JP2006184555A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of excellently forming a halftone image and a solid image even when the halftone image and the solid image coexist in images to be formed on a sheet of paper. <P>SOLUTION: A laser printer divides image data acquired from the outside and stored in a RAM into a plurality of data in a developing direction (S120), and generates an exposure ratio between an exposure area and a non-exposure area by a scanner part to divided control object areas for every control object area (S140). The laser printer controls the rotating speed of a developing roller in the case of supplying toner to an electrostatic latent image in the control object area based on the exposure ratio (S150 to S240). Therefore, even when the halftone image and the solid image coexist in the images to be formed on a sheet of paper, they are excellently formed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a laser printer.

  2. Description of the Related Art Conventionally, some image forming apparatuses such as laser printers switch print modes according to a user's selection, and form an image on a sheet according to the selected print mode.

  In other words, the image forming apparatus includes a printing mode for a solid image suitable for forming a solid image (so-called solid image) and a printing mode suitable for forming a halftone image that expresses light and shade with dot density. Is configured to be selectable by the user. In the image forming apparatus, when a printing mode is selected by the user, the amount of toner supplied from the developing roller to the photosensitive member is controlled by controlling the rotation speed of the developing roller according to the selected printing mode. And an image suitable for the selected print mode is formed on the paper (see, for example, Patent Document 1).

According to this, for example, when the printing mode for halftone images is selected, the rotation speed of the developing roller is made slower than the rotation speed of the developing roller in the printing mode for solid images, so that a small amount is obtained. Since the toner is supplied to the photosensitive member, a halftone image having sufficient contrast can be formed even in a thin line or a minute dot portion.
Japanese Patent Laid-Open No. 9-80896

  However, since the conventional image forming apparatus forms an image according to the selected print mode, when an image is formed in the print mode for halftone images, there is a solid image in a part of the image. In some cases, the amount of toner supplied to the portion is insufficient and a defective image is formed.

  On the other hand, when an image is formed in the solid image print mode, if there is a halftone image in a part thereof, the amount of toner supplied to the part increases, and fine lines and minute dot parts are removed. There is a case where the toner is sufficiently adhered and the portion is crushed after fixing, so that the contrast cannot be obtained.

  The present invention has been made to solve these problems, and even if a halftone image and a solid image are mixed in an image to be formed on one recording medium, each image is formed satisfactorily. An object of the present invention is to provide an image forming apparatus.

  In order to solve the above problems, the invention according to claim 1 is directed to a photoconductor, an exposure unit that selectively exposes the photoconductor to form an electrostatic latent image based on image data, and a photoconductor. By supplying the developer, a developing roller that develops the electrostatic latent image formed on the photosensitive member by the exposure unit to form a developer image, and an image area for one page represented by the image data Speed control for controlling the rotation speed of the developing roller when supplying the developer to the electrostatic latent image in the control target area based on the exposure ratio between the exposure area and the non-exposure area by the exposure unit with respect to the small control target area Means.

  According to this, the rotation speed of the developing roller when the speed control means supplies the developer to the electrostatic latent image in the control target area during one image forming operation is set to the exposure of the control target area. Since the control is based on the ratio, even if a halftone image and a solid image are mixed in an image to be formed on one recording medium, each image can be formed satisfactorily.

  Therefore, according to the image forming apparatus of the first aspect, the developer necessary for forming a good image can be supplied to the photoconductor, and a defective image is formed due to a shortage of developer or excessive developer. Can be suppressed.

  By the way, in the image forming apparatus, when the developer is supplied from the developing roller to the photosensitive member, the developer is deteriorated such that the charging performance of the developer is lowered due to friction between the developing roller and the photosensitive member. . As the developer rotates more rapidly, more developer is supplied to the photoconductor, so that more developer deteriorates.

  Therefore, in the image forming apparatus according to claim 1, the speed control unit, as described in claim 2, determines the rotation speed of the developing roller when supplying the developer to the control target area, as an exposure ratio. It is preferable that the smaller the size, the slower.

  According to this, for a region where the exposure ratio of the control target region is not 100% (that is, a region that is not a solid image), the speed control unit rotates the developing roller when supplying the developer to the control target region. In order to make the speed slower than the rotation speed of the developing roller when supplying the developer to the solid image area, the rotation speed of the developing roller is controlled by the rotation amount of the developing roller in one image forming operation. It is possible to reduce the number of image forming apparatuses that do not, and the deterioration of the developer can be minimized.

  In other words, in an image forming apparatus that does not control the rotation speed of the developing roller, the rotation speed of the developing roller is normally set so as not to run out of developer during image formation. Since the rotation speed of the developing roller is controlled to be slower as the exposure ratio of the control target area is smaller, an image suitable for the exposure ratio can be formed, and deterioration of the developer can be suppressed to the minimum. it can.

Therefore, according to the image forming apparatus of the second aspect, it is possible to suppress deterioration of the developer while forming a good image.
Further, according to the image forming apparatus of the second aspect, as the exposure ratio decreases, the rotation speed of the developing roller is decreased, so that the developer supply amount can be suppressed. For this reason, for example, it is possible to lengthen the period required to replace the storage unit storing the developer, or the period required to replenish the developer.

  In addition, the image forming apparatus according to claim 1 or 2 includes storage means for storing image data as described in claim 3, and the speed control means adds the image data stored in the storage means to the image data. Based on this, it is preferable that the exposure ratio of the control target region is generated.

In this way, even if a large amount of image data is input from the outside, it can be dealt with by the storage means storing the image data.
Next, an image forming apparatus according to a fourth aspect is the image forming apparatus according to any one of the first to third aspects, wherein the speed control unit divides the image data into a plurality along the developing direction. When the developer is supplied to the control target area for each control target area based on the exposure ratio for each control target area. The rotation speed of the developing roller is changed.

According to this, since the speed control unit generates an exposure ratio for each divided control target region, the supply amount of the developer supplied to the photoconductor can be controlled more optimally.
According to a fourth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the speed control unit divides each control target area into a plurality of areas along a direction perpendicular to the developing direction. An exposure ratio in each area may be generated, and an area having the largest exposure ratio among the control target areas may be generated as an exposure ratio of the control target area.

