JP2007011094A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform stable image formation and to prevent an image carrier from deteriorating by making corrections based upon information in a storage device by discriminating an improper value of a discharge current as an abnormal value if the discharge current calculated from an AC voltage peak value and an AC voltage differential peak value has the improper value under the effect of noise etc. <P>SOLUTION: An image forming apparatus has means of detecting an included abnormal value and taking measures if a proper discharge current amount can not be calculated because of noise when discharge is carried out by using discharge current control. In a method thereof, a calculated discharge current value is compared with values previously stored in the storage device to decide that a value which is not within a range of those values is an abnormal value and then ignore the current value, and a discharge current value used last is employed to perform control. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus. More specifically, the present invention relates to a charging control method in an image forming apparatus that charges an image carrier and an image forming apparatus.

  Conventionally, in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, a method of charging a surface of an image carrier as a charged body such as a photoreceptor or a dielectric is generated by applying a high voltage to a thin corona discharge wire. Corona charging, which is non-contact charging, in which charging is performed by causing a corona to act on the surface of an image carrier, is generally used.

  In recent years, from the viewpoints of low-pressure process, low ozone generation, and low cost, a roller-type or blade-type charging member is brought into contact with the surface of the image carrier, and a voltage is applied to the charging member to Contact charging methods for charging are becoming mainstream.

  In particular, a roller-type charging member can be stably charged over a long period of time. The voltage applied to the charging member may be only a DC voltage, but charging can be performed uniformly by applying an oscillating voltage and alternately causing discharge to the plus side and minus side. For example, an alternating voltage having a peak-to-peak voltage equal to or higher than the discharge start threshold voltage (charging start voltage) of the object to be charged when a DC voltage is applied, and an oscillating voltage superimposed with a DC voltage (DC offset bias) are applied. By doing so, it is known that there is an effect of leveling the charge of the member to be charged and uniform charging is performed. The waveform of the oscillating voltage is not limited to a sine wave, but may be a rectangular wave, a triangular wave, or a pulse wave. The oscillating voltage is a rectangular wave voltage formed by periodically turning on / off the DC voltage, or the same output as the superimposed voltage of the AC voltage and the DC voltage by periodically changing the value of the DC voltage. Including.

  As described above, a contact charging method in which an oscillating voltage is applied to the charging member for charging is hereinafter referred to as an “AC charging method”. A contact charging method in which only a DC voltage is applied for charging is referred to as a “DC charging method”. In the AC charging method, compared to the DC charging method, the total amount of discharge generated between the charging member and the image carrier increases due to voltage application, which promotes deterioration of the image carrier such as scraping of the image carrier, and is caused by discharge products. An abnormal image such as image flow in a high temperature and high humidity environment may occur. Therefore, if the discharge is performed more than necessary, discharge products that cause deterioration of the image carrier and image flow are excessively formed, and if the discharge is not performed sufficiently, a charging failure will occur. . Therefore, it is necessary to minimize the discharge that causes the plus side and the minus side to occur alternately by applying the minimum necessary charging voltage so that charging failure does not occur. However, in reality, the relationship between the voltage and the discharge amount is not always constant, and changes depending on the film thickness of the photosensitive layer and dielectric layer of the image carrier, the environmental variation of the charging member and air, and the like. In a low-temperature and low-humidity environment (L / L), the material dries and the resistance value rises, making it difficult to discharge. Therefore, in order to obtain uniform charging, a peak-to-peak voltage above a certain value is required. Even at the lowest voltage value at which charging uniformity can be obtained in the environment, if the charging operation is performed in a high-temperature and high-humidity environment (H / H), the material absorbs moisture and the resistance value decreases. Will cause a discharge. As a result, when the amount of discharge increases, problems such as image defects such as image flow, toner fusion, and image carrier scraping and shortening due to deterioration of the image carrier surface occur.

  In addition to the above-mentioned causes due to environmental fluctuations, problems due to changes in the discharge amount also occur due to fluctuations in charging member manufacturing and resistance values due to dirt, electrostatic capacity fluctuations of the image carrier due to durability, fluctuations in the main body high-voltage device, etc. I know that.

  In order to suppress such a change in the discharge amount, there is a “discharge current control method” devised in Patent Document 1. In this method, the discharge current amount is calculated and optimized in the pre-rotation process period, the printing process, and the inter-paper process, and the discharge current amount can be optimally controlled in real time.

