U.S. patent number 3,930,251 [Application Number 05/468,534] was granted by the patent office on 1975-12-30 for character image generation apparatus and crt phototypesetting systems.
This patent grant is currently assigned to Compugraphic Corporation. Invention is credited to Brian G. Eastman, George W. King, Roger F. Salava.
United States Patent |
3,930,251 |
Salava , et al. |
December 30, 1975 |
Character image generation apparatus and CRT phototypesetting
systems
Abstract
The scanning of the character generation apparatus is improved
by the generation of horizontal and coarse vertical automatic
position control signals subsequent to the initial accessing of a
character and prior to the actual scanning of a character image
whereby the speed of accessing a selected character is increased
and the logic and electronic control circuitry for operating the
system is simplified. Two different rate scanning rasters are used
with a fast scanning raster used to correct the position of the
character generator beam and a slower scanning raster is used to
actually scan the character. Provision is made for ensuring the
correct storage of width values in a memory. The width values
appear in coded format and are associated with at least one of the
indexing bars forming each of the character fields on a character
font. Increased speed and improved operation of the output
reproduction apparatus is obtained by jump scanning non-character
spaces which may include interword and intercharacter spaces used
for justification of a composed text.
Inventors: |
Salava; Roger F. (Andover,
MA), Eastman; Brian G. (Hampstead, NH), King; George
W. (Concord, MA) |
Assignee: |
Compugraphic Corporation
(Wilmington, MA)
|
Family
ID: |
23860200 |
Appl.
No.: |
05/468,534 |
Filed: |
May 9, 1974 |
Current U.S.
Class: |
345/467; 396/549;
178/15; 315/365; 396/550; 178/30 |
Current CPC
Class: |
B41B
19/01 (20130101); B41B 19/16 (20130101) |
Current International
Class: |
B41B
19/16 (20060101); B41B 19/01 (20060101); B41B
19/00 (20060101); G08B 005/36 () |
Field of
Search: |
;340/324AD,173LM,173CR
;178/15,30 ;354/5,6,7,8,9,11 ;315/365,367 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Trafton; David L.
Attorney, Agent or Firm: Watson, Cole, Grindle &
Watson
Claims
What is claimed is:
1. Apparatus for printing text by converting encoded electrical
signals into printed characters, comprising:
means for generating electron images of characters to be printed
from said coded input signals and including an arrangement of
characters with indexing bars forming a character field for each of
said characters;
means for controlling said means for generating electron images to
select characters from said arrangement of characters in accordance
with a desired character format;
said means for generating electron images further including means
for deflecting said electron images in accordance with a
predetermined scanning pattern in response to said means for
controlling, said scanning pattern having first and second
different scanning rasters wherein said first scanning raster scans
at least one of said indexing bars and said second scanning raster
scans said character associated with said at least one indexing
bar, and means for producing output signals representative of said
electron images;
first means responsive to said output signals for correcting the
position of said first scanning raster to improve the initial
position of said second scanning raster for scanning a selected
character, said first means including means for selectively varying
the rate of said position correction during said first scanning
raster; and
second means responsive to said output signals for generating a
visual image of said characters in accordance with said second
scanning raster and including means for recording said visual
image.
2. Apparatus as in claim 1 wherein said first means includes means
for repetitively scanning another of said indexing bars during the
second scanning raster and means for altering said second scanning
raster to correct the position thereof.
3. Apparatus as in claim 1 further comprising means for offsetting
the position of said second raster from said at least one indexing
bar to an edge of a character field associated with said indexing
bar.
4. Apparatus for composing printed characters from coded electrical
input signals, comprising:
means for generating electron images of selected characters from
said coded electrical signals;
means for generating output signals from said electron images;
output reproduction means for printing characters from said output
signals in accordance with a predetermined scanning pattern;
and
means for altering said predetermined scanning pattern to avoid
scanning of non-character areas of said output reproduction
means.
5. Apparatus as in claim 4 further comprising means for decoding
said coded electrical input signals and generating non-character
output signals and wherein said means for altering is responsive to
said non-character output signals.
6. Apparatus as in claim 5 further comprising means for calculating
justification of lines of said composed printed characters and
generating inter-character spacing signals and wherein said means
for altering is also responsive to said inter-character spacing
signals.
7. Apparatus as in claim 4 further comprising means for displacing
said scanning pattern by successive predetermined increments; and
wherein said means for altering increases the magnitude of said
increments.
8. Apparatus as in claim 4 wherein said output reproduction means
includes an electron beam and means for deflecting said electron
beam in accordance with said predetermined scanning pattern.
9. Apparatus as in claim 8 further comprising means for decoding
said coded electrical input signals and generating non-character
output signals and wherein said means for altering is responsive to
said non-character output signals.
10. Apparatus as in claim 9 further comprising means for
calculating justification of lines of said composed printed
characters and generating inter-character spacing signals and
wherein said means for altering is also responsive to said
inter-character spacing signals.
11. Apparatus as in claim 8 wherein said means for deflecting
includes means for displacing said electron beam by successive
predetermined increments; and wherein said means for altering
increases the magnitude of said increments.
12. Apparatus for printing characters from coded electrical input
signals comprising:
means for generating electron images of characters from said coded
input signals including a character grid and indexing bars defining
individual character areas, and each said character area including
encoded data representative of the width of the associated
character;
and means for reading and storing all of said encoded width data,
said means for reading re-reads all said encoded width data;
means for comparing said stored width data with said re-read
encoded width data;
means for generating an error signal for indicating a
non-comparison; and
means responsive to said error signal for repeating operation of
said reading and storage means, said means for comparing, and said
means for generating an error signal.
13. Apparatus for printing text by converting encoded electrical
signals into printed characters, comprising:
means for generating electron images of characters to be printed
from said coded input signals and including an arrangement of
characters with indexing bars forming a character field for each of
said characters;
means for controlling said means for generating electron images to
select characters from said arrangement of characters in accordance
with a desired character format;
said means for generating electron images further including means
for deflecting said electron images in accordance with a
predetermined scanning pattern in response to said means for
controlling, said scanning pattern having first and second
different scanning rasters wherein said first scanning raster scans
at least one of said indexing bars and said second scanning raster
scans said character associated with said at least one indexing
bar, and means for producing output signals representative of said
electron images;
first means responsive to said output signals for correcting the
position of said first scanning raster to improve the initial
position of said second scanning raster for scanning a selected
character, said first means including means for selectively varying
the rate of said position correction during said first scanning
raster;
second means responsive to said output signals for generating a
visual image of said characters in accordance with said second
scanning raster and including means for recording said visual
image;
wherein said means for producing output signals produces different
output signals from said indexing bars and the areas adjacent
thereto, respectively, and further comprising means for detecting
said different output signals during said first raster scan and
means for positioning said first scanning raster in accordance with
said detected output; and
wherein said first means first corrects the position of said first
scanning raster only when a predetermined one of said signals is
present and subsequently corrects the position of said first
scanning raster only when another of said different output signals
is present, whereby the useful range of position correction is
increased.
Description
BACKGROUND OF THE INVENTION
This invention relates to apparatus for improving certain functions
and operations of the character image generation apparatus and CRT
phototypesetting system as set forth in co-pending application Ser.
No. 467,536, filed May 6, 1974, and assigned to the same Assignee
as the present application. In particular, the present apparatus
provides an improved automatic position control for controlling the
electronic scanning of the selected character images over that
which is disclosed in the aforementioned co-pending application.
Additionally, this invention increases the speed of the cathode ray
tube by apparatus which causes the CRT beam to jump the actual
white spaces between the characters rather than scanning such white
spaces as does the CRT beam in the aforementioned co-pending
application. Finally, the present invention provides structure for
a read width cycle during which the width codes associated with
each of the respective characters on a font matrix are read and
compared to determine valid width values which are stored in a
memory for use during the printing of a character by the CRT
beam.
