RE: NT-Linux Comments

Bertho -

This is the approach that I've been starting to favor as well. I think with
the low cost DSP's out there, we should be able to move many of the
functions that an I/O card handles right onto the servo amp. Texas
Instruments is coming out with a motion control-oriented DSP, the
TMS320LC2402 at:

http://www.ti.com/sc/docs/apps/digital/index.htm TI DSPs
http://www.ti.com/sc/docs/products/dsp/tms320lc2402.html TMS320LC2402

that they sell for $2.95 in higher quantities that has tons of PWM channels,
A/D's, I/O pins, and a hardware quadrature encoder/counter port. This thing
would be overkill for what you're talking about, but at that price who
cares? You could program it to run any kind of axis drive motor (brushed,
brushless, steppers...) and also slap one on your spindle motor. The thing
I like about it is that they claim it is alot like a microcontroller as far
as programming, peripherals, etc., so with my meager 8051 experience I might
actually be able to understand what's going on in the code, and more
importantly, understand what is possible to do in code.

As many people will say about me, I know enough about electronics to be
dangerous. But I think with a DSP like this one, you could drastically
simplify hardware requirements and potentially boost performance as well.
Having velocity feedback without the tach is one nice start. The integrated
encoder interface would help keep the IC count to a minimum. I think you
could do so much with the DSP the biggest problem is knowing where to stop.

Anybody out there have intimate experience with this DSP??

Carlos Guillermo

> From: Bertho Boman <boman@...>
>
> Let me add a comment or two to Matt's & Hans and others' discussion:
>
> Real Time NT:
> In the June 1998 issue of "Embedded Systems Programming" magazine
> there was a detailed explanation of NT performance in RT
> applications, including an explanation of different RT software
> to buy and how to do it yourself. Also discussed was how to
> separate time critical task so screen redraws, mouse movements
> and other tasks would be done on a low priority basis.
>
> EMC features & function:
> Since you are talking about hardware improvements and accessories
> to EMC let me bring back one of my previous suggestions. I
> think Matt said the goal with EMC is to provide a low-cost, high
> performance CNC system. Part of that is defeated by the high
> cost of the Servo-to-Go interface board.
>
> As it is now, the digital output command is converted to an
> analog signal inside the PC and then the signal is feed to an
> external servo amp which also typically is expensive. If the
> output signal was left as digital and feed to an external micro-P
> that would be part of the Servo amp the internal A/D would not be
> needed. The shaft encoder for each channel would also be
> connected to the same board and signals cleaned up and then
> communicated back to the PC. I think a bi-directional printer port
> or a high speed serial port easily could handle the updates. The
> changes to EMC would be minimal, it would write the digital
> commands to the printer port instead of the I-O card and it
> would read the printer port for position data. A standard PC would
> be fine without modifications.
>
> Note, I am not proposing to use external motion calculations, EMC
> would operate as normal. Basically, what I suggest is to get
> an interface with a servo amp on one board for each channel.
>
> The board (one per axis) that I envision is actually a DSP
> programmed to do several things:
>
> 1. Interface with the PC for communication of data and status (a
> simple protocol is needed for the boards not to fight or they
> could be daisy chained)
>
> 2. Interface with the encoder, limit switches and home switch.
>
> 3. PWM generation. Since a DSP typically has a built in A/D it
> can sense the motor current and generate the PWM internally. A
> medium power output stage could be included on board with an
> option to feed the PWM control signal to an external high power
> stage.
>
> 4. A software tachometer calculated from the encoder signals.
> This is not new and works well. That will remove the need to add
> a mechanical tachometer to each servo channel with its cost and
> mechanical mounting problems.
>
> 5. The DSP software would replace the analog filter and gain pots
> and make a much more reliable system with the gain and filter
> constants accurately set in software.
>
> 6. We could even add one more PWM channel and the DSP could be
> programmed to run steppers, with or without encoder feedback.
>
> Summary: Basically one DSP chip with all its I-O pins can do all
> the interfacing to the PC, the encoders and via a FET driver
> chip the power output FETs. That would make a really high
> performance and low cost servo or stepper system.
>
> What do you guys think? My DSP programming experience is zero
> but I am not really suggesting something new or drastic. It
> really makes sense to combine the I-O functions with the PWM
> generation on one board and then just duplicate it for each
> channel as needed.
>
> Bertho Boman
> Vinland Corporation
>
>
>
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