JP4386828B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, or a printing machine that transfers and fixes a toner image reversely developed by an electrophotographic process onto a recording sheet. The present invention relates to an image forming apparatus that prevents adhesion.

  Generally, in a photosensitive drum of an electrophotographic image forming apparatus, an electrostatic latent image is formed on a surface layer, and the electrostatic latent image is developed with a developer such as toner to form an unfixed toner image. . Then, the transfer unit is brought into contact with a recording sheet, which is a sheet-like recording medium, on the photosensitive drum, and the toner image is transferred to the recording sheet. After the transfer, the toner image is recorded by heating and pressurizing by the fixing unit. Fix to paper.

  For example, the photoconductor drum forms a photoconductor layer by dispersing fine particles of a photoconductive material in a mixed liquid in which a charge transport material and a resin are melted, and applying this to the surface of the drum base and drying it. To do.

  If the remaining toner adheres to the surface layer of the photosensitive drum after transfer, there is a risk that filming, a black spot of the developer, or the like may occur.

  Therefore, since it is necessary to remove the toner adhering to the surface of the photosensitive drum, a cleaning device provided with a cleaning blade for scraping off the adhering toner is disposed downstream of the transfer process. .

  The cleaning method using a blade is not necessary for a rotating part or its driving part and has a simple structure as compared with a method using a brush, and is therefore widely used in popular machines.

  The cleaning blade is classified into a trading type in which the tip of the edge is directed to the rear side in the movement direction of the drum peripheral surface and a leading type in which the edge tip is directed to the front side in the movement direction depending on the direction in which the blade is applied to the photosensitive drum surface. . In the leading type blade, the blade faces the counter direction, and scrapes off the toner while allowing the blade to bite by the movement of the drum peripheral surface.

  The precision of the cleaning blade and the applied pressure must be appropriate so that the drum surface is not scraped off too much. Therefore, the edge portion of the blade is finished with a highly accurate angle and straightness, and a uniform pressure is applied over the entire length.

  In addition, if the cleaning blade is turned upside down (reversed), the cleaning performance deteriorates. Therefore, the blade is brought into contact with the photosensitive drum with an appropriate pressure so that the blade is not consumed quickly. It is desirable.

  In this case, it is preferable that silica of the toner component, for example, external additive, uniformly adheres to the surface of the photosensitive drum with an appropriate layer thickness and becomes a lubricant for the cleaning blade.

  FIG. 6 is a schematic diagram showing each device for the image forming process in the image forming apparatus. An image forming process will be described with reference to the image forming apparatus shown in FIG.

  As shown in FIG. 6, the photosensitive drum a rotates in the direction of the arrow b, and is uniformly charged to the charging voltage Vg by the charger c before forming the electrostatic latent image on the photosensitive drum a. The charging voltage Vg is substantially the same voltage as the grid voltage of the grid electrode c1 when the charger c is a scorotron.

  An electrostatic latent image is formed on the photosensitive drum a by irradiating the charged photosensitive drum a with laser light L modulated with an image signal.

  The developing roller e of the developing device rotating in the direction of the arrow d is opposed to the downstream side portion of the photosensitive drum a where the electrostatic latent image is formed. When the surface of the photosensitive drum a on which the electrostatic latent image is formed is in contact with the developer layer on the surface of the developing roller e, the toner in the developer adheres to the latent image portion on the photosensitive drum a, and the photosensitive drum a A toner image is developed on the surface of the body drum a.

  Usually, reversal development is performed in which the black and white of the electrostatic latent image is reversed.

  The developed toner image is transferred to the recording paper P by applying a transfer voltage Tc by the transfer roller f of the transfer device. After the toner image is transferred to the recording paper P, the cleaning blade h of the cleaning device comes into contact and scrapes off the remaining toner.

  A developing bias voltage Vb is applied to the developing roller e so that the threshold voltage at the start of development is changed with respect to the fluctuation of the background potential of the photosensitive drum a, so that a low-density character original is reproduced without background contamination. Is given.

  The potential difference between the charging voltage Vg of the charger c and the developing bias voltage Vb is related to the amount of residual toner on the photosensitive drum a and is called a cleaning field (potential). This cleaning field is a potential for cleaning by electrostatic force to prevent the toner from adhering to the charged portion of the photosensitive drum where the laser beam is not applied, and the charged charging voltage and the developing bias voltage. And the potential difference. If the cleaning field is not constant, the edge effect is increased, the toner adhesion amount at the edge portion is increased, and the stability of the image quality is lowered. In addition, problems such as trailing edge and fogging due to poor cleaning occur.

  Therefore, it is necessary to set the cleaning field appropriately.

  However, the cleaning field is not set so as to remove all toner components, but is set so that components such as silica remain to some extent on the surface of the photosensitive drum. As a result, the contact of the cleaning blade is made smooth so as to protect the surface of the photosensitive drum.

  As for the clean field, conventionally, the difference in the cleaning field of the difference between the charging voltage Vg by the charger and the developing bias voltage Vb is provided between the first and second rotations of the photosensitive drum, and the photosensitive drum A technique has been proposed in which the fluctuation of the potential is adjusted to prevent the trailing edge from being chipped (see Patent Document 1).

