Information
-
Patent Grant
-
6484008
-
Patent Number
6,484,008
-
Date Filed
Tuesday, December 19, 200023 years ago
-
Date Issued
Tuesday, November 19, 200221 years ago
-
Inventors
-
Original Assignees
-
Examiners
-
CPC
-
US Classifications
Field of Search
US
- 271 248
- 271 250
- 271 252
- 347 153
- 399 167
- 399 301
- 399 394
- 399 395
- 399 388
-
International Classifications
-
Abstract
A paper drive sheet feeder system includes an edge guide, a paper transport mechanism, a paper edge detector, and control circuitry. The edge guide serves to guide the edges of a sheet of paper along a travel path of a peripheral device. The paper transport mechanism is configured to move the sheet of paper along the travel path. The paper edge detector is provided along the travel path to detect a leading edge of the sheet of paper. The control circuitry communicates with the paper transport mechanism and the paper edge detector and is operative to locate the sheet of paper in response to the detected leading edge of the sheet of paper along the travel path to accurately superpose successive image planes during a multiple color image transfer process. A printing system and a method are also provided.
Description
FIELD OF THE INVENTION
This invention pertains to color printing. More particularly, this invention relates to color laser printing systems and to image plane registration for color printing systems.
BACKGROUND OF THE INVENTION
Color image printing systems are known in the art. One color image printing system comprises an inkjet printer. An inkjet printer prints color images incrementally, with a continuous inkjet printing process, piezoelectric inkjet printing process or bubble-jet printing process. However, these inkjet printing processes provide relatively low-cost printing that is often satisfactory for printing color graphics images, but is not necessarily of high enough quality for certain business applications.
Another color image printing system comprises a color laser, or electrophotographic, printer. Color laser printers generate sufficient text and graphics quality for most business applications. However, color laser printers typically require complex and expensive mechanisms when forming and aligning overlaid color frames. Hence, color laser printers are not sufficiently economical for many applications.
One problem encountered with color laser printers relates to registration of individual color image planes that generate a printed color page. A color image plane is an arrangement either in electronic or optical or other physical form representing a distinctive image in one color. One physical form comprises a single color of toner particles. Typically, three or four distinct color image planes are imaged using one of several known techniques and transferred onto a common piece of paper in order to generate a color image. In some cases, a yellow, a magenta and a cyan color image plane are each imaged and transferred onto a common piece of paper. In other cases, a black, a yellow, a magenta and a cyan color image plane are each imaged and transferred. Irrespective of whether individual color image planes are serially or concurrently transferred onto a piece of paper, registration of individual color image planes is very important.
One type of color image printing system builds up four different colored image planes onto a well-controlled substrate before transferring the generated image onto a piece of paper. One exemplary printing system comprises a Hewlett-Packard Color LaserJet 5, manufactured by Hewlett-Packard Co. of Palo Alto, Calif. Such exemplary printing system builds up a color image onto a page size photoconductor drum. The generated image comprises four distinct colors: yellow, magenta, cyan and black. Four developers are used to produce the four colors, with four distinct photoconductor drum rotations being needed to accumulate the four-color toner images.
Another exemplary printing system comprises a Tektronix Phaser 560, manufactured by Tektronix of Wilsonville, Oreg. Such exemplary printing system builds up a color image onto a page size intermediate transfer medium. However, the use of an intermediate transfer medium adds an additional processing step, which increases cost and complexity. Yet another type of color image printing system comprises a Xerox C55 color laser printer. Such laser printer fixes a sheet of paper onto a drum in order to achieve plane-to-plane registration of successively colored image planes.
Each of the above-mentioned printing systems increases the size of the printer or increases the complexity or cost of the printer. Therefore, there exists a need to provide a reduced cost and complexity technique for achieving a multiple pass color laser printer that realizes improved plane-to-plane registration and is usable with a wide range of media types.
SUMMARY OF THE INVENTION
A recirculating type paper drive provides a relatively low cost technique for achieving a multiple pass color laser printer having excellent planeto-plane registration and usable with a wide range of media types. According to one implementation, a four pass color laser printer achieves improved registration for most types of printable paper.
According to one aspect, a paper drive sheet feeder system includes an edge guide, a paper transport mechanism, a paper edge detector, and control circuitry. The edge guide cooperates with the paper transport mechanism to guide the edge of a sheet of paper along a travel path of a peripheral device. The paper transport mechanism is configured to move the sheet of paper along the travel path. The paper edge detector is provided along the travel path to detect the leading edge of the sheet of paper. The control circuitry communicates with the paper transport mechanism and the paper edge detector and is operative to locate the sheet of paper in response to the detected leading edge of the sheet of paper along the travel path to accurately superpose successive image planes during a multiple color image transfer process.
