Re: [CAD_CAM_EDM_DRO] EMC questions

samcoinc2001 wrote:

>I finally got emc installed on a computer to play with. It was the
>bdi_emc v2.20 cd. It took about 4 tries to get the right hardware
>combo. Ended up with a 450mhz pentium II with a 440 chipset and a s3
>video card. I have it installed and have been playing with the
>emc_sim Icon on the desktop.
>here are a few questions.
>
>I am new with linux and emc. What are some good beginers sources for
>info on it. The install/setup instructions are a little vauge.
>
>I am going to run stepping motors with emc.
>This little snippet is from the install/setup instructions.
>
>"Stepper motor control is implemented using a second real-time task
>that runs at 100 microseconds. This task writes the parallel port
>output with bits set or cleared based on whether the a pulse should
>be raised or lowered. This gives an effective period of 200
>microseconds for a full up-and-down pulse, or a 5 kilohertz
>frequency."
>
>If I calculate that right I can only have a max speed of 30ipm with a
>resolution of .0001/step. Am I correct with this. Is there any other
>solutions?
>
>

Yes, your calculations are correct. But, the 100 uS period is not fixed.
As long as you have sufficient CPU speed to keep up, the period can be
reduced. With a modest Pentium CPU, say 333 MHz, you can go to about
16 uS. When the mouse cursor gets sluggish, you are close to the limit.
If the system freezes completely, you have exceeded the limit, try a
larger period.

>What about an external step generator? How does that work.
>
>
>

When you get into higher resolutions, the external step pulse generator
starts to look real good. I have a product that makes the steppers look
much like a servo to the computer. The CPU sends out a step rate value
to the board, and reads back a position, which is maintained either by
counting the step pulses, or by reading an actual encoder on the motor.
Since the computer is not saddled with handling individual step pulses,
but is working at a higher level, just dealing with velocity, and the
hardware is working at the low level of the step pulses, the timing
jitter of the step pulses is made very small. Step pulse rates up to
300,000
steps/second are supported in the standard version. If you need more,
that can be arranged. See
http://jelinux.pico-systems.com/univstep.html for more info.

This board also provides 16 opto-isolated inputs for limit and home
switches, and place to plug up to 8 solid state relays for spindle
coolant etc. control. It also has an all-hardware E-stop circuit.

Jon