JP2010128174A - Image forming device - Google Patents

Abstract

An image forming apparatus capable of detecting a surface potential with high accuracy even when the response speed of a surface potential meter is changed.
In an image forming apparatus having a potential sensor 13 for measuring a surface potential of a photoreceptor 1, the photoreceptor 1 is output using an output of the potential sensor 13 after a set time has elapsed since the potential sensor 13 started measurement. Control means 100 for controlling the surface potential to be a target potential, and setting means for setting a set time according to the cumulative number of image formations.
[Selection] Figure 5

Description

  The present invention relates to an image forming apparatus such as an electrostatic recording type or electrophotographic type copying machine or printer, and more particularly to an image forming apparatus that controls the surface potential of a photosensitive drum with high accuracy.

  2. Description of the Related Art Conventionally, an image forming apparatus using electrophotography such as an electrophotographic copying machine or a printer includes a photosensitive drum, a charging unit, an exposure device, a developing device, and a transfer device.

  In such an image forming apparatus, the rotating photosensitive drum is uniformly charged by the charging device. Next, the surface of the charged photosensitive drum is selectively exposed according to the image pattern, and the electrostatic latent image on the photosensitive drum is developed by a developing device to be visualized to form a toner image.

  Thereafter, the charged state of the toner image is adjusted using the pre-transfer charging unit, and the toner image is primarily transferred to the intermediate transfer member by the transfer unit, and then secondarily transferred to the recording material. Thereafter, the recording material is conveyed to the fixing device via the conveyance path, and the toner image is fixed by applying pressure and a predetermined temperature.

  Further, in the image forming apparatus, the surface potential is controlled in order to make the surface potential unevenness of the photosensitive drum uniform or to reduce density fluctuation inherent in the image forming apparatus. In this case, in order to cope with the change of the VL potential and the change of the shape, it is necessary to measure the surface potential that is moved by the rotation operation of the photosensitive drum with high accuracy, and the surface potential is measured by a surface potential meter. The surface electrometer is used as means for correcting fluctuations in image density that change due to environmental fluctuations, usage conditions, and the like, that is, as means for adjusting imaging conditions.

  The surface electrometer detects a potential waveform between images (between sheets) during continuous image formation. That is, under the conditions of a paper interval of 40 mm and a drum rotation speed of 250 mm / s, the image trailing edge 10 msec and the potential measurement start timing are always fixed, and the potential waveform in the period up to the image leading edge 10 msec is measured. During the continuous output, the exposure portion potential for one rotation of the drum is measured, compared with the average potential for one rotation of the drum measured in advance, and the VL potential is corrected during image formation (see Patent Document 1).

JP 2001-281943 A

  However, since the conventional surface electrometer samples the potential waveform within a predetermined period, if the response speed changes due to the usage environment or durability of the surface electrometer, the change in the response speed is followed. Measurement is not possible. As a result, the surface potential of the photosensitive drum cannot be detected with high accuracy.

  The technical problem of the present invention has been made in view of the circumstances as described above, and is capable of detecting the surface potential with high accuracy even when the response speed of the surface electrometer changes. A device is provided.

  In order to achieve the above object, a typical configuration according to the present invention includes a photoconductor, a charger for charging the photoconductor to form an electrostatic image on the photoconductor, and a surface potential of the photoconductor. And controlling the surface potential of the photoconductor to be a target potential using an output of the potential sensor after a set time has elapsed since the potential sensor started measurement. It is characterized by comprising control means and setting means for setting a set time according to the cumulative number of image formation times.

  In the image forming apparatus, further comprising: a photoconductor; a charger that charges the photoconductor to form an electrostatic image on the photoconductor; and a potential sensor that measures a surface potential of the photoconductor. Control means for controlling the surface potential of the photosensitive member to be a target potential using the output of the potential sensor after a set time has elapsed since the start of measurement, and a predetermined potential difference between the photosensitive member and the photosensitive member. The charging unit includes an execution unit that executes a test mode for measuring a surface potential of a portion corresponding to a predetermined potential difference by the potential sensor, and a setting unit that sets a set time according to a measurement result in the test mode. It is characterized by that.

  According to the present invention, the potential waveform on the surface of the image carrier is read with high accuracy even when the response speed changes due to changes in the usage environment or durability deterioration of the surface electrometer, and the surface potential of the image carrier is accurately controlled. Can be done well.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram of an electrophotographic image forming apparatus according to an embodiment of the present invention.

  In the image forming apparatus shown in FIG. 1, a corona charging device 2 is provided at a facing portion of a rotating drum type photosensitive drum 1 that is an image carrier. In the corona charging device 2, two discharge wires 2a made of tungsten or the like and having a wire diameter of about 60 μm are stretched. A shield electrode 2c formed of a U-shaped sheet metal such as stainless steel is provided around the discharge wire 2a, and a predetermined opening is formed on the surface facing the photosensitive drum 1.

  This opening is provided with an electrode member called a grid electrode 2b set to a predetermined opening area ratio. For example, when the photosensitive drum 1 is formed in a cylindrical shape and has a photosensitive layer on the surface, the discharge wire 2 a is disposed long in the left-right direction along the generatrix on the surface of the photosensitive drum 1. The discharge wire 2a is disposed substantially parallel to the generatrix on the surface of the photosensitive drum 1, and the distance from the photosensitive drum 1 is maintained at a predetermined distance (1.25 mm in the present apparatus).

  A constant current of 1600 μA is applied to the two discharge wires 2a. The grid electrode 2b and the shield electrode 2c are connected to have the same potential, and a high voltage of 500V to 900V is applied to the grid electrode 2b and the shield electrode 2c so that the charging potential can be adjusted to a target value. .

