Image forming device

1. Field of the invention

The present invention relates to a mechanism for adjusting the focal position error of exposure heads in an image forming device with a wide exposure width by disposing plural exposure heads.

2. Description of the Related Art

Image forming devices which handle wide paper sizes such as A0 sized paper conventionally use a single A0 size LED head, but these LED heads have poor production yields and low demand quantities, so the cost is high and the LED head will be high priced.

Therefore, in recent years, technology to expose a wide region using multiple heads of a small common size has been used in order to reduce costs.

For instance, as shown in FIG. 9A , exposure device R 100 is made with heads h 101 , h 102 , h 103 fixed in a housing k 100 . As shown in FIG. 9B which is a view in the direction of arrow A in FIG. 9A , the light emitted from the LED contained in each of the heads h 101 , h 102 , h 103 passes through lenses r 101 , r 102 , r 103 respectively which are located at the external boundary regions, and the light is collected and exposed with connecting focal points on the outer circumferential surface of a cylindrical photosensitive drum kd.

In order to obtain an A0 size exposure width, the exposure device R 100 aligns three A3 size heads h 101 , h 102 , h 103 and longitudinally connects the exposure regions of the lenses r 101 , r 102 , r 103 of each head to ensure the desired exposure width.

At this time, image shift occurring at the seams of the exposure regions for each head h 101 , h 102 , h 103 will be a problem, and technology to reduce this effect, such as to randomly switch the image information from one head to another head for each scan line in order to make the image shift less noticeable, has been introduced in Japanese Patent Application Laid-open No. 6-255175.

Furthermore, the Japanese Patent Application Laid-open No. 2002-52727 shows a method for detecting and correcting image shift, as well as a method for correcting intensity variation at the head exposure region seams.

Incidentally, the method for determining the focal position of the LED head for focal position adjusting of an exposure device generally uses a method of establishing a focal direction striking member on both sides of the head and adjusting the position using this member. Technology where the striking member which contacts and rotates the photosensitive drum is a space roller is shown in Japanese Patent Application Laid-open No. 62-175782.

Furthermore, as a means for space roller application, Japanese Patent Application Laid-open No. 5-127465 introduces a technology where plural heads are connected and arranged on the inside of a transparent photosensitive drum, and each head is positioned on the drum inner circumferential surface by space rollers. This technology has an advantage in that wearing of the outer circumferential surface of the photoreceptor does not occur, but currently transparent photosensitive bodies are not common.

Therefore, as shown in FIG. 9A , when space rollers are used for a exposure device R 100 which has a housing with plural heads mounted in a staggered pattern, a method is conceivable wherein image formation dot lines kl 1 , kl 2 are divided into two columns, so rollers c are established in 4 locations as shown in FIG. 9A , and striking is performed on four points on the outer circumferential surface of the photosensitive drum kd.

On the other hand, when space rollers are not used for mounting of the exposure devices R 100 , a three-point support system which is the basis for component positioning is generally used for mounting of the exposure devices R 100 to the image forming device. Of these three points, two points are for focal positioning and receive the focal direction striking member of both sides of the LED head, and the third point is for controlling the angle of the head to point the exposure direction toward the center of the drum. This technology is shown in Japanese Patent Application Laid-open No. 2002-14524, and this technology has been commonly used in the past.

Note, there are also cases where one of the three-points is able to be adjusted in order to perform fine adjustments to the parallelism of the exposure line with regards to the rotational axis of the exposure drum in order to prevent color shifting of the heads in a color printer which uses plural heads.

Incidentally, when adjusting the focal position of the exposure device, as shown in Japanese Patent Application Laid-open No. 62-175782, when plural heads are joined together and used, the position on both sides of each of the heads will not necessarily be outside of the image area, and if the space roller is made to roll and contact inside the image area of the photosensitive drum, wearing of the photosensitive drum will be promoted, and image lines will occur.

On the other hand, if rollers c are established in four locations as shown in FIG. 9A , the method for striking the four points on the outer surface of the photosensitive drum kd is to simultaneously contact all for points on the drum, so either the orientation of the exposure device R 100 with regard to the axis of the drum will be made to vary, or the exposure devices R 100 must be forcefully pressed onto the drum and the housing k 100 must be deformed.

However, in this case, structural instability is possible for positioning with regards to the drum kd because the drum kd itself is the basis and is rotationally driven.

Furthermore, if plural LED heads are mounted on a common housing to make a wide exposure device, an exposure device R 100 , which for instance has three LED heads h 101 , h 102 , h 103 in a staggered arrangement on a housing k 100 as shown in FIG. 9A , has focal positions 101 a, 101 b, 102 a, 102 b, 103 a, 103 b to be optimized on both sides of each of the heads h 101 , h 102 , h 103 , or in other words at six locations.

With this structure, if there is error in the position of these six locations during the assembly of the exposure device R 100 , optimizing all of the focal positions for the LED heads h 101 , h 102 , h 103 by adjusting the mounting of the exposure device R 100 will not be possible. Furthermore, there is an individual difference in the position error on the photosensitive drum kd side for each device.

Therefore, in order to completely eliminate differences in intensity which occurs at the seam lines for the heads, or in other words at the edge region 101 b for head h 101 , edge region 102 b for head h 102 , and edge region 103 b for head h 103 , the focal point of each head must be readjusted while matching the individual differences of the devices.

However, the focal depth of the LED heads is only several tens of micrometers and great skill is required for such minute adjustments, and therefore there is a problem with long adjustment times.

The present invention has been made in view of the above circumstances and provides an image forming device with a simple structure which can prevent image intensity variation which occurs at the seam lines between heads and can eliminate focus relative error in plural LED heads.

An aspect of the present invention provides an image forming device, comprising: a cylindrical rotatable photoreceptor rotatably supported by an apparatus body; an exposure device in which plural exposure heads which expose an outer circumferential surface of the rotatable photoreceptor are disposed in a common housing in such a manner that exposure sections thereof are consecutively positioned; and a supporting unit having a position adjusting mechanism for adjusting a posture of the exposure device in at least two locations, which supports the exposure device and which is fixed on the apparatus body.

According to the image forming device of the above-mentioned aspect of the present invention, intensity variation at the seam lines between exposure heads can be eliminated by simply adjusting the orientation of the exposure devices using a position adjusting mechanism without performing detailed adjustments on each exposure head.

Furthermore, a position adjusting mechanism is provided on the side of the supporting unit which is secured to the apparatus body, so compatibility of the exposure device mounting is supported, and there is an advantage that re-adjusting the exposure devices will not be necessary when exchanging or recycling components.

Furthermore, the seam lines between exposure heads are not directly affected, so even if image shift adjustments have already been made for the seam line regions, adjustments can be made without affecting the positional relationship between seam regions.

Embodiments of the present invention will be described in detail based on the following figures, wherein:

FIG. 1 is a conceptual major component side cross section view showing the image forming device of an embodiment 1 of the present invention;

FIG. 2A and FIG. 2B are a conceptual side view showing an enlarged view of the area around the exposure devices and photosensitive drum of the image forming device shown in FIG. 1 , and a conceptual side view of the area around the exposure devices and photosensitive drum shown in FIG. 2A , as seen from the back side;

FIG. 3 is a view of the exposure device shown in FIG. 2A in the B direction;

FIG. 4 is a conceptual expanded side view showing a close-up of the region around the exposure device and photosensitive drum which are alternates of embodiment 1;

FIG. 5A and FIG. 5B are a top view showing the area around the exposure device and photosensitive drum shown in FIG. 4 , and a view in the direction of arrow C of the exposure device and photosensitive drum shown in FIG. 4 ;

FIG. 6A and FIG. 6B are a conceptual side view showing the area around the exposure device and photosensitive drum of embodiment 2 of the present invention, and a conceptual side view of the area around the exposure device and photosensitive drum shown in FIG. 6A ;

FIG. 7 is a diagram showing an exposure device of embodiment 3 (D direction view of the exposure device shown in FIG. 8A seen from the D direction);

FIG. 8A and FIG. 8B is a conceptual side view showing the region around the exposure device and photosensitive drum of embodiment 3 of the present invention, and a conceptual side view showing the region around the exposure device and photosensitive drum of embodiment 3 of the present invention seen from the back side; and

FIG. 9A and FIG. 9B are a diagram showing a conventional exposure device and a view in the direction of arrow A of the exposure device shown in FIG. 9A .

Embodiments of the present invention will be described in detail while referring to the attached drawings.

As shown in FIG. 1 , a conceptual critical unit side cross section view, the image forming device 1 of embodiment 1 which uses the present invention is roughly comprised of a paper feeder 2 which feeds paper for forming an image, and image forming unit 3 which forms an image on the paper sent from the paper feeder 2 , a control circuit for controlling the paper feeder 2 and the image forming unit 3 , and a storage units 4 for storing extra paper feeder rolls or the like.

Inside the image forming unit 3 , a photosensitive drum (rotating type photoreceptor) 5 which acts as an image information image support member for forming an image is rotatably supported by the apparatus body.

The photosensitive drum 5 has a cylindrical form approximately 100 mm in diameter with a center axis which is perpendicular to the surface of the paper in FIG. 1 , is coated with a photoreceptor made from an organic photosensitive agent such as OPC on the outer circumferential surface of the drum which is made from aluminum, and is rotationally driven at a prescribed rotational speed in the direction of the arrow shown in FIG. 1 .

Opposite the outer circumferential surface of the photosensitive drum 5 , a first LED print head (Hereinafter abbreviated as first LPH) (exposure head) 71 , a second LED print head (Hereinafter abbreviated as second LPH) (exposure head) 72 , and a third LED print head (Hereinafter abbreviated as third LPH) (exposure head) 73 are arranged in the exposure device R 1 in a form extending parallel to the width direction of the outer circumferential surface of the photosensitive drum 5 , in order to form an electrostatic latent image corresponding to the image information on the outer circumferential surface of the photosensitive drum 5 .

FIG. 2A is a conceptual side view showing an enlarged view of the area around the exposure device R 1 and the photosensitive drum 5 shown in FIG. 1 , and FIG. 3 is a view of the exposure device R 1 shown in FIG. 2A in the direction of arrow B.

LPH 71 , 72 , 73 are arranged in a row on a substrate, and house a mounted LED (not shown in the drawings), SELFOC® lenses 71 r, 72 r, 73 r are arranged at the boundary region to the outside opposite the LED series which are arranged in a row, and the light from each of the LED pass through and is collected by the SELFOC® lenses 71 r, 72 r, 73 r, and exposed onto the outer circumferential surface of the photosensitive drum 5 .

The photosensitive drum 5 is rotationally driven while images are successively formed on the region along the width direction of the outer circumferential surface to form the desired image on the circumferential surface, but because the dimensions of the outer circumferential surface of the photosensitive drum 5 are large in the width direction, the exposure regions of LPH 71 , 72 , 73 are joined together to form an image.

In other words, as shown in FIG. 3 , the SELFOC® lenses 71 r, 72 r, 73 r which are the exposure regions of each of the LPH 71 , 72 , 73 are provided in order to provide the prescribed wide exposure width, and opposite the photosensitive drum 5 outer circumferential surface, LPH 71 , 72 , 73 are arranged in a staggered position on exposure device housing tk such that the exposure regions are connected along the width direction of the outer circumferential surface.

Furthermore, the exposure edge 71 rb of the first LPH 71 and the exposure edge 72 ra of the second LPH 72 are arranged to overlap in the width direction of the outer circumferential surface of the photosensitive drum 5 such that the image between LPH 71 , 72 in the width direction of the outer circumferential surface of the photosensitive drum 5 is continuous without breaks.

Simultaneously, the exposure edge 72 rb of the second LPH 72 and the exposure edge 73 ra of the third LPH 73 are arranged to overlap in the width direction of the outer circumferential surface of the photosensitive drum 5 such that the image between LPH 72 , 73 in the width direction of the outer circumferential surface of the photosensitive drum 5 is continuous without breaks.

In this case, if the exposure regions of LPH 71 , 72 , 73 are used for forming the image, in the region where the exposure edge 71 rb of the first LPH 71 and the exposure edge 72 ra of the second LPH overlap, and in the region where the exposure edge 72 rb of the second LPH 72 and the exposure edge 73 ra of the third LPH overlap in the widthwise direction of the outer circumferential surface of the photosensitive drum 5 , the image will be doubled and proper image forming cannot be accomplished. Therefore, the image signal is controlled by a control unit so that an exposure region (shaded region in FIG. 3 ) is formed which connects without overlapping the exposure regions of LPH 71 , 72 , 73 .

Next, an outline of the process of forming an image using an image forming device 1 with the aforementioned structure will be described.

As shown in FIG. 1 , rolled paper p with an A0 or A1 size or the like which is stored in the paper feeder 2 is supplied from paper rolls 9 a, 9 b to the transfer roller 12 and the outer circumferential surface of the photosensitive drum 5 which rotates in the direction of the arrow.

The photosensitive drum 5 rotates in the direction of the arrow, and after the outer circumferential surface is temporarily charged to a prescribed potential by a charged roller 6 which is a primary charging unit, and image is exposed on the outer circumferential surface by plural image exposing units, namely first LPH 71 , second LPH 72 , and third LPH 73 , and an electrostatic latent image is formed with an electric potential difference corresponding to the image information. In this manner, an electrostatic latent image formed on the outer circumferential surface of the photosensitive drum 5 is developed and attached by a development device 8 to form a toner image.

The toner image formed on the outer circumferential surface of the photosensitive drum 5 is transferred to the roll paper p provided as described above by the transfer roller 12 , the roll paper p to which the toner image is transferred is transported to a fusing unit 15 by a transport belt 14 , and the toner image is then fixed using heat and pressure by the fusing unit 15 . If necessary, the roll paper is cut to a desired size such as size A0, and then discharged onto a paper discharged tray (not shown in the drawings) located on the outside of the image forming device body 1 .

Incidentally, LPH 71 , 72 , 73 are mounted on the metal exposure device housing tk as shown in FIG. 3 , and one end of the exposure device housing tk has a cylindrical pin p 11 which is crimped in place to form a single stud, while the other end of the exposure device housing tk has two studs formed by crimping cylindrical pins p 12 , p 13 in place, to form the exposure unit R 1 .

The exposure unit R 1 is manufactured as a single piece with a prescribed level of precision as a component part of the image forming device 1 , and is mounted and secured to the device body.

As shown in FIG. 2A , when mounted, LPH 71 , 73 are positioned parallel to the tangent line opposite the outer circumferential surface of the photosensitive drum 5 . Similarly, when LPH 72 is mounted, it is positioned parallel to the tangent line opposite the outer circumferential surface of the photosensitive drum 5 , and the design is such that the distance from the outer surface of the SELFOC® lenses 71 r, 72 r, 73 r of the LPH 71 , 72 , 73 to the outer circumferential surface of the photosensitive drum 5 is equal to the focal distance. The focal distance is between 2 and 3 mm, a variation level of ±50 μm is permissible, and the desired image is exposed on the outer circumferential surface in order to ensure the precision of the focal distance.

If the seam region of LPH 71 and LPH 72 cannot have the respective desired focal distances, intensity variation observed as tint intensity will occur, and similarly, if the seam region of LPH 72 and LPH 73 cannot have the respective desired focal distances, intensity variation will occur.

In order to mount the exposure unit R 1 in the prescribed location, one end of the exposure unit R 1 has a supporting member (supporting unit) s 11 which is the focus standard and has an adjusting hole (position adjusting mechanism) sp 11 into which pins p 12 , p 13 are fit and can slide to adjust as shown in FIG. 2A . Adjustment screws (position adjusting mechanism) b 11 , b 12 are screwed into both sides of the support member s 11 .

On the other hand, at the other end of the exposure unit R 1 , a support member (supporting unit) s 12 , which is the focus standard, is secured to the apparatus body and has an adjusting hole (position adjusting mechanism) sp 12 into which pin p 11 is fit and can slide to adjust as shown in FIG. 2B which is a view seen from the back side of FIG. 2A . Adjustment screws (position adjusting mechanism) b 13 , b 14 are screwed into both sides of the support member s 12 .

With this construction, as shown in FIG. 2A , the pins p 11 , p 13 of the exposure unit R 1 are fit into the adjustment hole sp 11 of the support member s 11 and pressed by adjustment screws b 11 , b 12 to adjust and set the position of one end of the exposure unit R 1 in the direction of the arrow, and as shown in FIG. 2B , the pin p 11 of the exposure unit R 1 is fit into the adjustment hole sp 12 of the support member s 12 and pressed by adjustment screws b 13 , b 14 to adjust and set the position of one end of the exposure unit R 1 in the direction of the arrow.

In other words, the pins p 12 , p 13 at one end of the exposure unit R are supported by support member s 11 , and one end of the exposure unit R can be moved and adjusted in the direction of the arrow by rotating the adjust screws b 11 , b 12 . Furthermore, the pin p 11 at the other end of the exposure unit R is supported by support member s 12 , and the other end of the exposure unit R can be moved and adjusted in the direction of the arrow by rotating the adjust screws b 13 , b 14 .

With the above structure, if the direction of movement of the exposure unit R is in the direction perpendicular to the exposure direction of LPH 71 , 73 , or in other words the direction tangential to the outer circumference surface of the photosensitive drum 5 , the image forming distance of LPH 71 , 73 will hardly change even though the exposure unit R is moved, so at this time, of the three LPH, the focus of LPH 71 and LPH 73 are almost optimized. On the other hand, the movement in the exposure direction which changes the image forming distance of LPH 72 will be large, so the image forming distance of LPH 72 can be significantly changed and adjusted.

Therefore, the relative error of the image forming distance of LPH 72 can be eliminated with LPH 71 , 73 as a standard. Note, the adjustment target is easily achieved because the LPH 71 , 73 standard is clearly seen.

However, the direction of adjustment of the exposure unit R 1 does not necessarily have to be in the same direction as the arrow shown in FIG. 2 . For instance, the direction may be perpendicular to the exposure direction of LPH 72 (tangential to the outer circumferential surface of the photosensitive drum 5 ), or in a direction between these two examples, and can be arbitrarily selected depending on the position and direction of the pins p 11 , p 12 , p 13 and the support members s 11 , s 12 of the exposure unit R 1 .

In this manner, regardless of the adjustment direction of the exposure unit R 1 , intensity variation at the seam between LPH 71 , 72 and the intensity variation at the seam between LPH 72 , 73 can be eliminated by eliminating the relative image forming distance error between LPH 71 , 72 , 73 .

Furthermore, FIG. 2 shows the method of striking adjust screws b 11 , b 12 , b 13 , b 14 in order to briefly describe the structure, but the adjustment mechanism is not restricted to this example and various other applications are possible, such as a method to strike and adjust the support part of the exposure unit R 1 using eccentric pins where the dimension from the center to the outer edge is eccentric, or a method to reduce the spacer thickness between the support members which hold the supports and the device body of the exposure unit R 1 in place.

Furthermore, with the conventional technology, the screw adjustment of the exposure unit is in only one location, so adjusting the image forming distance difference of the head seam region in two locations is not possible, but with the present invention, the adjustment is performed in two locations, namely both end supports of the exposure unit R 1 , so the image forming distance difference in two locations, namely the seam region of LPH 71 , 72 and the seam region LPH 72 , 73 , can be adjusted together.

Next, a method of adjusting the position of the exposure unit using eccentric pins which is an alternate of embodiment 1 will be described.

As shown in FIG. 4 , a conceptual side expanded view, FIG. 5A a top view of FIG. 4 , and FIG. 5B , a view in the direction of arrow C of FIG. 4 , a photoresistor R 1 ′ has a construction such that LPH (exposure heads) 71 ′, 72 ′, 73 ′are arranged in prescribed locations in the exposure unit housing tk′ of the exposure unit R 1 , a mounting bracket t 1 on one end of the exposure unit housing tk′ is secured by bolts b′, b′, and a mounting bracket t 2 on the other end of the exposure unit housing tk′ is secured by bolts b′, b′.

Mounting brackets t 1 , t 2 each have rectangular adjusting holes t 1 a , t 2 a which are sufficiently larger than the outer diameter of hexagonal eccentric pins (position adjusting unit) hp 1 , hp 2 which are vertically positioned in supports (supporting unit) s 11 ′, s 12 ′ on the sides of the apparatus body so that the eccentric pins hp 1 , hp 2 can pass through and fit with free play. These eccentric pins hp 1 , hp 2 are formed such that the dimension from the center line to each of the hexagonal edges increases in steps.

With this structure, as shown in FIG. 5A , one side of the adjusting hole t 1 a of the mounting bracket t 1 will strike on one of the hexagonal sides of the eccentric pin hp 1 , and mounting bracket t 1 is secured to the support s 11 ′ on the side of the apparatus body by bolts b 1 ′, b 1 ′, and furthermore, one side of the adjusting hole t 2 a of the mounting bracket t 2 will strike on one of the hexagonal sides of the eccentric pin hp 2 , and mounting bracket t 2 is secured to the support s 12 ′ on the side of the apparatus body by bolts b 2 ′, b 2 ′, and thereby exposure unit R 1 ′ is positioned and secured with regards to the outer circumferential surface of the photosensitive drum 5 .

Therefore, as shown in FIG. 5A , adjustment of the position of the mounting bracket t 1 in the direction of arrow a is possible by rotating the eccentric pin hp 1 to select one of the sides and then securing in place, and adjustment of the position of the mounting bracket t 2 in the direction of arrow b is possible by rotating the eccentric pin hp 2 to select one of the sides and then securing in place. Therefore, a sliding position adjustment is made on both sides of the exposure unit R 1 ′ and the respective image forming distances of the LPH 71 ′, 72 ′, 73 ′ with regards to the outer circumferential surface of the photosensitive drum 5 can be adjusted.

With the aforementioned construction, the eccentric pins hp 1 , hp 2 are secured to the side of the apparatus body as the position adjusting unit for the exposure unit R 1 , so even if any one of the LPH 71 ′, 72 ′, 73 ′ breaks down and is replaced with a new exposure unit R 1 ′, adjusting the position of the LPH 71 ′, 72 ′, 73 ′, of the new exposure unit R 1 ′ will not be necessary.

Furthermore, this alternate example will of course have the same functional effects as embodiment 1.

Embodiment 2 uses the exposure unit R 1 shown in embodiment 1, but changes the structure of the support member which adjusts and secures the exposure unit R 1 .

In other words, as shown FIG. 6A , on one side of the exposure unit R 1 , a conceptual side view, a support member (supporting unit) s 21 which is the focus standard has a hole (position adjusting mechanism) sp 21 through which a pin p 12 for exposure unit R 1 is inserted and rotatably supported, and an adjusting hole (position adjusting mechanism) sp 22 wherein a pin p 13 of the exposure unit R 1 can be fit and adjusted by sliding, and this support member s 21 is secured to the apparatus body where the photosensitive drum 5 and the like are established. Adjustment screws (position adjusting mechanism) b 21 are screwed into the bottom of the adjusting hole sp 22 of this support member s 21 .

On the other hand, on the other end of the exposure unit R 1 , as shown in FIG. 6B , a view from the back side of FIG. 6A , support member (supporting unit) s 22 which is the focus standard has an adjusting hole (position adjusting mechanism) sp 23 through which the pin p 11 of the exposure unit R 1 can fit and adjust by sliding, and this supporting member s 22 is secured to the apparatus body wherein the photosensitive drum 5 and the like is established. Both sides of this support member s 22 are screwed in place by adjusting screws (position adjusting mechanism) b 22 , b 23 .

With this construction, as shown in FIG. 6A , the pin p 12 of the exposure unit R 1 is inserted into and pivotally supports the hole sp 21 of the support member s 21 , and the pin p 13 of the exposure unit R 1 is inserted into the adjustment hole sp 22 and pressed upon by adjusting screw b 21 , so one end of the exposure unit R 1 is rotationally adjusted as shown by the arrow and positioned by the region around the pin p 12 which is supported by the hole sp 21 of the support member s 21 .

Furthermore, by fitting the pin p 11 of the exposure unit R 1 into the adjusting hole sp 23 of the support member s 22 and applying pressure by adjusting screws b 22 , b 23 , the other end of the exposure unit R 1 is adjusted by sliding and positioned in the direction of the arrow by adjusting screws b 22 , b 23 .

With this construction, the adjusting points of the exposure unit R 1 are in two locations at both supporting members, but embodiment 2 differs from the structure of embodiment 1 in that one of the studs is made to pivot so that one end of the exposure unit R 1 is adjusted by rotation.

With this mechanism, when the degree of adjustment of the two seam regions of LPH 71 , 72 and LPH 72 , 73 are to be changed, one end of the exposure unit R 1 is adjusted by sliding, and the other end of the exposure unit R 1 is adjusted by rotating. With embodiment 1, as shown in FIG. 2A , adjustments must be performed by the two adjusting screws b 11 , b 12 even if adjusting the left and right sides by the same amount, but with embodiment 2, as shown in FIG. 6A , adjusting can be completed by adjusting only one adjusting screw b 12 , so the number of adjusting steps can be reduced.

Therefore, the image forming distance of LPH 71 , 72 , 73 with regards to the outer circumferential surface of the photosensitive drum 5 can be adjusted, and therefore intensity variation at the edge of LPH 71 and the edge of LPH 72 , and intensity variation at the edge of LPH 72 and the edge of the LPH 73 can be prevented.

An exposure unit R 3 shown in embodiment 3 is identical to the exposure unit R 1 of embodiments 1 and 2 with regards to the arrangements of the LPH on the photoreceptor housing, and only the structure of the vertical pins on both sides of the exposure unit housing have been changed.

Therefore, structural elements which are identical in exposure unit R 3 and exposure unit R 1 have been assigned the same code, and only the structural differences will be discussed.

As shown in FIG. 7 , exposure unit R 3 is formed with two studs formed by crimping the cylindrical pins p 31 , p 32 at one end of the exposure unit housing tk of the exposure unit R 3 , and two studs formed by crimping the cylindrical pins p 33 , p 34 at the other end.

The structure of the apparatus body side which adjusts the position and secures the exposure unit R 3 is as shown below.

In other words, as shown in FIG. 8A , on one end of the exposure unit R 3 , a support member (supporting unit) s 31 which is the focus standard has a hole (position adjusting mechanism) sp 31 through which the pin p 33 of the exposure unit R 3 is inserted and rotatably supported, and an adjusting hole (position adjusting mechanism) sp 32 wherein the pin p 34 of the exposure unit R 3 is fit and adjusted by sliding, and this supporting member s 31 is secured to the apparatus body wherein the photosensitive drum 5 and the like are established. The top part and the bottom part of the adjusting hole sp 32 of this support member s 31 each have adjusting screws (position adjusting mechanism) b 31 , b 32 .

On the other hand, as shown in FIG. 8B , a view from the back side of FIG. 8A , on the other end of the exposure unit housing tk of the exposure unit R 3 , a support member (supporting unit) s 32 which is the focus standard has a hole (position adjusting mechanism) sp 34 through which the pin p 31 of the exposure unit R 3 is inserted and rotatably supported, and an adjusting hole (position adjusting mechanism) sp 34 wherein the pin p 33 of the exposure unit R 3 is fit and adjusted by sliding, and this supporting member s 32 is secured to the apparatus body wherein the photosensitive drum 5 and the like is established. The top part and the bottom part of the adjusting hole sp 34 of this support member s 32 each have adjusting screws (position adjusting mechanism) b 33 , b 34 .

With this construction, as shown in FIG. 8A , the pin p 33 of the exposure unit R 3 is inserted into and pivotally supports the hole sp 31 of the support member s 31 , and the pin p 34 of the exposure unit R 3 is inserted into the adjustment hole sp 32 and pressed upon by adjusting screws b 31 , b 32 , so one end of the exposure unit R 3 is rotationally adjusted as shown by the arrow and positioned by the area around the pin p 33 which is supported by the hole sp 31 of the support member s 31 .

With this construction, as shown in FIG. 8B , the pin p 31 of the exposure unit R 3 is inserted into and pivotally supports the hole sp 33 of the support member s 32 , and the pin p 32 of the exposure unit R 3 is inserted into the adjustment hole sp 34 and pressed upon by adjusting screws b 33 , b 34 , so the other end of the exposure unit R 3 is rotationally adjusted as shown by the arrow and positioned by the area around the pin p 31 which is supported by the hole sp 33 of the support member s 32 .

With this structure, the exposure unit R 3 is adjusted at both ends of the support position, and the adjustment is performed by rotation at the both ends.

Accordingly, both ends of the exposure unit R 3 are rotated in the same direction or both ends of the exposure unit R 3 are rotated in opposite directions, thereby the exposure unit R 3 is twisted and deformed, so that the image forming distance of the LPH 71 , 72 , 73 can be adjusted so that the intensity differences at the seam region of LPH 71 , 72 and the seam region of LPH 72 , 73 can be eliminated.

In other words, it is possible to twist and deform a straight exposure unit R 3 in order to align the image forming distance differences of LPH seams in two locations.

For the case of the slide adjustment of the embodiment 1 shown in FIG. 2 , if the focal point difference of the LPH seam is preferentially eliminated so that the amount of adjustment is large, the image forming distance at the ends of the LPH 71 and the LPH 73 will become slightly worse. However, by using the method of embodiment 3 shown in FIG. 8 , the image forming distance of LPH 72 can be changed while having almost no affect on the image forming distance of the LPH 71 and the LPH 73 . Therefore, this is an effective method if a big adjustment is to be made in LPH 72 .

In addition to the aforementioned embodiments 1 through 3, if the exposure unit has more than three LPH, the number of head seams will also increase, so a combination of only slide adjusting and rotation adjusting will be insufficient. In this case, the image forming distance difference of plural LPH seams can be adjusted for by a method of intentionally warping the exposure unit housing by having a screw strike the region of the seam of the LPH of the exposure unit housing.

The present invention can be effectively used for standard printers, plotters, devices which form an image on blank sheets such as paper bills, and securities or the like, as well as other types of image forming devices so long as the image forming device uses a rotating photoreceptor and exposure units.

The entire disclosure of Japanese Patent Application No. 2004-326502 filed on Nov. 10, 2004 including specification, claims, drawings, and abstract is incorporated herein by reference in its entirety.