JP2015014747A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent as much as possible the occurrence of CD white stripes in an image due to the charge defect of a photoreceptor.SOLUTION: An image forming apparatus includes a charging roller 12 that has a surface layer part 12a at a close distance from the surface of a photoreceptor 11 and a background part 12b at a distance farther than the surface layer part 12a from the surface of the photoreceptor 11, means for performing the formation of images at a plurality of printing speeds, resistance value detection means for detecting the resistance value of the charging roller 12, and control means. The control means calculates a potential stabilization time required for the potential of the surface layer part 12a and the potential of the background part 12b to become substantially equal to each other from a result of the detection by the resistance value detection means, calculates a discharge gap reaching time required for an area between the surface layer part 12a and photoreceptor 11 where discharge has occurred to reach an area between the background part 12b and photoreceptor 11 where discharge has occurred, compares the potential stabilization time with the discharge gap reaching time, and sets the printing speed low when the discharge gap reaching time is shorter than the potential stabilization time, so that the discharge gap reaching time becomes longer than the potential stabilization time.

Description

  The present invention relates to an image forming apparatus, and more particularly to an electrophotographic image forming apparatus such as a printer or a copying machine.

  In general, in an electrophotographic image forming apparatus, first, the surface of a photoreceptor is uniformly charged to a predetermined potential by a charging member. When a charging roller is used as the charging member, in a situation where the resistance value of the charging roller becomes high due to environmental conditions such as temperature and humidity or due to aging of the roller itself, the image is oriented in a direction perpendicular to the rotation direction of the photoconductor. There is a problem that white stripes (hereinafter referred to as CD white stripes) occur and the image quality is impaired.

  Conventionally, in order to eliminate the above-mentioned problem, Patent Document 1 discloses that the charge charge amount is obtained by integrating the time until the surface potential of the photoconductor is utilized, and the film thickness of the photoconductor is detected from the charge amount. In addition, there is described control for obtaining the life of the photoreceptor or correcting the charging potential. Japanese Patent Application Laid-Open No. 2004-228688 describes control for calculating the resistance value of the charging roller by detecting the voltage or current applied to the charging roller and correcting the applied voltage from the resistance value and temperature.

  However, as in Patent Documents 1 and 2, it is difficult to eliminate the possibility of the occurrence of CD white streak due to charging failure simply by performing output correction such as charging potential.

JP 2006-309144 A JP 2000-338749 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of preventing as much as possible the occurrence of CD white stripes in an image based on a charging failure of a photoreceptor.

An image forming apparatus according to an aspect of the present invention is
The surface of the photosensitive member rotating at a predetermined speed is uniformly charged, a desired image is exposed to form an electrostatic latent image, the electrostatic latent image is developed to form a toner image, and the toner In an image forming apparatus for transferring an image onto a recording material directly or via an intermediate transfer member,
A charging roller having a surface layer portion having a short distance from the surface of the photoconductor and a background portion having a distance from the surface of the photoconductor surface farther than the surface layer portion;
Means for performing image formation at a plurality of print speeds;
Resistance value detecting means for detecting a resistance value of the charging roller;
Control means;
With
The control means includes
From the detection result of the resistance value detection means, calculate the potential stabilization time until the potential of the surface layer portion and the potential of the background portion are substantially equal,
Calculating a discharge gap arrival time until a region where discharge occurs between the surface layer portion and the photoreceptor reaches a region where discharge occurs between the background portion and the photoreceptor,
Comparing the potential stabilization time with the discharge gap arrival time, if the discharge gap arrival time is shorter, the print speed is set to be low so that the discharge gap arrival time is longer than the potential stabilization time. ,
It is characterized by.

  The CD white stripe is caused by abnormal discharge generated between the background portion of the charging roller and the photosensitive member, and no abnormal discharge occurs if the potential of the surface portion of the charging roller is substantially equal to the potential of the background portion. Further, the potential stabilization time until the potential of the surface layer portion of the charging roller becomes substantially equal to the potential of the background portion changes based on the resistance value of the charging roller. Therefore, by comparing the potential stabilization time with the discharge gap arrival time, if the discharge gap arrival time is shorter, the print speed is set to a low speed so that the discharge gap arrival time is longer than the potential stabilization time. CD white streaks as image defects are effectively prevented.

  According to the present invention, it is possible to prevent CD white streaks from occurring in an image as much as possible based on a charging failure of a photoreceptor.

