 |
Claims  |
|
|
What is claimed is:
1. A thermal-fixing-unit temperature control method for an image forming
apparatus which includes (a) an interim-image forming section for forming
a succession of interim images one at a time onto each of successive
record mediums based on a plurality of items of input image data
representing various object images, the successive record mediums being
fed one after another with staggered timing intervals, and (b) a thermal
fixing unit, disposed downstream of the interim-image forming section, for
receiving from the interim-image forming section the successive record
mediums one at a time and fixing the interim image formed on the
individual record medium, the thermal fixing unit including a heat roller,
in which a heat source is mounted, and a pressure roller coating with the
heat roller for feeding the individual record medium while the interim
image is fixed to the individual record medium under heat originated from
the heat source, said method being operable to control a temperature of
the thermal fixing unit and comprising the steps of:
(I) detecting the intervals of feeding of the individual record mediums one
interval after another;
(II) counting how many image forming jobs have been carried out by the
image forming apparatus from start-up of the image forming apparatus by
incrementing a count of image forming jobs for every individual interval
which is longer than a predetermined value, each of which jobs is composed
of one or more individual-image formings sequentially performed without
any intervals longer than the predetermined value;
(III) setting a target temperature of the thermal fixing unit based on the
then-current total number of image forming jobs counted in said step (II)
and the then-current interval detected in said step (I);
(IV) detecting a then-current temperature of the thermal fixing unit; and
(V) controlling the thermal intensity of the heat source so as to adjust
the temperature of the thermal fixing unit to the target temperature set
in said step (III) using the then-current temperature detected in said
step (IV).
2. A thermal-fixing-unit temperature control method as defined in claim 1,
wherein, when the then-current interval is larger than a predetermined
value, the target temperature of said thermal fixing unit is set in said
step (III) to be lower than a predetermined target temperature for a
successive image formation.
3. A thermal-fixing-unit temperature control method as defined in claim 2,
wherein the target temperature to be set in said step (III) when the
then-current interval is larger than the predetermined value is a
predetermined target temperature for the start-up of the image foming
apparatus.
4. A thermal-fixing-unit temperature control method as defined in claim 3,
wherein
the intervals of feeding of the individual record mediums are detected in
said step (II) in terms of the intervals of arriving of the individual
input image data to a mechanism control section in the image formation
apparatus, and
when the then-current interval of arriving of the individual input image
data exceeds a time corresponding to the predetermined value for the
interval of feeding, the then-current interval of feeding of the
individual record medium interval is judged in said step (III) to be
larger than the predetermined value.
5. A thermal-fixing-unit temperature control method as defined in claim 2,
wherein
the intervals of feeding of the individual record mediums are detected in
said step (II) in terms of the intervals of arriving of the individual
input image data to a mechanism control section in the image formation
apparatus, and
when the then-current interval of arriving of the individual input image
data exceeds a time corresponding to the predetermined value for the
interval of feeding, the then-current interval of feeding of the
individual record medium is judged in said step (III) to be larger than
the predetermined value.
6. A thermal-fixing-unit temperature control system in an image forming
apparatus which includes (a) an interim-image forming section for forming
a succession of interim images one at a time onto each of successive
record mediums based on a plurality of items of input image data
representing various object images, the successive record mediums being
fed one after another with staggered timing intervals, and (b) a thennal
fixing unit, disposed downstream of the interim-image forming section, for
receiving from the interim-image forming section the successive record
mediums one at a time and fixing the interim image formed on the
individual record medium, the thermal fixing unit including a heat roller,
in which a heat source is mounted, and a pressure roller coating with the
heat roller for feeding the individual record medium while the interim
image is fixed to the individual record medium under heat originated from
the heat source, said system being operable to control a temperature of
the thermal fixing unit and comprising:
(I) an interval detecting section for detecting the intervals of feeding of
the individual record mediums one interval after another;
(II) a job counting section for counting how many image forming apparatus
from start-up of the image forming apparatus by incrementing a count of
image forming jobs for every individual interval which is longer than a
predetermined value, each of which jobs is composed of one or more
individual-image formings sequentially performed without any intervals
longer than the predetermined value;
(III) a target-temperature setting section for setting a target temperature
of the thermal fixing unit based on the then-current total number of image
forming jobs counted by said job counting section and the then-current
interval detected by said interval detecting section;
(IV) a temperature detecting section for detecting a then-current
temperature of the thermal fixing unit; and
(V) a temperature control section, operatively connected to the heat
source, for controlling the thermal intensity of the heat source so as to
adjust a temperature of the thermal fixing unit to the target temperature
set by said target-temperature setting section using the then-current
temperature detected by said temperature detecting section.