The improved image dissector and CRT phototypesetting system of the
present invention uses essentially the same basic apparatus as is
used in the aforementioned co-pending application and the
disclosure of that application is incorporated herein by
reference.
The character generation system of the present invention overcomes
certain difficulties of prior art systems by utilization of
character signal generation apparatus such as the basic image
dissector tube as conceived by Farnsworth in 1923, but with state
of the art improvements that provide enhanced performance. For
example, improved coil and dynamic focus assembly construction has
resulted in significantly higher signal resolution. Additionally,
geometric distortion has been reduced and there has been an overall
improvement in the signal output of such devices. Such an image
dissector tube is very simply constructed, is relatively
inexpensive compared to the prior art digital and analog type
character generation apparatus, and produces electronic signals
representative of character images with sufficient accuracy and
detail to provide characters in a desired text meeting modern
high-speed printing standards.
The image dissector used in the character generation apparatus of
the invention does not require additional complex electrode or
element structure, such as a grid structure for selecting one of a
number of channels each of which is associated with a given
character, for generating the necessary electron character images.
An example of such a system is Columbia Broadcasting System's Inc.
Linatron. One primary difficulty in using a single aperture image
dissector tube of the type described above resulted from the
inability to accurately locate a desired character among a group of
characters on a font matrix and accurately scan the character to
generate the necessary electron beam image representative of the
character.
A primary feature of the present invention which enables the use of
an image dissector tube for generating the character images resides
in the technique for providing quick and accurate access to a
selected character and for generating horizontal and vertical
automatic position control signals for controlling the vertical and
horizontal deflection so that the character may be scanned to
produce the necessary electronic signals representative of the
character.
The operation of the entire character generation and reproducing
system is enhanced by the generation of horizontal and coarse
vertical automatic position control signals prior to the actual
scanning of the character image by means of relatively simple
circuitry which senses the video. The use of such vertical and
horizontal automatic position control signals further enhances the
use of the basic image dissector tube, increases the speed of the
system with respect to the access of a selected character, and
decreases the complexity of the logic and electronic control
circuitry for operating the system.
In the present invention the character scanning is enhanced over
that which is disclosed in prior art systems and in particular that
which is disclosed in the aforementioned U.S. patent application.
The scanning is divided into a fast and a slow scan and during the
fast scan the scanning deflection voltages are adjusted so that the
actual character scanning begins at an optimum location adjacent a
character to be scanned. The two speed scanning increases the speed
and accuracy of character scanning. During the slow scan the
vertical deflection voltages are finely and repetitively corrected
to maintain the proper initial position of the vertical scanning
strokes.
Phototypesetting systems have used character fonts in which the
character widths are physically associated with the respective
characters and that width information is detected and stored for
proper escapement of the characters in the desired textual format.
The present invention utilizes a character font in which the
character widths appear in coded format adjacent the characters.
However, in the present invention the character widths are read and
stored in memory during a width read cycle in the prime mode of
operation of the system. The character widths are read twice in
sequence and compared to ensure that the character data stored in
memory is error free. In some previous phototypesetting systems,
the character width is read just prior to the scanning of a
character, as is for example utilized in the phototypesetting
description described in the aforementioned U.S. patent
application. The width reading as performed by this invention
enables the scanning of a selected character to be initiated more
readily as the width code is not read for each character during the
printing cycle.
Additionally, in the present invention the character font has been
modified to increase the area to which the initial scan of a
character is directed by the horizontal and vertical address
deflection voltages. Thus, the present system will accommodate a
larger initial deflection error than prior art systems of a similar
type.
An improvement of the invention includes a "jump scanning" of the
output CRT device in which the spaces between characters are not
scanned. The spaces include interword and intercharacter spaces
used for justification and fixed space. A technique for
automatically and accurately locating a desired character among a
group of characters on a font matrix is described in U.S. Pat. No.
3,497,761 entitled "Cathode-Ray Tube Apparatus" in the name of C.
A. Washburn,
Another improvement of the invention includes off-setting the
character generation scan after correcting the position of the scan
with respect to the indexing bar. This eliminates a lateral
positioning error of the first scanned edge of the reproduced
character.
OBJECTS OF THE INVENTION
It is a primary object of the present invention to provide improved
automatic position control circuitry for an electronic scanning
character generation system for use in a cathode ray tube
phototypesetting system.
It is another primary object of the present invention to provide
apparatus in a character image generation and CRT phototypesetting
system for reading and storing width data associated with
respective characters on a character font.
It is yet another primary object of the present invention to
improve the printing speed of a character image generation and CRT
phototypesetting system by causing the CRT beam to jump
non-character spaces between the characters of the text.
Still another object of the present invention is to provide an
improved automatic position control for the generation of
characters from an electronic scanning character generation system
by using a two-speed scan control.
Another object of the present invention is to provide an improved
automatic position control for scanning selected characters in a
system of the type specified herein wherein indexing bars and logic
circuitry are utilized to improve the accuracy of positioning the
character scanning and the allowable initial character deflection
error.
It is still yet another object of the present invention to minimize
errors in the reading of the width code from a character font.
A still further object of the invention is to increase the printing
speed of the cathode ray tube in a phototypesetting system of the
type specified herein by the employment of logic circuitry which
causes the CRT beam to jump for non-character spaces.
Yet another object of the invention is to eliminate lateral
positioning error of the reproduced character.
SUMMARY OF THE INVENTION
A font matrix of characters in a two-dimensional pattern is
irradiated by a lamp to provide simultaneous character light images
on the photocathode of an image dissector tube. The characters to
be reproduced are determined from a tape reader and stored in a
memory buffer thereby enabling the character generation system to
be independent of the source input as well as to enable the
justification of the text if that is desired. A selected character
is addressed by the application of major vertical and horizontal
deflection control signals to the image dissector tube, which are
representative of X and Y addresses of the characters on the font
matrix. Position correction circuitry utilizes the video output of
the image dissector tube to correct the position of the scan of the
character with respect to indexing bars which define individual
character areas. At least one of the indexing bars includes encoded
width data for each character. The scan of a character begins with
a fast scan of the indexing bars during which time the necessary
minor corrections are applied to the scanning deflection signals in
preparation for the actual scanning of the character.
The improved automatic position control utilizes a two-speed
scanning technique wherein a high-speed scanning is employed for
the first seven vertical strokes of the character image scanning
during which time the indexing bars are utilized to position the
stroke at a position immediately adjacent the upper left portion of
a selected character. Prior to scanning the character, the scanning
strokes are offset to position the first active stroke at the edge
of the character field. During the subsequent character scanning
strokes the vertical position is sensed using automatic position
control bars associated with the selected character on the
character font to control and finely adjust the vertical position
of the scanning.
The coded character widths are detected and stored in memory during
a read width cycle in a prime mode of operation of the
phototypesetting system in which each width code on the character
font matrix is read, stored, re-read, and compared to minimize
width error. Any comparison errors will generate a new read width
cycle. The width code on the character font is contained within and
in close proximity to automatic position control bars where the
beam position is most accurate. Additionally, the code reading
stroke video signal is highly filtered to minimize noise
errors.
The speed of the output reproducing system is increased by causing
the CRT beam to jump non-character space such as spacebands,
letterspaces, etc. in a given line of text. Such non-character
space is added to a line position counter by means of logical adder
circuitry. The horizontal position of the CRT beam is directly
controlled by the line position counter through a thirteen-bit D/A
converter and a deflection amplifier. Normally, each character is
formed by a great number of strokes, each of which advances the
actual beam one eighteenth point (0.00076 inches). In the
aforementioned co-pending application all fixed spaces (thin, EM
and EN) plus spacebands are also stroked as normal characters. The
improved apparatus and technique of the present invention result in
a speed improvement of the CRT phototypesetting system of
approximately two hundred lines per minute (from 300 to 470 LPM) in
six point, eleven pica stock market output which contain a
significant amount of non-character space.