1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment. FIG. 2 is a schematic configuration diagram illustrating a configuration of an image forming unit of the image forming apparatus. FIG. 2 is a block diagram illustrating a control unit of the image forming apparatus. (A), (b), (c) is explanatory drawing of the phenomenon of CD white stripe generation. FIG. 4 is a graph showing changes in potentials of a charging roller and a photosensitive member, where (a) shows a normal discharge time and (b) shows an abnormal discharge time. It is a graph which shows the relationship between the resistance value of a charging roller, and temperature. It is a graph which shows the relationship between the surface potential of the charging roller at the time of voltage application, and elapsed time. It is a flowchart figure which shows the 1st example of control. It is a flowchart figure (continuation of FIG. 8A) which shows the 1st control example. It is a flowchart figure which shows the 2nd example of control. It is a flowchart figure (continuation of FIG. 9A) which shows the 2nd example of control. It is a flowchart figure which shows the 3rd example of control. It is a flowchart figure (continuation of FIG. 10A) which shows the 3rd control example.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the same member and part in each figure, and the overlapping description is abbreviate | omitted.

(Refer to the outline of the image forming apparatus, FIGS. 1 and 2)
First, a schematic configuration of an electrophotographic image forming apparatus 1 according to an embodiment will be described with reference to FIG. The image forming apparatus 1 constitutes an image forming system including an image reading unit 60 and a post-processing unit (not shown) having a stapling function and a paper folding function.

  The image forming apparatus 1 is configured to form a color image by a tandem method, and includes four image forming units 10 (an image forming unit 10y for forming a yellow image and an image forming unit 10m for forming a magenta image). The image forming unit 10c for forming a cyan image and the image forming unit 10k for forming a black image are juxtaposed, and the toner images of the respective colors formed on the respective photoconductors 11 are transferred onto the intermediate transfer belt 31. / Composition (primary transfer), and the composite toner image is secondarily transferred onto the recording material by the electric field applied from the transfer roller 35.

  As shown in FIG. 2, a charging roller 12, an image exposure device 13 using an LED as a light source, a developing device 14 including a developing roller 14a, and the like are disposed around each photoconductor 11, and the electrophotographic system is used. To form an image. Such an image forming process is well known, and a description thereof will be omitted. Further, a temperature sensor 41 and a humidity sensor 42 are disposed in the vicinity of the image forming unit 10k. The functions of these sensors 41 and 42 are mainly to detect the ambient temperature and ambient humidity of the transfer roller 12.

  Recording materials (thin paper, thick paper, etc.) are stacked and housed in a paper feed cassette 50 and are fed one by one by a paper feed roller 51. The fed recording material is conveyed to the secondary transfer section via the registration roller pair 52, and the toner image is secondarily transferred. Thereafter, the recording material is heated and fixed with toner by the fixing device 55, and is discharged from the discharge roller pair 56 to the discharge portion 57.

  The image reading unit 60 is arranged on the upper part of the image forming apparatus 1 and includes a well-known image reading optical system (scanner, not shown). The image reading unit 60 reads an image of a document placed on the platen glass 61. The image of the original that is read and fed one by one from the original tray 63 and conveyed on the slit glass 62 is read and converted into digital image information. The document image (digital image information) read by the unit 60 is transferred to the control unit of the image forming apparatus 1, and the image is printed on the recording material. The image forming apparatus 1 prints digital image information transferred from a computer (not shown) on a recording material.

(Control unit, see FIG. 3)
As shown in FIG. 3, the control unit of the image forming apparatus 1 is roughly configured by a system controller unit 100 including a CPU 101 and an image forming controller unit 120 including a CPU 121. The CPU 101 controls the entire image forming system, and in particular instructs the CPU 121 to execute printing.

  The CPU 121 includes a ROM 122, a RAM 123, and a nonvolatile memory 124. The CPU 121 reads out a program from the ROM 122 and controls each operation of the image forming apparatus 1 in a unified manner while measuring the timing, and smoothly executes, for example, a print job. The ROM 122 stores programs such as a printing operation in the image forming unit 10 and a conveyance operation in the recording material conveyance unit. The RAM 123 functions as a work area in the CPU 121. The nonvolatile memory 124 functions as a data storage area when the CPU 121 executes a program.

  The CPU 121 controls a drive motor 131 that rotates the photoconductor 11, the transfer roller 12, and the like, a power source 132 that applies predetermined high voltages to the four charging rollers 12, and the like. The CPU 121 receives temperature information and humidity information from the temperature sensor 41 and the humidity sensor 42. Further, the controller unit 120 has a built-in counter 133 that accumulates the rotation amount of the charging roller 12, detects the accumulated rotation amount of the charging roller 12, and inputs it to the CPU 121.

