JPH09185207A - Color electrophotographic printer provided with many linear arrays for surface irradiation laser having identical wavelength - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a single monolithic light source for a color electrophotographic printer equipped with a simple and inexpensive optical system. SOLUTION: This color printer 100 uses many linear arrays of identical- wavelength surface irradiation laser in order to simultaneously expose widely distant positions on an identical or different photoreceptors 140-146. The images of the respective arrays are formed on the photoreceptors 140-146 by an identical telecentric spherical surface lens group 134, an aperture 136 and a telecentric spherical surface lens group 138. Then, linear beams are arranged around the aperture by angularly giving an interval. Many linear arrays are a monothlic structure body 102 and they can be closely arranged.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to color electrophotographic printers, and more particularly to a large number of surface emitting lasers having the same wavelength for simultaneously exposing widely spaced locations on the same or different photoreceptors. Color electrophotographic printer having a linear array monolithic structure of.

[0002]

2. Description of the Related Art A raster output scanner (RO) known as an image forming unit used in an electrophotographic printer.
S) or light emitting diode (LED) printbar
Are well known in the art. A ROS or LED printbar is placed in the optical scanning system to write an image on the surface of a moving photoreceptor belt.

In a ROS system, the modulated light beam is directed onto a facet of a rotating polygon mirror, which then sweeps the reflected light beam across the photoreceptor surface. Each sweep exposes a raster line into a linear segment of the video signal image.

[0004]

The use of rotating polygon mirrors, however, presents some inherent problems. Curvature and wobble of the light beam scanning across the photoreceptor surface may result from imperfections in the mirror, slight angular misalignment of the mirror, or instability in the rotation of the polygon mirror. These problems are typically complex, precise, between the light source and the rotating polygon mirror, and between the rotating polygon mirror and the photoreceptor surface.
Requires expensive optics. In addition to this, optically complex elements are also needed to correct the refractive index dispersion which causes a change in the focal length of the imaging optics of the ROS.

LED printbars generally consist of a linear array of light emitting diodes. L of each linear array
The ED is used to expose corresponding areas on the moving photoreceptor in response to video data information applied to the drive circuitry of the printbar. The photoreceptor is advanced in the process direction to provide the desired image with a continuous scan line configuration.

In electrophotographic printers, the plurality of light emitting elements of the LED printbar are typically "self-locking".
It is imaged onto the surface of the photoreceptor by closely spaced glass fibers of differing refractive index known as a (selfoc) lens.

Printing with LED bars requires a precisely manufactured "selfoc" lens for each light emitting element. Each full-length “selfoc” lens bar must be straight and parallel to the well-polished input and output facets. Each lens bar must have the same focal length and throughput efficiency. Even if these requirements are met,
“Selfoc” lenses have a short focal length and must therefore be placed close to the photoreceptor surface, but the lens may collect toner here, thus requiring an additional cleaning mechanism. Due to their optical properties, the depth of focus of "selfoc" lenses is very shallow and therefore requires very precise placement to produce a uniform spot exposure over the scan line.

Light-emitting diodes, by their nature, have large spatial divergence, broad spectrum, and are unpolarized, all of these factors being a single photoreceptor required for color electrophotographic printers. Alternatively, it severely limits the possibility of imaging multiple LED arrays at multiple locations on multiple photoreceptors. Prior art LED printbar electrophotographic line printers only teach line exposure at a single location on one photoreceptor.

Laser arrays have smaller spatial divergence and smaller emission apertures than LED arrays. Both of these factors increase spot density. As taught in the present application, the narrow spectrum of the laser beam allows for optical separation of the laser beam. The broad spectrum makes similar separation of LED radiation impossible.

It is an object of the present invention to provide a single monolithic light source for a color electrophotographic printer with simple and inexpensive optics.

[0011]

SUMMARY OF THE INVENTION In accordance with the present invention, a color printer allows a vertical cavity surface emitting laser of the same wavelength to simultaneously expose widely spaced locations on the same or different photoreceptors. VCSEL) multiple linear arrays are used. Full color printers use four or more linear laser arrays, while highlight color printers will use two or more linear laser arrays.

Each array has the same telecentric (t
(elecentric) Image is formed on the photoconductor by a spherical lens and an aperture. The linear beams are concentrically spaced around the axis of the imaging optics. Multiple linear arrays can be assembled and placed in close proximity within a monolithic structure or assembled in a precision unit. The light emitting elements of each array can be spaced or staggered for line imaging at the printed pixel density.

