JP7271210B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus such as a copying machine and a laser printer, and more particularly to a heating element switching control method for double-sided printing.

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, when a fixing device has a plurality of heating elements with different lengths and is configured to be able to exclusively switch the heating elements to which power is supplied, , the following heating element switching control is performed. That is, in the image forming apparatus, electric power is supplied by switching to a heating element having an appropriate length according to the width of the recording material in the direction perpendicular to the conveying direction. As a result, while preventing damage to the heating element and its peripheral members due to temperature rise in the non-paper-passing portion of the heating element through which the recording material does not pass, print jobs can be executed while suppressing a decrease in productivity of the image forming apparatus. can do. For example, Japanese Patent Application Laid-Open No. 2002-200002 discloses a fixing unit having a plurality of heating elements corresponding to the maximum width of a passable recording material and the width of a small size recording material. Japanese Patent Application Laid-Open No. 2002-200001 proposes a method of switching to a heating element having a length suitable for the width of the recording material and supplying electric power to the fixing unit, based on the relationship between the width of the recording material and the length of the heating element.

Japanese Unexamined Patent Application Publication No. 2001-100558

In the conventional method of supplying electric power to the fixing means by switching to a heating element having a length suitable for the width of the recording material, double-sided printing may be performed on a plurality of recording materials. In such a case, if an attempt is made to switch the heating element according to the width of the recording material, there is a possibility that the heating element cannot be appropriately switched depending on the conveying state of a plurality of recording materials printed on both sides. .

SUMMARY OF THE INVENTION The present invention has been made under such circumstances, and an object of the present invention is to switch a heating element in consideration of the conveying state of a plurality of recording materials when double-sided printing is performed on a plurality of recording materials. .

In order to solve the above problems, the present invention has the following configuration.

(1) image forming means for forming a toner image on a recording material; fixing means for fixing an unfixed toner image formed on a recording material by the image forming means; and the first heat generating element or the second heat generating element of the heater. switching means for switching a power supply path so that power can be supplied to any one of the heating elements; and control means for controlling the power supply path switched by the switching means. When double-sided printing is performed, an image is formed on the first surface of a first recording material, the first recording material is made to stand by on a double-sided conveying path, and a second recording material following the first recording material is printed. An image forming apparatus for forming an image on a first surface and forming an image on a second surface of the first recording material, wherein the control means controls the length of the first recording material in the longitudinal direction, and the electric power when fixing the first surface of the second recording material and the second surface of the first recording material by the fixing means based on the length of the second recording material in the longitudinal direction The power supply path is controlled, and the power supply path is not switched after the fixing means fixes the first surface of the second recording material until the second surface of the first recording material is fixed. An image forming apparatus characterized by controlling to :

According to the present invention, when double-sided printing is performed on a plurality of recording materials, the heating element can be switched in consideration of the conveying state of the plurality of recording materials.

Schematic cross-sectional view showing the configuration of the image forming apparatus of Examples 1 and 2. Schematic diagram showing a cross section of a fixing portion of Examples 1 and 2 Schematic diagram for explaining the configuration of the power control circuit of the fixing unit of Examples 1 and 2. FIG. FIG. 2 is a control block diagram showing the system configuration of the image forming apparatuses of the first and second embodiments; 4 is a timing chart showing the image forming operation of the image forming apparatus according to the first embodiment; 4A and 4B are diagrams for explaining the state of the recording paper in the reversing portion of the first embodiment; 4 is a timing chart showing the image forming operation of the image forming apparatus according to the first embodiment; 3 is a flow chart showing a control sequence for determining a heating element to which power is to be supplied according to the first embodiment; FIG. 10 is a diagram for explaining the positional relationship between the heating element and the recording paper width sensor of the second embodiment; 6 is a timing chart showing the image forming operation of the image forming apparatus according to the second embodiment; 3 is a flow chart showing a control sequence for determining a heating element to which power is to be supplied according to the second embodiment; Schematic diagram for explaining the configuration of the power control circuit of the fixing unit of the third embodiment. 10 is a flow chart showing a control sequence for determining a heating element to which power is to be supplied according to the third embodiment;

BEST MODE FOR CARRYING OUT THE INVENTION Below, embodiments of the present invention will be described in detail with reference to the drawings.

[Overview of Image Forming Apparatus]
FIG. 1 illustrates the overall configuration of a laser printer as an example of the image forming apparatus according to the first embodiment. The image forming apparatus shown in FIG. 1 has four image forming stations 4a, 4b, 4c, and 4d, and from the left in the figure, yellow (Y), magenta (M), cyan (C), and black (K). of toner. Also, the letters a, b, c, and d at the end of the symbols in the drawing denote yellow (Y), magenta (M), cyan (C), and black (K), respectively. The image forming stations 4a to 4d, which are image forming means, have the same configuration, and in the following description, the reference numerals a to d will be omitted unless particularly necessary. The image forming apparatus shown in FIG. 1 can form a full-color image or a monochrome image on a recording material. Here, recording materials include, for example, recording paper, OHP sheets, cloth, and the like. In this embodiment, the case of forming an image on recording paper will be described below.

(Image forming section)
The image forming section comprises a scanning optical member 5 , a photosensitive drum 8 , a charger 9 , a developing roller 7 and a cleaning device 10 . The photosensitive drum 8, which is an image bearing member, is constructed by applying an organic photoconductive layer to the outer periphery of an aluminum cylinder, and is rotated in the direction of the arrow (counterclockwise direction) by the driving force of a driving source (not shown). are arranged. Around the photosensitive drum 8, a charger 9, a scanning optical member 5, a developing roller 7, a primary transfer roller 15, and a cleaning device 10 are arranged. The charger 9 uniformly charges the surface of the photosensitive drum 8 . The scanning optical member 5 guides the light generated based on the image signal to the optical path 6, exposes the photosensitive drum 8, and forms an electrostatic latent image. The developing roller 7 attaches toner to the electrostatic latent image formed on the surface of the photosensitive drum 8 and visualizes it as a yellow (Y), magenta (M), cyan (C), and black (K) toner image. do. A primary transfer roller 15 transfers the toner image on the photosensitive drum 8 (on the photosensitive drum) to an intermediate transfer belt 11 as an intermediate transfer member. This is called primary transcription. The cleaning device 10 removes toner remaining on the surface of the photosensitive drum 8 without being transferred onto the intermediate transfer belt 11 . The cleaning device 10 removes the toner image remaining on the intermediate transfer belt 11 after transferring the toner remaining on the photosensitive drum 8 or the toner formed on the intermediate transfer belt 11 (on the intermediate transfer body) to the recording paper. collected and stored in a cleaner container.

The intermediate transfer belt 11 is stretched by support rollers 11 a and 11 b and arranged so as to contact the photosensitive drum 8 . The intermediate transfer belt 11 is rotated in the direction of the arrow (clockwise direction) by a drive source (not shown), and the toner image on the photosensitive drum 8 is transferred by the primary transfer roller 15 . A secondary transfer section (also referred to as a transfer section) transfers the toner image on the intermediate transfer belt 11 onto the recording paper while pinching and conveying the recording paper. This is called secondary transfer. The secondary transfer portion is arranged so that the transfer roller 11c contacts the intermediate transfer belt 11, and is arranged at a position facing the support roller 11b.

(Paper feed section)
The paper feed unit 1 has paper feeders ka and 1b for feeding recording paper (also referred to as recording material) stored in a paper feed cassette 1c. A paper feed cassette 1c as a storage unit stores recording paper on which an image is to be formed. The recording paper sent out from the paper feeding unit 1 passes through the registration sensor 17 and reaches the secondary transfer unit. The paper feed section 2, like the paper feed section 1, has a pair of paper feed rollers 2a and 2b for feeding recording paper stored in a paper feed cassette 2c. A paper feed cassette 2c as a storage unit stores recording paper on which an image is to be formed. The recording paper sent out from the paper feeder 2 connected to the lower part of the paper feeder 1 by the pair of paper feed rollers 2a and 2b passes through a part of the transport path of the paper feeder 1 and the registration sensor 17. It reaches the next transfer portion.

