JP2006139140A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize primary transfer efficiency and secondary transfer efficiency even against a rise of an internal temperature of an image forming apparatus and environmental variation around an image forming apparatus in many image forming operations, and to provide a stable image forming apparatus which ensures little change in image density. <P>SOLUTION: The image forming apparatus has: a first detection means 31 to detect the internal environment of the image forming apparatus; and a second detection means 32 to detect the external environment of the image forming apparatus, wherein primary transfer conditions of a primary transfer means 7 are variably controlled according to the detection results of the first detection means 31 without substantially using the detection results of the second detection means 32, and secondary transfer conditions of a secondary transfer means 11 are variably controlled according to at least the detection results of the second detection means 32. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic or electrostatic recording image forming apparatus such as a copying machine, a printer, or a facsimile, and is particularly visible on an image carrier by an electrophotographic method or an electrostatic recording method. The present invention relates to an image forming apparatus of an intermediate transfer system in which an image, that is, a developer image (toner image) is formed and this toner image is transferred to a transfer material via an intermediate transfer member.

  Conventionally, as a developer for developing an electrostatic image, an image forming apparatus using a one-component developer of a magnetic toner or a non-magnetic toner or a two-component developer in which a magnetic carrier and a non-magnetic toner are mixed at a predetermined ratio has been proposed. ing. In such a developer, the toner is charged by friction between the toner and the regulating blade or friction between the toner and the carrier at the time of stirring, and the electrostatic image is developed by a potential difference between the electrostatic image and the developer carrying member to form a toner image.

  Incidentally, the charge amount of toner in such an image forming apparatus is easily affected by environmental conditions, that is, temperature and humidity. For example, when the humidity changes, the amount of water adhering to the surface of the developer changes. The charge amount of the toner changes, and as a result, the density fluctuation of the output image occurs. For this reason, in order to always perform image formation under appropriate conditions and appropriate densities, it is necessary to continuously monitor the environment of the image forming apparatus and appropriately adjust various image forming conditions. Particularly, there is a great need for such adjustment in a color image forming apparatus.

  In view of this, image forming apparatuses that change image forming conditions depending on environmental conditions have been proposed. For example, in Patent Document 1 and Patent Document 2, the relative humidity in the apparatus is detected by a humidity detecting unit, and an image is thereby generated. A control method for changing the forming conditions is described.

Patent Document 3 discloses a control method for detecting the absolute humidity (water content per unit volume) in the apparatus and changing the image forming conditions.
JP-A-53-115233 Japanese Utility Model Publication No. 54-181954 JP-A-63-177178

  However, the environmental control of the conventional image forming apparatus as described above has a problem in determining the transfer condition of the intermediate transfer type image forming apparatus.

  That is, in the intermediate transfer type image forming apparatus, the toner image must be transferred twice, that is, primary transfer from the image carrier to the intermediate transfer member and secondary transfer from the intermediate transfer member to the transfer material. In the primary transfer, an intermediate transfer body and toner are interposed between the primary transfer apparatus for applying a primary transfer electric field and the image carrier, but in the secondary transfer, the intermediate transfer body, toner and transfer material are used. Intervenes.

  The change in the toner environment (mainly the change in charge amount) is easily affected by the humidity inside the image forming apparatus. The humidity condition inside the image forming apparatus is not limited to the surrounding environmental conditions of the image forming apparatus, that is, the external environmental conditions. It also changes depending on the temperature rise state of the forming apparatus main body.

  However, the environmental change (mainly resistance change) of the transfer material is easily affected by temperature and humidity changes around the image forming apparatus, that is, outside the image forming apparatus, because the transfer material is transported through the apparatus in a short time. It is hardly affected by the temperature rise state in the apparatus. Moreover, the environmental change of the transfer material is considerably larger than the environmental change of the toner.

