JP2017111326A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent reduction in chargeability under a low temperature environment in a configuration including a positive charging single layer-type photoreceptor and a charging roller.SOLUTION: A color printer 1 includes: a photoreceptor drum 11 which is provided in a rotatable manner; a charging part 12 having a charging roller 31 which charges the photoreceptor drum 11 with electricity by applying DC voltage to the photoreceptor drum 11; a destaticization part 15; a charging control part 53; and a destaticization control part 55. The charging control part 53 controls the charging part 12 so as to perform preliminary charging for charging the photoreceptor drum 11 with electricity during a prescribed preliminary charging period t1 before execution of the image formation operation using the photoreceptor drum 11. The destaticization control part 55 sets a delay period t2 from the start of preliminary charging to the start of preliminary destaticization as preliminary destaticization for destaticizing the photoreceptor drum 11 charged with electricity by the preliminary charging, and controls the destaticization part 15 so as to perform preliminary destaticization during a preliminary destaticization period t3 to execution of the image formation operation after the elapse of the delay period t2.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus including a charging roller that charges a surface of a photoreceptor with a DC voltage.

  In recent years, in an electrophotographic image forming apparatus, in consideration of environmental protection, instead of a scorotron charging (non-contact) charging member that generates a large amount of ozone, a contact charging method, for example, a rubber charging roller Are widely used (see, for example, Patent Document 1). In such a contact charging type charging roller, charging is realized by a discharge in a minute gap between the photosensitive member and the charging roller, and the amount of ozone can be reduced.

  Electrophotographic photoreceptors provided in an electrophotographic image forming apparatus include inorganic photoreceptors and organic photoreceptors. It is known that organic photoreceptors are easier to manufacture than inorganic photoreceptors, and have a wide variety of options for organic materials constituting the photosensitive layer and a high degree of freedom in structural design.

  In addition, the organic photoreceptor includes a multilayer photoreceptor in which a layer containing a charge generator and a charge transport layer are laminated, and a single layer including a photosensitive layer containing the charge generator and the charge transport agent in the same layer. Type photoreceptors. Single layer type photoreceptors generate carriers near the surface, so that the film thickness can be increased, which is suitable for extending the life, and furthermore, since single layer coating is used, it is easier and easier than the multilayer type. It can be manufactured at low cost. Accordingly, if a single-layer type photoreceptor and a contact charging type charging roller are combined, an image forming apparatus that is more suitable for the environment can be designed.

JP-A-5-303259

  However, the charging roller has a peculiar problem that image defects such as fogging occur with a decrease in charging ability in a low temperature environment. This is because the resistance of the charging roller increases in a low-temperature environment, so that it is difficult to increase the surface potential of the photoreceptor even when a constant charging voltage is applied to the charging roller. Such a decrease in charging ability is more likely to occur in a positively charged single layer type photoreceptor. The reason for this is that in a positively charged single layer type photoconductor, the charge generating agent is uniformly dispersed in the resin, and the photogenerated carrier is generated inside the photoconductor by static elimination light. This is because it remains and acts to cancel the surface charge during charging.

  Although it is possible to reduce the charging rise time by increasing the voltage applied to the charging roller in response to a decrease in charging performance, the discharge voltage (current flowing into the photoconductor) increases, so the film on the photoconductor is scraped. There is a risk that the service life will be shortened.

  In addition, by applying a superimposed voltage, which is a combination of DC voltage and AC voltage, to the charging roller, the trap carrier cancellation in the photoreceptor and the charging of the photoreceptor can be repeated in an AC voltage cycle, improving the charging performance Although the effect can be expected, there is a possibility that the amount of ozone generated increases or the film scraping of the photosensitive layer is promoted.

 Furthermore, increasing the diameter of the charging roller to expand the discharge area, or reducing the rotation speed of the image forming unit and extending the charging time can also reduce the charging performance, but it can reduce the size and speed of the product. Will be hindered.

  Conventionally, there is a technique for obtaining a desired surface potential by extending a preliminary charging (charging aging) time before starting a print job in a low temperature environment. However, this technique has a problem that the product life cannot be guaranteed for users who use in a low temperature environment because the preliminary charging is performed for a long time.

  In view of the above circumstances, an object of the present invention is to prevent a decrease in charging ability in a low temperature environment in a configuration including a positively charged single layer type photoreceptor and a charging roller.

