Mach spindle speed problem! Any ideas

[SimonRafferty]

I pretty much have my Easiturn running under the control of Mach now - but I'm having problems with the closed loop spindle control.

Essentially, it reads correctly up to 870rpm then if you up the demand speed to say 900rpm, the indicated speed halves to read 450rpm. In closed loop - mach thinks it's running too slow - and ramps up to 1800rpm (which it indicates as 900.

I've not stuck a scope on the index sensor yet - but I'm wondering if at low speeds it's triggering on both the leading and trailing edge of the pulse (due to ringing?) but above that speed it just reads it as a single pulse?

Interestingly, if you move the sensor to look at the little holes - it reads correctly regardless of the rpm - but this is obviously no good for things like thread cutting where it needs the phase as well as speed.


Has anyone else had this using the built in opto sensor and the disk with one big hole and loads of little holes?

What is the preferred solution?

Si

[cncbasher]

if my memory serves , Mach 3 only uses the sensor to count one rev of the spindle and works out the Rpm from that , this value is updated each rev , it works best with 2 holes at 180deg apart with one hole wider than the other , this acts as an Index pulse for mach3

their is a diagram on the yahoo groups forum
this works true with the results you are finding , as you are only picking up one pulse per rev instead of two

you may find siteing another sensor on your spindle exclusively for mach 3 may help

[SimonRafferty]

Solved it!

Mach seems to expect the ON (+5v at the input) time to be shorter than the OFF time.

I had assumed that the active high or low setting would fix that - but it seems not. Put the output of the opto or inductive sensor through a hardware inverter - and it works perfectly.

The inductive pickup used a disk with a 10mm slot cut in the circumference. and the output of the original opto sensor was high until light shone on the phototransistor which pulled the output low. Both therefore were high most of the time with a short 0v pulse.

Si

[dscolwill]

I have recently converted my easiturn. Initially I used an old vesion of mach 3 ( 1.84 ish ) and the spindle speed was ok then when I was getting the turret working I changed to a newer version and got the same problem that you have. I think this is a bug that they have fixed or are fixing if I have read some of the posts on the forum correctly. I haven't had time to sort my machine out but I was going to download the latest version of mach and see if all is well, perhaps you could try this and let me know.
Hope this helps
David.