Hey all,
For some time now I've been retrofitting a Deckel Maho DMU 50M to work with a Mesa 7i97t and 7i84u over LinuxCNC. I'm so close to being done with the machine, but there's just one major issue that I can't get past — the Z axis falls about 10mm on servo power on and brake release 3 out of 5 times on average, making it impossible to work with the machine. It falls no more than 10mm before what I assume is the emergency stop kicks in and catches it, leaving me with a bright red LED on the servo drive and no way to power the machine on without a hard restart.
Does anyone have any clue what I'm doing wrong? As I hope is obvious from the HAL (line 266), I am releasing the servo brake a short delay after the servo power on signal arrives (the AC power on and emergency circuit is separate from the Mesa entirely). I've tried connecting it with an and2 gate to what should be a signal for emergency circuit ok too, to no avail. What irks me is that this issue is inconsistent. I can't find a surefire way to get the axis to fall through or to work properly, it's different each time and every day.
I don't think it's the PID configuration that's causing this, as even on a stupidly incorrect calibration that makes the machine oscillate, whenever the axis falls through, it does so in the same way — as if it is merely doing so under its own weight.
I've exhaustively measured the analog out to the drive from the Mesa and don't see any relation to the issue. If I were to spam jog in a positive direction to get an analog out of 10V before AC power on and brake release, you'd expect the axis to shoot out at max speed upwards on release, but no. It falls through in the same way.
LinuxCNC itself, the Mesa and even the main servo controller seem to have no indication or idea a fault has occurred. The only indication is the red LED that I can't really find exact documentation for.
Coincidentally, I have the exact same machine with the original Heidenhain TNC 310 handy. Measured said signals there with an oscilloscope as well and I don't see the original controller handling it any differently than from what I am doing.
I'll attach the HAL, INI and some pictures of the servo drives and the relevant pages of the electrical documentation.
Many thanks for taking the time to read this.