JP2013080127A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that performs environmental history control, and reduces an influence of a change in image density due to an environmental change when the power is turned off to perform appropriate image formation.SOLUTION: An image forming apparatus includes: a delayed-change-in-humidity member, humidity of which changes with delay following a change in ambient humidity; and a control unit that sets a tentative image forming condition on the basis of former environmental information that is obtained before a previous turn-off of a power supply of the control unit and stored in a storage unit, and corrects the tentative image forming condition on the basis of the former environmental information and new environmental information obtained from the delayed-change-in-humidity member at the time of a current turn-on of the control unit so as to determine an image forming condition.

Description

  The present invention relates to an image forming apparatus such as a dry electrophotographic printer or a copying machine.

  In dry electrophotography, frictional charging of toner is used in the process of image formation. For this reason, the surrounding atmosphere (temperature, relative humidity, absolute water content, etc.) is an important parameter. Thus, many techniques for detecting the ambient atmosphere and controlling the image forming conditions have been disclosed. In particular, a number of so-called “environment history controls” that store past environment information and change the image forming conditions together with the current environment information have been disclosed (for example, see Patent Document 1).

JP 2001-147620 A

  In considering the environmental history control using the technique of Patent Document 1, the time when the image forming apparatus is turned on is considered. In FIG. 19, time is plotted on the horizontal axis and humidity is plotted on the vertical axis. Two curves (humidity example (1): solid line, humidity example (2): broken line) in the region of 50% to 80% with respect to humidity are examples of actual environmental conditions around the image forming apparatus. A solid line in the region of 10% to 30% shows a time-series graph simulating on / off of the power supply of the image forming apparatus. Since the environment changes, the values themselves in FIG. 19 are merely an example.

  Environmental history control uses current environmental information and older environmental information, and sets more appropriate image forming conditions for materials whose characteristics change historically with respect to environmental conditions such as photosensitive drums and developers. To do.

  The environment information that can be used in this case includes the environment information whose timing is indicated by an arrow as “current environment detection” on the right side of FIG. 19 and the older environment information, that is, “the previous environment” on the left side of FIG. Environmental information indicated by arrows as “detection”. The image forming apparatus estimates the humidity during that time from two pieces of information: “current environment detection” and “previous environment detection”. The simple method is to interpolate linearly or exponentially with the horizontal axis as time.

  When the environmental information does not change while the power of the image forming apparatus is turned off, for example, in the case of the humidity example (1), the interpolation as described above has almost no error with respect to the actual humidity example (1). It can be calculated. For this reason, setting of image forming conditions by this method is effective.

  However, as in humidity example (2), the environment may change significantly while the image forming apparatus is powered off. For example, the air conditioner is turned off while the image forming apparatus is turned off, the room is hot and humid, and the image forming apparatus is turned on after the air conditioning is turned on the next morning.

  In this case, the image forming apparatus cannot detect the environment while the power is off. On the other hand, the photosensitive drum and the developer are exposed to such a humidity change, and the characteristics thereof are changed. For this reason, setting of image forming conditions may not always be accurate. As a result, the obtained image has a problem such as a density fluctuation.

  As the simplest alternative to this, a means for intermittently driving only a part such as a printer control unit related to humidity measurement of the image forming apparatus even when the power is turned off can be considered. However, the drive itself and the control means for controlling on / off of the drive are turned on, and so-called standby power is consumed. At present, power saving performance is required for office machines and home appliances in various forms, and it is not preferable to perform control based on standby power. This is the same in that some power is consumed even when a (primary or secondary) battery is mounted on the main body of the image forming apparatus.

  An object of the present invention is to reduce an influence of an image density change due to an environment change when the power is turned off and perform an appropriate image formation in an image forming apparatus that performs environmental history control.

  A typical configuration of the present invention for achieving the above-described object includes an image carrier, a developer that visualizes an electrostatic latent image carried on the image carrier as a toner image, and obtains time A time acquisition unit, an environment measurement unit that measures the environment in the image forming apparatus, a storage unit that stores environment information obtained from the environment measurement unit and environment measurement time information obtained from the time acquisition unit, In an image forming apparatus having a control unit that determines image forming conditions and a control unit power source that supplies power to the control unit, the humidity changes so as to follow a change in ambient humidity with a delay. A humidity follow-up delay member, and the control unit sets an image formation provisional condition based on old environment information stored in the storage unit acquired before the previous power-off of the control unit power supply, Environmental information and the power supply By correcting the image forming temporary condition by at new environment information obtained from the humidity tracking delay member, and determines the image forming condition.

  With the above configuration, in an image forming apparatus that performs environmental history control, it is possible to reduce the influence of an image density change due to an environmental change when the power is turned off and to perform appropriate image formation.

1 is a schematic diagram of an image forming apparatus according to a first embodiment. The figure explaining the station for 1 color of 1st Embodiment. FIG. 3 is a block diagram corresponding to one color according to the first embodiment. 6 is a flowchart for explaining an outline of a printing operation according to the first embodiment. The flowchart explaining the discharge current control of 1st Embodiment in detail. The graph explaining the discharge current control of 1st Embodiment in detail. The graph which showed the humidity transition of the charging roller of 1st Embodiment. The graph showing the environmental fluctuation | variation which is a subject of 1st Embodiment. The graph explaining the time constants D and C of 1st Embodiment. The flowchart explaining the environmental log | history correction control which is the characteristics of 1st Embodiment. 10 is a flowchart for explaining a printing operation according to the second embodiment. 10 is a flowchart for explaining an outline of a printing operation according to a third embodiment. 9 is a flowchart for explaining transfer voltage setting control according to a third embodiment. The graph explaining the transfer voltage setting control of 3rd Embodiment in detail. The flowchart explaining the environmental log | history correction control which is the characteristics of 3rd Embodiment. 6 is a flowchart for explaining an outline of a printing operation of a comparative example. The flowchart explaining the humidity calculation of a comparative example. The flowchart explaining the humidity history control of a comparative example. The graph showing the environmental change which is a conventional subject.

[First Embodiment]
(Outline of image forming apparatus of this embodiment)
FIG. 1 is a schematic diagram of an image forming apparatus according to the first embodiment.

