Which sensor?

We are constantly moving truck trailers around the site using a special vehicle known as a yard mule. The mule has a hydraulic cylinder attached to the 5th wheel, so that the driver does not have to raise and lower the trailer jacks when he moves a trailer. He simply backs up to a trailer, couples the 5th wheel, and rasies the trailer by raising the 5th wheel. This makes the trailer a couple of feet higher than it would be, when connected to a standard tractor. This is not an issue for most of our bays. However, we have one building that has slightly lower overhead clearance, and if the driver forgets to lower the trailer a little, he hits the overhead.

The question is: What type of sensor could I use to shoot across three loading bays, about 50 feet. Ideally I could place a transmitter on one side of the building and a receiver at the other side, the beam would be set at the maximum allowable height, then when the truck is backing in and breaks the beam an alarm would sound. Then the driver could lower the trailer until the alarm stops. No alarm means height is okay, back on in.
I don't have any experience with sensors for this great a distance that has a beam tight enough to sense say +/- 1.0 inches. I'm looking for some recommendations, web links, etc...


thanks in advance,
Ken

We are using a Syc laser sensor for an overhead crane running 75 feet left/right and holding tolerance well under an inch.


I don't have the exact pn we use right now, but here's a link.

http://www.ferret.com.au/articles/52/0c01bc52.asp

I don't know of any single beam sensors with that kind of range (though I gotta believe they exist) but there is a line of safety curtains that advertise operating ranges up to 30m; see Guardscan. Pricier than a single sensor but maybe less than the cost of repairing the truck bay.

How about a piece of break away PVC pipe that the Mule driver has to reattach if he hits it?
Kind of like a Pole vault target.
Oh never mind.. I just noticed that it is 50 feet.
Would a light beam like they have at 7 eleven work?

Ken,

I would look into the SICK sensors. Here is a page that should help you search if you like.
http://www.sickusa.com/live/master/ss.asp?FAM=StandSensor

Hope this Helps,
Bob O.

We used some Honeywell sensors in '96 that were supposed to be good for 300'. We were acroos town from the Honeywell factory. They may have been prototypes, as I have not sen them on the market. We used them in lieu of a safety pull rope in case someone fell into a tire conveyor. There was not a big safety issue, just to stop the belt so the operator didn't get to bruised up by more tires faling onto him.

I am pretty sure that there are other manufacturers out there with something similar.

Would some of the ultrasonic detectors have a tight enough beam to put one at each bay?

regards.....casey

The Sick products appear to be exactly what I'm looking for, thanks for all the responses.

Hey Ken, how’s thinks?

I don’t want to complicate thing's but have you thought of putting say an ultra sonic sensor on the mule, set the required barrier distance and sound an alarm if distance is broken, similar to a reversing sensor on car.

Just a thought


Lance

Use a laser. They work really well with a very tight beam, if you select the right one.

You said that the lowest overhead is only slightly lower than the normal overhead. Why not install a hard limit in the lift of the mule? Make it so that the mule can lift no higher than allowed for the lowest overhead.

Having sensors and alarms in this arrangement is providing a false sense of security. Any sensor or alarm device could fail at any time.

Meanwhile, not hearing any alarms, the mule-skinner is feeling safe and secure as he high-balls down the path towards the lowest overhead on the lot.

One thing to be aware of is the effect of weather on optical and ultrasonic sensors. Rain for optical and wind for ultrasonc can be a problem.

Knowing that it may be difficult to limit the height the yard mule has when lifting it may be easier (and cheaper) to mount something, on the yard mule, like a limit switch (or ?) with an alarm buzzer to signal it has exceeded bay height.