JP4826246B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic system, for example.

  In an image forming apparatus such as a digital copying machine or a printer using an electrophotographic method, generally, the surface of a photosensitive drum rotating at a constant speed is uniformly charged by a charging device and then controlled based on image information. Laser light is scanned and exposed to form an electrostatic latent image. The electrostatic latent image formed on the photosensitive drum is developed by a developing device, and the developed toner image is electrostatically transferred onto the recording paper. Then, the toner image is fixed on the recording paper by the fixing device, and a print image is formed.

In recent years, as a charging device for uniformly charging the surface of the photosensitive drum, a contact charging device using a charging roll as a contact charging member, for example, is widely used in place of the conventional scorotron. A contact charging device using a charging roll has a configuration in which a charging roll in which a conductive elastic layer or a conductive surface layer is coated around a cored bar is disposed so as to be in contact with the surface of the photosensitive drum. . The surface of the photosensitive drum is uniformly charged by applying a DC voltage or a DC voltage on which an AC voltage is superimposed on the charging roll. Since such a contact charging device can set the voltage to be applied low, it has the advantages that less ozone is generated and that the high-voltage power supply can be downsized, and is particularly suitable for a small-sized image forming apparatus. Yes.
However, the resistance value of the conductive elastic layer and the conductive surface layer constituting the charging roll has a characteristic that it changes according to environmental conditions such as temperature and humidity. Therefore, the voltage applied to the charging roll in the contact charging device needs to be set according to the environmental conditions.

Therefore, conventionally, in the contact charging device, a technique for controlling the voltage and current applied to the charging roll according to environmental conditions such as temperature and humidity has been proposed. For example, in an image forming apparatus that optimizes and controls the applied voltage of the charging roll so that the charging voltage becomes constant at a timing corresponding to the non-image forming area, the environmental condition in the vicinity of the charging roll is detected, and the detected environmental condition There is a technique in which optimization control is performed again when it changes by a predetermined amount or more compared to the environmental conditions when optimization control is performed (see, for example, Patent Document 1).
In addition, it detects environmental conditions such as temperature and humidity, and switches between constant voltage control for applying a constant voltage to the charging roll and constant current control for applying a constant current to the charging roll in accordance with the detected environmental conditions. Technology exists (see, for example, Patent Document 2).

JP-A-7-209931 (page 4-5) JP-A-9-179383 (page 4-5)

  By the way, in the techniques described in Patent Document 1 and Patent Document 2 described above, an environmental sensor that detects environmental conditions is installed in the vicinity of a charging roll that is a contact charging member. As described above, in the configuration in which the environmental sensor can be installed in the vicinity of the charging roll, the environmental condition in the vicinity of the charging roll and the environmental condition in the position where the environmental sensor is disposed can be regarded as substantially the same. Therefore, by using the detection information from the environmental sensor as it is, the voltage and current applied to the charging roll can be easily controlled in accordance with the environmental conditions in the vicinity of the charging roll.

However, when trying to reduce the size of the image forming apparatus, it may be difficult to create a space for installing the environmental sensor in the vicinity of the charging roll due to the configuration of the apparatus. Furthermore, when an image forming apparatus is to be manufactured at a low cost, for example, it may be necessary to control the operation of a plurality of different components using detection information from one environmental sensor. Even in that case, a situation occurs in which the environmental sensor cannot be installed in the vicinity of the charging roll. As described above, when the environmental sensor cannot be installed in the vicinity of the charging roll, the environmental conditions in the vicinity of the charging roll and the environmental conditions at the position where the environmental sensor is installed are different. In particular, when shortening the warm-up time, the temperature rise near the fixing device at the start-up of the image forming device becomes abrupt. The deviation from the environmental conditions at the position tends to be large.
For this reason, in a configuration in which such an environmental sensor is installed at a position separated from the charging roll, if the voltage or current applied to the charging roll is controlled using the detection information from the environmental sensor as it is, the environmental conditions change rapidly. In addition, it becomes difficult to set the charging potential of the photosensitive drum within a predetermined range.

  Accordingly, the present invention has been made to solve the technical problems as described above, and an object of the present invention is to charge the photosensitive drum at a charging potential corresponding to a change in environmental conditions around the charging member. Is set within a predetermined range.

For this purpose, the image forming apparatus of the present invention is an image forming apparatus for forming a toner image on a recording material, and includes a photoreceptor on which an electrostatic latent image is formed, a charging member for charging the photoreceptor, A power supply that supplies power to the charging member, an environmental sensor that detects the environmental value inside the device, and a power control that sets the current value or voltage value supplied from the power source to the charging member in accordance with the environmental value around the charging member The power supply control unit determines an environmental value detected by the environmental sensor and a correspondence relationship between the environmental value detected by the preset environmental sensor and the environmental value around the charging member. It is characterized in that an assumed environmental value assumed around the charging member is calculated and a current value or a voltage value corresponding to the assumed environmental value is set.
The “environmental value” here is a value obtained by quantifying environmental state quantities such as temperature and humidity.

  Here, the power supply control unit changes the maximum value of the difference between the environmental value detected by the environmental sensor and the environmental value around the charging member from the environmental value detected by the environmental sensor, or the maximum value. It is possible to calculate an assumed environmental value by subtracting a value added with a predetermined margin. In addition, the power supply control unit determines, based on the environmental value detected by the environmental sensor, the difference generated between the environmental value detected by the environmental sensor and the environmental value around the charging member for each detected environmental value The estimated environment value can be calculated by subtracting a value obtained by adding a predetermined margin to the difference. Further, the power supply control unit determines the environmental value detected by the environmental sensor and the correspondence between the environmental value detected by the preset environmental sensor and the environmental value around the charging member. Assume that the estimated environmental value corresponding to the elapsed time is calculated by using the environmental value detected by the environmental sensor at each elapsed time and the above-described correspondence relationship in association with the elapsed time from the time of raising. It can also be.

The power control unit further includes a memory for storing a correspondence relationship between an environmental value detected by a preset environmental sensor and an environmental value around the charging member, and the power control unit includes an environment detected by the environmental sensor. An environmental value around the charging member can be assumed using the value and the above-described correspondence stored in the memory. Further, the power supply control unit sets a current value or a voltage value corresponding to the environmental assumed value within a predetermined time from the startup of the apparatus, and the environmental value detected by the environmental sensor after the predetermined time has elapsed. It is also possible to set a current value or a voltage value corresponding to.
In addition, a plurality of photoconductors are arranged, and a plurality of charging members corresponding to the photoconductors are arranged, and the power supply control unit sets the environmental value detected by the environment sensor and each of the plurality of charging members. Calculating an assumed environment value around each charging member using a correspondence relationship between the environment value detected by the environmental sensor and the environment value around the charging member. You can also In addition, the power supply control unit sets a current value or a voltage value corresponding to the assumed environmental value, either before the image forming operation in the apparatus, during the interval set during the image forming operation, or during the image forming operation. It can also be characterized by setting.

