U.S. patent application number 11/472418 was filed with the patent office on 2007-01-11 for image forming apparatus.
This patent application is currently assigned to BROTHER KOGYO KABUSHIKI KAISHA. Invention is credited to Daisuke Ogawa.
Application Number | 20070007717 11/472418 |
Document ID | / |
Family ID | 37583383 |
Filed Date | 2007-01-11 |
United States Patent
Application |
20070007717 |
Kind Code |
A1 |
Ogawa; Daisuke |
January 11, 2007 |
Image forming apparatus
Abstract
An image forming apparatus includes: a sheet transport mechanism
including: a sheet feeding unit; an attitude correction unit that
corrects an attitude of a sheet; and a drive source; a first
actuator that operates upon receipt of supply of power from a power
source, when a sheet feeding command is issued, and transmits power
of the drive source to the sheet feeding unit to commence driving
of the sheet feeding unit; a second actuator that operates upon
receipt of power from the power source and controls the attitude
correction unit into an attitude correctable state, when a
transported sheet has approached the attitude correction unit; and
a control unit that determines an operation start timing of the
first actuator, operation of the first actuator, which transports
the next sheet after transport of one sheet, starting after
operation of the second actuator for the one sheet has been
completed.
Inventors: |
Ogawa; Daisuke; (Nagoya-shi,
JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
BROTHER KOGYO KABUSHIKI
KAISHA
|
Family ID: |
37583383 |
Appl. No.: |
11/472418 |
Filed: |
June 22, 2006 |
Current U.S.
Class: |
271/226 |
Current CPC
Class: |
B65H 2404/7231 20130101;
B65H 2513/50 20130101; B65H 2513/50 20130101; B65H 5/062 20130101;
B65H 2220/02 20130101; B65H 2301/512125 20130101; B65H 2403/40
20130101; B65H 9/106 20130101; B65H 9/006 20130101; B65H 3/0669
20130101 |
Class at
Publication: |
271/226 |
International
Class: |
B65H 9/00 20060101
B65H009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 22, 2005 |
JP |
2005-182214 |
Claims
1. An image forming apparatus comprising: a sheet transport
mechanism including: a sheet feeding unit that feeds a sheet from a
sheet feeding cassette; an attitude correction unit that corrects
an attitude of the sheet fed from the sheet feeding unit; and a
drive source that drives the sheet feeding unit and the attitude
correction unit; a first actuator that operates upon receipt of
supply of power from a power source, when a sheet feeding command
is issued, and transmits power of the drive source to the sheet
feeding unit to commence driving of the sheet feeding unit; a
second actuator that operates upon receipt of power from the power
source and controls the attitude correction unit into an attitude
correctable state, when a transported sheet has approached the
attitude correction unit; and a control unit that determines an
operation start timing of the first actuator, operation of the
first actuator, which transports the next sheet after transport of
one sheet, starting after operation of the second actuator for the
one sheet has been completed.
2. The image forming apparatus according to claim 1, further
comprising: a storage unit that stores an operation status of the
second actuator, wherein the control unit determines whether or not
operation of the second actuator has been completed based on the
operation status of the second actuator.
3. The image forming apparatus according to claim 2, further
comprising: a detection sensor that detects an approach of a sheet
to the attitude correction unit, wherein operation of the second
actuator is controlled so as to stop after elapse of a
predetermined period of time since start of operation; the storage
unit stores a time when the detection sensor detects an approach of
a sheet; and the control unit uses the time when the detection
sensor detects an approach of a sheet as a time when the second
actuator is to start operation, and the control unit determines
whether or not operation of the second actuator has been completed
based on elapse of the predetermined period of time since the
operation start time of the second actuator stored in the storage
unit.
4. The image forming apparatus according to claim 2, wherein data
pertaining to an operating status of the second actuator with
regard to one sheet are erased before the first actuator starts
operation to transport the next sheet; and when operation of the
second actuator is again started in association with transport of
the next sheet, an operating status of the second actuator is
stored in the storage unit.
5. The image forming apparatus according to claim 1, further
comprising a relay roller that is rotated at all times, wherein:
the relay roller is interposed between the sheet feeding unit and
the attitude correction unit; and when transport of a sheet from
the sheet feeding unit has once been started, the sheet is
transported up to the attitude correction unit without being
stopped in a sheet transport path.
6. The image forming apparatus according to claim 1, further
comprising a transmission gear that transmits power, wherein: the
sheet feeding unit and the attitude correction unit are connected
to the drive source by the transmission gear; and the sheet feeding
unit and the attitude correction unit rotate upon receipt of a
supply of driving force from the drive source.
7. The image forming apparatus according to claim 1, further
comprising: an operation interval determination unit that
determines an operation interval time of the first actuator such
that the number of operations of the first actuator per unit time
does not exceed a preset number, wherein the control unit
determines the operation start timing of the first actuator to
start operation of the first actuator with regard to the next sheet
after operation of the second actuator for the one sheet has been
completed and the operation interval time has elapsed since the
start of operation of the first actuator for the one sheet.
8. An image forming apparatus comprising: a sheet transport
mechanism including: a sheet feeding unit that feeds a sheet from a
sheet feeding cassette; an attitude correction unit that corrects
an attitude of the sheet fed from the sheet feeding unit; and a
drive source that drives the sheet feeding unit and the attitude
correction unit; a first actuator that operates upon receipt of
supply of power from a power source every time a sheet feeding
command is issued and transmits power of the drive source to the
sheet feeding unit to commence driving of the sheet feeding unit; a
second actuator that operates upon receipt of power from the power
source, when a transported sheet has approached the attitude
correction unit, to control the attitude correction unit into an
attitude correctable state; and an operation interval determination
unit that determining an operation interval time of the first
actuator such that the number of operations of the first actuator
per unit time does not exceed a preset number; and a control unit
that determines operation start timing of the first actuator,
operation of the first actuator for the next sheet starting after
the operation interval time has elapsed since the start of
operation of the first actuator for one sheet.
9. The image forming apparatus according to claim 1, wherein the
sheet feeding unit is a sheet feeding roller; the attitude
correction unit is registration rollers; and the drive source is a
main motor.
10. The image forming apparatus according to claim 9, wherein
roller shafts of the sheet feeding roller and the registration
rollers are connected to the main motor by a transmission gear; and
the sheet feeding roller and the registration rollers rotate upon
receipt of a supply of driving force from the main motor.
