JP3803358B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image by an electrophotographic method, such as a copying machine or a printer.

  As an image forming apparatus, an electrophotographic copying machine, a printer, and the like are widely known. In an electrophotographic copying machine or the like, after the photosensitive drum is uniformly charged by a charging charger, the original on the document table is exposed, and the reflected light is imaged on the photosensitive drum. An electrostatic latent image is formed thereon. The electrostatic latent image on the photosensitive drum is supplied with toner particles by a developing device to perform electrostatic development, and the formed toner image is transferred onto transfer paper charged by a transfer charger to form an image. .

  In this type of electrophotographic copying machine, in recent years, the copying speed has been increased, but along with the increase in speed, the photosensitive drum has a larger diameter and a higher drum peripheral speed. There is a tendency that the transfer efficiency of the toner image electrostatically adhered on the photosensitive drum is deteriorated.

  That is, when the toner image formed on the photosensitive drum is transferred to the transfer paper, if the electrostatic adhesion force of the toner to the photosensitive drum is large, the toner image on the photosensitive drum is not sufficiently transferred on the transfer paper, Image defects such as image fading, image density shortage, image density deterioration, and transfer omission occur. Such image defects tend to increase as the copying speed increases.

  Therefore, in order to efficiently transfer the toner image electrostatically attached to the photosensitive drum onto the transfer paper, auxiliary neutralizing means is often provided after development and before transfer (for example, Patent Document 1). . This pre-transfer auxiliary static elimination means functions to efficiently transfer the toner onto the transfer paper by weakening the electrostatic adhesion between the toner on the photosensitive drum and the photosensitive drum by static elimination after development and before transfer.

  As this pre-transfer auxiliary means, the charge on the photoconductor is mainly neutralized by discharge from a pre-transfer neutralization light source (pre-transfer lamp, hereinafter referred to as PTL), which discharges the charge on the photoconductor with light, or a wire. In addition, it is roughly divided into two types: a pre-transfer charger (pre-transfer charger, hereinafter referred to as PTC) for improving the transferability of the toner itself.

  PTL is a means for neutralizing the charge on the photoconductor by means of static elimination light and weakening the electrostatic adhesion between the photoconductor and the toner, and a cold cathode tube, LED or the like is generally used. In addition, with the recent increase in the speed of electrophotographic copying machines, there is a need to increase the transfer efficiency. For this purpose, it is effective to increase the light quantity of the static elimination light source before transfer. As the PTL, a cold cathode tube having a larger light quantity than that of the LED is often used.

PTC is a means to neutralize the photosensitive member by charging to weaken the electrostatic adhesion between the photosensitive member and the toner, and to charge the toner more easily and transfer it. The PTC has a polarity opposite to that of the photosensitive member from an ultrafine wire such as platinum or tungsten oxide. A device that discharges DC charge of the same polarity as the toner or a device that discharges AC charge after DC biasing to a polarity opposite to that of the photoreceptor (same polarity as the toner) is used.
JP-A-64-59276

  As described above, in the electrophotographic copying machine, particularly the copying machine in which the speed of the photosensitive drum is increased in order to increase the copying speed, the transfer of the toner image is assisted in order to increase the transfer efficiency. In many cases, a cold cathode tube is used as a pre-transfer charge eliminating light source. However, when a cold cathode ray tube is used as a pre-transfer charge eliminating light source, the following problems are raised as characteristics of the cold cathode tube.

  That is, there is a large variation in the amount of light in the cold cathode tube. For example, if the cold-cathode tube is continuously lit, that is, after continuous copying with a copying machine, it is left unlit for a long time and then turned on, the amount of light immediately after lighting is low and it gradually becomes brighter. To go.

  Therefore, if the light intensity of the cold-cathode tube is set so that the light intensity during continuous lighting is the light intensity that can prevent image defects such as transfer failure, The amount of light is insufficient, leading to deterioration in transfer efficiency, and as a result, transfer omission occurs. For this reason, it is necessary to set the amount of light in the cold cathode tube immediately after lighting after standing for a long time to a sufficient amount of light that does not cause transfer omission, but in this case, the amount of light in the cold cathode tube during continuous lighting is Excessive image defects such as image memory occur. That is, in the case of using a cold cathode tube, the optimum light amount width that does not cause an image defect immediately after lighting and during continuous lighting is narrow (the amount of light missing in the transfer memory and image memory is small).

  In addition, the cold cathode tube has a characteristic that the amount of light decreases in a low temperature environment, for example, in an environment of 5 to 10 ° C. and 20 RH%. For this reason, when the cold cathode tube is used in a low temperature environment, the amount of light is insufficient, and image defects such as missing transfer occur.

  On the other hand, the PTC discharges the photosensitive drum by discharging a charge having a polarity opposite to that of the photosensitive drum. This is a charge of the same polarity as the toner, so that the toner in the image area is further charged to increase the transfer efficiency, but a slight amount of weakly charged toner adhering to the non-image area (white background area), So-called re-toner on the drum is also charged. The weakly charged toner is not transferred when there is no PTC, but is carried to the cleaning unit. However, when the toner is charged with PTC, the toner is easily transferred, so that the fog on the paper becomes very large. In this way, when PTC is used, there is a problem that the fog level is deteriorated.

