CHMT36VA seems to have a software issue with fiducial offset on penalized pcb. - Page 1
Forum section: electronics / general

author: BADASSLOUMD
author_rank: Newbie
timestamp: August 24, 2020, 07:15:58 pm
content: Ok, so I have been playing with my "new" chmt36va with varying degrees of success.Not a terrible machine, especially for the price. You can easily buy feeders for othermachines that cost more than this entire setup... but I digress.I use this machine (for now) to produce a very, very simple board that I havein a 5 panel array (1..5) arranged on the X axis with a 3 millimeter space betweenthe boards. I used the cool Sparkfun charm converter to get the data in the machine,and I have had reasonably good luck with it. Some days better than others..Some things I learned the *hard* way:1) you MUST shut off the FIFO buffering in the usb-serial converter thatis supplied with the unit. Admittedly I have a slow lap-top running themachine. What was happening with the default USB fifo buffer in turnedin was that the up-camera would end up taking a picture of the partas it was moving into the "center" of the camera. This resulted in it oftenfinding the centroid of the part *centimeters* away from the "center"of the camera, and causing gross placement errors.2) sometimes the drag-pin on the feeder just plain misses the componenttape, usually at the back of the machine, and continues to do so. I havefound that re-starting the software fixes this. WTF? It is workable but apain in the butt.3) On one of my more fussy days using this machine, I had a hunch thatthe fiducial offsets don't work right. Turns out, I am pretty sure thatthey DO NOT work right on penalized boards... let me explain what Ihave found.. First my setup:NORMAL setup:{Mark1}{ } { } { } { } { }{board1 } {board2} {board3 } {board4 } {board5 }{ } { } { } { } { }{mark3} {mark2}On a “normal” day when you go into the “pcb calibrate” menuand the fiducial are very close. No problem, hit run and all is well.I noted that on some boards, when the fiducals require movementof the head, the boards on the “end” don't seem to lign up as well.So, to prove this I performed this experiment, I shifted the entirepanel to the right about 1 CM:Experiment:<1cm> {Mark1}<1cm><1cm><1cm> { } { } { } { } { }<1cm> {board1 } {board2 } {board3 } {board4} {board5}<1cm> { } { } { } { } { }<1cm><1cm> {mark3} {mark2}I shifted the boards right 1 cm, and got some very surprising results:the components on Board1 were placed perfectly. The offset was accountedfor by the machine, and all was perfect. board 2, was ok, but has a visibleshift of the components being placed too far to the right. Board 3 was bad,parts were shifted quite a bit too far to the right. Boards 4 and 5 were totallyun-useable. The parts had been “over shifted” too far right and were literallyfalling off of the board.So, my question is, has any one else seen this problem? Is there somethngthat I am probably doing wrong?Cheers,---Lou

author: thinkfat
author_rank: Unknown
timestamp: August 25, 2020, 06:42:19 am
content: Not knowing anything about pick and place robots, but this looks like an axis scaling issue. There is maybe a calibration to be done. There is maybe a factor that translates input to output coordinates for each axis, and it seems to be off (slightly too large)