(Charging operation by charging roller, see FIGS. 4 to 7)
As shown in FIG. 4A, the charging roller 12 includes a surface layer particle portion 12a containing particles made of polyamide resin, a ground portion 12b made of polyimide resin, and a metal core (not shown). A predetermined high voltage is applied via gold, and the surface of the photoconductor 11 is charged to a predetermined potential by this voltage. The surface layer particle portion 12a is close to the surface of the photoconductor 11 (the surface layer particle portion 12a is in contact with the surface of the photoconductor 11 at a predetermined pressure), and the background portion 12b is more distant from the surface of the photoconductor 11 than the surface layer portion 12a. Is too far away.

  The photoconductor 11 rotates in the direction of arrow a, and the charging roller 12 rotates in the direction of arrow b. The initial potential of the photoconductor 11 is 0V, and when the surface layer particle portion 12a of the charging roller 12 becomes a certain distance (discharge gap) or less from the photoconductor 11, a discharge E is generated, and the surface of the photoconductor 11 in the normal discharge state Charge to -400V. Since the surface layer particle part 12a approaches the photoreceptor 11 earlier than the background part 12b, the surface layer particle part 12a discharges first. In the background portion 12b that is substantially in the same position as the surface particle portion 12a with respect to the photoreceptor 11, the time that the surface layer particle portion 12a and the background portion 12b are less than the discharge gap is different. That is, after the discharge at the surface particle portion 12a, the discharge at the background portion 12b.

  Specifically, as shown in FIG. 5A, the surface layer particle portion 12a of the charging roller 12 is −400V at the beginning of applying the charging voltage, but is stabilized at −1000V after 5 ms. The background portion 12b is stable at −1000 V from the beginning of application. In this case, the photoconductor 11 is stably charged uniformly at −400 V from the beginning of application.

  By the way, since the potential is reset when the discharge occurs, a potential difference is generated between the surface particle portion 12a and the background portion 12b due to the discharge at the surface particle portion 12a. If the potential difference between the surface layer particle portion 12a and the background portion 12b is not eliminated, the potential of the background portion 12b becomes higher than the potential of the surface layer particle portion 12a, and abnormal discharge occurs from the background portion 12b to the photoconductor 11. E ′ (see FIG. 4B) occurs. The abnormal discharge E ′ is generated by extending in the CD direction perpendicular to the rotation direction in which the surface of the charging roller 12 and the surface of the photoconductor 11 are in the same distance relationship (see FIG. 4C). The abnormal discharge E ′ is generated in the background portion 12b, but is generated beyond the scattered surface particle portions 12a.

  Specifically, when an abnormal discharge E 'occurs in the background portion 12b, the potential of the photoconductor 11 is changed from a normal value of -400V to -600V as shown in FIG. 5B. If the surface potential of the photoconductor 11 is −400V, the toner normally adheres to the exposed portion. However, if the surface potential is −600V, the toner hardly adheres even if the exposure is performed. The image quality deteriorates due to white lines.

  Whether or not the potential difference between the surface particle portion 12a and the background portion 12b can be eliminated before the background portion 12b becomes less than the discharge gap so that CD white stripes do not occur is determined by the charging roller 12 that varies depending on the resistance value of the charging roller 12. The surface potential change (see (1) and (2) below) and the time from the discharge of the surface particle portion 12a to the time when the ground portion 12b becomes less than the discharge gap (see (3) below).

(1) The relationship between the surface resistance value of the charging roller 12 and the temperature is as shown in FIG. 6, and the resistance value becomes higher as the temperature becomes lower. The relationship with humidity is the same, and the resistance value increases as the humidity decreases. The relationship with the integrated rotation amount is the same, and the resistance value decreases as the integrated rotation amount increases.
(2) The relationship between the surface potential and time when a voltage is applied to the charging roller 12 is as shown in FIG. In this case, the surface potential V of the charging roller 12 is expressed by the following equation. The surface potential V is determined by the resistance value of the cored bar and the roller 12, and the larger the resistance value, the longer it takes to reach the predetermined potential V.

V x exp (-t / CR)
V: surface potential of charging roller t: time C: capacitance R: charging roller resistance

  (3) The time from when the discharge is generated in the surface layer particle portion 12a until the background portion 12b becomes less than the discharge gap becomes shorter as the rotation (printing speed) of the photoconductor 11 becomes higher.

  Considering the relationship of (1), (2), (3), the surface portion 12b is less than the discharge gap in the low temperature environment where the surface resistance value of the charging roller 12 is high and the surface particle portion 12a is discharged. In particular, when the printing speed (high speed) cannot ensure the time until the surface layer particle portion 12a becomes a low potential, CD white stripes are particularly likely to occur. Specifically, CD white stripes are likely to occur when printing on plain paper (high-speed printing) in an environment of 10 ° C.

