Information
-
Patent Grant
-
6304731
-
Patent Number
6,304,731
-
Date Filed
Thursday, June 8, 200024 years ago
-
Date Issued
Tuesday, October 16, 200122 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 399 43
- 399 45
- 399 329
- 399 400
- 399 330
- 399 334
- 219 216
-
International Classifications
-
Abstract
A printer has a media feed path (12) for feeding sheets of media (14), with the path having a side reference edge (52) for aligning the media. A media transport mechanism feeds the sheets of media at a standard speed and at a reduced speed. A narrow media detector (38) generates a narrow media signal when sheets of narrow media are fed through the media feed path. A controller (68) adjusts the media transport mechanism to feed the narrow media aligned with the reference edge at the reduced speed. A method of printing sheets of narrow media in a printer comprises the steps of aligning the narrow media with a reference edge in a media feed path of the printer, sensing when the narrow media are present in the media feed path, and feeding the narrow media through the media feed path at the reduced sheet feeding speed and, particularly with a belt fuser, with increased inter-sheet gap.
Description
FIELD OF THE INVENTION
This invention relates to an electrophotographic printer, and more particularly, to a laser printer for printing narrow media with high throughput that does not overheat the fuser.
BACKGROUND OF THE INVENTION
An electrophotographic printer prints an image on media, such as sheets of paper, from toner contained in a toner cartridge. A developer roller or sleeve is mounted within the toner cartridge in proximity to a photoconductive drum. The photoconductive drum is charged, and a laser scans the charged photoconductive drum with a laser beam to discharge the surface and form a latent image thereon. The developer roller attracts statically charged toner from the toner container. Toner is transferred from the developer roller to the photoconductive drum to develop the latent image formed on the photoconductive drum. The developed image is then transferred to statically charged sheets of media. The sheets are fed through a heated fuser assembly, where the heat fixes the visible image.
Sheets of narrow media, such as envelopes, are aligned with a reference edge in the feed path of the printer. Because the narrow sheets do not extend across the full width of the feed path, the consecutive printing of several sheets of narrow media creates a temperature imbalance in the fuser assembly. The sheets of media, when fed past the fuser assembly to fuse the image to the sheets, remove heat therefrom. Since sheets of narrow media do not extend fully across the width of the fuser assembly, the portion of the fuser assembly away from the reference edge, where the narrow media do not contact the fuser assembly, becomes hotter than the portion adjacent the reference edge, where the narrow media contact the fuser assembly. The fuser assembly can overheat so much after printing several consecutive sheets of narrow media that it becomes damaged.
One proposed solution to the problem of the overheating in a fuser assembly with a hot roller has been to make the fuser roller out of very thick material, so that the heat diffuses more evenly across the entire width. This has been unsatisfactory, as the cost of a thick fuser roller is high. This solution, of course, is not applicable to a fuser assembly with a fuser belt.
A second proposed solution to the problem of the overheating of the fuser assembly has been the insertion of gaps between the sheets of narrow media. Inter-sheet gaps permit the fuser assembly to equilibrate between sheets. However, this solution has also been unsatisfactory, as the insertion of inter-sheet gaps for all sheets of narrow media dramatically reduces the throughput of the printer.
A third proposed solution to the problem of the overheating of the fuser assembly has been to reduce the operating temperature of the fuser assembly and the transport speed. Consequently, all the sheets of media, regardless of width, are fed past the fuser assembly at a very slow speed, so that enough heat is transferred to the media to fuse the image thereto. However, this solution has also been unsatisfactory, as the slow feeding speed for all the sheets of media severely reduces the throughput of the printer.
SUMMARY OF THE INVENTION
A printer in accord with the present invention overcomes the foregoing problems by determining when narrow media are to be printed, aligning the narrow media with a side reference edge of the media path, lowering the temperature of the fuser assembly and feeding the narrow media through the media path at a reduced speed, and, for certain conditions, increasing the gap between fed sheets.
In accord with one aspect of the present invention, a printer comprises a media feed path for feeding sheets of media through the printer, the path including a side reference edge, and a media transport mechanism for feeding the sheets of media at a standard speed and at a reduced speed along the media feed path. A narrow media detector generates a narrow media signal when sheets of narrow media are fed through the media feed path. A controller responds to the narrow media signal and adjusts the media transport mechanism to feed the narrow media aligned with the reference edge at the reduced speed.