Further, in a multicolor image forming apparatus, in order to suppress the tendency of the charging voltage of each color to decrease when developing on a single photosensitive drum by a multicolor developing device, the charging voltage is adjusted to adjust the charging voltage and the developing bias voltage. Alternatively, a technique for controlling the cleaning field by changing the developing bias voltage is also disclosed (see Patent Document 2).
JP 2002-55496 A JP 2001-125335 A

  However, in the image forming apparatus described above, a transfer voltage is applied by a transfer device such as a transfer roller. However, if the humidity increases or decreases due to changes in the surrounding environment, a + (plus) current during transfer is applied to the photosensitive drum a. The flowing amount increases and decreases, the residual + (plus) charge on the surface of the photosensitive drum a increases and decreases, and the amount of silica that remains and adheres to the surface of the photosensitive drum a also changes.

  Accordingly, when the humidity of the surrounding environment increases, the amount of silica adhering to the photosensitive drum increases. When the thickness of the silica layer adhering to the photosensitive drum is increased, the cleaning blade is caught, and the cleaning blade may be reversed (turned up).

  When such reversal occurs, the cleaning blade is chipped or damaged, and eventually the residual toner cannot be sufficiently removed, resulting in contamination of the toner image and deterioration of image quality printed on the recording paper. There was a problem of end.

  In view of the above-described problems, the present invention appropriately controls the residual component of the toner adhering to the surface of the photosensitive drum to prevent the cleaning blade contacting the surface of the photosensitive drum from reversing, and accordingly, the photosensitive drum An image forming apparatus capable of reliably preventing the deterioration of a toner image formed on the surface of a body drum is provided.

  The present invention relates to an image forming apparatus.

In the image forming apparatus according to the first aspect of the present invention, a negative charge is supplied to the surface of the photosensitive drum by the charger, the charging polarity of the photosensitive drum is negative, the charging voltage is Vg, and the charging voltage Vg After the electrostatic latent image is formed on the surface of the photosensitive drum, toner containing silica having a negative charge polarity as an external additive is supplied to the surface of the photosensitive drum by a developing unit that applies a developing bias voltage Vb. The electrostatic latent image on the surface is developed into a toner image, and a transfer voltage is applied to the transfer device to transfer the toner image from the surface of the photosensitive drum to the recording paper, and a cleaning blade is applied to the surface of the photosensitive drum after transfer. In an image forming apparatus that removes residual toner by contact,
A humidity detector that detects the humidity around the photosensitive drum, and a controller that controls the potential difference [Vg−Vb] between the charging voltage Vg of the photosensitive drum and the developing bias voltage Vb and the transfer voltage or transfer current of the transfer unit. Provided,
The control unit is configured to set a first predetermined humidity and a second predetermined humidity greater than the first predetermined humidity, and the humidity detected by the humidity detection unit is equal to or higher than the first predetermined humidity and is second. Is less than the predetermined humidity, the potential difference [Vg−Vb] between the charging voltage Vg of the photosensitive drum and the developing bias voltage Vb is obtained from the first potential difference [Vg−Vb] 1 when the humidity is less than the first predetermined humidity. Is set to a second potential difference [Vg−Vb] 2,
When the humidity detected by the humidity detector is equal to or higher than the second predetermined humidity, the potential difference [Vg−Vb] between the charging voltage Vg of the photosensitive drum and the developing bias voltage Vb is set to the second potential difference [Vg−Vb]. A third potential difference [Vg−Vb] 3 greater than 2 and a transfer voltage or transfer current of the transfer device is lowered as compared with a case where the transfer voltage or transfer current is lower than the second predetermined humidity. is there.

According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the potential difference control unit forms an electrostatic latent image from charging of the image forming area of the photosensitive drum by a charger. The potential difference [Vg−Vb] between the charging voltage Vg of the photosensitive drum and the developing bias voltage Vb is set at a timing other than the steps from the development of the electrostatic latent image to the toner and the transfer of the toner image onto the recording paper. Control is performed so that the second potential difference [Vg−Vb] 2 is obtained.

According to the image forming apparatus of the first or second aspect of the present invention, the control unit sets a first predetermined humidity and a second predetermined humidity that is higher than the first predetermined humidity. When the humidity detected by the humidity detector is equal to or higher than the first predetermined humidity and lower than the second predetermined humidity, the potential difference [Vg−Vb] between the charging voltage Vg of the photosensitive drum and the developing bias voltage Vb is set to the first. When the second potential difference [Vg−Vb] 2 is larger than the first potential difference [Vg−Vb] 1 when the humidity is less than the predetermined humidity, and the humidity detected by the humidity detector is equal to or higher than the second predetermined humidity. Because the potential difference [Vg−Vb] between the charging voltage Vg of the photosensitive drum and the developing bias voltage Vb is set to a third potential difference [Vg−Vb] 3 larger than the second potential difference [Vg−Vb] 2. , to increase the cleaning field Thus, it is possible to prevent components such as silica of the toner from adhering too much to the photosensitive drum.