According to another aspect, a printing system is provided for printing multiple colors on a sheet of print media. The printing system includes an electrophotographic print engine and a paper drive sheet feeder system. The electrophotographic print engine includes a photoconductor drum and a transfer roller configured to interact in co-rotation with the drum during transfer of a color image plane from the drum onto a sheet of print media passed therebetween. The paper drive sheet feeder system includes at least one edge guide, a sheet transport mechanism, a sheet edge detector, and control circuitry. The edge guide is configured to guide an edge of the sheet of print media along a travel path about the print engine. The sheet transport mechanism is configured to move the sheet of print media along the travel path. The sheet edge detector is provided along the travel path to detect the leading edge of the sheet of print media. The control circuitry communicates with the sheet transport mechanism and the sheet edge detector and is operative to locate the sheet of print media in response to the detected leading edge of the sheet of print media along the travel path to accurately superpose successive image planes during a multiple color image transfer process.
According to yet another aspect, a method is provided for aligning and positioning a sheet of print media to receive multiple, successive color image planes. The method includes: moving a sheet of print media along a travel path; while moving the sheet of print media along the travel path, accurately guiding the sheet of print media along an edge guide to prevent movement in a lateral direction; detecting the leading edge of the sheet of print media to accurately locate positioning of the sheet of print media along the travel path; while moving the accurately located sheet of print media, transferring a first color image onto the sheet of print media; moving and accurately guiding the sheet of print media along the travel path along the guide and about a print engine; following transferring the first color image and moving the sheet, detecting the leading edge of the sheet of print media to accurately locate positioning of the sheet of print media along the travel path; and while moving the accurately located sheet of print media, transferring a second color image onto the sheet of print media accurately aligned atop the first color image.
One advantage is provided by precisely transferring a sheet of print media between successive passes against a photoconductor drum while transferring successive color image planes onto the sheet of print media so as to ensure precise registration between successive color image planes when forming an image.
Other features and advantages of the invention will become apparent to those of ordinary skill in the art upon review of the following detailed description, claims, and drawings.
DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are described below with reference to the following accompanying drawings depicting examples embodying the best mode for practicing the invention.
FIG. 1
is a perspective view of a printing system in accordance with one embodiment of Applicant's invention.
FIG. 2
is a vertical sectional view of the printing system of
FIG. 1
taken along line
2
—
2
.
FIG. 3
is a flow chart illustrating logic employed by the paper drive system included in the printing system of
FIGS. 1-2
.
DETAILED DESCRIPTION OF THE INVENTION
This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts”. U.S. Constitution, Article 1, Section 8.
FIG. 1
shows a printing system
10
embodying Applicant's invention usable for printing color images onto a sheet or page of print media, such as a sheet of paper. Typically, printing system
10
is connected for control with a microprocessor-based computer (not shown). Printing system
10
comprises an electrophotographic printer configured to print monochrome and/or color images onto a sheet. As shown in
FIG. 1
, color laser printer
10
includes a housing
12
, a paper tray
14
, an output tray
16
and a user interface
18
. User interface
18
includes one or more of a keyboard, a display, and a keypad that enables a user to operate and/or configure printer
10
.
As shown in
FIG. 1
, according to one implementation color laser printer
10
is configured to generate four different, successively transferred colored image planes. The image planes cooperate to form an image. Alternatively, printer
10
can be configured to compose at least three different colored image planes. Even further alternatively, printer
10
can be configured to compose two different colored image planes. Optionally, such printer
10
can be used to generate a plurality of different or uniquely shaded image planes, each having a unique shade of a common color, such as two unique and distinguishable grey-scale image planes.
Irrespective of the total number of image planes, the ability to align such planes to one another is important to achieving precise color printing of a colored image. As used herein, the term “color printing” is understood to include the generation and transfer of a plurality of unique shades of a common color, or of different grey-scale image planes.
FIG. 2
illustrates recirculating type paper drive color laser printer
10
in vertical sectional view to enable description of internal operating components. As shown in
FIG. 2
, a recirculating paper travel path
26
is depicted within printer
10
, extending between a plurality of roller transport assemblies
34
-
37
each including an edge guide roller
39
which cooperates with a paper drive roller
38
to provide a paper transport mechanism
28
. Each pair of rollers
38
-
39
cooperate to provide an edge guide
29
. It is understood that assemblies
34
-
37
each include a pair of coacting rollers
38
,
39
provided along one lateral edge of travel path
26
. As shown in
FIG. 2
, travel path
26
encircles print engine
20
, including laser scanner
22
and toner cartridge
24
.
