JP2008213976A - Image forming device, controlling program, and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a problem in which print processing is wrongly stopped due to erroneous determination of a determining portion determining the presence of double feed, in an image forming device. <P>SOLUTION: The image forming device includes a double feed detecting sensor DD, and a control portion 100. The double feed detecting sensor DD judges whether a double feed state wherein two or more sheets of papers are superimposed and carried is occurred or not in a paper carrying passage before the print processing. The control portion 100 carries out control for stopping the print processing when the double feed state occurs by referring to the result of the judgement. The control portion 100 refers to the result of the determination executed before the first print processing, when double-sided print processing including the first printing processing for printing on a first surface of the paper and second printing processing for printing on a second surface of the paper is carried. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus provided with a double feed detection device.

  In image forming apparatuses such as printers, copiers, and multi-function machines, sheets are conveyed one by one to a printing unit where images are printed on the sheets. There is a case where a state of being overlapped and simultaneously transported (hereinafter, this state is referred to as “double feeding”) may occur. When double feeding occurs upstream of the printing unit in the image forming apparatus, printing failure occurs in the printing unit.

  Therefore, in the conventional image forming apparatus, a double feed detection device (double feed detection sensor) for determining whether or not double feed has occurred is provided on the upstream side of the printing unit, and double feed has occurred by the double feed detection device. If it is determined that the print processing is determined, control for canceling the print processing is performed in advance.

  In addition, various devices have been known as the above-described multifeed detection device, but recently, an ultrasonic multifeed detection device is frequently used. Hereinafter, the principle of the ultrasonic multifeed detection device will be described.

  FIG. 1A is a diagram illustrating a state in which a sheet is normally conveyed in the sheet conveyance path, and FIG. 1B is a diagram illustrating a state in which double feeding is occurring in the sheet conveyance path. It is.

  As shown in FIG. 1 (a) or FIG. 1 (b), ultrasonic double feed detection devices 500 are arranged to face each other across a paper conveyance path S on the upstream side of a printing unit. And an ultrasonic receiver 520. The ultrasonic transmitter 510 transmits an ultrasonic wave toward the ultrasonic receiver 520 at the timing when the paper P is conveyed between the ultrasonic transmitter 510 and the ultrasonic receiver 520. The ultrasonic wave transmitted in this way is greatly attenuated by passing through the paper P being conveyed, and the ultrasonic wave receiver whose intensity is greatly reduced by the attenuation is received by the ultrasonic receiver 520.

  Further, when double feeding occurs in the paper transport path S as shown in FIG. 1B, the paper is normally transported in the paper transport path S as shown in FIG. 1A (one by one). In addition, since the attenuation is larger than when only one sheet is conveyed, the intensity of the ultrasonic wave received by the ultrasonic receiver 520 is reduced.

Therefore, when the output of the ultrasonic receiver 520 is greater than the reference level (threshold), it is determined that no double feed occurs in the paper transport path S, and when the output of the ultrasonic receiver 520 is lower than the reference level, the paper is detected. If it is determined that double feed occurs in the transport path S, it is possible to detect that double feed has occurred.
JP-A-1-184490 (Publication date: July 24, 1991)

  By the way, the output of the ultrasonic receiver 520 fluctuates according to the change in the ambient temperature. Specifically, the output of the ultrasonic receiver 520 decreases as the ambient temperature increases. Therefore, when the ambient temperature is significantly increased due to some factor, the output of the ultrasonic receiver 520 is significantly decreased, and no double feed occurs in the paper transport path S as shown in FIG. However, it is erroneously determined that double feeding has occurred.

  Here, the ambient temperature rises significantly due to the self-heating of the ultrasonic receiver 520 and the self-heating of the peripheral circuits, but it should be noted that the ambient temperature rises significantly during the double-sided printing process. It is to end. In the following, the reason why the ambient temperature is greatly increased during the double-sided printing process will be described.

  When an execution command for double-sided printing processing is input in the image forming apparatus, first, the sheet is conveyed to the printing unit via the sheet conveying path S, and in this printing unit, the sheet surface (sheet front surface) is conveyed. On the other hand, the image is transferred and the image is thermally fixed on the paper surface, whereby the printing process is performed on the paper surface. Then, the sheet subjected to the heat fixing process is conveyed again to the printing unit via the sheet conveying path S, and the printing process is performed on the back surface of the sheet in the printing unit.

  That is, during the double-sided printing process, after the first printing process and before the second printing process (after the printing process on the paper surface and before the printing process on the paper back surface), the thermal fixing process in the paper transport path S The sheet having been subjected to the heat fixing process is transported, the atmosphere of the sheet transport path S is warmed by the sheet subjected to the heat fixing process, and the ambient temperature of the ultrasonic receiver 520 in the vicinity of the sheet transport path S is also increased. Will do.

  Therefore, during the double-sided printing process, after the first printing process and before the second printing process, due to the increase in the ambient temperature of the ultrasonic receiver 520, double feed does not occur in the paper transport path S. However, the double feed detection device 500 erroneously determines that double feeding has occurred, and the control unit of the image forming apparatus stops the printing operation based on this erroneous determination.

  The present invention has been made in view of the above problem, and the control unit of the image forming apparatus erroneously stops the printing process based on the erroneous determination of the determination unit (multifeed detection device) that determines the presence or absence of double feed. The purpose is to suppress the inconvenience.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a paper conveyance path, a printing unit that performs a printing process on a sheet that has passed through the paper conveyance path, and the printing unit before the printing process. A determination unit that determines whether or not a double feed state in which two or more sheets are transported in a paper transport path overlaps, and the double feed state occurs by referring to the determination result. A control unit that performs control to stop the printing process when the print data is printed, the control unit performs printing on the first side of printing on one side of the paper and printing on the other side of the paper 2 When the double-sided printing process including the first printing process is performed, only the result of the determination executed before the first printing process is referred to.

  When the double-sided printing process is performed, the fact that no double feeding has occurred before the first printing process means that the double feeding is performed after the first printing process and before the second printing process. Will not occur. In addition, if the multi-feed occurs before the first printing process, if the printing process proceeds as it is, the multi-feeding is performed after the first printing process and before the second printing process. Will occur. Therefore, when the double-sided printing process is performed, if it is determined whether double feeding has occurred before the first printing process, it is after the first printing process and before the second printing process. There is no need to determine whether or not the double feeding has occurred.

  Therefore, when the double-sided printing process is performed, even if only the result of the determination executed before the first printing process is referred to as in the above configuration, the double-feed state is accurate. Thus, the printing process can be canceled. Further, according to the above configuration, the determination is not performed after the first printing process and before the second printing process, or the determination result is not referred to even if a determination is made. Therefore, it is possible to suppress a problem that has occurred in the conventional double feed detection device in which the control unit erroneously stops the printing process based on the erroneous determination.

  In the image forming apparatus according to the aspect of the invention, the determination unit may be configured based on an ultrasonic transmitter and an ultrasonic receiver that are disposed to face each other across the paper conveyance path, and a signal output from the ultrasonic receiver. A configuration including a determination circuit that performs the determination may be employed.