  Such defective images due to PTC, that is, fogging, mainly occurs when the photosensitive drum approaches the end of its life (due to an increase in white background potential) or in a humid environment (due to a decrease in developer charge amount).

  The present invention has been made in view of the above points, and an object thereof is to provide an image forming apparatus capable of obtaining a good image without causing image defects such as transfer leakage, image memory, and fog. .

  In order to achieve the above object, an image forming apparatus according to an aspect of the present invention uses a pre-transfer neutralization light source and a pre-transfer neutralization charger in combination as a pre-transfer neutralization unit, so In addition to supplementing with a charger, it prevents fogging due to the pre-transfer static elimination charger.

  That is, an image forming apparatus according to an aspect of the present invention includes a latent image forming unit that forms an electrostatic latent image on the surface of an image carrier, and a developer that develops the electrostatic latent image formed on the image carrier. Developing means for forming a developer image, transfer means for transferring the developer image formed on the image carrier to a transfer material, and discharging the image carrier before transferring the developer image, A pre-transfer neutralization unit that reduces the electrostatic attraction force of the developer image to the image carrier, and a temperature detection unit that detects an environmental temperature.

  The pre-transfer neutralization unit includes a neutralization light source that irradiates the image carrier and the developer image with neutralization light, a neutralization charger that discharges and neutralizes the image carrier, and the discharge output can be changed. The discharge output of the charge removal charger is changed in accordance with fluctuations in the amount of light from the charge removal light source, and the discharge output of the charge removal charger is changed in accordance with the environmental temperature detected by the temperature detection means. Control means for adjusting the capability to a predetermined value.

  According to the image forming apparatus having the above configuration, the pre-transfer charge eliminating unit neutralizes the image carrier and the developer image immediately before the developer image formed on the image carrier by the developing unit is transferred to the transfer material. As a result, the electrostatic attraction force of the developer image to the image carrier is reduced, and the transfer efficiency is improved. The control means is characterized by changing the discharge output of the static elimination charger so as to maintain the static elimination capability of the pre-transfer static elimination means at a predetermined value.

  An image forming apparatus according to another aspect of the present invention includes a latent image forming unit that forms an electrostatic latent image on the surface of an image carrier and a developer that develops the electrostatic latent image formed on the image carrier. Developing means for forming a developer image, transfer means for transferring the developer image formed on the image carrier to a transfer material, and discharging the image carrier before transferring the developer image, A pre-transfer charge eliminating unit that reduces the electrostatic attraction force of the developer image to the image carrier, and a time detection unit that detects a pause time of the image carrier.

  The pre-transfer neutralization means includes a cold cathode tube that irradiates the image carrier and developer image with neutralization light, a neutralization charger that discharges and neutralizes the image carrier, and can change a discharge output; The initial discharge output of the static eliminator is set according to the pause time detected by the time detection means, and the discharge output of the static eliminator is changed from the initial discharge output according to fluctuations in the light quantity of the cold cathode tube. And a control means for maintaining the pre-transfer charge removal means at a predetermined charge removal capability.

  According to the image forming apparatus having the above configuration, the pre-transfer charge eliminating unit neutralizes the image carrier and the developer image immediately before the developer image formed on the image carrier by the developing unit is transferred to the transfer agent. As a result, the electrostatic attraction force of the developer image to the image carrier is reduced, and the transfer efficiency is improved. When lighting is started after the cold cathode tube is paused, the amount of light immediately after lighting varies depending on the pause time of the cold cathode tube. Therefore, the control means sets the initial discharge output of the static elimination charger according to the pause time detected by the time detection means, and thereafter the discharge output of the static elimination charger according to the fluctuation of the light quantity of the cold cathode tube. By changing from the initial discharge output, the pre-transfer charge removal means is maintained at a predetermined charge removal capability.

  An image forming apparatus according to another aspect of the present invention includes a latent image forming unit that forms an electrostatic latent image on the surface of an image carrier and a developer that develops the electrostatic latent image formed on the image carrier. Developing means for forming a developer image, transfer means for transferring the developer image formed on the image carrier to a transfer material, and discharging the image carrier before transferring the developer image, A pre-transfer charge eliminating unit that reduces the electrostatic attraction force of the developer image to the image carrier, and a temperature detecting unit that detects a temperature environment.

  The pre-transfer neutralization means includes a cold cathode tube that irradiates the image carrier and developer image with neutralization light, a neutralization charger that discharges and neutralizes the image carrier, and can change a discharge output; A time detection means for detecting the rest time of the image carrier and the continuous lighting time of the cold cathode tube, and setting an initial discharge output of the charge removal charger according to the rest time detected by the time detection means, In response to an increase in the continuous lighting time of the cold-cathode tube detected by the time detection means, the discharge output of the static elimination charger is reduced from the initial discharge output, and further, when a low temperature environment is detected by the temperature detection means The discharge output of the charge removal charger is maintained at a higher discharge output than that at room temperature, and when a high temperature environment is detected by the temperature detection means, Electrostatic charger discharge output was maintained at a low discharge power than that at normal temperature, and a, and a control means for maintaining the pre-transfer charge removing means to a predetermined neutralization capacity.

