JP2018162153A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of correctly determining whether or not feeding is in an overlapped state, without reducing productivity even for a JOB with mixed loading of different types of sheets.SOLUTION: An image forming apparatus has a document transportation motor that transports a sheet, an ultrasonic wave transmission part that is arranged on one side with respect to a transport passage through which the sheet is transported, and transmits an ultrasonic wave toward the transport passage, and an ultrasonic wave reception part that is arranged on the other side with respect to the transport passage and receives the ultrasonic wave transmitted from the ultrasonic wave transmission means. Also, the image forming apparatus compares a threshold determined on the basis of a reception signal received in a state that no sheet is being fed and that an ultrasonic wave is transmitted on the basis of a parameter matched to a type of a sheet to be transported from now on, with a reception signal the ultrasonic wave receiving means received in a state that a sheet is being transported and that an ultrasonic wave is transmitted, and determines whether or not overlapped sheets are fed according to a comparison result.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a technique for detecting double feeding of paper using ultrasonic waves in an image forming apparatus.

Some image forming apparatuses that convey a sheet (for example, a sheet) and form an image on the sheet detect an overlap of conveyed sheets. For example, an ultrasonic transmission sensor that transmits ultrasonic waves and an ultrasonic reception sensor that receives ultrasonic waves that have passed through the paper are provided on the paper conveyance path.
Then, the amount of attenuation is detected based on the amplitude level of the received wave (received wave amplitude level), and the conveyed paper is in a state of feeding one sheet (hereinafter referred to as single feed) or a plurality of sheets. It is determined whether or not they overlap (hereinafter referred to as double feeding).

  In this double feed detection process using ultrasonic waves, for example, when there is a variation in sensitivity (individual difference) of the ultrasonic reception sensor, the transfer characteristics vary from ultrasonic transmission to ultrasonic reception. For this reason, even when the same paper is a detection target, there is a possibility that it cannot be accurately determined whether or not it is a double feed state due to fluctuations in the amplitude level of the received wave.

  For such a problem, for example, before the paper is transported on a transport path sandwiched between the ultrasonic transmission sensor and the ultrasonic reception sensor, that is, in a state where there is no paper between the ultrasonic transmission sensor and the ultrasonic reception sensor (hereinafter referred to as “paper”). This is referred to as “no paper”. At this time, the detection characteristics (for example, the amplification factor of the amplification circuit, the threshold level, etc.) are corrected according to the amplitude level of the received wave received by the ultrasonic wave reception sensor. There is a method of performing such a paper absence correction and correctly determining whether or not the conveyed paper is in a double feed state (for example, Patent Document 1).

JP 2012-188177 A

However, the sheet to be detected has a different ultrasonic attenuation rate for each sheet type.
For example, it can be dealt with by changing the transmission wave number of the ultrasonic wave according to the paper type, but it becomes necessary to change the wave number to the transmission wave according to the paper to be detected later in the paper absence correction.
For this reason, in the case of a mixed JOB in which different types of paper are passed through in the same JOB, there remains a problem that correction cannot be performed unless the setting for paper absence correction is changed according to the paper type to be passed next. In addition, there is a problem that a correction time is required for performing the paper-out correction between the sheets (between the conveyed sheet and the next sheet) every time one sheet is conveyed, and productivity is lowered.

  The present invention provides an image forming apparatus capable of accurately determining whether or not a multi-feed state is achieved without reducing productivity even in a job in which different types of sheets (for example, paper) are mixedly loaded. The main purpose is to do.

