JP5901243B2 - Discriminating apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a discriminating apparatus that discriminates the type of a sheet and an image forming apparatus equipped with the apparatus.

  In image forming apparatuses such as printers and copiers, various types of sheets for forming images are used. Image forming conditions (transfer conditions, fixing conditions, conveying conditions, etc.) for obtaining good image quality vary depending on the type of sheet. Therefore, the image forming conditions are automatically set by determining with a type determining means for determining the type of sheet on which an image is formed. Here, as the type discriminating means, for example, there is one that detects the weight (thickness) of the sheet. In Patent Document 1, as a mechanism for detecting the thickness, a lever is brought into contact with the sheet, and the displacement (position) of the lever corresponding to the deflection of the sheet is detected by a plurality of sensors to determine the weight (thickness) of the sheet. It discloses what to do.

JP-A-10-236691

  However, the above-described prior art requires a plurality of photointerrupters in order to detect the displacement (position) of the lever according to the thickness of the sheet. Therefore, there is a problem in cost, and a space for arranging a plurality of photointerrupters. Is necessary and the device becomes larger.

  SUMMARY An advantage of some aspects of the invention is that it provides a low-cost and small-sized discriminating apparatus for discriminating the type of a sheet and an image processing apparatus equipped with the apparatus.

The discriminating apparatus of the present invention is pushed by a lever that is pushed and moved by the sheet conveyed by the conveying means, a photo interrupter whose ON / OFF state changes depending on the position of the lever, and a leading edge of the conveyed sheet. After the lever is moved and the photo interrupter is turned on, the measurement time until the lever moves and the photo interrupter is turned off when the rear end of the sheet moves away from the lever is measured. A discriminating unit that discriminates the thickness of the sheet, and the discriminating unit calculates an expected time calculated based on a length in the sheet conveying direction of the sheet conveyed by the conveying unit and a conveying speed, and the measurement time. When the difference is larger than a preset first reference value, the conveyed sheet is determined as thin paper .

  In the present invention, a low-cost and small-sized discriminating apparatus that discriminates the type of sheet can be provided.

1 is a cross-sectional view of an image forming apparatus according to the present invention. 1 is an explanatory diagram of a first embodiment of an image forming apparatus according to the present invention. 1 is a flowchart of a first embodiment of an image forming apparatus according to the present invention. 1 is a block diagram of a first embodiment of an image forming apparatus according to the present invention. Explanatory drawing of 2nd Embodiment of the image forming apparatus which concerns on this invention. Explanatory drawing of 2nd Embodiment of the image forming apparatus which concerns on this invention.

(First embodiment)
FIG. 1 is a sectional view of an image forming apparatus according to the present invention.
In the image forming apparatus 30 shown in FIG. 1, the sheets P stacked on the paper feed cassette 40 are transported by the paper feed roller 41 to the sensor unit 10 provided downstream in the transport direction from the paper feed roller 41. . The sheet P that has passed the sensor unit 10 is corrected in the skew of the sheet by aligning the leading end of the sheet P in the registration shutter unit 20 perpendicularly to the conveyance direction. After passing through the registration shutter unit 20, the sheet is sent to the transfer unit 50 by the registration roller pair 24. The sheet feeding roller 41, the registration roller pair 24, and the like constitute a conveying unit that conveys the sheet.

  The image on the photosensitive drum of the image forming unit 71 is transferred to the sheet in the transfer unit 50. The sheet on which the image is transferred is conveyed to the fixing unit 60. In the fixing unit 60, the transferred image is fixed to the sheet P by heat and pressure. The sheet P conveyed downstream from the fixing unit 60 is discharged to a discharge stacking tray 64 by a discharge roller pair 63.

  FIG. 2 is a cross-sectional view showing the configuration of the sensor unit 10 constituting the sheet type discrimination unit and its periphery. A sensor lever 11 is rotatably provided in the sensor unit 10. The sensor lever 11 is biased by the spring 14 in the direction of the initial stop position (arrow direction) which is a standby position (see FIG. 2A).

  A sensor shield 11 a is formed in the sensor lever 11, and a sensor (photo interrupter) 12 that reacts by the operation of the sensor lever 11 is disposed in the vicinity of the sensor lever 11. The ON / OFF state of the sensor 12 changes depending on whether or not the sensor 12 is shielded by the sensor shielding portion 11a of the sensor lever 11. The sensor 12 is OFF in a standby state where it is not shielded by the sensor shielding part 11a of the sensor lever 11. The sensor 12 is ON when the sensor 12 is shielded by the sensor shield 11a of the sensor lever 11. The guide 13 has a recess 13a in a part of the sheet conveying path so that the rear end of the sheet receiving the force from the sensor lever 11 can be deformed.