  For this reason, if the primary transfer, which is greatly affected by the environmental change of the toner, and the secondary transfer, which is greatly affected by the environmental change of the transfer material, are controlled with the same environmental parameters, the primary transfer efficiency and the secondary transfer efficiency are improved. Neither can be stabilized, and as a result, there has been a problem that when the environmental conditions and the operating conditions of the image forming apparatus change, the image density fluctuates.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to stabilize the primary transfer efficiency and the secondary transfer efficiency even when the temperature inside the image forming apparatus is increased or the environment around the image forming apparatus is changed in a large number of image forming operations. An object of the present invention is to provide a stable image forming apparatus with little change.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image carrier on which an electrostatic image is formed, developing means for developing the electrostatic image on the image carrier with a developer to form a developer image, and the image carrier on the image carrier. An image forming unit comprising: a primary transfer unit that primarily transfers a developer image to an intermediate transfer member; and a secondary transfer unit that secondarily transfers the developer image on the intermediate transfer member to a transfer material;
A transfer material feeding unit for feeding the transfer material to the image forming unit;
In an image forming apparatus having
A first detection unit that detects an internal environment of the image forming apparatus; a second detection unit that detects an external environment of the image forming apparatus;
Control means for variably controlling the primary transfer condition of the primary transfer means based on the detection result of the first detection means without substantially using the detection result of the second detection means; Control means for variably controlling secondary transfer conditions of the next transfer means based on at least the detection result of the second detection means;
An image forming apparatus comprising:

  According to the present invention, it is possible to stabilize transfer efficiency and form a stable image with little change in density even under any environmental conditions.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
FIG. 1 is a sectional view showing a schematic configuration of a color image forming apparatus of a tandem type intermediate transfer system which is an embodiment of the image forming apparatus of the present invention.

  In this embodiment, as shown in FIG. 1, the image forming apparatus 100 includes four image forming units, that is, image forming stations P (Pa, Pb, Pc, and Pd) in the image forming apparatus main body 100A. They are juxtaposed in series in the direction. Each image forming station P (Pa, Pb, Pc, Pd) is a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 1 (1a, 1b, 1c, 1d) as an image carrier. ) Charging device 2 (2a, 2b, 2c, 2d) as primary charging means, laser beam scanner exposure device 3 (3a, 3b, 3c, 3d) as exposure means, and developing device 4 (4a) as developing means 4b, 4c, 4d), a cleaning device 5 (5a, 5b, 5c, 5d) as a cleaning means, and a primary transfer device 7 (7a, 7b, 7c, 7d) as a primary transfer means. Yes.

  In this embodiment, the photosensitive drum 1 (1a, 1b, 1c, 1d) and the primary transfer device 7 (7a, 7b, 7c, 7d) of each image forming station P (Pa, Pb, Pc, Pd) are used. An intermediate transfer belt 12 as an intermediate transfer member is disposed so as to be movable in the direction of the arrow so as to pass between the two.

  In this embodiment, the charging device 2 is a charging roller configured as a roller as a whole, which contacts the surface of the photosensitive drum 1 and uniformly charges the surface of the photosensitive drum to a predetermined polarity and potential.

  In the upper part of the apparatus main body 100A, a light source device and a polygon mirror (not shown) constituting the laser beam scanner exposure apparatus 3 as exposure means in this embodiment are installed. The laser light emitted from the light source device is scanned by rotating the polygon mirror, the light beam of the scanning light is deflected by a plurality of reflection mirrors, and is generated on the bus of the photosensitive drum 1 (1a, 1b, 1c, 1d) by the fθ lens. When the light is condensed and exposed, an electrostatic image corresponding to the image signal is formed on the photosensitive drum 1 (1a, 1b, 1c, 1d).

  The developing devices 4 (4a, 4b, 4c, 4d) are filled with a predetermined amount of developer in which non-magnetic toners of yellow, magenta, cyan, and black and magnetic carriers are mixed at a predetermined mixing ratio, respectively. The electrostatic image on the drum 1 is sequentially developed with each color toner to form a developer image (toner image). This toner image is primarily transferred onto the intermediate transfer belt 12 by the primary transfer device 7.

