JP2010210994A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of quickly finding more accurate appropriate Vpp, corresponding to an environmental change. <P>SOLUTION: The image forming apparatus includes a charging device 34 for charging a photoreceptor drum 29; a charging bias generation part 41 for applying a charging bias obtained by superposing an AC voltage to a DC voltage to the charging device 34; a calibration mode execution part 54 for executing calibration at predetermined timing; a storage part 52 for storing a first AC inter-peak voltage (Vpp1), set previously in a table in each predetermined in-machine atmospheric temperature; and a control circuit part 51 for controlling the charging bias generating section 41 by utilizing the first AC inter-peak voltage (Vpp1) stored in the storage part 52, determining the first AC inter-peak voltage (Vpp1) necessary for the charging of the photoreceptor drum 29 at the timing of calibration execution by the calibration mode execution part 54, and charging the photoreceptor drum by a second AC inter-peak voltage (Vpp2) corrected by using the first AC inter-peak voltage (Vpp1) as a reference value at the start of printing. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a charging device that is arranged in contact with or close to an image carrier and charges the surface of the image carrier by applying a charging voltage in which a DC voltage generated by a charging bias applying means and an AC voltage are superimposed. The present invention relates to an image forming apparatus including

  2. Description of the Related Art Conventionally, there has been known an image forming apparatus in which a contact charging type or proximity charging type charging device using a charging principle as a charging principle is arranged to charge the surface of a photosensitive drum as an image carrier.

  At this time, the charging device of the contact charging method or the proximity charging method can realize a lower voltage of the power source and has less ozone generation than the non-contact charging device such as Scorotron. have.

  In addition, a contact charging method or a proximity charging method charging device includes a method in which a charging voltage obtained by superimposing an AC voltage (Vac) on a DC voltage (Vdc) is applied.

  This method of applying the charging voltage is characterized by excellent charging uniformity by applying Vac, while the discharge current of Vac superimposed on the discharge current of Vdc damages the surface of the photosensitive drum. Further, there has been a problem that the life of the image forming apparatus is shortened such that the surface of the photosensitive drum is easily scraped.

  At this time, it is known that the damage to the surface of the photosensitive drum has an adverse effect as the peak-to-peak voltage (Vpp) of the applied Vac increases.

  Therefore, it is preferable that Vpp is small. However, if Vpp is too small, uniform charging becomes difficult and image defects such as white spots are generated. For example, Vpp has a minimum value for uniform charging. The necessary Vpp (Vmin) is present.

  Further, Vmin varies greatly due to environmental variation and temporal variation of the resistance of the charging device, and is not constant.

  Therefore, as a technique for changing Vpp according to environmental changes, a technique for determining an appropriate Vpp based on the saturation point of DC current (Idc) (see, for example, Patent Document 1), or a current (Iac) generated by Vpp is detected. A technique for determining aptitude Vpp (see, for example, Patent Document 2) is known.

JP 2007-065401 A JP 2006-276056 A

  However, as described above, the image forming process (printing) environment changes only by changing the Vpp according to the environmental change, for example, the initial printing after the power is turned on, and the intermittent printing in which the time is opened so as not to enter the sleep mode. Vpp could not be changed in response to the occurrence of a deviation between the temperature change of the photosensitive drum such as continuous printing and the change in the atmosphere temperature in the apparatus.

  Further, in order to make it in time for the first printing (first print) after the power is turned on, there has been a problem that if Vpp is set based on the environmental temperature, only rough setting can be performed.

  Therefore, when a Vpp higher than the appropriate Vpp is set, the surface temperature of the photosensitive drum rises during continuous printing. Therefore, if the printing is continued, the appropriate value of Vpp will be further deviated, resulting in excess. There has been a problem that Vpp is applied.

  In particular, such a problem becomes conspicuous in a low temperature environment. When such an excessive application environment of Vpp continues, not only the surface of the photosensitive drum is contaminated by the adhesion of discharge products, but also, for example, the photosensitive drum This causes a problem that the cleaning blade in contact with the surface of the toner is damaged and the charging device is contaminated by the developer (toner) slipping through.

