Re: [CAD_CAM_EDM_DRO] Closed Loop PC Based CNC

Les,

A great job of answering my questions!!

I will look deeper into this.

gary

Les Newell wrote:

>Hi Gary,
>
>I don't know the Rutex drives all that well but I will try to answer
>your questions.
>
> > 1) Does the drive have a PID Loop to control following error
> > calculated between comanded steps and encoder feedback?
>
>Yes
>
>
>> 2) Do the drives have both Proportional and Intergral Gain (linear
>>error and time base error multipliers)?
>>
>>
>
>You can control P,I and D. With the current version this is via 3 pots
>but on the latest version it is all done by software via the PC parallel
>port.
>
>
>
>> 3) Do the drives attempt to reduce any following error by iterating
>>to near zero or only monitor a "lost steps" count?
>>
>>
>>
>
>The I part of the loop will try to keep the error within 1 count. I used
>some Rutex step/dir to +/- 10V converters a while back and with no input
>steps they slowly cycled between two encoder counts (i.e. +/- 1 count).
>
>
>
>> 4) If the drive cannot keep up or exceeds the "lost steps" error
>>count does it shut down and drop a "drive ok" signal? Can this signal be
>>used to take the other drives off line by controlling the "drive enable"
>>signal to the other drives?
>>
>>
>>
>
>They have a fault output. I can't remember off-hand if that o/p can be
>used as an input as well. I tied all the following error outputs into my
>EStop chain.
>
>
>
>> 5) If the drives fault and go down, the control may not know and
>>keep chugging along like it had good sense. Is there an drive output to
>>the software to prevnt this?
>>
>>
>>
>
>I used the fault signal to EStop the machine. The computer soon knows
>about it then :-) The new version drives allow you to define the maximum
>following error before a fault. The older version is fixed to 1024 counts.
>
>
>
>>Some other desired features possible with a closed loop system are "soft
>>limits" and homing based on the encoder marker pulse. I would want to
>>drive the axis in the direction of the home limit at traverse speed
>>until the mechanical limit is tripped, switch to a slow approach speed
>>and drive until the marker pulse (Z/ZNOT) is detected.
>>
>>
>>
>
>Mach2 http://www.artofcnc.ca has soft limits. It also has quite a few
>other really useful features. It is a bit of a steep learning curve to
>start with but it is worth the effort. I don't think it currently
>supports a marker pulse reliably.
>
>
>
>>All in all however, I completely agree that this is a much better
>>approach than where we are now.
>>
>>
>
>I hate steppers. I have used quite a few stepper driven machines and
>they have all lost steps at some point. No matter how careful you are
>tuning them you will eventually find a job that has just the right
>combination of moves to make them lose steps.
>
>Les
>
>
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