The characters are produced on a film which is positioned in proper
alignment and in contact with a fiberoptic face-plate on the
viewing surface of a cathode ray tube. During character
reproduction, the electron beam of the cathode ray tube is slaved
to the scanning pattern of the image dissector tube, with the
exception that the electron beam current of the cathode ray tube is
maintained constant (except during blanked intervals and for
producing pseudo-bold output) as is the velocity of the electron
beam.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustration of the phototypesetting
apparatus;
FIG. 2 is a simplified representation of the character
generator;
FIGS. 3A and B are block diagram representations of the image
dissector control circuitry;
FIG. 4 is a block diagram of the CRT control circuitry;
FIG. 5A is a block diagram of the control logic for the
phototypesetting apparatus;
FIG. 5B illustrates digital control signals for character
generation timing;
FIG. 6 is a block diagram representation of the CRT output jump
ahead circuitry;
FIG. 7A is a flow chart representing the sequence of operations for
width code reading;
FIG. 7B is a block diagram representation of the X and Y character
select circuitry;
FIG. 7C is a block diagram representation of the width decoder
circuitry;
FIG. 7D illustrates a portion of the character font showing an
example of the width code beside the character and the manner in
which the beam is positioned during the initial portions of the
character scan;
FIG. 7E illustrates the manner in which the deflection voltages are
assigned to the font grid;
FIG. 7F shows the digital control signals used for width read
timing;
FIG. 8 is a block diagram representation of the video processor
circuitry;
FIGS. 9A and 9B are block diagram illustrations of the vertical
stroke generation circuitry;
FIG. 10A is a block diagram representation of the vertical
automatic position control circuitry;
FIG. 10B illustrates the relationship of the character generator
beam to the indexing bar on the character font during the initial
strokes of the fast automatic position control sequence;
FIG. 11A is a block diagram illustrating the horizontal automatic
position control and stroke advance circuitry, and FIG. 11B
illustrates the advance of the strokes during horizontal automatic
position control;
FIG. 12 shows an embodiment of a character font matrix illustrating
the relationship of the character fields, the indexing bars and the
width code data.
GENERAL DESCRIPTION
The input to the phototypesetting system comprises a six-level
perforated tape containing justified text with line-ending codes.
FIG. 1 is a block diagram representation of the basic system
wherein control panel 20 provides the necessary data input to the
system such as the line measure, point size, set size, leading
value, and controls for letterspacing. The characters and width
data are contained on font grid 22 which is illuminated by lamp 24
and projected through the font grid to projection lens 26 and onto
the photocathode of image dissector 28. Initially the width value
on font 22 of a selected character is read by image dissector 28
and stored in a width memory. Paper tape 30, containing the
justified text, is read by reader 32 and provided to decoders in
memory 34. Calculation logic within memory 34 may be provided to
determined the spacing values to justify the copy to fit the
selected measure. Such logic circuitry is well known to those
skilled in the art and circuitry is well known to those skilled in
the art and forms no part of the present invention. Output control
logic 36 provides data and command signals to analog circuits 38,
which drive image dissector 28 and Cathode Ray Tube (CRT) 40 to
produce output copy on film 42 which is transported past
fiberoptics 44 from film supply 46 to film cassette 48, which
transport is controlled by film motor 50.
Image dissector 28 receives the light pattern from the font and
produces video (black and white) signals for controlling the CRT
beam by scanning the character image. The output copy on film 42 is
generated by vertical strokes of light transmitted through the
fiberoptics from the face of CRT onto film 42.
The input to the system may comprise, for example, a justified
six-level TTS coded, paper tape. The phototypesetting CRT system
preferably includes twelve type sizes, namely 5, 6, 7, 8, 9, 10,
12, 14, 18, 24, 30 and 36 point. The set size output is preferably
from 5 point to 36 point. In the preferred embodiment there may be
any line length of type up to 27 Picas, and leading is provided in
one-half point increments up to 631/2 points. Font 22 consists
preferably of one hundred six characters plus the special functions
em, en and thin. Film 42 preferably comPrises either three or 6
inch width paper.
The phototypesetting CRT system may be interfaced with a general
purpose computer which has the capability of operating a TTS
perforator. Additionally, tapes may be prepared on any TTS keyboard
perforator which has a measure-counting capability. The system may
also operate in conjunction with AP, UPI, or CPA transmitted paper
tape wire services.
Tape reader 32 reads six-level TTS coded paper or Mylar tape at a
rate of approximately five hundred characters per second and
presents a six-level TTS code input to decoder circuitry within
memory 34, which in turn controls the start/stop of reader 32. The
memory and logic within memory 34 comprises plug-in IC chips.
Analog circuit 38 processes video signals from image dissector 28,
provides the logic within memory 34 with an analog active clock
(AAC) control signal and raw unit widths from font grid 22. Analog
circuits 38 include the CRT horizontal and vertical deflection
amplifiers, CRT waveform generator, video processor, image
dissector horizontal and vertical deflection amplifiers, image
dissector video preamplifier, and other necessary control circuitry
to be more fully described below.
The character generator comprises font grid 22, lamp 24, projection
lens 26 and image dissector assembly 28, which preferably consists
of an image dissector tube and associated deflection and focus
coils. The character generation circuitry generates video
information by scanning font 22 with vertical strokes of an
electron beam.
The printer of the CRT phototypesetting system comprises cathode
ray tube CRT 40 having fiberoptics face-plate 44, film supply 46
and film cassette 48. Photocopy output is generated by exposing
film 42 with light transmitted from the CRT phosphor through a
fiberoptic face-plate contacting the film surface.
SEQUENCE OF OPERATION
Font grid 22 is installed within the machine and control panel 20
is formatted as desired. The prime button on control panel 20 is
depressed, thereby initializing logic circuits 34 within memory.
The system is placed in a "prime mode" during which the width
values on the font are read twice, and a comparison made to detect
any errors in the sensed widths. If an error is detected the width
read cycle is repeated. If no errors are detected the width values
are placed in memory for future reference and the operational
sequence proceeds as follows. The line measure inserted into the
system from control panel 20 is stored in a width counter within
memory 34. Justified paper tape 30 is placed within tape reader 32
and a start button on control panel 20 is depressed. Reader 32 runs
forward, the codes thereon are read and stored in memory 34 until
an end of line (return) code is sensed. The line may be processed
by the logic within memory 34 to determine spaceband and
letter-space values for justification. The line is then released to
the character generator and printer (CRT 40) for printing. The
logic within memory 34 provides the necessary controls and data to
analog circuits 38 for point size, italicizing, bolding, condensing
or expanding of the output copy produced on film 42.
IMAGE DISSECTOR
With reference to FIG. 2, the image of an entire font is projected
through the iris of lens 50, which has a two to one reduction ratio
and onto photocathode 52 of the image dissector tube. Photocathode
52 is coated with a material that emits electrons from the areas
that are struck by light. The electrons are attracted through an
accelerating mesh 54 into a drift tube area 56. Focus coil 64
focuses the electron stream to a fine electron beam image of the
font at the plane of aperture 62. Under the influence of horizontal
and vertical deflection coils 58 and 60, the electrons are
precisely allowed to pass through aperture 62 which has a diameter
of 0.001 inches.
