Re: Wish to add DRO to tube bender using rotary encoder and timing belt

Hello,
I was hoping just to plug the encoder into a propriatory display, if
those are too expensive then i could use an old pc. Happy to use
largish parts as there is plenty of room. Will the type of encoder
used for the length axis be suitable for the rotary axis?

Thanks for all your info, understand most of it. Could do with
someone from the UK recommending a good source of parts.

Many thanks.


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "gcode fi (hanermo)"
<yahoog@...> wrote:

>
> Q: How do you plan to interface it, and to what ?
>
> Any quality timing belt solution will work.
> All will have about 0.1 mm or much better accuracy - down to about

0.01 mm.

>
> If you are using mach3, for example,
> you can just buy belts and pulleys, and encoder, and fit all

together.

> You can then directly input the encoder reading into mach.
>
> It will display it with no work.
> With simple VB code, you can use it in a macro pump, to adjust your
> work/bending.
>
> Note-
> for good results, you must tension the belt.
> A few bearings on tensioner pulleys and the belt in tension about

10 kg,

> for 3 mm timing belt, and there you are.
>
> The encoder res you need depends on the diameter of pulley where it
> contacts the belt.
> You need 6 teeth min contact - its best to use 12 teeth pulley or

more.

> (Technically - it does not matter as this is a no load measuring
> application. Practically, its hard to work with very small parts,

shaft,

> pulleys and teeth).
>
> Circumference of circle is 2 x pi x r.
> So for say 14 teeth pulley, with 5 mm htd belt.
> D = 0.832 in ( 21.13 mm)
> Pitch D is = 0.877 in ( 22.27 mm)
> So belt circumference of this pulley is 2 x pi x pitch D / 2 = pi x

pitch D,

> = 3.14 x 22.27 / 2 mm = 69.92 mm circumference.
>
> 1 degree of angle moves the belt 1 / 360 degrees * circumference.
> = 69.92 mm / 360 = 0.194 mm.
> So a 1 degree or 360 quadrature count encoder resolves to this

resolution.

> So a 1 degree quadrature encoder, or 90 count (360 / 4 = 90 counts

or

> lines) would give you about 0.19 mm resolution.
>
> To achieve a given accuracy, you should generally count and resolve

to

> about 4 x theoretical resolution.
> Small res encoders from US digital, between 100 - 300 counts, have

the

> same cost.
> So a 200 lines encoder will give you the needed accuracy.
> Your speed and sampling rate is low - as bending will take seconds
> (compared to resolving a servo running at 5000 rpm) therefore you

do not

> need to worry about the sampling rate.
> As the cost is the same, and more accurate is better, get the 300

count

> encoder.
> The cheapest US digital encoder is more than adequate. About 20$.
>
> A 14 teeth HTD pulley of 5 mm teeth, 9 mm wide will be easy to fit,
> tension and will last for essentially forever in this application.
> You can use a smaller one if you want (like xl or mxl).
>
> Pulleys and belts from any of the usual us suppliers.
> Good luck.
>
>
> al.swift wrote:
> >
> > Need some advice. I want to add DRO to the length axis of our tube
> > bender. I have seen something similar which had a long toothed

timing

> > belt approx 3m runing thru a rotary encoder with a couple of small
> > wheels acting as tentioners. The encoder was fixed on a linear

guide

> > that allowed it to run up and down the timing belt. I' m looking

for

> > 0.5 mm acuracy / repeatability (I know they're different). A

similar

> > system can be used for the plain of bend angle but using a closed

belt

> > measureing perhaps 0.5 degree. Where shall i look first?
> >
> > __._,_.
>