Paper transport mechanism
28
moves a sheet
64
of paper along recirculating paper travel path
26
to provide a recirculating-type paper drive for a direct transfer color laser printer
10
. Accordingly, printer
10
comprises a recirculating-type paper drive configured to achieve a four-pass color printing process in a relatively low cost manner and having accurate plane-to-plane registration between color image planes. Furthermore, such recirculating-type paper drive is compatible with a relatively wide range of media types, such as various thicknesses of sheet
64
.
In order to accurately detect the positioning of a sheet
64
of paper along path
26
, a paper edge detector
30
is provided. Paper edge detector
30
is configured to accurately detect a leading edge of sheet
64
as sheet
64
is delivered along paper travel path
26
. According to one alternative construction, a trailing edge of sheet
64
can be detected via detector
30
. A microcontroller
31
communicates with paper edge detector
30
and paper transport mechanism
28
to provide a feedback control system operative to precisely move sheet
64
along the direction of travel path
26
during a multiple stage printing operation. More particularly, paper edge detector
30
comprises a precise slot photointerruptor
42
including a light source, or photodiode,
45
and an optical detector, or photodetector,
43
which are aligned such that sheet
64
interrupts detection of the light with the optical detector
43
.
Accordingly, movement of a sheet
64
of paper through photointerrupter
42
causes a change in output state for the optical detector
43
. Detection of such change of state enables a precise determination of the location of a leading edge of the sheet
64
of paper along travel path
26
. In response to receiving an output signal from photointerruptor
42
, microcontroller
31
generates a control signal that activates and deactivates paper transport mechanism
28
to move sheet
64
along path
26
in response to detected positioning of sheet
64
relative to precise slot photointerruptor
42
.
Roller
39
cooperates with paper drive roller
38
within each roller transport assembly
34
-
37
to precisely guide a sheet
64
of paper along paper travel path
26
in order to further ensure accurate registration between successive images that are printed onto sheet
64
using printer
10
. Roller
39
is skewed to guide a sheet of paper along a lateral edge. The construction of skew rollers is presently understood in the art. One exemplary construction for edge guide skew rollers is described in U.S. Pat. No. 6,118,465, assigned to Hewlett-Packard Company, and herein incorporated by reference. Hence, roller
39
cooperates with paper transport mechanism
28
, paper edge detector
30
, and microcontroller
31
to accurately move and present a sheet
64
of paper along paper travel path
26
and accurately transfer and superpose successive color image planes during a multiple color image transfer process.
Paper edge detector
30
provides an input to control circuitry
32
in order to regulate positioning of sheet
64
by regulating the drive signal for each paper drive roller of each assembly
34
-
37
of paper transport mechanism
28
. According to a color printing configuration, color laser printer
10
comprises at least three, and usually four, different color image planes. The alignment of these color image planes to one another is critical in order to achieve a resulting quality image on sheet
64
. Even slight variations between registration of different color image planes can result in hue and density shifts throughout the image that is printed onto the sheet
64
of paper.
In operation, individual sheets of paper are retrieved from a pressure plate
44
of a paper tray
14
via a pick roller
46
. A single sheet
64
of paper is then transferred between pick roller
46
and a transfer, or guide, roller
48
and deposited at roller transport assembly
34
, at a nip between edge guide skew roller
39
and paper drive roller
38
. Each paper drive
38
of assemblies
34
-
37
comprises a single, high friction elastomeric roller. Paper drive roller
38
is rotatably actuated so as to deliver a single sheet
64
of paper into position between a photoconductor drum (or roller)
50
and a transfer roller
52
such that a first color image plane can be printed onto the sheet
64
of paper from drum
50
. Accordingly, such sheet
64
of paper is presented between roller transport assembly
34
of roller
39
and paper drive roller
38
with roller transport assembly
34
driving sheet
64
through photointerruptor
42
and against photoconductor drum
50
. Paper drive roller
38
is driven via a drive motor (not shown), under control of microcontroller
31
and in response to detected position along travel path
26
, to accurately move sheet
64
of paper to receive a first image plane from photoconductor drum
50
.
As shown in
FIG. 2
, microcontroller
31
delivers an output control signal to roller transport assembly
34
. More particularly, microcontroller
31
delivers an output signal which drives rotation of paper drive roller
38
of roller transport assembly
34
. Although not shown in
FIG. 2
, it is understood that a similar output signal is provided to roller
38
of each respective remaining roller transport assembly
35
-
37
. Furthermore, according to one construction, each paper drive roller
38
is controllably driven using a high resolution stepper motor. According to one embodiment, a single high-resolution stepper motor is utilized to drive paper drive roller
38
of assembly
34
, with the remaining paper drive rollers
38
being geared together with the paper drive roller
38
of assembly
34
via a gear train, a toothed belt, or a band drive (not shown). According to an alternative embodiment, each paper drive roller
38
is driven by a dedicated, high-resolution stepper motor. It is further understood that photoconductor drum
50
comprises an optical photoconductor roller including a high-resolution stepper motor. Accordingly, the utilization of high-resolution stepper motors in transport mechanism
28
and as a drive for photoconductor drum
50
ensures accurate image plane registration between successive color image planes as they are deposited onto a sheet
64
of paper.