  An image forming apparatus according to the present invention includes a positively charged single layer type photoconductor provided rotatably, and a charging roller provided with a conductive charging roller that applies a DC voltage to the photoconductor to charge the surface of the photoconductor. A charge removal unit that removes the surface potential of the photoconductor; a charge control unit that controls charging of the photoconductor by the charging unit; and a charge removal control unit that controls charge removal of the photoconductor by the charge removal unit; The charging control unit controls the charging unit to perform preliminary charging for charging the photosensitive member for a predetermined preliminary charging period before an image forming operation using the photosensitive member is performed. The static elimination control unit provides a delay period from the start of the preliminary charging to the start of the preliminary static elimination as preliminary static elimination for neutralizing the photosensitive member charged by the preliminary charging, and after the delay period has elapsed, The image forming operation is executed During the pre-charge removal period, the and controls the electrostatic charge removing unit to perform the preliminary neutralization.

  In this way, by providing a delay period for preliminary static elimination at the start of preliminary charging, the static elimination unit is stopped and the static elimination lamp is extinguished, so that trap carriers staying in the photoreceptor are not generated, and normal image formation is performed. Compared to sometimes, the charging ability of the photoreceptor is improved even in a low temperature environment. As described above, since the charging ability of the photoconductor does not decrease, the charge rising time can be shortened without increasing the voltage applied to the charging roller more than necessary, and the desired surface potential of the photoconductor can be obtained in a short time. It becomes possible. Therefore, it is possible to extend the life by avoiding film abrasion of the photoreceptor due to discharge from the charging roller.

  In addition, there is no need to increase the charging roller diameter, expand the discharge area, or slow down the rotation speed of the image forming unit with the photoconductor to extend the charging time. Will not be disturbed.

  Furthermore, since a desired charging bias can be obtained quickly, the preliminary charging period itself can be shortened. As a result, there is no risk of damage to the charging roller and the photoconductor due to prolonged pre-charging even in a low temperature environment, and the product life can be guaranteed for users who use in a low temperature environment.

  Therefore, in a configuration including a positively charged single-layer type photoreceptor and a charging roller, it is possible to prevent a decrease in charging ability in a low-temperature environment and to avoid image defects such as fogging.

  Further, the static elimination control unit stops the static elimination unit during the delay period in the preliminary charging period, while the neutralization unit may be operated during the preliminary static elimination period. Therefore, a simple configuration that performs simple ON / OFF control of the static elimination lamp and the like. Can be adopted. In such a configuration, since it is only necessary to design a circuit so that the switching of the static elimination lamp can be switched on / off in accordance with a signal from the CPU, the strength of the static elimination lamp, that is, the input voltage to the static elimination section can be varied. No complicated circuit design is required.

  The neutralization control unit may set the preliminary neutralization period longer than the time required for one rotation of the photoconductor in the preliminary charging.

  By adopting such a configuration, it is possible to surely remove the charge charged on the photosensitive member by the charging unit during preliminary charging.

  The image forming apparatus further includes an apparatus main body that houses the photoconductor, the charging unit, and the charge eliminating unit, and a temperature sensor that detects an in-machine temperature of the apparatus main body, and the charge eliminating control unit includes The delay period and the preliminary static elimination period may be set based on temperature.

  By adopting such a configuration, it is possible to realize preliminary static elimination suitable for the environment.

  The static elimination control unit may set the delay period longer as the in-machine temperature becomes lower.

  By adopting such a configuration, it is possible to reliably prevent a reduction in charging ability of the photoconductor and the charging roller that is likely to occur in a low temperature environment. Since preliminary static elimination is performed, it is possible to prevent the surface potential of the photoreceptor from rising more than necessary. Therefore, the developing unit does not charge unnecessary carriers or reversely charged toner.

  According to the present invention, in a configuration including a positively charged single layer type photoreceptor and a charging roller, it is possible to prevent a decrease in charging ability in a low temperature environment.

1 is a cross-sectional view schematically illustrating a configuration of a color printer according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a photosensitive drum and its periphery in a color printer according to an embodiment of the present invention. 1 is a block diagram illustrating a configuration of a color printer according to an embodiment of the present invention. 6 is a graph showing a relationship between an in-machine temperature and a delay time in preliminary static elimination in the color printer according to the embodiment of the present invention. 6 is a flowchart illustrating an operation of performing preliminary charging and preliminary neutralization before image formation in the color printer according to the embodiment of the present invention. 6 is a timing chart illustrating an operation of performing preliminary charging and preliminary neutralization before image formation in the color printer according to the embodiment of the present invention. 4 is a graph showing the relationship between elapsed time and the surface potential of a photosensitive drum in a color printer according to an embodiment of the present invention.

  First, the overall configuration of a color printer 1 (image forming apparatus) according to an embodiment of the present invention will be described with reference to FIG. Hereinafter, for convenience of explanation, the front side of the sheet in FIG.

  The color printer 1 includes a box-shaped printer main body 2 (apparatus main body). A paper feed cassette 3 that stores paper (recording medium) is provided at the bottom of the printer main body 2. A paper tray 4 is provided.

