JP5253611B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic system. The present invention is suitable for an image forming apparatus such as a copying machine, a printer, and a facsimile machine.

  With the widespread use of image forming apparatuses such as laser printers, such image forming apparatuses are increasingly required to have higher image quality and lower costs. An image forming apparatus includes a primary charger that uniformly charges a photoconductor, a primary transfer unit that transfers a toner image formed on the photoconductor to an intermediate transfer belt, and a toner image on the intermediate transfer belt as a recording paper. And a secondary transfer portion to be transferred.

  As a configuration of the primary transfer unit and the secondary transfer unit, in recent years, a contact transfer type transfer member (contact transfer member) represented by a transfer roller has become mainstream. Compared with a corona charger or the like, the contact transfer member can realize a reduction in power source capacity and a reduction in the amount of discharge products (such as ozone). The transfer roller is composed of, for example, a cored bar and a medium-resistance elastic layer formed around the cored bar. The transfer roller is pressed against the intermediate transfer belt or the recording paper with a predetermined pressing force, and a transfer part (transfer nip part). Form. Further, while the toner image passes through the transfer portion (that is, from when the toner image reaches the transfer portion and then comes off), a predetermined transfer bias (transfer voltage) is applied to the core metal of the transfer roller from the transfer bias applying means. ) Is applied. Since the characteristics of the transfer roller change due to environmental changes and changes with time, it is necessary to appropriately control the transfer bias applied to the transfer roller (core metal) according to the characteristics of the transfer roller.

  In view of this, an image forming apparatus that controls a transfer bias applied to the transfer roller in accordance with the characteristics of the transfer roller has been proposed (see Patent Document 1). Such an image forming apparatus performs control (constant current control) so that the current flowing through the transfer roller becomes a predetermined value at the timing when the non-image area is positioned at the transfer site, and the image area is controlled based on the voltage applied at this time. Control transfer bias (constant voltage control). Here, the non-image area refers to an area in which an image on the front side of the front end of the image for one sheet on the photosensitive member or the intermediate transfer belt and the rear side of the rear end of the image is not formed. Further, a plurality of different voltages are applied while one non-image area is located at the transfer site to obtain the impedance of the transfer roller, a voltage at which the current flowing through the transfer roller becomes a predetermined value is calculated, and the voltage is applied to the image area. Also, an image forming apparatus using a transfer bias is proposed.

  On the other hand, as a primary charger, a contact charging type charging member represented by a charging roller is mainly used. The charging roller contacts the surface of the photoconductor and applies a charging bias (for example, a charging voltage obtained by superimposing an AC voltage on a DC voltage) to charge the surface of the photoconductor. At this time, by setting the AC voltage to be equal to or higher than the discharge start voltage, there is an effect of equalizing the charge of the photoreceptor, and the photoreceptor can be charged uniformly.

  However, when an AC voltage is superimposed and applied to the photoconductor, the amount of discharge to the photoconductor is increased compared to the case where only a DC voltage is applied to the photoconductor, thus accelerating the photoconductor deterioration (scraping, etc.). At the same time, image flow or the like in a high-temperature and high-humidity environment due to discharge products is generated. Therefore, it is necessary to suppress the discharge by minimizing the AC voltage superimposed on the DC voltage, but the relationship between the voltage applied to the charging roller and the discharge is not always constant, and the amount of discharge changes due to environmental changes, changes over time, etc. To do.

  In view of this, an image forming apparatus has been proposed in which the charging bias applied to the charging roller is controlled to suppress increase / decrease in the amount of discharge due to environmental changes or changes with time (see Patent Document 2). Such an image forming apparatus obtains the impedance and discharge amount of the charging roller by applying a plurality of different AC voltages in the undischarged area and the discharged area before forming an image. While an image is being formed, an AC voltage of one value in the non-discharged area is applied in the non-image area, and the current flowing through the charging roller at this time and the charging roller obtained before the image is formed The charging bias is determined based on the impedance and the discharge amount.

Japanese Patent Application Laid-Open No. 11-95581 JP 2001-201920 A

  However, the image forming apparatus disclosed in Patent Document 1 performs constant current control for a circuit that generates a transfer bias while the non-image area is located at the transfer site, and constant voltage while the image area is located. Control is in progress. Therefore, both a constant current control circuit and a constant voltage control circuit must be provided. Therefore, the cost of the image forming apparatus increases.

  Further, as described above, when obtaining the impedance of the transfer roller, it is very short while one non-image region is located at the transfer site, so that the voltage value applied to the transfer roller can be changed at high speed. A transfer bias applying means is required. Accordingly, it is necessary to mount a high-speed responsive high-voltage power source in the image forming apparatus, leading to an increase in the cost of the image forming apparatus.

  On the other hand, the image forming apparatus disclosed in Patent Document 2 determines the voltage to be applied in the image area based on the impedance and discharge amount of the charging roller predicted by applying an alternating voltage of only one value in the non-image area. Therefore, it is very difficult to control the charging bias with high accuracy.

  Therefore, an object of the present invention is to provide an image forming apparatus capable of controlling the bias (voltage) applied to the transfer roller and the charging roller with high accuracy without causing an increase in cost.

In order to achieve the above object, an image forming apparatus according to one aspect of the present invention forms an electrostatic latent image by exposing a photosensitive member, and develops the electrostatic latent image with toner to form the photosensitive member. An image forming means for forming a toner image thereon; a first transfer portion for transferring the toner image formed on the photoconductor by the image forming means to an intermediate transfer body at a first transfer position; and the intermediate transfer body. A second transfer unit that transfers the toner image transferred to the recording medium to a recording medium at a second transfer position; a voltage application unit that applies a voltage to the first transfer unit; and the voltage application unit applied a voltage. A current detection unit that detects a current that sometimes flows through the first transfer unit; and the voltage while a non-image area on which the toner image is not formed on the photoconductor passes through the first transfer position. By applying a plurality of different voltages to the application unit, the current detection unit And the current flowing through the first transfer portion when the toner image is transferred from the photosensitive member to the intermediate transfer member is set to a predetermined value based on the plurality of different voltages and the plurality of currents. Control means for controlling a voltage to be applied by the voltage application unit, and the control means is configured to form a plurality of toner images continuously on the photoconductor. The voltage applying unit distributes and applies the plurality of different voltages for each period in which a plurality of non-image areas between adjacent toner images on the photoconductor pass through the first transfer position. And

  Further objects and other features of the present invention will become apparent from the preferred embodiments described below with reference to the accompanying drawings.