  Therefore, in the image forming apparatus 1, the potential stabilization time until the potential of the surface layer particle portion 12 a and the potential of the background portion 12 b are substantially equal is calculated from the resistance value of the charging roller 12, and the surface layer particle portion 12 a, the photoconductor 11, and the like. The discharge gap arrival time until the region where discharge occurs between the base 12b and the photoreceptor 11 reaches the region where discharge occurs is calculated, and the potential stabilization time is compared with the discharge gap arrival time. Thus, when the discharge gap arrival time is shorter, the printing speed is set to be low so that the discharge gap arrival time is longer than the potential stabilization time. Thereby, it is possible to prevent the occurrence of CD white stripes in the image. In that case, it is preferable not to reduce the print productivity as much as possible. The resistance value of the charging roller 12 can be predicted from the ambient temperature and ambient humidity of the charging roller 12 or can be predicted from the accumulated rotation amount of the charging roller 12. Hereinafter, the first, second, and third control examples based on the prediction of the resistance value of the charging roller 12 will be specifically described.

(Refer to the first control example, FIGS. 8A and 8B)
In the first control example, printing is performed at a speed determined from the relationship between the potential stabilization time of the charging roller 12 and the discharge gap arrival time, which fluctuates depending on the ambient temperature, and the case where the printer is kept in a driving state before printing is started. In comparison, a control is selected so that the print job is completed earlier. More specifically, the rate of increase of the ambient temperature in the driving state of the charging roller 12 is predicted, a first time until the ambient temperature reaches a predetermined temperature is calculated, and one of the print speeds based on the print mode to be executed is calculated. The second time from the start to the end of the job is calculated. Then, it is set based on the standby job time obtained by adding the second time after waiting for the printing operation for the first time and the resistance value of the charging roller 12 without waiting for the printing operation for the first time. A print operation in which one job is completed earlier is selected by comparing the job time when the print operation is performed at the print speed.

  Here, it is assumed that 30 sheets are printed using A4 size plain paper and the ambient temperature of the charging roller 12 at the start of printing is in an environment of 15 ° C.

  When printing is started, the CPU 121 acquires the number N of jobs and the print mode from the system controller unit 100 (step S1), and sets the print mode speed determined by the print mode (steps S2, S3, S6). If the recording material is plain paper, it is set to high speed (step S3), and if it is thick paper, it is set to low speed (step S6). Note that the print mode speed may vary depending on the gloss designation and resolution designation in addition to the type of recording material.

  Next, a time t for discharging one sheet is obtained (steps S4 and S7). The time t for discharging one sheet is determined by the sheet size and the printing speed. When the printing speed is high and the paper size is letter size, it is 1.5 seconds, when it is A4 size, it is 1.6 seconds, and when it is legal size, it is 1.8 seconds. When the print speed is low and the paper size is letter size, it is 3.0 seconds, when it is A4 size, it is 3.2 seconds, and when it is legal size, it is 3.8 seconds. Here, since the A4 size of plain paper is assumed, the single sheet discharge time t is 1.6 seconds.

  Further, a standby release temperature twrt determined by the print mode is obtained (steps S5 and S8). The standby release temperature twrt represents the ambient temperature of the charging roller 12 as a condition for waiting for the print operation in a state where the drive motor 131 is started before the start of printing, and releasing this standby. When time elapses while the drive motor 131 is driven, the temperature around the charging roller 12 gradually increases. As a result, the resistance value of the charging roller 12 decreases, and as a result, CD white stripes do not occur. The standby release temperature twrt is 17 ° C. when the printing speed is high and 12 ° C. when the printing speed is low.

  Next, the current ambient temperature T of the charging roller 12 is detected (step S9), and the estimated standby time tw is calculated (step S10). In the first control example, the temperature rise when the drive motor 131 is driven and is on standby is obtained in advance from experimental data, and the temperature rise time is calculated as increasing by 1 ° C. in 30 seconds. The estimated standby time tw is obtained from the difference between the current ambient temperature T detected in step S9 and the standby release temperature twrt determined in steps S5 and S8. If the current ambient temperature is 15 ° C., the standby release temperature twrt is 17 ° C., so the difference is 2 ° C. In order to increase the temperature of the charging roller 12 by 2 ° C., the estimated standby time tw is 30 seconds × 2 and 60 seconds.

  Then, a standby job execution time twait is obtained when the printer is kept waiting before the printing operation is started and printing is performed at the printing speed (step S11). The time twait is obtained as follows. First, an execution time (one sheet discharge time t × number of jobs N) when printing is performed in a predetermined print mode without waiting is calculated. Here, since the time t is 1.6 seconds and N is 30, the job execution time without waiting is 48 seconds. If the standby time of 60 seconds is added to this, the standby job execution time twait is 108 seconds.

