Manage to do the line scan encoder disc and fitted a CNY70 reflective sensor/led as in the photo below. I coupled this onto a single transistor common emitter amplifier and go a decent square wave out of this. Also the sync separator has been completed and works as expected.
- line scan sensor.jpg (80.74 KiB) Viewed 15106 times
There is however a HUGE problem when trying to sync the line scan motor. After a lot of playing about I managed to get a sync - well sort of - but this is very shaky and can drift after a few minutes beyond the capture range of the 4046.
After a lot of checking, I believe the hard disc motor will not be suitable for the line scan motor, in its present form. Although the HDD motor is capable of very high speed and is excellently engineered, it has very low torque, meaning that any adjustment to its speed is slow and making the feedback loop time large. Perhaps with a phonic wheel it could work, but I don't know for sure. In addition the BLDC driver takes time to reach its final frequency, even if the voltage control to it is rapidly change, as it constantly monitors the rotor position before increasing its frequency.
The BLDC driver, although reasonably stable, can cause slight changes to its RPM as it is monitoring the rotor position constantly, and if this drifts, it can cause unexpected very small, but sudden changes to the speed.
I have looked into the possibility of using a stepper motor for the line scan. The 1.8 degree stepper motors unfortunately can only go to around 1000 RPM or thereabouts, but for 60 lines at even 12.5 frames/sec one needs 3000 RPM with the 15 sided mirror and 4800 RPM for 60 lines 20 frames/sec.
A second option is 7.5 degree stepper motors, and here for the same pulse rate the RPM is about 4 times as much. I have scavenged a Matsumi M49SP-2K stepper motor from an old laser copier and tried it out to see the maximum RPM unloaded. The spec shows a maximum of 2100 full steps per sec which corresponds to 2400 RPM.
After testing with a 25 volt supply with the stepper driver set to 0.8 Amps the best performance was with 1/16 micro steps, the motor reaching 5500 RPM before cutting off - if I got things right, which is quite a bit more than the spec
So major changes, I will need to re-mount the line scan mirror with the stepper motor, luckily it should fit into the existing base, provide I cut a hole in the base for the motor. Hopefully after this I should have a good sync, but will have to wait for another stepper motor driver to come.