  According to the present invention, for example, it is possible to provide an image forming apparatus capable of controlling the bias (voltage) applied to the transfer roller and the charging roller with high accuracy without causing an increase in cost.

1 is a schematic cross-sectional view illustrating a configuration of an image forming apparatus as one aspect of the present invention. FIG. 2 is a schematic block diagram illustrating a configuration of a primary transfer bias application mechanism that applies a transfer bias to a primary transfer roller of the image forming apparatus illustrated in FIG. 1. FIG. 2 is a diagram illustrating a primary transfer voltage and a primary transfer current at a timing at which an image region is positioned at a transfer site and a timing at which a non-image region is positioned at a transfer site during continuous operation of the image forming apparatus illustrated in FIG. 1. FIG. 2 is a diagram illustrating a relationship between a voltage (voltage value) applied to a primary transfer roller and a current (current value) flowing through the primary transfer roller in the image forming apparatus illustrated in FIG. 1. FIG. 2 is a schematic block diagram illustrating a configuration of a secondary transfer bias application mechanism that applies a transfer bias to a secondary transfer outer roller of the image forming apparatus illustrated in FIG. 1. FIG. 2 is a diagram illustrating a secondary transfer voltage and a secondary transfer current at a timing when an image region is positioned at a transfer site and a timing when a non-image region is positioned at a transfer site in the image forming apparatus illustrated in FIG. 1. FIG. 2 is a diagram illustrating a relationship between a voltage (voltage value) applied to a secondary transfer outer roller and a current (current value) flowing through the secondary transfer outer roller in the image forming apparatus illustrated in FIG. 1. FIG. 2 is a schematic block diagram illustrating a configuration of a primary charging bias application mechanism that applies a charging bias to a primary charging roller of the image forming apparatus illustrated in FIG. 1. FIG. 2 is a diagram illustrating a primary charging voltage and a primary charging current at a timing at which an image region is positioned at a transfer site and a timing at which a non-image region is positioned at a transfer site during continuous operation of the image forming apparatus illustrated in FIG. 1. FIG. 2 is a diagram illustrating a relationship between a voltage (voltage value) applied to a primary charging roller and a current (current value) flowing through the primary charging roller in the image forming apparatus illustrated in FIG. 1.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. In addition, in each figure, the same reference number is attached | subjected about the same member and the overlapping description is abbreviate | omitted.

  FIG. 1 is a schematic cross-sectional view showing a configuration of an image forming apparatus 1 as one aspect of the present invention. The image forming apparatus 1 is an image forming apparatus that forms an image (color image) on a recording medium PM using an electrophotographic method. In this embodiment, the image forming apparatus 1 superimposes and transfers yellow, magenta, cyan, and black toner images on the recording medium PM, and heats and pressurizes the recording medium PM to transfer the toner image to the recording medium PM. It is embodied as a color laser printer for fixing.

  As shown in FIG. 1, the image forming apparatus 1 includes a laser unit 10, an image forming unit 20, a transport unit 30, a paper feed cassette 40, and a paper discharge tray 50. The image forming apparatus 1 further includes a primary transfer bias applying mechanism 60 shown in FIG. 2, a secondary transfer bias applying mechanism 70 shown in FIG. 5, and a primary charging bias applying mechanism 80 shown in FIG.

  The laser unit 10 generates laser light modulated based on an image signal input from an image signal generation device such as an image reading device or a computer, and exposes the photosensitive drum 21 of the image forming unit 20 with the laser light. The laser unit 10 controls the exposure amount of the photosensitive drum 21 by ON / OFF control and PWM control, and forms an electrostatic latent image on the surface of the photosensitive drum 21 with a distribution of charge amount. In this embodiment, the laser unit 10 includes four laser units 10y, 10m, 10c, and 10bk corresponding to each color of yellow, magenta, cyan, and black.

  The image forming unit 20 develops the electrostatic latent image formed by the laser unit 10 with toner to form a visible image, and superimposes and transfers the visible image to form a color visible image. Further, the image forming unit 20 transfers the color visible image to the recording medium PM at the transfer site, and fixes the color visible image transferred to the recording medium PM to form an image on the recording medium PM.

  The image forming unit 20 includes a photosensitive drum 21, a primary charging roller 22, a developing sleeve 23, a primary transfer roller 24, an intermediate transfer belt 25, a secondary transfer inner roller 26, and a secondary transfer outer roller 27. And a fixing device 28. In the present embodiment, the photosensitive drum 21 includes four photosensitive drums 21y, 21m, 21c, and 21bk corresponding to each color of yellow, magenta, cyan, and black. Similarly, in the present embodiment, the primary charging roller 22 includes four primary charging rollers 22y, 22m, 22c, and 22bk corresponding to each color of yellow, magenta, cyan, and black. Similarly, in the present embodiment, the developing sleeve 23 includes four developing sleeves 23y, 23m, 23c, and 23bk corresponding to each color of yellow, magenta, cyan, and black. Similarly, in the present embodiment, the primary transfer roller 24 includes four primary transfer rollers 24y, 24m, 24c, and 24bk corresponding to each color of yellow, magenta, cyan, and black. Since the photosensitive drum 21, the primary charging roller 22, the developing sleeve 23, and the primary transfer roller 24 have the same configuration for each color, the photosensitive drum 21y, the primary charging roller 22y, and the developing sleeves 23y and 1 corresponding to yellow will be described below. The next transfer roller 24y will be described as an example.

