Patent Publication Number: US-7589751-B2

Title: Image forming apparatus and method for adjusting the interval between a write head and a photoreceptor

Description:
CROSS-NOTING PARAGRAPH 
   This Nonprovisional application claims priority under 35 U.S.C. §119 (a) on Patent Application No. 2005-350852 filed in JAPAN on Dec. 5, 2005, the entire contents of which are hereby incorporated herein by references. 
   FIELD OF THE INVENTION 
   The present invention relates generally to an image forming apparatus and an adjusting method of an image forming apparatus, and, more particularly, to an image forming apparatus with an adjusting mechanism that adjusts an interval between a write head writing an optical image on a photoreceptor and the photoreceptor to a reference interval, and an adjusting method of the image forming apparatus. 
   BACKGROUND OF THE INVENTION 
   A write head such as an LED (Light Emitting Diode) head is used in an electrophotographic image forming apparatus such as a digital multi-function peripheral (MFP), printer, and facsimile machine and is positioned and attached with a predetermined interval from a photoreceptor drum to achieve high-quality images. 
   However, it is difficult to assemble mass-produced image forming apparatuses such that intervals between the write heads and the photoreceptors become completely the same, and some variance is generated at the time of assembly. Therefore, the position of the write head must be adjusted in each apparatus after the assembly such that the interval between the write head and the photoreceptor falls within a certain tolerance to achieve images with a predetermined quality. 
   Therefore, in a conventional electrophotographic image forming apparatus such as an MPF, a mechanism adjusting the position of the LED head is disposed in a main body of the image forming apparatus. In a manufacturing line of the image forming apparatus, a photoelectric transducer such as a CCD is mounted on the photoreceptor mounting position and an adjustment work is performed by detecting an LED exposure spot shape from the CCD output and using a dedicated jig for adjusting the LED head position. 
   On the other hand, in electrophotographic image forming apparatuses, photoreceptors are consumables, and a variance is generated in a distance between the photoreceptor surface and the LED head due to an individual difference of the photoreceptor mounting position. A lens built into the LED head has a focal depth of only ±0.1 mm, and if the variance exceeds the focal depth, a desired image quality cannot be acquired unless focus adjustment is performed such that the focal point of the light emitted from the LED head conforms to the photoreceptor surface after replacing the photoreceptor. 
   Since the apparatus of the above dedicated jig is large and expensive, the dedicated jig cannot be used when a service person visits a customer&#39;s site to adjust the LED head position, and since the position is adjusted by performing test print and visually checking printed line widths, this operation takes a long time and adjustment accuracy is low in reality. 
   In view of the above situations, a clamshell image forming apparatus is known which can be opened at a lower portion of the LED head. Since the clamshell image forming apparatus can be opened at the lower portion of the LED head, when positioning the write head and the photoreceptor drum with a predetermined distance, the mounting position of the write head can easily be adjusted. 
   Japanese Laid-Open Patent Publication No. 2001-130047 discloses a technology of reducing a focal shift generated when correcting a position shift of a scanning line in an electrophotographic recording apparatus using an LED head by bring a contact rod into contact with a photoreceptor surface to maintain a constant distance between the LED head and the photoreceptor surface. Japanese Laid-Open Patent Publication No. 2003-173073 discloses a technology capable of adjusting a distance between a writing head and a photoreceptor drum, and the scanning inclination of the writing head relative to the photoreceptor drum from the side portion of a main body apparatus. 
   If a user must replace consumables or adjust parts in the electrophotographic image forming apparatuses during use, a skilled “service man” performs the operation. Conventionally, it has been insisted that the maintenance by a service man must be shifted to “user maintenance”, and the “user maintenance” is introduced in the case of a portion of parts, for example, a process kit, since the printing quality is not deteriorated and the apparatus is not damaged even when a user replaces the parts. However, in the case of parts that are a core of the electrophotographic mode, the operation is dependent on the “service man maintenance”. 
   Especially, with regard to the mounting adjustment of image writing members such as an optical unit and LED head using laser light which has an influence on the print quality, the operation is regarded as an essential item of the “service man maintenance”, not only since a lot of skill is required to perform dot diameter adjustment using a print image at a mounting site after the adjustment of the image forming apparatus at the time of factory shipment but also from a standpoint of having an influence on the print quality. The mounting adjustment of image writing members such as an optical unit and LED head must be performed every time an electrostatic latent image support (photoreceptor) is replaced in addition to the above maintenance and, since the adjustment operation is difficult, the adjustment has been omitted at the time of the replacement of the photoreceptor in a normal process. 
