Quad 4C MK2, Z axis drift

Hello everybody Lately our machine has been working pretty well, but it can’t last too long. Now, during this week’s production cycle, it began to increase the component’s reject rate to alarming levels (obviously the operators reported me when the machine became unable to place components at all). Trying to arrive to a diagnosis, I ran Function 30 and 31. I found that NOZZLE HEIGHT readings vary from each Function 30 run to the next, its figure diminished by one or two mils each time. I located a height gauge on the top-end of Z-rod, firmly fitted to the chassis with a magnetic stand. X-Y axis to 0,0, static. After each F30 run I physically checked the zero Z position and it remain constant despite the Nozzle Height variation of readings. I’m looking for a smaller gauge to attach it directly to the head casting and read the actual movement of Z axis at any X-Y position, now I just can check 0,0,0 coordinates. Just after RESET, Function 31 runs fine when I put a component by hand on the nozzle tip. ST1 and ST2 read 1Q85 and the component’s dimension appears. After the Z axis start to drift, ST1 and ST2 reads 30Q65, the X-Y dimension read equal, about 45-60 mils, which correspond to the nozzle tip diameter. I checked the Up and Down End optic sensors, clean and OK. All the mechanical parts: motor, pulleys, belt, screw, bearings, etc. are Ok. The movements are smooth, no slack, non sticky areas. Flex cables prima facie seem to be fine, however I did not examined them in depth yet. I did not detected lose or faulty connectors (not yet, at least). Laser head is a Quad Align type, it was provided by PPM in mid 2013. It has less than 300 run hours and is clean and well cared. Align system version is 1.6C. I have explored the whole forum in order to find any precedent about this phenomenon, but I was not lucky. Any help or advice shall be appreciated. Thanks.

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