JP2010044252A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, measuring a change in speed when a first conveying means rotated through a transfer position of a developing material conveys a medium to be recorded without damaging the medium to be recorded. <P>SOLUTION: Prior to conveying a paper sheet 4 from register rollers 16, 17, a first register patch is formed in a range shown in Fig.4(A) on the surface of a conveying belt 23. Then a change in speed of the conveying belt 23 during the period from the time when the leading end of the paper sheet 4 is nipped by a photoreceptor drum 31 corresponding to black (K) and the conveying belt 23 until the trailing end of the paper sheet 4 is passed between the register rollers 16, 17 is found according to the detection interval of the register sensor 83 for the first register patch. After the paper sheet 4 has passed by the photoreceptor drum 31 corresponding to the black (K), a second register patch is printed. Then the interval for forming the register patch varies with a change in speed when the paper sheet 4 is conveyed by cooperation of a heat roller 51, a pressure roller 52 and the conveying belt 23. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image by transferring a developer onto a recording medium. More specifically, the measurement image is transferred to the surface of a first conveying unit that rotates through a transfer position of the developer. The present invention relates to an image forming apparatus capable of detecting the measurement image.

2. Description of the Related Art Conventionally, in an image forming apparatus provided with a first conveying unit such as a belt that rotates on a recording medium after passing a developer transfer position by an image forming unit, an image for measurement is provided on the surface of the first conveying unit. It is considered to correct color misregistration and the like by transferring and detecting. Further, in this type of image forming apparatus, the rotational speed of the first transport unit may change depending on whether the recording medium is placed or not. Therefore, it has been proposed to perform color misregistration correction by forming a measurement image on both the first transport unit and the recording medium while the recording medium is actually placed on the first transport unit ( For example, see Patent Document 1).
JP 2007-292789 A

  However, the recording medium that easily affects the rotation speed of the first transport means is a thick cardboard or the like, and this type of recording medium may be an expensive image material. For this reason, if a measurement image is formed on a recording medium as in Patent Document 1, at least one recording medium is damaged, which is not preferable. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of measuring a change in speed when a recording medium is conveyed by a first conveying means that rotates through a transfer position of a developer without contaminating the recording medium. Was made.

  The image forming apparatus of the present invention made to achieve the above object has an image forming means for transferring a developer to form an image, and a surface rotating through a transfer position of the developer by the image forming means. A first conveying unit that conveys the recording medium; and a first conveying unit that is provided upstream or downstream of the first conveying unit in the recording medium conveying direction and that cooperates with the first conveying unit to convey the recording medium. 2 a transfer means, a measurement image transfer means for controlling the image forming means to transfer a measurement image onto the surface of the first transfer means, and a surface of the first transfer means by the measurement image transfer means. A measurement image detecting means for detecting the transferred measurement image, wherein the measurement image transfer means is used when the recording medium on the surface of the first conveying means is conveyed only by the first conveying means. Opposite to the measurement image detection means The measurement image is at least at two positions, a position where the recording medium is conveyed and the position where the recording medium is conveyed in cooperation with the first conveyance unit and the second conveyance unit. It is characterized by transferring.

  In the image forming apparatus of the present invention configured as described above, the first conveying unit has a surface that rotates through the transfer position of the developer by the image forming unit, and the recording medium is provided by the first conveying unit. An image is formed while being conveyed. The second transport means provided on the upstream or downstream side of the first transport means in the recording medium transport direction cooperates with the first transport means to transport the recording medium. Therefore, when the recording medium is transported only by the first transporting means, and when the recording medium is transported by the cooperation of the first transporting means and the second transporting means, the first transporting is performed. The speed of the means varies. Since the first conveying means rotates through the transfer position, measuring the change in speed is extremely important for forming an accurate image.

  Therefore, in the present invention, the measurement image transfer unit controls the image forming unit to face the measurement image detection unit when the recording medium on the surface of the first conveyance unit is conveyed only by the first conveyance unit. The measurement image is transferred to at least two positions, the position where the recording medium is conveyed and the position facing the measurement image detection unit when the recording medium is conveyed by the cooperation of the first conveyance unit and the second conveyance unit.

  Therefore, if the measurement image transferred to the surface of the first transport unit by the measurement image transfer unit is detected by detection of the measurement image detection unit, the change in speed when the recording medium is transported by the first transport unit is Can be measured as follows. That is, if the speed of the first transport unit changes between when the recording medium is transported only by the first transport unit and when the recording medium is transported by the cooperation of the first transport unit and the second transport unit, the first transport is performed. The speed at which the measurement image formed on the means moves on the opposing portion of the measurement image detection means also changes. Therefore, in the present invention, it is possible to detect a change in speed when the recording medium is conveyed by the first conveying means without fouling the recording medium.

  The image forming apparatus of the present invention includes an image forming unit that transfers an image of a developer to form an image, and a surface that rotates through a transfer position of the developer by the image forming unit, and conveys a recording medium. A first conveying means that is provided upstream or downstream of the first conveying means in the recording medium conveying direction, and that cooperates with the first conveying means to convey the recording medium; and A measurement image transfer means for controlling the image forming means to transfer a measurement image to the surface of the first transport means, and a measurement image transferred to the surface of the first transport means by the measurement image transfer means Measuring image detecting means for detecting the image, and the measuring image transfer means is arranged at the transfer position when the recording medium on the surface of the first conveying means is conveyed only by the first conveying means. Installed and the recording medium is not superimposed. At least two of the position and the position at which the recording medium is disposed when the recording medium is conveyed by the cooperation of the first conveying means and the second conveying means, and the recording medium is not superimposed. The measurement image may be transferred to a place.

  Also in the image forming apparatus of the present invention, the first conveying unit has a surface that rotates through the transfer position of the developer by the image forming unit, and the image is recorded on the recording medium while being conveyed by the first conveying unit. Is formed. The second transport means provided on the upstream or downstream side of the first transport means in the recording medium transport direction cooperates with the first transport means to transport the recording medium. In the image forming apparatus of the present invention, the measurement image transfer unit controls the image formation unit to transfer the measurement image to at least the following two locations on the surface of the first transport unit. That is, a position on the surface of the first transport unit that is disposed at the transfer position when the recording medium is transported only by the first transport unit, and the recording medium is not superimposed, and the recording medium is the first transport The measurement image is transferred to at least two positions, which are disposed at the transfer position when transported in cooperation with the means and the second transport means, and where the recording medium is not superimposed.

  Therefore, if the measurement image transferred to the surface of the first transport unit by the measurement image transfer unit is detected by detection of the measurement image detection unit, the change in speed when the recording medium is transported by the first transport unit is Can be measured as follows. That is, if the speed of the first transport unit changes between when the recording medium is transported only by the first transport unit and when the recording medium is transported by the cooperation of the first transport unit and the second transport unit, the first transport is performed. The position at which the measurement image is transferred to the surface of the means also changes. Therefore, also in the present invention, it is possible to detect a change in speed when the recording medium is transported by the first transport means without causing the recording medium to become dirty.

  The present invention is not limited to the following configuration, but in any one of the above image forming apparatuses, the recording medium is further based on the detection result of the measurement image by the measurement image detection means. The change in the speed of the surface of the first conveying means is calculated when the recording medium is conveyed by only one conveying means and when the recording medium is conveyed by the cooperation of the first conveying means and the second conveying means. And a correction unit that corrects an image formation timing by the image forming unit based on the speed change calculated by the speed change calculation unit. In this case, the change in speed of the first transporting unit is calculated when the recording medium is transported only by the first transporting unit and when the recording medium is transported by the cooperation of the first transporting unit and the second transporting unit. The image forming timing by the image forming unit can be corrected according to the speed change. Therefore, a more accurate image can be formed on the recording medium.

  The image forming unit includes a plurality of image carriers along the recording medium conveyance direction, and the first conveyance unit conveys the recording medium through a portion facing each of the image carriers. However, it may be a transfer belt that transfers the developer image carried on each image carrier to the recording medium. In this case, it becomes easy to match the transfer position of the developer image from each image carrier to the recording medium based on the detected speed change.

  Furthermore, the transfer of the measurement image by the measurement image transfer means may be executed only when the special mode is executed. In this case, the above control can be executed only in a special case such as cardboard printing, and the operability of the apparatus is further improved.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a side sectional view showing a schematic configuration of an image forming apparatus 1 to which the present invention is applied. In the following description, the left side in FIG. 1 is the front, and the near side in FIG. 1 is the right.