  Accordingly, the residual component of the toner adhering to the surface of the photosensitive drum is appropriately controlled to prevent the cleaning blade contacting the surface of the photosensitive drum from being reversed, and therefore, the toner image formed on the surface of the photosensitive drum is prevented. Deterioration can be reliably prevented.

  The point of adhesion of the toner component relating to the cleaning field will be described.

  In the electrophotographic image forming process shown in FIG. 6 described above, when the humidity around the photosensitive drum a of the image forming apparatus becomes high due to changes in the surrounding environment and atmosphere, the blade is inverted (turned up). End up. As a result of investigating the cause of the reversal, the silica adhered firmly on the photosensitive drum is greatly involved, and the cleaning blade becomes a hindrance to slip, and the reversal (turning) occurs due to being caught or shortened quickly. It has been found that blade reversal can be prevented by reducing the amount of silica on the photosensitive drum.

  The cleaning field is set in order to prevent the toner from adhering to the photosensitive drum a, but it is also effective to prevent the silica separated from the toner from adhering to the photosensitive drum a.

  Therefore, in the present invention, when the humidity becomes equal to or higher than the predetermined humidity, the potential difference [Vg−Vb] between the charging voltage Vg and the developing bias voltage Vb is increased, that is, the cleaning field is increased so that silica is the photosensitive member. The amount adhering to the drum a is reduced. In other words, silica or the like, which is an external additive of the toner, is hydrophobized by a surface treatment agent such as dimethyldichlorosilane, hexmethyldisilazane, or alkylsilane, so that the charging polarity is negative (−), and the photosensitive member by the charger is used. In the case where the drum a has a negative (−) polarity, the cleaning field is increased to increase the electrostatic repulsive force between the surface of the photosensitive drum a and silica and the electrostatic attraction force to the developing device and carrier. Silica is prevented from adhering to the surface of the photosensitive drum a. This prevents the silica from adhering too much, so that it is possible to reliably prevent the cleaning blade from being inverted.

In addition to the above effects, the present invention has the following effects.

According to the present invention, when the humidity detected by the humidity detecting portion is a second predetermined humidity above, since lowering than when the transfer voltage or transfer current of the transfer unit smaller than the second predetermined humidity, paper The surface of the photosensitive drum that does not come into contact with the recording paper, such as between, becomes positive (+) charged polarity by the voltage of the transfer device after passing through the transfer area, but the silica after passing through the transfer voltage is reduced by reducing the transfer voltage. The surface potential becomes almost zero, and silica reduces the adhesion force of silica from the photosensitive drum to the photosensitive drum, and prevents electrostatic attraction between the cleaning blade and the photosensitive drum, ensuring that the cleaning blade is reversed. Can be prevented.

  In the electrophotographic image forming process shown in FIG. 6 described above, when a positive transfer voltage is applied to the photosensitive drum a having a negative polarity charged by the charger c by the transfer roller f of the transfer device, the humidity As a result, a positive charge flows into the photosensitive drum a, and the photosensitive drum a is charged to a positive polarity. Due to this positive polarity, the negative polarity charged with silica is attracted and the adhesion of silica to the photosensitive drum a increases.

Accordingly, in the present invention of claim 1 , the adhesion force of silica to the photosensitive drum is reduced by decreasing the transfer voltage or the transfer current of the transfer device to reduce the positive charge flowing into the photosensitive drum. The electrostatic attraction force between the cleaning blade and the photosensitive drum can be reduced, and the cleaning blade can be reliably prevented from being reversed.

According to the invention of the image forming apparatus according to claim 2, the electrical potential difference control unit, the image forming region of the photosensitive drum, the charging by the charger, forming an electrostatic latent image, development by toner of the electrostatic latent image The potential difference [Vg−Vb] between the charging voltage Vg of the photosensitive drum and the developing bias voltage Vb is set to the second potential difference [Vg−Vb] at a timing other than the process until the transfer of the toner image to the recording paper. Therefore, in the image forming area, the potential difference is changed during the formation of the electrostatic latent image or the transfer of the toner image to prevent the image forming condition from changing, and the image forming condition is made constant. Thus, the image quality formed can be kept good.

  The timing includes the pre-rotation timing for charging the photosensitive drum with a uniform voltage before image formation, the timing between recording sheets in the case of continuous printing, and the image forming process is completed after the image is transferred to the recording sheet. There are timings for post-rotation, etc., and in either case, the voltage is switched at a timing that does not affect image formation, not during image formation, to prevent changes in image forming conditions and transfer conditions in the image forming unit Can do.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  1 to 5 show an example of an image forming apparatus according to an embodiment of the present invention. In the drawings, the same reference numerals denote the same components.

  FIG. 1 is an explanatory diagram showing an overall schematic configuration of an embodiment of an image forming apparatus according to the present invention, and FIG. 2 is an electrical control block diagram of the image forming apparatus of FIG.

