[0001] This invention relates to a color xerographic printer, and, more particularly, to
a color xerographic printer with a monolithic structure of multiple linear arrays
of surface emitting lasers with the same wavelengths to simultaneously expose widely
separated positions on the same or different photoreceptors.
[0002] A Raster Output Scanner (ROS) or a Light Emitting Diode (LED) print bar, known as
imagers, used in xerographic printers are well known in the art. The ROS or the LED
print bar is positioned in an optical scan system to write an image on the surface
of a moving photoreceptor belt.
[0003] In a ROS system, a modulated beam is directed onto the facets of a rotating polygon
mirror which then sweeps the reflected beam across the photoreceptor surface. Each
sweep exposes a raster line to a linear segment of a video signal image.
[0004] However, the use of a rotating polygon mirror presents several inherent problems.
Bow and wobble of the beam scanning across the photoreceptor surface result from imperfections
in the mirror or even slight misangling of the mirror or from the instability of the
rotation of the polygon mirror. These problems typically require complex, precise
and expensive optical elements between the light source and the rotating polygon mirror
and between the rotating polygon mirror and the photoreceptor surface. Additionally,
optically complex elements are also needed to compensate for refractive index dispersion
that causes changes in the focal length of the imaging optics of the ROS.
[0005] The LED print bar generally consists of a linear array of light emitting diodes.
Each LED in the linear array is used to expose a corresponding area on a moving photoreceptor
in response to the video data information applied to the drive circuits of the print
bars. The photoreceptor is advanced in the process direction to provide a desired
image by the formation of sequential scan lines.
[0006] In xerographic printer, a plurality of the light emitting elements of the LED print
bars are imaged to a photoreceptor surface usually by closely spaced radially indexed
glass fibers known as "selfoc" lenses.
[0007] Printing with LED bars requires a precisely fabricated "selfoc" lens for each light
emitting element. Each full length "selfoc" lens bar must be straight and parallel
with highly polished input and output facets. Each lens bar must have the same focal
length and throughput efficiency. Even if these requirements are met, the "selfoc"
lenses have short focal lengths and therefore must be positioned close to the photoreceptor
surface where the lenses can collect toner and thereby require an additional cleaning
mechanism. Due to their optical characteristics, the depth of focus of a "selfoc"
lens is very short and consequently requires very precise placement to produce uniform
spot exposures on the scan line.
[0008] Light emitting diodes, by their very nature, have a large spatial divergence, a broad
spectrum and are unpolarized, all factors which severely limit the possible imaging
of multiple LED arrays at multiple positions on a single photoreceptor or at multiple
photoreceptors as needed in color xerographic printers. Prior LED print bar xerographic
line printers have taught only line exposure at a single position on one photoreceptor.
[0009] US-A-5 337 074 and US-A-5 461 413 disclose using a single linear surface emitting
laser array as the light source for a line printer.
[0010] A laser array has a smaller spatial divergence than a LED array and a smaller radiating
aperture. Both of these factors increase the spot density. The narrow spectrum of
laser beams enables optical separation of the laser beams in accordance with the present
invention. The broad spectrum precludes similar separations of LED emissions.
[0011] It is an object of this invention to provide a single monolithic light source for
a color xerographic printer with simple and inexpensive optics.
[0012] It is yet another object of this invention to provide a multiple laser array light
source with the same wavelength for a color xerographic printer.
[0013] In accordance with one aspect of the present invention, there is provided a xerographic
printer comprising:- at least one photoreceptor, at least one linear laser array for
emitting modulated light beams having the same wavelength, a first telecentric lens
means for refracting the modulated light beams, an aperture at which the telecentric
lens means refracts the modulated light beams, and a second telecentric lens means
for focusing the modulated light beams passing through the aperture onto the photoreceptor(s)
to simultaneously expose a full scan line thereon.
