JP4272331B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus that charges a surface of an image carrier using a proximity or contact charging member.
[0002]
[Prior art]
In an electrophotographic image forming apparatus, the surface of an image carrier is uniformly charged by a charging member, and after a latent image is formed on the charged surface, a developer is supplied through the developing member to supply the latent image. The image is visualized. As a charging method for the surface of the image carrier, there are a wire type for charging by corona discharge and a contact type for charging by bringing a charging member close to or in contact with the surface of the image carrier. As the recent market situation, there is a demand for downsizing, space reduction and cost reduction of the main body of the image forming apparatus, and further, it is required to maintain a good image for a long time even with an inexpensive and small apparatus. ing. From this point of view, the proximity or contact type is more effective as the charging method. This is because the required voltage is lower than that of the wire type, so that the capacity of the high-voltage power supply, which is a charging power pack, can be reduced, and the high-voltage power supply can be reduced in size and cost. Further, the contact type has the advantage that the amount of ozone generated is smaller than that of the wire type.
[0003]
The proximity or contact type charging method has a characteristic that the electrical characteristics such as the resistance value and dielectric constant of the charging member vary depending on the usage environment such as temperature and humidity. Variations in the charged state are likely to occur. In Japanese Patent Application Laid-Open No. 11-95529, the reflection density of the surface when no toner is attached to the surface of the image carrier is Vsg, and the reflection density of the surface when the toner is slightly attached is Vsdp. Then, the charged state of the surface of the image carrier is detected from the reflection density Vsg and the reflection density Vsdp, and the applied voltage (charging voltage) to the charging member is varied so that the reflection density ratio Vsdp / Vsg becomes a certain value. I have control.
[0004]
[Problems to be solved by the invention]
As described in JP-A-11-95529, when the voltage applied to the charging member (charging voltage) is controlled so that the reflection density ratio Vsdp / Vsg becomes a certain value, the charging potential on the surface of the image carrier is decreased. Although variations in the charged state such as uneven charging can be reduced, there are the following problems. When a two-component developer comprising a toner and a carrier is used as the developer, the toner charge amount (hereinafter referred to as Q / M) caused by friction between the toner and the carrier gradually increases over time, and conversely there is almost no use frequency. In the state, Q / M decreases. That is, if the Q / M is increased too much, the binding force between the toner and the carrier is too strong. Therefore, if the charge on the surface of the image carrier is not increased, the toner hardly adheres to the latent image and the image becomes thin. If Q / M is too low, the binding force between the toner and the carrier is too weak, and toner scattering and background contamination are likely to occur.
[0005]
In order to stabilize the Q / M, development is performed using a toner density detecting means for magnetically detecting the mixing ratio of toner and carrier and an optical sensor as a reflection density detecting means for detecting the reflection density on the surface of the image carrier. It may be possible to stabilize the Q / M in the agent. However, the usage state of the image forming apparatus is difficult to control well because there are variations in users who use the apparatus.
[0006]
There is also an attempt to stabilize the Q / M in the developer by making the developing voltage for the developing member variable according to the Q / M. In general, the development voltage is set to a reference value (reference development bias) that does not cause problems such as scumming or carrier adhesion. Therefore, if the development voltage is increased or decreased from the reference value, problems such as scumming or carrier adhesion occur. It tends to occur.
[0007]
In the image forming apparatus that performs charging voltage control, the present invention does not cause scumming or carrier adhesion even if the developing bias is changed when the developer Q / M changes over time. An object of the present invention is to provide an image forming apparatus capable of obtaining a good image.
[0008]
[Means for Solving the Problems]
The present invention corrects the charging voltage when changing the Q / M or the developing voltage in order to solve the problem that occurs when the charging voltage applied to the charging member and the developing voltage applied to the developing member are changed. Focused on.
[0010]
  According to the first aspect of the present invention, there is provided a charging member that is disposed close to or in contact with the surface of the image carrier and uniformly charges the surface;Contains a two-component developer having toner and carrier,A latent image formed on a uniformly charged surface through a developing memberTonerDeveloping means for supplying and visualizing;Reflection density Vsg in the state where toner is not attached to the surface of the image carrier, density detection means for detecting the reflection density Vsdp and reflection density in the state where toner is attached, and charging voltage application for applying a charging voltage to the charging member Reflection ratio Vsdp between reflection density Vsg and reflection density Vsdp detected by the density detection means / Voltage control means for variably controlling the charging voltage to the charging member so that Vsg is constant is provided.