  Further, the transfer material P accommodated in the transfer material cassette (transfer material accommodating means) 13 constituting the transfer material feeding unit is conveyed to the secondary transfer device 11 as the secondary transfer means and transferred onto the intermediate transfer belt 12. The transferred toner image is secondarily transferred onto the transfer material P. The transfer material P carrying the toner image is conveyed to the fixing unit 9, and after fixing the toner image by heating and pressurization, it is discharged out of the apparatus as a recorded image.

  Further, an intermediate transfer belt cleaning device 14 is disposed downstream from the secondary transfer position to the transfer material P in the intermediate transfer belt traveling direction, and removes fog toner, secondary transfer residual toner, and the like adhering to the surface of the intermediate transfer belt 12. To do. On the other hand, the primary transfer residual toner or the like remaining on the photosensitive drum 1 (1a, 1b, 1c, 1d) is cleaned by a photosensitive drum cleaning device 5 (5a, 5b, 5c, 5d) such as a fur brush or blade means. The

  Next, transfer environment control in this embodiment will be described.

  In this embodiment, the image forming apparatus has two environmental sensors 31 and 32. In other words, the environment sensor 31 as a first detection unit that detects the environment inside the image forming apparatus is a relative humidity sensor, and is located near the center of the four image forming stations P (Pa, Pb, Pc, Pd). In the example, it is disposed between the image forming station Pb and the image forming station Pc, and the relative humidity in the apparatus is measured. An environment sensor 32 as a second detection unit that detects the environment outside the image forming apparatus is a temperature / humidity sensor that measures both temperature and relative humidity. In this embodiment, the environment sensor 32 is an external environment of the apparatus. Then, the temperature and relative humidity in the vicinity of the transfer material cassette 13 disposed near the outer periphery of the image forming apparatus are measured.

  As shown in FIGS. 2 (a) and 2 (b), the humidity sensor 31 includes a hygrometer 34 supported by an attachment member 33, and is fixed in the main body by a screw hole 37 and a connection plug 36 on the upper right. The temperature / humidity sensor 32 includes a hygrometer 34 and a thermistor 35 supported by a mounting member 33. The temperature / humidity sensor 32 is fixed in the main body by a screw hole 37 and a connection plug 36 on the upper right side. Has been.

  According to the present embodiment, in the above configuration, the high pressure condition applied to the primary transfer device 7 uses the first detection unit without substantially using the detection result of the environmental sensor 32 as the second detection unit. The high-pressure condition applied to the secondary transfer device 11 is variably controlled based on at least the detection result of the environmental sensor 32 as the second detection means.

  FIG. 3 shows an embodiment of a flowchart for performing environmental control of primary transfer and secondary transfer.

  First, when the operation of the image forming apparatus is started (S1), the environmental sensors 31 and 32 detect the relative humidity in the image forming apparatus and the temperature and relative humidity around the image forming apparatus, respectively (S2, S3).

  Next, the target primary transfer and secondary transfer conditions, that is, the primary and secondary transfer currents are determined based on the detection result (S4, S5). Then, before performing the image forming operation, the transfer voltage control (ATVC) is performed, and the high voltage condition applied to the primary transfer device 7 (7a, 7b, 7c, 7d) and the secondary transfer device 11 is performed. That is, the transfer voltage is determined (S6). Thereafter, the image forming operation starts and ends (S7, S8).

  In the transfer voltage control (ATVC), the drum is charged with the charging potential at the time of color image formation, a predetermined transfer voltage is applied at several points, and the current value corresponding to the transfer voltage is detected. The target transfer voltage corresponding to the target transfer current is calculated and set as the transfer voltage.