  In this way, for example, even if there is only one area of the solid image, the exposure ratio in the control target area where the area is arranged is generated by the speed control means as the area of the solid image. Further, it is possible to efficiently suppress the formation of a defective image due to a shortage of developer.

  By the way, the image forming apparatus according to claim 4 or 5 can form a better image as the length in the developing direction of the control target area divided by the speed control unit is smaller.

  For this reason, in the image forming apparatus according to claim 4 or 5, the length in the developing direction of each control target area divided by the speed control unit is set to the circumference of the developing roller. It is good to comprise so that it may become below length.

  In this way, even if a portion (solid image) having an exposure ratio of 100% is continuously generated by the speed control means, the supply amount of the developer supplied from the developing roller to the photoconductor is reduced. Can be prevented from occurring.

  That is, when the solid image continues continuously for longer than one rotation of the developing roller, when the developing roller enters the second rotation, the amount of developer supplied to the photosensitive member by the developing roller decreases. In the image forming apparatus according to the sixth aspect, the occurrence of this problem is prevented by setting the length of each control target area in the developing direction to be equal to or less than the circumferential length of the developing roller.

  In addition, in the image forming apparatus according to any one of claims 1 to 6, the speed control unit is configured so that, as described in claim 7, the speed between the necessary minimum rotation speed and the maximum rotation speed of the developing roller is You may comprise so that a rotation speed may be changed continuously according to the exposure rate of a control object area | region.

In this way, the rotation speed of the developing roller can be controlled to an optimum rotation speed corresponding to the exposure ratio for each control target area.
Further, in the image forming apparatus according to any one of claims 1 to 7, the speed control means develops when the exposure ratio of the control target area is 0% as described in claim 8. It is also possible to change the rotation speed of the roller to 0 and stop the developing roller.

In this way, the developing roller is stopped for the control target area where the image need not be formed, so that the deterioration of the developer can be further suppressed.
In addition, in the image forming apparatus according to any one of claims 1 to 8, as described in claim 9, a separation unit that separates the developing roller in contact with the photosensitive member from the photosensitive member; And a separation control unit that operates the separation unit when the exposure ratio of the control target area is 0%, the separation of the developing roller from the photosensitive member causes the separation between the photosensitive member and the developing roller. Deterioration of the developer due to friction can be suppressed.

Hereinafter, a laser printer according to an embodiment to which the present invention is applied will be described with reference to the drawings.
[First Embodiment]
<Overall Configuration of Laser Printer 1>
FIG. 1 is a side cross-sectional view showing a main part of a laser printer as an image forming apparatus of the present invention.

  In FIG. 1, a laser printer 1 includes a feeder unit 4 for supplying a sheet 3 as a recording medium and an image forming unit 5 for forming an image on a fed sheet 3 in a main body frame 2. Yes.

  The feeder unit 4 includes a paper feed tray 6 that is detachably attached to the bottom of the main body frame 2 and one end of the paper feed tray 6 (hereinafter, this one end is referred to as the front side and the opposite side as the rear side). A paper feed mechanism unit 7 provided on the downstream side of the paper feed mechanism unit 7 in the conveyance direction of the paper 3, and a conveyance direction of the paper 3 with respect to the conveyance rollers 8 to 10. And a registration roller 11 provided on the downstream side.

  The paper feed tray 6 has a box shape with an open upper surface capable of accommodating the sheets 3 in a stack, and is detachable in the horizontal direction with respect to the bottom of the main body frame 2. A sheet pressing plate 12 is provided in the sheet feeding tray 6. The sheet pressing plate 12 can stack the sheets 3 in a stacked manner, and is supported so as to be swingable at an end far from the sheet feeding mechanism unit 7, thereby being close to the sheet feeding mechanism unit 7. One end is movable in the vertical direction. A spring (not shown) is disposed below the paper pressing plate 12, and the paper pressing plate 12 is urged upward by the spring. Therefore, the paper pressing plate 12 is swung downward against the biasing force of the spring, with the end portion farther from the paper feeding mechanism unit 7 as a fulcrum as the amount of stacked sheets 3 increases.

  The paper feed mechanism unit 7 includes a paper feed roller 13, a separation pad 14 that faces the paper feed roller 13, and a spring 15 that is disposed on the back side of the separation pad 14. In the paper feed mechanism unit 7, the separation pad 14 is pressed toward the paper feed roller 13 by the biasing force of the spring 15.

  When the paper pressing plate 12 is biased upward by the spring, the uppermost paper 3 on the paper pressing plate 12 is pressed toward the paper feed roller 13. The leading edge of the sheet 3 is sandwiched between the sheet feeding roller 13 and the separation pad 14 by the rotation of the sheet feeding roller 13, and the sheet 3 is separated one by one by the cooperation of the sheet feeding roller 13 and the separation pad 14. The separated sheet 3 is sent to the registration roller 11 by the conveying rollers 8 to 10.

The registration roller 11 is composed of a pair of rollers, and corrects the skew of the sheet 3 and sends it to the image forming position (contact portion between the photosensitive drum 55 and the transfer roller 57).
The feeder unit 4 of the laser printer 1 further includes a multipurpose tray 16 that can stack sheets 3 of any size, and a multipurpose feed for feeding sheets 3 stacked on the multipurpose tray 16. A paper roller 17 and a multi-purpose separation pad 18 facing the multi-purpose paper feed roller 17 are provided. The multipurpose tray 16 is accommodated in a folded state in a front cover 32 described later.

The image forming unit 5 includes a scanner unit 20, a process unit 21 as a process device, and a fixing unit 22.
The scanner unit 20 is provided in the upper part of the main body frame 2 and includes a laser light emitting unit (not shown), a polygon mirror 23 that is driven to rotate, lenses 24 and 25, and reflecting mirrors 26, 27, and 28. A laser beam modulated based on image data representing an image to be formed on the paper 3 is emitted from the laser light emitting unit. The laser beam is a polygon mirror 23, a lens 24, The reflecting mirrors 26 and 27, the lens 25, and the reflecting mirror 28 are passed through or reflected in this order, and irradiated onto the surface of the photosensitive drum 55 of the process unit 21 described later.

