depth - With the camera focus set such that the largest part you will ever populate can fit in-frame, find the resulting camera height (distance from part) and set the depth of the shaft so that the camera is “in focus” maybe an inch or two above the placement position (that is, the position with the needle touching the board). This will allow the head to focus on parts without touching the needle down. This should cover 99.999% of all SMD assembly uses, but if you will be somehow using it to move very tall objects, set the focus height at least a bit higher than the tallest part you will place.
SOURCING MOTORS: The timing pulleys and stepper motors only come in a handful of diameters (imperial for the pulleys and usually metric for the small motors), so a 3mm (.118″) motor onto a .125″ ID pulley was the closest I could come up with in a reasonable amount of effort. Any small, el-cheapo permanent magnet (“tin can”) stepper motor should work here, but sourcing it may be annoying. Off-the-shelf 3mm-shaft motors I found are Jameco’s ValuePro 42BY48H08, Anaheim Automation’s TSM42 series, and Portescap’s 42/44 series e.g. 42×048 and 42S100. The surplus stepper at http://www.allelectronics.com/make-a-store/item/SMT-125/4-WIRE-STEPPER-MOTOR-W/GEARS/1.html is also worth a look, but you’ll have to remove a pre-attached plastic(?) gearhead. Beware, many of these smaller motors are 7.5deg/step, so even with the gear reduction, you will probably want to use a microstepping driver such as Linistepper to ensure adequate rotational resolution. On mine, I took a 2mm motor I had lying around (http://www.allelectronics.com/make-a-store/item/SMT-108/STEPPER-MOTOR-6-WIRE/1.html) and glued a bit of steel tubing onto its shaft to make it ~3mm for use with the pulley.
Final note: There have been slight improvements to the design files after building the one shown in the photo, so yours will not be 100% identical to the photo.
Final final note: "You do not have permission to edit this supplier" when trying to add suppliers, part numbers/URLs, etc. for the discrete parts. Anyone know what's going on with this? For now, please read from the parts list on my blog at http://tim.cexx.org/?p=728