JP2009229577A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase/decrease a developing voltage value applied to a toner carrier in an image forming apparatus, according to the extent of a leak so as to set the appropriate developing voltage value, in a short time. <P>SOLUTION: The image forming apparatus is provided with: a developing voltage generating means 108 applying developing voltage obtained by superimposing DC voltage on the AC voltage of rectangular wave to the toner carrier; a leak detection means 41 for detecting a waveform distortion portion which appears in the rectangular wave, when a leak occurs between an image carrier and the toner carrier, by sampling the waveform of the developing voltage, obtained by dividing the developing voltage by a voltage divider within a fixed period; a leakage degree calculation means 42 for measuring the number or distortion amount of the waveform distortion portion detected in the fixed period by the leak detection means and calculating the current extent of leakage from the measured number or distortion amount; and a developing voltage control means 43 performing developing voltage optimizing control that the value of the developing voltage is changed stepwise, according to the calculated present leak degree to the developing voltage value at the appropriate extent of leak at which occurrence of the leak is started or the developing voltage value, immediately preceding it. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact development type image forming apparatus that visualizes an electrostatic latent image by moving toner from a toner carrier to an image carrier, and more particularly to a technique for applying an optimum development voltage to the toner carrier. Is.

  2. Description of the Related Art Conventionally, in a non-contact development type image forming apparatus, a photosensitive member, which is an image carrier on which an electrostatic latent image is formed, and a developing roller, which is a toner carrier that carries toner, are arranged apart from each other. Then, a developing voltage obtained by superimposing a DC voltage and an AC voltage is applied to the developing roller, and the toner is moved from the developing roller to the photoconductor to visualize the electrostatic latent image.

  The reason why the AC voltage is superimposed is that the gap distance between the developing roller surface and the photoreceptor surface (hereinafter referred to as “gap”) is non-uniform in the longitudinal direction of the developing roller, so even when there is an in-plane difference in the gap, the developing roller This is because, if the amplitude of the AC voltage applied to is somewhat large, an electric field sufficient to cause the toner to fly to the photosensitive member can be obtained even if the gap is wide, so that density unevenness is less likely to occur.

  However, if the development voltage value, that is, the amplitude of the AC voltage is fixed, variations in the diameter of the developing roller and the photosensitive member (individual differences), surface potential fluctuations due to surface scraping, durability fluctuations, etc. Depending on the factor, a good image may not be formed.

  For example, if the value of the AC voltage is set to a high value, a leak (hereinafter referred to as “development leak”) occurs between the developing roller and the photoconductor even during image formation, and the electrostatic latent image exposed on the photoconductor surface is exposed. Regardless of the presence or absence of an image, toner adheres to the surface of the photoreceptor from the developing roller, resulting in a decrease in image quality.

  On the other hand, if the AC voltage value is set to a low value, there will be a portion where an electric field sufficient to cause the toner to fly to the photoreceptor due to in-plane difference of the gap, development characteristics, density unevenness, etc. As a result, density unevenness due to deterioration in development characteristics occurs. This is due to the flying property of the toner by applying an AC voltage. Thus, when the amplitude of the AC voltage is fixed, it is difficult to prevent density unevenness and discharge from occurring at the same time.

  Therefore, when setting the value of the developing voltage applied to the developing roller of the non-contact developing method, that is, the AC voltage value, the AC voltage of the reference amplitude is first applied to check the presence or absence of the developing leak. Is set to the reference amplitude, and when there is a development leak, a development voltage optimization control method is known in which the AC voltage is set to an amplitude smaller than the reference amplitude (Patent Document 1). In this method, initial development voltage optimization control is performed from the maximum amplitude of the AC voltage.

In addition, a charge / discharge circuit composed of a capacitor and a resistor is used as a leak detection circuit which is a prerequisite for such development voltage control.
Japanese Patent No. 3844384

  However, if development leakage is detected by a charge / discharge circuit consisting of a capacitor and a resistor, the time required for charge / discharge cannot be ignored.Therefore, the set value of the development voltage applied to the development roller can be increased or decreased to an appropriate development voltage value. It took time to make the transition. In particular, in an image forming apparatus using multi-color toner, a non-negligible time is generated until the developing voltage at which a developing leak of each color occurs in the leak detection operation, and an image can be formed after the power switch of the image forming apparatus is turned on. It takes a long warm-up time to reach the state.

  For example, in the case of a tandem image forming apparatus, a single circuit that amplifies the leakage current by converting it into a voltage is configured to reduce the cost. In this case, first, the DC voltage applied to the Y-color developing roller is set to a positive polarity, and the AC voltage is set to a voltage value at which development leakage does not occur as estimated from the cause of development leakage.

  The DC voltage applied to the other three developing rollers of M color, C color, and K color is set to 0 V that is neither positive nor negative, and the AC voltage is a voltage value that does not cause development leakage. Furthermore, a minimum value that can be set to a lower voltage value is set.

  Then, in the development voltage value in which development leakage never occurs in the Y color, the development voltage output value from the amplifier circuit is taken into the CPU, and the development voltage value is gradually increased after setting this output value as a reference, When a voltage higher than a certain level can be detected with respect to the reference, it is determined that a development leak has occurred, the voltage value of the AC voltage at that time is stored in the memory, and the Y-color leak detection operation, that is, the development voltage optimization control ends.