The process unit 21 is provided below the scanner unit 20 and is detachably attached to the main body frame 2.
That is, the main body frame 2 covers or covers the main body housing portion 30 for housing the process unit 21, the opening 31 leading to the main body housing portion 30 for detaching the process unit 21 from the main body frame 2, and the opening 31. And a front cover 32 for opening.

The main body accommodating portion 30 is provided as a space in which the process unit 21 can be accommodated below the scanner portion 20 in the main body frame 2.
The opening 31 is formed as a passage from the main body housing portion 30 to the front cover 32. The front cover 32 is provided over the front surface and the upper surface of the front side of the main body frame 2.

The front cover 32 swings between a closed position and an open position, opens the opening 31 in the open position, and covers the opening 31 in the closed position.
Then, the process unit 21 is attached to and detached from the main body housing portion 30 through the opening 31 with the front cover 32 positioned at the open position.

FIG. 2 is a configuration diagram showing the process unit 21.
As shown in FIG. 2, the process unit 21 includes a drum cartridge 33 that is detachably attached to the main body frame 2, and a developing cartridge 34 that is a developer that is detachably accommodated in the drum cartridge 33.

  As shown in FIG. 1, the developing cartridge 34 includes a housing 35, an agitator 36 as a stirring member provided in the housing 35, a supply roller 37, a developing roller 38, and a layer thickness regulating blade 39.

  The housing 35 is formed above the front wall 42, a bottom wall 43 that curves backward from the lower end of the front wall 42, a lower wall 44 that extends rearward from the rear end of the bottom wall 43, and the lower wall 44. The blade support wall 45 is provided.

  Both the front wall 42, the bottom wall 43, the lower wall 44, and the blade support wall 45, and both side walls 46 provided on both sides in the width direction thereof (the direction orthogonal to the front-rear direction and the width direction of the housing 35, the same applies hereinafter). And 47 are integrally formed. Further, the rear side of the casing 35 formed by the lower wall 44, the blade support wall 45, and both side walls 46 and 47 is opened so that a part of the rear side of the developing roller 38 described later is exposed.

  In the front side of the housing 35, a space surrounded by the front wall 42, the bottom wall 43 and the side walls 46 and 47 is formed as a toner storage chamber 40 as a developer storage chamber. On the rear side, a space surrounded by the lower wall 44, the blade support wall 45, and both side walls 46 and 47 is formed as the developing chamber 41.

  The housing 35 includes an upper cover 48 that covers the upper opening of the housing 35. The upper cover 48 is formed as a separate member from the housing 35, and includes an upper plate 49 that covers the upper opening of the housing 35 and an upper partition that extends downward from the rear end side of the upper plate 49. The plate 50 is integrally formed.

  The toner storage chamber 40 stores toner as a developer. The toner is a positively chargeable non-magnetic single component, which is a styrene monomer such as styrene, or an acrylic monomer such as acrylic acid, alkyl (C1 to C4) acrylate, or alkyl (C1 to C4) methacrylate. A polymerized toner obtained by copolymerizing a polymerizable monomer typified by a monomer by a known polymerization method such as suspension polymerization is used. The polymerized toner has a substantially spherical shape with an average particle diameter of about 6 to 10 μm, and has extremely good fluidity. The polymerized toner is blended with a colorant such as carbon black, wax or the like. Further, an external additive such as silica is added to improve the fluidity of the toner.

  An agitator 36 is provided in the toner storage chamber 40. The agitator 36 is made of a resin material such as ABS resin having flexibility, and is provided so as to rotate only in the clockwise direction in FIG.

In the developing chamber 41, a supply roller 37, a developing roller 38, and a layer thickness regulating blade 39 are provided.
The supply roller 37 is provided behind the toner storage chamber 40 along the width direction of the housing 35 and is rotatably supported on both side walls 46 and 47. The supply roller 37 is provided to be rotatable in the direction opposite to the rotation direction of the agitator 36. The supply roller 37 has a metal roller shaft covered with a conductive urethane sponge.

  The developing roller 38 is provided behind the supply roller 37 along the width direction of the housing 35, and rotates on both side walls 46 and 47 so that a part of the developing roller 38 is exposed from an opening provided behind the housing 35. Supported as possible. The developing roller 38 is provided to be rotatable in the same direction as the rotation direction of the supply roller 37.

  The developing roller 38 is coated with a conductive elastic material, conductive urethane rubber or silicone rubber containing carbon fine particles on the surface of a metal roller shaft, and fluorine is contained on the surface of the elastic material. It is formed by coating a coat layer of urethane rubber or silicone rubber. A power supply (not shown) is connected to the roller shaft of the developing roller 38, and a developing bias is applied during development.

  The supply roller 37 and the developing roller 38 are arranged to face each other, and are in contact with the developing roller 38 in a state where the supply roller 37 is compressed to some extent. The supply roller 37 and the developing roller 38 rotate in directions opposite to each other at their opposing contact portions.

  The layer thickness regulating blade 39 is above the supply roller 37 and between the position facing the supply roller 37 and the position facing the photosensitive drum 55 in the rotation direction of the developing roller 38, the blade support wall of the housing 35. 45.

  The layer thickness regulating blade 39 is disposed so as to face the developing roller 38 along the axial direction of the developing roller 38, is provided at the leaf spring member 51, and the tip of the leaf spring member 51, and contacts the developing roller 38. And a press-contact portion 52 made of insulating silicone rubber. The layer thickness regulating blade 39 is in pressure contact with the surface of the developing roller 38 by the elastic force of the leaf spring member 51 while the leaf spring member 51 is supported by the blade support wall 45.