The electrons emitted from other areas of the font image are
attracted to the plate portion of the aperture anode and are
separated from the signal stream. A multiplier section 66 includes
68, 70 . . . 78, first dynode 68 is struck by the signal electrons
to release secondary electrons which are greater in number than the
original stream of electrons. Each succeeding dynode is more
positive, thereby accelerating the stream of electrons and
generating additional secondary electrons. The multiplied signal
consisting of an electron stream is finally attracted to anode 80
and passes through a load resistor 82 thereby generating a video
signal that corresponds in time with the sequence of scanning the
character area of the font.
A character on the font is reproduced in video signal form as
follows. The area on the font containing the desired character is
coarsely located by selected horizontal and vertical deflection
currents generated by digital/analog converters actuated from the
tape input and connected to horizontal and vertical deflection
coils 58 and 60. The black and white areas of the character are
then scanned in linear vertical strokes from top to bottom, thereby
causing output signal electrons corresponding to white portions of
the scanned character area to be directed through aperture 62 and
no output signal electrons corresponding to the black portions of
the scanned character area. Each succeeding vertical stroke is
directed slightly to the right of the last, allowing a new portion
of the character to be scanned. Such stroking continues until the
relative width portion of the area containing the character has
been scanned. The variation in the number of electrons passing
through anode load resistor 82 produces a voltage which is input to
a preamplifier to provide a character generator output signal
representative of the selected character.
As will be apparent from the following description, the CRT
phototypesetting system is not limited to an image dissector tube
for generating the required signals representative of the
characters. Other devices capable of single channel operation such
as flying-spot scanners, or photodiode arrays can also be used as
part of the character generator apparatus.
IMAGE DISSECTOR CONTROL CIRCUITRY
With reference to FIG. 3A, a particular font character is accessed
by digital address signals HP1 - HP8 and VP1 - VP8 (four-bits
horizontal and four bits vertical) from four-bit digital analog
converter 90. Converter 90 converts the four-bit digital levels
into major horizontal and vertical deflection voltages. The X D/A
and Y D/A output voltages are provided to horizontal deflection
amplifier 92 and vertical deflection amplifier 94, which supply the
image dissector horizontal and vertical deflection coils 58, 60
with a current that directs the beam of image dissector 28 to the
approximate desired location on font 22. Digital/analog converter
90 also provides a focus-correcting waveform to focus
regulator/modulator 96, which supplies a focus correction current
while also regulating the basic focuc current in the image
dissector focus coil 98.
Point size register 100 provides a ten-bit output to vertical
stroke generator 102 to generate the appropriate vertical strokes
for directing the beam down through the character. It is noted that
the amplitude of the character generator strokes has been made
constant for all point sizes, but the velocity of the beam is
greatest for small point sizes, in other words, the velocity of the
beam is point size dependent. The constant amplitude is necessary
because the same font character image area and therefore height is
stroked for all point sizes of output copy. As previously noted,
the point size control has been established to provide a stroke
time interval proportional to point size. This interval controls
the timing of both the character generator and output CRT strokes.
The output CRT stroke generator is provided with a constant rise
time and therefore its stroke amplitude will be lower for short
intervals and greater for long intervals. Since the interval has
been made proportional to point size, the amplitude of the CRT
strokes and hence the characters reproduced will be proportional to
the selected point size. However, the beam velocity remains
constant and therefore, the rate of film exposure is constant and
uniform exposure results for a constant beam current.
The master stroke-timing signal SD (stroke drive) from vertical
stroke generator 102 synchronizes image dissector strokes and CRT
strokes. The blanking signal from vertical stroke generator 102
deactivates the video signal of the video processor circuit during
retrace of the image dissector beam. The video output of image
dissector 28 is preamplified by preamplifier 104. AAC signals are
generated by vertical stroke generator 102 for synchronizing the
operation of the analog and digital circuitry.
Signal RWG displaces the stroke horizontallly to properly read the
width codes as described hereinafter. The signal SAG displaces the
stroke horizontally to move from the indexing bar to the adjacent
character field prior to character scanning as described more fully
hereinafter.
With reference to FIG. 3B, set size register 110 provides ten-bit
data to horizontal stroke advance circuit 112 to generate stroke
advance signals. Horizontal stroke advance circuit 112 provides a
slightly greater horizontal deflection voltage after each stroke of
the image dissector beam, thereby enabling the beam to advance
slightly to the right for each new stroke so that a given character
on font 22 can be scanned. This stroke advance signal is applied to
horizontal deflection amplifier 92 (FIG. 3A). As the beam passes
through the black and white areas on font 22, the image dissector
28 generates a video signal which is amplified by video
preamplifier 104 (FIG. 3A) and forwarded to video processor 114
along with a blanking control signal from vertical stroke generator
102 (FIG. 3A) and a control signal (PREN). The output of video
processor 114 comprises a video (black or white) signal which is
input to the CRT printer and vertical automatic positioning control
and skew circuit 116, which is also controlled by signal VAPCG
generated by circuitry described below. The output of VAPC and skew
circuit 116 is a vertical automatic positioning control signal and
a skew signal, which are respectively provided to vertical
deflection amplifier 94 and to horizontal deflection amplifier 92
(FIG. 3A).
CRT PRINTER DESCRIPTION
With reference to FIG. 4, CRT 40 generates output copy by
projecting vertical strokes of light through fiber-optics
face-plate 44 which is in contact with film 42. The basic
horizontal position of the CRT beam is determined by a thirteen-bit
output from line counter 120 which is converted into an analog
voltage by horizontal digital/analog converter 122, the output of
which is in turn provided to horizontal deflection amplifier
124.
The basic vertical position of the CRT beam begins at the top-align
location of the character. The beam is driven downward by the CRT
stroke from waveform generator 128 by means of vertical deflection
amplifier 130. Signal SD input to waveform generator 128
synchronizes the CRT stroke with the image dissector stroke. The
digitized video output of video processor 114 is amplified by CRT
driver 126 and is used to modulate the beam in synchronism with the
font pattern (White on font equals beam On).
GENERAL DESCRIPTION OF LOGIC CIRCUITRY
The logic circuitry is illustrated in block diagram format in FIG.
6A. The phototypesetting apparatus has three basic sequences during
normal operation:
1. Input/storage cycle-read tape and store codes until Return is
read.
2. Justification calculation cycle-calculate for the unused space
to justify the preset line measure.
3. Print cycle reads the line from memory and print.
INPUT STORAGE CYCLE
With reference to FIG. 5A, when the prime switch on control panel
20 is actuated, the line measure from the control panel switches in
picas, points, is converted in line measure converter 138 to
machine units and stored in a width counter used during a
calculation cycle. With the depression of the start button on
control panel 20, reader 32 runs at a 500 cpm rate and applies a
six-bit TTS code to reader control 140. Reader control 140 buffers
the reader 32 output to character decoder 142 which determines if
the six-bits are character or function codes, letterspaceable,
space codes or super-shift functions. Character decoder 142 outputs
are input to data control and line store 144 for storage, and
simultaneously, address width control circuits 146 so that the
character width may be subtracted from the preset line measure.
Simultaneously with width handling, the other outputs of character
decoder 142 are input to space calculation control circuit 148 for
maintaining track of letterspaceable characters and the number of
spacebands or insert space codes in the line. Supershift outputs of
character decoder 142 enable automatic control of point size, set,
leading, and the setting of new line measures.
The phototypesetting system logic determines which codes are to be
stored and writes them sequentially into line storage 144 for use
during the print cycle of the system. The character code addresses
the width control circuitry 146 and the character width is provided
to line ending calculation circuitry 150. The width, at this time,
is multiplied by the set size selected and the result is subtracted
from the remaining line measure. Space control and calculation
circuitry 148 is utilized at this time for counting the number of
spacebands and letterspaceable characters in the line as this
information is necessary during the justification calculation.
