Re: [CAD_CAM_EDM_DRO] Re: Safety -- servo vs. stepper

jess@... wrote:

>Jon mentioned the Servo-To-Go ISA PC board
>
>What does the Servo-To-Go card attempt at replacing taking into
>consideration that
>generally:
>
>Servos are driven by say geckos or like
>and the geckos are driven by a breakout board connected to your parallel
>port under the control of EMC or MACH2.
>
>The picture I have in my head is that Servo_To-Go would replace the Parallel
>Port? Is this correct?
>
>

No. With the Servo-to-Go card, an analog voltage proportional to
desired velocity is sent to a velocity servo amplifier. That amplifier's
job is to provide movement of a velocity proportional to the applied
velocity command voltage. There are no step and direction signals
anywhere in this system.

The STG card also reads the encoder signals back into the PC, so the
computer always knows the exact position, even if the servo amps
are turned off.

>Assuming it is does Mach2 or EMC know how to talk to Servo-To-Go?
>
>

No, Mach2 cannot use the STG card, because all it knows is step and
direction pulses generated in software. It cannot handle real servo
systems where the computer reads position and tells the drives how
fast to move. In other words, Mach2 is open-loop from the ground up,
it sends step pulses and assumes the machine moves as it is told.

A true servo system is closed-loop, it assumes the machine is never
qhere it is supposed to be, and is always adjusting position to minimize
error. If you walk up to it and grab the motor pulleys and twist them,
it will sense the motion and fight back. If you move it far enough, it
will get a following error, and shut down. If you don't deflect it that
far, it will move right back on position as soon as you let go.

This is how EMC works with the STG card, and other true closed loop
motion interfaces.

Jon