JP2016157062A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that suppresses a user's waiting time from being unnecessarily extended, while maintaining image quality and suppressing wear of a photoreceptor drum.SOLUTION: There is provided an image forming apparatus printing images on media during a paper feed period, and comprising: an image carrier; charging means disposed in proximity to the image carrier; power supply means that sequentially applies during a non-paper feed period, to the charging means, a plurality of charging voltages each including an AC current, the plurality of charging voltages in which a plurality of AC voltages having peak-to-peak voltages in the respective AC currents different from each other are superimposed; current detection means that detects a value of an AC current flowing in the charging means during the application of the plurality of charging voltages; and processing means that, when a predetermined condition is satisfied, performs first charging voltage determination deriving a peak-to-peak voltage to be used in processes on the basis of a result of the detection performed by the current detection means. The predetermined condition is such that the current ambient temperature changes by a predetermined temperature threshold or more compared with an ambient temperature during execution of the previous first charging voltage determination.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus provided with a charging unit of a proximity charging method to which a charging voltage obtained by superimposing an AC voltage on a DC voltage is applied.

  In recent years, a proximity charging method is becoming mainstream as a charging method in an image forming apparatus. In the proximity charging method, for example, a roller-type charging unit is disposed in proximity to the surface of the photosensitive drum in contact or non-contact. A charging voltage in which an AC voltage is superimposed on a DC voltage is applied to the charging means so that the surface of the photosensitive drum is uniformly charged.

  It is known that the charging potential Vs on the surface of the photosensitive drum with respect to the peak-to-peak voltage value Vpp of the AC voltage Vac is as shown in FIG. That is, if the peak-to-peak voltage value Vpp is in the range of the voltage value 2 × Vth that is twice the charging start voltage value Vth, the charging potential Vs is approximately proportional to the AC voltage Vac. Here, the charging start voltage value Vth is a voltage value at which charging of the photosensitive drum is started by the DC voltage Vdc, and is determined by various characteristics of the photosensitive drum. FIG. 11 illustrates a case where Vth is 800V and 2 × Vth is 1600V.

  If it exceeds 2 × Vth, the charging potential Vs is saturated and becomes substantially constant Vs0. Therefore, in order to make the charging potential Vs uniform, it is necessary to apply a charging voltage on which the alternating voltage Vac having a peak-to-peak voltage value Vpp exceeding 2 × Vth is superimposed on the charging means. Further, the charging potential Vs0 at that time depends on the DC voltage Vdc included in the charging voltage.

  By the way, in the image forming apparatus, the discharge amount of the charging unit is always constant regardless of the influence of the environment or the like, or the manufacturing variation of the resistance value of the charging unit, and uniform without problems such as deterioration of the photosensitive drum or defective image. It is required to charge the photosensitive drum. For this purpose, the conventional image forming apparatus is provided with a means for measuring an alternating current flowing through the photosensitive drum through the charging means and a control means.

  The measuring means measures each alternating current value that flows through the charging means when a plurality of alternating voltages Vac having different peak-to-peak voltage values Vpp that are less than 2 × Vth and different peak-to-peak values are sequentially applied when the sheet is not passed. Similarly, each AC current value when a plurality of AC voltages Vac having different peak-to-peak voltage values Vpp of 2 × Vth or more are applied is also measured. In this specification, a region where the peak-to-peak voltage value Vpp is less than 2 × Vth is referred to as a positive discharge region in which only charge transfer from the charging means to the photosensitive drum (that is, unidirectional charge transfer) occurs. A region of × Vth or more is referred to as a reverse discharge region in which bidirectional charge transfer occurs alternately between the photosensitive drum and the charging unit.

  The control means determines the peak-to-peak voltage value Vppi of the alternating voltage Vaci to be superimposed on the charging voltage during the printing process from each alternating current value obtained by the measuring means. Such control is referred to as first charging voltage determination in this specification.

Hereinafter, a specific example of determining the first charging voltage will be described with reference to FIG.
The control means obtains the alternating current values Iac1 to Iac3 flowing in the charging means when the alternating voltages Vac1 to Vac3 in the positive discharge region are superimposed, and then linearly approximates the alternating current values Iac1 to Iac3 to the alternating voltage in the positive discharge region. A characteristic straight line L1 of the alternating current value is obtained. In the same manner, the control means obtains a characteristic line L2 of the alternating current value with respect to the alternating voltage for the reverse discharge region. The control means determines the intersection of the characteristic lines L1 and L2 as the AC voltage value Vaci to be superimposed during the printing process.

  When the alternating current value Iac is determined in determining the first charging voltage, variations in the film thickness of the photosensitive drum may be taken into consideration. More specifically, the control means measures the alternating current value Iac of a predetermined number of samplings at a plurality of different locations in the circumferential direction while rotating the photosensitive drum once. The control means sets the average value of the plurality of alternating current values Iac obtained by measurement as the alternating current value Iac when the alternating voltage Vac is applied.

  In the first charging voltage determination, the AC voltage Vac having different peak-to-peak voltage values Vpp is sequentially applied to the charging means, so that the fog toner adheres to the surface of the rotating photosensitive drum. The fog toner reaches the secondary transfer roller via the intermediate transfer belt and causes the secondary transfer roller to be contaminated. Therefore, after the first charging voltage is determined, the secondary transfer roller is cleaned.

  A considerable amount of time is required from the start of determination of the first charging voltage to the end of cleaning. This time varies depending on the productivity of the image forming apparatus and the system speed, but is about 20 seconds when the system speed is 165 mm / second.