  As shown in FIGS. 1 and 2, the image forming apparatus according to the embodiment supplies electric charges to the surface of the photosensitive drum 48 a by the charger 48 b and sets the charging voltage of the photosensitive drum 48 a to Vg. After the electrostatic latent image is formed on the surface of the photosensitive drum 48a, the electrostatic latent image on the surface of the photosensitive drum 48a is reversely developed and developed into a toner image by a developing device 48c that applies a developing bias voltage Vb to the toner. By applying a transfer voltage to the transfer device 48d, the toner image is transferred from the surface of the photosensitive drum 48a to the recording paper P, and residual toner is removed by bringing the cleaning blade 48e1 into contact with the surface of the photosensitive drum 48a after the transfer. In the image forming apparatus that performs the reversal development process, the humidity detector 66 that detects the humidity around the photosensitive drum 48a, and the humidity detector 66 Accordingly, when the detected humidity is equal to or higher than the first predetermined humidity, the potential difference [Vg−Vb] between the charging voltage Vg of the photosensitive drum and the developing bias voltage Vb is the first when the detected humidity is less than the first predetermined humidity. And a potential difference control unit 68 for controlling the charging voltage Vg or the developing bias voltage Vb so that the second potential difference [Vg−Vb] 2 is larger than the potential difference [Vg−Vb] 1.

  The image forming apparatus of the embodiment is a digital copying machine 30, and the main body of the digital copying machine 30 is roughly composed of a scanner unit 31 and a laser printer unit (laser recording unit) 32, which will be described in detail below. .

  The scanner unit 31 automatically places a document placing table 35 on which a fixed document made of transparent glass is placed, and automatically feeds a document placed on the document placing table 35 to a fixed document made of transparent glass for automatically feeding and reading the document. It comprises a double-sided automatic document feeder (RADF) 36 for feeding and conveying, and a document image reading unit for scanning and reading an image of a document placed on the document placement table 35, that is, a scanner unit 40. ing.

  The document image read by the scanner unit 31 is sent as image data to an image processing unit 47 described later, and predetermined image processing is performed on the image data.

  In the RADF 36, a plurality of documents are set at a time on a document tray provided at the top, and the set documents are automatically fed onto the document placing table 35 of the scanner unit 40 one by one. Device. Further, the RADF 36 passes through a conveyance path for a single-sided document, a conveyance path for a double-sided document, a conveyance path switching unit, and each unit so that the scanner unit 40 reads one or both sides of the document according to an operator's selection. It consists of a group of sensors that grasp and manage the state of the document, a control unit, and the like. Since many applications and commercialization of this RADF 36 have been made, further explanation will be omitted.

  A scanner unit 40 that constitutes a scanner unit 31 for reading an image of a document on the document table 35 is configured to guide a lamp reflector assembly 41 that exposes the document surface and a reflected light image from the document to the photoelectric conversion element 44. A first scanning unit 40a having a first reflecting mirror 42a for reflecting the reflected light of the original, and second and second light beams for guiding the reflected light image from the first reflecting mirror 42a to the photoelectric conversion element 44. A second scanning unit 40b having three reflecting mirrors 42b and 42c mounted thereon, and a reflected light image from the original guided through the reflecting mirrors 42a to 42c is condensed on the photoelectric conversion element 44 to form an image. Mainly from an optical lens 43 for making the image and a photoelectric conversion element 44 comprising an arrayed CCD (charge coupled device) for converting a reflected light image from the imaged original into an electrical image signal. It is made.

  The scanner unit 31 moves the scanner unit 40 along the lower surface of the document placing table 35 while sequentially placing the document to be read on the document placing table 35 by the operation related to the RADF 36 and the scanner unit 40. It is configured to read an image.

  In particular, the first scanning unit 40a travels from the left to the right along the document placement table 35 at a constant speed V, and the second scanning unit 40b is the same at a speed of V / 2 with respect to the speed V. Scan control is performed parallel to the direction. As a result, the image of the document placed on the document placement table 35 is sequentially formed on the CCD element 44 for each line, and the image is read.

  Image data obtained by reading the original image with the scanner unit 40 is sent to the image processing unit 47, where various processing is performed, and then temporarily stored in the memory of the image processing unit 47, in accordance with an output instruction. The image in the memory is read out and transferred to the laser printer unit 32 to form an image on the recording paper. Since various configurations of the image processing unit 47 can be used, description thereof will be omitted.

  The laser printer unit 32 includes a paper conveyance system 50 that is a recording material for forming an image, a laser writing unit 46, and an electrophotographic process unit 48 for forming an image.

  The laser writing unit 46 is a semiconductor laser light source that emits laser light in accordance with image data read from the memory after being read by the scanner unit 40 described above or image data transferred from an external device, and laser light. A polygon mirror that deflects the angular velocity, an f-θ lens that corrects the laser beam deflected at the uniform angular velocity so as to be deflected at a uniform angular velocity on the photosensitive drum 48a constituting the electrophotographic process unit 48, and the like. .

  The electrophotographic process section 48 mainly includes a charger 48b, a developing device 48c, a transfer device 48d, a cleaning device 48e, and a static eliminator (adjacent to the charger) around the photosensitive drum 48a.