  FIG. 4 is a block diagram of a control system of the image forming apparatus 30. A signal from the sensor 12 is input to the controller 32. Based on the signal from the sensor 12, the controller 32 discriminates the sheet type by the discriminating unit, and discriminates the sheet type, which will be described in detail later. The controller 32 controls the operation of each device related to image formation via the image formation control unit. That is, when the controller 32 receives a print command from the user, for example, through the operation panel, the controller sets a conveyance speed suitable for sheet conveyance, and sets a motor or the like related to sheet conveyance so that the sheet is conveyed at the set conveyance speed. Control is performed via an image formation control unit. Instead of receiving a print command through the operation panel, an image processing command may be received from a personal computer. The controller 32 controls the transfer current and voltage in the transfer unit 50, the fixing temperature in the fixing unit 60, and the like via the image formation control unit.

Next, an operation related to sheet type determination will be described with reference to FIG. 2 and FIG. 3 which is a control flowchart of the controller 32.
Estimated ON time, which is the time when the sensor 12 is ON when one sheet passes the sensor lever 11 by the controller 32 of the image forming apparatus 30 in the conveyance direction length and conveyance speed of the sheet to be conveyed. T1 is calculated (step 41. Hereinafter, step is abbreviated as S).

  In FIG. 2, when a sheet is fed by the sheet feed roller 41, the leading edge of the sheet P conveyed by the sheet feed roller 41 moves the sensor lever 11 (see FIG. 2B).

  At this time, the sensor shield 11a of the sensor lever 11 turns on the output state of the sensor 12. When the ON signal from the sensor 12 is input to the controller 32 (YES in S42), a timer, which is a measuring means built in the controller 32, starts measuring the sensor ON time of the sensor 12 (S43).

  Here, when the leading edge of the sheet comes into contact with the sensor lever 11 and starts to rotate, the behavior of the sheet is constant regardless of the thickness (stiffness) of the sheet. On the other hand, the behavior of the sheet when the trailing edge of the sheet passes through the sensor lever 11 (see FIG. 2C) varies depending on the thickness (stiffness) of the sheet. Note that the thickness and the size of the stiffness are in a substantially proportional relationship, and the thickness can be determined based on the size of the stiffness.

  The timing at which the sensor lever 11 turns off the sensor 12 varies depending on the thickness of the sheet due to the difference in the behavior of the sheet trailing edge, and the actual sensor ON time T2 varies depending on the thickness of the sheet. The actual sensor ON time T2 as the elapsed time here is that the rear end of the sheet passes through the sensor lever 11 from the time when the sensor 12 changes from the OFF state which is the standby state to the ON state. This is the time until returning to the OFF state.

  Thus, since the actual sensor ON time T2 differs depending on the difference in sheet thickness (strength and strength), the type of sheet can be determined from the difference ΔT between the expected ON time T1 and the actual sensor ON time T2. it can. Therefore, when the signal from the sensor 12 is switched off (S44), the controller 32 ends the measurement of the sensor ON time T2 (S45). Then, the type (thickness) of the sheet is determined by the determination unit of the controller 32 based on the actual ON time T2.

  Hereinafter, in the present embodiment, a method for discriminating the sheet thickness into three types from the difference in stiffness of the sheet will be described as an example.

First, the case where the sheet P is weak paper such as thin paper will be described.
The sheet P that has passed through the sensor lever 11 is conveyed along the guide 13. Immediately after the trailing edge of the sheet P passes through the pick roller 41, the portion on the trailing edge side of the sheet is bent in the arrow direction (direction toward the guide 13) by the sensor lever 11, as shown in FIG. The sensor lever 11 rotates toward the standby position by the urging force of the spring 14 and turns off the output of the sensor 12.

  Assuming that the expected sensor ON time is T1 and the actual sensor ON time is T2, when the sheet is bent as described above, a difference ΔT of ΔT = T1−T2 is generated.

  When ΔT is greater than or equal to the discrimination criterion Ta (YES in S46), the discrimination unit of the controller 32 discriminates the sheet type as thin paper (S47). Here, since ΔT includes measurement error, sheet behavior variation, and the like, a value that does not cause erroneous determination due to the difference is set in advance as the discrimination criterion Ta.

