CA1147382A - Scanning array configuration - Google Patents

Abstract

SCANNING ARRAY CONFIGURATION

ABSTRACT OF THE DISCLOSURE
A line scanning apparatus employing a multiplicity of linear arrays, the linear extent of which is less than the length of the scan line. To permit an entire line to be covered, the arrays are offset from one another in the direction of scan with adjoining array ends overlapped. To correct for the misalignment and redundancy introduced, the image data from the arrays is buffered until a line is completed when readout, is initiated.
During readout, cross over from one array to the next is effected within the overlapped areas and the redundant data discarded.

Description

3~2 This invention relates to raster input scanners and, more particularly to, raster input scanners having multiple linear arrays. Reference is herewith made to copending Canadian Patent Application Serial No. 301,787, filed on April 24, 1978, entitled "Crossover Arrangement For Multi-ple Scanning Arrays", inventor: Martin A. Agulnek.
Scanning technology has progressed rapidly in recent years and today arxays of fairly substantial linear extent are available for use in raster scanners. Indeed, the linear extent of new arrays are in some cases many times the linear extent of earlier array designs. However, the length of even these recent array designs is still not sufficient to enable a single array to span the entire width of the normal sized line, i. e. 8 1/2 inches.
Further, it appears improbable that arrays of sufficient length will be developed in the foreseeable future since fabrication of such arrays would appear to require a major breakthrough in semi-conductor fabrication technology.
As a result, raster input scanners are ~orced to ~- -rely on shorter arrays and must, therefore, employ a multiplicity of arrays if the entire line is to be scanned in one pass. This raises the question of how to place the arrays so as to cover the entire line yet provide data representative of the line which is free of aberrations at the array junctures. Recently, interest has been expressed in optically-butted arrays. However, optical and optical~mechanical arrangements often experience difficulty in meeting and maintaining the tight tole-rances necessary for aberration free scanning, partic-ularly in operating machine environments.

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It is, therefore, an object of an aspect of thepresent invention to provide a new and improved raster input scanner employing multiple arrays.
It is an object of an aspect of the present invention S to provide an improved single pass line scanner employing mul-tiple linear arrays.

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It is an object of an aspect of the present invention to provide a system designed to accommodate misalignment of plural linear arrays.
It is an object of an aspect of the present invention to provide, in a raster input scanner having multiple physical-ly offset and overlapping linear arrays, means for removing offset and redundancy rom the data produced.
It is an object of an aspect of the present invention to provide scanning apparatus with plural relatively short linear arrays, having a composite length at least equal to the scan width.
It is an object of an aspect of the present invention to provide a line scanner incorporating plural overlapping arrays whose composite length equals the length of the scanned lines, with electronic means for switching from one array to the next without introducing noticeable aberrations and stigma-tism.
It is an object of an aspect o the present invention to provide multiple linear arra~s having overlapping viewing fields with data readout bridging between arrays in the over-lapping fields th~reof.

An aspect of the invention is as follows:
An array for use in scanning apparatus of the type employing plural arrays disposed so that a finite portion of one array overlaps a finite portion of an adjoining array to provide a composite array having a linear extent at least equal to the length of the line to be scanned, comprising a. an array substrate, said substrate being generally rectangular in shape;
b. a multiplicity of photosensitive elements on said 1~ substrate, said photosensi~ive elements being disposed in succes-sion longitudinally of said substra~e;
c. the center-to-center distances between the portion of said photosensitive elements in said finite portion of said array being different than the center-to-center distances between the remainder of said photosensitiv~ elements whereby to provide a vernier-like spacing between said photosensitive elements in : said array portion facilitating alignment of one photosensi~ive .~ element with the corresponding photosensitive element of the ad~oin~ng array.

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Other ob~ects and advantages will be apparent from the following description and drawings in which:
Figure 1 is an isometric view showing a ras~er input ~canner incorporating tAe multiple array arrangement of the pre-sent invention;
Figure 2 is a schematic illustrating an exemplary array disposition;
Figure 3 is an schematic view of the scanner opera~ing control;
Figure 4 is a schematic representation of tbe memory buffer for temporarily storing image data;
Figure 5 is 2 schematic illustration of the data map-pi~ng arrangement to avoid bit shifting on readout from the tem-porary memory buffer of Figure ~; .
Figure 6 is a schematic view showlng the data reado~lt system;
Fi~ure 7 is a schematic illustration of the dat~ read-out with crossover and removal of redundant data;
Figure 8 is a schematic view illustrating a modi~ied array wherein the center-to-center dis~ances between the photo-sensitive elements of a portion of one array are changed to pro-vide a vernier useful for aligning arrays;
Figure 9 is a schematic view o~ an alternate array con-figuration wherein a bridging array is employed to effect contin-ui~y between adjoinins arrays; and ~4a-~ 38~