Additionally, or alternatively, encoders can be provided on a drive for photoconductor drum
50
, and in order to drive the paper drive rollers
38
of paper transport mechanism
28
.
After transfer of the first image plane onto sheet
64
of paper, each drive roller
38
of roller transport assemblies
34
-
37
is driven to move sheet
64
in a forward, advancing direction along travel path
26
. More particularly, sheet
64
is moved completely about so as to encircle print engine
20
until sheet
64
engages with assembly
34
and physically interrupts photointerruptor
42
. Hence, sheet
64
is again accurately located. Roller transport assembly
34
, along with the associated drive roller
38
, controllably drives sheet
64
in response to detected positioning of sheet
64
using photointerruptor
42
. Accordingly, sheet
64
is accurately advanced and positioned between photoconductor drum
50
and transfer roller
52
when delivering a subsequent image plane from drum
50
onto sheet
64
. The resulting subsequent image plane is aligned in accurate registry atop the first image plane. The same technique is used to move sheet
64
forward along travel path
26
in order to deliver additional, successive image planes accurately atop previously delivered image planes, on a first side of sheet
64
. Accordingly, subsequent additional color image planes are deposited onto drum
50
, then transferred onto sheet
64
of paper via the above technique.
FIG. 2
illustrates the workings of an electrophotographic color laser printer
10
. Laser scanner
22
is provided within printer
10
for generating an optical image via an imaging path or a slot
60
which is superposed onto photoconductor drum
50
after drum
50
has been charged with a charge roller
56
. Subsequently, one of four different colored toners is delivered from one of toner developers
62
,
162
,
262
and
362
.
Printer
10
is preferably connected for control with a microprocessor-based computer (not shown) which submits print jobs to printer
10
. Printer
10
includes an electrophotographic printer that is configured to print a color image onto sheet
64
, in the form of an image plane (e.g., including text and/or graphics). As used here, the term “image” is intended to mean text, graphics, or both text and graphics. One or more superposed image planes cooperate to provide a final image on sheet
64
.
As shown in
FIG. 2
, printer
10
comprises a color laser printer. In one embodiment, printer
10
includes internal components similar to those found in a LaserJet 5000 printer sold by Hewlett-Packard Company of Palo Alto, Calif.
Printer
10
includes housing
1
2
configured to support internal operating components. In the illustrated embodiment, printer
10
includes laser scanner
22
supported in housing
12
. A toner supply is contained within one of toner developers
62
,
162
,
262
, and
362
. A photoconductor drum
50
is provided which is acted upon by laser scanner
22
. A charge roller
56
is provided in contact with photoconductor drum
50
to impart charge to drum
50
upstream of where laser scanner
22
acts on photoconductor drum
50
. A developer roller
58
is provided in each of developers
62
,
162
,
262
, and
362
which acts on the photoconductor drum
50
downstream from where the laser scanner
22
acts on photoconductor drum
50
. A transfer roller
52
is provided at a location facing the photoconductor drum
50
downstream from the developer roller
58
and cooperating with the photoconductor drum
50
to impart an image onto sheet
64
. A cleaning blade
54
is configured to clean photoconductor drum
50
within a waste toner reservoir (not identified) after the image has been imparted to sheet
64
. Furthermore, a fuser
66
is provided spaced apart from and downstream of the photoconductor drum
50
.
According to the implementation depicted in
FIG. 2
, a rotating carousel toner cartridge assembly
67
is employed containing a “black” toner developer
62
, a “cyan” toner developer
162
, a “magenta” toner developer
262
, and a “yellow” toner developer
362
. Hence, each of developers
62
,
162
,
262
, and
362
contains a powder toner having a respective associated color for use in generating one color image plane.
A drive motor (not shown) rotates assembly
67
to present a desired developer roller
58
and toner developer
62
,
162
,
262
,
362
(containing a desired toner reservoir
59
containing toner) against drum
50
. Such rotation is controlled by microcontroller
31
. Additionally, waste toner is augered into a waste reservoir (not shown) by auger
55
. Auger
55
is also provided in the carousel cartridge assembly
67
for collecting waste toner that is removed by cleaner blade
54
from photoconductor drum
50
, after depositing an image plane onto sheet
64
of paper. Toner cartridge assembly
67
further includes an aperture, or slot, through which optical images are delivered via imaging path
60
onto charged photoconductor drum
50
. A charge roller
56
is supported in contact with drum
50
to deliver a charge to drum
50
.