  An image forming apparatus according to the present invention includes a conveyance unit that conveys a sheet, an ultrasonic wave transmission unit that is disposed on one side of a conveyance path through which the sheet is conveyed, and that emits ultrasonic waves toward the conveyance path direction, The ultrasonic wave receiving unit disposed on the other side of the conveyance path and receiving the ultrasonic wave transmitted from the ultrasonic wave transmitting unit, the acquiring unit for acquiring the type of the sheet, the ultrasonic wave transmitting unit, and the ultrasonic wave A state in which the ultrasonic wave is transmitted by the ultrasonic wave transmission unit based on a parameter corresponding to the sheet type acquired by the acquisition unit with respect to the sheet to be transported in the state where there is no sheet between the ultrasonic wave reception unit And a threshold value determined based on a reception signal which is an output of the ultrasonic wave receiving means, and the ultrasonic wave sending means with the sheet between the ultrasonic wave transmitting means and the ultrasonic wave receiving means A control means for comparing the reception signal of the ultrasonic wave receiving means in a state where the ultrasonic wave is further transmitted and determining whether or not the sheet is double fed according to the comparison result. Features.

  According to the present invention, the paper absence correction is performed in advance according to the sheet type, and it is determined whether or not the double feeding state is performed using the correction result of the paper absence correction according to the sheet to be conveyed. As a result, even if the job is a JOB in which different types of sheets are mixedly loaded, it is possible to accurately determine whether or not it is in a double feed state without reducing productivity.

1 is a schematic longitudinal sectional view for explaining an example of an image forming system according to a first embodiment. FIG. 3 is a block diagram for explaining a functional configuration of the image forming apparatus. The elements on larger scale for demonstrating the arrangement | positioning relationship of an ultrasonic transmission sensor and an ultrasonic reception sensor. The figure which shows an example of a function structure of a double feed detection part. (A), (b) is a figure for demonstrating the outline | summary of the identification method of the single feeding of the paper performed using an ultrasonic sensor, or double feeding. (A)-(f) is a graph for demonstrating the relationship between the transmission wave number of the ultrasonic wave to transmit, and the reception level of a received wave. (A), (b) is a graph for demonstrating the threshold value for identifying single feeding and double feeding. 6 is a flowchart illustrating an example of a processing procedure performed by the image forming apparatus. The flowchart for demonstrating an example of the process which determines double feed detection conditions. (A), (b), (c) is an example of a table (table) in which a paper feed position and a paper type are defined in association with each other. FIG. 11 is an example of a table (table) different from FIG. 10 in which a paper feed position and a paper type are defined in association with each other. The ultrasonic sensor is a graph for explaining that the peak value of the ultrasonic reception wave varies depending on the ambient temperature. 9 is a flowchart illustrating an example of a processing procedure performed by an image forming apparatus according to a second embodiment.

[First Embodiment]
<Printer system>
Hereinafter, an example of an embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a schematic longitudinal sectional view for explaining an example of an image forming system according to the present embodiment.
As shown in FIG. 1, the image forming system 1000 includes an image forming apparatus 10 and a sheet processing apparatus 500 connected to the sheet discharge side of the image forming apparatus 10. The image forming apparatus 10 includes an image reader 200, a document feeder 100, and an operation unit 400.

  The exposure control unit 110 included in the image forming apparatus 10 modulates and outputs a laser beam based on the input video signal. The output laser light is irradiated onto the photosensitive drum 111 while being scanned by the polygon mirror 110a. An electrostatic latent image corresponding to the scanned laser beam is formed on the photosensitive drum 111.

The electrostatic latent image formed on the photosensitive drum 111 is visualized as a developer image by the developer supplied from the developing device 113.
Also, synchronized with the start of laser light irradiation via each cassette 114, 115 functioning as a feeding means for feeding sheets (for example, paper), the manual paper feed unit 125, or the double-sided conveyance path 124. Paper is fed at the timing. The supplied paper passes through the path sensor 132 and is further conveyed toward the double feed detection unit 140.

  In addition, when the image forming apparatus 10 determines that the sheet to be conveyed is in a single-feed state via the multi-feed detection unit 140, the image forming apparatus 10 further conveys the sheet between the photosensitive drum 111 and the transfer unit 116. Details of the double feed detection unit 140 will be described later.

