JP6615288B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, a loop amount formed on a sheet between two conveyance units is detected by a loop sensor, and the conveyance rate of the sheet by the conveyance unit is set according to the detected loop amount. A changing loop control is known.

  Patent Document 1 describes loop control between a registration roller pair that synchronously conveys a sheet and an image forming unit. In the image forming apparatus disclosed in Patent Document 1, when it is determined that the loop amount formed on the sheet between the registration roller pair and the image forming unit is small, the conveyance speed of the sheet by the registration roller pair is increased. If it is determined that the loop amount formed on the sheet is large, the sheet conveyance speed by the registration roller pair is reduced.

  On the other hand, a sensor (hereinafter referred to as a media sensor) for determining the paper type is provided between the registration roller pair and the image forming unit, and the image forming conditions are changed according to the paper type determined by the media sensor. An image forming apparatus is known.

  Patent Document 2 describes a media sensor having a light emitting element that emits light to the surface of a sheet and a photodiode that receives light reflected from the surface of the sheet. Here, in Patent Document 2, in order to improve the followability of the media sensor to the paper, a pressing member that presses the paper against the guide surface with which the sensor contacts the paper is arranged. The pressing member is connected to a spring and presses the sheet by the biasing force of the spring. Accordingly, it is possible to prevent the sheet from being separated from the guide surface due to the influence of the conveyance flutter and the like, and the accuracy of determining the sheet type is reduced.

Japanese Patent No. 2535365 JP 2006-30736 A

  Here, when the loop sensor and the media sensor described above are arranged between the registration roller pair and the image forming unit, the posture of the paper is corrected because the paper is pressed against the guide surface by the spring provided in the media sensor. End up. As a result, it becomes difficult for the loop sensor to detect the loop amount formed on the sheet, and the loop control cannot be executed with high accuracy.

  An object of the present invention is to execute loop control with high accuracy between two conveyance units and prevent a decrease in detection accuracy of a sheet by a sensor different from a loop sensor arranged between the two conveyance units. It is.

  In order to achieve the above object, an image forming apparatus of the present invention is disposed between a first transport unit that transports a recording material, a second transport unit, and the first transport unit and the second transport unit. A flag that moves in contact with a recording material in which a loop is formed between the first transport unit and the second transport unit, a sensor that outputs a signal having a different output value according to the position of the flag, A loop control unit that changes a conveyance speed of the recording material by at least one of the first conveyance unit and the second conveyance unit according to a signal output from the sensor, the first conveyance unit, and the second conveyance unit And a detection unit that detects a recording material or an image formed on the recording material, and an image that changes an image forming condition when an image is formed on the recording material according to a detection result of the detection unit. And an image forming apparatus having a control unit. The detection unit includes a first contact member that comes into contact with one surface of the recording material and a second contact member that comes into contact with the other surface that can be sandwiched by being provided to face each other. Further, a first urging member that urges the first abutting member against the second abutting member, and a second attachment that urges the second abutting member against the first abutting member. The first abutting member and the second abutting member are movable in a direction to sandwich the recording material, and the first abutting member and the second abutting member move. The position of the flag at which the output value of the signal output from the sensor switches when viewed from a direction orthogonal to the possible direction and orthogonal to the recording material conveyance direction is the first contact member and the second The contact member is configured to be included in a movable range.

  According to the present invention, it is possible to accurately perform loop control between two transport units and prevent a decrease in detection accuracy of a sheet by a sensor different from the loop sensor disposed between the two transport units. Can do.

Sectional drawing which shows schematic structure of image forming apparatus The figure which shows the detailed structure and drive source of a registration roller pair and a secondary transfer conveyance part The figure which shows arrangement | positioning of each member in the longitudinal direction of the inner guide before transfer and the outer guide before transfer Sectional view showing the configuration of the sensor guide unit Sectional view showing the configuration of a registration loop sensor The figure which shows the output signal of a registration loop sensor at the time of registration loop control, and the change of the peripheral speed of a registration roller pair The figure which shows the relationship between the state of the sensor guide unit in case the sheet | seat S is conveyed in the balance point, and the force concerning a sheet | seat The figure which shows the relationship between the state of the sensor guide unit when the loop amount formed in the sheet | seat S is large, and the force concerning a sheet | seat The figure which shows the relationship between the state applied to the state of the sensor guide unit and the force applied to the sheet when the loop amount formed on the sheet S is small The figure which shows the relationship of the force applied to the state of a sensor guide unit when a balance point and a registration loop control point have shifted | deviated, and a sheet | seat Diagram showing relationship between balance point and registration loop control point for cardboard

[Example 1]
The configuration of the image forming apparatus in this embodiment will be described with reference to FIG. In this embodiment, an electrophotographic color laser beam printer 1 (hereinafter referred to as printer 1) is shown as an image forming apparatus.

  The printer 1 includes four drum-shaped image carriers, that is, photosensitive drums 2 (2a, 2b, 2c, and 2d) arranged side by side in a substantially horizontal direction. The photosensitive drum 2 is rotationally driven in a clockwise direction in FIG. 1 by a drive source (not shown). The printer 1 irradiates a laser beam based on the charging unit 3 (3a, 3b, 3c, 3d) for uniformly charging the surface of the photosensitive drum 2 and image information, and forms an electrostatic latent image on each photosensitive drum 2. The scanner unit 4 (4a, 4b, 4c, 4d) is provided. The printer 1 transfers the image to the developing unit 5 (5a, 5b, 5c, 5d) and the intermediate transfer belt 8 for developing the image by attaching toner to the electrostatic latent image, and then remains on the surface of the photosensitive drum 2. A cleaning unit 6 (6a, 6b, 6c, 6d) for removing toner is provided. The photosensitive drum 2, the charging unit 3, the developing unit 5, and the cleaning unit 6 are configured as an integral cartridge unit, and each cartridge unit forms images of different colors (yellow, cyan, magenta, black).

  The primary transfer roller 7 (7a, 7b, 7c, 7d) is in contact with the photosensitive drum 2 via the intermediate transfer belt 8, and the toner image on the photosensitive drum 2 is transferred to the intermediate transfer belt 8 by the primary transfer roller 7. Transcribed. The intermediate transfer belt 8 is stretched by a driving roller 9, a secondary transfer counter roller 10, and a tension roller 11, and is rotated counterclockwise in FIG. A secondary transfer roller 12 (transfer unit) provided at a position facing the secondary transfer counter roller 10 via the intermediate transfer belt 8 transfers the toner image transferred to the intermediate transfer belt 8 to the sheet S. The intermediate transfer belt 8, the secondary transfer counter roller 10, and the secondary transfer roller 12 constitute a secondary transfer conveyance unit 13 that conveys the sheet S, and transfers the sheet S and conveys the sheet S downstream. Have a role to play. A belt cleaning unit 14 is located at a position facing the tension roller 11 via the intermediate transfer belt 8, and removes and collects toner remaining on the surface of the intermediate transfer belt 8.

  The printer 1 is provided with a paper feed cassette 15 on which a sheet S (recording material) is placed and a multi-tray 18. The sheets S placed on the paper feed cassette 15 are separated one by one by the paper feed roller 16 and the separation roller 17 and fed to the drawing roller 21. The sheets S placed on the multi-tray 18 are separated one by one by the multi-feed roller 20 and the separation pad 19 and fed to the drawing roller 21. The sheet S fed to the drawing roller 21 is conveyed to a registration roller pair 30 (hereinafter referred to as a registration roller pair 30) that corrects the skew of the sheet S. On the conveyance path between the registration roller pair 30 and the secondary transfer roller 12, a sensor guide unit 40 that detects information regarding the characteristics of the sheet S is provided in order to determine the type of the sheet S. Details of the sensor guide unit 40 will be described later.

  The fixing unit 51 fixes the image transferred on the sheet S by the secondary transfer roller 12 to the sheet S. The fixing unit 51 fixes the image on the sheet S by applying heat and pressure to the sheet S. During single-sided printing, the sheet S is guided to the discharge conveyance path by the double-sided flapper 52, and during double-sided printing, the sheet S is guided to the reverse conveyance path and the double-sided conveyance path. The discharge roller pair 54 discharges the sheet S conveyed to the discharge conveyance path to the discharge tray 55.

  The control unit 60 includes circuits such as a CPU, a ROM, and a RAM (not shown), and executes a program that controls each device in the printer 1. The control unit 60 includes a conveyance control unit 61 and an image control unit 62 as functions. The conveyance control unit 61 controls a drive motor described later to change the conveyance speed of the sheet S. The image control unit 62 determines the type of the sheet S based on the information regarding the sheet S obtained from the sensor guide unit 40, and changes the image forming condition of the image forming unit according to the determined type. These detailed functions will be described later.

  FIG. 2 is a diagram illustrating a detailed configuration of a conveyance path between the registration roller pair 30 and the secondary transfer conveyance unit 13 and a driving source of each conveyance unit. The registration roller pair 30 includes a registration roller 30a (hereinafter referred to as a registration roller 30a) and a registration roller 30b. The registration roller 30b presses the registration roller 30a with a spring (not shown) to form a nip portion. The registration roller 30b is supported so as to be rotatable about the registration roller shaft 30c. The registration roller 30 a rotates by receiving a driving force from the paper feeding motor 31 and conveys the sheet S. The conveyance control unit 61 described above can change the conveyance speed of the sheet S by the registration roller pair 30 by controlling the paper feed motor 31.

  A registration shutter 32 for correcting the skew of the sheet S is provided on the upstream side of the registration roller pair 30 in the conveyance direction of the sheet S. The registration shutter 32 is supported rotatably about the registration roller shaft 30c, and is urged in a clockwise direction in FIG. 2 by a spring (not shown). When the leading edge of the sheet S enters the registration shutter 32, the registration shutter 32 is rotated counterclockwise in FIG. 2 against this urging force. When the sheet S is skewed, the sheet S uniformly contacts the registration shutter 32 in the width direction, and is pushed up the registration shutter 32 and then conveyed to the registration roller pair 30. That is, the skew of the sheet S is corrected when the leading edge of the sheet S hits the registration shutter 32.

  As described above, the secondary transfer conveyance unit 13 includes the intermediate transfer belt 8, the secondary transfer counter roller 10, and the secondary transfer roller 12. The secondary transfer roller pressing spring 38 presses the secondary transfer roller 12 against the secondary transfer counter roller 10, thereby forming a nip portion for transporting the sheet S by the intermediate transfer belt 8. The driving roller 9 rotates by receiving a driving force from the belt driving motor 39 and rotates the intermediate transfer belt 8 in the counterclockwise direction in FIG. Note that the conveyance control unit 61 described above controls the belt drive motor 39.

  Further, the pre-transfer inner guide 33 and the pre-transfer outer guide 34 form a conveyance path for guiding the sheet S from the registration roller pair 30 to the secondary transfer conveyance unit 13. The sensor guide unit 40 includes a first sensor holder 100 (first contact member) that contacts one surface of the conveyed sheet S and a second sensor holder 110 (second contact) that contacts the other surface of the sheet S. Contact member). The first sensor holder 100 is provided in the inner guide 33 before transfer, and the second sensor holder 110 is provided in the outer guide 34 before transfer. The first sensor holder 100 is biased in the direction in which the second sensor holder 110 is pressed, and is configured to be movable with respect to the pre-transfer inner guide 33. Further, the second sensor holder 110 is biased in the direction in which the first sensor holder 100 is pressed, and is configured to be movable with respect to the pre-transfer outer guide 34. The first sensor holder 100 and the second sensor holder 110 urge each other to sandwich the conveyed sheet S. A follower roller 112 is provided on the second sensor holder 110 and is configured to abut against the first sensor holder 100. When the sheet S passes through the sensor guide unit 40, the driven roller 112 rotates in contact with the sheet S, thereby reducing the conveyance resistance of the sheet S. Reference numeral 37 denotes a loop sensor flag, which is provided for detecting a loop amount formed on the sheet S by loop control described later.

  In this embodiment, the conveyance direction of the sheet S at the nip portion of the registration roller pair 30 is configured to be an oblique left direction in FIG. The conveyance direction of the sheet S at the nip portion of the secondary transfer conveyance unit 13 is configured to be an oblique right direction in FIG. By determining the conveyance direction of the sheet S in this way, the direction of the loop formed on the sheet S between the registration roller pair 30 and the secondary transfer conveyance unit 13 is directed to the pre-transfer inner guide 33 side (left side in FIG. 2). Limited. The conveyance guide shape of the pre-transfer inner guide 33 is a curved shape that forms a space that becomes a loop region.

  FIG. 3A is a view showing the arrangement of the respective members arranged in the pre-transfer inner guide 33 in the longitudinal direction (the width direction of the sheet S), and FIG. It is a figure which shows arrangement | positioning in the longitudinal direction of a member. Here, the conveyance direction of the sheet S is the arrow direction in FIGS. 3A and 3B, and the sheet S is conveyed along the arrow direction by the registration roller pair 30 (registration roller 30a, registration roller 30b).

  First, FIG. 3A will be described. In the pre-transfer inner guide 33, a paper width sensor flag 35 for detecting the paper width of the sheet S, a paper width sensor flag 36, and a loop sensor flag 37 for detecting the paper width of the sheet S and loop detection are arranged. That is, the loop sensor flag 37 is not only used for detecting the loop amount of the sheet S but also for detecting the paper width of the sheet S. In the pre-transfer inner guide 33, photo interrupters (described in FIG. 5) corresponding to the respective flags are arranged, and the paper width of the sheet S can be detected by the ON / OFF state of the photo interrupter.

  Protrusions 100a are provided at both ends in the longitudinal direction of the first sensor holder 100, and a groove 33a corresponding to the protrusion 100a is provided in the pre-transfer inner guide 33. The protrusion 100a is fitted in the groove 33a, and the protrusion 100a moves along the groove 33a so that the first sensor holder 100 can move relative to the pre-transfer inner guide 33. In the first sensor holder 100, a line sensor 101 (light receiving unit) that constitutes a surface property detection unit, an LED 102 (light emitting unit), and an ultrasonic wave reception unit 103 that constitutes a basis weight detection unit are arranged.

  The surface property detection unit detects the surface property of the sheet S as information on the characteristics of the sheet S, that is, the uneven state of the surface. When detecting the surface property, the light emitted from the LED 102 is polarized by a polarizer (not shown), and the polarized light is incident on the surface of the sheet S from an oblique direction. The reflected light reflected by the surface of the sheet S is collected and imaged by the line sensor 101. The line sensor 101 is an image sensor that extends along the width direction of the sheet S, and performs imaging a plurality of times while the sheet S is conveyed. From the surface image of the sheet S obtained in this way, the above-described image control unit 62 obtains a feature amount related to the surface property and determines the surface property (type) of the sheet S.

  Next, FIG. 3B will be described. Protrusions 110a are provided at both ends in the longitudinal direction of the second sensor holder 110, and a groove 34a corresponding to the protrusion 110a is provided in the pre-transfer outer guide 34. The protrusion 110a is fitted in the groove 34a, and the second sensor holder 110 can move relative to the pre-transfer outer guide 34 by the protrusion 110a moving along the groove 34a. The second sensor holder 110 is provided with an ultrasonic transmission unit 111 and two driven rollers 112 that constitute a basis weight detection unit.

The basis weight detection unit detects the basis weight of the sheet S as information on the characteristics of the sheet S. Here, the basis weight is the mass per unit area of the sheet S, and the unit is represented by [g / m ² ]. The ultrasonic transmission unit 111 and the ultrasonic reception unit 103 are provided at positions facing each other across the conveyance path of the sheet S. When detecting the basis weight, the ultrasonic wave transmitted from the ultrasonic wave transmission unit 111 propagates through the air and reaches the sheet S. When the ultrasonic wave reaches the sheet S, the sheet S is vibrated by the ultrasonic wave. The ultrasonic wave attenuates according to the basis weight of the sheet S and is received by the ultrasonic wave receiving unit 103. In this way, the ultrasonic waves generated by the ultrasonic transmission unit 111 reach the ultrasonic reception unit 103 via the sheet S. The ultrasonic receiving unit 103 outputs a voltage value corresponding to the amplitude value of the received ultrasonic wave, and the image control unit 62 determines the basis weight (type) of the sheet S based on this output voltage.

  The image control unit 62 determines the type of the sheet S according to the detection results obtained by the surface property detection unit and the basis weight detection unit, and controls the conditions for forming an image on the sheet S. The image forming conditions referred to here are the conveyance speed of the sheet S, the transfer voltage applied to the secondary transfer roller 12 when the image is transferred to the sheet S, and the fixing temperature of the fixing unit 51 when the image is fixed to the sheet S. And pressure. For example, since coated paper has a lower resistance value than bond paper, it is necessary to set a high transfer voltage when transferring a toner image. In addition, the coated paper has a lower fixing temperature necessary for fixing the toner image than the bond paper and requires a shorter fixing time, so that it is necessary to change the fixing conditions such as the fixing temperature and the sheet S conveyance speed. . As described above, the image quality of the image formed on the sheet S can be improved by controlling various image forming conditions.

  FIG. 4 is a cross-sectional view showing details of the sensor guide unit 40. 4A is a diagram showing a position holding configuration of the first sensor holder 100 and the second sensor holder 110, and FIG. 4B is a diagram showing a pressing configuration of the first sensor holder 100 and the second sensor holder 110. FIG. is there.

  First, FIG. 4A will be described. The groove 33a of the pre-transfer inner guide 33 is formed along the left-right direction in FIG. 4A, and the two protrusions 100a of the first sensor holder 100 are fitted in the groove 33a. Thus, the first sensor holder 100 is configured to be movable in the direction of the arrow in FIG. The second sensor holder 110 has the same configuration, and the groove 34a of the pre-transfer outer guide 34 is formed along the left-right direction in FIG. 4A, and the two protrusions 110a of the second sensor holder 110 are formed. Is fitted in the groove 34a. Thus, the second sensor holder 110 is configured to be movable in the arrow direction in FIG. 4A with respect to the pre-transfer outer guide 34.

  Next, FIG. 4B will be described. The first sensor holder 100 is biased in a direction of pressing the second sensor holder 110 by a first holder spring 104 that is a compression spring. The second sensor holder 110 is biased in the direction of pressing the first sensor holder 100 by a second holder spring 113 that is a compression spring. The driven roller 112 hits the first sensor holder 100. Thus, the 1st sensor holder 100 and the 2nd sensor holder 110 will be in the state pressed mutually, and will stop in the position where pressing force balances. The position where the pressing force is balanced is defined as a balancing point K. The biasing force of the first holder spring 104 and the second holder spring 113 is set so that the balance point K is included in a loop region formed by the pre-transfer inner guide 33 and the pre-transfer outer guide 34.

  The first sensor holder 100 and the second sensor holder 110 are pressed against each other and kept in contact with each other so that the sheet S can be sandwiched between them. The distance can be kept constant. For this reason, it is possible to reduce the effect of the sheet S conveyance fluctuation and to prevent the detection accuracy of the surface property detection unit and the basis weight detection unit from being lowered. Further, even when the stiffness of the sheet S such as thin paper or thick paper is different and the path along which the leading edge of the sheet S follows on the conveyance path is different, the sensor guide unit 40 moves following the position of the sheet S. For this reason, the influence by the difference in the hardness of the sheet | seat S can be reduced, and it can prevent that the detection precision of a surface property detection part or a basic weight detection part falls.

  FIG. 5 is a cross-sectional view showing details of the loop sensor flag 37 for performing the registration loop control. 5A is a standby state of the sheet S, FIG. 5B is a state where the sheet S reaches the loop sensor flag 37, and FIG. 5C is a state where the sheet S is conveyed by the registration roller pair 30 and the secondary transfer conveyance unit 13. Each state is shown.

  First, FIG. 5A will be described. A loop sensor flag 37 is provided between the registration roller pair 30 and the secondary transfer conveyance unit 13. The loop sensor flag 37 is centered on the pre-transfer inner guide 33 and is arranged in a rotatable state. The loop sensor flag 37 is pressed in the clockwise direction in FIG. 5A by a torsion coil spring (not shown). The loop sensor flag 37 is provided with a sheet detection unit 37a and a light shielding unit 37b. Reference numeral 41 denotes a registration loop sensor using a photo interrupter. When the light shielding portion 37b of the loop sensor flag 37 shields the photo interrupter 41a, the registration loop sensor 41 outputs an ON (first output value) signal, and outputs an OFF (second output value) signal when light is transmitted. In the standby state of the sheet S shown in FIG. 5A, the registration loop sensor 41 outputs an OFF signal.

  When the sheet S is conveyed by the registration roller pair 30 and reaches the loop sensor flag 37 (FIG. 5B), the sheet S pushes up the loop sensor flag 37, and the light blocking portion 37b blocks the photo interrupter 41b. The position of the loop sensor flag 37 at which the light shielding starts is set as a registration loop control point L. When the sheet S is further conveyed downstream and reaches the secondary transfer conveyance unit 13 (FIG. 5C), the loop amount formed on the sheet S between the registration roller pair 30 and the secondary transfer conveyance unit 13 is reduced. Residue loop control to keep constant is started. The loop sensor flag 37 and the registration loop sensor 41 are arranged so that the registration loop control point L is included in a loop region formed by the inner guide 33 before transfer and the outer guide 34 before transfer.

  FIG. 6 is a graph showing an example of the operation of the registration loop control. The upper graph shows the signal (ON / OFF) output from the registration loop sensor 41. The lower graph is a graph showing the ratio of the conveyance speed of the sheet S by the registration roller pair 30 (the peripheral speed of the registration roller pair 30) to the conveyance speed of the sheet S by the secondary transfer conveyance unit 13. Here, the conveyance speed of the sheet S by the secondary transfer conveyance unit 13 is the peripheral speed of the intermediate transfer belt 8, and when the peripheral speed of the intermediate transfer belt 8 and the peripheral speed of the registration roller pair 30 are the same in FIG. It is expressed as 100%. Note that the peripheral speed of the intermediate transfer belt 8 does not change during image formation.

  Time T1 is the timing when the leading edge of the sheet S pushes up the loop sensor flag 37 and the registration loop sensor 41 outputs an ON signal. Time T2 is the timing when the leading edge of the sheet S reaches the secondary transfer conveyance unit 13. The time T3 is a timing at which the registration loop control is started, and is started after the leading edge of the sheet S reaches the secondary transfer conveyance unit 13.

  In FIG. 6, since the registration loop sensor 41 outputs an ON signal at time T3, the loop amount formed on the sheet S is in a large state. For this reason, the conveyance speed of the registration roller pair 30 is decreased so that the loop amount is reduced, that is, the sheet S is moved to the pre-transfer outer guide 34 side. In this embodiment, the conveyance control unit 61 controls the paper feed motor 31 so that the peripheral speed of the registration roller pair 30 is 99%.

  Time T4 is the timing at which the registration loop sensor 41 outputs an OFF signal. This time, the conveying speed of the registration roller pair 30 is increased so that the loop amount is increased, that is, the sheet S is moved toward the pre-transfer inner guide 33 side. In this embodiment, the conveyance control unit 61 controls the paper feed motor 31 so that the peripheral speed of the registration roller pair 30 is 101%. In this way, the loop formed on the sheet S by the conveyance control unit 61 (loop control unit) changing the speed of the paper feed motor 31 in accordance with the signal (ON / OFF) output from the registration loop sensor 41. The amount can be kept constant near the registration loop control point L.

  Time T5 is the timing immediately before the trailing edge of the sheet S exits the registration roller pair 30, and time T6 is the timing when the trailing edge of the sheet S exits the registration roller pair 30. In this embodiment, the conveyance speed of the registration roller pair 30 is always set to 99% during the time T5 to T6. This is to prevent the phenomenon that if the trailing edge of the sheet S passes through the registration roller pair 30 when the loop amount is large, the sheet S may be violated by the slack of the loop and rubbed in contact with the intermediate transfer belt 8. is there. The conveyance speed of the registration roller pair 30 after time T6 is set to 100% again, so that the next sheet enters the registration roller pair 30.

  When the torque load on the secondary transfer conveyance unit 13 increases, it causes a color shift between the colors. By maintaining a constant loop at the registration loop control point L as described above, it is possible to prevent the sheet S from being pushed or pulled more than necessary between the registration roller pair 30 and the secondary transfer conveyance unit 13. Thereby, the torque load on the secondary transfer conveyance unit 13 is reduced.

  The speed between the times T5 and T6 can be changed according to the thickness of the sheet S and the shape of the conveyance path. For example, when the sheet S is excessively pulled between the secondary transfer conveyance unit 13 and the registration roller pair 30, the secondary transfer conveyance unit 13 causes a blur when the trailing edge of the sheet S passes through the registration roller pair 30. An image may occur. In this case, it is possible to prevent the occurrence of blurred images by increasing the conveyance speed of the registration roller pair 30 and creating a loop. Further, based on the detection result of the sensor guide unit 40, it is possible to change the peripheral speed increase rate or the deceleration rate of the registration roller pair 30 or change the peripheral speed according to the durable wear of the registration roller pair 30. .

  7 to 9 are cross-sectional views when the registration loop control point L and the balance point K of the sensor guide unit 40 are in the same position, the force that the first holder spring 104 and the second holder spring 113 apply to the sheet S, and both It is a figure which shows the force finally applied to the sheet | seat S by a spring. 7 to 9 are views when the sensor guide unit 40 is viewed from a direction perpendicular to the direction in which the sensor guide unit 40 can move in parallel and perpendicular to the conveyance direction of the sheet S. FIG. That is, the sensor guide unit 40 is movable in the direction of the arrow α in FIG. 7, and the sheet S is conveyed in the direction of the arrow β.

  FIG. 7 shows a state where the sheet S is being conveyed at the balance point K of the sensor guide unit 40. In FIG. 7, the first holder spring 104 (first urging member) pushes the sheet S to the right in FIG. 7 via the first sensor holder 100, and the second holder spring 113 (second urging member). The force that pushes the sheet S in the left direction in FIG. 7 through the second sensor holder 110 is equal. For this reason, the force that the sheet S receives from the sensor guide unit 40 becomes zero, and the conveyance of the sheet S is not affected. Therefore, if the registration loop control point L is arranged at the balance point K of the sensor guide unit 40, the registration loop control can be performed without being affected by the sensor guide unit 40.

  Next, the influence and operation of the sensor guide unit 40 on the sheet S when performing the registration loop control will be described with reference to FIGS.

  FIG. 8 shows a state where the sheet S is conveyed at a position on the left side of the balance point K of the sensor guide unit 40. In other words, this shows a state where the amount of loop formed on the sheet S is larger than that in the state of FIG. In FIG. 8, the force with which the first holder spring 104 pushes the sheet S in the right direction becomes larger because the spring is compressed as compared with the state of FIG. On the other hand, the force with which the second holder spring 113 pushes the sheet S to the left is smaller than the state of FIG. 7 because the spring is extended. For this reason, the force that the sheet S receives from the sensor guide unit 40 is directed rightward, that is, toward the registration loop control point L.

  As shown in FIG. 8, when the sheet S is on the left side of the registration loop control point L, an ON signal is output from the registration loop sensor 41, so that the conveyance control unit 61 decelerates the peripheral speed of the registration roller pair 30. The paper feed motor 31 is controlled. For this reason, the sheet S tends to move in the right direction. At this time, since the force received from the sensor guide unit 40 is also in the right direction, it assists the loop cancellation operation of the sheet S.

  FIG. 9 shows a state where the sheet S is conveyed at a position on the right side of the balance point K of the sensor guide unit 40. In other words, this shows a state in which the amount of loop formed on the sheet S is small compared to the state of FIG. In FIG. 9, the force with which the first holder spring 104 pushes the sheet S in the right direction is smaller than the state of FIG. 7 because the spring is extended. On the other hand, the force with which the second holder spring 113 pushes the sheet S to the left increases as the spring is compressed compared to the state of FIG. For this reason, the force that the sheet S receives from the sensor guide unit 40 is directed leftward, that is, toward the registration loop control point L.

  As shown in FIG. 9, when the sheet S is on the right side of the registration loop control point L, an OFF signal is output from the registration loop sensor 41, so that the conveyance control unit 61 increases the peripheral speed of the registration roller pair 30. The paper feed motor 31 is controlled. For this reason, the sheet S tends to move leftward. At this time, since the force received from the sensor guide unit 40 is also in the left direction, it assists the loop increasing operation of the sheet S.

  Thus, by making the registration loop control point L and the balance point K of the sensor guide unit 40 the same, when the sheet S is conveyed at the registration loop control point L, it is possible to prevent the sheet S from being loaded. Therefore, it is possible to realize loop control substantially equivalent to the state without the sensor guide unit 40. In addition, at the time of loop increase and loop cancellation operations, the sensor guide unit 40 can assist the registration loop control operation, and the number of loop control ON / OFF operations can be increased. When the number of ON / OFF increases, the sheet S is conveyed in the vicinity of the registration loop control point L. Therefore, the loop amount formed on the sheet S can be kept constant. That is, it is possible to stabilize the posture of the sheet S and reduce the occurrence of image defects in the secondary transfer conveyance unit 13.

  As described above, according to the present exemplary embodiment, the loop control is accurately performed between the two conveyance units, and the decrease in the detection accuracy of the sheet S by the media sensor disposed between the two conveyance units can be prevented. it can.

  In the above embodiment, the configuration in which the balance point K of the sensor guide unit 40 and the registration loop control point L coincide with each other has been described. However, the present invention is not limited to this. The registration loop control point L only needs to be included in the movable range M of the sensor guide unit 40 including the balance point K.

  FIG. 10 shows a case where the balance point K of the sensor guide unit 40 is provided on the left side with respect to the registration loop control point L. In FIG. 10, the registration loop control point L is included in the movable range M of the sensor guide unit 40. The movable range M of the sensor guide unit 40 is determined based on the spring constants of the first holder spring 104 and the second holder spring 113 around the balance point K. In this embodiment, the movable range M is assumed to be a range of ± 3 mm with the balance point K as the center.

  As shown in FIG. 10, when the balance point K is provided on the left side with respect to the registration loop control point L, the force on the sheet S at the registration loop control point L is not zero, and a force that pushes the sheet S leftward is generated. . When this force is increased, an extra force is required to release the sheet S in the right direction, that is, to eliminate the loop when performing the registration loop control. Since the force for eliminating the loop is formed by the pulling force of the secondary transfer conveyance unit 13 and the registration roller pair 30, if the torque load on the secondary transfer conveyance unit 13 becomes large at this time, the color misregistration or the like is affected. . For this reason, the spring constants of the first holder spring 104 and the second holder spring 113 are made as small as possible to reduce the influence on the torque load of the secondary transfer conveyance unit 13.

  In this way, even if the balance point K of the sensor guide unit 40 and the registration loop control point L do not match, the balance point K and the registration loop control point L are determined by looking at the balance with the influence on the secondary transfer conveyance unit 13. It is possible to dispose them.

  In the above embodiment, only the loop sensor flag 37 arranged at the center of the plurality of paper width sensor flags is used for the registration loop control. However, the flags arranged at other positions are used for the registration loop control. It is also possible to use it.

  For example, the paper width sensor flag 35 shown in FIG. 3A may be used as a loop sensor for thick paper, and the loop sensor flag 37 may be used as a loop sensor for plain paper and thin paper. Here, in consideration of the difference between thick paper, plain paper, and thin paper, the position where the paper width sensor flag 35 shields the photo interrupter and the position where the loop sensor flag 37 shields the photo interrupter 41a may be shifted. That is, the position where the loop sensor flag 37 shields the photointerrupter 41a is arranged at the same position as the balance point K as shown in FIG. It is arranged near the front outer guide 34.

  FIG. 11 is a diagram showing a state in which the paper width sensor flag 35 is a thick paper loop sensor, and the registration loop control point L is offset to the right in the drawing from the balance point K. As shown in FIG. 2, when the conveyance path configuration in which the nip direction of the registration roller pair 30 is directed toward the pre-transfer inner guide 33 and the sheet S is curved, when the thick paper is curved, the thick paper tends to return to a straight state due to the stiffness. That is, a force due to the stiffness of the thick paper is applied to the second sensor holder 110 side in FIG. For this reason, when the conveyance path configuration is affected by the stiffness of the thick paper, the registration loop control point L is offset toward the second sensor holder 110 with respect to the balance point K in consideration of the influence of the force due to the stiffness of the thick paper. As shown in FIG. 11, the force relationship at the registration loop control point L is that the registration loop control point L is on the right side of the balance point K, so that the force received by the sheet S from the first holder spring 104 is reduced, and the second holder spring 113 The force received by the sheet S increases. However, the stiffness of the thick paper is further added to the force of the first holder spring 104, and as a result, the force is balanced at the registration loop control point L.

  In this way, it is also possible to distinguish between a sheet S that is less affected by stiffness, such as thin paper and plain paper, and a sheet S that is affected by greater stiffness, such as thick paper, and a configuration in which a plurality of positions for performing registration loop control are arranged. is there. As a result, the registration loop control can be stably operated even in the case of thick paper.

  Further, in the above embodiment, the surface property and the basis weight of the sheet S are detected by the surface property detection unit and the basis weight detection unit, respectively, so that the type of the sheet S is determined, but only one of the detection units is detected. The structure which has this may be sufficient. Moreover, you may detect the other characteristic of the sheet | seat S different from the surface property and basis weight of the sheet | seat S. FIG. For example, a light emitting element that emits light to the first sensor holder 100 and a light receiving element that receives transmitted light that has passed through the sheet S are provided in the second sensor holder 110, and the thickness of the sheet S is determined from the amount of light that has passed through the sheet S. May be. In this case, the control unit 60 determines that the paper is thin if the amount of transmitted light is large, and is thick if it is small.

  In the above-described embodiment, the sensor for detecting the sheet S is described as an example of the media sensor (sensor guide unit 40) that detects information on the characteristics of the sheet S, but is not limited thereto. For example, the present invention may be applied to a color sensor that detects the color of an image formed on the sheet S. Since the color sensor is often arranged on a double-sided conveyance path or the like, the present invention can be applied when executing loop control in a section of the double-sided conveyance path. The detection result of the color sensor is fed back to the image control unit 62 and reflected in the next and subsequent image forming conditions.

  In the above embodiment, an example of a laser beam printer is shown. However, the image forming apparatus to which the present invention is applied is not limited to this, and a printer of another printing system such as an ink jet printer or a copying machine. But you can.