(fixing section)
The fixing unit 50 includes a fixing roller 51 that heats the recording paper and a pressure roller 53 that presses the recording paper against the fixing roller 51. The fixing unit 50 is arranged to rotate in the direction of the arrow by the motor 25 as driving means. It is A heater 54 is built inside the fixing roller 51 . The recording paper onto which the toner image has been transferred is conveyed by a fixing roller 51 and a pressure roller 53, and heat and pressure are applied to fix the fused toner image on the surface of the recording paper. A pair of discharge rollers 13a and 13b and a pair of discharge rollers 18a and 18b discharge the recording paper on which the toner image has been fixed to the paper discharge section 14. FIG.

(reversal part)
The reversing section, which is reversing means, reverses the conveying direction of the recording paper on which the toner image is fixed by the fixing section 50 . The reversing unit includes a flapper 19 for changing the transport path of the recording paper, and a reversing roller configured to transport the recording paper transported by the pair of discharge rollers 13a and 13b in the direction of pulling in or in the direction of the reversing path 28. 20a and 20b. The flapper 19 and the reversing rollers 20 a and 20 b are arranged so as to be driven by a motor 25 which is the same drive source as the fixing section 50 . A solenoid 27 is provided between the flapper 19, the reversing rollers 20a and 20b, and the motor 25, which is a drive unit, and the solenoid 27 switches the position of the flapper 19 and the rotation direction of the reversing rollers 20a and 20b. A solenoid 27 can switch the flapper 19 between the position indicated by the solid line in FIG. 1 and the position indicated by the dotted line. Further, the position of the flapper 19 and the rotation directions of the reversing rollers 20a and 20b are configured to be interlocked. When the flapper 19 is at the position indicated by the dotted line in FIG. 1, the reversing rollers 20a and 20b rotate in the direction of drawing the recording paper into the reversing portion. On the other hand, when the flapper 19 is positioned at the position indicated by the solid line in FIG.

(refeed unit)
The reversing path 28, which is a double-sided conveying path, includes conveying roller pairs 21a and 21b, conveying roller pairs 22a and 22b, conveying roller pairs 24a and 24b, and a clutch (not shown) that controls driving force transmission to each conveying roller pair. ) and a paper refeed waiting sensor 23 . Each transport roller pair 21a/21b, 22a/22b, 24a/24b is driven by a motor 26 and a clutch that controls the drive power supply of the motor 26. As shown in FIG. In addition, the pair of paper feed rollers 1a and 1b of the paper feed section 1 and the pair of paper feed rollers 2a and 2b of the paper feed section 2 also control the motor 26 and the supply of the driving force of the motor 26 in the same manner as the transport roller pair. driven by the clutch and

The operation of the reversing section is reversal of the conveying direction of the recording paper, transportation to a predetermined position within the reversing path 28 , and transportation from the reversing path to the registration sensor 17 . In the reversing operation of the conveying direction of the recording paper, the reversing section drives the solenoid 27 for changing the position of the flapper 19, changes the conveying direction of the recording paper after the toner image is fixed by the fixing section 50, and changes the conveying direction of the recording paper. to the reversing rollers 20a and 20b. After conveying the recording paper to a sufficiently downstream position in the conveying direction from the flapper 19, the reversing section stops the solenoid 27 to change the rotating direction of the reversing rollers 20a and 20b so that the recording paper passes through the reversing path. 28 directions.

During transport to a predetermined position in the reversing path 28, the reversing section drives a clutch (not shown) to apply driving force to the transport roller pairs 21a and 21b, the transport roller pairs 22a and 22b, and the transport roller pairs 24a and 24b. Feed and rotate. Then, the reversing section stops the clutch (not shown) when the re-feed waiting sensor 23 detects the recording paper, and stops the supply of driving force to each conveying roller pair.

During transport from the reversing path 28 to the registration sensor 17, the reversing section drives a clutch (not shown) to apply driving force to the transport roller pairs 21a and 21b, the transport roller pairs 22a and 22b, and the transport roller pairs 24a and 24b. Feed and rotate. After the registration sensor 17 detects the recording paper, the reversing section stops driving the clutch.

[Structure of Fixing Section]
Next, the configuration of the fixing section 50, which is the fixing means in the first embodiment, will be described with reference to FIG. Here, the longitudinal direction is the rotation axis direction of the pressure roller 53 which is substantially orthogonal to the sheet P conveying direction, which will be described later. Also, the length of the paper P in the direction (longitudinal direction) substantially perpendicular to the transport direction is called the width. FIG. 2 is a schematic cross-sectional view of the fixing section 50. As shown in FIG. The toner image T is fixed on the paper P by heating the paper P holding the unfixed toner image T from the left side of FIG. The fixing unit 50 in the first embodiment includes a fixing roller 51 that is a cylindrical film, a nip forming member 52 that holds the fixing roller 51, a pressure roller 53 that forms a fixing nip portion N together with the fixing roller 51, and a paper sheet. and a heater 54 for heating P.

The fixing roller 51 (first rotating body) is a fixing film as a heating rotating body. In Example 1, polyimide, for example, is used as the base layer. An elastic layer made of silicone rubber and a release layer made of PFA are used on the base layer. The inner surface of the fixing roller 51 is coated with grease in order to reduce the frictional force generated between the fixing roller 51 and the nip forming member 52 and the heater 54 due to the rotation of the fixing roller 51 .

The nip forming member 52 serves to guide the fixing roller 51 from the inside and form a fixing nip portion N with the pressure roller 53 via the fixing roller 51 . The nip forming member 52 is a member having rigidity, heat resistance, and heat insulation, and is made of liquid crystal polymer or the like. The fixing roller 51 is fitted onto the nip forming member 52 . The pressure roller 53 (second rotating body) is a roller as a pressing rotating body. The pressure roller 53 is composed of a metal core 53a, an elastic layer 53b, and a release layer 53c. The pressure roller 53 is rotatably held at both ends and is rotationally driven by a motor 25 (see FIG. 1) which is also a fixing motor. Further, the fixing roller 51 is driven to rotate by the rotation of the pressure roller 53 . A heater 54 that is a heating member is held by the nip forming member 52 and is in contact with the inner surface of the fixing roller 51 .

A heater 54 is a heating member. The heater 54 is held by the nip forming member 52 and is in contact with the inner surface of the fixing roller 51 . A fixing temperature sensor 59 is a thermistor and detects the temperature of the heater 54 . The fixing temperature sensor 59 is located on the surface of the substrate 54a of the heater 54 opposite to the protective glass layer 54e, and is installed at the longitudinal center position of the heating elements 54b1 and 54b2 having different lengths in the longitudinal direction, It is in contact with the substrate 54a.

[Control Circuit of Fixing Section]
FIG. 3 is a schematic diagram of a power control circuit that controls power supply to the fixing section 50. As shown in FIG. The power control circuit of the fixing section 50 has heating elements 54 b 1 and 54 b 2 , a bidirectional thyristor (hereinafter referred to as triac) 56 and a heating element switching device 57 . The heater 54 has a heating element 54b1 that is a first heating element and a heating element 54b2 that is a second heating element, and the heating element 54b1 is longer than the heating element 54b2 in the longitudinal direction. In this embodiment, the longitudinal lengths of the heating elements 54b1 and 54b2 are the widths (longitudinal lengths) of A4 size and A5 size recording paper, respectively. One end of the triac 56, which is a switch means, is connected to the AC power supply 55, and the other end is connected to terminals connected to the heating elements 54b1 and 54b2 of the heater 54. It supplies/shuts off power to 54b2. A heating element switching device 57, which is switching means, is a relay that connects the AC power supply 55 and the heating element 54b1 or 54b2 of the heater 54, and in this embodiment, a C-contact relay is used. The heating element switching unit 57 switches the terminal 54d1 connected to the heating element 54b1 or the terminal 54d2 connected to the heating element 54b2 to select either one of the heating elements 54b1 and 54b2 as the power supply destination from the AC power supply 55. Select exclusively. A power supply path is formed by the triac 56 and the heating element switch 57 so that power can be supplied to the heating element 54b1 or the heating element 54b2. It is assumed that the heating element switching device 57 is in a state in which power can be supplied from the AC power supply 55 to the heating element 54b1 side in the initial state. In order to prevent contact welding of the heating element switching device 57, which is a C-contact relay, switching of the heating element switching device 57 is performed in a state in which the power supply to the heating elements 54b1 and 54b2 by the triac 56 is surely cut off. done.

