JP4123174B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a technology of an image forming apparatus that enables double-sided printing by reversing a recording sheet that has passed through an image forming unit by a switchback method and passing the recording sheet again through the image forming unit.

Conventionally, a recording paper detection sensor is provided on the recording paper conveyance path in the image forming apparatus for detecting the position of the recording paper and detecting the length of the recording paper.
Since such a recording paper detection sensor is a contact type sensor that detects the presence or absence of recording paper by utilizing contact with the recording paper, chattering may occur when the recording paper is detected.
In order to eliminate this adverse effect of chattering, the technique disclosed in Patent Document 1 sets a predetermined delay time, and determines the presence or absence of recording paper when a signal continues during this time. In particular, in this technique, by making the delay time setting time variable, reliable detection is performed according to the difference in use, such as jam detection or recording paper size detection.

JP-A-6-56303

In the case of an image forming apparatus configured to be able to perform double-sided printing by the switchback method, a normal path for front side printing and a bypass path for the normal path are provided. When printing on the back side, the discharge roller located at the end of the recording paper transport direction of the normal path does not directly discharge the recording paper on which the front surface has been printed, but switches the recording paper transport direction to the opposite direction and removes the recording paper. Send back. The reversely fed recording paper is reversed and turned back to the normal path when passing the bypass path. Then, when the recording paper is transported again through the normal path, the back side printing process is performed this time.
Here, in the normal path, the part located on the discharge roller side from the connection point between the bypass path and the normal path is a reciprocating path in which the recording paper reciprocates during double-sided printing. A recording paper detection sensor is also provided on this reciprocating path. The recording paper detection sensor detects the recording paper conveyed in the paper discharge direction toward the discharge roller device, and detects the recording paper conveyed in the reverse direction from the discharge roller device.

When double-sided printing is performed, the recording paper passes through the recording paper detection sensor on the reciprocating path before and after the switchback. When the recording paper passes through the recording paper detection sensor before the switchback, chattering occurs in the recording paper detection sensor. Then, when the same recording paper passes through the recording paper detection sensor again at a time point after the switchback, if chattering at the time point before the switchback is not settled, a recording is performed based on the output signal of the recording paper detection sensor. The paper cannot be detected correctly.
That is, even if an ON signal is output from the recording paper detection sensor, it cannot be determined by the control device connected to the recording paper detection sensor whether the ON signal is due to chattering or true recording paper detection.

The above problem cannot be improved by the technique disclosed in Patent Document 1. Since the technology of Patent Document 1 eliminates the adverse effects of chattering by setting a delay time, the recording signal of the recording paper detection sensor is output for a certain time (the delay time) after the recording paper travels the forward path. I will ignore it. If the recording paper passes through the return path during this delay time, the recording paper passing through the return path cannot be detected.
In particular, when the path length of the reciprocating path is shorter than that of a general-purpose machine, a normal machine, or the like in a small machine or the like, the chattering duration cannot be ignored. In other words, the switch-backed recording paper passes through the recording paper detection sensor while chattering that occurred before the switch-back is continued.

On the other hand, recording paper detection sensors are provided not on the reciprocating path but on the bypass path and the normal path upstream of the reciprocating path to detect the recording paper moving in the paper discharge direction and the recording to be reversely sent. A configuration may be employed in which detection of paper is performed by a separate sensor.
In this case, movement of the recording paper in different directions is detected by different sensors, so that the influence of chattering of each recording paper detection sensor can be ignored. However, with such a configuration, the number of recording paper detection sensors increases, leading to an increase in cost.
In addition, in the configuration in which only two sensors are provided, jam detection cannot be performed on the reciprocating path. Therefore, it is necessary to separately provide a recording paper detection sensor on the reciprocating path for detecting the jam. This will lead to further cost increases.

Therefore, in the present invention, in the image forming apparatus configured to be capable of duplex printing by the switchback method, both the detection of the recording paper conveyed in the paper discharge direction and the detection of the recording paper conveyed in the reverse feed direction are both performed. An object is to prevent an increase in cost while ensuring the configuration .