  Next, the M color and other C and K colors are set as described above for the Y color, and the operation similar to that performed for the Y color is repeated in the same manner as the M color leak detection operation, that is, the development voltage. The optimization control is terminated. The C color and K color leak detection operations are performed in the same manner.

  Even if the voltage is increased step by step, there is a limit, and the maximum value that can be set by the AC voltage is reached. Even if the Y-color leakage occurrence voltage is close to the maximum value that can be set by the AC voltage, it starts from a voltage value at which development leakage does not occur, resulting in wasted time.

  Of course, the voltage value is not increased stepwise after setting the reference, but can be set at the center of the normal distribution of leak generation voltages that can be assumed in advance. However, if a development leak occurs at an early stage in which the voltage value is increased stepwise, the development voltage value that is considerably different from the development voltage at which the leak occurred is set. As a result, the configuration of the conventional leak detection circuit has a problem that an output from the amplifier circuit cannot be obtained. Therefore, an operation of increasing the voltage value step by step from a setting lower than the leakage occurrence voltage is always performed. This is because the conventional leak detection circuit is a circuit that converts the leak current into a voltage by using the charge and discharge of the capacitor and the resistor. Therefore, if an excessive leak current is detected, it takes a long time to discharge the capacitor charge. This is because the next development leak cannot be detected.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus that can increase and decrease the development voltage value applied to the toner carrier in accordance with the degree of development leakage, that is, the degree of leakage, and can set an appropriate development voltage value in a short time. is there.

  The above object of the present invention is achieved by the following means.

  (1) An image carrier on which an electrostatic latent image is formed and a toner carrier that carries toner are arranged apart from each other, and a rectangular wave AC voltage is applied to the toner carrier to carry the toner. In a non-contact development type image forming apparatus that visualizes an electrostatic latent image by moving toner from a body to an image carrier, a development voltage having a waveform in which a DC voltage is superimposed on the rectangular AC voltage is generated. And developing voltage generating means for applying the developing voltage to the toner carrier, a voltage divider for dividing the developing voltage, and sampling the waveform of the developing voltage divided by the voltage divider for a certain period, Leak detection means for detecting a waveform distortion portion appearing in the rectangular wave when a leak occurs between the image carrier and the toner carrier, and the waveform detected within the predetermined period by the leak detection means The number of distortion parts or Leak degree calculating means for measuring the distortion amount of the waveform distortion portion and calculating the current leak degree from the number or the amount of the waveform distortion portions, and according to the current leak degree calculated by the leak degree calculation means The development voltage value that the development voltage output from the development voltage generation means is changed in stages, and the development voltage value is set to the development voltage value at the appropriate leak level at which the leak starts to occur or the development voltage value just before that. An image forming apparatus comprising: a developing voltage control unit that performs image forming control.

  (2) The development voltage control means sets the development voltage value set to an appropriate value in the previous development voltage optimization control as an initial value, and starts the development voltage optimization control from the initial value. The image forming apparatus according to (1).

  (3) The development voltage control means obtains the development voltage value of the mode from the distribution of known development voltage values determined to be appropriate values in the past development voltage optimization control, and obtains the development voltage value of the mode. The image forming apparatus according to (1) or (2), wherein the development voltage optimization control is started as an initial value.

  (4) The image forming apparatus further includes detection means for detecting that the image carrier has been replaced with a new one, and the development voltage control means is configured to perform past development when the detection means determines that the image carrier is new. A mode development voltage value is obtained from a distribution of known development voltage values determined to be an appropriate value by voltage optimization control, and the development voltage optimization control is started with the mode development voltage value as an initial value. The image forming apparatus as described in any one of (1) to (3) above.

  (5) The leak detection means samples, as the fixed period, one cycle of the waveform of the AC voltage in the development voltage or N cycles of an integral multiple thereof. The image forming apparatus according to 4).

  According to the present invention, the number of waveform distortion portions appearing in a rectangular wave due to the occurrence of a development leak or the amount of distortion of the waveform distortion portion is measured, and the development voltage AC depending on the current degree of development leak, that is, the degree of leak. Since the voltage value is variably controlled step by step up to the development voltage value at which development leakage starts or the development voltage value just before it, the development voltage optimization control is required as compared with the case where development leakage is detected using a CR circuit. Time can be significantly reduced. In addition, since the development voltage becomes a level that can be easily observed by dividing the voltage with a voltage divider, it is possible to easily configure the leak detection circuit with a small number of parts compared to the case where development leak is detected using a CR circuit. it can.

  In addition, by performing development voltage optimization control with the development voltage value of the appropriate leak degree calculated last time as the initial value, it is possible to eliminate the occurrence of excessive development leak, and excessive noise due to the occurrence of excessive development leak. The leak detection operation can be shortened without causing it to occur or causing the image carrier to deteriorate.

  Also, the development voltage value of the most frequent value at which development leakage occurs is obtained from the distribution of development voltage values at which development leakage occurs in advance, and this development voltage value is used as the initial value for development voltage optimization control, so that the development voltage is appropriate. The development voltage value at which development leakage starts or the development voltage value immediately before the development leakage value can be obtained without greatly varying the development voltage value in the conversion control. This shortens the time in developing voltage optimization control.

