30 Jun
2010
30 Jun
'10
1:08 p.m.
Having played with a the Canon II printer series
scanners (the guts of =
both the Laserjet II and Apple Laserwriter II), some comments:
Not quite...
I was mis-rememebring last night, and thinking more of the CX, which I
did a lot more work with...
The CX scanner motor has a control board on the bottom, This contains the
brushless motor control chip and a PLL circuit [1]. The feedback is taken
Well, working backwards from DPI and print speed
gives about 3MHz dot =
clock:
=20
300DPI * 11 inches (paper height) * 3ppm =3D 9900 lines per minute
(thus, the line rate is 9900Hz, or 9.9kHz)
9900lpm * 300 dots per line =3D 2.97e6
(thus, the pixel rate is 2.97MHz)
Unless you are using the control board, the above calculation is moot: =
the scanner is a DC brushless motor - the speed is controlled by the =
input voltage. The control board closes a motor loop based on the = from an FG coil in the motor, not from the beam detect
pusel. The motor
runs fine -- and at the right speed -- without the laser bring
presnet.
The SX is actually similar, but the PLL is on the DC cotroller board (I
think it's a separate chip, not in the gate array, but In would have to
check the schematics). Again it takes the feedback from an FG coil in the
motor assembly (IIRC a wiggly track on the motor PCB)
[] The PLL chip, at least the one used in the CX (and IIRC it's used
there both in the scanner motor controller and the main motor controller)
was designed for use in record player turntables (phonographs?).
According to the data sheet, one of the pins is called '33/45' :-)
-tony