   In recent years, print resolution is increased from conventional 300 dpi to 600 and 1200 dpi as higher quality images are formed by image forming apparatuses, and it is difficult even for a skilled service man to respond such increment with the conventional adjustment technique. For reference, in the case of 1200 dpi, a dot diameter of one dot is generally 12 to 13 μm, which cannot be recognized. 
   Due to eccentricity, deformation, diameter variance, etc., of the photoreceptor drum including the photoreceptor, a distance between the write head and the photoreceptor is changed depending on a rotation angle. Therefore, if the interval adjustment is performed at a position where the distance is maximized between the write head and the photoreceptor, the distance between the write head and the photoreceptor drum becomes too small at other positions; contrary, if the interval adjustment is performed at a position where the distance is minimized between the write head and the photoreceptor, the distance between the write head and the photoreceptor drum becomes too large at other positions; and in either case, the optimum interval adjustment cannot be performed. 
   When adjusting the interval between the write head and the photoreceptor, if a line extended from a regulating member is shifted such that the line does not intersect with a center line of the drum rotation axis, i.e., if the position of the regulating member is shifted from the photoreceptor drum in the sub-scanning direction, the shape of the exposure spot applied to the photoreceptor does not become a perfect circle and a sharp latent image cannot be formed on the photoreceptor. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide an image forming apparatus that includes an adjusting mechanism enabling an unskilled user to easily and certainly check an interval between a write head and a photoreceptor to adjust the interval highly accurately, and a method of adjusting the interval between the write head and the photoreceptor. 
   Another object of the present invention is to provide an image forming apparatus that adjusts an interval between a write head and a photoreceptor when a photoreceptor drum is located at a predetermined rotation position to prevent the interval between the write head and the photoreceptor from becoming too small or too large in one rotation of the photoreceptor drum and making a photoreceptor surface out of a range of focal depth of the write head even if acceptable eccentricity, deformation, diameter variance, etc., are generated in the photoreceptor drum, and a method of adjusting the interval between the write head and the photoreceptor. 
   Another object of the present invention is to provide an image forming apparatus that corrects a shift between a regulating member and a photoreceptor drum in a sub-scanning direction when adjusting an interval between a write head and a photoreceptor and that subsequently adjusts the interval between the write head and the photoreceptor to accurately adjust the interval between the write head and the photoreceptor, and a method of adjusting the interval between the write head and the photoreceptor. 
   More specifically, an object of the present invention is to provide an image forming apparatus comprising an adjusting mechanism that adjusts an interval between a write head writing an optical image on a photoreceptor and the photoreceptor to a reference interval, the adjusting mechanism including a regulating member that integrally moves along with the write head in the direction of the photoreceptor to regulate the interval between the write head and the photoreceptor; a moving mechanism that integrally moves the regulating member along with the write head to bring the regulating member into contact with the photoreceptor; and a reverse-moving mechanism that integrally moves the regulating member along with the write head in the direction opposite to the photoreceptor by a predetermined distance after the regulating member comes into contact with the photoreceptor to set the interval between the write head and the photoreceptor to the reference interval. 
   Another object of the present invention is to provide the image forming apparatus, comprising: a contact detection mechanism that detects the contact between the regulating member and the photoreceptor from presence of electric conductivity; and a mechanism that performs notification of the detection result of the contact detection mechanism. 
   Another object of the present invention is to provide the image forming apparatus, wherein the regulating member contacts with a conductive non-image area disposed at both ends of the photoreceptor and the moving mechanism and the reverse-moving mechanism can independently move both ends of the write head. 
   Another object of the present invention is to provide the image forming apparatus, wherein when adjusting the interval between the write head and the photoreceptor, the regulating member is brought into contact with the photoreceptor while the photoreceptor is rotated. 
   Another object of the present invention is to provide an image forming apparatus comprising an adjusting mechanism that adjusts an interval between a write head writing an optical image on a photoreceptor and the photoreceptor to a reference interval, the adjusting mechanism including a regulating member that integrally moves along with the write head in the direction of the photoreceptor to regulate the interval between the write head and the photoreceptor; a mechanism that mounts a spacer with a predetermined thickness to the photoreceptor; a moving mechanism that integrally moves the regulating member along with the write head to bring the regulating member into contact with the spacer; and a mechanism that removes the spacer after the regulating member comes into contact with the spacer. 
