Re: [CAD_CAM_EDM_DRO] Re: VISUAL BASIC & CNC

On Sat, 12 Apr 2003 19:36:03 -0400, you wrote:

>
>All printers (serial & parallel) have a problem keeping up with the speed
>that the computer ports can output data. They use a technique called
>handshaking (in conjunction with a buffer in the printer. When the printer
>can't take any more data, it places voltage on one (or more) lines which
>communicate back to the computer to stop sending data. When the buffer
>empties, the handshaking signal goes low and the computer is able to send
>more data. In this way the printer's stepper driver always gets data at a
>constant acceptable rate.

The parameters for the stepper's driver are hidden in the printer's
processor. Windows and handshaking becomes irrelevant here, since
what you're looking at is the equivalent of downloading Gcode (as I
understand it) directly to the mill, and having a smart mill...

>
>There is generally no feedback used to keep track of the location of the
>stepper motor in a CNC system with a PC controller (I think encoders can
>address this, but haven't gotten there yet).

They can. The difference is between a closed loop and an open loop
servo system.

Open loop says: I am here, and I think it will take 455 steps to go
there. Once those are done, it hopes that it is there... Missing
steps and torque problems are not addressed.

Closed loop says: I am here, step until I am there. I know where
there is, and where I am at all times.

Harvey

>The speed the data is
>transmitted is controlled by software and lost steps are not accounted for.
>
>Regards,
>Jeff
>
>