  As a result, when the controller 32 determines that the determination unit is thin paper, the controller 32 sets the subsequent image forming conditions (for example, transfer current and voltage in the transfer unit 50, fixing temperature in the fixing unit 60, etc.) to be suitable for thin paper. To the conditions. For example, the temperature of the fixing unit 60 is set to be lower than the standard temperature.

Next, a case where the sheet is a strong sheet such as thick paper will be described.
The sheet P that has passed through the sensor lever 11 is conveyed along the guide 13. Since the sheet is strong, the sheet is conveyed along the guide 13 with little bending even if the trailing end of the sheet passes through the pick roller 41 and is pressed by the sensor lever 11 (see FIG. 2D). Then, after the rear end of the sheet is conveyed to a position beyond the front end of the sensor lever 11, the sensor lever 11 is rotated toward the standby position by the biasing force of the spring 14, and the output of the sensor 12 is turned off.

  Assuming that the expected sensor ON time is T1 and the actual sensor ON time is T2, the sheet P hardly bends as described above, and therefore the difference ΔT of ΔT = T1−T2 approaches almost zero.

  When ΔT is smaller than the discrimination criterion Tb (YES in S48), the discrimination unit of the controller 32 of the image forming apparatus discriminates the sheet type as thick paper (S49). Here, since ΔT includes measurement error, sheet behavior variation, and the like, a value that does not cause false detection due to the measurement error is set as the discrimination reference Tb.

  As a result, if the determination unit of the controller 32 determines that the sheet is thick paper, the controller 32 sets the subsequent image forming conditions (for example, transfer current and voltage in the transfer unit 50, fixing temperature in the fixing unit 60, etc.) suitable for the thick paper. To. For example, the temperature of the fixing unit 60 is set to be higher than the standard temperature.

  If the difference ΔT is between Ta and Tb (NO in S48), the determination unit of the controller 32 of the image forming apparatus determines that the sheet type is plain paper (S50). Then, the controller 32 sets the subsequent image forming conditions (for example, the transfer current and voltage in the transfer unit 50, the fixing temperature in the fixing unit 60, etc.) to conditions suitable for plain paper. For example, the temperature of the fixing unit 60 is set to the standard temperature.

  As described above, the type of the sheet P can be determined by the ON time of the sensor 12 being different depending on the strength of the sheet P being conveyed. Furthermore, it is possible to automatically set the optimum image forming conditions for the sheet P by using the determination result.

  In addition, by using a sensor for detecting the presence or absence of a sheet in an existing conveyance path to determine the sheet type, it is possible to provide an inexpensive image forming apparatus without requiring additional parts for determining the sheet. That is, the signal from the sensor 12 is also used for detecting a jam of a sheet and for aligning an image and a sheet when forming an image. Specifically, if the ON signal from the sensor 12 continues longer than a predetermined time, it is determined that the controller is a stay jam. Alternatively, when the controller 32 receives an ON signal from the sensor 12, it may be determined that a jam has occurred when another downstream sheet sensor does not receive a sheet arrival signal. Alternatively, the image forming unit may start image formation in response to receiving an ON signal from the sensor 12 to use the image and the sheet for alignment.

  In the first embodiment, the sensor lever is provided upstream of the nip portion of the registration roller pair 24. However, the sensor lever may be provided at another position on the conveyance path. For example, it may be provided in a fixing unit or a paper discharge unit. Further, the sensor may be operated by a registration shutter with which the front end of the sheet comes into contact for skew correction. Note that the skew of the sheet is corrected by forming a loop in the sheet with the leading edge of the sheet in contact with the registration shutter.

(Second Embodiment)
In the first embodiment, the determination of the thickness of the sheet is exemplified. It is also possible to determine the width size of the sheet by using the ON time of a sensor (photo interrupter) that is operated by a lever pushed by the sheet, which will be described as a second embodiment below. Further, in the following second embodiment, a mode in which a rest shutter with which the front end of the sheet contacts for skew correction is used as a lever for operating the sensor is illustrated. Note that the second embodiment is a configuration in which a sensor is turned ON / OFF with a resist shutter and a signal from the sensor is used to determine the width size in addition to the first embodiment described above. Except for the configuration described above, the first embodiment and the second embodiment are the same. Therefore, regarding the same configuration as that of the first embodiment, the same reference numerals as those of the first embodiment are given and detailed description thereof is omitted.