Reader 32 continues to run until a return code is sensed at the end
of the line and at that time reader 32 stops and the system logic
circuitry enters a justification calculation mode.
JUSTIFICATION CALCULATION MODE
The function of the calculation performed in the justification
calculation mode is to assign the remaining widths in the line to
spaceband and/or letterspace. In the space control and calculation
circuitry 148, the spaceband count is used to calculate how much
width is to be assigned to each spaceband. In the phototypesetting
system, the spaceband begins with no assigned width which is
expanded by the logic circuitry within the space control and
calculation circuitry 148. Such calculations continue until all the
width has been assigned and at that time, the print mode
begins.
PRINT MODE
The functions of the print mode are to enable selection of each
character to be printed, control the height and width of each
character, and control the number of horizontal steps to be used by
the cathode ray tube of the output reproduction unit. Subsequent to
the printing of a line, the print mode controls the paper advance
system (leading).
Data control and line store circuitry 144 provides the location of
each character to be printed from the image dissector tube 28 (FIG.
1), and character code to character decoder 142 and width control
146. Print and output control circuitry 152 counts the strokes for
each character, directs the CRT when to print, and informs the CRT
how many horizontal steps to move the beam.
Point/set control circuitry 154 is used during both the calculation
mode and the print mode and during the print mode it controls the
length of the vertical stroke on the CRT and each step of the
horizontal advance of image dissector tube 28. Subsequent to the
handling of all the character and space information for a given
line, the return code at the end of the line informs print and
output control circuitry 152 to allow leading to take place under
control of leading control 156.
DETAILED DESCRIPTION OF THE LOGIC CIRCUITRY
CHARACTER DECODER CIRCUITRY
Character decoder circuitry 142 determines which codes are EM
precedent or non-letter spaceable. Those codes which are not
letterspaceable inhibit a letterspace counter in space control and
calculation circuitry 148 from incrementing for those codes. Those
codes which are part of an EM precedent sequence increment a
letterspace counter in space control and calculation circuitry 148
and are written into line storage 144.
Character decoder 142 interprets the various supershift formats to
make changes from the fixed format of control panel 20. To select a
new line measure, via tape control, a supershift code followed by
SM and four decimal digits is read. Character decoder 142 senses
the sequence S followed by M, converts the TTS code for the decimal
quantity to BCD and ensures that it is placed in line measure
converter 138 according to pica and point representation.
In order to select a new point size via tape input, a supershift
code followed by a T and two decimal digits is read. The function
of character decoder 142 is to recognize that sequence and decode
the two decimal digits for use as the point size in point/set
control circuit 154.
In order to select a new line-space quantity for leading, a
supershift code followed by S, L and three digits is used. It is
the function of character decoder 142 to determine the proper
sequence and convert the BCD configuration of the line-space
quantity to standard binary representationn. This is input to
leading control 156.
DATA CONTROL AND LINE STORAGE CIRCUITRY
As codes are read from paper tape by tape reader 32, they must be
stored in sequential order for use by the print cycle after all
calculations are completed for each line. Data control and line
store circuitry 144 determines which codes are to be stored,
provides information to the analog circuits to locate the codes on
font grid 22, and provides addresses for a width memory for each
code's width so that calculations can be performed.
WIDTH CONTROL CIRCUITRY
Width control circuit 146 stores all widths from font grid 22 in
locations that are addressable from the TTS code of each character
and provides each width as it is addressed to line ending and
calculation circuitry 150. Width control 146 stores the width of
each code on font grid 22 which is installed in the phototypesetter
system. These widths are written from the font into a width memory
on lines RUI 1-8 during the prime sequence (as previously
described), and are capable of being read out of memory at any
other time.
POINT/SET CONTROL CIRCUITRY
The functions of point/set control circuit 154 are to provide:
1. A set size multiplication factor for line ending calculation
circuit 150.
2. The point digital/analog value to the analog circuits for
controlling the frequency of the vertical stroke of image dissector
28.
3. Set digital/analog values to the analog circuits for controlling
the horizontal advance of each image dissector stroke.
These digital/analog values depend upon settings of control panel
20 or control sequences input through reader 32 to character
decoder 142.
LINE MEASURE CONVERTER CIRCUITRY
Line measure converter circuitry 138 changes the BCD configuration
of the line measure to binary representation to produce total
machine units required for that measure. This resultant value is
provided to a width counter in line ending calculation circuitry
150 for use during line end calculation and space calculation.
Line measure converter circuitry gates either control panel switch
values or tape control line measure values to a line length
converter (not shown) the output of which is the machine unit value
of line measure in a complement form. For an example, using elevan
picas, the output of converter 138 is the one's complement of 2376
machine units.
LINE ENDING CALCULATION CIRCUITRY
The function of line ending calculation circuitry 150 is to
subtract the machine unit width of each character in a line from
the remaining line measure in a width counter until the return code
at the end of the line is sensed. At that time, line-ending
calculation circuitry 150 aids space control and calculation 148 in
assigning remaining width to spacebands, into inter-character
space, or insert space in order to justify the line. The width
counter (not shown) is initially set to a value determined by line
measure converter 138. The value of width to be subtracted is
determined by a multiplier (not shown) the inputs to which are
determined by point/set control 154 and width control 146.
SPACE CONTROL-CALCULATION CIRCUITRY
Space control/calculation circuitry 148 counts all spacebands and
letterspaceable characters (minus one) during the input/storage
cycle. If an insert space code is read, then space
control/calculation circuitry 148 counts the number of insert space
codes instead of letterspaceable characters. During justification
calculation, space control/calculation circuitry 148 controls
justification of the line by calculating the amount of space to be
added to each spaceband and/or letterspace position in order to
justify the line.
During justification calculations, space control and calculation
circuitry 148 determines how much width is to be assigned to:
1. A spaceband in the line;
2. An insert space in the line, or
3. An inter-character space.
When calculation is complete, space control and calculation circuit
148 indicates the value of one of the following:
1. The number of machine units to be assigned a spaceband if the
line was not letterspaced.
2. The number of machine units to be assigned to each
intercharacter space if the line was letterspaced.
3. The number of machine units to be assigned to each insert space
code if the line contained insert space codes.
If the number of machine units remaining in the line could not be
divided equally, then at the end of calculation a deficit value
would remain in space control and calculation circuit 148. If that
value represented spacebands, a count pulse for every spaceband is
generated during the print cycle. When the deficit is filled, the
value increments and all remaining spacebands in the line receive
one more unit. If the deficit represents letter-spaceable
characters, an increment during the print cycle is provided. If the
deficit represents insert space codes, an increment is provided
during the print cycle of each insert space.
PRINT OUTPUT CONTROL CIRCUITRY
Print output control circuitry 152 is used to interface the digital
signals developed by the results of calculation with the analog
components used to locate and scan a character on image dissector
28, and position and expose characters through CRT 40 on
photographic paper or film 42.
During the prime sequence print output control 152, in conjunction
with point/set control 154 and data control 144, counts the number
of image dissector vertical strokes to correctly position the scan
beam for reading each width bar on font 22. Data control 144
provides horizontal and vertical information for approximate ID
beam position, point/set control 154 provides information to
control the stroke rate of the beam, and output control 152 counts
fifteen strokes before allowing width to be read on the 16th
stroke. During the fifteen strokes, the analog components of the
apparatus prepare the beam to be positioned on the center of the
width bar during the sixteenth stroke ensuring accurate width
reading.
During normal operation, print output control 152 functions ONLY
after the calculation cycle of each line is finished. Reader 32 is
stopped during the entire calculate cycle and it is also stopped
for an entire print cycle if either an end-of-line (EL) function is
processed or a supershift code is read during a print cycle.