In accord with another aspect of the present invention, a printer system comprises a media feed path for feeding sheets of media through the printer, the path including a reference edge, and a media transport mechanism for feeding the sheets of media at a standard speed and at a reduced speed along the media feed path. A narrow media detector generates a narrow media signal when sheets of narrow media are fed through the media feed path. A programmed microcomputer responds to the narrow media signal and adjusts the media transport mechanism to feed the narrow media aligned with the reference edge at the reduced speed.
An advantage of a printer in accord with this invention is that sheets of narrow media are printed without damaging the printer even though use of a side reference edge adds to heat stress at the fixing mechanism when fixing narrow media.
Another advantage of a printer in accord with this invention is that sheets of narrow media are printed without overheating and damaging the fuser assembly.
A further advantage of a printer in accord with this invention is that narrow media are printed with a high printer throughput.
A still further advantage of the present invention is that it can be used in a printer with a fuser assembly having either a hot fuser roller or a fuser belt.
Other objects and advantages of the invention will be readily perceived from the following description, claims, and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The attached drawings illustrate preferred embodiments of the invention, in which:
FIG. 1
is a cutaway, diagrammatic side view of an electrophotographic printer;
FIG. 2
is a diagrammatic plan view of a fuser roller in the printer of
FIG. 1
;
FIG. 3
is a schematic diagram of the data flow in the printer of
FIG. 1
;
FIG. 4
is a block diagram of the electrical circuitry of the printer of
FIG. 1
; and
FIG. 5
is a flowchart illustrating programs used in the circuit of FIG.
4
.
FIG. 6
is illustrative of a belt fuser.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to the drawings, and initially to
FIG. 1
thereof, an electrophotographic printer
10
includes a media feed path
12
for feeding sheets of media
14
, such as paper, from a media tray
16
past a photoconductive drum
18
and a fuser assembly
20
to an output tray
22
. The fuser assembly
20
may be a nip roller fuser formed by a fuser roller
24
, which is heated to a relatively high temperature to fuse particles of toner to the sheets of media
14
, a backup roller
26
. U.S. Pat. No. 5,860,051 to Goto et al. is illustrative of a belt fuser. It will be appreciated that fuser assembly
20
could also be of the belt fuser type (see FIG.
6
), in which a polyamide belt
24
a
passes over a ceramic heater
24
b
with the media
14
in a nip between belt
24
a
and a backup roller
26
a
. Special media, such as envelopes, transparencies or checks, are fed into the media feed path
12
from an external, front-option tray
28
, sometimes referred to as a multi-purpose tray. Envelopes may also be fed from a separate, external tray (not shown). The photoconductive drum
18
forms an integral part of a replaceable toner cartridge
30
inserted in the printer
10
. A printhead
32
is disposed in the printer
10
for scanning the photoconductive drum
18
with a laser beam
34
to form a latent image thereon. The laser beam
34
places a spot of light on a facet of a rotating polygonal mirror
36
, which then redirects the laser beam
34
so that it ultimately sweeps of “scans” across a “writing line” on the photoconductive drum
18
, thereby creating, in a black and white laser printer, a raster line of either black or white print elements, also known as “pels.” The polygonal mirror
36
typically has six or eight facets, and each one-sixth or one-eighth rotation of the polygonal mirror
36
, respectively, creates an entire swept raster scan of laser light that ultimately becomes a writing line on a sheet of media
14
. The operation of the printhead
32
is more fully described in U.S. Pat. No. 5,877,798 to Clarke et al., also assigned to the assignee of the present application.
In the illustrated embodiment, the printer
10
has a narrow media sensor
38
located downstream, as viewed from the direction of flow of the media
14
, from the photoconductive drum
18
and the fuser assembly
20
. The narrow media sensor
38
detects the presence of sheets of narrow media in the media feed path
12
. The narrow media sensor
38
could alternatively be located upstream from the photoconductive drum
18
, as indicated in phantom
38
′. A plurality of rollers
40
,
42
,
44
,
46
,
48
function in a known manner to transfer the sheets of media
14
from the media tray
16
or multi-purpose tray
28
through the media feed path
12
.