  In order to charge the photosensitive drum, an image forming apparatus that applies a charging voltage in which an alternating voltage (Vac) is superimposed on a direct current voltage (Vdc), particularly a sensor that detects the surface temperature and humidity of the photosensitive drum, and the like. In a relatively inexpensive low-end model that is not arranged, if the AC voltage Vpp is determined only by the in-machine temperature, the difference between the surface temperature of the photosensitive drum and the in-machine temperature is even greater when continuous printing is performed. Thus, Vpp is applied more than necessary.

  Therefore, useless discharge is likely to occur, and the surface of the photosensitive drum is contaminated by discharge products, resulting in a problem that the coefficient of dynamic friction increases, causing damage to the cleaning blade and defective cleaning.

  Further, in recent image forming apparatuses, the first print has been shortened, and the time required for charging correction is limited. Therefore, it has been necessary to set an appropriate Vpp in a shorter time.

  In view of the above circumstances, an object of the present invention is to provide an image forming apparatus capable of obtaining a more accurate appropriate Vpp according to environmental changes in a short time.

  An image forming apparatus according to the present invention includes a charging device that charges an image carrier, a charging bias generator that applies a charging bias in which an AC voltage (Vac) is superimposed on a DC voltage (Vdc), and a predetermined timing. A calibration mode execution unit for executing calibration, a storage unit for storing a first AC peak-to-peak voltage (Vpp1) preset in a table in a predetermined in-machine atmosphere temperature unit, and a first stored in the storage unit And a control circuit unit that controls the charging bias generation unit using an AC peak-to-peak voltage (Vpp1) of 1. The control circuit unit performs calibration by the calibration mode execution unit The first AC peak-to-peak voltage (Vpp1) necessary for charging the image carrier is determined at the timing, and at the start of printing As it charged corrected second AC peak-to-peak voltage (Vpp2) first AC peak-to-peak voltage (Vpp1) as a reference value, and controlling the charging bias generator.

  At this time, it is preferable that the control circuit unit corrects the appropriate Vpp with a vertical width smaller than the vertical width of the first AC peak-to-peak voltage (Vpp1) stored in the storage unit.

Further, it is preferable that the control circuit unit determines the vertical width of the correction value of the appropriate Vpp based on the detection result of the direct current Idc flowing into the image carrier.
According to the image forming apparatus of the present invention, the first AC peak-to-peak voltage (Vpp1) is determined at the calibration execution timing, and based on the first AC peak-to-peak voltage (Vpp1) at the start of the printing operation. By determining the correct appropriate Vpp, the correction of the first AC peak-to-peak voltage (Vpp1) can be performed for each calibration performed periodically, and a stable appropriate Vpp can be determined. In particular, there is a difference between the surface temperature change of the photosensitive drum and the change in the atmosphere temperature in the machine when continuous printing is continued, and the first AC peak-to-peak voltage (Vpp1) determined by the change in the machine atmosphere temperature is actually necessary. The problem that the difference is different from Vpp can be solved.

  The image forming apparatus of the present invention can determine a more accurate appropriate Vpp in a short time according to environmental changes.

1 is an explanatory diagram of a printer as an image forming apparatus according to an embodiment of the present invention. FIG. FIG. 3 is an explanatory diagram of a main part in an image forming apparatus according to an embodiment of the present invention. It is explanatory drawing of the 1st alternating current peak-to-peak voltage (Vpp1) table in the image forming apparatus which concerns on one Embodiment of this invention. FIG. 6 is a flowchart showing a routine 1 of calibration execution timing in the image forming apparatus according to the embodiment of the present disclosure. FIG. 6 is a flowchart showing a routine 2 for calibration execution timing in the image forming apparatus according to the embodiment of the present disclosure. FIG. 10 is a flowchart showing a routine 3 for calibration execution timing in the image forming apparatus according to the embodiment of the present disclosure. FIG. 9 is a flowchart showing a routine 4 for calibration execution timing in the image forming apparatus according to the embodiment of the present disclosure. FIG. 6 is a flowchart of a Vpp correction control routine in the image forming apparatus according to an embodiment of the present invention. It is a graph which shows the example of a fluctuation | variation of Vpp at the time of continuous printing.