  For example, when a photoconductor as an image carrier is replaced with a new one alone or when a photoconductor is replaced with a new one in the form of an image forming unit integrated with a toner cartridge, a development voltage that causes a development leak in advance is generated. By obtaining the mode value at which development leak occurs from the distribution of values and setting the development voltage value of this mode value as the initial value of the development voltage optimization control, an excessive development leak is generated as described above. It is possible to set and control the development voltage value so that good image quality can be obtained in a short time compared to the case where a leak detection circuit using a CR circuit is used without causing excessive noise and without causing deterioration of the image carrier. it can.

  Examples of the present invention will be described below.

  FIG. 1 shows a schematic diagram of a color leather printer to which this embodiment is applied.

  As for the printing operation, when a print start request is transmitted from the image controller (not shown) to the image forming apparatus, the printing apparatus feeds the sheet from the sheet feeding cassette 1 by the sheet feeding roller 2, and feeds the sheet. The paper moves along the path 3 and waits at the position where it has reached the timing sensor 30. This is done by controlling the timing roller 4. At the same time, the transfer belt 8 is rotated by the transfer belt driving roller 9 and is formed on the transfer belt by the process units Y (yellow), M (magenta), C (cyan), and K (black) that form images of the respective colors. An image is formed.

  Each process unit includes, as each developing roller, a Y color toner developing roller 12, a M toner developing roller 17, a C toner developing roller 21, a K toner developing roller 27, and Y-color toner developing motor 36, M-color toner developing motor 35, C-color toner developing motor 34, and K-color toner developing motor 33.

  At the time of developing each color, each of the developing roller drive motors 33 to 36 is activated to rotate each of the developing rollers 12, 17, 21, and 27, and a high voltage for development is applied to these developing rollers, thereby The toner on the developing roller is developed on the Y color image carrier 11, the M color image carrier 16, the C color image carrier 22, and the K color image carrier 26. These image carriers are specifically photoconductors.

  An image developed by the process unit on the photoconductors 11, 16, 22, and 26 of each color is converted into a Y-color primary transfer roller 10, an M-color primary transfer roller 15, a C-color primary transfer roller 20, Transfer is sequentially performed on the transfer belt 8 by the primary transfer roller 25 for K color.

  The above-described timing roller 4 is driven in accordance with the timing at which the image position formed on the transfer belt 8 reaches the position of the secondary transfer roller 5 so that the leading edge position of the sheet coincides with the image position. The image on the transfer belt 8 is a toner that forms an image on the transfer belt 8 by applying a transfer voltage (about +2000 V) to the secondary transfer roller 5 (in this image forming apparatus, a negatively charged toner). ) On the sheet passing through the counter roller 6 and the secondary transfer roller 5. The transferred toner image is fixed onto a sheet by the fixing roller 7 and discharged onto a discharge tray at the top of the image forming apparatus.

  The image forming apparatus described above is provided with a toner concentration detection sensor 31 in the apparatus so that the toner density in printing is constant. In order to keep the print density constant, image stabilization control is performed when the main switch of the apparatus main body is turned on, when the toner cartridge is replaced, or when a predetermined number of sheets are printed.

  In the image stabilization control described above, several patches are formed on the transfer belt 8 by changing the developing voltage output of the developing unit, changing the toner density, and printing toner density detection toner patches (about 10 mm □). The toner density detection sensor 31 detects the density, and according to the result, feedback is provided to the development voltage output of the developing device, so that a stable toner density is always obtained during printing. This control is performed for each color in the case of a color printer.

  FIG. 2 shows a block diagram around the high-voltage power supply.

  A control board 100 that controls the color laser beam printer main body is provided with a CPU 101. When the image controller 103 receives a print request and image data from a host computer (not shown) by an external I / F (not shown), the image data is developed in an image memory (not shown) in the image controller 103. At the same time, a print request command is transmitted to the CPU 101 using the I / F line 110 with the CPU 101. Upon receiving the print request command, the CPU 101 activates the control line 112 at a predetermined timing to the image control unit 102 as described in the description of the print operation, and the image data from the image controller 103 is sent through the image data line 111. Image data is sent to the print head 104.

  The print head 104 and the image control unit 102 are connected by a connection line 113. The print head 104 comprehensively shows the Y-color print head 13, the M-color print head 18, the C-color print head 23, and the K-color print head 28, and each color photoconductor in the printing operation. 11, 16, 22, and 26 are exposed based on image data.

  The high-voltage power source shown in FIG. 2 will be described using only the K color as a representative.

  The CPU 101 controls a high voltage power supply around the printing process. A secondary transfer voltage value is controlled by a control line 114 with respect to a secondary transfer high-voltage power supply 105 that supplies a secondary transfer voltage (about +2000 V) to the secondary transfer roller 5. The charging voltage value (about −5000 V) to the charger 29 is controlled by the control line 115 with respect to the high voltage power supply 106 for charging. A primary transfer voltage value (about +1000 V) is controlled by a control line 116 for a primary transfer high-voltage power supply 107 that supplies a primary transfer voltage to the primary transfer roller 25. Further, the developing voltage value is controlled by the control line 117 with respect to the developing high-voltage power supply 108 that applies the developing voltage to the developing roller 27. Further, the development leak detection voltage from the development high-voltage power supply 108 is input to the AD port input line 119. The memory 109 is used for storing the development leak detection voltage value.