Figure 10 is a schematic view of another alternative array configuration wherein a bridging array is combined with a standard array to form a unitary structure, the photosensitive elements of the bridging array being on different center-to-center distances to provide a vernier.
Referring to Figure 1, an exemplary raster input scan-ning apparatus 10 is thereshown. Scanning appara~us 10, as will appear more fully herein scans an original document 12 line by line to produce a video signal representative of the original document 12. The video signal so produced may be thereafter used to reproduce or duplicate the original 12, or store3 in me~ory for later use, or transmitted to a remote source, etc~
Scanning apparatus 10 comprises a box-like frame or . .
housing 14, the upper surface of which includes a transparent pla~en section 16 on which the original document 12 to be scanned is disposed face down. A displaceable scanning mechanism desig-nated:generally by the numeral 18, ls suppor~ed on frame 14 below platen 16 for movement back and forth underneath the platen 16 and the original document 12 thereon ln the Y direction as shown by the solid line arrow in Flgure 1.
Scanning ~:echanism 18 includes a carriage 20 slidably supported upon parallel rods 21, 22 through journals 23. Rods 21, 22, which parallel the scanning direction along each side of platen 16, are suitably supported upon ~he frame 14.
Reciprocatory movement is imparted to carriage 20 by means of a screw type drive 24. Drive 24 includes a longitudir.-ally extending threaded driving rod 25 rotata~ly journalled on frame 14 below carriage 20. Dr1ving rod 25 is dri~ingly in~er-connected with carriage 20 through a cooperating internally threaded carriage segment 26. Driving rod 25 is driven by means L7~8Z

of a reversible motor 28.
, A plurality of photosensitive linear arrays 1, 2, 3, 4 are carried on plate-like portion 35 of carriage 20. Arrays 1, 2, 3, 4 each comprise a series of individual photosensitive picture elements or pixels 40 arranged in succession along the array longitudinal axis. The arrays scan the original document 12 on platen 14 as scanning mechanism 18 moves therepast, scanning movement being in a direction (Y) substantially perpendicular to the array longitudinal axis (X). As best seen in Figure 2, the arrays 1, 2, 3, 4 may, due to the difficulty in accurately align-ing the arrays one with the other, be orfset from one another in the direction of scanning movement (the Y direction). To ac~om-modate the relatively short length of the individual arrays, the arrays overlap. In the exemplary illustration, the end portion of arrays 2, lt 4 overlap t~e leading portion of the succeeding arrays 1, 4, 3 when looking from left to right in Figure 2 along the X direction.
As will be understood, the length of the individual arrays 1, 2, 3, 4 may vary with different types of arrays and from manufacturer to manufacturer. As a result, the number of arrays required to cover the entire width of the original document 12 may vary from that illustrated herein.
Photosensitive elemen~s or pixels 40 of arrays l, 2, 3, 4 are normally silicon with carrier detecti,on by means of photo-transistors, photodiode-MOS ampIifiers, or CCD de.ection cir cuits. One sui~able array is the fairchild CCD 121 - 1728 pixel

2-phase linear array manufactured by Fairchild Corporation. As described, arrays 1, 2, 3, 4 are offset from one another in the scanning or sagittal direction (Y direction) but with an end por-tion of each array overlapping the leading portion of the next ~4~38Z

