Hi Lou,
I understand that I don’t need to give the 7766 any encoder info at all but if I do then the DRO’S in Mach4 will display the actual machine position based on encoder input as opposed the commanded position. Just seems there has to be some value in that.
Sorry to burst your bubble but Mach is not a feedback controller. The Hicon unit does not routinely relay information back to Mach. If it were to do so the communication lag
would mean the DROs would always be out of date. Mach can read an MPG or encoder and display it in a DRO provided you don't mind it being a tenth of a second out of date.
Hooking the encoders to the 7766 is for the 7766's benefit only. The 7766 can use that to close a loop in realtime whereas Mach cannot, its way way WAY TO SLOW!
A communication loop in Mach3 is of the order of 25ms one way! Mach4 can do a lot better than that, about 10ms as default and you can push it to probably less than 5ms
but that is still to slow for genuine feedback control.
Just to give you some background: a feedback loop has a refresh rate (sometimes called bandwidth and various other terms). So every so often the control loops get a measurement
of the current error between commanded position verses actual position. Lets say that happens 100 times a second, ie every 10 ms.
The Nyquist sampling theorem assures us that the maximum frequency signal that can be represented by a 100 sample/second stream is half that or 50Hz. As a control engineer you
yawn, yes its theoretically possible to represent a 50 Hz signal with 100 sample/second but you get no 'discrimination', that is to say the fideility is very poor. You might get fair
representation of a 5 Hz signal with 100 samples per second, but even that would be very grainy or poor resolution. A feedback control loop with a 100 Hz refresh rate will have
at best a 5Hz bandwidth, ie it will be as slow as a wet week! And even a 5Hz bandwidth is pretty sketchy and grainy.....
A servo loop will have refresh rates of the order of 20kHz, for a Nyquist rate of 10 kHz, and an acceleration loop bandwidth of about 1kHz and a position loop bandwidth of about 100Hz.
Thus you can see Mach3 with a refresh rate of about 25 per second and even Mach4 at 100 per second is a long LONG way short of the speed necessary for a high fideility closed loop
control system.
I do understand the inclination to use the activation that you paid for and especially doing what is politic as far as 'her indoors' is concerned..... I would try the method I have outlined
given that it is mainly keystrokes and maybe a bit of wiring. Using the scope feature will teach you stuff in one afternoon that 100 books/videos/forum posts will never do.
Once you have that knowledge/understanding under your belt THEN try using the 7766 to close the loop, either with or without the closed loop stepper drive. That experience based
understanding of feedback control will allow you to dial in the 7766 really well, maybe as good as the stepper and its even remotely possible you could do better. Without that knowledge
you may find as many others have found that PID loop tuning is a Black Art never to be mastered!
Years ago at University I studied this stuff. We had whole labs set up with various servo systems and all manner of measuring and test gear. We were required to do certain experiments
but were encouraged to do a whole lot more than that. Basically we could fiddle with things as much as we liked....all of it adding to the intuitive understanding of feedback control.
Add that intuitive understanding to the mathematics, and there was a s*********t load of that....
Craig