  As shown in FIG. 1, the image forming apparatus A according to this embodiment uses yellow (Y), magenta (M), cyan (C), and black (K) photosensitive drums 28 (28Y, 28M, 28C, and 28K). This is a so-called tandem full-color image forming apparatus provided in parallel. The configuration of the photosensitive drum 28 (image carrier) and the process means corresponding to each photosensitive drum 28 is the same regardless of the image forming colors (Y, M, C, K). For this reason, in the following description, display of image forming colors (Y, M, C, K) is omitted as appropriate.

  First, the image forming apparatus A creates a toner image of each color at each color station (image forming unit), and visualizes the electrostatic latent image carried on each photosensitive drum 28. Then, four color toner images are superimposed on the intermediate transfer belt 24 by the primary transfer roller 23 (23Y, 23M, 23C, 23K), and then, the secondary transfer roller 23z collectively performs the secondary transfer on the transfer material 27. To do.

  Thereafter, the transfer material 27 on which the toner images for four colors are transferred is heated and pressed by the fixing device 25. Then, the toner image is fixed on the transfer material 27 and becomes a permanent image. Residual toner that has not been transferred to the transfer material 27 is removed by the photosensitive drum cleaner 26 (26Y, 26M, 26C, 26K). Further, before cleaning, the charge of the photosensitive drum 28 is discharged by the discharging member 29 (29Y, 29M, 29C, 29K).

  The configuration of each station will be described in detail with reference to FIGS. FIG. 2 is a diagram illustrating a station for one color according to the first embodiment. FIG. 3 is a block diagram corresponding to one color of the first embodiment.

  In the following description, the reference numerals are simply shown in common to each station. Each station has means for applying a charging bias, a developing bias, and a primary transfer bias. That is, a charging bias power source 41 (41Y, 41M, 41C, 41K), a developing bias power source 42 (42Y, 42M, 42C, 42K), and a primary transfer bias power source 43 (43Y, 43M, 43C, 43K) are provided. The printer control unit 300 (control unit) controls the operation of each part of the above-described image forming apparatus A and the bias power supply by the built-in CPU 301 and the like.

  The photosensitive drum 28 has a configuration in which three layers of an undercoat layer, a photocharge generation layer, and a charge transport layer (thickness of about 20 μm) are sequentially applied from the bottom to the surface of an aluminum cylinder.

  The surface of the photosensitive drum 28 is uniformly charged by the charging bias applied from the charging bias power source 41 to the charging roller 21 (charging member). This uniformly charged potential on the photosensitive drum 28 is referred to as a white background potential or Vd (V). The charging bias is obtained by superimposing an alternating current component on the direct current component Vchg (V), and details thereof will be described later, but the value of Vchg (V) is adjusted to be approximately Vd (V).

  Next, the irradiation position of the laser 22 (22Y, 22M, 22C, 22K) is controlled based on a signal corresponding to the level of the image data (image signal), and the Vd (V) portion on the photosensitive drum 28 is irradiated. Thereby, an electrostatic latent image is formed on the photosensitive drum 28. The potential of the portion subjected to the maximum exposure by the laser 22 is referred to as the maximum density portion potential or Vl (V).

  The developing device 1 will be described in detail. The developer of this embodiment employs a “two-component development method” in which a nonmagnetic toner and a magnetic carrier are mixed and used as a developer.

  The non-magnetic toner is mainly composed of polyester, and is obtained by pulverizing and classifying a resin in which a colorant corresponding to each color of black, cyan, magenta, and yellow and a wax as a fixing aid are mixed. As the toner resin, in addition to the polyester used in the present embodiment, a styrene acrylic type or a mixture thereof can be used.

  In addition to the pulverization and classification method used in the present embodiment, a spherical toner prepared using a polymerization method can also be used. As the magnetic carrier, a ferrite core coated with silicon resin is used. As the core, magnetic resin particles such as magnetite or the like, which are solidified with phenol resin or the like and made spherical, may be used. As the coating agent, styrene acrylic, fluorine, and other various materials may be used.

  Inside the developing device 1, two screw pairs 4 provided in parallel rotate. As a result, the developer is conveyed in directions opposite to each other in the direction perpendicular to FIG. 2, and the developer is delivered at both ends in the vertical direction in FIG. In this manner, the developer is circulated while being stirred in the developing device 1 due to the presence of the screw pair 4.

  A developing sleeve 3 is provided at the opening of the developing device 1 so as to face the photosensitive drum 28. The developing sleeve 3 carries a two-component developer and conveys it to the surface of the photosensitive drum 28 by the magnetic force of the magnet 5 provided inside.

  A developing bias in which an AC component is superimposed on a predetermined DC component Vdev (V) is applied to the developing sleeve 3 from a developing bias power source 42. The absolute value of the difference of Vl−Vdev is called Vcont, and indicates the potential of the maximum density portion of the electrostatic latent image viewed from the developing sleeve 3. The absolute value of Vd−Vdev is referred to as Vback, which is a potential difference provided to guarantee the toner fog on the white background.

  The sum of Vcont and Vback matches the difference between Vd and Vl, and this value is called the latent image contrast. If the maximum exposure amount is determined, Vl is uniquely determined with respect to Vd. That is, by adjusting Vd, the latent image contrast can be adjusted, and there is a predetermined relational expression. The printer control unit 300 stores the predetermined relational expression, and determines an appropriate value of Vd, that is, a DC component Vchg of the charging bias from a required value of Vcont / Vback. Further, the value obtained by subtracting the value of Vback from that value is the DC component Vdev of the developing bias.

  The toner images of the respective colors are primarily transferred to the primary transfer roller 23 while being superimposed on the intermediate transfer belt 24 (transfer member) by the primary transfer bias Vtr1 applied from the primary transfer bias power source 43.

  As shown in FIG. 3, the printer control unit 300 supplied with power from the control unit power supply 100 includes a CPU 301, a nonvolatile memory 302 and a ROM 303 as a storage unit, and a time acquisition unit 304 that acquires time. The storage unit stores environment information obtained from an environment measurement unit described later and environment measurement time information obtained from the time acquisition unit 304. The printer control unit 300 determines image forming conditions from these.

  The printer control unit 300 includes a developing device temperature sensor 51 and an environment sensor 53 as an environment measurement unit.