  In this embodiment, this transfer voltage control (ATVC) is performed independently for each color. The reason why the transfer voltage control (ATVC) is performed is that the volume resistance value of each member constituting the primary transfer device 7, the secondary transfer device 11, and the intermediate transfer body 12 changes due to temperature change. This is remarkable when an ion conductive material is used for adjusting the resistance value of the electrode.

In this embodiment, as the primary transfer device 7 (7a, 7b, 7c, 7d), a high molecular elastomer material such as rubber or urethane mixed with a cored bar and an ion conductive material such as sodium perchlorate, or a high molecular weight A transfer roller formed of an elastic material such as foam material was used. The volume resistance value of the transfer roller 7 is 1 × 10 ⁶ Ω · cm (23 ° C./50% RH environment).

On the other hand, a secondary transfer device 11 having the same structure was used, and a roller having a volume resistance value of 1 × 10 ⁸ Ω · cm (under an environment of 23 ° C./50% RH) was used.

As the intermediate transfer belt 12, a polyimide belt having an endless shape and having a surface resistance of 100 μm adjusted to 1 × 10 ¹² Ω / □ and a volume resistance of 1 × 10 ⁹ Ω · cm was used.

  FIG. 4 is a diagram showing the relationship between the relative humidity in the image forming apparatus by the humidity sensor 31 and the target of the primary transfer current.

  FIG. 5 is a graph showing the relationship between the relative humidity in the apparatus and the toner charge amount in the developer. “◯” in FIG. 5 is a change in the charge amount of the toner when the temperature is raised and the relative humidity is lowered in a 30 ° C./80% RH environment, and “Δ” is 23 ° C./50. Under the% RH environment, “□” is the change in the toner charge amount when the same operation is performed in the 23 ° C./5% RH environment.

  In an environment where the absolute humidity is constant, the saturated moisture content increases as the temperature rises, so the relative humidity decreases. As can be seen from the graph of FIG. 5, even if the absolute humidity of the surrounding environment is different, the relationship between the relative humidity in the apparatus and the toner charge amount has a correlation that can be approximated linearly. When the relative humidity is high, the charge amount of the toner is low, and as the relative humidity is low, the charge amount of the toner is high. This is because when the relative humidity changes, the amount of water adhering to the surface of the carrier and toner changes. That is, the charge amount of the toner changes as the relative humidity in the apparatus changes.

  Here, in order to make the image density constant even with respect to environmental changes in the image forming apparatus, it is necessary to develop a toner amount image that achieves the target density and to control to make the transfer efficiency constant. There is.

  However, since the relative humidity is lowered and the charge amount of the toner is increased due to the temperature rise in the apparatus accompanying the continuous image forming operation or the like, in this embodiment, as the relative humidity is lower, as shown in FIG. The primary transfer voltage was controlled so as to increase the target primary transfer current amount.

  FIG. 6 is a graph showing the relationship between the absolute humidity around the image forming apparatus by the temperature / humidity sensor 32 and the transfer voltage when the transfer current at the secondary transfer unit is fixed at 18 μA. In the figure, “◯” indicates a voltage when a solid white image is passed through, and “Δ” indicates a voltage when a solid black image is passed through a single color. Here, absolute humidity is a value determined by temperature and relative humidity.

  Here, it can be seen that the variation in the voltage shared by the transfer material is large with respect to the absolute humidity change around the apparatus, and the variation in the voltage shared by the toner (the difference between the transfer material + the transfer voltage of the toner and the transfer voltage of the transfer material) is small. .

The transfer material has a volume resistivity of about 10 ¹² Ω · cm in a 23 ° C./50% RH environment, depending on the paper type. The resistance value changes to about 1 × 10 ¹⁰ to 1 × 10 ¹³ Ω · cm as the transfer material absorbs moisture or dehumidifies. This is because the resistance value fluctuates more than the toner, and the contribution ratio in the transfer voltage is also large. That is, the resistance value of the transfer material changes as the absolute humidity around the apparatus changes.

  Since the resistance value of the transfer material is low in an environment where the absolute humidity is high, secondary transfer is performed with a transfer material having properties relatively close to a conductor interposed therebetween, and a secondary transfer current can be applied with a low potential difference. However, since the resistance value of the transfer material is high in an environment where the absolute humidity is low, secondary transfer is performed with a transfer material having properties close to that of a dielectric, and a high potential difference is required because current does not flow unless a predetermined potential difference is applied. It becomes.

  This problem is not a problem if constant current control can be performed during the secondary transfer. However, when ATVC is performed before image formation as in this embodiment, a transfer material is sandwiched. Since ATVC could not be performed, the transfer voltage shared voltage was determined by the ambient absolute humidity, and the secondary transfer voltage was controlled.

  The above control is performed as an operation timing at the start of the image forming operation or at predetermined intervals of the number of printed sheets. These environmental controls are performed by the controller 51 (FIG. 1), with the primary transfer condition environment table and the secondary transfer condition environment table stored in the RAM 41 (FIG. 1) provided in the image forming apparatus.

  With such a configuration, appropriate primary transfer and secondary transfer voltage can be applied even in an environment of the image forming apparatus or in a temperature rising state due to continuous image forming operation, the change in transfer efficiency is small, and the image density is reduced. It was possible to stabilize.

  As described above, the relative humidity in the image forming apparatus is detected, the primary transfer condition is determined based on the result, the temperature around the image forming apparatus and the relative humidity are detected, and the secondary transfer is performed based on the absolute humidity. By determining the conditions and applying them to perform primary transfer and secondary transfer, it was possible to provide a stable image forming apparatus with stable transfer efficiency and little change in image density.

Example 2
Next, another embodiment of the image forming apparatus of the present invention will be described with reference to FIGS. 6, 7 and 8. FIG.

  In the first embodiment, the applied high pressure condition of the primary transfer device 7 is determined by the relative humidity in the device, and the applied high pressure condition of the secondary transfer device 11 is determined by environmental control from the temperature and relative humidity around the device. In the second exemplary embodiment, the applied high-pressure condition of the secondary transfer device 11 is the temperature and relative humidity around the device, which is the detection result of the environmental sensor 31 as the first detection means inside the image forming device, and the image forming device. Environmental control is performed in such a manner as to determine the relative humidity in the apparatus, which is the detection result of the environmental sensor 32 as the second detection means for detecting the external environment.

  Since the configuration of the image forming apparatus of the present embodiment is the same as that of the image forming apparatus described in the first embodiment, the same components are denoted by the same reference numerals, and description thereof is omitted.

  As described with reference to FIG. 6 in the first embodiment, the transfer material sharing voltage and the toner sharing voltage in the secondary transfer greatly vary in the transfer material sharing voltage due to a change in the absolute humidity around the apparatus. However, the toner charge amount at the secondary transfer position varies depending on the relative humidity in the apparatus, and in order to make the secondary transfer efficiency constant, it is necessary to change the secondary transfer current in accordance with the change in the toner charge amount. .

  Therefore, in this embodiment, as shown in FIG. 7, the transfer voltage control (ATVC) is performed with the secondary transfer current determined by the relative humidity in the apparatus as a target, and the voltage determined from the ATVC result and the surroundings of the apparatus A high voltage condition to be applied to the secondary transfer device was calculated and determined from a shared voltage of the transfer material determined from the absolute humidity.

  Here, in the secondary transfer, unlike the primary transfer, it is necessary to transfer a plurality of color toner images to the transfer material, and charging of the toner carried on the intermediate transfer belt 12 by applying a primary transfer electric field. Since the amount changes, the secondary transfer current is different from the target current value of the primary transfer current.

  FIG. 8 shows a flowchart for performing environmental control of primary transfer and secondary transfer in the second embodiment.

  That is, when the operation of the image forming apparatus is started (S11), the environmental sensors 31 and 32 detect the relative humidity in the image forming apparatus and the temperature and relative humidity around the image forming apparatus, respectively (S12, S13).

  Next, a target primary transfer condition, that is, a primary transfer current is calculated and determined based on the detection result of the relative humidity in the apparatus (S14, S15). The secondary transfer conditions are determined by calculating the target secondary transfer conditions, that is, the secondary transfer current, based on the detection results of the ambient temperature and relative humidity (S16, S17).

  Then, before performing the image forming operation, the transfer voltage control (ATVC) is performed, and the high voltage condition applied to the primary transfer device 7 (7a, 7b, 7c, 7d) and the secondary transfer device 11 is performed. That is, the transfer voltage is determined (S18).

  In particular, the high voltage condition applied to the secondary transfer device 11 is such that the transfer voltage control (ATVC) is performed with the secondary transfer current determined by the relative humidity in the device as a target, the voltage determined from the ATVC result, A high voltage condition to be applied to the secondary transfer device is calculated and determined from the voltage assigned to the transfer material determined from the absolute humidity.

  Thereafter, the image forming operation starts and ends (S19, S20).

  The above control is performed as an operation timing at the start of the image forming operation or at predetermined intervals of the number of printed sheets. As a result, an appropriate secondary transfer voltage can be applied even in an environment of the image forming apparatus or in a temperature rising state due to continuous image forming operation, and the change in secondary transfer efficiency is less and the image density is stabilized. I was able to.

  In addition, since the amount of change in the volume resistance value with respect to the absolute humidity change around the apparatus varies depending on the type of transfer material, the calculation ratio of the transfer voltage of the transfer material was changed. For example, a transfer material in which the surface of a transfer material is coated with a resin, such as glossy paper, has a small resistance change with respect to a change in absolute humidity, so that the ratio of the shared voltage of the paper is made smaller than that of a normal transfer material.

  The image forming apparatus according to this embodiment includes a transfer material selection unit 61 (FIG. 1) that allows the user to select the type of transfer material to be used. Then, the controller 51 that controls the secondary transfer condition of the secondary transfer device 11 refers to the ratio of the detection result of the first detection unit and the detection result of the second detection unit that is referred to when controlling the secondary transfer condition. Is changed according to the type of transfer material selected by the transfer material selection means.

  Specifically, when a transfer material having a large resistance change due to a change in the environment around the apparatus, such as glossy paper, is selected by the transfer material selection means 61, the secondary transfer condition of the secondary transfer apparatus 11 is set to the controller 51. When the control is variably controlled, the ratio of referring to the second detection means is increased.

  As described above, the primary transfer condition is determined based on the relative humidity in the image forming apparatus, and the secondary transfer condition is determined based on the detection result of the relative humidity in the image forming apparatus as well as the absolute humidity around the image forming apparatus. In addition, by applying them to perform primary transfer and secondary transfer, it was possible to further stabilize the transfer efficiency and provide a stable image forming apparatus with little change in image density.

Example 3
Next, another embodiment of the image forming apparatus of the present invention will be described with reference to FIGS.

  In the first and second embodiments, a relative humidity sensor is arranged as the environmental sensor 31 in order to detect the relative humidity in the image forming apparatus, whereas in the third embodiment, a temperature sensor is used as the environmental sensor 31. (Temperature detection means) is arranged, and environmental control is performed by calculating the relative humidity in the apparatus by calculation.

  Since the configuration of the image forming apparatus of the present embodiment is the same as that of the image forming apparatus described in the first embodiment, the same components are denoted by the same reference numerals, and description thereof is omitted.

  The calculation and environmental control in this embodiment will be described below.

The temperature around the image forming apparatus detected by the environmental sensor 32 is T1, the relative humidity is H1, and the temperature inside the image forming apparatus detected by the temperature sensor 31 is T2. When the saturated water vapor pressure for the temperature T1 is P1, and the saturated water vapor pressure for the temperature T2 is P2, the relative humidity H2 in the apparatus is
H2 = H1 × P1 / P2 (1)
It can be shown by the relational expression.

  FIG. 9 shows the relationship between the temperature T and the saturated water vapor pressure P. For example, when the temperature in the apparatus is 23 ° C., the saturated water vapor pressure is 21 mgHg.

  Here, when the temperature in the apparatus is raised to 30 ° C., the saturated water vapor pressure changes to 31.9 mgHg, and when further raised to 40 ° C., it changes to 55.3 mgHg. At this time, the relative humidity H2 in the apparatus is calculated as 32.9% and 19.0% from the equation (1), assuming that the surrounding relative humidity H1 is 50% RH. Based on the relative humidity H2 in the apparatus thus calculated, environmental control of the primary transfer current as shown in FIG. 4 was performed in the same manner as in Example 1 or Example 2.

  FIG. 10 is a flowchart for performing environmental control of primary transfer and secondary transfer in the third embodiment.

  That is, when the operation of the image forming apparatus is started (S21), the environment sensors 31 and 32 detect the temperature inside the image forming apparatus, and the temperature and relative humidity around the image forming apparatus, respectively (S22, S23). ) Then, based on the temperature inside the image forming apparatus and the absolute humidity calculated from the temperature around the image forming apparatus and relative humidity, the relative humidity inside the apparatus is calculated (S24).

  Next, the target primary transfer condition, that is, the primary transfer current is determined based on the detection result of the relative humidity in the apparatus (S25). As the secondary transfer condition, a target secondary transfer condition, that is, a secondary transfer current is determined based on the detection result of the temperature and relative humidity around the apparatus (S26).

  Then, before performing the image forming operation, the transfer voltage control (ATVC) is performed, and the high voltage condition applied to the primary transfer device 7 (7a, 7b, 7c, 7d) and the secondary transfer device 11 is performed. That is, the transfer voltage is determined (S27). Thereafter, the image forming operation starts and ends (S28, S29).

  The relative humidity sensor 31 installed in the image forming apparatus in the first and second embodiments has a feature that the detection accuracy is poor in a low humidity environment. Accordingly, when the temperature inside the image forming apparatus rises and the relative humidity decreases, the measurement error of the relative humidity increases, and environmental control cannot be performed properly. Therefore, the primary transfer efficiency by the primary transfer current is increased. It becomes unstable and affects the stability of image density.

  However, since the temperature sensor 31 used in this embodiment has almost no detection error in a normal use environment (0 ° C. to 80 ° C.), there is little error in the relative humidity after calculation, and the primary transfer efficiency is also low. It can be stabilized.

  The relative humidity sensor is larger than a temperature sensor such as a thermistor, and is difficult to install when there is little space in the apparatus such as when the image forming apparatus is downsized. However, since the temperature sensor is small, it is easy to install at a desired position in the apparatus.

  As described above, the temperature rise in the image forming apparatus is detected by the temperature sensor, the relative humidity in the apparatus is calculated from the result and the absolute humidity around the image forming apparatus, and the primary is calculated based on the calculated relative humidity. By controlling the environment of the transfer current, it was possible to provide a stable image forming apparatus in which the transfer efficiency is further stabilized even in a low humidity environment and the image density change is small. In addition, even when the space in the apparatus is small due to the miniaturization, the restriction on the space for arranging the environmental sensor is reduced, and the environmental control can be similarly performed.

Example 4
In the third embodiment, the environmental control of the secondary transfer current determines the target secondary transfer condition, that is, the secondary transfer current, based on the detection results of the temperature and relative humidity around the image forming apparatus. However, the secondary transfer condition is determined not only from the absolute humidity around the image forming apparatus but also from the temperature detection result in the image forming apparatus, and the secondary transfer is performed. The primary transfer conditions are determined in the same manner as in Example 3.

  That is, in Example 4, the primary transfer condition is determined based on the ambient absolute humidity calculated from the temperature and relative humidity detection results of the image forming apparatus and the temperature detection result in the apparatus, and the secondary transfer conditions are: A determination is made based on the detection result of the temperature and relative humidity around the image forming apparatus and the detection result of the temperature in the image forming apparatus, and these are applied to perform primary transfer and secondary transfer. Accordingly, it is possible to provide a stable image forming apparatus in which the transfer efficiency is further stabilized and the image density change is small.

  In the above embodiment, the image forming apparatus is described as a quadruple tandem full-color image forming apparatus. However, the number of image forming stations (that is, image forming units) is smaller or smaller. Also good. Alternatively, the present invention can be equally applied to an image forming apparatus including a single image carrier and a plurality of developing devices corresponding thereto.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus according to the present invention. 1 is a schematic configuration diagram showing an environment sensor in an image forming apparatus according to the present invention. 6 is a flowchart illustrating an example of environmental control for primary transfer and secondary transfer. It is a figure which shows the relationship between the relative humidity in an apparatus in an environmental control, and a primary transfer current. It is a figure which shows the relationship between the relative humidity in an apparatus, and a toner charge amount. FIG. 4 is a diagram illustrating a relationship between absolute humidity around the apparatus and a shared voltage of a transfer material and toner in secondary transfer. It is a figure which shows the relationship between the relative humidity in an apparatus in an environmental control, and a secondary transfer current. It is a flowchart which shows the other Example of the environmental control of a primary transfer and a secondary transfer. It is a correlation diagram which shows a temperature-saturated water vapor pressure characteristic. It is a flowchart which shows the other Example of the environmental control of a primary transfer and a secondary transfer.

Explanation of symbols

1 (1a to 1d) Photosensitive drum (image carrier)
4 (4a to 4d) Developing device (developing means)
7 (7a-7d) Primary transfer device (primary transfer means)
11 Secondary transfer device (secondary transfer means)
12 Intermediate transfer belt (intermediate transfer member)
31 Environmental sensor inside device (first detection means)
32 Environmental sensor outside device (second detection means)
41 RAM
51 controller

Claims (5)

An image carrier on which an electrostatic image is formed, developing means for developing the electrostatic image on the image carrier with a developer to form a developer image, and the developer image on the image carrier to an intermediate transfer member An image forming unit comprising: a primary transfer unit for primary transfer; and a secondary transfer unit for secondary transfer of the developer image on the intermediate transfer member to a transfer material;
A transfer material feeding unit for feeding the transfer material to the image forming unit;
In an image forming apparatus having
A first detection unit that detects an internal environment of the image forming apparatus; a second detection unit that detects an external environment of the image forming apparatus;
Control means for variably controlling the primary transfer condition of the primary transfer means based on the detection result of the first detection means without substantially using the detection result of the second detection means; Control means for variably controlling secondary transfer conditions of the next transfer means based on at least the detection result of the second detection means;
An image forming apparatus comprising: The transfer material feeding unit has a transfer material accommodating means for accommodating a transfer material,
The first detection means is disposed closer to the developing means than the second detection means,
The image forming apparatus according to claim 1, wherein the second detection unit is disposed closer to the transfer material accommodation unit than the first detection unit.   The control unit that controls the secondary transfer condition of the secondary transfer unit variably controls the secondary transfer condition based on detection results of the first and second detection units. The image forming apparatus according to claim 1 or 2. The first detection means is a humidity detection means for detecting relative humidity,
The image forming apparatus according to claim 1, wherein the second detection unit is a temperature / humidity detection unit that measures temperature and relative humidity. The primary transfer condition is a condition of a bias applied to the primary transfer unit,
The image forming apparatus according to claim 1, wherein the secondary transfer condition is a condition of a bias applied to the secondary transfer unit.

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