  The photosensitive drum 48a is formed by forming a layer of Se alloy, zinc oxide or the like on a cylindrical aluminum alloy drum, and the laser beam emitted from the laser writing unit 46 is incident on the photosensitive drum 48a. As a result, photoelectric conversion occurs at the incident location to form an electrostatic latent image. Specifically, the laser beam is irradiated from the writing unit 46 onto the surface (image forming area) before reaching the developing unit 48b on the surface of the photosensitive drum 48a uniformly charged with negative charges by the charger 48b. Then, a positive charge is generated by photoelectric conversion at the portion irradiated with the laser light, the charge amount is changed, and an electrostatic latent image is formed by a set of portions where the charge amount is changed. A reversal development method is employed in which the amount of charge differs between a portion where the laser beam does not hit and a portion where the laser beam hits, and the portion where the laser beam hits is developed with toner.

  In the embodiment, the charger 48b is a scorotron having a grid electrode. A predetermined charging voltage Vg is applied to the charger 48b from a voltage source (not shown), and the surface of the photosensitive drum 48a is charged from the grid electrode by corona discharge. Since the charging voltage is substantially the same as the voltage of the grid electrode, the sign of the charging voltage is Vg. Specifically, the predetermined charging voltage Vg is normally −450 (v: volt) at low humidity, but the power supply unit 70 of the charger 48b has a structure that can be controlled to change the charging voltage Vg.

  In the embodiment, the developing device 48c causes the toner to adhere to the photosensitive drum 48a by an electrostatic force by a developing roller to which a predetermined developing bias voltage Vb is applied to the one-component developing toner or the two-component developing toner. Then, the electrostatic latent image on the photosensitive drum 48a is developed by a reversal development method. The developing device 48c may be a brush type that supplies toner to the photosensitive drum 48a by other brushes.

  Further, the voltage (developing bias voltage Vb) of the developing device 48c in the embodiment is smaller than the charging voltage Vg, and the difference between the charging voltage Vg and the developing bias voltage Vb is the cleaning field (Vg−Vg). ). Specifically, when the charging voltage Vg is −450 (v), the developing bias voltage Vb is −325 v under normal low humidity, and the cleaning field (Vg−Vb) is −125 (v). The power supply 72 of the developing device 48c has a structure that can be controlled so as to change the developing bias voltage Vb.

  The transfer device 48d brings the recording paper P into contact with the toner image forming portion of the photosensitive drum 48a, applies a positive high voltage, and causes the toner image to be attracted to the recording paper by electrostatic attraction force. The transfer machine 48d is a roller-type transfer roller, which normally applies a voltage of +2500 (v) (2.5 (kv: kilovolt) at low humidity, and the toner image on the surface of the photosensitive drum 48a is generated by the positive electric field. It is attracted and transferred by electrostatic force to the recording paper P. The power source 74 of the transfer device 48d has a structure that can be controlled to change the transfer voltage.

  A power supply unit for the transfer unit 48d can be used to control the transfer current.

  The cleaning device 48e scrapes off the toner remaining on the surface of the photosensitive drum 48a without being transferred by the cleaning blade 48e1. The cleaning device 48e accommodates the toner scraped by the cleaning blade 48e1 in the collection unit. The cleaning blade 48e1 is made of a leading rectangular resin or metal agent. Further, in the blade 48e1, the abutting side tip portion faces the counter direction of the rotation direction of the photosensitive drum 48a, and the developer is scraped off while the blade bites in by the movement of the peripheral surface of the photosensitive drum 48a. ing.

  On the other hand, the paper transport system 50 includes a registration roller (also referred to as “PS roller”) 33a that transports the paper to the transfer position where the transfer unit 48d is disposed in the electrophotographic process unit 48 that performs the above-described image formation. A transport unit 33, a cassette paper feeding device 51 for feeding paper to the transport unit 33, a fixing device 49 for fixing an image formed on the paper after transfer, particularly a toner image, and a back surface of the paper after fixing. And a re-feeding path 55 for re-feeding paper to form an image again.

  In FIG. 1, reference numerals 52 and 53 denote cassette feeding devices for storing other types of papers having different dimensions and the like, and feeding them to the transport unit 33, and 54 is a manual paper feed to the transport unit 33. This is a manual sheet feeding device for feeding the paper. The plurality of cassette paper feeding devices 51 to 53 constitute a multi-stage paper feeding unit.

  A post-processing device that receives the recording sheet P on which an image is recorded and performs a predetermined process on the recording sheet P is disposed downstream of the fixing device 49.

  In the laser writing unit 46 and the electrophotographic processing unit 48, the image data read from the image memory is formed as an electrostatic latent image on the surface of the photosensitive drum 48a by scanning the laser beam with the laser writing unit 46. The toner image visualized by the toner is electrostatically transferred and fixed on the surface of the sheet conveyed from any one of the sheet feeding units of the multi-stage sheet feeding unit.

  The sheet on which the image is formed in this way is conveyed from the fixing device 49 to the sheet discharge tray unit 34 (upper and lower trays 341 and 342 for sheet stacking) via the sheet discharge driving roller 57. .

  Next, a control configuration of the image forming apparatus according to the embodiment will be described.

  FIG. 2 is an electrical control block diagram of the image forming apparatus according to this embodiment. FIG. 3 is a control table of an embodiment for controlling the charging voltage Vg and the transfer voltage Tc with respect to the relative humidity area (region). In FIG. 3, the relative humidity of 0 to 100% is divided into seven equal areas, and correction values of the charging voltage Vg and the transfer voltage Tc in each of the areas 1 to 7 are shown.