  Further, the present invention is regarded as a charging device, and the charging device of the present invention is preset with a charging member that charges a member to be charged, a power source that supplies power to the charging member, and an environmental sensor that detects an environmental value. Memory that stores the correspondence between the environmental value detected by the environmental sensor and the environmental value around the charging member, and the current value or voltage value supplied from the power source to the charging member as the environmental value around the charging member A power control unit that sets correspondingly, and the power control unit uses the environmental value detected by the environmental sensor and the correspondence stored in the memory to assume the environment assumed around the charging member A value is calculated, and a current value or a voltage value corresponding to the assumed environmental value is set.

  Here, the power supply supplies electric power having a voltage waveform in which an alternating voltage is superimposed on a direct current voltage to the charging member, and the alternating current is supplied to the photosensitive member so that the amount of alternating current to the photosensitive member becomes a predetermined value set by the power supply control unit. The power supply can be characterized by being a constant current control type power source that controls the output voltage value of the voltage. In addition, the charging member may be a contact charging member that charges the member to be charged while being in contact with the member to be charged.

  According to the present invention, even when the environmental sensor cannot be installed in the vicinity of the charging member, the charging potential of the photosensitive drum can be set within a predetermined range. As a result, even if environmental conditions around the charging member fluctuate rapidly, a high-quality print image can be stably formed.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[Embodiment 1]
FIG. 1 is a diagram illustrating a configuration of a digital color printer 1 as an example of an image forming apparatus to which the exemplary embodiment is applied. A digital color printer 1 shown in FIG. 1 is a so-called tandem type, and an image forming process unit 20 that performs image formation corresponding to image data of each color, and a control unit 60 that controls the image forming process unit 20, such as a personal computer ( The image processing unit (IPS) 22 is connected to the PC 3 and the image reading device 4 and performs predetermined image processing on the image data received from these.

The image forming process unit 20 includes four image forming units 30Y, 30M, 30C, and 30K that are arranged in parallel at a predetermined interval. The image forming units 30Y, 30M, 30C, and 30K form an electrostatic latent image while rotating in the direction of arrow A, and further, a photosensitive drum 31 as an image carrier on which a toner image is formed, and the surface of the photosensitive drum 31 A charging roller 32 as an example of a contact charging member that uniformly charges the toner at a predetermined potential, developing units 33Y, 33M, 33C, and 33K that develop an electrostatic latent image formed on the photosensitive drum 31, and photosensitive after transfer. A drum cleaner 34 for cleaning the surface of the body drum 31 is included. Further, a laser exposure device 26 that exposes the respective photosensitive drums 31 of the image forming units 30Y, 30M, 30C, and 30K is provided.
Here, the image forming units 30Y, 30M, 30C, and 30K are configured in substantially the same manner except for the toner stored in the developing devices 33Y, 33M, 33C, and 33K. In each of the image forming units 30Y, 30M, 30C, and 30K, yellow (Y), magenta (M), cyan (C), and black (K) toner images are formed.

  In addition, the image forming process unit 20 includes an intermediate transfer belt 41 onto which the toner images of the respective colors formed on the photosensitive drums 31 of the image forming units 30Y, 30M, 30C, and 30K are transferred, and the image forming units 30Y and 30Y. A primary transfer roll 42 that sequentially transfers (primary transfer) each color toner image of 30M, 30C, and 30K to the intermediate transfer belt 41 at the primary transfer portion T1, and a superimposed toner image transferred onto the intermediate transfer belt 41 is a secondary transfer portion. A secondary transfer roll 40 that performs batch transfer (secondary transfer) onto a sheet P that is a recording material (recording sheet) at T2 and a fixing device 80 that fixes the second transferred image onto the sheet P are provided.

  In the digital color printer 1 of the present embodiment, the image forming process unit 20 performs an image forming operation based on a control signal supplied from the control unit 60. At that time, the image data input from the PC 3 or the image reading device 4 is subjected to predetermined image processing by the IPS 22 and supplied to the laser exposure device 26. In the yellow (Y) image forming unit 30Y, for example, the surface of the photosensitive drum 31 uniformly charged at a predetermined potential by the charging roll 32 is applied by the laser exposure device 26 based on the image data obtained from the IPS 22. An electrostatic latent image is formed on the photosensitive drum 31 by scanning exposure. The formed electrostatic latent image is developed by the developing device 33Y, and a Y toner image is formed on the photosensitive drum 31. Similarly, M, C, and K color toner images are also formed in the image forming units 30M, 30C, and 30K.

Each color toner image formed by each image forming unit 30Y, 30M, 30C, 30K is sequentially electrostatically transferred by the primary transfer roll 42 onto the intermediate transfer belt 41 rotating in the direction of arrow B in FIG. A toner image superimposed on the belt 41 is formed. As the intermediate transfer belt 41 moves, the superimposed toner image is conveyed toward the secondary transfer portion T2 where the secondary transfer roll 40 and the backup roll 49 are disposed. On the other hand, the paper P is taken out from the paper tray 71 by the pickup roll 72 and conveyed one by one to the position of the registration roll 74 by the conveyance roll 73.
When the superimposed toner image is conveyed to the secondary transfer portion T2, the paper P is supplied from the registration roll 74 to the secondary transfer portion T2 in accordance with the timing at which the toner image is conveyed to the secondary transfer portion T2. The superimposed toner images are collectively electrostatically transferred (secondary transfer) onto the paper P by the action of the transfer electric field formed between the secondary transfer roll 40 and the backup roll 49 in the secondary transfer portion T2. Is done.

Thereafter, the sheet P on which the superimposed toner image is electrostatically transferred is peeled from the intermediate transfer belt 41 and conveyed to the fixing device 80. The unfixed toner image on the paper P conveyed to the fixing device 80 is fixed on the paper P by being subjected to fixing processing by heat and pressure by the fixing device 80. Then, the paper P on which the fixed image is formed is conveyed to a paper discharge placement unit 91 provided in a discharge unit of the image forming apparatus. On the other hand, the toner (transfer residual toner) adhering to the intermediate transfer belt 41 after the secondary transfer is removed by the belt cleaner 45 in contact with the intermediate transfer belt 41 after the completion of the secondary transfer, and the next image forming cycle. Prepared for.
In this way, image formation is performed by the digital color printer 1.