Description
CROSS-REFERENCE TO THE RELATED APPLICATION(S)
[0001] This application is based upon and claims a priority from
prior Japanese Patent Application No. 2005-182214 filed on Jun. 22,
2005, the entire contents of which are incorporated herein by
reference.
TECHNICAL FIELD
[0002] Aspects of the present invention relate to an image forming
apparatus.
BACKGROUND
[0003] A conventional image forming apparatus transports a sheet
placed on a sheet feeding cassette to a transfer position (a nip
position between a photosensitive drum and a transfer roller) by a
plurality of rollers, thus forming a desired image on the sheet. As
disclosed in JP-A-2005-114754, a sheet feeding roller, registration
rollers, a transfer roller, a heating roller, a pressurization
roller and a sheet discharge roller are sequentially arranged along
a sheet transport path in the image forming apparatus. When
transport of the sheet is started by a driving action of the sheet
feeding roller, the transported sheet is delivered first to the
registration rollers. The registration rollers correct the attitude
of the transported sheet. The registration rollers normally rotate.
However, when the sheet approaches the registration rollers, the
registration rollers halt temporarily. When a leading end of the
sheet comes into contact with the stationary registration rollers,
the attitude of the sheet is corrected.
[0004] Subsequently, by means of a driving action of the
registration rollers, the sheet is delivered to the transfer
roller. In association with the sheet passing by the transfer
roller, a toner image is formed on the sheet. In association with
the sheet passing by the heating/pressurization roller, the toner
image is thermally fixed and subsequently discharged.
[0005] The respective rollers are connected to the motor, which
acts as a drive source, by way of a relay gear (a power
transmission mechanism), and receive power from the motor. The
sheet feeding roller and the registration rollers are each provided
with a clutch mechanism (of electromagnetic type having a solenoid
switch) that intermittently transmits power to the sheet feeding
roller or the registration roller. The reason why the sheet feeding
roller is provided with a clutch mechanism is that sheets must be
fed intermittently one at a time. When an excitation current is
supplied to the coil of the solenoid switch, the power transmission
mechanism is connected to the solenoid switch, to thus rotate the
sheet feeding roller.
[0006] In the meantime, as mentioned previously, the reason why the
registration rollers are provided with the clutch mechanism is for
temporarily stopping rotation of the roller in association with an
approach of the sheet. When an excitation current is supplied to
the coil of the solenoid switch for the registration rollers, the
power transmission mechanism is disconnected, whereupon rotation of
the rollers stops.
SUMMARY
[0007] As mentioned above, when solenoid switches are used for the
registration rollers and the sheet feeding roller respectively,
there is a potential risk of a coincidence arising between the
timings at which an electric current is supplied to coils of both
solenoid switches. Specifically, in the image forming apparatus, a
transport interval between sheets is determined in advance, and an
electric current is supplied to the solenoid for the sheet feeding
roller in synchronism with the transport interval. However, the
timing when the transported sheet approaches the registration
rollers may coincide with the timing when the next sheet is
transported (an area enclosed by a dashed line in FIG. 10A).
[0008] Exciting the coil of the solenoid switch usually requires a
comparatively large electric current. Hence, when the timings of
supply of an electric current to the coils of both solenoid
switches coincide with each other, there may arise a case where a
load exceeds the performance of the power source, thereby hindering
stable supply of power. In such a case, in order to offset the
timings of supply of an electric current to the coils of both
solenoid switches, it is better to control the timing when the
sheet, whose transport has been started, approaches the
registration rollers. To implement control of approach timing,
providing a mechanism for temporarily stopping transport of the
sheet between the sheet feeding roller and the registration rollers
is conceivable. However, this leads to an increase in the number of
components, which increases the cost.
[0009] In addition, in order to offset timings of an electric
current supply to the coils of both solenoid switches, setting
custom layouts for the respective registration rollers is
conceivable. Specifically, the layout of the registration rollers
is determined beforehand such that the timing of an approach of the
transported sheet to the registration rollers does not coincide
with the timing of transport of the next sheet.
[0010] In recent years, some image forming apparatus use sheet
feeding cassettes C1, C2 arranged in layers, pursuant to the user's
request (see FIG. 11). In this case, transporting a sheet from the
lower cassette C2 results in an increase in a transport length from
a transport start position to the registration rollers, when
compared with a case where a sheet is transported from the upper
cassette C1. As shown in FIG. 10B, when a sheet is fed from the
lower cassette C2, the timing of an approach of a sheet to the
registration rollers becomes delayed as compared with a case where
the sheet is fed from the upper cassette (the area enclosed by a
dashed line in FIG. 10B).
[0011] For instance, in a case where the sheet is fed from the
cassette C1, even when the timings of supply of an electric current
to the coils of the solenoid switches are offset from each other,
there will arise a case where the timings of supply of an electric
current to the coils of both solenoid switches coincide with each
other if a sheet is fed from the cassette C2.
[0012] Aspects of the present invention provide an image forming
apparatus that can avoid simultaneous supply of an electric current
to both solenoid switches, without increasing the number of
components.
[0013] In order to achieve the above object, according to an aspect
of the invention, there is provided an image forming apparatus
including: a sheet transport mechanism including: a sheet feeding
unit that feeds a sheet from a sheet feeding cassette; a attitude
correction unit that corrects an attitude of the sheet fed from the
sheet feeding unit; and a drive source that drives the sheet
feeding unit and the attitude correction unit; a first actuator
that operates upon receipt of supply of power from a power source,
when a sheet feeding command is issued, and transmits power of the
drive source to the sheet feeding unit to commence driving of the
sheet feeding unit; a second actuator that operates upon receipt of
power from the power source and controls the attitude correction
unit into an attitude correctable state, when a transported sheet
has approached the attitude correction unit; and a control unit
that determines an operation start timing of the first actuator,
operation of the first actuator, which transports the next sheet
after transport of one sheet, starting after operation of the
second actuator for the one sheet has been completed.
[0014] According to the aspect of the invention, the first and
second actuators are prevented from being simultaneously actuated;
namely, the actuators are prevented from being simultaneously
supplied with a drive current from the power source. As a result, a
load exceeding the performance of the power source is avoided.
Hence, power is stably supplied from the power source, thereby
rendering operation of the image forming apparatus stable.
[0015] Operation timings of the actuators is controlled by the
control unit. Hence, devices dedicated for the control unit are
minimized. Accordingly, there is no risk of a significant increase
in the number of components.