7. A thermal-fixing-unit temperature control system as defined in claim 6,
wherein, when the then-current interval is larger than a predetermined
value, said target-temperature setting section is operable to set the
target temperature of said thermal fixing unit to a value lower than a
predetermined target temperature for a successive image formation.
8. A thermal-fixing-unit temperature control system as defined in the claim
7, wherein the target temperature to be set by said target-temperature
setting section when said record medium interval is larger than the
predetermined value is a predetermined target temperature for the start-up
of the image forming apparatus.
9. A thermal-fixing-unit temperature control system as defined in claim 8,
wherein
said interval detecting section is operable to detect the intervals of
feeding of the individual record mediums in terms of the intervals of
arriving of the individual input image data to a mechanism control section
in the image forming apparatus, and
said target-temperature setting section is operable to judge, when the
then-current interval of arriving of the individual input image data
detected by said interval detecting section exceeds a time corresponding
to the predetermined value for the interval of feeding, that the
then-current interval of feeding of the individual record medium becomes
larger than the predetermined value.
10. A thermal-fixing-unit temperature control system as defined in claim 7,
wherein
said interval detecting section is operable to detect the intervals of
feeding of the individual record mediums in terms of the intervals of
arriving of the individual input image data to a mechanism control section
in the image forming apparatus, and
said target-temperature setting section is operable to judge, when the
then-current interval of arriving of the individual input image data
detected by said interval detecting section exceeds a time corresponding
to the predetermined value for the interval of feeding, that the
then-current interval of feeding of the individual record medium becomes
larger than the predetermined value.
11. An image forming apparatus comprising:
(A) an interim-image forming section for forming a succession of interim
images one at a time onto each of successive record mediums based on a
plurality of items of input image data representing various object images,
the successive record mediums being fed one after another with staggered
timing intervals;
(B) a thermal fixing section, disposed downstream of said interim-image
forming section, for receiving from said interim-image forming section the
successive record mediums one at a time and fixing the interim image
formed on the individual record medium, said thermal fixing section
including a heat roller, in which a heat source is mounted, and a pressure
roller coacting with said heat roller for feeding the individual record
medium while the interim image is fixed to the individual record medium
under heat originated from the heat source;
(C) an interval detecting section for detecting the intervals of feeding of
the individual record mediums one interval after another;
(D) ajob counting secfion for counting how many image forming jobs have
been carried out by said image forming apparatus from start-up of said
image forming apparatus by incrementing a count of image forming jobs for
every individual interval which is longer than a predetermined value, each
of which jobs is composed of one or more individual-image formings
sequentially performed without any intervals longer than the predetermined
value;
(E) a target-temperature setting section for setting a target temperature
of said thermal fixing unit based on the then-current total number of
image forming jobs counted by said job counting section and the
then-current interval detected by said interval detecting section;
(F) a temperature detecting section for detecting a then-current temperawre
of said thermal fixing unit; and
(G) a temperature control section, operatively connected to said heat
source, for controlling the thermal intensity of said heat source so as to
adjust a temperature of said thermal fixing unit to the target temperature
set by said target-temperature setting section using the then-current
temperature detected by said temperature detecting section.
12. An image forming apparatus as defined in claim 11, wherein, when the
then-current interval is larger than a predetermined value, said
target-temperature setting section is operable to set the target
temperature of said thermal fixing unit to a value lower than a
predetermined target temperature for a successive image formation.
13. An image forming apparatus as defined in claim 12, wherein the target
temperature to be set by said target-temperature setting section when said
record medium interval is larger than the predetermined value is a
predetermined target temperature for the start-up of said image forming
apparatus.