  An intermediate transfer belt 5 (image carrier) is installed between a plurality of rollers in the center of the printer main body 2, and an exposure unit composed of a laser scanning unit (LSU) is provided below the intermediate transfer belt 5. 6 is arranged. Below the intermediate transfer belt 5, four image forming units 7 are provided for each toner color (for example, four colors of magenta, cyan, yellow, and black). A secondary transfer unit 8 is provided at the right end of the intermediate transfer belt 5, and a belt cleaning unit 10 is provided at the left end of the intermediate transfer belt 5. The secondary transfer unit 8 includes a part on the right end side of the intermediate transfer belt 5 and a secondary transfer roller 8a.

  Each image forming unit 7 is rotatably provided with a photosensitive drum 11 (positively charged single layer type photosensitive member). Around the photosensitive drum 11, a charging unit 12, a developing unit 13, and a primary unit are provided. The transfer unit 14, the charge eliminating unit 15, and the photoconductor cleaning unit 16 are arranged in the order of the primary transfer process. Above the developing unit 13, a toner container 17 corresponding to each image forming unit 7 is provided for each toner color (for example, four colors of magenta, cyan, yellow, and black). Each image forming unit 7 will be described later.

  On one side of the printer main body 2 (on the right side in the drawing), a paper transport path 20 is provided in the vertical direction. A paper feed unit 21 is provided at the upstream end of the conveyance path 20, the secondary transfer unit 8 is provided in the middle part of the conveyance path 20, and a fixing unit 22 is provided in the downstream part of the conveyance path 20. A paper discharge port 23 is provided at the downstream end of the transport path 20.

  Next, an image forming operation of the color printer 1 having such a configuration will be described. When the color printer 1 is turned on, various parameters are initialized, and initial settings such as temperature setting of the fixing unit 22 are executed. When image data is input from a computer or the like connected to the color printer 1 and an instruction to start printing is given, an image forming operation is executed as follows.

  First, after the surface of the photosensitive drum 11 is charged by the charging unit 12, an electrostatic latent image is formed on the surface of the photosensitive drum 11 by laser light from the exposure unit 6 (see arrow P). Next, the electrostatic latent image is developed into a toner image of a corresponding color by the developing unit 13 with toner supplied from the toner container 17. This toner image is primarily transferred to the surface of the intermediate transfer belt 5 at the primary transfer portion 14. Each image forming section 7 sequentially repeats the above operation, whereby a full-color toner image is formed on the intermediate transfer belt 5. The charge and toner remaining on the photoconductor drum 11 are removed by the charge eliminating unit 15 and the photoconductor cleaning unit 16.

  On the other hand, the paper taken out from the paper feed cassette 3 or the hand tray (not shown) by the paper feed unit 21 is conveyed to the secondary transfer unit 8 in synchronization with the above-described image forming operation, and is subjected to secondary transfer. In the portion 8, the full color toner image on the intermediate transfer belt 5 is secondarily transferred to the paper. The sheet on which the toner image is secondarily transferred is conveyed downstream in the conveyance path 20 and enters the fixing unit 22 where the toner image is fixed on the sheet. The sheet on which the toner image is fixed is discharged from the discharge outlet 23 onto the discharge tray 4.

  Next, each image forming unit 7 will be described with reference to FIG. Since the four image forming units 7 corresponding to the four color toners of magenta, cyan, yellow, and black have the same configuration, one image forming unit 7 (for example, image formation corresponding to the black toner) will be described below. Part 7) will be described.

  In the image forming unit 7, the photosensitive drum 11 is formed in a long cylindrical shape in the front-rear direction, and includes a photosensitive layer in which a charge generating agent and a charge transporting agent are contained in the same layer. Consists of. The photoreceptor coating liquid for forming the photoreceptor drum 11 is, for example, 5 parts by mass of a charge generator (metal-free phthalocyanine), 50 parts by mass of a hole transport agent, 35 parts by mass of an electron transport agent, and a binder resin. It is adjusted by mixing and dispersing 100 parts by mass (viscosity average molecular weight 67000) together with 800 parts by mass of tetrahydrofuran in a ball mill for 50 hours. Then, this coating solution is applied on a conductive substrate by a dip coating method and then dried with hot air at 100 ° C. for 40 minutes to obtain a photosensitive member having a photosensitive layer thickness of 36 μm (diameter 30 mm). Used as a body drum 11.

  The charging unit 12 includes a housing 30, a charging roller 31, and a brush roller 32. The housing 30 is formed in a box shape that is long in the front-rear direction, has an opening 30 a at the upper end, and is disposed with the opening 30 a facing the lower side of the photosensitive drum 11. The charging roller 31 is formed in a long cylindrical shape in the front-rear direction, and is configured by laminating a rubber charging layer 31b mainly composed of epichlorohydrin rubber on the outer peripheral surface of the rotating shaft 31a, and has a diameter of 12 mm. The charging roller 31 is rotatably provided in the vicinity of the opening 30 a inside the housing 30, and a part of the peripheral surface is exposed to the outside from the opening 30 a and is in contact with the photosensitive drum 11. The brush roller 32 is configured by providing a plurality of brushes 32b on the outer peripheral surface of a columnar rotating shaft 32a that is long in the front-rear direction. The brush roller 32 is provided to be rotatable inside the housing 30 relative to the charging roller 31, and is arranged so that the tip of the brush 32 b contacts the charging roller 31 at a part of the outer periphery.

