JP2020126204A - Image forming device - Google Patents

Abstract

To switch a heating element from one to another considering the conveyance state of a plurality of recording media when printing to both sides of the plurality of recording media.SOLUTION: The present invention comprises: a fixing unit 50 including a heater having at least an image forming station 4 where a toner image is formed on a recording medium, a heating element 54b1 and a heating element 54b2 the longitudinal length of which is shorter than the heating element 54b1, for fixing an unfixed toner image on the recording medium; a heating element selector switch 57 for switching a power supply path to the heating element 54b1 or heating element 54b2 of the heater; and an engine control unit 201 for controlling the power supply path. When printing to both sides of a plurality of recording media, the engine control unit 201 controls the power supply path for the case where the first side of a second recording medium and the second side of a first recording medium are fixed by the fixing unit 50, on the basis of the longitudinal length of the first recording medium and the longitudinal length of the second recording medium (S1003-S1006).SELECTED DRAWING: Figure 8

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a laser printer, and more particularly to a heating element switching control method for double-sided printing.

Conventionally, in an image forming apparatus using an electrophotographic method, when the fixing device has a plurality of heat generating elements having different lengths and is configured to be capable of exclusively exchanging heat generating elements for supplying electric power, The following switching control of the heating element 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 in the direction orthogonal to the recording material conveyance direction. As a result, the print job is executed while preventing the productivity of the image forming apparatus from being reduced while preventing damage to the heating element and the surrounding members due to the temperature rise of the non-sheet passing portion of the heating element through which the recording material does not pass. can do. For example, Patent Document 1 discloses a fixing unit having a plurality of heating elements corresponding to the maximum width of a recording material through which a paper can pass and the width of a small-sized recording material. Patent Document 1 proposes a method of supplying electric power to the fixing unit by switching to a heating element having a length suitable for the width of the recording material, based on the relationship between the width of the recording material and the length of the heating element.

JP, 2001-100558, A

In a 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 depending on the width of the recording material, it may not be possible to switch the heating element appropriately depending on the conveyance state of the plurality of recording materials that are double-sided printed. ..

The present invention has been made under such circumstances, and it is an object of the present invention to switch the heating element in consideration of the conveyance state of a plurality of recording materials when performing double-sided printing on a plurality of recording materials. ..

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

(1) An image forming unit for forming a toner image on a recording material, a first heating element, and a first heating element having a length in a longitudinal direction which is a direction orthogonal to a conveying direction of the recording material, which is shorter than that of the first heating element. And a fixing unit configured to fix an unfixed toner image formed on the recording material by the image forming unit, and the first heating unit or the second heating unit of the heater. A switching means for switching the power supply path so that power can be supplied to any one of the heating elements, and a control means for controlling the power supply path switched by the switching means. When performing double-sided printing, an image is formed on the first surface of the first recording material, the first recording material is made to stand by in the double-sided conveyance path, and the 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 has a length in the longitudinal direction of the first recording material, And the electric power for 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. An image forming apparatus characterized by controlling a supply path.

According to the present invention, when performing double-sided printing on a plurality of recording materials, it is possible to switch the heating element in consideration of the transport 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 the fixing unit of Examples 1 and 2. Schematic diagram illustrating the configuration of the electric power control circuit of the fixing unit of Embodiments 1 and 2. Control block diagram showing the system configuration of the image forming apparatus of Embodiments 1 and 2. Timing chart showing the image forming operation of the image forming apparatus of the first embodiment FIG. 3 is a diagram illustrating a state of recording paper in a reversing unit according to the first exemplary embodiment. Timing chart showing the image forming operation of the image forming apparatus of the first embodiment The flowchart which shows the control sequence which determines the heating element which supplies the electric power of Example 1. FIG. 6 is a diagram illustrating a positional relationship between a heating element and a recording paper width sensor according to the second embodiment Timing chart showing the image forming operation of the image forming apparatus of the second embodiment The flowchart which shows the control sequence which determines the heating element which supplies the electric power of Example 2. FIG. 3 is a schematic diagram illustrating a configuration of a power control circuit of a fixing unit according to a third exemplary embodiment. The flowchart which shows the control sequence which determines the heating element which supplies the electric power of Example 3.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Overview of image forming apparatus]
In FIG. 1, as an example of the image forming apparatus of the first embodiment, the entire configuration of a laser printer will be described. The image forming apparatus shown in FIG. 1 includes four image forming stations 4a, 4b, 4c, and 4d. From the left side in the figure, yellow (Y), magenta (M), cyan (C), and black (K). Image forming station having the toner of Further, a, b, c, and d at the end of the reference numerals in the drawing mean yellow (Y), magenta (M), cyan (C), and black (K), respectively. The respective image forming stations 4a to 4d, which are image forming means, have the same configuration, and in the following description, the symbols a to d will be omitted unless particularly required. The image forming apparatus shown in FIG. 1 can form a full-color image or a monochrome image on a recording material. Here, the recording material includes, for example, recording paper, OHP sheet, cloth and the like. Hereinafter, in this embodiment, a case of forming an image on a recording sheet will be described.

(Image forming section)
The image forming unit includes 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 carrier is formed by applying an organic photoconductive layer on the outer circumference 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). It is 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 and exposes the photosensitive drum 8 to form an electrostatic latent image. The developing roller 7 attaches toner to the electrostatic latent image formed on the surface of the photosensitive drum 8 to visualize it as a toner image of yellow (Y), magenta (M), cyan (C), and black (K). To do. The primary transfer roller 15 transfers the toner image on the photosensitive drum 8 (on the photosensitive drum) to the intermediate transfer belt 11 which is an intermediate transfer body. This is called primary transfer. The cleaning device 10 removes the toner remaining on the surface of the photosensitive drum 8 without being transferred to the intermediate transfer belt 11. The cleaning device 10 transfers 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 and then the toner image remaining on the intermediate transfer belt 11. Is collected and stored in a cleaner container.

The intermediate transfer belt 11 is stretched by supporting rollers 11 a and 11 b and arranged so as to come into contact with the photosensitive drum 8. The intermediate transfer belt 11 is rotated in the arrow direction (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. The secondary transfer section (also referred to as a transfer section) transfers the toner image on the intermediate transfer belt 11 to the recording sheet while nipping and conveying the recording sheet. This is called secondary transfer. The secondary transfer portion is arranged such that the transfer roller 11c contacts the intermediate transfer belt 11, and is also arranged at a position facing the support roller 11b.