  According to the aspect of the present invention, the static elimination capability of the pre-transfer neutralization unit is maintained at a predetermined level by using the neutralization light source and the neutralization charger in combination as the pre-transfer neutralization unit and adjusting the discharge output of the neutralization charger. Therefore, it is possible to provide an image forming apparatus capable of obtaining a good image without causing image defects such as transfer leakage, image memory, and fog.

  Embodiments in which the present invention is applied to an electrophotographic copying machine will be described below in detail with reference to the drawings.

  First, the overall configuration of the copying machine will be schematically described. As shown in FIG. 1, the copying machine includes a casing 10, and an image carrier, such as arsenic selenium, is provided at a substantially central portion in the casing. A photosensitive drum 12 is rotatably provided. Around the photosensitive drum 12, a charging charger 11, a developing device 13 functioning as a developing means, a transfer charger 14 functioning as a transferring means, a peeling charger 15, a peeling claw 16, a cleaning device 17, and a static elimination lamp 18 are arranged in this order. Thus, the image forming unit 20 is configured.

  A document placing table 32 made of transparent glass and an automatic document feeder (hereinafter referred to as ADF) 80 that automatically feeds the document D onto the document placing table are provided on the upper surface of the housing 10.

  The ADF 80 is also configured to serve as a document presser that opens and closes the document placement table 32, a document tray 82 on which the document D is placed, and a conveyance belt 85 that is provided to face almost the entire surface of the document placement table and conveys the document. It is equipped with. Then, the document placed on the document tray 82 is guided onto the document placement table 32 via the conveyance path 84, and conveyed and positioned at a predetermined position by the conveyance belt 85. Then, a document read by a scanner, which will be described later, is discharged to a document discharge unit 88 on the upper surface of the ADF 80 by a transport belt 85 through a transport path 86.

  A scanner 22 for reading an image of the document D placed on the document placement table 32 is disposed below the document placement table 32 in the housing 10. The scanner 22 includes an exposure lamp 24 whose back is surrounded by a reflector 23, and a first reflection mirror 25 placed on the first carriage 33 together with the exposure lamp. The scanner 22 is mounted on the second carriage 34 and can move integrally therewith, the second and third reflecting mirrors 26 and 27, the lens 28, and the fixed fourth, fifth and sixth. Reflection mirrors 29, 30, and 31.

The first and second carriages 33 and 34 are moved at a predetermined speed along the document placing table 32, and scan the document D with the irradiation light from the exposure lamp 24. The reflected light from the document D is guided to the photosensitive drum 12 by the first to sixth reflecting mirrors and the lens 28 to expose the surface of the photosensitive drum. +-
As a result, an electrostatic latent image corresponding to the image of the original is formed on the surface of the photosensitive drum 12 uniformly charged by the charging charger 11 as will be described later. The formed electrostatic latent image is developed with toner as a developer by the developing device 13 to form a toner image. Thus, the charging charger 11 and the scanner 22 constitute a latent image forming unit in the present invention.

  An automatic exposure sensor 21 that measures the amount of exposure light is provided between the third reflection mirror 27 and the lens 28. A part of the light reflected by the third mirror 27 enters the automatic exposure sensor 21, and the automatic exposure sensor 21 outputs an output voltage corresponding to the image density to the CPU 92 described later as a document density signal.

  First and second paper feed cassettes 35 and 36 each containing a large number of sheets P as transfer materials are detachably mounted on the lower side of the side surface of the housing 10. Further, in the housing 10, a conveyance path for conveying the paper P taken out from the first and second paper feed cassettes 35 and 36 through a transfer unit located between the photosensitive drum 12 and the transfer charger 14. 38 is formed, and a fixing device 40 is provided at the end of the conveyance path. A discharge port 42 is formed in the side wall of the housing 10 facing the fixing device 40, and a discharge tray 43 is attached to the discharge port.

  The fixing device 40 includes a heat roller 40a with a built-in heater, a pressure roller 40b that is in rolling contact with the heat roller, a thermistor 40c that detects the temperature of the heat roller 40a, and the like.

  In the vicinity of the first and second paper feed cassettes 35 and 36, there are provided pickup rollers 44 for taking out the paper P from the paper feed cassettes, respectively, and on the upstream side of the photosensitive drum 12 in the transport path 38. A registration roller 46 for aligning P is provided. A sensor 48 that detects the arrival of the paper P is provided in the vicinity of the registration roller 46.

  The sheets P picked up one by one from the first or second sheet feeding cassette 35, 36 by the pickup roller 44 are aligned by the registration roller 46 and then sent to the transfer unit. In the transfer unit, the toner image on the photosensitive drum 12 is transferred onto the paper P by the transfer charger 14.