The developing cartridge 34 is provided with a gear mechanism (not shown) that rotationally drives the agitator 36, the supply roller 37, and the developing roller 38.
The gear mechanism section includes an input gear 53 (see FIG. 2) that is rotatably provided between the developing roller 38 and the agitator 36 on the outer wall of one side wall 46 of the developing cartridge 34. 53 is input with power from the developing cartridge motor 126 (see FIG. 7).

  When the power from the developing cartridge motor 126 is input to the input gear 53, the gear mechanism transmits the power to the agitator 36, the supply roller 37, and the developing roller 38, so that these 36 to 38 are transmitted. Rotation drive.

  The drum cartridge 33 includes a drum frame 54 as a photosensitive frame, a photosensitive drum 55 provided in the drum frame 54, a scorotron charger 56, and a transfer roller 57.

  As shown in FIG. 2, the drum frame 54 is formed at the rear as a drum accommodating portion 58 that accommodates a photosensitive drum 55, a scorotron charger 56, and a transfer roller 57. In addition, the drum frame 54 is formed as a process accommodating portion 59 that is open on the front and accommodates the developing cartridge 34 in a detachable manner. Further, an introduction portion 61 into which the roller shaft of the developing roller 38 can be introduced is formed on one side wall 60 of the drum frame 54, and the introduction portion 61 is located on the lower rear side from the upper end of the one side wall 60 of the drum frame 54. It is formed as a substantially fan-shaped notch extending in a curved shape toward the side.

  As shown in FIG. 1, the photosensitive drum 55 is disposed behind the developing roller 38 so as to face the developing roller 38. The photosensitive drum 55 is provided along the width direction of the drum frame 54 and is rotatably supported at both ends in the width direction of the drum frame 54. The photosensitive drum 55 is formed by forming a positively chargeable photosensitive layer made of polycarbonate or the like on the surface of a cylindrical aluminum base tube, and the cylindrical base tube is electrically grounded.

  The scorotron charger 56 is disposed above the photosensitive drum 55 so as not to come into contact with the photosensitive drum 55 at a predetermined interval and is provided along the width direction of the drum frame 54. The scorotron charger 56 is a positively charged scorotron charger that generates corona discharge from a tungsten charging wire, and uniformly charges the surface of the photosensitive drum 55 to a positive polarity.

  The transfer roller 57 is disposed below the photosensitive drum 55 so as to face the photosensitive drum 55, is provided along the width direction of the drum frame 54, and is rotatably supported at both ends in the width direction of the drum frame 54. The transfer roller 57 is formed by coating a metal roller shaft with a conductive rubber material, and a power source (not shown) is connected to the roller shaft. When the toner is transferred to the paper 3, a transfer bias is applied to the roller shaft.

  In the laser printer 1, first, the developing cartridge 34 is mounted on the drum cartridge 33. More specifically, the developing cartridge 34 is attached to the process accommodating portion 59 of the drum frame 54 of the drum cartridge 33 from above. Then, a portion 38 a protruding from the side wall 46 of the developing cartridge 34 on the roller shaft of the developing roller 38 is introduced from the upper side of the introducing portion 61 and disposed at the deepest portion of the introducing portion 61. In this way, the developing cartridge 34 is mounted on the drum cartridge 33, and the process unit 21 is configured.

And this process unit 21 is accommodated in the main body accommodating part 30 of the main body frame 2 through the opening 31 opened by the front cover 32 made into the open position.
In the laser printer 1, when the process unit 21 is mounted in the main body housing portion 30, a warm-up operation is started, and a glass turning operation in which the agitator 36 is rotationally driven is executed. When the warming-up operation is completed, a normal printing operation is then performed, and the toner stored in the toner storage chamber 40 is scraped up and conveyed into the developing chamber 41 by the rotation of the agitator 36.

  The toner conveyed into the developing chamber 41 is supplied to the developing roller 38 by the rotation of the supply roller 37. When the toner is supplied from the supply roller 37 to the developing roller 38, the toner is rubbed between the supply roller 37 and the developing roller 38 to be positively charged.

  The charged toner is carried on the surface of the developing roller 38 and enters between the developing roller 38 and the pressure contact portion 52 of the layer thickness regulating blade 39 as the developing roller 38 rotates. When the toner passes between the developing roller 38 and the pressure contact portion 52, the toner is further charged by friction, the thickness of the layer is regulated, and the toner is carried as a thin layer on the surface of the developing roller 38.

  On the other hand, in the drum cartridge 33, as the photosensitive drum 55 rotates, the surface of the photosensitive drum 55 is uniformly positively charged by the scorotron charger 56, and the laser beam emitted from the scanner unit 20 based on the image data. Are exposed to form an electrostatic latent image.

  Next, when the developing roller 38 rotates, the toner that is carried on the surface of the developing roller 38 and charged positively is formed on the surface of the photosensitive drum 55 when it contacts the photosensitive drum 55. An electrostatic latent image, that is, a visible image formed by being selectively carried on an exposed portion of the surface of the photosensitive drum 55 that is uniformly positively charged and exposed to a laser beam and having a lowered potential. It becomes.

  As the photosensitive drum 55 rotates, the sheet 3 conveyed from the registration roller 11 passes between the photosensitive drum 55 and the transfer roller 57 while being in contact with the surface of the photosensitive drum 55. The toner carried on the surface is transferred to the paper 3. The sheet 3 on which the toner has been transferred is conveyed toward the fixing unit 22.

  The fixing unit 22 is provided behind the process unit 21 and on the downstream side in the conveyance direction of the paper 3, and includes a heating roller 62, a pressure roller 63, and a conveyance roller 64. The heating roller 62 includes a halogen lamp as a heater in a metal base tube. The pressure roller 63 is disposed so as to face the lower side of the heating roller 62 and is provided so as to press the heating roller 62 from below. Further, the transport roller 64 is provided on the downstream side in the transport direction of the paper 3 with respect to the heating roller 62 and the pressure roller 63.