[0011]
  Claim1According to the described invention, the charging voltage applied to the charging member fluctuates in accordance with a change in development voltage or a change in toner charge amount that can be detected from the reflection density on the surface of the image carrier.Image carrierSince the correction according to the surface state is performed, the charged potential on the surface of the image carrier is in a good state even when the environmental change, the Q / M change, and the development voltage are varied.
[0012]
  Claim 1inventionThenA developing voltage applying means for applying a developing voltage to the developing means;The voltage control means is a developing voltage to the developing member.Variable,As the developing voltage of the developing member when detecting the reflection density on the surface of the image carrierWith density detection means using variable development voltageThe reflection density on the surface of the image carrierDetectFrom the concentration detection means at that timeThe charging voltage to the charging member is determined based on the output value. For this reason, the reflection density on the surface of the image carrier detected by the density detection means corresponds to the variable development voltage, and the charging voltage is corrected to a voltage corresponding to the development voltage after the development change.
[0013]
  In invention of Claim 2,And a two-component developer having a charging member that is disposed close to or in contact with the surface of the image carrier and uniformly charges the surface, and a toner and a carrier,A latent image formed on a uniformly charged surface through a developing memberTonerDeveloping means for supplying and visualizing;Reflection density Vsg in the state where toner is not attached to the surface of the image carrier, density detection means for detecting the reflection density Vsdp and reflection density in the state where toner is attached, and charging voltage application for applying a charging voltage to the charging member Reflection ratio Vsdp between reflection density Vsg and reflection density Vsdp detected by the density detection means / In the image forming apparatus having voltage control means for variably controlling the charging voltage to the charging member so that Vsg becomes constant,The voltage control means is a developing voltage to the developing member.When changing,right awayImage carrierThe density detection means uses the developing voltage at the time of variable as the developing voltage of the developing member when detecting the reflection density of the surface.The reflection density on the surface of the image carrierDetectFrom the concentration detection means at that timeThe charging voltage to the charging member is determined based on the output value. For this reason, the reflection density of the image carrier surface detected by the density detector corresponds to the development voltage immediately after the change, and the charging voltage corresponding to the development voltage changed immediately after the development voltage change is supplied to the charging member. Response delay is reduced.
[0014]
  In invention of Claim 3,A two-component developer having a charging member that is disposed close to or in contact with the surface of the image carrier and uniformly charges the surface, and a toner and a carrier is housed.A latent image formed on a uniformly charged surface through a developing memberTonerDeveloping means for supplying and visualizing;Reflection density Vsg in the state where toner is not attached to the surface of the image carrier, density detection means for detecting the reflection density Vsdp and reflection density in the state where toner is attached, and charging voltage application for applying a charging voltage to the charging member Reflection ratio Vsdp between reflection density Vsg and reflection density Vsdp detected by the density detection means / In the image forming apparatus having voltage control means for variably controlling the charging voltage to the charging member so that Vsg becomes constant,A developing voltage applying means for applying a developing voltage to the developing means is provided, and when the voltage control means changes the developing voltage to the developing member, the variable amount (difference of | reference value−variable output |) is supplied to the charging member. The variable charging voltage is determined in consideration of determining the charging voltage.
[0015]
  Claim4In the described invention, the claims3In the image forming apparatus described above, when the variable amount is larger in absolute value than the reference value of the developing voltage, the charging voltage after change becomes larger in absolute value than the charging voltage before change when determining the charging voltage. If the variable is an absolute value smaller than the reference value of the development voltage, the voltage control means controls the correction voltage to be applied so that the charging voltage after the variable becomes smaller in absolute value. Yes.
[0016]
  Claim3, 4According to the described invention, since the charging voltage for the charging member is varied in consideration of the variable amount of the developing voltage applied to the developing member, the charging voltage corresponding to the variable amount of the developing voltage is applied to the charging member.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a main configuration of an image forming apparatus to which the present invention is applied. This image forming apparatus is arranged in contact with a drum-shaped photosensitive member 1 as an image carrier and a surface 1a of the photosensitive member 1 (hereinafter referred to as "photosensitive member surface 1a"), and charging that uniformly charges the surface. Two-component development via a charging roller 2 as a member, a writing device 12 as a latent image forming means for forming a latent image on the uniformly charged photoreceptor surface 1a, and a developing roller 31 as a developing member on the latent image And developing means 3 for supplying the toner of the agent to visualize (develop) the latent image.