[0016] According to another aspect of the invention, there is
provided an image forming apparatus including: a sheet transport
mechanism including: a sheet feeding unit that feeds a sheet from a
sheet feeding cassette; an attitude correction unit that corrects
an attitude of the sheet fed from the sheet feeding unit; and a
drive source that drives the sheet feeding unit and the attitude
correction unit; a first actuator that operates upon receipt of
supply of power from a power source every time a sheet feeding
command is issued and transmits power of the drive source to the
sheet feeding unit to commence driving of the sheet feeding unit; a
second actuator that operates upon receipt of power from the power
source, when a transported sheet has approached the attitude
correction unit, to control the attitude correction unit into an
attitude correctable state; and an operation interval determination
unit that determining an operation interval time of the first
actuator such that the number of operations of the first actuator
per unit time does not exceed a preset number; and a control unit
that determines operation start timing of the first actuator,
operation of the first actuator for the next sheet starting after
the operation interval time has elapsed since the start of
operation of the first actuator for one sheet.
[0017] According to the aspect of the invention, the current supply
time during which a drive current is supplied to the first actuator
per unit time is maintained at an appropriate value. Consequently,
heating of the first actuator, which would otherwise be caused when
an electric current exceeding an appropriate amount of electric
current flows into the first actuator, can be prevented, whereby
operation of the image forming apparatus becomes stable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] These and other objects and advantages of the present
invention will be more fully apparent from the following detailed
description taken in conjunction with the accompanying drawings, in
which:
[0019] FIG. 1 is a side cross sectional view of a laser
printer;
[0020] FIG. 2 is a cross sectional view showing that an MP tray is
opened;
[0021] FIG. 3 is a view showing a power transmission mechanism;
[0022] FIG. 4 is a partially enlarged view of sheet transport
paths;
[0023] FIG. 5 is a block diagram showing an electrical
configuration of the laser printer;
[0024] FIG. 6 is a flowchart showing procedures by which an ASIC
determines a sheet transfer timing;
[0025] FIG. 7 is a timing chart showing a case where a sheet has
been transported from a sheet feeding cassette C1;
[0026] FIG. 8 is a view showing the configuration of memory;
[0027] FIG. 9 is a timing chart acquired when a sheet has been
transported from a sheet feeding cassette C2;
[0028] FIGS. 10A and 10B are views showing current supply timings
of a related art example; and
[0029] FIG. 11 is a view showing a related art image forming
apparatus.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE ASPECTS
[0030] One aspect of the present invention will be described by
reference to FIGS. 1 through 9.
[0031] FIG. 1 is a side cross sectional view of a laser printer
according to the aspect.
[0032] In a laser printer (an image forming apparatus) 10, a
cassette housing section 12 is provided at a bottom portion of a
main body casing 11. A sheet feeding cassette C1, where sheets
employed as a recording medium are accommodated in layers, is
loaded into the cassette housing section 12. This laser printer 10
can be additionally provided with other sheet feeding cassettes. In
the present aspect, the laser printer 10 is additionally provided
with another sheet feeding cassette; namely, a sheet feeding
cassette C2 is disposed beneath the sheet feeding cassette C1. In
the following descriptions, the right side in FIG. 1 is taken as a
front side of the apparatus.
[0033] Sheet transport paths are formed within the main body casing
11. During the course of the sheets fed from the respective sheet
feeding cassettes C1, C2 being transported over the sheet transport
paths, toner images are formed on the sheets. The thus formed toner
images are thermally fixed by a fixing unit 36, whereby desired
images are formed (detailed description thereof will be provided
later).
[0034] The sheet transport paths are routed as designated by dashed
lines in FIG. 1. In the case of a sheet transport path L1 for the
sheet feeding cassette C1, the sheet transport path is inverted
toward a rear side of the laser printer 10 at a front upper section
of the sheet feeding cassette C1 about 180.degree.. Then, the sheet
is horizontally transported toward the rear side of the laser
printer 10. The sheet is then inverted about 180.degree. toward the
front of the laser printer 10 at the rear side of the laser printer
10, and the sheet reaches a sheet discharge section 14 provided on
an upper wall surface of the main body casing 11.
[0035] In the case of a sheet transport path L2 of the sheet
feeding cassette C2, a sheet is fed in an obliquely upward
direction from the front edge of the sheet feeding cassette C2, and
the sheet travels upwardly over the path. After the sheet has
ascended by the amount essentially corresponding to the height of
the sheet feeding cassette C2, the sheet transport path L2 is
merged with the sheet transport path L1 for the sheet feeding
cassette C1. Specifically, the sheet transport path L2 for the
sheet transported from the sheet feeding cassette C2 is longer than
the sheet transport path L1 for the sheet feeding cassette C1 by
the amount corresponding to the distance from the start of
transport to the merge.
[0036] As shown in FIG. 2, in the laser printer 10 of the present
aspect, a portion of a front wall 15 rotates about a hinge 16 and
is maintained in a horizontal position as illustrated. This pivotal
portion corresponds to an MP tray 17, by means of which a sheet can
be manually inserted. As illustrated, the sheet on the MP tray 17
is delivered rearward of the laser printer 10 from the MP tray 17
and is subsequently merged with the sheet transport path L1 of the
sheet feeding cassette C1. A sheet transport path L3 of the MP tray
17 is shorter than the sheet transport path L1 of the sheet feeding
cassette C1. Of all the sheet transport paths L1 to L3, the sheet
transport path L3 is the shortest. Thus, the laser printer 10 is
provided with the three sheet transport paths L1 to L3 that differ
from each other in terms of a transport length.
[0037] A mechanism for forming an image on a sheet will now be
described briefly.
[0038] Various rollers (a sheet transport mechanism) are arranged
along the sheet transport path (a description is provided
hereinbelow while taking the sheet transport path L1 for the sheet
feeding cassette C1 as an example) in order to transport a sheet as
shown in FIG. 1. Specifically, a sheet feeding roller (a sheet
feeding unit) 21, a relay roller 23, registration rollers (an
attitude correction unit) 25, a transfer roller 27, a heating
roller 38 and a sheet discharge roller 39 are sequentially
arranged. The rotary shafts of the respective rollers are coupled
to a rotary shaft M1 of a main motor (a drive source) M by way of a
transmission gear G, and the respective rollers rotate upon receipt
of the driving force of the main motor M.