  The photosensitive drum 1 has a five-layered structure as shown in FIG. 2, in which an amorphous silicon photosensitive member is used and functions necessary for electrophotographic image formation are separated.

  In FIG. 2, reference numeral 101 denotes a conductive support, which is mainly made of a metal conductive material such as aluminium. On the conductive support 101, a blocking layer 105 for blocking charge injection from the conductive support 101 and a photosensitive layer 104 for generating charge pairs by light irradiation are sequentially laminated. Further, on the photosensitive layer 104, a charge transport layer 102 capable of moving generated charges and a charge holding layer 103 for holding charges on the outermost layer are sequentially laminated.

  The photosensitive drum 1 is rotationally driven in the direction of the arrow at a predetermined peripheral speed (process speed), and an image forming process for forming a normal image described later is repeatedly performed on the surface of the photosensitive drum 1. The process speed of the image forming apparatus is set to 665 mm / s.

  The photosensitive drum 1 is charged to a predetermined polarity and a predetermined surface potential by the corona charging device 2 in the rotation process in the direction of the arrow. Thereafter, image exposure by the exposure unit 11 is irradiated, and an electrostatic latent image (electrostatic image, latent image) corresponding to the target image is formed. The exposure unit 11 includes an imaging exposure optical system based on a document image and a scanning exposure optical system using a laser scanner that outputs a laser beam modulated in accordance with a time-series electric digital pixel signal of image information.

  In the figure, reference numeral 3 denotes a developing device adjacent to the photosensitive drum 1. The developing device 3 will be described with reference to FIGS. 3 (a) and 3 (b). 3A is a plan view of the developing device 3, and FIG. 3B is a cross-sectional view.

  That is, in the developing device 3, an alternating voltage in which alternating current is superimposed on direct current is applied as a developing bias from the developing bias applying device 37 between the developing sleeve 31 and the photosensitive drum 1 in the developing region. As a result, the toner 35 carried on the developing sleeve 31 is transferred to and adhered to the electrostatic latent image on the photosensitive drum 1, and the electrostatic latent image is visualized and developed as a developer image (toner image). .

  Next, corona discharge is performed on the toner image by the pre-transfer charger 15 disposed on the downstream side of the developing device 3 in the rotation direction of the photosensitive drum 1, and the toner image is transferred to the intermediate transfer belt 12 by the primary transfer unit 4. Is transcribed.

  Here, the pre-transfer charger 15 is a corotron type corona discharger in which AC high voltage and DC high voltage are superimposed. As the AC high voltage, a frequency of 1 KHz, Vpp = 5 to 8 KV is applied, and a high voltage in a range where the differential current is −100 to −500 μA is applied under the condition that the DC high voltage is superimposed.

  The difference current is controlled based on the measurement value of an environmental sensor (not shown) that detects temperature and humidity provided in the image forming apparatus.

  As with the corona charging device 2, the discharge wire uses a 60 μm tungsten wire, the shield electrode is 0 V, is grounded to the device body, and is in the GND state.

  The pre-transfer charger 15 adjusts the charge amount of the toner image on the photosensitive drum 1 so that proper transfer can be performed in the primary transfer unit 4 by variably controlling the difference current according to environmental conditions.

  Thereafter, the transfer material is conveyed from a feed cassette unit (not shown) to the secondary transfer unit, and the transfer material is fed to the secondary transfer unit at a predetermined timing. The secondary transfer means is a secondary transfer roller 8 arranged in pressure contact with the toner image carrying surface side of the intermediate transfer belt 12 and a counter electrode of the secondary transfer roller 8 arranged on the back side of the intermediate transfer belt 12. And a backup roll 7.

  In the secondary transfer unit, when transferring a toner image onto a transfer material fed at a predetermined timing, a transfer bias having a toner charging polarity (minus in this example) and a reverse polarity (plus) is applied by a bias power source. The

  By repeating the series of image forming processes described above, the toner image is transferred to subsequent transfer materials that are successively sent to the secondary transfer means.

  The transfer material onto which the toner image on the photosensitive drum 1 has been transferred is introduced into a fixing device (not shown) through a conveyance guide (not shown). Then, the toner image is fixed and heated by a fixing roller and a pressure roller (not shown) whose temperature is adjusted to a predetermined value, and the toner image is fixed and output as a final color image formed product.

  After the toner image has been transferred, the photosensitive drum 1 is cleaned by the cleaning device 5 and then neutralized by the light neutralizer 6 to erase the image history of the electrostatic latent image.

  This image forming apparatus employs a method in which a digitally processed image signal is exposed by background image exposure. Similar to the analog method, this method is a method in which a non-image portion is exposed to form a latent image, and a toner image is formed using a regular development method.

  A surface potential meter 13 for detecting the surface potential of the photosensitive drum 1 is provided downstream of the exposure unit 11 in the rotation direction of the photosensitive drum 1. The grid voltage of the corona charging device 2 is adjusted to a target Vd = 500V. The VL voltage is adjusted by adjusting the laser power of the exposure unit 11.

  The surface electrometer 13 is a small potential sensor used for electrophotography. The light emitting section of the light static eliminator 6 uses an LED array light source that is generally used in an electrophotographic apparatus. What is necessary is just to select the wavelength of LED according to the spectral sensitivity characteristic of a photoconductor timely.

  In this image forming apparatus, an LED having a wavelength of 660 nm is employed, and the wavelength is the same as that of the exposure unit 11. Further, a belt cleaner (not shown) is provided for removing residues on the intermediate transfer belt 12 after the secondary transfer.

  The intermediate transfer belt 12 is made of a resin such as polyimide, polyamide, polyester, polypropylene, polyethylene terephthalate, or various rubbers containing a suitable amount of a conductive agent such as carbon black. The volume resistivity is 5 to 110 log Ωcm, and the thickness is set to 0.1 mm.

