JP2019056860A - Charge control device and image forming apparatus - Google Patents

Abstract

To provide a charge control device and an image forming apparatus that can accurately determine a minimum optimal AC voltage required irrespective of measurement data.SOLUTION: A charge control device comprises: a charging member for a charge target body; means that controls the voltage value of a peak-to-peak voltage of a DC voltage or an AC voltage applied to the charging member; measuring means that measures the value of an AC current flowing to the charging member through the charging target body; average value calculation means that determines the average value of measurement data in a non-image forming period; and corrected data calculation means that determines the ratios of the measurement data acquired in a time-series manner to the average value and compares the ratios with measurement positions on the charging target member, thereby outputting as corrected data of the measurement positions. When a current value other than a predetermined current value is detected at a measurement position in the measurement data acquired in a time-series manner, the charge control device does not reflect a result of the current value on the average value of the measurement data acquired in a time-series manner and does not use the result for subsequent current measurement positions.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a contact charging method that uses discharge as a charging principle, a charging control device that charges an object to be charged by superimposing an AC current or an AC voltage on a DC voltage and supplying it to a charging member, and an image forming apparatus using the same About. In particular, the present invention relates to a technique for detecting an AC voltage or an AC current when a charged body is saturated even if a measurement current varies due to rotation of the charged body or charging member.

  Conventionally, as a charging device, there is a contact type charging device in which a charging member such as a roller or a blade to which a voltage is applied is brought into contact with a surface of a charged body such as a photoconductor to charge the charged body surface to a predetermined polarity and potential. It is used.

  In this contact-type charging device, a method of applying an AC voltage or AC current and a DC voltage or DC current to the charging device is employed. If only a DC voltage or DC current is applied, the current flows only where the resistance is low on the photosensitive member, so that uniform charging cannot be achieved. Further, when the surface of the photosensitive member is locally soiled, there arises a problem that only that portion is not charged. Therefore, a voltage obtained by superimposing the AC voltage on the DC voltage is applied to the charging device to charge the surface of the photoreceptor.

  However, if the AC voltage is too high, the photoreceptor wear will be affected. On the other hand, if it is too small, the uniformity of charging cannot be maintained, and unevenness occurs when printed. In addition, immediately after the machine is started up, the in-machine temperature rises rapidly, so that the optimum AC voltage value changes greatly. Therefore, it is necessary to correct the AC voltage to the minimum necessary optimum value as needed.

  In Patent Document 1, as shown in FIG. 7, at the time of non-image formation, a current value when a peak-to-peak voltage less than twice the discharge start voltage Vth of at least one point is applied to the charging member, and at least two points or more. Discloses a technique for measuring a current value when a peak-to-peak voltage more than twice Vth of Vth is applied, and determining a peak-to-peak voltage of the AC voltage applied to the charging means during image formation based on the measured AC current value. ing.

In Patent Document 2, as shown in FIG. 1, an AC current or an AC voltage is superimposed on a DC voltage and supplied to a charging roll member, and a current detection unit that measures a current flowing through the charging roll, and an AC voltage supplied to a photoreceptor. Alternatively, the AC current is swept, the average value of the obtained measurement data is obtained, the ratio of each measurement data to the average value is obtained, and the correction data for each measurement position is obtained by corresponding to each measurement position on the photoconductor. Is disclosed.
JP 2001-201921 A JP 2007-57988 A

  However, the photoreceptor has unevenness such as eccentricity and film thickness, and further, the measured current value shown in FIG. 7 fluctuates due to partial contamination of the photoreceptor and the charging roll. For example, as shown in FIG. 2, when the sampling point represented by the black circle interferes with the fluctuation associated with the photosensitive member, the current value with respect to the voltage supplied to the charging roll varies depending on the sampling point, and the minimum necessary optimum The AC voltage cannot be found. For this reason, a loss of image quality occurs, resulting in a significant lack of reliability.

  Further, when C set (outer diameter deformation) of the charging roller is caused by leaving the image forming apparatus for a long time, the sampling point to be measured is the same when the charging roller is set to C and when the C is not set. The flow value changes as the contact NIP width formed by the photosensitive drum and the charging roller becomes wider.

  Therefore, a current detection unit for measuring the current flowing through the charging roll, and an AC voltage or an AC current supplied to the photosensitive member are swept, and an average value of the obtained measurement data is obtained, and a ratio to the average value of each measurement data Even if each is obtained, corresponding to each measurement position on the photosensitive member, and correction data at each measurement position is output, the state of the C set of the charging roller gradually changes (recovers) by the rotation of the charging roller. Therefore, the correction value calculated in the initial stage of correction control may be shifted.

