Using flexible DRO scale

Good morning. I have a project where I need to accurately track a rotating element in a paper converting machine. I see various offerings of flexible scales but I have no experience with them. My plan is to attach the scale to a 12 inch diameter column and track the rotational position of a cutter head. Have any of you used these flexible scales and if so are there any pitfalls that you know of? I can't quite figure out how to join the two ends without losing indexing at the joint. Nothing from my search explains how to make that joint. It may be better to use an encoder disc but there is no access to the top or bottom of the rotating element. I need to measure from the side if possible. My other option is to say to heck with it and let the plant electricians figure it out. That is an issue in itself. I walked in here and there are eight guys standing around and I swear they don't have a full set of teeth between them. Thanks very much.

What's your positioning requirement? 0-90, 0-360, continuous? If under 360, I'd expect a gap is NBD as long as you have a precision homing method placed within the range you need.

I'd almost wonder (if the accuracy requirements aren't super high) if an appropriate pot with rubber tire bearing against the side of whatever you're rotating could work.

0-360 unfortunately Milland. I thought of a semi flexible rack with an encoder wheel but gave up on that for one reason or another. Perhaps a rubber wheel with an encoder would work. Let me kick that around.
Thanks.

Perhaps an actual rotary encoder would work for you. Renishaw makes a wide variety of relative and absolute rotary encoders with quite large diameters. The precision can be extraordinary. Here is a link: Rotary incremental encoders
The best thing would be to talk to an applications engineer. You need the OD of what you want to attach it to, the precision and/or resolution you need, the environment it will work in, and some idea of what is around it. The read heads are pretty small, but they do need to attach to something stable. Most likely you would need to fabricate a support structure to attach the encoder to the 12" element, but that may not be too difficult. I used these encoders in an extremely precise spectrometer I had to build- they were GREAT!!!
All the best,
Michael

Honestly 2 optical slot type readers and a simple slotted edged donut, if you get creative you can easily get sub degree accuracy this way. That said if you want tenths of degrees or better that's a whole different ball game.

adama said:

Honestly 2 optical slot type readers and a simple slotted edged donut, if you get creative you can easily get sub degree accuracy this way. That said if you want tenths of degrees or better that's a whole different ball game.

Click to expand...

Or a printed tape with a "bar code", then optical readers with angular offsets. Sounds like a relatively low accuracy application (i.e. not machine tool level), so many options...

^ Problem with a printed tape and those readers is cost and trying to get the tape to join up nicely, a circular collar even if split in half is a lot easier to do good joints on and also a lot easier to have very accurate spacing of the code across those joints. Retro-reflective sensors are normally way more a pain in the ass than simple broken beam sensors. Also if you go ferrous on the toothed ring you open up all sorts of induction based sensors that are noise, light and most importantly in the paper game dust immune.

Fair points...

If the max number of rotations built up is small, maybe use a straight scale attached to a metal tape or cable on a spool that wraps around the column with a spring return at the other end of the scale, and a stationary reader head. Or attach the tape to the head and move the head over the scale, whichever is easier. Won't work if the thing spins more than a few rotations or does not return to the original position in the opposite direction of course though...

Sorry for the delay in getting back to thank you for the replies. I was wondering if there was an optical pickup kind of like a computer mouse that does not require a "target". I have no idea how they work but a mouse can be used on just about any surface. Not sure of the resolution either. I need about .001" accuracy. Thanks again. Many good ideas here.