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

That is, in claim 1,
In the image forming apparatus which enables double-sided printing by inverting the front and back of the recording paper that has passed through the image forming unit and passing it again through the image forming unit,
A transport device capable of transporting recording paper in both the paper discharge direction and the reverse direction;
On the reciprocating path through which the recording paper passes in both directions, away from the connecting portion of the first path, the second path, and the reciprocating path by a predetermined distance, and more than the end position when the recording paper is switched back , Arranged on the back side in the reverse feed direction, supporting the feeler arm from above the reciprocating path vertically downward so that the feeler arm can be tilted in both the discharge direction and the reverse feed direction, A recording paper detection sensor for detecting the passage of the recording paper conveyed in both directions;
A control device for controlling the driving of the transport device based on an output signal from the recording paper detection sensor;
With
The control device detects a first passage of the recording paper based on a first output signal from the recording paper detection sensor, temporarily stops driving the conveyance device, and then records the recording paper in the reverse feeding direction. Based on the second output signal from the recording paper detection sensor, detects the second passage of the recording paper to be switched back, and based on the third output signal from the recording paper detection sensor In addition, the third passage of the recording paper in the double-sided printing state is detected, and control for discharging the recording paper to the conveying device is performed.

In claim 2,
The drive stop time that the control device commands the transfer device is:
More than the chattering continuation time by the recording paper detection of the recording paper detection sensor.

In claim 3,
The recording sheet detection sensor is provided only at one position in the recording sheet conveyance direction on the reciprocating path.

  As effects of the present invention, the following effects can be obtained.

The recording paper switchback according to claim 1, wherein the recording paper is on a reciprocating path through which the recording paper passes in both directions and is separated from a connection portion of the first path, the second path, and the reciprocating path by a predetermined distance. It is arranged on the back side in the reverse feed direction from the terminal position at the time, and the feeler arm is moved vertically from above the reciprocating path so that the feeler arm can be tilted in both the discharge direction and the reverse feed direction. The recording sheet detection sensor that supports the recording sheet and detects the passage of the recording sheet conveyed in both directions detects both the recording sheet conveyed in the paper discharge direction and the reverse feeding direction, thereby preventing an increase in cost. The

According to the second aspect of the present invention, since the drive stop time instructed by the control device to the transport device is equal to or longer than the chattering continuation time by the recording paper detection of the recording paper detection sensor, the recording paper at the recording paper detection sensor at the time after the switchback Is surely detected.

According to the third aspect of the present invention, since the recording sheet detection sensor is provided only at one place in the recording sheet conveyance direction on the reciprocating path, an increase in cost is prevented.

  A printer 1 which is an embodiment of an image forming apparatus of the present invention will be described with reference to the drawings.

First, the overall configuration of the printer 1 will be described with reference to FIG.
The printer 1 is an apparatus that forms an image by an electrophotographic process. In the printer 1, an apparatus that takes charge of each process of charging, exposure, development, transfer, cleaning, and fixing is provided.
These devices are provided along a recording paper transport path R from the paper feeding device 2 that stores recording paper for recording to the paper discharge tray 3, and specifically include the following devices.

First, a photosensitive drum 4 is disposed on the downstream side of the recording paper conveyance path R from the paper feeding device 2, and a print image is formed on the photosensitive drum 4 as an electrostatic latent image.
Around the photosensitive drum 4, there are a charger 5 for charging the surface (one side) of the photosensitive drum 4, and a laser scanning device 6 as an exposure means for irradiating the photosensitive drum 4 with light to form an electrostatic latent image. A developing roller 7 for supplying toner to the photosensitive drum 4, a transfer roller 8 for transferring a toner image in which an electrostatic latent image is visualized on a recording paper, and an eraser brush 9 for collecting the transferred toner. Yes.
A heat roller fixing type fixing device 10 is disposed downstream of the photosensitive drum 4 in the recording paper conveyance path R. The fixing device 10 includes a heat roller for heating the recording paper on which the toner image is transferred. 11 and a press roller 12 for pressing the recording paper. Then, the fixing device 10 performs a fixing process of the toner image on the recording paper.

  Further, a discharge roller device 13 is arranged on the downstream side of the fixing device 10 in the recording paper conveyance path R, and the recording paper that has passed through the fixing device 10 is transferred onto the paper discharge tray 3 by the discharge roller device 13. And discharged.