  There is a method of measuring only one measurement point by one rotation of the photosensitive member in order to eliminate the error due to the unevenness of the photosensitive member film thickness and the influence of the C set of the charging roller. The problem of increased wear arises.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a charge control device and an image forming apparatus capable of accurately obtaining a minimum necessary optimum AC voltage regardless of measurement data. To do.

  In order to achieve the above object, a charge control device according to the present invention comprises a charging member that is disposed in contact with or close to a member to be charged, and that charges the member to be charged following the rotation of the member to be charged. Means for applying either a DC voltage or an AC voltage to the member, or a superimposed voltage of the DC voltage and the AC voltage; means for controlling each voltage value of the DC voltage and the peak voltage of the AC voltage applied to the charging member; Measuring means for measuring an alternating current value flowing through the charging member through the charged body, and when the charging member and the charged body are rotated, the direct current voltage is applied to the charging member. When the discharge start voltage to the object to be charged is Vth, a peak-to-peak voltage less than twice Vth is applied during non-image formation, and the average value of the measurement data obtained in time series from the measurement means is calculated. An average value calculating means to be obtained; and A correction data calculating means for obtaining a ratio of the measurement data obtained in time series with respect to the average value and corresponding to each measurement position on the charged body, and outputting as correction data for each measurement position; And the current value result at the measurement position where a value outside the predetermined current value is detected in the measurement data obtained in time series is not reflected in the average value of the measurement data obtained in time series. And it is not used for the subsequent current measurement positions.

  In addition, an image forming apparatus according to the present invention includes the above charge control device.

  According to the present invention, the minimum necessary optimum AC voltage can be accurately obtained regardless of the measurement data. In addition, the applied AC voltage or AC current when the charged object is saturated can be obtained with high accuracy regardless of the measurement data.

It is a figure which shows an Iac-Idc curve, and is a figure which shows DC current measured when AC amplitude is changed. It is a figure which shows the wave | undulation of the DC current produced by rotation of a photoconductor. 1 is a schematic configuration model diagram of an image forming apparatus according to a first embodiment. Layer structure model of photoconductor Operation sequence diagram of image forming apparatus Block diagram of charging bias application system Measurement schematic of discharge current Relationship between peak-to-peak voltage and AC current measured during print preparation rotation Relationship between current fluctuation for one rotation of charging roller and current when C set is generated Charge control flow chart Relationship diagram between peak-to-peak voltage and alternating current measured during print preparation rotation in the second embodiment

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 3 is a schematic configuration diagram of the image forming apparatus according to the embodiment of the present invention. The image forming apparatus of this example is a laser beam printer having a transfer type electrophotographic process, a contact charging method, a reverse development method, and a maximum sheet passing size of A3 size.

(1) Overall Schematic Configuration of Printer a) Image carrier 1 is a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier. This photosensitive drum 1 is a negatively charged organic photoconductor (OPC), has an outer diameter of 25 mm, and rotates in the counterclockwise direction indicated by an arrow with a process speed (peripheral speed) of 100 mm / sec around the center support shaft. Driven.

  As shown in the layer configuration model diagram of FIG. 4, the photosensitive drum 1 has an undercoat layer 1b that suppresses light interference and improves the adhesion of the upper layer on the surface of an aluminum cylinder (conductive drum base) 1a. The photocharge generation layer 1c and the charge transport layer 1d are coated in order from the bottom.

b) Charging means 2 is a contact charging device (contact charger) as a charging means for uniformly charging the peripheral surface of the photosensitive drum 1, and in this example, a charging roller (roller charger). The charging roller 2 holds both ends of the cored bar 2a rotatably by bearing members (not shown), and is urged in the direction of the photosensitive drum by a pressing spring 2e to be applied to the surface of the photosensitive drum 1. It is brought into pressure contact with a predetermined pressing force, and rotates following the rotation of the photosensitive drum 1. A pressure contact portion between the photosensitive drum 1 and the charging roller 2 is a charging portion (charging nip portion) a.

  By applying a charging bias voltage of a predetermined condition from the power source S1 to the metal core 2a of the charging roller 2, the peripheral surface of the rotating photosensitive drum 1 is uniformly contact-charged to have a negative polarity in this example. The Reference numeral 100 denotes a control unit of the power source S1. The configuration of the charging roller 2 and the charging control method will be described in detail in section (3).

c) Information writing means 3 is an exposure apparatus as information writing means for forming an electrostatic latent image on the surface of the charged photosensitive drum 1, and this example is a laser beam scanner using a semiconductor laser. A laser beam modulated in response to an image signal sent from a host device such as an image reading device (not shown) to the printer side is output, and the uniformly charged surface of the rotating photosensitive drum 1 is laser-exposed at the exposure position b. Scan exposure L (image scan exposure) is performed. Due to the laser scanning exposure L, the potential of the surface of the photosensitive drum 1 irradiated with the laser light is lowered, so that an electrostatic latent image corresponding to the scanned and exposed image information is sequentially formed on the surface of the rotating photosensitive drum 1. Will be formed.

d) Developing means 4 is a jumping developing device (developing device) in this example as developing means for supplying a developer (toner) to the electrostatic latent image on the photosensitive drum 1 to visualize the electrostatic latent image. is there. The electrostatic latent image formed on the surface of the photosensitive drum 1 is reversely developed with the one-component magnetic toner (negative toner) negatively charged by the developing device 4.