  The development high-voltage power supply 108 includes three transformers 203, 204, and 205 and three control circuits 200, 201, and 202 that individually drive them. The transformer drive control circuit 200 controls the output of the AC transformer 203, and the output from the AC transformer 203 is output to the output terminal A217 as a rectangular wave AC voltage by the waveform shaping resistor 206 and the capacitor 207. . The transformer drive control circuit 201 controls the output of the DC transformer 204. The output from the DC transformer 204 is a DC minus output that is half-wave rectified by the rectifier diode 209 and the capacitor 210. A resistor 211 is a load resistor for stabilizing the output and coupling with a DC plus output described later.

  The transformer drive control circuit 202 controls the output of the DC transformer 205, and the output from the DC transformer 205 is a DC plus output that is half-wave rectified by the rectifier diode 212 and the capacitor 213.

  A resistor 214 is a load resistor for stabilizing the output. These AC output, DC minus output, and DC plus output are electrically connected, and become an output in which the AC output is superimposed on the DC output. Therefore, the circuit portion described above generates a developing voltage having a waveform obtained by superimposing a DC voltage on a rectangular AC voltage, and outputs the developing voltage from an output terminal A denoted by reference numeral 217 to develop a developing roller 27 as a toner carrier. It acts as a developing voltage generating means to be applied to.

  Reference numeral 216 indicates a power source DC24V of the high-voltage power source, and reference numeral 215 indicates a ground.

  FIG. 4 shows the waveform of the development voltage. For a rectangular wave AC voltage, the amplitude Vpp of the waveform is set from about 1000 V to 1700 V during development. Vdc in the drawing is a DC voltage superimposed on the rectangular wave AC voltage and represents the center of amplitude, and is set to a negative value during development during printing. This is because the developing toner uses a negatively charged toner. When the above-described photoconductor is charged to about −450 V and exposed by the print head 104, a potential close to 0 V is obtained. Here, in order to allow the developing toner to adhere and develop, the toner is negatively charged and the Vdc of the developing roller is negative. The development voltage waveform has a frequency f (about 2 kHz).

  In the leather color printer of this embodiment, a gap (gap) L is provided between the developing roller 27 and the photosensitive member 26 (see FIG. 2). The developing toner flies through the gap and develops on the photosensitive member 26.

  However, since this gap has a so-called gap difference in which the gap varies depending on the variation in the diameter of the developing roller and the diameter of the photoconductor, the amount of toner development differs even when the same development voltage is applied. If the gap is too narrow or the development voltage is set too high, the development voltage leaks between the developing roller and the photoconductor, resulting in an image abnormality.

  Therefore, the setting of the AC voltage applied to the developing roller of the non-contact developing system takes into account individual differences in gaps, changes due to durability of members of the developing roller and the photosensitive drum, and the ambient environment of the developing unit such as air. Thus, before each development process, it is necessary to reset the development voltage value optimum for the development process. For this reason, in order to provide an optimum development voltage even if there is such a variation as described above, the development voltage value is gradually increased, and the development voltage value at which development leakage occurs is detected and set to that voltage value. Optimization control means are provided.

  FIG. 3 shows a portion of the development high-voltage power supply 108 and a portion of a leak detection circuit that is a component of the development voltage optimization control means.

  A portion surrounded by a broken line in FIG. 3 is a leak detection circuit according to the present invention, and waveforms of the A portion, the P portion, and the C portion are shown in FIG.

  A developing roller 27 is connected to the developing voltage output terminal A. When a developing leak occurs between the developing roller 27 and the photosensitive member 26, the developing voltage output waveform observed at the developing voltage output terminal A (A part) is an AC output waveform of the developing voltage as described above. In the rectangular wave 52 having the frequency f, the waveform distortion portion 53 corresponding to the development leak is generated.

  FIG. 5A shows the development voltage output waveform at the development voltage output terminal A when the leak occurs. As shown in the figure, the waveform distortion portion 53 due to the development leak is from the peak level of the rectangular wave 52. Appears as a voltage drop.

  When the developing voltage output leaks, a developing leak occurs between the developing voltage output waveform and the photosensitive member on the plus side of the developing voltage output waveform. Therefore, a voltage drop that falls from the peak level occurs on the plus side of the developing voltage output waveform. As the leak detection means 41 (FIG. 2) for detecting the waveform distortion portion 53 appearing in the rectangular wave 52, a leak detection circuit surrounded by a dotted line in FIG. 3 is provided.

  In this leak detection circuit, in order to extract only the positive side of the development voltage output waveform, a voltage divider composed of a resistor 401 and a resistor 403 is connected between the development voltage output terminal A and the ground 215 via a diode 400. Yes. At that time, the diode 400 connects the anode side to the output terminal A side as shown in the figure, and extracts the analog voltage value on the positive side of the development voltage output waveform from the cathode side. The waveform of the P portion on the cathode side is shown in FIG.