  The developing unit 13 includes a housing 33, a first stirring screw 34, a second stirring screw 35, a magnetic roller 36, a developing roller 37, and a developer regulating blade 38. The casing 33 is formed in a box shape that is long in the front-rear direction, and has an opening 33 a at the upper end of the right end, and is disposed with the opening 33 a facing the left side of the photosensitive drum 11. A partition wall 33 b extending in the front-rear direction is provided on the inner bottom surface of the housing 33. The first agitation screw 34 and the second agitation screw 35 are screws each having a long rotating shaft 34 a and 35 a in the front-rear direction, and are provided to be rotatable on both the left and right sides with the partition wall 33 b sandwiched between the lower part inside the housing 33. It is done. The magnetic roller 36 is formed in a long cylindrical shape in the front-rear direction, and is rotatably provided above the second stirring screw 35 inside the housing 33. The developing roller 37 is formed in a long cylindrical shape in the front-rear direction, and is provided to be rotatable while being in contact with the upper side of the magnetic roller 36 inside the housing 33. A part of the peripheral surface is exposed to the outside from the opening 33a. In contact with the photosensitive drum 11. The developer regulating blade 38 is formed in a long plate shape in the front-rear direction, is attached to the lower edge portion of the opening 33 a of the housing 33, and one end is in contact with the outer peripheral surface of the magnetic roller 36.

  The primary transfer unit 14 includes a part of the intermediate transfer belt 5 and a primary transfer roller 14a. The primary transfer roller 14 a is formed in a long cylindrical shape in the front-rear direction, and is rotatably provided above the photosensitive drum 11 while being in contact with the inner peripheral surface of the intermediate transfer belt 5.

The charge removal unit 15 includes a mounting member 40 and a charge removal lamp 41. The attachment member 40 is formed in a long plate shape in the front-rear direction, and is attached to the upper surface of the casing 42 of the photoreceptor cleaning unit 16 described below. The static elimination lamp 41 is configured by arranging a plurality of (for example, twelve) LED chips at equal intervals in the front-rear direction and attaching the LED chip to the attachment member 40 so that the light emission direction is on the photosensitive drum 11 side. The static elimination lamp 41 is configured so that the static elimination light from the plurality of LED chips is uniformly irradiated in the longitudinal direction (front-rear direction) of the photosensitive drum 11 so that the photosensitive body surface light quantity satisfies ² to 10 μJ / cm ² .

  The photoconductor cleaning unit 16 includes a housing 42, a cleaning blade 43, and a collection roller 44. The casing 42 is formed in a box shape that is long in the front-rear direction, has an opening 42 a at the left end, and is disposed with the opening 42 a facing the right side of the photosensitive drum 11. The cleaning blade 43 is formed in a plate shape that is long in the front-rear direction, is attached to the lower edge portion of the opening 42 a of the housing 42, and one end is in contact with the outer peripheral surface of the photosensitive drum 11. The collection roller 43 is formed in a long cylindrical shape in the front-rear direction, and is provided to be rotatable inside the housing 42.

  Next, the control system of the printer 1 will be described with reference to FIG.

  The printer 1 is provided with a control unit 50 configured by a CPU or the like, and the control unit 50 is connected to a storage unit 51 including a ROM, a RAM, and the like. Based on the control program and control data stored in the storage unit 51, the control unit 50 is configured so that each unit of the printer 1 (exposure unit 6, secondary transfer roller 8 a, belt cleaning unit 10, photosensitive drum 11, charging unit 12, The developing unit 13, the primary transfer roller 14a, the charge removing unit 15, the photosensitive member cleaning unit 16, the paper feeding unit 21, the fixing unit 22, and the like are configured to be controlled.

  For example, the control unit 50 is connected to a drum drive unit 52, a charge control unit 53, a development control unit 54, a charge removal control unit 55, a temperature sensor 56, and the like. Note that the charging control unit 53, the development control unit 54, and the charge removal control unit 55 may be configured by a control program stored in the storage unit 51. The temperature sensor 56 detects the in-machine temperature T of the printer main body 2.

  The storage unit 51 stores temperature thresholds Ta, Tb, and Tc used in the charge removal control unit 55 and delay periods ta, tb, and tc in advance as described below.