FIG. 5 shows the configuration of the second embodiment, and FIG. 6 shows the operation of the sheet type discriminating apparatus applicable to the present invention.
First, a configuration related to the registration shutter unit 20 which is a size discrimination sensor unit will be described with reference to FIG.

  The resist shutter unit 20 includes a resist shutter 21. The registration shutter 21 is swingably supported on the axis of one roller of the registration roller pair 25. The resist shutter 21 is urged toward the initial stop position (arrow direction) by a spring. The registration shutter 21 has a sensor shielding part 21 a, and a size discrimination sensor (photo interrupter) 22 that reacts by the operation of the registration shutter 21 is disposed in the vicinity of the registration shutter 21.

  The registration shutter 21 has a plurality of sheet front end contact portions 21b, and the conveyed sheet front end portion contacts each of the contact portions 21b. The leading edge of the sheet is aligned to correct the skew of the sheet. Thereafter, the registration shutter 21 is rotated by being pushed by the leading edge of the conveyed sheet. The guide 23 has a sheet escape portion 23a in a part of the sheet conveyance path so that the rear end of the sheet that receives the force from the registration shutter 21 can be deformed.

Next, the operation will be described.
As described in detail in the first embodiment, the thickness of the sheet conveyed by the sheet feeding roller 41 is determined by the sensor unit 10. Thereafter, the sheet P is brought into contact with the contact portion 21b of the registration shutter 21 and enters the nip of the registration roller pair 24 while rotating the registration shutter 21 (FIG. 6A).

  At this time, the sensor shielding portion 21a of the registration shutter 21 turns on the size discrimination sensor 22, and at the same time, the measuring means built in the controller 32 starts measuring the ON time of the size discrimination sensor 22 (FIG. 6B). .

  The controller 32 of the image forming apparatus 30 calculates an expected ON time T91 from the sheet size set on the operation panel by the user, the sheet conveyance speed, and the thickness determined by the sensor unit 10. Instead of setting through the operation panel, an image processing command including sheet size information may be received from a personal computer.

  Here, the behavior of the portion on the trailing edge side of the sheet when the trailing edge of the sheet passes through the registration shutter 21 varies depending on the difference in the sheet width size. This is because the stiffness of the sheet differs depending on the width size of the sheet, and the bending shape of the portion on the rear end side of the sheet pressed by the resist shutter 21 varies depending on the strength of the sheet. That is, the OFF timing of the size discrimination sensor 22 changes depending on the sheet width size. As a result, the actual sensor ON time T92 changes.

  Thus, since the actual sensor ON time T92 differs depending on the difference in sheet width size (strength and strength), the sheet width size is determined from the difference between the expected ON time T91 and the actual sensor ON time T92. Can do. In the second embodiment, the width size determination result based on the signal from the size determination sensor 22 is used to check whether the width size set by the user on the operation panel is correct.

Hereinafter, a method for determining the sheet width size from the difference in strength of the sheet will be described.
First, a case where the sheet width size is smaller than the size set on the operation panel by the user will be described.

  The sheet P that has passed through the registration roller pair 24 is conveyed along the guide 23. Since the conveyed sheet width size is small, the sheet P contacts only a part of the resist shutter contact portion 21b. Therefore, the urging force of the spring urging the registration shutter 21 is concentrated on a part of the registration shutter contact portion 21b. Here, as the width size of the sheet P is narrower, the force from the resist shutter 21 that tries to deflect the sheet per sheet unit width increases. Therefore, a sheet having a narrow width size is more easily bent.

  As a result, immediately after the trailing edge of the sheet passes through the registration roller pair 24, the trailing edge of the sheet P bends in the direction of the arrow by pressing the registration shutter 21 (see FIG. 6D). That is, as shown in FIG. 6D, the rear end portion of the sheet whose front end side is in contact with the guide 23 is greatly bent by being pushed by the resist shutter 21 biased by the spring to the standby position. 22 is turned OFF. Immediately after the trailing edge of the sheet passes through the registration roller pair 24, the registration shutter 21 starts to rotate in the standby position direction, and the width determination sensor sensor 22 is turned off. That is, the return of the registration shutter 21 to the standby position is completed earlier than when a sheet having a large width size is conveyed.

Assuming that the expected ON time is T91 and the actual sensor ON time is T92, when the sheet P is bent as described above, a difference ΔT of ΔT = T91−T92 is generated.
Therefore, if ΔT is equal to or greater than the determination criterion Tc, the controller 32 determines that the sheet width size is narrower than the size set (designated) by the user. Here, since ΔT includes a measurement error, sheet behavior variation, and the like, a value that does not cause post-detection due to the measurement error is set as the discrimination criterion Tc.