FIG. 2
illustrates the fuser roller
24
and a reference edge
50
of the media feed path
12
. Sheets of narrow media
14
, such as envelopes, shown in phantom on
FIG. 2
, are left justified and aligned with the reference edge
50
as they are fed through the media feed path
12
. In one particular embodiment, the fuser roller
24
was slightly wider than 8½inches, so that it could accommodate full-width media, such as U.S. letter size paper and A4 paper. The narrow media sensor
38
was located between two edges
52
,
54
of the fuser roller
24
, at approximately three-quarters of the distance from the edge
52
, corresponding to the lateral position of the reference edge
50
, to the opposite edge
54
of the fuser roller
24
. The narrow media sensor
38
can be located at different positions across the width of the media feed path
12
. An exit sensor
56
is located adjacent the narrow media sensor
38
and detects the presence of any sheet of media
14
as it leaves the fuser assembly
20
.
It will be appreciated that the printer
10
can print different widths of narrow media
14
. In the preferred embodiment, the narrow media were classified into three categories, with each category having similar characteristics vis å vis the heating of the fuser assembly
20
when several sheets are consecutively printed. One category of narrow media is envelopes. A second category of narrow media is very narrow media. Very narrow media are media that the narrow media sensor
38
detects as narrow. Examples of very narrow media are A5 size paper and 3″×5″ index cards. A third category of narrow media is nearly narrow media. Nearly narrow media are media that have a width between very narrow media and normal media. Nearly narrow media engage the narrow media sensor
38
, but do not extend the full width of the fuser roller
24
. Nearly narrow media are determined by the standard paper sizes detected within the paper tray
16
. Examples of nearly narrow media are B5 size paper and executive size paper.
It will be recognized that other categories of media width for narrow media can be utilized with the present invention, with each category determined by the width of the media and the temperature characteristics of the fuser assembly
20
in printing them, and that the categories of media widths discussed hereinbefore are the preferred embodiment.
Turning now to
FIG. 3
, a print job is sent to the printer
10
from a variety of sources, such as, for example, a networked personal computer running a word processing program, and is identified in the drawing as being supplied from input data ports
60
. Each print job contains the image to be printed, and may contain additional information about the job, such as the media size and the media source. For example, a print job for an envelope may contain, in addition to the name and address to be printed, information indicating that the job is to be printed on a special size of media, i.e., an envelope. The media source information contained in the print job may specify which tray is to be used to supply the media to be printed.
A print job flows from the input data ports
60
to a raster image processor (RIP)
62
, where the print job is rasterized to form a bitmap suitable for printing on the sheets of media
14
. The bitmap from the raster image processor
62
is supplied to a print engine
64
for printing on the sheets of media
14
. The RIP
62
supplements the job information contained in the print job received from the input data ports
60
.
Referring to
FIG. 4
, the raster image processor (RIP)
62
sends the bitmap through an interconnect card
66
to an engine controller
68
. The engine controller
68
acts as a controller and data-manipulating device for the various hardware components within the print engine
64
. The engine controller
68
includes a programmed microcomputer
70
, a flash memory
72
and a random access memory (RAM)
73
, for storing programs to be run thereon. In the preferred embodiment, the programmed microcomputer
70
was a Toshiba TMP90CM38 microcontroller. Other devices, such as a hard drive
74
, can be connected to the RIP
62
via one of the integrated network adapters
76
,
76
′,
76
″ and the interconnect card
66
. A low voltage power supply (LVPS)
78
supplies the engine controller
68
and the RIP
62
with power via the interconnect card
66
.
The engine controller
68
is connected to an operator panel
80
, which is an input/output interface providing a user with a method to supply the printer
10
with configuration information. In one embodiment, the operator panel
80
was an LCD panel and input buttons. A user can use the operator panel
80
to supply the printer
10
with media information. The operator panel
80
can also display any of a large number of messages to the user, including status messages, e.g. ready/busy, output tray empty, output tray near full, output tray full, and error messages. The engine controller
68
is connected to a high voltage power supply (HVPS)
82
, which supplies high voltages to hardware components, such as the photoconductive drum
18
. A base input tray paper LED indicating a low paper condition
84
, a base input tray paper LED indicating a no paper condition
86
, a paper size sensor
88
, a multifunction paper tray LED indicating a no paper condition
90
, an output tray LED
92
indicating a near full output tray condition, an input sensor LED
94
, which indicates that a sheet of media
14
is about to be printed, and a multipurpose tray (MPT) solenoid
96
, which picks the sheets of media
14
out of the multipurpose tray
28
, are connected to the engine controller
68
. Additional components operated under control of the engine controller
68
include a main fan
98
, a transport motor assembly
100
, and an autocompensator picker motor
102
. A fuser assembly
104
, generally corresponding to the fuser assembly
20
of
FIG. 1
, operates under control of the engine controller
68
. A fuser on/off signal passes from the engine controller
68
through the interconnect card
66
to the low voltage power supply (LVPS)
78
. There, the on/off signal actuates a triac (not shown), thereby allowing AC current to flow into the fuser lamp or heater inside the fuser assembly
104
(depending on the type of fuser
104
employed in the printer
10
). An inductor
106
is connected to the fuser assembly
104
and the engine controller
68
. A laser printhead
108
is connected to the engine controller
68
and a top cover switch
110
, which is also connected to the engine controller
68
.