  The drum driving unit 52 is configured by a drum motor or the like that is controlled by the control unit 50 to rotationally drive the photosensitive drum 11.

  The charging control unit 53 controls charging of the photosensitive drum 11 by the charging unit 12. For example, when operating the charging unit 12, the charging control unit 53 applies a predetermined DC voltage (charging bias) from a charging bias power source (not shown) to the charging roller 31 and also drives a drive motor (not shown). The charging roller 31 and the brush roller 32 are rotated. Here, during the above-described image forming operation, the charging control unit 53 applies normal voltage for charging the photosensitive drum 11 by applying a DC voltage (for example, 520 V) suitable for image formation to the charging roller 31. The charging unit 12 is controlled to perform.

  On the other hand, before the image forming operation is executed, the charging control unit 53 applies a DC voltage to the charging roller 31 during a predetermined preliminary charging period to perform preliminary charging for charging the photosensitive drum 11. The charging unit 12 is controlled. The charging controller 53 applies the same DC voltage (preliminary charging voltage) to the charging roller 31 during preliminary charging as the DC voltage (normal charging voltage) applied to the charging roller 31 during normal charging. However, the preliminary charging voltage may be set smaller than the normal charging voltage. The charging control unit 53 may set the preliminary charging period t1 so as not to fall below the minimum period tmin regardless of fluctuations in the delay period t2 and the preliminary discharging period t3 set by the discharging control unit 55 described below. When the delay period t2 = 0, the preliminary charging period t1 = the preliminary static elimination period t3 = tmin. When the delay period t2 = tmin, the preliminary charging period t1 = the delay period t2 and the preliminary static elimination period t3 = 0. Become.

  The development control unit 54 controls development of the electrostatic latent image on the photosensitive drum 11 by the developing unit 13 into a toner image. For example, when the development control unit 54 operates the development unit 13, it applies a predetermined development bias from a development bias power source (not shown) to the magnetic roller 36 or the development roller 37 and also drives a drive motor (not shown). 1), the first stirring screw 34, the second stirring screw 35, the magnetic roller 36, and the developing roller 37 are rotationally driven.

  The neutralization control unit 55 controls the neutralization of the photosensitive drum 11 by the neutralization unit 15. For example, the static elimination control unit 55 turns on the static elimination lamp 41 when operating the static elimination unit 15. Here, during the above-described image forming operation, the charge removal control unit 55 turns on the charge removal lamp 41 in synchronization with the rotation of the photosensitive drum 11 and the operation of the charging unit 12, thereby normally charging the charging unit 12. Thus, the neutralization unit 15 is controlled so as to perform normal neutralization for neutralizing the charge applied to the surface of the photosensitive drum 11 and remaining on the surface of the photosensitive drum 11 after the toner image is formed.

  On the other hand, the charge removal control unit 55 turns on the charge removal lamp 41 for a predetermined preliminary charge removal period t3 before the image forming operation is performed, so that the charge on the surface of the photosensitive drum 11 is preliminarily charged by the charging unit 12. The neutralization unit 15 is controlled so as to perform preliminary neutralization to neutralize the applied charge. For such preliminary neutralization, the neutralization controller 55 provides a delay period t2 from the start of preliminary charging to the start of preliminary neutralization, and the preliminary neutralization until the image forming operation is executed after the delay period t2 elapses. During the period t3, the static elimination unit 15 is caused to perform preliminary static elimination.

  The static elimination control unit 55 sets a time longer than the time required to rotate the photosensitive drum 11 at least once as the preliminary static elimination period t3. This is because when the photosensitive drum 11 receives a history of the exposure process or the like by the exposure unit 6, there is a history corresponding to one rotation of the photosensitive drum 11 at the maximum, so that the potential unevenness on the surface of the photosensitive drum 11 is canceled. Because.

  Further, the static elimination control unit 55 sets the delay period t2 according to the in-machine temperature T of the printer main body 2 detected by the temperature sensor 56. For example, the lower the in-machine temperature T, the longer the delay period t2. The delay period t2 may be 1 to 2 seconds (2 to 4 rotations of the photosensitive drum 11).

  For example, as shown in FIG. 4, the charge removal control unit 55 predetermines temperature thresholds Ta, Tb, and Tc that have a relationship of Ta> Tb> Tc, and delay periods ta and tb that have a relationship of ta> tb> tc. , Tc are predetermined. The neutralization controller 55 sets the delay period t2 = 0 when the in-machine temperature T ≧ Ta, sets the delay period t2 = ta when Ta> the in-machine temperature T ≧ Tb, and Tb> the in-machine temperature. When T ≧ Tc, the delay period t2 = tb is set. When Tc> in-machine temperature T, the delay period t2 = tc is set. For example, the temperature threshold values Ta, Tb, and Tc are set to 15 ° C., 10 ° C., and 5 ° C., respectively, and the delay periods ta, tb, and tc are 0.51 sec (one rotation of the photosensitive drum 11), respectively. 02 sec (for two rotations of the photoconductive drum 11) and 1.53 sec (for three rotations of the photoconductive drum 11), and the minimum preliminary charging period tmin is set to 1.53 sec.