  The sheet P on which the toner image has been transferred is peeled from the photosensitive drum 12 by the AC corona discharge from the peeling charger 15 and the peeling claw 16, and is conveyed to the fixing device 40 via the conveyance belt 50 that constitutes the conveyance path 38. . Then, the paper P on which the toner image has been fused and fixed by the fixing device 40 is discharged onto the paper discharge tray 43 by the paper discharge roller 51.

  Further, below the conveyance path 38, an automatic double-side device 51 that reverses the paper P that has passed through the fixing device 40 and guides the paper P again to the transfer unit via the registration roller 46 is provided. The automatic duplexer 51 includes a reversing path 52 for reversing the paper P branched from the conveyance path 38, a temporary stacking unit 53 for temporarily stacking the reversed paper P, and a sheet from the temporary stacking unit to the registration roller 46. And a re-transport path 54 for transporting P.

  Between the fixing device 40 and the paper discharge roller 51, a sorting gate 55 for guiding the paper P to the reverse path 52 is provided, and a plurality of feed rollers 56 are provided in the reverse path 52 and the re-conveying path 54. Yes. Further, a pickup roller 57 is provided in the temporary stacking unit 53 to take out the stacked sheets P one by one and send them to the re-conveying path 54.

  When performing double-sided copying, the paper P that has passed through the fixing device 40 is guided to the inversion path 52 by the sorting gate 55, and after being inverted, is accumulated in the temporary accumulation unit 53. The accumulated paper P is taken out from the temporary accumulating portion 53 by the pickup roller 57, and then sent to the registration roller 46 through the re-conveying path 54. After being arranged there, the toner is again applied to the back surface of the paper P in the transfer portion. The image is transferred. Thereafter, the paper P is discharged to the paper discharge tray 43 via the conveyance path 38, the fixing device 40, and the paper discharge roller 51.

  Next, the configuration of the photosensitive drum 12 and the image forming unit 20 will be described in detail. As shown in FIG. 2, the charger 11 for uniformly charging the surface of the photosensitive drum 12 to a predetermined potential has a corona wire 11a and a grid 11b, and a voltage is applied to the corona wire to cause corona discharge. A power source (not shown) to be generated is connected. The grid 11b is connected to a high voltage transformer 60 that applies a grid voltage. These power supply and high voltage transformer 60 are connected to a CPU 62 as a control means.

  With respect to the rotation direction of the photosensitive drum 12, an exposure position 12a on the surface of the photosensitive drum 12 exposed by the reflected light from the scanner 22 is located on the downstream side of the charging charger 11, and at this exposure position, the photosensitive drum. An electrostatic latent image is formed on the surface.

  Between the exposure position 12a and the charging charger 11, a partial erasing LED 65 is disposed. The developing unit 13 has a developing roller 13a that supplies toner particles to the electrostatic latent image on the surface of the photosensitive drum 12 and develops the toner. The developing roller is controlled by a high-pressure transformer 76 under the control of the CPU 62. A development bias is applied.

  A thermistor 66 functioning as a temperature detecting means for detecting the temperature of the surface of the photosensitive drum 12 is provided between the developing device 13 and the LED 65, and an actuator 66a of the thermistor 66 contacts the drum surface at the end of the photosensitive drum. is doing. The thermistor 66 outputs a detection signal to the CPU 62.

  A surface potential sensor 67 for detecting the surface potential of the photosensitive drum 12 is provided between the developing device 13 and the LED 65.

  The transfer charger 14 for transferring the toner image formed on the photosensitive drum 12 onto the paper P, and the peeling charger 15 for separating the paper P from the photosensitive drum are a developing unit 13 with respect to the rotation direction A of the photosensitive drum 12. It is provided on the downstream side. The transfer charger 14 and the peeling charger 15 are integrally formed and connected to the CPU 62 via high-voltage transformers 68 and 70, respectively.

  A pre-transfer static eliminator 100 is provided between the developing device 13 and the transfer charger 14. The pre-transfer static eliminator 100 neutralizes the toner image formed on the surface of the photosensitive drum 12 and the photosensitive drum, and reduces the electrostatic adhesion of the toner image to the surface of the photosensitive drum. Functions as a means.

  The pre-transfer static eliminator 100 includes a cold cathode tube 102 as a pre-transfer static elimination lamp (PTL) that irradiates the photosensitive drum 12 with static elimination light, and a pre-transfer charger (PTC) 104 that discharges toward the photosensitive drum 12. And in combination.

  The cold cathode tube 102 is disposed along the axial direction of the photosensitive drum 12 and is connected to the CPU 62 via the light source driver 106. As the pre-transfer charger 104, a platinum clad wire (φ65 μm) extending along the axial direction of the photosensitive drum 12 is used, and connected to the CUP 62 via the power source 108.