Preferably, toner cartridge assembly
67
is designed as a replaceable toner/developer cartridge, with color being accomplished by using multiple development stations as provided by toner developers
62
,
162
,
262
, and
362
. One color is associated with each reservoir for the subtractive colors cyan, yellow and magenta, plus black. Typically, toners are colored with either a dye or a pigment. In operation, the four colored image planes are individually accumulated onto photoconductor drum
50
and transferred onto sheet
64
of paper, before transferring a successive color image plane. In this manner, according to the present embodiment, sheet
64
of paper is passed between photoconductor drum
50
and transfer roller
52
up to four separate times.
It is understood that printer
10
works as any presently understood electrophotographic, or laser, printing process. More particularly, charge roller
56
comprises a conductive elastomer charge roller that is placed in direct contact with photoconductor drum
50
. Charge roller
56
generates a charge on the surface of photoconductor drum
50
. Subsequently, laser scanner
22
traces the charged photoconductor drum
50
via imaging path
60
with a wavelength of exposing light source that matches the spectra sensitivity of photoconductor drum
50
. The developed photoconductor drum
50
imparts monocomponent image development by receiving powder toner onto the charged surface of photoconductor drum
50
, after which such toner is delivered onto sheet
64
when such sheet
64
is passed between transfer roller
52
and photoconductor drum
50
. Accordingly, monocomponent development is well understood in the art, and is carried out up to four different times in order to deliver up to four different color planes onto a single sheet
64
of paper.
The novelty of Applicant's invention lies in the manner in which a single sheet
64
of paper is repeatedly delivered in an accurate positional manner across photoconductor drum
50
when delivering successive, superposed image planes thereon.
Accordingly, the provision of paper edge detector
30
enables the accurate determination of the position of a sheet
64
of paper along the paper travel path
26
during the four electrophotographic print operations used to deliver four superposed color image planes onto sheet
64
. In order to achieve precise and accurate registration between success color planes, drive roller
38
on one edge of the sheet cooperates with an associated roller
39
to maintain accurate lateral positioning of sheet
64
which further ensures superposed, aligned registration between successive transferred image planes.
It is understood that a color print is composed of at least three, and usually four, different colored image planes. The precise alignment of these image planes to one another is critical to achieving a high-quality color image being placed onto a sheet of paper. Even slight variations in placement between successive image planes can cause hue and density shifts throughout the printed page.
Pursuant to the implementation depicted in
FIG. 2
, four color image planes are successively imaged and transferred directly onto sheet
64
of paper in essentially the same manner as a readily understood prior art monochrome laser printer. However, a recirculating type paper drive, or paper transport mechanism,
28
is provided in printer
10
consisting of drive roller
38
and edge roller
39
which clamp sheet
64
at one margin (along one edge) at each roller transport assembly
34
-
37
so as to impart precise registration and delivery of such sheet of paper therebetween. The accurate positioning of sheet
64
against drum
50
during successive image transfer operations is enabled via paper edge detector
30
.
In order to achieve accurate lateral alignment of sheet
64
during movement along paper travel path
26
, each roller
39
(for each assembly
34
-
37
) cooperates with each respective drive roller
38
to laterally align sheet
64
. More particularly, roller
39
comprises a previously mentioned edge-guide skew roller.
Additionally, a plurality of guide tracks
70
-
73
are provided within housing
12
. Guide tracks
70
-
73
serve to direct sheet
64
within housing
12
as sheet
64
travels along paper travel path
26
. Each guide track is formed from one or more rigid track walls, such as walls
74
-
79
.
A pair of paper redirection guides, or sheet diverter gates,
82
and
84
are also provided within housing
12
to further selectively redirect sheet
64
. More particularly, guide
82
is activated via a solenoid to advance sheet
64
along travel path
26
, and is retracted to advance sheet
64
into fuser
66
and between exit rollers
68
. Exit rollers
68
can be driven in forward and reverse. Accordingly, sheet
64
can be inverted in order to print on a back-side of such sheet
64
.
In order to invert sheet
64
, sheet
64
is delivered to exit rollers
68
sufficiently to clear redirection guide
84
. Subsequently, guide
84
is actuated via a solenoid to a raised position. Sheet
64
is then driven in reverse, guiding sheet
64
along track walls
77
and
79
and guide
84
for delivery into assembly
36
. Hence, sheet
64
is delivered, in an inverted configuration, back into travel path
26
. Sheet
64
is then delivered along travel path
26
via paper transport mechanism
28
to transfer one or more successive image planes onto a back side of sheet
64
, as previously discussed with respect to the front side of sheet
64
. Once printing is complete, sheet
64
is delivered from housing
12
via exit rollers
68
.
