Re: Re: Cheap Encoders

Jim GREGG wrote:

>
> From: Jim GREGG <gregg@...>
>
> Re the cable drive toan encoder-
>
> There is a commercial unit on the Australian market with a spring tensioned
> pulley system and a stainless wire attached to a point on the moving machine
> element.
>
> I was considering a scheme using a system I used on a servo driven chart
> recorder when I was with NASA. This had a drum on the (shaft type) encoder
> about 1" dia. with a coarse thread on it. The wire was clamped to the mid
> point of the drum thread, and wound round the thread equally both ways. As
> the cariage moved, the wire fed in on one end and off at the other, lying in
> the thread groove, so stacking was eliminated, and the wire was clamped to
> the drum so it could not slip.

I built a simular system, only it used a thin steel tape (0.375 wide,
0.005 thick) going around drums at each end of the table. One end of
the tape was fastened solidly to an arm on the saddle, the other end
fastened to that same arm through a strong spring.

The shaft encoder was connected to one of the drums. That drum must be
of an exact diameter to suit the encoder.

This system worked well for several years, but the drum with the encoder
had to be kept very clean or its diameter would change.

About a year ago I got a good deal on a used Bridgeport DRO and retired
to old system.