  The toner transferred to the paper 3 is melted by heat while passing between the heating roller 62 and the pressure roller 63 and is fixed to the paper 3. The sheet 3 is guided by a conveying roller 64 to a guide portion 65 disposed in the vertical direction behind the conveying roller 64 and is conveyed toward the paper discharge roller 66.

The paper 3 conveyed by the paper discharge roller 66 is then discharged onto the paper discharge tray 67 by the paper discharge roller 66.
Next, the laser printer 1 of the present embodiment is provided with a developing device contacting / separating mechanism for contacting / separating the developing cartridge 34 (specifically, the developing roller 38) with respect to the photosensitive drum 55.

<Developer contact / separation mechanism>
3 is a side view showing the process unit 21, FIG. 4 is a cross-sectional view of the main part of the process unit 21, and FIG. 5 shows the developing cartridge 34 (the developing roller 38, the photosensitive drum 55, and the like of the process unit 21. 6 is a side view showing the developing cartridge 34 of the process unit 21 (a state where the developing roller 38 and the photosensitive drum 55 are separated).

  The developing device contact / separation mechanism includes a developing device side contact / separation mechanism portion 70 provided on the developing cartridge 34 and a main body side contact / separation mechanism portion 82 provided on the main body frame 2. As shown in FIG. 3, the mechanism unit 70 includes a support shaft 71 as a support member, a lever 72 as an engaging body, and a spring 81 as an urging member.

As shown in FIGS. 3 and 5, the support shaft 71 is provided in a protruding shape so as to face each other toward the inner side in the width direction on both side walls of the front portion of the process accommodating portion 59.
The levers 72 are respectively arranged on the inner side in the axial direction of the photosensitive drum 55, more specifically, on both side walls of the front portion of the process accommodating portion 59 corresponding to each support shaft 71. Each lever 72 is opened in a substantially U-shaped groove shape downward from the center of the upper surface of the lever main body 72a, a lever main body 72a made of a plate body, a knob 73 formed on the upper front side of the lever main body 72a. A first receiving portion 74, a second receiving portion 75 opened substantially in a U-shaped groove toward the lower side below the front end portion of the lever main body 72a, and a knob 73 at the front end portion of the lever main body 72a. And the second receiving portion 75, and a spring receiving portion 76 formed in a concave shape toward the rear obliquely upward, and a contact surface formed in an inclined shape on the front side of the lower surface of the lever main body 72a. 77 is integrally formed.

Further, an inclined surface 79 for guiding the engagement shaft 78 is provided at the opening portion of the first receiving portion 74 of the lever 72.
The lever 72 is swingably supported by the support shaft 71 by fitting the second receiving portion 75 opened downward to the support shaft 71 of the process accommodating portion 59. In this state, the lever 72 can swing between a contact position where the developing roller 38 and the photosensitive drum 55 are brought into contact with each other and a separation position where the developing roller 38 and the photosensitive drum 55 are separated from each other. In this state, the lower end portion including the contact surface 77 of the lever 72 is communicated with the lower side via the notch portion 80 of the process accommodating portion 59.

Further, one end of the spring 81 is engaged with the front wall of the process accommodating portion 59 and the other end is received by the spring receiving portion 76 on both sides in the width direction of the front end portion of the process accommodating portion 59.
Thus, the lever 72 is always urged by the urging force of the spring 81 so that the upper side tilts backward and the front side tilts forward with the support shaft 71 as a fulcrum. Therefore, the lever 72 is always biased so as to be positioned at the contact position by the biasing force of the spring 81.

  Further, as shown in FIG. 4, the main body frame 2 includes a main body side contact / separation mechanism 82 for swinging each lever 72. The main body side contact / separation mechanism 82 includes a drive shaft 83 as a connecting member, a cam 84 as a pressing member and a moving member, a clutch 85, and a sensor for detecting the position of the developing cartridge 34 (specifically, the developing roller 38). 170 (hereinafter referred to as a position sensor) and a release plate 87 as a contact member.

  As shown in FIGS. 4 and 5, the drive shaft 83 is provided on the drive shaft 83 so as to face each lever 72 of the drum frame 54 that is mounted on the main body frame 2. Each cam 84 is made of a thick plate that is eccentric with respect to the drive shaft 83, and as shown in FIG. 6, a first cam surface 88 that contacts the contact surface 77 of the lever 72, and as shown in FIG. A second cam surface 89 that does not contact the contact surface 77 of the lever 72 is provided.

  Each cam 84 is provided on the drive shaft 83 such that the first cam surface 88 and the second cam surface 89 are in the same phase with respect to the lever 72, that is, in a side view. As a result, each cam 84 is rotated by the rotation of the drive shaft 83 so that the first cam surface 88 and the second cam surface 89 are alternately opposed to the contact surface 77 of each lever 72 at the same timing. The first cam surface 88 of the lever 84 contacts the contact surface 77 of the lever 72 (first position) and the second cam surface 89 of the cam 84 does not contact the contact surface 77 of the lever 72. Between the non-pressing position (second position), the position is alternately repeated and rotated so as to be engaged with and disengaged from the contact surface 77 of the lever 72.

  As shown in FIG. 4, the clutch 85 is provided on one side in the axial direction of the drive shaft 83 and on the outer side in the other direction from the shaft support portion 90. The clutch 85 receives power from the separation motor 128 (see FIG. 7), and transmits or blocks the power to the drive shaft 83. The clutch 85 is a well-known spring clutch, and transmits the power from the separation motor 128 to the drive shaft 83 via a gear train (not shown) in the on state.

In the off state, transmission of power from the separation motor 128 to the drive shaft 83 is interrupted.
The position sensor 86 includes a sensor disk 91 as a light shielding plate, a light emitting unit 92, and a light receiving unit 93.

  The sensor disk 91 is provided at one end portion in the axial direction of the drive shaft 83 outside the clutch 85 in the axial direction. The sensor disk 91 has a disk shape, and a substantially fan-shaped light shielding portion 94 bulging outward in the radial direction is integrally formed.