Next, a schematic configuration of the printer 1 related to double-sided printing will be described with reference to FIG.
The printer 1 is configured as an image forming apparatus that enables double-sided printing by a switchback method. In other words, while having the single-sided image forming unit 20 that forms an image on only one side of the recording paper in a single pass, the recording paper is switched back and forth by switching back (conveying direction), and again. By supplying the image forming unit 20 to the image forming unit 20, the recording paper can be printed on both sides.
Here, the image forming unit 20 means an assembly of process devices related to image formation. The photosensitive drum 4, the charger 5, the laser scanning device 6, the developing roller 7, and the transfer roller shown in FIG. 8 includes an eraser brush 9 and a fixing device 10.

First, the path through which the recording paper passes during front side printing is assumed to be three paths of a paper feed side path R0, a first path R1, and a reciprocating path R3. These paths R0, R1, R2, and R3 together with the second path R2 described later constitute the recording paper transport path R.
On the first path R1, the image forming unit 20 for one side is provided. When the front side printing is performed, the recording sheet is discharged from the sheet feeding device 2 to the sheet discharge tray 3 through the sheet feeding side path R0, the first path R1, and the reciprocating path R3 in this order.
Hereinafter, the direction in which the recording paper passes through the reciprocating path R3, that is, the direction in which the recording paper is discharged from the image forming unit 20 as it is to the paper discharge tray 3 in front surface printing is referred to as a discharge direction A.

A path that bypasses the upstream side and the downstream side of the image forming unit 20 of the first path R1 is a second path R2. That is, the second path R2 is connected to the connection part C1 between the paper feed side path R0 and the first path R1 and the connection part C2 between the first path R1 and the reciprocating path R3.
When printing on the back side, the recording paper is switched back by the discharge roller device 13 provided at the downstream end in the discharge direction A of the reciprocating path R3, and is sent back to the reciprocating path R3, the second path R2, the first The paper is discharged to the paper discharge tray 3 through one path R1. At this time, the front and back of the recording paper are reversed by returning to the first path R1 via the second path R2. Then, when the recording paper passes through the image forming unit 20 again with the front and back sides reversed, printing on the back side is performed and double-sided printing is performed.
Hereinafter, the direction in which the recording paper is switched back by the discharge roller device 13 and is fed back in the reciprocation path R3 with respect to the discharge direction A is referred to as a reverse feed direction B.

The discharge roller device 13 is a transport device that discharges the recording paper from the reciprocation path R3 to the paper discharge tray 3, and is also a transport device that reversely feeds the recording paper on the reciprocation path R3. The direction can be switched).
The discharge roller device 13 includes a discharge roller 14 that is rotated by applying a driving force, and a press roller 15 that is disposed so as to be in contact with the discharge roller 14 and rotates in a driven manner. The recording paper is nipped between the discharge roller 14 and the press roller 15 and conveyed.
Further, as a driving source for the discharge roller 14, a double-sided surface separate from a motor for driving a rotating member (photosensitive drum 4, developing roller 7, transfer roller 8, eraser brush 9, heat roller 11) provided in the image forming unit 20. A motor 22 is provided. The double-sided motor 22 is configured to be able to rotate in both forward and reverse directions. By switching the rotation direction, the conveyance direction of the recording paper nipped between the rollers 14 and 15 is changed between the discharge direction A and the reverse feed direction. It can be switched with B.

  The printer 1 is provided with a control device 21 for controlling the discharge roller device 13, and the drive of the discharge roller device 13 is controlled based on a control signal from the control device 21.

A recording paper detection sensor 16 that detects the presence or absence of recording paper is provided on the reciprocating path R3.
The arrangement position of the recording paper detection sensor 16 is between the arrangement position of the discharge roller device 13 and the connecting portion C2 in the reciprocating path R3. More specifically, the end position of the recording paper 30 at the time of switchback It is on the far side in the reverse feed direction B from P.
Here, since the recording paper 30 is nipped and conveyed by the rollers 14 and 15 provided in the discharge roller device 13, the recording paper 30 is held in a nipped state even when switched back. That is, the end position P is set to a position where the discharge roller device 13 can securely nip the recording paper. Therefore, the terminal position P (in the paper discharge direction A) of the recording paper 30 at the time of switchback is inevitably located on the connection portion C2 side (back side in the reverse feed direction B) from the nip position N.
Then, by setting the position of the recording paper detection sensor 16 on the back side in the reverse feed direction B from the end position P of the recording paper 30 at the time of switchback, the presence / absence of recording paper is detected before and after the switchback. Has been done. For example, when recording paper is detected both before and after the switchback during double-sided printing, it is recognized by the control side of the printer 1 that the recording paper is being conveyed correctly without jamming.