   Another object of the present invention is to provide the image forming apparatus comprising: a contact detection mechanism that detects the contact between the regulating member and the spacer from presence of electric conductivity; and a mechanism that performs notification of the detection result of the contact detection mechanism. 
   Another object of the present invention is to provide the image forming apparatus, wherein the regulating member contacts with the spacer mounted to both ends of the photoreceptor and the moving mechanism can independently move both ends of the write head. 
   Another object of the present invention is to provide an image forming apparatus comprising an adjusting mechanism that adjusts an interval between a write head writing an optical image on a photoreceptor on a drum and the photoreceptor to a reference interval, the adjusting mechanism including an adjusting member that integrally moves along with the write head to adjust the interval between the write head and the photoreceptor and a detecting member that comes into contact with the photoreceptor drum to detect the interval between the write head and the photoreceptor, the detecting member obtaining a place on the photoreceptor where the photoreceptor becomes closest to the write head and a place on the photoreceptor where the photoreceptor becomes farthest from the write head to adjust the interval between the write head and the photoreceptor to an intermediate position between the obtained places. 
   Another object of the present invention is to provide the image forming apparatus, comprising: a contact detection mechanism that detects the contact between the detecting member and the photoreceptor drum from presence of electric conductivity; and a mechanism that performs notification of the detection result of the contact detection mechanism. 
   Another object of the present invention is to provide an image forming apparatus comprising an adjusting mechanism that adjusts an interval between a write head writing an optical image on a photoreceptor on a drum and the photoreceptor to a reference interval, the adjusting mechanism including a regulating member that integrally moves along with the write head in the direction of the photoreceptor to regulate the interval between the write head and the photoreceptor; a sub-scanning direction position detecting member that detects a position of the regulating member in the sub-scanning direction relative to the photoreceptor drum; and a sub-scanning direction moving mechanism that moves the write head in the sub-scanning direction, after the sub-scanning direction position detecting member and the sub-scanning direction moving mechanism adjust a sub-scanning direction position of the write head, the apparatus using the regulating member to adjust the interval between the write head and the photoreceptor. 
   Another object of the present invention is to provide the image forming apparatus, wherein the sub-scanning direction position detecting member comes into contact with a rotation shaft of the photoreceptor drum when the write head reaches right above the photoreceptor. 
   Another object of the present invention is to provide the image forming apparatus, wherein the regulating member and the sub-scanning direction position detecting member are integrally formed and move closer or away in the direction of the photoreceptor along with the write head. 
   Another object of the present invention is to provide the image forming apparatus, wherein a distance between the center axis of the regulating member and a contact position bringing the sub-scanning direction position detecting member into contact with the rotation shaft of the photoreceptor drum is set larger than a radius of the rotation shaft of the photoreceptor drum by a predetermined distance and when detecting contact with the rotation shaft, the sub-scanning direction position detecting member is moved away from the contact position by the predetermined distance. 
   Another object of the present invention is to provide the image forming apparatus, comprising: an evacuation mechanism that evacuates the regulating member. 
   Another object of the present invention is to provide the image forming apparatus, wherein the photoreceptor is drum-shaped. 
   Another object of the present invention is to provide the image forming apparatus, wherein the write head is an LED head. 
   Another object of the present invention is to provide the image forming apparatus, wherein the photoreceptor is belt-shaped. 
   Another object of the present invention is to provide an adjusting method of an image forming apparatus, the apparatus comprising an adjusting mechanism that adjusts an interval between a write head writing an optical image on a photoreceptor and the photoreceptor to a reference interval, the adjusting mechanism including a regulating member that integrally moves along with the write head in the direction of the photoreceptor to regulate the interval between the write head and the photoreceptor, wherein after the regulating member is moved in the direction of the photoreceptor and brought into contact with the photoreceptor, the regulating member is integrally moved along with the write head in the direction opposite to the photoreceptor by a predetermined dimension to set the interval between the write head and the photoreceptor to the reference interval. 
