JP2627178B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention develops a latent image formed on a photosensitive drum, which is an image carrier, by a plurality of developing means containing multicolored developers. The present invention relates to an image forming apparatus for obtaining a color copy by an electrophotographic method.

[Background of the Invention]

Many methods and apparatuses have been proposed for obtaining a color image using electrophotography. For example, as disclosed in JP-A-61-100770, a latent image is formed and developed on a photosensitive drum in accordance with the number of color separations of an original image, and transferred to a transfer drum for each development. There is a method in which a multicolor image is formed on a drum and then transferred onto a recording sheet to obtain a color copy. In the apparatus according to this method, it is necessary to provide a transfer drum having a size capable of transferring one image on the peripheral surface in addition to the photosensitive drum, and the apparatus has a large and complicated structure. Inevitable.

Further, as disclosed in, for example, JP-A-61-149972, a latent image is formed and developed on a photosensitive drum in accordance with the number of separated colors of an original image, and is transferred onto a transfer material each time development is performed. This is a method of obtaining a multi-color copy. In this method, it is difficult to accurately superimpose multi-color images, and a high-quality color copy cannot be obtained.

Further, there is a method in which a latent image is formed on the photosensitive drum in accordance with the number of separated colors of the original image and development with a color toner is repeated, and a color image is obtained by superimposing and transferring color powder on the photosensitive drum. The basic process of this multicolor image formation is described in Japanese Patent Application Laid-Open Nos. 60-75850, 60-76766 and 60-95 by the present applicant.
Nos. 456, 60-95458 and 60-158475.

In a multi-color image forming apparatus that obtains a color image by such superposition, a plurality of developing devices that store color toners of different colors are arranged on the periphery of the photosensitive drum. Rotates the photoconductor drum several times,
The color image is obtained by developing the latent image on the photosensitive drum.

In this case, the length of the photosensitive drum needs to be at least longer than the length of the original.
In the case of (4 × 257), a drum having a diameter of about 130 mmφ is required in consideration of a margin generated in the image forming process. According to the study by the present applicant, Japanese Patent Application No. 60-296340
As described in detail in the specification, the latent image written on the photosensitive drum by the writing unit is transferred onto the developed image by superimposing the developed image. It is necessary that the cleaning means is in contact with the peripheral surface of the photosensitive drum for the first time after the transfer step. At this time, the cleaning means has an effect on the rotation of the photosensitive drum, and at this point, writing by the writing means is still impossible. If the continuation is continued, the image to be superimposed is shifted and the image quality is deteriorated. Therefore, it is required that the diameter of the photoconductor drum be large enough. The same applies to development, and when a plurality of developing means provided on the peripheral portion of the photosensitive drum perform development while simultaneously applying a development bias,
There is a difference between a single developing unit and a place where development is performed, which is not preferable. The size of the photosensitive drum is determined from these conditions, and a large-diameter drum is required as described above.

In a multi-color image forming apparatus in which a color image is superimposed on a photosensitive drum, it is not possible to use a developing unit that performs development by bringing a conventional magnetic brush into contact with an image bearing member as a developing unit. Can not. Applicant filed Japanese Patent Application Laid-Open
-147652 makes it possible to implement a multicolor image forming apparatus in which a toner image is superimposed on an image carrier using a non-contact developing method disclosed in Japanese Patent Application Laid-Open No. 147652 or the like.

[Problems to be solved by the invention]

In such a multi-color image forming apparatus, as is well known, each developing device containing a color toner of a different color is directed along the peripheral surface of the photoreceptor drum in the direction of rotation so that each developing sleeve has a predetermined gap with respect to the drum surface. It is set to the position where Dsd can be kept.

The developing sleeve of each developing unit is driven and rotated at the time of developing a specific color.On the other hand, regarding the magnetic roll included in the developing sleeve, the number of rotations and the rotating direction are different, and there are plural developing units. Since the power transmission mechanism is complicated, fixed magnetic rolls are generally used, and satisfactory results have been obtained. However, in the case of a fixed-type magnetic roll, it is necessary to set the magnetic pole of the north pole or the south pole to the drum surface in a specific condition close to or directly facing the magnetic pole. The phase of the magnetic pole must be adjusted, and the adjustment operation requires a lot of time and labor, and there is a problem that the developing device main body cannot be handled as a common unit.

The present applicant previously disclosed in Japanese Patent Application No. 62-331226, a plurality of developing devices having magnetic rolls in which magnetic poles of equal magnetic force were arranged at the same angle on the outer line of the photosensitive drum at the same angle. We have proposed an image forming apparatus that uses a common magnetic roll and can be used without the need for phase adjustment.However, by further developing that proposal, a magnetic roll with newly arranged magnetic poles at unequal angles It is another object of the present invention to provide an image forming apparatus which can use a plurality of developing devices in common and can be used without phase adjustment.

[Means for solving the problem]

An object of the present invention is to provide an image forming apparatus in which development is performed by a photosensitive drum and a plurality of developing devices arranged in parallel with each other so as to face the photosensitive drum, wherein the developing devices have the same shape and a plurality of fixed magnetic forces. One of the magnetic poles exists at a developing position on a line connecting the center of the photosensitive drum and the center of the developing sleeve of the developing device, and is adjacent to the center of the photosensitive drum. The included angle formed by the line connecting the center of the developing sleeve of the developing device is α ゜, β from the upstream in the rotation direction of the photosensitive drum.
゜, γ ゜, the included angle formed between the center of the sleeve of the developing sleeve and the adjacent magnetic pole has the relationship of γ ゜, β ゜, α ゜ in the same direction as the rotation direction of the photosensitive drum. The image forming apparatus is characterized in that the included angle on the photosensitive drum and the included angle on the developing sleeve have a point-symmetrical positional relationship at a point where the photosensitive drum and each developing unit oppose each other. .

Embodiment 1 FIGS. 1 (a) to 4 show a first embodiment in which three developing devices of the present invention are provided on the peripheral edge of a photosensitive drum. FIG. 1A shows a main configuration of a multicolor image forming apparatus, wherein A is an image reading system, B is each unit of a laser writing system, C is an image forming unit, D is a paper feeding unit, A color image is formed by the following process.

In the reading system A, reference numeral 11 denotes a platen.
The document stored in the carriage is slid horizontally.
Illuminated by a halogen lamp 13 attached to 12.
Mirrors 16 and 17 are mounted on the movable mirror unit 15 and slide in the horizontal direction in the same manner, and the optical image of the document is led out to the lens reading unit 20 in combination with the mirror 14 mounted on the carriage 12. I do.

The carriage 12 and the movable mirror unit 15 are driven via wires (both not shown) connected to a stepping motor, and are slid in the same direction at V and 1/2 V, respectively.

The lens reading unit 20 includes a lens 21, a prism 22, a first
Read substrate 24, red channel (hereinafter referred to as R-ch)
CCD 25, second reading substrate 26, cyan channel (hereinafter C
-Ch).

The light images of the original transmitted by the mirrors 14, 16 and 17 are converged by the lens 21 and separated into an R-ch image and a C-ch image by a dichroic mirror provided in a prism 22, and the first reading is performed. R-ch provided on substrate 24
C-ch C provided on CCD 25 and second reading substrate 26
An image is formed on the light receiving surface of the CD 27, respectively.

The image signals output from the R-ch CCD 25 and the C-ch CCD 27 are subjected to signal processing in a signal processing unit. In the signal processing unit, a color signal that is color-separated according to the color of the toner is output, and is input to the laser writing unit B that is an exposure unit.

In the laser writing unit B, a laser beam generated by a semiconductor laser (not shown)
Is rotated and scanned by a polygon mirror 32 rotated by a mirror, the optical path of which is bent by a mirror 34 via an Fθ lens 33, and projected onto the peripheral surface of an image carrier 30 to which electric charges have been applied in advance by a charger 35 as a charging means. Form a bright line.

On the other hand, when scanning is started, the beam is detected by the index sensor, the modulation of the beam by the first color signal is started, and the modulated beam is applied to the photosensitive drum 30.
Is scanned on the peripheral surface of. Accordingly, a latent image corresponding to the first color is formed on the peripheral surface of the photosensitive drum 30 by the main scanning by the laser beam and the sub-scanning by the rotation of the photosensitive drum 30. This latent image is developed by, for example, a developing device 36 loaded with red toner (visual medium) in the developing means, and a toner image is formed on the drum surface. The obtained toner image passes under the cleaning device 51 as cleaning means separated from the peripheral surface of the photosensitive drum 30 while being held on the drum surface, and enters the next copy cycle.

That is, the photosensitive drum 30 is charged again by the charger 35, and then the second color signal output from the signal processing unit is input to the writing unit B, and the case of the first color signal described above is used. Similarly, writing is performed on the drum surface to form a latent image. The latent image is developed by a developer 37 loaded with, for example, blue toner as the second color.

This blue toner image is formed in the presence of the previously formed red toner image.

Reference numeral 38 denotes a developing device having black toner, which forms a black toner image on the drum surface based on a control signal generated by a signal processing unit. AC and DC biases are applied to the sleeves of these developing units 36, 37, and 38, so that jumping development with a two-component developer is performed, and development is performed without contact with the grounded photosensitive drum 30. It has become.

Thus, the color image formed on the peripheral surface of the photosensitive drum 30 is a recording medium sent from the paper supply unit D by the paper supply belt 41 and the supply roller 42 at the transfer pole 40 provided as a transfer unit. Transferred to recording paper. The recording paper onto which the toner image has been transferred is separated from the drum surface by the separation pole 43, and is conveyed to the fixing device 45 via the transport belt 44 to fix the image.

On the other hand, a photosensitive drum that separates the recording paper from the drum peripheral surface
At 30, the blade 51 </ b> A of the cleaning device 51 comes into contact to remove the remaining toner, and after the end, the toner is separated from the drum peripheral surface again, and a new color image forming process is started.

Next, the layout of each of the above-mentioned main components will be described. As shown in FIG. 1, the image reading system A is housed in an independent exclusive housing 1 and mounted and mounted on an upper portion of a main body 2 which will be described later. I have.

The main body 2 incorporates an image recording system including the writing system B, the image forming unit C, the paper feeding unit D, and the like, and the image reading system A is connected to a flexible cable group connected to the housing 1. Color signal from the camera.

In the main body 2, the photosensitive drum 30 is located substantially at the center, and the developing units 36, 37, and 38 are respectively arranged in a horizontal state facing the right peripheral surface thereof, while the charging device is disposed on the left peripheral surface. 35 and the cleaning device 51 are arranged.

The photosensitive drum 30, the developing units 36, 37, 38, and the cleaning device 51 are not directly attached to the pair of front and rear substrates fixed to the main body 2, but are supported so as to be inserted into and removed from the main body 2. 3 is mounted on a bearing or detachably.

As shown in FIG. 3, the supporting member 3 is fixed to each other via a stay or the like and integrally formed into three similar shaped panels 3A, 3B,
A pair of left and right guide members 4 composed of a plurality of balls and rails, each of which is composed of 3C, can be easily taken out and attached to the main body 2.

That is, rails 4A are provided on the left and right side edges of the support member 3,
On the other hand, rails 4C are respectively fixed at positions of the main body 2 corresponding to the rails 4A, and each of them forms a slidable pair by engaging with the rail 4B via a plurality of balls.

A pair of left and right reference pins P are attached near the upper side edges of the rear surfaces of the panels 3A and 3B, respectively.
Is suspended by engaging with a hole provided in the hanging portion Q with respect to a hanging portion Q derived from the substrate before and after fixing, and the photosensitive drum 30 attached to the support member 3 in that state, Developing units 36, 37, 38 and cleaning device 51
The setting of the relation position with respect to the main body 2 is performed.

Accordingly, when the handle 5 on the front surface of the panel 3A is pulled, the support member 3 is largely pulled out to the front of the main body 2 by using the rail 4B as a relay member for the rolling operation of the ball. Is engaged with the hole of the hanging portion Q, and the support member 3 is again suspended and stored in the main body 2.

In this manner, the support member 3 is held in a suspended state with respect to the substrate of the main body 2, so that the support member 3 is transmitted from the motor or the like attached to the main body 2 to the photosensitive drum 30, each developing device, or the cleaning device. Even if the vibrations and shocks are greatly reduced and absorbed, and transmitted slightly to the scale, the equipment will receive uniform vibrations and shocks. Since the image is held in an appropriate state, there is no great trouble in image formation.

In particular, the photosensitive drum 30 and the cleaning device
The blade 51 which must be carried out in the cleaning device for superimposed development image formation by holding the 51 integrally
A, Substantially alleviates adverse effects such as vibrations and impacts on the delicate way of pressing, pressing, and loading conditions when the second cleaning roller 51B, etc., comes into contact with or separates from or presses against the cleaning blade for residual toner treatment. Absorbed. These effects can be said to be the same in the case where the reference pins P on the panels 3A and 3B and the holes of the hanging portions Q fitted to the main body are interchanged and combined. Further, it is sufficient that the panel plate is composed of two front and rear panels, and it is not always necessary to provide three panel plates as in this embodiment.

When the image forming process is performed by the superposition type as described above, the photosensitive drum 30 needs to have a peripheral surface length that is a length obtained by adding a margin to one page of B4 size or A3 size, which is the maximum recording material. Therefore, the outer diameter of the photosensitive drum is required to be at least about 130 mm to 150 mm. In this embodiment, the photosensitive drum of 150 mm is rotated at a peripheral speed of 140 mm per second.

On the other hand, as for the developing units 36, 37 and 38, as will be described later in detail, the outer diameter of the developing sleeve is reduced to 20 mm without deteriorating the image performance, and the thickness (height) of each developing unit is reduced to 40 mm.
mm or less, so that three or four developing units, that is, developing units 36, 37 and 38 in this embodiment,
Can be further integrated and arranged in a horizontal state in a space corresponding to the range of the outer diameter dimension of.

Therefore, the supporting member 3 is a member directly attached to and fixed to the main body 2, particularly the upper laser writing system B and the lower transfer pole 4.
0, even if the height above and below is limited to the minimum size enough to cover the photosensitive drum 30 so as not to affect the layout of each member of the transport system including the separation pole 43, the cleaning device 39 Needless to say, multiple developing units
It is possible to mount and store all of 36, 37, and 38 sufficiently, so that the recording paper transport path can be configured almost linearly, which is effective for jam prevention and also for jam prevention. Even if it occurs, its processing is easy.

Each of the developing units 36, 37, and 38 has the following configuration.

In this embodiment, the developing units 36, 37, and 38 use the same structure. The developing device used in the present invention will be described with reference to the sectional view of the developing device 37 shown in FIG.

370 is a housing, 371 is a developing sleeve, 372 is a magnetic roll, 373 is a developer layer thickness regulating plate, 373A is a layer thickness regulating plate 373.
376A and 376B are first and second stirring members, 374 is a supply roller, 375 is a scraper, and 377 is a stirring partition plate.

The toner replenished in the apparatus rotates in the direction of the arrow.
The developer is sufficiently stirred and mixed with the carrier by the stirring member 376A and the second stirring member 376B rotating so as to overlap with each other in the opposite direction, and is sent to the developing sleeve 371 via the supply roller 374 as the upper developer.

The first stirring member 376A and the second stirring member 376B are screw-shaped members having left-handed helical angles rotating in opposite directions to each other and conveyed to the back side by the thrust of the second stirring member 376B. The toner and the carrier sequentially move over the agitating partition plate 377 whose upper edge is inclined downward toward the back side, move to the first agitating member 376A side, and are conveyed to the near side by the thrust, and the mixing action of the toner and the carrier therebetween. It is a homogenous developer triboelectrically charged by
A sponge-like supply roller rotating in the direction of the arrow adheres to the peripheral surface of the developing sleeve 371 in a layered manner.

An elastic layer thickness regulating plate held on a surface of the developing sleeve 371 by a fixing member 373A extending from the housing 370.
373 is pressed against a portion of the surface close to the end, regulates the layer thickness of the developer to be conveyed, and regulates the layer thickness from 100 μm to 500 μm, preferably 15 μm.
A thin developing layer having a thickness of 0 μm to 400 μm is formed.

The fixed magnetic roll 372 and a thin layer of developer adhered on the peripheral surface of the developing sleeve 371 rotating in the direction indicated by the arrow (clockwise) on the outer side of the magnetic roller 372 are rotated in the developing region E in the direction indicated by the arrow. The latent images on the drum 30 are developed in a non-contact manner at intervals to form a toner image.

During this non-contact development, a developing bias containing an AC component is applied to the developing sleeve 371 from a power source (not shown),
As a result, only the toner in the developer on the developing sleeve 371 is selectively transferred to and adhered to the surface of the latent image.

The developer having consumed the toner component has a high carrier ratio, is conveyed by the developing sleeve 371, is separated and collected by the scraper 375, and is mixed again with the developer having a high toner ratio.

The specifications of the components included in the embodiment of the developing device shown in FIG. 2 are as follows.

The developing sleeve 371 is a thin cylindrical stainless steel material having an outer diameter of 20 mmφ and is blasted on the outer peripheral surface to a roughness of 3 μm, and is clockwise at 200 to 300 revolutions per minute, and 250 revolutions per minute in the present embodiment. Has been rotated. The developing sleeve diameter is required to be a small diameter sleeve in order to reduce the size of the developing device, but is set to 15 to 30 mmφ due to the limitation of the magnetic force of the built-in magnetic roll. Various experiments were also conducted on the number of rotations of the developing sleeve. When the number of rotations was low, the supply amount of the developer was small, and the image density when the latent image was developed was low. Outer diameter 20mm
Looking at the developing sleeve, the rotation speed is 0 to 200 per minute.
The maximum image density increases linearly during rotation and becomes saturated for more than 200 rotations per minute. However, when the ambient temperature is low, the maximum image density decreases, so it is necessary to set the maximum image density with some margin.

As shown in FIG. 2, the magnetic roll 372 is a 10-pole magnet of equal magnetic force in which S and N are alternately arranged clockwise in unequal intervals so that the central angles are α = 36 ° and β = 34 °, respectively. However, a repulsive magnetic field is formed at a portion where the supply roller 374 is in contact with the supply roller 374, and one pole is removed to facilitate the peeling of the developer to form nine poles.
Included in a fixed state within 1. The magnetic force of each magnet should be large to suppress carrier adhesion,
There is a limit in the production due to the shape of the magnetic roll, and about 500 to 700 gauss on the peripheral surface of the developing sleeve 371.
Gauss is kept.

Each of the developing devices 36, 37, and 38 is incorporated in the support member 3 so that it can be easily attached to and detached from the support member 3 by a mounting mechanism described below.

Hereinafter, the case of the developing device 37 will be described.
Is provided between the fixed handle 50A and the holding piece 52, and the movable handle 50B is slidably fitted to each of the guide pins 51.
To the right.

The movable handle 50B is fitted and supported on the guide pin 51 by a pair of bosses 50C provided vertically,
A pressing lever 54 urged in a counterclockwise direction by a torsion spring 53 is mounted on the lower boss 50C.

On the other hand, the support member 3 has a guide plate on which a developing device 37 is mounted.
37A is fixed, and a "key-shaped" notch 60 is provided at a side end corresponding to the pressing lever 54.

When the developing device 37 is mounted on the support member 3, the pressing lever 54 comes into contact with the linear portion 61 of the notch 60 and is pressed slightly clockwise. A configuration in which the distance (Dsd) between the image bearing surface and the developing sleeve is maintained at a specified value by pressing in the direction of the photosensitive drum 30 (for example, a roller provided concentrically with the developing sleeve against the photosensitive drum to make the gap (Not shown).

On the other hand, in order to remove the developing device 37 from the support member 3, when the movable handle 50B is slid leftward against the action of the compression spring, the pressing lever 54 reaches the inclined portion 62 and returns counterclockwise to project 54A is brought into contact with the movable handle 50B and stopped.

Therefore, when the boss 50C abuts on the fixed handle 50A and grips and pulls the fixed handle 50A and the movable handle 50B, the pressing lever 54 escapes from the opening of the notch 60 and the developing device 37 is removed. It can be taken out from the support member 3 and separated.

Further, when the developing device 37 is mounted on the support member 3,
Is placed on the guide plate 37A, and a pin 37B attached to the side surface of the developing device 37 is pushed in so as to engage with the groove 3A-2 provided in the panel 3A. The pressing piece 5 on the movable handle 50B located at the right end of
Reference numeral 4 abuts on the inclined portion 63 and slides leftward on the guide pin 51 together with the movable handle 50B according to the inclination angle.

When the pressing lever 54 reaches the opening of the notch 60, the developing device 37
Is further pushed, the movable handle 50B slides rightward due to the action of the compression spring, and the pressing lever 54 slides on the slope portion 62 and is slightly rotated clockwise. Then, the above-described biased state of the developing device 37 is obtained.
The developing units 36 and 38 are also attached to and detached from the support member 3 by a similar mounting mechanism.

Further, when mounting each of the developing units 36, 37, and 38 on the support member 3, the dimensions, length, depth, and width, or the relative position, the grooves, holes, notches, etc. A foolproof mechanism is employed in which one or more combinations of mechanical elements based on a combination of projections such as rails and a fitting mechanism based on the selection of the above specifications do not erroneously mount another type of developing device.

For example, the height of the position where the pin 37B engages with the groove 3A-2 is changed depending on the type of the developing device, so that a different type of developing device is not mounted by mistake.

When the developing units 36, 37, and 38 are mounted on the support member 3 in parallel and stored in the apparatus main body 2, the developing unit 37 moves the developing sleeve 371 to the axis of the photosensitive drum 30 as shown in FIG. The developing units 36 and 38 are arranged on the horizontal plane passing therethrough to form Dsd with the drum peripheral surface, while the developing units 36 and 38 are directed downward from above with respect to the horizontal plane passing through the axis of the photosensitive drum 30, that is, α = 36 in the clockwise direction.
The developing sleeves 361 and 381 are arranged at positions on the peripheral surface of the drum with a phase relationship forming a central angle of ゜, β = 34 °, and are arranged so as to form a developing area having a predetermined Dsd.

Therefore, even if the magnetic rolls 362, 372, and 382 having the same magnetic pole phase are commonly used for the developing units 36, 37, and 38, the magnetic roll 372 of the developing unit 37 faces the N pole to the peripheral surface of the photosensitive drum 30. In this case, the magnetic rolls 362 and 382 of the developing units 36 and 38 can face the respective south poles adjacent to the north pole.

That is, the central angle between the developing sleeves 361, 371 and 381 viewed from the axis of the photosensitive drum 30 is clockwise α = 36 °, β = 3
Each developing unit 36, 37, 38 is provided at each position on the drum peripheral surface under the condition that the center angle between the magnetic poles in each of the magnetic rolls 362, 372, 382, ie, clockwise, is equal to α = 36 °, β = 34 °. By installing the magnetic rolls, the magnetic rolls 362, 372, and 382 can be used in common with the roll main body as well as the mounting specifications for the developing device.

As a result, the angle between the magnetic poles of the magnetic roll can be freely determined, so that the magnetic pole position can be selected according to the purpose.

Embodiment 2 A second embodiment in which four developing devices are provided on the peripheral portion of the photosensitive drum will be described with reference to FIGS. 1 (b), 5 and 6. Four developing units are used instead of three developing units of the first embodiment, and the same functional parts as those of the first embodiment are indicated by the same part numbers.