  The pre-transfer charger 104 can change its discharge output, that is, the charge removal capability in accordance with the applied voltage. As will be described later, under the control of the CPU 62, the light quantity fluctuation, humidity fluctuation, and photosensitivity of the cold cathode tube 102 are controlled. The discharge output is adjusted according to the life of the body drum, and the charge removal capability of the pre-transfer charge remover 100 as a whole is maintained at a predetermined value.

  A peeling claw 16 is provided on the downstream side of the peeling charger 15, and a cleaning device 17 having a cleaning blade 78 is provided on the downstream side of the peeling claw. The cleaning blade 78 is provided in contact with the surface of the photosensitive drum 12 and scrapes off toner remaining on the drum surface without being transferred from the drum surface.

  A charger 77 having a corona wire for applying AC to the photosensitive drum 12 as an auxiliary cleaning mechanism is provided between the peeling claw 16 and the cleaning device 17.

  Further, a static elimination lamp 18 is disposed between the cleaning device 17 and the charging charger 11. The static elimination lamp 18 is connected to the CPU 62 via the light source driver 94, and the light quantity of the static elimination lamp 18 can be changed by changing the voltage applied to the light source driver 94 under the control of the CPU.

  Note that the CPU 62 includes a timer 96 that measures the operation time and pause time of the copying machine, that is, the time from when the copying operation is finished until the next copying operation is disclosed, and the heat roller 40a of the fixing device 40. A thermistor 40c for detecting the temperature of the photosensitive drum 12, a life counter 97 for counting the life of the photosensitive drum 12, and a memory 93 for storing various control data are connected.

  The timer 96 functions as time detecting means in the present invention for detecting the rest time and continuous lighting time, and the thermistor 40c also functions as means for detecting the rest time based on the temperature of the heat roller 40a. Further, the thermistor 40c functions as a temperature detection means for detecting the environmental temperature in accordance with the temperature of the photosensitive drum 12, and the life counter 97 functions as a life detection means.

  In the copying machine configured as described above, the pre-transfer static eliminator 100 controls the discharge output of the pre-transfer charger 104 in accordance with the light quantity fluctuation of the cold cathode tube 102, the environmental fluctuation, the life of the photosensitive drum, and the like. Therefore, the desired static elimination capability is maintained, and problems such as transfer omission, occurrence of image blur, and fogging are prevented.

  First, the relationship between the light quantity of the cold cathode tube 102 and the discharge output of the pre-transfer charger 104 will be described. The amount of light in the cold cathode tube 102 varies depending on the resting time or the environmental temperature.

  FIG. 3 shows a static eliminator 100 before transfer after leaving the copier for 60 minutes, that is, after 60 minutes of rest in a normal temperature environment (temperature 23 ° C., humidity 50%) and a low temperature environment (10 ° C., 20%). The change in the amount of light when the cold cathode tube 102 is turned on and the level of transfer omission at that time are shown.

  In FIG. 3, the horizontal axis represents the number of continuous copies corresponding to the continuous lighting time of the cold cathode tube 102, the first vertical axis represents the light quantity of the cold cathode tube, and the second vertical axis represents the transfer omission level.

  The copying machine used for the study was Toshiba's analog PP-CF154 (65 CPM machine), the developer was D-1710, the toner was T-2510, the OPC drum of φ100 was used as the photosensitive drum, and the evaluation of transfer omission was performed. Hammer mill Tidal-DP LT size paper was used. As the cold cathode tube 102, a tube having a maximum illuminance of 1200 LUX in a room temperature environment was used. As the illuminance meter used for measuring the light intensity, T-IM manufactured by Minolta was used, and the illuminance was measured by attaching a 3 × 10 mm slit to the probe of the illuminance meter.

  As is apparent from FIG. 3, when the copier is operated after being left for a long time in a room temperature environment, that is, when the cold cathode tube 102 is turned on, the cold cathode tube immediately after lighting is dark, and for several seconds from immediately after lighting. It can be seen that the light intensity does not reach the maximum output until several tens of seconds, and then gradually becomes brighter. Then, until the light quantity of the cold cathode fluorescent lamp 102 rises to about 1000 LUX, the transfer omission level is not bad, and the transfer omission level is gradually improved as the light quantity increases. There is a similar tendency in a low temperature environment, and the amount of light in the cold cathode fluorescent lamp 102 is generally lower than that in a normal temperature environment.

  The light quantity of the cold cathode tube 102 immediately after lighting depends on the downtime of the copying machine, that is, the downtime of the cold cathode tube 102. FIG. 4 shows changes in the amount of light in the cold cathode tubes when the cold cathode tubes are continuously lit after the pause when the pause times of the cold cathode tubes 102 are variously changed. As the copying machine and the illuminance measuring device used in this test, the same one as shown in FIG. 3 was used, and the test was performed under the same conditions.

  Here, the horizontal axis represents the continuous lighting time of the cold cathode tube 102, and the vertical axis represents the transition of the light quantity of the cold cathode tube during continuous lighting. As is apparent from this figure, the rise of the light amount of the cold cathode tube during continuous lighting changes due to the difference in the standing time of the cold cathode tube 102, and the light amount immediately after lighting is closer to the maximum light amount as the standing time is shorter. The longer it is left, the lower the light intensity.