A front feeder option
112
is connected to the engine controller
68
through a front feeder option autoconnect connector
114
. As noted hereinbefore, envelopes may be fed from the multi-purpose tray
28
(see FIG.
1
), or from a separate tray associated with the front feeder option
112
. The printer
10
has an optional output tray
116
and an optional input tray
118
with different options configurable under the control of a software program stored in the engine controller
68
. The output and input trays
116
,
118
are connected by an output stacker autoconnect connector
120
and a bottom tray option autoconnect connector
122
, respectively, which provide electrical connections to the engine controller
68
.
FIG. 5
depicts flowcharts for software programs or subroutines used in the engine controller
68
, and which assist in the operation thereof. In one embodiment, software programs were written in a suitable computer language, such as C, and stored in the flash memory
72
. As will be evident to those of ordinary skill in the art, the engine controller
68
could be replaced by an application specific integrated circuit (ASIC), which would operate as hereindescribed. Additionally, the software programs associated with
FIG. 5
could be run on a server and connected to the printer through one of the integrated network adapters
76
,
76
′,
76
″ of FIG.
3
.
As shown on
Figure 5A
, the software program begins at step S
100
, which is associated with the condition when a sheet of media
14
is positioned in the media feed path
12
proximate the narrow media sensor
38
. Program flow then continues at step S
102
, where the program determines whether the sheet of media
14
in the media feed path
12
is known to be an envelope. As discussed in connection with
FIG. 3
, the program does this by examining the information contained in the print job. If the program determines at step S
102
that the sheet of media
14
is an envelope, program flow continues at step S
104
, where the program increments a count, commonly identified as a meltometer, by an amount corresponding to an envelope. Program flow then continues at step S
106
, where the program sets a flag corresponding to the condition where the last sheet width was an envelope. Program flow then continues at step S
108
.
As noted hereinbefore, the engine controller
68
maintains a count, called the meltometer, associated with the temperature of the fuser assembly
20
. The meltometer is incremented or decremented according to the heat properties associated with each sheet of media
14
that the printer prints. When a sheet of media
14
is printed, it feeds past the heated fuser roller
24
(see FIG.
2
), where the heat from the fuser roller
24
fuses the image to the sheet
14
. In addition to fixing the image to the sheet
14
, this operation removes heat from the fuser roller
24
. Since sheets of narrow media, when aligned with the reference edge
50
, do not extend fully across the width of the fuser roller
24
, the portion of the fuser roller
24
away from the reference edge
50
, where the narrow media do not contact the fuser roller
24
, becomes hotter than the portion adjacent the reference edge
50
, where the narrow media contact the fuser roller
24
. The fuser roller
24
can overheat so much after printing several consecutive sheets of narrow media that it becomes damaged. Different widths of media remove different amounts of heat from the fuser assembly
20
when images are printed thereon, and the value of the meltometer is changed to reflect the sheets that have been printed on the printer
10
, and hence, the temperature of the fuser assembly
20
. It is to be appreciated that the value of the meltometer is not the actual temperature of the fuser assembly
20
, but rather, a numeric representation of the approximate or projected value thereof. The changes in the value of the meltometer are related to the width of the sheets of media
14
, as wider sheets of media
14
absorb greater amounts of heat from the fuser assembly
20
during the printing process, as discussed more fully hereinbelow.