14. An image forming apparatus as defined in claim 13, wherein
said interval detecting section is operable to detect the intervals of
feeding of the individual record mediums in terms of the intervals of
arriving of the individual input image data to a mechanism control section
in said image forming apparatus, and
said target-temperature setting section is operable to judge, when the
then-current interval of arriving of the individual input image data
detected by said interval detecting section exceeds a time corresponding
to the predetermined value for the interval of feeding, that the
then-current interval of feeding of the individual record medium becomes
larger than the predetermined value.
15. An image forming apparatus as defined in claim 12, wherein
said interval detecting section is operable to detect the intervals of
feeding of the individual record mediums in terms of the intervals of
arriving of the individual input image data to a mechanism control section
in said image forming apparatus, and
said target-temperature setting section is operable to judge, when the
then-current interval of arriving of the individual input image data
detected by said interval detecting section exceeds a time corresponding
to the predetermined value for the interval of feeding, that the
then-current interval of feeding of the individual record medium becomes
larger than the predetermined value. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to a thermal fixing unit which is for use in
an image forming apparatus including an electrophotographic recording
apparatus such as a copying machine, facsimile and laser printer using a
toner, and which thermally fixes an image transferred onto a record
medium, and more particularly, relates to a method and system for
controlling a temperature of the thermal fixing unit, and further to an
image forming apparatus based upon that temperature control technique for
the thermal fixing unit.
2) Description of the Related Art
In general, in an image forming apparatus (which will be referred
hereinafter to as a printer) including an electrophotographic recording
appartus such as a copying machine, a facsimile and a laser printer using
a toner, a thermal fixing unit, which thermally fixes a toner image
transferred onto a record medium (paper), is located along a record medium
conveyance path on the downstream side of a transferring system.
FIG. 16 is an illustration of a common construction of the thermal fixing
unit and a temperature control system therefor.
As shown in FIG. 16, a thermal fixing unit, designated at numeral 191, is
made up of a heating roller 192 containing a heat source 193 such as a
halogen lamp, and a pressure roller (backup roller) 194 for pressing a
record medium against the heating roller 192.
In addition, a temperature measuring section 195 and a temperature control
section 196 are provided as a temperature control system which takes
charge of controlling a surface temperature of the heating roller 192. The
temperature measuring section 195 is for measuring the surface temperature
of the heating roller 192, and is constructed with a thermo-sensitive
device such as a thermister, while the temperature control section 196 is
for executing the ON (lights)/OFF (lights-out) -control for the heat
source 193.
Secondly, referring to the flow chart (steps S1 to S8) of FIG. 17, a
description will be made hereinbelow of a prior control operation in a
printer including the aforesaid thermal fixing unit 191, and more
specifically, of an operation to be taken for when an operational
variation takes place from an ordinary printing operation to a Consecutive
printing operation or a stand-by mode.
After the completion of a predetermined initializing operation, upon
receipt of print data from a host unit such as a host computer, a printer
starts to print the print data onto a paper sheet (record medium) (step
S1). At this time, as will be described herein later, the surface
temperature of the heating roller 192 in the thermal fixing unit 191 is
controlled by the temperature control section 196 in accordance with
various kinds of printing conditions or requirements, for example, whether
or not the printer is in a consecutive printing operation and whether or
not being in a starting operation (intermittent printing; the first
printing to be done when the printing resumes from the stand-by mode).
After the completion of the printing of the print data from the host unit,
in the case of receiving the next print data before a paper discharge
sensor (not shown) detects a rear end portion of the paper sheet (YES
route from step S2), the temperature control section 196 sets the desired
temperature of the heating roller 192 to a target temperature to be
controlled for consecutive printing which will be mentioned herein later
(step S3), before a printing operation starts (step S1). Incidentally, the
aforesaid paper discharge sensor is designed to sense the fact that the
paper sheet rear end portion passes through the thermal fixing unit 191.