  The voltage across the resistor 403 is obtained from the output terminal C (C section) of the voltage divider. This is an analog voltage output (hereinafter referred to as a development leak detection signal 55) obtained by dividing the analog voltage value of the P section to a level that can be read by the AD converter of the CPU 101, that is, a level of DC 5V or less. FIG. 5C shows the waveform of the development leak detection signal 55 of the C section.

  A Zener diode 402 is connected in parallel to the output resistor 403 constituting the voltage divider. This Zener diode 402 has a Zener voltage of 5.0V, and is for protection so as not to damage the CPU 101 so that the output waveform of the development leak detection signal 55 does not exceed 5.0V.

  The development leak detection signal 55 having the development voltage waveform divided by the voltage divider is sampled for a certain period by the leak detection means 41 (FIG. 2) and discharged (development leak) between the photosensitive member and the development roller. ) Is detected, the waveform distortion portion 53 appearing in the rectangular wave is detected. Here, the certain period to be sampled is one cycle of a rectangular AC voltage waveform constituting the development leak detection signal 55.

  In this example, the development voltage waveform of the A portion is a 2 kHz rectangular wave, and the waveform of the development leak detection signal 55 is also a 2 kHz rectangular wave. The sampling frequency for sampling this waveform is 20 kHz, and sampling is performed 10 times in one cycle to determine whether or not there is a development leak. For example, the waveform distortion portion 53 appearing in the rectangular wave of the development leak detection signal 55 is treated as having development leak if the width (depth) of the voltage drop is not less than a predetermined width (here, 1 V or more).

  With the configuration as described above, development leak can be detected regardless of the time constant of the CR circuit, so that the time required for detection of development leak can be reduced compared to the case where the leak detection circuit is configured using the CR circuit. Can be planned.

  The CPU 101 further includes two arithmetic processing means. The first arithmetic processing means measures the number of waveform distortion portions or the amount of distortion of the waveform distortion portions detected within a predetermined period by the leak detection means 41, and calculates the current leak from the number of waveform distortion portions or the amount of distortion. This is a leak degree calculation means 42 for calculating the degree. Further, the second arithmetic processing means is a value of the developing voltage output outputted by the developing high-voltage power source 108 as the developing voltage generating means according to the current leak degree calculated by the leak degree calculating means, more precisely, an AC voltage. The development voltage control means 43 performs development voltage optimization control by changing the value stepwise and setting the development voltage value to the development voltage value of the appropriate leak level at which the leak starts to occur or the development voltage value just before that.

  Here, the “leakage” is the degree of development leak as seen from the occurrence frequency or the leak level. In the case of the same gap and environment, the leak degree varies depending on the development voltage value. In the case where there is no development leak or the leak level is such that the development leak is acceptable, there is room for further increase in the development voltage value. In the case of an unacceptable leak level, it is necessary to lower the development voltage value and change it to an appropriate development voltage value.

  The “appropriate leak level” is a leak level at a stage where development leak starts to occur when the applied development voltage value is increased, and the development voltage is the development voltage value of the appropriate leak level or the development just before it. Set to voltage value.

  FIG. 6 shows a flowchart of development voltage optimization control.

  In step S1, the development voltage output is set to the initial values Vpp = 1400V and Vdc = + 100V, and the development voltage output is turned ON. This is performed by instructing the developing high-voltage power supply 108 from the CPU 101 using the control line 117 (117a, 117b, 117c). In FIG. 2, 117a, 117b, and 117c in FIG.

  Next, the waveform of the development voltage divided by the voltage divider by the leak detection means 41 is sampled for a certain period, the development leak (waveform distortion portion 53) is detected, and the number of leaks is counted (S2). This is done by counting the waveform distortion portion 53 in the development leak detection signal 55 input from the input line 119 of the CPU 101 by the leak degree calculation means 42.

  The leak degree calculation means 42 is configured such that the count number, that is, the leak number is 0 (leak degree is zero), the leak number is in the range of 3 to 4 (leak degree is 3 to 4), the leak number is in the range of 5 to 6 or more (leak degree) 5 or more), which class is in the range of the number of leaks 1 to 2 (leakage degree 1 to 2) is sequentially examined (S3 to S6). Then, the development voltage control means 43 changes the value of the development voltage in a stepwise manner according to the current leak level, and the development voltage value of the appropriate leak level at which the leak starts to occur or the previous development voltage. Development voltage optimization control to be set to a value is performed (S3 ′ to S5 ′).

  In detail, the leak degree calculation means 42 determines whether or not the count number, that is, the leak number is 0 (S3). When the number of leaks is 0 (leakage is zero), that is, when the development voltage value can be increased, the development voltage control means 43 adds +100 V to the development voltage output Vpp, and returns to step S3 (S3 ').

  If the number of leaks is not 0, the leak degree calculation means 42 determines whether or not the leak number is in the range of 3 to 4 (leak degree 3 to 4) (S4). If the leak number is in the range of 3 to 4, the development voltage value is too high, so the development voltage control means 43 outputs the development voltage output Vpp by subtracting +200 V and returns to step S3 (S4 ').

  If the number of leaks is not 3-4, it is determined in step S5 whether the number of leaks is 5-6 or more (S5).