[0018]
A belt-like member may be used as the photosensitive member, and a brush member may be used as the developing member. In this embodiment, the charging roller 2 as a charging member is brought into contact with the surface of the photosensitive member. However, the charging roller 2 may be disposed and used in the proximity of several tens to several hundreds of micrometers.
[0019]
Around the photosensitive member 1, a transfer portion 18 for transferring the developed toner image onto a sheet 17 as a transfer material is formed between the transfer roller 5 as a transfer member formed between the photosensitive member surface 1a and photosensitive at the time of transfer. The neutralizing needle 13 and the separation claw 6 functioning as a separating means for separating the sheet 17 electrostatically attached to the body surface 1a, the cleaning means 7 for collecting the toner remaining on the photoreceptor surface 1a after the transfer, and the photoreceptor A static elimination lamp 8 is provided as a static elimination member that neutralizes and initializes the residual charges on the surface 1a. Among these members, the photosensitive member 1, the charging roller 2, the developing unit 3, the separation claw 6, the cleaning unit 7, and the charge eliminating lamp 8 are mounted on the same casing 100 and configured as one photosensitive unit. . The cleaning unit 7 includes a cleaning blade 71 that contacts the photoreceptor surface 1a and scrapes off residual toner, and a discharge screw 72 that sends the scraped toner to the developing unit 3 or a waste toner bottle (not shown). The photoreceptor unit is detachable from the image forming apparatus main body. Although omitted in FIG. 1, the casing 100 near the transfer unit 18 is opened when the photosensitive unit is mounted on the image forming apparatus main body, and the photosensitive member surface 1 a is exposed from the casing 100, so that the photosensitive unit is mounted. A shutter member that closes the casing 100 when it is detached from the image forming apparatus main body is provided.
[0020]
A well-known registration roller pair 14 for feeding the sheet 17 to the transfer unit 18 at a predetermined timing is disposed upstream of the transfer unit 18. The transfer roller 5, the charge eliminating needle 13, and the registration roller pair 14 are mounted on the image forming apparatus main body side.
[0021]
A toner replenishing device 20 containing replenishing toner is detachably attached to the developing means 3. The toner replenishing device 20 replenishes the developing means 3 with replenishing toner from the toner replenishing unit 15 via the toner hopper unit 16 when the toner replenishing time comes. The developing means 3 contains a developer carrying member having a developing roller 31 and a developing doctor 32, and a two-component developer having toner and carrier, and contains an agent having stirring members 33 and 34 for stirring the developer. Divided into parts. In the unused state of the photosensitive unit, the agent carrier and the agent container are separated by the seal member 36, and the seal member 36 is removed when the unit is used. In the developing unit 3, the two-component developer mixed substantially uniformly by the stirring members 33 and 34 is conveyed to the developing roller 31, and the amount of toner supplied to the photoreceptor 1 is regulated by the developing doctor 32. In the vicinity of the stirring member 34, a toner concentration detection sensor 35 for detecting the mixing ratio of the toner in the developer and the carrier magnetically (magnetic permeability) is mounted. As shown in FIG. 3, Q / M indicating the toner charge amount in the two-component developer has a proportional relationship in which the charge amount Q / M increases as the number of sheets 17 used for printing increases. . Therefore, the Q / M detection may be performed after a predetermined number of prints on the paper 17 are completed.
[0022]
  Charging roller2, An optical sensor 9 (hereinafter referred to as “P sensor 9”) as a density detecting means for detecting the reflection density of the photoreceptor surface 1a is disposed. The P sensor 9 is a reflection type photosensor. As shown in FIG. 6, the P sensor 9 detects the reflection density of the background portion of the photoreceptor surface 1a when no toner adheres to the photoreceptor surface 1a. The gain is adjusted so that an output of 4V can be obtained. As shown in the figure, when the amount of toner adhering to the photoreceptor surface 1a increases, the output of the P sensor 9 decreases, and almost no output is generated at about 0.5 mg / cm @ 2.