The developer image formed on the photosensitive drum 111 is transferred onto a sheet fed by the transfer unit 116. The sheet on which the developer image is transferred is conveyed to the fixing unit 117.
The fixing unit 117 fixes the developer image on the paper by heat-pressing the paper. The sheet that has passed through the fixing unit 117 is discharged from the image forming apparatus 10 to the outside through the flapper 121 and the discharge roller 118.

  When the sheet is discharged with its image forming surface facing down (face down), the sheet that has passed through the fixing unit 117 is once guided into the reverse path 122 by the switching operation of the flapper 121. Then, after the trailing edge of the sheet passes through the flapper 121, the sheet is switched back and discharged from the image forming apparatus 10 via the discharge roller 118. Hereinafter, this form of paper discharge is referred to as reverse paper discharge.

  This reverse discharge is performed when forming an image sequentially from the first page, such as when forming an image read via the document feeder 100 or when forming an image based on image information output from a computer. As a result, the paper order after paper discharge becomes the correct page order.

  Further, when a hard sheet such as an OHP sheet is fed from the manual sheet feeding unit 125 and image formation is performed on the sheet, the image forming surface is faced up without guiding the sheet to the reverse path 122. The paper is discharged via the discharge roller 118 at (face up).

  Further, when image formation is performed on both sides of the sheet, the sheet is guided to the reverse path 122 by the switching operation of the flapper 121 and then conveyed to the duplex conveyance path 124. Then, the sheet guided to the duplex conveyance path 124 is fed again between the photosensitive drum 111 and the transfer unit 116 at the timing described above.

FIG. 2 is a block diagram for explaining a functional configuration of the image forming apparatus 10.
As shown in FIG. 2, the image forming apparatus 10 includes a printer control unit 153 that controls the entire image forming apparatus 10.
The printer control unit 153 includes a CPU (Central Processing Unit) 150, a ROM (Read Only Memory) 151, and a RAM (Random Access Memory) 152. The CPU 150 reads out a control program stored in the ROM 151, and carries the conveyance motor 50, the document feeder control unit 101, the double feed detection unit 140, the path sensor 132, the image reader control unit 201, the image signal control unit 202, and the operation unit 400. To control.
The RAM 152 is used as a work area for temporarily holding control data.

The document feeder control unit 101 drives and controls the document feeder 100 based on an instruction from the printer control unit 153 via the CPU 150.
The image reader control unit 201 performs drive control of the scanner 200 via the CPU 150. The image signal output from the scanner 200 is transferred to the image signal control unit 202 via the image bus 203.

  The double feed detection unit 140 is controlled by the printer control unit 153 via the CPU 150. The double feed detection unit 140 transmits ultrasonic waves to the paper that has passed through the path sensor 132 and receives ultrasonic waves that have passed through the paper. Further, it is determined whether or not the paper transported is in a double feed state based on the received waveform of the ultrasonic wave.

  The carry motor 50 is controlled by the printer control unit 153 via the CPU 150. Note that if the CPU 150 determines that the paper to be transported is in the double feed state via the double feed detection unit 140, the CPU 150 stops the transport of the paper.

  The operation unit 400 outputs a signal corresponding to the received user operation to the printer control unit 153. Further, based on various information output from the printer control unit 153, for example, various information is notified to the user via the display unit of the operation unit 400. Further, for example, when it is determined that the sheet to be conveyed is in a double feed state, information indicating that the paper is being double fed is notified.

<Configuration of Double Feed Detection Unit 140>
FIG. 3 is a partially enlarged view for explaining the positional relationship between the ultrasonic transmission sensor T1 and the ultrasonic reception sensor T2.
As shown in FIG. 3, the ultrasonic transmission sensor T1 is disposed on one side of the conveyance path through which the paper 102 is conveyed, and transmits ultrasonic waves toward the conveyance path. The ultrasonic reception sensor T2 is disposed on the other side across the conveyance path, and receives ultrasonic waves transmitted from the ultrasonic transmission sensor T1. Thus, each of the ultrasonic transmission sensor T1 and the ultrasonic reception sensor T2 is arranged.