  If the number of leaks is in the range of 5 or more (leakage level 5 or more), the development voltage output Vpp is reduced by +400 V, and the process returns to step S3 (S5 '). If the number of leaks is not 5 or more, it is determined in step S6 whether the number of leaks is 1 or 2 (S6). If the leak number is in the range of 1 to 2 (leakage degree 1 to 2), the development voltage value at the current leakage degree is stored in the memory 109 via the line 118 (S7). If the number of leaks is not 1 or 2, error processing is performed (S6 ').

  In this error processing, the development voltage value set to the appropriate value in the previous development voltage optimization control is adopted as the voltage value set in the current development voltage optimization control. However, the developing voltage value may be optimized by performing the developing voltage optimization control again. An error may be displayed on the operation panel of the machine.

  The initial value 1400 V in this example is a voltage obtained in advance from the center of the normal distribution of development voltage values at which development leakage occurs.

  Further, as the initial value, the development voltage value that is set to the appropriate value in the previous development voltage optimization control may be used as the initial value, and the current development voltage optimization control may be started from this initial value.

  Further, in the case where a detecting means for detecting that the photoconductor as the image carrier is replaced with a new one is provided, a development voltage value that causes a development leak in advance when the image carrier is determined to be new. The mode value at which development leakage occurs is obtained from the distribution, and development voltage optimization control can be started with this mode as an initial value. That is, when it is determined that the photoconductor is new, the mode development voltage value is obtained from the distribution of known development voltage values that have been determined to be appropriate values in the past development voltage optimization control, and this mode development voltage is obtained. The development voltage optimization control is started with the value as an initial value.

  As described above, according to the present invention, the development voltage optimization control is performed using the development voltage value with an appropriate leak degree as an initial value, so that the development voltage optimization control can be completed in a short time. Therefore, it is possible to reduce deterioration of the photosensitive member and the developing device due to development leak detection and to shorten the waiting time for the user.

  7 and 8 show an example of how the development voltage output waveform is increased or decreased by the development voltage optimization control. This is because the AC voltage value of the developing voltage output from the developing high-voltage power supply 108 is changed stepwise in accordance with the current leak level calculated by the leak level calculating means, and the developing voltage value causes development leakage. The development voltage optimization control for performing the development voltage optimization control to set the development voltage value of the appropriate leak degree to be started or the development voltage value immediately before the development voltage value starts from the initial value and is executed by the development voltage control means 43. .

  FIG. 7 shows development voltage optimization control when the development voltage control means 43 increases the AC voltage value of the development voltage. As shown in FIG. 7, first, an initial value of 1400 V is set over a time width from the time T0 to the time T1 in the first stage, and it is determined whether or not development leakage has occurred. When it is determined that there is no development leak, the time between T1 and T2 in the second stage is set to 1500 V, which is increased by 100 V, and the presence or absence of development leak is determined. Further, if it is determined that there is no development leak, 1600V is set between T2 and T3 in the third stage, and the maximum voltage is set to 1700V between T3 and T4 in the fourth stage. The presence / absence of development leak is determined.

  FIG. 8 shows development voltage optimization control when the AC voltage value of the development voltage is lowered, contrary to FIG. As shown in FIG. 8, when it is determined that a development leak has occurred at a development voltage of 1400V between times T0 and T1, the development voltage is lowered by 100V between T1 and T2 to determine whether there is a development leak. To do. If it is determined that no development leak has occurred, the voltage is further set to 1200 V between times T2 and T3 to determine whether or not development leak has occurred. Similarly, 1100V is set between time T3 and T4, and 1000V is set between time T4 and T5 to determine whether or not development leakage has occurred.

  If sampling is performed at the above sampling frequency of 20 kHz, it is possible to detect a development leak in one cycle of the development voltage output waveform. However, with a sufficient margin, the development leak is detected for 20 cycles of the development voltage output waveform, that is, 10 ms. Set as a predetermined time for. Since switching of the voltage value of the development voltage output takes about 30 ms, a total of 40 ms is set. Therefore, according to this example, the development leak can be detected from the time T0 to T5 at 40 ms × 5 = 200 ms, and the time can be significantly reduced as compared with the conventional method.

  The development leak is different in frequency of occurrence or the degree of development leak (leak degree) as seen from the leak level depending on the development voltage value. In the case where there is no development leak at all or the leak degree is such that the development leak is acceptable, the development voltage value is further increased. If the leak rate is unacceptable, the developing voltage value is lowered and changed to an appropriate developing voltage value.

  As a criterion for judging whether the degree of leakage is good or bad, here, when the voltage drop of 1 V of the waveform distortion portion 53 is 1 to 2 in 10 ms corresponding to 20 cycles of the development voltage output waveform, FIG. As shown in steps S6 and S7 of the flow, it is determined that there is an allowable development leak. When the voltage drop of 1V is 3-4, the two-step (200V) voltage is lowered. Further, when the voltage drop of 1V is 5 to 6, it is possible to further reduce the time required for the development voltage optimization control by lowering the four-step (400V) voltage.

  On the other hand, when the voltage drop of 1V is 0, the voltage is increased step by step (100V), and it is determined that development leakage has occurred when the voltage drops to one or two. Further, if the development voltage at the time of the previous development leak is stored in the memory 109 and this development voltage is used as an initial value as the development voltage for the next development leak detection, the development leak detection time can be further shortened. Become.

