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Zevatech 740 RH Head - issues with rotation of component during laser recognition

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#79967

Zevatech 740 RH Head - issues with rotation of component during laser recognition | 13 March, 2018

I have an old Zevatech 740 machine that, until recently, was running well. In the last few weeks, the RH head has started giving me issues.

When it picks up a component (and early on in most of my programs it will be picking up chip resistors or capacitors), it seems to under- or over-rotate the component by 45 degrees when its doing the laser recognition check, meaning the component X and Y measurements don't match the component data and the machine kicks up a laser recognition error.

It does this at normal production speeds as well as if I slow things down (by opening the cover), so I know its not an issue related to pick or theta speeds. And its only an issue on the RH head. The LH head works fine.

For the moment, I've disabled the RH head and am using only one head for production, but I'd like to get to the bottom of the issue and get both heads working again.

Anyone got any experience with this sort of problem and can give me some tips as to where I should start looking?

Cheers, Mike

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#79974

Zevatech 740 RH Head - issues with rotation of component during laser recognition | 15 March, 2018

Unfortunately, I can't give any help but wanted to ask about your experience with the 740 machine? How reliable has it been for you? Would you buy another or upgrade to newer machine?

I just bought 2 pm570s arriving tomorrow. If they work out well I plan to buy 2 740/750/760 to run in full assembly line with conveyors.

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#79977

Zevatech 740 RH Head - issues with rotation of component during laser recognition | 15 March, 2018

Is the nozzle in good condition? If it is not flat because of damage or wear, it might loose vacuum and the part may have a tendency to shift.

I don't have experience with these machines but how do you know the spindle is spinning slower when the cover is open? That may not be the case. I would think there is a way to slow down the spin speed in software for that profile.

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#79979

Zevatech 740 RH Head - issues with rotation of component during laser recognition | 15 March, 2018

Possibly a loose grub screw on one of the shafts controlling rotation or the sensor ot gray code wheel on the rotation servo motor. or even a small fault in the program eprom,

Good luck

sarason

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#79980

Zevatech 740 RH Head - issues with rotation of component during laser recognition | 15 March, 2018

The 740 has been a great machine for us. We've been able to reliably load components as small as 0603 (we've not tried 0402, but I believe with a special nozzle adaptor, you can get it to work) and place a 7x7 56 pin QFN with 0.4mm pin pitch with high reliability.

The only issue is with support for these older machines. If something goes wrong, you're pretty much on your own and having to fault find things through trial and error. There are plenty of places on-line selling spare parts, and they can be of some assistance with regards to fault finding, but on the whole, you've got to sort these things out yourself.

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#79981

Zevatech 740 RH Head - issues with rotation of component during laser recognition | 15 March, 2018

Yep, checked the nozzle (that was my first port of call). Had a look at it under our microscope, and also swapped it out for another nozzle to be sure. The problem still exists.

You can set the theta speed, but only to Fast, Medium or Slow. I've got it set right down at Slow, and its still an issue. It seems to reliably get the component at about 45 degrees (obviously that's just me observing it - I've not got out my protractor to check!!) so its almost like there is something wrong with the part of the head that measures the rotation. Might be missing every second signal from the stepper motor or something.

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#79982

Zevatech 740 RH Head - issues with rotation of component during laser recognition | 15 March, 2018

Cheers. I have a suspicion its an error with whatever part of the machine measures shaft rotation, but the grub screw thing is an easy one to check and eliminate.

I'm only guessing from what I can see, but it looks like its setting the component at 45 degrees rather than 90 or 180, (it could be 30 or 60, I've not tried to measure it) which would suggest that its not seeing all the signals from the shaft encoder/decoder output

I'm guessing a fault in the EEPROM is going to be a difficult fix :-(

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#80027

Zevatech 740 RH Head - issues with rotation of component during laser recognition | 20 March, 2018

OK, with my masterful powers of deduction, I have been able to resolve the problem.

Upon further investigation, it became apparent that the issue was restricted to those components that had the laser alignment level in the component data set to -0.25. Even though I had been into the machine set up menu and got the machine to re-measure the height of both L and R heads, it seemed that the R head wasn't putting those components with a low laser alignment figure all the way into the beam.

By changing the laser alignment so it was always -0.4 or more, I was able to ensure all components when sufficiently far into the laser detection area to be picked up and correctly aligned.

The machine seems to default the laser alignment level to 1/2 the component height, so for chip resistors (0.5mm height), the default value was -0.25.

Not sure why my 740 suddenly started having this issue, and whilst the above fix means I can get the two heads working again, it doesn't actually resolve the underlying issue, which is that despite measuring the RH position, the machine isn't actually able to move it to the correct location and I need to add this "fudge factor"

Has anyone seen this sort of behaviour before, and is there a better way to resolve it? At the moment, I'm having to modify ALL component data in ALL my active production files, which is more than a little labourious!

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