I have a winch motor with a cable that is controlled by an arduino.
I would like to detect a marked point on the cable with the arduino. This marked point will stop the motor. It will have to be detected from about 6"-8" away due to the winch construction.
I have considered marking the stop point with Glint (IR Reflective Tape) and using the Sharp GP2Y0A21 IR Sensor to detect a voltage change when the Tape goes by the eye.
Anybody know if this would be possible or if there is a better way before I go buy parts? The Sharp sensor says it is supposed to be more resistant to reflection. If that is the case.. the reflective tape may not cause the motor to stop
I am not too familiar with a winch motor setup but I can imagine that the least thing you want is arduino fails to detect the marker and keeps rolling the cable. This makes me think of mechanical switches that can be triggered by an object secured on to the cable, not an optical sensor. But now just thinking about this switch, the cable is going to shift from side to side as it is rolled on the winch or do you have something that restricts the cable from shifting from side to side?
As should be obvious, this is going to require particularly rugged construction.
Generally, an industrial-grade microswitch pair actuated by a fork (or in fact, loop) straddling the cable at the desired point with a large clamp on the cable which will catch the fork every time. The fork would be made of rugged metal stock and pivoted such as to not be damaged even when it is dragged into the winch.
One microswitch directly stops the motor, whilst the other signals the Arduino that it has done so. The latter (but not the former) could be substituted with an opto-interrupter.
Thank you for the comments. I changed the spelling in my original post.
I have considered most all of the above in Regard to rugged construction, the Tape wearing off etc. Just to clarify, These illusive "Stop Points" are to stop on the way down(out), and are not being used a safety points. They are strictly to stop the motor at a specific point for a look/feel we are trying to create with a screen. The motors are remotely controllable thanks to the arduino so it can be manually stopped if a stop point is passed over.
There is already a physical mechanism to stop the motor at a specified point on the way up (in). It is exactly what is described by @Paul__B. There is a metal ring around the cable and then a large object attached to the cable. when the large object hits the ring, the motor shuts off.
My problem is replicating a similar mechanical stop action on the way down.
Because I'm using the arduino, I can set a run time etc on the motor so it will run the motor down for a specified period, however this is only reliable if the motor has been wound all the way up to the stop point. If, for some reason, it was parked part way up the cable, this fails.
Looking at that picture, there seems to be some kind of cable guide hanging down underneath. Is it fixed in position or can it move a little in the vertical direction? If you attached a plastic tie to the cable, would it move that guide a little as it passed through it? If so, a microswitch or optical detector could pick up that movement? An optical detector could be a low power ir led/laser one one side and an ir detector on the other. If the guide moves slightly, it would block the beam and this could be detected by the sensor?
jgiebler:
My problem is replicating a similar mechanical stop action on the way down.
Ah well, that is a different matter entirely. You want to detect a marker as it rolls off the winch, not onto it. That gets really tricky for the reasons previously discussed.
What about using the same object secured to the cable and a mechanical switch further away from the shut-off switch? This way the object on cable only moves between these two switches.
I'm almost thinking of something separate from the winch cable. Take a cheap tape measure and suspend it by a spring next to the winch. Have a switch closed when the spring gets pulled.. Now attach the other end to then screen. You just need to adjust the length of the tape in the tape measure. When it's fully extended at the length you want it pulls down and activates the switch..