(Overall configuration of image forming apparatus)
The image forming apparatus 1 is a direct transfer tandem type color printer, and includes a substantially box-shaped housing 2 as shown in FIG. A front cover 3 is provided on the front surface of the housing 2. A paper discharge tray 5A on which paper 4 as a recording medium after image formation is stacked is formed on the upper surface of the housing 2, and the paper discharge tray 5A is provided integrally so that the image forming apparatus 1 is located upward. The top cover 5 is provided so as to be openable and closable around the upper rear end of the image forming apparatus 1. By opening the top cover 5, an image forming unit 30 and a belt unit 20 to be described later can be drawn upward from the inside of the housing 2.

  A paper feed tray 7 that accommodates paper 4 for forming an image is attached to the lower portion of the housing 2 so as to be able to be drawn forward. In the paper feed tray 7, a pressure plate 9 is provided that can be tilted so as to stack and support the paper 4 and lift the front end side of the paper 4. A paper feed roller 11 that conveys the paper 4 is provided at a position above the front end of the paper feed tray 7. A separation roller 12 and a separation pad 13 are provided for separating the four pieces one by one.

  The uppermost paper 4 in the paper feed tray 7 is separated one by one by the separation roller 12, and is further conveyed by being sandwiched between the paper dust removing roller 14 and the opposing roller 15, and guided to the sheet metal chute 70. Then, the sheet is fed between the pair of registration rollers 16 and 17. The registration rollers 16 and 17 send the paper 4 onto the rear belt unit 20 at a predetermined timing.

  A part of the front cover 3 is configured to be openable as a manual feed tray 18 as shown in FIG. The sheet 4 directly inserted by the user via the manual feed tray 18 passes between the manual feed side chute surface 62 of the front chute unit 60 and the opposing surface 3A of the front cover 3 and between the registration rollers 16 and 17. Is inserted. The paper 4 inserted through the manual feed tray 18 in this way is also sent out onto the belt unit 20 by the registration rollers 16 and 17 in the same manner.

  The interval in the thickness direction of the paper 4 between the manual feed side chute surface 62 and the facing surface 3A of the front cover 3 is gradually narrowed toward the registration rollers 16 and 17, as shown in FIG. A contact portion 81 of a sheet sensor 82 (see FIG. 2) described later protrudes from the portion. The registration rollers 16 and 17 are driven and controlled to transport the paper 4 when the contact portion 81 is tilted by the paper 4 inserted through the manual feed tray 18, and the control will be described in detail later. To do.

  The belt unit 20 can be attached to and detached from the housing 2 and includes a first conveying unit and a transfer belt that are horizontally installed between a belt driving roller 21 and a tension roller 22 that are spaced apart from each other in the front-rear direction. As an example, a conveyance belt 23 (so-called transfer conveyance belt) is provided. The transport belt 23 is an endless belt made of a resin material such as polycarbonate, and the paper placed on the upper surface thereof is circulated in the clockwise direction in FIG. 1 when the rear belt drive roller 21 is rotationally driven. 4 is conveyed backward.

(Configuration of image forming unit)
Inside the conveyance belt 23, four transfer rollers 24 arranged to face each photosensitive drum 31 included in the image forming unit 30 to be described later are provided at regular intervals in the front-rear direction, and correspond to each photosensitive drum 31. The transfer belt 24 is sandwiched between the transfer roller 24 and the transfer roller 24. At the time of transferring a toner image, which will be described later, a transfer bias is applied between the transfer roller 24 and the photosensitive drum 31, and a predetermined amount of transfer current is applied.

  Four image forming units 30 are provided corresponding to the respective colors of black, yellow, magenta, and cyan in a pair with the LED unit 40, and the image forming unit 30 and the LED unit 40 are in the paper transport direction. Are provided in series. The image forming unit 30 and the LED unit 40 corresponding to each color correspond to an example of an image forming unit.

  Each image forming unit 30 includes a photosensitive drum 31 as an example of an image carrier, a scorotron charger 32, a developing cartridge 34, and the like. The photosensitive drum 31 includes a grounded metal drum main body, and is configured by covering the surface layer with a positively chargeable photosensitive layer. The scorotron charger 32 is disposed opposite to the photosensitive drum 31 at a predetermined interval so as not to come into contact with the photosensitive drum 31 in the diagonally upper rear side of the photosensitive drum 31. The scorotron charger 32 uniformly charges the surface of the photosensitive drum 31 to positive polarity by generating corona discharge.

  The developing cartridge 34 has a substantially box shape, and a toner storage chamber 35 is provided in an upper portion thereof, and a supply roller 36, a developing roller 37, and a layer thickness regulating blade 38 are provided below the developing cartridge 34. . In the toner storage chamber 35 of each developing cartridge 34, positively chargeable nonmagnetic one-component toner of each color of black, yellow, magenta, or cyan is stored as a developer.

  The toner discharged from the toner storage chamber 35 is supplied to the developing roller 37 by the rotation of the supply roller 36, and is positively frictionally charged between the supply roller 36 and the developing roller 37. Further, the toner supplied onto the developing roller 37 enters between the layer thickness regulating blade 38 and the developing roller 37 with the rotation of the developing roller 37, and is further sufficiently frictionally charged here to have a constant thickness. It is carried on the developing roller 37 as a thin layer.

  The surface of the photosensitive drum 31 is first uniformly charged positively by the scorotron charger 32 when rotating. Thereafter, the LED unit 40 is exposed to LEDs (not shown) arranged in a row in the paper width direction (left-right direction) at the lower end of the LED unit 40, and an electrostatic latent image corresponding to the image to be formed on the paper 4 is formed. .

  Next, when the developing roller 37 rotates and the positively charged toner carried on the developing roller 37 comes into contact with and faces the photosensitive drum 31, a static image formed on the surface of the photosensitive drum 31 is formed. The electric latent image is supplied. As a result, the electrostatic latent image on the photosensitive drum 31 is visualized, and a toner image as an example of a developer image in which toner adheres only to the exposed portion is carried on the surface of the photosensitive drum 31. .

  Thereafter, the toner image carried on the surface of each photosensitive drum 31 is transferred to the sheet by the transfer current when the sheet 4 conveyed by the conveying belt 23 passes between the photosensitive drum 31 and the transfer roller 24. 4 are sequentially transferred. The paper 4 on which the toner images of the respective colors are transferred in a superimposed manner is then conveyed to the fixing device 50.

  The fixing device 50 is disposed behind the conveyance belt 23 in the housing 2. The fixing device 50 includes a heating roller 51 that is rotationally driven with a heat source such as a halogen lamp, and a pressure roller 52 that is disposed below the heating roller 51 so as to face the heating roller 51 and is driven to rotate. It has. In the fixing device 50, the toner image is fixed to the paper 4 by heating the paper 4 on which the toner images of the respective colors are transferred while being nipped and conveyed by the heating roller 51 and the pressure roller 52. The sheet 4 on which the toner image is fixed is further conveyed by a conveying roller 53 disposed obliquely above and behind the fixing device 50, and is discharged by the discharge roller 54 provided on the upper portion of the housing 2. It is discharged onto the tray 5A. The above-described set of registration rollers 16 and 17 and the set of the heating roller 51 and the pressure roller 52 each correspond to an example of a second transport unit.

  In addition, a registration sensor 83 as an example of a measurement image detecting unit is provided at a position facing the surface of the conveyance belt 23 obliquely below the belt driving roller 21. The registration sensor 83 includes a light emitting unit that irradiates infrared light toward the conveyance belt 23 and a light receiving unit that detects reflected light from the conveyance belt 23, and a registration patch (described later) is formed on the conveyance belt 23 by the image forming unit 30. It is a well-known one that detects a registration patch or the like. Further, a well-known belt cleaner 84 for erasing the registration patch formed on the surface of the conveyor belt 23 is in contact with the lower surface of the conveyor belt 23 installed between the belt driving roller 21 and the tension roller 22. Yes.

(Configuration of control system of image forming apparatus)
Next, FIG. 2 is a block diagram showing the configuration of the control system of the image forming apparatus 1 configured as described above. As shown in FIG. 2, the paper sensor 82 that detects that the paper 4 has been inserted into the manual chute surface 62 based on the swinging of the contact portion 81 (see FIG. 1) is a control unit together with the registration sensor 83 described above. 90. The control unit 90 includes a main motor 85 that drives the belt driving roller 21, a clutch 86 that switches stop / drive of the registration rollers 16 and 17, a liquid crystal display, various buttons, and the like (all not shown). A well-known operation panel 87 provided on the surface of the body 2 and the four LED units 40 are also connected.

  The control unit 90 is mainly configured of a microcomputer including a CPU 91, a ROM 92, and a RAM 93, and controls the main motor 85, the clutch 86, each LED unit 40, and the like based on a program stored in the ROM 92. The control unit 90 also includes an EEPROM 94 that retains stored contents even when the power is turned off. The control unit 90 is also provided with various drive circuits, buffers, and the like. However, since these configurations are well known, illustration and description thereof are omitted.

(Control in the above control system)
Next, processing performed when the special mode is set on the operation panel 87 in the control executed by the control unit 90 will be described. In other words, in the image forming apparatus 1, when the paper 4 is transported only by the transport belt 23, and when the pair of registration rollers 16 and 17 or the pair of the heating roller 51 and the pressure roller 52 and the transport belt 23 cooperates, The speed of the conveyor belt 23 may change depending on when the conveyor belt 4 is conveyed. Such a speed change tends to increase when a thick cardboard or the like having a low stiffness is inserted as the paper 4 through the manual feed tray 18, and if the speed change is large, the image forming position on the paper 4 may change. There is sex.

  Therefore, the image forming apparatus 1 includes a special mode that is set when performing image formation on such a sheet 4. When the special mode is set via the operation panel 87, the controller 90 The process shown in the flowchart of FIG. 3 is executed. Hereinafter, the processing at the time of setting the special mode will be described. The main motor 85 is driven from the beginning of this process, and the conveyor belt 23 is circulated.

  As shown in FIG. 3, in this process, first, “Set special paper 1” is displayed on the liquid crystal display of the operation panel 87 in S1 (S represents a step: the same applies hereinafter). That is, a message prompting the user to set the special paper 4 as described above on the manual feed tray 18 is displayed. In this process, an exposure timing correction table is created for the special paper 4 as described above (see S11 to be described later). The table is a special paper 1, 2, 2, whose ordinal number increases with each process. 3 are stored in the EEPROM 94 in association with each other. Therefore, the message displayed in S1 changes to special paper 1, 2, 3,... Each time this process is executed.

  In subsequent S <b> 2, it is determined whether or not there is paper 4 in the manual feed tray 18 based on the detection signal of the paper sensor 82. If there is no paper 4 in the manual feed tray 18 (S2: N), the process waits in S2 as it is, and when the paper 4 is set (S2: Y), the process proceeds to S3. In S3, a driving signal is output to the clutch 86, whereby the leading edge of the paper 4 set on the manual feed tray 18 is nipped by the registration rollers 16 and 17, and in S4 as an example of the subsequent image transfer means for measurement, A first registration patch as an example of an image for measurement is printed (image formation) on a predetermined range of the conveyor belt 23.

  Here, in S4, the first registration patch in which the line segments extending in the left-right direction are arranged at regular intervals in the movement direction of the conveyance belt 23 in the range A indicated by the arrow in FIG. It is formed by outputting a drive signal to the LED unit 40 corresponding to (K). Further, as illustrated in FIG. 4A, the range A is a nip between the photosensitive drum 31 and the conveying belt 23 in which the leading end of the sheet 4 conveyed from the registration rollers 16 and 17 corresponds to black (K). The range from the position facing the registration sensor 83 to the position facing the registration sensor 83 when the rear end of the sheet 4 passes between the registration rollers 16 and 17 as illustrated in FIG. 4B. It is.

  In the subsequent S5, a drive signal is output to the clutch 86 and the conveyance of the paper 4 is started from the registration rollers 16 and 17, and the first registration patch is detected via the registration sensor 83 in S6. By this process, as described above, the leading end of the sheet 4 is nipped between the photosensitive drum 31 corresponding to black (K) and the conveying belt 23, and then the trailing end of the sheet 4 passes between the registration rollers 16 and 17. The speed change of the conveyor belt 23 until it passes is acquired from the detection result of the first registration patch. In the case of the stiff paper 4, normally, when the paper 4 is conveyed by the cooperation of the registration rollers 16 and 17 and the conveyance belt 23, the conveyance belt 23 is pushed by the amount that the paper 4 is pushed by the registration rollers 16 and 17. And the detection interval of the first registration patch is shortened. For this reason, it can be seen that the shorter the detection interval of the first registration patch in S6, the greater the speed increase of the conveyor belt 23 due to the pushing.

  In subsequent S8, based on the detection signal of the sheet sensor 82, it is determined whether or not the sheet 4 is present in the manual feed tray 18, that is, whether or not the rear end of the sheet 4 as the special sheet 1 has passed through the contact portion 81. Is done. If there is paper 4 on the manual feed tray 18 (S8: Y), the process waits in S8 as it is, and if there is no paper 4 from the manual feed tray 18 (S8: N), the process is an example of an image transfer unit for measurement. The process proceeds to S9. In S <b> 9, a second registration patch as an example of a measurement image is provided on the conveyance belt 23 at the timing when the sheet 4 passes through the nip portion between the photosensitive drum 31 (K drum) corresponding to black (K) and the conveyance belt 23. Printed.

  That is, in S9, the driving of the LED unit 40 is started earlier than the above timing by the time required for the photosensitive drum 31 to rotate from the surface facing the LED unit 40 to the surface facing the conveying belt 23, and the first unit is started. A second registration patch similar to the registration patch is printed on the conveyance belt 23. Further, the printing of the second registration patch is continuously executed until the timing at which the rear end of the sheet 4 passes through the nip portion between the photosensitive drum 31 and the conveyance belt 23 corresponding to cyan (C). Then, during the second registration patch printing, as shown in FIGS. 4C and 4D, the paper 4 is nipped by the heating roller 51 and the pressure roller 52, and finally cyan ( The nip portion between the photosensitive drum 31 and the conveyance belt 23 corresponding to C) is removed.

  In the case of the stiff paper 4, normally, when the paper 4 is conveyed by the cooperation of the heating roller 51, the pressure roller 52 and the conveying belt 23, it is conveyed by the resistance applied from the heating roller 51 and the pressure roller 52. The speed of the belt 23 is decreased, and the formation interval of the second registration patch is shortened. Therefore, in the subsequent S10, the second registration patch is detected via the registration sensor 83. For this reason, it can be seen that the shorter the detection interval of the second registration patch in S10, the greater the decrease in speed of the conveyor belt 23 due to the resistance.

  In S11 as an example of the subsequent speed change calculation means and correction means, an exposure timing correction table of the LED unit 40 corresponding to each color is created based on the detection results of the first registration patch and the second registration patch detected in S6 and S10. Then, the process ends. That is, as described above, the detection results of the first registration patch and the second registration patch detected at S6 and S10 favorably reflect the speed change of the conveyance belt 23. Therefore, in S11, the speed change is calculated (corresponding to the speed change calculating means), and a table for correcting the exposure timing of each LED unit 40 is created in order to cancel the speed change (correcting means). Equivalent). The exposure timing correction table created in this way is stored in the EEPROM 94 in association with “special paper 1 (may be special paper 2, 3,... As described above)”.

  After such processing, when an image is formed on the paper 4 as the special paper 1, “manual feed tray” is designated as the paper feed tray on the operation panel 87 or the user interface of the printer driver, and the paper type “Special paper 1” is designated. Then, the exposure timing correction table corresponding to the special paper 1 is read from the EEPROM 94, and the speed change can be canceled to form an accurate image without color misregistration on the paper 4.

(Effect of this embodiment and its modification)
Thus, in the present embodiment, when the paper 4 is transported only by the transport belt 23 and when it is transported in cooperation with the registration rollers 16 and 17 or the heating roller 51 and the pressure roller 52, The speed change of the conveyor belt 23 can be detected as described above. Therefore, the exposure timing correction table is created according to the speed change, and an accurate image without color misregistration or the like can be formed on the paper 4 such as thick paper. In addition, the positions where the first registration patch and the second registration patch are formed on the conveyance belt 23 are positions shifted from the sheet 4 upstream or downstream in the conveyance direction so as not to overlap the sheet 4. The paper 4 is not soiled when the speed change of the belt 23 is detected. Furthermore, in the present embodiment, since the above processing is executed only when the special mode is set, the above control can be executed only in a special case such as cardboard printing, and the operability of the apparatus is further improved. To do.

  In addition, this invention is not limited to the said embodiment at all, It can implement with a various form in the range which does not deviate from the summary of this invention. For example, the first conveying unit may be configured in a drum shape, and when applied to an image forming apparatus using a so-called intermediate transfer belt or intermediate transfer drum, the intermediate transfer belt or intermediate transfer drum is the first transfer unit. This corresponds to one transport means. In addition, the printer driver or the like can be configured to create the exposure timing correction table as described above or to correct the image formation timing by other methods. Further, the correction by the exposure timing correction table or other methods as described above is performed when the registration rollers 16 and 17 and the transport belt 23 work together, during transport using only the transport belt 23, or when the transport belt 23 and the heating roller 51 are transported. , A rough one of about three stages may be used, such as during conveyance by cooperating with the pressure roller 52.

  Furthermore, as the measurement image, various forms other than the first registration patch and the second registration patch can be considered. In addition, the timing of formation of the registration sensor 83 can be changed variously by devising the position of the registration sensor 83 or forming a measurement image via the photosensitive drum 31 corresponding to cyan (C). The image forming unit may form an image by a method other than the electrophotographic method.

1 is a side sectional view showing a schematic configuration of an image forming apparatus to which the present invention is applied. 2 is a block diagram illustrating a configuration of a control system of the image forming apparatus. FIG. It is a flowchart showing the process performed with the control system. It is explanatory drawing which represents the principle of the process typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 4 ... Paper 16, 17 ... Registration roller 18 ... Manual feed tray 20 ... Belt unit 21 ... Belt drive roller 22 ... Tension roller 23 ... Conveying belt 24 ... Transfer roller 30 ... Image forming unit 31 ... Photoconductor drum 34 ... Developing cartridge 40 ... LED unit 50 ... Fixing device 51 ... Heating roller 52 ... Pressure roller 82 ... Paper sensor 83 ... Registration sensor 85 ... Main motor 86 ... Clutch 87 ... Operation panel 90 ... Control unit

Claims (5)

Image forming means for transferring a developer to form an image;
A first conveying unit having a surface rotating through a transfer position of the developer by the image forming unit and conveying a recording medium;
A second conveying means provided upstream or downstream in the recording medium conveying direction of the first conveying means, for conveying the recording medium in cooperation with the first conveying means;
A measurement image transfer means for controlling the image forming means to transfer a measurement image to the surface of the first transport means;
Measurement image detection means for detecting the measurement image transferred to the surface of the first transport means by the measurement image transfer means;
With
The measurement image transfer means includes a position on the surface of the first conveyance means that faces the measurement image detection means when the recording medium is conveyed only by the first conveyance means, and the recording medium is the first conveyance means. An image forming method characterized in that the measurement image is transferred to at least two positions, that is, a position facing the measurement image detection unit when the first conveyance unit and the second conveyance unit are carried together. apparatus. Image forming means for transferring a developer to form an image;
A first conveying unit having a surface rotating through a transfer position of the developer by the image forming unit and conveying a recording medium;
A second conveying means provided upstream or downstream in the recording medium conveying direction of the first conveying means, for conveying the recording medium in cooperation with the first conveying means;
A measurement image transfer means for controlling the image forming means to transfer a measurement image to the surface of the first transport means;
Measurement image detection means for detecting the measurement image transferred to the surface of the first transport means by the measurement image transfer means;
With
The measurement image transfer unit is disposed at the transfer position on the surface of the first transport unit when the recording medium is transported only by the first transport unit, and a position where the recording medium is not superimposed. The recording medium is disposed at the transfer position when the recording medium is conveyed by the cooperation of the first conveying means and the second conveying means, and at least two positions where the recording medium is not superimposed. An image forming apparatus for transferring the measurement image. Furthermore,
Based on the detection result of the measurement image by the measurement image detection means, when the recording medium is conveyed only by the first conveyance means, the recording medium is the first conveyance means, the second conveyance means, A speed change calculating means for calculating a speed change of the surface of the first transport means when transported in cooperation with each other;
Correcting means for correcting the image forming timing by the image forming means based on the speed change calculated by the speed change calculating means;
The image forming apparatus according to claim 1, further comprising: The image forming means includes a plurality of image carriers along the recording medium conveyance direction,
The first conveying means is a transfer belt for transferring a developer image carried on each image carrier to the recording medium while conveying the recording medium through a portion facing each image carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus is provided.   5. The image forming apparatus according to claim 1, wherein the transfer of the measurement image by the measurement image transfer unit is executed only when the special mode is executed.

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