Re: Rotary to linear translation - an interesting idea.

On 12 Apr 00 at 0:36, CAD_CAM_EDM_DRO@egroups.com scribbled
furtively:

> Message: 16
> Date: Tue, 11 Apr 2000 13:35:35 EDT
> From: ptengin@...
> Subject: Re: Re: Rotary to linear translation - an interesting idea.
>
> In a message dated 04/11/2000 4:16:29 AM Hawaiian Standard Time,
> dafKite@... writes:
>
> << and by adjusting the deflection you
> can indeed adjust the 'encoder counts per linear unit travel'.
> >>
>
> I understood the straight versus curved part but this portion is tough for me to
> comprehend....

sorry, I was getting tired of typing by that time..... it was a long
morning...

because the tape is attached to the table and must move at the same
speed, and when you deflect the tape with the wheel it now
travels around a radius, and that circumferential distance is
larger than the straight line distance, the tape must travel around
the radius faster in order to maintain it's length since the tape is
not stretchy (to that degree anyway).

now, if you increase the deflection, more tape is around the wheel =
greater circumferential distance, ergo it must go past faster,
turning the wheel faster = increasing the counts per linear unit
moved by the table/tape assembly.

that's why you make the encoder wheel slightly smaller than you
think hence giving you too few counts per linear unit, and adjust for
correct count by pressing it further into the tape.

hope that clarifies?

PS: I say 'unit' above because some work in inches and some in thou
and some in mm and if I use one it becomes too specific and I have to
give actual values that are true but I'm trying to convey the concept
and theory, not actual values....

BTW I spoke this problem and my explaination of it to my wife last
night and she understood it and agreed with me on the principal.
she's into dogs and horses and so I must think that either
a) I'm correct
b) I should have been a lawyer cos my argument was convincing even if
incorrect (-:

IMHO it's not about how the tape stretches on the inside/outside etc,
but just about the circumferential distance travelled as compared to
the straight line distance the tape would have traversed if the wheel
wasn't there.

also note the whole system depends on the spacing of the support
rollers. if one moves, you'll have to recalibrate....


--
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