   Another object of the present invention is to provide an adjusting method of an image forming apparatus, the apparatus comprising an adjusting mechanism that adjusts an interval between a write head writing an optical image on a photoreceptor and the photoreceptor to a reference interval, the adjusting mechanism including a mechanism that mounts a spacer with a predetermined thickness to the photoreceptor and a regulating member that integrally moves along with the write head in the direction of the photoreceptor to regulate the interval between the write head and the photoreceptor, wherein after the spacer is mounted to the photoreceptor and the regulating member is moved along with the write head in the direction of the photoreceptor and brought into contact with the spacer, the spacer is removed. 
   Another object of the present invention is to provide an adjusting method of an image forming apparatus, the apparatus comprising an adjusting mechanism that adjusts an interval between a write head writing an optical image on a photoreceptor on a drum and the photoreceptor to a reference interval, the adjusting mechanism including an adjusting member that integrally moves along with the write head to adjust the interval between the write head and the photoreceptor and a detecting member that comes into contact with the photoreceptor to detect the interval between the write head and the photoreceptor, wherein the detecting member obtains a place on the photoreceptor where the photoreceptor becomes closest to the write head and a place on the photoreceptor where the photoreceptor becomes farthest from the write head to adjust the interval between the write head and the photoreceptor to an intermediate position between the obtained places. 
   Another object of the present invention is to provide an adjusting method of an image forming apparatus, the apparatus comprising an adjusting mechanism that adjusts an interval between a write head writing an optical image on a photoreceptor on a drum and the photoreceptor to a reference interval, the adjusting mechanism including a regulating member that integrally moves along with the write head in the direction of the photoreceptor to regulate the interval between the write head and the photoreceptor, a sub-scanning direction position detecting member that detects a position of the regulating member in the sub-scanning direction relative to the photoreceptor drum, and a sub-scanning direction moving mechanism that moves the write head in the sub-scanning direction, wherein after the sub-scanning direction position detecting member and the sub-scanning direction moving mechanism adjust a sub-scanning direction position of the write head, the regulating member is used to adjust the interval between the write head and the photoreceptor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of an overall configuration of a digital color copier that is an image forming apparatus of an embodiment of the present invention; 
       FIG. 2  is a sectional view of a write head adjustment apparatus in an image forming apparatus of a first embodiment, taken along line P-P of  FIG. 1 ; 
       FIG. 3A  is a sectional view of  FIG. 2 , taken along line Q-Q of  FIG. 2 ; 
       FIG. 3B  is a sectional view of  FIG. 2 , taken along line R-R of  FIG. 2 ; 
       FIG. 4  is a perspective view of the write head adjustment apparatus; 
       FIG. 5  is a partial sectional view enlarging a positional relationship between a write head and a photoreceptor surface; 
       FIG. 6  depicts a contact detection mechanism; 
       FIGS. 7A to 7D  depict a procedure of adjusting an interval between the write head and the photoreceptor in the image forming apparatus of the first embodiment; 
       FIGS. 8A to 8D  depict screens displayed on a display apparatus in the process of the interval adjustment shown in  FIGS. 7A to 7D ; 
       FIG. 9  is a flowchart of a process when adjusting the interval between the write head and the photoreceptor in the image forming apparatus of the first embodiment; 
       FIG. 10  is a perspective view of a second adjusting mechanism that adjusts, the scanning inclination of the write head; 
       FIG. 11A  is a side view of a write unit disposed on a body frame, depicting movement when adjusting the scanning inclination; 
       FIG. 11B  is a side view of the write unit disposed on the body frame, depicting movement when the adjusting mechanism is evacuated; 
       FIG. 12A  depicts how the write head adjustment apparatus is rotated and evacuated around a support shaft when the interval between the write head and the photoreceptor drum surface is adjusted; 
       FIG. 12B  depicts how the write head adjustment apparatus is rotated and evacuated around the support shaft when the interval between the write head and the photoreceptor drum surface is not adjusted; 
       FIGS. 13A to 13D  depict a procedure of adjusting the interval between the write head and the photoreceptor in an image forming apparatus of a second embodiment; 
       FIGS. 14A to 14D  depict screens displayed on a display apparatus in the process of adjusting the interval between the write head and the photoreceptor; 
       FIGS. 15A to 15C  depict defective shapes generated in the photoreceptor drum; 
       FIG. 16  is a sectional view of a write head adjustment apparatus in an image forming apparatus of a third embodiment, taken along line P-P of  FIG. 1 ; 
       FIGS. 17A and 17B  depict a configuration of a movable pin and a relationship between the movable pin and the photoreceptor drum surface; 
       FIGS. 18A to 18C  depict a method of adjusting amounting position of the write head in the image forming apparatus of the third embodiment; 
       FIG. 19  depicts a relationship among a regulating member, a positioning member, and the photoreceptor drum in an image forming apparatus of a fourth embodiment; 
       FIG. 20  depicts a contact detection mechanism for the regulating member and the positioning member used in the image forming apparatus of the fourth embodiment; 
       FIG. 21A  is a side view of operation of shifting the write head in the sub-scanning direction, corresponding to a sectional view taken along line P-P of  FIG. 16 ; 
       FIG. 21B  is a side view of operation of shifting the write head in the sub-scanning direction, corresponding to a sectional view taken along line Q-Q of  FIG. 16 ; 
       FIGS. 22A to 22E  depict a method of correcting a shift between the regulating member and the rotation shaft of the photoreceptor drum; 
       FIG. 23  depicts an image forming apparatus of a fifth embodiment; and 
       FIG. 24  depicts a modified image forming apparatus of the fifth embodiment. 