  Furthermore, in the image forming apparatus according to the aspect of the invention, the control unit may instruct the determination unit until the second printing process is completed after the determination is performed before the first printing process. It is preferable to prohibit the execution of the determination. Thereby, it is possible to suppress a situation in which the determination unit makes an erroneous determination.

  In the image forming apparatus according to the aspect of the invention, the control unit may instruct the determination unit until the second printing process is completed after the determination is performed before the first printing process. It is preferable to stop supplying power.

  Accordingly, it is possible to prohibit the determination unit from executing the determination after the determination is performed before the first printing process until the second printing process is completed. In addition, the amount of power supplied to the determination unit is suppressed, thereby reducing the amount of self-heating of each component included in the determination unit, and suppressing an increase in the ambient temperature of the ultrasonic receiver included in the determination unit. It is possible to suppress a decrease in the output of the ultrasonic receiver due to an improvement in the ambient temperature.

  Further, the control unit may cause the determination unit to perform the determination at a timing when a front end of the paper transport direction reaches between the ultrasonic transmitter and the ultrasonic receiver in the paper transport path. The determination unit may cause the determination to be performed at a timing when a rear end in a sheet transport direction reaches between the ultrasonic transmitter and the ultrasonic receiver in the sheet transport path. In addition, when the determination unit performs the determination at a timing when the rear end in the paper transport direction reaches between the ultrasonic transmitter and the ultrasonic receiver in the paper transport path, the front end in the paper transport direction is Compared with the case where the determination unit performs the determination at the timing reached between the ultrasonic transmitter and the ultrasonic receiver in the paper transport path, the driving period of the determination unit can be shortened, and each of the determination units included in the determination unit There is an advantage that the self-heating amount of the configuration can be reduced.

  Furthermore, in the image forming apparatus of the present invention, a registration roller for temporarily stopping the transported paper and re-transporting the paper is arranged on the upstream side of the paper transport direction in the paper transport path. Preferably, the control unit causes the determination unit to perform the determination when the sheet is temporarily stopped. In the image forming apparatus of the present invention, a registration roller for temporarily stopping the transported paper and re-transporting the paper is disposed upstream of the printing unit in the paper transport path in the paper transport path. Preferably, the control unit causes the determination unit to perform the determination before the sheet is transported again.

  When the determination is performed on a sheet being conveyed, there is a problem in that the output of the ultrasonic receiver included in the determination unit varies due to the flapping of the sheet due to the sheet conveyance, and the determination unit erroneously determines. Although it may occur, according to the said structure, generation | occurrence | production of such an inconvenience can be avoided. Further, according to the above configuration, if it is determined that double feeding has occurred and the printing process is interrupted, the printing process is interrupted while the sheet is temporarily stopped. There is a merit that the restoration work can be easily performed (if the printing process is suddenly interrupted while the paper is being conveyed, a jam or the like occurs and the restoration work such as paper removal becomes difficult).

  Further, in the image forming apparatus of the present invention, a temperature detection unit that detects the temperature of the atmosphere of the ultrasonic receiver is provided, and the determination unit amplifies a signal output from the ultrasonic receiver, An amplification circuit that inputs the amplified signal to the determination circuit may be provided, and the control unit may be configured to adjust the amplification factor of the amplification circuit according to the temperature.

  According to the above configuration, even if the output of the ultrasonic receiver decreases due to an increase in the ambient temperature of the ultrasonic receiver, it is possible to suppress the disadvantage that the determination accuracy in the determination circuit decreases. .

  Furthermore, in the image forming apparatus of the present invention, a temperature detector that detects the temperature of the atmosphere of the ultrasonic receiver is provided, and the determination circuit includes a value of a signal output from the ultrasonic receiver and a threshold value. It is a comparator which performs the said determination by comparing, and the said control part may be comprised so that the said threshold value may be adjusted according to the said temperature.

  According to the above configuration, even if the output of the ultrasonic receiver decreases due to an increase in the ambient temperature of the ultrasonic receiver, it is possible to suppress the disadvantage that the determination accuracy in the determination circuit decreases. .

  In the image forming apparatus of the present invention, when a print command is input, the temperature detector that detects the temperature of the atmosphere of the ultrasonic receiver, and when a print command is input, the sheet is picked up from the tray on which the sheet is placed. A pickup roller that feeds a sheet into the sheet conveyance path, and the control unit determines whether the temperature is equal to or higher than a predetermined value. If the temperature is equal to or higher than a predetermined value, the operation of the pickup roller is performed. It may be configured to be prohibited. Further, the control unit determines whether or not the temperature falls below a predetermined value while prohibiting the operation of the pickup roller, and releases the prohibition when the temperature falls below a predetermined value. It may be configured.

  As a result, if the ambient temperature of the ultrasonic receiver has risen before the first printing process due to some factor, the determination unit erroneously makes a determination by not feeding the paper to the paper transport path. Can be prevented. Then, by feeding the paper to the paper conveyance path after the atmospheric temperature of the ultrasonic receiver becomes appropriate, it is possible to cause the determination unit to determine the double feed under an appropriate condition.

  Further, the image forming apparatus of the present invention includes a paper conveyance path, a printing unit that performs a printing process on the paper that has passed through the paper conveyance path, and two or more sheets in the paper conveyance path before the printing process. A determination unit that determines whether or not a multi-feed state in which sheets are overlapped and transported is generated, and the print processing is stopped when the multi-feed state occurs with reference to the determination result. A control unit that performs control, and the control unit includes a first printing process that performs printing on one side of a sheet and a second printing process that performs printing on the other side of the sheet. In the printing process, the determination unit is prohibited from executing the determination until the second printing process is completed after the determination is performed before the first printing process. To do.

  Further, the image forming apparatus of the present invention includes a paper conveyance path, a printing unit that performs a printing process on the paper that has passed through the paper conveyance path, and two or more sheets in the paper conveyance path before the printing process. A determination unit that determines whether or not a double feed state in which sheets are being conveyed is generated, a first printing process that performs printing on one side of the sheet, and printing on the other side of the sheet In the double-sided printing process including the second printing process, the determination is made to the determination unit after the determination is performed before the first printing process until the second printing process is completed. And a control unit that prohibits the execution of.

  The control unit of the image forming apparatus described above may be realized by a computer. In this case, a control program that causes the computer to function as the control unit, and a computer-readable recording medium that records the control program are also provided. It falls within the scope of the present invention.

  As described above, the image forming apparatus according to the present invention includes a paper conveyance path, a printing unit that performs a printing process on the paper that has passed through the paper conveyance path, and the paper conveyance path before the printing process. A determination unit that determines whether or not a double feed state in which two or more sheets are transported overlapped with each other, and a result of the determination is referred to. A control unit that performs control to stop the printing process, and the control unit performs a first printing process that performs printing on one side of the sheet and a second printing process that performs printing on the other side of the sheet. When the double-sided printing process including the above is performed, only the result of the determination executed before the first printing process is referred to.