[0014] In one embodiment of the present invention, the printer is a highlight color xerographic
printer comprising first and second linear laser arrays for emitting first and second
modulated light beams, each modulated light beam being angularly spaced from the other
by the aperture, the second telecentric lens means focusing the first and second modulated
light beams onto respective first and second regions of the photoreceptor to simultaneously
expose a full scan line thereon.
[0015] In another embodiment of the present invention, the printer is a highlight color
xerographic printer comprising first and second photoreceptors and first and second
linear laser arrays for emitting first and second modulated light beams, each modulated
light beam being angularly spaced from the other by the aperture, the second telecentric
lens means focusing the first and second modulated light beams onto a respective one
of the first and second photoreceptors to simultaneously expose a full scan line thereon.
[0016] In a further embodiment of the present invention, the printer is a full color xerographic
printer comprising first, second, third and fourth linear laser arrays for emitting
first, second, third and fourth modulated light beams, the second telecentric lens
means focusing each of the first, second, third and fourth modulated light beams onto
a respective one of first, second, third and fourth regions of the photoreceptor to
simultaneously expose a full scan line thereon.
[0017] In yet a further embodiment of the present invention, the printer is a full color
xerographic printer comprising first, second, third and fourth photoreceptors and
first, second, third and fourth linear laser arrays for emitting first, second, third
and fourth modulated light beams, the second telecentric lens means focusing each
of the first, second, third and fourth modulated light beams onto a respective one
of first, second, third and fourth photoreceptors to simultaneously expose a full
scan line thereon.
[0018] Moreover, the invention also provides a color xerographic printer comprising at least
two photoreceptors, at least two linear laser arrays for emitting at least two arrays
of modulated light beams of the same wavelength, first telecentric lens means for
refracting said at least two arrays of modulated light beams, an aperture, said telecentric
lens means refracting said at least two arrays of modulated light beams at said aperture,
each of said arrays of modulated light beams being angularly spaced from the other
arrays of said modulated light beams at the aperture, and second telecentric lens
means for focusing said at least two arrays of modulated light beams through said
aperture onto said at least two photoreceptors to simultaneously expose a full scan
line.
[0019] The invention further provides a color xerographic printer comprising a photoreceptor,
at least two linear laser arrays for emitting at least two arrays of modulated light
beams of the same wavelength, first telecentric lens means for refracting said at
least two arrays of modulated light beams, an aperture, said telecentric lens means
refracting said at least two arrays of modulated light beams at said aperture, each
of said arrays of modulated light beams being angularly spaced from the other arrays
of said modulated light beams at the aperture, and second telecentric lens means for
focusing said at least two arrays of modulated light beams through said aperture onto
different regions of said photoreceptors to simultaneously expose a full scan line.
[0020] In accordance with the present invention, a color printer uses multiple linear arrays
of Vertical Cavity Surface Emitting Lasers (VCSELs) of the same wavelength to simultaneously
expose widely separated positions on the same or different photoreceptors. A highlight
color printer would use two or more linear laser arrays while a full color printer
would use four or more linear laser arrays.
[0021] Each array is imaged by the same telecentric spherical lens and aperture to the photoreceptor.
The linear beams are concentrically spaced around the axis of the imaging optics.
The multiple linear arrays can be closely spaced in a monolithic structure or assembled
in a precise unit. Light emitting elements in each array can be spaced or staggered
for line imaging at the printed pixel density.