[0023]
  The image forming apparatus body has a charging roller2A charging high-voltage power supply 10 as charging voltage applying means for applying a charging voltage (hereinafter referred to as “charging bias”) to the developing roller, and a developing voltage applying means for applying a developing voltage (hereinafter referred to as “developing bias”) to the developing roller 31. A high-voltage power supply 11 for charging and a high-voltage power supply for transfer for applying a transfer bias to the transfer roller 5 are arranged.
[0024]
As shown in FIG. 2, the image forming apparatus is provided with voltage control means 30 that variably controls the charging bias applied to the charging roller 2 and the developing bias applied to the developing roller 31. The voltage control means 30 is configured by well-known computer hardware including a ROM, RAM, and CPU (not shown). On the input side of the voltage control means 30, an operation section 19 having various keys and a display section for performing input operations on the toner density detection sensor 35, the P sensor 9, and the image forming apparatus is connected through a circuit (not shown). Yes. To the output side of the voltage control means 30, a charging high voltage power source 10, a developing high voltage power source 11, a writing device 12, and a toner replenishing device 20 are connected through a circuit (not shown).
[0025]
The basic operation of the image forming apparatus having such a configuration will be described. When the operator operates the operation unit 19 to input the number of prints and output a print command, the photosensitive member 1 shown in FIG. 1 is driven to rotate in the direction of the arrow by a drive motor (not shown), and a predetermined charging bias (standard charging bias) ) Is uniformly charged to a predetermined charging potential by the charging roller 2 applied. Then, the exposure light 4 corresponding to the image information is irradiated from the writing device 12 to the charged photoreceptor surface 1a to form a latent image corresponding to the image, and a predetermined developing bias (reference developing bias) is applied. The toner is supplied through the developing roller 31 and the latent image is visualized to form a toner image. The transfer unit 18 is fed with a sheet 17 conveyed from a paper supply unit (not shown) by the registration roller pair 14 at a timing coincident with the position of the toner image by the transfer unit 18 and applied to the transfer roller 5. As a result, the toner image is transferred to the paper 17 and separated from the photoreceptor surface 1 a by the action of the charge eliminating needle 13 and the separation claw 6. The separated paper 17 is conveyed to a fixing unit (not shown), and heat and pressure are applied to fix the toner image. Residual toner is removed from the photoreceptor surface 1a after the transfer by the cleaning means 7, and the residual potential is neutralized by the neutralizing lamp 8, and is prepared for the next image formation.
[0026]
The voltage control means 30 controls each part so as to form a predetermined density pattern on the photoreceptor surface 1a and periodically detect this density pattern with the P sensor 9, and the output value from the P sensor 9 is preset. When the value is reached, the toner replenishing device 20 is operated to replenish the toner for replenishment to the agent container of the developing means 3, and the toner replenishment operation is stopped when the output value from the toner density detection sensor 35 reaches a preset value. It has a function to let you. For this reason, the toner density supplied from the developing roller 31 to the photoreceptor surface 1a is maintained in a substantially uniform state by this toner density control.
[0027]
  The voltage control means 30 is based on the output value of the P sensor 9 and the charging bias applied to the charging roller 2 and the developing roller.31Has a function of determining a developing bias to be applied to. That is, the voltage control means 30 has a function of changing the charging bias and the developing bias and determining the charging bias and the developing bias according to the output ratio from the P sensor 9 before and after the variable. More specifically, the developing roller31Developing roller for detecting the reflection density of the photoreceptor surface 1a when the developing bias to the surface is varied31As the developing bias, density detection is performed by the P sensor 9 using the developing bias at the time of variable, and the charging bias to the charging roller 2 is determined based on this output value. Such a charging bias control function is performed by a voltage control routine stored in the voltage control means 30 in advance.