  FIG. 4 is an explanatory diagram of high density correction of the development density of the development bias according to the embodiment. FIG. 5 is a control flowchart of charging voltage / transfer voltage of the image forming apparatus according to the embodiment.

  As shown in FIG. 2, the image forming apparatus according to the embodiment performs read processing, image processing, image formation processing, and transfer processing as well as change processing for changing the charging voltage, development bias voltage, and transfer voltage in ROM (Read-Only). The central processing unit (CPU) 62 of the control unit executes the program using a temporary storage unit such as a RAM (Random-access Memory) 64 according to a program stored in the memory 60 in advance. Instead of the ROM 60 and the RAM 64, a storage means such as an HDD (Hard Disk Drive) can be used.

  The program of the image forming apparatus according to the present invention supplies a charge to the surface of the photosensitive drum by a charger, sets the charging voltage of the drum to Vg, and forms an electrostatic latent image on the surface of the photosensitive drum with the charging voltage Vg. Later, the electrostatic latent image on the surface of the photosensitive drum is developed into a toner image by a developing device that applies a developing bias voltage Vb, and the toner image is transferred from the surface of the photosensitive drum to recording paper by applying a transfer voltage to the transfer device. In a program of an image forming apparatus that removes residual toner by bringing a cleaning blade into contact with the surface of the photosensitive drum after transfer, the humidity detection function that detects the humidity around the photosensitive drum and the humidity detection function When the measured humidity is equal to or higher than the first predetermined humidity, a potential difference [Vg−V between the charging voltage Vg of the photosensitive drum and the developing bias voltage Vb is obtained. The charging voltage Vg or the developing bias voltage Vb is controlled so that the second potential difference [Vg−Vb] 2 is larger than the first potential difference [Vg−Vb] 1 when the temperature is less than the first predetermined humidity. The potential difference control function is realized.

  Each of the above functions is achieved by controlling the voltage control unit of the electrophotographic process unit 48 according to the program stored in the ROM 60 by the CPU 62 of the control unit of the image forming apparatus. Input / output of signals to / from the CPU 62 is performed via an interface.

  In the embodiment, the humidity detector 66 can detect the humidity based on the output signal of the humidity sensor 66a provided around the photosensitive drum 48a of the image forming apparatus so that the humidity of the atmosphere can be detected. The sensor can be selected from various types such as a ceramic type, a polymer resin type, and an electrolyte type.

  In the embodiment, the potential difference control unit 68 is configured such that when the humidity detected by the humidity detection unit 66 is equal to or higher than the first predetermined humidity, the potential difference [Vg−Vb] between the charging voltage Vg of the photosensitive drum 48a and the developing bias voltage Vb. ] Is charged by the power supply unit 70 of the charger 48b so that the second potential difference [Vg−Vb] 2 is larger than the first potential difference [Vg−Vb] 1 when the humidity is lower than the first predetermined humidity. The developing bias voltage Vb is controlled by Vg or by the power supply unit 72 of the developing device 48c.

  In the embodiment, as shown in FIG. 3, the first predetermined humidity is set to two relative humidity values of 42% and 57%, and the environmental humidity changes based on these two first predetermined humidity values. The charging voltage (grid voltage) Vg is controlled to increase or decrease in two steps according to the above. The first predetermined humidity can be set to a plurality of three or more, and the correction amount can be set for each of them.

  In the embodiment, as shown in FIG. 3, the potential difference control unit 68 controls the potential difference [Vg−Vb] by increasing or decreasing the charging voltage Vg of the charger 48 b by the power supply unit 70. Yes. The developing bias voltage Vb is kept constant at −325 (v). In addition, the charging voltage Vg of the charger 48b can be kept constant and the development bias voltage Vb can be corrected to increase or decrease, or the charging voltage Vg and the development bias voltage Vb can be corrected together to increase or decrease.

  In FIG. 3, numerical values −25 and −50 (v) are voltage correction amounts for changing the charging voltage Vg, the charging voltage Vg before correction is −455 (v), and the charging voltage Vg after correction is −480 (v). ), −505 (v).

  Specifically, when the relative humidity is less than 42% (less than area 4: areas 1 to 3) under low humidity, the charging voltage Vg is not corrected and is set to −455 (v) constant, and the first potential difference [Vg −Vb] 1 is assumed to be −130 (= (− 455) − (− 325)) (v).

  On the other hand, when the humidity increases and the relative humidity becomes 42% to 56% (less than 57%) (area 4), the charging voltage Vg is corrected by −25 (v) to −480 (v) The second potential difference [Vg−Vb] 2 is increased to −155 (= (− 480) − (− 325)) (v).

  Further, when the humidity increases to become high humidity and the relative humidity becomes 57% or more (areas 5 to 7), the charging voltage Vg is corrected by −50 (v) and becomes large as −505 (v). However, the second potential difference [Vg−Vb] 2 is increased to −180 (= (− 505) − (− 325)) (v).