  Next, the surface potential meter 13 will be specifically described. The surface potential meter 13 is disposed between the exposure unit 11 and the developing device 3 and is provided at a position facing the photosensitive drum 1.

  The gap between the photosensitive drum 1 and the surface potential meter 13 is set to 2.0 mm. As shown in FIG. 4, the surface electrometer (sensor) 13 is connected to a sensor control board 13a, amplifies the detected potential signal with an amplifier 13b, and A / D converts it with an A / D converter 13c. Send to. Further, as shown in FIG. 5, the CPU 100 is connected with a storage unit 111, a correction unit 112 for correcting the transmitted potential signal value, and an exposure apparatus control unit 21.

  Inside the surface potentiometer 13, a detection electrode 13e, an opening / closing part 13g for changing the electrostatic capacity at a predetermined cycle, and a signal processing circuit 13f are provided. The surface potential meter 13 uses an open / close area modulation method such as the open / close portion 13g, but may use a distance-changing type capacitance adjustment. The opening / closing part 13g operates at a cycle of 500 Hz, and the surface potential of the photosensitive drum 1 is measured using the charge induced in the detection electrode.

  Here, the principle of the surface electrometer 13 will be described. That is, the detection electrode 13e faces the surface potential of the photosensitive drum 1, and the electrostatic capacitance between the detection electrode 13e and the detection electrode 13e is made minute by an electric field generated between the detection electrode 13e and the surface potential portion of the photosensitive drum 1. Vibrate. Thereby, a current signal having an amplitude proportional to the surface potential of the measurement target is obtained.

  The detection electrode 13e is induced with a charge Q having a charge amount proportional to the surface potential of the object to be measured. The relationship between Q and V is expressed by the following equation (1).

Q = CV (1)
Here, C is the electrostatic capacitance between the detection electrode 13e and the photosensitive drum 1, and by measuring the charge amount Q induced in the detection electrode 13e from the above equation (1), the photosensitive drum 1 is measured. The surface potential is obtained.

  However, it is actually difficult to directly measure the quantity of electricity Q induced in the detection electrode 13e at high speed and accurately. As a practical method, an alternating current signal generated at the detection electrode 13e is measured by periodically changing the capacitance between the detection electrode 13e and the photosensitive drum 1. Thereby, the surface potential of the photosensitive drum 1 is measured.

  Further, when the capacitance changes at time t, the current I of the potential detection signal is a time differential value of the amount of charge induced in the detection electrode 13e. Furthermore, when the change rate of the surface potential V of the photosensitive drum 1 is sufficiently slower than the change rate of the capacitance C, V is considered to be constant in the minute time dt, and is expressed by the following equation (2). To express.

I (t) = dQ (t) / dt = V · dC (t) / d (t) (2)
From the above equation (2), the detection current I is a linear function of the target surface potential V. Therefore, the surface potential of the measurement target can be obtained by measuring the amplitude of the AC signal.

  Further, from the above equation (2), if the change rate of the capacitance (C) is the same, the magnitude of the alternating current signal with respect to the surface potential of the photosensitive drum 1, that is, the sensitivity of the potential measurement device changes the capacitance. Proportional to quantity.

  Further, since the measurement of the surface potential meter 13 observes a change in current detected by a change in positive capacitance, a change in the operation of the opening / closing part 13g is affected by a change in use environment and durability.

  In addition, since it has a fixed field of view determined by the aperture area, when measuring the target surface potential, measure the potential in consideration of the size of the field of the surface electrometer 13 detected by the detection electrode 13e. It is necessary to do.

  Further, when the potential signal of the surface potential meter 13 is read by the CPU 100, a minute signal value is amplified and detected as a surface potential through the A / D converter 13c. Therefore, the response including the amplifier 13b and the sensor control board 13a is also included. Need to consider speed.

  Further, such a response speed is generated by a time constant determined by the entire system such as the surface electrometer 13, the sensor control board 13a, and the amplifier 13b. Then, it exists as a response speed unique to the image forming apparatus, and the response speed changes due to environmental fluctuations, durability deterioration, etc., so it is difficult to always read the surface potential at the same response speed.

[Embodiment 1]
The response speed correction of the surface electrometer 13 will be described. The measurement accuracy according to the response speed of the surface potential meter 13 and the latent image contrast potential difference of the surface potential is experimentally measured in advance, and the correction amount according to the environmental change, durability variation, etc. is measured.

  After the correction data is stored in the storage means 111, the potential is measured in consideration of the response speed until the surface potential is detected by the surface potential meter 13 and the CPU 100 during the surface potential measurement. Further, correction control is performed on the surface potential measurement value corresponding to the contrast potential difference of the surface potential.

  First, a measuring apparatus and a measuring method for measuring the response speed will be described. 6A and 6B are explanatory diagrams of the sensor response speed measuring device.

  In FIG. 6, a reference surface in which different biases V1 and V2 are applied to the surface of the photosensitive drum 1 is driven at the rotational speed of the photosensitive drum 1, and the response speed to the rectangular bias is measured. In this case, the response speed when the latent image potential passes immediately below the surface electrometer 13 is measured.

  Further, the photosensitive drum 1 is provided with electrodes to which V1 and V2 are applied in the entire longitudinal direction, and has an electrode configuration extending in the longitudinal direction. At the end, a contact terminal 51 is attached to the center position of the surface potentiometer 13, and the electrode surface monitors the voltage at the sensor center position. Further, the control unit connected to the recorder 52 can select a set voltage of V1 and V2, a response speed, and a voltage to be measured for measurement error.

  Using the timing at which the voltage value of the measurement object is detected as a reference time, the response time and the measurement error with respect to the potential data read by the image forming apparatus from the measurement value of the surface electrometer 13 are transmitted.