[0039] FIG. 3 shows a portion of the drive system of the laser
printer 10. Reference symbol M in the drawings designates the main
motor; M1 designates the rotary shaft of the main motor; 21A
designates a rotary shaft of the sheet feeding roller 21 for the
sheet feeding cassette C1; 23A designates a rotary shaft of the
relay roller 23; 25A designates a rotary shaft of the registration
rollers 25; and G1 to G8 designate transmission gears. For example,
in the case of the rotary shaft 21A for the sheet feeding roller,
driving force of the main motor M is transmitted by way of the
transmission gear G1.fwdarw.the transmission gear G2.fwdarw.the
transmission gear G3.fwdarw.the transmission gear G4.fwdarw.the
transmission gear G5. The group of transmission gears is called a
power transmission mechanism in the following descriptions.
[0040] The sheet feeding roller 21 is for feeding a sheet placed on
the sheet feeding cassette C1 to the relay roller 23. The sheet
must be transport one sheet at a time. When a plurality of sheets
are sequentially transported, the rotation of the roller must be
temporarily stopped during the course of transport of the sheets.
The power transmission mechanism of the sheet feeding roller 21 is
provided with an electromagnetic clutch mechanism (corresponding to
a first actuator of the present invention) 60A (see FIG. 3).
[0041] The clutch mechanism 60A is formed chiefly from a
transmission gear (i.e., the transmission gear G5 in the present
aspect), which has along an outer periphery thereof a
lock-receiving section 71; a lock arm 61 for regulating rotation of
the transmission gear G5; and a solenoid switch 65A. The lock arm
61 is provided so as to be pivotable about a hinge 62. A latch claw
63 is provided at the extremity of the lock arm 61, and the latch
claw 63 engages with the lock receiving section 71 of the
transmission gear G5.
[0042] A partial notch is formed in each of a large diameter teeth
section 73 and a small diameter teeth section 74, which are
provided on the transmission gear G5 (FIG. 3 shows only a notch of
the large diameter teeth section 73, and this notch is hereinbelow
taken as a notch section 75). When the latch claw 63 remains
engaged with the lock receiving section 71, settings are made such
that the notch section 75 of the large diameter teeth section 73
and the notch section 75 of the small diameter teeth section 74
exactly come to positions where the notch sections 75 engage with
other, adjacent transmission gears (a gear provided on the rotary
shaft 21A and the transmission gear G4).
[0043] By means of these settings, the large diameter teeth section
73 of the transmission gear G5 and the adjacent transmission gear
G4 are maintained so as not to mesh with each other, and the small
diameter teeth section 74 and the gear section of the rotary shaft
21A are maintained so as not to mesh with each other. Thereby,
power transmission between the shaft M1 and the shaft 21A is
disconnected (hereinafter described as interrupted); namely,
driving (rotation) of the sheet feeding roller 21 is stopped.
[0044] It is better to activate the solenoid switch 65A, when the
sheet feeding roller 21 is rotated from such a state. The solenoid
switch 65A has an advancing-and-receding shaft 66A. The
advancing-and-receding shaft 66A can be withdrawn upwardly in the
drawing by means of supplying an excitation current to the coil.
Thus the entire lock arm 61 pivots in an unlocking direction about
the hinge 62, whereupon the latch claw 63 is disengaged from the
lock receiving section 71, so that the transmission gear G5 becomes
pivotable.
[0045] At that time, as a result of the transmission gear G5
receiving impelling force from the impelling unit, the transmission
gear G5 rotates through a predetermined angle in the direction of
arrow A in the drawing, whereby the notch sections 75 come out of
the position where the notch sections 75 mesh with the other,
adjacent transmission gears. Thus, the teeth of the respective
gears mesh with each other, so that a power transmittable state
(hereinafter called a "connected state") is achieved.
[0046] The sheet feeding cassette C2 is provided with the custom
designed sheet feeding roller 41, and the MP tray 17 is provided
with a sheet feeding roller 45. Moreover, the sheet feeding roller
41 is provided with a custom designed electromagnetic clutch
mechanism and a solenoid switch 65C, and the sheet feeding roller
45 is provided with a custom designed electromagnetic clutch
mechanism and a solenoid switch 65D (see FIG. 5).
[0047] The relay roller 23 is for relaying the sheet fed by the
sheet feeding roller 21 so as to reach the registration rollers 25,
and the relay roller 23 is rotated all times. Here, "rotated at all
times" means that, when the main motor M is rotating, the relay
roller is in a rotating state at all times. Mechanically, a clutch
mechanism is not provided in the path by way of which power is
transmitted from the rotary shaft M1 of the main motor M to the
rotary shaft 23A of the relay roller 23, and the teeth sections of
the respective adjacent transmission gears remain in a meshed state
at all times. In the case of the relay roller employed in the
present aspect, the sheet feeding cassette C2 is provided with a
custom designed relay roller 42, and the MP tray 17 is also
provided with a custom designed relay roller 46.
[0048] Before transporting the sheet, which has been transported by
way of the sheet feeding roller 21 and the relay roller 23, to the
transfer roller 27, the registration rollers 25 are for correcting
the attitude of the sheet to a proper attitude and, subsequently,
transporting the sheet to the transfer roller 27. Although the
registration rollers 25 usually remain in a rotating state, the
registration rollers 25 are temporarily suspended when the sheet
has approached the registration rollers 25 (the approach is
detected by a second detection sensor S2 which will be described
later). As a result of the edge of the sheet coming into collision
with the suspended registration rollers 25, the attitude of the
sheet is corrected. Subsequently, the registration rollers 25 are
again driven. Thus, the sheet is delivered to the transfer roller
27. As mentioned above, the registration rollers 25 also need to be
stopped when necessary, as in the case of the sheet feeding roller
21. Therefore, an electromagnetic clutch mechanism 60B
(corresponding to a second actuator of the present invention) is
provided specifically for use with the registration rollers 25 (see
FIG. 3).
[0049] The clutch mechanism 60B for use with the registration
rollers is essentially identical to the clutch mechanism 60A for
use with a sheet feeding roller. The clutch mechanism 60B is formed
chiefly from the transmission gear G6, which has along an outer
periphery thereof a lock receiving section, a lock arm (not shown)
and a solenoid switch 65B. The clutch mechanism 60B differs from
the clutch mechanism 60A for use with a sheet feeding roller in
that the clutch mechanism 60B is set such that transmission of
power is disconnected (interrupted) by means of supplying an
excitation current and in that the transmission gear G6 is formed
from a differential gear and is not provided with a notch
section.
[0050] A state where supply of an excitation current to the
solenoid switch 65B of the clutch mechanism 60B has been completed
corresponds to the state of "completion of operation of the second
actuator" in the present invention.