Accordingly, the implementation depicted in
FIG. 2
delivers a sheet
64
of paper from within tray
14
, off a pressure plate
44
by way of a pick roller
46
. Pick roller
46
cooperates with a plurality of guide rollers
48
to guide such delivered sheet of paper between edge guide skew roller
39
and paper drive roller
38
of assembly
34
. Assembly
34
moves paper
64
into the nip between drive roller
38
and roller
39
for transfer along paper travel path
26
.
Once a sheet
64
of paper has been delivered into the nip between each pair of-rollers
38
,
39
, sheet
64
is moved forward via respective motors under control of microcontroller
31
, into assembly
35
, and into contact with photoconductor drum
50
. Hence, the sheet
64
of paper is passed between drum
50
and roller
52
, after drum
50
has been charged and an image plane has been applied and a single color toner has been adhered thereto. Accordingly, full forward delivery of paper
64
during a first pass imparts such toner thereon in the form of a single color image plane, with such paper being delivered in a forward direction about path
26
.
After depositing the first color image plane, sheet
64
is moved forward about path
26
until paper edge detector
30
detects the presence of a forward edge of sheet
64
. Microcontroller
31
is then used to accurately drive sheet
64
forward for presentment at the nip between photoconductor
50
and transfer roller
52
. While moving sheet
64
about path
26
, photoconductor drum
50
is recharged, a second color image plane is applied thereon, and a second toner is applied thereto, after which sheet
64
is accurately delivered against drum
50
and paper
64
is delivered in a forward direction via drive roller
38
and roller
39
to deposit the second color image thereon and registration therewith and delivery of such paper
64
forward along path
26
. Such operation is carried out two more times in order to deliver the remaining two color image planes onto paper
64
.
However, prior to application of the last color image plane onto paper
64
, paper redirection guide
82
is actuated to a downwardly biased position such that paper
64
is delivered into a fuser
66
, comprising a pair of heated rollers that fuse the resulting colored image onto paper
64
. Fuser
66
delivers such paper
64
to a pair of advancement rollers, and finally to a pair of exit rollers
68
where the printed and fused sheet
64
of paper is ejected into an output tray for retrieval by a user who has submitted a print job thereto.
As shown in
FIG. 2
, pick roller
46
comprises any of a number of pick roller constructions that are presently understood in the art. One exemplary pick roller construction is depicted in U.S. Pat. No. 5,462,373 to Chia, herein incorporated by reference, and illustrating construction of a heat advancement system having a roller arrangement with first and second rollers that impart in phase and out of phase rotation for engaging and gripping a sheet of paper for delivery from a stack while eliminating roller drag as such sheets pass beneath the rollers. However, it is understood that any of a number of pick roller constructions can be utilized to retrieve a sheet
64
of paper from paper tray
14
and delivery to drive roller
38
and edge roller
39
of assemblies
34
-
37
.
Each roller
38
(provided along one lateral edge of path
26
) is driven in rotation to induce movement of a sheet
64
of paper which is engaged along an edge by a respective roller
39
.
Edge guide skew roller
39
comprises a pinch or pressure roller that is spring-biased into engagement with drive roller
38
via action of a spring loaded arm, on which each edge roller
39
is carried for rotatably biased engagement and co-rotation with roller
38
. Preferably, roller
39
comprises a semi-resilient material such as a neoprene, nylon or plastic material.
Preferably, drive roller
38
is driven for rotation via a high-resolution stepper motor, and/or includes encoders that will ensure excellent image plane registration between successive image planes.
According to the range depicted in
FIG. 2
, four successive color image planes are imaged and transferred directly onto sheet
64
of paper in a manner similar to that implemented on a traditional monochrome laser printer. Utilization of the recirculating-type paper drive in the form of paper transport mechanism
28
utilizes multiple edge-guide skew rollers
39
within assemblies
34
-
37
in order to transport sheet
64
along opposite edges in a path circling electrophotographic (EP) print engine
20
.
According to such implementation, process-wise registration of sheet
64
is established utilizing a precise slot photointerruptor provided by paper edge detector
30
. Additionally, cross-process registration is maintained utilizing edge guide skew roller
39
of assemblies
34
-
37
which cooperates to provide an edge guide paper path.
In summary, a four-color imaging process is implemented according to the following six steps: First, a sheet
64
of paper is picked utilizing pick roller
46
from tray
14
and introduced into precise slot photointerruptor
42
. Microcontroller
31
precisely establishes the path-wise location of sheet
64
by determining the exact location of the top edge of sheet
64
.
Secondly, the optical photoconductive (OPC) drum
50
(or roller) is rotated and exposed by a laser of laser scanner
22
along imaging path
60
, and development of a first color image plane is begun on the outer surface of drum
50
. Thirdly, as the top of the first color image plane rotates into a transfer area, sheet
64
is driven in a forward direction using one or more of drive rollers
38
. Accordingly, a leading edge of sheet
64
is directed into a nip between transfer roller
52
and photoconductor drum (or OPC)
50
.