  As an example, when the in-machine temperature T is 15 ° C. or higher, the delay period t2 = 0, so that the static elimination control unit 55 performs static elimination while the drum driving unit 52 rotates the photosensitive drum 11 three times during preliminary charging. The lamp 41 is turned on to perform preliminary charge removal. When the in-machine temperature T is 10 ° C. or more and less than 15 ° C., the delay period t2 = 0.51 sec (one rotation of the photosensitive drum 11), so that the photosensitive drum 11 is rotated for the first rotation during preliminary charging. In the meantime, the static elimination control unit 55 turns off the static elimination lamp 41, and during the second to third rotations of the photosensitive drum 11, the static elimination control unit 55 turns on the static elimination lamp 41 to perform preliminary static elimination. When the in-machine temperature T is 5 ° C. or more and less than 10 ° C., the delay period t2 = 1.02 sec (two rotations of the photosensitive drum 11), so that the photosensitive drum 11 rotates once or twice during preliminary charging. Between the eyes, the static elimination control unit 55 turns off the static elimination lamp 41, and during the third rotation of the photosensitive drum 11, the static elimination control unit 55 turns on the static elimination lamp 41 to perform preliminary static elimination. When the in-machine temperature T is less than 5 ° C., the delay period t2 = 1.53 sec (for three rotations of the photosensitive drum 11), so that the photosensitive drum 11 is in the first to third rotations during preliminary charging. In other words, the static elimination control unit 55 turns off the static elimination lamp 41, and during the fourth rotation of the photosensitive drum 11, the static elimination control unit 55 turns on the static elimination lamp 41 to perform preliminary static elimination.

  Next, in the color printer 1 having such a configuration, an operation of performing preliminary charging and preliminary neutralization before image formation will be described with reference to a flowchart of FIG. 5 and a timing chart of FIG.

  First, the control unit 50 of the color printer 1 receives a print job command from an operation unit (not shown) provided in the color printer 1, a computer connected to the color printer 1, or the like (step S1 in FIG. 5, time in FIG. 6). T1).

  Here, the control unit 50 acquires the in-machine temperature T of the printer main body 2 detected by the temperature sensor 56 (step S2), and the static elimination control unit 55 calculates the preliminary static elimination delay period t2 based on the in-machine temperature T. (Step S3).

  Then, the control unit 50 controls each unit so as to start preliminary charging of the photosensitive drum 11, the drum driving unit 52 rotationally drives the photosensitive drum 11, and the charging control unit 53 detects the charging unit 12. The surface of the body drum 11 is precharged (step S4 in FIG. 5, time T1 in FIG. 6). In this preliminary charging stage, the development control unit 54 has not yet started the operation of the development unit 13, that is, does not start application of the development bias to the magnetic roller 36 or the development roller 37. Further, since the static elimination control unit 55 does not perform preliminary static elimination until the delay period t2 elapses from the start of preliminary charging, has the delay period t2 elapsed since the start of preliminary charging using a timer (not shown)? Whether or not is monitored (step S5 in FIG. 5).

  When the delay period t2 has elapsed from the start of preliminary charging (step S5 in FIG. 5: YES), the static elimination control unit 55 causes the static elimination unit 15 to perform preliminary static elimination on the surface of the photosensitive drum 11 (step in FIG. 5). S6, time T2 in FIG. Here, the static elimination control unit 55 controls the static elimination unit 15 to perform preliminary static elimination during the preliminary static elimination period t3 until the image forming operation is performed after the delay period t2.

  When the preliminary neutralization period t3 has elapsed after the delay period t2 has elapsed, that is, when the preliminary charging period t1 has elapsed since the start of preliminary charging (step S7 in FIG. 5: Yes, time T3 in FIG. 6), preliminary charging and preliminary The static elimination ends (step S8 in FIG. 5), and the process proceeds to an image forming operation (step S9 in FIG. 5). In the image forming operation, the charging controller 53 causes the charging unit 12 to perform normal charging while the drum driving unit 52 continues to rotate the photosensitive drum 11, and the charge removal control unit 55 performs normal charge removal to the charge removal unit 15. Make it. At this time, the development control unit 54 also starts the operation of the development unit 13 and starts applying a development bias to the magnetic roller 36 and the development roller 37.