succeeding array to form in effect a composite unbroken array.
To focus ~he image onto the arrays 1, 2, 3, 4 a lens 43 is provided for each array. Lenses 43 are supported on carriage 20 in operative disposition with the array 1, 2, 3, 4 associated therewith. Mirrors 44, 45 on carriage 20 transmit the light images of the original via lenses 43 to arrays 1, 2, 3, 4. Lamp 48 is provided for illuminating the original document 12, lamp 48 being suitably supported on carriage 20. Reflector 49 focuses the light emitted by lamp 48 onto ~he surface of platen 16 and the original document 12 resting thereon.
In operation, an original document 12 to be scanned is disposed on platen 16. The scanning mechanism 18 including motor 28 is actuated, motor 28 when energized operating driving mecha-nism 24 to move carriage 20 back and forth below platen 16. Lam~
48 is energized during the scanning cycle to illuminate the orig-inal docllment 12.
To correlate movement of carriage 20 with operation of arrays 1, 2, 3, 4 an encoder 60 is provided. Encoder 60 gener~tes timing pulses proportional to the velocity of scanning mechanism 18 in the Y direction. ncoder 60 includes a ~iming bar 61 havins a succession o~ cpaced apertures 62 therethrough disposed along one side of the path of movement of carriage 20 in parallel with the direction of movement of carriage 20. A suitable signal generator in the form o~ a photocell-lamp combination 64, 55 is provided on carriage 20 of scanning mechanism 18 with timing bar 61 disposed therebetween.
As carriage 20 of scanning mechanism 18 traverses back and forth to scan platen 16 and any document 12 thereon, photo-cell-lamp pair 64, 65 of encoder 60 moves there~ith. Movement o~
the photocell-lamp pair 64, 65 past timing bar 61 generates a 738~

pulse-like output signal in output lead 66 of photocell 64 directly proportional to the velocity of scanning mechanism 18.
As can be envisioned by those skilled in the art, sup-porting arrays 1, 2, 3, 4 in e~act linear or tangential alignment talong the X-axis) and maintaining such alignment throughout the operating lif~ of the scanning apparatus is extremely difricult and somewhat impracticable. To obviate this difficulty, arrays 1, 2, 3, 4 are initially mounted on carriage 20 in substantial tangential alignment. As can be seen in the exemplary showing of Figure 2, this nevertheless often results in tangential array misalignment alons the x-axis. If the disposition of the arrays 1~ 2, 3, 4 is compared to a predetermined reference, such as the s.art of scan line 101 in Figure 2, i~ can be s~en that each array 1, 2, 3t 4 is displaced o. ofset from line 101 by some offset distance dl, d2, d3, d4, respectively. As will appear more fully herein, the individual offset distances of each array 1, 2, 3, 4 is determined and the result programmed in an offset counter 120 (Figure 3) associated with each array. Offset counters 120 serve, at the start of the scanning cycle, to delay activation of the array associa~ed therewith until the interval dl, d2, d3, d4, therefor is taken up.
Referring to Figure 3, the pulse-like signal output of encoder 60 which is generated in response to movement of carriage in the scanning direction (Y-direction), is inputted to a phase locked frequency multlplier network 100. Network 100, which is conventional, serves to multiply the relatively low fre-quency pulse-like signal input of encoder 60 to a high frequenry clock signal in output lead 103. Feedback loop 104 of ne~work 100 serves to phase lock the frequency of the signal in lead 103 wi-th the frequency of the signal input from encoder 6Q.

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7~82 As will be understood, changes in the rate of scan of carxiage 20 produce a corresponding change in the freque~cy of the pulse-like signal generated by encoder 60. The frequency of the clock signal produced by network 100 undergoes a correspond-ing change. This resultq in a high frequency clock signal in output lead 103 directly related to the scanning velocity of car-riage 20, and which accommodates variations in that velocit~.
The clock signal in output lead 103 is inpu~ted to pro-grammable multiplexer 106. The output of a second or alternate clock signal source such as crystal controlled clock 108 is inputted via lead 109 to multiplexer 106. Multiplexer 106 selects either network 100 or clock 108 as the clock signal source in response to control instructions (CLOCR SEL2CT) from a suitable programmer (not shown). The selected clock signal ~appears in output lead 111 of mul~iplexer 106.
An operating circuit 114 is provided for each array 1, 2, 3, 4. Since the circuits 114 are the same for each array, the circuit 114 for array 1 only is described in detail. It is ~nder-stood that ~he number o~ circuits 114 lS equal to the number of arrays used.
Operating circuit 114 includes a line transfer counrer 115 for controlling the array imaging line shutter or sample time for each scan. Counter 115 is driven by the clock signal in output lead 111 of multiplexer 106. It is understood that where the si~nal input to counter 115 comprises the clock signal pro-duced by network 100, array sample size remains constant irres-pective of variations in the velocity of carriage 20. In other words, where carriage 20 slows down, array shutter time becomes longer. If carriage 20 speeds Up7 array shutter time becomes shorter.

