"DoN. Nichols" wrote:

On 2010-02-25, Jon Elson wrote:
Ignoramus26960 wrote:
On 2010-02-24, Jon Elson wrote:

[ ... ]

There are several servo interfaces available for EMC that you can choose
from (I make one kind).

Tell us about it Jon.

i
OK, I have two flavors. One is for use with
velocity servo amps that take +/- 10 V analog
velocity command signals. It is a very flexible
board set, meaning you can mix and match boards
for the actual number of I/Os you need. It runs
$780 for the
basic 4-axis set, that gives 4 encoder counters, 4
16-bit 10 V DACs and 16 digital inputs and 8 SSR
output locations, plus an E-stop circuit.

See
http://pico-systems.com/oscrc4/catal...ex.php?cPath=8
for a look at this system.

Intesting. I see that it expects to be driven by a parallel
port, and is not on cards which plug directly into the system bus, which
suggests that I could use it with on of my Sun workstations instead of
requiring an Intel based system. This I would like. I should be able
to compile EMC2 to run under Solaris 10 (which has a real-time feature).

I am curious about the power supply shown. The voltages are
specified, but I see no current capacity to suggest whether it would
serve better than the many other power supplies which I already have.

Is there anyplace where I can download the communication
protocols being used with the parallel port?

Most of these systems send step and direction signals from the parallel
port, not any sort of protocol. They rely on low level drivers to
control the parallel port and generate the pulses.

Pete C. wrote:

Most of these systems send step and direction signals from the parallel
port, not any sort of protocol. They rely on low level drivers to
control the parallel port and generate the pulses.
Right, a lot of people do that. But, EMC also
supports real servo systems where the CPU is in
the middle of the servo loop. That is the kind of
interface I make. The computer sends a velocity
command to the interface, it generates either steps,
a DC voltage or a PWM pulse train where pulse
width is proportional to desired velocity.
Encoders feed back position to encoder counters
which are read periodically by the CPU. If you
choose the PWM or analog interface, then there are
NO steps anywhere in the system. With these
systems, you can hit E-stop, move the machine
manually while EMC2 acts as a DRO, then clear the
E-stop and go back
to CNC, while the system maintains the coordinate
system all the time.

With my boards, the parallel port is a
communications channel, and the CPU can read and
write banks of registers, representing position
and velocity.

Jon

On 2010-02-26, Jon Elson wrote:
Pete C. wrote:

Most of these systems send step and direction signals from the parallel
port, not any sort of protocol. They rely on low level drivers to
control the parallel port and generate the pulses.

Right, a lot of people do that. But, EMC also
supports real servo systems where the CPU is in
the middle of the servo loop. That is the kind of
interface I make. The computer sends a velocity
command to the interface, it generates either steps,
a DC voltage or a PWM pulse train where pulse
width is proportional to desired velocity.
Encoders feed back position to encoder counters
which are read periodically by the CPU. If you
choose the PWM or analog interface, then there are
NO steps anywhere in the system. With these
systems, you can hit E-stop, move the machine
manually while EMC2 acts as a DRO, then clear the
E-stop and go back
to CNC, while the system maintains the coordinate
system all the time.

With my boards, the parallel port is a
communications channel, and the CPU can read and
write banks of registers, representing position
and velocity.

Just what I want.

Thanks,
DoN.

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