  According to the present embodiment, as described above, the color printer 1 includes the photosensitive drum 11 (positively charged single layer type photosensitive member) that is rotatably provided, the charging unit 12, the charge eliminating unit 15, and the charge control. Unit 53 and a charge removal control unit 55. The charging unit 12 includes a conductive charging roller 31 that applies a DC voltage to the photosensitive drum 11 to charge the surface of the photosensitive drum 11. The neutralization unit 15 neutralizes the surface potential of the photosensitive drum 11. The charging control unit 53 controls charging of the photosensitive drum 11 by the charging unit 12. The neutralization control unit 55 controls the neutralization of the photosensitive drum 11 by the neutralization unit 15. Further, the charging control unit 53 performs precharging to charge the photoconductive drum 11 during a predetermined precharging period t1 before the image forming operation using the photoconductive drum 11 is executed. To control. The neutralization control unit 55 provides a delay period t2 from the start of preliminary charging to the start of preliminary neutralization as preliminary neutralization for neutralizing the photosensitive drum 11 charged by preliminary charging. After the delay period t2, the image forming operation is performed. The static eliminator 15 is controlled so as to perform preliminary static elimination during the preliminary static elimination period t3 until is executed.

  Thus, by providing the preliminary static elimination delay period t2 at the start of preliminary charging, the static elimination unit 15 is stopped and the static elimination lamp 41 is extinguished, so that trap carriers staying in the photosensitive drum 11 are not generated. Compared with normal image formation, the charging ability of the photosensitive drum 11 is improved even in a low temperature environment. As described above, since the charging ability of the photosensitive drum 11 does not decrease, the charging rise time can be shortened without increasing the voltage applied to the charging roller 31 more than necessary, and the desired surface potential of the photosensitive drum 11 can be reduced. Can be obtained in a short time. Therefore, it is possible to extend the life by avoiding film scraping of the photosensitive drum 11 due to the discharge from the charging roller 31.

  Further, there is no need to increase the diameter of the charging roller 31, expand the discharge area, or extend the charging time by reducing the rotation speed of the image forming unit 7 (photosensitive drum 11). There is no hindrance to speed and speed.

  Furthermore, since a desired charging bias can be obtained quickly, the preliminary charging period t1 itself can be shortened. As a result, there is no risk of damage to the charging roller 31 and the photosensitive drum 11 due to prolonged precharging even in a low temperature environment, and the product life can be guaranteed for users who use in a low temperature environment.

  Therefore, in the configuration including the positively charged single-layer type photosensitive drum 11 and the charging roller 31, it is possible to prevent a decrease in charging ability of the photosensitive drum 11 and the charging roller 31 in a low temperature environment, such as fogging. Image defects can be avoided.

  Further, in the preliminary charging period t1, the static elimination control unit 55 stops the static elimination unit 15 in the delay period t2, while the static elimination unit 15 only needs to be operated in the preliminary static elimination period t3. A simple configuration for OFF control can be employed. In such a configuration, since it is sufficient to design the circuit so that the switch of turning on / off of the charge removal lamp 41 can be performed in accordance with a signal from the CPU (control unit 50), the strength of the charge removal lamp 41, that is, to the charge removal unit 15 is determined. No complicated circuit design is required to vary the input voltage.

  As an example of the color printer 1 of the present embodiment as described above, the surface of the photosensitive drum 11 after the start of a print job after the color printer 1 is left in an environment having an outside air temperature of 10.0 ° C. for 4 hours. The result of measuring the time transition of the potential is shown in the graph of FIG. In this embodiment, the optimum value of the surface potential of the photosensitive drum 11 at the time of image formation corresponding to the print job is set to 520 V, and each of the charging unit 12, the developing unit 13, and the primary transfer unit 14 is set accordingly. Set the bias value. In this embodiment, a surface potential sensor for measuring the surface potential of the photosensitive drum 11 is installed at the contact position between the photosensitive drum 11 and the developing roller 37.

  After the color printer 1 was left for 4 hours, the temperature sensor 56 detected 9 ° C. as the in-machine temperature T of the printer body 2. Therefore, the charge removal control unit 55 obtains a delay time tb = 1.02 sec for two rotations of the photosensitive drum 11 from the relationship between the in-machine temperature T and the delay period t2 as shown in FIG. The time transition of the surface potential of the photosensitive drum 11 when such a delay time tb of the static eliminating unit 15 is provided is shown by a solid line in FIG. As shown in FIG. 7, the static elimination control unit 55 stops the preliminary static elimination for two rotations of the photosensitive drum 11 and turns off the static elimination lamp 41 of the static elimination unit 15 in the preliminary charging period t1, and then the photosensitive drum The preliminary charge removal is executed for one rotation of 11 to turn on the charge removal lamp 41 of the charge removal unit 15. When the photosensitive drum 11 was rotated three times under this condition (after 1.53 seconds had elapsed), the surface potential of the photosensitive drum 11 reached approximately 520 V, and an image could be formed.