  As a result, the controller 32 changes the subsequent image forming conditions (for example, the transfer current and voltage in the transfer unit 50, the fixing temperature in the fixing unit 60, the heater heat generation area in the fixing unit 60, etc.) to conditions suitable for small-size sheets. To do. For example, in the fixing unit 60, a heater at the center is heated to stop the heater at the end of the fixing unit, or control is performed such that continuous feeding is performed with a long gap between sheets. In addition, since the size determined by the controller 32 does not match the size specified by the user, a display prompting confirmation of the size specification is displayed on the operation panel, and the apparatus is stopped by determining that an incorrect operation has been performed. Also good.

Next, a case where the sheet width size is wider than the size set (specified) by the user will be described.
The sheet P that has passed through the registration roller pair 24 is conveyed along the guide 23. If the conveyed sheet P is wide, the sheet P comes into contact with a large number of resist shutter contact portions 21b. Therefore, the urging force of the spring urging the registration shutter 21 is distributed to a number of registration shutter contact portions 21b. As the width of the sheet increases, the force per sheet unit width from the resist shutter 21 that attempts to bend the sheet decreases. Therefore, the wider the sheet, the more difficult it is to bend.

  As a result, even after the trailing edge of the sheet passes through the registration roller pair 24, the sheet is conveyed along the guide 23 in a state where the deflection due to the force from the registration shutter 21 is small. That is, as shown in FIG. 6C, the portion on the rear end side of the sheet whose front end side is in contact with the guide 23 is pushed and bent by the resist shutter 21 biased by the spring to the standby position. Is small, the sensor 22 remains ON. When the trailing edge of the sheet is conveyed to a position beyond the leading edge of the registration shutter 21, the registration shutter 21 rotates toward the standby position by the biasing force of the spring, and the width determination sensor sensor 22 is turned off.

Therefore, assuming that the expected sensor ON time is T91 and the actual sensor ON time is T2, as described above, the difference ΔT of ΔT = T91−T92 changes from 0 to minus when the sheet hardly bends.
When ΔT is equal to or less than Td, the controller 32 of the image processing apparatus determines that the sheet width is wider than the size set by the user. Here, since ΔT includes measurement error, sheet behavior variation, and the like, a value that does not cause post-detection due to the measurement error is set as the discrimination reference Td.

  As a result, the controller 32 is suitable for a large size of subsequent image forming conditions (for example, a transfer current and voltage in the transfer unit 50, a fixing temperature in the fixing unit 60, a heater heat generation area of the fixing unit 60), etc. To the conditions. For example, in the fixing unit 60, not only the heater at the center but also the heater at the end of the fixing unit generates heat. In addition, since the size determined by the controller 32 does not match the size specified by the user, guidance for confirming the size specification is displayed on the operation panel, and it is determined that an incorrect operation has been performed and the apparatus is stopped. It may be.

A case where the sheet width size is the same as the size set (specified) by the user will be described.
In this case, the deflection of the trailing edge of the sheet is as expected. When the expected sensor ON time is T1 and the actual sensor ON time is T2, the difference ΔT of ΔT = T1−T2 approaches almost zero.

  When the difference ΔT is between Tc and Td, the controller 32 of the image processing apparatus determines that the sheet width size is the size set by the user. Therefore, the controller 32 sets the subsequent image forming conditions (for example, the transfer current and voltage in the transfer unit 50, the fixing temperature in the fixing unit 60, the heater heat generation area in the fixing unit 60, etc.) according to the size set by the user. To do.

  The sensor 22 is also used for sheet jam detection and alignment of an image and a sheet when forming an image. Specifically, if the ON signal from the sensor 22 continues for longer than a predetermined time, the controller 32 determines that a jamming has occurred. Further, when the controller 32 receives an ON signal from the sensor 22, it is determined that a jam has occurred when another downstream sheet sensor does not receive a paper arrival signal. In addition, the image forming unit starts image formation in response to receiving an ON signal from the sensor 22 to use the image and the sheet for alignment. As described above, the sensor 22 is also used for detecting a jam and determining the position of the sheet, so that it is possible to provide an inexpensive apparatus without requiring additional parts only for sheet determination.