  The light emitting unit 92 and the light receiving unit 93 are configured as optical sensors, and are disposed to face each other at a position sandwiching the light shielding unit 94 of the sensor disk 91. As a result, the light shielding portion 94 of the sensor disk 91 passes between the light emitting portion 92 and the light receiving portion 93 by the rotation of the drive shaft 83.

  In the position sensor 86, light traveling from the light emitting unit 92 to the light receiving unit 93 is blocked while the cam 84 presses the lever 72, and light traveling from the light emitting unit 92 to the light receiving unit 93 while the cam 84 does not press the lever 72. Is passed. Thus, it is detected whether the cam 84 is in a pressing position where the lever 72 is pressed or whether the cam 84 is in a non-pressing position where the lever 72 is not pressed.

  Then, as shown in FIG. 3, the developing cartridge 34 is received from above into the process receiving portion 59 of the drum cartridge 33 and the first receiving portion 74 of each lever 72 having the engaging shaft 78 opened upward. Store as if

  At this time, in a state where the developing cartridge 34 is accommodated in the process accommodating portion 59 of the drum cartridge 33, the lever 72 is pressed backward with the support shaft 71 as a fulcrum by the biasing force of the spring 81, and the contact position Therefore, the engagement shaft 78 engaged with the lever 72 is disposed rearward. As a result, as shown in FIG. 5, the developing cartridge 34 is disposed rearward with respect to the drum cartridge 33, and the developing roller 38 and the photosensitive drum 55 come into contact with each other.

<About the control device 100>
Next, FIG. 7 is a block diagram showing a configuration of a control device 100 built in the laser printer 1 for controlling the above-described units.

  The control device 100 includes an image forming unit 5 including a scanner unit 20, a process unit 21, a fixing unit 22, a main motor 124 serving as a power source for a paper conveyance system of the laser printer 1, and a toner conveyance system of a developing cartridge 34 (more specifically, , A developing cartridge motor 126 serving as a power source for the agitator 36, supply roller 37, developing roller 38), a separation motor 128 serving as a power source for the developer contact / separation mechanism, and the like. The CPU 102, the ROM 104, the RAM 106, and a bus line 188 for connecting these units are controlled in accordance with commands from the computer or commands from various information processing devices (personal computers, etc.) input via the network. It is comprised with the well-known microcomputer centering on.

  In addition, the control device 100 drives an image formation control unit 110 for controlling the image forming unit 5 in accordance with a command from the CPU 102, and a main motor 124, a developing cartridge motor 126, and a separation motor 128 in accordance with a command from the CPU 102, respectively. Motor display units 112, 114, and 116, and a display control unit 118 for displaying the operating state of the printer 1 and the like on the display unit 130 including a liquid crystal display device in accordance with a command from the CPU 102, and an operation unit 132. A command input from a user and a signal input unit 120 for taking in a detection signal from the position sensor 86 described above into the control device 100, and an external information processing device (such as a personal computer) via a network. Network interface for network data communication (network I / F) 122 are also provided, these units via a bus line 188, is connected to the CPU 102, ROM 104, RAM 106.

  When the CPU 102 receives a print request from the external information processing apparatus via the network, the image formation control unit 110, the main motor 124, the developing cartridge motor 126, By driving and controlling the separation motor 128, an image based on the image data is formed on the paper 3 while the paper 3 is being conveyed.

  The CPU 102 also controls a rotational speed control process for controlling the rotational speed of the developing roller 38 when supplying toner to the electrostatic latent image generated on the photosensitive drum 55 based on image data acquired via the network. Execute.

<Rotational speed control process>
Next, the rotational speed control process performed by the CPU 102 of the laser printer 1 of the first embodiment will be described based on the flowchart shown in FIG. This process is a process that is repeatedly executed from when the laser printer 1 is started to when it is stopped.

  When the CPU 102 starts the rotation speed control process, first, in S110, the CPU 102 waits until image data is acquired. When acquired, the image data is stored in the RAM 106, and the process proceeds to S120.

  In S120, one page is captured from the image data stored in the RAM 106, and is divided into five along the developing direction of the electrostatic latent image by the developing roller 38, as shown in FIG. By generating five control target areas 1 to 5 and further dividing the control target area into six along the direction perpendicular to the developing direction for each control target area 1 to 5, a total of 30 control target areas 1 to 5 are generated. Create a region.

In the first embodiment, the length in the developing direction in each region divided by the processing of S120 is shorter than the circumferential length of the developing roller 38.
Further, in FIG. 9, the numbers given in the respective areas of the image data are the values of the exposure ratio, and the exposure ratio is 0% for the areas not given the numbers.

  In subsequent S130, for each area obtained by the division (that is, an area generated by dividing the control target area), an exposure area and a non-exposure area of the laser beam by the scanner unit 20 corresponding to that area. An exposure ratio representing the ratio is generated.

  Specifically, for each area divided in S120, the CPU 102 irradiates dots that the scanner unit 20 emits a laser beam when an electrostatic latent image corresponding to the area is generated on the photosensitive drum 55. The number and the number of non-irradiated dots that are not irradiated are measured, and the ratio of the number of irradiated dots to the total number of dots in that area (that is, the exposure ratio) is generated.

  In S120, it may be generated by calculating the exposure ratio as described above. For example, a table in which the number of irradiation dots is associated with the exposure ratio is stored in the ROM 104, and in S120, the number of irradiation dots. And the exposure ratio may be generated from the number of irradiated dots with reference to a table stored in the ROM 104. Further, for example, a nonvolatile memory may be provided in the control device 100, and a table in which the number of irradiation dots and the exposure ratio are associated with each other may be stored in the memory.

  Subsequently, in S140, the area having the highest exposure ratio among the respective control target areas is selected as the exposure ratio of the control target area, and stored in the RAM 106. Then, for example, the exposure ratio of the control target area 1 in the image data of FIG. 9 is generated as 80%.