  In addition, the time transition of the surface potential of the photosensitive drum 11 when the delay time tb of the static elimination unit 15 is not provided is indicated by a two-dot chain line in FIG. As shown by a two-dot chain line in FIG. 7, when the delay time tb of the static eliminating unit 15 is not provided, the photosensitive drum 11 is moved until the surface potential of the photosensitive drum 11 reaches the target surface potential of about 500V. It is necessary to rotate 5 times. Therefore, according to the color printer 1 of the present embodiment, it can be seen that the effect of reducing the driving distance for two rotations of the photosensitive drum 11 can be obtained.

  Further, according to the present embodiment, the static elimination control unit 55 sets the preliminary static elimination period t3 longer than the time for rotating the photosensitive drum 11 once in preliminary charging. As a result, the charge charged by the charging unit 12 on the photosensitive drum 11 during the preliminary charging can be reliably eliminated.

  Furthermore, according to the present embodiment, the color printer 1 includes a printer main body 2 (apparatus main body) that houses the photosensitive drum 11, the charging unit 12, and the static elimination unit 15, and a temperature sensor that detects an in-machine temperature T of the printer main body 2. 56. Then, the static elimination control unit 55 sets a delay period t2 and a preliminary static elimination period t3 based on the in-machine temperature T. Thereby, preliminary static elimination suitable for the environment can be realized.

  Further, according to the present embodiment, the static elimination control unit 55 sets the delay period t2 to be longer as the in-machine temperature T is lower. This reliably prevents a decrease in charging ability of the photosensitive drum 11 and the charging roller 31 that is likely to occur in a low temperature environment, and in a normal environment with high charging ability, the preliminary static elimination period t3 is lengthened and the static elimination unit 15 performs preliminary static elimination. Therefore, the surface potential of the photosensitive drum 11 can be prevented from rising more than necessary. Therefore, the developing unit 13 does not charge unnecessary carriers or reversely charged toner.

  In the present embodiment, the static elimination control unit 55 predetermines the temperature thresholds Ta, Tb, and Tc and predetermines the delay periods ta, tb, and tc, and determines the in-machine temperature T of the printer main body 2 stepwise (stepwise). Although the method for determining the delay period t2 has been described, the method for determining the delay period t2 is not limited to this. For example, in another embodiment, the static elimination control unit 55 may set a finer temperature threshold in advance and set a delay period more finely by previously setting a delay period corresponding to each temperature threshold. Alternatively, in another embodiment, the static elimination control unit 55 may determine the delay period t2 based on the in-machine temperature T using a mathematical formula in which the delay period t2 is inversely proportional to the in-machine temperature T.

  In this embodiment, the case where the configuration of the present invention is applied to the color printer 1 has been described. However, in other different embodiments, the present invention is applied to other image forming apparatuses such as a monochrome printer, a copier, a facsimile machine, and a multifunction machine. A configuration may be applied.

1 Color printer (image forming device)
2 Printer body 5 Intermediate transfer belt 7 Image forming section 11 Photosensitive drum (photosensitive body)
DESCRIPTION OF SYMBOLS 12 Charging part 13 Developing part 15 Static elimination part 31 Charging roller 41 Static elimination lamp 50 Control part 51 Memory | storage part 52 Drum drive part 53 Charging control part 54 Development control part 55 Static elimination control part 56 Temperature sensor

Claims (4)

A positively charged single-layer photoreceptor provided rotatably;
A charging unit including a conductive charging roller that applies a DC voltage to the photosensitive member to charge the surface of the photosensitive member;
A charge eliminating portion for eliminating the surface potential of the photoreceptor;
A charge control unit for controlling charging of the photoconductor by the charging unit;
A static elimination control unit that controls static elimination of the photoconductor by the static elimination unit;
With
The charging control unit controls the charging unit to perform preliminary charging for charging the photosensitive member for a predetermined preliminary charging period before an image forming operation using the photosensitive member is performed;
The neutralization control unit provides a delay period from the start of preliminary charging to the start of preliminary neutralization as preliminary neutralization for neutralizing the photosensitive member charged by the preliminary charging, and after the delay period has elapsed, the image An image forming apparatus that controls the static eliminator so as to perform the preliminary static elimination during a preliminary static elimination period until a forming operation is performed.   The image forming apparatus according to claim 1, wherein the static elimination control unit sets the preliminary static elimination period longer than a time for rotating the photosensitive member once in the preliminary charging. An apparatus main body that houses the photosensitive member, the charging unit, and the charge eliminating unit;
A temperature sensor for detecting an in-machine temperature of the apparatus main body,
The image forming apparatus according to claim 1, wherein the static elimination control unit sets the delay period and the preliminary static elimination period based on the in-machine temperature. The image forming apparatus according to claim 3, wherein the static elimination control unit sets the delay period to be longer as the in-machine temperature is lower.

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