  Temperature information is acquired from the developing device temperature sensor 51 (51Y, 51M, 51C, 51K), and annular information is acquired from the environment sensor 53. As shown in FIG. 1, the developing device temperature sensor 51 is arranged in each color developing device 1 and detects the temperature t (tY, tM, tC, tK) of each developing device 1.

  The environmental sensor 53 is provided in the image forming apparatus, and detects environmental temperatures T (° C.) and RH (%) from the surrounding environment. It is more preferable that the environmental sensor 53 is disposed at a position close to the outer wall of the image forming apparatus A and as far as possible from various heat sources in the apparatus. The detected temperature t, T (° C.), and RH (%) are notified to the printer control unit 300.

  In many existing image forming apparatuses, the image forming apparatus itself controls on / off of the printer control unit 300. That is, the printer control unit 300 operates only when the image forming apparatus is powered on and the printer control unit 300 is also powered on. In the following description, in order to simplify the description, in the present embodiment, it is assumed that the power on / off of the main body of the image forming apparatus is the on / off of the printer control unit 300. The description here is for one image forming station, and the printer controller 300 actually performs the operations for four stations in parallel.

[Comparative Example]
In order to explain the features of this embodiment in an easy-to-understand manner, first, a conventional image forming apparatus having a device configuration similar to that of this embodiment will be described as a comparative example. FIG. 16 is a flowchart for explaining the outline of the printing operation of the comparative example.

  The printer control unit 300 is in a print standby state in step S101. When the power is turned on, the flow starts from this step S101. Conversely, the power is turned off when the process always returns to step S101.

  Upon receiving a print instruction command, the printer control unit 300 obtains the current ambient environment temperature TMPn value and relative humidity RHn value from the environment sensor 53 in the image forming apparatus main body. Further, the developer temperature tmpn is acquired from the developer temperature sensor 51. The printer controller 300 obtains the humidity rhn (relative humidity) around the developing device from these values (step S102, details will be described later).

  Subsequently, the printer control unit 300 reads the temperature tmpm and humidity rhm previously measured and calculated as the temperature and humidity of the developer from the nonvolatile memory 302 which is a built-in nonvolatile RAM, and the time tm at which the temperature was obtained. And between humidity rhm and humidity rhn is complemented based on current time tn and stored time tm. Then, the “average developer current” humidity rhr is calculated (step S103, details will be described later). The process of step S103 is “environment history control”.

  Based on the humidity rhr, the printer control unit 300 performs “discharge current control” (step S104) and “transfer voltage setting control” (step S105) as described later. Thereafter, the obtained image forming conditions (charging, exposure, development, transfer) are set (step S106), and then a printing operation is performed (step S107). At the end of the printing operation (step S108), the printer control unit 300 stores the value of the humidity rhr used here in the nonvolatile memory 302 as the humidity rhm and the calculated time as tm (step S109).

  Next, the detailed operation of step S102 will be described. FIG. 17 is a flowchart for explaining the humidity calculation of the comparative example.

  As shown in FIG. 17, first, the printer control unit 300 determines that the current ambient environment temperature TMPn value, the relative humidity RHn value, the developing device temperature sensor 51 to the developing device temperature tmpn from the environmental sensor 53 in the image forming apparatus main body. Is acquired (step S201).

  In general, in order to obtain the absolute water content from the temperature and relative humidity, it is first necessary to obtain the saturated water vapor pressure based on the temperature of the air. Since the image forming apparatus of the present invention is used in an environment of approximately 1 atm and a temperature of approximately 0 ° C. to 60 ° C., the printer control unit 300 obtains the saturated water vapor pressure at that temperature using the Tetens approximation (step S202). ).

E (τ) = 611 × 10 ^ (7.5 × τ / (τ + 237.3)) (1)
(E (τ): saturated water vapor pressure (Pa), τ: Celsius temperature (° C.))
There are two methods for obtaining the absolute humidity from the vapor pressure, and there are a method using the absolute weight humidity (g / kg DryAir) and a method using the absolute volume humidity (g / m ³ ). Here, a calculation method using absolute volume humidity will be described.

Since water vapor in the air has a small partial pressure, it follows the equation of state of an ideal gas. That is,
PV = nRT (2)
Where P: partial pressure (Pa), V: volume (m ³ ), n: number of moles (mol),
R: Gas constant (Pa · m ³ / K · mol), T: Temperature (K)
Can be used.

Saturation value of absolute volume humidity used for humidity calculation in this embodiment is ABS (σ) (g / m ³ ), and the weight of water at that time is M (g).
Since ABS (σ) = M / V, number of moles n = M / (molecular weight of water), and P = E (τ),
ABS (σ) = molecular weight of water × E (τ) / R × (τ + 273.15) (3)
Furthermore, since the molecular weight of water = 18.0154 (1 / mol) and the gas constant R = 8.31447 (Pa · m ³ / K · mol), the absolute humidity saturation value at the ambient temperature TMPn is
ABS (σ) (g / m ³ )
= 2.1668 × E (TMPn) / (TMPn + 273.15) (4)
It becomes.

Further, by multiplying the absolute humidity saturation value ABS (σn) by the relative humidity RHn (% RH), the moisture content ABSn (g / m ³ ) of the current air is obtained,
ABSn = ABS (σ) × RHn (5)
Therefore, the printer control unit 300 calculates ABSn according to equations (2) to (5) (step S203).

Next, the printer control unit 300 substitutes the developing device temperature tmpn, which is the temperature measurement value of the developing device temperature sensor 51, into the formula (1), and sets the saturated water vapor pressure at the developing device temperature tmpn to ABS (σ (tmpn)). (Step S204),
rhn = ABSn / ABS (σ (tmpn)) (6)
Thus, the humidity rhn (relative humidity) around the current developing device 1 is obtained (step S205).

  Next, details of step S103 will be described. FIG. 18 is a flowchart for explaining the humidity history control of the comparative example.

  As shown in FIG. 18, first, the printer control unit 300 reads out the humidity rhm used in the previous image formation condition setting and the time tm when the humidity rhm was calculated, which is stored in the nonvolatile memory 302. (Step S301). Next, the humidity rhn of the calculation result in step S102 and the time tn at which the calculation was performed are read (step S302).