[System Configuration of Image Forming Apparatus]
FIG. 4 is a control block diagram showing a system configuration for controlling the image forming apparatus shown in FIG. The printer controller 200 receives a print command including an image code from an external device such as a host computer, and develops the received image code into bit data necessary for printing. The printer controller 200 also reads internal information of the engine control unit 201 through serial communication with the engine control unit 201, and displays the read internal information on a display unit (not shown). The engine control unit 201, which is control means, receives control instruction information through serial communication with the printer controller 200, and controls each control unit described below based on the control instruction information received from the printer controller 200. FIG.

Based on instructions from the engine control unit 201, the image forming control unit 202 drives and stops the charger 9, the developing roller 7, and the primary transfer roller 15, and drives and stops the scanning optical member 5 of the image forming station 4. conduct. Further, the image forming control unit 202 controls flickering of laser light for scanning the photosensitive drums 8 by the scanning optical member 5 according to an image signal from the printer controller 200 to form a toner image on the intermediate transfer belt 11 . Let

The transfer control unit 203 controls driving and stopping of the transfer roller 11c and the support roller 11b of the secondary transfer unit based on instructions from the engine control unit 201, and records the toner image formed on the intermediate transfer belt 11. Transfer to paper.

Based on instructions from the engine control unit 201, the paper feed control unit 204 controls the motor 26, which is also a pickup solenoid and a paper feed motor, of the paper feed unit 1 and the paper feed unit 2. The recording paper loaded in the section 2 is fed toward the registration sensor 17 .

Based on instructions from the engine control unit 201, the fixing control unit 205 adjusts the temperature of the heating elements 54b1 and 54b2 of the heater 54 by the triac 56 and the heating element switching unit 57, and drives and stops the motor 25, which is also the fixing motor. . As a result, the fixing unit 50 fixes the toner image transferred onto the recording paper (recording material) onto the recording paper.

The reverse control unit 206 drives and stops the solenoid 27 that changes the position of the flapper 19 based on instructions from the engine control unit 201 . The reverse control unit 206 also drives and stops clutches (not shown) that control the rotation of the transport roller pairs 21a and 21b, the transport roller pairs 22a and 22b, and the transport roller pairs 24a and 24b. Thereby, the reversing control unit 206 controls reversing the recording paper, conveying the reversing recording paper to the standby position on the reversing path 28 , and conveying the recording paper waiting at the standby position to the registration sensor 17 .

[Operation of each control unit by print job execution]
Next, in the image forming apparatus having the fixing section 50 having a configuration in which the heating element can be switched as described above, the printer controller 200 instructs the engine control section 201 to perform double-sided printing on recording paper of different sizes, particularly different widths of recording paper. The operation of each control unit in this case will be described.

FIG. 5 is a timing chart for explaining a print reservation command transmitted from the printer controller 200 to the engine control unit 201 and the operation of the engine control unit 201 that sequentially executes the contents of the print reservation command in this embodiment. In FIG. 5, the timing chart shown at the top shows transmission and reception of signals (print reservation command, print start command, /TOP signal, etc.) between the printer controller 200 and the engine control unit 201 . The timing chart shown at the bottom shows the operations of the image forming section, transfer section, fixing section, reversing section, paper feeding section 1 and paper feeding section 2 . Note that in FIG. 5, the horizontal axis indicates time, and T2001 to T2012 in the figure indicate operation timings.

The print job shown in FIG. 5 is for double-sided two-sheet alternate printing. The first sheet is A4 size recording paper, the second sheet is A5 size recording paper, the third sheet is A5 size recording paper, and the fourth sheet is A4 size recording paper. The print job is for recording paper of the size. In addition, it is assumed that A4 size recording paper and A5 size recording paper are previously stacked in the paper feeding unit 1 and the paper feeding unit 2, respectively. Further, of the heating elements 54b1 and 54b2 of the fixing unit 50, the heating element 54b1 has a width capable of fixing A4 size recording paper, and the heating element 54b2 has a width capable of fixing A5 size recording paper. shall have.

The contents (print information) of the print reservation commands transmitted from the printer controller 200 and acquired by the engine control unit 201 under the conditions described above and the order of execution thereof are as follows.
・Paper feed unit 1/1 side/A4
・Paper feed unit 2/1 side/A5
・Reversed part / 2 sides / A4
・Paper feed unit 2/1 side/A5
・Reversed part / 2 sides / A5
・Paper feed unit 1/1 side/A4
・Reversed part / 2 sides / A5
・Paper feed unit 1/2 sides/A4
In the content of the print reservation command, among the three specification items separated by slashes (/), the first specification item specifies which paper source (paper source 1, paper source) is used for printing. 2, whether the paper is conveyed from the reversing section). The second specification item indicates which side of the recording paper the image is to be formed on. For the first side, the image is to be formed on the front side of the recording paper, and for the second side, the image is to be formed on the back side of the recording paper. means. It should be noted that the instruction is not limited to this, and 1-sided may mean an instruction to form an image on the back side of the recording paper, and 2-sided may mean an instruction to form an image on the front side of the recording paper. The third specification item indicates the size of the recording paper.

By executing the print reservation command described above, double-sided printing is performed in the following order. That is, the first side of the first sheet of recording paper, the first side of the second sheet of recording paper, the second side of the first sheet of recording paper, the first side of the third sheet of recording paper, and the second side of the second sheet of recording paper. Duplex printing is performed on the first side, the first side of the fourth recording sheet, the second side of the third recording sheet, and the second side of the fourth recording sheet.

[Example of image forming operation that causes printing failure]
FIG. 5 shows image formation when the above-described print reservation command is transmitted from the printer controller 200 to the engine control unit 201, and the heating element of the fixing unit 50 is switched according to the recording paper size specified by the print reservation command. It is a timing chart explaining operation.

Upon receiving the print start command from the printer controller 200, the engine control unit 201 starts startup processing of each component of the image forming apparatus described with reference to FIG. 1 (T2001). Since the recording paper size specified in the first print reservation command is A4, the fixing unit 50 supplies electric power to the heating element 54b1 capable of fixing A4-size recording paper in the start-up process. Start controlling.

In the fixing section 50, when the temperature of the fixing roller 51 in the longitudinal direction has risen to the temperature required for fixing the toner image by the heating element 54b1 (T2002), the engine control section 201 sends the printer controller 200 a /TOP signal ( image request signal). Upon receiving the /TOP signal, the printer controller 200 starts transmitting image signals to the engine control unit 201 . Upon receiving the image signal transmitted from the printer controller 200, the engine control unit 201 sequentially instructs the image formation control unit 202 to form Y, M, C, and K toner images. The paper feed unit 1 feeds a first sheet of recording paper (first recording material) of A4 size in synchronization with the arrival timing of the toner images sequentially formed on the intermediate transfer belt 11 to the secondary transfer unit. Then, the secondary transfer unit starts transferring the toner image onto the fed recording paper (T2003). When the first sheet of recording paper that has passed through the secondary transfer section passes through the fixing section 50 and reaches just before the reversing section, the reversing section drives the solenoid 27, changes the position of the flapper 19, and records the first sheet. The operation of drawing the paper to the reversing portion is started (T2004). After performing the pull-in operation according to the length of the recording paper, the reversing section stops driving the solenoid 27, changes the position of the flapper 19, and starts reversing the first recording paper (T2006). . When the re-feed waiting sensor 23 on the reversing path 28 detects the first sheet of recording paper, the reversing section stops conveying the first sheet of recording paper and transitions to a standby state (T2008).

