I have a standard recliner chair that spins in a circle. I need to stop the chair quickly when some person large or small nears the chair to prevent injury. The chair is on a standard I beam 16 inch center, particle board carpeted floor. I have full access above and below. I have looked in the area of capacitive as in the floor, pressure mats, infared, and PIR. The room is occupied most of the time. I do not wish to stop the chair if some one is in the room. I only want to stop the chair when someone is in danger of being struck especially in the case of a small child at risk of being struck by the footrest. The sensor system can be installed in the chair or the room. Keep in mid taht a person is always in the chair spinning.

 

Maybe the following work for you?
http://www.edpcompany.com/pdf/Mini.pdf

 

Easiest, most positive way might be to use a circle of retro reflective photo sensors in a base the size of your zone and a sheet of reflective sign material on the ceiling. A vertical light curtain. There are ways to do this yourself at practical cost, the packaged sensors would be kinda spendy for a home installation. Most of the area sensors would be affected by the spinning and kinda broad. A capacitive ring bonded to a piece of carpet might work, but could be stepped over, etc. There are small, inexpensive, narrow angle PIR sensors that could be used as well. I saw those at Jameco electronics, I believe. My personal favorite would be a camera and, but it would require software that could mask the spinning area, otherwise it would be straightforward movement detection by frame to frame comparison. This might be the cheapest way. If you can't write the software, security companies use this type of stuff to turn on a VCR when there is movement to be monitored.

Regards

cww

 

Tim,

I think there are any number of ways to solve this application (Curt has some great ideas), but your description begs another question... what IS this application? I have not run into many spinning Lazy-Boys that cause injury.

Thanks,

Garrett

 

This is a spinning Lazy-Boy chair with substantial modification. It belongs to a 16 year old boy who was born with only a brain stem. He thrills with spinning motion. The prototype system currently in place has bumper sensors. Theses are not satisfactory for the final version as it spins at top speed of 30 RPM. This is more than a chair. It has a plc on board and a plc in the wall which communicate to each other. It also has an audio system and runs various motion programs. The weak link is bystanders can get hurt.

Imagine this chair in your living room. Since it runs programs and can be started by him, out of the blue it takes off. If a toddler is standing near you can see the predicament. I am looking for something failsafe that will prevent the rotation motion only if someone is in danger of being struck. Since people will be all around, in and out, I don't want to stop the chair with normal occupancy.

I would like it to be as simple as a 8 foot loop of copper in the floor that would sense the capacitance change. I originally was going to use a camera but It needs to see in the dark and have not found a viable solution. I also have not found and PIRs that will give me the coverage since its not really motion I am trying to sense.
Thanks for any suggestions...

 

Use a safety floor mat.
They are used in the industry for applications just like the one you describe.
One thing though, you have to make sure it can sense the weight of a small child.
As it is a safety application, I wouldnt compromise anyhow, or do something homegrown. That capacitive thing doesnt seem to be 100% failsafe to me.

 

For small children or anyone who might move quickly without thinking it might be necessary to use physical barriers. 30rpm sounds slow but for a human being it is quite fast and stopping suddenly presents a few problems and risks. However, if there is ample space around the chair I wouldn't dismiss the camera idea. Security cameras usually have the filters removed. The peak response is in the near infra-red and these cameras operate at extremely low light levels. You could use a very inexpensive camera mounted above the chair.
Have a look at the little board cameras sold by the security companies and others. If necessary you could illuminate with a small bank of LED's. There are plenty of diodes available in the 800 to 900+nm range. The camera will respond to these but they won't be noticable to the human eye. You might see a dull reddish glow.

Does the stationary PLC have image input capability?

If you enjoy writing software you could probably get really smart about slowing it down as something approaches, stopping when the object is within a certain range, resuming as the object/s move out of range. Slowing based on position, direction and speed etc.

Vince Dooley

 

My camera proposal would include LED IR "floodlights" to overcome
the dark problem. you would want to do this in any case to swamp
the effects of room light and variable shadows. I have built several
arrays from IR LEDS and they work quite well with filtering on the
camera. Look at Jameco PN 157964CF for an example illuminator. I have
an approximately 6" x 6" array that I have boards for. I'm still
tracking down where I saw the IS sensors. I am willing to contribute
what knowledge and experience I can.

Regards

 

One solution is to look at photoelectric optical sensors. Several different types of "convergent - reflective" sensors could be mounted in the chair or room which would sense a person at a certain distance from the chair, and not beyond. Look at http://www.sunx-ramco.com for more ideas.

Blake

 

How about a custom-made toroidal air pillow (in one or more segments)... something like a pool toy, only larger, and surrounding the air. It would need to be low profile or it'd be a trip hazard... Each segment would have
a tubing port connecting it to an air pressure operated limit switch. When something/someone wanders onto it one of the switches would pulse on.

Along the same line - I've seen pressure-sensitive tape switches, although they are long rectangular things.

In either case I don't know if a toddler would have enough weight to trip the switch... just brainstorming.

Bob

 

Thanks for all the suggestions. Right now I am looking at the camera approach, ceiling mounted, a Digispec box (with the chair masked out).

Detecting the circle being infringed in a wide area that would deaccel the spin motor. Also I would have some photo detectors mounted around the chair base and footrest that would brake the chair instantly if anyone comes closer than 6" within say 5 seconds after the perimiter breach. The chair will de-accel nominally in 5 sec. I could de-accel faster but there is time req for the PLC/s to communicate.

Still looking for ideas... I am still looking for the right infrareds that could reach out a little further and insight for the best camera and controller and if the infareds would interfere with the camera?