Next, with respect to the standby job execution time twait, the speed change job execution time tspd when printing is performed at a speed determined from the relationship between the potential stabilization time of the charging roller 12 and the discharge gap arrival time (step S19). . Specifically, the charging output is acquired (step S12), and the resistance value of the charging roller 12 is acquired based on the ambient temperature of the charging roller 12 at the start of printing (step S13). As shown in Table 1, the resistance value of the charging roller 12 is a value obtained experimentally in advance. Here, since the ambient temperature T at the start of printing is 15 ° C., the resistance value of the charging roller 12 is 7.0 × 10 ⁵ Ω.

  Then, a potential stabilization time tstb until the potential is restored after the discharge is generated on the surface of the charging roller 12 is acquired (step S14). The potential stabilization time tstb is a value obtained experimentally in advance as shown in Table 1. Here, since the ambient temperature T at the start of printing is 15 ° C., the potential stabilization time tstb is 5.00 seconds.

  Further, for each printing speed, discharge gap arrival times tH and tL until the background portion 12b becomes less than the discharge gap after the discharge is generated in the surface particle portion 12a of the charging roller 12 are calculated (step S15). The discharge gap arrival time is a value experimentally measured in advance, the discharge gap arrival time tH at high speed is 3.04 ms, and the discharge gap arrival time tL at low speed is 6.08 ms.

  Thereafter, the potential stabilization time tstb and the discharge gap arrival times tH and tL are compared (step S16), and a normal image speed at which no CD white stripe occurs is obtained. The normal image speed is high when tstb ≦ tH (step S17), and low when tH <tstb ≦ tL (step S18). Further, when tstb> tL, it is not necessary to consider the normal image speed, and step S22 and subsequent steps are executed.

  Next, a job execution time tspd at the time of speed change when the printing operation is executed at the speed obtained in step S17 or S18 is calculated (step S19). If the print speed when the standby job execution time twait is calculated is replaced with the normal image speed and the speed change job execution time tspd is calculated as a low speed operation, 30 sheets are discharged at 3.2 seconds. , Tspd is 96 seconds.

  Therefore, the job execution time tspd at the time of speed change and the standby job execution time twait are compared (step S20), and when tspd ≦ twait, that is, when printing is performed at a normal image speed without waiting at the start of printing, the job is executed. If the time is short, the printing speed is set to the normal image speed (step S21), and the printing operation is executed (step S26).

  On the other hand, if tspd> twait, that is, if the job execution time is shorter when printing is performed in the print mode that is set to wait before starting printing, the print speed is set to the set print mode speed. (Step S22). In this case, the ambient temperature T of the charging roller 12 is detected before printing (step S23), and if the detected temperature T is higher than the standby release temperature twrt (step S24), the printing operation is executed (step S26). Further, the standby time is counted until the detected temperature T reaches the standby release temperature twrt. When the standby time exceeds twice the standby standby time tw (step S25), the printing operation is executed (step S26). .

  Specifically, when comparing the standby job execution time twait of 108 seconds with the speed change job execution time tspd of 96 seconds, the speed change job execution time tspd is shorter. Set a certain low speed and execute the print operation. That is, in the first control example, the time required for one job is shorter in the case of printing at a low speed from the beginning without waiting before the printing operation than in the case of waiting before the printing operation and then printing at a high speed. .

(Refer to the second control example, FIGS. 9A and 9B)
In the second control example, printing is performed at a speed determined from the relationship between the potential stabilization time of the charging roller 12 and the discharge gap arrival time, which fluctuates depending on the ambient humidity, and the case of waiting in a driving state before starting printing. In comparison, a control is selected so that the print job is completed earlier. More specifically, the rate of increase of the ambient humidity in the driving state of the charging roller 12 is predicted, a first time until the ambient humidity reaches a predetermined humidity is calculated, and one of the print speeds based on the print mode to be executed is calculated. The second time from the start to the end of the job is calculated. Then, it is set based on the standby job time obtained by adding the second time after waiting for the printing operation for the first time and the resistance value of the charging roller 12 without waiting for the printing operation for the first time. A print operation in which one job is completed earlier is selected by comparing the job time when the print operation is performed at the print speed.

  As shown in FIGS. 9A and 9B, the second control example executes basically the same procedure as the first control example described in FIGS. 8A and 8B. Therefore, in FIG. 9A and FIG. 9B, the same processing is executed at the same step number as FIG. 8A and FIG. 8B. The difference is that the standby release humidity twhr determined by the print mode in steps S5a and S8a is obtained. The standby release humidity twrh represents the ambient humidity around the charging roller 12 as a condition for waiting for the print operation in a state where the drive motor 131 is started before the start of printing, and releasing the standby. When time elapses while the drive motor 131 is driven, the humidity around the charging roller 12 gradually increases. As a result, the resistance value of the charging roller 12 decreases, and as a result, CD white stripes do not occur. The standby release humidity twhrh is 25% when the printing speed is high and 20% when the printing speed is low.