  When the peak-to-peak voltage value Vpp of the AC voltage Vaci is small, an image defect occurs. On the contrary, if this is large, the wear of the photosensitive drum is increased. Therefore, it is desirable that the first charging voltage determination is performed not only during the printing process but also in other processes that require the photosensitive drum to be activated. Examples of this type of process include image stabilization control during warm-up, forced toner replenishment or TCR (Toner to Carrier Ratio) adjustment. However, if the first charging voltage determination is performed in these processes, the waiting time of the user becomes long. For example, in Patent Document 1, the ambient temperature at the time of the previous determination of the charging voltage, the current ambient temperature, Based on the result, the starting voltage of the peak-to-peak voltage value Vpp used in determining the first charging voltage is changed, thereby shortening the required time.

JP 2014-085405 A

  By the way, in various processes, if the peak-to-peak voltage Vpp of the AC voltage Vac is too small, an image defect occurs. Conversely, if it is too large, the wear of the photosensitive drum is increased. However, Patent Document 1 does not show an appropriate execution condition in consideration of this matter for determining the first charging voltage. That is, in the method of Patent Document 1, whenever the peak-to-peak voltage value Vpp is derived, the first charging voltage determination that requires the measurement result of the alternating current value and requires a large amount of calculation is performed, so the user wants to print. Sometimes it was impossible to print immediately and a waiting time occurred.

  In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of suppressing an unnecessarily long waiting time for a user while maintaining the image quality and suppressing the wear of the photosensitive drum.

  One aspect of the present invention is an image forming apparatus that prints an image on a medium when a sheet is passed, and an image carrier, a charging unit that is disposed in proximity to the image carrier, and a plurality of charging voltages each including an alternating current A plurality of charging voltages obtained by superimposing a plurality of AC voltages having different peak-to-peak voltages of each AC current from each other, a power supply unit that sequentially applies to the charging unit when paper is not passed, and a plurality of the charging voltages A current detecting means for detecting an alternating current value flowing through the charging means during application, and a first charging for deriving a peak-to-peak voltage to be used in the process based on a detection result of the current detecting means when a predetermined condition is satisfied. Processing means for performing voltage determination, and the predetermined condition is that the current ambient temperature changes by a predetermined threshold value or more compared to the ambient temperature at the time of execution of the previous first charging voltage determination.

  According to the above aspect, it is possible to provide an image forming apparatus capable of suppressing an unnecessarily long waiting time of the user while maintaining the image quality and suppressing the wear of the photosensitive drum.

1 is a schematic diagram illustrating a schematic configuration of an image forming apparatus. 1 is a schematic diagram illustrating a configuration of a main part of an image forming apparatus. FIG. 2 is a schematic diagram illustrating a detailed configuration of the photosensitive drum in FIG. 1. It is a main flowchart which shows the process of CPU (processing means) of FIG. It is a flowchart which shows the process of CPU in a printing process. It is a flowchart which shows the process of CPU in 1st charging voltage determination. It is a figure which shows the process of S215 of FIG. It is a flowchart which shows the process of CPU in 2nd charging voltage determination. It is a figure which shows the reason for which a 2nd threshold value is defined as 10 degreeC. FIG. 10 is a flowchart showing processing of a CPU when performing any one of image stabilization, forced toner supply, and TCR adjustment processes. It is a figure which shows the characteristic of the charging potential of the photoconductive drum surface with respect to the voltage value between peaks. It is a figure which shows the specific example of 1st charging voltage determination.

  Hereinafter, embodiments of the image forming apparatus will be described in detail with reference to the drawings.

<< First column: Definition >>
Some figures show an x-axis, a y-axis and a z-axis that are orthogonal to each other. The x axis and the z axis indicate the left and right direction and the up and down direction of the image forming apparatus 1. The y-axis indicates the front-rear direction of the image forming apparatus 1.

<< Second column: Overall configuration of image forming apparatus / printing process >>
1 and 2, an image forming apparatus 1 is, for example, a copying machine, a printer, a facsimile machine, or a multifunction machine having these functions. Various types of images (typically, by a known electrophotographic system and tandem system). Specifically, a full-color image or a monochrome image) is printed on a print medium (paper or OHP sheet) M. Therefore, the image forming apparatus 1 includes a yellow (Y), magenta (M), cyan (C), and black (K) image forming unit 2, an intermediate transfer belt 3, a secondary transfer roller 4, and a power source. Means 10, control means 11, environment detection means 12, and at least one current detection means 13 are further provided.

  The image forming units 2 for the four colors are juxtaposed in the left-right direction, for example, and include corresponding photosensitive drums 5. Each photoconductor drum 5 has, for example, a cylindrical shape extending in the front-rear direction, and rotates about its own axis, for example, in the direction of arrow α.

  As shown in FIG. 3, the photosensitive drum 5 includes, for example, a charge generation layer (hereinafter referred to as CGL) 51, a charge transport layer (hereinafter referred to as CTL) 52, and an aluminum substrate extending in the front-rear direction. An organic photoreceptor in which a protective layer (hereinafter referred to as OCL) 53 is laminated in this order. Note that the photosensitive drum 5 may not have the OCL 53. The photoconductor drum 5 may be an amorphous silicon photoconductor (a-Si photoconductor). Here, the α value, which is an index of the ease of scraping of the surface of the photosensitive drum, is defined as a scraping amount (amount of wear) (μm) per 100,000 revolutions. The α values of various photosensitive drums are as shown in Table 1 below.

  Reference is again made to FIGS. Around each photosensitive drum 5, at least a charging unit 6, a developing unit 8, and a primary transfer roller 9 are arranged from the upstream side to the downstream side in the rotation direction α.

  Each charging unit 6 is typically a charging roller that extends in the front-rear direction, and is a charging roller that is disposed close to or in contact with the peripheral surface of the photosensitive drum 5. Each charging means 6 uniformly charges the peripheral surface of the rotating photosensitive drum 5 with the charging voltage Vg from the power supply means 10.