[0028]
It is assumed that the charging roller 2 used in this embodiment has charging characteristics as shown in FIG. That is, when a charging bias as a charging application voltage for the charging roller 2 is applied at −1600 V when the humidity is 90% at a room temperature of 30 ° C. as shown by a solid line, for example, the photosensitive member surface 1 a is set to a charging potential of −900 V. When charged and applied at -1600 V at a room temperature of 10 ° C. and a humidity of 16% as indicated by the broken line, the photosensitive member surface 1 a is charged to a charged potential of −700 V. For this reason, in the case of the environment indicated by the solid line, the amount of change in the charge potential of the photoreceptor surface 1a with respect to the unit amount of the charging bias is large. It tends to grow. Further, in the case of the environment shown by the broken line, since the change amount of the charging potential of the photoreceptor surface 1a with respect to the unit amount of the charging bias is small, the change in the toner adhesion amount (toner density) is small and the output ratio of the P sensor 9 is small. It becomes a trend. Therefore, charging bias control may be performed to increase the charging bias when the output ratio of the P sensor 9 is small, and to reduce the charging bias when the output ratio of the P sensor 9 is large.
[0029]
At this stage, since the change in the development bias is not taken into consideration, the correction corresponding to the change in the development bias is performed next. If the increase / decrease width of the developing bias is constant with the general charging bias being constant, the change in the toner adhesion amount (toner density) is large and the output ratio of the P sensor 9 is large when the charging potential on the surface of the photoreceptor is high. When the charged potential on the surface of the photoreceptor is low, the change in the toner adhesion amount (toner density) is small and the output ratio of the P sensor 9 is also small. For this reason, if the output ratio of the P sensor 9 is small, the charging bias is corrected in a direction to increase the charging bias. If the output ratio of the P sensor 9 is large, the charging bias control is performed to correct the charging bias in a decreasing direction. Good.
[0030]
FIG. 7 shows a reference toner image formed when the charging bias is set and a detection pattern for controlling the charging bias. In FIG. 7, the vertical axis indicates the relationship between the charging bias as the charging application voltage, the developing bias, the writing operation by the writing device 12, and the output of the P sensor 9, and the horizontal axis indicates the circumferential position of the photoreceptor surface 1a. The charging bias Vt is a voltage value applied to the charging roller 2 in the charging process, and a normal value is −1600 V in this embodiment, and this value is set as a reference value (reference charging bias). ΔV is a charging bias level change value, which is −200 V in this embodiment.
[0031]
In the voltage control means 30, when the charging bias is set, the surface of the photosensitive member 1a is neutralized by the neutralizing lamp 8 shown in FIG. 1, and data of the charging bias Vt is given to a charging circuit (not shown). After a predetermined time elapses, data of Vt−ΔV = Vt + 200V is applied to a charging circuit (not shown), and then data of charging bias Vt is applied to a charging circuit (not shown) after the elapse of time T1 and T2. Then, the developing bias, writing on / off, and reading of the detection output of the P sensor 9 are performed in a relationship where the positions in the circumferential direction of the photosensitive member surface 1a are matched. This reading is performed a predetermined number of times in each of the sections T1, T2, and T3, and the average values are calculated as Vsp, Vsdp, and Vsg, respectively. The charging bias can be set when the apparatus is started or after a certain number of prints have elapsed.
[0032]
For example, the charging bias Vt is normally −1600 V (reference value), ΔV is −200 V, the developing bias is normally −600 V (reference value), the reference toner image portion is −400 V, and the writing operation is turned on (light irradiation). ) When the potential of the photosensitive member surface 1a is −140V, the P sensor 9 detects the following state in this embodiment. That is, when Vt = −1600V and ΔV = −200V, the charging bias is −1400V, the charging potential of the photosensitive member surface 1a is −700V, the developing bias is −400V, and the writing-on potential is −140V. As a result, a halftone pattern having a development potential of 260 V is detected (Vsp).
[0033]
Next, when the developing bias is increased to -600 V (reference value) while the charging bias is kept as it is and writing is turned off (light irradiation is stopped), the developing bias is -600 V with respect to the charging potential of -700 V on the surface 1a of the photosensitive member, that is, development. A ground dirt pattern having a potential of 100 V is detected (Vsdp). When the charging bias is returned from −1400V, which is Vt−ΔV, to −1600V, which is Vt, the charged potential of the photoreceptor surface 1a becomes approximately −900V. That is, a background portion (white portion) having a development potential of −300 V is detected (Vsg).
