Proximity Sensors

Question

Silly project but fun...

I want to get some ideas for proximity sensing in a particular application. I am trying to get my dog to run on a modified treadmill and automate his reward. My goal is to be able to keep him centered (with respect to the direction of travel). I need to be able to detect his position and alter the speed of the treadmill accordingly. So:

• When he is centered the speed is at the set point
• As he begins to tire and fall back the speed of the treadmill will slow
• When he disappears from the treadmill, it will stop completely

Most treadmills (including the one I have) come with a safety switch which tethers the jogger and when pulled out, stops the machine. This is not an option in my case because I desire him to get off and on at specified intervals without the assistance of a human. The sides of the treadmill should not be obstructed because he likes to bail to the sides when he is done (or getting his reward).

My current thoughts:

• Use a series of IR LEDs modulated at different frequencies along the side with matched receivers on the other side. So, I can figure where he is at by the missing frequency. This is not ideal because it would require something along the side at least as high as his body which prevents him from bailing.
• Use ultrasonic transducers from the front (facing head), which I could use to determine distance from the front of the treadmill. This sounds great but as I understand it, that frequency is quite annoying to dogs. Don't know if this is accurate.
• Use RFID with one piece being attached to his collar... again, I think this would require sensors along the side which prevent him from bailing. I also don't think I could get position as accurate as I could with the IR LEDs.
• Another thought was to build some sort of canopy and have sensors look downward. Perhaps paint the belt of the treadmill with a specific grid and bounce light off of it.
• Finally, and this is more complex than I'd like, but I could use a web cam and some open source software (like motion) to track the position of a target on his collar.

One last note, the maximum speed is between 8 and 10 mph.

Any thoughts?

EDIT:

Though not the same treadmill, this video shows the same breed of dog (for size) and he also bails from the treadmill in a similar fashion.

I stumbled across these IR proximity sensors from Sharp. These could be mounted at the head of the treadmill facing the tail to get a distance from the head. The specifications seem to fit (distance). Has anybody had any experience with these? He's not exactly reflective so I wonder if these would work well in my application.

Answer 1

Depending on what the shape of the treadmill is (could you provide a picture?) you could use the LEDs by making diagonal lines between the side bars and the floor of the treadmill.

Something like this:

where red circles are IR LEDs and green circles are receivers or vice versa, with some logic work should give you the control over the position of the dog.

You will have some interference between the LEDs but you can use modulation or some form of synchronization to deal with it.