  The photosensitive drum 21y is a photosensitive drum that carries a yellow electrostatic latent image, and rotates counterclockwise in this embodiment.

  The primary charging roller 22y applies a high voltage to the photosensitive drum 21y, and uniformly charges (minus) the surface of the photosensitive drum 21y that has passed through the primary charging roller 22y. The primary charging roller 22y is superposed with an AC component voltage (AC voltage) of 1300V to 2000V on a DC component voltage (DC voltage) of -300V to -700V via a primary charging bias applying mechanism 80 described later. Applied voltage. Thereby, the primary charging roller 22y can uniformly charge the surface of the photosensitive drum 21y.

  As described above, the surface of the photosensitive drum 21y that has been uniformly charged through the primary charging roller 22y is exposed to the laser light emitted from the laser unit 10y. The surface of the photosensitive drum 21y exposed by the laser light is exposed to light, and the impedance (charge amount) decreases.

  The developing sleeve 23y is arranged with a gap (gap) with respect to the photosensitive drum 21y. Further, the gap between the photosensitive drum 21y and the developing sleeve 23y is managed with high accuracy. A voltage obtained by superimposing a DC component voltage of −1000 V to −2000 V on a DC component voltage of −150 V to −500 V is applied to the developing sleeve 23y. As a result, an electric field is generated between the photosensitive drum 21y and the developing sleeve 23y.

  Even when a voltage is applied to the developing sleeve 23y, a DC component voltage and an AC component voltage are generated as in the charging process of the photosensitive drum 21y. In particular, the AC component voltage greatly affects the image quality in the developing process. To do.

  The direction and strength of the electric field generated between the photosensitive drum 21y and the developing sleeve 23y are affected by the amount of charge on the surface of the photosensitive drum 21y. For example, an electric field from the developing sleeve 23y toward the photosensitive drum 21y is generated on the surface portion of the photosensitive drum 21y having a large charge amount (minus) (that is, not exposed to laser light). On the other hand, an electric field from the photosensitive drum 21y toward the developing sleeve 23y is generated on the surface portion of the photosensitive drum 21y having a small charge amount (that is, strongly exposed to laser light).

  The negatively charged yellow toner on the developing sleeve 23y receives a force in the direction opposite to the direction of the electric field generated between the photosensitive drum 21y and the developing sleeve 23y. Therefore, yellow toner adheres to the electrostatic latent image formed on the photosensitive drum 21y due to the direction and strength of the electric field generated between the photosensitive drum 21y and the developing sleeve 23y to form a toner image (visible image). To do. In other words, the developing sleeve 23y develops the electrostatic latent image formed on the photosensitive drum 21y. The developing sleeve 23y can be replaced with a developing blade.

  The primary transfer roller 24y is disposed on the opposite side of the photosensitive drum 21y with the intermediate transfer belt 25 interposed therebetween. The intermediate transfer belt 25 is disposed in contact with the surface of the photosensitive drum 21y.

  A voltage of + 150V to + 1500V is applied to the primary transfer roller 24y via a primary transfer bias applying mechanism 60 described later. As a result, the negatively charged yellow toner is drawn toward the primary transfer roller 24y from the photosensitive drum 21y, and the yellow toner image formed on the photosensitive drum 21y is transferred to the intermediate transfer belt 25.

  Similarly, magenta, cyan, and black toner images are transferred to the intermediate transfer belt 25. As a result, a full-color toner image formed of yellow, magenta, cyan, and black toner is formed on the intermediate transfer belt 25.

  The secondary transfer inner roller 26 and the secondary transfer outer roller 27 are disposed to face each other with the intermediate transfer belt 25 interposed therebetween. Accordingly, the intermediate transfer belt 25 on which the toner image is formed passes between the secondary transfer inner roller 26 and the secondary transfer outer roller 27. At this time, the conveyance unit 30 conveys the recording medium PM between the intermediate transfer belt 25 and the secondary transfer outer roller 27. The conveyance unit 30 includes, for example, a conveyance belt and a conveyance roller, and the recording medium PM stored in the paper feed cassette 40 is indicated by arrows 30a, 30b, 30c, 30d, 30e, 30f, 30g, 30h, and 30i. Convey along.

  A voltage of +500 V to +7000 V is applied to the secondary transfer outer roller 27 via a secondary transfer bias applying mechanism 70 described later. As a result, the negatively charged toner image on the intermediate transfer belt 25 is transferred to the recording medium PM.

  The fixing device 28 fixes the unfixed toner image transferred to the recording medium PM (that is, the toner image easily peeled off from the recording medium PM) to the recording medium PM. The fixing device 28 is constituted by, for example, a heat roller, heats the recording medium PM to soften the toner image, and fixes the toner image to the recording medium PM by applying pressure.

  The recording medium PM on which the toner image has been fixed (image is formed) is transported by the transport unit 30 and discharged onto the paper discharge tray 50. The paper discharge tray 50 stacks the recording medium PM on which an image is formed.

  Hereinafter, in the image forming apparatus 1, control of bias applied to members related to image formation or image transfer (that is, the primary transfer roller 24, the secondary transfer outer roller 27, and the primary charging roller 22) will be described. .

  FIG. 2 is a schematic block diagram showing a configuration of a primary transfer bias applying mechanism 60 that applies a transfer bias to the primary transfer roller 24. The primary transfer bias application mechanism 60 includes a voltage application unit 62 and a current detection unit 64, as shown in FIG.

  The voltage application unit 62 is controlled by the control unit 90 and has a function of applying a voltage to the primary transfer roller 24 that is a member related to image transfer. The voltage application unit 62 generates and applies a voltage (primary transfer voltage) to be applied to the primary transfer roller 24 based on the primary transfer bias control signal TBC1 input from the control unit 90. For example, the voltage application unit 62 generates a voltage to be applied to the primary transfer roller 24 from a voltage (for example, 24 V) for operating the motor of the image forming apparatus 1 using a high voltage transformer.