  FIG. 7 shows a state in which a pseudo rectangular voltage waveform is created by applying the DC bias voltages V1 and V2 to the photosensitive drum 1. FIG. 8 shows a voltage waveform in the case where 500 V corresponding to the VD potential of the image forming apparatus is applied to V1, and the exposure part potentials are 100 v, 250 v, and 300 v as V2.

  Next, how to obtain the response speed and the error will be described. The response time and measurement error are obtained experimentally using the configuration of the measuring instrument as shown in FIGS. 6 (a) and 6 (b). The voltage signal conditions of the reference rectangular bias waveform of the exposure portion potential (V2 = 200V) with respect to the reference VD potential (V1 = 500V) will be described using measured cases.

  First, as shown in FIG. 6B, the values of V1 and V2 are input to the control unit 53 connected to the recorder 52. Thereafter, the rotational drive of the measuring device shown in FIG. 6A is started, and the potential measured by the surface potentiometer 13 from the image forming apparatus is started to be measured by the recorder 52.

  Thereafter, the V1 and V2 voltages of the high-voltage power supplies 54 and 55 are applied from the control unit 53 of the recorder 52. Further, the recorder 52 starts detecting the voltage of the contact terminal 51 after applying the V2 voltage, and measures the voltage from the contact terminal 51 by setting the detected timing to t = 0.

  At this time, the voltage at the contact terminal 51 is recorded in the recorder 52 as a continuous waveform. The voltage data of the image forming apparatus is also taken into the recorder 52 together with the waveform of the contact voltage, with t = 0 ms as a reference time.

  The control unit 53 records the data obtained from the surface potential measurement of the surface potentiometer 13 and the voltage signal of the contact voltage transmitted from the image forming apparatus at intervals of about 2 ms, and stores the data.

  Next, a method of calculating response speed and measurement error data based on the measurement data of the surface potential meter 13 and the voltage data of the detection electrodes will be described. Fig. 9 shows the calculation flow of response speed and measurement error. FIG. 10 is a model diagram of measurement data when the recorder 52 measures the conditions of V1 = 0V and V2 = 500V.

  FIG. 8 is a diagram showing the V2 voltage of 500 V as an input waveform and the electrometer measurement data as a response waveform. The potential data obtained when the waveform of the surface electrometer 13 converges and the reference voltage V2 are shown. The potential difference is taken as a measurement error.

  Further, the reference time t = 0 ms, and the timing t1 is set as the settling time at the timing within the range of ± 5 V with respect to the convergence value of the surface electrometer 13, and this is handled as the response speed of the surface electrometer 13.

  In FIG. 9, first, response speed calculation control is started. In step S1, the measurement data of the surface potentiometer 13 and the potential data of the detection electrode are measured. Next, in step S2, potential data with a time t of 100 to 120 ms is extracted.

  In step S3, the average value of the potential data is calculated, and the result is Vs. In step S4, time t and N = 0 are set, and variables used in the calculation formula are reset. Thereafter, in step S5, the difference between the VL potential response data for each time, V (t), and the average VL potential Vs is calculated. In step S6, whether or not the potential difference is 5 V or less in absolute value. Judging.

  In the case of 5V or more, it is considered that the VL response data cannot follow the average value of the VL potential, the process moves to step S7, t = 2 (ms) is added, and the data after 2 ms is used. Steps S5 and S6 are repeatedly calculated and judged.

  In step S6, when the condition that the difference is 5V or less is obtained, the process moves to step S8, the variable N = N + 1, and the process proceeds to step S10 to confirm the potential difference after the next 2 ms. Return to step S5. Next, in step S9, in order to omit an error factor in the response speed measurement, N = 4, that is, control is repeated until the difference between the response speed data for 4 data and the average potential Vs becomes 5V or less. ing. In this embodiment, N = 4 is set, but it may be adjusted as appropriate, or may be handled as response speed data when N = 1.

  In step S9, when N = 4 is reached, the process proceeds to step S11, and t of the data is stored as a response speed time Ts.

  Next, a method for obtaining the measurement error and the response speed will be described with reference to FIGS. FIG. 11 shows the data of the surface electrometer 13 shown in FIG. 12 and the data obtained under the detection electrode setting conditions of V1 = 0V and V2 = 500V.

  In order to obtain a convergence value in which the waveform of the measurement data of the surface electrometer 13 is stable, as shown in FIG. 12, the average value Vs of the potential data in the section ta = 100 ms and Tb = 120 ms is used. Here, the average calculation sections ta and tb may be adjusted as appropriate, and data for a sufficiently converged period may be used.

  Next, a method for calculating the response speed will be described. The waveform of the surface electrometer 13 becomes the waveform shown in FIGS. 12 and 8 when the detection electrode is suddenly switched. As a method for determining the response speed, the time within the range of ± 5 V with respect to the convergence potential Vs is set as the response time.

  A method for obtaining the response time will be described with reference to FIG. FIG. 11 shows potential data measured at intervals of 2 ms with respect to the reference time recorded in the recorder. As response speed data 1, 4 data of potentials up to 6 ms with reference to t = 0 ms are compared with Vs, and in the form of ΔV = V (t = 0) −Vs, ΔV = V (t = 2) −Vs, The difference between the four potential data and the convergence potential Vs is calculated. For the response speed 2, a difference from the convergence potential Vs is calculated using potential data of 2 ms to 8 ms.

  The potential differences described above are calculated as response speed 1, response speed 2..., And the time when the difference ΔV <± 5 with respect to the convergence potential Vs is obtained at all four points of potential data. , Defined as response time.

  By performing the above calculations, the response speed Δts = 30 ms is obtained in the potential measurement results shown in FIGS. Further, this data is transmitted from the recorder 52 to the image forming apparatus through the communication path shown in FIG. 6B in the form shown in FIGS. 10 and 13 in association with the information on the potential difference between V1 and V2.

