Linear encoders

Buerste · 2010-06-24T05:08:36+00:00

In previous posts I've mentioned that I'm pushing to replace relay logic control systems on some machines with PLCs. The more I think about the advantages, the more advantages I see in increased safety, speed, quality, reliability, etc. While just surfing for linear encoders I don't see any that are cheap enough to buy by the dozen. I don't need more accuracy than .005" nor fast speeds. Most encoders will replace limit switches that sense end-of-stroke or position within the stroke.Setting limit switch positions to adjust a process such as the way a knot-brush is twisted is a bitch! There are multiple knot configurations from fluffy (technical term) to cable-twist and there are multiple wire diameters and tensile. Especially because there are multiple switches that are interdependent...change one and it throws others out of whack. So, I think PLCs and encoders would greatly simplify set-up and make the different configurations easily reproducible. I also envision compensation for oil temps in the hydraulics. Cold or hot machines make entirely different knots even with heaters in the tanks and coolers in-line on the returns.I think by putting encoders on cylinders and slides I can boost productivity and decrease set-up time. Any suggestions for inexpensive encoders? No, I can't afford the time to disembowel computer mice and roll my own. I need an off-shelf continuing supply that will directly interface with standard PLCs.

Linear encoders

Jun 24, 2010 24 Replies

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Buerste 16 years ago

A quick look shows about the same cost as a good limit switch.

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Buerste 16 years ago

I see, and what ever we do will be better than the "Kentucky Windage" on the limit switches and the articulating strikers. I'd post pix but you would laugh! I'll post pix anyway!

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Pete C. 16 years ago

Then that may be your answer. Read them with an analog input on the PLC and you can adjust your trip point to whatever position you want. Resolution based on the PLCs A/D bits and your scaling of the signal from the position sensor.

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Wes 16 years ago

Bimba makes an air cylinder with a linear pot inside. We have been using it for about

200,000 cycles looking for a sealing washer. We feed the output it to an analog input of a plc. Washer is about 0.062" thick and their are some tolerance stacks so it has to working a reasonably tight degree of precision.

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On another line I see we are using a stick on tape and a mag scanner head to measure to

0.005 mm if I remember correctly, I'd have to look that up tomorrow in my files. I just ordered a meter of spare tape and a scanning head the other day. I think that head has RS422 output but I'd have to read the documentation. I really didn't care, I just wanted to order a spare to keep on hand. If I have spares it won't break.

Wes

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