>That 2.5µS value is experimental? Or how did you calculated it? Which is
>after all the size off the printed dot?
>I was following Adam Seychell. 2mils dot (~0.005cm) printing a 20cm line
>(~8") (like a A4 laser printer) is 0.1cm² area so is 6mJ and with 85mW
>laser is ~0.07s which gives the 14Hz (lines per second) and 140rpm with
>the 6faces mirror. With the 30% loss slowing to 100rpm is a good number.
>And there is the thing you can't use all mirror surface but that needs
>higher accuracy and longer distance from mirror to pcb and not slower
>rpm. You have to wast a portion off the surface for start counting only
>when the reflected beam touch the light sensor on side off your
>lenses/printed material.
>But still is almost 10times faster than your actual machine. Making a
>20x30cm (~100inch²) printed in 7minutes plus turnover mechanical delays
>in each line (ok 10minutes). Which is as good as 30.000+eur film
>photoplotters (ok those make 8000dpi not 720) but directly on pcb!
>Your 2.5µS number is about 5 times faster, so please tell me i am wrong
>because i want to be :>
2.5 microsecond value is both calculated and experimentally verified.
Here is the calculation
Dry film requires 10-15mJ/cm2, let's take 15mJ (because of wavelength of blue laser is
405nm). 720 dpi resolution corresponds 35micron-meters spot size, actually it should be
larger than that since on a continuous line there shouldn't be any discontinuity.
Let's assume it is 50 micron-meters and laser output power=150mW. So,
Spot area~= 20e-6 cm^2
Energy required=15∗20e-6=300e-6 mJ
Exposure time= Energy required/Laser_power= 300e-6/150=2e-6=2 micro-seconds.
According to my experiments below 1.5 microseconds, dry film couldn't stay
in a developing bath, it is not strong enough.
BTW, this 8000dpi is it equivalent resolution or real hw resolution? If it is equivalent
resolution it doesn't have so much sense.
>But can't the actual machine print in both directions? If the
>misalignment is because delay between encoder signal and firing the
>laser, which makes printing differ in the reverse directions. You could
>try (if you not made it yet) synchronise the laser with the signals
>coming from the encoder directly. Between positions it 'loads' (shifts)
>the next bit, and is the encoder signal which will fire it.
Here is a simple demonstration of the problem,
|=encoder pulse
.=no pulse
-> =direction is left to right
<- = direction is right to left
∗=laser dot
Unidirectional printing, lets print 2 dot in 2 rows
->
.......|.......
........∗
<-
->
.......|.......
........∗
Output
........∗
........∗
Bidirectional printing
->
.......|.......
........∗
<-
.......|.......
......∗
Output
........∗
......∗
Actual positioning error will be more that, because of state machine delay.
There is a solution which I implemented on inkjet printer and similar concept
can be applied to this case. The solution is, instead of actual encoder signal
estimate encoder position by time delay using previous encoder durations and
generate a pseudo encoder pulse to compensate position error by time delay.
Another method digital pll can be used for this purpose.
> I think it is a good idea, as far as I
> know Sun Microsystems used similar concept in their laser printers.
They were using VGA port as far as I know to generate/transfer raster image.
I don't know the implementation details.
Volkan
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