  Next, the response speed and the potential correction amount stored in the storage means will be described. The response speed and the measurement error with respect to the reference voltage are stored in the storage unit in the image forming apparatus in the form shown in FIGS.

  Although the detailed explanation is omitted, the correction value of the response speed time is the same as the embodiment shown in FIG. 10, and the photosensitive member is at 0 V or a predetermined potential difference with respect to the reference exposure portion potential (VL). A correction TBL in the case of corresponding to is also provided.

Similarly, the potential error correction value is also stored in the storage unit as “change from VL potential to VD potential”. If the relationship between the response speed and the measurement error with respect to the potential difference can be clarified, it is possible to store only the reference and data and use a method such as linear interpolation or other calculation methods. The effect of correction will be described. FIG. 14 shows an example of the potential waveform read by the surface potentiometer 13 when a rectangular voltage is applied to the photosensitive drum 1, and shows the result when the voltages of 0V and 600V are switched.

  When a rectangular bias voltage is applied, it can be seen that the read waveform of the surface electrometer 13 is sent and responding. In addition, the response speed when the potential of the surface electrometer 13 increases is 13 ms, and the response characteristic when the potential drops is 9 ms.

  The response speed as described above varies depending on the difference in potential difference, and the greater the potential difference, the greater the response speed, or the fluctuation of the current signal from the detection electrode signal and the fluctuation of the control circuit and amplification circuit as shown in FIG. In some cases, overshoot or undershoot.

  FIG. 16 shows a surface potential waveform measured with a Trek 344 surface potential meter manufactured by Trek and a potential waveform for one cycle of the photosensitive drum 1 of the surface potential measured with the surface potential meter 13. In this case, the surface potential waveform shows the case where the surface potential VD = 500V and the exposure portion potential VL = 200V.

  At this time, the measured potential waveform is measured under the condition that the VL potential is continued from the VD potential as shown in the model diagram of FIG. It can be seen that when the potential is measured at a timing when the surface electrometer 13 is not sufficiently responding, the exposure portion potential in the section from 0 ms to 80 ms in FIG. 16 cannot be measured with high accuracy.

  FIG. 18 shows the result of measuring the potential of the exposure potential VL = 200 V, similarly to FIG. 16, under the condition of VD = 350V. It can be seen that although the VD potential is small, the measurement accuracy of the potential of 0 to 80 ms is improved, but it is still insufficient. In the image forming apparatus of the present invention, the VD potential side is a black solid image portion, and the blank paper portion is an exposure portion potential.

  Next, a result when the potential between papers is measured when a black solid image is continuously output without correcting the response speed, for example, when an A4 size image is continuously output is shown.

  FIG. 19 is a diagram showing the rotational position of the photosensitive drum 1 and the potential measurement point between papers when an A4 size image is output continuously. FIG. 19 shows the number of output sheets on the horizontal axis, and the vertical axis is shown in FIG. 20 when continuous images are formed at the reference position detected by the rotation reference position detecting means (not shown) of the photosensitive drum 1. FIG. 6 is a diagram plotting the position at which the VL potential measurement between papers is performed with respect to the rotation point of the photosensitive drum 1 with respect to the starting point Q of the paper-to-paper potential.

  The measurement of the inter-paper VL potential starting at the position of the plot point in FIG. 19 shows that in the case of A4 size, it is possible to measure the drum potential across the entire photosensitive body with about 150 continuous outputs. Although the detection position varies depending on the size of the output size, it is possible to measure the entire area of the photoreceptor with the output number of about several hundreds at any size.

  FIG. 21 shows the measurement results under the paper-to-paper VL potential condition of FIG. Here, the time VL between the papers in this image forming measure is 110 ms regardless of the paper size, and the potential is measured at intervals of about 2 ms.

  As shown in FIGS. 16 and 18, the VL potential measured under the continuous black solid condition where “VD → VL potential” changes, as shown in FIG. 21, the overall VL potential of the photosensitive drum 1 increases and fluctuates. It can be seen that a simple potential waveform is measured. In this case, the potential is measured without sufficiently considering the response speed of the surface electrometer 13. Thus, it can be seen that a large potential measurement error occurs under the condition that the response speed is delayed.

  Next, potential measurement using the response speed and measurement error of the surface electrometer 13 will be described. In order to adjust to the target VD potential and the target VL potential as a pre-stage for applying the response speed and measurement error, the potential control configuration will be described first.

  FIG. 22 is a diagram showing a potential waveform model of potential control executed to measure the VD potential of the photosensitive drum 1 and adjust the VD potential and VL potential to target values. In order to adjust VD and VL to the target potential, the relationship of the VD potential to the grid voltage of the corona charging device 2 and the relationship of the VL potential to the exposure amount are obtained.

  This potential control is performed for the purpose of adjusting the average potential for the period of the photosensitive drum 1 to the target potential, and detailed measurement of the profile shape of the potential unevenness is not performed.

  The adjustment to the target potential is performed at a timing such as after the main SW-ON of the image forming apparatus. For this reason, adjustment to the target potential at the time of potential control has a time margin. Therefore, with respect to the response speed of the surface potential meter 13, it is possible to measure and adjust the average value of the surface potential in consideration of sufficient time.

  The potential control shown in FIG. 22 will be described. Driving of the photosensitive drum 1 is started, and at the same time, the light static eliminator 6 is turned on, and 500 V is applied to the grid electrode of the corona charging device 2. Thereafter, after the photosensitive drum 1 reaches steady rotation, a high voltage is applied to the discharge electrode 2a of the corona charging device 2 to start the formation of a charged potential.

