Browse Prior Art Database

Synchronizing a Reciprocating Lens With a Cathode Ray Beam

IP.com Disclosure Number: IPCOM000074004D
Original Publication Date: 1971-Mar-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 4 page(s) / 71K

Publishing Venue

IBM

Related People

Bachman, DE: AUTHOR [+4]

Abstract

In the apparatus shown, characters are generated by performing a vertical raster scan 1 on the face of cathode-ray tube 2. During each vertical scan, the cathode-ray beam is turned on and off to produce black and white segment lengths on film 3. The length of black and white vertical segments in each scan is specified by segment counts which are passed from a computer over data bus 30. Horizontal displacement of the scans is taken care of by lens 4 which reciprocates horizontally in front of cathode-ray tube 2.

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Synchronizing a Reciprocating Lens With a Cathode Ray Beam

In the apparatus shown, characters are generated by performing a vertical raster scan 1 on the face of cathode-ray tube 2. During each vertical scan, the cathode-ray beam is turned on and off to produce black and white segment lengths on film 3. The length of black and white vertical segments in each scan is specified by segment counts which are passed from a computer over data bus
30. Horizontal displacement of the scans is taken care of by lens 4 which reciprocates horizontally in front of cathode-ray tube 2.

Tachometer 40 indicates when the reciprocating lens is in the range between margins relative to the recording film, as is indicated by arc 42, and tachometer 50 indicates when a recording position has been reached. Tachometer 50 produces a pulse for each movement of the reciprocating lens that is equivalent to the horizontal spacing taken up by approximately 16-vertical scans. Coincidence of outputs from tachometers 40, via flip-flop 44, and 50 will set latch 54 so that pulses from oscillator 56 will commence to be counted in counter 58. The first count present in 58 will cause initial synchronization of ramp generator
60. The counter 58 will continue to count for a number of counts equivalent to one full vertical scan, and then will produce a reset signal on lines 72 and 73 for causing ramp generator 60 to reset and also to reset counter 58. The output of ramp generator 60 is used to cause vertical sweeping of the CRT beam.

Base line definition register 16 is loaded from the line register with a count equivalent to the distance above a horizontal base line at which the line of print is to begin. Register 16 must contain a count sufficient to ensure that the ramp from 60 has passed its initial nonlinear portion before an output is produced. When the counts in register 16 and counter 58 are equal, compare circuit 17 produces an output at which point in time the ramp generator output has at least reached the beginning of its linear range. This sets FF 62 and conditions AND 64 so that pulses from oscillator 65 will begin decrementing the content of counter 35.

Threshold detector 61 is used to ensure that the ramp has reached a minimum level when compare 17 produces a signal. Otherwise, a failure of ramp generator 60 to produce a ramp would result in unblanking of the CRT beam while it was in a fixed position on the CRT face and, thus, cause a spot burn-out in the phosphor.

The initial instruction for any line of characters to be recorded on the film will always be a space character. Accordingly, the control logic will present a signal on the start of line terminal which will cause latch 82 to be set. This deconditions gates 83 and 84 so that pulses from oscillator 65 will not be introduced to counter 35, and flip-flop 66 will be isolated from the output of zero detector 36. In addition, the set side of latch 82 will condition gate 85 so that pulses from line 73 out of...