  Next, embodiments of the image forming apparatus according to the present invention will be described with reference to the drawings. The following embodiments are preferred specific examples of the image forming apparatus of the present invention, and may have various technically preferred limitations. However, the technical scope of the present invention is particularly limited to the present invention. As long as there is no description which limits, it is not limited to these aspects.

  FIG. 1 is an explanatory diagram of a printer as an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of a main part of the image forming apparatus according to an embodiment of the present invention.

(Overall configuration of image forming apparatus)
As shown in FIG. 1, a printer 11 as an image forming apparatus according to an embodiment of the present invention includes a paper feed cassette 13 that is slidably stored inside a printer main body 12, and a storage space for the paper feed cassette 13. 14, a paper feed unit 15 for taking out transfer paper (not shown) stored in the paper 14, a manual paper feed tray 16 disposed in front of the printer main body 12, and a transfer paper (not shown) set in the manual paper feed tray 16. A manual paper feed unit 17 for taking out the paper, a transport path 18 for transporting the transfer paper supplied from each of the paper feed units 15 and 17, and an upstream side (hereinafter referred to as transfer paper transport direction of the transport path 18). A registration roller pair 19 disposed on the downstream side of the merging portion of each of the paper feeding units 15 and 17 and a toner container disposed on the downstream side of the conveyance path 18 relative to the registration roller pair 19. Supply from 20 An image forming unit 21 that forms a transfer image on one surface of the transfer paper with a developer such as toner, and a toner image that is disposed on the downstream side of the conveyance path 18 relative to the image forming unit 21 and formed on one surface of the transfer paper In the double-sided printing mode in which a transfer image is also formed on the other surface of the transfer paper that has passed through the fixing device 22, the registration roller pair 19 from the downstream side of the fixing device 22 in the conveyance path 18. A reversing path 23 for pulling back the transfer paper to the upstream side of the transport path 18 and a paper discharge section 24 provided at the terminal end (most downstream end) of the transport path 18 are provided.

(Configuration of toner container 20)
The toner container 20 stores replenishment toner inside the container body 25. The replenishing toner is agitated by a paddle 26 made of a flexible resin material or the like, and is conveyed by the spiral 27 in the transfer paper width direction (the depth direction in FIG. 1), and then forms an image at the predetermined position. Supplied to the developing device 28 of the section 21.

(Configuration of developing device 28)
The developing device 28 supplies the toner for replenishment supplied from the toner container 20 to the photosensitive drum 29 of the image forming unit 21 while stirring, and a pair of spirals 31 is partitioned inside by a partition wall 30. , 32 are arranged.

  Both ends of the partition wall 30 (in the depth direction in FIG. 1) are open so as to communicate between both ends of the spirals 31 and 32, and are directed toward one side of the developing device 28 by the spiral 31 provided below the spiral 27. After the toner is agitated and conveyed (forward path), the toner is turned back at the open end of the partition on one side, and the replenishing toner is agitated and conveyed (return path) toward the other side of the developing device 28 by the spiral 32. A circulation conveyance path is formed that is turned back again at the open end of the partition wall. In parallel with the spiral 32, a developing roller 33 for supplying replenishing toner is disposed in the vicinity of the photosensitive drum 29.

  The developing roller 33 is disposed so that the peripheral surface thereof faces the peripheral surface of the photosensitive drum 29. Accordingly, the replenishment toner being conveyed to the developing roller 33 is supplied to the peripheral surface of the photosensitive drum 29 via the developing roller 33, thereby forming a toner image on the peripheral surface of the photosensitive drum 29. Become. At this time, the developing roller (magnet roller) 33 supplies the toner to the photosensitive drum 29 while appropriately stirring so as not to aggregate the toner.

(Configuration of the image forming unit 21)
The image forming unit 21 includes, for example, a charging device 34, an exposure device 35, and a developing device 28 in the order of the image forming process along the rotation direction of the photosensitive drum 29 (see the arrow in the drawing) around the photosensitive drum 29 made of amorphous silicon. (Developing roller 33)-Transfer device 36-Cleaning device 37-Static elimination device 38 are provided.