   

   PREFERRED EMBODIMENTS OF THE INVENTION 
   Embodiments of the present invention will now be described. 
   First Embodiment 
     FIG. 1  is a sectional view of an overall configuration of a digital color copier that is an image forming apparatus of an embodiment of the present invention. An image forming apparatus  1  of the embodiment includes a document table  111  and an operation panel in the upper portion of the main body and includes an image reading portion  110  and an image forming portion  210  within the main body. On the upper surface of the document table  111 , a reversing automatic document feeder (RADF)  112  is disposed and supported openable/closable to the document table  111  with a predetermined positional relationship with the document table  111 . 
   The image forming apparatus  1  is an electrophotographic digital color copier that can copy a color image, reads an image of a document placed on the document table  111  or an image of a document fed by the reversing automatic document feeder  112  with the image reading portion  110 , and reproduce the image of the read document on recording paper  100  with first to fourth image forming stations Pa, Pb, Pc, Pd of the image forming portion  210 . The first image forming station Pa reproduces an image of a black component of the document image on the recording paper  100 ; the second image forming station Pb reproduces an image of a cyan component of the document image on the recording paper  100 ; the third image forming station Pc reproduces an image of a magenta component of the document image on the recording paper  100 ; and the fourth image forming station Pd reproduces an image of a yellow component of the document image on the recording paper  100 . The first to fourth image forming stations Pa, Pb, Pc, Pd have the same configuration and are collectively described as an image forming station P. 
   The image forming station P is an unit that forms a toner image on the recording paper  100  and includes a cylindrical photoreceptor drum  222  supported rotatably and horizontally within a frame of the image forming apparatus  1 , a charging device  223  that uniformly charges the photoreceptor, a developing device  224  that attaches toner to an electrostatic latent image formed on the surface of the photoreceptor for development, a transfer discharging device  225  that transfers the developed toner image on the photoreceptor surface to the recording paper  100 , and a cleaning device  226  that removes toner remaining on the surface of the photoreceptor drum  222 . The charging device  223 , the developing device  224 , the transfer discharging device  225 , and the cleaning device  226  are sequentially arranged along the rotation direction of the photoreceptor drum  222 . A transfer feed belt  215  feeding the recording paper  100  is disposed between the photoreceptor drum  222  and the transfer discharging device  225  and is driven by feed rollers  214 ,  216  to feed the recording paper  100  in a direction of an arrow Z. The photoreceptor drum  222  rotates in a direction of an arrow F around a rotation shaft extending in a direction perpendicular to the paper surface. 
   The image forming station P includes an LED head  227  that is a write head. The LED head  227  is disposed above the photoreceptor drum  222  such that the longitudinal direction thereof is substantially parallel to the axis direction of the photoreceptor drum  222 , is located between the charging device  223  and the developing device  224  that are disposed along the rotation direction of the photoreceptor drum  222 , and applies light to the photoreceptor surface charged by the charging device  223  to form the electrostatic latent image. 
     FIG. 5  is a partial sectional view enlarging a positional relationship between the write head and the photoreceptor surface. The LED head  227  includes an LED substrate unit  231  including light emitting diodes (LED) that emit dot light modulated in accordance with image data and that are formed into a line shape on a substrate, a Selfoc lens array  232  that makes the light from the light emitting diodes focus on the surface of the photoreceptor drum  222 , and a base member that is a framework of the LED head  227 . The base member extends in the longitudinal direction of the LED head  227  and is made of a metal block with high rigidity. Since the LED head  227  generates heat, the base member is made of aluminum, which has a good thermal conductivity. Therefore, the heat generation of the LED head  227  can be suppressed. Since aluminum is used for the base member, the LED head  227  can have sufficient rigidity and the LED head can be configured with a lighter weight. The both ends of the base member project from the both ends of the LED head  227  to configure head supporting portions  2 . 