  First, the potential at a grid voltage (Vgrid) of 500 V is measured, and one revolution of the photosensitive drum 1 is measured to obtain the average potential VD1. Thereafter, while switching the grid voltage between 750 V and 900 V, the surface potentials VD2 and VD3 under each grid condition are measured, the grid high voltage at which the target potential Vd = 500 V is calculated, and the VD potential is formed.

  Thereafter, as shown in FIG. 22, the amount of light is changed from the state of the target Vd potential, and the exposure portion potential is measured for one cycle of the photosensitive drum 1 as in the case of the VD potential. Calculate the average potential at. Thereafter, the target VL potential = 200V is obtained.

  At this time, the relationship between the grid high voltage and the VD potential and the relationship between the exposure amount and the VL potential are recorded in the storage unit of the image forming apparatus, and the potential can be corrected using the relationship from the next time. ing.

  Next, surface potential measurement using response speed correction and potential measurement error correction of the surface potential meter 13 will be described. FIG. 23 is a model diagram showing the shape of the potential when the image exposure is turned on from the state in which the surface potential VD is formed on the photosensitive drum 1 with respect to the image exposure position and the position of the surface potential meter 13. At t = 0, image exposure is started and VL potential formation is started. Thereafter, the image exposure is continuously turned on, and the exposure portion potential VL reaches the visual field of the potential sensor at the timing of time t = t1.

  Thereafter, at time t = 2, the VL potential reaches the entire visual field of the surface electrometer 13. The surface electrometer starts to respond to the condition where the entire field of view or the counter potential is VL at time t2. Thereafter, the response speed of the electrometer is from time t2 to time t3.

  Next, response speed correction and potential measurement error correction will be described with reference to the flowchart shown in FIG. Since the basic operation at the start of potential formation is described in the section of potential control, description thereof is omitted. FIG. 24 is a flowchart of the control operation for measuring the response speed and measurement error of the potential sensor by starting image exposure and measuring the VL potential from the state where the charged potential VD is formed as shown in FIG. It is explained. The details of the control shown in FIG. 24 will be described below in detail.

  First, in step S1, measurement of VL potential unevenness is started. Next, temperature and humidity are read from an environmental sensor (not shown) provided in the apparatus, and the amount of water contained in the air is calculated (step S2).

  Then, counter information is read from an output number storage unit (not shown) in the apparatus (step S3). Thereafter, the control unit in the apparatus reads the environment information, the output number information, the response speed Δts of the potential formation condition of VD = 500 V and VL = 200 V and the potential measurement error information ΔV formed this time from the storage unit 111 (step S4 , S5).

  Thereafter, image exposure is started (step S6), and response speed calculation control is started. This time corresponds to time t = 0 in FIG. After the image exposure is started, the measurement of the VL potential is started from the timing of the response speed information Δts read from the storage unit 111 (step S7). The potential measurement interval is 4 ms (step S8), and 128-point potential data is acquired for the period of the photosensitive drum 1 (step S9).

  Thereafter, using the potential measurement error ΔV read from the storage unit 111 (step S10), the measured potential data is corrected (steps S11 and S12), stored (step S13), and the measurement of the potential profile is completed. (Step S14). In the image forming apparatus, the potential unevenness profile of the exposure portion potential is stored, the VL potential between the papers during image formation is measured, and the potential fluctuation is monitored while performing comparative examination.

  As for the VL potential between papers, the potential between papers is measured from the timing when the exposure is turned on and the timing after the response speed correction amount Δts in the same method and between the papers when measuring the potential unevenness profile shape.

  FIG. 25 is a diagram schematically showing how the potential between papers is measured. The image forming apparatus can measure a large number of highly reliable potential data by measuring only the potential in the potential measurable region.

  In the present embodiment, the surface potential of the photosensitive drum 1 is controlled to be the target potential using the output of the surface potential meter 13 after a set time has elapsed since the surface potential meter 13 started measurement, and the cumulative image is displayed. A set time is set according to the number of formations.

  Then, a potential unevenness profile by an electrometer using the response speed correction and the potential error correction of the surface electrometer 13 is used. As a result, even when the solid black (VD potential) and the inter-paper potential (VL), which are the conditions for the largest potential difference shown in FIG. 26, are continuously formed, the potential shape conforms to the profile shape of the surface potential of the photosensitive drum 1. Can be measured accurately according to the ambient environment.

  Further, during continuous image formation, the VL potential fluctuation can be accurately captured by comparing and monitoring the profile shape of the VL potential for one cycle of the photosensitive drum 1 with the measurement result of the inter-paper potential. . Further, even when a partial potential fluctuation occurs at the peripheral position of the photosensitive drum 1, the fluctuation amount is confirmed, and the position of the photosensitive drum 1 is determined based on the relational data between the light amount and the VL potential measured during the potential control. Even partial correction control is possible.

  Even when the response speed of the surface potential meter 13 changes due to the environment or durability, the data used for potential control can be changed from the beginning by variably controlling the surface potential following the change in response speed. Accurate measurement can be performed up to durability. As a result, the image density of the photosensitive drum 1 can be controlled with high accuracy.

[Embodiment 2]
In the invention of the second embodiment, the configuration of the image forming apparatus and the measurement configuration of the surface electrometer 13 are the same as those of the first embodiment, and therefore only the parts different from the first embodiment will be described.

  In the surface potential measurement method of the first embodiment, the response speed and surface potential error measurement of the surface potentiometer 13 was previously determined experimentally by using the measuring instrument shown in FIG.

  In the second embodiment, in response to experimentally obtained correction information, when the image forming apparatus is used for a longer period of time than expected or when it is used in an environmental condition that is not guaranteed, the response speed is different from the experimental value. The point which correct | amends a speed differs from Embodiment 1. FIG.

