The Craftmans Shop > New from Old
The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
RussellT:
Hi Andrew
Thanks for the explanation.
That bit of maths is more or less what I was wondering about. I've also been back and looked at the diagram on post 541.
The diagram makes it clear it's supposed to overshoot - that makes sense as the inertia will change with the size of the workpiece.
The diagram only shows two iterations but presumably it will do as many as it takes or hunt if it can't stop in the zone - depending on the variable tv which is probably explained on one of the other images I skipped when reading the whole thread at one go.
I'm confident you'll work it out
Russell
awemawson:
The delay 'tv' is timer T1 in segment 69 of the program, which is triggered by 'on target' and is the 300 mSec period during which 'on target' has to be asserted.
awemawson:
--- Quote from: PekkaNF on November 07, 2018, 01:35:48 PM ---From which OB that control loop is called? Normally only HMI and secondary functions are on the normal loop and tight controllers are put to 20 ms or such loop.
--- End quote ---
Pekka,
The actual control loop seems to be implemented in hard ware on the Measuring Card as far as I can tell but the boundaries between hardware and software are a bit fuzzy to me at the moment. I have no technical information on the Measuring card other than what I can infer by looking at it :scratch:
RussellT:
Hi Andrew
On reflection I think that the angle measuring is working fine but it needs to go slower, or accelerate more slowly from the overshoot, it seems to me that it's the momentum of the system that's the problem.
Russell
awemawson:
Russell, yes I agree. The parameters that I managed to get from the lathe user had the approach speed (cut off speed) at 5 rpm but as I'm sure that you are aware from reading my posts I cannot get it turning reliably lower than 8 or 10 rpm.
When I can 'scope the Mentor analog drive voltage triggered from the Drive Enable signal it should let me see if any actual control is being exercised at the few milliseconds of arriving at set point - I'm not convinced that it is!
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