Table of Contents
Advertisement
Detailed Operation of the A4 GALVO BD
??All apologies to Doug. Below is an attempt to provide a more detailed description, but to make it less technical. I don't know how well I've succeeded.
This illustration is a more detailed block diagram, but not as complex as
Doug's. It will, I hope, include all that is useful, but no more than is
useful to describe the function of the A4.
1234563 – 12/12/94
1. To set up for a PLATE scan, the system (WHAT?) sets the plate-size-select
inputs to the State Machine for the PLATE being scanned, that is, the plate
width and the number of lines to be scanned ?? is this true?.
2. It then writes the values for that plate size, which were set up in calibration to
the Offset and Amplitude D/A Converters. The values loaded will vary from
machine to machine (??why?). What are these values, do the values include
the # of pixels plus the dwell time and the ramp up??
3. When the Galvo Clock starts running, the 13 bit counter starts counting up
and sends the current value of the count to the State Machine.
4. As the count progresses, the State Machine outputs a 12 bit value indicating
the desired current position of the GALVO between the beginning and end of
the scan line, as defined by the offset and amplitude signals. See ?? signal??
what should I call this??
5. The Closed-Loop Servo Circuit receives input about:
a. The desired GALVO ??shaft, mirror??position from the State Machine
b. The actual GALVO position which is derived from signals of the Galvo-
Position-Sensors.
6. The Servo Circuit compares the Desired Galvo Position against the Actual
Galvo Position. The resulting error (difference) is combined with the Desired
Galvo Position to determine the amount of current that is delivered to the
GALVO coil. The more current that is passed through the coil, the further the
GALVO will turn the MIRROR.
7. At the end of the cycle (which includes ramp up, trace, retrace, dwell time??),
a. the State Machine sends a line-start signal back to the DIGITIZER BD to
indicate that the full GALVO sweep is complete for that line and it is ready
to start another one.
b. At the same time, the counter-reset signal ?pulses? to set the 13 bit
counter back to "0" zero. If the Galvo Clock continues to run, the cycle
will continue and another sweep of the GALVO will begin. This will
continue until all the lines are read ?? how does it know how many??
OPTICAL Subsystem
9–41
Advertisement
Table of Contents