DUring the print cycle, print output control 152, in conjunction
with point/set control 154 and data control 144, counts the number
of vertical strokes to correctly position the ID beam, unblanks the
CRT beam, and controls the CRT beam horizontal deflection as
indicated in FIG. 5A. Again, during the print cycle, data control
144 provides horizontal and vertical information to ID 28 to locate
each character of a line. Point/set control 154 affects the scan
stroke of the ID beam which has a direct bearing on CRT stroke
length. Print output control 152 counts eight strokes before
unblanking the CRT beam. During the first seven of these strokes,
the ID beam position is being horizontally and vertically corrected
to create accurate beam position before scanning of a character
takes place. One actual character scanning takes place, print
output control 152 counts the number of strokes for each character
which, in turn, horizontally deflects the CRT beam. If any space is
encountered, or letterspace, insert space, spacebands, thin, etc.,
instead of stroking for the width of each space, print output
control 152 immediately deflects the beam by the amount of space
indicated which will be more fully described hereinafter.
Output control circuitry 152 is used to interface logic timing with
analog timing and at the completion of the justification
calculation cycle, the first character in a line is ready to be
stroked onto the CRT. Output control 152 provides the signals
necessary to read each code of a line from line store 144 for use
to locate the character on font 22, to load each code width into
output counter 160 for control of CRT horizontal deflection, and to
vertically and horizontally correct the image dissector 28 beam
position in preparation for character scanning.
To read any code out of line store 144 for use during printing, the
proper location of the code must be addressed. The code's width is
addressed in width control 146 while the code's position on font
grid 22 is being located by data control 144. The code's width is
multiplied by set-size in line ending calculation 150 to obtain
total machine width and then is loaded into output counter 160 as a
deficit. When the code's position on font grid 22 has been located,
the image dissector beam must be vertically and horizontally
corrected before enabling character scanning. After loading output
counter 160 with the code's width times set size, beam position
correction takes place, after the completion of which actual
printing of the character begins.
An AAC pulse is developed by vertical stroke generator 102 (FIG.
3A) for every vertical ID stroke and the frequency of these pulses
is point size dependent. However, during the beam position
correction the frequency of the AAC pulses is always based on
fifteen point (the same as during width reading).
Output control counter 162 is enabled to count AAC pulses. Each
count is immediately decoded to produce the OCC signals indicated
on FIG. 5B. For the first seven strokes of the image dissector
beam, high speed automatic vertical position correction takes place
under control of signal VAPCG (Ref. FIG. 5B). Signal VAPCG is
provided directly to VAPC and skew control 116 (FIG. 3B)
controlling vertical position of the image dissector beam. For the
fifth, sixth and seventh strokes, the image dissector beam is
corrected horizontally during signals HAPC1 and HAPC2 (FIG. 5B).
Signal SAG is generated during beam correction and is used to
advance the final ID beam position just prior to character scan.
The eighth stroke ensures correct beam position before printing of
a character by off-setting the ID beam to the edge of the character
field.
During print control signal PREN (FIG. 5B) enables the image
dissector video to control the beam of the CRT. Once the image
dissector beam is positioned to begin a character scan, print
control circuitry 152 (FIG. 5A) enables the video of the image
dissector to control the CRT beam until the proper number of
strokes have been counted which equal the width of the character.
If a spacing operation is performed, the print control will not
enable the image dissector control of the CRT. Instead print
control circuit 152 will directly deflect the CRT beam the required
amount of machine units. One machine unit is equal to a CRT beam
deflection of 0.000765 inch.
Signal PREN is generated to enable the ID video to control the CRT
beam. Signal OCOVF indicates an overflow of output counter 160.
Output counter 160 is loaded with the complement of the character
width. Signal OCOVF occurs when the exact number of AAC pulses have
been generated during signal PREN. The occurrence of signal OCOVF
indicates that one character has been completely scanned on font
grid 22 and one character has been exposed by the CRT onto film or
paper 42. Signal OCOVF immediately removes signal PREN. Had the
code indicated a space code, signal PREN would not have been
generated. The output of output counter 160 would be sent in
parallel to line counter 120.
LINE POSITION COUNTER CONTROL CIRCUITRY
The line position counter 120 provides a thirteen-bit output to the
horizontal control of the CRT for purposes of deflecting the beam
one machine unit for each count. The normal function of line
position counter 120 is to count each stroke of the image dissector
beam which, in turn, deflects the CRT beam for each machine unit of
character width. Output counter 160 will inhibit line counter 120
by signal OCOVF after the image dissector beam character strokes
are completed.
For spacing a different method of changing line position counter
120 is used. Instead of blank-stroking for space by counting the
width into line position counter 120, a space value from either
space control 148 or output counter 160 is selected by SC/OC MUX
166 and immediately added by ADD circuit 168 to the present line
position count and parallel-loaded into line position counter 120.
This provides an instantaneous beam deflection equal in value to
the number of machine units of space.
With line counter 120 at zero, the CRT beam is caused to be
deflected to the left margin of the film 42. Line counter 120 is
incremented by AAC pulses for each vertical stroke of the image
dissector beam. Corresponding values from counter 120 are provided
to the analog circuitry for CRT beam deflection. Whenever a space
code is sensed, a parallel enable signal is generated to line
counter 120 to allow immediate deflection of the CRT beam the
amount of space necessary. The input to adder 168 is via space
counter/output counter MUX circuit 166. The input from space
control 148 is used for CRT beam deflection for insert space,
normal spacebands or letterspacing, while the input from output
counter 160 is used for fixed space (TH, EM, EN, etc.).
CRT OUTPUT JUMP AHEAD
The present invention includes circuitry for increasing the CRT
system speed by not stroking the "white space" in each line, i.e.,
spacebands, letterspaces, etc. The circuitry for jumping the white
spaces is illustrated in FIG. 6 and operates such that the actual
non-character space between characters is jumped by the CRT by
adding the space to line position counter 120 by logical
thirteen-bit adder 168. Line position counter 120 is a thirteen-bit
counter which directly controls the horizontal position of the CRT
beam through thirteen-bit digital/analog converter 122 and the
corresponding CRT deflection amplifier. The output of line position
counter 168 is buffered by buffer 172. As has been previously
described, each character is formed by many strokes each of which
advances the actual beam one unit of one set (0.000765 inch). In
the phototypesetting apparatus described in co-pending application
Ser. No. 467,536, filed May 6, 1974, all fixed spaces, i.e., thin,
EM and EN, plus the spacebands, are also stroked as though they
were normal characters. It is noted that there is no letterspace or
insert space capability in the phototypesetting apparatus described
in the aforementioned co-pending application. The calculation of
fixed spaces from either output counter 160 or the calculation from
space counter 170 (a component of space control and calculation
148, FIG. 5A) is selected by multiplexer 166 and added directly to
line position counter 120 by means of thirteen-bit adder 168. The
detailed description of the operation of space control 148, output
counter 160, multiplexer 166, adder 168 and line position counter
120 has been previously described.
The above described technique results in a net speed improvement of
approximately two hundred lines per minute (from 300 to 475 LPM) in
six point eleven Pica stock market output which contain a
significant amount of non-character space.
WIDTH CODE READING
The width code in binary notation is located on font 22 (FIG. 12)
to the left of each character. The width code represents the actual
relative unit width minus three in an 8-4-2-1 binary code. During
the prime cycle the program sequence illustrated in FIG. 7A is
executed. That sequence of events comprises a read width cycle
which is completed only when each width code is read exactly the
same in two successive scans of the width codes on the font. The
double read cycle minimizes width errors.