[0013]

DETAILED DESCRIPTION OF THE INVENTION Here, the color printer 10 shown in FIG.
Referring to 0, it utilizes a monolithic structure 102 of four linear arrays of vertical cavity surface emitting lasers (VCSELs) to expose four photoreceptors simultaneously to enable one-pass full color printing.

The monolithic array structure 102 of the printer 100 creates an electronic subsystem (ES) to produce a modulated light beam from each individual VCSEL of the array.
S) 104 and selectively addressed by a video image signal that is modulated by drive circuit 106.

The laser array structure 102 of FIG. 2 is arranged in parallel (or in the scanning direction) within the monolithic array 102.
Four linear VCSEL arrays 10 arranged in series
8, 110, 112, and 114. Individually spaced individual Vs in each of the four linear arrays
The CSELs 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 arranged to provide a sufficient viewing angle for vignetting-free scan beam separation for the optics for color printer 100.

Individual linear VCSEL arrays 108, 1
The length of 10, 112, and 114 is equal to the scan length along the photoreceptor divided by the optical system magnification, and the length is resolution independent.

VCSEL1 of the first linear array 108
18 emits light 120 at a first wavelength. The VCSEL 122 of the second linear array 110 emits light 124 at the same first wavelength. V of the third linear array 112
CSEL 126 emits light 128 at the same first wavelength. The VCSEL 130 of the fourth linear array 114 is
Emit light 132 at the same first wavelength. VCSEL is
It has a half-power output beam divergence angle of approximately 8 to 10 degrees.

The laser array structure 102 is a monolithic combination of four linear arrays, each emitting at the same wavelength.

Four linear arrays 108, 110, 11
The monolithic VCSEL array structure 102 with 2 and 114 can be made in many different ways. A dense array of vertical cavity surface emitting lasers, as taught in US Pat. No. 5,062,115, commonly assigned to the same assignee as the present application and incorporated herein by reference, is an array of arrays. It can be emitted from the epitaxial side. US Pat. No. 5,211, commonly assigned to the same assignee as this application and incorporated herein by reference.
As taught in 6,263, a dense array of vertical cavity surface emitting lasers can emit from the substrate side of the array. In both cases, all elements of the array emit at substantially the same wavelength and are not prepared for control over the polarization state.

Four linear arrays 108, 110, 11
The VCSEL with 2 and 114 may be a monolithic diode laser array, or two non-monolithic closely arranged in a single integrated array, as will be discussed fully later in the application. It can be any of the laser sub-arrays. In either type of light source, the laser array structure 102 provides a substantially common spatial origin for all four laser beams.

Returning to the color printer 100 of FIG. 1, the monolithic array structure 102 is arranged symmetrically about the optical axes of both meridians and the VCSEL arrays 108 and 110 are oriented from one side of the optical axis in the process direction. Evenly spaced VCSELs 112 and 114
Are also equally spaced from the opposite optical axis in the process direction. In the scanning direction, the central portions of the monolithic structure 102 in the longitudinal direction are spaced on the optical axis of the imaging lens.

The monolithic array structure 102 includes a linear array of modulated first beam 120, a linear array of modulated second beam 124, a linear array of modulated third beam 128, and a modulated third beam. It emits a linear array of four beams 132, all beams having the same wavelength. Only the extreme rays of the beam are shown.

The linear beams 120, 124, 128 and 132 diverge from the array 102 and the circular aperture 13
6 through which it is refracted by a multi-element spherical telecentric lens 134.

Spherical lenses are telecentric in both tangential and sagittal meridians. The telecentric nature of lens 134 in both axes provides a flat field of view for good depth of focus while simultaneously passing all beams from four linear arrays 120, 124, 128 and 132 without vignetting. And thus provide high power throughput for all beams.

The main reason for being telecentric is the uniform output collection from all laser arrays, but it also provides other essential requirements.
The telecentric projection lens can image well-angled and widely-spaced VCSEL arrays, which allows the outgoing beams from each array to be spatially separated. Can be directed to the electrophotographic stations to which they are assigned.

VCS for Monolithic Array Structure 102
The EL array is in the object plane of the spherical telecentric lens 134.

Telecentric lens 134 collects the cones of light from the four linear beams 120, 124, 128, and 132 and "bends" them toward (and through) the circular aperture 136.