  When the developing device is replaced with a new one, the default value (1400 V) at the time of factory shipment is used instead of the default value.

  In the above-described embodiment, the description has focused on the K color process unit K. However, similar development voltage optimization control is performed individually for other Y color, M color, and C color process units, and appropriate development is performed. Set to voltage.

[Comparative example]
Next, a comparative example will be described. FIG. 9 shows the circuit configuration of the developing high-voltage power supply 108, which is the same as that shown in FIG. 3 except for the portion of the leak detection circuit surrounded by a broken line. FIG. 10 shows waveforms of the respective parts of the P1, P2, and P3 parts of the leak detection circuit.

  The current supplied from the power source DC24V denoted by reference numeral 216 reaches the developing voltage output terminal A denoted by reference numeral 217 via the resistor 301. When the developing voltage is gradually increased and a developing leak occurs, the electric charge is charged from the capacitor 302. Moves, and the potential of the capacitor 302 (P1 portion potential) drops from V1 (V) to V1 ′ (V) (see FIG. 10A).

  When the potential of the capacitor 302 (P1 portion potential) drops, a charge current flows into the capacitor 302 from the power source DC24V indicated by reference numeral 216 through the resistor 301, and the potential is increased. As a result, the potential after the capacitor 303 and the resistor 304 (the potential at the P2 portion) rises from 0 V to V2 (V) (see FIG. 10B).

  The capacitor 306 holds the charge at this time, and the operational amplifier 307 amplifies the potential at the P2 portion and outputs it as a leak detection output B (potential at the P3 portion) (see FIG. 10C). The amplifier circuit by the operational amplifier 307 is a non-inverting amplifier circuit, and outputs B = (1 + resistance value of resistor 308 / resistance value of resistor 309) × (P2 part) as a leak detection output B indicated by reference numeral 310 by resistors 308 and 309. Amplified to a potential of 1). The output B is V3 (V) shown in FIG.

  As described above, the leak detection circuit of the comparative example is configured to be affected by the time constant of CR, and the capacitor 306 is discharged via the resistor 305 to discharge the charge charged by the development leak. However, if the resistance value of the resistor 305 is made small, the time for holding the charge charged in the capacitor 306 may be too short. In addition, if the resistance value of the resistor 305 is excessively increased, there is a problem that the leak cannot be detected if there is a second or subsequent development leak before discharging the electric charge held in the capacitor 306. For this reason, a time constant of about 50 ms is generally set.

  Thus, it is necessary to set a time longer than the above time constant and gradually increase the development voltage to detect the presence or absence of development leak. In the comparative example, the development voltage for development leak detection set in the development voltage optimization control is increased every 500 ms to detect the presence or absence of development leak.

  FIG. 11 shows a sequence example in which the development voltage is raised until the development leak is detected in the comparative example.

  In this example, the initial value is set to Vpp = 1000V from time T0 to T1, 1100V from T1 to T2, 1200V from T2 to T3, 1300V from T3 to T4, 1400V from T4 to T5, 1400V from T5 to T6 The development voltage Vpp is increased every predetermined time (every 500 ms) such that the voltage is 1500V, the time from T6 to T7 is 1600V, and the time from T7 to T8 is 1700V. Vdc is set to a constant DC voltage + 100V. In this example, by setting Vdc to the plus side, leakage is caused on the plus side of Vpp with respect to the surface potential of −450 V of the photoconductor. This is because it is desired to detect a development leak in a state closer to the printing state, in a state where the surface potential of the photosensitive member is -450V.

  In this comparative example, it takes a maximum of 4000 ms until the development voltage Vpp is increased from 1000 V to 1700 V to detect a development leak. This is because in the development voltage optimization control for detecting the development voltage that causes an appropriate development leak, the photosensitive member and the developing device are driven for a relatively long time, which is preferable in terms of promoting the deterioration of the life of these. Absent. Further, in the case of the comparative example, the development voltage optimization control is performed every predetermined number of printed sheets or in the image stabilization control at the time of replacement of the developing device and the photosensitive member. Absent. It is better to make it as short as possible.

  On the other hand, according to the above embodiment of the present invention, the number of waveform distortion portions that appear in a rectangular wave due to the occurrence of a leak is counted rather than a charge / discharge circuit using a capacitor and a resistor as in the leak detection circuit of the comparative example. Alternatively, since the circuit configuration measures the distortion amount of the waveform distortion portion, it is possible to shorten the time required for the leak degree detection operation.

[Modification]
In the above embodiment, the number of waveform distortion portions that appear in a rectangular wave due to the occurrence of a leak is measured and the current leakage degree is determined from the number. However, the present invention is not limited to this, and the distortion of the waveform distortion portion is not limited thereto. The amount of leakage may be measured, and the current leak degree may be determined from the amount of distortion.

  In the above-described embodiment, the AC voltage value of the development voltage is variably controlled step by step up to the development voltage value at which the development leak starts to occur according to the current leak level, but the development voltage value immediately before the development leak starts to occur. Variable control may be performed step by step.