After the apparatus is reset by the prime control, data control 144
(FIG. 5A) addresses every character on font 22 in sequence under
control of print control 152. Each character is addressed and the
width read as described hereinafter. The width values are stored in
width control 146. Subsequent to the leading and storing of widths
for all of the characters, each character is again addressed by
data control 144 and the width codes re-read. The re-read width
values are compared to those stored in width control 146 and tested
for error. In case of error, data control 144 repeats the
aforementioned cycle until two successive width read and compare
cycles produce the same data. If there are no errors, the cycle is
completed at the end of the second read-compare sequence. Methods
and apparatus for data storage and comparison are well known to
those skilled in the art and are not therefore described in detail
herein.
The circuitry illustrated in FIGS. 7B and 7C is utilized to read
each character width value on the font. A character is accessed via
horizontal and vertical digital/analog converters 180, 182 which
receive coded data from character select ROM 184 within data
control 144 (FIG. 5A) and operate in the same manner as for normal
character exposure which will be described more fully hereinafter.
The vertical and horizontal automatic position control signals
function normally for the first seven strokes (OCC1 - OCC7, (FIG.
7F). Eight additional strokes (OCC8, FIG. 7F) are added thereby
enabling vertical APC to bring the beam to a more accurate position
on the bottom edge of the indexing bar above the selected
character. This is illustrated in FIG. 7D. Characters on font 22
are accessed by deflection voltages as shown in FIG. 7E. Read width
gate signal RWG (FIG. 7F) moves the beam to the left so that it is
centered on the width code bars during the sixteenth stroke.
The above width code reading strokes are performed at the same
stroke frequency as the APC strokes (the frequency used for a
fifteen point character). However, in actual practice the slower
frequency as compared to the frequency of smaller point sizes such
as five or six point, enables a greater amount of signal
integration thereby improving signal detection accuracy. The video
output from video preamplifier 104 (FIG. 3A) is provided to filter
186 through amplifier 188. The vertical ID stroke from vertical
stroke generator 102 (FIG. 3A) is input into a clock generator
which comprises IC comparator 190, flip-flops 192, 194, resistor
ladder 196 and one-shot multivibrator 198. Resistor ladder 196
utilizes transistor switches 200, 202, 204, which are driven by the
indicated logic outputs from flip-flops 192, 104 to generate four
trigger points for IC comparator 190. Each trigger point
corresponds to the center sampling point of a width code. The width
codes are in an 8-4-2-1 sequence to minimize errors as the stroke
amplitude/deflection is most accurate at the start of a sweep.
Therefore, the largest binary value is placed nearest to the
initiation of deflection.
The transistor switch/comparator approach illustrated in FIG. 7C is
only one manner of implementing the generation of four trigger
pulses. Clock generators based on time (rather than amplitude) may
be used just as effectively. For example, timing generators used to
convert data from serial-to-parallel in data communication networks
could also be used instead of the transistor switch/comparator
circuitry illustrated in FIG. 76.
The features of the width code reading are:
1. The width code is contained within and in close proximity to the
indexing bars where the beam position is most accurate;
2. The high degree of filtering of the code reading video minimizes
errors; and
3. The double reading and error control minimizes errors.
ANALOG CIRCUITRY
The video processor circuitry is illustrated in FIG. 8 and receives
the raw video signals from video preamplifier 104 (FIG. 3A) and
provides two basic functions, namely, the decoding of the width
value during the prime mode and the generation of the CRT beam
ON/OFF levels which are synchronous with the video during the print
mode (black on font equals CRT beam Off). The circuitry includes
width filter 210 having a long-time constant, video filter 212
having a short-time constant, and an auto threshold control (ATC)
214, which ensures a constant percentage threshold level into the
reference inputs of comparator amplifiers 216, 218. ATC circuit 214
compensates for any variation of font illumination. The raw video
output from video preamplifier 104 is provided to the high input of
amplifier 220 which has a gain of approximately three. The output
of amplifier 220 is input to width filter 210, the output of which
is provided to the low input of comparator amplifier 216. The
reference input of comparator amplifier 216 is connected to the
output of ATC circuit 214 and the output of that amplifier
comprises the width data during the prime mode of operation. The
output of amplifier 220 is provided both to ATC 214 and video
filter 212. The output of video filter 212 is input to the low
input of comparator amplifier 218 and the reference input of
amplifier 218 is the automatic threshold signal. The output of
comparator amplifier 218 comprises one input to AND gate 222, the
other inputs of which are a print enable signal (PREN) and a
blanking signal from vertical stroke generator 102 (FIG. 3A). The
output of AND gate 22 is a digitized video signal. The output of
comparator amplifier 218 is inverted by inverter 224 and provides a
signal to the automatic position control circuitry which will be
described hereinafter.
At video filter 212, the noisy video signal is smoothed into a
sharper square wave which is input to comparator 218. When the
image dissector beam is scanning a white area on the font, the
resulting positive video level causes the output of comparator 218
to switch positive. This switching video signal is sent through AND
gate 222 to CRT driver 126 (FIG. 4) where the cathode of the CRT is
turned on and off according to the video level.
WIDTH DECODING
The width code to the left of each character on font 22 is scanned
during the prime mode and the black on the font is the active width
value. One single scanning stroke (the sixteenth stroke) generates
the four-bit width values which is based on fifteen units.
Automatic horizontal and vertical beam positioning occurs prior to
the sixteenth stroke.
The width decoder circuitry is illustrated in FIG. 7C. During the
prime mode read width gate signal (RWG) FIG. 7F) which is enabled
for the sixteenth stroke, is produced by pulse signal OCC 15 to
prepare shift register 226 to receive the four-bits of width code
during the sixteenth stroke. Flip-flops 192, 104 are both reset so
that switch 200 is closed, placing a step "one" voltage to the
positive input of comparator amplifier 190. When the stroke ramp
voltage is equal to step one, the output of comparator 190 goes
negative thereby triggering clock 198 and at this time the image
dissector beam is sampling the topmost width code (8) which in FIG.
7D is black or "one." Clock 198 shifts the 8 bit into shift
register 226 and toggles A and B flip-flops 192, 194. Thereby
switch 200 opens and switch 202 closes, presenting a step 2 voltage
to comparator 109. When the stroke equals step two, clock 198
shifts the second width code (4) into register 226, thereby
shifting the eight-bit to the second stage thereof. The
aforementioned sequence continues until the four bits are shifted
into shift register 226. The four-bit width code (1001) equals nine
units. The "raw unit" width value (4 bits) is stored in width
control 146 (FIG. 5A) at the location that corresponds to the TTS
code of the character h.
X AND Y CHARACTER SELECT CIRCUITRY
The X and Y character select circuit is illustrated in FIG. 7B. The
position of a font character as viewed by the image dissector is
located by its TTS code which generates a deflection voltage in the
X and Y planes. For example, the lower case e is located at the
center of the font, so no significant deflection voltage is
required in either the X or Y planes for that character. The TTS
code on lines OR0 to OR6 at the input of character select ROM 184
generates four positional bits for the horizontal (HP1 to HP8) and
vertical (VP1 to VP8). These digital codes are input to
digital/analog converters 180, 182, each of which provides an
output voltage somewhere between minus 7 and plus 6 volts DC. The
maximum deflection voltages are shown in FIG. 7E. This positional
voltage is used to deflect the image dissector beam onto the
approximate target area of the font. Automatic positioning control
then occurs. During the prime mode, signal RWG offsets the beam to
the left so that the sixteenth stroke will pass through the middle
of the width code (FIG. 7D). When preparing to stroke a character,
signal SAG (FIG. 5B) offsets the beam to the right of the indexing
bar, to the left edge of the character field. The output voltages
from converters 180, 182 are provided to horizontal deflection
amplifier 92 and vertical deflection amplifier 94 (FIG. 3A) where
they are combined with the signals HAPC, VAPC and skew correction
signals.