  Here, the humidity of the “developer” when the environment “around the developing device” changes will be considered. For example, a portion of the developing device 1 exposed to the surrounding air easily follows the surrounding environment, but a portion far from the air such as the bottom of the container does not easily follow the surrounding environment. Considering this phenomenon as a whole, the current humidity “rhr” of the “developer” is a value of the currently calculated humidity rhn around the developing device 1 and the “developer” humidity rhm calculated in step S102. It is expected to be located between.

According to the above-mentioned consideration and the examination results of the present applicants based on the above consideration, the humidity (rhr) of the current developer (time tn) is
rhr = (rhm−rhn) × exp (− (tn−tm) / βd) + rhn (7)
Can be obtained approximately.

  Here, βd is a time constant having a time dimension (dimension), which is determined by the configuration of the developing device 1, the physical properties of the developer, the amount of the developer, or the like, or is obtained experimentally. This is the speed at which you are familiar. In this embodiment, βd = 240 (min).

  Based on equation (7), the printer controller 300 obtains the current humidity rhr of the developer from the humidity rhm, the humidity rhn, the time tm, and the time tn (step S303). By performing complementation using an exponential function, for example, it is possible to set image forming conditions with high accuracy even when the interval for acquiring environmental information is long.

  As described above, the current humidity rhr of the developer and the time tn at which it is calculated are stored in the nonvolatile memory 302 as the humidity rhm and the time tm, respectively (step S304).

  However, as described in the section “Problems to be Solved by the Invention”, if the image forming apparatus main body is turned off, the printer controller 300 is not turned on. For this reason, the environmental sensor 53 and the developing device temperature sensor 51 cannot acquire the ambient environmental temperature TMPn, the relative humidity RHn, and the developing device temperature tmpn therebetween.

  However, this problem can be solved by a configuration unique to the present invention as described below.

(Characteristic part of this embodiment)
In the present embodiment, the property that the electrical resistance of the charging roller 21 is related to “environmental temperature and humidity” and the humidity changes with a delay with respect to the surrounding environment is used. That is, even when the image forming apparatus A is powered off, the charging roller 21 (humidity tracking delay member) changes its humidity value while being delayed with respect to the surrounding environment. When the humidity value changes, the charging roller 21 has a portion where the electrical characteristics change. For this reason, it is considered that the electrical resistance of the charging roller 21 at the next power-on reflects the humidity history during the power-off period.

  Therefore, the environmental humidity history during the power-off period can be estimated by measuring and comparing the electrical resistance characteristics of the charging roller 21 when the power is finally turned off and when the power is turned on. Then, the calculated humidity value of the developer (when the power is turned on) can be corrected as necessary, and the humidity of the developer can be calculated with high accuracy.

  FIG. 4 is a flowchart for explaining the outline of the printing operation of the first embodiment. An outline of the printing operation of the present embodiment will be described based on the flowchart of FIG.

  As shown in FIG. 4, the printer control unit 300 is in a print standby state in step T101. When the printer control unit 300 receives a print instruction command, the humidity rhn is obtained in the same manner as in step S102, and image forming conditions are set once from the value of the humidity rhn (step T102).

  The settings here are provisional conditions (image formation provisional conditions) for performing subsequent steps T103 and T104, and the set values here are corrected in step T106 described later. In this embodiment, before performing an operation corresponding to “environment history control” shown in step S103 of the comparative example, “discharge current control” is performed as step T103, and “transfer voltage setting control” is performed as step T104.

  Thereafter, the “environment history correction control” in step T105, which is a feature of the present embodiment, is performed to correct the image formation provisional condition that is the partial set value described above, and then the image formation condition is set (step T106). Steps T107 to T109 are the same as steps S107 to S109 of the comparative example.

  Next, “discharge current control” in step T103 will be described in detail.

  In this embodiment, as the charging roller 21, for example, a roller in which a foamed EPDM rubber roller made conductive by carbon dispersion is coated on a core metal is used. The charging roller 21 is applied with a charging bias from a charging bias power source 41. The charging bias power supply 41 is a low voltage power supply that can control the output voltage value (DC component and AC component), and can measure the current value (DC component and AC component) by the applied bias.

  Such a charging roller 21 is brought into contact with and energized with the photoconductive drum 28, and the surface of the photoconductive drum 28 is made uniform by utilizing a discharge phenomenon generated in a small gap between the photoconductive drum 28 formed on both sides of the contact portion. It is charged like this.

  A charging bias in which a sine wave having a peak-to-peak voltage Vac and a frequency of 2.3 kHz is superimposed on the DC component Vchg is applied to the core of the charging roller 21 from the charging bias power supply 41. The magnitude of Vac can be obtained as a voltage at which the above-described “discharge phenomenon that occurs in the minute gap between the photosensitive drums 28 formed on both sides of the contact portion” starts to occur.

  Further, a method of determining Vac by “discharge current control” will be described with reference to the flowchart of FIG. 5 and the graph of FIG. This corresponds to step S104 in FIG. 16 in the comparative example and step T103 in FIG. 4 in the present embodiment. FIG. 5 is a flowchart for explaining in detail the discharge current control of the first embodiment. FIG. 6 is a graph illustrating in detail the discharge current control of the first embodiment.

  First, the printer control unit 300 does not drive the developing sleeve 3 and sets Vchg = Vdev = Vtr1 = 0 (V) (step T301). This is to avoid unnecessary toner and carrier adhesion to the photosensitive drum 28 and unnecessary charging of the photosensitive drum by the primary transfer roller 23 during the discharge current control.

  Next, the photosensitive drum 28 is rotated (step T302), and the discharge current target value Ictgt corresponding to the developer temperature tmpn and the developer humidity rhn (relative humidity) is read from the ROM 303 (step T303).

  The discharge current target value Ictgt is a value sufficient to uniformly charge the surface of the photosensitive drum 28 by generating a discharge phenomenon. The discharge material is generated due to excessive discharge, and the photosensitive member by the photosensitive drum cleaner 26 is used. The value is set to minimize the wear of the drum 28. In this case, Ictgt = 50 μA. The dischargeable material is, for example, ozone or nitrogen oxide.

  Next, in the area “undischarged area” in FIG. 6, the value of Vac is applied to the charging roller 21 in three steps (step T304). Specifically, in FIG. 6, they are 566V, 766V, and 966V.