  The ultrasonic wave emitted from the ultrasonic wave transmission sensor T1 is transmitted through the paper 102 on the document conveyance path and propagates toward the ultrasonic wave reception sensor T2, and the propagated ultrasonic wave is received by the ultrasonic wave reception sensor T2. Is done. The strength of the ultrasonic wave (reception signal) received by the ultrasonic wave reception sensor T2 is converted into a voltage amplitude.

FIG. 4 is a diagram illustrating an example of a functional configuration of the double feed detection unit 140.
The double feed detection unit 140 includes an ultrasonic transmission unit 130 that functions as an ultrasonic transmission sensor that transmits ultrasonic waves, and an ultrasonic reception unit 131 that functions as an ultrasonic reception sensor that receives ultrasonic waves.

  The ultrasonic transmission unit 130 includes an ultrasonic transmission sensor T <b> 1 and a transmission drive circuit 3. The ultrasonic receiving unit 131 includes an ultrasonic reception sensor T2, a reception amplification circuit 4 that amplifies a reception signal, and an AD converter 5 that AD converts a reception wave. Moreover, it has the ultrasonic control part 6 which performs control of the transmission timing of an ultrasonic wave, calculation of the peak value of a received wave, etc. The operation control of the ultrasonic control unit 6 is controlled by the CPU 150 via the printer control unit 153.

  For example, in the image forming measure 10 according to the present embodiment, the ultrasonic transmission sensor T1 has a natural frequency of 300 [kHz]. The ultrasonic reception sensor T2 is sensitive to ultrasonic waves having a frequency of 300 [kHz], and converts the sound pressure of the received ultrasonic waves into an electrical signal.

FIG. 5 is a diagram for explaining an overview of a method for identifying single-feed or double-feed of the paper 102 using an ultrasonic sensor.
The ultrasonic wave transmitted from the ultrasonic wave transmission unit 130 toward the conveyed paper is transmitted through the paper and propagated to the ultrasonic wave reception unit 131. The ultrasonic receiving unit 131 converts the strength of the received ultrasonic wave into voltage amplitude, and amplifies the conversion result by the amplifier circuit 4. The ultrasonic receiving unit 131 performs AD conversion on the amplification result via the AD converter 5, and then outputs the result to the CPU 150. Based on the output result, the CPU 150 determines whether or not the sheet to be conveyed is in a double feed state.

  Here, when the ultrasonic wave passes through the paper, the amplitude of the ultrasonic wave is greatly attenuated. At this time, if the sheet is conveyed in a double feed state in which a plurality of sheets are conveyed, this large attenuation occurs a plurality of times. Therefore, the amplitude of the ultrasonic wave transmitted through a plurality of sheets is further attenuated (see FIG. 5B) as compared with the case where there is one sheet (see FIG. 5A). In this way, when the attenuation is different, the amplitude of the received received wave is also greatly different. Based on this difference (comparison result), it is possible to detect whether or not the sheet to be conveyed is in a double feed state.

Further, the attenuation rate of the ultrasonic wave varies depending on the thickness and type (sheet type) of the paper. In general, the attenuation rate increases as the paper thickness increases.
For example, when the transmission energy of ultrasonic waves to be transmitted is small, the output level of the reception sensor when transmitting ultrasonic waves to one sheet and the reception sensor when transmitting ultrasonic waves to two sheets The difference in the output level becomes smaller. In this case, double feed detection cannot be performed accurately.

  In addition, when the transmission energy of the ultrasonic wave to be transmitted is large, the output level of the reception sensor when the ultrasonic wave is transmitted to one sheet and the reception sensor when the ultrasonic wave is transmitted to two sheets Both output levels may reach the upper limit. Even in this case, double feed detection cannot be performed accurately.