30 registration roller pair 37 loop sensor flag 41 registration loop sensor 61 transport control unit 62 image control unit 100 first sensor holder 101 line sensor 102 LED
103 Ultrasonic Receiver 104 First Holder Spring 110 Second Sensor Holder 111 Ultrasonic Transmitter 113 Second Holder Spring

Claims (12)

A first transport unit that transports the recording material, a second transport unit,
A flag that is disposed between the first transport unit and the second transport unit and moves in contact with a recording material in which a loop is formed between the first transport unit and the second transport unit;
A sensor that outputs a signal of a different output value according to the position of the flag;
A loop control unit that changes a conveyance speed of the recording material by at least one of the first conveyance unit and the second conveyance unit in accordance with a signal output from the sensor;
A detection unit that is disposed between the first conveyance unit and the second conveyance unit and detects a recording material or an image formed on the recording material;
In an image forming apparatus comprising: an image control unit that changes an image forming condition when an image is formed on a recording material according to a detection result of the detection unit.
The detection unit includes a first contact member that contacts one surface of the recording material and a second contact member that contacts the other surface, which are provided opposite to each other and can sandwich the recording material. Furthermore, a first urging member that urges the first abutting member against the second abutting member, and a second attachment that urges the second abutting member against the first abutting member. A force member,
The first abutting member and the second abutting member are movable in a direction in which the recording material is sandwiched, and are orthogonal to the direction in which the first abutting member and the second abutting member are movable. The position of the flag at which the output value of the signal output from the sensor is switched when viewed from the direction orthogonal to the conveyance direction of the recording material is movable between the first contact member and the second contact member. An image forming apparatus configured to be included in a wide range. The second transport unit is a transfer unit that transfers an image formed on the image carrier to a recording material, and is provided on the downstream side of the first transport unit in the transport direction of the recording material,
The image forming apparatus according to claim 1, wherein the loop control unit changes a conveyance speed of the recording material by the first conveyance unit in accordance with a signal output from the sensor. When a loop amount formed on the recording material between the first transport unit and the transfer unit is large, a signal of a first output value is output from the sensor, and the loop control unit outputs a signal of the first output value. Accordingly, the recording material conveyance speed by the first conveyance unit is decreased,
When the loop amount formed on the recording material between the transfer portion and the first conveyor is small, the output signal of the second output value from the sensor, the loop controller, the signal of the second output value 3. The image forming apparatus according to claim 2, wherein the recording material conveyance speed of the first conveyance unit is increased in accordance with the image forming apparatus. The detection unit detects information on characteristics of the recording material before the image is formed,
The image control unit, based on the detection result of the detection unit, the recording material conveyance speed, the voltage value applied to the transfer unit when the image is transferred to the recording material, or the time when the image is fixed on the recording material. The image forming apparatus according to claim 1, wherein the image forming condition including the temperature of the fixing unit is changed.   The detection unit includes an ultrasonic transmission unit provided in one of the first contact member and the second contact member, and an ultrasonic reception unit provided in the other, and the ultrasonic transmission The ultrasonic wave transmitted by the unit passes through the recording material and is received by the ultrasonic wave reception unit, and the image control unit performs the image forming condition based on the amplitude of the ultrasonic wave received by the ultrasonic wave reception unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is changed.   The detection unit includes a light emitting unit provided on one of the first contact member and the second contact member, and a light receiving unit provided on the other, and the light emitted from the light emitting unit 2. The image forming condition is changed based on the transmitted light received by the light receiving unit through the recording material, and the image control unit changes the image forming condition. The image forming apparatus according to claim 5.   The detection unit includes a light emitting unit and a light receiving unit provided on one of the first contact member and the second contact member, and light emitted from the light emitting unit is a surface of the recording material. 7. The image forming unit according to claim 1, wherein the image control unit changes the image forming condition based on reflected light received by the light receiving unit. 2. The image forming apparatus according to item 1.   The flag and the detection unit are arranged side by side along a direction orthogonal to the direction in which the first contact member and the second contact member are movable and orthogonal to the recording material conveyance direction. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. A plurality of the flags, and a plurality of the sensors corresponding to the plurality of flags,
The plurality of flags are arranged side by side along a direction orthogonal to the direction in which the first contact member and the second contact member are movable and orthogonal to the conveyance direction of the recording material. The image forming apparatus according to claim 1, wherein a length of the recording material in a width direction is detected by the flag and the sensor. When the type of the recording material is the first type, the loop control unit transports the recording material by using the first flag and the first sensor corresponding to the first flag among the plurality of flags. When the speed is changed and the type of the recording material is the second type thicker than the first type, the loop control unit corresponds to the second flag and the second flag among the plurality of flags. Using the second sensor to change the recording material conveyance speed,
The conveyance guide between the first conveyance section and the second conveyance section is curved, and the tip position of the second flag at which the output value of the signal output from the second sensor is switched is the first position. The image forming apparatus according to claim 9, wherein the image forming apparatus is located inside the conveyance guide that is curved with respect to a tip position of the first flag at which an output value of a signal output from the sensor is switched.   The first urging member and the second urging member are springs, and the range in which the first abutting member and the second abutting member are movable is the first urging member and the second urging member. The image forming apparatus according to claim 1, wherein the image forming apparatus is determined based on a spring constant of the member.   The output value of the signal output from the sensor is switched when viewed from a direction orthogonal to the direction in which the first contact member and the second contact member are movable and orthogonal to the conveyance direction of the recording material. The position of the flag matches the position where the urging force by the first urging member and the urging force by the second urging member are balanced and the first abutting member and the second abutting member are stopped. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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