  At this time, no discharge is generated in the above-mentioned minute gap, and an AC current Iac corresponding to the AC resistance of the functional layer existing between the cored bar of the charging roller 21 and the cylinder of the photosensitive drum 28 is charged with the charging bias. It can be detected by the power source 41 (step T305). The detected values are 954 μA, 1273 μA, and 1599 μA, and are stored in the nonvolatile RAM of the printer control unit 300 (step T306).

  Next, in the area indicated as “discharge area” in FIG. 6, the value of Vac is applied to the charging roller 21 while being changed in three stages (step T307). Specifically, in FIG. 8, they are 1489V, 1567V, and 1606V. At this time, discharge in the above-mentioned minute gap has occurred, and the charging bias power supply 41 detects a value obtained by adding the discharge current generated in association with the non-discharge current detected in step S305 (step T308). ). The detected values are 2459 μA, 2612 μA, and 2698 μA, and the values are stored in the nonvolatile RAM of the printer control unit 300 (step T309).

  As described above, three points for the “undischarged region”, three points for the “discharged region”, and data indicating the correlation between Vac and Iac were obtained. Next, the printer control unit 300 obtains an approximate line for the “undischarged area” and the “discharged area” by the least square method (step T310).

Undischarge area: Iac = 1.6125 × Vac + 40.158 (8)
Discharge region: Iac = 2.0311 × Vac−566.720 (9)
The inclination and intercept of the right side of Expressions (11) and (12) are stored in the nonvolatile memory 302 by the printer control unit 300 (Step T311). A point where these two approximate lines intersect is a “discharge start point” at which discharge in a minute gap is started, and is a point of Vac = 1455V. Further, in the upper right region of the discharge start point, the difference between the approximate straight line of “discharge region” and the approximate straight line of “undischarged region” Iac = 0.4186 × Vac−606.878 (10)
Indicates the “current value for the discharge” generated in the minute gap. Here, if the discharge current target value Ictgt is 50 μA, the setting of Vac is calculated as 1574 V by the printer control unit 300 (step T312).

  Since FIG. 6 is a graph of the AC applied voltage and the AC current generated thereby, the reciprocal of the slope of these approximate expressions is the AC resistance which is the electrical resistance of the charging roller 21 (hereinafter referred to as resistance value ZC (MΩ)). Means. In particular, since the reciprocal of the slope of the formula (11) does not cause an additional phenomenon of discharge into the air, the reciprocal of the slope of the formula (11): 0.620 (V / μA). The resistance value ZC is preferably set (step T313). In addition, the resistance value ZC includes the resin layer component of the photosensitive drum 28 and the elastic layer of the charging roller 21, but the photosensitive drum 28 may be ignored in consideration of the film pressure and the dielectric constant.

  In addition to the humidity, the resistance value ZC of the charging roller 21 has a characteristic that varies with temperature and charging bias application time. In the present embodiment, by comparing the resistance value ZC immediately before the power-off and the resistance value ZC immediately after the power-on, the correction based on the charging bias application time is unnecessary by comparing the values close to the charging bias application time. . This is because the total charging bias application time hardly changes between immediately before the power is turned off and immediately after the power is turned on.

  Further, the resistance value ZC is a slow change that changes about 10 times as the resistance value over about 200 hours as the total charging bias application time. For this reason, even if the time from the last discharge current control to the power-off and the time from the power-on to the first discharge current control are taken into account, there is almost no error. That is, a change in the resistance value ZC due to a slight increase in the total charging bias application time during this period may be ignored.

  For these reasons, if the resistance value ZC immediately before the power is turned off is compared after correcting the temperature change, the change in environment between the resistance value ZC immediately before the power is turned off and immediately after the power is turned on can be estimated. The latest resistance value ZC obtained by the discharge current control is stored in the nonvolatile memory 302 as a resistance value ZCr (for example, 0.620 (V / μA)) (step T314).

  Next, details of the “environment history correction control” in step T105, which is a characteristic part of this embodiment, will be described.

  First, the behavior of the resistance value ZC with respect to ambient humidity changes will be described. FIG. 7 is a graph showing the humidity transition of the charging roller of the first embodiment. Specifically, it is a graph in which the resistance value ZC is measured immediately after a certain charging roller 21 moves from an environment of 50% humidity to an environment of 5%.

  From such a plot, the change in the ZC value can be approximated as follows using an exponential function with respect to time.

ZCr = (ZCm−ZCi) × exp (− (tn−tm) / βc) + ZCi (11)
However, ZCm is the ZC value at time tm, and ZCi is the convergence value of the ZC value. From FIG. 7, the time constant βc is obtained as 1700 min. Also, the resistance value ZCi (convergence value) of this equation is obtained for each environmental humidity, and the charging roller 21 is familiar with the surrounding environment (a period of leaving for about 3 days or more is required at a time). It is obtained by measuring. When expressed with respect to a humidity difference between a certain humidity rhm and a virtual humidity rhi, an approximate expression can be established as follows.

ZCi = ZCm × (1−ε × (rhi−rhm)) (12)
As shown in FIG. 7, in the present embodiment, the ZC value that was 0.62 MΩ at the initial stage (at a humidity of 50%) converged to ZCn = 0.68 MΩ. As a result, the coefficient γ in Expression (12) is obtained as 0.00215 (1 /% RH).

  Next, a virtual humidity convergence value called virtual humidity rhi will be described. FIG. 8 is a graph showing environmental fluctuations, which is a problem of the first embodiment. FIG. 8 shows the ambient humidity (vertical axis) around the image forming apparatus A with respect to time (horizontal axis).

  For example, assume that the humidity behaves like the humidity example (3) during the power-off period. In order to represent this history on average, there is a method of taking the integral (area S) of the transition represented by the humidity example (3) in FIG. In this example, since the area S is 40500 (RH% · min), the value (= 45% RH) becomes the virtual humidity rhi in that period when divided by the time 900 min corresponding to the power-off time.

Assuming that “the ambient humidity during power-off was a constant virtual humidity rhi immediately after time tm to immediately before time tn”, the humidity rhr to be obtained at this time is
rhr = (rhm−rhi) × exp (− (tn−tm) / βd) + rhi (13)
It is required in the form of Here, from the expressions (11), (12), and (13), under the condition of tm <tn, rhr = (1 / ε) × ((1-D) / (1-C)) × (1-ZCr / Zcm) + rhm (14)
However, D≡exp (− (tn−tm) / βd) and C≡exp (− (tn−tm) / βc).