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine or printer having a non-contact developing type image forming unit that moves toner from a toner carrier to an image carrier to visualize an electrostatic latent image. Suitable.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus illustrated in FIG. 1. FIG. 2 is a circuit diagram illustrating a configuration of a high-voltage power supply for development of the image forming apparatus illustrated in FIG. 1. It is the figure which showed the waveform of the developing voltage obtained at the output terminal A of the high voltage power supply for development of FIG. It is the figure which showed the waveform of each part of the leak detection circuit of this invention. 3 is a flowchart illustrating an example of development voltage optimization control according to the present invention. It is the figure which showed the case where the developing voltage value is made high in the developing voltage optimization control of this invention. It is the figure which showed the case where the developing voltage value is made low in the developing voltage optimization control of this invention. It is the circuit diagram which showed the structure of the high voltage power supply for development of a comparative example. It is the figure which showed the waveform of each part of the leak detection circuit of a comparative example. FIG. 10 is a diagram illustrating an example of a sequence in which a development voltage is raised until a development leak is detected in a comparative example.

Explanation of symbols

1 paper cassette,
2 paper feed rollers,
3 Paper feed path,
4 Timing roller,
5 Secondary transfer roller,
6 Opposing roller,
7 Fixing roller,
8 Transfer belt,
10 Y-color primary transfer roller,
11 Y color image carrier (photosensitive member),
12 Development roller (toner carrier) for developing Y color toner,
13 Y color print head,
15 primary transfer roller for M color,
16 image carrier for M color (photoconductor),
17 Development roller (toner carrier) for developing M color toner,
18 M color print head,
Primary transfer roller for 20 C color,
Development roller (toner carrier) for 21 C color toner development,
22 C color image carrier (photosensitive member),
23 C color print head,
Primary transfer roller for 25 K color,
26 K color image carrier (photoconductor)
27 developing roller for K color toner development (toner carrier),
28 K color print head,
30 Timing sensor,
31 toner density detection sensor,
Development motor for developing 33 K color toner,
Development motor for 34 C color toner development,
Development motor for 35 M toner development,
36 Development motor for Y toner development,
41 leak detection means,
42 Leak degree calculation means,
43 Development voltage control means,
52 square wave,
53 Waveform distortion portion 55 Development leak detection signal 100 Control board,
101 CPU,
102 image control unit,
103 Image controller,
104 print head,
105 High-voltage power supply for secondary transfer,
106 high-voltage power supply for charging,
107 high-voltage power supply for primary transfer,
108 High-voltage power supply for development,
109 memory,
111 image data lines,
112, 114-117 control line,
113 connection lines,
119 AD port input line,
200-202 transformer drive control circuit,
203 AC transformer,
204, 205 DC transformer,
206, 211 resistance,
207, 210, 213 capacitors,
209, 212 Rectifier diode,
214, 301 resistors.

Claims (5)

An image carrier on which an electrostatic latent image is formed and a toner carrier that carries toner are arranged apart from each other, and a rectangular wave AC voltage is applied to the toner carrier, and the image is transferred from the toner carrier. In an image forming apparatus of a non-contact development system that visualizes an electrostatic latent image by moving toner to a carrier,
Developing voltage generating means for generating a developing voltage having a waveform in which a DC voltage is superimposed on the AC voltage of the rectangular wave, and applying the developing voltage to the toner carrier;
A voltage divider for dividing the developing voltage;
The waveform of the developing voltage divided by the voltage divider is sampled for a certain period, and a waveform distortion portion appearing in the rectangular wave is detected when a leak occurs between the image carrier and the toner carrier. Leak detection means to
The degree of leakage that measures the number of waveform distortion portions or the amount of distortion of the waveform distortion portions detected within the predetermined period by the leak detection means, and calculates the current leakage degree from the number of waveform distortion portions or the amount of distortion. A calculation means;
The development voltage value output from the development voltage generation unit is changed stepwise according to the current leak level calculated by the leak level calculation unit, and the development voltage value is set to an appropriate leak level at which the leak starts to occur. Development voltage control means for carrying out development voltage optimization control to set the development voltage value of
An image forming apparatus comprising:   2. The developing voltage control unit according to claim 1, wherein the developing voltage control means sets the developing voltage value, which is set to an appropriate value in the previous developing voltage optimizing control, as an initial value, and starts the developing voltage optimizing control from the initial value. The image forming apparatus described.   The development voltage control means obtains a development voltage value of a mode value from a distribution of known development voltage values set to an appropriate value in the past development voltage optimization control, and uses the development voltage value of the mode value as an initial value. The image forming apparatus according to claim 1, wherein the development voltage optimization control is started. It further has a detecting means for detecting that the image carrier is replaced with a new one,
When the image bearing member is determined to be new by the detection means, the development voltage control means determines the most frequent development voltage from the distribution of known development voltage values determined as appropriate values in the past development voltage optimization control. 4. The image forming apparatus according to claim 1, wherein a value is obtained, and the developing voltage optimization control is started with the mode developing voltage value as an initial value.   5. The leak detection unit according to claim 1, wherein the leak detection unit samples one cycle of the waveform of the AC voltage in the development voltage or N cycles of an integral multiple thereof as the fixed period. The image forming apparatus described.

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