The aperture 136 in FIG. 1 also functions as a diaphragm for controlling the spot size. Opening 1 in FIG.
36 provides a round spot on the photoreceptor,
It is circular.

Four converging linear beams 120, 12
4, 128, and 132 pass through aperture 136 and are focused onto the photoreceptor by spherical lens group 138. The spherical lens group 138 is a spherical lens composed of three lenses combined with the lens group 134, and focuses the beam on an appropriate position of the photoconductor with uniform size, energy, and linearity.

The spherical lens 138 has a first photoconductor 140.
Will focus the first modulated linear beam 120. The spherical lens 138 is used for the second photoconductor 14
A second modulated linear beam 124 will be focused on the top of the two. The spherical lens 138 is the third photoconductor 1
A third modulated linear beam 128 will be focused on 44. The spherical lens 138 will focus the fourth modulated linear beam 132 onto the fourth photoreceptor 146.

Four beams 120 from four arrays,
124, 128 and 132 are imaged onto the photoreceptor with good energy, uniform energy and linearity without curvature. The position of the VCSELs of the individual arrays is well controlled in the image plane and the characteristics of the telecentric spherical lens groups 134 and 138 have high quality imaging capabilities.

The combination of spherical lenses 134 and 138 results in four linear beams 120, 12 along four corresponding photoreceptors 140, 142, 144, and 146.
It also provides good linearity to each of 4, 128, and 132.

Since each laser beam is independently modulated with image information, a separate latent image is printed on each photoreceptor simultaneously. All VCSELS of the linear array will be addressed simultaneously so that the linear array simultaneously exposes the entire line on the photoreceptor.

Photoreceptors 140, 142, 144, and 1
46 is the beam 120, 124, 128, and 132.
Prior to exposure by means of a charging station (not shown), each is charged. After exposure, a development station (also not shown) develops the latent image formed in the associated image area on the photoreceptor. The fully developed image is then transferred from each of the two photoreceptors 130 and 134 to an output sheet (not shown) at a transfer station (not shown). Charging, developing, and transfer stations are conventional in the art.

The full-color printer 100 of FIG. 1 uses a monolithic structure 102 of four linear arrays of vertical cavity surface emitting lasers (VCSELs) of the same wavelength to simultaneously expose four photoreceptors for one-pass full-color printing. to enable. Only a monochrome laser is needed, where no specific polarization direction is required for the beam. No special thin film coating is required for the separation of the rays.

In the illustrated embodiment, four linear VCSEL arrays 108, 110, 112, and
114 are equally spaced 10 mm within the monolithic array structure 102, for a total distance of about 30 mm across the four arrays. This 30 mm width gives sufficient angular divergence of the four scanning beams for a clear and eclipse-free separation. The preferred length of each array is approximately 35 m
m. The object area of a complete VCSEL array would be approximately 30 × 35 mm. This size would require a system magnification of about 8.5 times for a 11.7 inch long scan line.

The wavelength of the four linear beams 120, 124, 128 and 132 produced by VCSELS is 780 nm.

The combined system magnification of lens 134 and lens 138 is approximately 8.5 times to produce the required 11.7 inch long scan.

Common Monolithic Array Structure Light Source 10
2 to individual photoreceptors 140, 142, 144, and 1
The total optical path length to 46 will be about 633 mm. The distance from the last surface of the lens 138 to the photoconductor is about 460 m.
m.

Perfect imaging lens (134 and 138)
Can be designed to produce an acceptable pixel placement and differential curvature, or can be modified by the insertion of parallel plate glass windows.

All four linear beams 120, 124,
Beams of similar dimensions enter the aperture 136 because 128 and 132 are from well controlled positions. Thus, the problem of maintaining an equal optical path length for each ray is a concern from the aperture 136 through the individual photoreceptors 140, 1.
42, 144, and 146 can be translated into the problem of maintaining substantially equal optical path lengths.

As shown in FIG. 4, a spherical lens 138.
The use of folding mirrors in the subsequent optical path length allows the size of color printer 100 to be reduced. The first modulated linear beam 120 is reflected by mirrors 148 and 150.
Is reflected by the second photoconductor 142.
The second modulated linear beam 122 will be reflected by the mirrors 152 and 154 onto the first photoreceptor 140. The third modulated linear beam 124 is reflected by the mirror 15
6 and 158 will be reflected to the fourth photoconductor 146. The fourth modulated linear beam 126 is
It will be reflected by the mirrors 160 and 162 to the third photoreceptor 144.