  4a is a developing container, 4b is a non-magnetic developing sleeve, and this developing sleeve 4b is rotatably arranged in the developing container 4a with a part of its outer peripheral surface exposed to the outside. 4c is a non-rotating magnet roller fixedly inserted in the developing sleeve 4b, 4d is a developer coating blade, 4e is a one-component magnetic toner as a developer contained in the developing container 4a, and S2 is a developing for the developing sleeve 4b. This is a bias application power source.

  Accordingly, the surface of the developing sleeve 4b rotating in the counterclockwise direction indicated by the arrow is coated as a thin layer, and the one-component magnetic toner conveyed to the developing unit c is electrostatically latentized on the surface of the photosensitive drum 1 by the electric field due to the developing bias. The electrostatic latent image is developed as a toner image by selectively adhering to the image. In the case of this example, toner adheres to the exposed bright portion of the surface of the photosensitive drum 1 and the electrostatic latent image is reversely developed.

  The developer thin layer on the developing sleeve 4b that has passed through the developing portion c is returned to the developer reservoir in the developing container 4a with the subsequent rotation of the developing sleeve.

e) Transfer means / fixing means / cleaning means 5 is a transfer device, and in this example is a transfer roller. The transfer roller 5 is brought into pressure contact with the photosensitive drum 1 with a predetermined pressing force, and the pressure nip portion is a transfer portion d. A transfer material (a member to be transferred, a recording material) P is fed to the transfer portion d from a paper feed mechanism portion (not shown) at a predetermined control timing.

  The transfer material P fed to the transfer part d is nipped between the rotating photosensitive drum 1 and the transfer roller 5 and conveyed. In the meantime, the transfer roller 5 is applied with a positive transfer bias having a polarity opposite to the negative polarity that is the normal charge polarity of the toner from the power source S3, whereby the surface of the transfer material P that is nipped and conveyed by the transfer portion d. The toner images on the surface of the photosensitive drum 1 are sequentially electrostatically transferred.

  The transfer material P that has received the transfer of the toner image through the transfer portion d is sequentially separated from the surface of the rotating photosensitive drum 1 and conveyed to the fixing device 6 (for example, a heat roller fixing device), where the toner image is fixed. And output as an image formed product (print, copy).

  Reference numeral 7 denotes a cleaning device. The surface of the photosensitive drum 1 after the transfer of the toner image onto the transfer material P is rubbed by the cleaning blade 7a to be cleaned to remove the transfer residual toner, and repeatedly used for image formation. The e is a photosensitive drum surface contact portion of the cleaning blade 7a.

(2) Printer Operation Sequence FIG. 5 is an operation sequence diagram of the printer.

a. Initial rotation operation (front multiple rotation process)
This is a start operation period (start operation period, warming period) when the printer is started. When the power switch is turned on, the photosensitive drum is rotationally driven, and a preparatory operation of a predetermined process device such as starting up the fixing device to a predetermined temperature is executed.

b. Print preparation rotation operation (pre-rotation process)
Print signal-This is a preparatory rotation operation period before image formation from when the image formation (printing) process operation is actually performed, and is executed following the initial rotation operation when a print signal is input during the initial rotation operation. Is done. When the print signal is not input, the main motor is temporarily stopped after the initial rotation operation is completed, and the photosensitive drum is stopped from rotating. The printer is kept in a standby (standby) state until the print signal is input. When the print signal is input, the print preparation rotation operation is executed.

  In the present embodiment, a calculation / determination program for an appropriate peak-to-peak voltage value (or alternating current value) of the applied AC voltage in the charging process of the printing process is executed during the printing preparation rotation operation period. This will be described in detail in section (3) below.

c. Printing process (image forming process, image forming process)
When the predetermined print preparation rotation operation is completed, an image forming process for the rotating photosensitive drum is subsequently executed, and the toner image formed on the surface of the rotating photosensitive drum is transferred to a transfer material, and the fixing process of the toner image by the fixing device is performed. The image formation is printed out.