   In an example of the Selfoc lens array  232  built into the LED head  227 , if the Selfoc lens has a focal length of 4 mm, an interval between each Selfoc lens and the photoreceptor surface of the photoreceptor drum  222  is set to 4 mm, and an error of ±0.5 mm must be anticipated at the position of the photoreceptor surface due to dimensional accuracy of the photoreceptor drum  222 . However, to keep a certain print quality, the focal depth of ±0.1 mm must be maintained for the Selfoc lens to the photoreceptor surface regardless of the position of the photoreceptor surface. Therefore, when replacing the photoreceptor drum  222 , the position of the LED head  227  must be set such that the interval between the LED head  227  and the photoreceptor surface is, for example, 4±0.1 mm for each photoreceptor drum  222 . 
     FIG. 2  is a sectional view of a write head adjustment apparatus in an image forming apparatus of a first embodiment, taken along line P-P of  FIG. 1 .  FIGS. 3A and 3B  are sectional views of  FIG. 2 ;  FIG. 3A  is taken along line Q-Q of  FIG. 2 ; and  FIG. 3B  is taken along line R-R of  FIG. 2 .  FIG. 4  is a perspective view of the write head adjustment apparatus. The write head adjustment apparatus  3  holds the LED head  227 , adjusts the distance between the LED head  227  and the photoreceptor drum  222 , and adjusts the scanning inclination of the LED head  227  relative to the photoreceptor drum  222 . The adjustment of the scanning inclination is to adjust the longitudinal direction of the LED head  227  on a cylindrical surface around the rotation shaft of the photoreceptor drum  222  to become parallel to the axis direction of the photoreceptor drum  222 . The both longitudinal ends of the write head adjustment apparatus  3  are attached to the frame of the image forming apparatus  1  supporting the photoreceptor drum  222 . 
   The write head adjustment apparatus  3  includes a support shaft  4  located substantially in parallel with the photoreceptor drum  222 , a moving member  5  that is movably disposed along the support shaft  4  to move substantially parallel to the axis of the photoreceptor drum  222 , a frame member  6  supported by the support shaft  4  and including first to third frames  20  to  22 , a regulating member  7  disposed at the both ends of the LED head  227  to contact with the moving member  5  and to move and contact to the non-photoreceptor area of the photoreceptor drum, and a spring  8  that energizes the regulating member  7  toward the moving member  5  and the frame member  6 . The write head adjustment apparatus  3  includes a first adjusting mechanism  9  including an interval adjustment screw  30  near the frame of the image forming apparatus  1 , i.e., at the both longitudinal ends of the frame member  6  to adjust an interval H between the LED head  227  and the photoreceptor drum  222 , and one end of the apparatus  3  includes a second adjusting mechanism  10  including an adjustment screw  42  to adjust the scanning inclination of the LED head  227  relative to the photoreceptor drum  222 . 
   In the following description, as shown in  FIG. 2 , the X-axis direction is the axis direction of the photoreceptor drum  222 ; the Y-axis direction is a direction perpendicular to the X-axis direction and is a direction from the axis of the photoreceptor drum  222  toward the moving member  5 ; and the Z-axis direction is a direction perpendicular to the X-axis direction and the Y-axis direction. In this embodiment, the X-axis and Y-axis directions are horizontal directions and the Z-axis direction is a vertical direction. 
   (First Adjusting Mechanism  9 ) 
   The regulating member  7  is fixed to the head supporting portion  2  at the both ends of the LED head  227 , is a pin-shaped member extending in a direction perpendicular to the longitudinal direction (horizontal direction of  FIG. 2 ) of the LED head  227 , and is formed as a conductive member. The regulating member  7  extends in the Y-axis direction to contact with the moving member  5  at an upper end that is one end in the Y-axis direction and to penetrate the frame member  6  and contact with surfaces of non-photoreceptor application portions  234   a ,  234   b  of the photoreceptor drum  222  at a lower end that is the other end in the Y-axis direction. The regulating member  7  includes a first regulating member  7   a  disposed at one end of the LED head  227  and a second regulating member  7   b  disposed at the other end of the LED head  227 . 
   If it is assumed that a reference interval A is an interval between the LED head  227  and the photoreceptor drum  222  held at the time of forming an image in the image forming apparatus and that H is an interval between the LED head  227  and the surface of the photoreceptor drum  222  when the lower end of the regulating member  7  contacts (touches) the surface of the photoreceptor drum  222 , a predefined interval B for adjustment is selected to establish B=A−H. 
   The moving member  5  is disposed for both the first and second regulating members  7   a ,  7   b  disposed at the both ends of the LED head  227 . The moving member  5  includes a first moving member  5   a  in contact with the first regulating member  7   a  disposed at one end of the LED head  227  and a second moving member  5   b  in contact with the second regulating member  7   b  disposed at the other end of the LED head  227 . The moving member  5  is movably disposed substantially parallel to the axis of the photoreceptor drum  222  along the support shaft  4 . Specifically, the first and second moving members  5   a ,  5   b  are disposed by inserting the support shaft  4  to them and are energized by springs  11  toward the both ends in the axis direction of the support shaft  4 . The springs  11  are coil springs and are disposed by inserting the support shaft  4  to them. 
   The moving member  5  includes an inclined surface  15  inclined in the axis direction of the photoreceptor drum  222 , i.e., the X-axis direction. The inclined surface  15  is formed on the moving member  5  toward the photoreceptor drum  222 , i.e., on the lower portion of the moving member  5 . In the first embodiment, the first moving member  5   a  and the second moving member  5   b  include the inclined surfaces  15  with different inclination directions. That is, the inclined surface  15  of the first moving member  5   a  is upwardly formed from one end toward the other end of the support shaft  4 , and the inclined surface  15  of the second moving member  5   b  is upwardly formed from the other end toward one end of the support shaft  4 . By disposing the inclined surfaces of the moving member  5  in this way, the LED head  227  can be stabilized in the X-axis direction. 
   In the first moving member  5   a , the inclined surface  15  is formed to contact with the first regulating member  7   a  at one point. In the second moving member  5   b , the second moving member  5   b  includes a recessed portion  16  in the lower portion to contact with the second regulating member  7   b  at two or more points and the inclined surface  15  is formed on the bottom of the recessed portion  16 . In this embodiment, the recessed portion  16  is formed in a groove shape extended in the X-axis direction. By disposing the recessed portion  16  to contact with the second regulating member  7   b  in this way, the regulating member  7  can be positioned by the inclined surface  15  formed on the bottom of the recessed portion  16  and the side surfaces of the recessed portion  16 . 
   The frame member  6  is disposed to cover the LED head  227 . The frame member  6  includes a first frame  20  at one end in the longitudinal direction, a second frame  21  at the other end in the longitudinal direction, and a third frame  22  between the first frame and the second frame. The first to third frames  20  to  22  are integrally configured by bending one metal plate member. A through-hole is disposed in the both longitudinal ends of the frame member  6 , i.e., the first frame  20  and the second frame  21 , and the support shaft  4  is inserted through the through-holes to support the frame member  6 . 
   The frame member  6  is rotatably supported by the support shaft  4 . A locking portion  25  is disposed on the side of the frame member  6  facing to the photoreceptor drum  222 , i.e., the lower portion of the frame member  6  and is in contact with the other end in the Y-axis direction (lower end) of the regulating member  7 . The locking portion  25  is formed in the third frame  22 . A first locking portion  25   a  is the locking portion  25  at one end of the frame member  6  in contact with the first regulating member  7   a  disposed at one end of the LED head  227 , and a second locking portion  25   b  is the locking portion  25  at the other end of the frame member  6  in contact with the second regulating member  7   b  disposed at the other end of the LED head  227 . 
   The first locking portion  25   a  and the second locking portion  25   b  have different shapes. The first locking portion  25   a  is configured by a substantially U-shaped cut having a fore-end in the Z-axis direction, and the lower end of the first regulating member  7   a  can be positioned in the Z-axis direction by the first locking portion  25   a . The second locking portion  25   b  is configured by a wedge-shaped (substantially V-shaped) cut having a fore-end in the Z-axis direction, and the lower end of the second regulating member  7   b  can be positioned in the X-axis and Z-axis directions by the second locking portion  25   b . Although the locking portion  25  is formed by a cut opened toward the front side of the write unit in this embodiment, the locking portion  25  may be formed by a through-hole or a recessed portion having a cut. 