  That is, in FIG. 27, the VL potential in the case of image exposure is measured with respect to the VD potential, and the response speed of the surface electrometer 13 is measured from the result of measuring the potential waveform of the surface electrometer 13 from the image exposure timing. ing.

  That is, first, a surface potential (VD) is formed, a potential of one or more cycles of the photosensitive drum 1 is formed, and then the VD potential from the second turn (position A) of the photosensitive drum 1 is measured. The average value is stored.

  Next, image exposure is started, a VL potential for two revolutions of the photosensitive drum 1 is formed, and a VL potential is applied at intervals of 2 ms from the second revolution (position B). As shown in FIG. 28, data at intervals of 2 ms are stored as profile data.

  Thereafter, the image exposure is turned OFF at the HP reference of the photosensitive drum 1 at the detection (C position) timing, the potential measurement is started with the next HP detection timing (D position) set to t = 0 ms, and the photosensitive drum 1 is started. Are measured and stored in the array form of FIG. Also, the average potential of the VD potential and VL potential for one cycle of the photosensitive drum 1 is calculated and stored in the storage unit 111.

  Thus, as a test mode, the surface potential meter 13 compares and measures the response performance with respect to the latent image potential from the potential waveform measured from the timing of the B position and the D position by measuring the rectangular potential waveform according to time. It becomes possible.

  In this control, the VD potential and VL potential, which are the reference for measuring the response speed, are the average potential for one cycle of the photosensitive drum 1 having the VD potential and the VL potential. The response speed of the surface electrometer 13 is compared with the VL response data to calculate the response speed.

  The response speed of the surface electrometer 13 is obtained by measuring each period data of VD and VL measured with reference to the HP of the photosensitive drum 1 and VL response data measured with reference to t = 0 ms when image exposure is started based on the HP. Compare and calculate. Note that the average value of the VD and VL potentials is used as the HP reference of the photosensitive drum 1.

  By using the measurement method described above, the image exposure timing and the potential data corresponding to the position of the photosensitive drum 1 as the HP reference are measured. As a result, as shown in FIG. 29, the reference VL cycle data is compared with the VL response data for the VL potential. Therefore, the response speed of the surface electrometer 13 can be obtained, and the response speed data stored in the storage unit 111 can be corrected.

  Regarding the potential measurement of response speed measurement, response speed calculation, and response speed correction, the correction amount is calculated according to the flowcharts shown in FIGS.

  In FIG. 30, first, potential formation is started on the photosensitive drum 1 (step S1). In step S2, drum driving is started, the surface potentiometer 13 is activated in synchronization with the driving, and the light static eliminator 6 is turned on.

  In step S3, a high voltage is applied to the discharge wire 2a and the grid electrode 2b to form a charging potential (VD). In step S4, phase detection of the drum rotation cycle is started using the detection sensor (HP). In step S5, the HP detection measures the VD potential at an interval of 2 ms from the timing A shown in FIG. 27, and stores it as VD cycle data in the storage unit 111 in the arrangement form of FIG. In step S6, the average potential for one revolution of the drum is calculated.

  Thereafter, at the timing of HP detection (step S7) when the VD potential measurement is completed, in step S8, image exposure is turned on to form a VL potential. Measurement of the VL potential is started at the timing of B in FIG. 27 from the start of exposure, and is stored in the storage unit 111 as VL cycle data shown in FIG. 28 (steps S9 and S10).

  In step S11, the average VL potential is calculated and stored in the storage unit 111. In step S12, the image exposure is turned off at the timing of C in FIG. 27, and the VD potential is formed once around the drum. In step S13, image exposure is turned ON, and in synchronization with this, a timer is started (t = 0) in step S14.

  Measurement of the VL potential is started at the timing of t = 0, and the measurement result is recorded in the storage means 111 as “VL response data” shown in FIG. 28 (step S15), and the operation is terminated in step S16. To do.

  Next, a flow for calculating the response speed of the surface electrometer 13 using the potential data shown in FIG. 28 will be described with reference to FIG. By implementing this control, the response speed data stored in the device can be corrected. At the time of shipment from the main unit, the response speed according to the environmental fluctuation and the number of durable sheets is shown in the form shown in FIG. The correction control of the data stored as the initial condition is executed.

  That is, in step S1, response speed calculation control is started. In step S2, the current environmental information (temperature, humidity) is measured, and the amount of water contained in the air is calculated from the result. Next, in step S3, the current number of output sheets is read from the storage means 111.

  In step S4, time data is read at intervals of 2 ms with reference to t = 0. In step S5-a, the cycle data of the VL potential is read for one cycle of the drum, the average value is calculated, and the result is Vs. In step S5-b, the VL response data corresponding to the time ts read in step S4 is read and stored as V (t) for each time.

  Thereafter, in step S6, time t and N = 0 are set, and variables used in the calculation formula are reset. In step S7, the difference between the VL potential response data for each time, V (t), and the average VL potential Vs is calculated. In step S8, whether or not the potential difference is 5 V or less in absolute value. Judging.

  In the case of 5V or more, it is considered that the VL response data cannot follow the average value of the VL potential, the process moves to step S9, t = 2 (ms) is added, and the data after 2 ms is used. Steps S7 and S8 are repeatedly calculated and judged.

  In step S8, when the condition that the difference is 5V or less is obtained, the process moves to step S10, variable N = N + 1, and the process proceeds to step S12 to confirm the potential difference after the next 2ms. Return to step S7. In the present embodiment, in step S11, in order to omit an error factor in the response speed measurement, N = 4, that is, the control is repeated until the difference between the response speed data for 4 data and the average potential Vs becomes 5V or less. Is doing. In this embodiment, N = 4 is set, but it may be adjusted as appropriate, or may be handled as response speed data when N = 1.