Next, a contact charging device 50 that uniformly charges the surface of the photosensitive drum 31 at a predetermined potential will be described. FIG. 2 is a diagram illustrating a configuration of the contact charging device 50 according to the present embodiment. As shown in FIG. 2, the contact charging device 50 includes a charging roll 32 as an example of the above-described contact charging member, a primary power supply 51 that supplies a current to the charging roll 32, and image forming units 30Y, 30M, 30C, The temperature sensor 65, which is disposed outside the 30K and detects the environment inside the apparatus (temperature in the present embodiment) as an example of the environment sensor, is configured inside the control unit 60, and the temperature data detected by the temperature sensor 65 Based on this, a power supply control unit 62 that generates a control signal for controlling the amount of current supplied to the charging roll 32 and outputs the control signal to the primary power supply 51, and an environmental temperature in the vicinity of the charging roll 32 and a temperature sensor 65 described later. The memory 63 is configured to store a maximum value (temperature difference) of a difference (temperature difference) from the temperature to be stored.
In FIG. 2, the contact charging device 50 disposed in the image forming unit 30K is shown as an example, but the same contact charging device 50 is also disposed in the image forming units 30Y, 30M, and 30C.

  The charging roll 32 is a roll member formed by sequentially laminating a conductive elastic body layer and a conductive surface layer on a conductive core bar such as aluminum or stainless steel. The conductive elastic layer is composed of urethane rubber, epichlorohydrin rubber, polyether urethane rubber, polyester urethane rubber, chloroprene rubber, NBR rubber, SBR rubber, butyl rubber, etc., and conductive particles such as carbon black and metal oxide. Are distributed. The conductive surface layer is made of polyester, polyamide, polyurethane, melamine resin, acrylic resin such as PMMA or PMBA, polyvinyl butyral, polyvinyl acetal, polyarylate, polycarbonate, phenoxy resin, polyurea, polyvinyl acetate and the like as a binder. In addition, conductive particles such as carbon black and metal oxide are dispersed. The charging roll 32 comes into contact with the photosensitive drum 31 while being driven to rotate, and supplies a current to the charging roll 32.

The primary power supply 51 supplies power having a voltage waveform in which an AC voltage is superimposed on a DC voltage, and outputs an AC voltage so that the AC current amount to the photosensitive drum 31 becomes a predetermined value set by the power supply control unit 62. This is a constant current control type power supply that controls the voltage value. Then, a current having a predetermined alternating current (AC) current value Iac is supplied to the charging roll 32. Since the primary power supply 51 of such a constant current control method can keep the amount of charge supplied to the photosensitive drum 31 constant, the charged potential of the photosensitive drum 31 can be stabilized.
The temperature sensor 65 is installed on the side of the image forming unit 30K. Then, the temperature inside the digital color printer 1 is detected, and the detected temperature data is output to the power supply control unit 62.

The power supply control unit 62 stores a CPU (Central Processing Unit) that performs arithmetic processing, a primary power supply 51, a temperature sensor 65, and an I / O circuit that manages input / output with the memory 63, and a processing program. It includes a ROM (Read Only Memory) and a RAM (Random Access Memory) as a primary storage unit. Then, the current value supplied to the charging roll 32 is determined based on the temperature data detected by the temperature sensor 65. Further, a control signal for setting the current value supplied to the charging roll 32 to the determined current value is output to the primary power source 51.
The memory 63 stores a maximum value (including a margin in some cases) of a difference between an environmental temperature in the vicinity of the charging roll 32 described later and a temperature detected by the temperature sensor 65.

Here, processing for determining the alternating current (AC) current set value Iac_set supplied to the charging roll 32 performed by the power supply control unit 62 of the contact charging device 50 of the present embodiment will be described.
First, the relationship between the AC current value Iac supplied from the charging roll 32 to the photosensitive drum 31 and the ambient temperature T around the charging roll 32 will be described. FIG. 3 shows an AC current value Iac (mA) supplied from the charging roll 32 to the photosensitive drum 31 and the environment around the charging roll 32 when the charging potential of the photosensitive drum 31 is set to a predetermined value (for example, −450 V). It is the figure which showed an example of the relationship with temperature T (degreeC).

  As described above, the charging roll 32 is formed by sequentially laminating a conductive elastic layer and a conductive surface layer. The resistance value of the conductive elastic layer and the conductive surface layer depends on the temperature. It has changing characteristics. That is, when the temperature of the conductive elastic layer and the conductive surface layer increases, the resistance value decreases. Therefore, the AC current value Iac supplied from the charging roll 32 to the photosensitive drum 31 is reduced in response to the temperature rise of the charging roll 32. In this way, by controlling the AC current value Iac in accordance with the temperature of the charging roll 32, the charging roll 32 supplies the photosensitive drum 31 even when the ambient temperature T around the charging roll 32 changes. The amount of current (charge amount) to be maintained can be kept constant. As a result, the charged potential of the photosensitive drum 31 can be maintained at −450 V, for example.

  The AC current value Iac to be supplied from the charging roll 32 to the photosensitive drum 31 corresponding to the environmental temperature T around the charging roll 32 is the resistance in the conductive elastic layer and the conductive surface layer of the charging roll 32. It varies depending on the temperature characteristics of the value, the material and layer structure of the photosensitive layer in the photosensitive drum 31, the latent image potential to be set, and the like. Therefore, the relationship between the AC current value Iac (mA) supplied from the charging roll 32 to the photosensitive drum 31 and the ambient temperature T (° C.) around the charging roll 32 as shown in FIG. It will vary depending on. That is, FIG. 3 is for the present embodiment. If the configuration of the image forming apparatus is different, a different relationship is exhibited.

  By the way, in the digital color printer 1 of the present embodiment, by downsizing the apparatus, a space for installing the temperature sensor 65 in the vicinity of the charging roll 32 inside the image forming units 30Y, 30M, 30C, 30K is created. This is difficult due to the configuration of the apparatus. Further, by using the temperature data detected by one temperature sensor 65, the AC current value Iac supplied from the charging roll 32 inside the image forming units 30Y, 30M, 30C, and 30K is all controlled, thereby manufacturing the apparatus. We are trying to reduce costs. Therefore, the digital color printer 1 of the present embodiment employs a configuration in which only one temperature sensor 65 is installed on the side of the image forming unit 30K.

  However, since the temperature sensor 65 is not installed in the vicinity of the charging roll 32 in the present embodiment, the environmental temperature T in the vicinity of the charging roll 32 is different from the environmental temperature in the position where the temperature sensor 65 is installed. It will be a thing. 4 shows the environmental temperature T around the charging roll 32 provided in the image forming unit 30K after the main power supply is turned on and the apparatus is started up in the digital color printer 1 of the present embodiment. FIG. 6 is a diagram showing a change with time of (° C.) and a change with time of temperature Ts (° C.) detected by a temperature sensor 65; As shown in FIG. 4, the temperature sensor 65 is disposed closer to the fixing device 80 that is a heat generation source than the image forming unit 30 </ b> K and a drive source (not shown) of the paper transport system, or the charging roll 32. Is shielded by the frame of the image forming unit 30K, the temperature Ts detected by the temperature sensor 65 is higher than the environmental temperature T around the actual charging roll 32. Similarly, the environmental temperature T in the vicinity of the charging roll 32 disposed in the image forming units 30Y, 30M, and 30C is different from the temperature Ts detected by the temperature sensor 65, and is usually separated from the temperature sensor 65. The image forming unit disposed at a different position has a larger temperature difference.