  In the continuous printing (continuous printing) mode, the above-described printing process is repeatedly executed for a predetermined set number n of prints.

d. Inter-sheet process In the continuous printing mode, after the trailing edge of one transfer material passes the transfer position d, the recording paper at the transfer position until the leading edge of the next transfer material reaches the transfer position d. This is a non-paper passing period.

e. Post-rotation operation This is a period during which a predetermined post-operation is executed by continuing to drive the main motor for a while after the last transfer material printing process is completed and rotating the photosensitive drum.

f. Standby When the predetermined post-rotation operation is completed, the drive of the main motor is stopped, the rotation of the photosensitive drum is stopped, and the printer is kept in a standby state until the next print start signal is input.

  In the case of printing only one sheet, after the printing is completed, the printer goes into a standby state through a post-rotation operation.

  When the print start signal is input in the standby state, the printer proceeds to the pre-rotation process.

  The printing process of c is the time of image formation, and the initial rotation operation of a, the pre-rotation operation of b, the paper gap process of d, and the post-rotation operation of e are non-image formation.

(3) Detailed description of charging means A) Charging roller 2
The longitudinal length of the charging roller 2 as the contact charging member is 320 mm. As shown in the layer configuration model diagram of FIG. 3, the lower layer 2b, the intermediate layer 2c, and the surface layer 2d are disposed around the core metal (support member) 2a. Is a three-layer structure in which are sequentially stacked from the bottom. The lower layer 2b is a foamed sponge layer for reducing charging noise, the intermediate layer 2c is a conductive layer for obtaining uniform resistance as a whole of the charging roller, and the surface layer 2d is a defect such as a pinhole on the photosensitive drum 1. This is a protective layer provided to prevent the occurrence of leaks even if there is.

More specifically, the specification of the charging roller 2 of this example is as follows.
Core bar 2a; stainless steel round bar lower layer 2b with a diameter of 6 mm; foamed EPDM with carbon dispersion, specific gravity 0.5 g / cm ³ , volume resistivity 10 ³ Ωcm, layer thickness 3.0 mm, length 320 mm
Intermediate layer 2c: carbon-dispersed NBR rubber, volume resistivity 10 ⁵ Ωcm, layer thickness 700 μm
Surface layer 2d; tin oxide and carbon dispersed in resin resin of fluorine compound, volume resistivity 10 ⁸ Ωcm, surface roughness (JIS standard 10-point average surface roughness Ra) 1.5 μm, layer thickness 10 μm
B) Charging Bias Application System FIG. 6 is a block circuit diagram of a charging bias application system for the charging roller 2. A predetermined vibration voltage (bias voltage Vdc + Vac) obtained by superimposing an AC voltage of frequency f on a DC voltage from the power source S1 is applied to the charging roller 2 through the core metal 2a, so that the peripheral surface of the rotating photosensitive drum 1 is It is charged to a predetermined potential. A power source S 1 that is a voltage application unit for the charging roller 2 includes a direct current (DC) power source 11 and an alternating current (AC) power source 12.

  Reference numeral 13 denotes a control circuit which controls the DC power supply 11 and the AC power supply 12 of the power supply S1 so as to apply a DC voltage, an AC voltage, or a superimposed voltage of both to the charging roller 2. And a function of controlling the DC voltage value applied to the charging roller 2 from the DC power source 11 and the peak-to-peak voltage value of the AC voltage applied from the AC power source 12 to the charging roller 2.

  Reference numeral 14 denotes an AC current value measurement circuit as means for measuring the AC current value flowing through the charging roller 2 via the photosensitive member 1. The measured AC current value information is input from the circuit 14 to the control circuit 13.

  Reference numeral 15 denotes an environment sensor (thermometer and hygrometer) as means for detecting the environment where the printer is installed. The detected environmental information is input from the environmental sensor 15 to the control circuit 13.

  Then, the control circuit 13 determines from the AC current value information input from the AC current value measurement circuit 14 and further from the environmental information input from the environmental sensor 15 between appropriate peaks of the AC voltage applied to the charging roller 2 in the charging process of the printing process. It has a function of executing a voltage value calculation / determination program.

C) Control Method for Peak Voltage of AC Voltage Next, a control method for the peak voltage of the AC voltage applied to the charging roller 2 during printing will be described.
The amount of discharge current quantified by the following definition represents the actual amount of AC discharge, and has been found to have a strong correlation with scraping of the photosensitive drum, image flow, and charging uniformity.

  That is, as shown in FIG. 7, the alternating current Iac is in a linear relationship with respect to the peak-to-peak voltage Vpp, less than the discharge start voltage Vth × 2 (V) (undischarged region), and gradually increases from that point toward the discharge region. In the direction of increasing current. In a similar experiment in a vacuum where no discharge occurs, a straight line is maintained, so this is considered to be the increment ΔIac of the current involved in the discharge.

