Re: [CAD_CAM_EDM_DRO] Interfacing EMC with Bandit drives

The Bandit in discussion here is on a Bridgeport mill and I would
like to hopefully replace the control circuitry with a PC while
retaining the present Bandit drivers and thought that EMC may be the
appropriate software for this.

The Bandit driver uses a sense resistor for sensing current and
controls it by varying the duty factor of the voltage pulse applied
to the motor windings. The control board does put out a command
coupled into the driver board via an opto-isolator to cut the holding
current in half.

I found that the resolution is .0002 in. per step and the rapid
traverse is 60 ipm. This calculates out to a 5 Khz for the step
input. It would seem to me that the chop frequency should be several
times the max step frequency. I don't know why they used 5 Khz, it
is very noisy.

There are 5 input signals to the Bandit driver. The position signal
input consists of 4 opto-isolators. A move signal is coupled to the
5th opto-isolator which terminates the hold mode. After the move
signal is goes to zero, there is a 5 second delay via a 555 timer
before it reduces the current to the hold level.

The step signal sequence into the two channels is as follows:
A B
01 01
01 10
00 10
10 10
10 00
10 01
00 01
repeating beginning with 01 01

Direction depends on which way you go through the above sequence.

With this information, can EMC handle this task? If not, what other
software might be appropriate?

Jack Ensor



Jon Elson wrote:

>
> jensor@... wrote:
>
> > Is it possible to interface a PC running EMC with a Bandit Stepper
> > drive which operates at about 5 KHZ. I think it would be possible to
> > raise the frequency in the Bandit driver, but I don't know what the
> > limit might might be. The frequency is set by a 555 timer.
>
> You are saying the chopping frequency is 5 KHz? It may cause some
> additional heating of the driver transistors or the energy absorbing
> components (resistors, Zener diodes, etc.) if you raise the freq.
> But, if it runs cool enough, you may be able to do that. Is it noisy?
>
> Depending on what signals come out of the Bandit control to drive
> the stepper drivers, it may be very easy to do this. Does the Bandit
> have some form of current control that lowers motor current when
> holding? EMC does not currently have such a feature, but it could
> probably be added. It can also be done externally, fairly easily.
>
> Jon