Pursuant to a fourth step, once a first image plane has been completely transferred, sheet
64
continues in a circular path
26
around EP print engine
20
until sheet
64
is, again, introduced into slot photointerruptor
42
, precisely establishing the location of a top edge of sheet
64
.
According to a fifth step, the first four steps above are repeated once for each of three remaining color planes. Finally, paper is directed into fuser
66
, and all four transferred color image planes are fused simultaneously onto a first side of sheet
64
. Sheet
64
is then delivered from housing
1
2
via exit roller
68
. Alternatively, sheet
64
is turned upside down via exit roller
68
and paper redirection guide
84
for printing on a second, or back, side of sheet
64
via delivery about path
26
and repetition of the above steps on the second side.
Accordingly, integrated duplexing can be implemented utilizing the techniques of the present invention. As discussed above, paper redirection guide
84
is actuated by a solenoid downstream of fuser
66
. Exit rollers
68
are actuated in a reverse direction to redirect sheet
64
back into the recirculating paper path
26
where the back side of sheet
64
can be subsequently printed.
Accordingly, numerous inherent advantages are provided by a recirculating-type paper drive color laser printer. The above-described recirculating-type paper drive system provides a relatively low cost, compact size, and relatively high print quality for a color laser printer. Because such printer is capable of facilitating direct-to-paper transfer, the need for a page-size belt or photoconductor drum is eliminated. According to alternative techniques, photoconductor drum
50
needs to be constructed such that the outer surface is sufficiently large so that an entire page can be built thereon when transferring four color image planes successively thereto. Accordingly, a much smaller sized photoconductor drum can be utilized which provides a relatively less expensive printer construction.
FIG. 3
is a flow chart illustrating logical operations employed when implementing the recirculating-type paper drive color laser printing features of Applicant's invention. In Step “S
1
”, the method of aligning and positioning a sheet of print media to receive multiple, successive color image planes entails moving a sheet of print media along a travel path. After performing Step “S
1
”, the process proceeds to Step “S
2
”.
In Step “S
2
”, the method entails moving the sheet of print media along the travel path, accurately guiding the sheet of print along an edge guide to prevent movement in a lateral direction. After performing Step “S
2
”, the process proceeds to Step “S
3
”.
In Step “S
3
”, the method entails detecting the leading edge of the sheet of print media to accurately locate positioning of the sheet of print media along the travel path. After performing Step “S
3
”, the process proceeds to Step “S
4
”.
In Step “S
4
”, the method entails, while moving the accurately located sheet of print media, transferring a first color image onto the sheet of print media. After performing Step “S
4
”, the process proceeds to Step “S
5
”.
In Step “S
5
”, the process entails moving and accurately guiding the sheet of print media along the travel path against the edge guides and about a print engine. After performing Step “S
5
”, the process proceeds to Step “S
6
”.
In Step “S
6
”, the method entails following transferring of the first color image and moving the sheet, detecting the leading edge of the sheet of print media to accurately locate positioning of the sheet of print media along the travel path. After performing Step “S
6
”, the process proceeds to Step “S
7
”.
In Step “S
7
”, the method entails, while moving the accurately located sheet of print media, transferring a second color image onto the sheet of print media accurately aligned atop the first color image.
In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.
Claims
- 1. A paper drive sheet feeder system, comprising:an edge guide including a paper drive roller and an edge-guide skew roller to guide the edge of a sheet of paper along a travel path of a peripheral device; a paper transport mechanism configured to move the sheet of paper in a forward direction along the travel path and circumferentially about a print engine of peripheral device; a paper edge detector provided along the travel path to detect a leading edge of the sheet of paper; control circuitry communicating with the paper transport mechanism and the paper edge detector and operative to locate the sheet of paper in response to the detected leading edge of the sheet of paper along the travel path to accurately superpose successive image planes during a multiple color image transfer process; a sheet guide track for redirecting a sheet of paper from the travel path back into the travel path in an inverted configuration; a first sheet diverter gate for guiding the sheet from the travel path into the sheet guide track; a second paper transport mechanism along the sheet guide track to selectively move the sheet in forward and reverse directions; and a second sheet diverter gate for opening the sheet guide track to receive the sheet in a forward direction and eject the sheet in a reverse direction that is in an inverted position relative to the travel path.
- 2. The paper drive sheet feeder system of claim 1 wherein the paper transport mechanism comprises a plurality of edge-guide skew rollers configured to transport the sheet of paper by accurately guiding the sheet of paper along the travel path.
- 3. The paper drive sheet feeder system of claim 1 wherein the edge guide comprises a pair of adjacent flanges cooperating to retain and guide one edge of the sheet of paper therebetween, and wherein the travel path encircles the print engine.