More specifically, current detection means for detecting the amount of alternating current flowing through the charging member, a capacitor A connected to the output section of the AC application means, a resistor connected in series with the capacitor A, and the capacitor A An average current detecting means for detecting an average value of the alternating current flowing through the capacitor, an AC high voltage peak voltage detecting means for detecting a peak value of the alternating high voltage from the average current detected value, and a peak value of the alternating current flowing through the capacitor A A peak current detecting means for detecting, and an AC high voltage differential peak voltage value detecting means for calculating a peak value of a differential waveform of the AC high voltage from the result of the peak current detecting means, the current detecting means, and the AC high voltage peak voltage detecting The pseudo discharge current generated between the drum and the charging roller is calculated from the result of the means and the AC high voltage differential peak voltage value detecting means. Hereinafter, the calculated pseudo discharge current is assumed to be a discharge current actually generated between the charging member and the image carrier. Then, the output of the AC high voltage applying means is adjusted so that the calculated discharge current becomes a desired value.
JP 2004-157501 A

  However, the above-described “discharge amount control method” has the following problems.

  When the discharge current value is calculated in real time, the AC voltage differential peak value is easily affected by noise due to the developing bias, and the waveform is distorted when affected by the noise, resulting in an error in the discharge current value.

  Therefore, even if the discharge current value selection cannot be performed properly due to the influence of noise, the object of the present invention is to identify the value as an abnormal value and make corrections so that the discharge current control is always kept good and stable. An object of the present invention is to provide an image forming apparatus capable of forming an image.

  The present invention includes an image carrier, a charging member that charges the image carrier, an AC voltage application unit that applies an AC voltage to the charging member, and a current detection unit that detects an AC current value flowing through the charging member. A peak voltage detecting means for detecting a peak value of the AC voltage, a differential peak voltage detecting means for calculating a peak value of a differential waveform of the AC voltage, a pseudo discharge from the peak voltage of the AC voltage, and the differential peak voltage value. Means for calculating a current value; means for controlling an applied AC voltage so that the calculated pseudo discharge current value becomes a predetermined value; and a storage area for storing information relating to the calculated pseudo discharge current value. In the image forming apparatus included in the process cartridge, the abnormal value of the calculated pseudo discharge current value is identified, and when the abnormal value is detected, the AC voltage value used last time or the main body is stored. To achieve the above object by performing charging using a preset AC voltage is.

  According to the present invention, even when the voltage differential peak value in the circuit is affected by noise or the like and an appropriate discharge current cannot be obtained, they are identified as abnormal values, and the information in the storage device By performing the correction based on the above, stable image formation can be achieved and deterioration of the image carrier can be prevented.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

(1) Overview of Configuration and Operation of Image Forming Apparatus FIG. 2 is a schematic configuration diagram of the image forming apparatus of this embodiment. The image forming apparatus according to the present exemplary embodiment is an electrophotographic type and a process cartridge detachable laser printer.

  Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (photosensitive drum) as an image carrier. The photosensitive drum 1 of this example is a negatively charged organic photosensitive member, and is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed by a driving motor (not shown).

  The photosensitive drum 1 is uniformly charged to a predetermined negative potential by a charging device during its rotation. In this example, the charging device is a contact charging device using a charging roller 2 as a charging member. The charging roller 2 rotates following the photosensitive drum 1. A bias voltage is applied to the charging roller 2 from a charging bias power source (not shown). As the charging bias voltage, a method is used in which a DC voltage corresponding to a desired on-drum potential is superimposed on an AC voltage having a peak-to-peak voltage that is twice or more the discharge start voltage. This charging method aims to eliminate local potential unevenness on the photosensitive drum by applying an AC voltage superimposed on the DC voltage, and to uniformly charge the photosensitive drum to a potential equal to the DC applied voltage.

  Next, image exposure by the exposure device 21 is performed. The exposure device 21 forms an electrostatic latent image on the uniformly charged photosensitive drum 1, and in this example, a semiconductor laser scanner is used. The exposure device 21 outputs a laser beam L modulated in accordance with an image signal sent from a host device (not shown) in the image forming apparatus, and passes through an exposure window portion of a process cartridge C described later. The uniformly charged surface of the photosensitive drum 1 is subjected to scanning exposure (image exposure). On the surface of the photosensitive drum, an electrostatic latent image corresponding to image information is sequentially formed as the absolute value of the potential of the exposed portion becomes lower than the absolute value of the charging potential.

  Next, the electrostatic latent image is developed by the reversal developing device 5 to be visualized as a toner image. In this example, a jumping development method is used. In this method, a developing bias voltage in which alternating current and direct current are superimposed is applied to a developing sleeve 7 from a developing bias power source (not shown), and friction charging is performed at a contact portion between the developer layer thickness regulating member 6 and the developing sleeve 7. The negatively charged toner is applied to the electrostatic latent image on the surface of the photosensitive drum to reversely develop the electrostatic latent image.