_g_ Initial actuation of line transfer counter 115 is con-trolled by the offset counter 120 associated therewith. Offset counter 120, which is driven ~y the clock signal in output lead 111, is ~reset to toll a count representing the time interv~l required ~or array 1 to reach start of scan line 101 following start up of carriage 20. On tolLing the preset count, offset counter 120 generates a signal in lead 122 enabling line transfer counter 115. -It will be understood that the offset counters 115 associated with the circuits 114 for the remainina arrays 2, 3, 4 : are similarly preset to a count representing ~he distance d2, d3, d4, respectively by which arrays 2, 3, 4 are offset from start OL
scan line 101.
Referring particularly to Figure 2 each array 1~ 2, 3, 4 scans a portion of each line of the original document 12, the sum total of the data (less overlap as will appear more fully - ~ ~herein) produced by arrays l, 2, 3, 4 representing the entire line. Preferably, arrays 1, 2, 3, 4 are of the same size with the same number of pixels 40. A~ descrlbed, the line transfer counters 115 of cir~uits 114 control the array imaging line shut-ter time for each scan, counters 115 being pr`eset to ac~;ivate the array asscciated therewith for a preselected period for this pur-pose. 5canned data from the arrays 1, 2, 3, 4 is clocked out by clock signals derived from a suitable pixel clock 118.
Sampled analog video data from the arrays 1, 2, 3, 4 is fed to a suitable video proGessor 148 which converts the video signals to a binary code representative of pixel image intensity.
~he binary pixel data from processor 148 is mapped into segments or words by Pixel Data Bit Mapper 149 for storage in o~fset rela-tion in RAM 175 as will appear. Bit Mapper 149 i~ driven by clock ~L~4~3~2 signals from pixel clock 118. Data from Rit Mapper 149 is passed via data bus 174 to R~ 175 where the data is temPorarily stored pending receipt of data from the array which last views the line.
In the exemplary arrangement illustrated, the last array wouid be array 4.
Multiple~er 150 may be provided in data bus 174 to per-mit data from other sources (OTHER DATA) to be inputted to R~M
175.
The binary data is stored in sequential addresses in RAM 175 (see Figure 4), the data being addressed into RAM 175 on a line by line basis by the .~ address pointers 165 throug~.
Address Bus 180. The clock signal output from pixel clock 118 is used to drive address pointers 165. Line scan countsr 170, which is driven by the output from line transfer counter 115, controls the number of full scan lines that will be stored in RA~ 175 before recy~ling. The output of counter 170 is fed to R~M Address pointer 165 vi~ lead 119. It is under~tood that line scan coun-ters 170 are individually preset to reflect the degree of array offset in the Y-direction~
Ram 175 provides a buffer for scanned data fro~ each array, RAM 175 buffering the data untll a full line is completed following which the data is read out. ~ sui~able prio~ity encoding system (not shown~ may be used to multiplex the data input from arrays 1, 2, 3, 4 with the address associ`ated ~here-with. Ram 175 has input and ou~put ports for input and output of data thereto.
Since thq degree of misalignment of arrays 1, 2, 3, 4 in the Y-direction may vary, the storage capacity of R~M 175 must be sufficient to accommodate the maximum misalignment anticipated~ A worst case misalignment is illustrated in Figure 73~2 4 wherein it is presumed ~ha~ arrays 1, 2, 3, 4 are each mis-aligned by a full line. In that circumstance and presuming scan-ning of line 1 is completed, RAM 175 then s~ores ~he line data for lines 1, 11, 12, 13, 14 from array 1, lines 1, 11, 12, i3 from array 2, lines 1, 11, 12 from array 3, and lines 1, 11 from array 4. The blocks of binary data that comprise the completed line 1 are in condition to ~e read out of ~ 175. In the above example, an extra line of data s~orage is provided.
Line scan counters 170 are recycling counters which are i~dividually preset for the number of lines of data to be s~ored for the array associated therewi~h. As a result, address pointers 165 operate in round robin fashion on a line by line basis. On reaching a preset count, the signal from counters 17Q
recycle the address pointer 165 associated therewith ~ack to the first storage line to repeat the process. It is understood that prior thereto, that poxtion of RA~ 175 has been cleared of da~a.
As described, da~a from video processing hardware 148 is stored temporarily in RAM 175 pending completion a the line.
In placing the data in RAM 175~, the data is prefera~ly mapped in -such a way as to avoid the need for subsequent data bit shiftins when outputting the data. Referr~lng to Figure 5, wherein mapping of pixel data from arrays 1, 2 is illustrated, da~a from an earlier array (i.e. array 1) is mapped by Pixel Data Bit Mapper 149 (Figure 3) into segments or words 180 before being stored in RAM 17i. The first pixel (Pl - 1) of the array within the array overlap 181 is mapped into a known bit position within the seg-ment or word 180 at the point of overlap.
At the end of line transfer, the first pixel (Pl - 2) of the succeeding array (i.e. array 2) is clocked into the bi~ posi-tion (Pl - 1) of the first overlapped pixel of the previous array.