(Configuration of charging device 34)
As shown in FIG. 2, the charging device 34 includes a charging roller 39 that comes into contact with the surface of the photosensitive drum 29, and a removing roller 40 such as a fur brush that removes surface deposits on the charging roller 39.

  Further, a charging bias obtained by superimposing an AC voltage (Vac) on a DC voltage (Vdc) is applied to the charging roller 39 from the charging bias generator 41.

  The charging bias generator 41 includes an AC power source 42 and a DC power source 43 arranged in parallel. The voltmeter 44 detects the AC voltage Vpp of the AC power source 42, and the ammeter 45 flows into the photosensitive drum 29. A direct current Idc of the DC power supply 43 is detected.

(Configuration of exposure device 35)
The exposure device 35 processes image data included in print data transmitted from a personal computer (not shown), for example, and irradiates the surface of the photosensitive drum 29 with the laser light P. In addition to the above-described image data, the print data here includes, for example, data relating to various settings such as the number of image forming processing copies, enlargement / reduction ratio, and image density.

(Configuration of transfer device 36)
A transfer voltage is applied to the transfer device 36 from a DC power supply 46, and a toner image formed on the surface of the photosensitive drum 29 is applied in cooperation with the photosensitive drum 29 while the transfer paper S is conveyed through the nip. Transfer by voltage.

(Configuration of static elimination device 38)
For example, an LED light source or the like is used as the charge removal device 38, and the photosensitive drum 29 charged by the charging device 34 is discharged.

(Configuration of Fixing Device 22)
The fixing device 22 includes a pair of a fixing roller 47 and a pressure roller 48 that are disposed to face each other with the conveyance path 18 therebetween, and a heating source 49 such as a halogen heater that is disposed inside the fixing roller 47 and directly heats the fixing roller 47. And a fixing thermistor 50 that detects the surface temperature (fixing temperature) of the fixing roller 47.

(Example)
In the above configuration, in the image forming unit 21, the photosensitive drum 29 is rotationally driven at a predetermined process speed (circumferential speed) by a driving unit (not shown), and the surface thereof is charged by the charging device 34.

  An electrostatic latent image is formed on the surface of the charged photosensitive drum 29 by the exposure device 35. Here, the exposure device 35 irradiates the surface of the photosensitive drum 29 with the laser beam P based on the image data included in the print data output from the personal computer or the like, and irradiates the surface of the photosensitive drum 29 with the laser beam. An electrostatic latent image corresponding to the image information is formed by removing the charge of the portion.

  The electrostatic latent image formed on the surface of the photosensitive drum 29 is developed as an unfixed toner image by electrostatically attaching the toner having the charge supplied from the toner container 20 by the developing device 28. Further, the unfixed toner image is transferred onto the transfer paper S by the transfer device 36 as a transfer image.

  At this time, the photosensitive drum 29 on which the unfixed toner image is transferred onto the transfer sheet S is subjected to a removal process of residual toner and the like by the cleaning device 37, and then is charged by the charge removal device 38 for charging at the next image formation. A static elimination process is performed.

  On the other hand, the surface temperature of the fixing roller 47 detected by the fixing thermistor 50 is output to the control circuit unit 51, and the temperature of the heating source 49 is controlled according to the detected temperature.

  At this time, the heating temperature management of the heating source 49 by the control circuit unit 51 is based on the fixing temperature control data associated with the surface detection temperature of the fixing roller 47 and the heating temperature of the heating source 49 stored in the storage unit 52. Managed.

  The storage unit 52 includes a control program for charging bias control related to the charging bias generation unit 41 of the present invention, and detection using a temperature monitoring sensor 53 and a fixing thermistor 50 that are disposed inside the printer main body 12 and detect the in-machine temperature. A control program for controlling the calibration mode execution unit 54 for executing the calibration mode according to the temperature is also stored, and the control circuit unit 51 for executing these various control programs constitutes a microcomputer.

  In addition, as shown in FIG. 3, the storage unit 52 stores control data in which the in-machine atmosphere temperature detected by the temperature monitoring sensor 53 and the first AC peak-to-peak voltage (Vpp1) by the AC power source 42 are associated in a table manner. Stored.