  The toner image on the photosensitive drum surface is transferred by a transfer device to a recording medium (transfer material) such as paper fed from a paper supply unit (not shown). In this example, a contact transfer device using a transfer roller 22 is used. The transfer roller 22 is pressed against the photosensitive drum 1 in the central direction of the photosensitive drum by an urging means such as a pressing spring (not shown). When the transfer material is conveyed and the transfer process is started, a positive transfer bias voltage is applied to the transfer roller 22 from a transfer bias power source (not shown), and the toner on the photosensitive drum 1 is charged to a negative polarity. Is transferred onto the transfer material.

  The transfer material that has received the transfer of the toner image is separated from the surface of the photosensitive drum and introduced into the fixing device 23 to undergo the fixing process of the toner image. The fixing device 23 fixes the toner image transferred onto the transfer material to a permanent image using means such as heat or pressure.

  The photosensitive drum surface after separation of the transfer material is cleaned by scraping off the transfer residual toner by the cleaning device 4 and is repeatedly used for image formation. The cleaning device 4 of this example uses a cleaning blade 3. The cleaning blade 3 collects transfer residual toner that has not been completely transferred from the photosensitive drum 1 to the transfer material during the transfer process, and contacts the photosensitive drum 1 with a constant pressure to collect the transfer residual toner. Clean the surface. After completion of the cleaning process, the photosensitive drum surface again enters the charging process.

  The image forming apparatus forms an image by repeating the steps of charging, exposure, development, transfer, fixing, and cleaning using the above-described means.

  Here, the process cartridge is a cartridge in which a charging unit, a developing unit or a cleaning unit and an electrophotographic photosensitive member are integrally formed, and this cartridge can be attached to and detached from the image forming apparatus main body. In addition, at least one of the charging unit, the developing unit, and the cleaning unit and the electrophotographic photosensitive member are integrally formed into a cartridge that can be attached to and detached from the main body of the image forming apparatus. Further, it means that at least the developing means and the electrophotographic photosensitive member are integrated into a cartridge so that it can be attached to and detached from the apparatus main body.

(3) Charging high voltage output method and determination of appropriate charging bias 3-1) Charging high voltage output control method (charging high voltage power supply circuit)
Next, charging high voltage output control will be described based on the circuit diagram of the charging output circuit of FIG. The charging output circuit generates a charging high voltage in which the AC high voltage is superimposed on the DC high voltage, and outputs it from the output terminal 299 in the figure. The output terminal is connected to a charging roller in contact with the photosensitive drum. When a clock pulse (PRICLK) is output from the CPU 245, it is amplified to a clock pulse having an amplitude corresponding to the output of the operational amplifier 265. When this amplitude is large, the drive voltage amplitude of a sine wave input to the high voltage transformer 204 described later also increases, and as a result, the high voltage AC voltage level also increases. The clock pulse is input to the filter circuit 235, and a sine wave centered at + 12V is output from the filter circuit 235. This output is input to the primary winding of the high-voltage transformer 204 via the push-pull high-voltage transformer drive circuit 205, and a sinusoidal AC high voltage is generated on the secondary winding side. Further, since one of the secondary sides of the high voltage transformer 204 is connected to the DC high voltage generation circuit 247, a high voltage bias in which the AC high voltage is superimposed on the DC high voltage is output from the output terminal via the output protection resistor 203, Power is supplied to the charging roller.

  Next, the current detection unit of the AC high voltage circuit will be described. The AC charging current generated by driving the AC high voltage generating circuit passes through the capacitor 248, and the half wave in the direction of arrow A flows through the diode 250 and the half wave in the direction of arrow B flows through the diode 249. The half-wave current in the direction of arrow A is converted into a DC voltage by an integrating circuit. The voltage Vn at the negative input terminal of the operational amplifier 265 has the following characteristics.

  Here, Imean is the average value of the half wave of the charging alternating current, and Rs is the resistance value of the resistor 257.

  On the other hand, the current control signal (PRICNT) output from the CPU 245 is input to the positive input terminal of the operational amplifier 265. The current control signal (PRICNT) is a signal for setting an alternating current level, and is an analog signal that changes between 0V and 5V.

  When the voltage Vn at the negative input terminal of the operational amplifier 265 is smaller than the current control signal PRICNT, the output of the operational amplifier 265 increases. As described above, when the output of the operational amplifier 265 increases, the amplitude of the clock pulse input to the filter circuit 235 increases and the high-voltage AC voltage increases. With this configuration, the level of the high-voltage AC voltage is controlled so that the AC current has a value corresponding to the current control signal PRICNT. That is, constant current control according to the current control signal: PRICNT is performed. The control value of the charging alternating current has the following characteristic.

  The charging high voltage drive signal (PRION) is a signal for switching between driving and stopping of the charging high voltage output. When the signal is HIGH level, the transistor is turned on, and the positive input of the operational amplifier 265 becomes 0V, so that the output of the operational amplifier 265 becomes 0V. Thereby, the charging AC output is stopped.

  Next, the voltage detection unit of the charging output circuit will be described. In the present charging output circuit, there are two voltage detection circuits, a voltage detection circuit A and a voltage detection circuit B.

(A) Voltage detection circuit A (voltage peak detection circuit)
The voltage detection circuit A detects the peak voltage value of the charging AC voltage. FIG. 4 shows the relationship between the charging AC waveform and the peak voltage value detected by the voltage detection circuit A. FIG. 4A-1 shows a case where the charging AC waveform is a sine wave. In this case, the level of Vp1 is detected by the voltage detection circuit A. On the other hand, FIG. 4A-2 shows the waveform when distortion occurs at the peak portion of the AC waveform. The broken line indicates the waveform of (A-1) which is a sine wave, and distortion occurs at the peak portion, and the peak voltage is lower by Δh than Vp1. The voltage detection circuit A detects the value of Vp2. Next, the operation of the voltage detection circuit A will be described. The peak voltage is detected by detecting the current flowing in the capacitor 271 connected to the same potential line as the charging high voltage output terminal 299. An alternating current flows through the capacitor 271 when a charging alternating voltage is applied, and is shunted by the diodes 276 and 289.

  A half-wave current in the direction of arrow D flows through diode 276, and a half-wave current in the direction of arrow C flows through diode 289. The average value of the half-wave currents of arrows C and D: Icap (av) can be expressed by the following equation.

  Here, C271 is the capacitance value of the capacitor C271, f is the frequency of the charging AC output, and Vp is the peak voltage value of the charging AC output. As is clear from (Equation 2-1), the average value of half-wave current: Icap (av) is a level corresponding to the peak value of the charging AC voltage.

  The half-wave current in the direction of arrow D is input to the integrating circuit. The half-wave current is rectified and a DC voltage is generated between the terminals of the capacitor 288.

  The voltage generated between the terminals of the capacitor 288: V288 can be expressed by the following equation.

  The inter-terminal voltage V288 of the capacitor 288 is input by the operational amplifier 281 to the analog input terminal 245f of the CPU 245 as a peak voltage detection signal: PRIVS. The level of the peak voltage detection signal: PRIVS is expressed by the following equation from (Equation 2-1) and (Equation 2-2).

(B) Voltage detection circuit B (voltage differential peak detection circuit)
The voltage detection circuit B detects the peak voltage value of the differential waveform of the charging AC voltage waveform.

  FIG. 4B shows a differential waveform of the AC voltage waveform (A-2). A broken line part shows the shape of a sine wave. In the region near the peak where the distortion occurs in (A-2), the differential waveform (B) is also distorted from the sine wave. On the other hand, in the phase region where no distortion occurs in (A-2), the differential waveform (B) has a sine wave shape, and its peak value is Vp1 which is the same as the peak value of the (A-2) waveform. . That is, the voltage detection circuit B detects the voltage of Vp1 obtained by adding the distortion amount Δh to the peak voltage value of the charging AC waveform in which distortion has occurred. Next, the operation of the voltage detection circuit B will be described. The charging output voltage is divided by the capacitor 271 and the resistor 273 and converted to a low voltage level. Since the diode 289 is interposed between the capacitor 271 and the resistor 273, a half-wave AC waveform is input to the positive input of the operational amplifier 286. Here, the impedance of the capacitor 271 is set to be sufficiently larger than the impedance of the resistor 273. In other words, an AC waveform half-wave waveform is generated at the positive input portion of the operational amplifier 286 by dividing the differential waveform of the charging AC voltage. The differentiated waveform is further converted into a DC voltage corresponding to the peak value of the AC waveform generated at the negative input terminal of the operational amplifier 281 by the peak voltage detection circuit, and input to the CPU 245 as a differential voltage detection signal: PRIDVS. The level of the differential voltage detection signal: PRIDVS can be expressed by the following equation.

  Here, C271 is the capacitance value of the capacitor C271, f is the frequency of the charging AC output, R273 is the resistance value of R273, π is the circumference, and Vd is the peak voltage of the differential value of the charging AC voltage. From the above (Expression 2) and (Expression 3), the peak voltage detection signal: PRIVS and the differential voltage detection signal: PRIDVS are both proportional to the capacitance value of the capacitor C271. That is, even when the capacitance value of the capacitor C271 fluctuates due to environmental conditions or the like, the relative value between both signals is constant.