  The current detection unit 64 detects a current flowing through the primary transfer roller 24 when the voltage application unit 62 applies a voltage. In this embodiment, the current detection unit 64 detects a current (primary transfer current) that flows through the primary transfer roller 24, the intermediate transfer belt 25, the photosensitive drum 21, and the like, and indicates a current value of the current. The next transfer current detection signal TCD1 is output to the control unit 90.

  The control unit 90 includes a CPU and a memory (not shown) and controls the operation of the image forming apparatus 1. The control unit 90 controls the voltage application unit 62 in the primary transfer bias application mechanism 60 based on the detection result of the current detection unit 64 (that is, the current value of the current flowing through the primary transfer roller 24). In other words, the control unit 90 indicates the primary voltage value that the voltage application unit 62 should apply to the primary transfer roller 24 based on the primary transfer current detection signal TCD1 input from the current detection unit 64. A transfer bias control signal TBC 1 is generated and output to the voltage application unit 62.

  Here, the transfer bias control of the primary transfer bias applying mechanism 60 during the continuous operation of the image forming apparatus 1 (when an image is formed) will be described with reference to FIGS.

  FIG. 3 is a diagram illustrating the primary transfer voltage and the primary transfer current at the timing when the image area is located at the transfer site and the timing when the non-image area is located at the transfer site during the continuous operation of the image forming apparatus 1. . In FIG. 3, the transfer portion is a portion where the primary transfer roller 24 and the intermediate transfer belt 25 are in contact with each other. The image area is an area where a toner image can be formed from the leading edge of the image on the photosensitive drum 21 to the trailing edge. The non-image area is the leading edge of the image on the photosensitive drum 21. This is an area where there is no toner image after the front and rear edges.

  Referring to FIG. 3, at the timing when the image region is located at the transfer site, the control unit 90 causes the voltage application unit 62 to apply a voltage having a voltage value Vo (normal primary transfer voltage) to the primary transfer roller 24. Thus, the voltage application unit 62 is controlled.

  At the timing when the non-image region a and the non-image region b are located at the transfer site, the control unit 90 sets the voltage application unit 62 so that the voltage application unit 62 applies the voltage value Va to the primary transfer roller 24. Control. At this time, the control unit 90 applies the voltage of the voltage value Va by the voltage application unit 62 at the timing when the non-image region a and the non-image region b are located at the transfer site. The current values Ia and Ib are acquired via the current detection unit 64. Further, the control unit 90 calculates an average current value Iab that is an average of the current value Ia and the current value Ib.

  Further, at the timing when the non-image region c and the non-image region d are located at the transfer site, the control unit 90 causes the voltage application unit 62 to apply the voltage Vc to the primary transfer roller 24. 62 is controlled. At this time, the control unit 90 applies the voltage of the voltage value Vc by the voltage application unit 62 at the timing when the non-image region c and the non-image region d are positioned at the transfer site. Current values Ic and Id are acquired via the current detector 64. In addition, the control unit 90 calculates an average current value Icd that is an average of the current value Ic and the current value Id.

FIG. 4 is a diagram showing the relationship between the voltage (voltage value) V applied to the primary transfer roller 24 and the current (current value) I flowing through the primary transfer roller 24. In FIG. 4, the horizontal axis represents the voltage V applied to the primary transfer roller 24, and the vertical axis represents the current I flowing through the primary transfer roller 24. Referring to FIG. 4, the control unit 90 calculates the following from the average current values Iab and Icd that flow through the primary transfer roller 24 when the voltage application unit 62 applies voltage values Va and Vc to the primary transfer roller 24. The equation of the straight line L1 is obtained according to Equation 1 below. In other words, the control unit 90 calculates the impedance characteristic (straight line L1) of the primary transfer roller 24 from the voltage values Va and Vc and the average current values Iab and Icd.
(Equation 1)
V-Va = {(Vc-Va) / (Icd-Iab)}. (I-Iab)
Next, the control unit 90 calculates a voltage value Vo at which the current flowing through the primary transfer roller 24 becomes a predetermined current value Io based on the straight line L1 indicating the impedance characteristic of the primary transfer roller 24, and the voltage value Vo. Is determined as a voltage value applied to the primary transfer roller 24 by the voltage application unit 62. Then, the control unit 90 controls the voltage application unit 62 so that the voltage application unit 62 applies the voltage of the voltage value Vo to the primary transfer roller 24 at the timing when the image region is located at the transfer site.

  As described above, the control unit 90 applies the first voltage value (first voltage value) to the primary transfer roller 24 at the timing when the first non-image area (non-image areas a and b) among the plurality of non-image areas is located at the transfer site. The voltage application unit 62 is controlled to apply the voltage Va). In addition, the control unit 90 applies the second voltage value (Vc) to the primary transfer roller 24 at the timing when the second non-image area (non-image areas c and d) among the plurality of non-image areas is positioned at the transfer site. The voltage application unit 62 is controlled so as to apply the above voltage. At this time, the controller 90 applies a first current value (Ia and Ib) flowing through the primary transfer roller 24 by applying a voltage having a first voltage value and a voltage having a second voltage value. The second current values (Ic and Id) flowing through the primary transfer roller 24 are acquired. Then, the control unit 90 calculates the impedance characteristic of the primary transfer roller 24 from the average current value (Iab) of the first current value and the average current value (Icd) of the second current value. Further, the control unit 90 controls the primary transfer roller 24 so that the current value of the current flowing through the primary transfer roller 24 becomes a predetermined value (Io) at the timing when the image region is located at the transfer site based on the impedance characteristics. The voltage value (Vo) of the voltage to be applied is determined.

