JP3884460B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer that forms an image by superimposing a plurality of color toner images, and more particularly to a technique for correcting a positional deviation of each color toner image during toner image transfer.

  Conventionally, there is an image forming apparatus such as a copying machine or a printer that forms an image by transferring toner images from an image carrier for each color and superimposing them. In this image forming apparatus, recording paper is placed on the image carrier. If there is a speed difference between the traveling speed of the transfer belt that is transported and the recording paper transport speed by the registration rollers that transport the recording paper from the paper feed mechanism toward the transfer belt, the transport speed of the recording paper that is carried into the transfer belt Therefore, the recording paper is not transported to the image carrier of each color at an appropriate speed, and when each color toner image is transferred, there is a positional deviation in the overlay of the color toner images. It sometimes occurred. Therefore, the recording paper conveyance speed by the registration roller is set to a speed slightly faster than the recording paper conveyance speed by the transfer belt (about 0.5 to 1% faster), and the registration roller is inclined in the vertical direction with respect to the transfer belt. When the recording paper leading edge is carried between the transfer belt and the suction roller arranged to face the transfer belt and the transfer speed by the transfer belt is slightly slowed, The recording paper is bent between the transfer belt and the registration roller so that the speed difference between the transfer belt running speed and the recording paper conveyance speed by the registration roller is absorbed.

  However, in order to reduce the size of the image forming apparatus, the distance between the transfer belt and the suction roller and the registration roller must be shortened. Therefore, the recording paper is bent by an amount sufficient to absorb the speed difference. It is difficult. Also, in the case of stiff paper such as thick paper, even if a certain distance is secured between the transfer belt and the suction roller and the registration roller, the recording paper is bent by an amount that can sufficiently absorb the above speed difference. Is difficult. Furthermore, the recording paper conveyance speed by the registration roller is the recording paper conveyance speed by the registration roller due to a change in the diameter of the registration roller depending on the ambient environment such as temperature and humidity, or a decrease in gripping force due to the wear of paper powder or the like over time. Therefore, it is difficult to maintain the transfer belt running speed set as described above and the recording paper conveyance speed by the registration rollers for a long period of time.

  The present invention has been made to solve the above-described problems, and the transfer belt running speed is independent of the distance between the transfer belt and the registration roller, the quality of the recording paper, and the temporal change in the performance of the registration roller. It is an object of the present invention to provide an image forming apparatus capable of reducing the positional deviation of the color toner image superposition at the time of transferring the color toner images by accurately adjusting the relationship between the color toner image and the recording paper conveyance speed by the registration rollers.

In order to achieve the above object, according to the first aspect of the present invention, a recording paper conveyed by a registration roller is conveyed to an image carrier provided for each color by a transfer belt, and a toner on each image carrier is provided. An image forming apparatus that forms an image by transferring an image onto a recording paper,
Transfer belt driving means for running the transfer belt;
Registration roller driving means for rotationally driving the registration roller;
Transfer belt speed detecting means for detecting the running speed of the transfer belt;
A conveyance speed detecting means for detecting a conveyance speed of a recording sheet conveyed from the registration roller to the transfer belt;
The registration roller driving is performed so that the conveyance speed of the recording paper detected by the conveyance speed detection unit is higher than the traveling speed of the transfer belt detected by the transfer belt speed detection unit while maintaining a predetermined speed difference. Or a control means for drivingly controlling at least one of the transfer belt driving means,
The transfer belt speed detecting means detects a running speed of the transfer belt based on a rotation speed of a suction roller disposed facing the transfer belt.

  According to this configuration, the control means causes the recording paper transport speed by the registration rollers to differ from the travel speed of the transfer belt by a predetermined speed difference (for example, in an experiment, the recording paper transport speed by the registration rollers determines the transfer belt travel speed). At least one of the registration roller driving unit and the transfer belt driving unit is driven and controlled so as to increase the speed while maintaining a speed of approximately 0.2%. The difference from the conveyance speed can be kept almost constant. As a result, when the recording paper is carried into the transfer belt from the registration roller, fluctuation of the running speed of the transfer belt due to the influence of the recording paper carry-in speed by the registration roller is reduced. In addition, since the difference between the transfer belt running speed and the recording paper conveyance speed by the registration rollers is kept substantially constant, the recording paper is bent between the transfer belt and the registration rollers when the recording paper is carried into the transfer belt. Furthermore, when absorbing the speed difference between the transfer belt running speed and the recording paper carry-in speed by the registration rollers, it is possible to absorb the speed difference even if the amount of deflection of the recording paper is small.

  Even if the recording paper transport force by the registration roller changes due to changes over time such as wear of the registration roller or adhesion of paper dust, the transfer belt travel speed and the recording paper transport speed by the registration roller Occurrence of fluctuations in the speed difference is prevented.

  Therefore, regardless of changes in the registration roller performance over time, the distance between the transfer belt and the registration roller, the quality of the recording paper, the recording paper is conveyed to each color image carrier by the transfer belt at a stable speed, and each color toner image It is possible to prevent misalignment of each color toner image at the time of transfer.

  In the above, the registration roller driving means or the transfer belt driving means is driven and controlled so that the recording paper conveyance speed by the registration rollers is faster than the running speed of the transfer belt. In the drive control of the roller driving means, the time required for the recording paper conveyed by the registration roller to move a certain distance and the time required for the transfer belt to move a certain distance have a predetermined time difference. It also includes driving control of the registration roller driving means or the transfer belt driving means.

  Also, since the transfer belt running speed is detected without forming a registration mark on the transfer belt based on the number of rotations of the suction roller that rotates following the transfer belt, the transfer belt running speed without image forming processing is detected. Can be detected.