[0034]
If the development characteristics in the case of development using a two-component developer are examined with reference to FIG. 5, the development characteristics indicated by a solid line or the development characteristics indicated by a broken line are obtained depending on the toner density. The voltage control means 30 controls the charging bias so that 0.90 ≦ Vsdp / Vsg ≦ 0.95. When the resistance value changes due to the environmental fluctuation of the charging roller 2, the charging potential is indicated by a broken line in FIG. It changes as follows. Therefore, when Vsdp / Vsg <0.90, the charging potential of the photosensitive member surface 1a is low, so correction control is performed so that the charging bias Vt is increased by a predetermined amount, for example, 50V. Conversely, when Vsdp / Vsg> 0.95, correction control is performed so that the charging bias Vt is lowered by 50V. In the development bias control, the signal from the toner density detection sensor 35 is controlled so that Vsp / Vsg becomes constant. However, the Vsp / Vsg does not become constant due to the fluctuation of Q / M of the two-component developer. A phenomenon occurs in which the density becomes thin.
[0035]
For this reason, when Vsp / Vsg does not become constant and the image density becomes dark, the development bias is variably controlled so that the voltage control of the development bias is out of order so that problems such as background contamination do not occur. The charging bias is corrected to an appropriate value.
[0036]
FIG. 8 shows a reference toner image formed at the time of setting the charging bias and a detection pattern for controlling the charging bias when the developing bias −600 V is increased by 100V. In the figure, the vertical axis represents the relationship between the charging bias, the developing bias, the writing operation by the writing device 12 and the output of the P sensor 9, and the horizontal axis represents the circumferential position of the photoreceptor surface 1a.
[0037]
When the developing bias is changed from −600 V to −700 V, the charging bias at −600 V is used as the charging bias at this time. That is, when Vt = −1600V and ΔV = −200v, the charging bias is −1400V, the charging potential on the surface 1a of the photoreceptor is −700V, the developing bias is −400V, and the potential after writing is −140V. Like the development potential shown in FIG. 7, a halftone pattern of 260 V is detected in section T1 (Vsp).
[0038]
Even when the developing bias is changed to -700 V, the control of the toner density detecting sensor 35 can be maintained in the normal state by using the developing bias of -400 V in the detection of Vsp in the section T1. In the detection of Vsdp in the section T2, if the developing bias is −700V, the developing potential becomes 0V, so the background stains become severe. In the detection of Vsg in the section T3, the developing potential is reduced to −200 V, but as shown in FIG. 5, the charged potential on the surface 1a of the photosensitive member 1a is increased because Vsdp / Vsg is significantly lower than 0.90. As a result, it is not necessary to cause background contamination on the image.
[0039]
FIG. 9 shows a flowchart of the charging bias control routine according to this embodiment. In the figure, X is ΔV = −200 V, Y is a variable amount of the charging bias, 50 V, and Z is an upper limit value of the charging bias. Hereinafter, it demonstrates along this flowchart.
[0040]
  In FIG. 9, in step S1, it is determined whether the photoconductor unit is a new product, for example, based on an output from the toner concentration detection sensor 35. If the photoconductor unit is a new product, the process proceeds to step S2 and the charge application voltage correction value VcP is returned to the default. In S3, 0.90 ≦ Vsdp / Vsg ≦ 0.95 is determined, and if this condition is satisfied, in step S4, X is subtracted from the charge application voltage correction value VcP, that is, −200 V is subtracted from the reference value −1600V. . Then, the charging bias information Vt ′ corrected in step S3 and the maximum value of the charging biasZIf the maximum value X is not exceeded, the process proceeds to step S6 and the value is stored in a memory (not shown) as the latest charging bias information Vt ′. Maximum value in step S6ZIf this is the case, no further charge bias variable control is possible.Z the mostThe new charging bias information Vt ′ is stored in a memory (not shown).
[0041]
  When this flowchart is started for the second time, the photosensitive unit is not new, so that X is added to the charging bias information Vt ′ stored in the memory to obtain the charging applied voltage correction value VcP, and 0 in step S3. .90 ≦ Vsdp / Vsg ≦ 0.95 is determined. If this condition is satisfied, the process proceeds to steps S4 and S5, and the subsequent processing is changed depending on whether or not the maximum value Z is reached. On the other hand, if the condition in step S3 is not satisfied, the process proceeds to step S8 to determine Vsdp / Vsg <0.90. If this condition is satisfied, the charging bias variable Y is subtracted from the charge application voltage correction value VcP, and the process proceeds to step S8. If the condition is not satisfied, the charge application voltage correction value VcP is determined. Add variable Y and step S5Proceed to Step S5The corrected charging bias information Vt ′ is the maximum value.ZCompared to the maximum valueZThen maximumZIs stored in the memory as the latest charging bias information Vt 'and the maximum value is stored.ZIf not, the charging bias information Vt ′ in step S5 is stored in the memory and the process is terminated.
[0042]
In this embodiment, since the output of the P sensor 9 is detected when the apparatus is started up or after a certain number of prints have elapsed, there is a time lag between the reading of the first detection voltage and the next reading. It may occur. Therefore, in order to prevent such a problem, when the developing bias Vt is changed by the voltage control means 30, the reflection density of the photoreceptor surface 1a is immediately detected by the P sensor 9, and the information is read. By changing the charging bias Vt applied to the charging roller 2 based on the output value, the charging bias Vt that matches the state of the latest photoreceptor surface 1a can be supplied to the charging roller 2 at all times. The charging potential can always be in a good state.
[0043]
As another form of the present invention, when the developing bias to the developing roller 31 is varied by the voltage control means 30 instead of considering the charging bias variable Y as in the above-described form, the developing bias variable Y1 is changed. Can be considered when determining the charging bias Vt. In this case, if the variable Y1 is larger in absolute value than the reference value of the developing bias, for example, −600, the charging bias after the change is more absolute than the charging bias before the change when determining the charging bias. When the variable voltage Y1 is smaller than the reference value of the developing bias by an absolute value, the correction voltage X2 is adjusted so that the charging bias after the variable becomes smaller by the absolute value. What is necessary is just to control so that it may add to developing bias.
[0044]
When the charging bias for the charging roller 2 is varied in consideration of the variable amount of the developing bias applied to the developing roller 31 as described above, a charging bias corresponding to the variable amount of the developing bias can be applied to the charging roller 2.
[0045]
【The invention's effect】
According to the present invention, with respect to the charging voltage applied to the charging member, the surface of the photoconductor that fluctuates in accordance with the change in the developing voltage that can be detected from the reflection density on the surface of the image carrier and the change in the toner charge amount Since correction is performed according to the state, even when the environment changes, the toner charge amount changes, or the development voltage is varied, the charged potential on the surface of the image carrier is kept in a good state, and background contamination, carrier adhesion, etc. occur. And a good image can be obtained.
[0046]
According to the present invention, the density of the surface of the image carrier detected by the density detecting unit corresponds to the variable development voltage, and the charging voltage is corrected to a voltage corresponding to the development voltage after the development change. Therefore, even when the environmental change, the change in toner charge amount, or the development voltage is varied, the charged potential on the surface of the image carrier can be in a good state, and there is no occurrence of background contamination, carrier adhesion, etc. Can be obtained.
[0047]
According to the present invention, the density of the surface of the image carrier detected by the density detector corresponds to the development voltage immediately after the change, and the charging voltage corresponding to the development voltage changed immediately after the change of the development voltage is the charging member. Since the response delay is reduced, the charged potential on the surface of the image carrier can be immediately brought into a good state even when the environment changes, the toner charge amount changes, or the development voltage is varied. Good images can be obtained without the occurrence of background stains or carrier adhesion.
[0048]
According to the present invention, since the charging voltage for the charging member is changed in consideration of the variable amount of the developing voltage to the developing member, the charging voltage corresponding to the variable amount of the developing voltage is applied to the charging member. Even when environmental changes, toner charge changes, and development voltages are varied, the charge potential on the surface of the image carrier can be in a good state, and there is no occurrence of background contamination or carrier adhesion, and a good image can be obtained. It is done.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus to which the present invention is applied.
FIG. 2 is a block diagram of a voltage control means of the present invention and a configuration connected thereto.
FIG. 3 is a diagram showing characteristics of developer charge amount.
FIG. 4 is a diagram showing a relationship between a charging applied voltage and a charging potential on the surface of an image carrier according to the present invention.
FIG. 5 is a diagram showing the relationship between the charged potential on the surface of the image carrier and the output ratio of the detection signal of the reflection density detection means.
FIG. 6 is a graph showing toner density detection characteristics on the surface of an image carrier by reflection density detection means.
FIG. 7 is a diagram showing changes in charging bias, developing bias, latent image writing on / off, and output of reflection density detecting means;
FIG. 8 is a diagram showing changes in charging bias, developing bias, latent image writing on / off, and output of reflection density detecting means when the developing bias is variable.
FIG. 9 is a flowchart showing one form of charging voltage control performed by the voltage control means of the present invention.
[Explanation of symbols]
1 Image carrier
1a Surface
2 Charging member
3 Development means
9 Concentration detection means (P sensor)
10 Charging voltage application means
11 Development voltage application means
12 Latent image forming means
30 Voltage control means
31 Development member
Vsdp / Vsg output ratio
X1, X2 correction voltage
Y1 Variable development voltage

Claims (4)

A charging member that is disposed close to or in contact with the surface of the image carrier and uniformly charges the surface;
A developing unit that stores a two-component developer having a toner and a carrier and supplies the toner to a latent image formed on the uniformly charged surface through a developing member to visualize the latent image;
Density detecting means for detecting a reflection density Vsg in a state where toner is not attached and a reflection density Vsdp in a state where toner is attached on the surface of the image carrier;
Charging voltage applying means for applying a charging voltage to the charging member;
In the image forming apparatus having voltage control means for variably controlling the charging voltage to the charging member so that the reflection density ratio Vsdp / Vsg between the reflection density Vsg and the reflection density Vsdp detected by the density detection means is constant .
A developing voltage applying means for applying a developing voltage to the developing means;
The voltage control means varies the developing voltage to the developing member and uses the developing voltage at the time of variable as the developing voltage of the developing member when detecting the reflection density on the surface of the image carrier. An image forming apparatus for detecting a reflection density on a surface of the image carrier and determining a charging voltage to the charging member based on an output value from the density detecting means at that time . A charging member that is disposed close to or in contact with the surface of the image carrier and uniformly charges the surface;
A developing unit that stores a two-component developer having a toner and a carrier and supplies the toner to a latent image formed on the uniformly charged surface through a developing member to visualize the latent image;
Density detecting means for detecting a reflection density Vsg in a state where toner is not attached and a reflection density Vsdp in a state where toner is attached on the surface of the image carrier;
Charging voltage applying means for applying a charging voltage to the charging member;
In the image forming apparatus having voltage control means for variably controlling the charging voltage to the charging member so that the reflection density ratio Vsdp / Vsg between the reflection density Vsg and the reflection density Vsdp detected by the density detection means is constant .
When the developing voltage to the developing member is varied , the voltage control means detects the density using the developing voltage at the time of variable as the developing voltage of the developing member when immediately detecting the reflection density on the surface of the image carrier. An image forming apparatus for detecting a reflection density on the surface of the image carrier by means and determining a charging voltage to the charging member based on an output value from the density detecting means at that time . A charging member that is disposed close to or in contact with the surface of the image carrier and uniformly charges the surface;
A developing unit that stores a two-component developer having a toner and a carrier and supplies the toner to a latent image formed on the uniformly charged surface through a developing member to visualize the latent image;
Density detecting means for detecting a reflection density Vsg in a state where toner is not attached and a reflection density Vsdp in a state where toner is attached on the surface of the image carrier;
Charging voltage applying means for applying a charging voltage to the charging member;
In the image forming apparatus having voltage control means for variably controlling the charging voltage to the charging member so that the reflection density ratio Vsdp / Vsg between the reflection density Vsg and the reflection density Vsdp detected by the density detection means is constant .
A developing voltage applying means for applying a developing voltage to the developing means;
The voltage control unit is an image forming apparatus that determines a variable charging voltage in consideration of the variable amount when determining the charging voltage to the charging member when the developing voltage to the developing member is varied. The image forming apparatus according to claim 3.
In the case where the variable portion is larger in absolute value than the reference value of the development voltage, the voltage control means is configured such that when the charging voltage is determined, the charging voltage after the change is an absolute value than the charging voltage before the change. An image forming apparatus that applies a correction voltage so as to increase, and applies the correction voltage so that the variable charging voltage becomes smaller in absolute value when the variable amount is smaller in absolute value than the reference value of the development voltage.

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