The recording paper detection sensor 16 is a contact type sensor that detects the presence or absence of recording paper using contact with the recording paper. The feeler arm 17 that swings in contact with the recording paper and the swinging of the feeler arm 17. And an optical sensor unit 18 for detecting the state.
The feeler arm 17 is swingably supported by the casing 19 of the recording paper detection sensor 16. The optical sensor unit 18 is a transmissive photo interrupter, and an optical path formed between a light emitting unit and a light receiving unit included in the optical sensor unit 18 is transmitted or transmitted according to the swinging position of the feeler arm 17. It is a configuration that is blocked.
In a natural state where no external force is applied to the feeler arm 17, the optical path is cut off and an OFF signal is output from the recording paper detection sensor 16, and the recording paper comes into contact with the feeler arm 17 and the feeler arm 17 is tilted. In this state, the optical path is in a transmissive state, and an ON signal is output from the recording paper detection sensor 16.

Basically, the ON signal is output from the recording paper detection sensor 16 is a state in which the passage of the recording paper is detected, and the OFF signal is output from the recording paper detection sensor 16 The passage is not detected.
Here, “basic” is because an ON signal and an OFF signal are output from the recording paper detection sensor 16 also in the case of chattering described later.

The feeler arm 17 is supported by the casing 19 so as to be inclined in both the discharge direction A and the reverse feed direction B, and hangs vertically downward by its own weight in a natural state where no external force acts.
For this reason, the recording paper detection sensor 16 detects the recording paper regardless of whether the recording paper passing through the recording paper detection sensor 16 comes from the discharge direction A or the reverse feeding direction B.

During duplex printing, the recording paper 30 passes through the detection position D of the recording paper detection sensor 16 a total of three times. In the case of the recording paper detection sensor 16 having the above-described configuration, the detection position D is a portion that overlaps the swing range of the feeler arm 17 on the reciprocating path R3.
The first pass and the second pass are performed before and after the switchback after the front surface printing is completed, and the third pass is performed at the time of discharging after the back surface printing.
In particular, the first pass is performed when the recording paper is transported through the reciprocating path R3 and moves to the discharge roller device 13, and the second pass is discharged immediately after the first pass. This is performed when the roller device 13 is switched back and fed back.
That is, the time interval between the first pass and the second pass is shorter than the time interval between the second pass and the third pass.

If the sensor detects the presence or absence of recording paper using contact with the recording paper, such as the recording paper detection sensor 16, chattering occurs when the input changes (when the recording paper and the feeler arm 17 are in contact). Inevitable.
The chattering generated by the recording paper detection sensor 16 having the above-described configuration means that the recording paper 30 swings like a pendulum when the recording paper 30 and the feeler arm 17 come into contact with each other (particularly at the time of separation). Until the oscillation is attenuated and stabilized, the optical sensor unit 18 repeatedly transmits and blocks the optical path, and the recording paper detection sensor 16 alternately and intermittently generates ON / OFF signals.
Since the feeler arm 17 is tilted during the passage of the recording paper, the ON signal is continuously output from the recording paper detection sensor 16. In addition, when the feeler arm 17 is stable (stationary) without swinging after the chattering duration, an OFF signal is continuously output from the recording paper detection sensor 16. The chattering duration is substantially determined by the type of the detection sensor 16, the shape of the feeler arm 17, and the frictional force between the feeler arm 17 and its mounting portion. That is, the chattering duration can be measured in advance.