  Therefore, according to the present embodiment, the CPU 62 as the control means increases the discharge output of the pre-transfer charger 104 immediately after the start of copying to compensate for the insufficient light quantity of the cold-cathode tube 102 immediately after the start of copying. The neutralization capability of the entire electric device 100 is set to a predetermined level that does not cause transfer omission.

  The discharge output of the pre-transfer charger 104 can be adjusted by controlling the voltage applied by the power source 108, and the discharge output of the pre-transfer charger 104 can be represented by the change in the light amount of the cold cathode tube 102 as shown in FIG. The reverse control is performed, that is, the discharge output of the pre-transfer charger is maximized immediately after the cold cathode tube 102 is turned on, and the discharge output is gradually lowered as the light quantity of the cold cathode tube increases, thereby transferring the transfer. The static eliminator capability of the pre-charger 100 is kept constant at a predetermined value.

  Here, the discharge output value of the pre-transfer charger 104 immediately after the cold-cathode tube 102 is turned on, that is, the initial value, is set according to the idle time of the copying machine as shown in FIG. That is, as the pause time is longer, the initial output value of the pre-transfer charger 104 is set higher. Then, after the cold cathode tube 102 is turned on, the discharge output is gradually reduced, and after the cold cathode tube 102 reaches the maximum light amount, the discharge output is maintained at a constant value.

  For example, when a cold cathode tube having a maximum light quantity in the range of 500 to 2000 LUX is used, the discharge output of the PTC 104 is set in the range of 1 to 20 μA according to the standing time of the cold cathode tube from the start of copying to 120 seconds. Decrease gradually.

  Thereby, the total static elimination capability of the cold cathode tube 102 and the pre-transfer charger 104, that is, the static elimination capability of the pre-transfer static eliminator 100 can be kept substantially constant regardless of the downtime of the copying machine.

  Further, as described above, in the low temperature environment, the light quantity of the cold cathode tube 102 is reduced as a whole in comparison with the normal temperature environment, so the discharge output of the pre-transfer charger 104 needs to be higher than that in the normal temperature environment. . On the contrary, in a high temperature and high humidity environment (for example, temperature 30 ° C., humidity 85%), the charge amount of the developer is lowered, so that the fog on the photosensitive drum is increased. If excessive discharge is applied from the pre-transfer charger 104 in this state, the toner on the white background portion should pass through the transfer position and be collected by the cleaning device 17 because of its weak charge. It becomes charged and all of it is drawn on the transfer paper, resulting in white background fog on the transfer paper. Therefore, in a high temperature and high humidity environment, it is necessary to reduce the discharge output of the pre-transfer charger 104.

  Therefore, according to the present embodiment, as shown in FIG. 6, the discharge output of the pre-transfer charger 104 is controlled to be increased in the low temperature environment as compared with the normal temperature environment, and conversely in the high temperature and high humidity environment. Controls to lower the discharge output. For example, the discharge output of the PTC 104 is varied in the range of 1 to 20 μA according to the detected environmental temperature.

  By such control, it becomes possible to eliminate the difference from the room temperature environment, and it is possible to prevent occurrence of transfer omission and image memory. In the drawing, N / N represents a normal temperature and normal humidity environment, L / L represents a low temperature and low humidity environment, and H / H represents a high temperature and high humidity environment.

  Further, the CPU 62 performs control so as to reduce the discharge output of the pre-transfer charger 104 according to the life of the photoconductor drum 12, that is, as the photoconductor drum approaches its life. That is, as the photoconductor drum 12 approaches the end of its life, the white background potential increases due to the increase in the permanent residual potential and the decrease in sensitivity, and the fog on the drum increases. Therefore, as shown in FIG. 7, the CPU 62 performs control to gradually decrease the discharge output of the pre-transfer charger 104 after the life of the photosensitive drum reaches a predetermined value based on the count of the life counter 97. Do. In this case, for example, the discharge output is gradually reduced in the range of 0 to 5 μA.

  FIG. 8 shows specific control operations of the copying machine based on the various test results described above. First, after starting the control, the CPU 62 calculates a pause time of the copying machine, that is, a time during which the cold cathode tube 102 is left unattended. For example, when the rest mode is ready-to-stand, the timer 96 of the copier is used to calculate the rest time in which the cold cathode tube 102 is left.

  On the other hand, when the copying machine is powered off, when the power is turned on, first, the temperature of the heat roller 40a is detected based on a signal from the thermistor 40c, and how much the copying machine is left to stand by the temperature. Estimate whether or not, and thereby calculate the downtime.

  Then, the CPU 62 determines the initial discharge output (1) of the PTC 104 based on the calculated pause time and the control data shown in FIG.

  Next, the CPU 62 detects the temperature of the photosensitive drum 12 when the power of the copying machine is turned on based on a signal from the thermistor 66. Based on the detected drum temperature, it is estimated what kind of environment the copying machine is in, and the discharge output (2) of the PTC 104 is determined based on the control data shown in FIG.