  The transmitted energy can be controlled by changing the parameters of the transmitted ultrasonic wave (wave number (transmitted amplitude), amplitude, center frequency, etc. of the transmitted wave). Therefore, it is possible to accurately detect double feed by changing the parameter of the ultrasonic wave to be transmitted according to the type of paper to be detected.

FIG. 6 is a graph for explaining the relationship between the number of transmitted ultrasonic waves and the reception level of received waves.
The transmitted energy increases as the wave number of ultrasonic waves increases. Accordingly, the transmission wave number is set to a relatively large value for a sheet having a relatively low attenuation rate of ultrasonic waves, and the transmission wave number is set to a relatively small value for a sheet having a relatively high attenuation rate. Control to do. That is, the transmission wave number for a sheet having a relatively low attenuation rate is controlled to be larger than the transmission wave number for a sheet having a relatively high attenuation rate. This makes it possible to improve the accuracy of double feed detection (see FIGS. 6A and 6B).

  The transmitted energy increases as the amplitude of the ultrasonic wave increases. Therefore, the amplitude of the transmitted ultrasonic wave is set to a relatively large value for a paper having a relatively low attenuation rate, and the amplitude is set to a relatively large value for a paper having a relatively high attenuation rate. Control to a small value. That is, the amplitude for a sheet having a relatively low attenuation rate is controlled to be larger than the amplitude for a sheet having a relatively high attenuation rate. This makes it possible to improve the accuracy of double feed detection (see FIGS. 6C and 6D).

Further, the transmission energy increases as the center frequency of the ultrasonic wave is closer to the natural frequency of the ultrasonic sensor 1. Therefore, the ultrasonic sensor 1 is driven at a frequency close to the natural frequency of the ultrasonic sensor 1 for a sheet having a relatively low ultrasonic attenuation rate. Further, the ultrasonic sensor 1 is driven at a frequency deviating (far) from the natural frequency for a sheet having a relatively high attenuation rate. That is, control is performed so that the center frequency of the transmission wave for a sheet having a relatively low attenuation rate is closer to the natural frequency than the center frequency of the transmission wave for a sheet having a relatively high attenuation rate. This makes it possible to improve the accuracy of double feed detection (see FIGS. 6E and 6F).
In the description of this embodiment, control for changing the wave number of the transmitted ultrasonic wave among the ultrasonic parameters will be described. Further, the image forming apparatus 10 determines a threshold value, which will be described later, and identifies single-feed and double-feed based on this threshold. Hereinafter, this point will be described in detail.

FIG. 7 is a graph for explaining the difference between the case where the threshold is determined without performing the paper-out correction (a) and the case where the threshold is determined according to the result of the paper-out correction (b).
For example, if the relative position of the ultrasonic transmitter 130 and the ultrasonic receiver 131 has deviated from a predetermined position due to sensor mounting tolerances, etc., the ultrasonic reception level will decrease, and false detection will occur as it is. There is a possibility of triggering (see FIG. 7A).
For this reason, at the start of JOB (at the start of printing), ultrasonic waves are transmitted in a state where there is no paper on the conveyance path sandwiched between the ultrasonic transmission sensor T1 and the ultrasonic reception sensor T2, that is, in the absence of paper. A value obtained by multiplying the sound wave reception level by a predetermined value is used as a threshold value for identifying single feeding and double feeding.
By using this threshold value, it is possible to prevent the occurrence of erroneous detection due to a shift in the relative position between the ultrasonic transmission sensor and the ultrasonic reception sensor at the time of starting JOB (see FIG. 7B).

  Note that the paper out correction is intended to adjust a threshold value used when detecting double feed. For this reason, it is necessary to transmit ultrasonic waves under the same conditions as when ultrasonic waves are transmitted to a sheet to be detected. The conditions for transmitting an ultrasonic wave include the amplitude and frequency of the ultrasonic wave and the wave number.