  Therefore, assuming that the temperature Ts detected by the temperature sensor 65 is equal to the environmental temperature T around the charging roll 32 (that is, Ts = T), the temperature Ts detected by the temperature sensor 65 is used as it is. When the AC current set value Iac_set in the charging roll 32 is determined based on the relationship shown in FIG. 3, the following inconvenience occurs. That is, since the environmental temperature T around the actual charging roll 32 is lower than the temperature Ts detected by the temperature sensor 65, the AC current setting in the charging roll 32 determined based on the relationship shown in FIG. The value Iac_set is lower than the AC current value necessary for forming a predetermined latent image potential. For this reason, the latent image potential formed on the photosensitive drum 31 is set lower than a predetermined value, and there arises a situation where a predetermined image density and gradation cannot be obtained.

  Therefore, in the contact charging device 50 of the present embodiment, when the power supply control unit 62 determines the AC current set value Iac_set supplied from the primary power supply 51 to the charging roll 32, the ambient temperature T around the charging roll 32 and Correction for correcting the temperature difference from the temperature Ts detected by the temperature sensor 65 is performed. Hereinafter, as an example, the case where the AC current set value Iac_set supplied from the primary power supply 51 to the charging roll 32 in the charging roll 32 provided in the image forming unit 30K will be described.

In FIG. 4 described above, in the digital color printer 1 of the present embodiment, the temporal change of the environmental temperature T around the charging roll 32 provided in the image forming unit 30K and the temperature Ts detected by the temperature sensor 65 are shown. The change with time is shown. In the temporal change shown in FIG. 4, the temperature difference between the environmental temperature T around the charging roll 32 and the temperature Ts detected by the temperature sensor 65 becomes the maximum temperature difference ΔT _Kmax after 150 minutes from the start-up of the apparatus. It is the time that has passed. After 150 minutes have elapsed since the start-up of the apparatus, the temperature difference between the environmental temperature T around the charging roll 32 and the temperature Ts detected by the temperature sensor 65 converges to be smaller than the maximum temperature difference ΔT _Kmax. Go.

This is because the temperature gradually becomes uniform throughout the entire digital color printer 1. That is, the temperature Ts detected by the temperature sensor 65 gradually becomes saturated. On the other hand, the environmental temperature T around the charging roll 32 gradually approaches the temperature saturation value detected by the temperature sensor 65 as the entire interior of the digital color printer 1 is warmed. Therefore, in the state where the measurement in FIG. 4 is performed, the maximum temperature difference ΔT _Kmax shows 7.9 ° C. at the time when 150 minutes have elapsed since the start-up of the apparatus, and no further temperature difference occurs. Therefore, in the contact charging device 50 according to the present embodiment, the memory 63 has an actual measurement in which the temperature difference between the environmental temperature T around the charging roll 32 and the temperature Ts detected by the temperature sensor 65 in FIG. 8 (° C.) obtained by adding a predetermined margin, for example, 0.1 (° C.) to the maximum temperature difference ΔT _Kmax = 7.9 (° C.) is stored as the maximum temperature difference ΔT _Kmax . In the present embodiment, the correspondence relationship between the environmental temperature T around the charging roll 32 and the temperature Ts detected by the temperature sensor 65 is set in advance using the maximum temperature difference ΔT _Kmax stored in the memory 63. Keep it.
When the temperature difference between the environmental temperature T around the charging roll 32 and the temperature Ts detected by the temperature sensor 65 changes stably, the actually measured maximum temperature difference ΔT _Kmax = 7.9 (° C.). Can also be stored in the memory 63.

Next, the power supply control unit 62 sets the AC current value Iac (mA) supplied from the charging roll 32 to the photosensitive drum 31 and the charging roll 32 when the charging potential of the photosensitive drum 31 is set to a predetermined value (−450 V). As a relational expression for defining the relation with the ambient environmental temperature T (° C.), the following expression (1) representing the correspondence shown in FIG. 3 is set. Then, equation (1) is stored in the ROM of the power supply control unit 62 as a part of the processing program.
Iac = −0.01 × T + 1.80 (1)
Further, the power supply control unit 62 has a memory 63 for obtaining an environmental temperature (environmental temperature estimated value) T ′ (° C.) assumed around the charging roll 32 from the temperature Ts (° C.) detected by the temperature sensor 65. Next, the following equation (2) using the maximum temperature difference ΔT _Kmax stored in is set. Similarly, equation (2) is stored in the ROM of the power supply control unit 62 as a part of the processing program.
T ′ = Ts−ΔT _Kmax (2)
Further, the power supply control unit 62 regards the estimated environmental temperature value T ′ obtained by the expression (2) as the environmental temperature T around the charging roll 32 in the expression (1) (that is, T ′ = T). . Then, the AC current set value Iac_set supplied from the primary power supply 51 to the charging roll 32 is determined by the following equation (3).
Iac_set = −0.01 × (Ts−ΔT _Kmax ) +1.80 (3)

As described above, in the power supply control unit 62 according to the present embodiment, the temperature Ts detected by the temperature sensor 65 and the maximum temperature difference ΔT _Kmax stored in the memory 63 are used around the charging roll 32. The assumed environmental temperature T ′ is calculated (Equation (2)). Further, the estimated environmental temperature T ′ is regarded as the environmental temperature T around the charging roll 32 (T ′ = T). Then, an AC current value Iac corresponding to the estimated environmental temperature T ′ around the charging roll 32 is supplied to the photosensitive drum 31 (equation (1)), and supplied from the primary power source 51 to the charging roll 32. The AC current set value Iac_set is set by equation (3).
Then, the power supply control unit 62 outputs a control signal for setting the obtained AC current set value Iac_set to the primary power supply 51.
Therefore, even if the temperature sensor 65 is not installed in the vicinity of the charging roll 32, the AC current value Iac corresponding to the environmental temperature in the vicinity of the charging roll 32 can be supplied to the photosensitive drum 31. . As a result, even if the environmental temperature around the charging roll 32 fluctuates, the latent image potential on the photosensitive drum 31 can be maintained within a predetermined range, and high-quality image formation can be performed.