If the program determines at step S
102
that the sheet of media
14
is not an envelope, program flow continues at step S
110
, where the program interrogates the narrow media sensor
38
to determine whether the sheet of media
14
is very narrow, that is, whether it does not engage the narrow media sensor
38
. If the program determines at step S
110
that the sheet of media
14
is very narrow, program flow continues at step S
112
, where the program increments the meltometer by an amount corresponding to a sheet of very narrow media. Program flow continues at step S
114
, where the program stores a value to indicate that the input source for the sheet of media
14
is one that contains very narrow media. Program flow continues at step S
116
, where the program sets a flag to indicate that the last sheet width was a sheet of narrow media. Program flow continues at step S
108
.
If the program determines at step S
110
that the sheet of media
14
is not very narrow media, program flow continues at step S
118
, where the program determines whether the sheet of media
14
is a sheet of nearly narrow media. As noted hereinbefore, nearly narrow media are media that have a width between very narrow media and normal media. If the program determines at step S
118
that the sheet of media
14
is a sheet of nearly narrow media, program flow continues at step S
120
, where the program increments the meltometer by an amount corresponding to a sheet of nearly narrow media. Program flow continues at step S
122
, where the program sets a flag to indicate that the last sheet width was a sheet of nearly narrow media. Program flow continues at step S
124
, where the program stores a value to indicate that the input source for the sheet of media
14
is one that does not contain narrow media. Program flow continues at step S
108
.
If the program determines at step S
118
that the sheet of media
14
is not nearly narrow media, program flow continues at step S
126
, where the program increments the meltometer by an amount corresponding to a sheet of full-width media. Program flow continues at step S
128
, where the program sets a flag to indicate that the last sheet width was a sheet of full-width media. Program flow continues at step S
124
, where the program stores a value in the RAM
73
to indicate that the input source for the sheet of media
14
is one that does not contain narrow media. Program flow continues at step S
108
.
At step S
108
, the program tests to determine whether the meltometer is greater than an upper threshold value. If the program determines that the meltometer is greater than the upper threshold value, program flow continues at step S
130
, where the program sets a reduced throughput flag, i.e., a value is stored in the RAM
73
to indicate that subsequent sheets of narrow media are to be fed through the media feed path
12
at a reduced rate. Program flow then continues at step S
132
, where the program has completed its task of looking at the input signals from the narrow media sensor
38
.
If the program determines at step S
108
that the value of the meltometer is not greater than the upper threshold value, program flow continues at step S
134
, where the program tests to determine whether the value of the meltometer is less than a lower threshold value. If the program determines at step S
134
that the value of the meltometer is not less than the lower threshold value, program flow continues at step S
132
. If the program determines at step S
134
that the value of the meltometer is less than the lower threshold value, program flow continues at step S
136
, where the program clears the reduced throughput flag. Program flow continues at step S
132
, where the program has completed its task of looking at the input signals from the narrow media sensor
38
.
From step S
132
on
FIG. 5B
, program flow continues at step S
138
, where the program tests to determine whether the reduced throughput flag has been set. If the program determines at step S
138
that the reduced throughput flag has not been set, program flow continues a step S
140
, where the program determines that the narrow media calculations have been completed. If the program determines at step S
138
that the reduced throughput flag has been set, program flow continues at step S
142
, where the program tests to determine whether the reduced throughput flag for the last sheet width should include a setting to indicate a reduced media sheet feeding speed. In a current embodiment, set reduced speed is done for all categories of narrow media except for nearly narrow media being printed in a nip-roller-fuser version of the highest speed printer (35 pages per minute). If the program determines at step S
142
that the reduced throughput flag for the last sheet width should be set, program flow continues at step S
144
, where the program sets the reduced speed flag. Program flow continues at step S
146
.
If the program determines at step S
142
that the reduced throughput flag for the last sheet width should not be set, program flow continues at step S
146
.
At step S
146
, the program tests to determine whether the reduced throughput for the last sheet width includes a larger inter-sheet gap. In a current embodiment, this set enlarged gap is not done for any narrow media with a nip roller fuser and is done for all categories of narrow media for a belt fuser (except for nearly narrow media with the nip-roller-fuser 35 ppm printer the gap is enlarged, but the speed is not reduced). If the program determines at step S
146
that the reduced throughput for the last sheet width does not include a larger inter-sheet gap, program flow continues at step S
140
. If the program determines at step S
146
that the reduced throughput for the last sheet width includes a larger inter-sheet gap, program flow continues at step S
148
, where the program sets the enlarged gap flag. Program flow continues at step S
150
, where the program sets a value indicating that the selected gap is an increased gap for the last sheet width. Program flow continues at step S
140
, where the program has completed the narrow media calculations.
