Moderators: Dave Moll, Andrew Davie, Steve Anderson
What steppers are you using ? bipolar ,unipolar ..hard to get the the line speed with a stepper be fine for framing mirror drum ,i used a pulley system to get the line speed when i used that idea but gave the idea up using just a DC motor no clogging...never tried the Chinese stepper drivers might be better than my go Keep working on it Watching with interest !
Gregory wrote:I have been re-thinking the electronics for driving the frame and line scan stepper motors, but I am not sure.
s steppers motors are synchronous motors, the thought is to drive these directly from the sync signals using the 4046 IC as a frequency multiplier to obtain the correct stepper frequency.
The process would consist of:
1) Initially to obtain the stepper pulses using a 4046 as a free running VCO slowly ramping up to the required speed.
2) To disconnect the output of the first 4046 and replace this with the output of a second 4046 configured to operate as a frequency multiplier of the incoming sync pulse frequency (using a frequency divider), so the output frequency would be an exact multiple frequency of the sync frequency. This should provide a very stable sync as the stepper frequency would be generated directly from the sync pulse frequency and there would not be any need for speed correction, as with a phase comparator.
he only problem is that although would be in sync, the mirror position would not neccessarily be in phase with sync signal. This could be overcome by using the mirror photo diode to initially trigger "process 2" only when the sync pulse and photo diode pulse coincide which would be at the start of the mirror scan.
Does this sound feasible?
Steve Anderson wrote:Well the 'Eureka MkI' as before does all that, less the 60-line/750Hz/12.5fps. If you need more input gain (how much?) that can be included as a couple of minor changes, the existing circuit has a gain if between 1 and 3 (VR101). No need to build any of the circuit above.
To add 60/750/12.5 would probably require a change of micro to a 14-pin device (a PIC16F688 or PIC16F684, with extra pin(s) to select which standard) but the vast majority of the rest would be unchanged...and a fairly simple update to the code.
The only additional thing I would need to know is the nominal width of the line-sync pulses at 750Hz.
Steve A.
smeezekitty wrote:Detecting the line rate and sync pulse width is certainly doable though.
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