Thus, in the contact charging device 50 of the present embodiment, when the environmental temperature T around the charging roll 32 is assumed, the environmental temperature T in the vicinity of the charging roll 32 and the temperature sensor 65 obtained by actual measurement performed in advance. The maximum temperature difference ΔT _Kmax with the temperature Ts detected by the above is used. As a result, it is possible to always supply an AC current value Iac greater than the necessary current from the charging roll 32 to the photosensitive drum 31. For this reason, even if the temperature sensor 65 is not installed in the vicinity of the charging roll 32, a decrease in the latent image potential on the photosensitive drum 31 due to insufficient charge can be stably suppressed. In addition, it is possible to obtain an appropriate image gradation and guarantee the provision of a high-quality print image.
In particular, a margin is added to the maximum temperature difference ΔT _Kmax stored in the memory 63. Thus, by _using a value equal to or greater than the actually measured maximum temperature difference ΔT _Kmax as the maximum temperature difference ΔT _{Kmax in the} expression (2), 150 minutes have elapsed since the start-up of the apparatus in which the temperature difference indicates the maximum temperature difference ΔT _Kmax. Even when the AC current set value Iac_set is insufficient, it is possible to stably suppress the shortage.

Here, FIG. 5 shows the AC current set value Iac_set (mA) supplied from the primary power supply 51 to the charging roll 32 and the temperature sensor 65 when the charging potential of the photosensitive drum 31 is set to a predetermined value (−450 V). It is the figure which showed an example of the relationship with temperature Ts (degreeC) detected by this. The relationship between the AC current set value Iac_set shown in FIG. 5 and the temperature Ts detected by the temperature sensor 65 is such that the AC current value Iac supplied to the photosensitive drum 31 from the charging roll 32 shown in FIG. A straight line (a straight line in FIG. 3) indicating the relationship with the ambient temperature T is shifted to the plus side by the maximum temperature difference ΔT _Kmax stored in the memory 63.

Incidentally, in the contact charging device 50 provided in the image forming unit 30K, the memory 63 stores the maximum temperature difference ΔT _Kmax . On the other hand, in the contact charging device 50 disposed in the image forming units 30Y, 30M, and 30C, the maximum temperature differences stored in the memory 63 are different maximum temperature differences ΔT _Ymax , ΔT _Mmax , ΔT, respectively. _Cmax can be set. In that case, each of the maximum temperature difference may be a relationship between _{△ T Kmax <△ T Cmax <} △ T Mmax <△ T Ymax. In the digital color printer 1 according to the present embodiment, since the position from the temperature sensor 65 is separated in the order of the image forming unit 30Y, the image forming unit 30M, and the image forming unit 30C, the maximum temperature difference corresponds to the arrangement position distance. This is because it becomes larger.

However, depending on the configuration of the image forming apparatus, there may be a case where there is no great difference in the environmental temperature T around the charging roll 32 provided in the image forming units 30Y, 30M, 30C, and 30K. In that case, ΔT _Kmax = ΔT _Cmax = ΔT _Mmax = ΔT _Ymax may be set. Further, according to the temperature difference between the environmental temperatures T around the charging rolls 32 arranged in the image forming units 30Y, 30M, 30C, and 30K, ΔT _Kmax = ΔT _Cmax <ΔT _Mmax = ΔT _Ymax Can also be set. Hereinafter, the maximum temperature differences ΔT _Kmax , ΔT _Cmax , ΔT _Mmax , ΔT _Ymax are collectively referred to as ΔT _max .

Further, the calculation of the above-described expression (3) by the power supply control unit 62 can be set to be executed only during a period until a predetermined time elapses after the digital color printer 1 is started up, for example. is there. As described above, when a predetermined time elapses from the start-up, the temperature gradually becomes uniform throughout the digital color printer 1, so that the ambient temperature T around the charging roll 32 and the temperature Ts detected by the temperature sensor 65 are detected. The difference between and tends to be smaller. Therefore, depending on the configuration of the digital color printer 1, even if the temperature sensor 65 is not installed in the vicinity of the charging roll 32, it is detected by the temperature sensor 65 after a predetermined time has elapsed since startup. The AC current value Iac of the charging roll 32 can also be determined using the temperature Ts.
That is, during a period from when the digital color printer 1 is started up until a predetermined time elapses, the power supply control unit 62 performs the calculation of the above-described equation (3) and supplies the charging roll 32 from the primary power supply 51. The AC current set value Iac_set to be set is set.
Then, after a predetermined time has elapsed since the digital color printer 1 was started up, the following equation (4) is calculated to set the AC current set value Iac_set supplied from the primary power supply 51 to the charging roll 32. It is also possible.
Iac_set = −0.01 × Ts + 1.80 (4)

  The timing for setting the AC current set value Iac_set by the power supply control unit 62 is the interval before or during the image forming operation in the digital color printer 1, or the image forming operation. It may be any time during image formation during operation.

  In the power supply control unit 62 of the present embodiment, the AC current value Iac (mA) supplied from the charging roll 32 to the photosensitive drum 31 and the ambient temperature T (° C.) around the charging roll 32 shown in FIG. The above equation (1) was used in defining the relationship. 3 is stored as a look-up table (LUT) in which the relationship shown in FIG. 3 is defined by discrete numerical values, and the power supply control unit 62 refers to the LUT and refers to the primary power supply. The AC current set value Iac_set supplied from 51 to the charging roll 32 can also be set. In that case, the power supply control unit 62 can determine the AC current set value Iac_set by performing linear interpolation or the like while referring to the LUT.

In the power supply control unit 62 of the present embodiment, the temperature sensor 65 is used as an environmental sensor. However, an AC current setting that is supplied from the primary power supply 51 to the charging roll 32 in response to humidity fluctuations using a humidity sensor. It is also possible to set the value Iac_set. This is because the conductive elastic layer and the conductive surface layer constituting the charging roll 32 have a characteristic that the resistance value changes depending on humidity.
Furthermore, although the primary power supply 51 of this Embodiment was comprised by the constant current control system, it can also be comprised by a constant voltage control system. In that case, the ambient temperature around the charging roll 32 is set by setting the AC voltage Vp-p, the DC voltage Vdc, etc. corresponding to the estimated environmental temperature T ′ around the charging roll 32 assumed by the equation (2). Even if fluctuates, the latent image potential on the photosensitive drum 31 can be maintained within a predetermined range.
In addition, the present invention can be applied to environmental conditions such as temperature and humidity by using some function or look-up table such as setting of transfer current / transfer voltage in the transfer roll, setting of development bias, setting of process control conditions, etc. It is also possible to apply to the one that needs to change the set value accordingly.