On the other hand, in the case that the reception of the next print data
does not take place before the paper discharge sensor detects the paper
sheet rear end portion (NO route from step S2), the temperature control
section 196 gets the controlled target temperature for the beating roller
192 to a tempetature Tsb for a stand-by mode which will be mentioned
herein later (step S4). Incidentally, in the step S4, in order to prevent
the excessive heating resulting from the event that the pressure roller
194 comes into contact with the heating roller 192, the controlled target
temperature by the heating roller 192 is merely set to the stand-by mode
temperature Tsb lower than the controlled target temperature for the
regular printing, which does not signify the actual advancement to the
stand-by mode.
Following this, a decision is made as to whether the next print data is
received or not (step S5), and a further decision is made on whether the
time t elapsed after the paper sheet rear end portion passes by the paper
discharge sensor of the thermal fixing unit 191 exceeds a predetermined
time (for example, 5 seconds) (step S6).
If the reception of the next print data occurs before the time t exceeds 5
seconds (NO route from step S6 and YES route from step S5), the
operational flow advances to the step S3 to continue the printing in a
consecutive printing mode.
On the other hand, if no transmission of the next print data takes place
although the time t exceeds 5 seconds (NO route of step S5 and YES route
of step S6), the printer stops in accordance with a given stop sequence,
and issues a stop command or the like to stop the rotation of its
photosensitive drum (step S7) and then goes into the stand-by mode to wait
for the next print data (print instruction) from the host unit (step S8).
Meanwhile, in case where the host unit such as a host computer makes a
request for printing to a printer, the print data is evolved in the host
unit or in a controller of the printer, and then transferred, together
with a print instruction, from the controller to a mechanism control
section within the printer. At this time, since the evolution or
development time of the print data depends upon printing patterns, the
evolution can be shorter or longer than the time required for the
preceding printing (preceding print time).
In the case of accomplishing the printing of a plurality of identical
patterns, or in the case that a print data evolution time is shorter than
the preceding print time as mentioned above, for example as shown in FIG.
18A, the printer implements the consecutive printing while conveying paper
sheets at its maximum print speed and at the minimum interval (distance)
between the paper sheets. FIG. 18A is an illustration of an example of an
output of a paper discharge sensor attainable when the printer conducts
the consecutive printing while conveying the paper sheets at the maximum
print speed and at the minimum interval.
On the other hand, if the next printing instruction (print data) does not
arrive in the printer because of no completion of the evolution of the
print data, although a predetermined time (for example, 5 seconds)
elapses, as mentioned before with reference to FIG. 17, the printer stops
the operations of the rotating system such as the photosensitive drum in
accordance with a given stop sequence, and proceeds to the stand-by mode
to go into the ready condition until receiving the next printing
instruction. Thereafter, when the printing instruction comes, the printing
is done in a predetermined printing start sequence. In an extreme example,
in the case that a printing instruction comes immediately after a
predetermined stand-by time elapses, after once stopping the printing in
accordance with a stop sequence, the printer immediately resumes the
printing through a restart sequence.
Furthermore, even in the case that the print data evolution time exceeds
the preceding print time, for example as shown in FIG. 18B, the printer
waits for the arrival of the next printing instruction by a predetermined
time (for example, 5 seconds) after the completion of the preceding
printing while operating the rotational drive system such as the rollers
192, 194 of the fixing unit 191, thereby surely suppressing the decrease
in throughput. FIG. 18B is an illustration of an output of a paper
discharge sensor when consecutive printing takes place in a state where
the interval between paper sheets (inter-paper interval) vanes.
In the case of assuming a ready condition while operating the rotational
drive system after the completion of the preceding printing as described
above, as mentioned with the step S4 of FIG. 17, fot the purpose of
avoiding even oxfly a little extra heating of the pressure roller 194, the
controlled target temperature for the fixing unit 191 (the controlled
target temperature for the heating roller 192) is switched to the stand-by
mode temperature Tsb at the time that the paper sheet rear end portion
passes by the paper discharge sensor. Since this stand-by mode temperature
Tsb is naturally set to be lower than the controlled target temperature
for the regular printing operation, the heat source 193 within the heating
roller 192 is virtually cut off forcedly by the temperature control
section 196. However, because the surface temperature of the heating
roller 192 does not immediately drop even if the heat source 193 is cut
off forcedly, the pressure roller 194 rotates while coining into contact
with the heating roller 192 whose temperature is substantially kept at the
controlled target temperature for the regular printing operation
The controlled target temperature to be given during the consecutive
printing is set to be higher than the controlled target temperature for
the first printing (at the printing start) to be taken for when the
printing resumes in response to the arrival of a printing instruction
during the stand-by mode, and for the following reason or situation.
