Hi,
The ESS can read a fast pulsed digital signal; it reads spindle speed/position triggers, rotary encoders, etc all the time. So it should be possible to read the current "speed" (in pulses per second, or pulses per time window if it is being polled at a known interval) and, knowing the PWM frequency, do a little math to convert that into a 0-100% value.
No ADC required.
Good trick if you can pull it off. Remember that and ESS encoder or MPG input measures input pulse frequency, not duty cycle. Its not clear to me how you would contort the ESS
to measure duty cycle.
I had another idea as a workaround....an ESS can very happily produce an analogue voltage from a PWM input from Mach. If that voltage is in a closed loop
with an external comparator you could get a low bandwidth ( sub 1Hz) approximation of the Clearpath analog voltage.
Even if either of these techniques could be used to 'push' an ESS to a quasi analog input capability....is it really worth it? A PoKeys 57E is about 60GBP, if you want analog inputs
that would be cost effective, and so so much easier. Note that the 57E is the plain 'vanilla' PoKeys data input board and the 57CNC is an extension of the core 57E.
Well in this case, because ClearPath is clever and encodes the left/right load into the single PWM signal, most of the time it should be at 50% PWM with blips towards either 0 or 100 depending on if the load is left/right.
Well spotted, you are correct, the voltage will be 50% normally and only deviate from that at times of peak load. My Delta servo drives have two (programmable) analog outputs.
As a matter of interest I hooked a simple moving coil voltmeter to each output just to monitor servo load. It was as boring as hell, the servos operate at near 0% load for 99.99% of the time
and only occasionally blip up to a few %. I came to the conclusion that it was a wasted effort, I was not learning anything particularly useful about my machine. It was for this reason that
I suggested OP try hooking a simple voltmeter and filter to the Clearpath out just to see what happens. He may well come to the conclusion I did, ie that its just not that bloody
interesting.
It might be if you had a large highspeed production machine where you might expect moderately high and near continuous servo load would such metering be useful. With my hobby machine
my 750W servos operate at 50W or less, on average, for hours at a time.
That is not to say however that I could not or would not be interested in extending my machine to have several analog inputs. Monitoring spindle load, especially my high torque/low speed spindle I
use for steel and stainless, I can draw 1kW to 1.5kW for long periods of time, and that's with a servo based spindle motor rated at 1.8kW.
Another place I would like to monitor motor load would be my coolant pump. If the load drops really low, that would suggest the coolant is running low and the pump is cavitating and a high
load indicates that the coolant delivery pipe is getting blocked with micro-swarf. I seem to suffer both problem on a regular basis, and any system that would help me automate the response
would save me headaches. It would be quite nice to have a slider or two for FeedRate Override etc as well.
None of these reasons is compelling.....what I really want is another 750W Delta B2 servo for my fourth axis. The stepper with which it is equipped now works but is a slow as a wet
week. I want another servo...they kick arse. The problem is that while the servo kit is (or rather was....has the price gone up?) $438USD, plus DHL shipping, say $100USD for a total
of $540USD. The New Zealand dollar has slipped to just 57cents relative to the USD so the servo would cost me something like $950NZD, and then I should allow another 15%
for GST, the local NZ tax for a total of $1090.00NZD. I have the annual rates bill due in a couple of weeks......a man should probably pay the city rates bill BEFORE he spends money on his
hobby obsession!
Craig
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