Therefore, in order to accurately detect the presence or absence of recording paper using the recording paper detection sensor 16, output signals generated by chattering (that is, ON / OFF intermittent portions) are excluded from the output signals of the recording paper detection sensor 16. There is a need.
As a hardware countermeasure, there is a method in which a filter circuit is connected to the recording paper detection sensor 16 to smooth and remove the intermittent portion of the output signal due to chattering (filter method).
Further, as a software (control) countermeasure, for example, when there is a change in the output signal from the recording paper detection sensor 16, a fixed waiting time is provided and the output signal after the change is changed thereafter. If this is continued, there is a method (delay method) in which the change is regarded as effective. In addition, there is a method (sampling method) in which the output signal of the recording paper detection sensor 16 is validated at regular intervals that are sufficiently longer than the chattering duration.
In any of the methods, basically, an output signal during chattering is ignored to prevent the adverse effects caused by chattering.

Here, in the recording paper detection sensor 16, when the time interval of the recording paper passage before and after the switchback described above is shorter than the duration of the chattering, the recording at the time of moving in the second reverse feeding direction is performed. Paper detection cannot be performed properly.
In other words, if the output signal during chattering is ignored in order to eliminate the adverse effects of chattering, the recording paper passes during that time, so the output signal due to passage of the recording paper is also ignored.

Therefore, before and after the switchback, by setting so that the second passage of the recording paper is performed after the duration of the chattering by the first passage, an appropriate passage of the recording paper by the recording paper detection sensor 16 is performed. Detection can be performed.
In addition, it is not always necessary that the second passage of the recording paper is performed after the duration of chattering by the first passage. That is, it is only necessary that the output of the ON signal in the second pass continues until after the duration of chattering by the first pass.
In each of the above-described countermeasures (delay method, etc.), in order to eliminate the adverse effects of chattering, the output signal during the chattering duration is ignored, but the output signal after the chattering duration is valid. Therefore, if the ON signal due to the passage of the recording paper is output from the recording paper detection sensor 16 after the chattering duration time, whether or not the recording paper is appropriate while eliminating the harmful effects of chattering using each of the above-described countermeasures. Detection can be performed.
In this embodiment, the delay method is applied as a method of ignoring the output signal during the chattering duration.

The chattering countermeasure structure of the recording paper detection sensor 16 will be described.
The control device 21 is a control device that controls the drive of the discharge roller device 13, and this drive control is performed based on an output signal from the recording paper detection sensor 16.
In particular, as a countermeasure against chattering, the control device 21 controls the driving of the discharge roller device 13 so as to appropriately delay the second recording paper passage based on the detection of the first recording paper passage.
Then, when the recording paper detection sensor 16 detects the second recording paper passage, the adverse effect of chattering due to the first recording paper passage is prevented.

The drive control of the discharge roller device 13 by the control device 21 will be described with reference to FIG.
First, printing processing is started in the printer 1 (step 101). The printing process here is more specifically a duplex printing process. Next, the recording paper passes through the image forming unit 20 in a state where the surface is printed (step 102).
The print start information in step 101 is transmitted from the overall control device that controls the entire printing process to the control device 21 related to the control of the discharge roller device 13. Further, the passage of the recording paper in the image forming unit 20 in step 102 can be detected by a recording paper detection sensor provided on the first path R1, and this detection information is transmitted to the control device 21.
Then, the control device 21 recognizes the start of double-sided printing and the conveyance of the recording paper to the discharge roller device 13 side.

  In the present specification, the control device 21 related to the control of the discharge roller device 13 is described separately from the overall control device, but this is only for characterizing the function of the control device 21 for convenience of explanation. That is, it is not limited whether the overall control device and the control device 21 are integrated or separate.

  In step 103, the passage of the recording paper at the time before the switchback in the recording paper detection sensor 16 is detected by the control device 21 based on the output signal from the recording paper detection sensor 16. The recording paper at this time is in a state where the surface is printed and conveyed toward the discharge roller device 13, and this is the first detection of the recording paper by the recording paper detection sensor 16.