  Next, a method for detecting the discharge current in this embodiment will be described. In the image forming apparatus according to this embodiment, the peak value of the charging AC voltage and the peak value of the charging AC voltage differential value are detected, and a pseudo discharge current value is calculated.

  FIG. 6A is a diagram showing the characteristics of the charging AC voltage peak value and charging AC voltage differential peak value, charging AC current value: Ic applied to the charging roller. A charging current: Ic flows by applying a charging AC voltage to the charging roller. In a region where the charging AC voltage is equal to or lower than the discharge start voltage: Vh (non-discharge generation region), the charging AC current increases linearly in proportion to the level of the charging AC voltage as the charging AC voltage increases. In this region, only the nip current corresponding to the resistive load and capacitive load between the charging roller and the photosensitive drum flows. When the charging AC voltage further rises and reaches a region (discharge generation region) exceeding the discharge start voltage: Vh, a discharge occurs between the charging roller and the photosensitive drum, and a charging current obtained by adding the discharging current to the nip current described above: Ic flows. In the non-discharge generation region, the charging AC voltage peak value and the charging AC voltage differential peak value coincide with each other. However, in the discharge start region, the charging AC voltage peak value is LINE-A, and the charging AC voltage differential peak value is LINE-B. Thus, a difference occurs between the two characteristics.

  The cause of the difference between the characteristics of LINE-A and LINE-B will be described with reference to FIG. FIG. 4 shows a charging AC voltage waveform when the charging AC voltage is set to Vp1 higher than the discharge starting voltage Vh. A waveform distortion occurs near the peak of the AC waveform. This waveform distortion occurs because the output of the transformer 204 is distorted by the occurrence of discharge. When the charging AC voltage exceeds the discharge start voltage, discharge occurs at a timing near the peak of the AC voltage, and a discharge current flows. This discharge current flows instantaneously with a sudden rise. When a discharge current flows through the transformer 204 that generates the charging AC voltage, a voltage drop occurs between the output terminals of the transformer 204 due to the leakage inductance of the transformer 204, and the output voltage waveform is distorted.

  At this time, the peak value of the charging AC voltage is Vp2. On the other hand, the peak value of the charging AC voltage differential value is Vb [1] obtained by adding the distortion amount to Vp2, and the LINE-A and LINE-B have different characteristics. LINE-A has discontinuous characteristics with the discharge start voltage Vh as a boundary. On the other hand, LINE-B has a characteristic that changes linearly with respect to the peak value of the charging AC voltage differential value. This is because, due to the operational characteristics of the transformer, the output power of the transformer operates at a constant regardless of the presence or absence of discharge.

  The discharge current value can be calculated from the relationship between LINE-A and LINE-B. In the case of charging AC voltage peak value: Vp, charging AC voltage differential peak value: Vd, and charging current: Ic, the relationship of the following equation holds with the discharge current value: Is.

  Furthermore, the discharge current can be calculated from the following formula from (Formula 4-1), (Formula 2), and (Formula 3).

  In the image forming apparatus of this embodiment, the charging AC voltage peak value: Vp is detected by the voltage detection circuit A, the charging AC voltage differential peak value: Vd is detected by the voltage detection circuit B, and the charging current: Ic is the constant current. Set by the control circuit and calculate the discharge current value. FIGS. 6B and 6C show detection characteristics of the PRIVS signal and the PRIVDS signal corresponding to FIG. Charging AC current: When Ic is Ic [1], the charging AC voltage peak value is Va [1], and the PRIVS signal is PRIVS (1). The charging AC voltage differential peak value is Vb [1], and the PRIDVS signal is PRIDVS (1). From the level of the PRIDS signal and the PRIDVS signal detected by the CPU 245, the discharge current: Is is calculated using (Equation 4-2).

  Next, a process for bringing the discharge current value close to a desired value in the present embodiment, and detection and correction when an abnormal value occurs during the process will be described. The image forming apparatus according to the present embodiment is characterized in that when an abnormal value is included in the discharge current value calculated from the AC voltage differential peak value and the AC voltage peak value, it is detected and corrected.