FIG. 8 is a flowchart illustrating an example of a processing procedure performed by the image forming apparatus. Each process shown in FIG. 8 is mainly performed by the CPU 150.
When the CPU 150 receives a job start instruction (print start instruction), the CPU 150 performs a process of determining a double feed detection condition (S1201).
Hereinafter, the process of determining the double feed detection condition will be described with reference to FIG.

FIG. 9 is a flowchart for explaining an example of processing for determining the double feed detection condition.
This processing is performed with each of the paper feed positions, specifically, the cassette 114, the cassette 115, the ultrasonic wave number, the wave amplitude, and the ultrasonic wave for each paper type (each sheet type) loaded in the manual paper feed unit 125. This is a process for determining a threshold value.

The CPU 150 determines the wave number 1 that is the oscillation wave number corresponding to the cassette 114 and the amplitude 1 that is the transmission wave amplitude (S1301).
Here, an example of the procedure for determining the oscillation wave number and the transmission wave amplitude will be described with reference to FIG.

FIG. 10 is an example of a table (table) in which a paper feed position (cassette 114 or the like) and a paper type (sheet type) are defined in association with each other.
FIG. 10A is a table showing an example of combinations of paper feed positions and papers loaded therein. In the image forming apparatus 10, for example, the paper loaded in the cassette 114 is plain paper having a basis weight of 108 [gsm], and the paper loaded in the cassette 115 is coated paper having a basis weight of 90 [gsm]. . In addition, it is assumed that the paper loaded in the manual paper feeding unit 125 is loaded with a coated paper having a basis weight of 110 [gsm]. In addition, the sheet setting for each sheet feeding position is set by the user via the operation unit 400, for example. As described above, the sheet type is set in association with each feeding unit on which the sheet is mounted.

  FIG. 10B is a table in which the paper type is defined by, for example, characteristics of the paper surface (surface property of the sheet surface). Based on the table shown in FIG. 10B, the paper is classified into paper types A, B, C, and the like. Each paper type is determined based on surface properties and basis weight, for example. For example, it can be seen that the paper loaded on the cassette 114 (plain paper of basis weight 108 [gsm]) is the paper type C.

Based on the paper type and the table showing the ultrasonic parameters shown in FIG. 10C, the optimum transmission wave number and transmission wave amplitude are determined for each paper type. For example, the transmission wave number of the ultrasonic wave transmitted to the paper fed from the cassette 114, that is, the wave number 1 is determined to be “6”. Similarly, the transmission wave amplitude 1 is determined to be 20 [V].
In the case of this embodiment, the transmitted wave amplitudes are all 20 [V] regardless of the paper type, and the same conditions are met.

  Returning to the description of FIG. 9, the CPU 150 transmits an ultrasonic wave using the transmission wave number and the transmission wave amplitude determined according to the sheet type in the process of step S1301 (S1302). At this time, there is no sheet at the position of the double feed detector 140. Thereafter, the CPU 150 receives the ultrasonic wave transmitted through the paper via the ultrasonic wave reception sensor T2 (S1303).

The CPU 150 determines the threshold 1 based on the received reception level of the ultrasonic wave (S1304).
The threshold value 1 is a threshold value corresponding to the paper loaded in the cassette 114, that is, the sheet type of the cassette 114. Similarly, it is assumed that threshold 2 is a threshold corresponding to the paper loaded in the cassette 115 and threshold 3 is a threshold corresponding to the paper loaded in the manual paper feed unit 125.

Similarly, the CPU 150 determines the wave number 2, amplitude 2 and threshold 2 corresponding to the cassette 115 in the processing of steps S1305 to S1308, and the wave number 3 and amplitude corresponding to the manual sheet feeder 125 in the processing of steps S1309 to S1312. 3 and threshold 3 are determined.
Even if there is no paper at the paper feed position, this processing is executed corresponding to the paper type set via the operation unit 400.