(Paper feeder)
The paper feed unit 1 has paper feeds ka and 1b for feeding out recording paper (also referred to as recording material) stored in a paper feed cassette 1c. The paper feed cassette 1c as a storage unit stores recording paper on which an image is formed. The recording paper delivered from the paper supply unit 1 reaches the secondary transfer unit via the registration sensor 17. Like the paper feed unit 1, the paper feed unit 2 has a pair of paper feed rollers 2a and 2b for feeding the recording paper stored in the paper feed cassette 2c. The paper feed cassette 2c as a storage unit stores recording paper on which an image is formed. The recording paper sent by the paper feed roller pair 2 a and 2 b from the paper feed unit 2 connected to the lower part of the paper feed unit 1 passes through a part of the conveyance path of the paper feed unit 1 and the registration sensor 17 and is fed to the recording paper. The next transfer portion is reached.

(Fixer)
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, and is arranged so as to rotate in the arrow direction by a motor 25 that is a driving unit. Has been done. A heater 54 is built in the fixing roller 51. The recording paper on which the toner image has been transferred is conveyed by the fixing roller 51 and the pressure roller 53, and heat and pressure are applied to fix the fused toner image on the surface of the recording paper. The paper discharge roller pair 13a and 13b and the paper discharge roller pair 18a and 18b discharge the recording paper after the toner image is fixed to the paper discharge unit 14.

(Inversion part)
The reversing unit, which is a reversing unit, reverses the conveying direction of the recording paper on which the toner image is fixed by the fixing unit 50. The reversing unit is configured to convey the recording paper conveyed by the paper discharge rollers 13a and 13b in a direction in which the flapper 19 that changes the recording paper conveyance path and the reversing path 28 are conveyed. It is equipped with 20a and 20b. The flapper 19 and the reversing rollers 20a and 20b are arranged so as to be driven by a motor 25 that is the same drive source as the fixing unit 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. The solenoid 27 switches the position of the flapper 19 and the rotation direction of the reversing rollers 20a and 20b. The solenoid 27 can switch the flapper 19 between the position shown by the solid line and the position shown by the dotted line in FIG. Further, the position of the flapper 19 and the rotation direction of the reversing rollers 20a and 20b are configured to interlock with each other. When the flapper 19 is located at the position shown by the dotted line in FIG. 1, the reversing rollers 20a and 20b rotate in the direction in which the recording sheet is drawn into the reversing section. On the other hand, when the flapper 19 is located at the position shown by the solid line in FIG. 1, the reversing rollers 20a and 20b rotate in the direction in which the recording paper is conveyed to the reversing path 28.

(Refeed unit)
The reverse path 28, which is a double-sided conveyance path, includes conveyance roller pairs 21a and 21b, conveyance roller pairs 22a and 22b, conveyance roller pairs 24a and 24b, and a clutch (not shown) that controls transmission of driving force to each conveyance roller pair. ) And a refeed standby sensor 23. Each of the conveying roller pairs 21a/21b, 22a/22b, 24a/24b is driven by the motor 26 and a clutch that controls the supply of the driving force of the motor 26. The paper feed roller pairs 1a and 1b of the paper feed unit 1 and the paper feed roller pairs 2a and 2b of the paper feed unit 2 also control the motor 26 and the driving force supply of the motor 26, similarly to the transport roller pair. Driven by the clutch and.

The operation of the reversing unit is reversing the conveyance direction of the recording paper, conveying to a predetermined position in the reversing path 28, and conveying from the reversing path to the registration sensor 17. In the reversing operation of the recording paper conveyance direction, the reversing unit drives the solenoid 27 that changes the position of the flapper 19 to change the conveyance direction of the recording paper after the toner image is fixed by the fixing unit 50 to change the recording paper. Is guided to the reversing rollers 20a and 20b. Then, the reversing unit conveys the recording sheet to a position sufficiently downstream of the flapper 19 in the conveying direction, stops the solenoid 27, and changes the rotation direction of the reversing rollers 20a and 20b, thereby reversing the recording sheet. It is conveyed in the direction of 28.

During conveyance to a predetermined position in the reversing path 28, the reversing unit drives a clutch (not shown) to apply a driving force to the conveying roller pairs 21a and 21b, the conveying roller pairs 22a and 22b, and the conveying roller pairs 24a and 24b. Supply and rotate. Then, the reversing unit stops the clutch (not shown) at the time when the re-feed standby sensor 23 detects the recording sheet, and stops the supply of the driving force to each pair of the transport rollers.

During the conveyance from the inside of the reversing path 28 to the registration sensor 17, the reversing unit drives a clutch (not shown) to apply a driving force to the conveying roller pairs 21a and 21b, the conveying roller pairs 22a and 22b, and the conveying roller pairs 24a and 24b. Supply and rotate. Then, the reversing unit stops driving the clutch after the registration sensor 17 detects the recording paper.

[Configuration of fixing unit]
Next, the configuration of the fixing unit 50, which is the fixing unit 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 that is substantially orthogonal to the conveyance direction of the paper P described later. The length of the paper P in the direction (longitudinal direction) substantially orthogonal to the transport direction is called the width. FIG. 2 is a schematic sectional view of the fixing unit 50. The sheet P holding the unfixed toner image T from the left side of FIG. 2 is heated while being conveyed from the left side to the right side in the figure in the fixing nip portion N, so that the toner image T is fixed to the sheet P. The fixing unit 50 according to the first exemplary 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 the fixing nip portion N together with the fixing roller 51, and a 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. Grease is applied to the inner surface of the fixing roller 51 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 plays a role of guiding the fixing roller 51 from the inside and forming a fixing nip portion N between the fixing roller 51 and the pressure roller 53. 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 rotary body) is a roller as a pressure rotary body. The pressure roller 53 includes a core metal 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. The fixing roller 51 is driven to rotate by the rotation of the pressure roller 53. The heater 54, which 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.

The 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. The 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 heater 54 opposite to the protective glass layer 54e with respect to the substrate 54a, and is installed at the center position in the longitudinal direction of the heating elements 54b1 and 54b2 having different lengths in the longitudinal direction. It is in contact with the substrate 54a.