  As described above, according to the first aspect of the present invention, the control means causes the recording paper conveyance speed by the registration rollers to be a predetermined speed difference from the running speed of the transfer belt (for example, in the experiment, the recording paper is fed by the registration rollers). Since at least one of the registration roller driving means and the transfer belt driving means is driven and controlled so that the conveying speed is preferably higher than the traveling speed of the transfer belt by about 0.2%, the transfer belt is controlled. It becomes possible to keep the difference between the running speed and the conveyance speed of the recording paper by the registration rollers substantially constant. As a result, when the recording paper is carried into the transfer belt from the registration roller, fluctuation of the running speed of the transfer belt due to the influence of the recording paper carry-in speed by the registration roller is reduced. Therefore, when the recording paper is carried into the transfer belt, the recording paper is bent between the transfer belt and the registration roller to absorb the speed difference between the transfer belt running speed and the recording paper carrying speed by the registration roller. Even if the amount of bending of the paper is small, the speed difference can be absorbed.

  Even if the recording paper transport force by the registration roller changes due to changes over time such as wear of the registration roller or adhesion of paper dust, the transfer belt travel speed and the recording paper transport speed by the registration roller Occurrence of fluctuations in the speed difference is prevented.

  Therefore, regardless of changes in the registration roller performance over time, the distance between the transfer belt and the registration roller, the quality of the recording paper, the recording paper is conveyed to each color image carrier by the transfer belt at a stable speed, and each color toner image It is possible to prevent misalignment of each color toner image at the time of transfer.

  Further, since the transfer belt traveling speed is detected without forming a registration mark on the transfer belt based on the number of rotations of the suction roller that rotates following the transfer belt, the transfer belt is not subjected to image forming processing. The traveling speed can be detected.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an example of a schematic configuration of an image forming apparatus according to the present invention. As shown in FIG. 1, a printer (an example of an image forming apparatus) 1 includes a developing device 3 for each of cyan, magenta, yellow, and black in a printer main body 2. Each developing device 3 includes a photosensitive drum (image carrier) 4 made of a-Si (amorphous silicon) or the like, and rotates in the direction of the arrow in the drawing. The photosensitive drum 4 is uniformly charged by the charging unit 5, and LED light based on document image data input from an external PC (personal computer) or the like is sent from the exposure unit (LED print head unit or the like) 6 to the photosensitive drum 4. An electrostatic latent image is formed by irradiating the surface of the toner, and toner adheres to the electrostatic latent image to form a toner image.

  The toner is supplied from the toner supply containers 7C, 7M, 7Y, and 7B. A transfer belt 8 for conveying recording paper is disposed below the photosensitive drums 4 arranged for each color. The transfer belt 8 is pressed against each photosensitive drum 4 by the transfer roller 9, and is driven by a drive roller 10 that is rotated by a motor (not shown) and the like, and driven rollers 11 and 24 that rotate according to the transfer belt 8. The photosensitive drum 4 is rotated endlessly in the forward direction of the rotation direction.

  Then, the recording sheet is conveyed from the sheet feeding mechanism 12 to the transfer belt 8 via the recording sheet conveying path 13, and the image transfer operation and sheet feeding by the photosensitive drum 4 and the transfer roller 9 are performed by the registration rollers 17. The timing with the operation is adjusted. After adjusting the timing, the recording paper is conveyed between the photosensitive drum 4 and the transfer belt 8 by the registration roller 17. While the recording paper is being conveyed between the photosensitive drums 4 and the transfer belt 8, the toner images of the respective colors on the surfaces of the photosensitive drums 4 are successively transferred onto the recording paper by applying a transfer bias of the transfer roller 9. .

  The recording paper onto which the toner image has been transferred by all the photosensitive drums 4 is conveyed to the fixing roller pair 14 where the toner image is fixed and a color image is formed. The recording paper that has passed through the fixing roller pair 14 is sent to the recording paper conveyance path 15 and is discharged from the discharge unit 16. Each of the photosensitive drums 4 includes a cleaning mechanism 21 that removes residual toner and the like on the photosensitive drum 4.

  Further, the image forming unit for each color (photosensitive drum 4, charging unit 5, exposure unit 6, developing device 3, transfer roller 9, etc.) further upstream of the cyan image forming unit arranged on the most upstream side. On the side, a suction roller 18 that electrostatically attracts the recording paper to the transfer belt 8 is provided. The suction roller 18 is provided at a position facing the transfer belt 8 and the driven roller 11 so as to contact the driven roller 11 via the transfer belt 8. The suction roller 18 is driven to rotate along the travel of the transfer belt 8.

  FIG. 2 is a block diagram illustrating an example of a schematic configuration of the printer 1. The printer 1 includes a control unit 110 that controls the entire printer 1. The control unit 110 is connected to a ROM 112 that stores an operation program and the like of the entire apparatus, and is connected to a RAM 113 that temporarily stores image data and the like and functions as a work area. In addition, the image forming units 20B, 20Y, 20M, and 20C for the respective colors are connected to the control unit 110, and the control unit 110 is a charging unit that is provided in each of the image forming units 20B, 20Y, 20M, and 20C. 5, the exposure unit 6, the developing device 3, the transfer bias unit 114 for applying a transfer bias to the transfer roller 9 to transfer the toner image on the photoconductive drum 4 to the recording paper, and the drive source of the photoconductive drum 4. The drum motor 115 is controlled.

  The fixing motor 120 rotates the fixing roller pair 14 and is controlled by the control unit 110 via a driver 120a. A clock signal is sent from the control unit 110 to the driver 120a, and the fixing motor 120 rotates at a rotation speed corresponding to the frequency of the clock signal. Therefore, the rotation speed of the fixing motor 120 can be controlled by changing the frequency of the clock signal sent from the control unit 110 to the driver 120a. The fixing heater 121 is provided in a heat roller that constitutes one of the fixing roller pair 14, and is turned on / off by the control unit 110. In FIG. 2, each image forming unit for yellow, magenta, and cyan is shown as one image forming unit, but actually, each image forming unit for each color is connected to the control unit 110 and controlled. ing.

  The transfer belt drive motor 125 is a drive source of the drive roller 10 that causes the transfer belt 8 to travel, and is controlled by the control unit 110 via the driver 125a. A clock signal is sent from the controller 110 to the driver 125a, and the transfer belt drive motor 125 rotates at a rotational speed corresponding to the frequency of the clock signal. Therefore, the rotation speed of the transfer belt drive motor 125 can be controlled by changing the frequency of the clock signal sent from the control unit 110 to the driver 125a.

  The suction roller bias unit 126 applies to the suction roller 18 a bias necessary to apply a charge for electrostatically attracting the recording paper to the transfer belt 8 to the recording paper. The operation unit 127 includes an operation panel for inputting a print instruction from the user and a display unit for displaying various messages. The control unit 110 is connected to a PC (personal computer) 130 via an interface 129. The printer 1 forms an image based on the image data input from the PC 130.

  The registration motor 133 rotates the registration roller 17 (FIG. 1), and is controlled by the control unit 110 via the driver 133a. A clock signal is sent from the control unit 110 to the driver 133a, and the registration motor 133 rotates at a rotational speed corresponding to the frequency of the clock signal. Therefore, the rotation speed of the registration motor 133 can be controlled by changing the frequency of the clock signal sent from the control unit 110 to the driver 125a.

  The registration sensor 137 detects that the recording paper is at the position of the registration roller 17. The first sensor 135a and the second sensor 135b are optical sensors or the like arranged in parallel in the recording sheet conveyance direction between the transfer belt 8 and the registration roller 17 in order to detect the leading and trailing ends of the recording sheet. The sensor 135a is disposed upstream of the second sensor 135b in the recording paper conveyance direction. The timer 136 performs various time measurements. The registration sensor 137 detects a registration mark formed on the transfer belt 8 (for example, an area outside the recording paper placement area or an area between the placed recording papers).

  The fixing roller sensor 140 is disposed on the downstream side of the fixing roller pair 14 and detects the leading edge and the trailing edge of the recording paper nipped by the fixing roller pair 14. The suction roller sensor 141 is a sensor that detects that a recording sheet is carried between the suction roller 18 and the transfer belt 8, and is disposed in the vicinity of the suction roller 18.

  The suction roller mark sensor 142 is a sensor for detecting a marking formed on the peripheral surface of the suction roller 18. The recording sheet counter 143 counts the number of recording sheets conveyed by the registration roller 17. The temperature / humidity sensor 145 detects the temperature and humidity inside the printer 1 (particularly near the registration roller 17). The driven roller sensor 146 is a sensor for detecting a marking formed on the peripheral surface of the driven roller 24.

  Next, the outline of the speed adjustment between the transfer belt running speed and the registration paper conveyance speed by the registration roller 17 when transferring the color toner images by the color photosensitive drums 4 will be described. FIG. 3 is a flowchart showing the speed adjustment process. The speed adjustment is caused by a difference in speed between the recording paper conveyance speed by the registration roller 17 and the running speed of the transfer belt 8 when the recording paper is carried from the registration roller 17 between the transfer belt 8 and the suction roller 18. This is performed to prevent fluctuations in the running speed of the transfer belt 8 (recording paper conveyance speed by the transfer belt 8).

  First, the traveling speed of the transfer belt 8 and the recording paper conveyance speed by the registration roller 17 are detected (S1, S2), and the recording paper conveyance speed by the registration roller 17 is different from the traveling speed of the transfer belt 8 by a predetermined speed difference (for example, In the experiment, it is preferable that the recording paper transport speed by the registration roller 17 is preferably about 0.2% higher than the traveling speed of the transfer belt 8), and the relationship of being slightly higher is maintained. Is determined (S3). If the predetermined speed difference is not maintained (NO in S3), the registration motor 133 is rotated so that the recording paper conveyance speed by the registration roller 17 and the running speed of the transfer belt 8 have the predetermined speed difference. The speed is corrected (S4). For example, when the recording paper conveyance speed by the registration roller 17 is a high speed having a speed difference exceeding the predetermined speed difference with respect to the traveling speed of the transfer belt 8, the rotation speed of the registration motor 133 is decreased. Further, when the recording paper conveyance speed by the registration roller 17 is a low speed that does not have the predetermined speed difference with respect to the traveling speed of the transfer belt 8, the rotation speed of the registration motor 133 is set high. If these speed differences are maintained (YES in S3), the process is terminated because there is no need to correct the rotational speed of the registration motor 133.

  An example of processing for detecting the traveling speed of the transfer belt 8 in the speed adjustment will be described. FIG. 4 is a flowchart showing the speed detection process, and FIG. 5 is a diagram showing a state of registration mark formation on the transfer belt 8. First, the transfer belt drive motor 125 is rotationally driven to run the transfer belt 8 (S21). Then, the first registration mark is formed on the transfer belt 8 by any one of the image forming units for each color (for example, the most upstream cyan image forming unit) (S22), and another image forming unit (for example, the most upstream image forming unit). The second registration mark is simultaneously formed on the transfer belt 8 from the downstream black image forming unit) (S23). As a result, a fixed interval (in the above example, the distance from the transfer position by the cyan photoconductor drum 4 to the transfer position by the black photoconductor drum 4) is set on the transfer belt 8 from the first registration mark. A second resist mark is formed at the position.

  When the first registration mark is detected by the registration sensor 137 (YES in S24), the timer 136 starts counting (S25). When the second registration mark is detected by the registration sensor 137 (YES in S26), the count by the timer 136 is stopped (S27). The count value of the timer 136 is acquired (S28), and the time from when the first registration mark is detected to when the second registration mark is detected is detected. The count value of the timer 136 (the time from the detection of the first registration mark to the detection of the second registration mark) and the interval between the first registration mark and the second registration mark (in the above example, the photosensitive drum 4 for cyan). The travel speed of the transfer belt 8 is calculated based on the distance from the transfer position to the transfer position by the black photosensitive drum 4 (S29).

  The first and second registration marks in S22 and S23 are formed, for example, after the first registration mark is formed by the cyan photosensitive drum 4, and then the first registration mark is the black photosensitive drum 4. The second registration mark may be formed by the black photosensitive drum 4 after a predetermined time α has passed after passing through the transfer position (the first registration mark by the cyan photosensitive drum 4 is formed). When the time required to reach the transfer position by the black photoconductor drum 4 is T, the second resist mark is formed by the black photoconductor drum 4 when T + α time elapses from the formation of the first resist mark. Will be.) In this case, based on the ratio between the actual measurement time (timer count value) from the time when the first mark is detected by the registration sensor 137 to the time when the second mark is detected and the fixed time α, the reference speed corresponding to the time α is The traveling speed of the transfer belt 8 is calculated.

  Another example of the process for detecting the traveling speed of the transfer belt 8 will be described. FIG. 6 is a flowchart showing the speed detection process. The detection of the traveling speed of the transfer belt 8 is to calculate the traveling speed of the transfer belt 8 based on the rotational speed of the driven roller 24 that rotates following the transfer belt 8.

  First, the transfer belt drive motor 125 is driven to rotate and the transfer belt 8 travels (S31), and the driven roller 24 is rotated together with the transfer belt 8. When one marking provided on the outer peripheral surface of the driven roller 24 is detected by the driven roller sensor 146 (YES in S32), counting by the timer 136 is started (S33). When the driven roller 24 makes one round and the marking is detected again by the driven roller sensor 146 (YES in S34), the count by the timer 136 is stopped (S35). The count value of the timer 136 is acquired (S36), and the time from when the mark is first detected until the mark is detected again (the time required for the driven roller 24 to make one revolution) is detected. Based on this, the rotational speed of the driven roller 24 is calculated (S37). Based on the rotational speed of the driven roller 24 and the outer peripheral length of the driven roller 24, the running speed of the transfer belt 8 is calculated (S38).

  Still another example of the process for detecting the traveling speed of the transfer belt 8 will be described. FIG. 7 is a flowchart showing the speed detection process. The travel speed detection of the transfer belt 8 is to calculate the travel speed of the transfer belt 8 based on the rotational speed of the suction roller 18 that rotates following the transfer belt 8.

  First, the transfer belt drive motor 125 is rotationally driven to cause the transfer belt 8 to travel (S41), and the suction roller 18 is rotated together with the transfer belt 8. When one marking provided on the outer peripheral surface of the suction roller 18 is detected by the suction roller sensor 141 (YES in S42), the timer 136 starts counting (S43). When the suction roller 18 makes one round and the marking is detected again by the suction roller sensor 141 (YES in S44), the timer 136 stops counting (S45). The count value t2 of the timer 136 is acquired (S46), and the time from when the mark is first detected until the mark is detected again (the time required for the suction roller 18 to make one revolution) is detected. Based on this, the rotation speed of the suction roller 18 is calculated (S47). Then, based on the rotational speed of the suction roller 18 and the outer peripheral length of the suction roller 18, the traveling speed of the transfer belt 8 is calculated (S48).

  Processing for detecting the recording paper conveyance speed by the registration roller 17 in the speed adjustment will be described. FIG. 8 is a flowchart showing the recording paper conveyance speed detection process. First, the registration motor 133 is driven to convey the recording paper toward the transfer belt 8 (S51), and the first sensor 135a disposed between the registration roller 17 and the transfer belt 8 detects the leading edge of the recording paper. Then (YES in S52), the timer 136 starts counting (S53), and when the leading edge of the recording paper is detected by the second sensor 135b downstream of the first sensor 135a (YES in S54), the timer 136 The count is stopped (S55). The count value t3 of the timer 136 is acquired (S56), the moving time of the leading edge of the recording paper between the first sensor 135a and the second sensor 135b is detected, and this time and the distance between the first sensor 135a and the second sensor 135b. Based on the above, the recording paper conveyance speed is calculated (S57).

  Next, another example of speed adjustment processing between the traveling speed of the transfer belt 8 and the recording paper conveyance speed by the registration rollers 17 at the time of transferring each color toner image will be described. FIG. 9 is a flowchart showing the speed adjustment processing, and FIG. 10 is a schematic side view showing a first sensor and a second sensor disposed between the transfer belt 8 and the registration roller 17. In the speed adjustment process described above, the running speed of the transfer belt 8 and the recording paper conveyance speed by the registration roller 17 are detected, and the rotation speed of the registration motor 133 is controlled so that both speeds have a predetermined speed difference. However, a difference in the recording paper conveyance speed before and after the recording paper is carried between the transfer belt 8 and the suction roller 18 is detected, and the rotation speed of the registration motor 133 is adjusted so that the speed difference has a predetermined speed difference. You may make it control.

  In this speed adjustment processing, when the leading edge of the recording paper has passed the registration roller 17 and the trailing edge of the recording paper has not yet passed the registration roller 17, the leading edge of the recording paper is already between the transfer belt 8 and the suction roller 18. The present invention is applied to the printer 1 having a structure that is carried in between. The recording paper conveyance speed before carrying the recording paper between the transfer belt 8 and the suction roller 18 is detected based on the time required for the recording paper leading edge to move between the first sensor 135a and the second sensor 135b. The recording paper conveyance speed after the recording paper is carried between the belt 8 and the suction roller 18 is detected based on the time during which the trailing edge of the recording paper moves between the first sensor 135a and the second sensor 135b.

  First, the registration motor 133 is driven and the recording paper is conveyed toward the transfer belt 8 (S61). When the first sensor 135a detects the leading edge of the recording paper (YES in S62), the timer 136 starts counting. (S63) When the second sensor 135b downstream of the first sensor 135a detects the leading edge of the recording paper (YES in S64), the counting by the timer 136 is stopped (S65). The count value t4 of the timer 136 is acquired (S66), and the moving time of the leading edge of the recording paper between the first sensor 135a and the second sensor 135b is detected.

  Subsequently, when the first sensor 135a detects the trailing edge of the recording paper (YES in S67), the timer 136 starts counting (S68), and when the leading edge of the recording paper is detected by the second sensor 135b (YES in S69). ), The count by the timer 136 is stopped (S70). The count value t5 of the timer 136 is acquired (S71), and the moving time of the trailing edge of the recording paper between the first sensor 135a and the second sensor 135b is detected.

  Then, the movement times (count values t4 and t5) between the first sensor 135a and the second sensor 135b at the leading and trailing ends of the recording paper are compared (S72), and the difference between the count value t4 and the count value t5 will be described later. If it is not the predetermined value (NO in S72), the rotation of the registration motor 133 is performed so that the recording paper conveyance speed by the registration roller 17 is higher than the running speed of the transfer belt 8 while maintaining the above-mentioned predetermined speed difference. The speed is corrected (S73). That is, the difference between the count value t4 and the count value t5 represents the speed difference between the recording paper conveyance speed by the registration roller 17 and the traveling speed of the transfer belt 8, and thus the difference between the count value t4 and the count value t5 is adjusted. As a result, the speed difference between the recording paper conveyance speed by the registration roller 17 and the traveling speed of the transfer belt 8 can be adjusted. Therefore, a predetermined speed difference between the recording paper conveyance speed by the registration roller 17 and the traveling speed of the transfer belt 8 (the recording paper conveyance speed by the registration roller 17 exceeds the traveling speed of the transfer belt 8 by about 0.2%. The difference value between the count value t4 and the count value t5 corresponding to the predetermined value is held as a predetermined value so that the difference between the actually measured count value t4 and the count value t5 becomes the predetermined value. If the rotational speed of the registration motor 133 is controlled, it is possible to obtain a state in which the recording paper conveyance speed by the registration roller 17 is higher than the traveling speed of the transfer belt 8 while maintaining the above-described predetermined speed difference.

  For example, when the value obtained by subtracting the count value t4 from the count value t5 exceeds the predetermined value, the rotation speed of the registration motor 133 is decreased, and the value obtained by subtracting the count value t4 from the count value t5 exceeds the predetermined value. If not, the rotation speed of the registration motor 133 is increased.

  If the difference between the count value t4 and the count value t5 is the predetermined value (YES in S72), it is not necessary to correct the rotation speed of the registration motor 133, and the process ends.

  Still another example of speed adjustment processing between the running speed of the transfer belt 8 and the recording paper conveyance speed by the registration rollers 17 at the time of transferring the color toner images will be described. FIG. 11 is a flowchart showing the speed adjustment process. The speed adjustment process between the running speed of the transfer belt 8 and the recording paper conveyance speed by the registration roller 17 at the time of transferring the color toner images is performed by the suction roller 18 before and after the recording paper is carried between the transfer belt 8 and the suction roller 18. , And the registration motor 133 may be driven and controlled so that the rotational speed difference has a predetermined speed difference described later.

  First, the transfer belt drive motor 125 is driven (S81), and the suction roller 18 is rotated together with the transfer belt 8. The application of the suction roller bias and the transfer roller bias is stopped (S82). Then, when the recording sheet is not conveyed between the transfer belt 8 and the suction roller 18 and one marking provided on the outer peripheral surface of the suction roller 18 is detected by the suction roller mark sensor 142 (S83). (YES), counting by the timer 136 is started (S84). When the suction roller 18 makes one revolution and the marking is detected again by the suction roller mark sensor 142 (YES in S85), the count by the timer 136 is stopped (S86), and the count value t6 of the timer 136 is acquired. (S87).

  Thereafter, the registration motor 133 is driven (S88), the recording paper is conveyed between the transfer belt 8 and the suction roller 18, and when the leading edge of the recording paper is detected by the suction roller sensor 141 (YES in S89), the suction roller. Mark detection of one marking provided on the outer peripheral surface of the suction roller 18 by the mark sensor 142 is started (S90). When the marking of the suction roller 18 is detected by the suction roller mark sensor 142 (YES in S91), the timer 136 starts counting (S92). When the driven roller 24 makes one round and the marking is detected again by the suction roller mark sensor 142 (YES in S93), the count by the timer 136 is stopped (S94), and the count value t7 of the timer 136 is acquired. (S95).

  Then, by comparing the count value t6 with the count value t7, the rotation speed of the suction roller 18 before and after the recording paper conveyance is compared (S96). When the difference between the count value t6 and the count value t7 is not a predetermined value described later (NO in S96), the recording paper conveyance speed by the registration roller 17 maintains the above-described predetermined speed difference rather than the traveling speed of the transfer belt 8. The rotational speed of the registration motor 133 is corrected so as to be a high speed (S97).

  That is, in the state where there is no recording paper between the suction roller 18 and the transfer belt 8, the suction roller 18 is driven and rotated by the transfer belt 8. Therefore, the count value t6 measured in this state is the running speed of the transfer belt 8. In the state where the recording paper exists between the suction roller 18 and the transfer belt 8, the suction roller 18 is driven to rotate by the recording paper, and the count value t7 measured in this state is This corresponds to the recording paper conveyance speed by the registration roller 17.

  Therefore, the difference between the count value t6 and the count value t7 represents the speed difference between the traveling speed of the transfer belt 8 and the recording paper conveyance speed by the registration roller 17, and thus the difference between the count value t6 and the count value t7. By adjusting this, it is possible to adjust the speed difference between the recording paper conveyance speed by the registration roller 17 and the traveling speed of the transfer belt 8. Therefore, a predetermined speed difference between the recording paper conveyance speed by the registration roller 17 and the traveling speed of the transfer belt 8 (the recording paper conveyance speed by the registration roller 17 exceeds the traveling speed of the transfer belt 8 by about 0.2%. The difference value between the count value t6 and the count value t7 corresponding to (a) is held as a predetermined value so that the difference between the actually measured count value t6 and the count value t7 becomes the predetermined value. If the rotational speed of the registration motor 133 is controlled, it is possible to obtain a state in which the recording paper conveyance speed by the registration roller 17 is higher than the traveling speed of the transfer belt 8 while maintaining the above-described predetermined speed difference.

  For example, when the value obtained by subtracting the count value t6 from the count value t7 exceeds the predetermined value, the rotation speed of the registration motor 133 is decreased, and the value obtained by subtracting the count value t6 from the count value t7 exceeds the predetermined value. If not, the rotation speed of the registration motor 133 is increased.

  If the difference between the count value t6 and the count value t7 is the predetermined value (YES in S96), it is not necessary to correct the rotation speed of the registration motor 133, and the process ends.

  Next, processing for warning the replacement of the registration roller 17 according to the rotational speed correction amount of the registration motor 133 will be described. FIG. 12 is a flowchart showing the processing. When the rotational speed control of the registration motor 133 is performed in the processing (FIGS. 4, 9, and 11) for making the traveling speed of the transfer belt 8 and the recording paper transport speed by the registration rollers 17 substantially equal ( YES in S101), the rotational speed correction amount r of the registration motor 133 (that is, the correction amount of the recording paper conveyance speed by the registration roller 17) is confirmed (S102).

  When the rotational speed correction amount r has reached a certain amount (for example, about + 1%) from the initial rotational speed value of the registration motor 133 (a preset fixed value) (YES in S103), the registration roller 17 After a message for prompting replacement is displayed on the display unit of the operation unit 127 (FIG. 2) (S105), the rotation speed of the registration motor 133 is corrected (S104). If the rotational speed correction amount r has not reached a certain amount from the initial rotational speed value of the registration motor 133 (the initial value of the recording paper conveyance speed by the registration rollers 17) (NO in S103), a message prompting the replacement of the registration rollers 17 Is displayed, and the rotational speed of the registration motor 133 is corrected (S104). If the rotational speed correction amount r reaches a predetermined amount from the initial rotational speed value of the registration motor 133 and a message prompting the replacement of the registration roller 17 is displayed, the rotational speed correction of the registration motor 133 is not performed. Processing for prohibiting the image forming operation may be performed until the registration roller 17 is replaced.

  Next, a process for determining whether or not to adjust the transfer belt running speed at the time of transferring each color toner image and the recording paper transport speed by the registration roller 17 according to the surrounding environment will be described. FIG. 13 is a flowchart showing the processing. When the count value of the recording paper counter 143 is acquired (S111) and this counter value has reached a predetermined value, for example, the total counter value is (1) every 5000 (sheets) count, and (2) at the time of the previous adjustment. When counting from 1000 (sheets) (YES in S112), adjustment of the running speed of the transfer belt 8 and the recording paper conveyance speed by the registration roller 17 is executed (S115).

  Subsequently, the temperature and humidity are detected by the temperature / humidity sensor 145 (S113), and when the detected change amount of the temperature or humidity reaches a predetermined value, for example, the change amount of the temperature is about 8 from the time of the previous correction. When the temperature has changed, or when the amount of change in humidity has changed by about 20% from the previous correction (YES in S114), the running speed of the transfer belt 8 and the recording paper conveyance speed by the registration roller 17 are adjusted. (S115). If neither the counter value (number of recording paper transported sheets) nor the amount of change in temperature and humidity has reached the predetermined values (NO in S112, NO in S114), the running speed of the transfer belt 8 and the registration roller The processing ends without adjusting the recording paper conveyance speed by 17.

  The adjustment timing of the recording paper conveyance speed is not limited to when the count by the recording paper counter 143 reaches a predetermined value, but may be when the printer 1 is turned on.

  Next, an outline of speed adjustment between the running speed of the transfer belt 8 and the recording paper conveyance speed by the fixing roller pair 14 at the time of transferring each color toner image by each color photosensitive drum 4 will be described. FIG. 14 is a flowchart showing the speed adjustment process. In this speed adjustment, when the recording paper is carried from the transfer belt 8 to the nip portion of the fixing roller pair 14, the traveling speed of the transfer belt 8 (recording paper conveyance speed by the transfer belt 8) and the recording paper conveyance by the fixing roller pair 14. This is to prevent fluctuations in the running speed of the transfer belt 8 (recording paper conveyance speed by the transfer belt 8) due to the speed difference from the speed.

  First, the running speed of the transfer belt 8 and the recording paper conveyance speed by the fixing roller pair 14 are detected (S121, S122), and the recording paper conveyance speed by the transfer belt 8 is a predetermined speed than the recording paper conveyance speed by the fixing roller pair 14. It is possible to maintain the relationship of slightly higher speed while maintaining the difference (for example, it is preferable that the running speed of the transfer belt 8 exceeds the recording paper conveyance speed by the fixing roller pair 14 by about 0.2% in the experiment). Is determined (S123). If the predetermined speed difference is not maintained (NO in S123), the fixing motor is set so that the recording paper conveyance speed by the transfer belt 8 and the recording paper conveyance speed by the fixing roller pair 14 have the predetermined speed difference. The rotational speed of 120 is corrected (S124). That is, when the running speed of the transfer belt 8 (recording paper transport speed by the transfer belt 8) is a high speed having a speed difference exceeding the predetermined speed difference with respect to the recording paper transport speed by the fixing roller pair 14, The rotation speed of the fixing motor 120 is increased. When the running speed of the transfer belt 8 (recording paper transport speed by the transfer belt 8) is a slow speed that does not have the above-described predetermined speed difference with respect to the recording paper transport speed by the fixing roller pair 14, the rotation of the fixing motor 120 is performed. Set the speed slower. If these speed differences are maintained (YES in S123), it is not necessary to correct the rotation speed of the fixing motor 120, and the process ends. The traveling speed of the transfer belt 8 is detected in the same manner as in FIGS. The detection of the recording paper conveyance speed by the fixing roller pair 14 is performed as follows.

  FIG. 15 is a flowchart showing a process for detecting the recording paper conveyance speed by the fixing roller pair 14, and FIG. 16 is a schematic side view showing a fixing roller sensor disposed in the vicinity of the fixing roller pair 14. When the fixing roller sensor 140 detects the leading edge of the recording sheet (YES in S131), the timer 136 starts counting (S132). When the fixing roller sensor 140 detects the trailing edge of the recording sheet (YES in S133), the count of the timer 136 is stopped (S134), and the count value t8 of the timer 136 is acquired (S135). Subsequently, the recording size information is acquired (S136), and the length in the conveyance direction of the recording paper being conveyed is confirmed. Based on the timer count value t8 and the recording paper size information (recording paper length in the transport direction), the recording paper transport speed by the fixing roller pair 14 is calculated (S137).

  It should be noted that whether or not to adjust the traveling speed of the transfer belt 8 and the recording paper conveyance speed by the fixing roller pair 14 is determined based on the same process as that shown in FIG. Good.

  As described above, according to the printer 1, the registration motor 133 is driven and controlled so that the recording paper conveyance speed by the registration roller 17 is slightly higher than the traveling speed of the transfer belt 8 while maintaining a predetermined speed difference. The difference between the running speed of the transfer belt 8 and the recording paper conveyance speed by the registration rollers 17 is kept substantially constant, and the recording paper conveyance speed by the registration rollers 17 when the recording paper is carried from the registration rollers 17 to the transfer belt 8. The fluctuation of the running speed of the transfer belt 8 due to the influence of the above is reduced. Further, since the difference between the running speed of the transfer belt 8 and the conveyance speed of the recording paper by the registration roller 17 is kept substantially constant, when the recording paper is carried into the transfer belt 8, the transfer belt 8 and the registration roller 17 When the recording paper is bent between the two to absorb the speed difference between the traveling speed of the transfer belt 8 and the recording paper carry-in speed by the registration roller 17, the speed difference is absorbed even if the amount of bending of the recording paper is small. Is possible. As a result, regardless of the distance between the transfer belt 8 and the registration roller 17 and the paper quality of the recording paper, the recording paper is conveyed to the photosensitive drum 4 of each color by the transfer belt 8 at a stable speed. In this case, misalignment of toner images of each color is prevented.

  The present invention is not limited to the configuration of the above embodiment, and various modifications can be made. For example, in the above-described embodiment, the speed adjustment between the traveling speed of the transfer belt 8 and the recording paper conveyance speed by the registration roller 17 at the time of transferring each color toner image, and the recording paper conveyance by the fixing belt pair 14 by the traveling speed of the transfer belt 8. The speed adjustment is performed when the recording paper counter 143 reaches a predetermined value or when the amount of change in temperature and humidity in the printer 1 reaches a predetermined value. It may be performed each time the recording paper conveyance from the registration roller 17 to the transfer belt 8 is started when the color misregistration correction process is performed or when image formation is performed.

  In the above embodiment, the registration motor 133 is driven and controlled so that the rotational speed difference of the suction roller 18 before and after the recording paper is carried between the transfer belt 8 and the suction roller 18 is eliminated. In the process of adjusting the traveling speed and the recording paper conveyance speed by the registration roller 17 (FIG. 11), the rotation speed of the suction roller 18 is detected in a state where the application of the suction roller bias and the bias of the transfer roller is stopped. However, the rotation speed of the suction roller 18 is reduced in a state where the application of the suction roller bias and the transfer roller bias is reduced, or in a state where the application of either the suction roller bias or the transfer roller bias is stopped. It may be detected.

  Further, in the above embodiment, when the speed adjustment of the running speed of the transfer belt 8 at the time of transferring each color toner image and the recording paper conveyance speed by the registration roller 17 is performed, by controlling the rotation speed of the registration motor 133, The recording paper conveyance speed by the registration roller 17 is set to be slightly faster than the running speed of the transfer belt 8 while maintaining a predetermined speed difference. The speed adjustment is performed by controlling the rotation speed of the transfer belt drive motor 125. May be performed.

  In the above embodiment, when the speed adjustment of the running speed of the transfer belt 8 at the time of transferring the color toner images and the recording paper conveyance speed by the fixing roller pair 14 is performed, the rotation speed of the fixing motor 120 is controlled. The traveling speed of the transfer belt 8 is set to be slightly faster than the recording paper transport speed by the fixing roller pair 14 while maintaining a predetermined speed difference. By controlling the rotational speed of the transfer belt drive motor 125, Speed adjustment may be performed.

  Further, a guide member that suppresses the recording paper being conveyed from shaking up and down or left and right at a position where the first sensor 135a and the second sensor 135b for detecting the leading edge and the trailing edge of the recording paper are disposed. The leading and trailing edges of the recording paper may be accurately detected by the first sensor 135a and the second sensor 135b by regulating the posture of the recording paper being provided and being conveyed.

  In the above embodiment, the registration motor 133 or the transfer belt drive motor 125 is driven and controlled so that the recording paper conveyance speed by the registration roller 17 is slightly higher than the running speed of the transfer belt 8 while maintaining a predetermined speed difference. However, in this drive control, the time required for the recording paper conveyed by the registration roller 17 to move a certain distance and the time required for the transfer belt 8 to move a certain distance are predetermined. It also includes driving control of the registration motor 133 or the transfer belt drive motor 125 so as to have a time difference.

  In the above embodiment, the transfer belt drive motor 125 or the fixing motor 120 is set so that the running speed of the transfer belt 8 is slightly higher than the recording paper transport speed by the fixing roller pair 14 while maintaining a predetermined speed difference. The drive control is performed. For this drive control, the time required for the recording paper conveyed by the fixing roller pair 14 to move a certain distance and the time required for the transfer belt 8 to move a certain distance are used. And driving control of the fixing motor 120 or the transfer belt driving motor 125 so that there is a predetermined time difference.

1 is a schematic diagram illustrating an example of a schematic configuration of an image forming apparatus according to the present invention. 1 is a block diagram illustrating an example of a schematic configuration of an image forming apparatus according to the present invention. 10 is a flowchart of a speed adjustment process between a transfer belt running speed at the time of transferring each color toner image and a recording paper conveyance speed by a registration roller. 6 is a flowchart of a process for detecting the transfer belt traveling speed in the speed adjustment between the transfer belt traveling speed and the recording paper transport speed by the registration rollers. FIG. 6 is a diagram illustrating a state of registration mark formation on the transfer belt when the transfer belt traveling speed is detected. 10 is a flowchart illustrating another example of processing for detecting a transfer belt traveling speed. 12 is a flowchart illustrating still another example of processing for detecting a transfer belt traveling speed. 6 is a flowchart illustrating processing for detecting a recording paper conveyance speed by a registration roller in a speed adjustment between a transfer belt traveling speed and a recording paper conveyance speed by a registration roller. 12 is a flowchart showing another example of speed adjustment processing between the transfer belt running speed and the recording paper transport speed by the registration rollers when transferring the color toner images. FIG. 6 is a schematic side view showing a first sensor and a second sensor disposed between a transfer belt and a registration roller. 14 is a flowchart showing still another example of speed adjustment processing between the transfer belt running speed and the recording paper conveyance speed by the registration rollers when transferring the color toner images. 6 is a flowchart showing processing when a warning is given for replacement of a registration roller in accordance with the rotation speed correction amount of the registration motor. 10 is a flowchart showing processing for determining whether or not to adjust the speed of the transfer belt at the time of transferring each color toner image and the recording paper conveyance speed by the registration rollers according to the surrounding environment. 6 is a flowchart of a speed adjustment process between a running speed of a transfer belt and a recording paper conveyance speed by a pair of fixing rollers when transferring toner images of respective colors. 6 is a flowchart showing a process for detecting a recording paper conveyance speed by a fixing roller pair in a speed adjustment between a transfer belt traveling speed and a recording paper conveyance speed by a fixing roller pair. FIG. 4 is a schematic side view showing a fixing roller sensor disposed in the vicinity of a fixing roller pair.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printer 4 Photoconductor drum 8 Transfer belt 9 Transfer roller 24 Driven roller 14 Fixing roller pair 17 Registration roller 18 Adsorption roller 20B, 20Y, 20M, 20C Image formation unit 110 Control part 114 Transfer bias part 120 Fixing motor 120a Driver 123 Registration motor 125 Transfer Belt Drive Motor 125a Driver 126 Adsorption Roller Bias Unit 127 Operation Unit 133 Registration Motor 133a Driver 135a First Sensor 135b Second Sensor 136 Timer 137 Registration Sensor 140 Fixing Roller Sensor 141 Adsorption Roller Sensor 142 Adsorption Roller Mark Sensor 143 Recording Paper Counter 145 Temperature / humidity sensor 146 Driven roller sensor

Claims (1)

An image forming apparatus that transports a recording sheet conveyed by a registration roller to an image carrier provided for each color by a transfer belt and transfers a toner image on each image carrier onto the recording sheet to form an image. There,
Transfer belt driving means for running the transfer belt;
Registration roller driving means for rotationally driving the registration roller;
Transfer belt speed detecting means for detecting the running speed of the transfer belt;
A conveyance speed detecting means for detecting a conveyance speed of a recording sheet conveyed from the registration roller to the transfer belt;
The registration roller driving is performed so that the conveyance speed of the recording paper detected by the conveyance speed detection unit is higher than the traveling speed of the transfer belt detected by the transfer belt speed detection unit while maintaining a predetermined speed difference. Or a control means for drivingly controlling at least one of the transfer belt driving means,
The transfer belt speed detecting unit is an image forming apparatus that detects a running speed of the transfer belt based on a rotation speed of a suction roller disposed to face the transfer belt.

Images