  FIG. 7 is a graph showing the voltage-current characteristics applied to the charging member. For example, in FIG. 7, the discharge current value is calculated as Is1 from the AC voltage peak value Vp1 and the AC voltage differential peak value Vd1 obtained from the charging current Ic1. Since this value is smaller than the target discharge current value Is (cnt), the charging current Ic1 is increased and the calculation is performed again to gradually approach the target discharge current value Is (cnt). Here, the AC voltage differential peak value is more unstable than the AC voltage peak value and is easily affected by noise or the like, and when affected by noise, an abnormal value different from the actual calculated value may be detected. Therefore, actually, the current voltage differential peak value when the charging current Ic2 is applied should be Vd2, but if the value is greatly measured and becomes Vd2 ′ due to the influence of noise, for example, the calculation is performed at that time. The discharge current value thus calculated is calculated to be larger than the actual discharge current value: Is2, and there is a possibility that proper control cannot be performed.

  As described above, in the present invention, in order to gradually bring the discharge current value closer to the desired value, the desired discharge current value: Is (cnt) is compared with the calculated latest discharge current value: Is, and the target is obtained. If the discharge current value is smaller than the discharge current value, the charging current Ic applied to the charging member is increased, and if the discharge current value is larger than the target discharge current value, the control is repeated such that the charging current is reduced to approach the desired value. In addition, in order to approach the desired value in a short time, when the difference between the target discharge current value and the calculated discharge current amount is large, the charging current applied to the charging member is changed greatly, and when the difference is small, fine adjustment is performed. . Therefore, if control is performed as it is when a discharge current value that is clearly different from the target discharge current value is calculated, the charging current applied to the charging member can be greatly changed in a direction far from the desired value. There is sex. As a result, an abnormal value may cause charging failure or excessive charging. Therefore, when such a value is detected, it is necessary to identify the value as an abnormal value and take measures.

  Therefore, the present invention is characterized in that an abnormal value in such a case is detected and corrected. As shown in FIG. 8, the storage element of the main body or process cartridge has two areas for storing the previously calculated discharge current value Is (n-1) and the applied charging current Ic (n-1) at that time. It is possible to detect and correct an abnormal value using this storage device. The abnormal value identifying method is such that the difference between the latest discharge current value Is calculated from the AC voltage peak value and the AC voltage differential peak value sequentially updated in the storage device and the target discharge current value Is (cnt) is as follows. When it is above a certain level, the calculated discharge current amount Is is identified as an abnormal value. When an abnormal value is detected, the value at that time is ignored and the previous charging current value is adopted. Further, for example, when such abnormal values are continuously detected, a default value of the charging current stored in the memory in the main body or the process cartridge may be adopted.

  Next, a series of charging high voltage control processing procedures during the printing operation of the image forming apparatus of the present embodiment will be described.

  FIG. 5 is a diagram showing a sequence during the printing operation of the image forming apparatus. When the main power supply of the main body of the device is turned on, a pre-multi-rotation process is performed in which a series of processes such as driving the fixing device and raising the fixing device to a predetermined temperature is performed. In this process, the main motor rotates the photosensitive drum While being driven, the presence or absence of a process cartridge is detected, the transfer roller is cleaned, and the like. When the front multi-rotation is completed, a standby (standby) state is entered. Next, when a print start command is received from an external personal computer or the like, the main motor drives the main body of the image forming apparatus and enters a pre-rotation process. In the pre-rotation process, printing preparation operations of various process devices are performed. Mainly, preliminary charging on the photosensitive drum, startup of the laser scanner, determination of the transfer print bias, temperature adjustment of the fixing device, and the like are performed. Thereafter, a printing process is performed in which a printing operation is performed on recording paper by a series of electrophotographic processes. Here, in the mode in which a plurality of printing operations are performed, a predetermined process is performed in the inter-sheet process until the printing operation for the next recording sheet is performed, and then the process proceeds to the second and subsequent printing processes. . If there is no next print signal after the printing operation is completed, the image forming apparatus enters a post-rotation process. In the post-rotation process, processes such as charge removal on the surface of the photosensitive drum and discharge of toner adhering to the transfer roller to the photosensitive drum (transfer roller cleaning) are performed. When the post-rotation process is completed, the image forming apparatus again enters a standby (standby) state and waits for the next print signal. In the image forming apparatus according to the present embodiment, the process for determining the charging AC high voltage level is continuously executed in the pre-rotation process period, the printing process, and the inter-paper process, and the charging AC high voltage level is controlled in real time based on the result. To do.

  FIG. 1 shows a series of control flow for charging and high voltage during a printing operation in the image forming apparatus of this embodiment. When the printing operation is started, in step 702, a discharge current control value: Is (cnt) is set. The control value: Is (cnt) is set using a value stored in advance in the memory of the main body or process cartridge.