  Further, the CPU 62 determines the discharge output (3) of the PTC 104 based on the count value of the life counter 97 and the control data shown in FIG. Then, the final discharge output value of the PTC 104 is calculated based on the determined discharge outputs (1), (2), and (3).

  When the copying operation is started, the CPU 62 starts discharging the PTC 104 with the initial discharge output (1) while irradiating the cold-cathode tube 102 with static elimination light. When continuous copying is performed, the discharge output of the PTC 104 is gradually reduced in accordance with the continuous copy time detected by the timer 96 of the copying machine, and then maintained at the calculated final discharge output value.

  FIGS. 9 and 10 show the level of transfer omission and the occurrence of fog when the discharge output of the PTC 104 in the pre-transfer static eliminator 100 is controlled as described above.

  As can be seen from FIG. 9, the discharge output of the PTC 104 is changed in accordance with the light amount fluctuation of the cold cathode tube 102 and the environmental temperature to adjust the static elimination capability of the pre-transfer static eliminator 100 to a predetermined value. It is possible to improve the transfer efficiency by maintaining the transfer omission level at a level where there is no problem both in the initial lighting of the cathode tube 102 and during continuous copying.

  Further, as can be seen from FIG. 10, the discharge output of the PTC 104 is changed according to the environmental change and the life of the photosensitive drum 12 to adjust the charge removal capability of the pre-transfer charge remover 100 to a predetermined value. In the environment and even when the photosensitive drum 12 is nearing the end of its life, it is possible to reduce image fogging and form a high-quality image.

  The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the present invention. For example, in the present embodiment, a cold cathode tube is used as a static elimination light source. However, the present invention is not limited to this, and other light sources such as an LED array may be used. For example, when an LED array is used, the discharge output of the pre-transfer charger is adjusted in accordance with environmental fluctuations and the life of the photoconductor drum, so that the photoconductor drum can be used in a high-temperature and high-humidity environment as in the above embodiment. However, even in a situation where the lifetime is approaching, it is possible to reduce image fogging and form a high-quality image.

  In addition, the pre-transfer charger of the pre-transfer static eliminator 100 can obtain the same operation and effect when using either a DC charger or an AC charger. The cold cathode tube is not limited to a maximum light quantity of 1200 LUX, and can be changed as necessary. By adjusting the discharge output of the PTC according to the difference in the maximum light quantity, the same effect as described above can be obtained. Obtainable.

  Furthermore, the present invention is not limited to an analog copying machine, and may be applied to other image forming apparatuses such as a digital copying machine and a laser printer. In addition, the photosensitive drum is not limited to the organic type such as the above-described OPC drum, and similar effects can be obtained when an inorganic type photosensitive drum is used.

1 is a cross-sectional view showing an entire copying machine according to an embodiment of the present invention. FIG. 2 is a diagram schematically showing an image forming unit and a control system of the copying machine. The graph which shows the relationship between the lighting time of a cold cathode tube, a light quantity, and a transfer omission level. The graph which shows the relationship between the lighting time of a cold-cathode tube, and a light quantity when a pause time differs, respectively. The graph which shows the PTC output value controlled according to various rest time. The graph which shows the PTC output value controlled according to various environments. 6 is a graph showing the relationship between the life (travel distance) of a photosensitive drum and the PTC output value. 6 is a flowchart showing a control operation of discharge output of a static elimination charger in the copying machine. The graph which shows the transfer omission level at the time of controlling the discharge output of the said static elimination charger. The graph which shows the state of fog in case the discharge output of the said static elimination charger is controlled.

Explanation of symbols

DESCRIPTION OF SYMBOLS 12 ... Photosensitive drum, 13 ... Developing device, 20 ... Image forming part, 40 ... Fixing device,
40c ... Thermistor 62 ... CPU 66 ... Thermistor 93 ... Memory,
96 ... Timer, 97 ... Life counter, 100 ... Pre-transfer static eliminator,
102 ... Cold cathode tube, 104 ... Static elimination charger, 106 ... Power supply,
108: Light source driver

Claims (5)