On the other hand, the recording paper size of the second print reservation command from the printer controller 200 is A5. Therefore, the engine control unit 201 performs switching operation of the heating element that supplies power to the fixing unit 50 at the timing when the first recording sheet passes the fixing roller 51 (T2005). In the operation of switching the heating element to which power is supplied, the triac 56 is turned off, and the heating element switching device 57 switches the power supply destination from the heating element 54b1 to the heating element 54b2. Therefore, the triac 56 is turned on after waiting for the heating element switch 57, which is a C-contact relay, to switch with a sufficient margin. When the temperature of the fixing roller 51 rises to the temperature required for fixing the toner image by the heating element 54b2 (T2007), the engine control unit 201 causes the printer controller 200 to A TOP signal (image request signal) is output. Upon receiving the /TOP signal, the printer controller 200 starts transmitting image signals to the engine control unit 201 . The engine control unit 201 instructs toner image formation.

The paper feeding unit 2 feeds a second sheet of recording paper (second recording material) of A5 size in synchronization with the arrival timing of the toner images sequentially formed on the intermediate transfer belt 11 to the secondary transfer unit. Then, the secondary transfer unit starts transferring the toner image onto the fed second sheet of recording paper (T2009). When the second sheet of recording paper that has passed through the secondary transfer section passes through the fixing section 50 and reaches just before the reversing section, the reversing section drives the solenoid 27, changes the position of the flapper 19, and transfers the second recording sheet to the reversing section. The pull-in operation of the first sheet of recording paper is started (T2010). After performing the pull-in operation corresponding to the length of the second sheet of recording paper, the reversing unit stops driving the solenoid 27, changes the position of the flapper 19, and completes the pull-in operation (T2012).

FIG. 6 shows the state of two sheets of recording paper in the image forming apparatus at timing T2012. FIG. 6 is an enlarged schematic diagram of the fixing section 50, the reversing section, and the reversing path 28 and their surroundings. In the figure, P1 is the first sheet of A4 size recording paper, which is waiting at the position of the paper re-feed waiting sensor 23 at timing T2012. On the other hand, in the figure, P2 is the second sheet of A5 size recording paper, and indicates the moment when the pull-in operation is completed at time T2012 and then the reversing operation in the direction of the reversing path 28 is started. As described above, in this embodiment, the drive source for the fixing section 50 and the reversing section is the motor 25 (see FIG. 1), and the drive force from the motor 25 is transmitted to the pair of rollers 20a and 20b by a clutch or the like. It is a configuration that cannot be stopped (blocked). As a result, the roller pairs 20a and 20b either rotate clockwise and counterclockwise, respectively, or rotate counterclockwise and clockwise, respectively. In the former case, the reversing section continues the operation of pulling in the second sheet of recording paper P2, after which the second sheet of recording paper P2 is discharged outside the apparatus. On the other hand, in the latter case, although the reversing section starts reversing the second sheet of recording paper P2, the reversing second sheet of recording paper P2 is then replaced by the first sheet of recording paper waiting on the reversing path 28. It collides with P1, causing a jam, which may damage both recording papers P1 and P2.

Therefore, in order to avoid the occurrence of defective printing, the instruction to form the toner image for the second side of the first sheet of recording paper (P1 in the drawing) waiting in the reverse path 28 is delayed by switching the heating element. It must be done without being forced. That is, instead of delaying the toner image formation instruction for the second side of the first recording sheet P1 by the switching operation of the heating element at T2005 in FIG. The contents of the print instruction for both the second side of the first sheet of recording paper P1 and the content of the print instruction are considered. Then, the heating element is selected so as not to switch the heating element when printing on the second side of the subsequent first sheet of recording paper P1. Therefore, in the case of the above-described print reservation command, A5, which is the specified size of the second sheet of recording paper on which the image to be formed second is fixed, and A5, which is the designated size of the second sheet of recording paper on which the image to be formed thirdly is fixed, The following control is performed in consideration of A4, which is the designated size of . In other words, the electric power is kept supplied to the heating element 54b1 which does not need to be switched to fix the third image to be formed. At this time, the heating element 54b1 for A4, which has a wider recording paper width, performs the fixing operation for A5, which is the designated size of the second recording paper on which the second formed image is to be fixed. With about one sheet, the temperature does not rise to the point where the fixing unit 50 is damaged, and there is no problem.

[Example of image forming operation that does not cause printing failure]
FIG. 7 is a timing chart for explaining an image forming operation for selecting a heating element in consideration of the size of recording paper designated by the print reservation command and the situation of double-sided printing. The horizontal axis in FIG. 7 indicates time, and T3001 to T3013 indicate timing. Note that the instruction content of the print reservation command transmitted from the printer controller 200 to the engine control unit 201 is the same as that in FIG. 5, so the description is omitted.

Upon receiving the print start command from the printer controller 200, the engine control unit 201 starts startup processing of each component of the image forming apparatus described with reference to FIG. 1 (T3001). Since the recording paper size of the first sheet of recording paper to which the first print reservation instruction is directed is A4, the fixing unit 50 can fix A4 size recording paper in the start-up process. Power is supplied to the heating element 54b1 to start temperature control.

In the fixing unit 50, the temperature of the entire length of the fixing roller 51 rises due to the heating element 54b1, and when the temperature exceeds the output permission temperature of the image signal (T3002), the engine control unit 201 sends the /TOP signal to the printer controller 200. Output. Upon receiving the /TOP signal, the printer controller 200 starts transmitting image signals to the engine control unit 201 . Upon receiving the image signal transmitted from the printer controller 200, the engine control unit 201 sequentially instructs the image formation control unit 202 to form Y, M, C, and K toner images. The paper feeding unit 1 feeds the first sheet of recording paper of A4 size in accordance with the arrival timing of the toner images sequentially formed on the intermediate transfer belt 11 to the secondary transfer unit. Transfer of the toner image to the first sheet of recording paper that has been fed is started (T3003). When the first sheet of recording paper that has passed through the secondary transfer section passes through the fixing section 50 and reaches just before the reversing section, the reversing section drives the solenoid 27, changes the position of the flapper 19, and records the first sheet. The operation of drawing the paper to the reversing portion is started (T3004). After performing the pull-in operation corresponding to the length of the first sheet of recording paper, the reversing unit stops driving the solenoid 27, returns the position of the flapper 19, and starts the reversing operation of the first sheet of recording paper. (T3007). When the re-feed waiting sensor 23 on the reversing path 28 detects the first sheet of recording paper, the reversing section stops conveying the first sheet of recording paper and transitions to a standby state (T3009).

The engine control unit 201 confirms the contents of the second print reservation command from the printer controller 200 at the timing when the first recording sheet passes the fixing roller 51 of the fixing unit 50 (T3005). Since the recording paper size of the second sheet of recording paper targeted by the second print reservation command is A5 and the first side, the engine control unit 201 then instructs the third print reservation command. Check the contents. The engine control unit 201 determines that the third print reservation instruction designates A4 for the first sheet of recording paper and the second side, and the recording paper size (A5) of the second sheet of recording paper for the second print reservation instruction. , it is determined that the heating element switching operation of the fixing unit 50 is unnecessary. Therefore, the engine control unit 201 does not perform the heating element switching operation of the fixing unit 50 . Engine control unit 201 supplies toner for A5 size recording paper, which is the second recording paper, to image formation control unit 202 at a predetermined interval in double-sided printing from the start of toner image formation on the first recording paper. The start of image formation is instructed (T3006). Next, the engine control unit 201 issues a third print reservation command, ie, the third print reservation command, after the start of toner image formation on the second sheet of recording paper. The start of toner image formation for one side is instructed (T3008).