  Since the impedance characteristic of the primary transfer roller 24 does not change abruptly, the impedance of the primary transfer roller 24 can be obtained from the current value acquired at the timing when each of the plurality of non-image areas is located at the transfer site. Is possible. Therefore, in this embodiment, instead of applying a plurality of different voltages to the primary transfer roller 24 at the timing when one non-image area is located at the transfer site, each of the plurality of non-image areas is located at the transfer site. Different voltages are applied to the primary transfer roller 24 at the timing. In other words, the impedance characteristics of the primary transfer roller 24 are calculated by synthesizing current values when different voltages are applied to the primary transfer roller 24 at the timing when each of the plurality of non-image areas is located at the transfer site. To do. As a result, the image forming apparatus 1 does not require a constant current control circuit or a transfer bias application circuit capable of changing the voltage value at high speed in the primary transfer bias application mechanism 60, and can prevent an increase in cost. Further, since the impedance characteristic of the primary transfer roller 24 is calculated from a plurality of current values flowing through the primary transfer roller 24, the impedance characteristic is applied to the primary transfer roller 24 rather than when the impedance characteristic is calculated from one current value. The voltage to be controlled can be controlled with high accuracy. However, according to the time when the non-image area is located at the transfer site, the current of the primary transfer roller 24 is determined from the current value when the voltage is applied to the primary transfer roller 24 at the timing when one non-image area is located at the transfer site. It is also possible to calculate impedance characteristics.

  The transfer bias control in the primary transfer bias applying mechanism 60 is preferably performed every predetermined time (for example, every 5 minutes) or every output number of the recording medium PM (for example, every 200 sheets). Further, the transfer bias control in the primary transfer bias applying mechanism 60 is preferably performed at a timing different from the density correction control and other correction controls.

  Next, the secondary transfer bias applying mechanism 70 for applying a transfer bias to the secondary transfer outer roller 27 will be described. FIG. 5 is a schematic block diagram showing the configuration of the secondary transfer bias applying mechanism 70. As shown in FIG. 5, the secondary transfer bias application mechanism 70 includes a voltage application unit 72 and a current detection unit 74.

  The voltage application unit 72 is controlled by the control unit 90 and has a function of applying a voltage to the secondary transfer outer roller 27 which is a member related to image transfer. The voltage application unit 72 generates and applies a voltage (secondary transfer voltage) to be applied to the outer secondary transfer roller 27 based on the secondary transfer bias control signal TBC2 input from the control unit 90.

  The current detection unit 74 detects a current flowing through the secondary transfer outer roller 27 when the voltage application unit 72 applies a voltage. In this embodiment, the current detection unit 74 detects a current (secondary transfer current) flowing through the secondary transfer outer roller 27, the intermediate transfer belt 25, the secondary transfer inner roller 26, and the like, and the current of the current is detected. A secondary transfer current detection signal TCD2 indicating the value is output to the control unit 90.

  The control unit 90 controls the voltage application unit 72 in the secondary transfer bias application mechanism 70 based on the detection result of the current detection unit 74 (that is, the current value of the current flowing through the secondary transfer outer roller 27). In other words, the control unit 90 indicates the voltage value of the voltage that the voltage application unit 72 should apply to the secondary transfer outer roller 27 based on the secondary transfer current detection signal TCD2 input from the current detection unit 74. Next transfer bias control signal TBC 2 is generated and output to voltage application unit 72.

  Here, the transfer bias control of the secondary transfer bias applying mechanism 70 during the continuous operation of the image forming apparatus 1 (when an image is formed) will be described with reference to FIGS.

  FIG. 6 is a diagram illustrating the secondary transfer voltage and the secondary transfer current at the timing at which the image region is positioned at the transfer site and the timing at which the non-image region is positioned at the transfer site during the continuous operation of the image forming apparatus 1. . In FIG. 6, the transfer portion is a portion where the secondary transfer outer roller 27 and the intermediate transfer belt 25 (recording medium PM) are in contact with each other. The image area is an area where a toner image from the leading edge to the trailing edge of one image on the intermediate transfer belt 25 can exist, and the non-image area is one image on the intermediate transfer belt 25. This is an area where there is no toner image before the front end and after the rear end.

  Referring to FIG. 6, at the timing when the image region is located at the transfer site, the control unit 90 applies the voltage (normal secondary transfer voltage) of the voltage value Vp to the secondary transfer outer roller 27 by the voltage application unit 72. Thus, the voltage application unit 72 is controlled.

  At the timing when the non-image region e and the non-image region f are located at the transfer site, the control unit 90 causes the voltage application unit 72 to apply the voltage value Ve to the secondary transfer outer roller 27. To control. At this time, the control unit 90 causes the current to flow through the secondary transfer outer roller 27 when the voltage application unit 72 applies the voltage value Ve at the timing when the non-image region e and the non-image region f are located at the transfer site. Current values Ie and If are obtained via the current detector 74. Further, the control unit 90 calculates an average current value Ief that is an average of the current value Ie and the current value If.

  Further, at the timing when the non-image region g and the non-image region h are located at the transfer site, the control unit 90 applies the voltage so that the voltage application unit 72 applies the voltage Vg to the secondary transfer outer roller 27. The unit 72 is controlled. At this time, the controller 90 applies a voltage value Vg to the secondary transfer outer roller 27 when the voltage application unit 72 applies the voltage Vg at the timing when the non-image region g and the non-image region h are located at the transfer site. Current values Ig and Ih are obtained via the current detector 74. Further, the control unit 90 calculates an average current value Igh that is an average of the current value Ig and the current value Ih.

