Re: Kulago/Mauch DRO ISA quadrature feedback kit with new timer

[Doug Fortune <pentam-at-home.com>]

Jon Elson wrote:

> Matt Shaver wrote:
> > > From: Doug Fortune <pentam-at-home.com>
> > > Ok, I know there is a limit to how fast you can step a stepper (in rpm).
> >
> > It's more a problem of the granularity of the frequency control ....

> > 2. Use special hardware to either increase the granularity of interrupt
> > scheduling (this may be the Ahha method, I haven't reverse engineered their
> > stuff), or to implement a programmable frequency generator controlled by the
> > PC (the Flashcut method). The only drawbacks to these methods are (at the
> > present time), cost and having to live with proprietary systems. Of these two
> > methods, I like the programmable frequency generator best.
>
> I intend to do this later this summer, as an extension to our parallel
> port interfaced motion system.  What I have in mind is a FPGA which
> has a fast digital counter running at, perhaps 1 MHz.  The CPU sends a
> velocity command to this unit, which schedules step pulses with a
> granularity of 1 uS, and counts those steps with an up/down counter.
> The computer thinks it is driving a velocity servo system with a shaft
> encoder, because it sends velocity commands, and gets back a position
> count.  The CPU doesn't need to update this quickly, 1 KHz would be fine,
> so the demand on the CPU is drastically reduced.
>
> >From experience with the Xilinx Spartan-series chips, I can get 4 channels
> of quadrature counter, plus some other interface logic on one $18 chip
> (which needs a $6 serial PROM to load the configuration).  I suspect I can
> get 2 channels of this stepper control logic on the same $18 chip.
>
> With a granularity of 1 uS, we could reduce Matt's ~4% velocity step
> (from 3617 to 3741 Hz) to about 0.4% with 1 uS steps.

Why not just add that functionality onto the Kulago/Mauch quadrature
feedback (DRO) ISA board?   The raw pcb board is cheap enough at $20
(probably still be $20 after the new circuit traces are added) and if
some people don't want the quadrature feedback features, they just
leave those related IC's off.   Later if they need it, they can add the IC's.

Doug