I am designing a system, where I would like to add an absolute position encoder. But, my idea does not need the high resolution, or cost of the encoders I am finding in the market so far. I prefer optical over a pot, for its reliability.
The object I am motorizing needs to spin slowly around an axis in continuous rotation, but will normally stop at 90 deg increments. It won't go faster than 3 RPM.
Mechanical CAM switches;
One option I was considering was to use mechanical cam switches, and maching a wheel with detents at the 90 deg mark. There would be 3 cam swtiches for each of the 90 deg positions, so that my system can know when it is approaching a stop, so that it knows to slow down.
It does need to know where "home" is, so I would need an additional cam wheel and switch, to mark home.
It occured to me that I might find something off the shelf. I can find and higher resolution absolute position sensors, but I really don't need any more than 2 bits of resolution.
Electronic position sensors;
Note that I already have a motor encoder, which will primarily be used to control speed, but I can use it for position control after I have homed. However, I don't want the device to have to spin the object up to 360 deg to do the homing. I figured if I had a very coarse optical encoder, I could just home to what ever is the closest point to the current position. E.g. if I am somewhere between 0 and 90 deg, I could just move forward slowly untill I hit the 90 deg location.
It just occured to me, that if I had a 2 pulse-per-rev quadrature encoder at the shaft of the output, I would have exactly what I am asking about. So, it seems that asking the quesitons, has lead me to an answer.
I could just delete the above posting, but since I typed it, I might as well leave it up for others to benefit. Also, if you have any cautions about this approach, let me know.
-Joe