It will be appreciated from the foregoing description that the present invention can be utilized with an enlarged inter-sheet gap to provide additional opportunities for the fuser assembly
20
to cool between consecutive sheets of narrow media.
Turning now to
FIG. 5C
, program flow continues at step S
152
, where the sheet of media
14
is staged to be picked from an input source, such as a particular tray containing envelopes or other narrow media. At step S
154
, the program tests to determine whether the sheet of media
14
is known to be an envelope. If the program determines that the sheet of media
14
is an envelope, program flow continues at step S
156
, where the program tests to determine whether an envelope must always be picked and fed at a reduced speed. In a current embodiment, this is set to require reduced speed only when the fuser is a belt fuser. If the program determines at step S
156
that an envelope must always be picked and fed at a reduced speed, program flow continues at step S
158
, where the reduced speed flag is set. Program flow continues at step S
160
.
If the program determines at step S
156
that an envelope need not be picked and fed at a reduced speed, program flow continues at step S
162
, where the program tests to determine whether the sheet of media
14
is known to be very narrow media. If the program determines at step S
162
that the sheet of media
14
is known to be very narrow media, program flow continues at step S
164
, where the program tests to determine whether sheets of very narrow media must always be picked and fed at a reduced speed. However, in a current embodiment, an envelope is the only category of narrow media which is picked and fed at a reduced speed. If the program determines at step S
164
that sheets of very narrow media must always be picked and fed at a reduced speed, program flow continues at step S
158
, where the program sets the reduced speed flag. Program flow continues at step S
160
. If the program determines at step S
164
that sheets of very narrow media are not always picked and fed at a reduced speed, program flow continues at step S
160
.
At step S
160
, the program tests to determine whether the reduced speed flag has been set. If the program determines at step S
160
that the reduced speed flag has been set, program flow continues at step S
166
, where the program sets the printer to require the sheet of media
14
to be picked and fed at a reduced speed. Program flow continues at step S
168
, where the program sets the temperature of the fuser assembly
20
to a reduced temperature for the sheet of media
14
. Program flow continues at step S
170
.
If the program determines at step S
160
that the reduced speed flag has not been set, program flow continues at step S
172
, where the program sets the temperature of the fuser assembly
20
to a normal (or unreduced) temperature for the sheet of media
14
. Program flow continues at step S
170
.
At step S
170
, the program tests to determine whether the enlarged inter-sheet gap flag has been set. If the program determines at step S
170
that the enlarged inter-sheet gap flag has been set, program flow continues at step S
174
, where the program sets the printer
10
to require the sheet of media
14
to be picked and fed with the enlarged inter-sheet gap. Program flow continues at step S
178
, where the program has completed its operations with regard to staging the sheets of media
14
prior to the picking and feeding operation. Accordingly, with a belt fuser, the first envelopes are fed at a reduced speed and temperature, and subsequent envelopes are fed with increased gap by action of steps
148
in response to step S
108
being “yes” when the amount of meltometer count is above the predetermined threshold value. In a current embodiment for the belt fuser, standard speed is 20 pages per minute (ppm), reduced speed is 10 ppm, and reduced speed with inter-sheet gap is 5 ppm.
If the program determines at step S
170
that the enlarged inter-sheet gap flag has not been set, program flow continues at step S
176
, where the program sets the printer
10
to require the sheet of media
14
to be picked and fed at the normal inter-sheet gap. Program flow continues at step S
178
, where the program has completed its operations with regard to staging the sheets of media
14
prior to the picking and feeding operation.
It will be appreciated from the foregoing that the engine controller
68
has three sources of information about the width of a sheet of media
14
to be printed: the narrow media sensor
38
, the information in the print job as it comes from the raster image processor
62
, and historical data about the media source stored in the RAM
73
. It will be further appreciated that the computer program of
FIG. 5
utilizes information from the three sources in operating the printer
10
. In the preferred embodiment, in the calculations performed above, the output from the narrow media sensor
38
overruled any information contained within the print job. In addition, in the calculations performed above, the printing of an envelope overruled any other categorization, such as very narrow media.