Therefore, when the ratio of the current Iac to the peak-to-peak voltage Vpp less than the discharge start voltage Vth × 2 (V) is α, AC current such as current flowing to the contact portion (hereinafter referred to as nip current) other than current due to discharge The current is α · Vpp. The difference between Iac measured when a voltage equal to or higher than the discharge start voltage Vth × 2 (V) is applied, and this α · Vpp,
Formula 1... ΔIac = Iac−α · Vpp
To ΔIac is defined as a discharge current amount that indicates the amount of discharge instead.

  The amount of discharge current changes as the environment and durability are increased when charging is performed under the control of a constant voltage or a constant current. This is because the relationship between the peak-to-peak voltage and the discharge current amount and the relationship between the alternating current value and the discharge current amount are fluctuating.

  In the AC constant current control method, control is performed with the total current flowing from the charging member to the member to be charged. As described above, the total current amount is the sum of the nip current α · Vpp and the discharge current amount ΔIac that flows by discharging at the non-contact portion. In constant current control, the charged object is actually charged. In addition to the discharge current, which is the current required for the control, the nip current is controlled.

  For this reason, the amount of discharge current cannot actually be controlled. Even if the constant current control is performed with the same current value, the discharge current amount naturally decreases as the nip current increases due to the environmental variation of the charging member material, and the discharge current amount increases as the nip current decreases. Even with the current control method, it is impossible to suppress the increase / decrease in the amount of discharge current ideally, and it has been difficult to realize both the shading of the photosensitive drum and the charging uniformity when aiming for a long life.

Therefore, in order to always obtain a predetermined amount of discharge current, control was performed as follows. A method of determining the peak-to-peak voltage that becomes the discharge current amount D when the predetermined discharge current amount is D will be described.
In this embodiment, the control circuit 13 executes a calculation / determination program for an appropriate peak-to-peak voltage value of the AC voltage applied to the charging roller 2 in the charging process during the printing process during the printing preparation rotation operation.

  Specifically, a description will be given with reference to the Vpp-Iac graph in FIG. 8, the AC current data for one rotation of the charging roller in FIG. 9, and the control flow diagram in FIG. As shown in FIG. 8, the control circuit 13 controls the AC power source 12 to provide the charging roller 2 with three peak-to-peak voltages (Iα1 to Iα3) that are undischarged regions and peak-to-peak voltage (Vpp) that is a discharge region. Three points (Iβ1 to Iβ3) are sequentially applied, and the alternating current value flowing through the charging roller 2 via the photosensitive member 1 at that time is measured by the alternating current value measuring circuit 14 and input to the control circuit 13.

D) Method for Determining AC Current Value Next, a method for determining the AC current value of the AC current value flowing through the charging roller 2 will be described. First, the AC current flowing through the charging roller 2 at Iα1 in the Vpp-Iac graph of FIG. 8 is measured over one rotation of the charging roller 2 at the timing of 1 to 8 as shown in FIG.

  Next, an average value of the measured AC current is obtained. In calculating the average value, a predetermined current value range is determined and set for each environment. As shown in 5 of FIG. 9, when the charging roller 2 detects a current value out of the current value range, it is determined that the portion is set to C, and the current value data at that position is the AC current value. The average value is not reflected. The average value obtained from the result is taken as the alternating current value of Iα1.

  It should be noted that the position where there is a possibility of C set in the charging roller 2 is not used for the subsequent measurement points at the positions Iα2 to Iα3 and Iβ1 to Iβ3.

  Next, the ratio of the average value to the average value for each measurement position, which is the correction value, is obtained from the result of measuring the AC current flowing through the charging roller 2 at Iα1 over one turn of the charging roller 2, and the charging roll 2 The correction data at each of the above positions is used.

  Next, a method for determining AC current values of Iα2 to 3 and Iβ1 to Iβ3 in the Vpp-Iac graph of FIG. 8 will be described. Each position on the charging roller 2 with respect to the charging roller 2 with respect to two points (Iα2 to Iα3) of the peak-to-peak voltage which is an undischarged region and three points (Iβ1 to Iβ3) of the peak-to-peak voltage (Vpp) which is a discharging region. The voltage is sequentially applied based on the correction data at.

  Specifically, bias is applied at position 1 of charging roller 2, position Iα3 at position 2, position Iβ1 at position 3, position Iβ2 at position 4, and position Iβ3 at position 6. Thereafter, the AC alternating current is read, and the AC alternating current value is corrected and determined for each measurement position based on the correction data.

  Note that the position 5 of the charging roller 2 is not used for AC AC current value measurement because there is a possibility of C setting.

  Next, the control circuit 13 linearly approximates the relationship between the peak-to-peak voltage in the discharged and undischarged regions and the alternating current from the measured current values at the three points using the least square method, and the following equation 2 And Equation 3 is calculated.

