Re: Constant Velocity unwinder

A simple analog method is have a tach (tiny DC motor) attached to a
capstan wheel. Form a summing node of the tach feedback (- voltage)
with a velocity command (+ voltage). Use an op-amp to PID amplify the
difference voltage (error signal) and drive the VFD analog speed
input with the output. You should be able to regulate the feedrate to
within 1% that way. A quad op-amp and a dozen resistors/capacitors
should do it. About $0.99 of parts.:-)

Mariss


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Fernando" <fer_mayrl@...>
wrote:

>
> Hello,
> I think this would be off topic, dont know so if you think it is,
> please add the OT on the subject on your replies.
>
> I have a client that has an unwinder, it unwinds flatstock

about .25"

> thick, it has a 5HP motor with a reducer, and a VFD. The client has

it

> right now as to supply the max amount of material it can, but
> obviously, as the diameter of the roll gets smaller the less

material

> is being delivered. What would be a good way to supply constant
> material flow? I was kind of thinking of replacing the motor and

VFD,

> with a servo operating in velocity mode, and attaching the encoder

to

> a following wheel that is in contact with the material being
> delivered. Does anyone know if there are VFD that can accept a

signal

> that regulates the speed, that signal being an encoder or tach
> attached to the advancing material?
> Any suggestions would be greatly appreciated.
> Regards
> Fernando
>