That is, since it takes a long time to warm up the pressure roller 194 at
the start of printing, the fixing rate required is securable irrespective
of a low temperature of the heating roller 192. Conversely, if the
temperature of the heating roller 192 is not set to a relatively low
value, an excessive fixing condition is liable to occur to produce
wrinkles on paper sheets.
On the other hand, since the pressure roller 194 comes into contact with
paper sheets for a longer time but coming into contact with the heating
roller 192 for a shorter time during the consecutive printing, the
temperature of the pressure roller 194 does not easily rise. Particularly,
such a situation occurs noticeably in the case of performing the
consecutive printing while conveying the paper sheets at the maximum print
speed and at the minimum inter-paper interval (distance) as shown in FIG.
18A Accordingly, as mentioned above, the controlled target temperature to
be taken during the consecutive printing is set to be higher than the
controlled target temperature for the start of the printing.
However, when the inter-paper interval is prolonged halfway because of the
problems about the data evolution time or the like even during the
consecutive printing, since the pressure roller 194 is heated in a state
of rotating while coming into contact with the heating roller 292
maintained substantially at the controlled target temperature for the
regular printing operation as mentioned before, the temperature of the
pressure roller 194 naturally tends to rise.
Meanwhile, in the recent years, as the pressure roller 194, there has been
employed a roller made of a sponge (which will be referred hereinafter to
as a sponge roller). The sponge roller is easier to warm up as compared
with a prior toiler made of a rubber, and therefore, the employment of the
spouse roller as the pressure roller 194 permits the temperature of the
heating roller 192 to be set to a relatively low value. In addition, since
the entire fixing unit also becomes easy to warm up, the shortening of the
time period needed for the warming-up of the printer at the initial
operation becomes feasible.
However, in the case that the aforesaid easy-to-warm sponge roller with a
high thermal insulation effect is employed as the pressure roller 194, if
the inter-paper interval is prolonged (varies) during the consecutive
printing as shown in FIG. 18B, the temperature of the pressure roller 194
has a stronger tendency to rise.
The fixing conditions depend upon the temperature of the pressure roller
194 as well as the temperature of the heating roller 192, and hence, if
the sponge roller is used as the pressure roller 194, the fixing is liable
to go into an excessive condition. That is, the prolongation of the
inter-paper interval destroys the balance between the fixing rate and the
occurrence of wrinkles, which is excellent in a short inter-paper interval
condition, so that wrinkles appear on the paper sheet after the fixing.
For instance, if the maximum paper sheet conveying speed is set to 83
mm/sec, even in the consecutive printing, the shortest inter-paper
interval is at 39 mm while the longest inter-paper interval assumes
39+83.times.5=454 mm, the range therebetween becomes extremely wide. When
the inter-paper interval approaches the longest, as mentioned previously,
the temperature of the pressure roller 194 reaches a considerable high
value. Nevertheless, in the case of the prior temperature control
technique described with reference to FIG. 17, since, when print data
arrives within 5 seconds after the passage of a paper sheet, the printing
is implemented in a manner that the controlled target temperature for the
heating roller 192 is set to the controlled target temperature to be taken
during the consecutive printing, the next paper sheet is excessively
heated by the heating roller 192 and the pressure roller 194. with the
result that wrinkles appear on the paper sheet after the fixing.
Particularly, due to the recent progress of OA (Office Automation), there
is a greater tendency for the print data evolution time to greatly vary
because various types of data mixes on one page. Accordingly, the
expectation exists that, even if the print data evolution time thus
greatly varies, that is, even if the inter-paper interval within the
printer greatly varies the occurrence of wrinkles on paper sheets after
the fixing is certainly preventable to enhance the print quality.
In addition, in recent years, in general, there is an environmental
tendency for a plurality of users to make a request, to printers connected
to a network, for various kinds of printing processing at an arbitrary
time. Accordingly, the expectation in the thermal fixing also exists that,
even under such an environment, the maintenance of the print quality and
the prevention of the decrease in throughput are achievable to improve the
performance of an information processing system.