The primary benefit of reducing the speed at which the sheets of media
14
are fed through the media feed path
12
of the printer
10
is that, at a reduced speed, the operating temperature of the fuser assembly
20
can be reduced. The energy transferred from the fuser roller
24
to the sheet of media
14
is proportional to the fusing temperature and the time spent in contact with the fuser roller
24
. Thus, when the speed at which the sheets of media
14
are fed through the media feed path
12
is reduced, the time each sheet of media
14
spends in contact with the fuser roller
24
is increased, and the fusing temperature can be reduced while providing the same amount of energy for the fusing process properly to occur. Lowering the temperature of the fuser assembly
20
avoids temperature extremes for the fuser assembly
20
when printing narrow media.
However, lowering the fusing temperature and accompanying sheet feeding speed for all sheets of media
14
severely reduces throughput of the printer
10
. Hence, in the printer of the present invention, only selected sheets of media
14
are printed at the reduced sheet feeding speed, so that throughput of the printer
10
is greater than the case in which all the sheets of media
14
are printed at the reduced sheet feeding speed.
It was found that a single threshold was not sufficient to implement the desired control of the temperature of the fuser assembly
20
. A pair of thresholds, on the other hand, provided an adequate hysteresis. With a single threshold, intermixing different categories of media width resulted in the printer
10
repeatedly switching between the normal sheet feeding speed and the reduced sheet feeding speed. It will be recognized that substantial amounts of time are required to change from one printing speed to another, so that numerous speed changes in rapid succession severely reduce the throughput of printer
10
. The upper threshold (Step S
108
) was selected so that the precision of the value of the meltometer was maximized without using large amounts of the available memory. The lower threshold (Step S
134
) was set some distance below the upper threshold to provide an appropriate hysteresis.
Many different reduced speeds can be selected to feed the sheets of media
14
through the printer
10
. However, the engine controller
68
must adjust all the speed-related parameters for the printer
10
for each speed selected. These parameters include, for example, gamma correction, laser duty cycle, laser power, and developer voltage. This is very complicated for many different speeds. Since the memory space available in the flash memory
72
for storing the associated parameters is limited, it has not been found to be practical to have a large number of different sheet feeding speeds implemented in the printer
10
. One solution is to limit the different sheet feeding speeds to a small number. In the preferred embodiment, a single speed of about one-half the normal sheet feeding speed was selected as the reduced sheet feeding speed.
It is to be appreciated that additional advantages accrue from the selection of a single reduced sheet feeding speed of one-half the normal sheet feeding speed. Video processing for each writing line is comparatively simple for a speed of one-half normal sheet feeding speed. Gamma correction, laser duty cycle, laser power, and developer voltage are also relatively simply handled.
Different methods of video processing in the printer
10
can be utilized for one-half normal sheet feeding speed. One method of video processing is to reduce the printhead scanning motor velocity so that each writing line of an image to be printed on a sheet of media
14
will take twice as long as at normal sheet feeding speed. A second method of video processing is to interlace a blank scan with each information-bearing scan during printing. This is sometimes called “skip-a-scan” or “scan-skipping”operation.
The skip-a-scan operation of the printer
10
can be implemented by different methods. According to one method, the raster image processor
62
alternately supplies the blank scans with the information-bearing scans. According to a second method, the engine controller
68
prints a blank scan by not asking the raster image processor
62
for an information-bearing scan. According to a third method, the control signal for sync pulses for the laser beam
34
is delayed for one cycle, corresponding to one facet of the polygonal mirror
36
. In the preferred embodiment, the engine controller
68
skipped a scan of one facet of the polygonal mirror
36
during the reduced sheet feeding speed operation by delaying the sync pulses for the laser beam
34
.
An additional advantage of skip-a-scan operation is that video switching times remain unchanged between the reduced sheet feeding speed and the normal sheet feeding speed, since the printhead scanning motor can operate at the same velocity as at normal sheet feeding speed. A second advantage of skip-a-scan operation is that unique parameters for gamma correction, laser duty cycle, laser power, and developer voltage are not necessarily required.
In operation, whenever any sheet of media
14
is printed, the computer program of
FIG. 5
adds a value associated with the width category of the media to the meltometer (Steps S
112
, S
120
, and S
126
). The value of the meltometer is then compared to a pair of thresholds (Steps S
108
and S
134
). The result of the comparisons determines whether over-temperature compensation of the fuser assembly
20
is invoked, if not currently active (Step S
130
), or ceased, if currently active (Step S
136
).