- 4. The paper drive sheet feeder system of claim 1 wherein the paper edge detector comprises a slot photointerruptor.
- 5. The paper drive sheet feeder system of claim 4 wherein the slot photointerruptor comprises an optical photodetector and a light source each provided on opposite sides of the travel path, the optical photodetector operative to detect the light source, wherein presence of one of the leading edge of the sheet of paper causes a change in state of the detected light source corresponding with movement of the sheet of paper through an optical detection path of the optical photodetector.
- 6. The paper drive sheet feeder system of claim 1 further comprising a sheet diverter gate operative to invert the sheet of paper along the paper travel path for duplex imaging.
- 7. A printing system for printing multiple colors on a sheet of print media, comprising:an electrophotographic print engine including a photoconductor drum and a transfer roller configured to interact in coacting rotation with the drum during transfer of a color image plane from the drum onto a sheet of print media passed therebetween; and a paper drive sheet feeder system having at least one edge guide to guide an edge of the sheet of print media along a travel path about the print engine, a sheet transport mechanism configured to move the sheet of print media along the travel path and circumferentially about a print engine of the printing system, a sheet edge detect or provided along the travel path to detect the leading edge of the sheet of print media, and control circuitry communicating with the sheet transport mechanism and the sheet edge detector and operative to locate the sheet of print media in response to the detected leading edge of the sheet of print media along the travel path t o accurately superpose successive image planes during a multiple color image transfer process.
- 8. The printing system of claim 7 wherein the at least one edge guide comprises edge-guide skew rollers cooperating to transport the sheet of print media by accurately guiding the sheet of print media along an edge for transport along the travel path.
- 9. The printing system of claim 7 wherein the sheet edge detector comprises a light source provided along a first side of the sheet travel path and a photodetector along a second side of the sheet travel path configured to detect light from the light source, wherein movement of the sheet of print media along the travel path interrupts the beam so as to provide a detectable change at the photodetector corresponding to presence of a leading edge of the sheet of print media.
- 10. The printing system of claim 9 wherein the sheet edge detector comprises a slot photointerruptor interposed across the sheet travel path.
- 11. The printing system of claim 7 wherein process-wise registration is provided by the sheet edge detector, and wherein cross-process registration is provided by an edge guide.
- 12. The printing system of claim 7 further comprising a sheet diverter gate downstream of a fuser and operative to redirect the sheet into the travel path upside down and in an opposite direction so as to provide duplex image transfer.
- 13. A method of aligning and positioning a sheet of print media to receive multiple, successive color image planes, the method comprising:moving a sheet of print media along a travel path in a first direction; while moving the sheet of print media along the travel path, accurately guiding the sheet of print media along an edge guide to prevent movement in a lateral direction; detecting the leading edge of the sheet of print media to accurately locate positioning of the sheet of print media along the travel path; while moving the accurately located sheet of print media, transferring a first color image onto the sheet of print media; moving and accurately guiding the sheet of print media along the travel path along the guide and about a print engine; following transferring the first color image and moving the sheet, detecting the leading edge of the sheet of print media to accurately locate positioning of the sheet of print media along the travel path; while moving the accurately located sheet of print media, transferring a second color image onto the sheet of print media accurately aligned atop the first color image; moving the sheet of print media from the travel path into a sheet guide track that inverts the sheet; inverting the sheet of print media; and moving the inverted sheet of print media from the sheet guide track to the travel path to present an opposed surface of the sheet of print media to receive an image plane.
- 14. The method of claim 13 wherein, after transferring the first color image, the steps of moving and accurately guiding, detecting, and transferring are carried out three times in series to transfer the second color image, a third color image, and a fourth color image successively and accurately aligned atop the first color image so as to accurately register four color images atop the sheet of print media.
- 15. The method of claim 13 wherein accurately guiding the sheet of print media along the guide to prevent movement in a lateral direction comprises moving the sheet of print media between a pair of edge-guide skew rollers operative to transport the sheet of print media along an edge in a path circling an electrophotographic print engine.
- 16. The method of claim 13 wherein the initial step of moving the sheet of print media along a guide and along a travel path comprises picking the sheet of media from a paper tray and moving the sheet of media into a slot photointerruptor.
- 17. The method of claim 16 wherein detecting the leading edge of the sheet of print media to accurately locate positioning of the sheet of print media along the travel path comprises detecting movement of the sheet of media into the slot photointerruptor.
- 18. The method of claim 17 wherein the slot photointerruptor comprises a light source and a photodetector provided on opposite sides of the paper travel path such that movement of the sheet of media between the light source and the photodetector interrupts detection of a light beam from the light source by the photodetector.
- 19. The method of claim 18 wherein a change in state of detection of the light source corresponds with the leading edge of the sheet of media.
US Referenced Citations (5)