The state of the reversing section during this period and the movement of the recording paper conveyed by the reversing section are as follows. At timing T3006, the image formation control unit 202 starts forming toner images on the intermediate transfer belt 11 in sequence. The paper feed unit 2 feeds the second sheet of A5 size recording paper in synchronism with the arrival timing of the toner image formed on the intermediate transfer belt 11 at the secondary transfer unit. Then, the transfer of the toner image to the second sheet of A5 size recording paper is started (T3010). When the second sheet of recording paper that has passed through the secondary transfer section passes through the fixing section 50 and reaches just before the reversing section, the reversing section drives the solenoid 27 to change the position of the flapper 19, thereby transferring the second sheet. The operation of drawing the recording paper into the reversing portion is started (T3011). On the other hand, at timing T3008, the reversing unit waits on the reversing path 28 in synchronization with the arrival timing (T3012) of the toner images sequentially formed on the intermediate transfer belt 11 by the image formation control unit 202 at the secondary transfer unit. Start conveying the first sheet of A4 size recording paper. After that, the reversing section performs a pull-in operation corresponding to the length of the second sheet of recording paper, stops driving the solenoid 27, returns the position of the flapper 19, and reverses the second sheet of recording paper. Start (T3013). At timing T3013, the reversing section starts conveying the first sheet of recording paper waiting in the reversing path 28 toward the secondary transfer section. Therefore, even if the reversing section starts reversing the second sheet of recording paper having a different size, the reversing section does not collide with the preceding first sheet of recording paper and does not cause printing defects. Duplex printing can continue.

[Control sequence for switching heating elements]
FIG. 8 is a flow chart showing a control sequence for switching the heating elements that supply electric power to the fixing section 50 . The processing shown in FIG. 8 is started when a print reservation command is received from the printer controller 200 and executed by the engine control unit 201 in order to execute a print job.

At step (hereinafter referred to as S) 1001, the engine control unit 201 performs the following processing. That is, the engine control unit 201 selects a print reservation command for which a heating element to be supplied with electric power to the fixing unit 50 is not determined among the print reservation commands received from the printer controller 200 for image formation. print instructions). If the engine control unit 201 determines that there is a print reservation command for which a heating element to which power is to be supplied has not been determined, the process advances to step S1002. If it is determined that there is no such, the process is terminated. In S1002, the engine control unit 201 determines whether or not there is a print reservation command (denoted as print instruction in the drawing) for which two or more heating elements to which power should be supplied have not been determined. If the engine control unit 201 determines that there is a print reservation command for which two or more heating elements to which power should be supplied has not been determined, the process advances to step S1003. On the other hand, if the engine control unit 201 determines that there are less than two print reservation commands for which the heating element to be supplied with power has not been determined, that is, one print reservation command, the process advances to step S1006.

In S1003, the engine control unit 201 determines that the first print reservation command is a print instruction for the first side of the second (subsequent) recording sheet of the two consecutive sheets of recording paper, and the second print reservation It is determined whether the command is a print instruction for the second side of the first (preceding) recording sheet. The first print reservation command (denoted as first print instruction in the figure) is also called the first print reservation command, and the second print reservation command (denoted as second print instruction in the figure) is 2 It is also called the second print reservation command. When the engine control unit 201 determines that the first print reservation command is for the first side of the second sheet of recording paper and the second print reservation command is for the second side of the first sheet of recording paper, The process proceeds to S1004. On the other hand, when the engine control unit 201 determines that the first print reservation command is for the first side of the second sheet of recording paper and the second print reservation command is not for the second side of the first sheet of recording paper. , the process proceeds to S1006. When the engine control unit 201 advances the process to S1006, for example, the first print reservation command is for the second side of the first sheet of recording paper, or the first print reservation command is for the second side of the recording paper (for example, the second sheet). The second print reservation command for the first side is also for the first side of the recording paper (for example, the third sheet).

In S1004, the engine control unit 201 determines whether the size of the second sheet of recording paper specified by the first print reservation command is different from the size of the first sheet of recording paper specified by the second print reservation command. Please judge. If the engine control unit 201 determines that the recording paper sizes specified by the first print reservation command and the second print reservation command are different, the process advances to step S1005, and the specified recording paper size is If it is determined that they are the same, the process advances to S1006.

In S1005, the engine control unit 201 selects the larger one of the second sheet of recording paper specified by the first print reservation command and the first sheet of recording paper specified by the second print reservation command. Power supply to the heating element 54b1 of the fixing unit 50 corresponding to the paper size is determined. Then, the engine control unit 201 controls the fixing control unit 205 to switch the power supply destination to the heating element 54b1 by the heating element switching device 57, and the process returns to S1001.

In S1006, the engine control unit 201 determines power supply to the heating element of the fixing unit 50 according to the size of the second sheet of recording paper specified by the first print reservation command. Here, the heating element corresponding to the recording paper size is determined as the heating element 54b2 when the recording paper size is A5 or less, and is determined as the heating element 54b1 when the recording paper size is larger than A5 and A4 or less. It is assumed that Then, the engine control unit 201 controls the fixing control unit 205 to switch the power supply destination to the heating element determined by the heating element switching unit 57, and returns the process to S1001.

As described above, according to this embodiment, when the drive source for the fixing unit and the reversing unit are the same, when a double-sided print job including recording sheets of different widths is executed, the heating element to which power is to be supplied is The heating element is determined so as not to introduce delays associated with switching. Specifically, when image formation is performed on two consecutive sheets of recording paper, the first side of the recording paper fed from the paper feed cassette first, and the second side of the recording paper waiting in the reverse path 28 are printed next. When performing image formation on one side, the heating element is determined so that it is not necessary to switch the heating element. In this way, when the first side of the recording paper fed from the paper feed cassette is printed and then the second side of the recording paper in the reverse path 28 is printed, a delay due to the switching of the heating element is caused. The heating element is determined so that switching of the heating element does not have to be performed. As a result, it is possible to perform double-sided printing on two continuous recording sheets without causing printing failures due to jamming or the like.

In this embodiment, the length of the heating element 54b1 is the width of A4 recording paper (longitudinal length), and the heating element 54b2 is the width of A5 recording paper (longitudinal length). However, for example, the width of the B5 recording paper (the length in the longitudinal direction) may be used as the heating element 54b2. The length of the heating element may be, for example, A3 width or postcard width, and is not limited to the length of the recording paper. Furthermore, in this embodiment, an image forming apparatus capable of forming a full-color image is shown as an example, but the present invention can also be applied to a configuration of a monochrome image forming apparatus.

As described above, according to this embodiment, when double-sided printing is performed on a plurality of recording materials, the heating element can be switched in consideration of the conveying state of the plurality of recording materials.

In the first embodiment, an example of a print job including a print reservation command from the printer controller 200 in which the size of recording paper is determined in advance has been described. In the second embodiment, when a print reservation command is received from the printer controller 200 in which the width of the recording paper on which the image is to be formed is not specified, such as an unspecified width of the recording paper or an irregular width, the heating element of the fixing unit 50 is operated. A determination method will be described.

[Recording paper width sensor]
FIG. 9 is a schematic diagram of a control circuit that controls power supply to the fixing section 50. As shown in FIG. FIG. 9 shows a recording paper width sensor for detecting the length (width) of the heating elements 54b1 and 54b2 of the fixing section 50 in the longitudinal direction and the width of the recording paper introduced into the fixing section 50 in the direction orthogonal to the conveying direction. is a diagram for explaining the positional relationship of . Note that the configuration of the fixing unit 50 is the same as that in FIG. 3 described in the first embodiment, and thus description thereof is omitted here.