[Fixer control circuit]
FIG. 3 is a schematic diagram of a power control circuit that controls power supply to the fixing unit 50. The electric power control circuit of the fixing unit 50 includes heating elements 54b1 and 54b2, a bidirectional thyristor (hereinafter referred to as a 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 longitudinal length of the heating element 54b1 is longer than that of the heating element 54b2. In the present embodiment, the lengths of the heating elements 54b1 and 54b2 in the longitudinal direction are the widths (lengths in the longitudinal direction) of recording sheets of A4 size and A5 size, respectively. The triac 56, which is a switch means, has one end connected to the AC power supply 55 and the other end connected to a terminal connected to the heating element 54b1 and the heating element 54b2 of the heater 54, and the AC power supply 55 to the heating element 54b1 or the heating element. The power is supplied to or cut off from 54b2. The heating element switch 57, which is a switching unit, is a relay that connects the AC power supply 55 and the heating element 54b1 or the heating element 54b2 of the heater 54, and in this embodiment, a C contact relay is used. The heating element switching device 57 switches the terminal 54d1 connected to the heating element 54b1 or the terminal 54d2 connected to the heating element 54b2 so that either one of the heating elements 54b1 and 54b2 is supplied with power from the AC power supply 55. Select exclusively. An electric power supply path is formed by the triac 56 and the heating element switch 57 so that the electric power can be supplied to the heating element 54b1 or the heating element 54b2. In the initial state, the heating element switching unit 57 is in a state in which electric power from the AC power supply 55 can be supplied to the heating element 54b1 side. In order to prevent contact welding of the heating element switching unit 57, which is a C-contact relay, switching of the heating element switching unit 57 is performed in a state in which power supply to the heating elements 54b1 and 54b2 by the triac 56 is reliably 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 expands the received image code into bit data required for printing. Further, the printer controller 200 reads the 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 a control unit, receives the 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.

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 included in the image forming station 4 based on an instruction from the engine control unit 201. To do. Further, the image forming control unit 202 controls the blinking of the laser light that the scanning optical member 5 scans each photosensitive drum 8 according to the image signal from the printer controller 200, and forms a toner image on the intermediate transfer belt 11. Let

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

The paper feed control unit 204 controls the pickup solenoids of the paper feed units 1 and 2 and the motor 26 that is also a paper feed motor based on an instruction from the engine control unit 201, and the paper feed unit 1 and the paper feed unit 2 are fed. The recording sheets stacked in the unit 2 are fed toward the registration sensor 17.

The fixing control unit 205 controls 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 that is also a fixing motor, based on an instruction from the engine control unit 201. .. As a result, the fixing unit 50 fixes the toner image transferred onto the recording paper (recording material) onto the recording paper.

The reversal control unit 206 drives and stops the solenoid 27 that changes the position of the flapper 19 based on an instruction from the engine control unit 201. The reversal control unit 206 also drives and stops a clutch (not shown) that controls 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. As a result, the reversal control unit 206 controls the reversal of the recording paper, the transportation of the reversed recording paper to the standby position of the reversal path 28, and the transportation of the recording paper waiting at the standby position to the registration sensor 17.

[Operation of each control unit by executing print job]
Next, in the above-described image forming apparatus having the fixing unit 50 capable of switching the heating element, the printer controller 200 instructs the engine control unit 201 to perform double-sided printing on recording papers having different recording paper sizes, particularly different paper widths. The operation of each control unit in the case of being described will be described.

FIG. 5 is a timing chart for explaining the 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 in the upper part 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 in the lower part shows the operations of the image forming unit, the transfer unit, the fixing unit, the reversing unit, the paper feeding unit 1, and the paper feeding unit 2. In FIG. 5, the horizontal axis represents time, and T2001 to T2012 in the figure represent operation timings.

The print job shown in FIG. 5 is a double-sided two-sheet alternating printing, the first sheet is A4 size recording sheet, the second sheet is A5 size recording sheet, the third sheet is A5 size recording sheet, and the fourth sheet is A4 size recording sheet. It is a print job for recording paper of a size. Further, it is assumed that A4 size recording paper is loaded in the paper feed unit 1 and A5 size recording paper is loaded in the paper feed unit 2 in advance. Further, of the heating elements 54b1 and 54b2 included in 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. I have it.

The contents (print information) of the print reservation command transmitted from the printer controller 200 and acquired by the engine control unit 201 and the execution order thereof are as shown below under the above conditions.
・Paper feeder 1/1 side/A4
・Paper feeder 2/1 side/A5
・Reversing part/2 sides/A4
・Paper feeder 2/1 side/A5
・Reversing part/2 sides/A5
・Paper feeder 1/1 side/A4
・Reversing part/2 sides/A5
・Feeding unit 1/2 side/A4
In the content of the print reservation command, the first designated item among the three designated items separated by slashes (/) is the paper feeding unit (paper feeding unit 1, paper feeding unit 1) for which the recording paper to be printed is. 2, the reversing unit). The second designation item indicates on which side of the recording paper the image is to be formed, and if it is one side, it is an instruction to form an image on the front side of the recording paper or two sides. means. Note that the present invention is not limited to this, and may mean that the one side is the back side of the recording paper and the two sides are the image forming instructions on the front side of the recording paper. The third designated 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 recording sheet, the first side of the second recording sheet, the second side of the first recording sheet, the first side of the third recording sheet, the second side of the second recording sheet. Double-sided printing is performed on 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 is an image formation in the case where 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 designated by the print reservation command. It is a timing chart explaining operation.

When the engine control unit 201 receives the print start command from the printer controller 200, the engine control unit 201 starts the startup process of each component of the image forming apparatus described in FIG. 1 (T2001). Since the recording paper size of the first print reservation command is A4 designation, the fixing unit 50 supplies power to the heating element 54b1 side capable of fixing the recording paper of A4 size in the startup process, and Start control.

At the fixing unit 50, when the temperature of the entire lengthwise direction of the fixing roller 51 rises to the temperature required for fixing the toner image by the heating element 54b1 (T2002), the engine control unit 201 informs the printer controller 200 of the /TOP signal ( Image request signal) is output. Upon receiving the /TOP signal, the printer controller 200 starts transmitting the image signal to the engine control unit 201. When the engine control unit 201 receives the image signal transmitted from the printer controller 200, the engine control unit 201 instructs the image formation control unit 202 to sequentially form Y, M, C, and K toner image. The paper feeding unit 1 feeds the first A4 size recording paper (first recording material) at the timing of arrival of the toner images sequentially formed on the intermediate transfer belt 11 at the secondary transfer unit. Then, the secondary transfer unit starts transferring the toner image to the fed recording paper (T2003). When the first sheet of recording paper that has passed through the secondary transfer unit passes through the fixing unit 50 and reaches just before the reversing unit, the reversing unit drives the solenoid 27, changes the position of the flapper 19, and changes the position of the first recording sheet. The operation of pulling the paper to the reversing unit is started (T2004). The reversing unit performs the pulling-in operation according to the length of the recording paper, stops the driving of the solenoid 27, changes the position of the flapper 19, and starts the reversing operation of the first recording paper (T2006). .. The reversing unit stops the conveyance of the first sheet of recording paper when the re-feeding standby sensor 23 on the reversing path 28 detects the first sheet of recording paper, and transits to the standby state (T2008).