  The power supply means 10 includes a DC power supply circuit 101 for each color, an AC power supply circuit 102 common to a plurality of colors (for example, three colors Y, M, and C), and an AC power supply circuit 103 for the remaining colors (for example, K). ,including.

  Each DC power supply circuit 101 outputs a predetermined DC voltage Vdc under the control of the control means 11. The DC power supply circuit 101 is individually provided for each color, so that the DC voltage Vdc can be adjusted for each color. However, in the present embodiment, since there is no interest in changing the DC voltage Vdc for each color, the DC voltage Vdc will be described with the same value for each color for convenience.

  The AC power supply circuits 102 and 103 are constituted by, for example, an AC transformer, and output an AC voltage Vac having a variable peak-to-peak voltage value Vpp under the control of the control unit 11. In the following description, it is assumed that each AC voltage Vac has the same value from the same viewpoint as the DC voltage Vdc.

  The output terminal of the AC power supply circuit 102 is connected to each output terminal of the DC power supply circuit 101 for Y, M, and C, thereby generating a charging voltage Vg in which the AC voltage Vac is superimposed on the DC voltage Vdc. , M, C charging means 6. Similarly, the output terminal of the AC power supply circuit 103 is connected to the output terminal of the K DC power supply circuit 101, whereby the same charging voltage Vg is applied to the K charging means 6.

  An exposure device 7 is provided below each photosensitive drum 5. Each exposure device 7 irradiates a light beam B based on the image data to an exposure area immediately downstream of the charging area of the photosensitive drum 5, thereby forming an electrostatic latent image of a corresponding color.

  Each developing means 8 forms a corresponding color toner image by supplying a corresponding color developer to the developing area immediately downstream of the exposure area of the corresponding photosensitive drum 5.

  The intermediate transfer belt 3 is looped over the outer peripheral surfaces of at least two rollers arranged in the left-right direction, for example, and rotates in the direction indicated by the arrow β, for example. For example, the outer peripheral surface of the intermediate transfer belt 3 is in contact with the upper end of each photosensitive drum 5.

  Each primary transfer roller 9 opposes the corresponding photosensitive drum 5 with the intermediate transfer belt 3 interposed therebetween, and presses the intermediate transfer belt 3 from above so that the primary transfer roller 9 is primary between the photosensitive drum 5 and the intermediate transfer belt 3. A transfer nip 91 is formed. A primary transfer bias voltage is applied to each primary transfer roller 9 during the printing process. As a result, the toner image on the photosensitive drum 5 is transferred to the rotating intermediate transfer belt 3 at the corresponding primary transfer nip 91. Is done.

  The secondary transfer roller 4 is configured to be rotatable about its own axis. A secondary transfer bias voltage is applied to the secondary transfer roller 4 during the printing process. The secondary transfer roller 4 presses the outer peripheral surface of the intermediate transfer belt 3 in the vicinity of the right end of the intermediate transfer belt 3, for example, so that the secondary transfer nip is brought into contact with the secondary transfer roller 4 and the intermediate transfer belt 3. 41 is formed. The secondary transfer nip 41 is fed with the print medium M during the printing process.

  Since the secondary transfer bias voltage is applied to the secondary transfer roller 4 while the printing medium M is passing through the secondary transfer nip 41 (that is, during paper passing), the toner image carried on the intermediate transfer belt 3 is transferred to the secondary transfer roller 4. It moves to the printing medium M and is transferred. The print medium M passes through the secondary transfer nip 41, passes through a known fixing device, and is then discharged as a printed matter to the tray.

  The control unit 11 includes, for example, a ROM 111, a CPU 112 as an example of a processing unit, an SRAM 113, and an NVRAM 114 as an example of a storage unit. The CPU 112 controls various processes by executing a control program stored in advance in the ROM 111 while using the SRAM 113 as a work area. This embodiment is particularly related to the following four processes (that is, printing, image stabilization, forced toner replenishment, and TCR adjustment). Even in the following four processes, the photosensitive drum 5 needs to be charged, and therefore the charging voltage Vg is applied to the charging means 6.

(1) Printing: Printing an image on the printing medium M (2) Image stabilization: Controlling the toner density to a target value based on the density of a known pattern image (3) Forced toner supply: Forcing the developing means (4) TCR adjustment: controlling the toner to carrier ratio to the target value

  In addition, the CPU 112 selectively performs first charging voltage determination and second charging voltage determination, which will be described later in detail, and is a peak-to-peak voltage value Vpp to be used in each of the above processes, and is superimposed on the charging voltage Vg. A peak-to-peak voltage value Vpp (hereinafter referred to as a reference peak-to-peak voltage Vpp0) serving as a reference for the AC voltage Vac to be determined is determined. Further, in order to determine the peak-to-peak voltage Vpp (hereinafter referred to as the actual peak-to-peak voltage Vpp1) of the AC voltage Vac that is actually superimposed in each of the above processes, the CPU 112 causes the NVRAM 114 to make a total rotation of each photosensitive drum 5. The number is held as an example of usage status information Irot (see Table 2 below). Although details will be clarified later, in this embodiment, the reference peak-to-peak voltage value Vpp0 is different from the actual peak-to-peak voltage Vpp1, so care should be taken.

  In addition, the CPU 112 holds, in the NVRAM 114, the reference peak voltage Vpp0 derived in the previous determination of the first charging voltage and the correction value Vpp0 ′ of the reference peak voltage Vpp0. Further, the CPU 112 holds the in-machine temperature St (that is, the temperature in the image forming apparatus 1) St when the previous first charging voltage determination is executed as the previous in-machine temperature St ′ (see Table 3 below).

