Re: [CAD_CAM_EDM_DRO] Re: Manual Control

roboticscnc wrote:

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "James Peck" <jamesgpeck@y...>
>wrote:
>
>
>>Thanks James, a schematic is exactly what I'm after. What I had in
>>
>>
>mind was somehow converting the quad signal from the encoders to a
>step / direction signal ( using a switch to select either manual or
>cnc control ). Maybe there is a simple circuit to do this. This way
>the computer doesn't have to be switched on. Any information anyone
>can send me would be greatly appreciated.
>Thanks, Glen.
>
>

Actually, an encoder is already step/direction, as long as you don't
spin it too fast (which you can't by hand ;) )

Just connect phase A to the direction input, and phase B to the step
input. If it runs backwards, switch the two wires.

Here's why it works. This is the pattern of phase signals from an
encoder (note that they always specify whether it's for clockwise or
counterclockwise rotation in the datashets):

A B
0 0
0 1
1 1
1 0

The stepper drive will only be looking for one edge of the step signal -
let's pick the negative-going edge.
If you apply the sequence above (dir=A, step=B) to the drive, then it'll
see a 1 on DIR when the negative step edge appears.
If you spin it backwards, you get the reverse sequence:

A B
1 0
1 1
0 1
0 0

Now, every time the step pulse goes to 0, there's a 0 on the DIR pin.

The disadvantage is that you get only one pulse per full cycle - there's
no "resolution multiplication" that we're used to.

Oh - and the speed limit is due to changing the direction line during a
step. With 1000 CPR encoders, you'd have to spin it at about 12000 RPM
to have a problem ;)

- Steve