SUMMARY OF THE INVENTION
The present invention has been developed with a view to eliminating these
problems, and it is therefore an object of this invention to provide a
temperature control method and system for a thermal fixing unit and an
image forming apparatus which arc capable of adjusting the balance between
the fixing rate and the occurrence of wrinkles irrespective of a great
variation of an interval between paper sheets within a printer to surety
prevent the occurrence of wrinkles on paper sheets after the fixing so
that the print quality is improbable.
For this purpose, in accordance with this invention, there is provided a
thermal fixing unit temperature control method of controlling a
temperature of a thermal fixing unit which is equipped with a heating
roller containing a heat source and a pressure roller for pressing a
record medium against the heating roller to thermally fix an image
transferred onto the record medium in an image forming apparatus. the
temperature control method comprising the steps of, when image formation
is consecutively effected onto a plurality of record mediums without
stopping the image forming apparatus, detecting an interval between the
plurality of record mediums, switching and setting a controlled target
temperature for the thermal fixing unit in accordance with the interval
between the record mediums, and controlling the heat source so that the
temperature of the thermal fixing unit reaches the controlled target
temperature.
In addition, in accordance with this invention, there is provided a
temperature control system for controlling a temperature of a thermal
fixing unit including a heating roller containing a heat source and a
pressure roller for pressing a record medium against the heating roller to
thermally fix an image transferred onto the record medium in an image
forming apparatus, the temperature control system comprising an interval
detecting section for, when an image formation is consecutively effected
onto a plurality of record mediums without stopping an operation of the
image forming apparatus, detecting an interval between the plurality of
record mediums, a controlled target temperature switching and setting
section for switching and setting a controlled target temperature for the
thermal fixing unit in accordance with the interval between the record
mediums detected by the interval detecting section, a temperature
detecting section for detecting a temperature of the thermal fixing unit,
and a temperature control section for controlling the heat source so that
the detection result by the temperature detecting section coincides with
the controlled target temperature set by the controlled target temperature
switching and setting section.
Furthermore, in accordance with this invention, there is provided an image
forming apparatus comprising an image forming section for transferring and
forming an image on a record medium, a thermal fixing unit including a
heating roller containing a heat source and a pressure roller for pressing
the record medium against the heating toiler to thermally fix the image
transferred by the image forming section on the record medium, an interval
detecting section for, when an image formation is consecutively effected
onto a plurality of record mediums without stopping the image forming
section, detecting an interval between the plurality of record mediums, a
controlled target temperatare switching and setting section for switching
and setting a controlled target temperatnre for the thermal fixing unit in
accordance with the interval between the record mediums detected by the
interval detecting section, a temperature detecting section for detecting
a temperature of the thermal fixing unit, and a temperature control
section for controlling the heat source so that the detection result by
the temperature detecting sectioa coincides with the controlled target
temperature set by the controlled target temperature switching and setting
section.