VERTICAL STROKE GENERATION
Vertical stroke generation circuit 102 (FIG. 3A) is more fully
described in FIGS. 9A, 9B and generates the wave shapes and timing
pulses that influence or control the majority of the analog
circuits throughout the phototypesetting system. Point size
register 100 provides a ten bit output that is converted by D/A
converter 230 to a signal supplied to all circuits that are point
size dependent. Signals STK and SD control both the image dissector
and CRT stroke timing. Signal AAC occurs at the top of the image
dissector stroke and is used as the clock in all analog circuits
and generates the signal OCC0-15 in the digital circuits.
With reference to FIG. 9A, the vertical stroke (STK) for the image
dissector is generated as follows. The ten-bit code to D/A 230
results in a negative voltage which is greatest (minus ten V) for
five point, and least (minus 1.5 V) for thirty-six point. This
voltage is provided to integrator 232 which charges capacitor 234
at the rate of five microseconds/PT towards plus seven volts.
Comparator 236 monitors the level of the vertical stroke output of
integrator 232 and when it reaches plus seven volts, the output of
the comparator goes negative. The negative output triggers one-shot
MV 238 to produce the signals SD and SD, and one-shot MV 240
produces signals RD (retrace delay) and RD. Stroke drive signal SD
activates field effect transistor switch 242, which discharges
capacitor 234. This is a significant time, as both the image
dissector stroke and cathode ray tube stroke voltages are driven to
zero, thereby creating the retrace or return of the beam. Signal SD
is a constant 12 microsecond width as illustrated in FIG. 9A.
With reference to FIG. 9B, comparator 244 also monitors signal STK
but is adjusted to approximately plus 6.8 volts. When the level of
signal STK reaches that voltage, comparator 244 goes negative
thereby generating the analog active clock (AAC) signal (Ref. FIGS.
5B and 7F). The duration of signal AAC is about two percent of
signal STK and is point-size dependent because of the slope of STK
at the negative input of comparator 244. Blanking is a signal that
turns off the CRT beam during its retrace and is generated at the
output of NOR gate 246. The duration of blanking is from the lead
edge of an AAC signal to the fall of signal SD, plus 3
microseconds. Retrace delay signal RD is used by VAPC and skew
circuit 116 (FIG. 3B) to establish the time for VAPC. The other
inputs to NOR gate 246 are signals SD and the output of one-shot MV
248.
VAPC AND SKEW CIRCUITRY
Signal VAPC is the automatic positioning of the image dissector
beam on the font in the vertical plane and occurs at two different
rates; fast VAPC (for the second through seventh strokes) and slow
VAPC (for the remainder of the strokes of a character.) VAPC and
skew circuit 116 (FIG. 3B) are illustrated schematically in FIG.
10A where the video signal from video processor circuit 114 (FIG.
3B) is monitored at time SD .sup.. RD. If the positioning voltage
directs the beam to the white area above the width code frame (as
illustrated in FIG. 10B) white is monitored by AND gate 250. Switch
252 is thereby closed, applying plus fifteen volts through resistor
254 to capacitor 256. Capacitor 256 is charged positive which acts
to lower the beam toward the desired target (the black and white
border). A signal corresponding to the stroke from the digital
circuitry previously described has discharged capacitor 256 through
switch 258 at time OCCO (FIGS. 5B, 7F) to establish zero during the
first stroke. Capacitor 256 is now charged positive and the voltage
thereof is applied to voltage follower 260 and to vertical
deflection amplifier circuit 94 (FIG. 3A) to drive the beam
slightly downward toward the black area. After the next stroke at
time SD .sup.. RD, the font position is again monitored for black
or white, and charges capacitor 256 accordingly positively or
negatively. If black is sensed then switch 262 is closed by AND
gate 264 to apply minus 15 volts to capacitor 256 through resistor
266. During the second through seventh strokes, signal VAPCG from
the digital circuitry, closes switches 268, 270 to provide fast
VAPC by placing resistors 272 and 274 into the charge circuit,
thereby charging capacitor 256 at a faster rate.
HAPC AND STROKE ADVANCE CIRCUIT
Stroke advance refers to the displacement of the image dissector
beam to the right after each stroke. The amount displaced is
set-sized dependent. Signal HAPC is the analog automatic
positioning voltage for the image dissector beam in the horizontal
plane and is generated during the fifth, sixth and seventh strokes.
The purpose of signal HAPC is to locate the right side (black-white
border) of the indexing bar containing the width code as
illustrated in FIG. 11B. The horizontal stroke advance and HAPC
circuitry is illustrated in detail in FIG. 11A. Set-size register
110 provides a ten bit output of set-size data to digital/analog
converter 280, which develops a negative output voltage that is
greatest for the small set sizes. The first signal from the digital
circuitry previously described discharges capacitor 282 during the
first stroke by closing switch 284. Signal SAG inhibits signal SD
at gate 286 for the second through seventh strokes to enable signal
HAPC to be generated.
Continuing with FIG. 11A, after the deflection voltage has directed
the image dissector beam to the approximate target area on the
font, the right side of the width code frame is located before the
end of the seventh stroke as follows. Signal HAPC1 (signal OCC4
from the logic circuitry previously described, (Ref. FIG. 5B)
conditions AND gate 288 to monitor the fifth stroke. As the image
dissector beam is driven downward on the font, black video enables
AND gate 288 and OR gate 290 to activate field effect transistor
292 which provides minus fifteen volts through resistor 294 to
integrator 296. Capacitor 282 is charged while black is monitored
on the fifth stroke. This drives the image dissector beam to the
right which differs from general stroke advance, which occurs
during stroke signal SD. On the sixth and seventh strokes, white
video is monitored by AND gate 298 and signal HAPC2 activates
switch 292 through OR gate 290 to charge capacitor 282, thereby
directing the image dissector beam further to the right. When black
has been sensed, signal HAPC becomes ineffective, allowing the
image dissector beam to rest on the border as shown in FIG. 11B.
Signal BLANKING ensures that gate 290 does not generate signal HAPC
during beam retrace.
After the seventh stroke signal SAG goes high, allowing stroke
advance. Signal SAG at the input to digital analog converter 180
(FIG. 7B) produces a small deflection of the image dissector beam
just to the left of the character field to prepare for the
character stroking. Video is now on at the CRT and output copy will
be produced (white on the font equals CRT beam On).
After signal SAG goes high, signal SD closes switch 300 for twelve
microseconds, applying the output from digital/analog converter 280
to integrator 296. The resulting current through switch 300 charges
capacitor 28 for twelve microseconds, thereby resulting in a
step-change in voltage at the output of integrator 296. This
voltage is provided to horizontal deflection amplifier 92 (FIG. 3A)
to direct the image dissector beam one stroke to the right to
stroke a new area of the same character on the font. This step
varies with set size and is greatest for five set. This results in
fewer image dissector strokes and fewer CRT strokes, which are
synchronized when the video is on. Thus, the width (set) of the
output copy carrier is inversely proportional to the size of the
image dissector beam step. After all of the signals SD have charged
capacitor 282 to about plus 6.7 volts, the image dissector beam has
stroked the entire character field and some of the black area to
the right thereof. The next first stroke signal then discharges
capacitor 282 to prepare for the next character.
FONT GRID
Font grid 22 is a precision optical glass plate containing the
characters and spaces that are used to generate output copy. An
example of a font layout is illustrated in FIG. 12 which contains
109 characters and spaces. The width values are coded and appear to
the left of each character or space. The width code is arranged in
four bits (vertically) where black is the active bit.
* * * * *