  As a result, the determination is not performed after the first printing process and before the second printing process, and even if a determination is made, the determination result is not referred to. It is possible to suppress a problem that has occurred in the conventional multi-feed detection apparatus in which the control unit erroneously stops the printing process based on the determination.

  First, the overall configuration of an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a diagram illustrating the overall configuration of the image forming apparatus 11 of the present embodiment.

[Overall configuration of image forming apparatus]
The image forming apparatus 11 is an electrophotographic laser printer that forms a monochrome image (single color and black image) on a sheet based on digital image data received from an external terminal or the scanner 1 installed on the image forming apparatus 11. is there.

  As shown in FIG. 2, the image forming apparatus 11 includes an exposure unit 13, a developing device 15, a photosensitive drum 17, a charger 19, a cleaner unit 21, a fixing unit 23, a paper feed tray 25, a paper transport path 31, and a refeed. The paper conveyance path 83, the reverse conveyance path 99, the paper discharge tray 33, and the like are included.

  Note that the paper transport path 31 passes from the paper feed tray 25 to the junction C (a connection point between the paper transport path 31 and the re-feed transport path 83), the image transfer unit 47, and the fixing processing unit 66, and the paper discharge tray 33. It is formed in the range to reach. The re-feed conveyance path 83 is a conveyance path that branches from a branch point T between the fixing unit 23 and the paper discharge tray 33 in the paper conveyance path 31, and is formed so as to reach the junction C from the branch point T. This is the transport path that is being used. The registration roller 29 is disposed on the upstream side of the image transfer unit 47 in the paper conveyance path 31.

  The charger 19 is a charging means for uniformly charging the surface of the photosensitive drum 17 to a predetermined potential. In the image forming apparatus 11 shown in FIG. 2, the charger-type charger 19 is used. A type charger or a brush type charger may be used.

  The exposure unit 13 is a laser scanning unit (LSU) provided with a laser irradiation unit 35 and a reflection mirror 37 as shown in FIG. 2, but is not limited to LSU. For example, the light emitting elements are arranged in an array. The exposure unit may be an EL or LED writing head.

  The LSU may be either a one-beam LSU, a two-beam LSU for high-speed printing, or a four-beam LSU. In this embodiment, two lasers are used as shown in FIG. A two-beam LSU in which the irradiation units 35 and 35 are configured is employed.

  The exposure unit 13 exposes the photosensitive drum 17 uniformly charged by the charger 19 based on the input image data, so that the electrostatic latent image corresponding to the input image data is formed on the surface of the photosensitive drum 17. Is formed.

  The developing device 15 visualizes (develops) the electrostatic latent image formed on the photosensitive drum 17 with toner. The cleaner unit 21 removes and collects toner remaining on the surface of the photosensitive drum 17 after development and image transfer.

  The toner image (image) visualized on the photosensitive drum 17 is transferred onto the paper in the image transfer unit 47. The transfer belt unit 39 for performing the transfer is applied with an electric field having a polarity opposite to that of the charge on the toner on the photosensitive drum 17, and the toner on the photosensitive drum 17 is applied to the sheet by the electric field. Is transcribed. For example, when the toner on the photosensitive drum 17 has a negative polarity charge, the polarity of the electric field applied to the transfer belt unit 39 becomes a positive polarity.

  The transfer belt unit 39 includes a drive roller 41, a driven roller 43, an elastic conductive roller 49, a roller 96, and a transfer belt 45 that spans these rollers 41, 43, 49, and 96.

The transfer belt 45 is a belt member having a volume resistance value in the range of 1 × 10 ⁹ Ω · cm to 1 × 10 ¹³ Ω · cm.

  An elastic conductive roller 49 for applying a transfer electric field is disposed in the vicinity of the image transfer portion 47, which is a region where the photosensitive drum 17 and the transfer belt 45 are in contact with each other. The elastic conductive roller 49 has elasticity. As a result, the photosensitive drum 17 and the transfer belt 45 are not in line contact but in surface contact with each other with a predetermined width (referred to as a transfer nip). As a result, the transfer efficiency to the conveyed paper can be improved.

  Further, on the downstream side of the image transfer section 47 of the transfer belt 45, a charge eliminating roller is used to neutralize the sheet charged by the voltage applied when passing through the image transfer section 47 and smoothly carry it to the next process. 51 is arranged. The neutralizing roller 51 is disposed on the back surface of the transfer belt 45.

  Further, the transfer belt unit 39 is provided with a cleaning unit 53 that removes toner stains on the transfer belt 45 and a static elimination mechanism 55 that neutralizes the transfer belt 45. As a charge removal method by the charge removal mechanism 55, there is a method in which the transfer belt 45 is grounded through an apparatus, or a method in which an electric field having a polarity opposite to the polarity of the transfer electric field is positively applied to the transfer belt 45. The sheet on which the toner image (image) is transferred by the transfer belt unit 39 is conveyed to the fixing unit 23.

  The fixing unit 23 includes a heating roller 57 and a pressure roller 59, and a sheet peeling claw 61, a thermistor 63 (roller surface temperature detection member), and a roller surface cleaning member 65 are disposed on the outer periphery of the heating roller 57. . A heat source 67 for heating the surface of the roller to a predetermined temperature (fixing set temperature: approximately 160 to 200 ° C.) is disposed inside the heating roller 57.

  At both ends of the pressure roller 59, a mechanism such as a load spring is configured, and the pressure roller 59 is pressed against the heating roller 57 with a predetermined load by this mechanism. Further, similarly to the outer periphery of the heating roller 57, a sheet peeling claw and a roller surface cleaning member are disposed on the outer periphery of the pressure roller 59.

  The fixing unit 23 has a fixing processing unit (also referred to as a fixing nip unit) 66 that is a pressure contact portion between the heating roller 57 and the pressure roller 59. The unfixed toner image is thermally fixed on the paper.

  The paper feed tray 25 is a tray for storing sheets (recording paper) used for printing. In the image forming apparatus 11 according to the present embodiment, the paper feed tray 25 includes the photosensitive drum 17, the transfer belt unit 39, and the like. It is provided below the image forming unit and in the vicinity of the side wall of the apparatus.

  Further, in the image forming apparatus 11 of the present embodiment, a plurality of paper feed trays 25 capable of storing 500 to 1500 fixed-size sheets are arranged so that continuous printing can be performed even for an extremely large amount of sheets. . Further, on the side of the apparatus, there is a large-capacity paper feed cassette 73 that can store a plurality of different types of paper in large quantities, and a manual feed tray 75 that is mainly used for printing on irregular-size paper. Has been placed.

  The paper discharge tray 33 is disposed on the side of the apparatus opposite to the manual feed tray 75. However, the paper discharge tray 33 is removed, and a post-processing device (stapling, punching, etc.) of discharged paper or a multi-stage paper discharge is performed. The tray can be arranged as an option.

  Next, a paper conveyance path when printing processing is performed in the image forming apparatus 11 will be described.

  When a print request (print request command) is input to the image forming apparatus 11, the paper is supplied to the paper transport path 31 by the pickup roller 70 from the paper feed tray 25 in which the paper conforming to the print request is stored. The Then, the sheet is conveyed to the registration roller 29 disposed upstream of the image transfer unit 47 in the sheet conveyance path 31 via the junction C, and is temporarily stopped.

  Further, the registration roller 29 is rotated again at a timing such that the leading edge of the sheet coincides with the leading edge of the toner image (image) on the photosensitive drum 17 in the image transfer unit 47, and the sheet is conveyed to the image transfer unit 47. As a result, the toner image on the photosensitive drum 17 is transferred to the surface (front surface) of the sheet in the image transfer unit 47, and the sheet is guided to the fixing unit 23 and transferred to the sheet in the fixing unit 23. The toner is fixed (thermally fixed) on the paper.

  Thereafter, the paper transport path is switched according to the single-sided printing mode / double-sided mode. Specifically, in the single-sided printing mode, the gate of the transport path switching mechanism 80 in FIG. 2 is turned so that the front and back of the paper discharged from the fixing unit 23 are reversed and then the paper is guided to the paper discharge tray 33. The direction is switched. In the double-sided printing mode, the direction of the gate of the transport path switching mechanism 80 is switched so that the paper discharged from the fixing unit 23 is turned upside down and then the paper is sent to the refeed transport path 83. . Then, the sheet sent to the sheet refeed conveyance path 83 passes through the sheet refeed conveyance path 83 and is sent again to the sheet conveyance path 31 via the junction C. Thereafter, the sheet is conveyed again to the image transfer unit 47, and the image transfer unit 47 transfers the image to the back surface. Thereafter, the sheet is discharged to the discharge tray 33 through the fixing unit 23.

  As described above, in the image forming apparatus 11, the printing process is performed by performing both the image transfer process in the image transfer unit 47 and the fixing process in the fixing process unit 66. In other words, the printing process includes an image transfer process and a fixing process, and the image transfer unit 47 and the fixing processing unit 66 may be collectively referred to as a printing unit.

  Further, in the image forming apparatus 11 of the present embodiment, in addition to the various configurations described above, as shown in FIGS. 2 and 3, a double feed detection sensor DD is configured in the paper transport path 31, thereby conveying the paper. In this way, it is possible to detect a double feed occurring on the upstream side of the printing unit in the path 31, and when this double feed occurs, the printing process is stopped. Hereinafter, the details of the image forming apparatus 11 will be described focusing on the double feed detection sensor DD.

[About double feed detection sensor]
FIG. 3 is a diagram illustrating a detailed configuration of the sheet conveyance path 31. As shown in FIGS. 2 and 3, the sheet conveyance path 31 is located on the sheet conveyance path 31 from the upstream side in the sheet conveyance direction to the downstream side between the junction C and the printing unit (the image transfer position 47 and the fixing processing unit 66). The sheet detection sensor PD1, the double feed detection sensor DD, the sheet detection sensor PD2, and the registration roller 29 are arranged in this order.

  The paper detection sensor PD1 is a transmission type optical sensor provided between the merging point C and the double feed detection sensor DD. The paper detection sensor PD1 passes through the merging point C and reaches the double feed detection sensor DD. It is a sensor that detects the leading edge and further transmits a paper detection signal indicating that this detection has been performed to the control unit 100.

  The double feed detection sensor DD is an ultrasonic double feed detection device that determines whether or not double feed is occurring in the paper transport path 31 and transmits a determination signal indicating the determination result to the control unit 100. It is a device to do. Here, double feeding means a state in which two or more sheets overlap and are simultaneously conveyed as shown in FIG. Details of the configuration of the double feed detection sensor DD will be described later.

  The sheet detection sensor PD2 is a reflection type optical sensor provided between the double feed detection sensor DD and the registration roller 29. The sheet detection sensor PD2 passes through the double feed detection sensor DD and reaches the registration roller 29. It is a sensor that detects the leading edge and further transmits a paper detection signal indicating that this detection has been performed to the control unit 100.

  Next, the control unit of the image forming apparatus 11 and various hardware controlled by the control unit will be described in detail. FIG. 4 is a functional block diagram showing various hardware configured in the image forming apparatus 11.

  As shown in FIG. 4, the image forming apparatus 11 includes a gate drive solenoid 101, a conveyance motor 102, drivers 103 and 104, in addition to the above-described control unit 100, double feed detection sensor DD, and paper detection sensors PD <b> 1 and PD <b> 2. A temperature sensor 105 is provided.

  The gate drive solenoid 101 drives the gates 80a, 80b, 80c, 80d, and 80e (see FIG. 9) included in the transport path switching mechanism 80. The driver 103 is a driver circuit for operating the gate drive solenoid 101 and is connected to the control unit 100. In other words, the control unit 100 operates the gate drive solenoid 101 by transmitting a drive signal to the driver 103, thereby driving and controlling the gates 80a, 80b, 80c, 80d, and 80e.

  The transport motor 102 is a motor that applies torque to each of the paper transport rollers provided along the transport paths 31, 83, and 99. The driver 104 is a driver circuit for operating the transport motor 102 and is connected to the control unit 100. That is, the control unit 100 transmits a drive signal to the driver 104 and operates the transport motor 102 to rotate the paper transport roller, thereby performing control to transport the paper inside the image forming apparatus 11. is there.

  The temperature sensor 105 is a sensor that detects an ambient temperature of an ultrasonic receiver 120 (described later) configured in the double feed detection sensor DD, and transmits a temperature signal indicating the ambient temperature to the control unit 100.

  The switching circuit 106 is connected to the power source and the control unit 100 and the double feed detection sensor DD, and by connecting the power source and the double feed detection sensor DD in response to a command from the control unit 100, the double feed detection sensor DD. Is a circuit that switches between an operating state in which power is supplied to the power supply and a non-operating state in which power supply to the double feed detection sensor DD is stopped by disconnecting the power supply and the double feed detection sensor DD.

  Next, details of the double feed detection sensor DD will be described. As shown in FIG. 3, the double feed detection sensor DD includes an ultrasonic transmitter 110 and an ultrasonic receiver 120 that are disposed to face each other with the paper transport path 31 interposed therebetween, and a control circuit 121.

  As shown in FIG. 4, the ultrasonic transmitter 110 includes an ultrasonic drive circuit 111 and a transmitter 112. As illustrated in FIG. 4, the control circuit 121 includes an amplifier circuit 122, a smoothing circuit 123, a threshold setting circuit 124, and a comparison circuit 125.

  The ultrasonic drive circuit 111 is a drive circuit that drives the transmitter 112 at the switching timing when the double feed detection sensor DD is switched to the operating state by the switching circuit 106. The transmitter 112 is a device that transmits ultrasonic waves toward the ultrasonic receiver 120 by being driven by the ultrasonic driving circuit 111.

  The ultrasonic receiver 120 is a device that receives the ultrasonic wave transmitted from the transmitter 112, converts the received ultrasonic wave into a signal, and transmits this signal to the amplifier circuit 122. The amplifier circuit 122 is a circuit that receives a signal from the ultrasonic receiver 120, amplifies the signal, and transmits the amplified signal to the smoothing circuit 123. The smoothing circuit 123 is a circuit that smoothes the signal sent from the amplifier circuit 122 and transmits the smoothed signal to the comparison circuit 125.

  The threshold setting circuit 124 is a circuit that sets a threshold for a signal transmitted from the smoothing circuit 123 to the comparison circuit 125 under the control of the control unit 100. The threshold value is a threshold value for determining whether or not double feeding is occurring in the paper transport path 31.

  The comparison circuit 125 is a comparator that compares the signal transmitted from the smoothing circuit 123 with the threshold set in the threshold setting circuit 124 and transmits a determination signal indicating the comparison result to the control unit 100. When the signal sent from the smoothing circuit 123 is equal to or greater than the threshold value, the comparison circuit 125 determines that no double feed has occurred in the paper transport path 31 and generates a determination signal indicating that no double feed has occurred. When the signal transmitted to the control unit 100 and sent from the smoothing circuit 123 is less than the threshold value, it is determined that double feeding has occurred in the paper transport path 31, and a determination signal indicating that double feeding has occurred is controlled. To the unit 100.

  The control unit 100 controls the overall operation of the image forming apparatus 11, and includes (a) a microcomputer, (b) a ROM that stores a control program that describes a processing procedure executed by the microcomputer, and (c) (1) RAM serving as a data development area during data processing, (d) non-volatile memory for storing data necessary for controlling the image forming apparatus 11, (e) a peripheral device such as a sensor, and the like An input buffer that receives the signal of the signal, an input circuit including an A / D conversion circuit that digitizes the signal, (f) an output circuit that outputs a drive signal to the drivers 103 and 104 for driving the motor and solenoid, etc. Consists of

  Next, various processes executed by the control unit 100 will be described in detail with reference to flowcharts. 5 and 6 are flowcharts showing the flow of the printing process in the single-sided printing mode or the printing process for the paper surface in the double-sided printing mode. FIG. 7 is a flowchart showing the flow of the printing process for the back side of the sheet in the duplex printing mode. FIG. 8 is a timing chart showing driving timings of various hardware included in the image forming apparatus 11.

  As shown in FIG. 5, when a print request is input (YES in S <b> 1), the control unit 100 drives the pickup roller 70 to pick up the paper in the paper feed tray 25 and sends it to the paper transport path 31 ( S2).

  When the leading edge of the sheet supplied to the sheet conveyance path 31 passes through the junction C and reaches the vicinity of the sheet detection sensor PD1, the sheet detection sensor PD1 detects the leading edge of the sheet, and the sheet detection signal is transmitted to the control unit. To 100. Thereby, the control unit 100 can recognize the timing when the leading edge of the sheet is detected by the sheet detection sensor PD1 (YES in S3). Then, after S3, the control unit 100 executes the processes (S4 to S17) shown in A of FIG. 6 and the processes (S31 to S36) shown in B in parallel. In the following, the process indicated by B will be described first, and then the process indicated by A will be described.

  After recognizing the timing when the leading edge of the sheet is detected by the sheet detection sensor PD1 in S3, the control unit 100 recognizes the double feed detection sensor DD when a predetermined time T1 has elapsed from this timing, as shown in the pattern 1 of FIG. To the operating state. In other words, after recognizing the timing when the leading edge of the sheet is detected by the sheet detection sensor PD1, the control unit 100 waits for a predetermined time T1 (S31), and switches the double feed detection sensor DD to the operating state after this waiting (S32). ).

  The predetermined time T1 is the time required for the leading edge of the paper being conveyed to reach the double feed detection sensor DD from the paper detection sensor PD1. Therefore, the double feed detection sensor DD is switched to the operating state when the leading edge of the paper reaches between the ultrasonic transmitter 110 and the ultrasonic receiver 120 in the double feed detection sensor DD.

  The double feed detection sensor DD that has been switched to the operating state transmits a determination signal indicating that double feed has occurred to the control unit 100 when double feed has occurred in the paper transport path 31, and When the paper is normally transported in the transport path 31, a determination signal indicating that no double feed has occurred is transmitted to the control unit 100.

  Here, the control unit 100 refers to the determination signal transmitted from the double feed detection sensor DD, and when the double feed is occurring in the paper transport path 31 (YES in S33), the control unit 100 turns the double feed detection sensor DD off. Switching to the operation state (S35) and sending a print prohibition command to the exposure unit 13, the transfer belt unit 39, the fixing unit 23, and the driver 104 to perform a control for stopping the paper transport operation and the printing process (S36). . Thereby, the process of S4-S17 demonstrated later will be interrupted.

  On the other hand, the control unit 100 refers to the determination signal transmitted from the double feed detection sensor DD, and when the paper is normally transported in the paper transport path 31 (NO in S33), the double feed detection sensor DD. Is switched to the non-operating state (S34), but the control for stopping the printing process as in S36 is not performed. Therefore, when the paper is normally conveyed in the paper conveyance path 31, the printing process is performed without interrupting the processes of S4 to S17 described later.

  Next, the process shown in FIG. 6A will be described. As shown in FIG. 3, the leading edge of the paper being conveyed to the paper conveyance path 31 reaches the paper detection sensor PD2 after passing through the paper detection sensor PD1 and the double feed detection sensor DD. The paper detection sensor PD2 detects the leading edge of the paper and transmits a paper detection signal to the control unit 100.

  Thereby, the control unit 100 can recognize the timing when the leading edge of the sheet is detected by the sheet detection sensor PD2 (YES in S4).

  After recognizing the timing when the leading edge of the sheet is detected by the sheet detection sensor PD2 in S4, the control unit 100 detects the leading edge of the sheet by the sheet detection sensor PD2 as shown in “image writing timing” of FIG. The exposure unit 13 is controlled so that writing of a latent image on the photosensitive drum 17 is started when a predetermined time T4 has elapsed from the timing. In other words, after recognizing the timing when the leading edge of the sheet is detected by the sheet detection sensor PD2, the control unit 100 waits for a predetermined time T4 (S5), and starts writing a latent image on the photosensitive drum 17 after this waiting. (S6).

  After S6, the control unit 100 causes the registration roller 29 to rotate when a predetermined time T5 elapses from the timing when writing of the latent image on the photosensitive drum 17 is started, as shown in "Registration roller" in FIG. Control driver 104 to begin. In other words, the control unit 100 waits for a predetermined time T5 after starting the writing of the latent image on the photosensitive drum 17 (S7), and after this waiting, starts the rotation of the registration roller 29 (S8).

  Further, after S8, the control unit 100 transfers the image to the transfer belt unit 39 when a predetermined time T6 has elapsed from the rotation start timing of the registration roller 29, as shown in “transfer output” of FIG. Is applied (transfer output operation). In other words, the control unit 100 waits for a predetermined time T6 from the start of rotation of the registration roller 29 (S9), and starts the transfer output operation after this standby (S10). By this transfer output operation, the image is transferred to the surface of the paper. Further, the sheet having the image transferred on the surface thereof is conveyed to the fixing unit 23 and subjected to a fixing process.