  In step S9a, the current ambient humidity H of the charging roller 12 is detected, and in step S10, the estimated standby time tw is calculated. In the second control example, the humidity increase during the standby while driving the drive motor 131 is obtained in advance from experimental data, and the humidity increase time is calculated as 1.0% increase in 30 seconds. The standby standby time tw is obtained from the difference between the current ambient humidity H detected in step S9a and the standby release humidity twrh determined in steps S5a and S8a. If the current ambient humidity is 23%, the standby release temperature twhr is 25%, so the difference is 2%. In order to increase the humidity of the charging roller 12 by 2%, the estimated standby time tw is 30 seconds × 2 and 60 seconds.

  The process for obtaining the standby job execution time twait when the print operation is made to stand by before the print operation is started is the same as in the first control example (step S11), and there is no standby and a predetermined print mode. In this case, the job execution time when printing is executed is 48 seconds, and the standby job execution time twait is 108 seconds obtained by adding 60 seconds.

The first control also determines the job execution time tspd when changing the speed when printing is performed at a speed determined from the relationship between the potential stabilization time of the charging roller 12 and the discharge gap arrival time with respect to the standby job execution time twait. This is the same as the example (step S19). Specifically, the resistance value of the charging roller 12 is acquired based on the humidity around the charging roller 12 at the start of printing (step S13). As shown in Table 2, the resistance value of the charging roller 12 is a value obtained experimentally in advance. Here, since the ambient humidity H at the start of printing is 23%, the resistance value of the charging roller 12 is 7.0 × 10 ⁵ Ω.

  Then, a potential stabilization time tstb until the potential is restored after the discharge is generated on the surface of the charging roller 12 is acquired (step S14). The potential stabilization time tstb is a value obtained experimentally in advance as shown in Table 2. Here, since the ambient humidity H at the start of printing is 23%, the potential stabilization time tstb is 5.00 seconds.

  Further, the discharge gap arrival times tH and tL are calculated for each printing speed as in the first control example (step S15). Similarly, in step S16, S17, S18, an image normal speed at which no CD white stripe occurs is obtained. If the job execution time is shorter when printing is performed at a normal image speed without waiting at the start of printing, the normal printing speed is set (step S21), and the printing operation is performed (step S26).

  On the other hand, if the job execution time is shorter when printing is performed in the print mode set by waiting before starting printing, the print speed is set to the set print mode speed (step S22). In this case, the ambient humidity H of the charging roller 12 is detected before printing (step S23a), and if the detected humidity H is higher than the standby release temperature twhr (step S24a), the printing operation is executed (step S26). Further, the standby time is counted until the detected humidity H reaches the standby release temperature twhr. If the standby time exceeds twice the standby standby time tw (step S25), the printing operation is executed (step S26). .

  Specifically, when comparing the standby job execution time twait of 108 seconds with the speed change job execution time tspd of 96 seconds, the speed change job execution time tspd is shorter. Set a certain low speed and execute the print operation. That is, in the second control example, the time required for one job is shorter when printing is performed at a low speed from the beginning without waiting before the printing operation than when waiting at a high speed after the printing operation. .

(Refer to the third control example, FIGS. 10A and 10B)
In the third control example, printing is performed at a speed determined from the relationship between the potential stabilization time of the charging roller 12 and the discharge gap arrival time, which fluctuates depending on the accumulated rotation amount, and a case where the printer is kept in a driving state before printing is started. Are selected so that the print job is completed early. More specifically, a first time until the accumulated rotation amount of the charging roller 12 reaches a predetermined amount is calculated, and a second time from the start to the end of one job at the print speed based on the print mode to be executed is calculated. Calculate time. Then, it is set based on the standby job time obtained by adding the second time after waiting for the printing operation for the first time and the resistance value of the charging roller 12 without waiting for the printing operation for the first time. A print operation in which one job is completed earlier is selected by comparing the job time when the print operation is performed at the print speed.

  As shown in FIGS. 10A and 10B, the third control example executes basically the same procedure as the first control example described in FIGS. 8A and 8B. Therefore, in FIG. 10A and FIG. 10B, the same process is performed by the same step number as FIG. 8A and FIG. 8B. The difference is that the standby release rotation amount twrr determined by the print mode in steps S5b and S8b is obtained. The standby release rotation amount twrr represents the integrated rotation amount of the charging roller 12 as a condition for waiting for the print operation in a state where the drive of the drive motor 131 is started before the start of printing, and releasing this standby. When time elapses while the drive motor 131 is driven, the rotation amount of the charging roller 12 gradually increases. As a result, the resistance value of the charging roller 12 decreases, and as a result, CD white stripes do not occur. The standby release rotation amount twrr is set to 1200000 rotations when the printing speed is high and 1000000 rotations when the printing speed is low.

