Just had an idea that we could use a sawtooth interval strip to give frequent position checks with one of the optoswitches. The other optoswitch would be used for both endstops.
The sawtooth interval strip would look like the ascii diagram below. The 'O' is for the opaque part of the strip and the 'T' for the transparent part.
OOOOOOOOOOTTTTTTTTTTOOOOOOOOOTTTTTTTTTOOOOOOOOTTTTTTTTOOOOOOOTTTTTTTOOOOOOTTTTTTOOOOOTTTTT
Whenever the interval switch showed that an interval has been crossed, the microprocessor would check to see that the stepper is at an interval location, which would be in a lookup table. If it is not, then it would go home to reset the stepper position.
When the endstop optoswitch is triggered, the microprocessor would check the interval optoswitch. If the interval switch was off (when it is on the opaque 'O'), that means the tool head was on the far left and if the interval switch was on(on the transparent 'T'), that means the tool was on the far right.
So with this setup, without additional electronic components, we could get frequent position checks. This would be enough to handle occasional stepper motor slips. The extra hardware needed is an interval strip and an extra optical endstop. There would be extra software needed to compare the interval crossings with the stepper positions.
After an interval crossing which does not match the stepper position, it would also be possible with additional software to determine the absolute position by counting the steps and therefore measuring the distance to the next interval to determine which of the intervals was just crossed. However, there could be a measurement error if another step was missed, so going home would be more reliable, although slower.
Cheers,
Enrique
Edited 1 time(s). Last edit at 09/26/2009 04:48AM by Enrique.