FIG. 5 shows the arrangement of the magnetic poles of the magnetic rolls 362, 372, 382, 392 used in common for the developing units 36, 37, 38, 39.
FIG. 6 shows four developing units 36, 37,
It shows the arrangement relationship between 38 and 39.

In the present embodiment, the photosensitive drum 30 is a cylindrical body having a diameter of 180 mm coated with an organic photoconductive layer (OPC), and rotates clockwise at a peripheral speed of 140 mm per second. Developing units 36, 37, 38, 3
Reference numeral 9 denotes a built-in two-component developer including yellow, magenta, cyan, and black toners and a magnetic carrier, and performs non-contact development on the latent image on the photosensitive drum 30. Developer 36
(37,38,39) developing sleeve 361 (371,381,391) is 20φ
Magnetic roll 362, fixed inside with a cylindrical body of mm
(372, 382, 392) have the magnetic pole arrangement shown in FIG. Here, alpha = 30 °, beta = 28 °, from the lower gamma = 28 poles N ₄ and S ₃ have ° comprise angle horizontally, upwardly poles N ₃ and S ₂ from the horizontal, the magnetic pole N _4, S ₃ , N ₃ and S ₂ are arranged in the clockwise direction.

The developing units 36, 37, 38, and 39 are arranged in a positional relationship as shown in FIG. 6 with respect to the photosensitive drum 30, and perform non-contact development. That is, at a position where the photoconductor drum 30 is divided in a symmetrical manner from the horizontal plane, α = 30 ° and β = 28 in the clockwise direction.
The developing units 36, 37, 38, and 39 are installed horizontally in a positional relationship of ゜, γ = 28 °. With this configuration, it is possible to use the magnetic rolls 362, 372, 382, and 392 as completely common ones including not only the roll main body but also the specification for mounting to the developing device.

〔The invention's effect〕

According to the present invention, it is possible to use a magnetic roll having exactly the same magnetic pole phase as the roll body in each developing unit arranged in the rotation direction of the photosensitive drum, thereby reducing the manufacturing cost of the developing unit and sharing parts. As a result, a practically useful image forming apparatus that is extremely advantageous in terms of service and maintenance has been provided.

[Brief description of the drawings]

FIG. 1A is a sectional view of a first embodiment of the image forming apparatus of the present invention. FIG. 1B is a cross-sectional view of a second embodiment of the image forming apparatus of the present invention. FIG. 2 is a cross-sectional view of a developing device used in the apparatus. FIG. 3 is a perspective view of a support member for housing the developing device. FIG. 4 is a layout view of the developing device with respect to the photosensitive drum. FIG. 5 is a magnetic pole arrangement diagram of the magnetic roll of the second embodiment. FIG. 6 is a layout diagram of the developing device of the second embodiment with respect to the photosensitive drum. DESCRIPTION OF SYMBOLS 1 ... Housing, 2 ... Main body 3 ... Support member, 30 ... Photoconductor drum 36,37,38 ... Developer 36A, 37A, 38A ... Guide plate 361,371,381 ... Development sleeve 362,372,382 ... Magnetic roll

Claims (1)

(57) [Claims] 1. An image forming apparatus in which development is performed by a photosensitive drum and a plurality of developing devices arranged in parallel with each other to face the photosensitive drum, wherein the developing devices have a same shape and a plurality of uniform magnetic forces. A fixed magnetic pole is provided in the developing sleeve, and one of the magnetic poles exists at a developing position on a line connecting the center of the photosensitive drum and the center of the developing sleeve of the developing device. When the included angle formed by a line connecting the centers of the developing sleeves of the adjacent developing devices is α ゜, β ゜, and γ ゜ from the upstream in the rotation direction of the photosensitive drum, between the magnetic poles adjacent to the center of the sleeve of the developing sleeve. Is included in the same direction as the rotation direction of the photosensitive drum.
含 み, β ゜, α ゜, wherein the included angle on the photosensitive drum and the included angle on the developing sleeve are in a point-symmetrical positional relationship at the point where the photosensitive drum and each developing unit face each other. An image forming apparatus, comprising: