JP2007025407A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can set an appropriate compensation timing according to the state of use, while estimating temperature variation inside an optical scanning apparatus, regardless of the operating mode of the apparatus. <P>SOLUTION: When the counted value of a printed number of pages counter 17 reaches a compensation executing value, a control signal is transmitted from an integral control part 15 to each part of the image forming apparatus. A registration mark for each color is created, based on the control signal, and detected by a registration mark detecting sensor 11. The detected result is transmitted to a compensation operation part 16, an operation process is carried out and the result of the operation is stored within NVRAM18 as color-smearing compensation value data 21. The integral control part 15 carries out scanning position compensation, based on the color-smearing compensation data 21. The date for carrying out the scanning position compensation are stored to a compensation control counter 19. Furthermore, a reserved number of times for compensation which is executed thereafter is determined, based on the compensation executing number of times within a predetermined time and stored to a compensation control reserve counter 20. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on an image carrier using a plurality of scanning lines, and more particularly to a timing determination method for correcting the scanning position of each scanning line.

  In image forming apparatuses such as copying machines, printers, and facsimiles, color image forming apparatuses that form a color image by sequentially superimposing images of a plurality of colors are rapidly spreading. As such a color image forming apparatus, yellow, cyan, magenta, and black toner images are formed on separate photoconductors (image carriers) using a plurality of image forming units, and are recorded on a recording medium or an intermediate medium. A tandem type image forming apparatus that sequentially transfers onto a transfer body to form a full color image or a toner image of each color is sequentially formed on one photoconductor, and then sequentially transferred onto an intermediate transfer body to form a full color image. One-drum type image forming apparatus can be mentioned.

  In recent years, there has been an increasing demand for higher processing speed and higher image quality in image forming apparatuses. In the tandem type color image forming apparatus as described above, a method of forming a full color image using a plurality of image forming units. For this reason, there is a possibility that the color registration will be deteriorated due to deterioration in the alignment when the toner images of the respective colors formed by the respective image forming units are superimposed. The main causes of color misregistration are the position of each image forming unit itself or the components in the image forming unit due to changes in the internal temperature of the color image forming apparatus due to heat generated from a drive motor that rotates at high speed or heat generated from the fixing unit, or external force It is mentioned that the size changes slightly.

  In particular, in a scanning optical device that writes an image on a photosensitive member, it is necessary to rotate a motor that rotates a polygon mirror, which is a deflection device of a scanning system, with the recent increase in speed and resolution of an image forming apparatus. Occurs. As the motor speed increases in this manner, the internal temperature of the scanning optical device rises significantly due to the heat generated from the motor rotor and the circuit board that controls the motor rotation. For this reason, the optical members such as the semiconductor laser light source and the lens disposed therein are affected by the temperature change, and the scan start position may change after being mounted on the image forming apparatus.

  In order to prevent the occurrence of such color misregistration, conventionally, a color misregistration detection mark (hereinafter referred to as a registration mark) is formed on a transfer body conveyance unit or an intermediate transfer body, and this registration mark is detected by a detecting means. A method of detecting a color misregistration amount and executing a color misregistration correction process by changing a laser lighting timing or a lighting interval based on a detection result is employed.

  However, since this color misregistration correction process needs to be executed other than during normal image formation, for example, if correction is performed when a predetermined number of prints has been reached, the number of executions has been reached during continuous image formation. In this case, the image forming process is interrupted, and the waiting time of the user is increased. Further, if correction processing is performed at regular time intervals, the frequency of color misregistration varies depending on the use state and usage environment of the apparatus, so unnecessary correction processing is frequently performed or correction is required. Nevertheless, there is a problem that correction processing is not performed.

  In view of this, there has been proposed a method for correcting a scanning start position in each image forming unit in accordance with a temperature change in the image forming apparatus and preventing color misregistration. For example, Patent Document 1 discloses a frame that supports image forming means. Disclosed is an image forming apparatus capable of executing color misregistration correction processing at an appropriate timing as compared with the prior art by disposing a temperature detecting means near the image sensor and detecting the temperature inside the apparatus at a position closer to the image forming means. .

  However, the temperature rise inside the image forming apparatus does not necessarily coincide with the temperature rise inside the scanning optical apparatus. For example, only the heater of the fixing unit is heated during image formation in which both the scanning optical device and the fixing unit operate. Depending on the operation mode of the image forming apparatus, such as when the apparatus is on standby. Further, in a tandem type color image forming apparatus having a plurality of scanning optical devices, the drive time of each image forming unit differs depending on the image to be printed, so the temperature rise inside the scanning optical device also varies from unit to unit. For this reason, even if the color misregistration correction timing is set according to the temperature inside the apparatus by the method of Patent Document 1, it is difficult to make it coincide with the actual occurrence timing of the scan start position deviation.

  Further, a method of setting a correction timing by directly detecting a temperature rise inside the scanning optical device by providing a temperature detection means in the scanning optical device is also conceivable. For example, each image forming unit is provided with a scanning optical device. In this color image forming apparatus, it is necessary to install an expensive temperature sensor in each of the four scanning optical devices, which leads to an increase in cost. Furthermore, it is necessary to constantly monitor the temperature change of the four temperature sensors, which increases the burden on the control unit such as a CPU.

On the other hand, Patent Document 2 is provided with a speed detection means for detecting the speed of the transfer material conveyance body or the intermediate transfer body, and a table showing the relationship between the detected speed and the amount of color misregistration, and using the speed detection result. An image forming apparatus that performs color misregistration correction without requiring temperature measurement inside the apparatus is disclosed. However, although the temperature rise in the apparatus can be estimated to some extent from the speed of the transfer material conveyance body or the intermediate transfer body, it does not always coincide with the temperature rise inside the scanning optical device as described above. It was difficult to make the correction timing coincide with the actual occurrence timing of the scan start position deviation.
JP-A-8-286666 Japanese Patent Laid-Open No. 2002-221841

  In view of the above problems, the present invention provides an image forming apparatus capable of accurately estimating a temperature change inside a scanning optical apparatus regardless of the operation mode of the apparatus and setting an appropriate correction timing according to the use state. It is aimed.

  In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention scans an image carrier and scans the image carrier using a plurality of scanning lines deflected by a deflecting means and writes an image. In the image forming apparatus comprising one or more scanning optical devices and a control unit that corrects a scanning position on the image carrier by the scanning optical device, the control unit is estimated from a driving state of the image forming device The correction execution timing is automatically set using at least one of the temperature information or the correction execution frequency information in the scanning optical device.

  According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the number of printed sheets counter for counting the number of printed sheets, the correction control counter for counting the number of corrections executed by the control means, and the number of reserved corrections. A correction control reservation counter for storing, and the control means performs correction based on the count value of the printed sheet counter and sets the number of corrections counted within a predetermined time by the correction control counter. The number of times of reservation for correction is determined and stored in the correction control reservation counter, and the correction of the number of times stored in the correction control reservation counter is executed at a predetermined timing.

  According to a third aspect of the present invention, there is provided an image forming apparatus according to the first aspect, wherein a toner image formed by attaching toner to an electrostatic latent image written on the image carrier by the scanning optical device is provided. A transfer unit that transfers the toner image onto the recording medium directly or via an intermediate transfer member; a fixing unit that fixes the toner image by heating and pressurizing the recording medium onto which the toner image has been transferred; And a calculation unit for calculating the estimated temperature, a continuous printing mode for driving the scanning optical device and the fixing unit, a non-printing mode for stopping the driving of the scanning optical device and the fixing unit, and the fixing A standby mode in which only the temperature control of the means is performed, and the computing means generates the amount of heat generated by the scanning optical device in the continuous printing mode and the scanning optics in the non-printing mode. An estimated temperature in the scanning optical device is calculated based on a heat radiation amount from the device and a heat generation amount from the fixing unit in the standby mode, and the control unit is based on the estimated temperature calculated by the calculation unit. Correction is performed.

According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the third aspect, wherein the calculation means calculates an estimated temperature T in the scanning optical apparatus using the following conditional expression (1). To do.
T = G + {k1 × (A + C−Y0) / A × B × t1} + {k2 × (C−Y0) / C × D × t2} + {k3 × (E + C−Y0) / E × F × t3} ... (1)
However,
Y0: temperature in the scanning optical device obtained from the previous calculation A: difference between the saturation temperature and the outside air temperature in the scanning optical device in the continuous printing mode B: temperature increase per unit time in the continuous printing mode C: calculation Outside air temperature during execution D: Temperature drop per unit time in non-printing mode E: Difference between saturation temperature and outside air temperature in scanning optical device in standby mode F: Temperature rise per unit time in standby mode G; Outside air temperature k1 at power-on; calculation coefficient k2 in print mode; calculation coefficient k3 in non-print mode; calculation coefficient t1 in standby mode; drive time t2 of deflection means; stop time t3 of deflection means and fixing means; Temperature control time.

  In the image forming apparatus according to a fifth aspect of the present invention, in the configuration of the fourth aspect of the invention, the calculation means uses the driving time t1 of the deflection means predicted from the reserved number when a predetermined number of print reservations are input. Based on the estimated temperature T in the scanning optical apparatus after printing calculated in this manner, it is determined whether or not correction execution is necessary, and if the correction is necessary, the control means executes it before the start of printing. Features.

  According to a sixth aspect of the present invention, in the configuration of the fourth or fifth aspect of the invention, the computing unit multiplies the amount of change in the estimated temperature T in the scanning optical device by a positional deviation amount per unit temperature. An estimated scanning position deviation amount is calculated, and the control unit corrects the scanning position based on the calculated estimated scanning position deviation amount.

  According to a seventh aspect of the present invention, in the configuration of the sixth aspect, the image forming apparatus is provided with a detecting unit that detects a scanning position deviation amount of the scanning optical device, and the control unit is calculated by the calculating unit. The first correction for correcting the scanning position using the estimated scanning position deviation amount and the second correction for correcting the scanning position using the scanning position deviation amount detected by the detecting means can be executed. It is characterized by.

  According to an eighth aspect of the present invention, in the image forming apparatus according to the seventh aspect, the calculation means includes the estimated scanning position shift amount calculated in the first correction and the scanning detected in the second correction. It is characterized in that the calculation coefficients k1, k2, and k3 are optimized by averaging the positional deviation amounts.

  An image forming apparatus according to a ninth invention is characterized in that, in the configuration of the seventh or eighth invention, the execution frequency of the first correction is higher than the execution frequency of the second correction.

  According to the configuration of the first invention, regardless of whether the image forming apparatus is continuously printing or printing is stopped, it is determined whether or not correction is necessary without providing a temperature sensor inside the pressing difference optical device. Scanning position correction can be executed at an appropriate timing.

  According to the configuration of the second invention, in the image forming apparatus of the first invention, the operation state of the apparatus is determined based on the number of correction executions within a predetermined time, and the subsequent correction reservation is made by the number corresponding to the operation state. By inserting, the scanning position correction can be executed at an appropriate timing even during printing stop when the number of printed sheets is not counted, and color misregistration after resuming printing can be effectively prevented.

  According to the configuration of the third invention, in the image forming apparatus of the first invention, the amount of heat generated by the scanning optical device in the continuous printing mode, the amount of heat released from the scanning optical device in the non-printing mode, and the standby mode The estimated temperature in the scanning optical device is calculated based on the amount of heat generated from the fixing means in the scanning optical system, and the correction is executed based on the calculated estimated temperature in the scanning optical device, so that the scanning optics can be used without using the temperature sensor. It is possible to accurately grasp the temperature change inside the apparatus and execute the scanning position correction at an appropriate timing according to the temperature change.

  According to the configuration of the fourth aspect of the invention, in the image forming apparatus of the third aspect of the invention, the calculated scanning optical device is calculated by calculating the estimated temperature in the scanning optical device using the conditional expression (1). The estimated temperature inside becomes more accurate.

  Further, according to the configuration of the fifth invention, in the image forming apparatus of the fourth invention, before the start of printing, the operation status of the image forming apparatus is predicted at the stage when a predetermined number of print reservations are entered. By determining whether or not correction is necessary and executing the correction in advance, it is possible to provide an output with good image quality from the start of printing without interrupting the printing process.

  According to the configuration of the sixth aspect of the invention, in the image forming apparatus of the fourth or fifth aspect of the invention, the amount of change in estimated temperature in the scanning optical device is calculated by multiplying the amount of positional deviation per unit temperature. By correcting the scanning position based on the estimated scanning position deviation amount, the scanning position deviation amount can be estimated without creating a registration mark, so the printing waiting time due to the correction is shortened and the printing process is interrupted even during continuous printing. The scanning position can be corrected without doing so.

  According to the configuration of the seventh invention, in the image forming apparatus of the sixth invention, the first correction for calculating the estimated scanning position deviation amount and the second measurement for actually measuring the scanning position deviation amount by the detecting means. By making it possible to execute both corrections, it is possible to perform correction with higher accuracy by absorbing individual differences between the scanning optical apparatus and the image forming apparatus.

  According to the configuration of the eighth invention, in the image forming apparatus of the seventh invention, the estimated scanning position deviation amount and the actual scanning position deviation amount are averaged, and the calculation coefficient in the conditional expression (1) is calculated. By optimizing k1, k2, and k3, the calculation coefficient can be corrected to a value corresponding to each scanning optical device, and the estimated scanning position deviation amount can be made closer to the actual measurement value.

  According to the configuration of the ninth invention, in the image forming apparatus of the seventh or eighth invention, the registration mark is created by increasing the execution frequency of the first correction compared to the second correction. The overall correction time can be further shortened by reducing the frequency.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of a color image forming apparatus and its control circuit according to the first embodiment of the present invention. First, the operation of the image forming apparatus will be described with reference to FIG. In the main body of the color image forming apparatus 1, four photosensitive drums 2a, 2b, 2c, and 2d corresponding to images of four different colors (yellow, magenta, cyan, and black) are located upstream in the transport direction (in FIG. 1). Arranged in order from the upper side.

  Around the photosensitive drums 2a to 2d, there are chargers (not shown) for uniformly charging the surfaces of the photosensitive drums 2a to 2d, and electrostatic latent images based on image information on the photosensitive drums 2a to 2d. A developing unit (not shown) for forming a toner image by attaching toner to the electrostatic latent image, and a cleaning for removing the developer (toner) remaining on the photosensitive drums 2a to 2d. A portion (not shown) is provided. In the exposure unit 3, four scanning optical devices 4a, 4b, 4c, and 4d for irradiating the respective photosensitive drums 2a to 2d with laser light are arranged.

  When the start of image formation is input by the user, first, the surfaces of the photosensitive drums 2a to 2d are uniformly charged by a charger, and then light is irradiated by the scanning optical devices 4a to 4d, thereby the photosensitive drums 2a to 2d. An electrostatic latent image corresponding to the image signal is formed on the top. Each of the developing units is filled with a predetermined amount of yellow, magenta, cyan, and black toners, and is supplied onto the photosensitive drums 2a to 2d to electrostatically adhere to the electrostatic latent image. A toner image corresponding to the above is formed.

  An intermediate transfer roller (not shown) facing the photosensitive drums 2a to 2d with the intermediate transfer belt 5 interposed therebetween causes yellow, magenta, cyan, and black toner images on the photosensitive drums 2a to 2d to be transferred to the intermediate transfer belt. 5 is transferred. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, residual toner on the surfaces of the photosensitive drums 2a to 2d is removed by the cleaning unit in preparation for a new image forming process to be subsequently performed.

  The transfer paper on which the toner image is transferred is accommodated in a paper cassette (not shown) at the lower part of the apparatus, and is conveyed to the transfer roller 9 via a paper feed roller (not shown) and a resist roller pair 8. The intermediate transfer belt 5 is stretched between an upstream conveyance roller 6 and a downstream drive roller 7. When the intermediate transfer belt 5 starts to rotate clockwise as the drive roller 7 rotates, the transfer paper is transferred. Is transferred from the registration roller pair 8 to a transfer roller 9 provided adjacent to the intermediate transfer belt 5 at a predetermined timing, and a full color image is transferred. The transfer sheet on which the toner image is transferred is conveyed to the fixing unit 10. The transfer paper conveyed to the fixing unit 10 is discharged to the outside of the apparatus after the toner image is fixed on the surface by heating and pressing.

  The registration mark detection sensor 11 detects the positional relationship of registration marks formed on the intermediate transfer belt 5. The detection result is transmitted to a color misregistration correction calculation unit 16 described later, and color misregistration correction is performed for each color by correcting the scanning position by the scanning optical devices 4a to 4d in comparison with a predetermined reference position. As the registration mark detection sensor 11, an optical sensor having a light emitting element such as an LED and a light receiving element such as a photodiode is generally used. The registration mark detection sensor 11 can also have a function of detecting the toner density.

  Next, the control circuit 12 of the image forming apparatus 1 will be described. The control circuit 12 is roughly composed of an image control board 13 and an overall control board 14. The image control board 13 converts an image signal input from an image input unit (not shown) into image data by performing scaling processing or gradation processing as necessary. The scanning optical devices 4a to 4d in the exposure unit 3 irradiate laser light based on the processed image data, and form latent images on the photosensitive drums 2a to 2d.

  The overall control board 14 generally controls the operation of each part of the image forming apparatus 1 such as the photosensitive drums 2a to 2d, the intermediate transfer belt 5, the fixing unit 10 and the registration mark detection sensor 11 according to the set program. The overall control board 14 includes an overall control unit 15, a color misregistration correction calculation unit 16, a printed sheet counter 17, and an NVRAM (nonvolatile memory) 18.

  The print number counter 17 accumulates and stores the number of prints in the image forming apparatus 1. When the count value of the printed sheet counter 17 reaches a predetermined correction execution value, a control signal is transmitted from the overall control unit 15 to each part of the image forming apparatus 1. Based on this control signal, the scanning optical devices 4a to 4d write a predetermined pattern on the photosensitive drums 2a to 2d, and are further developed into toner images, which are then transferred onto the intermediate transfer belt 5 to be registered marks of the respective colors. Is created. This registration mark is detected by a registration mark detection sensor 11. The detection result is transmitted to the color misregistration correction calculation unit 16 to perform calculation processing, and the calculation result is stored as color misregistration correction value data 21 in the NVRAM 18.