  In the embodiment, when the humidity detected by the humidity detector 66 is equal to or higher than the second predetermined humidity, the transfer unit controller that lowers the transfer voltage or transfer current of the transfer unit 48d than when the humidity is lower than the second predetermined humidity. 76 is provided.

  In the embodiment, the transfer device controller 76 controls to increase or decrease the transfer voltage Tc of the transfer device 48d under a constant current. The present invention can also control to increase or decrease the transfer current of the transfer device 48d under a constant voltage.

  In the embodiment, as shown in FIG. 3, the second predetermined humidity is set to 57% as a relative humidity, and the second predetermined humidity is set according to a change in the humidity of the environment based on the one second predetermined humidity. Control is performed to increase or decrease the transfer voltage Tc in one stage.

  In the present invention, a plurality of second predetermined humidity can be set and a correction amount can be set for each of them. In addition, the second predetermined humidity may be the same as the first predetermined humidity as described above (such as when the relative humidity is 57%) or may be different (such as when the relative humidity is 42%).

  Specifically, in the transfer voltage control of the transfer device controller 76, as shown in FIG. 3, a numerical value −250 (v) is a voltage correction amount for changing the transfer voltage Tc. In the embodiment, the transfer voltage is 2.5 (kv) before correction.

  Specifically, when the relative humidity is less than 57% (less than area 5: areas 1 to 4) under low humidity, the transfer voltage Tc is set to 2.5 (kv) without correction. On the other hand, when the humidity increases under high humidity and the relative humidity is 57% or more (area 5 or more: areas 5 to 7), the transfer voltage Tc is reduced by −250 (v) to +2.25 (kv). It is said.

  In the embodiment, a difference is provided in the control of increase / decrease between the charging voltage Vg and the transfer voltage Tc. In other words, when the detected humidity is within the range of area 4 (relative humidity 42 to 56%), only the charging voltage Vg is corrected to −25 (v) to be −480 (v), which is detected by a change in environment. When the humidity is within the range of area 5 or more (relative humidity 57% or more), the correction amount of the charging voltage Vg is set to −50 (v) and the correction amount of the transfer voltage Tc is set to −250 (v). It is said. In other words, the first predetermined humidity has two relative humidity of 42% and 57% for the charging voltage Vg, but the second predetermined humidity is one of the relative humidity 57% for the transfer voltage (transfer current). Yes. In addition, of course, the first predetermined humidity and the second predetermined humidity can be appropriately set according to the characteristics of the image forming environment of the image forming apparatus.

  In the embodiment, the potential difference control unit 68 changes the charging of the image forming area of the photosensitive drum 48a by the charger 48b to the formation of the electrostatic latent image, the development of the electrostatic latent image with toner, and the recording sheet P of the toner image. The potential difference [Vg−Vb] between the charging voltage Vg of the photosensitive drum and the developing bias voltage Vb is controlled to be the second potential difference [Vg−Vb] 2 at a timing other than the process until the transfer of the toner. .

  In the embodiment, the timing other than the process from the charger 48b to the transfer includes the pre-rotation of the photosensitive drum 48a, the interval between recording sheets, and the post-rotation.

  FIG. 4 is an explanatory diagram of high density correction of the developing bias voltage Vb.

  Note that, after controlling the potential difference [Vg−Vb] to be the second potential difference, in the embodiment, high density correction is performed in which the developing bias voltage is corrected based on the patch that has produced the density of the developed toner image.

This high density correction is performed by the following procedure. In the embodiment, this density correction is performed by an automatic sequence every time the condition is satisfied.
(1) The laser power (PWM) is fixed to 100%.
The charging voltage Vg is fixed to −600V.
As shown in FIG. 4, the development bias voltage Vb is switched (switched) to -275v, -325v, and -375v to create three patches.
Specifically, the patch is formed at a predetermined location on the intermediate transfer member.
(2) Read the reflected light (scattered light) I1, I2, and I3 of the patch.

(3) As shown in FIG. 4, I1, I2, and I3 are connected by a straight line.

(4) A development bias Vbo that becomes the reference reflected light Io is obtained.

(5) The development bias voltage is set to -Vbo.

    Finish development bias correction

    Then, the high density correction ends.

In the next high density correction, based on Vbo obtained this time,
Three patches are made with Vbo + 50v, Vbo, and Vbo-50v, and the procedure (1) is performed.

  Note that the timing for performing the high density correction can be performed after the potential difference correction by the humidity according to the above-described embodiment. However, the fixing is performed when the power to the image forming apparatus is turned on or the slip mode is released. When the temperature of the container 49 is 45 ° C. or more, when the number of printed sheets of recording paper P reaches 1000 after changing the previous developing bias voltage to the correction (second [Vg−Vb] 2), the photosensitive drum For example, after replacement of 48a, after replacement of the developer.

  FIG. 5 is a flowchart of a control process for the potential difference [Vg−Vb] between the charging voltage Vg of the photosensitive drum 48a and the developing bias voltage Vb and the transfer voltage Tc according to the embodiment. In this flowchart and the following description, each “step” is abbreviated as “S”. If the determination result is positive, it is abbreviated as “Y”, and if it is not, it is abbreviated as “N”.

