Re: Constant Velocity unwinder

THanks for you reply Mark,
The VFD does have analog input it is a Yaskawa VFD, I had thought of
using the capstan and pinch rolls to feed the material, I just wanted
to know if it could be done by just adding some electronics to it
instead of building a whole feeder. The $0.99 suggestion from mariss
does not seem too far off, providing I can design the circuit and tune
the op amp PID components to my application.
Thanks again!
Fernando

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Mark Whitis <whitis@...> wrote:
>
>
>
> On Mon, 17 Jul 2006, Fernando 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.
>
> If you were to take a typical DC servo drive (either DC input
> or pulse direction input) that might be used in a CNC application
and hook
> it up as you are suggesting, there is a good chance you would have
> serious oscillation problems because of the loose coupling
> between the encoder and the motor which the typical servo
> drive is expecting to be tightly coupled. Not that there aren't
> servo motor controllers that can do the job or ways to fix
> the problem with ones that are less well suited. But you
> are likely to buy a high performance product expecting smooth
> operation and end up with performance you could have gotten
> just by flipping the on/off switch.
>
> Oscillation can be a problem with just about any configuration
> but your typical VFD is probably more closely tuned to your
> application. Speed changes on the order of a second rather
> than a millisecond. But remember to ask your vendor
> about oscillation in your application and you will probably
> need to configure the drive for slow response times or
> low pass filter your signal input (in 0-10V or digital form).
>
> Your existing VFD has no inputs of any sort to control the speed
> other than a keypad/display? What is the make/model? Even
> a $320 VFD has a 0-10V input and external run/stop signals
> and modbus inputs and a remote up/down inputs.
>
http://www.driveswarehouse.com/Drives/AC+Drives/Compact+VFD/L200-037LFU.html
> Not even a front panel or remote operator control box potentiometer
that
> can be disconnected and connected to your source?
>
> Mechanical solutions:
> - Move the motor from the reel to where the feed material exits
> and put a capstan/pinch roller there (i.e. one wide tire on
> the motor shaft and one spring loaded or weighted).
>
> - On good reel to reel tape decks, they ran the tape around
> a swing arm roller between two fixed rollers. The position of the
> swing arm measured the tension and told the reel servo how fast
to move.
> Note that this doesn't just give you a constant feed, it gives
> you the speed required by whatever machinary is processing
> the stock, assuming it has motors to move the stock but not
> strong enough to run the reel. Depending on the stiffness of
> the material you might need several feet of space for the sensing
> setup. Use the swing arm position with a potentiometer, optical
> sensor, switch or switches to generate a 0-10V, 4-20ma, start/stop
> signal, or speed select signals, or up/down signals.
>
> If you know how to use microcontrollers, they can be used as
> an interface between encoders and whatever inputs your system
> needs. Or a PLC.
>
> PC solution:
> you might be able to use the spindle speed control features on
EMC or
> other milling servo controller to drive either a motor or
> a 0-10V input.
>
> Frequency to voltage converters are availible as ICs or as
> industrial modules that mount on a DIN rail. google
> "frequency to voltage converter DIN rail". Can be used
> with a decoded output (usdigital sells converters) from an
> optical encoder - don't use the raw signal as it suffers
> from "bounce" when you are on the edge of line - to produce
> a 0-10V output from the encoder signal. Polarity will probably
> be opposite what you want but you may find some that can
> invert.
>
> Check out http://web2.automationdirect.com/. I have not used their
> products, they were just the first match with an encoder input. But
> their drives have a number of features that are applicable:
> - Digital inputs (start/stop, speed selection, etc) standard
> - 0-10V or 4-20ma analog inputs: standard
> - encoder feedback: optional on some models
> - modbus: standard on most models, optional on others
> - ethernet optional on most models
> You might find other model that have PWM or reference frequency inputs.
>
> google "variable frequency drive "encoder input" OR "encoder feedback"
> for more VFDs.
>
> You should not need to replace the motor if you change drives; you
> should be able to find a drive that will work with your motor, assuming
> that your motor can turn fast enough (with the aid of a VFD that
> can produce a high enough frequency).
>