Recording paper width sensors, which are detecting means, are arranged at respective positions indicated by the dashed line A in the figure, and are configured to detect the passage of the recording paper P conveyed from the secondary transfer portion in the direction of the arrow in the figure. there is In this embodiment, if the width of the recording paper P (the length in the left-right direction in the figure) is greater than the length between the dashed-dotted lines AA, the recording paper width sensor has the same length as the heating element 54b1. It is detected as recording paper having a paper width. On the other hand, if the width of the recording paper P is smaller than the length between the dashed-dotted lines AA, the recording paper width sensor detects the recording paper as having a width equal to that of the heating element 54b2. In this embodiment, the recording paper width sensor is arranged between the fixing section 50 and the secondary transfer section composed of the transfer roller 11c and the support roller 11b in FIG. Note that the configuration of the image forming apparatus and the system configuration are the same as those described in the first embodiment, and description thereof will be omitted here.

[Operation of each control unit by print job execution]
Next, in the image forming apparatus configured as described above, the operation of each control unit when a double-sided print job in which the paper width of the recording paper is not specified is transmitted from the printer controller 200 to the engine control unit 201 will be described. In this embodiment, it is assumed that A5-size recording paper is loaded in the paper feeding unit 1 and A4-size recording paper is loaded in the paper feeding unit 2 in advance.

The contents (printing information) of the print reservation commands transmitted from the printer controller 200 and acquired by the engine control unit 201 and their execution order are as follows.
・Paper feed section 1/side 1/unspecified ・Paper feed section 2/side 1/unspecified ・Reversing section/side 2/unspecified ・Paper feed section 2/side 1/unspecified Specified Paper feed unit 1/side 1/Unspecified/Reversed/side 2/Unspecified Paper feed unit 1/2 side/Unspecified Of the three specification items, the first specification item indicates from which paper supply unit (paper supply unit 1, paper supply unit 2, reversing unit) the recording paper to be printed is conveyed. The second specification item indicates which side of the recording paper the image is to be formed on. For the first side, the image is to be formed on the front side of the recording paper, and for the second side, the image is to be formed on the back side of the recording paper. means. It should be noted that the instruction is not limited to this, and 1-sided may mean an instruction to form an image on the back side of the recording paper, and 2-sided may mean an instruction to form an image on the front side of the recording paper. The third specification item indicates the size of the recording paper.

By executing the print reservation command described above, double-sided printing is performed in the following order. That is, side 1 of sheet 1, side 1 of sheet 2, side 2 of sheet 1, side 1 of sheet 3, side 2 of sheet 2, sheet 4 Duplex printing is performed on the first side of the first sheet, the second side of the third sheet, and the second side of the fourth sheet.

If the size of the recording paper is not specified, the width of the paper is unknown. Therefore, the image forming apparatus selects the wide heat generating element 54b1 as the heat generating element for supplying power to the fixing unit 50, and starts the preparatory operation. do. Further, in the image forming apparatus, when the toner image is fixed on the recording paper in the fixing section 50, the heating element 54b1 is used. When the first sheet of recording paper fed from the paper feeding unit 1 reaches the fixing unit 50, the width of the recording paper is determined to be equivalent to A5 size by the recording paper width sensor. For image formation on the second side of the same first sheet of recording paper, the heating element 54b2 corresponding to the A5 size recording sheet width of the fixing section 50 has an appropriate length. However, the second sheet of recording paper fed from the paper feeding unit 2 to be printed next is also unspecified, and the width of the paper is unknown. selects the heating element 54b1 to perform the fixing operation. Therefore, when the heating element of the fixing unit 50 is switched from the heating element 54b1 to the heating element 54b2 for the printing on the second side of the A5 size recording paper, which is the first recording paper, which is the third printing, , the printing failure (jam) described in FIG. 6 of the first embodiment occurs. Therefore, even in the case of a double-sided printing job in which the recording paper width is not specified and the recording paper width is not specified in this embodiment, the heating element 54b1 is used as it is so that the switching of the heating element for supplying power to the fixing unit 50 is not required. Power is supplied to perform the fixing operation.

FIG. 10 is a timing chart for explaining the image forming operation when the above-described print reservation command is transmitted from the printer controller 200 to the engine control unit 201. As shown in FIG. The horizontal axis indicates time, and T4001 to T4016 indicate timing. Since the flow of the basic image forming operation is the same as that of FIG. 7 described in the first embodiment, the same description will be omitted. Selection of the heating element after the width of the recording paper is detected by the recording paper width sensor will be described. The recording paper width sensor shown in the lower part of the figure indicates the output of the recording paper width sensor explained in FIG. outputs an ON signal, and outputs an OFF signal when the recording paper width is smaller than the width between AA.

Upon receiving the print start command from the printer controller 200, the engine control unit 201 starts startup processing of each component of the image forming apparatus (T4001). Since the recording paper size is not specified in the first print reservation command, the fixing unit 50 supplies power to the heating element 54b1, which is capable of fixing any recording paper width, in the start-up process, thereby controlling the temperature. to start. When the temperature of the fixing section 50 detected by the fixing temperature sensor 59 exceeds the image signal output permission temperature (T4002), the engine control section 201 outputs the /TOP signal to the printer controller 200. FIG. When the engine control unit 201 receives an image signal transmitted from the printer controller 200, the engine control unit 201 forms a toner image on the intermediate transfer belt 11, feeds the first sheet of A5 size recording paper by the paper feed unit 1, and performs secondary transfer unit A toner image is transferred to the first sheet of recording paper (T4003). Then, the engine control unit 201 causes the fixing unit 50 to fix the toner image on the first sheet of recording paper, the reversing unit to pull in the first sheet of recording paper (T4005), the reversing operation (T4007), and the refeeding operation. Conveyance stop by standby sensor 23 (T4009) is sequentially executed.

In the process of executing this duplex print job, when the first recording sheet reaches the fixing unit 50 (T4004), the OFF signal is output from the recording sheet width sensor, so the width of the first recording sheet is A5 size. It turns out to be reasonable. However, since the recording paper size of the second recording paper in the second print reservation command is not specified, power is not supplied at the timing (T4006) when the first recording paper passes through the fixing unit 50. The fixing operation is performed with the heating element 54b1 as it is without switching the heating element. Next, the instruction content of the third print reservation instruction is for printing on the second side of the first sheet of recording paper. The heating element 54b2 is suitable for the recording paper width (A5 size) of the first recording sheet found at timing T4004. However, at the timing (T4015) when the second sheet of recording paper passes through the fixing section 50, the power supply destination is not switched from the heating element 54b1 to the heating element 54b2, and the fixing operation is performed with the heating element 54b1. This is because the switching operation from the heating element 54b1 to the heating element 54b2 as described above causes a collision (jam) between the two recording sheets in the reversing path 28, resulting in printing failure.

[Control sequence for switching heating elements]
FIG. 11 is a flow chart showing a control sequence for switching the heating elements that supply power to the fixing section 50 . The processing shown in FIG. 11 is started when a print reservation command is received from the printer controller 200 and executed by the engine control unit 201 in order to execute a print job. When the print instruction from the printer controller 200 does not specify the recording paper size, the engine control unit 201 executes the processing shown in FIG.

In step S<b>2001 , the engine control unit 201 selects, among the print reservation commands received from the printer controller 200 , a print reservation command for which a heating element to which electric power should be supplied to the fixing unit 50 is not determined for image formation. , print instructions). If the engine control unit 201 determines that there is a print reservation command for which a heating element to which power is to be supplied has not been determined, the process advances to step S2002. If it is determined that there is no such, the process is terminated. In S2002, the engine control unit 201 determines whether or not there is a print reservation command (denoted as print instruction in the figure) for which two or more heating elements to which power should be supplied have not been determined. If the engine control unit 201 determines that there is a print reservation command for which two or more heating elements to which power should be supplied has not been determined, the process advances to step S2003. On the other hand, if the engine control unit 201 determines that there are less than two print reservation commands for which the heating element to be supplied with power has not been determined, that is, one print reservation command, the process advances to step S2009.