  In step S11, when N = 4 is reached, the process proceeds to step S13, and t of the data is stored as a response speed time tso. Thereafter, in step S14, the response speed data Δts stored in the storage means 111 is read in accordance with the environmental conditions in steps S2 and S3 and the conditions of the durable number, and the time difference from the response speed data measured this time Δt is calculated.

  In step S15, the response speed correction calculation value Δt obtained in step S14 is added to the data stored in the form shown in FIG. The rewriting and control are finished (step S16).

  By performing the above control flow, the reference potential for measuring the response speed of the surface electrometer 13 and the response speed of the surface electrometer 13 can be measured.

  Next, a potential sampling method using the corrected response speed for control will be described. FIG. 29 shows the VL period data corresponding to the phase of the photosensitive drum 1 and the response data of the surface potentiometer 13 when the potential waveform is switched from the VD potential to the VL potential.

  Considering the response speed of the surface electrometer 13, the VL potential can be accurately measured by measuring the potential from the timing when the response time of 25 ms has elapsed. Here, the potential data sampling period may be a method in which the potential is sampled from time t = 0 ms, and the correction data at the timing after 25 ms is used for the potential control.

  The response speed correction control described above can be executed in a timely manner by a serviceman from an operation unit (not shown) provided in the image forming apparatus. As a service mode from the operation panel of the main unit, it can be performed at an arbitrary timing and is performed when the main unit is activated.

  In this device, it is set to operate at startup after being left for a long period of time, the main switch is turned on, the condition that the temperature of the fixing device is less than 50 ° C. is determined to be left for a long time, the response speed is measured, And the calculation control is implemented. In addition, after the main SW of the image forming apparatus is turned on, the potential control shown in FIG. 22 is executed, and then it can be executed automatically.

  As described above, by executing the correction control described above, it is possible to perform timely confirmation and correction control on the response speed data stored in the apparatus, thereby maintaining the potential measurement accuracy.

1 is a configuration diagram of an image forming apparatus according to Embodiment 1 of the present invention. FIG. 3 is a cross-sectional view illustrating a layer structure of a photosensitive drum. (A) is a top view of a developing device, (b) is sectional drawing of a developing device. It is a block diagram of a surface electrometer. It is a block diagram of a surface electrometer. (a) And (b) is explanatory drawing of a sensor response speed measuring device. It is a figure which shows the waveform example of the rectangular voltage applied to a counter electrode. It is explanatory drawing of the response speed of a surface electrometer, and measurement error measurement. It is a flowchart of response speed and potential error measurement. It is a figure which shows the example of a correction value of the response speed memorize | stored in the apparatus. It is a figure which shows the example of measurement data preservation | save of Embodiment 1. FIG. It is a figure which shows the example of a measurement data waveform of Embodiment 1. FIG. It is a figure which shows the example of a correction value of the electric potential measurement error memorize | stored in the apparatus. It is a figure which shows the response example 1 of the sensor at the time of a rectangular voltage application to a counter electrode. It is a figure which shows the example 2 of a response of the sensor at the time of a rectangular voltage application to a counter electrode. It is explanatory drawing of the exposure part electric potential measurement result 1 (VD = 500, VL = 200V conditions). It is a figure which shows the drum potential measurement condition example (switching from VD => VL potential). It is explanatory drawing of exposure part electric potential measurement result 2 (VD = 350, VL = 200V conditions). It is a figure which shows the sampling relationship of the position of the photoconductive drum at the time of A4 continuous image formation, and the position between paper. It is explanatory drawing of a paper gap position and a plot position. It is explanatory drawing of the VL electric potential measurement result 1 between sheets (When a black solid image is continuous, there is no correction). It is a figure which shows the electric potential formation at the time of electric potential control. It is a figure which shows an image exposure position and sensor response time. It is a flowchart which shows the correction | amendment with respect to a paper potential measurement value. It is explanatory drawing of the measurement timing of a paper-to-paper potential. It is explanatory drawing of the VL electric potential measurement result 2 between sheets (When a black solid image is continuous, with correction | amendment). 6 is a diagram illustrating an example of a potential waveform at the time of response speed measurement according to Embodiment 2. FIG. It is a figure which shows the example of response speed data measurement of Embodiment 2. FIG. It is a relationship diagram of VL period data and response speed data of Embodiment 2. 10 is a flowchart for explaining response speed correction data measurement according to the second embodiment. 10 is a flowchart illustrating response speed correction control according to the second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Corona charger 2a Discharge wire 2b Grid electrode 2c Shield electrode 3 Developing device 4 Primary transfer means 5 Cleaning device 6 Photostatic device
11 Exposure section
13 Surface electrometer
15 Pre-transfer charger
111 Storage means

Claims (3)

In an image forming apparatus comprising: a photoconductor; a charger that charges the photoconductor to form an electrostatic image on the photoconductor; and a potential sensor that measures a surface potential of the photoconductor.
Control means for controlling the surface potential of the photosensitive member to be a target potential using the output of the potential sensor after a set time has elapsed since the potential sensor started measurement, and according to the cumulative number of image formation times An image forming apparatus comprising: a setting unit that sets a set time.   The image forming apparatus according to claim 1, wherein the setting unit is set according to an atmosphere environment. In an image forming apparatus comprising: a photoconductor; a charger that charges the photoconductor to form an electrostatic image on the photoconductor; and a potential sensor that measures a surface potential of the photoconductor.
Control means for controlling the surface potential of the photosensitive member to be a target potential using the output of the potential sensor after a set time has elapsed since the potential sensor started measurement; and a predetermined potential difference between the photosensitive member and the photosensitive member. And executing means for executing a test mode for measuring a surface potential of a portion corresponding to a predetermined potential difference by the potential sensor, and setting for setting a set time according to the measurement result in the test mode. And an image forming apparatus.

Images