Re: digital servo controller to offload the Parallel Port?

[Jon Elson <elson-at-pico-systems.com>]

John Griessen wrote:

>  
>
>>>If a feedback loop is too much for emc on a PC via standard ports, has
>>>anyone made a microcontroller digital servo loop controller for emc
>>>yet?
>>>
>>>      
>>>
>On Wed, 2002-12-18 at 13:11, Jon Elson wrote:
>  
>
>>Why do you want to add more computers?  It only adds to the confusion 
>>factor.
>>    
>>
>
>Oh... one good reason is to allow for safety shutdowns, and also have
>everything handled by messages and all the speed, time, actual position
>data loggable, and requested toolpaths tweakable and all switches
>throwable from the emc screen for debugging and performanc increasing
>reasons.  And then another reason to redesign anything is to improve on
>what came before by making it all tougher, simpler, more like a hockey
>puck.  And then there's price.
>  
>
I have completely hardware estop circuitry, and it has a watchdog to 
stop the whole system
if the computer fails to update the servo DACs or step rate generators 
frequently enough.
All of this IS controllable from EMC, either for logging or tuning! 
 Well, my step rate
generator essentially has ONE chip on it.  (Actually, there is a gate 
chip that mostly acts
as a reset generator, a one shot to time the watchdog, a crystal 
oscillator and a serial PROM
to load the config into the FPGA.  But, the rest are cheap parts.  To 
keep cost down, I even
used real cheap wire terminals.  I just looked into making a version of 
my stepper controller
with 2-part screw terminals, and it would add $60 to the parts cost!

If you really think you can make a stepper controller with encoder 
inputs, 4 axes of step/dir
outputs, 16 opto-isolated digital inputs and mounting locations for 8 
solid state relays all
for only $200 list price - and still make money at it - then go to work! 
 I'm basically selling these
at cost to get the product going.

By the way, my stepper controller has a step timing resolution of 100 
nS, so you DEFINITELY
can't do that in software, even on a DSP.

Jon