JP4326859B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
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 in particular, due to fluctuations in the running speed of a transfer belt when a recording sheet is carried from a registration roller to the transfer belt. In addition, the present invention relates to a technique for preventing the occurrence of misalignment in the superposition of toner images of respective colors.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there are image forming apparatuses such as copiers and printers that form images by transferring toner images from an image carrier for each color and superimposing them. In this image forming apparatus, if there is a speed difference between the traveling speed of the transfer belt that transports the recording paper to the image carrier and the recording paper transport speed by the registration roller that transports the recording paper from the paper feed mechanism toward the transfer belt. Since the running speed of the transfer belt fluctuates due to the influence of the conveyance speed of the recording paper carried into the transfer belt, the recording paper is not conveyed to the image carrier of each color at an appropriate speed, and each color toner image is transferred. In some cases, the color toner images may be misaligned.
[0003]
Therefore, for example, as shown in Patent Document 1, the laser beam P irradiated from the image writing unit 20 is reflected on the transfer unit 51 by the laser beam control units 22 and 24 and is reflected by the transfer unit 51. An image forming apparatus that improves the image quality by receiving the reflected light of P by the light receiving means 28, detecting the Doppler frequency of the reflected light, and using the speed of the transfer means calculated based on the Doppler frequency for each part speed control. Has been proposed.
[0004]
[Patent Document 1]
JP-A-8-137293
[0005]
[Problems to be solved by the invention]
However, according to the image forming apparatus disclosed in Patent Document 1, in addition to the configuration of the image writing means 20 and the like originally provided for image formation, the laser light control means 22 for detecting the speed of the transfer means. 24, the light receiving means 28, etc., the configuration becomes complicated and the manufacturing cost increases.
[0006]
The present invention has been made to solve the above-described problems, and enables the speed adjustment between the transfer belt and the registration roller at a low cost without complicating the configuration, so that the recording paper from the registration roller to the transfer belt can be obtained. An object of the present invention is to provide an image forming apparatus capable of preventing color misregistration at the time of transfer of each color toner image onto a recording sheet due to a change in speed of the transfer belt at the time of carry-in.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, a toner image is transferred onto a recording sheet delivered from a registration roller to a transfer belt via an image carrier for each color. directly In an image forming apparatus that forms an image by transferring,
Registration roller driving means for rotating the registration roller at a predetermined speed;
Transfer belt driving means for running the transfer belt at a predetermined speed;
Before the recording paper is delivered to the transfer belt directly Mark forming means for forming a plurality of marks at regular intervals on the transfer belt;
A plurality of marks formed on the transfer belt by the mark forming means, From the registration roller Before or after the recording paper is delivered to the transfer belt Was One of the later non-delivery periods, From the registration roller Recording paper is delivered to the transfer belt. While Mark detection means for detecting the delivery period;
The mark detection interval in the non-delivery period and the delivery period is obtained from the mark detection signal detected by the mark detection means, and the fluctuation amount of the mark detection interval in the delivery period with respect to the non-delivery period is calculated from the mark detection interval of both periods. Mark detection interval fluctuation calculating means;
And a control unit that controls at least one of the registration roller driving unit and the transfer belt driving unit to eliminate the mark detection interval variation calculated by the mark detection interval variation calculating unit.
[0008]
When the recording paper is transported from the registration roller to the transfer belt, if the recording paper transport speed of the registration roller is faster than the recording paper transport speed of the transfer belt, the recording paper pushes the transfer belt and the transfer belt traveling speed increases. When the recording paper transport speed of the registration rollers is slower than the recording paper transport speed of the transfer belt, the transfer belt is pulled by the recording paper having a low transport speed, and the travel is hindered, and the transfer belt travel speed increases. Therefore, due to the difference between the recording paper transport speed of the registration rollers and the recording paper transport speed of the transfer belt, the speed fluctuation occurs in the transfer belt when the recording paper is transported to the transfer belt.
[0009]
For this reason, when a plurality of marks are formed on the transfer belt at regular intervals, the mark interval varies between a state in which the recording paper is applied to the transfer belt and a state in which the recording paper is not applied. The present invention detects the variation in the mark interval and controls the speed of at least one of the transfer belt driving unit or the registration roller driving unit to eliminate the variation in the mark interval, thereby causing the recording paper to be carried in. This eliminates fluctuations in the recording belt conveyance speed of the transfer belt (traveling speed of the transfer belt) and prevents the occurrence of misalignment when the color images are superimposed.
[0010]
Thus, for example, the mark forming means is composed of an image forming mechanism such as an image carrier, the mark detecting means is composed of a photosensor for detecting density, and the mark interval detecting means and the control means are used for the entire image forming apparatus. If the image forming apparatus includes a control unit that controls the operation of the image forming apparatus, the structure of the present invention can be realized by the mechanism originally provided in the image forming apparatus for image formation. Therefore, it is possible to adjust the recording paper conveyance speed of the registration roller or the recording paper conveyance speed of the transfer belt at low cost, and to prevent color misregistration at the time of transferring each color toner image.
[0011]
The invention according to claim 2 is the image forming apparatus according to claim 1, wherein the transfer belt driving means includes a transfer belt driving roller for rotating the endless transfer belt in a stretched state. And the interval between the marks generated by the mark forming means is equal to the circumferential length of the transfer belt drive roller.
[0012]
According to this configuration, the interval between the marks generated by the mark forming means is set equal to the circumference of the transfer belt drive roller. For example, the transfer belt is caused by the eccentricity of the transfer belt drive roller. Due to the difference between the recording paper transport speed of the registration roller and the recording paper transport speed of the transfer belt without being affected by the speed fluctuation of the transfer belt that occurs in the rotation cycle of the drive roller, when the recording paper is transported to the transfer belt The resulting change in the speed of the transfer belt can be accurately detected by the mark interval detection means as a change in the interval between the marks formed on the transfer belt. Thereby, it is possible to reliably suppress the positional deviation when the color toner images are superimposed due to the speed fluctuation of the transfer belt that occurs when the recording paper is carried into the transfer belt.
[0013]
The invention according to claim 3 is the image forming apparatus according to claim 1 or 2, wherein a mark formation start time on the transfer belt by the mark forming unit is conveyed by the registration roller. The mark formed on the transfer belt by the mark forming means can reach the mark detecting means before the recording paper to reach the transfer belt.
[0014]
According to this configuration, since the mark on the transfer belt reaches the mark detection unit before the recording paper is carried into the transfer belt, the mark detection unit starts from the point before the recording paper arrives on the transfer belt. A plurality of marks on the transfer belt can be detected.
[0015]
According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the third aspect, wherein the recording paper conveyed by the registration rollers is transferred to the transfer belt when the mark is formed on the transfer belt by the mark forming means. It ends before it reaches the belt.
[0016]
According to this configuration, mark formation on the transfer belt is completed by the mark forming means before the recording paper reaches the transfer belt and the running speed of the transfer belt fluctuates. Can be accurately formed at uniform intervals. For this reason, fluctuations in the running speed of the transfer belt before and after the recording paper reaches the transfer belt can be accurately detected as fluctuations in the intervals between the marks on the transfer belt that move with the transfer belt.
[0017]
The invention according to claim 5 is the image forming apparatus according to any one of claims 1 to 4, wherein the mark forming means has a temperature change around the image forming apparatus equal to or higher than a reference value. The mark is formed when the image forming apparatus is turned on, when the image forming apparatus is turned on, or when the number of recording sheets onto which the toner image has been transferred reaches a predetermined number.
[0018]
According to this configuration, by setting the period during which the mark is formed, it is possible to suppress the toner consumption related to the mark formation and reduce the processing load on the control unit that controls the speed of the transfer belt driving unit or the registration roller driving unit. Can do.
[0019]
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the mark detection means is a photosensor for density detection.
[0020]
According to this configuration, the speed control of the transfer belt driving unit or the registration roller driving unit can be easily and inexpensively performed by using the density detection photosensor conventionally used for toner patch density detection as the mark detection unit. be able to.
[0021]
A seventh aspect of the present invention is the image forming apparatus according to any one of the first to sixth aspects, wherein the mark forming means comprises the image carrier.
[0022]
According to this configuration, since the image carrier originally provided in the image forming apparatus for image formation is used as the mark forming unit, the image forming apparatus according to the present invention can be manufactured at low cost without complicating the configuration. be able to.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1A is a schematic view showing an outline of an image forming apparatus according to the present invention in a side view, and FIG. 1B is a plan view schematically showing a state of speed detection mark formation and recording paper conveyance on a transfer belt. is there. As shown in FIG. 1A, a printer (an example of an image forming apparatus) 1 includes image forming units 2M, 2C, 2Y, and 2K for magenta, cyan, yellow, and black colors, respectively. Each of the image forming units 2M, 2C, 2Y, and 2K is provided with a photosensitive drum (image carrier) 3 made of a-Si (amorphous silicon) or the like, and rotates in the direction of an arrow in the figure. . The photosensitive drum 3 is uniformly charged by the charging unit 4, 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) 5 to the photosensitive drum 3. An electrostatic latent image is formed by irradiating the surface of the toner, and toner supplied from the developing device 6 adheres to the electrostatic latent image to form a toner image. The photosensitive drum 3 includes a cleaning mechanism 7 that removes residual toner and the like on the photosensitive drum 3.
[0024]
A transfer belt 8 for conveying the recording paper is disposed below the photosensitive drums 3 for the respective colors. The transfer belt 8 is pressed against each photosensitive drum 3 by the transfer roller 9 and is driven to rotate at a predetermined speed (predetermined speed) by a motor (not shown) or the like (transfer belt drive roller, The transfer belt drive means) 10 and 11 are driven to rotate endlessly in the forward direction of the rotation direction of the photosensitive drum 3.
[0025]
On the upstream side of the transfer belt 8 in the recording paper conveyance direction, a registration roller 12 is provided for adjusting the timing of the image transfer operation by each photoconductive drum 3 and the transfer roller 9 and the paper feed operation to the transfer belt 8. ing. The registration roller 12 adjusts the timing of a recording sheet conveyed from a sheet feeding cassette (not shown) through a sheet conveying path, and then is a photosensitive drum on the transfer belt 8 at a predetermined speed (predetermined speed). 3 and the transfer belt 8. While the recording paper is being conveyed between the photosensitive drums 3 and the transfer belt 8, the toner images of the respective colors on the surfaces of the photosensitive drums 3 are successively transferred onto the recording paper by applying a transfer bias of the transfer roller 9. . An adsorption roller 13 for electrostatically adsorbing the recording paper to the transfer belt 8 is provided at the most upstream portion of the transfer belt 8 in the conveyance direction of the recording paper.
[0026]
The recording paper on which the toner images are transferred from all the photosensitive drums 3 and superimposed is conveyed to a fixing device (not shown) to fix the toner images and form a color image. The recording paper that has passed through the fixing device is discharged to a discharge portion provided on the upper surface of the printer 1 or the like.
[0027]
As shown in FIG. 1B, the photosensitive drum 3 of the image forming unit 2Y of the printer 1 also functions as a mark forming unit that forms a mark m for detecting the running speed of the transfer belt 8 on the transfer belt 8. . The photosensitive drum 3 that functions as the mark forming means may be the photosensitive drum 3 provided in any of the image forming units 2M, 2C, 2Y, and 2K, but in this embodiment, the photosensitive drum 3 of the image forming unit 2Y. 3.
[0028]
A mark detection sensor (mark detection means) 15 including a reflection type photosensor is provided above the transfer belt 8 on the further downstream side than the image forming unit 2K disposed on the most downstream side in the recording paper conveyance direction. Is provided. The mark detection sensor 15 also functions as a density detection sensor. In the present invention, the mark detection sensor 15 detects a plurality of marks m formed on the transfer belt 8 by the photosensitive drum 3 of the image forming unit 2Y. It also functions as a sensor. As shown in FIG. 1B, the mark detection sensor 15 is disposed above a position where a mark for detecting a traveling speed is formed by the photosensitive drum 3 of the image forming unit 2Y. A cleaning mechanism 16 is provided at a position that has passed through the mark detection sensor 15 and the transfer belt drive roller 11 to remove a running speed detection mark m formed on the transfer belt 8.
[0029]
In the printer 1 according to the present invention, a plurality of marks m formed on the transfer belt 8 by the photosensitive drum 3 of the image forming unit 2Y are detected by the mark detection sensor 15, and based on the detection result, each mark is detected. By calculating the interval, and when the interval of each mark fluctuates before and after the recording paper is carried into the transfer belt 8, by controlling the rotational driving speed of the registration roller 12 according to the ratio of the mark interval before and after the change, Color misregistration correction processing (processing for preventing occurrence of misregistration in the superposition of the color toner images when the toner images are transferred from the image forming units 2M, 2C, 2Y, and 2K to the recording paper) is performed.
[0030]
2 is an example of a functional block diagram for color misregistration correction control by the printer 1, FIG. 3 is a diagram showing an example of a plurality of marks m formed on the transfer belt 8, and FIG. FIG. 8B is a diagram illustrating an output waveform of the mark detection sensor 15 when the running speed of the transfer belt 8 does not change before and after the recording paper is carried into the transfer belt. FIG. It is a figure which shows the output waveform of the mark detection sensor 15 when a speed fluctuates.
[0031]
As shown in FIG. 2, the printer 1 includes a correction management unit 20, a sensor control unit 21, a correction calculation unit 22, a paper feed control unit 23, a mark generation unit (mark formation unit) 24, and an image formation unit control unit (mark Forming means) 25 and the like.
[0032]
The correction management unit 20 determines whether or not to perform the color misregistration correction process. Ambient temperature changes of the image forming units 2M, 2C, 2Y, and 2K, the transfer belt 8, the transfer roller 9, and the like are greater than a reference value. When the printer 1 is turned on, when the number of printed sheets reaches a predetermined number (for example, 100 sheets), or when a color misregistration correction execution instruction is input manually by the user, Allows execution of color misregistration correction processing.
[0033]
The sensor control unit 21 is connected to the mark detection sensor 15 and includes a sensor driving unit 211 and a sampling processing unit 212 (mark interval detection means). The sensor driving unit 211 controls driving of the mark detection sensor 15. The mark detection sensor 15 outputs a waveform indicating a peak as shown in FIGS. 4A and 4B in response to detection of each mark m on the transfer belt 8. The sampling processing unit 212 has a counter function for performing A / D conversion processing of the detected waveform obtained from the mark detection sensor 15 and measuring time for measuring the mark position (mark arrival time).
[0034]
The correction calculation unit 22 includes a mark interval calculation unit (mark interval detection unit) 221 and a registration roller speed adjustment value calculation unit (control unit) 222. The mark interval calculation unit 221 calculates the interval between marks based on the processing result by the sampling processing unit 212. That is, each peak position is detected from data indicating the detection waveform of the mark detection sensor 15, and the arrival time of each peak is obtained from each peak position and the count value input from the counter of the sampling processing unit 212. Based on the difference between the arrival times, the time from when one mark is detected until the next mark is detected is calculated.
[0035]
The registration roller speed adjustment value calculation unit 222 compares the time calculated from the detection of one mark to the detection of the next mark calculated by the mark interval calculation unit 221, and changes to a value indicating each time. If there is, a new driving speed (registration roller driving speed adjustment value) of the registration roller 12 is calculated from the ratio of the values. For example, when the time from mark to mark is 10% longer than the mark interval calculated so far (as shown in FIG. 4B, when the mark interval that was 100 msec is changed to 110 msec, etc.) ), It is assumed that the speed of the registration roller is 9.1% slower than the speed of the transfer belt 8, and based on this calculation result, the rotational driving speed of the registration roller is 110% (100 msec / 90.9 msec = 1.10) ). Thereby, the recording paper conveyance speed by the transfer belt 8 and the recording paper conveyance speed by the registration rollers are made the same.
[0036]
The paper feed control unit 23 includes a registration clutch control unit 231 and a registration motor control unit (control means) 232. The registration clutch control unit 231 controls the operation of a registration clutch 29 that turns on / off transmission of rotational driving force from the registration motor (registration motor driving means) 28 to the registration roller 12. The registration motor control unit 232 controls driving of the registration motor 28, and the driving speed of the registration roller 12 is variable based on the registration roller driving speed adjustment value calculated by the registration roller speed adjustment value calculation unit 222. Let
[0037]
The mark generation unit 24 generates image data of a plurality of marks to be formed on the transfer belt 8 by the photosensitive drum 3 of the image forming unit 2Y. For example, as shown in FIG. 3, the mark has a long shape extending in the direction of the rotation axis of the photosensitive drum 3, and has a length of about 15 mm and a width of about 2 mm. The interval (Int) between the marks on the transfer belt 8 is the same as the circumference of the transfer belt drive roller 10. For example, when the circumference of the transfer belt drive roller 10 is 10 mm, the interval between the marks is as follows. Is also 10mm.
[0038]
The image forming unit controller 25 controls operation of the image forming units 2M, 2C, 2Y, and 2K. The image forming unit control unit 25 drives and controls the image forming units 2M, 2C, 2Y, and 2K based on image data input from an external personal computer or the like during normal printing, and performs the color misregistration correction process. In this case, the image forming unit 2Y is controlled based on the mark image data input from the mark generation unit 24.
[0039]
Next, color misregistration correction processing by the printer 1 will be described. FIG. 5 is a flowchart showing color misregistration correction processing by the printer 1. When changes in the ambient temperature of the image forming units 2M, 2C, 2Y, 2K, the transfer belt 8, the transfer roller 9, and the like become a certain value or more, when the printer 1 is turned on, the number of prints is a predetermined number (for example, 100 When a preset condition is satisfied, such as when the image has reached the number of sheets, image data of the mark m is generated by the mark generation unit 24 (S1), and the image data of this mark is sent to the image forming unit 2Y. The image forming unit 2Y forms a plurality of mark images on the transfer belt 8 from the photosensitive drum 3 based on the image data sent from the mark generating unit 24 under the control of the image forming unit control unit 25 (S2). ).
[0040]
Subsequently, an operation of reading a plurality of marks by the mark detection sensor 15 is started (S3). Here, when the plurality of marks formed on the transfer belt 8 reach the mark reading position of the mark detection sensor 15 as the transfer belt 8 travels, the recording paper conveyed by the registration roller 12 is transferred to the transfer belt. It is set to be before the time of reaching 8. As a result, the mark m is detected from a point in time before the recording sheet is conveyed onto the transfer belt 8 and the traveling speed of the transfer belt 8 is likely to fluctuate.
[0041]
After completion of the mark transfer to the transfer belt 8 by the photosensitive drum 3 of the image forming unit 2Y (S4) and after the mark reading by the mark detection sensor 15 has already started, the operation control by the registration clutch control unit 231 is performed. Thus, the rotational driving force of the registration motor 28 is transmitted to the registration roller 12 (S5). Thus, the mark is detected by the mark detection sensor 15 before and after the recording paper is carried into the transfer belt 8.
[0042]
As described above, after the mark detection sensor 15 detects the mark before and after conveying the recording paper to the transfer belt 8, the mark detection by the mark detection sensor 15 is finished (S6). For example, the marks on the transfer belt 8 are detected 10 to 11 before and after the recording paper is conveyed onto the transfer belt 8. Based on the mark detection result by the mark detection sensor 15, the mark interval calculation unit 221 calculates each mark interval (time from detection of one mark to detection of the next mark) (S7).
[0043]
As shown in FIG. 4A, when the mark interval is constant without any change (NO in S8), it is assumed that there is no change in the running speed of the transfer belt 8 before and after the recording paper is carried into the transfer belt 8. The process ends without adjusting the rotation speed of the registration roller 12.
[0044]
If there is a change in each mark interval (YES in S8), the registration roller speed adjustment value calculation unit 222 calculates a rotation speed adjustment value of the registration roller 12 based on the ratio of the mark intervals before and after the change (S9). . For example, as shown in FIG. 5B, when the time from the detection of the peak of a certain mark to the detection of the peak of the next mark varies from 100 msec to 110 msec, and the mark interval is increased by 10%. Suppose that the recording paper conveyance speed by the registration roller 12 is 9.1% slower than the recording paper conveyance speed of the transfer belt 8, and based on this detection result, the rotational driving speed of the registration roller is 110.0% ( The speed is adjusted to 100 msec / 90.9 msec = 1.10) (S10). That is, a speed that is 110% of the rotational driving speed of the registration roller up to that time is set as the registration roller speed adjustment value. By setting the rotation speed of the registration roller 12 to this registration roller speed adjustment value, the recording paper conveyance speed by the transfer belt 8 and the recording paper conveyance speed by the registration roller are made the same.
[0045]
As described above, according to the printer 1 according to the present invention, the transfer is performed by a mechanism such as the photosensitive drum 3, the developing device 6, and the density correction sensor originally provided in the printer 1 for image formation and density correction. Since the recording paper conveyance speed by the belt 8 and the recording by the registration roller 12 can constitute a mechanism for adjusting the conveyance speed, color misregistration at the time of transferring each color toner image can be prevented at low cost without complicating the configuration of the printer 1.
[0046]
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 rotational driving speed of the registration roller 12 is adjusted when the mark interval on the transfer belt 8 varies, but the rotational driving speed of the transfer belt driving rollers 10 and 11 is adjusted. (And image forming speeds of the image forming units 2M, 2C, 2Y, and 2K) may be adjusted.
[0047]
Further, the mark forming means may not be composed of the photosensitive drum 3 of the image forming units 2M, 2C, 2Y, and 2K, but a mechanism separate from the photosensitive drum 3 may be provided in the printer 1.
[0048]
Further, in the above embodiment, when the interval between the marks on the transfer belt 8 detected by the mark detection sensor 15 fluctuates before and after the recording paper is carried into the transfer belt 8, the rotational driving speed of the registration roller 12 is controlled. However, the rotational drive speeds of the transfer belt drive rollers 10 and 11 may be controlled, or the rotational drive speeds of both the registration roller 12 and the transfer belt drive rollers 10 and 11 may be controlled. May be.
[0049]
【The invention's effect】
As described above, according to the first aspect of the present invention, a plurality of marks are formed on the transfer belt at regular intervals, and fluctuations in the mark interval between the state in which the recording paper is on the transfer belt and the state in which the recording paper is not on the transfer belt are achieved. By detecting the minute and controlling the speed of either the transfer belt driving means or the registration roller driving means so that the fluctuation of the mark interval is eliminated, the recording paper conveyance speed by the registration roller and the recording by the transfer belt are controlled. By making the paper conveyance speed the same, it is possible to prevent a positional deviation from occurring when the color images are superimposed.
[0050]
For example, the mark forming means is composed of an image forming mechanism such as an image carrier, the mark detecting means is composed of a photosensor for detecting density, and the mark interval detecting means and the control means are used to control the operation of the entire image forming apparatus. If the image forming apparatus includes a control unit that controls the image forming apparatus, the structure of the present invention can be realized by the mechanism originally provided in the image forming apparatus for image formation, so that the structure of the image forming apparatus is not complicated. By adjusting the recording paper conveyance speed of the registration rollers or the recording paper conveyance speed of the transfer belt at low cost, it is possible to prevent color misregistration at the time of transferring each color toner image.
[0051]
According to the second aspect of the present invention, the interval between the marks generated by the mark forming means is set equal to the circumference of the transfer belt drive roller. Transfer due to the difference between the recording paper transport speed of the registration roller and the recording paper transport speed of the transfer belt without being affected by the speed fluctuation of the transfer belt that occurs in the rotation cycle of the transfer belt drive roller due to eccentricity etc. The change in the speed of the transfer belt that occurs when the recording paper is carried into the belt can be accurately detected by the mark interval detection means as the change in the interval between the marks formed on the transfer belt. Thereby, it is possible to reliably suppress the positional deviation when the color toner images are superimposed due to the speed fluctuation of the transfer belt that occurs when the recording paper is carried into the transfer belt.
[0052]
According to the third aspect of the present invention, since the mark on the transfer belt reaches the mark detection means before the recording paper is carried into the transfer belt, the recording paper before the recording paper reaches the transfer belt. From the time, a plurality of marks on the transfer belt can be detected by the mark detection means.
[0053]
According to the fourth aspect of the present invention, mark formation on the transfer belt by the mark forming means is completed before the recording paper reaches the transfer belt and the running speed of the transfer belt fluctuates. The marks can be accurately formed at uniform intervals on the transfer belt. For this reason, fluctuations in the running speed of the transfer belt before and after the recording paper reaches the transfer belt can be accurately detected as fluctuations in the intervals between the marks on the transfer belt that move with the transfer belt.
[0054]
According to the fifth aspect of the present invention, the control means for controlling the speed of the transfer belt driving means or the registration roller driving means by setting the period during which the mark is formed, thereby suppressing the toner consumption related to the mark formation. The processing load on can be reduced.
[0055]
According to the invention described in claim 6, the transfer belt driving means or the registration roller can be simply and inexpensively used by using the density detection photosensor conventionally used for toner patch density detection as the mark detection means. Speed control of the driving means can be performed.
[0056]
According to the seventh aspect of the present invention, since the image carrier originally provided in the image forming apparatus for image formation is used as the mark forming means, the configuration of the image forming apparatus according to the present invention is complicated. It can be manufactured at low cost without the need to make it.
[Brief description of the drawings]
FIG. 1A is a schematic diagram showing an outline of an image forming apparatus according to the present invention in a side view, and FIG. 1B is a plan view schematically showing a state of speed detection mark formation and recording paper conveyance on a transfer belt. FIG.
FIG. 2 is an example of a functional block diagram for color misregistration correction control by a printer according to the present invention.
FIG. 3 is a diagram illustrating an example of a plurality of marks m formed on a transfer belt.
4A is a diagram showing an output waveform of a mark detection sensor when the running speed of the transfer belt is not changed before and after the recording paper is carried into the transfer belt, and FIG. 4B is a drawing of the recording paper into the transfer belt. It is a figure which shows the output waveform of a mark detection sensor when the running speed of a transfer belt fluctuates before and after.
FIG. 5 is a flowchart showing color misregistration correction processing by the printer according to the present invention.
[Explanation of symbols]
1 Printer (image forming device)
2M, 2C, 2Y, 2K image forming unit
3 Photosensitive drum
10, 11 Transfer belt driving roller (transfer belt driving means)
12 Registration roller
15 Mark detection sensor (mark detection means)
24 Mark generator (mark forming means)
25 Image forming unit controller (mark forming means)
28 Registration motor (registration motor drive means)
21 Sensor controller
211 Sensor drive unit
212 Sampling processing unit (mark interval detection means)
22 Correction calculator
221 Mark interval calculation unit (mark interval detection means)
222 Registration roller speed adjustment value calculation unit (control means)
23 Paper Feed Control Unit
231 Registration clutch controller
232 Registration motor controller (control means)

Claims (7)

In an image forming apparatus that forms an image by directly transferring a toner image to a recording paper delivered from a registration roller to a transfer belt via an image carrier for each color,
Registration roller driving means for rotating the registration roller at a predetermined speed;
Transfer belt driving means for running the transfer belt at a predetermined speed;
Mark forming means for directly forming a plurality of marks on the transfer belt at regular intervals before recording paper is transferred to the transfer belt;
A plurality of marks, one of the non-delivery period before or after the receive pass the recording paper to the transfer belt from the resist roller is passed, which is formed on the transfer belt by said mark forming means, wherein Mark detection means for detecting a transfer period while the recording paper is being transferred from the registration roller to the transfer belt;
The mark detection interval in the non-delivery period and the delivery period is obtained from the mark detection signal detected by the mark detection means, and the fluctuation amount of the mark detection interval in the delivery period with respect to the non-delivery period is calculated from the mark detection interval of both periods. Mark detection interval fluctuation calculating means;
Control means for controlling the driving speed of at least one of the registration roller driving means and the transfer belt driving means so as to eliminate the mark detection interval fluctuation calculated by the mark detection interval fluctuation calculating means. Image forming apparatus.   The transfer belt driving unit includes a transfer belt driving roller that rotates the endless transfer belt in a stretched state, and the interval between the marks generated by the mark forming unit is a circumferential length of the transfer belt driving roller. The image forming apparatus according to claim 1, wherein   The mark formation start time on the transfer belt by the mark forming means is such that the mark formed on the transfer belt by the mark forming means before the recording paper conveyed by the registration rollers reaches the transfer belt. The image forming apparatus according to claim 1, wherein a time when the mark detection unit can be reached is set.   The image forming apparatus according to claim 3, wherein the mark formation on the transfer belt by the mark forming unit is finished before the recording paper conveyed by the registration roller reaches the transfer belt.   The mark forming means has a predetermined number of recording sheets on which the toner image is transferred when the temperature change around the image forming apparatus becomes a reference value or more, or when the image forming apparatus is turned on. The image forming apparatus according to claim 1, wherein the mark is formed when the number reaches a predetermined number.   The image forming apparatus according to claim 1, wherein the mark detection unit is a photosensor for density detection.   The image forming apparatus according to claim 1, wherein the mark forming unit includes the image carrier.

Images