  In step S9b, the current accumulated rotation amount R of the charging roller 12 is detected, and in step S10, the estimated standby time tw is calculated. In the third control example, it is assumed that the charging roller 12 rotates once in 130 ms when the printing speed is high and 260 ms when the printing speed is low. The estimated standby time tw is obtained from the difference between the current integrated rotation amount R detected in step S9b and the standby release rotation amount twrr determined in steps S5b and S8b. If the current accumulated rotation amount is 1199700 rotations, the standby release rotation amount twrr is 1200000 rotations, so the difference is 300 rotations. In order for the charging roller 12 to rotate 300 times, the estimated standby time tw is 39 seconds at 130 ms × 300 rotations.

  The process for obtaining the standby job execution time twait when the print operation is made to stand by before the print operation is started is the same as in the first control example (step S11), and there is no standby and a predetermined print mode. In this case, the job execution time is 48 seconds when the print is executed, and the standby job execution time twait is 87 seconds obtained by adding 39 seconds thereto.

The first control also determines the job execution time tspd when changing the speed when printing is performed at a speed determined from the relationship between the potential stabilization time of the charging roller 12 and the discharge gap arrival time with respect to the standby job execution time twait. This is the same as the example (step S19). Specifically, the resistance value of the charging roller 12 is acquired based on the accumulated rotation amount of the charging roller 12 at the start of printing (step S13). As shown in Table 3, the resistance value of the charging roller 12 is a value obtained experimentally in advance. Here, since the accumulated rotation amount R at the start of printing is 1199700 rotations, the resistance value of the charging roller 12 is 5.00 × 10 ⁵ Ω.

  Then, a potential stabilization time tstb until the potential is restored after the discharge is generated on the surface of the charging roller 12 is acquired (step S14). The potential stabilization time tstb is a value obtained experimentally in advance as shown in Table 3. Here, since the accumulated rotation amount R at the start of printing is 1199700 rotations, the potential stabilization time tstb is 5.00 seconds.

  Further, the discharge gap arrival times tH and tL are calculated for each printing speed as in the first control example (step S15). Similarly, in step S16, S17, S18, an image normal speed at which no CD white stripe occurs is obtained. If the job execution time is shorter when printing is performed at a normal image speed without waiting at the start of printing, the normal printing speed is set (step S21), and the printing operation is performed (step S26).

  On the other hand, if the job execution time is shorter when printing is performed in the print mode set by waiting before starting printing, the print speed is set to the set print mode speed (step S22). In this case, the accumulated rotation amount R of the charging roller 12 is detected before printing (step S23b), and if the accumulated rotation amount R is higher than the standby release rotation amount twrr (step S24b), the printing operation is performed (step S24b). S26). Further, the standby time is counted until the integrated rotation amount R reaches the standby release rotation amount twrr. If the standby time exceeds twice the standby standby time tw (step S25), the printing operation is executed (step S25). S26).

  Specifically, comparing the standby job execution time twait of 87 seconds with the speed change job execution time tspd of 96 seconds, the standby job execution time twait is shorter, so the print speed is set to a higher speed. Execute the print operation. That is, in the third control example, the time required for one job is shorter in the case of waiting before the printing operation and then printing at high speed than when printing at low speed from the beginning without waiting before the printing operation. .

(Speed priority or image quality priority)
In the first, second, and third control examples, the speed priority mode and the image quality priority mode may be set. That is, when the speed priority mode is selected, the printing operation is executed at a printing speed based on the print mode to be executed, and when the image quality priority mode is selected, the printing according to the first, second, or third control example is performed. Run the action. The speed priority mode is selected by the user when the image quality is not so important.

(Other examples)
The image forming apparatus according to the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the gist thereof.

  In particular, the image forming apparatus may be a monochrome image forming apparatus in addition to a color image forming apparatus, or may be a multifunction machine having a communication function or a facsimile function. Further, the detailed configuration of the image forming unit is arbitrary.