  Next, at step 703, the initial value of the constant current control level of the charging current is set. The set value is set using the previously used charging current value Ic value. Next, in step 704, the charging DC bias is driven at a predetermined timing during the pre-rotation, and in step 705, the charging AC bias driving signal: PRION signal is switched to the LOW level. As a result, a charging AC bias is output. Subsequently, in steps 706 to 708, the discharge current is measured.

  In step 706, the detection value of the voltage detection circuit A: PRIVS is read, and in step 707, the detection value of the voltage detection circuit B: PRIDVS is read. In step 708, the discharge current value is calculated from the PRIVS and PRDVS values read in the previous step by the method described above.

  Next, in step 709, the discharge current value calculated in step 708: Is and the control value set in step 702: Is (cnt) are compared, and a value with a difference (Is−Is (cnt)) is less than α. If it is equal to or greater than β, the Is is determined to be an abnormal value and ignored, and the process proceeds to step 714 using the previous Ic read in step 703 to perform printing. The values stored in advance in the main body or the process cartridge are used as the values α and β that are determined as abnormal values at this time. For example, when the target discharge current value Is (cnt) is 80 μA and the limit at which charging failure occurs is 30 μA, α uses the difference −50 μA. The upper limit β can be set to 100 μA in consideration of image carrier scraping and blade turning.

  When the difference between Is and Is (cnt) is greater than or equal to α and less than or equal to β, the process proceeds to step 710, where Is and Is (cnt) calculated in step 708 are compared. If Is is greater than Is (cnt), the process proceeds to step 711, where the current control signal level is reduced by a predetermined level. Thereby, the level of the charging AC output is controlled to be small. On the other hand, if Is is smaller than Is (cnt) in step 710, the process proceeds to step 710, where a process for increasing the current control signal level by a predetermined level is performed, whereby the level of the charging AC output is largely controlled. Then, the discharge current amount Is determined in step 713 and the applied AC voltage value Ic at that time are stored in the memory.

  Subsequently, in step 715, it is determined whether printing is completed. If printing is continued, the process returns to step 706, and the same processing is repeated. On the other hand, if printing is completed in step 715, the charging AC bias drive signal: PRION signal is switched to HIGH level to stop the charging AC bias (step 716), and the charging DC bias is stopped (step 717). To complete. Since the above series of processes is continuously executed in the pre-rotation process period and the inter-sheet process, the charging AC high voltage level is controlled in real time so that the discharge current value always becomes a desired value.

  As described above, in the charging high voltage control in this embodiment, one capacitor is provided in the charging high voltage output section, and the charging AC voltage peak value is detected by measuring the current flowing through the capacitor, and is connected in series with the capacitor. The charging AC voltage differential peak value is detected by measuring the voltage generated in the resistance, and the discharge current is calculated from the detected charging AC voltage peak value and the charging AC voltage differential peak value. The charging AC level is controlled as follows. With such a configuration, the discharge current value can always be optimally controlled in real time during the pre-rotation process period, the printing process, and the paper-to-paper process, regardless of environmental fluctuations and variations in the characteristics of the charging member during manufacturing. Therefore, uniform charging can be achieved while suppressing deterioration of the photosensitive drum. Furthermore, even if the capacitance of the capacitor fluctuates due to environmental changes, the relative relationship between the charging AC voltage peak value and the charging AC voltage differential peak value does not change, so accurate discharge current control can be achieved even when environmental fluctuations occur. it can. In addition, when the AC voltage differential peak value is affected by noise, etc., and the calculated discharge current value is significantly different from the actual value, control is performed by ignoring that value, thereby ensuring stable charging. Control becomes possible.

  The basic configuration of the image forming apparatus, the discharge current value control method, and the determination method of the alternating current value flowing through the charging member in the present embodiment are the same as those in the first embodiment, and the method for detecting abnormal values is different. The control flow of the present embodiment will be described with reference to FIG. The control method is almost the same, but step 709 different from the first embodiment will be described.

  In Example 1, the abnormality was determined based on the difference between the discharge current value Is calculated from the charging AC voltage peak value and the charging AC voltage differential peak value and the target discharge current amount value Is (cnt). In this embodiment, the difference between the previously calculated discharge current value Is (n−1) stored in the storage device of the main body and the latest discharge current value Is sequentially updated is equal to or greater than a certain value ( When | Is (n−1) −Is | ≧ γ), an abnormal value is determined, and charging is performed using the previous charging current value or the default value stored in the main body or the process cartridge.

  As a result, when the discharge current value is converged to a desired value in real time, the alternating current value is gradually changed. Therefore, it is not normal that the discharge current value becomes extremely large compared to the previous value. Compared to the first embodiment, it is possible to have a narrower range of values to be determined as abnormal values.