  Note that print data, image data, and the like when executing the image forming process are temporarily stored in a storage device (not shown) such as another RAM or HDD when the storage unit 52 is a ROM. However, in the present embodiment, description will be made as a writable functionally one storage device that stores the in-machine temperature detected by the temperature monitoring sensor 53 for the control of the charging bias generator 41.

  The calibration mode execution unit 54 also prevents the above-described fixing thermistor from changing in print results (image quality) due to changes in the environment such as the ambient temperature and humidity in the apparatus and the use of consumable members such as toner. 50, the temperature monitoring sensor 53, or the control circuit 51 based on output information from the print counter 55 that counts the number of printed sheets, for example, the charging device 34 that uniformly charges the photosensitive drum 29, the photosensitive drum Control of potential and bias of an exposure device 35 that exposes 29 to form an electrostatic latent image, a developing device 28 that visualizes the electrostatic latent image into a toner image, and a transfer device 36 that transfers the visualized toner image onto a transfer medium In addition, the calibration of the erase light quantity of the static elimination device 38 is executed.

  Specifically, as shown in FIG. 4, the control circuit unit 51 monitors whether or not the main power source of the printer main body 12 is turned on (step S11), and when the main power source is turned on, the fixing thermistor 50 is turned on. Is compared with the threshold temperature (eg, 50 ° C.) of the calibration execution timing stored in the storage unit 52 (step S12), and calibration is executed when the detected temperature is equal to or lower than the threshold temperature (step S12). S13).

  If the detected temperature of the fixing thermistor 50 when the main power is turned on is equal to or higher than the threshold temperature of the calibration execution timing, the temperature monitoring sensor 53 detects the ambient temperature in the apparatus (step S14), and the detection. The charging roller 39 is charged by a charging bias using the first AC peak-to-peak voltage (Vpp1) corresponding to the temperature (step S15).

  Further, as shown in FIG. 5, the control circuit unit 51, for example, inputs print data from a personal computer in a case where a known sleep mode is being executed with the main power turned on. In response to this (step S21), the temperature monitoring sensor 53 detects the internal atmosphere temperature before starting printing (step S22), and the internal atmosphere temperature before the start is stored in the storage unit 52 (step S23). In addition, printing is started and printing count of the printing counter 55 is started for use in a continuous printing state to be described later (step S24), and every time printing on the transfer sheet S or a predetermined number of sheets (for example, every 5 sheets) is started. The temperature monitoring sensor 53 detects the current atmospheric temperature inside the machine at the timing (step S25), and the current atmospheric temperature inside the machine is stored in the storage unit 52. In step S26, the in-machine atmosphere temperature at the start of printing is compared with the current in-machine atmosphere temperature (step S27), and the temperature difference (absolute value) of each in-machine atmosphere temperature is stored in the storage unit 52 at the calibration execution timing. Calibration is performed when the temperature becomes a threshold temperature (for example, 5 ° C.) or more (step S28).

  If the temperature difference (absolute value) between the in-machine atmosphere temperature at the start of printing and the current in-machine atmosphere temperature is equal to or lower than the threshold temperature of the calibration execution timing during printing, for example, in step S15 described above. The charging roller 39 is charged by the charging bias based on the first AC peak-to-peak voltage (Vpp1) used or the first AC peak-to-peak voltage (Vpp1) used last time stored in the storage unit 52 described later (step S29). .

  The routine shown in FIG. 5 is used for continuous printing with a relatively small number of printed sheets.

  Further, in parallel with the routine for continuous printing with a relatively small number of printed sheets shown in FIG. 5, the control circuit unit 51 performs continuous printing with a relatively large number of sheets as shown in FIG. In addition, calibration is executed as necessary even during the printing.

  That is, the control circuit unit 51 continuously performs the print count up by the print counter 55 (step S31), monitors the continuous print count number (step S32), and executes the calibration execution timing stored in the storage unit 52. The charging roller 39 is continuously charged with the charging bias using the first AC peak-to-peak voltage (Vpp1) such as the initial (step S15 or step S29) until reaching the continuous printing number (for example, 100 sheets) (step S33). ) When the number of continuous prints at the calibration execution timing is reached, calibration is executed (step S34).