  After the fixing process, in the single-sided printing mode (YES in S11), the control unit 100 causes each sheet of the conveyance path switching mechanism 80 to guide the sheet discharged from the fixing unit 23 to the reverse conveyance path 99 (switchback-in). The orientations of the gates 80a, 80b, 80c, 80d, and 80e are switched to the orientations shown in FIG. 9 (S12). As a result, the paper discharged from the fixing unit 23 is sent to the reverse conveyance path 99, and the front surface and the back surface of the paper are reversed.

  Further, the control unit 100 waits for a predetermined time after performing the process of S12 (S13), and then guides the paper in the reverse conveyance path 99 to the paper discharge tray 33 (switchback → discharge), the conveyance path switching mechanism 80. The direction of each of the gates 80a, 80b, 80c, 80d, and 80e is switched to the direction shown in FIG. 10 (S14). Then, the control unit 100 reverses the transport roller 97 in the reverse transport path 99 (S15), thereby discharging the paper in the reverse transport path 99 to the paper discharge tray 33 (S16). As a result, the paper that has been subjected to the printing process on the front surface is discharged to the paper discharge tray 33, and the single-sided printing process for one sheet is completed. Thereafter, the control unit 100 shifts the process to S2 when printing the next page (Y in S17), and ends the process when there is no next page (NO in S17).

  Further, after S10, the control unit 100, when in the duplex printing mode (NO in S11), guides the sheet discharged from the fixing unit 23 to the reverse conveyance path 99 (switchback-in), and the conveyance path switching mechanism 80. The direction of each of the gates 80a, 80b, 80c, 80d, and 80e is switched to the direction as shown in FIG. 9 (S44, see FIG. 7). As a result, the paper discharged from the fixing unit 23 is sent to the reverse conveyance path 99, and the front surface and the back surface of the paper are reversed.

  Then, after waiting for a predetermined time after performing the process of S44 (S45), the control unit 100 switches the conveyance path so as to guide the sheet in the reverse conveyance path 99 to the refeed conveyance path 83 (switchback → recycle). The directions of the gates 80a, 80b, 80c, 80d, and 80e of the mechanism 80 are switched to the directions as shown in FIG. 11 (S46). Further, the control unit 100 can guide the sheet in the reverse conveyance path 99 to the refeed conveyance path 83 by reversing the conveyance roller 97 in the reverse conveyance path 99 (S47). As a result, the sheet whose surface has been subjected to the printing process is sent to the sheet conveyance path 31 via the refeed conveyance path 83 and the junction C.

  Thereafter, when the leading edge of the sheet supplied to the sheet conveyance path 31 reaches the vicinity of the sheet detection sensor PD1, the sheet detection sensor PD1 detects the leading edge of the sheet and transmits a sheet detection signal to the control unit 100. 100 does not switch the double feed detection sensor DD to the operating state, as shown in the back side printing of the pattern 1 in FIG. Therefore, when the paper is re-conveyed to the paper conveyance path 31 at the time of printing on the back side, the operation of the double feed detection sensor DD is prohibited.

  And S48-S54 will be performed, but since this S48-S54 is the same processing as S4-S10, the description is abbreviate | omitted here. However, printing is performed also on the back surface of the sheet by executing S48 to S54.

  After S54, the control unit 100 directs the paper discharged from the fixing unit 23 directly to the paper discharge tray 33 (discharge), and the direction of each gate 80a, 80b, 80c, 80d, 80e of the transport path switching mechanism 80. Are switched to the orientation shown in FIG. 12 (S55). As a result, the paper discharged from the fixing unit 23 is discharged to the paper discharge tray 33 (S56), and the double-sided printing process for one sheet ends. Thereafter, control unit 100 proceeds to S2 when printing the next page (YES in S57), and ends the process when there is no next page (NO in S57).

  As described above, the image forming apparatus 11 according to the present exemplary embodiment includes the paper conveyance path 31, the image transfer unit 47 serving as a printing unit that performs printing processing on the paper that has passed through the paper conveyance path 31, and fixing. A processing unit 66, a double feed detection sensor DD as a determination unit for determining whether or not a double feed state has occurred in the paper transport path 31 before the printing process, and the double feed detection sensor DD as a result of the determination. When the feeding state has occurred, a control unit 100 that performs control to stop the printing process is provided. Then, the control unit 100 performs the first printing process for printing on one side (front surface) of the paper and the second printing process for printing on the other side (back side) of the paper. When the double-sided printing process including is performed, only the result of the determination executed before the first printing process is referred to.

  Here, when the double-sided printing process is performed, the fact that no multi-feed has occurred before the first printing process means that after the first printing process and before the second printing process, Double feed will not occur. In addition, if the multi-feed occurs before the first printing process, if the printing process proceeds as it is, the multi-feeding is performed after the first printing process and before the second printing process. Will occur. Therefore, when the double-sided printing process is performed, if it is determined whether double feeding has occurred before the first printing process, it is after the first printing process and before the second printing process. There is no need to determine whether or not the double feeding has occurred.

  Therefore, when the double-sided printing process is performed, even if only the result of the determination executed before the first printing process is referred to as in the control unit 100 of the present embodiment, double feeding occurs. If so, the printing process can be canceled accurately. Note that “refer only to the result of the determination performed before the first printing process” means that the determination performed by the double feed detection sensor DD is performed for the first time when the double-sided printing process is performed. This means that only the result of the determination executed before the printing process is referred to, and the detection result by a sensor other than the double feed detection sensor DD after the first printing process and before the second printing process. It does not mean that the judgment result is not referred to. For example, when the double-sided printing process is performed, the control unit 100 refers to the determination result of the occurrence of a paper jam by a jam detection sensor (not shown) after the first printing process and before the second printing process. Various controls may be performed.

  The double feed detection sensor DD serving as the determination unit includes an ultrasonic transmitter 110 and an ultrasonic receiver 120 that are disposed to face each other across the paper conveyance path 31, and signals output from the ultrasonic receiver 120. And a comparison circuit 125 for making the above determination.

  Further, after the first printing process and before the second printing process, the sheet subjected to the heat fixing process is transported to the sheet transport path 31, whereby the double feed detection sensor DD Since the ambient temperature of the ultrasonic receiver 120 rises and the output of the ultrasonic receiver 120 decreases, the possibility that the double feed detection sensor DD makes an erroneous determination increases. On the other hand, according to the present embodiment, the control unit 100 performs at least a double feed detection sensor from when the determination is performed before the first printing process until the second printing process ends. By switching the DD to the non-operating state, the execution of the determination is prohibited with respect to the double feed detection sensor DD. Thereby, it is possible to suppress a situation in which the double feed detection sensor DD makes an erroneous determination.