  As described above, the present invention is useful for an image forming apparatus, and is particularly excellent in that CD white streaks can be prevented from being generated in an image based on poor charging of a photoreceptor.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 10 ... Image forming unit 11 ... Photoconductor 12 ... Charging roller 12a ... Surface particle part 12b ... Background part 13 ... Exposure apparatus 14 ... Developing device 41 ... Temperature sensor 42 ... Humidity sensor 121 ... CPU
133 ... Rotation amount integration counter

Claims (8)

The surface of the photosensitive member rotating at a predetermined speed is uniformly charged, a desired image is exposed to form an electrostatic latent image, the electrostatic latent image is developed to form a toner image, and the toner In an image forming apparatus for transferring an image onto a recording material directly or via an intermediate transfer member,
A charging roller having a surface layer portion having a short distance from the surface of the photoconductor and a background portion having a distance from the surface of the photoconductor surface farther than the surface layer portion;
Means for performing image formation at a plurality of print speeds;
Resistance value detecting means for detecting a resistance value of the charging roller;
Control means;
With
The control means includes
From the detection result of the resistance value detection means, calculate the potential stabilization time until the potential of the surface layer portion and the potential of the background portion are substantially equal,
Calculating a discharge gap arrival time until a region where discharge occurs between the surface layer portion and the photoreceptor reaches a region where discharge occurs between the background portion and the photoreceptor,
Comparing the potential stabilization time with the discharge gap arrival time, if the discharge gap arrival time is shorter, the print speed is set to be low so that the discharge gap arrival time is longer than the potential stabilization time. ,
An image forming apparatus. Furthermore, a temperature detection means for detecting the ambient temperature of the charging roller is provided,
The resistance value detecting means determines a resistance value of the charging roller based on a detection result of the temperature detecting means,
The control means calculates the discharge gap arrival time for each of a plurality of print speeds, and sets the print speed to a speed at which the discharge gap arrival time is longer than the potential stabilization time;
The image forming apparatus according to claim 1. Furthermore, a humidity detecting means for detecting the ambient humidity of the charging roller is provided,
The resistance value detecting means determines a resistance value of the charging roller based on a detection result of the humidity detecting means,
The control means calculates the discharge gap arrival time for each of a plurality of print speeds, and sets the print speed to a speed at which the discharge gap arrival time is longer than the potential stabilization time;
The image forming apparatus according to claim 1. Furthermore, it comprises an accumulated rotation amount detecting means for detecting the accumulated rotation amount by counting the rotation amount of the charging roller,
The resistance value detecting means determines a resistance value of the charging roller based on a detection result of the integrated rotation amount detecting means,
The control means calculates the discharge gap arrival time for each of a plurality of print speeds, and sets the print speed to a speed at which the discharge gap arrival time is longer than the potential stabilization time;
The image forming apparatus according to claim 1. Means for determining each print speed based on a plurality of print modes;
Means for predicting the rate of increase in ambient temperature in the driving state of the charging roller;
First time calculating means for calculating a time until the ambient temperature of the charging roller reaches a predetermined temperature;
Second time calculating means for calculating a time from the start to the end of one job at a print speed based on the print mode to be executed;
With
The control unit calculates the waiting job time obtained by adding the time calculated by the second time calculating unit after waiting for the printing operation for the time calculated by the first time calculating unit, and the first time calculating unit. Compared with the job time when the printing operation is performed at the printing speed set based on the detection result of the resistance value detecting means without waiting for the printing operation for the time, the printing operation in which one job is completed earlier To select,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. Means for determining each print speed based on a plurality of print modes;
Means for predicting the rate of increase in ambient humidity in the driving state of the charging roller;
First time calculating means for calculating a time until the ambient humidity of the charging roller reaches a predetermined humidity;
Second time calculating means for calculating a time from the start to the end of one job at a print speed based on the print mode to be executed;
With
The control unit calculates the waiting job time obtained by adding the time calculated by the second time calculating unit after waiting for the printing operation for the time calculated by the first time calculating unit, and the first time calculating unit. Compared with the job time when the printing operation is performed at the printing speed set based on the detection result of the resistance value detecting means without waiting for the printing operation for the time, the printing operation in which one job is completed earlier To select,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. Means for determining each print speed based on a plurality of print modes;
First time calculating means for calculating a time until the accumulated rotation amount of the charging roller reaches a predetermined amount;
Second time calculating means for calculating a time from the start to the end of one job at a print speed based on the print mode to be executed;
With
The control unit calculates the waiting job time obtained by adding the time calculated by the second time calculating unit after waiting for the printing operation for the time calculated by the first time calculating unit, and the first time calculating unit. Compared with the job time when the printing operation is performed at the printing speed set based on the detection result of the resistance value detecting means without waiting for the printing operation for the time, the printing operation in which one job is completed earlier To select,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. It has speed priority mode and image quality priority mode,
The control means causes a print operation to be executed at a print speed based on a print mode to be executed when the speed priority mode is selected, and according to any one of claims 1 to 7 when the image quality priority mode is selected. To execute a printing operation under the control described above;
An image forming apparatus.

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