  As described above, in the digital color printer 1 according to the present embodiment, the temperature sensor 65 is disposed at a position separated from the charging roll 32 and is preset by the power supply control unit 62 of the contact charging device 50. By using the correspondence relationship between the environmental temperature T around the charging roll 32 and the temperature Ts detected by the temperature sensor 65, the estimated environmental temperature is assumed around the charging roll 32 from the temperature Ts detected by the temperature sensor 65. Find T '. Further, the estimated environmental temperature T ′ is regarded as the environmental temperature T around the charging roll 32 (T ′ = T). Then, an AC current set value Iac_set supplied from the primary power source 51 to the charging roll 32 is supplied so as to supply the AC current value Iac corresponding to the estimated environmental temperature T ′ around the charging roll 32 to the photosensitive drum 31. It is set.

Therefore, even when the temperature sensor 65 is not arranged around the charging roll 32, the AC current value Iac corresponding to the environmental temperature T around the charging roll 32 can be supplied to the photosensitive drum 31. It becomes possible. As a result, even if the environmental temperature T around the charging roll 32 fluctuates, the latent image potential on the photosensitive drum 31 can be maintained within a predetermined range, and high-quality image formation can be performed. .
In particular, using the maximum temperature difference ΔT _max (which may include a margin) between the environmental temperature T around the charging roll 32 and the temperature Ts detected by the temperature sensor 65, the environmental temperature T around the charging roll 32 is determined. As a result, it is possible to suppress a decrease in the latent image potential on the photosensitive drum 31 due to insufficient charge. Therefore, sufficient image density and appropriate image gradation can be obtained, and provision of a high-quality print image can be guaranteed.

[Embodiment 2]
In the first embodiment, the maximum temperature difference ΔT _max between the temperature Ts detected by the temperature sensor 65 and the temperature Ts detected by the temperature sensor 65 and the ambient temperature T in the vicinity of the charging roll 32 measured in advance. Based on the above, the case where the ambient temperature T around the charging roll 32 is assumed and the AC current set value Iac_set supplied from the primary power supply 51 to the charging roll 32 is determined has been described. In the second embodiment, each detected temperature Ts between the temperature Ts detected by the temperature sensor 65 and the ambient temperature T around the charging roll 32 measured in advance and the temperature Ts detected by the temperature sensor 65. A case where the environmental temperature T around the charging roll 32 is assumed will be described based on the temperature difference ΔT. In addition, the same code | symbol is used about the structure similar to Embodiment 1, and the detailed description is abbreviate | omitted here.

  Also in the contact charging device 50 of the present embodiment, the alternating current (AC) current value Iac (mA) supplied from the primary power source 51 to the charging roll 32 and the environment around the charging roll 32 are the same as in the first embodiment. It is assumed that the relationship with the temperature T (° C.) is as shown in FIG. Further, since the apparatus is turned on with the main power turned on, the temporal change of the environmental temperature T in the vicinity of the charging roll 32 provided in the image forming unit 30K and the temporal change of the temperature Ts detected by the temperature sensor 65 are performed. The change is assumed to be the one shown in FIG.

  In the contact charging device 50 of the present embodiment, the temperature difference ΔT between the environmental temperature T in the vicinity of the charging roll 32 and the temperature Ts detected by the temperature sensor 65 is measured for each detected temperature Ts from the measurement in FIG. Calculate in advance. In the memory 63, the temperature Ts (° C.) detected by the temperature sensor 65 and the temperature difference ΔT (deg) at the detected temperature Ts are stored in association with each other. That is, the memory 63 stores them in association with each other as (Ts0, ΔT0), (Ts1, ΔT1), (Ts2, ΔT2), (Ts3, ΔT3),. In the present embodiment, the ambient temperature T around the charging roll 32 and the temperature Ts detected by the temperature sensor 65 using the temperature difference ΔT (deg) for each detected temperature Ts stored in the memory 63. Is set in advance.

And in the power supply control part 62 of this Embodiment, above-described (3) Formula is set for every temperature Ts (degreeC) detected by the temperature sensor 65 as follows. That is, the AC current set value Iac_set supplied from the primary power supply 51 to the charging roll 32 is, for each temperature Ts detected by the temperature sensor 65,
Iac_set (Ts0) = − 0.01 × (Ts0−ΔT0) +1.80 (5)
Iac_set (Ts1) = − 0.01 × (Ts1−ΔT1) +1.80 (6)
Iac_set (Ts2) = − 0.01 × (Ts2−ΔT2) +1.80 (7)
Iac_set (Ts3) = − 0.01 × (Ts3−ΔT3) +1.80 (8)
Etc. are determined.

Specifically, from FIG. 4, when Ts0 = 12.6, Ts1 = 23.8, Ts2 = 30.8, and Ts3 = 35.2, ΔT0 = 0, ΔT1 = 3.6, Since ΔT2 = 7.0 and ΔT3 = 7.9, the equations (5) to (8) are
Iac_set (12.6) = − 0.01 × (12.6-0) +1.80 (5a)
Iac_set (23.8) = − 0.01 × (23.8-3.6) +1.80 (6a)
Iac_set (30.8) = − 0.01 × (30.8−7.0) +1.80 (7a)
Iac_set (35.2) = − 0.01 × (35.2-7.9) +1.80 (8a)
It becomes. Then, the AC current set value Iac_set to be supplied from the primary power supply 51 to the charging roll 32 is determined for each temperature Ts detected by the temperature sensor 65 using the equations (5a) to (8a).
At that time, in the region of Ts0 to Ts1, Ts1 to Ts2, and Ts2 to Ts3, the power supply control unit 62 can be configured to set the AC current set value Iac_set using linear interpolation or the like.

In this case, a predetermined margin δ can be set for the temperature difference ΔT between the environmental temperature T in the vicinity of the charging roll 32 and the temperature Ts detected by the temperature sensor 65. That is, in the memory 63, the temperature Ts detected by the temperature sensor 65 and the value (ΔT + δ) obtained by adding the margin δ to the temperature difference ΔT at the temperature Ts can be stored in association with each other. Specifically, the memory 63 stores them in association with each other like (Ts0, ΔT0 + δ), (Ts1, ΔT1 + δ), (Ts2, ΔT2 + δ), (Ts3, ΔT3 + δ),.
In this way, by setting the predetermined margin δ in the temperature difference ΔT, it is possible to always supply an AC current value Iac greater than the necessary current from the charging roll 32 to the photosensitive drum 31. For this reason, even if the temperature sensor 65 is not installed in the vicinity of the charging roll 32, a decrease in the latent image potential on the photosensitive drum 31 due to insufficient charge can be stably suppressed. In addition, it is possible to obtain an appropriate image gradation and guarantee the provision of a high-quality print image.

