Messages

1131

General Mach Discussion / Re: G31 Probe problem

« on: December 13, 2011, 04:26:08 AM »

I too used accept the Mach urban lore that IsMoving was was a misnamed sync call, and that it was an API sync mechanism.
It seems to do no harm if used for an API that does not cause movement, as in that case there is no movement in process and so the IsMoving call just returns false and your wait loop exits quickly. 

Here is how I learned that it really, truely, is only a wait for movement to stop.

I understand what you're saying Dave, but if you're correct and isMoving() really is only a wait for MOVEMENT to stop. Why does this code fragment count? There's no movement here.

Code: [Select]

cnt=0
setOEMDRO(800, 1000)
While isMoving()
  cnt=cnt+1
Wend
message cnt

Ian

1132

Modbus / Re: multiple serial modbus slaves

« on: December 13, 2011, 04:06:02 AM »

No one ever used more than one serial slave?

1133

General Mach Discussion / Re: Reverse RUN problem in second pass

« on: December 13, 2011, 04:02:32 AM »

OK bit the bullet and upgraded to R3.042.022 and it's still broken. Pretty please?

Ian

1134

General Mach Discussion / Re: Steppers are too slow

« on: December 07, 2011, 12:44:25 PM »

Ray - if only I'd said "ONLY when the current through the motor reaches the set point will the chopper start to chop. drive start to limit the current" I really must be more careful. But in the context of the thread surely to goodness it's clear what I meant. It was never about how a chopper works. (have you read the thread?)

The discussion had reached a point where we were discussing whether LOAD affects coil current. I stated... well I guess you'll read it if you're interested.

But then Ray YOU actually re-stated the EXACT point of where we'd got to when you said...

At low pulsewidths, and/or low loads, you'll never reach the limit

I thought EUREKA!  - Ray knows the answer we've been searching for - we're about to get somewhere. BUT you then said in your last post...

For a stepper, I don't believe motor load does affect current, unless there is some small effect related to back-EMF/slip angle, but I'm not sure about that.  It's been a loooooong time since I studied the details of the operation of motors...

So it appears after all this we've made zilch progress - marvelous....

Cheers

Ian

1135

General Mach Discussion / Re: Brushless DC Servo Spindle Speed Control w/ Smooth Stepper and Leadshine

« on: December 07, 2011, 11:33:55 AM »

For a rotary axis, isn't acceleration in RPM/sec^2?  If so, 500 is not very high.

Revs per minute per sec per sec? That would be a 3rd order derivative, which would be jerk but with mixed time units - curious.

Hmmmm....  I wonder what the units are then?

Well whatever it is it has to be in terms of angular-displacement/sec^2 so revs/sec^2 or radians/sec^2 or degrees/sec^2 perhaps.

Ian

1136

General Mach Discussion / Re: Steppers are too slow

« on: December 07, 2011, 06:39:01 AM »

That's not how choppers typically work.  They normally run at a constant switching rate, with the pulse width varying based on commanded output.  Current limiting will prematurely turn off the output current, ONLY if the limit is exceeded.  At low pulsewidths, and/or low loads, you'll never reach the limit, because the current is not turned on long enough to saturate the coil, due to the coil inductance .  The whole idea is to vary RMS voltage, allowing the current to do what it will, provided it does not exceed the set limit.

Ray - I'm not sure where your reply contradicts anything I said. If you check out the attached pic I think I described it adequately for the purposes of the thread. However if we're being Mr. Picky... 

Current limiting will prematurely turn off the output current

Actually current limiting turns off the output VOLTAGE. current decays as a result.

because the current is not turned on long enough to saturate the coil, due to the coil inductance

As above, it's because the VOLTAGE is not turned on long enough to allow the current to rise to saturation because of the effects of inductance. We use a larger than rated VOLTAGE to "combat" inductance by reducing the rise time of the current and hence why we need current LIMITING in the first place.

But enough of this merry banter... now to the bit in your reply which is really pertinent to the point we were discussing... (please read post #33)

What I was asking was... please explain how the LOAD on the stepper motor affects the coil current? and in particular because you've said it here... please explain how a LOW load would result in a lower coil current. You may well be correct - as I said earlier in the thread I've had this stated to me before but no one has ever explained (or been able to explain) why. Personally I don't get it - and that's why I'd LOVE to have someone explain this.

Cheers

Ian

1137

Modbus / multiple serial modbus slaves

« on: December 06, 2011, 08:25:08 AM »

In his vid, Art alludes that Mach can communicate with 2 or possibly 4 serial modbus slaves at a time. However I can't see anywhere in either brains or macros or in setup how you would do this. For example in a brain there's nowhere I can see where you specify the slave address. The slave address used by brains seems to be set only in the modbus config dialog and that only allows one. i.e. you don't appear to be able to say slave 1 has these regs and slave 2 has these etc. Does anyone know how to address more than one slave?

Thanks

Ian

1138

General Mach Discussion / Re: G31 Probe problem

« on: December 06, 2011, 06:52:46 AM »

Just and update to what I said about FIFO and one-shot. I'm not sure but I think this has changed at some time. I THINK you can now send multiple CODE statements without an isMoving() after each one. I THINK you can now get away with a series of CODE statements with just one while isMoving() after the last one. i.e. I THINK Mach buffers the CODE requests in order. Is it reliable? - your guess is as good as mine - which version do I think it changed in? - I don't know. I still stick an isMoving() after each one - but that's just me.

Ian

1139

General Mach Discussion / Re: Steppers are too slow

« on: December 06, 2011, 06:42:10 AM »

Thanks for this Sargon - definitely sounds the way to go for Stuart to really find out what's going on.

Ian

1140

General Mach Discussion / Re: Reverse RUN problem in second pass

« on: December 06, 2011, 06:31:40 AM »

Any update on this please? I'm loathe to move from R3.042.020 for the gazillion reasons discussed in other threads but reverse run is very much a nice to have for plasma when the fire goes out.

Thanks

Ian