In S150, “1” is substituted for the value n representing the control target area to be controlled this time.
Next, in S160, it is determined whether or not the exposure ratio of the control target area n is 0%. If it is determined that the exposure ratio of the control target area n is not 0%, the process proceeds to S170 and vice versa. On the other hand, when it is determined that the exposure ratio of the control target area n is 0%, the process proceeds to S230.

  In S170, the rotation speed of the developing roller 38 is generated based on the exposure ratio of the control target area n. In the first embodiment, the rotation speed of the developing roller 38 is decreased as the exposure ratio decreases.

Subsequently, in S180, a driving amount of the developing cartridge motor 126 is generated based on the rotation speed of the developing roller 38 generated in the processing of S170.
In S190, the process waits until the timing for supplying toner to the electrostatic latent image in the control target area n generated on the photosensitive drum 55 by the scanner unit 20 is reached. The drive amount generated by the process is output to the motor drive unit 114.

Then, the rotation speed of the developing roller 38 when supplying toner to the electrostatic latent image in the control target area n becomes the rotation speed of the control target area n generated in the process of S170.
Then, in S210, it is determined whether or not the value n representing the control target region to be controlled this time is larger than “5”, and if it is determined that the value n is larger than “5”, S110 On the other hand, if it is determined that the value n is smaller than “5”, the process proceeds to S220, “1” is added to the value n, and the process returns to S160.

  In the rotational speed control process of the first embodiment, when the image data acquired in S110 is one page or more, when an affirmative determination is made in S160 and the process proceeds to S110, the image data is determined in S110. Is determined to have been acquired. In the subsequent S120, the next page of the previously fetched page is fetched from the image data, and the image data is divided as described above.

  Next, in S230, the process waits until the timing for supplying toner to the electrostatic latent image in the control target area n generated on the photosensitive drum 55 by the scanner unit 20 is reached.

In S240, the rotation of the developing roller 38 is stopped and the developing roller 38 is separated from the photosensitive drum 55, and the process proceeds to S210.
More specifically, in S240, the motor driving unit 114 stops the rotation of the developing roller 38 and the motor driving unit 116 drives the separation motor 128. When the position sensor 86 detects the separation of the developing roller 38 from the photosensitive drum 55 while the separation motor 128 is rotating, the motor driving unit 116 stops the rotation of the separation motor 128. Thus, in S120, the rotation of the developing roller 38 is stopped and the developing roller 38 is separated from the photosensitive drum 55.

  In S190, when it is determined that it is time to supply toner to the electrostatic latent image in the control target area n generated on the photosensitive drum 55 by the scanner unit 20, the developing roller 38 is moved from the photosensitive drum 55. If they are separated (that is, when the position sensor 86 detects the separation of the developing roller 38 from the photosensitive drum 55), the position sensor 86 detects the contact of the developing roller 38 with the photosensitive drum 55. Then, after the separation motor 128 is driven by the motor driving unit 116, the process proceeds to S200.

  In the laser printer 1 of the first embodiment as described above, the rotation speed of the developing roller 38 when supplying toner to the electrostatic latent image in each control target area during one image forming operation is Since the control is performed based on the exposure ratio of the control target area, even if a halftone image and a solid image are mixed in an image to be formed on one sheet 3, each image can be formed satisfactorily.

  Therefore, according to the laser printer 1 of the first embodiment, the toner necessary for forming a good image can be supplied to the photosensitive drum 55, and a defective image is formed due to insufficient toner or excessive toner. Can be suppressed.

  Further, the laser printer 1 of the first embodiment is configured so that the rotation speed of the developing roller when supplying toner to each control target area is decreased as the exposure ratio is smaller. For areas where the exposure ratio is not 100% (that is, areas that are not solid images), the rotation speed of the developing roller 38 when supplying toner to the control target area is set, and toner is supplied to the solid image areas. Therefore, the rotational operation amount of the developing roller 38 in one image forming operation can be made smaller than that of a laser printer that does not control the rotational speed of the developing roller 38. Toner deterioration can be minimized.

  Furthermore, according to this, since the rotation speed of the developing roller 38 is decreased as the exposure ratio decreases, the amount of toner supply can be suppressed. For this reason, for example, it is possible to lengthen the period required to replace the developing cartridge 34 or the period required to replenish the toner.

  Further, according to the laser printer 1 of the first embodiment, since the exposure ratio is generated for each divided control target region, the supply amount of toner supplied to the photosensitive drum 55 can be controlled more optimally.

  Furthermore, according to the laser printer 1 of the first embodiment, for example, as shown in FIG. 9, even when there is only one area of the solid image in the control target area 2, the control target area 2 is generated with an exposure ratio of 100%, it is possible to efficiently suppress the formation of a defective image due to lack of toner.

  In the first embodiment, since the length of the control target area in the developing direction is shorter than the circumferential length of the developing roller 38, a portion (solid image) having an exposure ratio of 100% is continuously generated. Even so, it is possible to prevent the amount of toner supplied from the developing roller 38 to the photosensitive drum 55 from dropping.

  When the exposure ratio of the control target area is 0%, the rotation speed of the developing roller 38 is changed to 0, the rotation of the developing roller 38 is stopped, and the developing roller 38 is separated from the photosensitive drum 55. Therefore, the developing roller 38 can be stopped in the control target area where the image need not be formed, and toner deterioration can be further suppressed.

In the first embodiment, the scanner unit 20 corresponds to an exposure unit, the rotation speed control process corresponds to a speed control unit, and the RAM 106 corresponds to a storage unit.
[Second Embodiment]
Next, a laser printer according to the second embodiment will be described with reference to FIG. In the second embodiment, the same components as those of the laser printer 1 of the first embodiment described above are described with the same reference numerals, and detailed description thereof is omitted. This also applies to a third embodiment described later.

The laser printer according to the second embodiment differs from the laser printer according to the first embodiment in the following points.
In step S130, the CPU 102 determines whether there is text data in each area based on the image data stored in the RAM 106 when generating the exposure ratio. Then, an area determined to have text data is generated assuming that the exposure ratio is 80%. On the other hand, an exposure rate is generated for an area determined to have no text data, as in the first embodiment, but an exposure rate of 100 is generated for an area whose exposure rate is not 0%. .