Specifically, the case where the margin δ is set to 0.1 (° C.) is shown. From FIG. 4, when Ts0 = 12.6, Ts1 = 23.8, Ts2 = 30.8, and Ts3 = 35.2, ΔT0 = 0.1, ΔT1 = 3.7, ΔT2, respectively. = 7.1 and ΔT3 = 8.0, so the equations (5) to (8) are
Iac_set (12.6) = − 0.01 × (12.6−0.1) +1.80 (5b)
Iac_set (23.8) = − 0.01 × (23.8-3.7) +1.80 (6b)
Iac_set (30.8) = − 0.01 × (30.8−7.1) +1.80 (7b)
Iac_set (35.2) = − 0.01 × (35.2-8.0) +1.80 (8b)
It becomes. Then, the AC current set value Iac_set to be supplied from the primary power supply 51 to the charging roll 32 is set for each temperature Ts detected by the temperature sensor 65 using the equations (5b) to (8b).

  Here, FIG. 6 shows that the temperature difference ΔT for each temperature Ts detected by the temperature sensor 65 is transferred from the primary power source 51 to the charging roll 32 by the equations (5b) to (8b) in this embodiment. When the AC current setting value Iac_set (mA) to be supplied is set, the AC current setting value Iac_set (mA) supplied from the primary power source 51 to the charging roll 32 and the temperature Ts (° C.) detected by the temperature sensor 65 It is the figure which showed an example of the relationship.

In the present embodiment, the temperature difference ΔT at each detected temperature Ts between the environmental temperature T around the charging roll 32 and the temperature Ts detected by the temperature sensor 65 measured in advance is used to determine the temperature. An estimated environmental temperature value T ′ assumed around the charging roll 32 is obtained from the temperature Ts detected by the sensor 65. Further, the estimated environmental temperature T ′ is regarded as the environmental temperature T around the charging roll 32 (T ′ = T). Then, an AC current set value Iac_set supplied from the primary power source 51 to the charging roll 32 is supplied so as to supply the AC current value Iac corresponding to the estimated environmental temperature T ′ around the charging roll 32 to the photosensitive drum 31. It is set.
Even when such a temperature difference ΔT for each temperature Ts detected by the temperature sensor 65 is used, when the configuration in which the temperature sensor 65 is not arranged in the vicinity of the charging roll 32 is adopted, the environment in the vicinity of the charging roll 32 is adopted. An AC current value Iac corresponding to the temperature T can be supplied to the photosensitive drum 31. As a result, even if the environmental temperature around the charging roll 32 fluctuates, the latent image potential on the photosensitive drum 31 can be maintained within a predetermined range with higher accuracy, and high-quality image formation can be performed. It becomes possible.
In particular, by setting a predetermined margin δ in the temperature difference ΔT, it is possible to suppress a decrease in the latent image potential on the photosensitive drum 31 due to insufficient charge. Therefore, sufficient image density and appropriate image gradation can be obtained, and provision of a high-quality print image can be guaranteed.

[Embodiment 3]
In the second embodiment, the temperature Ts detected by the temperature sensor 65 and the detected temperature Ts between the environmental temperature T around the charging roll 32 and the temperature Ts detected by the temperature sensor 65 measured in advance. The case where the AC current set value Iac_set supplied from the primary power supply 51 to the charging roll 32 is determined on the basis of the temperature difference ΔT has been described assuming the environmental temperature T around the charging roll 32. In the third embodiment, the temperature Ts detected by the temperature sensor 65 at the elapsed time t from the startup of the digital color printer 1 and the ambient temperature around the charging roll 32 at the elapsed time t from the startup. Based on the temperature difference ΔT between T and the temperature Ts detected by the temperature sensor 65, a case where the environmental temperature T around the charging roll 32 is assumed for each elapsed time t will be described.

  Also in the contact charging device 50 of the present embodiment, the alternating current (AC) current value Iac (mA) supplied from the primary power source 51 to the charging roll 32 and the environment around the charging roll 32 are the same as in the first embodiment. It is assumed that the relationship with the temperature T (° C.) is as shown in FIG. Further, since the apparatus is turned on with the main power turned on, the temporal change of the environmental temperature T in the vicinity of the charging roll 32 provided in the image forming unit 30K and the temporal change of the temperature Ts detected by the temperature sensor 65 are performed. The change is assumed to be the one shown in FIG.

  In the contact charging device 50 of the present embodiment, the temperature difference ΔT between the environmental temperature T in the vicinity of the charging roll 32 and the temperature Ts detected by the temperature sensor 65 is determined by a predetermined time step (for example, from the measurement in FIG. , Every 30 min). Then, in the memory 63, the elapsed time t (min) from the start of the digital color printer 1, the temperature Ts (° C.) detected by the temperature sensor 65 at that time t, and the temperature difference at that time t. ΔT (deg) is stored in association with each other. In other words, the memory 63 stores them in association with each other like (t0, Ts0, ΔT0), (t1, Ts1, ΔT1), (t2, Ts2, ΔT2), (t3, Ts3, ΔT3),. Is done. In this embodiment, the detected temperature Ts and the temperature difference ΔT (deg) for each elapsed time t stored in the memory 63 are used to determine the elapsed temperature t and the environmental temperature T around the charging roll 32. Is set in advance.

Then, the above-described expression (3) is set for each elapsed time t (min) from the startup as follows. That is, the set value of the AC current set value Iac_set supplied from the primary power source 51 to the charging roll 32 is set at every elapsed time t from the startup.
Iac_set (t0) = − 0.01 × (Ts0−ΔT0) +1.80 (9)
Iac_set (t1) = − 0.01 × (Ts1−ΔT1) +1.80 (10)
Iac_set (t2) = − 0.01 × (Ts2−ΔT2) +1.80 (11)
Iac_set (t3) = − 0.01 × (Ts3−ΔT3) +1.80 (12)
And so on as a function of the elapsed time t.

Specifically, from FIG. 4, when t0 = 0, t1 = 30, t2 = 60, and t3 = 150, Ts0 = 12.6, Ts1 = 23.8, Ts2 = 30.8, Ts3 = Since 35.2 and ΔT0 = 0, ΔT1 = 3.6, ΔT2 = 7.0, and ΔT3 = 7.9, the equations (9) to (12) are
Iac_set (0) = − 0.01 × (12.6-0) +1.80 (9a)
Iac_set (30) = − 0.01 × (23.8-3.6) +1.80 (10a)
Iac_set (60) = − 0.01 × (30.8−7.0) +1.80 (11a)
Iac_set (150) = − 0.01 × (35.2-7.9) +1.80 (12a)
It becomes. Then, the AC current set value Iac_set supplied from the primary power supply 51 to the charging roll 32 is set for each elapsed time t by the equations (9a) to (12a).
At that time, in the region of t0 to t1, t1 to t2, and t2 to t3, the power supply control unit 62 can be configured to set the AC current set value Iac_set using linear interpolation or the like.