  The environment detection unit 12 includes a temperature sensor 121 and a humidity sensor 122. The temperature sensor 121 detects the temperature (that is, the in-machine temperature) St in the image forming apparatus 1 and outputs it to the CPU 112. On the other hand, the humidity sensor 122 detects relative humidity (hereinafter referred to as “in-machine humidity”) Sh in the image forming apparatus 1 and outputs it to the CPU 112.

  Further, the current detection means 13 detects, for example, an alternating current value Iac flowing through the Y-color charging means 6 when the charging voltage Vg is applied to each charging means 6, and outputs it to the CPU 112.

<< 3rd column: Operation of image forming apparatus >>
Next, the operation of the image forming apparatus 1 will be described with reference to FIGS.
In FIG. 4, the CPU 112 determines whether or not the process to be performed is a printing process at a predetermined timing during the operation of the image forming apparatus 1 (S01).
If an affirmative determination is made in S01 (ie, Y), the CPU 112 performs the processing of FIG. 5 (S02), and if a negative determination is made (ie, N), the process to be performed will be image stabilization, forced toner supply, and TCR adjustment. It is determined whether or not any one of them (S03).
If the CPU 112 makes an affirmative determination in S03, the process of FIG. 10 is performed (S04), but if a negative determination is made, the process returns to S01.

  In FIG. 5, after starting the execution of the print job, the CPU 112 starts a printing process, starts rotation of each photosensitive drum 5 and the like (S11), and acquires the previous in-machine temperature St ′ from the NVRAM 114 (S12). ). Further, the CPU 112 acquires the current in-flight temperature St from the temperature sensor 121 (S13). Next, the CPU 112 subtracts the current in-machine temperature St from the previous in-machine temperature St ′. Next, the CPU 112 determines whether or not the difference (ie, temperature change) ΔSt1 obtained as a result satisfies the first example of the predetermined condition (S14). That is, in S14, the CPU 112 determines whether or not the temperature change ΔSt1 is 10 ° C. or more as a typical example of the first threshold value Tref1.

  When the CPU 112 makes an affirmative determination in S14, it determines the first charging voltage, and determines the actual peak-to-peak voltage value Vpp1 of the AC voltage Vac to be output from the AC power supply circuits 102 and 103 in S17 (S15).

  Here, the first charging voltage determination will be described in detail with reference to FIG. In FIG. 6, the CPU 112 acquires the current in-machine humidity Sh from the humidity sensor 122 (S21). The CPU 112 acquires the environmental steps corresponding to the in-machine temperature St and the in-machine humidity Sh obtained in S13 and S21 from the environment step table T1 previously stored in the ROM 111 or the NVRAM 114 (S22). As shown in Table 4 below, the table T1 describes an environmental step that is an index indicating the magnitude of the absolute humidity for each combination of the in-machine temperature and the in-machine humidity. In this embodiment, the environmental steps are divided into sixteen stages, the environmental steps 1 to 3 are a low temperature and low humidity environment (so-called LL environment), the environmental steps 4 to 7 are a normal temperature and normal humidity environment (so-called NN environment), Environmental steps 8 to 12 indicate a slightly high temperature and high humidity environment, and environmental steps 13 to 16 indicate a high temperature and high humidity environment (so-called HH environment).

  Next, the CPU 112 selects one set of peak-to-peak voltage values Vpp corresponding to the environmental step obtained in S22 from the peak-to-peak voltage value table T2 previously stored in the NVRAM 114 or the like (S23). In the table T2, as shown in Table 5 below, a set of eight different peak-to-peak voltage values Vpp is described for each environmental step range. Each set includes four peak-to-peak voltage values Vpp for each of the positive discharge region and the reverse discharge region. For example, a set A of peak-to-peak voltage values Vpp is assigned to the environmental steps 1 to 3, and the set A includes 600V, 700V, 800V and 900V included in the normal discharge region and 1850V included in the reverse discharge region. , 1950V, 2050V and 2150V. The environmental steps 4 to 7, 8 to 12, and 13 to 16 are assigned the combinations B, C, and D of the peak-to-peak voltage values Vpp as shown in Table 5.

  Next, the CPU 112 initializes the first counter value n to 1 (S24), and acquires the peak-to-peak voltage value Vpp corresponding to the current first counter value n in the selected set (S25).

  The CPU 112 sets the peak-to-peak voltage value Vpp of the AC voltage Vac to be output from the AC power supply circuits 102 and 103 to the value acquired in S25. Further, the CPU 112 sets the DC voltage Vdc to be output from each DC power supply circuit 101 to a predetermined value (S26).

  As a result of S26, the charging voltage Vg is applied from the power supply means 10 to each charging means 6. When the AC voltage Vac of the AC power supply circuits 102 and 103 is stabilized (S27), the CPU 112 initializes the second counter value m to 1 (S28). Next, the CPU 112 acquires the alternating current value Iac from the current detection means 13 and temporarily stores it in the SRAM 113 (S29). Next, the CPU 112 determines whether or not the second counter value m is y (S210). Here, y is the number of samplings per rotation of each photosensitive drum 5, and is a natural number of 1 or more. If the CPU 112 makes a negative determination in S210, it increments the second counter value m by 1 (S211), and performs S29.

  As a result of S28 to S211, the SRAM 113 holds the alternating current values Iac measured at y different locations in the circumferential direction while rotating each photosensitive drum 5 once. When the CPU 112 makes an affirmative determination in S210, the CPU 112 derives an average value of the y AC current values Iac (S212). Next, the CPU 112 determines whether or not the first counter value n is 8, and determines whether or not the processing of S25 to S212 has been performed for all the peak-to-peak voltage values Vpp included in the set selected in S23. (S213). If a negative determination is made in S213, the CPU 112 increments the first counter value n by 1 (S214), and performs S25.

  As a result of the above S25 to S213, each charging voltage Vg superposed with the AC voltage Vac having the peak-to-peak voltage value Vpp included in each of the positive discharge region and the four reverse discharge regions is sequentially applied to the SRAM 113. A total of eight alternating current values Iac flowing through the means 6 are held.

  The CPU 112 derives the reference peak-to-peak voltage value Vpp0 to be used in the printing process or the like based on the eight AC current values Iac in the SRAM 113, and stores it in the NVRAM 114 as the previous one (S215).

Here, the process of S215 will be described in detail with reference to FIG.
The CPU 112 linearly approximates each AC current value Iac in the positive discharge region based on the least square method or the like to obtain a characteristic line L1 (Iac = a × Vac + b) of the AC current value with respect to the applied AC voltage in the positive discharge region. In a similar manner, the CPU 112 linearly approximates each AC current value Iac in the reverse discharge region to obtain a characteristic line L2 (Iac = c × Vac + d) of the AC current value with respect to the applied AC voltage in the reverse discharge region. Here, a to d are constants, in particular, a and c are inclinations, and b and d are intercepts. Thereafter, the CPU 112 derives the AC voltage value Vac at the intersection of the characteristic lines L1 and L2 (that is, (db) / (ac)) as the reference peak voltage value Vpp0, and the previous first charging voltage. It is stored in the NVRAM 114 as a value at the time of determination (see Table 2).

  FIG. 6 will be referred to again. Since the reference peak-to-peak voltage value Vpp0 stored in S215 is a value based on the environmental step, it is difficult to say that the value matches the current environmental conditions with high accuracy. Therefore, the CPU 112 selects one set of slope and intercept corresponding to the in-machine temperature St and the in-machine humidity Sh obtained in S13 and S21 from the correction value table T3 previously stored in the NVRAM 114 or the like (S216). In the correction value table T3, as shown in Table 6, for each combination of temperature range and relative humidity range, a combination of slope and intercept is described. For example, if the in-machine humidity Sh is less than 20% and the in-machine temperature St is 10.5 ° C. or more and less than 12.5 ° C., (slope, intercept) is described as (−0.0054,269).

Next, the CPU 112 acquires the rotation speed of the Y-color photosensitive drum 5 from the usage status information Irot of the NVRAM 114 (S217).
Next, the CPU 112 derives a correction value based on the following equation (1) (S218).
Correction value = tilt × rotation speed + intercept (1)
Next, the CPU 112 adds the correction value of the corresponding color to the reference peak-to-peak voltage value Vpp0 derived in S215, and the actual peak-to-peak voltage that matches the current environmental conditions (ie, temperature and relative humidity) with high accuracy. The value Vpp1 is derived, and this actual peak-to-peak voltage value Vpp1 is stored in the NVRAM 114 as the correction value Vpp0 ′ of the reference peak-to-peak voltage value Vpp0 at the time of the previous first charging voltage determination (see S219, Table 2). .
Next, the CPU 218 stores the in-machine temperature St obtained in S13 in the NVRAM 114 as the value at the time of the previous determination of the first charging voltage (see S220, Table 2), and ends the process of FIG.

  Reference is again made to FIG. If the CPU 112 determines that the temperature change ΔSt1 is not greater than or equal to the first threshold value Tref1 (ie, 10 ° C.) in S14, the CPU 112 determines the second charging output, and in S17, determines the AC voltage Vac to be output from the AC power supply circuits 102 and 103. The actual peak-to-peak voltage value Vpp1 is determined (S16).

  Here, the second charging voltage determination will be described in detail with reference to FIG. In FIG. 8, the CPU 112 acquires the reference peak-to-peak voltage Vpp0 at the time of the previous first charging voltage determination from the NVRAM 114 (see Table 2) (S31).

Next, the CPU 112 acquires the current in-machine humidity Sh from the humidity sensor 122 (S32). Thereafter, the CPU 112 performs processing similar to that of S216 to S218 described above, and derives a correction value (S33 to S35).
Next, the CPU 112 adds the correction value to the reference peak-to-peak voltage value Vpp0 acquired in S31 to derive an actual peak-to-peak voltage value Vpp1 that matches the current environmental conditions with high accuracy (S36). The process of 8 is finished. As described above, the determination of the second charging voltage does not require the execution of S215 (see FIG. 7), which requires a large amount of computation. Vpp1 can be derived.

  Reference is again made to FIG. The CPU 112 outputs the peak-to-peak voltage value Vpp of the AC voltage Vac to be output from the AC power supply circuits 102 and 103 next to one of S15 and S16, and the actual peak-to-peak voltage value derived in one of S15 and S16. Vpp1 is set (S17). Further, the CPU 112 sets the DC voltage Vdc to be output from each DC power supply circuit 101 to a predetermined value (S18).

  Thereafter, the CPU 112 controls the printing process as described in the first column (S19). More specifically, in S19, as described in the first column, the CPU 112 controls paper passing and prints an image on the print medium M. When S19 is completed, the CPU 112 acquires the previous in-machine temperature St ′ from the NVRAM 114 and the current in-machine temperature St from the temperature sensor 121 (S110, S111). Next, the CPU 112 subtracts the previous in-machine temperature St ′ from the current in-machine temperature St, and determines whether or not the difference (ie, temperature change) ΔSt2 obtained as a result satisfies the second example of the predetermined condition ( S112). That is, in S112, the CPU 112 determines whether or not the temperature change ΔSt2 is 10 ° C. or more as a typical example of the second threshold Tref2 (S112).

  If the CPU 112 makes an affirmative determination in S112, it performs the first charging voltage determination similar to S15 (S113). However, in S113, unlike S15, the reference peak-to-peak voltage value Vpp0, its correction value Vpp0 ′, and the in-machine temperature St obtained in S111 are simply stored in the NVRAM 114 as values at the time of the previous determination of the first charging voltage. is there. In other words, the reference peak voltage value Vpp0 and the correction value Vpp0 ′ are not used in the current printing process as the actual peak voltage value Vpp1. This is because the purpose of storing the reference peak-to-peak voltage value Vpp0, its correction value Vpp0 ′ and the in-machine temperature St in S113 is used in a process (printing process, image stabilization, etc.) executed next to the current printing process. Because of that. As can be understood from the above, the reference peak-to-peak voltage value Vpp0 is only stored in the NVRAM 114 in this process, and may not be set in the AC power supply circuits 102 and 103 in this process. The value Vpp1 is set in the AC power supply circuits 102 and 103 in this process. In this respect, the reference peak voltage value Vpp0 is different from the actual peak voltage value Vpp1.

  The CPU 112 makes a negative determination in S112 or, after S113, stops the printing process (that is, stops applying the charging voltage Vg or stops the photosensitive drum 5) (S114), and ends the process of FIG. To do.

  Next, the reason why the first threshold value Tref1 and the second threshold value Tref2 in FIG. 5 are preferably 10 ° C. will be described with reference to FIG. FIG. 9 shows characteristic curves C1 and C2. The characteristic curve C1 shows the peak-to-peak voltage value Vpp derived by the first charging voltage determination with respect to the in-machine temperature. On the other hand, the characteristic curve C2 indicates the lower limit value of the peak-to-peak voltage value Vpp at which no image defect occurs on the printed matter with respect to the in-machine temperature. According to the experiment of the present inventor, it has been found that an image defect due to charging failure occurs in a printed matter in a temperature range where the characteristic curve C1 is lower than the characteristic curve C2.

  Further, in the region where the in-machine temperature is 10 ° C. or higher in the characteristic curve C2, the peak-to-peak voltage value Vpp changes by about 50 V when the in-machine temperature changes by about 10 ° C. When the AC voltage Vac is changed by about 50 V, it has been found by an experiment by the present inventors that an image defect occurs in the printed matter.

  From the above, when the in-machine temperature has changed by 10 ° C. or more since the previous determination of the first charging voltage, the first charging voltage determination is performed again, and an appropriate AC voltage Vac (between peaks) is determined according to the current in-machine temperature. The voltage value Vpp) needs to be derived again. On the other hand, if not, the correction value is added to the reference peak-to-peak voltage value Vpp0 stored at the previous determination of the first charging voltage without executing the first charging voltage determination again, and the AC voltage Vac (between peaks) is determined. It has been found by experiments of the present inventors that no image defect occurs in the printed matter even if the voltage value Vpp) is derived. Further, when the internal temperature does not change by 10 ° C. or more, the time from the start to the end of the printing process can be shortened unless the first charging voltage determination is performed again.

  Again, if the AC voltage Vac superimposed on the charging voltage Vg is too small, an image defect occurs on the printed matter (see the characteristic curve C2 in FIG. 9). On the contrary, if the AC voltage Vac is too large, the wear of the photosensitive drum 5 is increased. Further, as is apparent from the characteristic curve C2 of FIG. 9, the AC voltage Vac must be set relatively large when the in-machine temperature decreases. Conversely, when the in-machine temperature rises, the AC voltage Vac must be set relatively small. Further, when the internal temperature changes by about 10 ° C., the peak-to-peak voltage value Vpp changes by about 50 V, and as a result, an image defect occurs on the printed matter.

  From the above, when the internal temperature has changed by 10 ° C. or more in the current printing process from the time of the previous determination of the first charging voltage, the CPU 112 temporarily determines the second charging voltage and determines the reference in the NVRAM 114. Assume that the actual peak-to-peak voltage value Vpp1 is determined using the peak-to-peak voltage Vpp0. In this case, an actual peak-to-peak voltage value Vpp1 lower than the AC voltage Vac suitable for the temperature environment of the current printing process is obtained, and there is a high possibility that an image defect will occur on the printed matter.

  On the other hand, when the internal temperature rises by 10 ° C. or more, it is assumed that the second charging voltage determination is performed. In this case, an actual peak-to-peak voltage value Vpp1 higher than the AC voltage Vac suitable for the temperature environment of the current printing process is obtained, and the possibility that the photosensitive drum 5 is excessively worn out increases.

  In consideration of the above, the first threshold Tref1 used in S14 of FIG. 5 is set to 10 ° C., and if the temperature change ΔSt1 is 10 ° C. or more in S14, the first charging voltage determination is executed. Otherwise, the second charging voltage determination is executed with priority given to reducing the waiting time of the user.

  When the temperature change ΔSt1 rises by 10 ° C. or more in S14, the first charging voltage may be determined in consideration of excessive wear of the photosensitive drum 5. However, in this embodiment, in this case, priority is given to reducing the waiting time of the user, and the second charging voltage is determined in consideration of the low possibility of image failure.

Reference is now made to FIG. 4 again. As described above, when an affirmative determination is made in S03, the processing of FIG. 10 is performed.
In FIG. 10, when executing any one of image stabilization, forced toner replenishment, and TCR adjustment, the CPU 112 determines the previous in-machine temperature St ′ and the current in-machine temperature St in the same manner as S12 and S13 described above. Is acquired (S41, S42). Next, the CPU 112 determines whether or not the absolute value | ΔSt | of the difference (that is, temperature change) obtained as a result satisfies the third example of the predetermined condition (S43). That is, in S43, the CPU 112 determines whether or not the absolute value | ΔSt | of the temperature change is 10 ° C. or more as a typical example of the third threshold Tref3 (S43). In image stabilization and the like, paper is not passed but image formation is performed. Therefore, the third threshold value Tref3 is preferably 10 ° C., which is the same as the first threshold value Tref1. However, the present invention is not limited to this, and the third threshold value Tref3 may be different from the first threshold value Tref1.