  Further, after the calibration is executed, if there is print data that has not been subjected to the printing process (step S35), the printing is performed more than the number of continuous prints at the calibration execution timing. After performing a Vpp correction routine to be described later (step S36), printing is resumed (step S37), the count of the print counter 55 is reset, and printing count-up is resumed (step S38).

  Further, after the calibration is executed, if there is no print data that has not been subjected to the printing process, the first AC peak-to-peak voltage (Vpp1) used is stored in the storage unit 52 (step S39). The process proceeds to step S38.

  The control circuit unit 51 uses a timer (not shown) for executing a known sleep mode, for example, during a predetermined time period from the end of printing in each use mode described above to entering the sleep mode ( For example, in the case of intermittent printing in which print data is input during 15 minutes), for example, instead of monitoring the continuous print count in step S32 of FIG. 6 described above, as shown in FIG. When the count of the print counter 55 since the previous calibration has reached the number of continuous prints (for example, 200) at the calibration execution timing stored in the storage unit 52 (step S42), the calibration is executed. For example, a known control example can be used for the calibration execution timing itself.

  Next, a control routine of charging bias control (Vpp correction control) for the charging bias generator 41 according to the present invention by the control circuit 51 will be described with reference to FIG.

  In the following description, due to a large number of printing processes associated with continuous printing and intermittent printing, the atmospheric temperature inside the machine is 35 ° C. or more, which is the maximum setting, and the first AC peak-to-peak voltage (Vpp1) is 1000V. It will be explained as a thing.

(Step S51)
In step S51, the control circuit unit 51 receives the calibration at 35 ° C. or higher, which is the maximum setting of the internal atmospheric temperature, and boosts the first AC peak-to-peak voltage (Vpp1) from 1000V to 200V to 1200V. Then, the process proceeds to step S52.

(Step S52)
In step S52, the control circuit 51 determines whether or not the direct current Idc of the DC power source 43 flowing into the photosensitive drum 29 detected by the ammeter 45 has reached the saturation state, and the change amount of the direct current Idc is stored in the storage unit. 52. When the DC current Idc has not reached the saturation state, the process loops to step S41 to further increase the voltage Vpp by 200 V to determine whether the DC current Idc has reached the saturation threshold (for example, 10 μA) stored in 52 or not. When Idc reaches a saturated state, the process proceeds to step S53.

(Step S53)
In step S53, the control circuit unit 51 stores Vpp (saturated Vpp) when the direct current Idc reaches the saturation state in the storage unit 52, and proceeds to step S54.

(Step S54)
In step S54, the control circuit unit 51 starts a printing operation with the boosted first AC peak-to-peak voltage (Vpp1), and proceeds to step S55.

(Step S55)
In step S55, the control circuit unit 51 reduces the saturated Vpp stored in the storage unit 52 by 200V, boosts Vpp by 50V, and proceeds to step S56.

(Step S56)
In step S56, the control circuit unit 51 continuously monitors the DC current Idc of the DC power supply 43 flowing into the photosensitive drum 29 detected by the ammeter 45, and the DC current Idc changes in a state where it is boosted by 50V in step S45. It is monitored whether or not the amount is equal to or less than the boost stop threshold (for example, 3 μA) stored in the storage unit 52. If the change amount of the direct current Idc does not reach the boost stop threshold, the process loops to step S45. Then, Vpp is further boosted by 50 V, and when the change amount of the DC current Idc reaches the boost stop threshold or less, the process proceeds to step S57.

(Step S57)
In step S57, the control circuit unit 51 determines Vpp when the change amount of the direct current Idc has reached the boost stop threshold value or less in step S56 as the appropriate Vpp, and stores the corrected aptitude Vpp in the storage unit 52. This routine ends.

  The appropriate Vpp stored in the storage unit 52 is applied as the appropriate Vpp at the time of resuming printing in step S37 described above.