Thus, in the thermal fixing unit temperature control method and system and
the image forming apparatus according to this invention, since the
controlled target temperature is switched and set in accordance with the
interval between the recotd mediums, even if the interval between the
record mediums greatly varies within the image forming apparatus, it is
possible to certainly suppress the occurrence of a problem in that the
pressure roller is excessively heated by the heating roller to produce
excessive fixing, which allows the balance between the fixing rate and the
occurrence of wrinkles to be suitably adjustable, thus surely preventing
the occurrence of wrinkles on paper sheets after the fixing to noticeably
enhance the print quality.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an illustration useful for describing an aspect of a temperature
control method for a thermal fixing unit according to the present
invention;
FIG. 2 is a block diagram showing an aspect of a temperature control system
for a thermal fixing unit according to this invention;
FIG. 3 is a block diagram showing an aspect of an image forming apparatus
according to this invention:
FIG. 4 is a perspective view showing an appearance of a printer (image
forming apparatus) according to an embodiment of this invention;
FIG. 5 is a side-elevational and cross-sectional view showing an internal
structure of the printer according to this embodiment;
FIG. 6 is a block diagram showing an arrangement of a control system in the
printer according to this embodiment;
FIG. 7 is a block diagram showing a functional arrangement of a thermal
fixing unit temperature control section (temperature control system)
provided in the printer according to this embodiment;
FIG. 8 is a flow chart useful for explaining an operation of the thermal
fixing unit temperature control section in the printer according to this
embodiment;
FIG. 9 is a flow chart available for explaining an operation of the printer
in a stand-by mode and at a printing start according to this embodiment;
FIG. 10 is a flow chart available for describing an operation of the
printer in a sleep mode according to this embodiment;
FIG. 11 is a flow chart useful for describing an operation of the printer
at a printing start according to this embodiment;
FIG. 12 is a flow chart useful for describing an operation of the printer
at a print start according to this embodiment;
FIG. 13 is a flow chart useful for explaining an operation of the printer
at a printing start according to this embodiment;
FIG. 14 is a flow chart useful for explaining an operation of the printer
at a printing start according to this embodiment;
FIG. 15 is a flow chart available for describing an operation of the
printer at a consecutive printing according to this embodiment;
FIG. 16 is a block diagram showing a common construction and temperature
control system of a thermal fixing unit;
FIG. 17 is a flow chart for describing a prior control operation of a
printer including a thermal fixing unit;
FIG. 18A is an illustration of an output of a paper discharge sensor to be
taken when a consecutive printing is conducted in a state where paper
sheets are fed at a maximum print speed and at a minimum interval between
paper sheets; and
FIG. 18B is an illustration of an output of a paper discharge sensor to be
taken when a consecutive printing is done in a state where the interval
between paper sheets varies.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[A] Description of an Aspect of this Invention
FIG. 1 is an illustration useful for describing an aspect of a temperature
control method for a thermal fixing unit according to the present
invention. As shown in FIG. 1, the thermal fixing unit temperature control
method according to this invention is for controlling a temperature of a
thermal fixing unit including a heating roller containing a heat source
and a pressure roller for pressing a record medium against the heating
roller to thermally fix an image transferred onto the record medium in an
image forming apparatus, and comprises the steps of detecting an interval
between record mediums (record medium interval) in case where consecutive
image formation is done onto a plurality of record mediums without
stopping an operation of the image forming apparatus (step S11), switching
and setting a target temperature to be controlled (controlled target
temperature) for the thermal fixing unit in accordance with the record
medium interval (step S12), and controlling the heat source so that the
temperature of the thermal fixing unit becomes equal to the controlled
target temperature (step S13).
In the step S12, when the record medium interval is greater than a
predetermined value, the controlled target temperature for the thermal
fixing unit can also be switched and set to be lower than a controlled
target temperature preset for a consecutive image formation. In this case,
that controlled target temperature can be the controlled target
temperature preset for the start of printing.
Furthermore, in the step S11, the record medium interval is detected as an
arrival time interval of image formation data at a mechanism control
section within the image forming apparatus, and in the step S12, when the
arrival time interval detected exceeds a time interval corresponding to
the aforesaid predetermined value, a decision can be made to that the
record medium interval becomes longer than the aforesaid predetermined
value so that the switching and setting of the controlled target
temperature for the thermal fixing unit are done.
FIG. 2 is a block diagram showing one aspect of a temperature control
system for a thermal fixing unit according to this invention. As shown in
FIG. 2, the temperature control system for a thermal fixing unit according
to this invention is for controlling a temperature of a thermal fixing
unit 10 comprising a heating roller 11 having a heat source 12 therein and
a pressure roller 13 for pressing a record medium 1 against the heating
roller 11 to thermally fix an image transferred onto the record medium 1
in an image forming apparatus, and is composed of an interval detecting
section 21, a controlled target temperature switching and setting section
22, a temperature detecting section 23 and a temperature control section
24.
In this arrangement, in the case that image formation is consecutively
performed with respect to a plurality of record mediums without stopping
the operation of the image forming apparatus, the interval detecting
section 21 detects the interval between the record mediums 1. The
controlled target temperature switching and setting section 22 switches
and sets the controlled target temperature for the thermal fixing unit 10
| | |