Latent image forming means for forming an electrostatic latent image on the surface of the image carrier;
Developing means for developing the electrostatic latent image formed on the image carrier with a developer to form a developer image;
Transfer means for transferring the developer image formed on the image carrier to a transfer material;
Before transfer of the developer image, the image carrier is neutralized, and a pre-transfer neutralization unit that reduces the electrostatic attraction force of the developer image to the image carrier;
Temperature detection means for detecting the environmental temperature;
With
The pre-transfer charge eliminating means is
A static elimination light source for irradiating the image carrier and developer image with static elimination light;
A discharger that discharges and discharges the image carrier, and that can change the discharge output;
The discharge output of the charge removal charger is changed according to the change in the light amount of the charge removal light source, and the discharge output of the charge removal charger is changed according to the environmental temperature detected by the temperature detection means. Control means for adjusting the static elimination capability to a predetermined value;
An image forming apparatus comprising: Latent image forming means for forming an electrostatic latent image on the surface of the image carrier;
Developing means for developing the electrostatic latent image formed on the image carrier with a developer to form a developer image;
Transfer means for transferring the developer image formed on the image carrier to a transfer material;
Before transfer of the developer image, the image carrier is neutralized, and a pre-transfer neutralization unit that reduces the electrostatic attraction force of the developer image to the image carrier;
Time detecting means for detecting the rest time of the image carrier;
With
The pre-transfer charge eliminating means is
A cold cathode tube for irradiating the image bearing member and the developer image with static elimination light;
A discharger that discharges and discharges the image carrier, and that can change the discharge output;
The initial discharge output of the static eliminator is set according to the pause time detected by the time detection means, and the discharge output of the static eliminator is changed from the initial discharge output according to fluctuations in the light quantity of the cold cathode tube. A control means for maintaining the pre-transfer static elimination means at a predetermined static elimination capability;
An image forming apparatus comprising: Latent image forming means for forming an electrostatic latent image on the surface of the image carrier;
Developing means for developing the electrostatic latent image formed on the image carrier with a developer to form a developer image;
Transfer means for transferring the developer image formed on the image carrier to a transfer material;
Before transfer of the developer image, the image carrier is neutralized, and a pre-transfer neutralization unit that reduces the electrostatic attraction force of the developer image to the image carrier;
With
The pre-transfer charge eliminating means is
A cold cathode tube for irradiating the image bearing member and the developer image with static elimination light;
A discharger that discharges and discharges the image carrier, and that can change the discharge output;
Time detecting means for detecting the rest time of the image carrier and the continuous lighting time of the cold cathode tube;
The initial discharge output of the static elimination charger is set according to the pause time detected by the time detection means, and the static elimination charger is adjusted according to an increase in the continuous lighting time of the cold cathode tube detected by the time detection means. Control means for reducing the discharge output from the initial discharge output and maintaining the pre-transfer charge removal means at a predetermined charge removal capacity;
An image forming apparatus comprising: Latent image forming means for forming an electrostatic latent image on the surface of the image carrier;
Developing means for developing the electrostatic latent image formed on the image carrier with a developer to form a developer image;
Transfer means for transferring the developer image formed on the image carrier to a transfer material;
Before transfer of the developer image, the image carrier is neutralized, and a pre-transfer neutralization unit that reduces the electrostatic attraction force of the developer image to the image carrier;
Temperature detection means for detecting the temperature environment;
With
The pre-transfer charge eliminating means is
A cold cathode tube for irradiating the image bearing member and the developer image with static elimination light;
A discharger that discharges and discharges the image carrier, and that can change the discharge output;
Time detecting means for detecting the rest time of the image carrier and the continuous lighting time of the cold cathode tube;
The initial discharge output of the static elimination charger is set according to the pause time detected by the time detection means, and the static elimination charger is adjusted according to an increase in the continuous lighting time of the cold cathode tube detected by the time detection means. The discharge output is reduced from the initial discharge output, and when the low temperature environment is detected by the temperature detection means, the discharge output of the charge removal charger is maintained at a discharge output higher than that in the normal temperature environment and the temperature detection is performed. When a high temperature environment is detected by the means, the discharge output of the charge removal charger is maintained at a discharge output lower than that at room temperature, and the control means for maintaining the pre-transfer charge removal means at a predetermined charge removal capability;
An image forming apparatus comprising: Latent image forming means for forming an electrostatic latent image on the surface of the image carrier;
Developing means for developing the electrostatic latent image formed on the image carrier with a developer to form a developer image;
Transfer means for transferring the developer image formed on the image carrier to a transfer material;
Before transfer of the developer image, the image carrier is neutralized, and a pre-transfer neutralization unit that reduces the electrostatic attraction force of the developer image to the image carrier;
Temperature detection means for detecting the temperature environment;
A lifetime detecting means for measuring the lifetime of the image carrier;
With
The pre-transfer charge eliminating means is
A cold cathode tube for irradiating the image bearing member and the developer image with static elimination light;
A discharger that discharges and discharges the image carrier, and that can change the discharge output;
Time detecting means for detecting the rest time of the image carrier and the continuous lighting time of the cold cathode tube;
The initial discharge output of the static elimination charger is set according to the pause time detected by the time detection means, and the static elimination charger is adjusted according to an increase in the continuous lighting time of the cold cathode tube detected by the time detection means. The discharge output is reduced from the initial discharge output, and when the low temperature environment is detected by the temperature detection means, the discharge output of the charge removal charger is maintained at a discharge output higher than that in the normal temperature environment and the temperature detection is performed. When the high temperature environment is detected by the means, the discharge output of the static elimination charger is maintained at a discharge output lower than that at the normal temperature environment, and the detection result of the life detection means indicates that the image carrier approaches the end of its life. Control means for reducing the discharge output of the static elimination charger;
An image forming apparatus comprising:

Images