Categories of media width that have a tendency to increase the temperature of the fuser assembly
20
are assigned positive weighting factors (Steps S
112
, S
120
, and S
126
). Positive weighting factors are determined for each category of media width by:
Categories of media width that have a tendency to reduce the temperature of the fuser assembly
20
are assigned negative weighting factors (Steps S
112
, S
120
, and S
126
). Negative weighting factors are determined for each category of media width by:
In some special printing situations, it is advantageous immediately to invoke the reduced sheet feeding speed in order to prevent the fuser assembly
20
from reaching a high temperature. For these specific instances, the reduced sheet feeding speed is invoked when the sheets of media
14
are picked from the tray
16
,
28
. An example of a special printing situation in which the reduced sheet feeding speed is immediately invoked is the printing of an envelope on a belt-type fuser. Envelopes printed by such a belt-type fuser also require the reduced speed in order to provide sufficient energy to fuse properly.
It is to be appreciated that the value of the meltometer is not involved in selecting the reduced sheet feeding speed in special printing situations. However, the present invention does recognize that over-temperature compensation may be appropriate for special printing situations. In the preferred embodiment, if the value of the meltometer exceeds the upper threshold (Step S
108
) while the reduced sheet feeding speed is invoked, thus indicating that over-temperature compensation is appropriate, an inter-sheet gap is inserted in the printing of the sheets of media
14
to prevent overheating of the fuser assembly
20
.
Since the computer program can invoke different over-temperature compensation methods to reduce the temperature of the fuser assembly
20
, e.g. Employing a reduced sheet feeding speed or inserting an inter-sheet gap between consecutive sheets of media
14
, once an over-temperature method is invoked, it remains in operation until the program determines that over-temperature compensation is no longer required.
If the value of the meltometer is below the lower threshold value (Step S
134
), over-temperature compensation is eliminated, and normal sheet feeding operation is resumed.
If the printing of the sheets of media
14
is paused, and the temperature of the fuser assembly
20
drops below a reset temperature, the computer program resets the value of the meltometer to an initial, minimal value.
For purposes of exemplification, particular embodiments of the invention have been shown and described according to the best present understanding thereof. However, it will be apparent that various changes and modifications in the arrangement and construction of the parts thereof may be made without departing from the spirit and scope of the invention as defined in the appended claims.
Claims
- 1. A printer comprising:a media feed path for feeding sheets of media through said printer; a media transport mechanism for feeding said sheets of media at a standard speed and at a reduced speed along said media feed path; a media fixing mechanism for fixing toned images on said sheets of media at a standard temperature and at a reduced temperature; a media transport initiating mechanism for initiating feed of sheets of media at a standard gap and at an increased gap; means for detecting narrow media and for generating a narrow media signal when sheets of narrow media are fed through said media feed path; means for counting narrow media and for generating a signal representing the sheets of narrow media that have been fed through said printer; and a controller responsive to said narrow media detection means detecting media of a predefined category of narrow media for adjusting said media transport mechanism to feed sheets of said category at reduced speed and for adjusting said media fixing mechanism to fix at said reduced temperature, while said media transport initiating mechanism initiates sheet feed at said standard gap, until said counting means reaches a predetermined amount representing repetitive feeding of narrow media, said control also then adjusting said media fixing mechanism to initiate sheet feed at said increased gap.
- 2. The printer as in claim 1 in which said predefined category is envelopes.
- 3. The printer as in claim 2 in which said media fixing mechanism is a belt fuser.
- 4. The mechanism as in claim 2 in which said sheets are fed with side registration through said media fixing mechanism.
- 5. The printer as in claim 1 in which said media fixing mechanism is a belt fuser.
- 6. The mechanism as in claim 5 in which said sheets are fed with side registration through said media fixing mechanism.
- 7. The mechanism as in claim 1 in which said sheets are fed with side registration through said media fixing mechanism.
- 8. The mechanism as in claim 7 in which said sheets are fed with side registration through said media fixing mechanism.
US Referenced Citations (15)
Foreign Referenced Citations (9)
Number |
Date |
Country |
2-132481 |
May 1990 |
JP |
2-275483 |
Nov 1990 |
JP |
3-18883 |
Jan 1991 |
JP |
3-163464 |
Jul 1991 |
JP |
4-178677 |
Jun 1992 |
JP |
6-186875 |
Jul 1994 |
JP |
7-199694 |
Aug 1995 |
JP |
8-220928 |
Aug 1996 |
JP |
11-133790 |
May 1999 |
JP |