Re: Manual Control

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Stephen Wille Padnos
<spadnos@s...> wrote:

>
> 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
>

I connected the encoders as explained but when I switch the power on
the servos just run at maximum speed without the drivers showing a
position error. Maybe there is something missing in the circuit. I'm
trying to finish my lathe retrofit during this week before I have to
go back to work so I don't want to order anything from overseas. Is
there a simple way to get the required signal from the encoders ?
Thanks, Glen.