  The overall control unit 15 corrects the scanning position by mechanical or electrical correction means based on the color misregistration correction value data 21. Examples of the mechanical correction unit include a method of adjusting the relative positional relationship between the scanning optical devices 4a to 4d and the photosensitive drums 2a to 2d. Examples of the electrical correction unit include a laser lighting timing and a lighting interval. And a method of correcting the main scanning magnification by changing the frequency of the dot writing clock. The date and time when the scanning position correction is performed is stored in the correction control counter 19.

  In this embodiment, in addition to the control of the correction execution timing based on the number of printed sheets, the number of correction reservations to be executed thereafter is determined based on the number of correction executions within a predetermined time. A large number of correction executions within a predetermined time indicates that the number of printed sheets is large and the operation state of the image forming apparatus (scanning optical apparatus) is close to continuous operation (hereinafter referred to as continuous printing mode). Therefore, by monitoring the number of correction executions within a predetermined time, it is possible to determine whether the apparatus is in a severe operating state, that is, whether the temperature rise in the scanning optical apparatus is large.

  When the number of printed sheets is large, that is, in the continuous printing mode in which the temperature rise in the scanning optical apparatus is large, the number of correction executions within a predetermined time is increased, and the scanning position is corrected according to the temperature at that time. On the other hand, when the apparatus is stopped from the continuous printing state (hereinafter referred to as a non-printing mode), the temperature in the scanning optical apparatus rapidly decreases. However, since the printing operation is not performed in the non-printing mode, the number of printed sheets is not counted, and the scanning position correction is not performed. Therefore, the printing is resumed due to the change in the dimension and refractive index of the optical member inside the scanning optical device accompanying the temperature drop. Sometimes the scanning position shifts.

  Therefore, after the power is turned on, the correction execution timing is controlled by the number of printed sheets until the first correction is performed, and after the correction is performed, the number of correction executions within a predetermined time is added to the control by the number of printed sheets. Based on the control for reserving the number of corrections to be performed thereafter, scanning according to the state in the scanning optical device is performed without using a temperature sensor even in the non-printing mode in which the temperature in the scanning optical device decreases. Position correction can be executed.

  FIG. 2 is a flowchart illustrating a scanning position correction control procedure in the image forming apparatus according to the first embodiment. A specific correction control example of the first embodiment will be described with reference to FIG. 1 according to the steps of FIG. Here, it is assumed that the correction of the scanning position is executed when the count value of the print sheet counter 17 reaches the correction execution value (for example, 200 sheets).

  First, the total control unit 15 inquires the correction date and time in the correction control counter 19 every 10 minutes, and counts the number of correction executions within a predetermined time (here, within the past one hour) (step S1). Next, it is determined whether or not the number of corrections is 0 (step S2). If the number of corrections is not 0, the process proceeds to C. Then, it is determined whether or not the number of corrections is 4 or more (step S7), and if it is less than 4, it is determined whether or not it is 2 or more (step S8). If the number of corrections is two times or more, one correction reservation is entered in the correction control reservation counter 20 (step S9), and if it is less than two times, the process returns to A as it is and the correction control counter 19 stores the value every 10 minutes. The correction date and time is inquired, and the number of correction executions within the past one hour is counted to determine whether or not the correction number is 0 (steps S1 and S2).

  When the image forming apparatus is in a non-printing mode in which printing is not performed, the count value of the printed sheet counter is not accumulated and no new correction is performed, so that a new correction date and time is not recorded in the correction control counter 19. Therefore, if there is a correction date and time exceeding 1 hour when the correction date and time in the correction control counter 19 is inquired, the corresponding data is deleted. That is, the number of correction executions within the past one hour decreases with the passage of time.

  If it is determined in step S2 that the number of corrections within the past hour is zero, the overall control unit 15 then inquires about the number of correction reservations in the correction control reservation counter 20 (step S3). If the number of correction reservations is 0, the process returns to step S1 and the same procedure is repeated. If the number of correction reservations is 1 or more in step S3, scanning position correction is executed (step S4), and the correction date and time is recorded in the correction control counter 19 (step S5). Thereafter, the number of correction reservations in the correction control reservation counter 20 is subtracted (-1), and the process returns to step S1.

  On the other hand, if the number of corrections is 4 or more in step S7, the process proceeds to D, and two correction reservations are entered in the correction control reservation counter 20 (step S10). Then, the correction date and time in the correction control counter 19 is inquired every 10 minutes (step S11), and the number of correction executions within the past one hour is counted to determine whether or not the correction number is 0 (step S12). ). When the number of corrections within the past hour decreases with time and reaches 0, the process proceeds to B to perform scanning position correction, and the correction date and time is recorded in the correction control counter 19, and the correction reservation in the correction control reservation counter 20 is recorded. The number of times is subtracted (-1) (steps S4 to S6), and the process returns to step S1 again.

  For example, when the number of correction reservations is 2, the first correction is executed when the correction execution number in the correction control counter 19 becomes 0 after 1 hour from the previous correction execution, and the correction reservation number is set to 1. Subtracted. At this point, the number of correction executions becomes 1 again, and when the number of correction executions becomes 0 after one hour has passed, the remaining correction is executed, the number of correction reservations is subtracted to 0, and the reservation correction control ends. To do. Note that the relationship between the number of corrections within a predetermined time and the number of correction reservations may be set according to the specifications and characteristics of the image forming apparatus. It may be settable.

  In the present embodiment, the exposure unit 3 is composed of four independent scanning optical devices 4a to 4d. For example, a beam deflected and scanned by one polygon mirror (deflecting means) 22a is used as a plurality of mirrors 23. As shown in FIG. 3 in which the light is guided to each of the photosensitive drums 2a to 2d using the light source, and the structure of FIG. 4 in which the light is guided to each of the photosensitive drums 2a to 2d using the two polygon mirrors 22a and 22b. The unit 3 may be one scanning optical device provided with one or a plurality of polygon mirrors.

  FIG. 5 is a schematic diagram showing the configuration of a color image forming apparatus and its control circuit according to the second embodiment of the present invention. Portions common to FIG. 1 of the first embodiment are denoted by the same reference numerals and description thereof is omitted. As shown in FIG. 5, the image forming apparatus 1 includes a temperature sensor 24 that measures the outside air temperature, and the overall control board 13 includes a calculation result storage address 25 and a calculation coefficient storage address 26.

  In the present embodiment, correction is executed based on both the number of printed sheets counted by the number of printed sheets counter 17 and the estimated temperature information in the scanning optical devices 4a to 4d. As described above, when the continuous printing mode is shifted to the non-printing mode, the temperature in the scanning optical device rapidly decreases. However, in the non-printing mode, the scanning position is not corrected, and thus the scanning position shifts.

  Further, since the scanning optical device (scanning optical device 4d in FIG. 5) closer to the fixing unit 10 that is a heat source is more susceptible to temperature changes, the scanning optical devices 4a to 4d have different frequency of occurrence of scanning position deviation. Further, even when one scanning optical device as shown in FIG. 3 is used, the size and refractive index change become larger as the optical member is closer to the polygon mirror 22a which is a heat generation source. Therefore, the frequency at which the scanning position correction is required for each color also differs.

  The temperatures in the scanning optical devices 4 a to 4 d vary depending on the amount of heat generated in the scanning optical device due to rotation of the polygon mirror, the amount of heat released from the scanning optical device when the polygon mirror is stopped, and the amount of heat generated from the heater of the fixing unit 10. . Therefore, it is only necessary to estimate the temperature in the scanning optical device based on these three factors and determine the correction execution timing of the scanning position for each of the scanning optical devices 4a to 4d.

If the temperature change in the scanning optical device in the continuous printing mode is Y1,
Y1 = k1 * (A + C-Y0) / A * B * t1 (a)
It can be expressed as In the formula (a), Y0 is the temperature in the scanning optical device obtained from the previous calculation. A is the difference between the saturation temperature in the scanning optical device and the outside air temperature in the continuous printing mode. The saturation temperature means that when the image forming apparatus is continuously operated (continuous printing), the amount of heat generated and the amount of heat released in the scanning optical device are balanced, and the temperature does not exceed that temperature even if the operation is continued further. Temperature. The temperature change in the scanning optical device is mainly caused by heat generated from the polygon mirror, but A is an experimental value obtained in the actual printing state, and other factors such as fixing away from the scanning optical device. This value is unique to the apparatus, taking into account the heat generated by the motor, the motor driving the photosensitive drum, various electric boards, and the like.

  B is the amount of temperature change per unit time in the continuous printing mode, that is, the amount of temperature rise per unit time in the scanning optical apparatus mainly due to heat generation from the polygon mirror. The value of B is an experimental value obtained in the actual printing state similarly to A, and is a value unique to the apparatus. C is the outside air temperature at the time of calculation based on the formula (a), and is a value measured by the temperature sensor 24. t1 represents the driving time of the polygon mirror (continuous printing mode duration), and k1 represents the calculation coefficient in the continuous printing mode.

If the temperature change in the scanning optical device in the non-printing mode is Y2,
Y2 = k2 * (C-Y0) / C * D * t2 (b)
It can be expressed as Y0 and C are the same as in formula (a). D is a temperature change amount per unit time of the scanning optical device in the non-printing mode (at the time of heat radiation), and image formation is performed when the operation is shifted from the state sufficiently warmed to the outside air temperature by the continuous operation to the operation stop state. This is the amount of temperature drop per unit time in the scanning optical device due to heat radiation from the device to the outside air. Similarly to A and B, the value of D is an experimental value obtained in the actual apparatus operating state, and is a value unique to the apparatus. t2 represents the stop time (non-printing mode continuation time) of the polygon mirror and the fixing unit, and k2 represents a calculation coefficient in the non-printing mode.

In addition, when the printing process is started by the user, the heater temperature is controlled to a predetermined temperature in order to raise the heating roller of the fixing unit to the fixing temperature in a short time so that printing can be performed (hereinafter referred to as a standby mode). ) If the temperature change in the scanning optical device due to heat generation from the fixing unit is Y3,
Y3 = k3 × (E + C−Y0) / E × F × t3 (c)
It can be expressed as Y0 and C are the same as those in the formulas (a) and (b).

  E is the difference between the saturation temperature in the scanning optical device and the outside air temperature in the standby mode. Even if the image forming apparatus is not in a printing state, the fixing unit is in a temperature control state, so that the temperature in the image forming apparatus rises due to heat generated from the fixing unit, and consequently the temperature in the scanning optical device rises. The value E represents the difference between the saturation temperature in the scanning optical apparatus and the outside air temperature in such a state. The value E is also an experimental value obtained in the actual apparatus operating state, and is a value unique to the apparatus. This temperature control is not necessarily the temperature during printing, and may be controlled to a temperature lower than the temperature during printing within a range where printing can be started in a short time.

  F is the amount of temperature rise per unit time in the scanning optical apparatus due to heat generated from the fixing unit in the standby mode. Similarly to E, the value of F is an experimental value unique to the apparatus obtained in the actual apparatus operating state. t3 represents the temperature control time (standby mode duration) of the fixing unit, and k3 represents a calculation coefficient in the standby mode.

Therefore, the amount of temperature change in the scanning optical device is the amount obtained by adding the above Y1, Y2, and Y3, and the estimated temperature T in the scanning optical device is expressed using Y1, Y2, and Y3.
T = G + {k1 × (A + C−Y0) / A × B × t1} + {k2 × (C−Y0) / C × D × t2} + {k3 × (E + C−Y0) / E × F × t3} ... (1)
It becomes. Here, G is the outside air temperature when the power is turned on. Since t1 = t2 = t3 = 0 when the power is turned on, T = G.

  FIG. 6 is a graph comparing the measured value of the temperature in the scanning optical apparatus when the image forming apparatus of the second embodiment is continuously operated and the calculated value obtained by the conditional expression (1). The measured value of the temperature in the scanning optical device when the image forming apparatus of the second embodiment is intermittently operated (repeated operation of printing one sheet and stopping for 20 seconds) is compared with the calculated value obtained by the conditional expression (1). It is a graph.

  Here, A = 21 ° C., B = 0.03 ° C./min, k1 = 0.5, C = 33 ° C., D = −0.01 ° C./min, k2 = 0.2, E = 12 ° C. F = 0.03 ° C./min and k3 = 0.5. In FIG. 6, t1 = 5 min and t2 = t3 = 0 min. In FIG. 7, t1 = 1.7 min and t2 = t3 = 3.3 min.

  As is apparent from FIGS. 6 and 7, the measured value of the temperature in the scanning optical apparatus (broken line in the figure) during both continuous operation and intermittent operation is a calculated value obtained by the conditional expression (1) (FIG. (Solid line). From this result, it was confirmed that the temperature in the scanning optical device can be estimated by calculation without mounting an expensive temperature sensor in the scanning optical device.

  Further, in the tandem type color image forming apparatus as in this embodiment, for example, all four scanning optical devices 4a to 4d are operated during color printing, but only the scanning optical device 4d corresponding to the black image is operated during monochrome printing. When the other scanning optical devices 4a to 4c are not operated, an internal temperature difference occurs between the scanning optical devices 4a to 4c and 4d, and the scanning lines of the scanning optical devices 4a to 4c and the scanning optical device 4d However, according to the present embodiment, the temperatures of the scanning optical devices 4a to 4d can be grasped separately, and accurate scanning position correction corresponding to each temperature change amount can be performed. It becomes executable.

  Further, in the correction using the measured value by the temperature sensor, the correction operation cannot be performed unless the temperature is directly measured. However, in this embodiment, the estimated temperature in the scanning optical apparatus can be obtained from the operation time of the image forming apparatus. The scanning position correction control in anticipation of this operation is also possible. That is, if a large number of print reservations are input immediately before the temperature inside the scanning optical device rises and reaches the correction execution temperature, the correction execution temperature is reached during the printing operation, and correction is executed. Although the processing must be interrupted, in the control of this embodiment, the operation status of the image forming apparatus is predicted at the stage when the print reservation is entered. Therefore, the operation status predicted before starting printing is taken into account. Starts printing without interrupting the printing process by determining whether or not correction is necessary, and if correction is required, the correction that minimizes the amount of color misregistration during printing is performed prior to printing. From time to time, the output can be provided to the user with good image quality.

  FIG. 8 is a flowchart illustrating a scanning position correction control procedure in the image forming apparatus according to the second embodiment. A specific correction control example of the second embodiment will be described with reference to FIG. 5 according to the steps of FIG. In the second embodiment, in addition to the case where the temperature change in the scanning optical apparatus exceeds a predetermined range, the scanning position is also detected when the count value of the printed sheet counter 17 reaches the correction execution value (for example, 200 sheets). Although correction is performed, for the sake of simplicity, FIG. 8 shows only correction control based on a temperature change in the scanning optical apparatus. First, it is determined whether or not a predetermined number of print reservations have been input by the overall control unit 15 (step S1). If there is no print reservation for a predetermined number or more, it is next determined whether or not a predetermined time (here, 10 minutes) has elapsed (step S2).

  Conditional expression (1) is stored in the color misregistration correction calculation unit 16, and when 10 minutes have elapsed, the inside of the scanning optical device obtained from the previous calculation stored in the calculation result storage address 25 Temperature Y0 and calculation coefficients k1, k2, and k3 stored in the calculation coefficient storage address 26 are read, and the outside air temperature G at the time of power-on, the current outside air temperature C, and image formation measured by the temperature sensor 24 are read. The estimated temperature T in the scanning optical devices 4a to 4d is calculated based on the polygon mirror drive time t1, the stop time t2, and the standby mode duration time t3 after the power is turned on (step S3). The calculated estimated temperature T is overwritten on Y0 in the calculation result storage address 25 and stored as a new Y0 (step S4).

  On the other hand, when a print reservation of a predetermined number or more is input in step S1, the operation state of the image forming apparatus is predicted from the reserved number and the polygon mirror drive time t1 is calculated (step S6). Next, the estimated temperature T in the scanning optical devices 4a to 4d is calculated using the calculated value of t1 (step S3). The calculated estimated temperature T is stored as a new Y0 in the calculation result storage address 25 (step S4).

  Next, it is determined whether or not the estimated temperature T calculated for each of the scanning optical devices 4a to 4d is within a preset allowable range (step S5). The processes of S1 to S4 are repeated. If it is determined in step S5 that there is a scanning optical device that exceeds the allowable range, a control signal is transmitted from the overall control unit 15 to each part of the image forming apparatus 1.

  Based on this control signal, a registration mark of a color corresponding to the scanning optical device whose estimated temperature T exceeds the allowable range is created on the intermediate transfer belt 5 (step S7) and detected by the registration mark detection sensor 11. . The detection result is transmitted to the color misregistration correction calculation unit 16 to perform calculation processing, and the amount of scan position deviation is measured (step S8). The calculation result is stored as color misregistration correction value data 21 in the NVRAM 18 (step S9). Based on the color misregistration correction value data 21, the overall control unit 15 corrects the scanning position for the corresponding scanning optical device (step S10).

  In the present embodiment, the correction control based on the count value of the printed sheet counter 17 and the correction control based on the estimated temperature T in the scanning optical apparatus are performed in parallel, but the estimation in the scanning optical apparatus is performed. It is also possible to determine whether or not the scanning position can be corrected only by the correction control based on the temperature T. The allowable range of the estimated temperature T and the time interval for executing the calculation of the estimated temperature T can be arbitrarily set according to the specifications and characteristics of the image forming apparatus.

  FIG. 9 is a schematic diagram showing the configuration of a color image forming apparatus and its control circuit according to the third embodiment of the present invention. In the present embodiment, correction is executed based on the estimated temperature information in the scanning optical devices 4a to 4d in the same manner as in the second embodiment. However, a registration mark is created on the intermediate transfer belt 5 and is actually used. The present invention is characterized in that it is possible to perform a scanning position correction by calculating an estimated value of a positional deviation amount of a scanning line from a temperature change amount in the scanning optical device without detecting a color deviation amount.

  For this reason, the NVRAM 18 in the overall control board 14 of FIG. 9 creates the color misregistration correction value data S21a in which the correction data when the deviation amount is calculated from the temperature change without creating the registration mark, and the registration mark. Color misregistration correction value data M21b in which correction data for calculating an actual misregistration amount is stored. Since the configuration of other parts is the same as that of FIG. 5 of the second embodiment, description thereof is omitted.

  FIG. 10 is a graph showing the relationship between the temperature change in the scanning optical apparatus and the amount of scanning position deviation. As can be seen from FIG. 10, the scanning position deviation amount is proportional to the temperature change in the scanning optical apparatus. That is, when the estimated scanning position deviation amount is H and the positional deviation amount per unit temperature is ΔH, H = ΔT × ΔH. Here, ΔT is a change amount of the estimated temperature T obtained by the conditional expression (1) stored in the color misregistration correction calculation unit 16. Note that ΔH is stored in advance in the NVRAM 18.

  Normally, the correction performed by creating a registration mark requires a correction time of about 30 seconds to 1 minute. However, according to the configuration of the present embodiment, the creation of the registration mark on the intermediate transfer belt 5 can be omitted. The scanning position correction can be executed without interrupting the printing process. Accordingly, it is possible to increase the substantial operation time of the image forming apparatus by eliminating the waiting time for executing correction.

  The positional deviation amount ΔH per unit temperature has individual differences between the respective scanning optical devices, and the error in the estimated scanning positional deviation amount H due to the individual difference increases as the temperature increases. Therefore, when performing the scanning position correction operation, it is preferable to absorb the individual difference of the scanning optical device by actually creating a registration mark once every few times and actually measuring the amount of positional deviation. In the measurement of the misregistration amount by detecting the registration mark, the misregistration amount including not only the scanning optical device but also the error factor of the entire image forming apparatus can be detected, so that individual differences of the image forming apparatus are also absorbed simultaneously. be able to.

  Further, the actual value of the scanning position deviation amount detected by the registration mark detection and the estimated scanning position deviation amount calculated from the temperature change are compared and averaged, and the arithmetic coefficients k1, k2 and the arithmetic coefficients stored in the arithmetic coefficient storage address 26 are stored. If k3 is corrected sequentially, the coefficient in the conditional expression (1) can be optimized to a value corresponding to each scanning optical device, and the estimated scanning position deviation amount can be brought close to the actual measurement value. Optimal correction control can be performed in consideration of individual differences.

  FIG. 11 is a flowchart illustrating a scanning position correction control procedure in the image forming apparatus according to the third embodiment. A specific correction control example of the third embodiment will be described according to the steps of FIG. 11 with reference to FIG. It is determined whether or not a predetermined number of print reservations have been input by the overall control unit 15 and whether or not a predetermined time has elapsed, and the estimated temperature T in the scanning optical devices 4a to 4d is calculated and allowed. The procedure (steps S1 to S6 in FIG. 8) until it is determined whether or not is the same as in FIG. 8 is omitted. Here, two of the three corrections are corrected to calculate an estimated scanning deviation amount from the temperature change (hereinafter referred to as a first correction), and the remaining one time is a registration mark to create a scanning deviation amount. It is assumed that correction that is directly detected (hereinafter referred to as second correction) is performed.

  If the estimated temperature T exceeds the allowable range, the overall control unit 15 next determines whether or not the number of corrections is a multiple of 3 (step S7). When the number of corrections is a multiple of 3, the second correction is executed. A control signal is transmitted from the overall control unit 15 to each part of the image forming apparatus 1, and based on the control signal, a color registration mark corresponding to the scanning optical device whose estimated temperature T exceeds the allowable range is placed on the intermediate transfer belt 5. It is created (step S8). The registration mark is detected by the registration mark detection sensor 11, and the detection result is transmitted to the color misregistration correction calculation unit 16, where calculation processing is performed, and the amount of scan position deviation is measured (step S9). The calculation result is stored in the NVRAM 18 as color misregistration correction value data M21b (step S10).

  Next, an average of the color misregistration correction value data M21b and the total correction amount (color misregistration correction value data S21a) obtained by the first two corrections in the past is taken and stored in the calculation coefficient storage address 26. The calculation coefficients k1, k2, and k3 are optimized (step S11). Then, the overall control unit 15 performs scanning position correction for the corresponding scanning optical device based on the color misregistration correction value data M21b (step S12).

  On the other hand, if the number of corrections is not a multiple of 3 in step S7, the first correction is executed. The estimated temperature T is calculated by multiplying the calculated estimated temperature T by the positional deviation amount ΔH per unit temperature (step S13). The calculation result is stored in the NVRAM 18 as color misregistration correction value data S21a (step S14). Then, the overall control unit 15 performs scanning position correction for the corresponding scanning optical device based on the color misregistration correction value data S21a (step S12).

  In this example, one of the three corrections is a second correction that creates a registration mark and actually measures the amount of positional deviation. However, the number of times of the second correction and the estimated positional deviation are calculated. The ratio with the number of times of the first correction for obtaining the amount can be arbitrarily set. However, in order to reduce the registration mark creation frequency and shorten the correction time, it is preferable to set the first correction execution frequency higher than the second correction.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in each of the above embodiments, an image forming apparatus has been described in which each color toner image is sequentially stacked on an intermediate transfer belt to form a color image, and then transferred onto a transfer sheet at once. The present invention can also be applied to an image forming apparatus using another intermediate transfer member such as an intermediate transfer drum instead of the belt.

  The present invention also relates to a direct transfer type in which a transfer sheet is conveyed to each image forming unit by a conveying unit, and a toner image of each color is sequentially formed on the transfer sheet, or a one-drum type color image forming apparatus having one photoconductor. Of course, the same effect can be obtained, and it can be applied not only to the color image forming apparatus but also to the correction of the scanning position of a monochrome type copying machine, printer, facsimile or the like.

  As described above, according to the present invention, the correction execution timing using at least one of the temperature information in the scanning optical apparatus or the correction execution frequency information estimated from the driving time of the scanning optical apparatus and the control time of the fixing temperature. By automatically setting the color image forming apparatus, it is possible to accurately estimate the temperature change in the scanning optical apparatus regardless of the operation mode of the apparatus and to set an appropriate correction timing according to the use state, and to provide a color image forming apparatus with little color misregistration. .