In S2003, the engine control unit 201 determines that the first print reservation command of the two consecutive recording sheets is a print instruction for the first side of the second (subsequent) recording sheet, and the second print reservation It is determined whether or not the command is a print instruction for the second side of the first (preceding) recording sheet. In FIG. 11, the first print reservation command is indicated as the first print instruction, and the second print reservation command is indicated as the second print instruction. When the engine control unit 201 determines that the first print reservation command is for the first side of the second sheet of recording paper and the second print reservation command is for the second side of the first sheet of recording paper, The process advances to S2004. On the other hand, when the engine control unit 201 determines that the first print reservation command is for the first side of the second sheet of recording paper and the second print reservation command is not for the second side of the first sheet of recording paper. , the process proceeds to S2009. When the engine control unit 201 advances the process to S2009, for example, the first print reservation command is for the second side of the first sheet of recording paper, or the first print reservation command is for the second side of the recording paper (for example, the second sheet). Regarding the first side, the second print reservation command is also for the first side of the recording paper (for example, the third sheet).

In S2004, the engine control unit 201 determines whether the size of the second sheet of recording paper specified by the first print reservation command is known. If the engine control unit 201 determines that the size of the second sheet of recording paper specified by the first print reservation command is detected by the recording paper width sensor and is known, the process advances to step S2005. On the other hand, if the engine control unit 201 determines that the size of the second sheet of recording paper specified by the first print reservation command is unknown, the process advances to step S2008.

In S2005, the engine control unit 201 determines whether the size of the first sheet of recording paper instructed by the second print reservation command is known. If the engine control unit 201 determines that the size of the first sheet of recording paper instructed by the second print reservation command is detected by the recording paper width sensor and is known, the process advances to step S2006. On the other hand, if the engine control unit 201 determines that the size of the first sheet of recording paper instructed by the second print reservation command is unknown, the process advances to step S2008.

In S2006, the engine control unit 201 determines whether the size of the second sheet of recording paper specified by the first print reservation command is the same as the size of the first sheet of recording paper specified by the second print reservation command. Please judge. If the engine control unit 201 determines that the recording paper sizes designated by the first print reservation command and the second print reservation command are the same, the process advances to step S2007, and the designated recording paper size is If it is determined that they are different (not the same), the process advances to S2008.

In step S2007, the engine control unit 201 designates the heating element corresponding to the recording paper instructed by the first and second print reservation commands by the first and second print reservation commands whose recording paper sizes are known. The heating element is determined according to the selected recording paper size. Then, the engine control unit 201 controls the fixing control unit 205 to switch the power supply destination to the heating element determined by the heating element switching unit 57, and returns the process to S2001.

In step S2008, the engine control unit 201 selects a heating element corresponding to the recording paper designated by the first and second print reservation commands as a heating element corresponding to a large recording paper size among the heating elements of the fixing unit 50. (In this embodiment, the heating element 54b1) is determined. Then, the engine control unit 201 controls the fixing control unit 205 to switch the power supply destination to the heating element 54b1 determined by the heating element switching unit 57, and returns the process to S2001. When the process of S2008 is executed, the recording paper width of the recording paper instructed by the first print reservation command or the recording paper width of the recording paper instructed by the second print reservation command is unknown, or This is the case where the known recording paper widths of the recording paper specified by the print reservation command are different. Therefore, the engine control unit 201 selects the heat generating element 54b1 capable of fixing any recording paper width as the heat generating element to which electric power is to be supplied.

In S2009, the engine control unit 201 determines whether the size of the second sheet of recording paper specified by the first print reservation command is known. If the engine control unit 201 determines that the size of the second sheet of recording paper instructed by the first print reservation command is detected by the recording paper width sensor and is known, the process advances to step S2010. On the other hand, if the engine control unit 201 determines that the size of the second sheet of recording paper specified by the first print reservation command is unknown, the process advances to step S2011.

In S2010, the engine control unit 201 instructs the heating element corresponding to the second sheet of recording paper instructed by the first print reservation command by the first print reservation command whose recording paper size is known. The heating element is determined according to the size of the recording paper. Then, the engine control unit 201 controls the fixing control unit 205 to switch the power supply destination to the heating element determined by the heating element switching unit 57, and returns the process to S2001.

In step S2011, the engine control unit 201 selects a heat generating element corresponding to the second sheet of recording paper instructed by the first print reservation command to generate heat corresponding to a large recording paper size among the heat generating elements of the fixing unit 50. The body (the heating element 54b1 in this embodiment) is determined. Then, the engine control unit 201 controls the fixing control unit 205 to switch the power supply destination to the heating element 54b1 determined by the heating element switching unit 57, and returns the process to S2001. Since the engine control unit 201 does not know the size of the second sheet of recording paper instructed by the first print reservation command, the engine control unit 201 selects the heating element 54b1 that can fix any recording sheet width as the heating element to which power should be supplied. are choosing.

As described above, in this embodiment, in a configuration in which the drive source for the fixing section and the reversing section are the same, recording sheets of different widths are stacked in each paper feed cassette, and the width of the recording sheet is not specified by the printer controller 200. The processing when a double-sided job execution command is issued has been described. As described above, when image formation is performed on two consecutive sheets of recording paper, the first side of the recording paper first fed from the paper feed cassette and the second side of the recording paper waiting in the reverse path 28 are printed next. When performing image formation on one side, the heating element is determined so as not to switch the heating element. In this way, when the first side of the recording paper fed from the paper feed cassette is printed and then the second side of the recording paper in the reverse path 28 is printed, a delay due to the switching of the heating element is caused. The heating element is determined so that switching of the heating element does not have to be performed. As a result, double-sided printing can be performed without causing printing defects.

In this embodiment, the heating element 54b1 has the width (length in the longitudinal direction) of A4 recording paper, and the heating element 54b2 has the width (length in the longitudinal direction) of A5 recording paper. I gave an example. The length of the heating element may be A3 width and postcard width, and is not limited to the length of the recording paper. Furthermore, although an apparatus capable of forming a full-color image has been shown as an example, the present invention can also be applied to a configuration of a monochrome image forming apparatus.

As described above, according to this embodiment, when double-sided printing is performed on a plurality of recording materials, the heating element can be switched in consideration of the conveying state of the plurality of recording materials.

In the present embodiment, the selection of heating elements will be described in the case of image formation using a power control circuit having a larger number of heating elements constituting the heater 54 than the power control circuit shown in the first embodiment. Since the basic configuration is the same as that of the first embodiment, different points will be explained.

[Control Circuit of Fixing Section]
FIG. 12 shows the power control circuit 97 used in this embodiment. The power control circuit 97 is composed of the heater 54 , the AC power supply 55 , the triacs 56 a and 56 b and the heating element switch 57 . The heater 54 is composed of heating elements 54m1 to 54m3 and contacts 54n1 to 54n4. The heating elements 54m1 to 54m3 are resistors that generate heat when supplied with power from an AC power supply 55 such as a commercial AC power supply. The contacts 54n1 and 54n2 are provided on one end side in the longitudinal direction of the substrate 54a, and the contacts 54n3 and 54n4 are provided on the other end side in the longitudinal direction of the substrate 54a. In this embodiment, the longitudinal lengths of the heating elements 54m1 to 54m3 are the widths (longitudinal lengths) of A4 size, B5 size, and A5 size recording paper, respectively. The heat generating elements are arranged in the order of heat generating element 54m1, heat generating element 54m2, heat generating element 54m3, and heat generating element 54m1 in the lateral direction of substrate 54a (from the top to the bottom in FIG. 12).

The heating element switch 57 has a contact 57a connected to the contact 54n2, a contact 57b1 connected to the triac 56b and the contact 54n3, and a contact 57b2 connected to the AC power supply 55 and the contact 54n4. When the contact 57a and the contact 57b1 are connected, the heating element switching device 57 is in a state capable of supplying electric power to the heating element 54m2. On the other hand, when the contact 57a and the contact 57b2 are connected to each other, the heating element switch 57 is ready to supply electric power to the heating element 54m3.

The triac 56a has one end connected to the contact 54n1 and the other end connected to the AC power supply 55 and the triac 56b. When the triac 56a is conductive, power is supplied to the heating element 54m1 (first heating element). On the other hand, the triac 56b has one end connected to the AC power supply 55 and the triac 56a, and the other end connected to the contacts 57b1 and 54n3 of the heating element switch 57. FIG. When the triac 56b is turned on, power is supplied to either the heating element 54m2 (second heating element) or the heating element 54m3 (third heating element) according to the connection state of the heating element switch 57. .

[Control Sequence for Heating Element Switching]
FIG. 13 shows a processing flow regarding the determination of the heating element of the engine control section 201. As shown in FIG. Since steps S3001 to S3004 of the flow are the same as steps S1001 to S1004 of the flow shown in FIG. 8, description thereof will be omitted, and steps S3005 and S3006 for determining the heating element will be described. In S3005, the engine control unit 201 selects the larger one of the second sheet of recording paper specified by the first print reservation command and the first sheet of recording paper specified by the second print reservation command. The power supply to the heating element of the fixing unit 50 corresponding to the paper size is determined. In FIG. 13, the first print reservation command is indicated as the first print instruction, and the second print reservation command is indicated as the second print instruction. In S3005, if the recording paper sizes of the recording papers of the first and second print reservation commands are A5 and B5, respectively, the heating element 54 m2 corresponding to the larger B5 is used for the first and second printing. Determined as a heating element for a reserved command. If the recording paper sizes for the first and second print reservation instructions are B5 and A4, respectively, the heating element 54m1 corresponding to the larger A4 size is used as the heating element for the two print reservation instructions. Determined as Furthermore, if the recording paper sizes for the first and second print reservation instructions are A5 and A4, respectively, the heating element 54m1 corresponding to the larger A4 size is used as the heating element for the two print reservation instructions. Determined as In S3006, the engine control unit 201 determines power supply to the heating element of the fixing unit 50 according to the size of the second sheet of recording paper instructed by the first print reservation command. Here, the heating element corresponding to the recording paper size is determined to be a 54m3 heating element when the recording paper size is A5 or less, and is determined to be a 54m2 heating element when the recording paper size is larger than A5 and B5 or less. If the size is larger than B5 and equal to or smaller than A4, the heating element is determined to be 54m1.

As described above, according to the present embodiment, when the drive source for the fixing section and the reversing section are configured to be the same, when the printer controller 200 issues a command to execute a double-sided printing job without specifying the width of the recording paper, the heating element is operated as follows. decide. In other words, the heating element is determined so as not to cause a delay due to the switching of the heating element between the formation of the toner image on the first side of the second sheet of recording paper and the formation of the toner image on the second side of the first sheet of recording paper, thereby causing printing defects. Double-sided printing can be performed without

In this embodiment, the heating element 54m1 has the width of A4 recording paper, the heating element 54m2 has the width of B5 recording paper, and the heating element 54m3 has the width of A5 recording paper. I gave an example. The length of the heating element may be A3 width and postcard width, and is not limited to the length of the recording paper. Furthermore, although an apparatus capable of forming a full-color image has been shown as an example, the present invention can also be applied to a configuration of a monochrome image forming apparatus.

As described above, according to this embodiment, when double-sided printing is performed on a plurality of recording materials, the heating element can be switched in consideration of the conveying state of the plurality of recording materials.

4 Image Forming Station 50 Fixing Unit 54b1 Heating Element 54b2 Heating Element 57 Heating Element Switch 201 Engine Control Unit

Claims (14)

an image forming means for forming a toner image on a recording material;
a heater having at least a first heat generating element and a second heat generating element having a length in a longitudinal direction perpendicular to the conveying direction of the recording material that is shorter than that of the first heat generating element; fixing means for fixing the unfixed toner image formed on the recording material by means;
switching means for switching a power supply path so that power can be supplied to either the first heating element or the second heating element of the heater;
and a control means for controlling the power supply path switched by the switching means,
When double-sided printing is performed on a plurality of recording materials, an image is formed on a first surface of a first recording material, the first recording material is made to wait on a double-sided conveying path, and a second printing material following the first recording material is formed. 2. An image forming apparatus for forming an image on a first surface of a recording material and forming an image on a second surface of the first recording material,
Based on the length of the first recording material in the longitudinal direction and the length of the second recording material in the longitudinal direction, the control means controls the first surface of the second recording material and the second recording material. The power supply path is controlled when the second surface of the recording material of No. 1 is fixed by the fixing means, and after the fixing means has fixed the first surface of the second recording material, the first recording material is fixed. An image forming apparatus , wherein control is performed so as not to switch the power supply path until the second surface of the image forming apparatus is fixed . When the length of the first recording material in the longitudinal direction and the length of the second recording material in the longitudinal direction are different, the control means supplies power to the first heating element. 2. The image forming apparatus according to claim 1 , wherein said switching means switches said power supply path. When the length of the first recording material in the longitudinal direction and the length of the second recording material in the longitudinal direction are the same, the control means controls the first heating element or the second heating element. The power supply path is switched by the switching means so that power is supplied to a heating element corresponding to the length of the first recording material or the second recording material in the longitudinal direction. The image forming apparatus according to claim 1 , wherein: A detecting means for detecting the length of the recording material in the longitudinal direction,
2. An image forming apparatus according to claim 1 , wherein said detection means is arranged between said image forming means and said fixing means. When the length of the first recording material in the longitudinal direction is not specified, the control means controls whether power is supplied to the first heating element when performing image formation on the first recording material. 5. The image forming apparatus according to claim 4 , wherein the power supply path is switched by the switching means such that the power supply path is switched. When the length of the second recording material in the longitudinal direction is not specified, the control means controls whether power is supplied to the first heating element when performing image formation on the first recording material. 5. The image forming apparatus according to claim 4 , wherein the power supply path is switched by the switching means such that the power supply path is switched. 2. The image forming apparatus according to claim 1 , wherein the heater has a third heating element whose length in the longitudinal direction is shorter than that of the second heating element. the fixing means has a substrate on which the first heating element, the second heating element, and the third heating element are arranged;
The first heat generating element includes one first heat generating element arranged at one end in the width direction of the substrate and the other first heat generating element arranged at the other end. and
3. The first heating element on one side, the second heating element, the third heating element, and the first heating element on the other side are arranged in this order in the lateral direction. 7. The image forming apparatus according to 7 . When the length of the first recording material in the longitudinal direction and the length of the second recording material in the longitudinal direction are different, the control means controls the first heating element and the second heating element. , of the third heating elements, the heating element corresponding to the length in the longitudinal direction of the recording material having the longer length in the longitudinal direction, out of the first recording material and the second recording material. When the length of the first recording material in the longitudinal direction and the length of the second recording material in the longitudinal direction are the same, the power supply path is switched by the switching means so that the power is supplied to is the heating element selected from the first heating element, the second heating element, and the third heating element according to the length of the first recording material or the second recording material in the longitudinal direction; 9. The image forming apparatus according to claim 8 , wherein the power supply path is switched by the switching means so that power is supplied to the image forming apparatus. The fixing means includes a first rotating body heated by the heater;
a second rotating body forming a nip with the first rotating body;
10. The image forming apparatus according to any one of claims 1 to 9 , comprising: 11. The image forming apparatus according to claim 10 , wherein said first rotating body is a film. The heater is arranged in the internal space of the film, and the film is sandwiched between the heater and the second rotating body. 12. The image forming apparatus according to claim 11 , wherein the film is heated at a nip formed therebetween. The image forming means transports a plurality of photosensitive drums on which images are formed, an intermediate transfer member to which the images formed on the plurality of photosensitive drums are transferred, and the image transferred on the intermediate transfer member. 13. The image forming apparatus according to any one of claims 1 to 12 , further comprising transfer means for transferring the image onto the first recording material or the second recording material. a reversing unit for reversing the first recording material or the second recording material on which the image is fixed by the fixing unit and conveying the first recording material or the second recording material to the double-sided conveying path; ,
driving means for driving the reversing means and the fixing means;
with
14. The image forming apparatus according to claim 1, wherein when said driving means drives said fixing means, said driving means also drives said reversing means.

Images