[0051] As shown in FIG. 1, a photosensitive drum 28 is disposed
opposite the transfer roller 27. A scanner section 31, which can
radiate a laser beam in order to form an electrostatic latent image
on the photosensitive drum 28, is placed at a position above the
photosensitive drum 28. Moreover, a development roller 33 and a
toner storage section 35 are arranged side by side in front of (at
right positions in FIG. 1) of the photosensitive drum 28. The
photosensitive drum 28, the scanner section 31, the development
roller 33, and the toner housing section 35 constitutes an image
forming section and exhibit a function of forming a toner image on
a sheet.
[0052] A press roller 37 is placed opposite the heating roller 38.
The heating roller 38 has an elemental metal tube acting as a
cylindrical member, and a halogen lamp is incorporated in the
heating roller along the axial direction thereof. The surface of
the heating roller 38 is heated to a fixing temperature by means of
the halogen lamp. The press roller 37 is formed by means of coating
the surface of a metal roller shaft with a rubber material, and the
press roller 37is rotated so as to follow rotation of the heating
roller 38 while being elastically pressed against the heating
roller 38. The fixing unit 36 for thermally fixing a toner image on
a sheet is formed from the press roller 37 and the heating roller
38. The transfer roller 27 and the heating roller 38 are rollers
which are rotated at all times.
[0053] The sheet discharge roller 39 is located at a boundary that
acts as a partition between the inside of the main body casing 11
and the sheet discharge section 14, and the sheet discharge roller
39acts to discharge the sheet, which has been transported by way of
the fixing unit 36 and on which an image has been formed, to the
sheet discharge section 14.
[0054] Three detection sensors S1 to S3 are provided in a path from
the sheet feeding roller 21 to the sheet discharge roller 39. These
three detection sensors S1 to S3 detect a transported state of the
sheet, and all the three detection sensors perform detection
operation by utilization of the same detection principle.
Specifically, each of the detection sensors is formed from a
photoelectric sensor consisting of a light emitting element and a
light receiving element, which are disposed opposite each other to
pair up each other and a pivotal member, which is a counterpart of
the photoelectric sensor.
[0055] Reference numeral 81 in FIG. 4 designates a photoelectric
sensor for use as the first detection sensor S1, 82 designates a
photoelectric sensor for use as the second detection sensor S2, and
83 designates a photoelectric sensor for use as the third detection
sensor S3. Reference numeral 85 designates a pivotal member for use
with the first detection sensor S1, 86 designates a pivotal member
for use with the second detection sensor S2, and 87 designates a
pivotal member for use with the third detection sensor S3.
[0056] Each of the pivotal members 85 to 87 is pivotable about a
hinge. The pivotal member 85 has a light blocking section for the
photoelectric sensor 81 and a protruding section which protrudes
into the sheet transport path. The pivotal member 86 has a light
blocking section for the photoelectric sensor 82 and a protruding
section that protrudes into the sheet transport path. The pivotal
member 87 has a light blocking section for the photoelectric sensor
83 and a protruding section that protrudes into the sheet transport
path. As the transported sheet travels across the protruding
sections, the pivotal members 85 to 87 are pivotally displaced to
thus change their attitudes. Thereby, the light blocking sections
enter the detection areas of the photoelectric sensors to thus
block the projected light, or recede from the detection areas to
thus release optical paths. Thus, a change arises in the level at
which detection light is received by the light receiving element,
and hence passage of the sheet can be detected on the basis of the
change in the receiving level of the light.
[0057] The detection functions of the respective detection sensors
are sequentially described. First, the first detection sensor S1 is
located between the sheet feeding roller 21 and the relay roller
23. The first detection sensor S1 detects completion of feeding of
the sheet performed by the sheet feeding roller 21. Specifically,
when the leading edge of the sheet collides against the pivotal
member 85 of the first detection sensor S1, output of a detection
signal is commenced. When the trailing edge of the sheet passes by
the pivotal member 85, the output of the detection signal is
stopped. Hence, the time at which the sheet feeding roller 21 has
finished feeding a sheet can be detected at a point in time ts1
when the detection signal falls (see FIG. 7).
[0058] Next will be described the second detection sensor
(corresponding to a detection sensor for detecting an approach of a
sheet of the present invention) S2. This second detection sensor is
placed at a position close to the registration rollers 25 between
the relay roller 23 and the registration rollers 25. The second
detection sensor S2 detects an approach of a sheet to the
registration rollers 25. Specifically, when the leading end of the
sheet reaches the second detection sensor S2 to thus pivotally
displace the pivotal member 86, an output of the detection signal
is commenced. Hence, an approach of a sheet can be detected at a
point in time ts2 when the signal rises (see FIG. 7).
[0059] The third detection sensor S3 is placed between the
registration rollers 25 and the transfer roller 27. Besides, the
third detection sensor S3 is placed at a position close to the
registration rollers 25. This third detection sensor S3 is for
detecting an approach of a sheet to the transfer roller 27.
[0060] Reference numeral S4 in FIG. 4 designates a fourth detection
sensor which acts in the same manner as does the first detection
sensor S1. Specifically, the fourth sensor detects that the sheet
feeding roller 41 has completed feeding a sheet from the sheet
feeding cassette C2.
[0061] The electrical configuration of a laser printer will now be
described.
[0062] As shown in FIG. 5, the laser printer 10 includes various
circuit boards such as a main board 100, a front relay board 150, a
rear relay board 160 and an additional tray board 170. A main CPU
120, RAM 121, ROM 122 and three types of timers 123A to 123C, each
of which is formed from a counter circuit, are mounted on the main
board 100. Further, the main motor M1, a polygon motor M2, a laser
light source, the first detection sensor S1, the second detection
sensor S2, and the third detection sensor S3 are electrically
connected to the main board 100.
[0063] The main board 100 is provided with an interface 129, and
the main board 100 is communicable with a higher level device
(e.g., an unillustrated personal computer or the like) by way of
the interface 129. Upon receipt of print data and a print command
by way of the interface 129, the main board 100 controls the
entirety of the laser printer 10, and the main board 100 causes the
laser printer 10 to form a desired image on a sheet.
[0064] The front relay board 150 is provided in the front section
of the laser printer 10, and the rear relay board 160 is provided
in the rear section of the same. The solenoid switch 65A for use
with the sheet feeding cassette c1, the solenoid switch 65B for use
with the registration rollers 25, and the solenoid switch 65C for
use with the MP tray 17 are electrically connected to the front
relay board 150. A fixing thermistor, a DX unit sensor, and a sheet
discharge sensor are electrically connected to the rear relay board
160. The solenoid switch 65D for use with the sheet feeding
cassette C2 and the fourth detection sensor S4 are electrically
connected to the additional tray board 170.