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This correlates the first overlapping pixel (Pl - 2) of t:ne succeeding array (i.e. array 2) with the first overlapped pixel tPl - 1) of the preceding array (i.e. array 1). Crossover from one array to the succeeding array on data readout may then be effected without the need to shift bits.
Referring now to Figures 6 and 7, video data held in RAM 175 is read out to a user (not shown) via RAM output bus 176, in both tangen~ially and spatially corrected form, line by line, through output channel 200. Data readout is controlled by a microprocessor, herein CPU 204 in accordance with address program instru~tions in memory 2060 CPU 204 may comprise any suitable commercially available processor ~uch as a Model M6800 manufac-tured by Motorola, Inc.
The address program instructions in memory 206 include a descriptor list 207. List 207 contains in~orma~ion identifying the number of bits to be read out (Nn), the address of the first word (A), and other user information (U)O The ~ATA OUT address information is fed ~o address multiplexer 208 via address bus 209.
As described heretofore, exact tangential alignment and end to end abutment of mul~iple arrays is difficult to achieve.
In the arrangement shown/ sagittal misalignment (in the Y
direction) among the arrays is accommoda~ed by offset counters 120 of the individual array operating circuits 114. The need to accurately abut the arrays end to end is obviated by overlapping succeeding arrays.
As a result of the above, the sequence in which vldeo data is inputted to RAM 175 offsets sagittal misalignments between the several arrays. By outputting the data from RA~ 175 on a line by line basis, the lines are reconstructed without ~47382 sagittal misalignment.
Due to the overlapping disposition of arrays 1, 2, 3, 4, data within the overlapping portions of the arrays is redun-dant. To obviate this and provide a complete line of data without repeated or redundant portions, bit crossover on readout within the overlapping regions is used.
Referring now to the embodiment shown in Figure 7, data bit crossover within the overlapping portions of arrays 1, 2, 3, 4 is effected by an algorithm which picks a predetermined last cell to be sampled within the overlapped region and automatically picks the next bit in the succeeding array. In the descriptor list 207 illustrated in Figure 7, the totaL bit output from the first array is Nl by~es ~ nl bits with the bit output from the second ar~ay N2 bytes - n2 bitsO In the example shown in Figure 7, crossover ~rom array 2 to array 1 is effected between bit 4 and bit 5.
In the arrangement described heretofore, the center-to-cen~er distance between successive photosensitive elements or pixels 40 is constan~. Referring to Figure 87 wher~in like numerals refer ~o the like parts a pair of arrays 300, 301 are there shown with the end portions overlapped. The photosensitive elements or pixels 40 that comprise arrays 300, 301, except for the end 308 of array 300, are on normal center-to-center dis-tance~s d. The photosensitive elements 40' in the end 308 of array 300 are set on a slightly reduced center-to-center distance d'.
The reduction in center-to-center distances between the photosen-sitive elements 40' in end 308 of array 300 provide in effect a vernier scale which normally provides at least one point where opposing arrays are in alignment irrespective of the degree of overlap between the arrays. In the exemplary arrangement shown, ~7382 the end of photosensitive elemen~ 40 - 3 of array 301 is in suo-stantial alignment with the start of photosensitive element 40' -5 o array 300, and crossover would be set at this ~oint.
It will be understood that vi~ual i~entification of the individual ~hotosensitive elemen.s or pixels 40, 40' to determine the optimum crossover point may be made through microscopic e:~a.m-ination of the arrays. It is further unders~ood that or.ce the optimum crossover point is determined, the descriptor list of memory 206 (Figures 6, 7) is programmed to provide crossover from pixels 44 - 8 of array 301 to pi~el 40' - S of array 300 on readout.
; While the vernier scale is illustrated as being at one end 308 of array 300 only, it is understood that vernier scales may be provided at ~oth ends of the array. In that event, in a scanning arrangement employing four arrays such as shown in Figure 2, array 1 may have a vernier scale of the type described at each end, array 3 a vernier scale at one end only, with remain-in~ arrays 2, 4 conventional.
While the vernier scale described is established by reducing center-to-center distances between adjoinin~ pixels, it is understood that a vernier scale may be created by incre~sing slightly the center-to-center dis~ances between adjoining array pixels.
- Referrin`g to the embodiment shown in Figure ~, there a pair of relatively long lin~ar arrays 350, 351 are disposed end to end. This may be effected optically as ~y means of lenses 43 in the scanning apparatus 10 of Figure 1 or mechanically throuyh physical contact of the array ends with one another. To accom-modate any gaps betwe~n the array ends or misalignments along the X axis and to assure continuity of the composite array so formed, .

