Re: [CAD_CAM_EDM_DRO] Re: software/hardware for laser engraver

Oh, er, I guess I thought it would be an easy hack at first to control the galvos with step and direction. My mill is set up with Gecko G340 step/direction servo drives running straight from the parallel port. I am not sure I want to try and modify EMC to ouput both steppermod and servomod (or whatever the analog servo amps use in EMC) at the same time. I figured I could just hook the x and y of the galvos up to the 4th and 5th axis in EMC with this step/direction to analog signal converter. It seemed like and easy starting point at least. And cheap.

Richard

Jon Elson wrote:skykotechnologies wrote:

> As a reply to my post, upon further reflection, I think that emc can
> actually control my galvos after all. A few calculations:
>
> realistic galvo speed for engraving - 20 inches/second
> realistic resolution - 1000 dots per inch
>
> At this speed, I could vector scan the entire range of the galvos (4
> inchs by 4 inchs) in 800 seconds. This would be worst case with a
> 100% fill graphic. Most things would be max 10% fill, meaning 80
> seconds for a 4x4 inch square. My mill travel is 28 inches by 16
> inches, meaning 28 squares over the entire area, or 2240 seconds or
> about 34 minutes for a 28 inch by 16 inch engraving. I can live with
> that.
>
> So, I am thinking about using an atmel running a short program to
> take step and direction from emc and output +/-10V through a fast
> serial DAC connected to its sync serial port. Should be a simple
> board.

Why on EARTH would you use step and direction signals to control
purely analog devices? Why not just drive it with a DAC, right off the bat?

It would be a fairly easy hack to change the output drive scheme to allow
several axes to be position rather than the usual velocity. Or, you could use
an analog integrator (op amp + capacitor + resistor) to convert the
velocity signal from the servo DACs to position to feed your galvo amps.
This way, you'd actually have FAST control of the galvos in velocity mode.
If you told it to sweep the galvo at x IPS, you'd get a very smooth sweep at
that rate - EXACTLY.

Jon


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