  Since time tn, time tm, and Zcm are values stored or acquired by the printer control unit 300, and ZCr is also a value obtained by the printer control unit in step T103, the humidity rhr can be calculated in this way. .

  Considering the meaning of equation (14), the difference between humidity rhr and humidity rhm is an exponential function of resistance value ZCm (memory value) and resistance value ZCr (measured value), and further, time constant D and time constant C. Calculated by value.

  FIG. 9 is a graph for explaining the time constants D and C of the first embodiment. In FIG. 9, only the index part of the developer and the charging roller 21 is plotted.

  For example, focusing on the horizontal axis 500 min, in the case of the present embodiment, by using the value of the time constant D related to the developer and the value of the time constant C related to the charging roller 21, the humidity rhr of the developer at time tn can be obtained. Can be calculated. In other words, the time constants D and C used here are indices indicating how much the members are familiar with the atmospheric humidity between times tm and tn.

  For example, when the resistance value ZCr, which is an actually measured value of the resistance value ZC of the charging roller 21, corresponds to 0.74 in the index value of FIG. 9, in this embodiment, the environmental history in the middle is used in FIG. Determine as follows.

  That is, when the resistance value ZCr, which is an actual measurement value of the resistance value ZC of the charging roller 21, corresponds to 0.74, the resistance value ZC of the charging roller 21 corresponds to an index value (0.74) Δt ( 500 min). The developer also uses a temporary time Δt obtained from the resistance value ZC in which the humidity history remains. Thereby, it is possible to apply a humidity history that has been unknown until now, and to set image forming conditions with high accuracy.

  As for the temperature change, it is more accurate to correct the temperature change for the resistance value ZCr, the resistance value ZCm, and the resistance value ZCn in the equations (11) to (14). However, it is not mentioned here for the sake of simplicity.

  The above operation will be described from the viewpoint of the operation of the printer control unit 300. FIG. 10 is a flowchart for explaining environmental history correction control, which is a feature of the first embodiment. FIG. 10 describes details of step T105.

  First, the printer control unit 300 reads out old environment information used for setting image forming conditions at time tm before the last power-off stored in the nonvolatile memory 302 (step T501). Here, specific old environment information is the humidity rhm and the resistance value ZCm of the charging roller 21. It should be noted that the time when the humidity rhm and the resistance value ZCm are calculated differs from each other strictly, but is assumed to be substantially the same at the time tm.

  The time point at which the old environment information is measured and stored is the latest one of the environment information (first old environment information, second old environment information, third old environment information) acquired at the following three times. Is preferred. Here, the first old environment information is environment information acquired by the image forming unit from before the last image forming operation performed before the control unit power is turned off to after the end of image formation. The second old environment information is environment information at the end of the last image forming condition adjustment operation performed by the image forming unit before the control unit power is turned off last time. The third old environment information is the environment obtained by the control unit at a predetermined time interval after the time when the first old environment information and the second old environment information are acquired and before the control unit power is turned off. Information.

  Next, the printer control unit 300 reads out the humidity rhn, which is the calculation result in step T102, the resistance value ZCr obtained in the previous step T314, and the time tn at which the calculation was performed (same time as tm). (Step T502). Subsequently, the printer control unit 300 obtains the current developer humidity rhr based on the equation (14) (step T503).

  Returning to FIG. 4, the image forming conditions are reset based on the environmental information (new environmental information) such as the humidity rhr at the time of the current image formation obtained in step T105 (step T106), and the printing operation is performed (step T107). . At the end of the printing operation, the printer control unit 300 stores the value of the humidity rhr used here and the time at which it was calculated in the nonvolatile memory 302 as the humidity rhm and time tm (step T108).

  As described above, in this embodiment, the time constants D and C indicating the influence of the environmental transition during the power-off period of the image forming apparatus A are calculated by actually measuring the resistance value ZC that is the AC resistance value of the charging roller 21. It is used for environmental history control for developer humidity.

  Here, the humidity rhn obtained from the equation (7) at the time tn is not used in the equation (14). That is, the humidity rhr and the humidity rhn do not restrict each other mathematically, but can be used to determine whether or not the values are likely.

  As another feature, since the value used for the actual measurement of the AC resistance is a value obtained in the operation already used in the original image formation, it is not necessary to provide a separate operation for it. For this reason, it is advantageous in terms of productivity.

  Further, the discharge current control in step T103 and the transfer voltage setting control in step T104 can be omitted if it is not necessary to perform each print. In that case, the environmental history correction control in step T105 cannot be used, but it is not necessarily required as long as the main body is turned on, and can be omitted in the same manner.

[Second Embodiment]
A second embodiment of the present invention will be described.

(Characteristic part of this embodiment)
The outline of the image forming apparatus A of the present embodiment is substantially the same as that of the first embodiment, except that the flowchart of FIG. 11 is used instead of the flowchart of FIG. 4 as a basic operation. In brief, in the first embodiment, the resistance value ZCr value is not measured immediately after receiving an instruction to start printing. For this reason, there is a high possibility that the resistance value ZCr is different from the actual power-off value when time has passed since the last print or when the number of prints is large. In this case, the present embodiment is characterized in that the resistance value ZCr is acquired again.

  An outline of the printing operation of the present embodiment will be described based on the flowchart of FIG. FIG. 11 is a flowchart for explaining the printing operation of the second embodiment.

  The printer control unit 300 is in a print standby state in step T121. If the waiting time continues to some extent, it is confirmed in step T122 whether there is a print instruction. If there is a print instruction (in the case of Y), the process proceeds to step T123. On the other hand, if there is no print instruction (N), the process proceeds to step T129. Steps T123 to T127 are the same as steps T102 to T106 of the first embodiment, respectively.

  When the printing operation is completed in step T128, the “resistance value ZCr reacquisition flag” is confirmed in step T129. The resistance value ZCr reacquisition flag normally takes a value of 0, but becomes 1 when the resistance value ZCr needs to be measured and acquired. As a case where the resistance value ZCr reacquisition flag becomes 1, there are the following two cases in the present embodiment.