~7382 a relatively short bridging array 360 is provided to overlap the adjoining ends of each array 350, 351.
Bridging array 360 comprises a relatively short li.ne~r array, preferably ~ith the minimum quantitv o~ ~ixel- 40 needed to provide ef~ective overlap of the adjoinin~ arrays. Typically, bridging array 360 may be comprised of the order of 100 pixei~
whereas arrays 350, 35L comprise some 1700 pixels.
In use, data from arrays 350, 351, 360 may be readout as described earlier, the data being stored temporarily in R~M
175 (Figure 3) pending completion of the line. By choosing r~la-tively short bridging arrays 360, the amount of data to be stored in R~M 175 and hence the size of RAM 175 may be substantiall~
reducsd. The da~a held in RAM 175 is, on completion of the line, read out from RAM 175 into bus 176 (Figure 6), with crossover made ;from array 350 to bridging array 360 and thereafter from bridging array 360 to array 351 in the overlapping areas ~o assu.e cnntin-uity. ~
Referring to the embodiment shown in Figure 10, where like numerals refer to like parts, an array structure 400 is thereshown. Array structure 400 includes relatively long and short ar~ays 402, 404 respectively mounted upan a common sub-strate or mask 406. Array 404 is disposed in parallel with array 402, with a portion 409 of array 404 overlapping one end 403 o~
array 402. The remainder of arr~y 404 projects beyond end 403 of array 402 and is adapted to overlay the leading end of the next suc-essive array structure 400' as seen in drawing Figure 10. To accommodate overlapping of successive array structures 400, sub-strate 406 is inse~ at 407.
To enhance alignment between the arrays and provlde undistorted crossover be~ween arrays, photosensitive elements or 73~2 pixels 40' of array 404 are disposed on a center-to-center dis-tance d' different from the center-to-center distance d of pix~la 40 of array 402. This in effect establishes a vernier scale which ena~les at least one pi~el 40' of array 404 to be aligned with a corresponding pixel 40 of array 402. In the exemplary arrange-ment shown, pixel 40 - 5 of array 402 is in substantial alignment with pixeL 40' - 4 of array 404 and crossover would be effec~ed at this point.
Simil~rly, when associating the array structure 400 with the next succeeding array structure 400', crossover from array 404 to array 402' is selected a~ the point of slosest pixel alignment. In the embodiment shown, crossover would be between pixel 40' - 7 of array 404 and pixel 40 - 3 of array 402.
While the center-to-center distance d' between pixels 40' of array 404 is illustrated as being less than the center-to-center distance d between the pixels 40 of array 402, it is under-stood that dimension dl may be greater than dimension While the invention has been described with reference to the s.ructure disclosed, it is not confined to the details se' forth, but is intended to cover such modifications or changes as may come within the scope of the following claims.
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Claims

WHAT IS CLAIMED IS:

1. An array for use in scanning apparatus of the type employing plural arrays disposed so that a finite portion of one array overlaps a finite portion of an adjoining array to provide a composite array having a linear extent at least equal to the length of the line to be scanned, comprising a. an array substrate, said substrate being generally rectangular in shape;
b. a multiplicity of photosensitive elements on said substrate, said photosensitive elements being disposed in succes-sion longitudinally of said substrate;
c. the center-to-center distances between the portion of said photosensitive elements in said finite portion of said array being different than the center-to-center distances between the remainder of said photosensitive elements whereby to provide a vernier-like spacing between said photosensitive elements in said array portion facilitating alignment of one photosensitive element with the corresponding photosensitive element of the adjoining array.