Returning to the explanation of FIG. 8, the CPU 150 sets the double feed detection condition in the ultrasonic control unit 6 (step 1202).
This setting is the transmission wave number and the transmission wave amplitude. However, since only the transmission wave number is different for each paper type, only the transmission wave number is controlled.
Also, the transmitted wave number and the transmitted wave amplitude to be set are wave numbers 1, 2, 3, and amplitude 1 according to which paper feed position the paper transported to the position of the double feed detection unit 140 is transported next. One of 2, 3 is selected and set.

The CPU 150 waits until the paper is detected by the path sensor 132 (S1203).
The CPU 150 waits for a predetermined time from the timing when the path sensor 132 detects the sheet (S1204). This predetermined time is the time for the sheet to move to a position where the double feed can be stably detected at the position of the ultrasonic sensor 140 after the sheet is detected by the path sensor 132. Specifically, it is determined according to the sheet conveyance speed and the attachment distance from the path sensor 132 to the ultrasonic sensor 140.

The CPU 150 transmits an ultrasonic wave (S1205). At this time, the transmitted wave number and the transmitted wave amplitude of the ultrasonic wave are the values set in the process of step S1202.
The CPU 150 determines whether or not the reception level when the transmitted ultrasonic wave is received is equal to or less than a threshold value (S1206). As the threshold used in this process, a threshold (any one of thresholds 1 to 3) corresponding to the paper feed position of the detection target paper is selected.

  When the CPU 150 determines that the reception level is equal to or lower than the threshold (S1206: No), the CPU 150 determines that the paper to be conveyed is in a double feed state. Thereafter, the process proceeds to step S1207. If not (S1206: Yes), it is determined that the conveyed paper is in a single-feed state. Thereafter, the process proceeds to step S1209.

When the CPU 150 determines that the paper to be transported is in the double feed state, the CPU 150 stops the transport of the paper (S1207).
The CPU 150 notifies information indicating that the sheets are being double-fed through the operation unit 400 (S1208).

  If the CPU 150 determines that the sheet to be conveyed is in a single-feed state, the CPU 150 determines whether there is a next page (S1209). If it is determined that there is a next page (S1209: Yes), the process returns to step S1202.

As described above, the image forming apparatus 10 according to the present embodiment performs the process of determining the double feed detection condition in advance according to the acquired sheet type, and receives the ultrasonic control parameter and the reception for each sheet to be conveyed. A threshold used for identifying whether or not a double feed state is determined according to the level.
As a result, even if the job is a JOB in which different types of paper are mixedly loaded, it is possible to detect double feed with high accuracy without increasing the interval of the paper to be conveyed.

Of the ultrasonic parameters, the transmitted wave number and the transmitted wave amplitude can be changed.
FIG. 11 is an example of a table (table) that is defined in association with a paper feed position (cassette 114 or the like) and a paper type, which is different from FIG. As shown in FIG. 11C, it is possible to select more optimal parameters by changing the transmission wave and the transmission wave amplitude according to the paper type.
In addition, the transmission center frequency, which is one of the parameters of the transmitted ultrasonic wave, can be configured to be changeable.

[Second Embodiment]
For example, the ultrasonic sensor has a characteristic that the sensitivity changes depending on the ambient temperature. Therefore, there is a possibility that the ultrasonic reception level changes due to environmental changes and false detection is induced.

For example, as shown in the graph shown in FIG. 12, the peak value of the ultrasonic wave varies in the ultrasonic sensor depending on the ambient temperature. Therefore, it is desirable to calculate the threshold value again when a certain temperature change occurs.
Here, an image forming apparatus capable of performing double feed detection with high accuracy without reducing productivity even in such a case will be described. In addition, the same thing as the functional structure demonstrated in 1st Embodiment attaches | subjects the same code | symbol, and abbreviate | omits the description.