  For this reason, when the laser printer of the second embodiment acquires image data as shown in FIG. 10, for example, the control target areas 1, 3, and 4 are generated with an exposure ratio of 100%. The control target area 2 is generated with an exposure ratio of 80%, and the control target area 5 is generated with an exposure ratio of 0%.

  Even with the laser printer of the second embodiment as described above, it is assumed that a halftone image and a solid image are mixed in an image to be formed on one sheet 3 as in the laser printer 1 of the first embodiment. In addition, each image can be formed satisfactorily and toner deterioration can be suppressed.

[Third Embodiment]
Next, a laser printer according to a third embodiment will be described with reference to FIG.
The laser printer according to the third embodiment differs from the laser printer 1 according to the first embodiment in the following points.

  First, the CPU 102 according to the third embodiment does not divide the control target area along the direction perpendicular to the developing direction in S120. That is, the CPU 102 of the third embodiment generates a control target area by dividing the image data into five along the development direction in S120.

In S130, an exposure ratio is generated for each control target area. At this time, if the exposure ratio is other than 0%, the exposure ratio is generated as 100%.
For this reason, when the laser printer of the third embodiment acquires image data as shown in FIG. 11, for example, the control target areas 1, 2, and 3 are generated with an exposure ratio of 100%. The control target areas 4 and 5 are generated assuming that the exposure ratio is 0%.

  According to the laser printer of the third embodiment, it is possible to more efficiently suppress the formation of a defective image due to the lack of toner than in the first and second embodiments described above. However, regarding the suppression of toner deterioration, the first and second embodiments are more advantageous than the third embodiment.

As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that this invention can take a various form.
In the above embodiment, the case where the present invention is applied to a monochrome laser printer has been described. However, the present invention is a color laser printer or a facsimile apparatus (so-called laser fax) equipped with an image forming unit 5 similar to the above embodiment. Even in the case of a printer / fax compound machine, the same effect can be obtained by applying the same as in the above embodiment.

  Further, for example, in the first and second embodiments, the image data is divided into five along the development direction and into six along the direction perpendicular to the development direction. Not limited to this, it may be divided into any number.

  When the exposure ratio of the control target area is 0%, it is not necessary to separate the photosensitive drum 55 from the developing roller 38 only by stopping the rotation of the developing roller 38. In this case, since it is not necessary to provide a developing device contact / separation mechanism, the components can be simplified as compared with the image forming apparatus of the above-described embodiment. The embodiment is more advantageous.

It is a block diagram showing the apparatus of 1st Embodiment. It is a block diagram showing the process unit of the laser printer shown in FIG. It is a side view which shows the process unit of the laser printer shown in FIG. It is principal part sectional drawing of the process unit shown in FIG. FIG. 11 is a side view showing a developing cartridge (a state where a developing roller and a photosensitive drum are in contact with each other) of the process unit shown in FIG. 10. FIG. 11 is a side view showing a developing cartridge (a state where a developing roller and a photosensitive drum are separated from each other) of the process unit shown in FIG. 10. It is a block diagram showing the structure of the control apparatus incorporated in the laser printer. It is a flowchart showing the rotational speed control process which CPU of a control apparatus performs. It is explanatory drawing explaining the rotational speed control process of 1st Embodiment. It is explanatory drawing explaining the rotational speed control process of 2nd Embodiment. It is explanatory drawing explaining the rotational speed control process of 3rd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Laser printer, 2 ... Main body frame, 3 ... Paper, 5 ... Image forming part, 6 ... Paper feed tray, 20 ... Scanner part, 21 ... Process unit, 33 ... Drum cartridge, 34 ... Developing cartridge, 38 ... Developing roller 55 ... photosensitive drum, 70 ... developer side contact / separation mechanism, 82 ... main body side contact / separation mechanism, 100 ... control device, 110 ... image formation controller, 126 ... developing cartridge motor, 128 ... separation motor.

Claims (9)

A photoreceptor,
Exposure means for selectively exposing the photoconductor to form an electrostatic latent image based on image data;
A developing roller that develops an electrostatic latent image formed on the photosensitive member by the exposure unit to form a developer image by supplying the developer to the photosensitive member;
Based on the exposure ratio between the exposure area and the non-exposure area by the exposure means for the control target area smaller than the image area for one page represented by the image data, the electrostatic latent image of the control target area Speed control means for controlling the rotation speed of the developing roller when supplying the developer;
An image forming apparatus comprising: The speed control means slows down the rotation speed of the developing roller when supplying the developer to the control target area as the exposure ratio is smaller;
The image forming apparatus according to claim 1. Storage means for storing the image data;
The speed control unit generates an exposure ratio of the control target region based on the image data stored in the storage unit;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The speed control means is
The image data is divided into a plurality along the developing direction of the electrostatic latent image by the developing roller, and an exposure ratio in each of the divided control target regions is generated.
Furthermore, based on the exposure ratio for each of the control target areas, controlling the rotation speed of the developing roller when supplying the developer to the control target area for each of the control target areas;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The speed control unit divides each control target area into a plurality of areas along a direction perpendicular to the developing direction, generates an exposure ratio in each of the divided areas, and further, in each of the control target areas. And generating the area having the largest exposure ratio as the exposure ratio of the control target area,
The image forming apparatus according to claim 4. A length in the developing direction of each control target area divided by the speed control unit is equal to or less than a circumferential length of the developing roller;
The image forming apparatus according to claim 4, wherein: The speed control means continuously changes the rotation speed in accordance with the exposure ratio of the control target area between the minimum required rotation speed and the maximum rotation speed of the developing roller.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The speed control means, when the exposure rate of the control target area is 0%, changes the rotation speed of the developing roller to 0 and stops the developing roller;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. Separating means for separating the developing roller in contact with the photoreceptor from the photoreceptor;
A separation control means for operating the separation means when the exposure ratio of the control target area is 0%;
The image forming apparatus according to claim 1, further comprising: