THEORY GUIDE Optical
10DEC05
TG4825-1
Page
61 of 120
Traces of the GALVO Description
Desired position
trace
• position A - the DIGITIZER BOARD has sent a signal to the
GALVO to retrace
• between Positions A and B - the system is waiting for the GALVO
to complete the retrace
• between Positions B and C - the speed of the GALVO is
increasing to operating speed
• position C - the PIXEL CLOCK starts and the PMT/DAS BOARD
starts measuring the pixel data from the SCREEN. The laser
beam is at the edge of the SCREEN.
• between Positions C and D - the complete line of pixels is
scanned
• position D - the laser beam is at the other edge of the PLATE and
the PIXEL CLOCK stops
Actual position trace • matches the desired position trace during scanning of the
SCREEN
• does not match the desired position trace between Positions A
and B, indicating the time necessary for the GALVO to be stable
and start moving across the next line
Velocity trace • GALVO is moving in the scanning direction when the trace is
above the “0 Velocity” line in the diagram
• GALVO is moving in the retrace direction when the trace is below
the “0 Velocity” line
• GALVO is moving at a continual speed during scanning
• the speed of the GALVO increasing to operating speed between
Positions B and C
• the difference between the scanning and retrace speed is larger
than it appears in the diagram
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