Equation 2 ... Approximate straight line of discharge region: Y _α = αX + A
Equation 3 ... Approximate straight line of undischarged region: Y _β = βX + B
After that, the peak-to-peak voltage Vpp at which the difference between the approximate straight line of the discharge area of Expression 2 and the approximate straight line of the undischarged area of Expression 3 becomes the discharge current amount D is determined by Expression 4.

Formula 4... Vpp = (D−A + B) / (α−β)
Here, the peak-to-peak voltage (Vpp) -alternating current (Iac) functions fI1 (Vpp) and fI2 (Vpp) in the undischarged region and the discharged region described in the claims are expressed by Y _β = βX _β Corresponds to + B and Y _α = αX _α + A in Equation 2. The constant D described in the claims corresponds to the predetermined discharge current amount D.

Therefore, fI2 (Vpp) −fI1 (Vpp) = D described in the claims is Y _α −Y _β = (αX _α + A) − (βX _β + B) = D
It becomes.

Further, from fI2 (Vpp) −fI1 (Vpp) = D, Vpp of the expression 4 is equal to (D−A + B) / (α−β).
Induction is as follows.

fI2 (Vpp) −fI1 (Vpp) = Y _α −Y _β = D
(ΑX _α + A) − (βX _β + B) = D
Now looking for the value of X that becomes D, and if that point is Vpp,
(ΑVpp + A) − (βVpp + B) = D
Therefore, Vpp = (D−A + B) / (α−β).

  Then, the peak-to-peak voltage applied to the charging roller 2 is switched to Vpp obtained by the above equation 4, the constant voltage control is performed, and the process proceeds to the printing process described above.

  In this way, every time printing preparation rotation is performed, the influence of the C set of the charging roller 2 due to long-term standing is removed, the AC AC current unevenness of the charging roller 2 is accurately recognized as a correction value, and correlated with the position of the charging roller. By calculating the AC alternating current values from Iα2 to Iα3 and Iβ1 to Iβ3 in a shorter time with higher accuracy than before, the peak-to-peak voltage required to obtain a predetermined amount of discharge current during printing is calculated and printed. By applying the obtained peak-to-peak voltage with constant voltage control, it absorbs fluctuations in the resistance value due to manufacturing variations of the charging roller 2 and environmental variations of the material, and high-voltage variations in the main unit, and is reliably determined. It became possible to obtain the amount of discharge current.

  When durability was examined under this control, no deterioration or abrasion of the photosensitive drum as an image carrier occurred in any environment, and about 10% of the photosensitive drum compared with the conventional constant current control. Long service life can be realized.

  In this embodiment, the discharge current amount is controlled by switching the peak-to-peak voltage of the AC voltage applied to the charging roller. However, the present invention is not limited to this, and conversely, the peak-to-peak voltage of the AC voltage is measured by applying the AC current. (The AC current value measurement circuit 14 in FIG. 6 is changed to a peak-to-peak voltage value measurement circuit), and the AC current output AC current is set so that the AC current necessary for obtaining a predetermined discharge current amount can always be applied during printing. It is also possible to perform constant current control by the control circuit 13.

  Furthermore, in this embodiment, the predetermined discharge current amount D and the peak-to-peak voltage value applied during the print preparation rotation are made constant in each environment. However, in the apparatus in which the environment sensor (thermometer and hygrometer) 15 is installed, By varying the respective values for each environment, it is possible to perform more stable and uniform charging.

  Thus, during printing preparation rotation, several points in the undischarged area and several points in the discharging area are sequentially applied to the charging roller 2 to measure the AC voltage value, and the peak-to-peak voltage applied during printing is determined. By applying a peak-to-peak voltage or an alternating current that can always obtain a predetermined amount of discharge current, it is possible to achieve both deterioration and shaving of the photoconductor and charging uniformity, thereby extending the life and improving the image quality. It became feasible.

  Furthermore, since variations at the time of manufacturing can be absorbed, the permissible range of materials and accuracy is widened, so that the cost of manufacturing can be reduced and products can be provided to users at low cost.

(Second Embodiment)
This embodiment is a system of three-point control and constant current control, and a method for determining an alternating current value that becomes the discharge current amount D when D is a predetermined discharge current amount will be described. As shown in FIG. 11, the image forming apparatus sequentially applies three points of alternating current (Iac) that is a discharge region and three points of alternating current that is an undischarged region to the charging roller during printing preparation rotation. Measure the peak-to-peak voltage at that time.

  The concept of the method for determining the peak-to-peak voltage values of Iα1 to Iα3 and Iβ1 to Iβ3 is the same as that of the first embodiment.