FIG. 13 is a flowchart illustrating an example of a processing procedure performed by the image forming apparatus according to the present embodiment. Each process shown in FIG. 13 is mainly performed by the CPU 150.
Further, the process shown in FIG. 13 is different from the process after determining that “there is a next page” (S1209: Yes) in the process of step S1209 when compared with the double feed detection process described in FIG. Hereinafter, this point will be described.

  If the CPU 150 determines that there is a next page in the process of step S1209 (S1209: Yes), the CPU 150 determines whether there is an adjustment (S1401). This adjustment is an adjustment that temporarily stops the conveyance of the sheet.

For example, when the number of prints in JOB increases, the temperature in the vicinity of the center decreases as the sheet passes through the center of the fixing unit 117. In contrast, the temperature of the end of the fixing unit 117 continues to rise. Therefore, when it reaches a certain temperature, it may be kept waiting until it cools. This is referred to as edge temperature increase adjustment.
Such an adjustment sequence is controlled so as to be started every predetermined time or every predetermined number of sheets, and at that time, the conveyance of the paper is stopped only during that time. The double feed detection condition determination sequence is performed again during this stop time, and the reception level threshold is calculated again. As a result, it is possible to correct the characteristics of the ultrasonic sensor again with respect to environmental changes such as temperature fluctuations, and to perform double feed detection with high accuracy.

  The embodiment described above is for explaining the present invention more specifically, and the scope of the present invention is not limited to these examples.

  DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus, 100 ... Document feeder, 200 ... Image reader, 400 ... Operation part, 500 ... Sheet processing apparatus, 1000 ... Image forming system.

Claims (8)

Conveying means for conveying the sheet;
Disposed on one side of a conveyance path where the sheet is conveyed, and an ultrasonic transmission means for transmitting an ultrasonic wave toward the conveyance path;
Disposed on the other side of the conveyance path, ultrasonic receiving means for receiving ultrasonic waves transmitted from the ultrasonic transmission means,
Obtaining means for obtaining the type of the sheet;
The ultrasonic wave transmitting means based on parameters according to the sheet type acquired by the acquiring means for the sheet to be conveyed in the state where the sheet is not present between the ultrasonic wave transmitting means and the ultrasonic wave receiving means. A state in which the sheet is between the threshold value determined based on a reception signal that is an output of the ultrasonic wave reception unit in a state where the ultrasonic wave is transmitted by the ultrasonic wave transmission unit and the ultrasonic wave reception unit And a control means for comparing the received signal of the ultrasonic wave receiving means in a state where the ultrasonic wave is transmitted by the ultrasonic wave transmitting means and determining whether or not the sheets are double-fed according to the comparison result. And characterized by comprising:
Image forming apparatus. The parameter is a value representing a wave number, a center frequency, and a transmission amplitude of an ultrasonic wave to be transmitted, and the control unit determines one or more values of the parameters according to the type of the sheet. To
The image forming apparatus according to claim 1. The type of the sheet is defined according to the characteristics or basis weight of the sheet surface,
The image forming apparatus according to claim 1. A feeding means for feeding the sheet;
The type of the sheet is set in association with each of the feeding means on which the sheet is mounted,
The image forming apparatus according to claim 1. The control means determines the threshold corresponding to each sheet type based on a parameter corresponding to the sheet type before starting feeding the sheet.
The image forming apparatus according to claim 4. The transporting unit stops driving when it is determined by the determining unit that the double feeding is performed,
The image forming apparatus according to claim 1. A notification means for notifying the user of various information;
The notifying means notifies information indicating that the sheet is in a double feed state when the control means determines that the double feed is performed.
The image forming apparatus according to claim 1. The control means, again during the stop time when the conveyance of the sheet is stopped, the sheet type acquired by the acquisition means without the sheet between the ultrasonic transmission means and the ultrasonic reception means. A threshold value is determined based on a reception signal which is an output of the ultrasonic wave reception unit in a state where an ultrasonic wave is transmitted by the ultrasonic wave transmission unit based on a parameter according to
The image forming apparatus according to claim 1.