[0022] Other objects and attainments together with a fuller understanding of the invention
will become apparent and appreciated by referring to the following description, by
way of example only, with reference to the accompanying drawings, in which:-
Figure 1 is a schematic illustration of the cross-section side view of a full color
xerographic printer with monolithic multiple linear arrays of vertical cavity surface
emitting lasers (VCSELs) and four photoreceptors formed according to the present invention;
Figure 2 is a schematic illustration of the front view of the monolithic multiple
linear arrays of vertical cavity surface emitting lasers (VCSELs) of Figure 1 formed
according to the present invention;
Figure 3 is a schematic illustration of the cross-section top view of the aperture
of the linear light beams of the color xerographic printer with monolithic multiple
linear arrays of vertical cavity surface emitting lasers (VCSELs) of Figure 1 formed
according to the present invention;
Figure 4 is a schematic illustration of the cross-section side view of a full color
xerographic printer of Figure 1 with fold mirrors formed according to the present
invention;
Figures 5A to 5D are schematic illustrations of the cross-section top view of the
apertures for the color xerographic printer with monolithic multiple linear arrays
of vertical cavity surface emitting lasers (VCSELs) of Figure 1 formed according to
the present invention; and
Figure 6 is a schematic illustration of the front view of the nonmonolithic structure
combination of two monolithic multiple linear arrays of vertical cavity surface emitting
lasers (VCSELs) formed according to the present invention.
[0023] Reference is now made to a full color printer 100 shown in Figure 1 which utilizes
a monolithic structure 102 of four linear arrays of vertical cavity surface emitting
lasers (VCSELs) to simultaneously expose four photoreceptors to enable one pass full
color printing.
[0024] The monolithic array structure 102 of the printer 100 is selectively addressed by
video image signals processed through Electronic Sub System (ESS) 104 and modulated
by drive circuit 106 to produce a modulated beam from each individual VCSEL in the
array.
[0025] The laser array structure 102, shown in detail in Figure 2, consists of a combination
of four linear VCSEL arrays 108, 110, 112 and 114 arranged in parallel (or series)
in the scan direction within the monolithic array 102, each array 108,110,112,114
emitting light at the same wavelength. The equally spaced individual VCSELs within
each of the four linear arrays are arranged linearly in the scan plane direction with
equal center to center spacing 116 between the individual VCSELs. The sagittal distance
between the VCSEL arrays and the length of the arrays are such that they provide sufficient
field angle for untruncated scanning beam separation for the optical system for the
color printer 100.
[0026] The length of the individual linear VCSEL arrays 108, 110, 112 and 114 will equal
the scan length along the photoreceptor divided by the optical system magnification
and the length is independent of resolution.
[0027] Referring to both Figures 1 and 2, the VCSELs 118 in the first linear array 108 emit
light 120, the VCSELs 122 in the second linear array 110 emit light 124, the VCSELs
126 in the third linear array 112 emit light 128, and the VCSELs 130 in the fourth
linear array 114 emit light 132. The VCSELs have a half power beam divergence of about
8 to 10 degrees.
[0028] The monolithic VCSEL array structure 102 with its four linear arrays 108, 110, 112
and 114 can be made in many different ways. A high density array of vertical cavity
surface emitting lasers can emit from the epitaxial side of the array, as described
in US-A-5 062 115. A high density array of vertical cavity surface emitting lasers
can emit from the substrate side of the array, as described in US-A-5 216 263. In
both cases, all elements of the array emit at substantially the same wavelength and
have no provision for control of the polarization state.
[0029] The VCSEL array structure 102 with its four linear arrays 108, 110, 112 and 114 may
be either a monolithic diode laser array or two non-monolithic laser subarrays closely
spaced into a single integrated array, as will be described fully later. With either
type of source, the laser array structure 102 provides a substantially common spatial
origin for all four laser beams.
[0030] Returning to the full color printer 100 of Figure 1, the monolithic array structure
102 is arranged symmetrically about the optical axis in both meridians with VCSEL
arrays 108 and 110 equally spaced from the optical axis on one side in the process
direction and VCSEL arrays 112 and 114 equally spaced from the optical axis on the
opposite side also in the process direction. In the scan direction the mid-length
of the monolithic structure 102 is spaced on the optical axis of the imaging lens.
[0031] The monolithic array structure 102 emits a linear array of modulated beams 120, 124,
128 and 132, at the same wavelength. Only the extreme rays of the beams are shown.
[0032] The linear beams 120, 124, 128 and 132 are diverging from the array 102 and are refracted
by a multiple element spherical telecentric lens 134 through the circular aperture
136.
[0033] The spherical lens is telecentric in both tangential and sagittal meridians. The
telecentric nature of the lenses 134 in both axes provides a flat field for good depth
of focus and, at the same time, permits the passage all of the beams from the four
linear arrays 120, 124, 128 and 132 without truncation, thus providing high power
throughput of all the beams.
[0034] Although the main reason for the telecentricity is uniform power collection from
all laser arrays, it also provides other essential requirements. A telecentric projection
lens can image widely spaced VCSEL arrays with sufficient angular separation that
permits the spatial separation of the emerging beams from each array, in order to
direct them to their assigned xerographic stations.
[0035] The VCSEL arrays in the monolithic array structure 102 are at the object plane of
the spherical telecentric lens 134.
[0036] The telecentric lens 134 collects the light cones from the four linear beams 120,
124, 128 and 132 and "bends" them toward (and through) the circular aperture 136.
[0037] The aperture 136 shown in Figure 1 also functions as a stop to control the spot size.
The aperture 136 shown in Figure 3 is circular to provide round spots on the photoreceptor.
[0038] The four converging linear beams 120, 124, 128 and 132 pass through the aperture
136 and are focused by the spherical lens group 138 upon photoreceptors 140, 142,
144, 146. The spherical lens group 138 is a spherical triplet, which, in combination
with lens group 134, focuses the beams 120, 124, 128, 132 with uniform size, energy
and linearity in the proper position on the photoreceptors 140,142,144,146.
[0039] The spherical lens 138 will focus the first modulated linear beams 120 upon a first
photoreceptor 140. The spherical lens 138 will focus the second modulated linear beams
124 upon a second photoreceptor 142. The spherical lens 138 will focus the third modulated
linear beams 128 upon a third photoreceptor 144. The spherical lens 138 will focus
the fourth modulated linear beams 132 upon a fourth photoreceptor 146.
[0040] The four beams 120, 124, 128 and 132 from the four arrays 108, 110, 112, 114 are
imaged on the photoreceptors 140, 142, 144, 146 in good focus, without bow, with uniform
energy and high linearity because the position of the VCSELs in the individual arrays
are well controlled in the image plane and the characteristics of the telecentric
spherical lens groups 134 and 138 are capable of high quality imaging.
[0041] The combination of spherical lenses 134 and 138 also provides good linearity to each
of the four linear beams 120, 124, 128 and 132 along the corresponding four photoreceptors
140, 142, 144 and 146.
[0042] Since each laser beam is independently modulated with image information, a distinct
latent image is simultaneously printed on each photoreceptor. All the VCSELs in the
linear array will be addressed at the same time so that the linear array will simultaneously
expose the entire line on the photoreceptor.
[0043] The photoreceptors 140, 142, 144 and 146 are charged by charging stations (not shown)
prior to exposure by beams 120, 124, 128 and 132 respectively. After exposure, a development
station (also not shown) develops the latent image formed in the associated image
area on the photoreceptors 140, 142, 144, 146. A fully developed image is then transferred
to an output sheet (not shown) at a transfer station (not shown) from each photoreceptor
140, 142, 144, 146. The charge, development and transfer stations are conventional
in the art. Further details of xerographic stations in a multiple exposure single
pass system are disclosed in US-A-4 661 901; US-A-4 791 452; and US-A4 833 503.
[0044] The full color printer 100 of Figure 1 utilizes a monolithic structure 102 of four
linear arrays of vertical cavity surface emitting lasers (VCSELs) of the same wavelength
to simultaneous expose four photoreceptors to enable one pass full color printing.
Only monochrome lasers are needed with no specific polarization orientation to the
beams required. No special thin film coatings are needed for the separation of beams.
[0045] In an illustrative embodiment, the four linear VCSEL arrays 108, 110, 112 and 114
are equally spaced 10mm apart in the monolithic array structure 102 with the total
distance across the four arrays being approximately 30mm. This 30mm width gives sufficient
angular divergence of the four scanning beams for clear, truncation free separation.
The preferred length of each array is approximately 35mm. The object area of the complete
VCSEL array will be approximately 30mm x 35mm. This geometry would require approximately
8.5X system magnification for a 297mm (11.7in) long scan line.
[0046] The wavelength of the four linear beams 120, 124, 128 and 132 produced by the VCSELs
is 780nm.
[0047] The combined system magnification of lens 134 and lens 138 will be approximately
8.5 X to produce the required 297mm (11.7in) long scan.
[0048] The total optical path length from the common monolithic array structure source 102
to the individual photoreceptors 140, 142, 144 and 146 will be approximately 633mm.
The distance from the last surface of lens 138 to the photoreceptors 140, 142, 144,
146 will be approximately 460mm.
[0049] The complete imaging lens (134 and 138) can be designed to produce acceptable pixel
placement and differential bow, or can be corrected by the insertion of parallel plate
glass windows as described in U.S. Patent Application No. 08/354,080, "Method and
Apparatus for Elimination of Bow in a Raster Scanning System".
[0050] Since all four linear beams 120, 124, 128 and 132 are from a well controlled location,
similarly dimensioned beams are input to the aperture 136. Thus the problem of maintaining
equal optical path lengths for each beam reduces to the problem of maintaining substantially
equal optical path lengths from the aperture 136 to the individual photoreceptors
140, 142, 144 and 146.
[0051] The size of the color printer 100 can be reduced by the use of folding mirrors in
the optical path length after the spherical lens 138 as shown in Figure 4. First modulated
linear beam 120 will be reflected by mirrors 148 and 150 to the second photoreceptor
142. Second modulated linear beam 124 will be reflected by mirrors 152 and 154 to
the first photoreceptor 140. Third modulated beam 128 will be reflected by mirrors
156 and 158 to the fourth photoreceptor 146. Fourth modulated beam 132 will be reflected
by mirrors 160 and 162 to the third photoreceptor 144.
[0052] Only a total of eight plane mirrors with standard coatings are required for light
path folding.
[0053] The 630mm total optical path length is sufficient to accommodate the folding for
up to 254mm (10 inch) photoreceptor separation in the process direction.
[0054] The object distance for the four photoreceptors do not have to be the same since
the folding can accommodate the differences, but the projected scan length from start-of-scan
(SOS) to end-of-scan (EOS) must be the same.
[0055] Similarly, the folding mirrors can be aligned so that the four linear beams expose
four different positions on a single photoreceptor (not shown).
[0056] All of the VCSELs in the linear array will be addressed simultaneously so that the
linear array will simultaneously expose all the pixels in a line on the photoreceptor.
The term of art used to describe the entire line of pixels on the photoreceptor is
the "scan line", although, technically, in this application the beam is not being
scanned along a line. However, this application will conform to conventional nomenclature
and describe the simultaneously exposed pixel line on the photoreceptor as a "scan
line".
[0057] A ROS will scan a beam along the scan line of the photoreceptor sequentially exposing
each pixel, one at a time. The present application with a linear laser array simultaneously
exposes all the pixels along the scan line at the same time. The present application
does not have the rotating mirror scanning element like the ROS and the linear laser
array prints a line at a time while the ROS prints a pixel at a time.
[0058] The optical system of the color printer 100 shown in Figure 1 works equally well
with only two linear VCSEL arrays, rather than four, and only two corresponding photoreceptors,
rather than four, to provide a highlight color printer which prints black and white
and a highlight color. Ideally, the VCSEL arrays would be arranged symmetrically about
the optical axis such as linear VCSEL arrays 110 and 112 or linear VCSEL arrays 108
and 114.
[0059] However, because the lens 134 is spherical and telecentric and the lens 138 is spherical,
any two of the linear VCSEL arrays 108, 110, 112 and 114 could be used despite being
asymmetric about the optical axis or even on the same side of the optical axis. However,
the extreme off-axis position of the VCSELs does influence the complexity of the imaging
lens.
[0060] Also, the highlight color printer can be adapted with the proper folding of the beams
by mirrors to expose two separated positions on a single photoreceptor.
[0061] Similarly, the optical system of the color printer 100 shown in Figure 1 works equally
well with only one linear VCSEL arrays, rather than four, and only one corresponding
photoreceptors, rather than four, to provide a black and white printer. The single
linear array can be at any of the four spatial positions of the four linear VCSEL
arrays. Alternately, the single linear array could be along the optical axis of the
xerographic printer. Telecentric lenses will still be need for flat field, linearity,
uniform spot size and uniform power and focusing is still needed in both meridians
but cross-cylinder lenses could be used.
[0062] The aperture 136 (Figure 3) also functions as a stop to control the spot size by
controlling the effective F/number of the imaging system. The aperture 136 in Figure
3 is circular to provide round spots in the scan line on the photoreceptor.
[0063] Spots that are narrower (or wider) in either in the sagittal or in the process direction
can be generated by the usage of an aperture that is larger in the meridian where
the smaller spot is required. This arrangement permits "high addressability" (higher
scan line density with smaller spots) and/or overlapping larger spots of the same
scan line density for "hyperacuity" printing in the process direction.
[0064] As shown in Figures 5A to 5D, the aperture 134 can be rectangular (Figures 5A and
5C) or ellipsoidal (Figures 5B and 5D).
[0065] The long axis of the rectangle or ellipse can be along the cross-scan or process
or sagittal direction in Figures 5A and 5B to provide spots smaller in that cross-scan
or process or sagittal direction on the photoreceptor for hyperacuity or other type
of highly addressed printing. The narrow dimension of the aperture has sufficient
value to produce the required overlapping spot size in the fast scan (tangential)
direction.
[0066] Larger than conventional overlapping spots of the same density can also be generated
in the fast scan direction by narrowing the width of the aperture in that direction.
[0067] A laser array structure 200 shown in Figure 6 is a non-monolithic combination of
two monolithic structures 202 and 204 of VCSEL arrays. Each monolithic array structure
202, 204 contains two linear arrays of VCSELs emitting at the same wavelength. Monolithic
array structure 202 has linear VCSEL arrays 206, 208 and monolithic array structure
204 has linear VCSEL arrays 210, 212.
[0068] Thus, the laser array structure 200 shown in Figure 6 emits the same wavelengths,
similar to the monolithic array structure 102 shown in Figure 2. The advantage of
this non-monolithic combination is that monolithic array structures 202 and 204 are
easier to fabricate.
[0069] The sagittal separation between adjacent arrays on different monolithic array structures
can be much larger than the tangential spacing between the VCSEL elements, since each
array is imaged at a different exposure position. The sagittal spacing between monolithic
subarray structures is minimized by locating the linear arrays near the edge of each
monolithic subarray structure. However it is important to have the array elements
on different monolithic subarray structures aligned parallel along the fast scan,
and their SOS and EOS pixels to be aligned in the process or sagittal direction in
order to avoid scan line misalignment on the four photoreceptors.
[0070] Gain guided VCSELs are well suited for the color printing applications of the embodiments
because they exhibit essentially no astigmatism, although desired controlled astigmatism
can be introduced by non-circular apertures. In addition, variation of the imaging
lens' focal length due to the wavelength dependence of its refractive index can be
compensated by (1) adding a glass plate to one array or by (2) monolithically adding
an appropriate diffractive lens to individual elements of one array, as described
in US-A-5 073 041.
[0071] A monolithic structure of two or four VCSEL arrays of the present invention is cheaper
to manufacture than the two or four separate LED print bars of the prior art. The
VCSEL arrays are accurately aligned within the monolithic structure as opposed to
the prior art four separate LED print bars which must be accurately aligned with each
other.
[0072] A monolithic structure of two or four VCSEL arrays considerably reduces the size
and total spatial volume of a color xerographic printer. And monolithic source arrays
are cost-effective since assemblies of multiple chips is reduced or in some cases
eliminated.
[0073] While the invention has been described in conjunction with specific embodiments,
it is evident to those skilled in the art that many alternatives, modifications and
variations will be apparent in light of the foregoing description.
1. A xerographic printer (100) comprising:-
at least one photoreceptor (140, 142, 144, 146),
at least one linear laser array (102, 108, 110, 112, 114; 200, 202, 204, 206, 208,
210, 212) for emitting modulated light beams (120, 124, 128, 132) having the same
wavelength,
a first telecentric lens means (134) for refracting the modulated light beams (120,
124, 128, 132),
an aperture (136) at which the telecentric lens means (134) refracts the modulated
light beams (120, 124, 128, 132), and
a second telecentric lens means (138) for focusing the modulated light beams (120,
124, 128, 132) passing through the aperture (136) onto the photoreceptor(s) (140,
142, 144, 146) to simultaneously expose a full scan line thereon.
2. A printer according to claim 1 wherein the first telecentric lens means (134) is a
cross-cylindrical triplet and the second telecentric lens means (138) is a cross-cylindrical
triplet.
3. A printer according to claim 1 wherein the first telecentric lens means (134) is a
spherical triplet and the second telecentric lens means (138) is a spherical triplet.
4. A printer according to claim 3 wherein the printer is a highlight color xerographic
printer comprising first and second linear laser arrays (110, 112; 108, 114) for emitting
first and second modulated light beams (124, 128; 120, 132), each modulated light
beam (124, 128; 120, 132) being angularly spaced from the other by the aperture (136),
the second telecentric lens means (138) focusing the first and second modulated light
beams (124, 128; 120, 132) onto respective first and second regions of the photoreceptor
(140, 142, 144 ,146) to simultaneously expose a full scan line thereon.
5. A printer according to claim 3, wherein the printer is a highlight color xerographic
printer comprising first and second photoreceptors (140, 142, 144, 146) and first
and second linear laser arrays (110, 112; 108, 114) for emitting first and second
modulated light beams (124, 128; 120, 132), each modulated light beam (124, 128; 120,
132) being angularly spaced from the other by the aperture (136), the second telecentric
lens means (138) focusing the first and second modulated light beams (124, 128; 120,
132) onto a respective one of the first and second photoreceptors (140, 142, 144,
146) to simultaneously expose a full scan line thereon.
6. A printer according to claim 3, wherein the printer is a full color xerographic printer
comprising first, second, third and fourth linear laser arrays (108, 110, 112, 114;
206, 208, 210, 212) for emitting first, second, third and fourth modulated light beams
(120, 124, 128, 132), the second telecentric lens means (138) focusing each of the
first, second, third and fourth modulated light beams (120, 124, 128, 132) onto a
respective one of first, second, third and fourth regions of the photoreceptor to
simultaneously expose a full scan line thereon.
7. A printer according to claim 3, wherein the printer is a full color xerographic printer
comprising first, second, third and fourth photoreceptors (140, 142, 144, 146) and
first, second, third and fourth linear laser arrays (108, 110, 112, 114; 206, 208,
210, 212) for emitting first, second, third and fourth modulated light beams (120,
124, 128, 132), the second telecentric lens means (138) focusing each of the first,
second, third and fourth modulated light beams (120, 124, 128, 132) onto a respective
one of first, second, third and fourth photoreceptors (140, 142, 144, 146) to simultaneously
expose a full scan line thereon.
8. A printer according to any one of claims 4 to 7 wherein the linear laser arrays (108,
110, 112, 114) are equally spaced and symmetric about the optical axis of the printer.
9. A printer according to any one of claims 4 to 7 wherein the linear laser arrays (108,
110, 112, 114) are nonsymmetric about the optical axis of the printer.