On the other hand, the recording paper size of the second print reservation command from the printer controller 200 is A5 designation. Therefore, the engine control unit 201 performs the switching operation of the heating element that supplies the electric power of the fixing unit 50 at the timing (T2005) when the first recording sheet passes the fixing roller 51. In the switching operation of the heating element that supplies electric power, 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. At the time 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 is set to the printer controller 200 as in the case of the first recording sheet. A TOP signal (image request signal) is output. Upon receiving the /TOP signal, the printer controller 200 starts transmitting the image signal to the engine control unit 201. The engine control unit 201 gives an instruction to form a toner image.

The paper feeding unit 2 feeds a second recording sheet of A5 size (second recording material) at the timing of arrival of the toner images sequentially formed on the intermediate transfer belt 11 at the secondary transfer unit. Then, the secondary transfer unit starts the transfer of the toner image onto the fed second recording sheet (T2009). When the second sheet of recording paper that has passed through the secondary transfer portion passes through the fixing portion 50 and reaches just before the reversing portion, the reversing portion drives the solenoid 27 to change the position of the flapper 19 and to the reversing portion. The drawing operation of the first recording sheet is started (T2010). The reversing unit performs the retracting operation according to the length of the second recording sheet, then stops driving the solenoid 27, changes the position of the flapper 19, and completes the retracting operation (T2012).

FIG. 6 shows the state of two recording sheets in the image forming apparatus at timing T2012. FIG. 6 is an enlarged schematic diagram of the periphery of the fixing unit 50, the reversing unit, and the reversing path 28. In the figure, P1 is the first recording sheet of A4 size, and is waiting at the position of the refeed standby sensor 23 at the timing T2012. On the other hand, in the figure, P2 is the second recording sheet of A5 size, and indicates the moment when the pulling-in operation is completed at the time of T2012 and then the reversing operation is started in the direction of the reversing path 28. As described above, in the present embodiment, the driving source for the fixing unit 50 and the reversing unit is the motor 25 (see FIG. 1), and the roller pair 20a, 20b transmits the driving force from the motor 25 by the clutch or the like. It is a configuration that cannot be stopped (shut off). Therefore, the roller pairs 20a and 20b are either in the clockwise direction and the counterclockwise direction, or in the counterclockwise direction and the clockwise direction, respectively. In the former case, the reversing unit continues the pulling-in operation of the second recording paper P2, and then the second recording paper P2 is discharged outside the apparatus. On the other hand, in the latter case, the reversing unit starts reversing the second recording paper P2, but thereafter, the reversed second recording paper P2 is the first recording paper waiting in the reversing path 28. There is a risk that the recording paper P1 and P2 on both sides will be damaged due to a collision with the paper P1.

Therefore, in order to avoid a situation in which a printing failure occurs, the toner image formation instruction for the second side of the first recording sheet (P1 in the figure) waiting in the reversing path 28 is delayed by switching the heating element. It must be done without letting it happen. That is, instead of delaying the instruction to form the toner image on the second side of the first recording sheet P1 by the switching operation of the heating element in T2005 of FIG. Both print instruction contents on the second side of the first recording sheet P1 are considered. Then, when printing the second surface of the subsequent first recording sheet P1, the heating element is selected so as not to switch the heating element. Therefore, in the case of the print reservation command described above, A5, which is the designated size of the second recording sheet on which the second image to be formed is fixed, and the first recording sheet on which the third image to be formed is fixed. The following control is performed in consideration of A4, which is the specified size of. That is, the heating element 54b1 that does not require switching of the heating element for fixing the third image to be formed is kept supplied with power. At that time, the fixing operation is performed by the heating element 54b1 for A4 having a large recording paper width with respect to A5 which is the designated size of the second recording paper on which the second image to be formed is fixed. With about one sheet, the temperature does not rise to a temperature at which the fixing unit 50 is damaged, and there is no problem.

[Example of image forming operation in which printing failure does not occur]
FIG. 7 is a timing chart for explaining the image forming operation for selecting the heating element in consideration of the designated size of the recording paper in the print reservation command and the situation of double-sided printing. The horizontal axis of 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 in FIG.

When the engine control unit 201 receives the print start command from the printer controller 200, the engine control unit 201 starts the startup process of each component of the image forming apparatus described in FIG. 1 (T3001). Note that the fixing unit 50 can fix the recording sheet of A4 size in the start-up process because the recording sheet size of the first recording sheet subjected to the first print reservation command is A4 designation. Electric power is supplied to the heating element 54b1 side to start temperature control.

In the fixing unit 50, the temperature of the entire region of the fixing roller 51 in the longitudinal direction is increased by the heating element 54b1 and exceeds the output permission temperature of the image signal (T3002), and 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 the image signal 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 toner images of Y, M, C, and K. The paper feeding unit 1 feeds the first recording sheet of A4 size at the timing when the toner images sequentially formed on the intermediate transfer belt 11 arrive at the secondary transfer unit. The transfer of the toner image to the first recording sheet fed is started (T3003). When the first sheet of recording paper that has passed through the secondary transfer unit passes through the fixing unit 50 and reaches just before the reversing unit, the reversing unit drives the solenoid 27, changes the position of the flapper 19, and changes the position of the first recording sheet. The operation of pulling the paper to the reversing unit is started (T3004). The reversing unit performs the pulling operation according to the length of the first recording sheet, then stops the driving of the solenoid 27, returns the position of the flapper 19, and starts the reversing operation of the first recording sheet. Yes (T3007). The reversing unit stops the conveyance of the first sheet of recording paper when the re-feeding standby sensor 23 on the reversing path 28 detects the first sheet of recording paper, and transits to the standby state (T3009).

The engine control unit 201 confirms the instruction content of the second print reservation command from the printer controller 200 at the timing (T3005) when the first recording sheet passes the fixing roller 51 of the fixing unit 50. Then, since the engine control unit 201 specifies the A5 size of the recording paper size of the second recording paper for which the second print reservation command is targeted and is the first side, the instruction of the third print reservation command is issued. Check the contents. The engine control unit 201 specifies that the third print reservation command is the A4 designation of the first recording paper and is the second side, and the recording paper size (A5) of the second recording paper of the second print reservation command. Therefore, 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. The engine control unit 201 sets a predetermined interval for double-sided printing from the start of toner image formation on the first sheet of recording paper, and causes the image formation control unit 202 to use the toner for the A5 size recording sheet, which is the second sheet of recording paper. An instruction to start image formation is given (T3006). Next, the engine control unit 201 makes a second print reservation command, that is, the second A4 size recording sheet, which is the third print reservation command, with a predetermined interval in double-sided printing from the start of toner image formation on the second recording sheet. The start of toner image formation on the first side is instructed (T3008).