  Further, according to the present embodiment, the control unit 100 controls the switching circuit 106 from the time when the determination is made before the first printing process until the second printing process is completed. Therefore, the supply of power to the double feed detection sensor DD is stopped. Accordingly, it is possible to prohibit the double feed detection sensor DD from executing the determination after the determination is performed before the first printing process until the second printing process is completed. become. In addition, the amount of power supplied to the double feed detection sensor DD is suppressed, whereby the self-heating amount of the double feed detection sensor DD can be reduced, and the ultrasonic receiver 120 included in the double feed detection sensor DD can be reduced. An increase in the atmospheric temperature can be suppressed, and a decrease in the output of the ultrasonic receiver 120 due to the increase in the atmospheric temperature can be suppressed.

  Furthermore, according to the present embodiment, the control unit 100 detects the double feed detection sensor at a timing when the leading end of the sheet (the leading end in the transport direction) reaches between the ultrasonic transmitter 110 and the ultrasonic receiver 120 in the paper transport path 31. Although the DD makes the determination, it is not limited to such timing.

  For example, the control unit 100 makes the determination to the double feed detection sensor DD at the timing when the rear end of the paper (rear end in the transport direction) reaches between the ultrasonic transmitter 110 and the ultrasonic receiver 120 in the paper transport path 31. It may be done. In order to realize such control, for example, as shown in “Pattern 2” in FIG. 8, the overlap is performed at a timing when a predetermined time T2 elapses from when the leading edge of the sheet is detected by the sheet detection sensor PD1. The feed detection sensor DD may be switched to the operating state. Here, the predetermined time T2 is the time required for the trailing edge of the paper to reach the double feed detection sensor DD after the leading edge of the paper being conveyed reaches the paper detection sensor PD1.

  In the case where the double feed detection sensor DD makes the determination at the timing when the trailing edge of the paper reaches between the ultrasonic transmitter 110 and the ultrasonic receiver 120 in the paper conveyance path 31 (pattern 2 in FIG. 8), Compared with the case where the double feed detection sensor DD makes the determination at the timing when the leading edge of the paper reaches between the ultrasonic transmitter 110 and the ultrasonic receiver 120 in the paper conveyance path 31 (pattern 1 in FIG. 8), There is an advantage that the driving period of the feed detection sensor DD can be shortened and the self-heating amount of the double feed detection sensor DD can be reduced.

  Further, the image forming apparatus 11 is provided with a registration roller 29 that temporarily stops the transported paper and re-transports the paper on the upstream side of the paper transport path 31 with respect to the paper transport direction in the paper transport path 31. Yes. Therefore, the control unit 100 may cause the double feed detection sensor DD to perform the determination when the sheet is temporarily stopped (before the sheet is re-conveyed). In order to realize such control, for example, as shown in “Pattern 3” in FIG. 8, the overlap is performed at a timing when a predetermined time T3 elapses from when the leading edge of the sheet is detected by the sheet detection sensor PD1. The feed detection sensor DD may be switched to the operating state. Here, the predetermined time T3 is a time required for the leading edge of the paper to reach the registration roller 29 after the leading edge of the paper being conveyed reaches the paper detection sensor PD1.

  When the double feed detection sensor DD determines double feed for the paper being transported as in pattern 1 or pattern 2 in FIG. 8, the output of the ultrasonic receiver 120 fluctuates due to paper flapping due to paper transport. However, there is a possibility that the double feed detection sensor DD makes an erroneous determination. However, when the sheet is temporarily stopped at the position of the registration roller 29 (before the sheet is re-conveyed). When the double feed detection sensor DD makes the determination, it is possible to avoid the above-described inconvenience.

  In the configuration in which the double feed detection sensor DD makes the determination when the paper is temporarily stopped at the position of the registration roller 29 (before the paper is re-conveyed), if double feed is temporarily generated. If the printing process is interrupted and the printing process is interrupted, the printing process is interrupted while the sheet is stopped, so that there is a merit that a recovery operation such as sheet removal can be easily performed (the printing process is suddenly performed while the sheet is being conveyed). If it is interrupted, a jam or the like occurs, and recovery work such as paper removal becomes difficult).

  The image forming apparatus 11 includes a temperature sensor (temperature detection unit) 105 that detects the ambient temperature of the ultrasonic receiver 120, and a signal output from the ultrasonic receiver 120 is output to the double feed detection sensor DD. Is amplified and input to the comparison circuit 125. Therefore, the control unit 100 may be configured to perform control to adjust the amplification factor of the amplifier circuit 122 according to the temperature detected by the temperature sensor 105. Specifically, if the control unit 100 adjusts the amplification factor so that the amplitude of the signal output from the amplifier circuit 122 increases when the ambient temperature increases, the ambient temperature of the ultrasonic receiver 120 increases. As a result, even if the output of the ultrasonic receiver 120 is lowered, it is possible to suppress the disadvantage that the determination accuracy in the comparison circuit 125 is lowered.

  Further, the comparison circuit 125 configured in the double feed detection sensor DD is a circuit that compares the value of the signal output from the ultrasonic receiver 120 with a threshold value. Therefore, the control unit 100 may be configured to adjust the threshold value according to the temperature detected by the temperature sensor 105. Specifically, if the control unit 100 adjusts the threshold value so as to decrease the threshold value when the ambient temperature increases, the output of the ultrasonic receiver 120 increases as the ambient temperature of the ultrasonic receiver 120 increases. Even if it decreases, it is possible to suppress the disadvantage that the determination accuracy in the comparison circuit 125 decreases.

  Further, the image forming apparatus 11 includes a pickup roller 70 that picks up a sheet from the sheet feeding tray 25 on which the sheet is placed and feeds the sheet into the sheet conveyance path 31. Therefore, the control unit 100 is configured to determine whether or not the temperature detected by the temperature sensor 105 is equal to or higher than a predetermined value, and prohibit the operation of the pickup roller 70 when the temperature is equal to or higher than the predetermined value. May be. Further, the control unit 100 determines whether or not the temperature falls below a predetermined value while the operation of the pickup roller is prohibited, and cancels the prohibition when the temperature falls below a predetermined value. May be configured.

  As a result, if the ambient temperature of the ultrasonic receiver 120 is increased before the first printing process due to some factor, the double feed detection sensor DD does not perform the paper feed itself to the paper transport path 31. It is possible to prevent erroneous determination. Then, by feeding paper to the paper transport path 31 after the atmospheric temperature of the ultrasonic receiver 120 becomes appropriate, it is possible to make the double feed detection sensor DD determine double feed under appropriate conditions.

  Further, when performing the double-sided printing, the control unit 100 performs the second printing process (backside printing) after the determination of the double feed detection is performed before the first printing process (front side printing). The double feed detection sensor DD is controlled so that the determination of the double feed detection is not performed until the end. However, it is not necessary to perform such control every time double-sided printing is performed. For example, the control unit 100 may be caused to execute a program that performs control more than 9 times out of 10 times of duplex printing and does not perform the above control once for the remaining time.