FIG. 7 is a diagram showing the relationship between the voltage (voltage value) V applied to the secondary transfer outer roller 27 and the current (current value) I flowing through the secondary transfer outer roller 27. In FIG. 7, the horizontal axis represents the voltage V applied to the secondary transfer outer roller 27, and the vertical axis represents the current I flowing through the secondary transfer outer roller 27. Referring to FIG. 7, the control unit 90 determines from the average current values Ief and Igh that flow through the secondary transfer outer roller 27 when the voltage application unit 72 applies the voltage values Ve and Vg to the secondary transfer outer roller 27. In accordance with the following formula 2, the formula of the straight line L2 is obtained. In other words, the control unit 90 calculates the impedance characteristic (straight line L2) of the secondary transfer outer roller 27 from the voltage values Ve and Vg and the average current values Ief and Igh.
(Equation 2)
V-Ve = {(Vg-Ve) / (Igh-Ief)}. (I-Ief)
Next, the control unit 90 calculates a voltage value Vp at which the current flowing through the secondary transfer outer roller 27 becomes a predetermined current value Ip based on the straight line L2 indicating the impedance characteristic of the secondary transfer outer roller 27. Further, the control unit 90 determines the voltage value Vp as the voltage value that the voltage application unit 72 applies to the secondary transfer outer roller 27. Then, the control unit 90 controls the voltage application unit 72 so that the voltage application unit 72 applies the voltage of the voltage value Vp to the secondary transfer outer roller 27 at the timing when the image region is located at the transfer site.

  As described above, the control unit 90 applies the first voltage value to the secondary transfer outer roller 27 at the timing when the first non-image area (non-image areas e and f) among the plurality of non-image areas is located at the transfer site. The voltage application unit 72 is controlled so as to apply a voltage of (Ve). In addition, the control unit 90 applies the second voltage value (Vg) to the secondary transfer outer roller 27 at the timing when the second non-image area (non-image areas g and h) among the plurality of non-image areas is positioned at the transfer site. The voltage application unit 72 is controlled so as to apply a voltage of). At this time, the controller 90 applies the first current value (Ie and If) flowing through the secondary transfer outer roller 27 and the voltage of the second voltage value by applying the voltage of the first voltage value. Thus, the second current values (Ig and Ih) flowing through the secondary transfer outer roller 27 are acquired. Then, the control unit 90 calculates the impedance characteristic of the secondary transfer outer roller 27 from the average current value (Ief) of the first current value and the average current value (Igh) of the second current value. Further, the controller 90 controls the outer secondary transfer roller so that the current value of the current flowing through the outer secondary transfer roller 27 becomes a predetermined value (Ip) at the timing when the image region is located at the transfer site based on the impedance characteristics. The voltage value (Vp) of the voltage to be applied to 27 is determined.

  Since the impedance characteristic of the secondary transfer outer roller 27 does not change abruptly, the impedance of the secondary transfer outer roller 27 is obtained from the current value acquired at the timing when each of the plurality of non-image areas is located at the transfer site. It is possible. In this embodiment, instead of applying a plurality of different voltages to the secondary transfer outer roller 27 at the timing when one non-image region is located at the transfer site, the timing when each of the plurality of non-image regions is located at the transfer site. , Different voltages are applied to the secondary transfer outer roller 27. In other words, at the timing when each of the plurality of non-image areas is located at the transfer site, the impedance values of the secondary transfer outer roller 27 are synthesized by combining current values when different voltages are applied to the secondary transfer outer roller 27. Is calculated. As a result, the image forming apparatus 1 does not require a constant current control circuit or a transfer bias application circuit capable of changing the voltage value at high speed in the secondary transfer bias application mechanism 70, and can prevent an increase in cost. Further, since the impedance characteristic of the secondary transfer outer roller 27 is calculated from a plurality of current values flowing through the secondary transfer outer roller 27, the secondary transfer outer roller is more effective than the case where the impedance characteristic is calculated from one current value. The voltage applied to 27 can be controlled with high accuracy. However, the secondary transfer outer roller is determined from the current value when a voltage is applied to the secondary transfer outer roller 27 at the timing at which one non-image area is positioned at the transfer site in accordance with the time at which the non-image region is positioned at the transfer site. It is also possible to calculate 27 impedance characteristics.

  Next, the primary charging bias application mechanism 80 that applies a charging bias to the primary charging roller 22 will be described. FIG. 8 is a schematic block diagram showing the configuration of the primary charging bias applying mechanism 80. As shown in FIG. 8, the primary charging bias application mechanism 80 includes a voltage application unit 82 and a current detection unit 84.

  The voltage application unit 82 is controlled by the control unit 90 and has a function of applying a voltage (a voltage obtained by superimposing an AC voltage on a DC voltage) to the primary charging roller 22 which is a member related to image formation. The voltage application unit 82 generates and applies a voltage (primary charging voltage) to be applied to the primary charging roller 22 based on the primary charging bias control signal CBC1 input from the control unit 90.

  The current detector 84 detects a current flowing through the primary charging roller 22 when the voltage application unit 82 applies a voltage. In the present embodiment, the current detection unit 84 detects a current (primary charging current) flowing through the primary charging roller 22, the photosensitive drum 21, and the like, and a primary charging current detection signal indicating the current value of the current. The CCD 1 is output to the control unit 90.

  The control unit 90 controls the voltage application unit 82 based on the detection result of the current detection unit 84 (that is, the current value of the current flowing through the primary charging roller 22) in the primary charging bias application mechanism 80. In other words, the control unit 90 indicates the primary voltage value that the voltage application unit 82 should apply to the primary charging roller 22 based on the primary charging current detection signal CCD1 input from the current detection unit 84. A charging bias control signal CBC 1 is generated and output to the voltage application unit 82.

  Here, the control of the primary charging bias applying mechanism 80 during the continuous operation of the image forming apparatus 1 (when an image is formed) will be described with reference to FIGS.

  FIG. 9 is a diagram illustrating the primary charging voltage and the primary charging current at the timing when the image area is positioned at the transfer site and the timing when the non-image area is positioned at the transfer site during the continuous operation of the image forming apparatus 1. . In FIG. 9, the transfer site is a site where the primary transfer roller 24 and the intermediate transfer belt 25 are in contact with each other. The image area is an area where a toner image from the leading edge to the trailing edge of one image on the photosensitive drum 21 is to be formed. The non-image area is an area where a toner image is not formed before the front end and the rear end of the image for one sheet on the photosensitive drum 21.

  Referring to FIG. 9, at the timing when the image region is located at the transfer site, the control unit 90 causes the voltage application unit 82 to apply the voltage (normal primary charging voltage) of the voltage value Vq to the primary charging roller 22. Thus, the voltage application unit 82 is controlled.

