OT: Sensor Question

ANSI 40 chain, has anyone sensed an individual link (or maybe the pins for 2 per link)? What sensor have you used?

It's this or a prox with a sprocket.

I would look at something in this family:
http://www.keyence.com/products/sensors/fiberoptic/fiberoptic.php
with an appropriate fiber.

I have only tried to use a prox to detect a pre-existing sprocket. I didn't have a whole lot of luck. You will need a fairly small diameter prox to resolve individual teeth. Unless you machine a sprocket, the normal axial and radial runout of an off-the-shelf sprocket can often carry the sprocket out of the range of the prox. This will cause you to miss counts.

How fast is this chain going? If you go with the sensors I linked to above you can get 20 microsecond response if needed. Will your controller be fast enough to pick up individual links?

Keith

There are several ways I have done this depending on situation. One method obtain wide attachmets for the chain and use a prox etc to detect it; http://www.daidocorp.com/pdfs/page120.pdf

Another method is use a double roller at the master location then adjust/mount your sensor for sensing it....I recommend sensing when the chain is ON the sprocket. http://www.grainger.com/Grainger/wwg/itemDetailsRender.shtml?xi=xi&ItemId=1611708383&ccitem=

ANOTHER method is to mount another sprocket onto the original sprocket, this can allow more than one sensor to be used.

Depending on application you may want to look at mag pickups too.

kamenges said:

I would look at something in this family:
http://www.keyence.com/products/sensors/fiberoptic/fiberoptic.php
with an appropriate fiber.

I have only tried to use a prox to detect a pre-existing sprocket. I didn't have a whole lot of luck. You will need a fairly small diameter prox to resolve individual teeth. Unless you machine a sprocket, the normal axial and radial runout of an off-the-shelf sprocket can often carry the sprocket out of the range of the prox. This will cause you to miss counts.

How fast is this chain going? If you go with the sensors I linked to above you can get 20 microsecond response if needed. Will your controller be fast enough to pick up individual links?

Keith

Click to expand...

I won't be moving very fast linearly, somewhere around the 4 in/sec range. 40 chain is what, maybe 2 links per inch, so say 16 signals per second max? Not all that fast.

I do have a full machine shop here at my disposal, so making a sprocket is just a matter of providing a drawing.

I was thinking about putting a second sprocket on, an analog prox, and setting up a window in the analog value.

I've got a system that moves 22 inches linear/rev, and I need to be able to stop it within +-.5, which is perrty darned forgiving.

mmmmhhhhhhhhhhhh.

I'd go for a second sprocket. Turn the OD down so that the arc length of the turned down tooth equals the arc length of the gap between teeth. Mount the prox switch axially. That way, you can count both the off-to-on transitions and the on-to-off transitions and your resolution is better. By making the prox's on time equal to the off time, you're able to sense the maximum speed possible for the PLC's scan time.

I usually make something from a two piece clamp collar like steve described. Put as many flags on it as you need for the resolution, and make the gaps such that the on-time and off-time are equal at the PLC input. Clamp it on the shaft against the sprocket and sense it from the side so runout isn't a problem. Beware that this method isn't 100% accurate, error can accumulate unless there is some way provided to reset or establish known values at a particular point in the sequence. The reason is, when stopping, if there is any backlash at all it can cause an extra transition and the PLC can't know the direction. It may count a backlash pulse as a forward pulse. Just program a method to deal with it and it works great.

I think this should be no problem if you get the right prox switch and mount it close enough. A #40 roller chain has a pitch of 1/2". Red Lion has magnetic proximity pickups that get down to 32 pitch gears - much smaller targets than the #40 chain.

www.redlion-controls.com