Next, stop control of the discharge roller device 13 is performed by the control device 21 so that the recording paper that has passed the recording paper detection sensor 16 stops correctly at the end position P.
Specifically, first, an elapsed time T after the recording paper passes through the recording paper detection sensor 16 is measured by a timer 21 a provided in the control device 21. When the elapsed time T reaches the drive duration time T1, the timer 21a instructs the double-sided motor 22 (discharge roller device 13) to stop driving (step 105), and the recording paper is discharged until the drive duration time T1 is reached. The conveyance in the direction A is continued (no drive stop is commanded). This process is the process of step 104.
Here, the drive continuation time T1 means the time required for the recording paper conveyed by the discharge roller device 13 to reach the terminal position P from the recording paper detection sensor 16. The length of this time can be predicted based on the speed at which the discharge roller device 13 conveys the recording paper and the distance from the recording paper detection sensor 16 to the end position P.

Next, the control device 21 switches back the recording paper. In order to eliminate the adverse effect of chattering, the discharge roller device 13 is temporarily stopped to delay the start of reverse feeding.
Specifically, an elapsed time T after the driving of the discharge roller device 13 is stopped is measured by the timer 21a. When the elapsed time T reaches the drive stop time T2, the timer 21a commands the drive start of the discharge roller device 13 in the reverse feed direction B (step 107), and the double-sided motor 22 (discharge) until the drive stop time T2 is reached. The drive stop of the roller device 13) is continued (no start of drive is commanded). This process is the process of step 106.
Here, the drive stop time T2 is set to about the chattering continuation time in the recording paper detection sensor 16. Then, the recording paper that is sent back to the recording paper detection sensor 16 at the time after the switchback and the chattering caused by the passage of itself (recording paper) at the time before the switchback has definitely settled. The paper detection sensor 16 is reached.
Since the elapsed time T means the time measured by the timer 21a, the same term and the same sign are used in step 105 and step 107.

  In step 108, the passage of the recording paper after the switchback in the recording paper detection sensor 16 is detected by the control device 21 based on the output signal from the recording paper detection sensor 16. The recording paper at this time is in a state where the surface is printed and is switched back and fed backward from the discharge roller device 13, and this is the second detection of the recording paper by the recording paper detection sensor 16. .

Then, the recording paper fed back from the discharge roller device 13 is returned to the first path R1 through the second path R2, and the front and back are reversed, and the back side is printed by the image forming unit 20 (step 109). After the printing on the back side is finished, the recording paper on which the printing on both sides is finished is discharged onto the paper discharge tray 3 via the reciprocating path R3 (step 110).
Here, the passage of the recording paper in the image forming unit 20 in step 109 can be detected by a recording paper detection sensor provided on the first path R 1, and this detection information is transmitted to the control device 21.
In addition, between step 109 and step 110, the recording paper is in a double-sided printing state and passes the recording paper detection sensor 16 for the third time, but the control device 21 receives the detection information in step 109, Correctly recognize the third passage of the recording paper and perform control accordingly. That is, the control device 21 drives the discharge roller device 13 in the paper discharge direction A until the recording paper is discharged onto the paper discharge tray 3.

When the recording paper is discharged onto the paper discharge tray 3, the control device 21 and the overall control device shift to a standby state (step 111).
For example, after the recording paper passes through the recording paper discharge sensor 16 for the third time, when the time required for the recording paper to be discharged to the paper discharge tray 3 elapses, the control device 21 or the overall control device “records”. It is recognized that the paper has been discharged onto the paper discharge tray 3.

The chattering countermeasure structure of the recording paper detection sensor 16 described above will be summarized.
First, this chattering countermeasure structure is a printer 1 (image forming apparatus) that enables double-sided printing by reversing the recording paper that has passed through the image forming unit 20 by the switchback method and passing it again through the image forming unit 20. ).
The printer 1 includes a discharge roller device 13 (conveyance device) capable of conveying the recording paper in both the paper discharge direction A and the reverse feed direction B with respect to the paper discharge direction A, and a reciprocating path R3 through which the recording paper passes. In addition, the recording paper detection sensor 16 disposed on the rear side in the reverse feed direction B from the end position P at the time of recording paper switchback, and a control device 21 for controlling the driving of the discharge roller device 13 are provided. It has been.
Then, the control device 21 instructs the discharge roller device 13 to stop driving once at the time of switchback to switch the conveyance direction from the discharge direction A to the reverse direction B, and then conveys the recording paper in the reverse direction B. Command to drive.