Also in this case, a predetermined margin δ can be set for the temperature difference ΔT between the environmental temperature T in the vicinity of the charging roll 32 and the temperature Ts detected by the temperature sensor 65. That is, in the memory 63, the temperature Ts detected by the temperature sensor 65 and the value (ΔT + δ) obtained by adding the margin δ to the temperature difference ΔT at the temperature Ts can be stored in association with each other. Specifically, the memory 63 stores (t0, Ts0, ΔT0 + δ), (t1, Ts1, ΔT1 + δ), (t2, Ts2, ΔT2 + δ), (t3, Ts3, ΔT3 + δ), and so on. Store it in association.
In this way, by setting the predetermined margin δ in the temperature difference ΔT, it is possible to always supply an AC current value Iac greater than the necessary current from the charging roll 32 to the photosensitive drum 31. For this reason, even if the temperature sensor 65 is not installed in the vicinity of the charging roll 32, a decrease in the latent image potential on the photosensitive drum 31 due to insufficient charge can be stably suppressed. In addition, it is possible to obtain an appropriate image gradation and guarantee the provision of a high-quality print image.

Specifically, the case where the margin δ is set to 0.1 (° C.) is shown. From FIG. 4, when t0 = 0, t1 = 30, t2 = 60, and t3 = 150, Ts0 = 12.6, Ts1 = 23.8, Ts2 = 30.8, and Ts3 = 35.2, respectively. And ΔT0 = 0.1, ΔT1 = 3.7, ΔT2 = 7.1, and ΔT3 = 8.0. Therefore, the equations (9) to (12) are
Iac_set (0) = − 0.01 × (12.6−0.1) +1.80 (9a)
Iac_set (30) = − 0.01 × (23.8-3.7) +1.80 (10a)
Iac_set (60) = − 0.01 × (30.8−7.1) +1.80 (11a)
Iac_set (150) = − 0.01 × (35.2-8.0) +1.80 (12a)
It becomes. Then, an AC current set value Iac_set to be supplied from the primary power supply 51 to the charging roll 32 is set for each elapsed time t by the equations (9b) to (12b).

In the present embodiment, the temperature Ts detected by the temperature sensor 65 measured in advance at the elapsed time t from the startup of the digital color printer 1 and the measurement in advance at the elapsed time t from the startup. Using the temperature difference ΔT between the ambient temperature T around the charging roll 32 and the temperature Ts detected by the temperature sensor 65, the environmental temperature assumed around the charging roll 32 at each elapsed time t. An assumed value T ′ is obtained. Further, the estimated environmental temperature T ′ is regarded as the environmental temperature T around the charging roll 32 (T ′ = T). Then, an AC current set value Iac_set supplied from the primary power source 51 to the charging roll 32 is supplied so as to supply the AC current value Iac corresponding to the estimated environmental temperature T ′ around the charging roll 32 to the photosensitive drum 31. It is set.
By assuming the environmental temperature T around the charging roll 32 in correspondence with the elapsed time t from the start-up, when the configuration in which the temperature sensor 65 is not arranged in the vicinity of the charging roll 32 is adopted, The AC current value Iac corresponding to the environmental temperature T in the vicinity of the charging roll 32 can be supplied to the photosensitive drum 31. As a result, even if the environmental temperature around the charging roll 32 fluctuates, the latent image potential on the photosensitive drum 31 can be maintained within a predetermined range with higher accuracy, and high-quality image formation can be performed. It becomes possible.
In particular, by setting a predetermined margin δ in the temperature difference ΔT, it is possible to suppress a decrease in the latent image potential on the photosensitive drum 31 due to insufficient charge. Therefore, sufficient image density and appropriate image gradation can be obtained, and provision of a high-quality print image can be guaranteed.

1 is a diagram illustrating a configuration of a digital color printer of the present invention. It is the figure which showed the structure of the contact charging device. FIG. 6 is a diagram illustrating an example of a relationship between an AC current value Iac (mA) supplied from a charging roll to a photosensitive drum and an environmental temperature T (° C.) around the charging roll. It is the figure which showed the time-dependent change of environmental temperature T (degreeC) around a charging roll, and the time-dependent change of temperature Ts (degreeC) detected by a temperature sensor. It is the figure which showed an example of the relationship between AC current setting value Iac_set (mA) supplied to a charging roll from a primary power supply, and temperature Ts (degreeC) detected by a temperature sensor. When the temperature difference ΔT for each temperature Ts (° C.) detected by the temperature sensor is used, the AC current set value Iac_set (mA) supplied from the primary power source to the charging roll and the temperature Ts ( It is the figure which showed an example of the relationship with (degreeC).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Digital color printer, 20 ... Image formation process part, 30Y, 30M, 30C, 30K ... Image formation unit, 31 ... Photosensitive drum, 32 ... Charging roll, 33Y, 33M, 33C, 33K ... Developer, 34 ... Drum Cleaner 40 ... secondary transfer roll 41 ... intermediate transfer belt 42 ... primary transfer roll 50 ... contact charging device 51 ... primary power source 60 ... control unit 62 ... power control unit 63 ... memory 65 ... temperature Sensor, 80 ... Fixer

Claims (2)

An image forming apparatus for forming a toner image on a recording material,
A photoreceptor on which an electrostatic latent image is formed;
A charging member for charging the photoreceptor;
A power source for supplying power to the charging member;
An environmental sensor that detects environmental values inside the device;
A power control unit configured to set a current value or a voltage value supplied from the power source to the charging member according to an environmental value around the charging member;
The power supply control unit is configured such that the maximum value of the difference generated between the environmental value detected by the environmental sensor and the environmental value around the charging member or the maximum value from the environmental value detected by the environmental sensor. By subtracting a value obtained by adding a predetermined margin to the calculated environmental assumed value around the charging member, the current value or the voltage value corresponding to the assumed environmental value is set. An image forming apparatus. An image forming apparatus for forming a toner image on a recording material,
A photoreceptor on which an electrostatic latent image is formed;
A charging member for charging the photoreceptor;
A power source for supplying power to the charging member;
An environmental sensor that detects environmental values inside the device;
A power control unit configured to set a current value or a voltage value supplied from the power source to the charging member according to an environmental value around the charging member;
The power supply control unit determines the environmental value detected by the environmental sensor and the correspondence between the environmental value detected by the environmental sensor set in advance and the environmental value around the charging member. It is assumed to be around the charging member corresponding to the elapsed time by using the detected environmental value and the corresponding relationship at each elapsed time in association with the elapsed time from the start-up of the apparatus. An image forming apparatus that calculates an assumed environmental value and sets the current value or the voltage value corresponding to the assumed environmental value .

Images