  In the image forming apparatus, the initial charging voltage Vg is −455 (v) and the transfer voltage Tc is +2.5 (kv) in the image forming process.

  First, the humidity around the photosensitive drum (relative humidity) is detected (S1).

  It is determined whether the detected humidity is equal to or higher than 42% relative humidity which is one of the first predetermined humidity h1 (S2).

  If the detected humidity is 42% or higher (S2: Y), it is determined whether or not the detected humidity is within the range of area 4 (42 to 56% (less than 57%)) (S3). .

  On the other hand, if the detected humidity is less than 42% relative humidity (S2: N), the charging voltage Vg and the transfer voltage Tc are not corrected (correction amount 0), and the process returns to S1.

  If the detected humidity is within the range of area 4 (S3: Y), the charging voltage Vg is corrected by −25 (v) and increased to −480 (v), and the second potential difference [Vg−Vb] 2 is − 155 (= (− 480) − (− 325)) (v) (S4). After correction to the second potential difference [Vg−Vb] 2, the process returns to S1 to prepare for the next humidity change.

  If the detected humidity is not within the range of area 4 (S3: N), the relative humidity is 57% or more which is the other h2 of the first predetermined humidity. In this case, the charging voltage Vg is corrected by −50 (v) to increase to −505 (v), and the second potential difference [Vg−Vb] 2 is −180 (= (− 505) − (− 325)) ( v), and the transfer voltage Tc is set to -250 (v) to obtain 2.25 (kv) (S5). And after processing, it returns to S1.

  Note that the image forming apparatus of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

1 is an explanatory diagram showing an overall schematic configuration of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is an electrical control block diagram of the image forming apparatus in FIG. 1. It is a control table of an embodiment which controls charging voltage Vg and transfer voltage Tc to a relative humidity area (area). It is explanatory drawing of the high density correction | amendment of the developing density of the developing bias which concerns on embodiment. 3 is a control flowchart of the image forming apparatus according to the embodiment. It is explanatory drawing of an image formation process with each apparatus arrange | positioned around a photoreceptor drum and its periphery.

Explanation of symbols

30 Digital copier 31 Scanner unit 32 Laser printer unit 33 Conveying unit 40 Scanner unit 46 Laser writing unit 47 Image processing unit 48 Electrophotographic process unit 48a Photosensitive drum 48b Charger 48c Developer 48d Transfer device 48e Cleaning device 48e1 Cleaning blade 49 Fixing device 60 ROM
62 CPU (control unit)
64 RAM
66 Humidity detector 68 Potential difference controller 70 Power supply (for charger)
72 Power supply (for developer)
74 Power supply (for transfer device)
76 Transfer Device Controller Io Reference Reflected Light P Recording Paper Tc Transfer Voltage Vb Development Bias Voltage Vg Charging Voltage

Claims (2)

A negative charge is supplied to the surface of the photoconductive drum by the charger, the charge polarity of the photoconductive drum is negative, the charging voltage is set to Vg, and an electrostatic latent image is formed on the surface of the photoconductive drum having the charged voltage Vg. After that, a developer containing a developing bias voltage Vb supplies toner containing silica having a negative charge polarity to the external additive to the surface of the photosensitive drum to develop the electrostatic latent image on the surface of the photosensitive drum into a toner image, In an image forming apparatus that transfers a toner image from a surface of a photosensitive drum to a recording sheet by applying a transfer voltage to a transfer device, and removes residual toner by bringing a cleaning blade into contact with the surface of the photosensitive drum after transfer. ,
A humidity detector that detects the humidity around the photosensitive drum, and a controller that controls the potential difference [Vg−Vb] between the charging voltage Vg of the photosensitive drum and the developing bias voltage Vb and the transfer voltage or transfer current of the transfer unit. Provided,
The control unit is configured to set a first predetermined humidity and a second predetermined humidity greater than the first predetermined humidity, and the humidity detected by the humidity detection unit is equal to or higher than the first predetermined humidity and is second. Is less than the predetermined humidity, the potential difference [Vg−Vb] between the charging voltage Vg of the photosensitive drum and the developing bias voltage Vb is obtained from the first potential difference [Vg−Vb] 1 when the humidity is less than the first predetermined humidity. Is set to a second potential difference [Vg−Vb] 2,
When the humidity detected by the humidity detector is equal to or higher than the second predetermined humidity, the potential difference [Vg−Vb] between the charging voltage Vg of the photosensitive drum and the developing bias voltage Vb is set to the second potential difference [Vg−Vb]. An image forming apparatus characterized in that a third potential difference [Vg−Vb] 3 greater than 2 is set, and the transfer voltage or transfer current of the transfer unit is lowered as compared with a case where the transfer voltage or transfer current is lower than the second predetermined humidity .   The potential difference control unit is a process other than the process from charging by the charger to the image forming area of the photosensitive drum, formation of the electrostatic latent image, development of the electrostatic latent image with toner, and transfer of the toner image to the recording paper. The potential difference [Vg−Vb] between the charging voltage Vg of the photosensitive drum and the developing bias voltage Vb is controlled to be the second potential difference [Vg−Vb] 2 at the timing of (1). The image forming apparatus described in 1.

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