  At the timing when the non-image region i is located at the transfer site, the control unit 90 controls the voltage application unit 82 so that the voltage application unit 82 applies the voltage value Vi of the undischarged region. At this time, the controller 90 applies the current value Ii of the current flowing through the primary charging roller 22 when the voltage application unit 82 applies the voltage of the voltage value Vi at the timing when the non-image region i is located at the transfer site. Obtained via the detector 84.

  At the timing when the non-image region j is located at the transfer site, the control unit 90 controls the voltage application unit 82 so that the voltage application unit 82 applies the voltage value Vj of the undischarged region. At this time, the control unit 90 applies the current value Ij of the current flowing through the primary charging roller 22 when the voltage application unit 82 applies the voltage value Vj at the timing when the non-image region j is located at the transfer site. Obtained via the detector 84.

  In addition, at the timing when the non-image region k is located at the transfer site, the control unit 90 controls the voltage application unit 82 so that the voltage application unit 82 applies the voltage value Vk of the discharge region. At this time, the controller 90 applies the current value Ik of the current flowing through the primary charging roller 22 when the voltage application unit 82 applies the voltage Vk at the timing when the non-image region k is located at the transfer site. Obtained via the detector 84.

  Further, at the timing when the non-image region 1 is located at the transfer site, the control unit 90 controls the voltage application unit 82 so that the voltage application unit 82 applies the voltage value Vl of the discharge region. At this time, the control unit 90 determines the current value Il of the current flowing through the primary charging roller 22 when the voltage application unit 82 applies the voltage of the voltage value Vl at the timing when the non-image region l is located at the transfer site. Obtained via the detector 84.

  FIG. 10 is a diagram showing the relationship between the voltage (voltage value) V applied to the primary charging roller 22 and the current (current value) I flowing through the primary charging roller 22. 10, the voltage V applied to the primary charging roller 22 is adopted on the horizontal axis, and the current I flowing through the primary charging roller 22 is adopted on the vertical axis.

Referring to FIG. 10, the control unit 90 includes current values Ii and Ij that flow through the primary charging roller 22 when the voltage application unit 82 applies the voltages Vi and Vj in the undischarged region to the primary charging roller 22. From this, the equation of the straight line L3 is obtained according to the following Equation 3. In other words, the control unit 90 calculates the first impedance characteristic (straight line L3) of the primary charging roller 22 from the voltage values Vi and Vj and the current values Ii and Ij.
(Equation 3)
I-Ii = {(Ij-Ii) / (Vj-Vi)}. (V-Vi)
Similarly, the control unit 90 calculates the following formula from the current values Ik and Il flowing in the primary charging roller 22 when the voltage applying unit 82 applies the voltage values Vk and Vl in the discharge region to the primary charging roller 22. 4 is used to obtain the equation of the straight line L4. In other words, the control unit 90 calculates the second impedance characteristic (straight line L4) of the primary charging roller 22 from the voltage values Vk and Vl and the current values Ik and Il.
(Equation 4)
I−Ik = {(Il−Ik) / (Vl−Vk)} · (V−Vk)
Next, the control unit 90 flows to the primary transfer roller 24 based on the straight line L3 indicating the first impedance characteristic of the primary charging roller 22 and the straight line L4 indicating the second impedance characteristic of the primary charging roller 22. A voltage value Vq at which the current becomes a predetermined current value Iq is calculated. Further, the control unit 90 determines the voltage value Vq as the voltage value that the voltage application unit 82 applies to the primary transfer roller 24. Then, the control unit 90 controls the voltage application unit 82 so that the voltage application unit 82 applies the voltage of the voltage value Vq to the primary charging roller 22 at the timing when the image region is located at the transfer site.

  As described above, the control unit 90 applies the first voltage of the undischarged area to the primary charging roller 22 at the timing when the first non-image area (non-image area i) among the plurality of non-image areas is located at the transfer site. The voltage application unit 82 is controlled so as to apply a voltage having a value (Vi). At this time, the control unit 90 acquires the first current value (Ii) flowing through the primary charging roller 22 by applying a voltage having the first voltage value. In addition, the control unit 90 controls the primary charging roller 22 to output the second voltage value of the non-discharged area at the timing when the second non-image area (non-image area j) among the plurality of non-image areas is positioned at the transfer site. The voltage application unit 82 is controlled to apply the voltage Vj). At this time, the control unit 90 obtains a second current value (Ij) flowing through the primary charging roller 22 by applying a voltage having the second voltage value. In addition, the control unit 90 applies the third voltage value (Vk) of the discharge region to the primary charging roller 22 at the timing when the third non-image region (non-image region k) among the plurality of non-image regions is located at the transfer site. The voltage application unit 82 is controlled so as to apply the voltage of). At this time, the control unit 90 acquires a third current value (Ik) flowing through the primary charging roller 22 by applying a voltage having a third voltage value. In addition, the control unit 90 applies the fourth voltage value (Vl) of the discharge region to the primary charging roller 22 at the timing when the fourth non-image region (non-image region l) among the plurality of non-image regions is located at the transfer site. The voltage application unit 82 is controlled so as to apply the voltage of). At this time, the control unit 90 obtains a fourth current value (Il) flowing through the primary charging roller 22 by applying a voltage having a fourth voltage value. Then, the controller 90 calculates the first impedance characteristic of the primary charging roller 22 from the first current value and the second current value, and calculates the primary charging roller from the third current value and the fourth current value. 22 second impedance characteristics are calculated. Further, the control unit 90 controls the current value of the current flowing through the primary charging roller 22 to be a predetermined value (Iq) based on the first and second impedance characteristics at the timing when the image region is positioned at the transfer site. The voltage value (Vq) of the voltage applied to the primary charging roller 22 is determined.