  In the second embodiment, an example in which the detection result of the thickness in the sensor unit 10 is used in calculating the expected ON time T91 is illustrated. However, the thickness may be input to the operation panel, and the thickness input to the operation panel may be used for calculating the expected ON time T91.

  Further, it is exemplified that the object to be confirmed by the determination result by the size determination sensor 22 is the width size set by the user on the operation panel. However, the object to be confirmed by the determination result of the size determination sensor 22 may be the width size included in the image processing command from the personal computer. Moreover, the structure using the discrimination | determination result in the size discrimination | determination sensor 22 as follows may be sufficient. A width size detection unit is provided that detects the position of the side regulating plate that is moved by the user to a position corresponding to the width of the sheets stacked on the paper feed cassette 40. In order to confirm whether or not the width size determination result based on the signal from the size determination sensor 22 matches the detection result in the width size detection unit, that is, whether the side regulating plate is set correctly. use. And if a controller presumes that the side regulation board is not set correctly, that will be displayed on an operation panel, for example.

Further, an example in which the determination result based on the signal from the size determination sensor 22 is used to confirm the width size input from the operation panel or the personal computer is also an example. In other words, needless to say, the width size may be detected solely from the signal from the size discrimination sensor 22.
As described in the first and second embodiments, the type (thickness and width size) of the sheet is determined by the detection time of the sensors 12 and 22 being different from the difference in thickness and width size of the conveyed sheet P. Is possible. Further, by using the determination result, it is possible to automatically set an optimum image forming condition corresponding to the type of sheet.

  In the first and second embodiments, the example in which the thickness or width of the sheet is detected by the sensor that detects jamming is shown, but the sensor of the sheet is different from the sensor that detects jamming. You may make it detect thickness or width size. Further, another type of sheet thickness detection unit and the sensor configuration for detecting the sheet width size described in the second embodiment may be combined. Another type of sheet size detection unit and the sensor configuration for detecting the thickness of the sheet described in the first embodiment may be combined.

DESCRIPTION OF SYMBOLS 10 Sensor part 11 Sensor lever 11a Sensor shielding part 12 Sensor (photo interrupter)
13 Guide 13a Recess 20 Registration shutter part 21 Registration shutter 21a Sensor shielding part 22 Sensor 23 Guide 23a Escape part

Claims (8)

A lever that is pushed and moved by the sheet conveyed by the conveying means;
A photo interrupter whose ON / OFF state changes according to the position of the lever;
The lever is moved by being pushed by the leading edge of the conveyed sheet and the photo interrupter is turned on. Then, the lever is moved by turning the rear end of the sheet away from the lever and the photo interrupter is turned off. A measuring unit for measuring the measurement time until the determination, and determining the thickness of the sheet ,
The determination unit is configured such that a difference between an expected time calculated based on a length of a sheet conveyed in the sheet conveyance direction and a conveyance speed, and a difference between the measurement times is a preset first reference value. If it is large, the conveyed sheet is judged to be thin paper . The discriminating unit determines that the conveyed sheet is cardboard when the difference is smaller than the second reference value set in advance and smaller than the first reference value. Item 4. The discrimination device according to Item 1. The determination apparatus according to claim 2, wherein the determination unit determines that the conveyed sheet is plain paper when the difference is smaller than the first reference value and larger than the second reference value . A spring for urging the lever to the standby position;
The conveying means includes a roller pair,
The lever is provided upstream in the transport direction from the nip portion of the roller pair,
And characterized in that said rollers over pair and said lever are arranged so that the nip rear end portion than the portion of the sheet which is nipped by the roller pair, wherein the lever is deflected by the biasing force of the spring The discrimination device according to any one of claims 1 to 3 . A guide for guiding the sheet, provided upstream of the pair of rollers in the transport direction;
The discriminating apparatus according to claim 4 , further comprising: a concave shape formed at a position corresponding to a rear end side portion of the sheet bent by the lever in the guide. A spring for urging the lever to the standby position;
A guide that guides a sheet to be conveyed, which is disposed downstream of the lever in the conveyance direction,
Request rear end portion of the sheet leading end side is in contact by the guide, from claim 1, characterized in that the guide and the lever are arranged to deflect said lever by the urging force of the spring Item 4. The determination device according to any one of Items 3 to 3 . The discriminating apparatus according to claim 6 , wherein the skew of the sheet is corrected by forming a loop in the sheet by abutting the leading end of the sheet on the lever. A discrimination device according to any one of claims 1 to 7, the image forming apparatus characterized by having an image forming unit for forming an image on a sheet is determined by the determination device.

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