  One is a case where a predetermined time (in this embodiment, 30 min) or more has elapsed from the time tm when the resistance value ZCr was measured and acquired last. The other is a case where a predetermined number of sheets (1000 sheets in this embodiment) have been printed since the last time when the resistance value ZCr was acquired. In such cases, the resistance value ZCr is likely to be different from the actual power-off value, so the resistance value ZCr reacquisition flag is set to 1.

  If the resistance value ZCr reacquisition flag = 1 is determined in step T129, the printer control unit 300 proceeds to step T130 and performs the same discharge current control as in step T124. However, the detection operation in a region larger than the start of AC discharge may be omitted.

  Here, using the newly obtained resistance value ZCr, environmental history correction control is performed (step T131), and the newly calculated resistance value ZCr, humidity rhr, and time tn at that time are defined as resistance value ZCm, humidity rhm, and time tm. Store (step T132).

  If the resistance value ZCr is not 1 in step T129, steps T130 and T131 are not performed, and the resistance value ZCr, humidity rhr, and time tn stored up to that point are stored as resistance value ZCm, humidity rhm, and time tm. .

  Even in the case of N in step T122, the resistance value ZCr reacquisition flag may become 1 in step T129. This indicates that a predetermined time has elapsed while waiting for printing. Also at this time, the process proceeds to step T130, and the subsequent processes are sequentially performed, and then the process returns to the print standby.

  As described above, in the present embodiment, necessary operations (discharge current control and environmental history correction control) are performed so that the resistance value ZCr does not deviate from the value at the time of power-off.

[Third Embodiment]
A third embodiment of the present invention will be described.

(Characteristic part of this embodiment)
The outline of the image forming apparatus A of this embodiment is substantially the same as that of the first embodiment, but has the following features.

  The first feature is that the time constant βd in Expression (7) is switched between βi / βo (= 30 min / 600 min) depending on whether the developing device is driven (time constant β switching). The second feature is that the primary transfer roller 23 is used as a humidity follow-up delay member instead of the resistance value ZC which is the resistance value of the charging roller 21 used in the first embodiment, and based on the resistance value of the primary transfer roller 23, It is a point that determines environmental information.

  First, the time constant βd switching will be described. As shown in the block diagram of FIG. 3, the development device 1 is driven by controlling the development drive motor 54 by the printer control unit 300. The printer controller 300 reads βi = 30 (min) when reading the value of the time constant βd while outputting a drive command to the development drive motor 54, and βo = 360 while not outputting the development command. Read the value (min).

  The speed at which the developer adapts to the surrounding environment varies depending on the driving state of the developing device 1. For this reason, the time constant βd is switched according to the driving state of the developing device 1. This makes it possible to optimize the time constant with and without the developer driving, and to set the time constant when the developing device is not driven more precisely.

  The operation of the image forming apparatus A of this embodiment using the time constant β switching method will be described with reference to the flowchart of FIG. FIG. 12 is a flowchart for explaining the outline of the printing operation of the third embodiment.

  The printer control unit 300 is in a print standby state in step T141. When the printer control unit 300 receives a print instruction command, the controller determines a humidity rhn in the same manner as in step S102, and performs step T142 for setting image forming conditions once from the humidity rhn.

  The settings in step T141 are provisional setting conditions (image formation provisional conditions) for performing subsequent steps T143 and T144. After performing the “environment history correction control” in step T145, the printer controller 300 resets the image forming conditions again in step T146.

  One of the characteristic parts in this embodiment is that when the printer control unit 300 determines the image forming condition, the image forming condition change amount is set as follows in the time interval used for the determination. That is, assuming that the first image forming condition change amount when the developing device 1 is driven and the second image forming condition change amount when the developing device 1 is not driven, “first image forming condition change amount> The amount of change in the second image forming condition ”.

  Specifically, the time constant β is switched and used as β in Equation (7) so that the value becomes βi / βo (= 30 min / 600 min) depending on whether the developing device is driven. Since the developing device 1 is not driven at the time of Step T145, βd = βo may be calculated according to Expression (7).

  In the present embodiment, the developing device 1 is driven only when a printing operation is performed. Therefore, prior to the printing operation being performed in step T148, the humidity rhr until immediately before the printing operation is calculated in step T147 with β = βo.

  The calculation of the humidity rhr in step T147 is recalculated for a short time elapsed from step T145. For this reason, although the calculation accuracy is improved by this recalculation, it may be omitted when the necessity is low.

  When printing starts and ends in step 148, the driving of the developing device 1 is stopped at this point. Then, the humidity rhr so far driven by the developing device 1 is calculated as βd = βi in equation (7) (step T149). Since this step uses βi whose order constant βd is an order of magnitude less than βo during non-driving during the operation of the developing device 1, if it is omitted, the specific effect of this embodiment cannot be obtained.

  Another feature of the present embodiment is that the environmental change history when the power is turned off is obtained by measuring the resistance of the primary transfer roller 23 instead of the charging roller 21.

  The “transfer voltage setting control” in step T144 will be described in detail.

  In this embodiment, as the primary transfer roller 23, for example, a roller in which a core metal is coated with urethane foam made conductive by carbon dispersion is used. The primary transfer roller 23 is applied with a transfer bias from a primary transfer bias power source 43. The primary transfer bias power source 43 is a low voltage power source that can control its output voltage value (DC component), and can measure a current value (DC component) due to an applied bias.

  Further, a method for determining Vtr will be described with reference to the drawings. FIG. 13 is a flowchart illustrating transfer voltage setting control according to the third embodiment. FIG. 14 is a graph illustrating in detail the transfer voltage setting control of the third embodiment.

  First, the printer control unit 300 reads the stored humidity rhm and resistance value ZTm from the nonvolatile memory 302 at time tm (step T401).

  Next, the developer humidity rhn is read out at the current time tn. The surface of the photosensitive drum 28 that has already been rotated in the previous stage of this flow is charged to a predetermined potential Vd by the charging roller 21 (step T402). When the region charged to Vd reaches a position where a nip is formed with the intermediate transfer belt 24, a predetermined primary transfer bias is applied by the primary transfer roller 23 (step T403). Here, four points of + 1050V, + 1425V, + 1941V, and + 2156V are taken as shown in FIG.

  At this time, the primary transfer current is measured by the primary transfer bias power source 43 (step T404). The measured values here are 18.9 μA, 28.6 μA, 42.4 μA, and 48.2 μA, and are stored in the nonvolatile RAM of the printer control unit 300 (step T405). An approximate straight line is obtained from these four points by the least square method (step T406). The obtained formula is as follows.

Itr1 = 0.0265 × Vtr1−9.045 (15)
At this time, since the target primary charging current Ittgt in the environment of the humidity rhn is 47.5 μA, the printer control unit 300 calculates Vtr = 2134V (step T407).

  Subsequently, the printer control unit 300 calculates the reciprocal (37.7 MΩ) of the slope of the equation (15) (step T408), subtracts the resistance value ZB = 11 MΩ for the intermediate transfer belt 24, and the resistance value of the primary transfer roller 23. ZT (= 26.7 MΩ) is set (step T409). In this embodiment, since carbon dispersion PI is used for the intermediate transfer belt 24, the resistance change due to temperature and humidity or energization time is small, and in the case of this embodiment, it is calculated as approximately 11 MΩ.

The calculation of the resistance value ZT is the same as in the description of the first embodiment, and the equation for measuring the resistance value ZTr of the primary transfer roller 23 in time is:
ZTr = (ZTm−ZTi) × exp (− (tn−tm) / βt) + ZTi (16)
Next, considering the correction value for the environmental fluctuation that the resistance value ZTr is adapted to the surrounding humidity,
ZTn = ZTm × (1−δ × (rhi−rhm)) (17)
Here, βt = 1000 min and δ = 0.004 (1 /% RH).

The following is calculated in the same manner as in the first embodiment,
rhr = (rhm−rhi) × exp (− (tn−tm) / βd) + rhi (18)
Therefore,
rhr = (1 / ε) × ((1-D) / (1-T)) × (1-ZCr / Zcm) + rhm (19)
Where D≡exp (− (tn−tm) / βd), T≡exp (− (tn−tm) / βt)
It is.

  FIG. 15 is a flowchart for explaining environmental history correction control, which is a feature of the third embodiment. The operation of the printer control unit 300 is as shown in the flowchart of FIG. 15, but the resistance value ZCm and the resistance value ZCr described in step T105 of the first embodiment are converted into the resistance value ZTm and the resistance value ZTr, and the calculation formula of T503 is calculated. The only difference is that Eq. Therefore, the description is omitted.

  As described above, in this embodiment, based on the actual measurement and estimation of the resistance value of the primary transfer roller 23, the environmental transition during the power-off period of the image forming apparatus A is calculated as Δt to control the environmental history with respect to the developer humidity. Used for. This solves the problem of the present invention.

  In the above embodiment, the “image forming conditions” include the following. For example, the output value of the charging bias power source 41, the output value of the developing bias power source 42, and the maximum exposure amount of the laser 22. It is also conceivable to adjust a table (γ look-up table) for converting the level of the image data into a signal corresponding to the driving time of the laser 22, the output value of the primary transfer bias power source 43, and the like.

[Other Embodiments]
In the above-described embodiment, the humidity follow-up delay member is the charging roller 21 or the primary transfer roller 23, but is not limited thereto. For example, the developing sleeve 3 (developing member) for transporting toner to the intermediate transfer belt 24 or the photosensitive drum 28 to form a toner image may be used. Alternatively, a photosensitive drum cleaner 26 (cleaning member) that collects residual toner that has not been transferred to the transfer medium as a toner image from the photosensitive drum 28 may be used. Further, the static elimination member 29 may be used as the humidity follow-up delay member.

A ... Image forming apparatus 1 ... Developer 24 ... Intermediate transfer belt 28 ... Photoconductor drum 51 ... Developer temperature sensor 53 ... Environmental sensor 100 ... Control unit power supply 300 ... Printer control unit 301 ... CPU
302: Non-volatile memory 304 ... Time acquisition unit

Claims (6)

An image carrier, a developing unit that visualizes the electrostatic latent image carried on the image carrier as a toner image, a time obtaining unit that obtains time, and an environment measurement that measures the environment in the image forming apparatus A storage unit that stores environmental information obtained from the environmental measurement unit and environmental measurement time information obtained from the time acquisition unit, a control unit that determines image forming conditions, and supplies power to the control unit An image forming apparatus having a control unit power supply
With a humidity tracking delay member that changes so that the humidity follows a change in the surrounding humidity with a delay,
The controller is
An image forming provisional condition is set according to the old environment information stored in the storage unit acquired before the previous power-off of the control unit power source, and the old environment information and the control unit are turned on this time An image forming apparatus that determines an image forming condition by correcting the temporary image forming condition based on new environment information obtained from the humidity tracking delay member. The old environment information stored in the storage unit is
First old environment information: environmental information acquired from before the last image forming operation started by the image forming unit before the control unit power was turned off to after the end of image formation.
Second old environment information: Environment information at the end of the last image forming condition adjustment operation performed by the image forming unit before the control unit power was turned off last time.
Third old environment information: Environmental information obtained by the control unit at a predetermined time interval after the time when the first old environment information and the second old environment information are acquired and before the control unit power is turned off. .
The image forming apparatus according to claim 1, wherein the oldest environment information is the latest. The humidity tracking delay member includes a portion where electrical characteristics change with respect to a change in humidity,
A bias power source for applying a bias to the humidity tracking delay member;
3. The image formation according to claim 1, wherein the control unit applies a bias to the humidity tracking delay member by the bias power source, and obtains electrical resistance information from the humidity tracking delay member. apparatus.   As the humidity tracking delay member, at least a charging member for charging the image carrier, a static elimination member for neutralizing the charge of the image carrier, a developing member for conveying toner to the image carrier to form a toner image, Either a transfer member that transfers a toner image formed on the image carrier to a transfer material, or a cleaning member that collects residual toner that has not been transferred to the transfer material as the toner image from the image carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus is used.   The said control part re-acquires the said new environment information in a predetermined case after the power-on of this control part power supply this time, The one of Claim 1 thru | or 4 characterized by the above-mentioned. Image forming apparatus.   When determining the image forming condition, the control unit changes the first image forming condition when the developing device is driven in the time interval used for the determination, and the second image when the developing device is not driven. 5. The image forming apparatus according to claim 1, wherein the first image forming condition change amount> the second image forming condition change amount is set between the forming condition change amounts.

Images