[0065] The relay boards 150, 160 and the additional tray board 170
are respectively connected with the main board 100 in a
communicable manner by means of a signal line. The relay boards
150, 160 and the additional tray board 170 control respective
connected devices in accordance with a command from the main board
100.
[0066] An ASIC (Application Specific Integrated Circuit) 130 is
provided on the main board 100. The ASIC 130 has a CPU
(corresponding to a control unit of the present invention) 131 and
memory (e.g., nonvolatile memory such as flash memory or EEPROM and
corresponds to a storage unit of the present invention) 132. The
ASIC 130 is connected with the main CPU 120 in a communicable
manner, and the ASIC 130chiefly controls sheet transport timing.
Namely, operation start timings when the respective solenoid
switches 65A to 65D are operated. A program storage area and a
sheet transport data storage area are provided in the memory 132. A
processing program for executing a control flow to be described
below is written into the program storage area.
[0067] Subsequently, control of sheet transport timing performed by
the ASIC 130 will now be described by reference to FIGS. 6 through
8. FIG. 6 is a flowchart of a processing program performed by the
ASIC.
[0068] When processing is started, the ASIC 130 awaits a print
command as indicated by step 10, and the ASIC 130enters an idle
state. When a PC; i.e., a higher level device, has issued a print
command, the print command is transmitted to the ASIC 130 by way of
the interface 129 and the main CPU 120 of the main board 100.
Thereby, processing proceeds to step 20. In the idle state, the
sheet transport data storage area in the memory 132 remains in an
initialized state. In the following descriptions, the sheet of the
sheet feeding cassette C1 is selected by the higher level device as
an object of printing.
[0069] In step 20, a control signal (corresponding to a sheet
feeding command of the present invention) is sent to the solenoid
switch 65A for use with the sheet feeding cassette C1 along the
path formed from the ASIC 130 and the front relay board 150.
Thereby, an excitation current is supplied from the power source to
the solenoid switch 65A for use with the sheet feeding cassette C1
for only a given period of time t1 (see FIG. 7). The solenoid
switch 65A is thus activated, and the power transmission mechanism
is brought into a connected state. As a result, power is
transmitted from the main motor M to the sheet feeding roller 21,
whereby rotation of the sheet feeding roller 21 and transport of a
sheet are commenced.
[0070] Subsequently, processing in the ASIC 130 proceeds to step
30, where a determination is made as to whether or not the
transported sheet has approached the registration rollers 25. Once
transport of the sheet has been started, time processing
(processing for detecting a transported status of a sheet), which
will be provided below, is performed by the main CPU 120. Moreover,
determination processing pertaining to step 30 and steps 60 to 80
is performed by use of data pertaining to time processing.
Therefore, time processing will be described prior to processing
pertaining to step 30.
[0071] When transport of a sheet is commenced, the main CPU 120
counts three preset times ta, tb, and tc, which will be described
below, from a predetermined reference time by use of the timers
123A to 123C (see FIG. 7). Respective reference times and a count
completion time are stored in specified addresses R in the sheet
transport data storage area in the memory 132.
[0072] More specifically, the rotation start time ts0 of the sheet
feeding roller 21 is taken as a first reference time. The timer
123A counts a time for only the present time ta while taking the
first reference time as a reference. Simultaneously with
acquisition of the first reference time ts0 and the time when
counting of the preset time ta has been completed, these times are
written into respective specified addresses R1, R2.
[0073] The preset time (hereinafter also called "operation interval
time") ta is previously set by the main CPU (corresponding to an
operation interval determination unit of the present invention)
such that an interval between transport of sheets does not become
shorter; namely, the number of operations of the solenoid switch
65A per unit time, which operates in association with transport of
a sheet, does not exceed a preset number. The preset time is used
in determination processing pertaining to step 70 which will be
described later.
[0074] A time ts1 when the detection signal output from the first
detection sensor S1 falls is taken as a second reference time. The
timer 123B counts a time for only the preset time tb while taking
the second reference time as a reference time. Simultaneously with
acquisition of the second reference time ts1 and the time when
counting of the preset time tb has been completed, these times are
written into respective specified addresses R3, R4. The reason why
the preset time tb is counted is that the preset time is used in
determination processing pertaining to step 60, which will be
described later.
[0075] A time ts2 when the detection signal output from the second
detection sensor S2 rises; i.e., a time when an approach of a sheet
to the registration rollers 25, is taken as a third reference time.
The timer 123C counts a time for only the preset time tc while
taking the third reference time as a reference time. Simultaneously
with acquisition of the third reference time ts2 and the time when
counting of the preset time tc has been completed, these times are
stored into respective specified addresses R5, R6. The reason why
the preset time tc is counted is that the preset time is used in
determination processing pertaining to step 80 which will be
described later.
[0076] When processing proceeds to processing pertaining to step
30, the ASIC 130 accesses the specified address R5 in the sheet
transport data storage area in order to determine whether or not
the transported sheet has approached the registration rollers 25.
If the third reference time (a time when an approach of a sheet has
been detected) ts2 is stored, the sheet is determined to have
approached the registration rollers, and processing proceeds to
step 40.
[0077] In step 40, the control signal is delivered to the solenoid
switch 65B for use with the registration rollers 25 by way of the
ASIC 130 and the front relay board 150. Thereby, the excitation
current is supplied from the power source to the solenoid switch
65B, whereupon the solenoid switch 65B is activated. The power
transmission mechanism, which has remained in a power transmittable
connected state, is disconnected, whereby the registration rollers
25 are temporarily stopped. At this time, the leading end of the
transported sheet collides against the registration rollers 25. As
a result, even when the sheet has been transported from the sheet
feeding roller 21 in an inclined position, the attitude of the
sheet is properly corrected by the registration rollers.
[0078] As shown in FIG. 7, supply of the excitation current to the
solenoid switch 65B for use with the registration rollers 25 is
maintained for only the period of time t2 (corresponding to a
predetermined time since operation of the present invention was
started). Therefore, after elapse of the predetermined period of
time, the power transmission mechanism is restored to a power
transmittable connected state. Hence, the registration rollers 25
resume rotation. Therefore, the registration rollers 25, which have
resumed rotation, resume the temporarily suspended transport of the
sheet.
[0079] Subsequent to operation of the solenoid switch 65B,
processing proceeds to step 50 by means of processing pertaining to
the ASIC 130. In this step, a determination is made as to whether
or not a next print job exists. When no next print job exists, No
is selected through determination. Processing pertaining to control
of the solenoid switches 65A to 65D, which are under control of the
ASIC 130, is thereby completed. A case where the next job exists
will be described later.
[0080] In the meantime, the sheet remains at any position along the
sheet transport path L1 at this point in time, and the main CPU 120
performs print processing subsequent to this point in time.
Specifically, when the leading edge of the sheet is detected by the
third detection sensor S3, the main CPU 120 causes the image
forming section to start print processing. Thereby, the
photosensitive drum 28 is exposed to a high speed scan of a laser
beam emitted from the scanner section 31. As the toner of the
development roller 33 adheres to the surface of the photosensitive
drum 28, a toner image is formed on the surface of the drum by
means of negative development.
[0081] Subsequently, the sheet is transported between the
photosensitive drum 28 and the transfer roller 27, whereby the
toner image carried on the surface of the photosensitive drum 28 is
transferred to the sheet. After having undergone a fixing process,
the sheet is discharged to the sheet discharge section 14.
[0082] There will now be described a case where Yes is selected
through determination in step S50; namely, where the next print job
exists.
[0083] In step 60, a determination is made as to whether or not
counting of the preset time tb has been completed. When processing
proceeds to step 60, the ASIC 130 accesses the specified address R4
of the memory 132, to thus read the stored data from the address
R4. At this time, when the timer 123B has not yet finished counting
a time, no data will be written into the address R4. To prevent
this, the timer 123B is determined to be still performing counting
operation (No is selected through determination). When the timer
123B has finished counting the time and the time--at which the
counting operation has been completed--is written into the address
R4, the preset time tb is determined to have elapsed (Yes is
selected through determination), and processing proceeds to step
70.
[0084] The reason why elapse of the preset time tb is determined is
to set an appropriate interval between the trailing edge of the
sheet that has already been sent and the leading edge of the sheet
that will be sent now (the first condition).
[0085] In step 70, a determination is made as to whether or not the
preset time ta has elapsed. To this end, when processing has
proceeded to step 70, the ASIC 130 accesses the specified address
R2 of the memory 132, to thus read the stored data. When the timer
123A has not yet finished counting the time, the time at which the
counting operation has been completed is written into the specified
address R2, whereby the preset time ta is determined to have
elapsed (Yes is selected through determination), and processing
proceeds to step 80.
[0086] The reason why elapse of the preset time ta; i.e., an
operation interval time, is determined is to prevent the solenoid
switch 65A from becoming heated and to seek stable operation of the
clutch mechanism, and by extension, stable operation of the sheet
transport system. Namely, the preset time (operation interval time)
ta is an interval of supply of an excitation current that must be
ensured to prevent the solenoid switch 65A (including the solenoid
switches 65C, 65D) from becoming heated. If a sheet is supplied
without adoption of such an operation interval time, the
interval--at which sheets are transported--becomes excessively
short, which in turn renders the interval--at which the excitation
current is supplied to the solenoid switch--shorter (i.e., an
average current value becomes greater), which heats the solenoid
switch. In the present aspect, the operation interval time ta is
set to about two seconds (the second condition).
[0087] By means of processing pertaining to step 70, the operation
stated in the present aspect "an operation start timing of the
first actuator is determined such that operation of the first
actuator for the next sheet is started after elapse of the
operation interval time since the start of operation of the first
actuator for one sheet" is implemented.
[0088] In step 80, a determination is made as to whether or not the
preset time tc has elapsed. When processing proceeds to step 80,
the ASIC 130 accesses the specified address R6 of the memory 132,
to thus read the stored data. When the timer 123C has not yet
completed counting a time, the timer is determined to be performing
counting operation (No is selected through determination). However,
when the timer 123C has finished counting a time and the time when
the counting operation has been completed is written into the
specified address R6, the preset time tc is determined to have
elapsed (Yes is selected through determination) and processing
proceeds to step 90.
[0089] The reason why elapse of the preset time tc is determined is
to ascertain that operation of the solenoid switch 65B for use with
the registration rollers 25 with regard to the sheet has already
been sent (i.e., a preceding job), i.e., supply of the excitation
current to the solenoid switch 65B, has been completed (the third
condition).
[0090] Completion of supply of the excitation current can be
ascertained by means of counting the preset time tc. The reason for
this is that counting of the preset time tc is performed
simultaneously with initiation of the excitation current for the
solenoid switch 65B (the third reference time ts2) and that the
duration of the preset time tc is set so as to become longer than
the time t2 during which supply of the excitation current is
maintained (see FIG. 7). As above, the third reference time ts2
corresponds to the operation start time of the clutch mechanism
60B, in which supply of the excitation current to the solenoid
switch 65B has been initiated. The time at which counting of the
preset time ts has been completed corresponds to the state where
operation of the clutch mechanism 60b, in which supply of power to
the solenoid switch 65B is disconnected, has been completed. Hence,
access is made to the specified addresses R5, R6 of the sheet
transport data storage area in the memory 132, to thus ascertain
the state of supply of the current to the solenoid switch 65B of
the clutch mechanism 60B (corresponding to "operating status of the
second actuator" of the present invention). By means of processing
pertaining to step 80, "operation start timing of the first
actuator is determined such that operation of the first actuator,
which is to be started to transport the next sheet after transport
of one sheet, is started after completion of operation of the
second actuator for the one sheet" in the present invention is
implemented.
[0091] In step 90, respective sets of data pertaining to the
transported state of the sheet in the memory 132, namely, all the
data stored in the specified addresses R1 to R6, are erased
(initialized). Subsequently, processing proceeds to step 20. A
control signal (corresponding to the "sheet feeding command" of the
present invention) is sent to the solenoid switch 65A for use with
the sheet feeding cassette C1 by way of the ASIC 130 and the front
relay board 150. Thus, the excitation current is supplied to the
solenoid switch 65A for use with the sheet feeding cassette C1 from
the power source for only a given period of time t1. In subsequent
processes, the main CPU 120 and the ASIC 130 perform processing in
accordance with the previously described procedures. Thus,
transport of the next sheet is started, and a desired image is
formed.
[0092] Through processing pertaining to step 90, "the data
pertaining to the operating status of the second actuator with
regard to one sheet, which are stored in the storage unit, are
deleted before the first actuator starts operation in order to
transport the next sheet."
[0093] The above aspect has been described by taking a case, where
a sheet is supplied from the sheet feeding cassette C1, as an
example. Processing is performed even in the case where a sheet is
fed from the sheet feeding cassette C2 and the case where the sheet
is fed from the MP tray 17, as in the case of the sheet feeding
cassette C1. Thus, transport timing of a sheet is determined, and
printing is also performed on the basis of this timing.
[0094] As mentioned above, according to the present aspect, three
conditions are imposed on initiation of the next sheet after
transport of one sheet. The first condition is that transmission of
the previously sent sheet (one sheet) has already been completed
(step 60). The second condition is that the operation interval time
ta has elapsed since commencement of transport of the preceding
sheet (step 70). The third condition is that the solenoid switch
65B for use with the registration rollers 25 has completed
operation with regard to the previously sent sheet (step 80).
Transport of a sheet is allowed only when all of these conditions
have been fulfilled.
[0095] Thus, so long as the transport timing of the sheet is
determined, delivery of superimposed sheets is avoided (an
advantage of the first condition). Further, the operation interval
time ta does not become excessively short. Hence, the mean value of
the excitation current supplied to the solenoid switches 65A, 65B
is maintained at an appropriate value, and hence the solenoid
switches do not become heated (an advantage of the second
condition).
[0096] Since transport of the next sheet is commenced after the
clutch mechanism 60 has finished operation with regard to the
previously sent sheet, simultaneous supply of an excitation current
to both the solenoids 65A, 65B from the power source is avoided.
Namely, load exceeding the performance of the power source can be
avoided, and hence stable supply of power from the power source is
achieved, so that operation of the laser printer 10 becomes stable
(an advantage of the third condition).
[0097] The advantage of the third condition will be further
described. The image forming apparatus of the present aspect is
provided with the sheet feeding cassettes C1, C2 and the MP tray
17. Further, the sheet transport paths L1 to L3 differ from each
other in terms of the length of the transport path from the sheet
feeding start position to the registration rollers 25. When the
sheet feeding start time ts0 is taken as a reference, the
time--which elapses from when an approach of the sheet to the
registration rollers 25 is detected until when supply of the
excitation current to the solenoid switch 65B for use with the
registration rollers is started--changes according to the sheet
transport paths L1 to L3. FIG. 9 shows a timing chart achieved in a
case where a sheet is transported from the sheet feeding cassette
c2. In this case, when compared with the case where a sheet is
transported from the sheet feeding cassette c1, the time ts2--when
an approach of the sheet to the registration rollers 25 is
detected--is seen to be delayed.
[0098] In consideration of this point, completion of operation of
the solenoid switch 65B for use with the registration rollers is
taken as a condition for transporting a sheet. Supply of an
excitation current to the solenoid-switch 65A for use with a sheet
feeding roller is always performed after completion of supply of
the excitation current to the solenoid switch 65B for use with the
registration rollers, regardless of the sheet transport paths L1 to
L3.
[0099] The image forming apparatus of the present aspect controls
operations of these solenoid switches 65A to 65D (control of sheet
transport timings) by use of the custom designed ASIC 130 other
than the main CPU 120 of the main board 100. As mentioned above, so
long as operation is controlled by means of the custom designed
ASIC 130, operation control (control of sheet transport timing) can
be incorporated into an existing laser printer which does not
control operation, without involvement of significant modifications
to the printer.
[0100] According to the present aspect, the relay roller 23 is
interposed between the sheet feeding roller 21 and the registration
rollers 25 in each of the sheet transport paths L1, L2. When the
sheet feeding roller 21 has started transporting operation, the
sheet reaches the registration rollers 25 without being stopped by
action of the relay roller 23. By means of such a configuration,
the time which elapses from when transport of a sheet is started
until when the sheet is subjected to image forming operation
becomes shorter, and hence formation of an image can be performed
efficiently. When compared with control performed in a case where
the sheet is stopped during transport, control becomes simpler.
[0101] In addition, according to the present aspect, supply of
power to the rollers 21, 23, 25, 27, 28, 37, 38, and 39 is
implemented by a single drive source; namely, the main motor M.
Hence, a smaller number of components is required.
[0102] The present invention has been described by reference to the
descriptions and drawings. However, for instance, the following
aspect is included in the technical scope of the present invention.
Moreover, in addition to the following modifications, the present
invention can be implemented while being modified in various
manners within the scope of the invention.
[0103] In the present aspect, the object to be controlled by the
ASIC 130 is set to the solenoid switch 65B for use with the
registration rollers 25 and the solenoid switch 65A (including 65C,
65D) for use with the sheet feeding roller 21. Operation timings
are controlled such that the solenoid switches 65A, 65B of the
rollers 21, 25 are not operated simultaneously. However, the object
of control is not limited to these, and various objects of control
can be applied.
[0104] The present aspect has been described on the condition that
sheets are sequentially sent from a single sheet feeding cassette.
For instance, however, a plurality of sheets may be transported a
long different sheet transport paths such that, after a sheet has
been transported from the sheet feeding cassette C1, the next sheet
is transported from the sheet feeding cassette C2 or the MP tray
17.
[0105] In such a case, a sheet transport timing is determined in
accordance with the procedures of the present aspect (step 60 to
step 80). Subsequently, when the solenoid switch is again activated
in step 20, it is better to selectively switch the solenoid
switches.
[0106] As the above, when sheets are sequentially transmitted from
the different sheet feeding cassettes C1, C2, and MP17, sheets of
different sizes are set in the respective cassettes, and the sheets
of different sizes may be sequentially transported.
[0107] In the above aspect, the sheet feeding cassettes C1, C2 are
constructed in two layers. However, the sheet feeding cassettes are
not limited to this configuration. The sheet feeding cassettes may
be formed into three or more layers.
[0108] In the present aspect, the times when the respective timers
123A, 123B, and 123C have completed counting operations are stored
in the sheet transport data storage area in the memory 132.
However, a bit flag (1 is set for completion of operation, and 0 is
set for other cases) maybe employed, so long as completion of
operation can be ascertained.
[0109] In the present aspect, supply of the excitation current to
the solenoid switch 65C is determined to have been completed by
means of the timer 123C counting the preset time tc. However,
completion of supply of the excitation current may be detected
directly. For instance, a custom designed circuit may be
incorporated into the supply circuit that supplies an excitation
current to the solenoid switch 65C, to thus detect completion of
supply of the excitation current.
[0110] In the present aspect, the custom designed timers 123A,
123B, and 123C are provided for counting the preset times ta, tb,
and tc. However, any timers are applicable, so long as they can
count a time. For instance, the timers may be a loop timer embodied
by software. When the loop timer is used, it is desirable to cause
a CPU other than the CPU 131 of the ASIC 130 to perform counting
operation.
* * * * *