For this reason, the time when the recording paper passes the recording paper detection sensor 16 after the switchback is delayed with respect to the chattering start time generated by the recording paper detection sensor 16 before the switchback. Become. That is, the recording paper passes through the recording paper detection sensor 16 with the influence of chattering reduced.
Therefore, the detection accuracy of the recording paper by the recording paper detection sensor 16 at the time after the switchback is improved.

  In particular, the drive stop time instructed by the control device 21 to the discharge roller device 13 (conveyance device) is longer than the chattering continuation time by the recording paper detection of the recording paper detection sensor 16.

For this reason, when the recording paper passes through the recording paper detection sensor 16 after the switchback, the chattering generated by the recording paper detection sensor 16 is settled before the switchback.
Therefore, the detection of the recording paper by the recording paper detection sensor 16 at the time after the switchback is ensured.

  The recording paper detection sensor 16 is provided only at one location in the recording paper conveyance direction on the reciprocating path R3.

For this reason, a single sensor detects both the recording paper conveyed in the paper discharge direction and the reverse feeding direction.
Therefore, an increase in cost is prevented.

In the double-sided printing method in this embodiment, after the transfer and fixing of the front side are completed, the transfer and fixing of the back side are performed to perform double-sided printing. For this reason, the image forming unit 20 includes both a transfer-related device and a fixing-related device, and a conveying device (switching back to the discharge side (discharge tray 3 side) with respect to the image forming unit 20 ( A discharge roller device 13) is provided.
Here, the devices related to the transfer are the photosensitive drum 4, the charger 5, the laser scanning device 6, the developing roller 7, the transfer roller 8, the eraser brush 9, and the like. An apparatus related to fixing is the fixing apparatus 10.

On the other hand, instead of the double-sided printing method in the present embodiment, a method may be used in which both surfaces are fixed simultaneously after the front and back surfaces are transferred.
In other words, it is switched back between the device related to transfer and the device related to fixing, the transfer of the front side is finished, the front and back are reversed, the transfer of the back side is performed, and then both sides are fixed It is.
In this case, only the apparatus related to the transfer is an image forming unit (corresponding to the image forming unit 20 of the printer 1), and the recording paper is fed back in the paper discharge direction between the image forming unit and the apparatus related to fixing. A conveying device (corresponding to the discharge roller device 13) capable of conveying in both directions is provided.

It is front sectional drawing of a printer. FIG. 2 is a schematic configuration diagram of a printer related to double-sided printing. It is a flowchart in connection with drive control of the discharge roller apparatus by a control apparatus.

Explanation of symbols

1 Printer (image forming device)
13 Discharge roller device (conveyance device)
16 Recording paper detection sensor 20 Image forming unit 21 Control device 30 Recording paper A Discharge direction B Reverse feed direction P End position R3 Reciprocating path

Claims (3)

In the image forming apparatus which enables double-sided printing by inverting the front and back of the recording paper that has passed through the image forming unit and passing it again through the image forming unit,
A transport device capable of transporting recording paper in both the paper discharge direction and the reverse direction;
On the reciprocating path through which the recording paper passes in both directions, away from the connecting portion of the first path, the second path, and the reciprocating path by a predetermined distance, and more than the end position when the recording paper is switched back , Arranged on the back side in the reverse feed direction, supporting the feeler arm from above the reciprocating path vertically downward so that the feeler arm can be tilted in both the discharge direction and the reverse feed direction, A recording paper detection sensor for detecting the passage of the recording paper conveyed in both directions;
A control device for controlling the driving of the transport device based on an output signal from the recording paper detection sensor;
With
The control device detects a first passage of the recording paper based on a first output signal from the recording paper detection sensor, temporarily stops driving the conveyance device, and then records the recording paper in the reverse feeding direction. Based on the second output signal from the recording paper detection sensor, detects the second passage of the recording paper to be switched back, and based on the third output signal from the recording paper detection sensor Detecting the third passage of the recording paper in the double-sided printing state, and performing control for discharging the recording paper to the transport device;
An image forming apparatus. The drive stop time that the control device commands the transfer device is:
More than the chattering continuation time by the recording paper detection of the recording paper detection sensor,
The image forming apparatus according to claim 1. The recording paper detection sensor is provided only at one location in the recording paper conveyance direction on the reciprocating path.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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