FIG. 1 is a schematic diagram illustrating a configuration of a color image forming apparatus and a control circuit thereof according to a first embodiment of the present invention. These are the flowcharts which show the correction | amendment control procedure of the scanning position in the image forming apparatus of 1st Embodiment. These are the schematic which shows the other structure of a scanning optical apparatus. These are the schematic which shows the other structure of a scanning optical apparatus. These are the schematic diagrams which show the structure of the color image forming apparatus in 2nd Embodiment of this invention, and its control circuit. These are graphs comparing measured values of the temperature in the scanning optical apparatus and calculated values obtained by the conditional expression (1) when the image forming apparatus of the second embodiment is continuously operated. These are graphs comparing measured values of the temperature in the scanning optical device and calculated values obtained by conditional expression (1) when the image forming apparatus of the second embodiment is intermittently operated. These are the flowcharts which show the correction control procedure of the scanning position in the image forming apparatus of 2nd Embodiment. These are the schematic diagrams which show the structure of the color image forming apparatus in 3rd Embodiment of this invention, and its control circuit. These are the graphs which show the relationship between the temperature change in a scanning optical apparatus, and the amount of scanning position shifts. These are the flowcharts which show the correction control procedure of the scanning position in the image forming apparatus of 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2a-2d Photosensitive drum (Image carrier)
4a to 4d scanning optical device 5 intermediate transfer belt (intermediate transfer member)
9 Transfer roller (transfer means)
10 Fixing part (fixing means)
11 Registration mark detection sensor (detection means)
12 Control Circuit 13 Image Control Board 14 Overall Control Board 15 Overall Control Unit (Control Unit)
16 Color misregistration correction calculation unit (calculation means)
17 Print number counter 18 NVRAM
19 Correction control counter 20 Correction control reservation counter 21 Color misregistration correction value data 21a Color misregistration correction value data S
21b Color misregistration correction value data M
22a, 22b Polygon mirror (deflection means)
24 Temperature sensor 25 Calculation result storage address 26 Calculation coefficient storage address

Claims (9)

An image carrier, and one or more scanning optical devices that scan the image carrier using a plurality of scanning lines deflected by a deflection unit to write an image;
A control unit that corrects a scanning position on the image carrier by the scanning optical device;
The control unit automatically sets the correction execution timing using at least one of temperature information or correction execution frequency information in the scanning optical apparatus estimated from a driving state of the image forming apparatus. apparatus. A print number counter for counting the number of prints, a correction control counter for counting the number of corrections executed by the control means, and a correction control reservation counter for storing the number of correction reservations,
The control means performs correction based on a count value of the printed sheet counter, and determines a correction reservation count based on a correction count counted within a predetermined time by the correction control counter, thereby correcting the correction control reservation counter. The image forming apparatus according to claim 1, wherein the number of times stored in the correction control reservation counter is corrected at a predetermined timing. Transfer means for transferring a toner image formed by adhering toner to an electrostatic latent image written on the image carrier by the scanning optical device onto a recording medium directly or via an intermediate transfer body;
Fixing means for fixing the toner image by heating and pressing the recording medium onto which the toner image has been transferred by the transfer means;
Computing means for calculating an estimated temperature in the scanning optical device, and
A continuous printing mode for driving the scanning optical device and the fixing unit, a non-printing mode for stopping the driving of the scanning optical device and the fixing unit, and a standby mode for performing only temperature control of the fixing unit can be executed. And
The computing means is based on the amount of heat generated by the scanning optical device in the continuous printing mode, the amount of heat released from the scanning optical device in the non-printing mode, and the amount of heat generated by the fixing means in the standby mode. The image forming apparatus according to claim 1, wherein an estimated temperature in the scanning optical apparatus is calculated, and the control unit performs correction based on the estimated temperature calculated by the calculation unit. The image forming apparatus according to claim 3, wherein the calculation unit calculates an estimated temperature T in the scanning optical apparatus using the following conditional expression (1).
T = G + {k1 × (A + C−Y0) / A × B × t1} + {k2 × (C−Y0) / C × D × t2} + {k3 × (E + C−Y0) / E × F × t3} ... (1)
However,
Y0: temperature in the scanning optical device obtained from the previous calculation A: difference between the saturation temperature and the outside air temperature in the scanning optical device in the continuous printing mode B: temperature increase per unit time in the continuous printing mode C: calculation Outside air temperature during execution D: Temperature drop per unit time in non-printing mode E: Difference between saturation temperature and outside air temperature in scanning optical device in standby mode F: Temperature rise per unit time in standby mode G; Outside air temperature k1 at power-on; calculation coefficient k2 in print mode; calculation coefficient k3 in non-print mode; calculation coefficient t1 in standby mode; drive time t2 of deflection means; stop time t3 of deflection means and fixing means; Temperature control time.   The calculation means is based on the estimated temperature T in the scanning optical apparatus after printing calculated using the driving time t1 of the deflection means predicted from the reserved number when a print reservation of a predetermined number or more is input. 5. The image forming apparatus according to claim 4, wherein it is determined whether or not correction execution is necessary, and the control unit executes the correction prior to the start of printing when correction is necessary.   The arithmetic means calculates an estimated scanning position deviation amount by multiplying a change amount of the estimated temperature T in the scanning optical device by a positional deviation amount per unit temperature, and the control means calculates the estimated estimated scanning position deviation amount. The image forming apparatus according to claim 4, wherein the scanning position is corrected based on the image quality.   Detection means for detecting a scanning position deviation amount of the scanning optical apparatus is provided, and the control means uses a first correction for correcting the scanning position using the estimated scanning position deviation amount calculated by the calculation means. The image forming apparatus according to claim 6, wherein a second correction that corrects a scanning position using the amount of scanning position deviation detected by the detecting unit can be executed.   The arithmetic means averages the estimated scanning position deviation amount calculated in the first correction and the scanning position deviation amount detected in the second correction, and optimizes the arithmetic coefficients k1, k2, and k3. The image forming apparatus according to claim 7.   The image forming apparatus according to claim 7, wherein an execution frequency of the first correction is higher than an execution frequency of the second correction.

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