Only plane mirrors with a total of eight standard coatings are needed for the optical path folding.

An overall optical path length of 630 mm is sufficient to accommodate folding for photoreceptor separation up to 10 inches in the process direction.

Since the folds can accommodate differences, the objective distances for the four photoreceptors need not be the same, but the projected scan length from SOS to EOS must be the same. .

Similarly, the folding mirrors can be aligned so that the four linear beams expose four different locations on a single photoreceptor (not shown).

All VCSELs in the linear array will be addressed simultaneously so that the linear array simultaneously exposes all pixels in a line on the photoreceptor. Technically, in this application, the beam is not scanned along a line, but the technical term used to describe the entire line of pixels on the photoreceptor is "scan line". . However, this application will, in accordance with conventional nomenclature, describe simultaneously exposed pixel lines on the photoreceptor as "scan lines".

ROS is a line along the scan line of the photoreceptor.
Each pixel will be exposed one at a time. The present application with a linear laser array does not have a rotating mirror scanning element like the ROS and the ROS prints one pixel at a time, whereas the linear laser array has one line at a time. To print.

The optical system of the color printer 100 shown in FIG.
A highlight color printer that prints black, white, and highlight colors that works well with only two linear VCSEL arrays instead of four, and with only two corresponding photoreceptors instead of four. provide. Ideally VC
The SEL arrays are linear VCSEL arrays 110 and 1.
12 or linear VCSEL arrays 108 and 11
4 are arranged symmetrically with respect to the optical axis.

However, since lens 134 is spherical and telecentric, and lens 138 is spherical,
Linear VCSEL array 10 whether asymmetric about the optical axis or on the same side of the optical axis
Any two of 8, 110, 112, and 114 can be used. However, the extreme off-axis position of the VCSEL affects the complexity of the imaging lens.

It can also be adapted to highlight color printers by appropriately adapting the beam with a mirror to expose two separate locations on a single photoreceptor.

Similarly, the optical system of the color printer 100 of FIG. 1 works well with only one linear VCSEL array instead of four, and with only one corresponding photoconductor instead of four. And provide a black and white printer. The single linear array can be anywhere in the four spatial locations of the four linear VCSEL arrays. Alternatively, a single linear array can be along the optical axis of the electrophotographic printer. Telecentric lenses have a flat field of view,
A cross-cylinder lens can be used, although linearity, uniform spot size, and uniform output are still required and focusing is still required for both meridians.

The aperture 134 in FIG. 3 also functions as a diaphragm for controlling the spot size by controlling the effective F value of the image forming system. The aperture 134 in FIG. 3 is circular to provide a round spot on the scan line above the photoreceptor.

Narrower (or wider) spots in either the sagittal or process directions can be produced by the use of larger apertures in meridians where smaller spots are required. With this arrangement, "high addressability" (higher scan line density with smaller spots) and / or larger overlap of the same scan line density for "hyperacuity" printing in the process direction. Spotting is possible.

As shown in FIGS. 5A-5D, the openings 134 can be rectangular (FIGS. 5A and 5C or ellipsoidal (FIGS. 5B and 5D)).

To provide smaller spots on the photoreceptor in the direction transverse to the scan, ie the process direction, ie the sagittal direction, for super sharp or other types of well addressed printing. 5A and 5B, the long axis of the rectangle or ellipse can be along the direction intersecting the scan, ie the process direction, ie the sagittal direction. The narrow dimension of the aperture has sufficient value to produce the required overlapping spot size in the main scanning direction (tangential direction).

By narrowing the width of the opening in the main scanning direction, it is possible to generate in the main scanning direction also spots larger than the conventional overlapping spots of the same density.

The laser array structure 200 shown in FIG.
A non-monolithic combination of two monolithic structures 202 and 204 of a CSEL array. Each monolithic array structure is a VCS that emits at the same wavelength.
Includes two linear arrays of EL. The monolithic array structure 202 is a linear VCSE emitting at a first wavelength.
It has an L array 206 and a linear VCSEL array 208. The monolithic array structure 204 includes a linear VCSEL array 210 and a linear VSEL array that emits at a first wavelength.
It has a CSEL array 212.

Thus, the laser array structure 200 of FIG. 6 becomes the monolithic array structure 102 of FIG.
And emits the same wavelength. The advantage of this non-monolithic combination is that the monolithic array structure 2
02 and 204 are easier to manufacture.

Since each array is imaged at a different exposure location, the sagittal separation between adjacent arrays on different monolithic array structures results in a VCS
It can be made larger than the tangential distance between the EL elements. The sagittal spacing between the monolithic subarray structures is minimized by placing the linear array near the edges of each monolithic subarray structure. However, array elements are aligned on the different monolithic sub-array structures along the main scan direction and their SOS and EOS pixels are aligned in the process direction,
That is, alignment in the sagittal direction is important for preventing scan line shift on the four photoconductors.

Gain-inducing VCSELs are well suited for embodiment color printing applications. Because they can cause the desired controlled astigmatism at the non-circular aperture, they are essentially free of astigmatism. In addition, the change in the focal length of the imaging lens due to the wavelength dependence of the refractive index is appropriate for (1) adding a glass plate to one array, or (2) to individual elements of one array. It can be corrected by adding a different diffractive lens.

The monolithic structure of the two or four VCSEL arrays of the present invention is less expensive than the prior art two or four separate LED printbar fabrication. VCSEL arrays are precisely aligned in a monolithic structure, as opposed to the four separate LED printbars of the prior art, which must be precisely aligned with each other.

The monolithic structure of two or four VCSEL arrays significantly reduces the size and overall space volume of a color electrophotographic printer. Also, monolithic source arrays are cost effective because the assembly of multiple chips is reduced or eliminated in some cases.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional side view of a full-color electrophotographic printer with multiple monolithic linear arrays of vertical cavity surface emitting lasers (VCSELs) and four photoreceptors formed in accordance with the present invention.

2 is a schematic view of a front view of a monolithic multiple linear array of vertical cavity surface emitting lasers (VCSELs) of FIG. 1 formed in accordance with the present invention.

3 is a schematic cross-sectional plan view of the aperture of a linear light beam of a color electrophotographic printer with a monolithic multiple linear array of vertical cavity surface emitting lasers (VCSELs) of FIG. 1 formed in accordance with the present invention. is there.

4 is a schematic cross-sectional side view of the full-color electrophotographic printer of FIG. 1 with a folding mirror formed in accordance with the present invention.

5A-5D are schematic cross-sectional plan views of apertures for a color electrophotographic printer having a monolithic multiple linear array of vertical cavity surface emitting lasers (VCSELs) of FIG. 1 formed in accordance with the present invention. is there.

FIG. 6 is a schematic view of a front view of a non-monolithic structural combination of two monolithic multiple linear arrays of a vertical cavity surface emitting laser (VCSEL) formed in accordance with the present invention.

[Explanation of symbols]

100 color printer, 102 monolithic structure, 104 electronic subsystem, 106 driving circuit, 1
08,110,112,114 linear VCSEL array, 116 spacing, 118 VCSEL, 120 light,
122 VCSEL, 124 light, 126 VCSE
L, 128 light, 130 VCSEL, 132 light, 13
4 Telecentric lens, 136 circular aperture, 13
8 spherical lens group, 140, 142, 144, 146
Photoreceptors 148, 150, 152, 154, 156, 1
58,160,162 mirror, 200 laser array structure, 202,204 monolithic structure, 206,
208, 210, 212 Linear VCSEL array

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location // H01S 3/18

Claims (1)

[Claims] 1. A first, a second, a third, and a fourth photoreceptor, a first linear laser array for emitting a first modulated light beam, a second modulated light. A second linear laser array for emitting a beam, a third linear laser array for emitting a third modulated light beam, and a fourth for emitting a fourth modulated light beam. Linear laser array, wherein the first, second, third, and fourth modulated beams have the same wavelength, and the first, second, third, and A first telecentric lens means for refracting the fourth modulated light beam, an aperture in which the telecentric lens means comprises the first, second, third and fourth telecentric lens means. Refraction of the modulated light beam at the aperture Each of the modulated light beams being angularly spaced from the other modulated light beam; and opening the first modulated light beam to simultaneously expose an entire scan line. Through the aperture to focus on the first photoreceptor to expose the entire scan line at the same time and onto the second photoreceptor through the aperture to provide the entire scan line. Focus the third modulated light beam through the aperture onto the third photoreceptor for simultaneous exposure, and the fourth modulated light beam for simultaneous exposure of the entire scan line. Full color electrophotographic printer including second telecentric lens means for focusing on the fourth photoreceptor through the aperture.