The state of the reversing unit and the movement of the recording paper conveyed by the reversing unit during this period are as follows. At timing T3006, the image formation control unit 202 sequentially starts forming toner images on the intermediate transfer belt 11. The paper feeding unit 2 feeds the second A5 size recording paper at the timing when the toner image formed on the intermediate transfer belt 11 arrives at the secondary transfer unit, and the secondary transfer unit feeds the recording paper. Then, the transfer of the toner image to the second recording sheet of A5 size is started (T3010). When the second sheet of recording paper that has passed through the secondary transfer unit passes through the fixing unit 50 and reaches just before the reversing unit, the reversing unit drives the solenoid 27 to change the position of the flapper 19 and the second sheet of recording paper. The operation of pulling the recording paper to the reversing unit is started (T3011). On the other hand, at timing T3008, the reversing unit waits on the reversing path 28 at the timing (T3012) when the toner images sequentially formed on the intermediate transfer belt 11 by the image forming control unit 202 arrive at the secondary transfer unit. The conveyance of the first recording sheet of A4 size is started. After that, the reversing unit performs the pulling-in operation according to the length of the second recording sheet, and then stops the driving of the solenoid 27 to return the position of the flapper 19 to perform the reversing operation of the second recording sheet. It starts (T3013). It should be noted that at timing T3013, the reversing unit starts transporting the first recording sheet waiting on the reversing path 28 toward the secondary transfer unit. Therefore, even if the reversing unit starts the reversing operation of the second recording sheet having a different recording sheet size, the reversing unit does not collide with the preceding first recording sheet and print defects do not occur. Double-sided printing can be continued.

[Control sequence for switching heating elements]
FIG. 8 is a flowchart showing a control sequence for switching the heating element that supplies electric power to the fixing unit 50. The process illustrated in FIG. 8 is executed when the print reservation command is received from the printer controller 200 to execute the print job, and is executed by the engine control unit 201.

In 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 from the print reservation command received from the printer controller 200 in which the heating element to which the power of the fixing unit 50 is to be supplied in order to perform image formation is not determined (in the figure, Judge whether there is a print instruction and notation). If the engine control unit 201 determines that there is a print reservation command in which a heating element to which power is to be supplied is not determined, the process advances to step S1002, and a print reservation command in which a heating element to which power is to be supplied is not determined. If it is determined that there is not, the processing ends. In step S1002, the engine control unit 201 determines whether or not there is a print reservation command (indicated as a print instruction in the drawing) for which a heating element to which more than two powers are to be supplied has not been determined. If the engine control unit 201 determines that there is a print reservation command in which a heating element to which more than one power is to 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 elements to which power is to be supplied have not been determined, that is, one, then the process proceeds to S1006.

In S1003, the engine control unit 201 determines that the first print reservation command is the print instruction for the first side of the second (subsequent) recording paper among the two continuous recording papers, and the second print reservation is performed. The instruction determines whether or not it is a print instruction for the second side of the first (preceding) recording sheet. The first print reservation command (indicated as first print instruction in the figure) is also called the first print reservation command, and the second print reservation instruction (indicated 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 the first side of the second recording sheet and the second print reservation command is the second side of the first recording sheet, The process proceeds to S1004. On the other hand, when the engine control unit 201 determines that the first print reservation command is not the first side of the second recording sheet and the second print reservation command is not the second side of the first recording sheet. If so, the process proceeds to S1006. When the engine control unit 201 advances the process to S1006, for example, when the first print reservation command is for the second side of the first recording sheet, or when the first print reservation command is for the recording sheet (for example, the second sheet). The second print reservation command on the first side is also the case of the first side of the recording paper (for example, the third sheet).

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

In step S1005, the engine control unit 201 records the larger one of the second recording sheet designated by the first print reservation command and the first recording sheet designated by the second print reservation command. The 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 unit 57, and returns the processing to S1001.

In step 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 recording sheet designated by the first print reservation command. The heating element according to the recording paper size is determined as the heating element 54b2 when the recording paper size is A5 or smaller, and as the heating element 54b1 when the recording paper size is larger than A5 and A4 or smaller. I will. 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 processing to S1001.

As described above, according to the present exemplary embodiment, when the double-sided print job in which the recording papers having different paper widths are mixed is executed in the configuration in which the driving sources of the fixing unit and the reversing unit are the same, the heating elements to be supplied with power The heating element is determined so as not to cause a delay due to switching. Specifically, in the case of performing image formation on two continuous recording papers, the first surface of the recording paper first fed from the paper feed cassette and the second recording paper waiting on the reversing path 28 next. When forming an image on the surface, the heating element is determined so that the heating element does not need to be switched. In this way, when the first side of the recording paper fed from the paper feeding cassette is printed and then the second side of the recording paper of the reversing path 28 is printed, a delay due to switching of the heating element is caused. The heating element is determined so that it is not necessary to switch the heating element. As a result, it is possible to carry out double-sided printing of two continuous recording sheets without causing a printing failure due to a jam or the like.

In the present embodiment, the length of the heating element is such that the heating element 54b1 is the width of A4 recording paper (length in the longitudinal direction) and the heating element 54b2 is the width of A5 recording paper (length in the longitudinal direction). However, for example, the heating element 54b2 may have the width (length in the longitudinal direction) of the B5 recording paper. 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. Further, in the present embodiment, the image forming apparatus capable of forming a full-color image is shown as an example, but the present invention can be applied to the configuration of a monochrome image forming apparatus.

As described above, according to the present embodiment, when performing double-sided printing on a plurality of recording materials, it is possible to switch the heating element in consideration of the transport state of the plurality of recording materials.

In the first embodiment, the embodiment of the print job including the print reservation command from the printer controller 200 in which the size of the recording paper is determined in advance has been described. In the second embodiment, when the print reservation command that does not specify the paper width of the recording paper on which an image is to be formed, such as the recording paper width not specified or the irregular width, is received from the printer controller 200, the heating element of the fixing unit 50 receives the print reservation command. The 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 unit 50. 9 is a recording paper width sensor for detecting the length (width) in the longitudinal direction of the heating elements 54b1 and 54b2 of the fixing unit 50 and the width in the direction orthogonal to the conveying direction of the recording paper introduced into the fixing unit 50. It is a figure explaining the positional relationship of. The configuration of the fixing unit 50 is the same as that of FIG. 3 described in the first embodiment, and thus the description thereof is omitted here.

The recording paper width sensor, which is a detecting means, is arranged at each position of the alternate long and short dash line A in the drawing, and detects the passage of the recording paper P conveyed from the secondary transfer portion in the direction of the arrow in the drawing. There is. In this embodiment, if the width of the recording paper P (the length in the left-right direction in the figure) is larger than the length between the alternate long and short dash lines AA, the recording paper width sensor has the same length as the heating element 54b1. It is detected as a 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 alternate long and short dash lines AA, the recording paper width sensor detects it as a recording paper having a paper width equal to that of the heating element 54b2. In this embodiment, the recording paper width sensor is arranged between the fixing unit 50 and the secondary transfer unit including the transfer roller 11c and the support roller 11b in FIG. The configuration of the image forming apparatus and the system configuration are the same as the configurations described in the first embodiment, and the description thereof is omitted here.

[Operation of each control unit by executing print job]
Next, in the image forming apparatus having the above-described configuration, the operation of each control unit when a double-sided print job in which the paper width of the recording paper is unspecified 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 feed unit 1 and A4 size recording paper is loaded in the paper feed unit 2 in advance.

The content (print information) of the print reservation command transmitted from the printer controller 200 and acquired by the engine control unit 201 and its execution order are as follows.
-Paper feed section 1/1 side/Unspecified-Paper feed section 2/1 side/Unspecified-Reversal section /2 side/Unspecified-Paper feed section 2/1 side/Unspecified-Reverse section /2 side/Unspecified Specified/Paper feed section 1/1 side/Undesignated/Inverted section/2 sides/Undesignated/Paper feed section 1/2 side/Undesignated In the contents of the print reservation command, 3 separated by a slash (/) The first designated item of the designated items indicates from which sheet feeding unit (sheet feeding unit 1, sheet feeding unit 2, reversing unit) the recording paper to be printed is conveyed. The second designation item indicates on which side of the recording paper the image is to be formed, and if it is one side, it is an instruction to form an image on the front side of the recording paper or two sides. means. Note that the present invention is not limited to this, and may mean that the one side is the back side of the recording paper and the two sides are the image forming instructions on the front side of the recording paper. The third designated 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, the first side of the second sheet, the second side of the first sheet, the first side of the third sheet, the second side of the second sheet, the fourth side Double-sided printing is performed on the first side of the third sheet, the second side of the third sheet, and the second side of the fourth sheet.

Since the paper width is unknown when the size of the recording paper is not specified, the image forming apparatus selects the wide heating element 54b1 as the heating element that supplies the electric power of the fixing unit 50, and starts the preparatory operation. To do. The image forming apparatus also uses the heating element 54b1 to fix the toner image on the recording paper in the fixing unit 50. When the first sheet of recording paper fed from the paper supply unit 1 reaches the fixing unit 50, the recording paper width sensor described above determines that the recording paper width is equivalent to A5 size. For the image formation on the second side of the same first recording sheet, the heating element 54b2 corresponding to the A5 size recording sheet width of the fixing section 50 becomes a heating element of an appropriate length. However, since the second recording sheet fed from the sheet feeding section 2 for the next printing is not designated and the sheet width is unknown, the heating element of the fixing section 50 continues. 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 second printing of the A5 size recording sheet which is the first printing sheet as the third printing. The printing defect (jam) described in FIG. 6 of the first embodiment occurs. Therefore, even in the case of a double-sided print job in which the recording paper is not specified in the present embodiment and the recording paper width is not specified, the heating element 54b1 is directly used so that the switching of the heating element for supplying the electric power of the fixing unit 50 is unnecessary. The fixing operation is performed by supplying electric power.

FIG. 10 is a timing chart illustrating an image forming operation when the above print reservation command is transmitted from the printer controller 200 to the engine control unit 201. The horizontal axis represents time, and T4001 to T4016 represent timing. Since the basic flow of the image forming operation is the same as that in FIG. 7 described in the first embodiment, the same description is omitted, and the selection of the heating element when the designation of the recording paper width is not designated, and The selection of the heating element after the recording paper width sensor detects the recording paper width will be described. Further, the recording paper width sensor shown in the lower part of the figure shows the output of the recording paper width sensor described in FIG. 9, and when a recording paper having a paper width larger than the width AA shown in FIG. Outputs an ON signal, and outputs an OFF signal in the case of recording paper having a paper width smaller than the width between AA.

When the engine control unit 201 receives the print start command from the printer controller 200, the engine control unit 201 starts the startup process of each component of the image forming apparatus (T4001). Since the recording paper size of the first print reservation command is not specified, the fixing unit 50 supplies electric power to the heating element 54b1 side capable of fixing any recording paper width in the start-up process to control the temperature. To start. When the temperature detected by the fixing temperature sensor 59 by the fixing unit 50 exceeds the image signal output permission temperature (T4002), the engine control unit 201 outputs the /TOP signal to the printer controller 200. When the engine control unit 201 receives the 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 recording sheet of A5 size by the paper feeding unit 1, and transfers the secondary transfer unit. Then, the toner image transfer (T4003) to the first sheet of recording paper is performed. Then, the engine control unit 201 fixes the toner image on the first recording sheet by the fixing unit 50, pulls in the first recording sheet by the reversing unit (T4005), reverses the operation (T4007), and re-feeds the sheet. The conveyance stop at the standby sensor 23 (T4009) is sequentially executed.

In the execution process of this double-sided printing job, since the OFF signal is output from the recording paper width sensor when the first recording paper reaches the fixing unit 50 (T4004), the first recording paper width is A5 size. It turns out to be considerable. However, since the recording paper size of the second recording paper of the second print reservation command is not specified, power is supplied at the timing (T4006) when the first recording paper passes 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 command is for printing the second side of the first recording sheet. The heating element suitable for the recording sheet width (A5 size) of the first recording sheet found at timing T4004 is the heating element 54b2. However, at the timing (T4015) when the second recording sheet passes through the fixing unit 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 when the switching operation from the heating element 54b1 to the heating element 54b2 is performed as described above, a printing failure occurs due to a collision (jam) between two recording sheets in the reversing path 28.

[Control sequence for switching heating elements]
FIG. 11 is a flowchart showing a control sequence for switching the heating element that supplies electric power to the fixing unit 50. The process illustrated in FIG. 11 is executed when a print reservation command is received from the printer controller 200 to execute a print job, and is executed by the engine control unit 201. When the recording paper size of the print instruction from the printer controller 200 is not specified, the engine control unit 201 executes the process shown in FIG.

In step S<b>2001, the engine control unit 201 determines, out of the print reservation commands received from the printer controller 200, a heat generation unit to which power of the fixing unit 50 is to be supplied to form an image (a print reservation command in the drawing). , Print instruction and notation). When the engine control unit 201 determines that there is a print reservation command in which a heating element to which power is to be supplied is not determined, the process advances to step S2002, and a print reservation command in which a heating element to which power is to be supplied is not determined. If it is determined that there is not, the processing ends. In S2002, the engine control unit 201 determines whether or not there is a print reservation command (indicated as a print instruction in the drawing) for which a heating element to which more than two powers are to be supplied has not been determined. If the engine control unit 201 determines that there is a print reservation command in which the heating elements to which more than two powers are to be supplied are not 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 which power is to be supplied has not been determined, that is, one print reservation command, the process advances to step S2009.

In step S2003, the engine control unit 201 determines that the first print reservation command is the print instruction for the first surface of the second (subsequent) recording paper among the two continuous recording papers, and the second print reservation is performed. It is determined whether the command is a print command for the second side of the first (preceding) recording sheet. In FIG. 11, the first print reservation command is described as a first print instruction, and the second print reservation command is described as a second print instruction. When the engine control unit 201 determines that the first print reservation command is the first side of the second recording sheet and the second print reservation command is the second side of the first recording sheet, The process proceeds to S2004. On the other hand, when the engine control unit 201 determines that the first print reservation command is not the first side of the second recording sheet and the second print reservation command is not the second side of the first recording sheet. If so, the process proceeds to S2009. When the engine control unit 201 advances the process to S2009, for example, when the first print reservation command is for the second side of the first recording sheet, or when the first print reservation command is for the recording sheet (for example, the second sheet). Although it is the first side, the second print reservation command is also the case of the first side of the recording paper (for example, the third sheet).

In step S2004, the engine control unit 201 determines whether the size of the second recording sheet designated by the first print reservation command is known. When the engine control unit 201 determines that the size of the second sheet of recording paper designated by the first print reservation command is detected by the recording paper width sensor and is known, the process proceeds to step S2005. On the other hand, if the engine control unit 201 determines that the size of the second recording sheet designated by the first print reservation command is not known, the process advances to step S2008.

In step S2005, the engine control unit 201 determines whether the size of the first recording sheet designated 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 designated 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 recording sheet designated by the second print reservation command is not known, the process advances to step S2008.

In step S2006, the engine control unit 201 determines whether the size of the second recording sheet designated by the first print reservation command is the same as the size of the first recording sheet designated by the second print reservation command. Make a decision. If the engine control unit 201 determines that the sizes of the recording papers 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 proceeds to S2008.

In step S2007, the engine control unit 201 instructs the heating elements corresponding to the recording sheets designated by the first and second print reservation commands by the first and second print reservation commands whose recording sheet sizes are known. The heating element is determined according to the 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 processing to S2001.

In step S2008, the engine control unit 201 sets the heating element corresponding to the recording sheet designated by the first and second print reservation commands to the heating element corresponding to the larger recording sheet size of the heating elements of the fixing unit 50. (The heating element 54b1 is selected in this embodiment). 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 processing to S2001. When the process of S2008 is executed, the recording paper width of the recording paper specified by the first print reservation command or the recording paper specified by the second print reservation command is unknown, or the first and second This is a case where the identified recording paper width of the recording paper designated by the print reservation command is different. Therefore, the engine control unit 201 selects the heat generating element 54b1 capable of fixing with any recording paper width as the heat generating element to which power is to be supplied.

In step S2009, the engine control unit 201 determines whether the size of the second recording sheet designated 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 designated by the first print reservation command is detected by the recording paper width sensor and is determined, the process advances to step S2010. On the other hand, if the engine control unit 201 determines that the size of the second recording sheet designated by the first print reservation command is not known, the process advances to step S2011.

In S2010, the engine control unit 201 designates the heating element corresponding to the second recording sheet designated by the first print reservation command by the first print reserve command whose recording paper size is known. Select a heating element according to the 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 processing to S2001.

In step S2011, the engine control unit 201 causes the heating element corresponding to the second recording sheet designated by the first print reservation command to generate heat corresponding to a larger recording sheet size of the heating elements of the fixing unit 50. The body (in the present 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 processing to S2001. Since the size of the second recording sheet specified by the first print reservation command is not known, the engine control unit 201 determines that the heating element 54b1 that can fix the recording sheet with any width as the heating element to be supplied with power. Is selected.

As described above, in the present embodiment, when the fixing unit and the reversing unit have the same drive source, the recording paper width is not specified by the printer controller 200 when the recording papers having different paper widths are stacked in the respective paper feed cassettes. The processing when the execution of the double-sided job is instructed has been described. As described above, in the case of performing image formation on two continuous recording sheets, the first side of the recording sheet fed first from the sheet feeding cassette and the second recording sheet waiting on the reversing path 28. When forming an image on the surface, 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 feeding cassette is printed and then the second side of the recording paper of the reversing path 28 is printed, a delay due to switching of the heating element is caused. The heating element is determined so that it is not necessary to switch the heating element. As a result, double-sided printing can be performed without causing print defects.

In the present 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. An example was given. The length of the heating element may have a configuration of 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 be applied to the configuration of a monochrome image forming apparatus.

As described above, according to the present embodiment, when performing double-sided printing on a plurality of recording materials, it is possible to switch the heating element in consideration of the transport state of the plurality of recording materials.

In this embodiment, as compared with the power control circuit shown in the first embodiment, selection of a heating element when an image is formed by using the power control circuit having a larger number of heating elements forming the heater 54 will be described. Since the basic configuration is the same as that of the first embodiment, only different points will be described.

[Fixer control circuit]
FIG. 12 shows a power control circuit 97 used in this embodiment. The power control circuit 97 includes a heater 54, an AC power supply 55, triacs 56a and 56b, and a heating element switch 57. The heater 54 includes 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 the present embodiment, the lengths of the heating elements 54m1 to 54m3 in the longitudinal direction are the widths (lengths in the longitudinal direction) of recording papers of A4 size, B5 size, and A5 size, respectively. The heating elements are arranged in the lateral direction of the substrate 54a (from the upper side to the lower side in FIG. 12) in the order of the heating element 54m1, the heating element 54m2, the heating element 54m3, and the heating element 54m1.

The heating element switching unit 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. The heating element switch 57 is in a state in which electric power can be supplied to the heating element 54m2 when the contact 57a and the contact 57b1 are connected. On the other hand, the heating element switch 57 is in a state in which electric power can be supplied to the heating element 54m3 when the contact 57a and the contact 57b2 are connected.

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 conducts, electric 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 contact 57b1 and the contact 54n3 of the heating element switching unit 57. When the triac 56b becomes conductive, power is supplied to either the heating element 54m2 (second heating element) or the heating element 54m3 (third heating element) depending on the connection state of the heating element switch 57. ..

[Control sequence for heating element switching]
FIG. 13 shows a processing flow regarding determination of a heating element of the engine control unit 201. It should be noted that steps S3001 to S3004 of the flow are the same as steps S1001 to S1004 of the flow shown in FIG. 8, and therefore description thereof will be omitted, and steps S3005 and S3006 for determining the heating element will be described. In step S3005, the engine control unit 201 records the larger one of the second recording sheet designated by the first print reservation command and the first recording sheet designated 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. Note that, in FIG. 13, the first print reservation command is described as a first print instruction, and the second print reservation command is described as a second print instruction. In S3005, when the recording paper sizes of the recording paper of the first and second print reservation commands are A5 and B5, respectively, the heating element 54m2, which is a heating element corresponding to the larger B5, is printed on the first and second prints. Determined as a heating element for a reservation order. Further, when the recording paper sizes of the first and second print reservation commands are B5 and A4, respectively, the heating element 54m1 which is a heating element corresponding to the larger A4 is used as the heating element for the two print reservation commands. To decide. Furthermore, when the recording paper sizes of the first and second print reservation commands are A5 and A4, respectively, the heating element 54m1 which is a heating element corresponding to the larger A4 is used as the heating element for the two print reservation commands. To decide. In step 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 recording sheet designated by the first print reservation command. Here, the heating element according to the recording sheet size is determined to be the heating element 54m3 when the recording sheet size is A5 or smaller, and is determined to be the heating element 54m2 when the recording sheet size is larger than A5 and B5 or smaller. When the size is larger than B5 and smaller than A4, it is determined as the heating element 54m1.

As described above, according to the present exemplary embodiment, when the fixing controller and the reversing unit have the same drive source, when the double-sided print job execution is instructed from the printer controller 200 without specifying the recording paper width, the heating element is set as follows. decide. That is, a printing defect occurs by determining the heating element so as not to cause a delay due to switching of the heating element between the toner image formation on the first surface of the second recording paper and the second surface of the first recording paper. It becomes possible to perform double-sided printing without doing so.

In this embodiment, the length of the heating element is such that 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. An example was given. The length of the heating element may have a configuration of 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 be applied to the configuration of a monochrome image forming apparatus.

As described above, according to the present embodiment, when performing double-sided printing on a plurality of recording materials, it is possible to switch the heating element in consideration of the transport state of the plurality of recording materials.

4 image forming station 50 fixing unit 54b1 heating element 54b2 heating element 57 heating element switching unit 201 engine control section

Claims (15)

Image forming means for forming a toner image on the recording material,
The image forming apparatus includes a heater having at least a first heating element and a second heating element having a length in a longitudinal direction which is a direction orthogonal to a recording material conveyance direction and shorter than the first heating element. Fixing means for fixing the unfixed toner image formed on the recording material by the 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;
Control means for controlling the power supply path switched by the switching means,
When performing double-sided printing on a plurality of recording materials, an image is formed on the first surface of the first recording material, the first recording material is made to stand by in the double-sided conveyance path, and the first recording material is connected to the first recording material. An image forming apparatus for forming an image on the first surface of a second recording material and forming an image on the second surface of the first recording material,
The control means, 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 first surface of the second recording material and the first recording material. An image forming apparatus, wherein the power supply path is controlled when the second surface of the first recording material is fixed by the fixing unit. The control unit does not switch the power supply path until the fixing unit fixes the first surface of the second recording material and then fixes the second surface of the first recording material. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled according to claim 1. When the length of the first recording material in the longitudinal direction is different from the length of the second recording material in the longitudinal direction, the control means is configured to supply power to the first heating element. The image forming apparatus according to claim 2, wherein the switching means switches the power supply path. The control means, when the length of the first recording material in the longitudinal direction is the same as the length of the second recording material in the longitudinal direction, the first heating element or the second heating element. Among the bodies, the switching means switches the power supply path so that power is supplied to a heating element according to the length of the first recording material or the second recording material in the longitudinal direction. The image forming apparatus according to claim 2. A recording means for detecting the length of the recording material in the longitudinal direction,
The image forming apparatus according to claim 2, wherein the detecting unit is arranged between the image forming unit and the fixing unit. When the length of the first recording material in the longitudinal direction is not designated, the control means supplies power to the first heating element when forming an image on the first recording material. The image forming apparatus according to claim 5, wherein the switching means switches the power supply path. When the length of the second recording material in the longitudinal direction is not specified, the control means supplies power to the first heating element when forming an image on the first recording material. 6. The image forming apparatus according to claim 5, wherein the switching means switches the power supply path. The image forming apparatus according to claim 2, wherein the heater has a third heating element having a length in the longitudinal direction shorter than that of the second heating element. The fixing unit has a substrate on which the first heating element, the second heating element, and the third heating element are arranged,
The first heating element includes one of the first heating elements arranged at one end portion in the lateral direction of the substrate and the other of the first heating element arranged at the other end portion. And
The one first heating element, the second heating element, the third heating element, and the other first heating element are arranged in this order in the lateral direction. 8. The image forming apparatus according to item 8. When the length of the first recording material in the longitudinal direction is different from the length of the second recording material in the longitudinal direction, the control unit controls the first heating element and the second heating element. A heating element according to the longitudinal length of the recording material of the first recording material or the second recording material, which has the longer longitudinal length, of the third heating elements, When the power supply path is switched by the switching means so that the power is supplied to the first recording material, the length of the first recording material in the longitudinal direction is the same as the length of the second recording material in the longitudinal direction. Among the first heating element, the second heating element, and the third heating element, is a heating element corresponding to the length of the first recording material or the second recording material in the longitudinal direction. 10. The image forming apparatus according to claim 9, wherein the switching unit switches the power supply path so that the power is supplied to the image forming apparatus. The fixing unit includes a first rotating body heated by the heater,
A second rotating body that forms a nip portion together with the first rotating body;
The image forming apparatus according to claim 1, further comprising: The fixing device according to claim 11, wherein the first rotating body is a film. The heater is provided in contact with the inner surface of the film,
The fixing device according to claim 12, wherein the nip portion is formed by the heater and the second rotating body via the film. The image forming unit conveys a plurality of photosensitive drums on which an image is 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. 14. The image forming apparatus according to claim 1, further comprising: a transfer unit configured to transfer the transferred first recording material or the second recording material. Reversing means for reversing the first recording material or the second recording material on which the image has been fixed by the fixing means, and conveying the first recording material or the second recording material to the double-sided conveyance path; ,
Drive means for driving the reversing means and the fixing means,
Equipped with
15. The image forming apparatus according to claim 1, wherein when the driving unit drives the fixing unit, the reversing unit is also driven by the driving unit.

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