  Since the impedance characteristic of the primary charging roller 22 does not change abruptly, the impedance of the primary charging roller 22 can be obtained from the current value acquired at the timing when each of the plurality of non-image areas is located at the transfer site. Is possible. Therefore, in the present embodiment, different undischarged area and discharged area voltages are applied to the primary charging roller 22 at the timing when each of the plurality of non-image areas is located at the transfer site. In other words, at the timing when each of the plurality of non-image areas is positioned at the transfer site, the current values when the voltages of the different undischarged areas and the discharged areas are applied to the primary charging roller 22 are combined to perform the primary charging. The impedance characteristic of the roller 22 is calculated. Accordingly, the image forming apparatus 1 does not require a constant current control circuit or a transfer bias application circuit that can change the voltage value at high speed in the primary charging bias application mechanism 80, and can prevent an increase in cost. In addition, since the impedance characteristic of the primary charging roller 22 is calculated from a plurality of current values flowing through the primary charging roller 22, it is applied to the primary charging roller 22 rather than when the impedance characteristic is calculated from one current value. The voltage to be controlled can be controlled with high accuracy. However, according to the time at which the non-image area is located at the transfer site, the current of the primary charging roller 22 is determined from the current value when the voltage is applied to the primary charging roller 22 at the timing at which one non-image area is located at the transfer site. It is also possible to calculate impedance characteristics.

  As described above, according to the image forming apparatus 1, the bias (voltage) applied to the transfer roller and the charging roller can be controlled with high accuracy without increasing the cost. In this embodiment, the image forming apparatus 1 has a primary transfer bias applying mechanism 60, a secondary transfer bias applying mechanism 70, and a primary charging bias applying mechanism 80 separately. However, the image forming apparatus 1 may have one bias application mechanism that has the functions of the primary transfer bias application mechanism 60, the secondary transfer bias application mechanism 70, and the primary charging bias application mechanism 80.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist.

Claims (6)

Image forming means for forming an electrostatic latent image by exposing the photosensitive member and developing the electrostatic latent image with toner to form a toner image on the photosensitive member;
A first transfer unit that transfers the toner image formed on the photoconductor by the image forming unit to an intermediate transfer body at a first transfer position;
A second transfer unit that transfers the toner image transferred to the intermediate transfer member to a recording medium at a second transfer position;
A voltage application unit for applying a voltage to the first transfer unit;
A current detection unit for detecting a current flowing in the first transfer unit when the voltage application unit applies a voltage;
By applying a plurality of different voltages to the voltage application unit while a non-image area where a toner image on the photoconductor is not formed passes through the first transfer position, the current detection unit has a plurality of voltages. Based on the plurality of different voltages and the plurality of currents, a current flowing through the first transfer unit when the toner image is transferred from the photosensitive member to the intermediate transfer body is set to a predetermined value based on the plurality of different voltages and the plurality of currents. Control means for controlling the voltage to be applied by the voltage application unit,
When the image forming unit continuously forms a plurality of toner images on the photoconductor, the control unit applies the plurality of different voltages to the adjacent toner images on the photoconductor by the voltage application unit. An image forming apparatus characterized in that a plurality of non-image areas are distributed and applied for each period passing through the first transfer position. Image forming means for forming an electrostatic latent image by exposing the photosensitive member and developing the electrostatic latent image with toner to form a toner image on the photosensitive member;
A first transfer unit that transfers the toner image formed on the photoconductor by the image forming unit to an intermediate transfer body at a first transfer position;
A second transfer unit that transfers the toner image transferred to the intermediate transfer member to a recording medium at a second transfer position;
A voltage application unit for applying a voltage to the second transfer unit;
A current detection unit for detecting a current flowing in the second transfer unit when the voltage application unit applies a voltage;
By applying a plurality of different voltages to the voltage application unit while a non-image area on which the toner image on the intermediate transfer body has not been transferred passes through the second transfer position, a plurality of voltages are applied to the current detection unit. And a current flowing through the second transfer portion when the toner image is transferred from the intermediate transfer member to the recording medium is set to a predetermined value based on the plurality of different voltages and the plurality of currents. Control means for controlling the voltage to be applied by the voltage application unit,
When the second transfer unit sequentially transfers each of the plurality of toner images carried on the intermediate transfer member to a recording medium, the control unit applies the plurality of different voltages to the intermediate voltage by the voltage application unit. An image forming apparatus, wherein a plurality of non-image areas between adjacent toner images on a transfer body are distributed and applied for each period passing through the second transfer position. The control means calculates a characteristic between a voltage applied to the first transfer unit and a current flowing through the first transfer unit based on the plurality of different voltages and the plurality of currents, and based on the characteristic A voltage to be applied by the voltage application unit is determined in order to set the current flowing through the first transfer unit when the toner image is transferred from the photosensitive member to the intermediate transfer member to the predetermined value. The image forming apparatus according to claim 1. The control unit calculates a characteristic between a voltage applied to the second transfer unit and a current flowing through the second transfer unit based on the plurality of different voltages and the plurality of currents, and based on the characteristic A voltage to be applied by the voltage application unit is determined in order to set a current flowing through the second transfer unit when the toner image is transferred from the intermediate transfer member to the recording medium to the predetermined value. The image forming apparatus according to claim 2. When the plurality of different voltages are distributed and applied for each period during which the plurality of non-image areas pass through the first transfer position, the control unit applies one of the plurality of different voltages by the voltage application unit. The same voltage is applied in different periods in which different non-image areas pass through the first transfer position, and the average value of the current detected by the current detector is applied in each period. 4. The image forming apparatus according to claim 1, wherein the image forming apparatus calculates the current flowing in the first transfer portion when the image is transferred. In the case where the control unit distributes and applies the plurality of different voltages for each period in which the plurality of non-image regions pass the second transfer position, one of the plurality of different voltages is applied by the voltage application unit. The same voltage is applied in different periods in which different non-image areas pass through the second transfer position, and the same voltage is applied to the average value of the current detected by the current detector in each period. 5. The image forming apparatus according to claim 2, wherein the image forming apparatus calculates the current flowing in the second transfer portion when the image is transferred.

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