  Next, the image forming apparatus linearly approximates the relationship between the peak-to-peak voltage and the alternating current in the discharged and undischarged regions from the measured current values at the three points using the least square method, Equation 3 is calculated.

Equation 2 ... Approximate straight line of discharge region: Y _α = αX _α + A
Formula 3 ... Approximate straight line in the undischarged region: Y _β = βX _β + B
Then, the difference between the approximate line Y _beta approximate straight line Y _alpha and undischarged areas of the discharge region, the alternating current as a discharge current amount D a (Iac) is determined by Equation 4.
Assuming that the alternating current value for D is Iac1 and the peak-to-peak voltage at that time is Vpp, Equation 2 and Equation 3 are expressed as Iac1 = αVpp + A.
Iac2 = βVpp + B Formula b
It becomes.

Here, Iac2 is an AC current value becomes the Vpp of the approximate straight line Y _beta undischarged areas.
Iac1 = Iac2 + D (Formula c)
From the equations a, b, and c, the alternating current (Iac) that becomes the discharge current amount D is determined by the equation 4.
Formula 4... Iac = (αD + αB−βA) / (α−β)
Then, the AC current applied to the charging member is switched to the obtained Iac, the constant current is controlled by the Iac, and the process proceeds to the image forming operation described above.

<Others>
1) In the above-described embodiments, only the mono-color (single color) printing operation has been described. However, the present invention is not limited to this, and the same effect can be exhibited in a full-color printing operation. is there.

  2) In the above-described embodiment, during the printing preparation rotation operation period when the printer is not forming an image, an appropriate peak-to-peak voltage value or alternating current value calculation / determination program in the charging process of the printing process is executed. It is not limited to the print preparation rotation operation period as in the printer of the embodiment. Other non-image formation, that is, an initial rotation operation, a sheet-to-sheet process, a post-rotation process, or a plurality of non-image formation can be performed.

3) The image carrier may be of a direct injection charging type provided with a charge injection layer having a surface resistance of 10 ⁹ to 10 ¹⁴ Ω · cm. Even when the charge injection layer is not used, for example, the same effect can be obtained when the charge transport layer is in the above resistance range. An amorphous silicon photoreceptor having a surface layer volume resistance of about 10 ¹³ Ω · cm may be used.

  4) In addition to the charging roller, a flexible contact charging member having a shape or material such as a fur brush, felt, or cloth can be used. Further, a combination of various materials can provide more appropriate elasticity, conductivity, surface property, and durability.

  5) As the waveform of the alternating voltage component (AC component, voltage whose voltage value periodically changes) of the oscillating electric field applied to the contact charging member and the developing member, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. It may be a rectangular wave formed by periodically turning on / off a DC power supply.

  6) The image exposure means as the information writing means for the charging surface of the photosensitive member as the image carrier is a digital exposure means using a solid light emitting element array such as an LED, in addition to the laser scanning means of the embodiment. There may be. An analog image exposure unit using a halogen lamp or a fluorescent lamp as a document illumination light source may be used. In short, any device capable of forming an electrostatic latent image corresponding to image information may be used.

  7) The image carrier may be an electrostatic recording dielectric or the like. In this case, after the dielectric surface is uniformly charged, the charged surface is selectively discharged by a discharging means such as a discharging needle head or an electron gun to write and form an electrostatic latent image corresponding to target image information. .

  8) The toner developing method and means for the electrostatic latent image are arbitrary. A reversal development method or a regular development method may be used.

  In general, as a method for developing an electrostatic latent image, a non-magnetic toner is coated on a developer carrying member such as a sleeve with a blade or the like, and a magnetic toner is magnetically coated on a developer carrying member. There is a method (one-component non-contact development) in which an electrostatic latent image is developed by coating and conveying by force and applying to the image carrier in a non-contact state. Further, there is a method (one-component contact development) in which the toner coated on the developer carrying member as described above is applied in contact with the image carrier to develop the electrostatic latent image. Further, a toner carrier mixed with a magnetic carrier is used as a developer (two-component developer) and conveyed by magnetic force and applied in contact with an image carrier to develop an electrostatic latent image. There is a method (two-component contact development). Further, there is a method (two-component non-contact development) in which the above-described two-component developer is applied to the image carrier in a non-contact state to develop an electrostatic latent image, and is roughly classified into these four types.

  9) The transfer means is not limited to the roller transfer of the above embodiment, but may be a blade transfer, a belt transfer, other contact transfer charging methods, or a non-contact transfer charging method using a corona charger.

  10) The present invention can be applied not only to the formation of a single color image by using an intermediate transfer member such as a transfer drum or a transfer belt but also to an image forming apparatus that forms a multicolor, full color image by multiple transfer or the like.

  In the above-described embodiment, even if the current to be measured varies due to the film thickness variation or eccentricity of the object to be charged, or even if the C set occurs in the charging member and the current amount of the C set portion changes over time, It is possible to generate accurate correction data for correcting the error superimposed on the current. Therefore, the AC current or the AC voltage supplied to the member to be charged can always be set to an optimum value to generate an image free from image quality loss and extend the life of the member to be charged.

  In the charging control device, the average value calculating means obtains an average value of measurement data obtained over a plurality of circumferences of the charging member or the object to be charged, and the correction data calculating means calculates the measurement data for each measurement on the object to be charged. An average value for each position may be calculated, and a ratio of the average value to the average value for each measurement position may be obtained.

  In the charging control, the correction means may obtain correction data from the measurement data obtained in time series and the ratio to the average value.

  In the charging control device, the current that contributes to charging of the member to be charged may be any one of a DC current that flows into the member to be charged, a discharge current to the member to be charged, and an AC current that flows into the member to be charged.

The charging control method is obtained by setting D as a predetermined constant, reflecting the correction data, and connecting the current value when a peak-to-peak voltage less than twice Vth of two points is applied to the charging means. The peak-to-peak voltage-alternating current function fI1 (Vpp) and the peak-to-peak voltage-alternating current function fI2 (Vpp) obtained from the current value when at least two peak-to-peak voltages more than twice Vth are applied By comparing with
A peak-to-peak voltage value satisfying fI2 (Vpp) −fI1 (Vpp) = D is determined, and the peak-to-peak voltage of the AC voltage applied to the charging unit at the time of image formation is controlled by constant voltage based on the determined peak-to-peak voltage value. .

  According to the above-described embodiment, with respect to an image forming apparatus in which charging of the image carrier is performed by a charging unit that is arranged in proximity to or in contact with the image carrier and to which a voltage is applied, the resistance value of the charging member varies depending on the environment and manufacturing. Regardless of, etc., a voltage applied to the charging means so that a constant amount of discharge is always generated without causing excessive discharge and uniform charging can be performed without problems such as deterioration of the image carrier, toner fusion, and image flow. The current can be appropriately controlled, and this can stably maintain high image quality and high quality over a long period of time.

1 .... Photosensitive drum, 2 .... Contact charging device, 14 .... AC current measurement circuit

Claims (5)

A charging member that is arranged in contact with or in proximity to the member to be charged, and charges the member to be charged following the rotation of the member to be charged;
Means for applying either a DC voltage or an AC voltage or a superimposed voltage of the DC voltage and the AC voltage to the charging member;
Means for controlling each voltage value of the DC voltage applied to the charging member and the peak-to-peak voltage of the AC voltage;
Measuring means for measuring an alternating current value flowing through the charging member via the charged body;
When the charging member and the member to be charged rotate, when a discharge start voltage to the member to be charged when a DC voltage is applied to the charging member is Vth, Vth An average value calculating means for applying a voltage between peaks less than twice and obtaining an average value of measurement data obtained in time series from the measuring means;
Correction data calculation means for obtaining the ratio of the measurement data obtained in time series with respect to the average value and corresponding to each measurement position on the object to be charged, and outputting as correction data for each measurement position; ,
Have
The current value result at the measurement position where a value outside the predetermined current value is detected in the measurement data obtained in time series is not reflected in the average value of the measurement data obtained in time series, and thereafter The charging control device is not used at the current measurement position. The average value calculating means obtains an average value of the measurement data obtained over a plurality of circumferences of the charging member or the charged object,
The correction data calculation means calculates an average value for each measurement position on the member to be charged, and calculates a ratio of the average value to the average value for each measurement position. 2. The charge control device according to 1.   The charging control apparatus according to claim 1, wherein the correction data calculation unit outputs the correction data from the measurement data obtained in time series and a ratio to the average value.   The current that contributes to charging of the member to be charged is any one of a DC current that flows into the member to be charged, a discharge current to the member to be charged, and an AC current that flows into the member to be charged. 2. The charge control device according to 1. A charge control device according to any one of claims 1 to 4, comprising:
The peak-to-peak voltage-alternating current function fI1 (Vpp) obtained by connecting the current value when D is a predetermined constant and a peak-to-peak voltage less than twice Vth at two points is applied to the charging means; By comparing the peak-to-peak voltage-alternating current function fI2 (Vpp) obtained from the current value when the peak-to-peak voltage more than twice the Vth of at least two points is applied
fI2 (Vpp) −fI1 (Vpp) = D
An image forming apparatus comprising: determining a peak-to-peak voltage value, and subjecting the determined peak-to-peak voltage value to constant voltage control of the peak-to-peak voltage of an AC voltage applied to the charging unit during image formation.