  An actual example is shown below.

  FIG. 10 shows the transition of each parameter when affected by noise. AC current applied to the charging member: Ic, AC voltage peak value: Vp, AC voltage differential peak value: Vd, and discharge current value calculated from the AC voltage peak value and AC voltage differential peak value: Is. Each parameter is assumed to be when noise enters after sampling of T (1) when control is performed with a stable transition. In the sampling of T (2), Vd is measured higher due to the influence of noise. Thereby, Is is calculated to be considerably larger than the actual value. In the next measurement T (3), since Is was previously calculated to be larger than the target value Is (cnt), processing is performed to reduce Ic to a desired value by coarse adjustment. Thereby, Vd, Vp, and Is are also reduced. Then, at T (4), on the contrary, in order to bring Is that has become smaller than the target closer to a desired value, Ic is increased finely.

  As described above, even when the control is stably performed, the control becomes unstable due to the influence of noise once. Therefore, in this embodiment, when the amount of change in Is between T (1) and T (2) is greater than or equal to a certain value γ, the discharge current value at that time (T (2)) is ignored. By using the charging current of the previous time (T (1)) and shifting to the control of T (3), stable charging becomes possible.

  Here, the value γ determined to be an abnormal value changes at that time, for example, if the amount of change in the charging current is changed at 20 μA when the current value is brought close to a desired value in a coarse adjustment. In the discharge amount region where normal image formation is performed, the discharge current value is 20 μA or less at most. Therefore, it is possible to recognize a value larger than this as an abnormal value. Therefore, in such a setting, γ can be set to 20 μA. Thus, for example, the value of γ is preferably set to be equal to or greater than the change width of the charging current value when changing in coarse tone.

  As described above, according to the present invention, when an abnormal value has been calculated due to the influence of noise, stable charge control can be performed by detecting and correcting the abnormal value, Due to the accelerated deterioration of the image carrier due to excessive discharge applied to the image carrier, image deterioration such as deterioration of wear, shortening of the life, image flow due to increased generation of discharge products, and sufficient charging Problems such as charging failure due to not being performed can be eliminated, and appropriate control can be performed so that uniform charging can be performed, whereby stable image formation can be maintained over a long period of time.

Process flow diagram in printing process of first embodiment 1 is a configuration diagram of an image forming apparatus according to a first embodiment. Configuration diagram of charging output circuit of first embodiment Explanatory drawing of the charging alternating voltage waveform of 1st Embodiment Sequence diagram during printing operation of the first embodiment Characteristic diagram of charging AC voltage and charging current of the first embodiment Special drawing of charging current voltage and charging current of the first embodiment Configuration diagram of storage device according to first and second embodiments Process flow diagram in printing process of second embodiment Transition diagram of each parameter under the influence of noise in the second embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Cleaning blade 4 Cleaning apparatus 5 Developing apparatus 6 Developer layer thickness control member 7 Developing sleeve 21 Exposure apparatus 22 Transfer roller 23 Fixing apparatus 203 Output protection resistance 204 High voltage transformer 205 High voltage transformer drive circuit 248,256, 271,284,288 Capacitors 265, 280, 281,286 Operational amplifiers 246,257,273,278,282,283,285,290,298 Resistor 235 Filter circuit 249,250,272,276,279,289 Diode 245 CPU
299 Output terminal

Claims (3)

An image carrier, a charging member that charges the image carrier, an AC voltage application unit that applies an AC voltage to the charging member, and a current detection unit that detects an AC current value flowing through the charging member;
A peak voltage detecting means for detecting a peak value of the AC voltage;
Differential peak voltage detection means for calculating the peak value of the differential waveform of the AC voltage;
Means for calculating a pseudo discharge current value from the peak voltage of the AC voltage and the differential peak voltage value;
Means for controlling the applied AC voltage so that the calculated pseudo-discharge current value becomes a predetermined value;
In an image forming apparatus having a storage area for storing information about the calculated pseudo discharge current value in a main body or a process cartridge,
The abnormal value of the calculated pseudo-discharge current value is identified, and charging is performed using the previously applied AC current or the preset AC voltage value stored in the main body when the abnormal value is detected. An image forming apparatus.   2. The image according to claim 1, wherein the calculated information on the pseudo discharge current value is the updated pseudo discharge current value that is sequentially updated and an applied AC current or an applied AC voltage at that time. Forming equipment.   The abnormal value is characterized in that the calculated pseudo discharge current value is outside a predetermined upper / lower limit range, or the amount of change from the previous pseudo discharge current value is a certain value or more. The image forming apparatus according to 1.

Images