  By the way, the charging bias control (Vpp correction control) shown in the present embodiment is different in the numerical value (for example, boost stop threshold = 3 μA, etc.) depending on the system, but the transfer sheet S is in direct contact with the photosensitive drum 29. In particular, when the double-side printing is performed by the transfer method, the surface temperature of the photosensitive drum 29 is likely to fluctuate, which is very effective.

  In the system in which the transfer sheet S contacts the photosensitive drum 29, as shown in FIG. 9, when printing starts in a low temperature environment, Vpp requires an output of 1700 V or more, but 500-sided printing ends. Around 1300V changes to a sufficient state.

  At this time, if the dynamic friction coefficient of the surface of the photosensitive drum 29 immediately after the start of printing is about 0.3, if Vpp is applied excessively by 400 V, the photosensitive drum after 500 transfer sheets S are printed. The surface 29 has a high dynamic friction coefficient of 0.6 to 0.7.

  Therefore, if printing is continued in such a high state, the cleaning device 37 that comes into contact with the surface of the photosensitive drum 29 is damaged such as chipping or wobbling, abnormal noise is generated, image defects due to toner slipping, Since it becomes a factor which causes the contamination of the charging device 34, it is very important to set an appropriate Vpp.

  As described above, according to the image forming apparatus of the present invention, the first AC peak-to-peak voltage is obtained when the calibration associated with the in-machine temperature fluctuation is performed when the main power is turned on or when continuous printing is performed. (Vpp1) is boosted in units of 200 V, and the saturation point is when the amount of change in the direct current Idc of the DC power supply 43 flowing into the photosensitive drum 29 becomes equal to or less than a specified amount (saturation threshold = 10 μm).

  During subsequent printing, the amount of change in the DC current Idc of the DC power source 43 flowing into the photosensitive drum 29 is changed below the boost stop threshold (for example, 3 μA) by changing Vpp in units of 50 V from the determined saturation Vpp-200 V. By determining this as the correct appropriate Vpp, it is possible to determine the optimum Vpp that matches the current state of the photosensitive drum 29, rather than determining Vpp based only on the in-machine atmospheric temperature.

  In the above-described embodiment, the image forming apparatus of the present invention is applied to the printer 11 that is a monochrome printer. However, the image forming apparatus can be applied to all image forming apparatuses such as a color printer and a multifunction machine. It is.

  At this time, especially in a relatively inexpensive low-end model that does not have a sensor or the like for detecting the surface temperature or humidity of the photosensitive drum 29, a deviation occurs between the in-machine atmosphere temperature and the surface temperature of the photosensitive drum 29. Even so, the corrected second AC peak-to-peak voltage (Vpp2) can be applied, and the first print time can be shortened by the optimum proper Vpp.

29 ... Photosensitive drum (image carrier)
34 ... Charging device 41 ... Charging bias generating unit 51 ... Control circuit unit 52 ... Storage unit 54 ... Calibration mode execution unit

Claims (3)

A charging device that charges the image carrier, a charging bias generator that applies a charging bias in which an AC voltage (Vac) is superimposed on a DC voltage (Vdc), and a calibration that executes calibration at a predetermined timing A mode execution unit, a storage unit for storing a first AC peak-to-peak voltage (Vpp1) preset in a table in a predetermined internal atmospheric temperature unit, and a first AC peak-to-peak voltage (Vpp1) stored in the storage unit And a control circuit unit that controls the charging bias generation unit using
The control circuit unit determines the first AC peak-to-peak voltage (Vpp1) necessary for charging the image carrier at the calibration execution timing by the calibration mode execution unit, and at the start of printing, the first AC peak. An image forming apparatus, wherein the charging bias generator is controlled so as to be charged with a second AC peak-to-peak voltage (Vpp2) corrected using an inter-voltage (Vpp1) as a reference value.   The control circuit unit corrects the second AC peak-to-peak voltage (Vpp2) with a vertical width smaller than the vertical width of the first AC peak-to-peak voltage (Vpp1) stored in the storage unit. The image forming apparatus according to claim 1.   The control circuit unit determines the vertical width of the correction value of the second AC peak-to-peak voltage (Vpp2) based on the detection result of the DC current Idc flowing into the image carrier. Item 3. The image forming apparatus according to Item 2.

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