  In the image forming apparatus 11 described above, the control unit 100 is configured by a PC-based computer. Various processes in the control unit 100 are performed by causing a computer to execute a program. This program may be in a form of reading out and using a program recorded on a removable medium (computer-readable recording medium) such as a CD-ROM, or reading out and using a program installed on a hard disk or the like. It may be a form to do. Further, when the control unit 100 is configured to be connected to a communication network such as the Internet, a mode in which the program is downloaded via the communication network, installed on a hard disk, and the like can be considered.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and the embodiments can be obtained by appropriately combining the respective technical means disclosed in the above-described embodiments. The form is also included in the technical scope of the present invention.

  The image forming apparatus of the present invention is suitable for electrophotographic printers, copiers, multifunction machines, facsimiles, and the like, but is not limited thereto, and is a printing apparatus that is provided with a paper conveyance path and capable of duplex printing. The present invention can be applied as long as it is present. For example, the present invention can also be applied to an ink jet printer capable of duplex printing.

(A) is a diagram illustrating a state in which a sheet is normally conveyed in the sheet conveyance path, and (b) is a diagram illustrating a state in which double feeding occurs in the sheet conveyance path. 1 is a diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a diagram illustrating a sheet conveyance path configured inside the image forming apparatus illustrated in FIG. 2. FIG. 3 is a functional block diagram illustrating various hardware configured in the image forming apparatus illustrated in FIG. 2. 6 is a flowchart illustrating a flow of a printing process in a single-sided printing mode or a printing process on a sheet surface in a double-sided printing mode. FIG. 6 is a flowchart showing a flow of a printing process in a single-sided printing mode or a printing process for a sheet surface in a double-sided printing mode, and is a flowchart showing a continuation of the flow shown in FIG. 5. 6 is a flowchart illustrating a flow of a printing process for the back side of a sheet in a duplex printing mode. 6 is a timing chart showing driving timings of various hardware included in the image forming apparatus. FIG. 4 is a diagram illustrating a state in which a sheet is sent from a fixing unit to a reverse conveyance path. FIG. 6 is a diagram illustrating a state where a sheet on a reverse conveyance path is discharged from an image forming apparatus. FIG. 6 is a diagram illustrating a state in which a sheet on a reverse conveyance path is sent to a refeed conveyance path. FIG. 4 is a diagram illustrating a state in which a sheet is discharged from the fixing unit to the outside of the image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Image forming apparatus 29 Registration roller 31 Paper conveyance path 47 Image transfer part (printing part)
66 Fixing processing section (printing section)
70 pickup roller 100 control unit 105 temperature sensor (temperature detection unit)
110 Ultrasonic Transmitter 120 Ultrasonic Receiver 122 Amplification Circuit 125 Comparison Circuit (Determination Circuit)
DD Double feed detection sensor (determination unit)

Claims (16)

A paper transport path;
A printing unit that performs a printing process on a sheet that has passed through the sheet conveyance path;
A determination unit for determining whether or not a double feed state in which two or more sheets are overlapped and conveyed in the sheet conveyance path before the printing process;
A control unit that performs control to stop the printing process when the double feed state occurs with reference to the determination result;
When the double-sided printing process including the first printing process for printing on one side of the paper and the second printing process for printing on the other side of the paper is performed, the control unit An image forming apparatus characterized by referring only to the result of the determination executed before printing processing.   The determination unit includes an ultrasonic transmitter and an ultrasonic receiver that are arranged to face each other across the paper conveyance path, and a determination circuit that performs the determination based on a signal output from the ultrasonic receiver. The image forming apparatus according to claim 1.   The control unit prohibits the determination unit from executing the determination after the determination is performed before the first printing process until the second printing process ends. The image forming apparatus according to claim 2.   The control unit stops supplying power to the determination unit after the determination is performed before the first printing process until the second printing process is completed. The image forming apparatus according to claim 3.   The control unit causes the determination unit to perform the determination at a timing at which a front end in a paper transport direction reaches between the ultrasonic transmitter and the ultrasonic receiver in the paper transport path. The image forming apparatus according to 2.   The control unit causes the determination unit to perform the determination at a timing when a rear end in a sheet transport direction reaches between the ultrasonic transmitter and the ultrasonic receiver in the sheet transport path. Item 3. The image forming apparatus according to Item 2. A registration roller that temporarily stops the transported paper and re-transports the paper is disposed upstream of the printing unit in the paper transport direction in the paper transport path.
The image forming apparatus according to claim 2, wherein the control unit causes the determination unit to perform the determination when the sheet is temporarily stopped. A registration roller for temporarily stopping the transported paper and re-transporting the paper is disposed upstream of the printing unit in the paper transport direction in the paper transport path.
The image forming apparatus according to claim 2, wherein the control unit causes the determination unit to perform the determination before the sheet is conveyed again. A temperature detection unit for detecting the temperature of the atmosphere of the ultrasonic receiver;
The determination unit includes an amplification circuit that amplifies a signal output from the ultrasonic receiver and inputs the amplified signal to the determination circuit.
The image forming apparatus according to claim 2, wherein the control unit adjusts an amplification factor of the amplifier circuit according to the temperature. A temperature detection unit for detecting the temperature of the atmosphere of the ultrasonic receiver;
The determination circuit is a comparator that performs the determination by comparing a value of a signal output from the ultrasonic receiver with a threshold value,
The image forming apparatus according to claim 2, wherein the control unit adjusts the threshold value according to the temperature. A temperature detector for detecting the temperature of the atmosphere of the ultrasonic receiver;
When a print command is input, a pickup roller is provided that picks up the paper from the tray on which the paper is placed and feeds the paper into the paper conveyance path,
3. The image formation according to claim 2, wherein the control unit determines whether or not the temperature is equal to or higher than a predetermined value, and prohibits the operation of the pickup roller when the temperature is equal to or higher than a predetermined value. apparatus.   The control unit determines whether or not the temperature is lower than a predetermined value while the operation of the pickup roller is prohibited, and releases the prohibition when the temperature falls below a predetermined value. The image forming apparatus according to claim 11. A paper transport path;
A printing unit that performs a printing process on a sheet that has passed through the sheet conveyance path;
A determination unit for determining whether or not a double feed state in which two or more sheets are overlapped and conveyed in the sheet conveyance path before the printing process;
A control unit that performs control to stop the printing process when the double feed state occurs with reference to the determination result;
In the double-sided printing process including a first printing process for printing on one side of the paper and a second printing process for printing on the other side of the paper, the control unit performs the first printing process. The image forming apparatus, wherein the determination unit is prohibited from executing the determination until the second printing process is completed after the determination is performed before. A paper transport path;
A printing unit that performs a printing process on a sheet that has passed through the sheet conveyance path;
A determination unit configured to determine whether or not a double feed state in which two or more sheets are overlapped and conveyed in the sheet conveyance path before the printing process;
In a double-sided printing process including a first printing process for printing on one side of a sheet and a second printing process for printing on the other side of the sheet, the determination is performed before the first printing process. An image forming apparatus comprising: a control unit that prohibits the determination unit from executing the determination until the second printing process is completed.   The control program for an image forming apparatus according to claim 1, wherein the control program causes a computer to function as the control unit.   The computer-readable recording medium which recorded the control program of Claim 15.

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