Multi-beam raster scan display monitor

A vertically aligned array of electron scanning beams independently modulated by individual sources of video signals are employed to significantly increase display definition in conventional cathode ray tube type monitors. Precise vertical alignment of scanning spots produced by the beam array is achieved by synchronizing the relative timing of the video signals associated with each of the beams using delay circuits. Vertical spacing between the scanning spots produced by the beam array may be selectively adjusted by electrostatic deflection plates. Vertical alignment and vertical spacing of the scanning spots are respectively sensed though the provision of narrow, vertical and diagonal slits in the fluorescent coating of the CRT screen. A photodetector positioned at the rear of the screen produces output signals in accordance with light delivered through the slits as the scanning spots traverse the slits. The relative timing and magnitude of the timing signals are indicative of the vertical alignment and vertical spacing of the scanning spots. Character generation circuitry comprises a plurality of discrete matrix memories which are simultaneously addressed using the same character designation derived from a single refresh memory. Superimposed screen images may be created by using different data sources to modulate the scanning beams in order to generate differing picture fields, each corresponding to an image on the screen.

TECHNICAL FIELD 
The present invention generally relates to raster scan, cathode ray tube 
type monitors, and deals more particularly with a device implemented 
method for significantly improving the definition of display images 
produced by such monitors. 
BACKGROUND ART 
The use of CRTs (cathode ray tubes) for displaying various types of 
alphanumeric and pictorial information has increased rapidly during recent 
years along with the expanding role of computers and data processing 
equipment. CRT display monitors are finding increasing use particularly in 
the area of computer generated graphics in which pictorial or graphics 
information generated by a computer is displayed on the CRT screen for 
analysis. In many of these applications, particularly those involving 
graphical analysis, definition of the display image on the screen is less 
than completely satisfactory. 
In connection with conventional television type raster scanning, definition 
is defined as the number of scanning lines which comprise each picture 
frame of the image to be displayed. Definition is dependent, in part, on 
the thinness of each scanning line; current conventional CRT display 
monitors produce scanning lines having a thickness typically between 0.015 
and 0.0075 inches, and state of the art monitors may achieve a line 
thickness of 0.005 inches. Scanning lines of this thickness are well 
within the range necessary to produce extremely high definition display 
images. Definition, as defined above however, does not reflect the total 
amount of information, i.e. the total number of discrete elements or 
"pixels" which can be utilized, but rather merely deals with a measure of 
minimum line width, regardless of the number of lines actually displayed. 
In contrast, the present invention relates to increasing the overall 
amount of information which can be displayed; the quality of information 
density will therefore be hereinafter referred to as image "definition". 
Prior art CRT display monitors typically utilize a picture frame comprising 
262 non-interlaced lines of image data interlaced to form a picture field. 
Objectionable flicker occurs at refresh rates below approximately 50 Hz in 
connection with non-interlaced scanning. Flicker may be eliminated through 
the use of persistance phosphors, but this approach suffers from certain 
drawbacks such as decreased image brightness and the tendency to "burn". 
The deflection yokes employed in conventional monitors for moving the 
electron beam of the tube across the screen are limited in the rate at 
which the beam may be moved across each line; currently, the maximum 
scanning rate of prior art, single beam monitors operating at 60 Hz 
refresh and using a special deflection yoke and drive circuit is 
approximately 60,000 lines per second. 
Although specially designed CRT monitors of the type having a single 
scanning beam have, in the past, been adapted to exceed the conventional 
15,720 scanning lines per second, such monitors are particularly expensive 
to produce due to the additional high speed logic and control circuitry 
required by their design, and in any event such specially designed 
monitors are not compatible with many computer installations which are 
based on standard television type formats. 
In connection with many types of computer generated and computer aided 
graphics, it is often necessary to simultaneously display a plurality of 
superimposed images on the screen which are generated from different data 
sources. In the past, it has been necessary to provide relatively complex 
mixing circuits for combining the video signals in a manner which allows a 
single electron beam to form each of the images to be displayed. This 
approach to the problem has not gained widespread acceptance because it 
was relatively expensive in terms of the hardware which was required. 
Multiple beam CRTs are known per se in the art, as exemplified by U.S. Pat. 
Nos. 2,978,608, 3,140,473 and 3,671,957. However, none of these prior 
patents disclose raster scan type monitors capable of generating high 
definition images. The device shown in U.S. Pat. No. 2,978,608 is not of a 
true raster scan type and is not capable of producing grey scales. U.S. 
Pat. No. 3,671,957 discloses a monitor in which each gun paints different 
areas of the screen, rather than adjacent lines on the screen. 
Accordingly, it is a primary object of the present invention to provide a 
raster scan type CRT display capable of providing high definition display 
images, but which is relatively simple in design and is readily compatible 
with existing data processing and television systems. 
Another object of the present invention is to provide a monitor of the type 
described above which employs a plurality of electron scanning beams in 
which the associated scanning spots are maintained in precise vertical 
alignment with each other. 
A still further object of the invention is to provide a monitor of the type 
discussed above which includes provision for adjusting the vertical 
spacing between the scanning lines. 
Another object of the invention is to provide a raster scan display monitor 
having character generation circuitry comprising a plurality of discrete 
matrix memories which may be simultaneously addressed using the same 
character designation. 
A further object of the invention is to provide a multi-beam scanning 
display as discussed above in which each of the beams is controlled by 
different sets of data sources thereby eliminating the need for special 
circuitry for mixing signals derived from differing data sources. 
DISCLOSURE OF INVENTION 
According to the present invention, a vertically aligned array of electron 
scanning beams simultaneously scan adjacent lines of a cathode ray tube 
type display monitor in order to significantly increase the definition of 
the images to be displayed. Each of the beams in the array thereof is 
independently modulated by separate sources of video signals. The monitor 
screen is provided with both a vertical and diagonally extending slit in 
the metalized coating thereon. As the beams traverse the slits during the 
scanning process, light generated by the layer of fluorescent material 
registrating with the slits is transmitted rearwardly into the tube and is 
detected by a photodetector. The photodetector produces a series of 
electrical signals whose timing and magnitude provide an indication of 
both the degree of vertical alignment and the scanning spots as well as 
the vertical spacing between such spots. The scanning spots may be brought 
into vertical alignment with each other by selectively delaying delivery 
of video signals to certain of the electron beam guns. Vertical spacing 
between the scanning spots produced by the beam array may be selectively 
adjusted by means of electrostatic deflection plates. Simplified character 
generation circuitry suitable for use in producing alphanumeric characters 
employs a plurality of discrete, matrix memories for generating the 
characters which may be simultaneously addressed using the same character 
designation derived from a single refresh memory. Images derived from 
separate data sources may be displayed in superimposed relationship on the 
monitor screen by driving the beams using different video signals such 
that the images are interlaced on various sets of lines of each picture 
frame.

BEST MODE FOR CARRYING OUT THE INVENTION 
Attention is first directed to FIG. 1 wherein the multi-beam raster scan 
display monitor of the present invention is depicted. The display monitor 
will typically include means for generating video signals which is 
generally indicated within the broken line 20 and comprises a clock 22 
delivering clock pulses to a plurality of independent circuits for 
generating video signals, respectively designated by the numerals 24-30, 
as well as to a horizontal sync signal generator 32, and a vertical sync 
signal generator 34. It is noted that although separate vertical and 
horizontal sync lines are shown, the vertical and horizontal sync signals 
may be combined with one or more video signals and then extracted using a 
conventional sync separator. 
The video signal generators 24-30 have outputs for delivering video signals 
on respectively corresponding lines 36-42 to the inputs of respectively 
associated, adjustable delay circuits 44-50 whose construction will be 
discussed later in more detail. Video generator circuits 24-30 are 
essentially conventional in design and may be employed for producing video 
signals from completely independent data sources, as will become clearly 
apparent hereinafter. Delay circuits 44-50 are each selectively operable 
for altering the timing of the video signals delivered thereto in order to 
compensate for timing variations in the respective sets of video signals 
generated by circuits 24-30. In this manner, the timing of the resulting 
signals output by delay circuits 44-50 to the respective corresponding 
amplifiers 52-58 is synchronized. Delay circuits 44-50 may be incorporated 
as integral parts of the corresponding video amplifiers 52-58 if desired. 
The synchronized, amplified video signals are delivered via lines 60-66 to 
a CRT partially indicated by the numeral 68, and more particularly to 
means for producing a plurality of electron scanning beams 70-76; as shown 
in FIG. 1, four conventional electron beam guns, 78-84 respectively, 
operably coupled with lines 60-66 are employed for producing the 
corresponding scanning beams 70-76. It is to be understood, however, that 
other methods may be employed for producing the plurality of scanning 
beams, such as the use of a single cathode to supply a stream of electrons 
which then may be divided into separate, discrete beams by deflection and 
focusing devices which are well known in the art. 
The horizontal sweep signal produced by horizontal sweep signal generator 
88 is synchronized with, or is triggered by the horizontal sync pulse 
signal, and the resulting signal is amplified by amplifier 90 and 
delivered to the input of a conventional deflection yoke indicated by the 
numeral 92. Similarly, a vertical sync signal derived from the vertical 
sync signal generator 34 is delivered by line 94 to a vertical sweep 
signal generator 96 thereby synchronizing or triggering a vertical sweep 
signal. Synchronized sweep signals are then amplified by amplifier 90 and 
delivered to the inputs of deflection yoke 92. 
Deflection yoke 92 functions to deflect the beams 70-76 to produce raster 
scanning of a display screen 100. Each of the scanning beams 70-76 is 
modulated to produce formation of images on the screen 100 using the 
respectively corresponding, synchronized video signals delivered on lines 
60-66 to the electron beam guns 78-84. 
Referring also to FIGS. 2 and 3, the scanning beams 70-76 are adapted to 
produce vertically spaced scanning spots 102-108 on the display screen 100 
which results in a series of four, vertically spaced, parallel, generally 
horizontal traces 109 upon each sweep of the screen 100 by scanning spots 
102-108. As in the conventional television format, scanning may be 
initiated in the upper left hand corner of the screen 100 at a starting 
frame 110 and is successively drawn across the screen 100 from left to 
right and slightly downward until the end of the frame 111 is reached at 
the lower right hand corner of the screen, at which point the scanning 
spot array returns along the vertical retrace path 112 to the starting 
frame 110. The width indicated by the letters "WB" in FIG. 3 of each trace 
may be altered by varying the diameter of the scanning spots 102-108 using 
a conventional focusing adjustment which controls each of the electron 
guns 78-84. The vertical spacing between adjacent traces and each sweep, 
designated by the letter "B" in FIG. 3, as well as the distance between 
the traces in adjacent sweeps, designated by the letter "S", may also be 
readily adjusted in a manner to be described below. 
As mentioned previously, the video signals produced by circuits 24-30 are 
normally not precisely synchronized, partially due to the fact that signal 
timing may be slightly altered by differences in the values of components 
in the respective circuits. Thus, in the absence of any provision for 
synchronizing the video signals, the timing of the modulation of scanning 
beams 70-76 may not be synchronized; the effect of the variation in the 
timing of the video signals is manifested in a lack of vertical alignment 
of the scanning spots 102-108. Consequently, the scanning spots 102-108 
are horizontally displaced from each other to positions (shown for 
illustrative purposes by broken lines) designated by the numerals 116-122. 
Distortions in the deflection of the scanning beams 70-76 as a result of 
imperfect deflection geometry and the like also significantly contributes 
to the lack of vertical alignment of the scanning spots. This lack of 
vertical alignment of the scanning spots results in a blurred, distorted 
display image which significantly reduces picture resolution and quality. 
The present invention provides a novel means of sensing the presence of 
vertical alignment of the scanning spots and allows appropriate adjustment 
of the lateral positions of the scanning spots to be made, in order to 
bring the same into precise vertical alignment, and in this connection, 
reference is also now made to FIGS. 6, 7 and 8. As shown in FIGS. 6 and 7, 
the CRT 68 is defined by a glass envelope 124, in which the screen 100 has 
a layer of fluorescent material 126, such as phosphor, on the inner face 
thereof. A metalized coating 128, as of aluminum, is provided on the 
interior face of the fluorescent layer 126 which forms a reflective 
surface for reflecting fluorescent light forwardly toward the viewer. The 
coating 128 is opaque as viewed from the inside of glass envelope 124 and 
prevents light from being reflected from fluorescent layer 126 inwardly to 
the interior of the CRT 68. A narrow, elongate, vertically extending slit 
130 is provided in the metal coating 128 adjacent one lateral side of the 
screen 100. The vertical slit 130 is disposed horizontally within the 
trace path produced by at least one of the sweeps by the beam array, but 
is preferably spaced beyond the lateral edge of the viewing area, which is 
designated by the numeral 132 in FIG. 6; in this manner, the slit 130 is 
traversed by at least one sweep of the beam array, but yet is not visible 
to the viewer. 
A diagonal slit 134, similar to slit 130, is provided in the metal coating 
128 near the top of the screen 100, above the upper edge 136 of the 
viewing area. The diagonal slit 134 is inclined with respect to the 
vertical slit 130, and as shown in FIG. 8, is adapted to be diagonally 
traversed by each of the trace lines in at least the first and second 
sweeps of the beam array. 
The CRT 68 is provided with a photodetector 138 confined in a housing 140 
which is mounted on a rear wall of the envelope 124. The rear wall of the 
glass envelope 124 is provided with a graphite coating on opposite sides 
thereof, except at an area adjacent one end of the housing 140 whereat 
transparent conductive coatings are applied to opposite surfaces of the 
envelope 124. The photodetector 138 is therefore in optical communication 
with the interior of the glass envelope 124 and is disposed in a position 
to detect light emanating from the rear surface of the screen 100. An 
optical lens 146 may be disposed in front of the photodetector 138 within 
the housing 140 to magnify and focus light passing through the transparent 
coating 144, in order to increase the detection sensitivity of 
photodetector 138. 
Attention is now directed to FIGS. 4 and 5 wherein one configuration of a 
circuit suitable for use as each of the delay circuits 44-50 is displayed. 
As shown in FIG. 4, the delay circuit has an input terminal 148 and an 
output terminal 150. A parallel-T arrangement of resistors and capacitors, 
consisting of resistors R1, R2 and R4, and capacitors C1, C2 and C3, is 
coupled within the input terminal 148 and the positive terminal of 
operational amplifier 152. The output of operational amplifier 152 is 
coupled in feedback to the negative input thereof as well as to the 
positive input of operational amplifier 154 through resistor R7. Resistor 
R9 is of the variable type and functions to allow adjustment of the amount 
of delay imposed upon the incoming video signals. The output of 
operational amplifier 154 is coupled via line 156 to the parallel-T 
arrangement mentioned previously, as well as to the negative input thereof 
through resistor R8. The negative input of operational amplifier 154 is 
coupled through resistor R5 to input terminal 148, and to the positive 
input thereof through resistors R5 and R6. Equalization and selection of 
amplitude may be obtained by adding the single stage operational amplifier 
shown in FIG. 5; in this case, the positive input of operational amplifier 
158 would be coupled to terminal 160 while the output thereof would be 
coupled to terminal 162. The output of operational amplifier 158 is 
coupled through a variable resistor R11 to the negative input thereof, the 
negative input of operational amplifier 158 being connected to ground 
through resistor R10. If desired, resistor R4 may be of the variable type 
to permit adjustment of the center frequency of the equalizer. 
Turning now to a description of the operation of the monitor, with 
reference being particularly made to FIGS. 1, 2, 6, 6a, 7 and 8, video 
signals generated by video generator circuit 24-30 are operated upon by 
delay circuits 44-50 and are then delivered to electron guns 78-80, after 
having been amplified by video amplifiers 52-58. The scanning beams 70-76 
are deflected by yoke 92 to produce a plurality or array of vertically 
aligned, spaced apart scanning spots 102-108 on the screen 100 which are 
then controlled by yoke 92 to produce raster scanning of the screen 100 in 
the normal manner. During the first two sweeps of the scanning spot array, 
each of the spots 102-108 traverse the vertical slit 130 to produce 
fluorescense of the fluorescent layer 126 registering with vertical slit 
130. The fluorescent light traveling rearwardly into the interior of the 
tube through vertical slit 130 is detected by photodetector 138 which 
produces an output signal on line 164 whose magnitude varies in accordance 
with the level of light which is sensed. The light level sensed by 
photodetector 138 varies in accordance with the number of the scanning 
spots 102-108 which traverse the vertical slit 130 at the same instant; 
thus, a maximum level of light will be sensed when all four of the 
scanning spots 102-108 traverse the slit 130 at exactly the same time. 
Assuming, for the moment, that the scanning spots 102-108 are not 
vertically aligned (due, for example, to deflection errors or the like), 
the quantity of light sensed by the photodetector 138 will be less than 
the predetermined, maximum level thereof corresponding to a condition of 
vertical alignment. The resulting signals indicative of a lack of vertical 
alignment are delivered via line 164 to means for automatically correcting 
vertical alignment, indicated by the numeral 166 in FIG. 1. Correcting 
means 166 may comprise a conventional control circuit having the output 
thereof on line 168 operatively coupled with a control input of each of 
the delay circuits 44-50. Correcting means 166 may comprise, for example, 
a conventional circuit for converting the signal on line 164 to an output 
signal whose voltage varies in accordance with the output of photodetector 
138; resistor R9 may be of the voltage controlled type whose value varies 
in accordance with the magnitude of the voltage on line 168. 
Alternatively, the output of photodetector 138 on line 164 could be 
delivered to a visual or audible indicator (not shown) which simply alerts 
the user of an out-of-alignment condition. In this case, the user would 
correct the out-of-alignment condition by manually controlling certain 
ones of the delay circuits 44-50. 
As is apparent from FIG. 8, the scanning spots 102-108 traverse the 
diagonally extending slit 134 at horizontally spaced locations along the 
first two sweeps of the scanning spot array, the points of intersection of 
the beam traces and the diagonal slit 134 being indicated by the short 
hash marks 170 in FIG. 8. As the scanning spots 102-108 traverse the 
diagonal slit 134, a corresponding series of light waves will be delivered 
through the slit 134 into the interior of the glass envelope 124 and are 
detected by the photodetector 138. It may be appreciated that the timing 
between successive light pulses sensed by photodetector 138 traveling 
through slit 134 is directly proportional to the vertical spacing between 
the scanning spots 102-108. A reduction of the vertical spacing between 
each of the scanning spots 102-108 increases the frequency of the light 
pulses, while greater spacing between the scanning spots decreases light 
pulse frequency. The light pulses detected by photodetector 138, which are 
indicative of the relative vertical spacing between the scanning spots 
102-108 are converted by photodetector 138 to a train of pulses which are 
output on line 164 to a means for adjusting the vertical spacing between 
the scanning spots 102-108, which adjustment means is designated by the 
numeral 172 in FIG. 1. Adjustment means 172 may comprise a conventional 
circuit automatically controlled by the pulse train received on line 164, 
which circuit is operative to vary the voltage on a pair of vertical 
deflection plates 174. Vertical deflection plates 174, in turn, control 
the vertical spacing between the scanning spots 102-108. 
It is appropriate to note at this point that, although the vertical and 
diagonal slits 130 and 134 respectively have been disclosed herein for 
detecting vertical alignment and spacing of the scanning spots 102-108, 
alternate means may be employed to perform this same function. For 
example, either of the slits 130 and 134 may be replaced by conductive, 
thin wire elements which themselves produce the necessary output signals 
when impinged by the beams 70-76. Also, alignment can be achieved by 
providing a video test pattern (such as cross-hatching and/or diagonal 
lines) and making the appropriate adjustments based on visual inspection 
of the image, using the naked eye or an optical system. 
Although the display monitor of the present invention discussed above is 
indicated as employing a raster scan pattern wherein scanning commences at 
the upper left hand corner of the viewing screen, it is to be noted that 
the present invention is readily adaptable for commencing scanning in any 
one of the four corners of the screen and may proceed in any of four 
directions. For example, the beginning of each scanning frame might 
commence at the lower right hand corner of the screen and proceed 
vertically upward on each successive sweep, or, scanning of each frame 
might commence at the lower right hand corner of the screen and proceed 
horizontally toward the left thereof on each successive sweep. Thus, while 
the terms "vertical" and "horizontal" are used herein to respectively 
designate the alignment axis of scanning spots 102-108 and the direction 
of scanning, it is to be understood that these terms are relative and the 
directions thereof are dependent on the frame of references established by 
the particular scanning pattern selected. 
As indicated in FIG. 3, successive sweeps are vertically spaced apart a 
distance "S", the distance S being determined by the amplitude of the 
vertical sweep signal. Normally, it will be desirable to have the distance 
S equal distance B. In some cases it may be desirable to reduce vertical 
spacing between each beam B, to a value less than the width WB, of each 
beam in order to produce overlapping of the traces produced by each beam. 
Attention is now directed to FIGS. 9 and 10 which relate to a system for 
generating alphanumeric characters suitable for use in connection with the 
display monitor previously described. The character generation system is 
driven by clock 176 whose pulse output is divided by a series of counters 
178-184 in order to provide a plurality of sources of pulse trains, each 
having different pulse timing. A refresh memory control 186 receives 
timing signals from counters 180 and 184 respectively corresponding to the 
column and text line addresses, and further interfaces with an external 
means (not shown) such as a keyboard to provide user control. The memory 
control 186 provides memory address signals, data signals and control 
signals to a refresh memory 188 which has stored therein character codes 
or designations corresponding to each character which may be displayed on 
the monitor. Character codes are delivered on an output bus 190 to the 
character address inputs of a plurality of matrix memories, respectively 
designated by the numerals 190-196. Each of the memories 190-196 includes 
a sweep address input which is coupled by a data bus to the output of 
counter 182. In operation, a character code output from refresh memory 188 
on data bus 190 is simultaneously delivered to the character addresses of 
each of the matrix memories 190-196. Each of the matrix memories 190-196 
has stored therein portions of the data necessary to generate a given 
character and deliver character data on their outputs to respectively 
corresponding shift registers 198-204. Each of the shift registers 198-204 
has a dot clock input coupled to the output of clock 176 and a load clock 
output coupled to the output of counter 178. Shift registers 198-204 
output the respectively corresponding portions of the character data on 
the corresponding video lines 206-212 which are operably coupled with the 
display monitor, and more particularly to the inputs of delay circuits 
44-50 shown in FIG. 1. From the foregoing, it may be appreciated that the 
data for producing each character is sliced or divided up into a plurality 
of portions which are stored in respectively corresponding, discrete 
memories, which memories may be addressed using a signal character code or 
designation. The resulting image display on the monitor screen is shown in 
FIG. 10 where it can be seen that each text line comprises five sweeps of 
the beam array to produce twenty traces or lines, each column 
corresponding to a particular character being divided into sixteen 
separate display dots. 
Referring now to FIGS. 11 and 12, the multibeam display monitor of the 
present invention is suitable for use in practicing a novel method of 
simultaneously displaying alphanumeric and graphical data so as to give an 
impression of superimposition on the display screen. A character generator 
214, either of conventional design or of the type described immediately 
above, is employed in cooperation with a graphics generator 216. Graphics 
generator 216 will typically include a controllable input (not shown) 
coupled with a bus 218 for receiving coded graphics information 
corresponding to particular graphics or pictorial information to be 
displayed. Character generator 214 and graphics generator 216 are 
controlled by a pair of timing inputs 220 and 222 derived from controller 
and timing circuitry 224 of the conventional type which is driven by a 
clock 226. Controller and timing circuitry 224 also provides horizontal 
and vertical sync pulses on output line 228 to the display monitor broadly 
designated by numeral 230. Character generator 214 is controlled by a 
suitable control (not shown) which delivers coded character designations 
on hub 232 in a manner similar to that described previously. The output of 
character generator 214 is delivered on video lines 234 and 236 to the 
display monitor 230, and more particularly to the respective inputs of one 
pair of delay circuits 44-50. The video signal outputs of graphic 
generator 216 are delivered on video lines 238 and 240 to the respective 
inputs of the other pair of delay circuits 44-50. Thus, it may be 
appreciated that video signals corresponding to character type information 
is processed by two "channels" of the multi-beam display monitor, while 
graphics information is processed by the other two "channels" thereof. The 
result of this method of information processing is shown in a typical 
example of a display pattern shown on the screen 110 in FIGS. 11 and 12, 
wherein the axes 242 and stair-step chart 244 represent graphics 
information generated by two channels of the display monitor and derived 
from graphics generator 216, while the remaining alphanumeric information 
is produced by the other two channels and is derived from the character 
generator 214. As is apparent from the simulated displays on screen 100, 
the graphics and character type images give the impression of being 
superimposed. This overlay effect of graphics and character information 
may be accomplished by delivering the respective character and graphics 
video signals to alternate channels of the display monitor. For example, 
as shown in FIG. 12, on the first sweep of the beam array, beams 70 and 74 
produce graphics information while beams 72 and 76 do not produce any 
image whatsoever. On the third sweep of the beam array (sweep .sub.n+2) 
beams 70 and 74 continue to produce graphics information while beams 72 
and 76 produce character information which is interlaced on alternate 
lines with the graphics information. 
By virtue of the use of independent video channels of the present 
multi-beam scan monitor, a novel method of displaying superimposed images 
produced from separate data sources, such as television cameras, is 
possible. This method is particularly useful for noncontact position 
sensing of a target object, as illustrated in FIGS. 13 and 14. As shown in 
FIG. 13, a reference object 246 is viewed by a first and second television 
camera 248 and 250 respectively, from preselected, known positions 
relative to the position of reference object 246. The video outputs are 
respectively operatively coupled with an alternate pair of video channels 
of the display monitor 230. Simultaneously, a target object 252 is viewed 
by a pair of cameras 254 and 256 from preselected positions relative to 
the target object 252. The video outputs of cameras 254 and 256 are 
respectively operably coupled to the remaining alternate pair of video 
channels of the display monitor 230. As shown in FIG. 14, the reference 
and target objects 246 and 252 are displayed in superimposed relationship 
by two separate sets of images thereof corresponding to the viewing 
positions of cameras 248, 250, 254 and 256. More particularly, the target 
object 252 displayed on the left hand side of screen 100 corresponds to 
the image televised by camera 254; the reference object 246 on the left 
hand side of screen 100 corresponds to the image televised by camera 248; 
target object 252 shown on the right hand side of screen 100 corresponds 
to the image televised by camera 256, and; the image of reference object 
246 shown on the right hand side of screen 100 corresponds to that 
televised by camera 250. Each of the cameras 248, 250, 254 and 256 are 
synchronized in their timing, relative to each other. 
With the arrangement described above, the positions of the images of the 
reference and target objects 246 and 252 shown on screen 100 correspond 
exactly to the actual positions of such objects themselves; any deviation 
of the position of the target object 252 will result in the apparent 
movement of at least one of the two images thereof shown on screen 100. In 
lieu of the reference object 246 and corresponding cameras 248 and 250, a 
suitable reference image may be created on screen 100 using artificial 
images generated by graphic data stored in a memory. 
Still another significant application of the present multi-beam raster scan 
display monitor involves its use in combination with many types of 
currently available television cameras which possess a resolution 
capability exceeding conventional display monitors. As shown in FIG. 15, a 
high resolution television camera 258 of the type having 4-1 interlace 
scanning delivers a multiplex output on line 260 consisting of four 
individual video signals. A demultiplexer 262 separates the individual 
video signals and respectively delivers the same on output lines 246-270 
to the inputs of respectively corresponding frame memories 272-278, 
wherein video signals corresponding to respectively associated frames 
recorded by the camera 258 are stored. A controller 280 is operatively 
coupled to the camera 258, demultiplexer 262, and each of the memories 
272-278, for controlling data transfer. The video signal outputs 
representing each frame recorded by the camera 258 are then respectively 
amplified by amplifiers 282-288 and delivered on lines 290-296 to 
respectively corresponding channels of the multi-beam display monitor 
which simultaneously displays all four frames recorded by the camera 258 
in a single scanning frame of the display monitor. Each of the frame 
memories 272-278 are updated with video signal information once for every 
four picture frames recorded by camera 258. 
In view of the foregoing, it is apparent that the multi-beam raster scan 
display monitor system of the present invention not only provides for 
reliable accomplishment of the objects of the invention but does so in a 
particularly simple and effective manner. It is recognized, of course, 
that those skilled in the art may make various modifications or additions 
to the preferred embodiment chosen to illustrate the invention without 
departing from the spirit and scope of the present contribution to the 
art. Accordingly, it is to be understood that the protection sought and to 
be afforded hereby should be deemed to extend to the subject matter 
claimed and all equivalents thereof fairly within the scope of the 
invention.