  If the CPU 112 makes an affirmative determination in S43, the CPU 112 acquires the correction value Vpp0 ′ from the NVRAM 114 in order to reduce the waiting time of the user (S44). Thereafter, the CPU 112 starts up a process (S45). Specifically, when each photosensitive drum 5 is activated and its rotation speed is stabilized, the CPU 112 corrects the peak-to-peak voltage value Vpp of the AC voltage Vac to be output from the AC power supply circuits 102 and 103 in S44. Temporarily set to Vpp0 ′, the DC voltage Vdc to be output from each DC power supply circuit 101 is set to a predetermined value. As a result, the charging voltage Vg is applied from the power supply means 10 to each charging means 6 to charge each photosensitive drum 5.

Next, the CPU 112 performs first charging voltage determination (refer to FIG. 6 for details), and determines the actual peak-to-peak voltage value Vpp1 of the AC voltage Vac to be output in S47 (S46).
Next, the CPU 112 switches the set value of the peak-to-peak voltage value Vpp of the AC voltage Vac to be output from the AC power supply circuits 102 and 103 to the actual peak-to-peak voltage value Vpp1 determined in S46 (S47).

  On the other hand, when the CPU 112 makes a negative determination in S43, the CPU 112 performs second charging voltage determination (refer to FIG. 8 for details) and determines the actual peak-to-peak voltage value Vpp1 of the AC voltage Vac to be output in S49. (S48). Here, the determination of the second charging voltage is significantly shorter than the determination of the first charging voltage with respect to the processing time. Therefore, it is not necessary to temporarily set the AC voltage Vac before determining the second charging voltage.

  Thereafter, the CPU 112 starts up a process (S49). Specifically, when each photosensitive drum 5 is started and its rotational speed is stabilized, the CPU 112 obtains the peak-to-peak voltage value Vpp of the AC voltage Vac to be output from the AC power supply circuits 102 and 103 in S48. The peak-to-peak voltage value Vpp1 is set, and the DC voltage Vdc to be output from each DC power supply circuit 101 is set to a predetermined value. As a result, charging of each photosensitive drum 5 is started.

  When one of S47 and S49 ends, the CPU 112 performs processing necessary for the process (image stabilization, forced toner supply, TCR adjustment) (S410).

<< Column 4: Actions and effects of image forming apparatus >>
According to the image forming apparatus 1, if the current in-machine temperature St changes by a predetermined threshold or more compared to the previous in-machine temperature St ′, the CPU 112 causes an image failure or the photosensitive drum 5 is excessive. The first charging voltage is determined and the reference peak-to-peak voltage value Vpp0 is derived. Since the reference peak-to-peak voltage value Vpp0 is based on the detection result of the current detection means 13, it is a value that matches the current environmental conditions, so that it is possible to suppress the occurrence of image defects on the printed matter, and the photosensitive drum 5 is excessively excessive. Can also be suppressed. Specifically, when the temperature change ΔSt1 is 10 ° C. or higher in S14 of FIG. 5, the temperature change ΔSt2 is 10 ° C. or higher in S112 of FIG. 5, or the temperature change | ΔSt | In the above case, the first charging voltage is determined, and the reference peak-to-peak voltage value Vpp0 as described above is derived.

  On the other hand, if the current in-machine temperature St does not change by a predetermined threshold or more compared to the previous in-machine temperature St ′, the first charging voltage determination that requires a large calculation is not performed, and as a result, the waiting time of the user is reduced. Reduced. More specifically, if the temperature change ΔSt1 is not 10 ° C. or more in S14 of FIG. 5 or if the temperature change | ΔSt | is not 10 ° C. or more in S43 of FIG. When the voltage determination is performed and the temperature change ΔSt2 is not 10 ° C. or more in S112 of FIG. 5, S114 is executed without performing the first charging voltage determination or the second charging voltage determination.

  Further, particularly in the printing process, in S14 of FIG. 5, if the internal temperature has decreased by the first threshold value Tref1 or more in the current printing process from the time of the previous determination of the first charging voltage before passing paper, As described above, in order to suppress image defects in the image formation immediately after that, the first charging voltage determination is performed to obtain the reference peak-to-peak voltage value Vpp. Also, in S112 of the figure, if the internal temperature has risen by the second threshold value Tref2 or more in the current printing process after the sheet is passed, as described above, in order to suppress excessive wear of the photosensitive drum 5, the first The charging voltage is determined to obtain the reference peak voltage value Vpp. As a result, for example, during continuous execution of a print job, an appropriate reference peak-to-peak voltage value Vpp is set in the subsequent printing process even if the subsequent printing process is performed in a state where the internal temperature has increased in the previous printing process. It can be derived.

  Further, according to the image forming apparatus 1, the first charging voltage determination and the second charging voltage determination are selectively executed according to the difference value ΔSt1 and the absolute value | ΔSt | of the difference value. When performing the second charging voltage determination, the peak-to-peak voltage value Vpp of the AC voltage Vac to be superimposed on the charging voltage Vg can be derived without performing the first charging voltage determination that requires a large amount of calculation. As a result, various processes can be executed quickly, so that it is possible to provide the image forming apparatus 1 that can reduce the waiting time of the user.

  In determining the second charging voltage, the CPU 112 performs steps S31 to S35 in FIG. 8 based on the current environmental conditions (in-machine temperature St and in-machine humidity Sh) and the usage status of the photosensitive drum 5 (for example, the number of revolutions). A correction value is derived. Thereafter, in S36, the CPU 112 corrects the reference peak-to-peak voltage value Vpp0 obtained in the previous determination of the first charging voltage, and the appropriate actual peak-to-peak interval according to the current environmental conditions and the usage state of the photosensitive drum 5 is corrected. The voltage Vpp1 can be derived. In the above description, the environmental conditions are the temperature and relative humidity in the image forming apparatus 1. However, when the environment detection unit 12 includes an absolute humidity sensor, a correction value may be obtained by selecting an inclination and an intercept from the correction table T3 (see Table 6) based on the absolute humidity.

  In determining the first charging voltage, the CPU 112 derives a correction value based on the current environmental conditions and the usage state of the photosensitive drum 5 through S216 to S218 in FIG. Thereafter, in S219, the CPU 112 corrects the reference peak-to-peak voltage value Vpp0 obtained in the determination of the first charging voltage this time, and the appropriate actual peak-to-peak interval according to the current environmental conditions and the usage state of the photosensitive drum 5 is corrected. The voltage Vpp1 can be derived.

<5th column: Appendix>
In the description of the above embodiment, the current detection unit 13 is described as being provided in the Y-color charging unit 6. However, the present invention is not limited to this, and when the power supply unit 10 includes the AC power supply circuits 102 and 103, the current detection unit 13 may be provided in any one of the charging units 6.

  The image forming apparatus 1 may be provided with two current detection means 13. In this case, one of the current detection means 13 is the YMC color charging means 6 and the other current detection means 13 is the other current detection means 13. , K charging means 6 may be provided. In this case, the CPU 112 may derive the peak-to-peak voltage value Vpp for the AC power supply circuit 102 shared by the YMC colors and the peak-to-peak voltage value Vpp for the K-color AC power supply circuit 103.

  In the description of the above embodiment, the power supply unit 10 has been described as including the AC power supply circuit 102 shared by the YMC colors and the K power supply circuit 103. However, the present invention is not limited to this, and the power supply means 10 may include individual AC power supply circuits in the YMCK color. In this case, four current detection means 13 may be provided in the image forming apparatus 1, and the CPU 112 may derive the peak value voltage Vpp for each AC power supply circuit.

  Moreover, in the said embodiment, 1st threshold value Tref1 and 2nd threshold value Tref2 were demonstrated as the same 10 degreeC. However, the present invention is not limited to this, and both threshold values Tref1 and Tref2 may be different. For example, the second threshold value Tref2 may be other than 10 ° C.

  The image forming apparatus according to the present invention can suppress an unnecessarily long waiting time of a user when determining a peak-to-peak voltage value, regardless of whether it is a color machine or a monochrome machine. It is suitable for a multifunction machine having the above functions.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 5 Photosensitive drum (image carrier)
6 Charging means 10 Power supply means 112 CPU (Processing means)
121 Temperature sensor 122 Humidity sensor

Claims (7)

An image forming apparatus that prints an image on a medium when passing paper,
An image carrier;
Charging means disposed in proximity to the image carrier;
A plurality of charging voltages each including an alternating current, and a plurality of charging voltages obtained by superimposing a plurality of alternating voltages having different peak-to-peak voltages of each of the alternating currents are sequentially applied to the charging unit when paper is not fed When,
Current detecting means for detecting an alternating current value flowing through the charging means during application of each of the plurality of charging voltages;
When a predetermined condition is satisfied, based on the detection result of the current detection means, a processing means for determining a first charging voltage for deriving a peak-to-peak voltage to be used in the process, and
The image forming apparatus, wherein the predetermined condition is that the current ambient temperature changes by a predetermined threshold or more compared to the ambient temperature at the time of the previous first charging voltage determination. The process is a printing process for printing an image on a medium when a paper is passed,
The predetermined condition includes a first condition that the current ambient temperature decreases by a first threshold or more compared to the ambient temperature at the time of the previous first charging voltage determination, and the ambient condition at the time of the previous first charging voltage determination. A second condition that the current ambient temperature rises by more than a second threshold value compared to the temperature, and
The processing means performs the first charging voltage determination when the first condition is satisfied before paper passing in the printing process, and the first charging voltage is satisfied when the second condition is satisfied after paper passing in the printing process. The image forming apparatus according to claim 1, wherein the determination is performed.   The processing means performs a second charging voltage determination capable of deriving a peak-to-peak voltage to be used in the process in a shorter time than the first charging voltage determination if the predetermined condition is not satisfied. The image forming apparatus described in 1.   In the second charging voltage determination, the processing means corrects the peak-to-peak voltage determined in the previous first charging voltage determination based on the current environmental conditions and the usage status of the image carrier, thereby the process. The image forming apparatus according to claim 3, wherein a peak-to-peak voltage to be used is derived.   The image forming apparatus according to claim 4, wherein the environmental condition is at least one selected from temperature, relative humidity, and absolute humidity.   The image according to any one of claims 1 to 3, wherein the processing means corrects the derived peak-to-peak voltage based on the current environmental conditions and the usage state of the image carrier in the first charging voltage determination. Forming equipment. A range of AC voltage in which only charge transfer from the charging means toward the image carrier occurs as a positive discharge region, and a range of AC voltage in which bidirectional charge transfer occurs alternately between the image carrier and the charging means. In the reverse discharge region,
The power supply means is a plurality of charging voltages each including an alternating current, and sequentially applying a plurality of charging voltages in which the peak-to-peak voltages of the alternating currents are different from each other in each of the positive discharge region and the reverse discharge region,
In the first charging voltage determination, the processing means determines the intersection of the characteristic line of the alternating current value with respect to the alternating voltage in the positive discharge region and the characteristic line of the alternating current value with respect to the alternating voltage in the reverse discharge region. The image forming apparatus according to claim 1, wherein the image forming apparatus is derived as a peak-to-peak voltage to be used in the above.

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