   The regulating members  7   a ,  7   b  are pin-shaped conductive members, and the tips thereof contact (touch) the non-photoreceptor application portions  234   a ,  234   b  near both ends of the photoreceptor drum  222  during the adjustment process of the interval between the LED head  227  and the photoreceptor. The non-photoreceptor application portions  234   a ,  234   b  of the photoreceptor drum  222  are, for example, conductive portions without a photoreceptor layer in a photoreceptor retaining member retaining the photoreceptor layer and may be the rotation shaft of the photoreceptor drum. A contact (touch) detection mechanism can electrically detect whether the tip of the regulating member  7  comes in contact with the conductive portion of the surface of the photoreceptor drum  222 . 
     FIG. 6  depicts the contact detection mechanism. The base consisting of an aluminum tube and the rotation shaft of the photoreceptor drum  222  are electrically connected, and if the tip of the regulating member  7  is not in contact with the non-photoreceptor application portion  234  on the surface of the photoreceptor drum  222 , a high-level signal (voltage Vcc) is output to the output terminal  236 . In the adjustment process of the LED head  227 , if the tip of the regulating member  7  comes in contact with the non-photoreceptor application portion  234  of the photoreceptor drum  222 , the output terminal  236  of the contact detection mechanism is grounded and a low-level signal (voltage  0 ) is output to the output terminal. The contact of the regulating members  7   a ,  7   b  and the surface of the photoreceptor drum  222  can be visually or auditorily notified by signals acquired from first and second output terminal  236   a ,  236   b  of the contact detection mechanism. 
   Description will be made of operation of adjusting the interval between the LED head  227  and the photoreceptor drum  222  with the write head adjustment apparatus  3 . Although the following description is based on the adjustment operation using the first adjusting mechanism  9  at on end (front side) of the write head adjustment apparatus  3 , the adjustment can be based on the first adjusting mechanism  9  at the other end (rear side) in exactly the same way. 
     FIGS. 7A to 7D  depict a procedure of adjusting the interval between the write head and the photoreceptor in the image forming apparatus of the first embodiment;  FIGS. 8A to 8D  depict screens displayed on a display apparatus in the process of the interval adjustment shown in  FIGS. 7A to 7D ; a pin F represents the front regulating member  7   a ; a pin R represents the rear regulating member  7   b ; a symbol “∘” indicates that the regulating member comes in contact with the photoreceptor drum; and a symbol “×” indicates that contact is not made. 
   (First Process): To keep a substantially large interval between the LED head  227  and the surface of the photoreceptor drum  222  when adjusting the interval between the LED head  227  and the photoreceptor drum  222 , the interval adjustment screw  30  is used to move the first moving member  5   a  and the second moving member  5   b  toward the end of the support shaft  4  to hold the LED head  227  at a high position. For example, as shown in  FIG. 7A , an interval X between the LED head  227  and the surface of the photoreceptor drum  222  is made larger than a distance of a reference interval A. That is, the LED head  227  is moved away from the surface of the photoreceptor drum  222  by the reference interval A or more. The adjustment screen indicates that the regulating members  7   a ,  7   b  do not contact with the photoreceptor drum  222  as shown by “pin F: ×” and “pin R: ×” of  FIG. 8A . 
   In the image forming apparatus of the first embodiment, a display apparatus including a liquid crystal panel, etc., located on the operation panel disposed in the image forming apparatus is used as a mechanism that visually displays when the first and second regulating members  7   a ,  7   b  comes in contact with the surface of the photoreceptor drum  222 . The display apparatus shown in  FIGS. 8A to 8D  shows the adjustment screen on the liquid crystal panel on the operation panel in a mode of adjusting the interval between the LED head and the photoreceptor drum. In the first process, since both the first and second regulating members  7   a ,  7   b  do not contact (touch) the photoreceptor drum  222 , the display indicates that both the first regulating member (front pin F)  7   a  and the second regulating member (rear pin R)  7   b  do not contact, as shown in  FIG. 8 . 
   (Second Process): In  FIG. 2 , the interval adjustment screw  30  is used to move the first moving member  5   a  toward the center of the support shaft  4 ; the first regulating member  7   a  is moved closer to the photoreceptor drum  222 ; and the tip of the first regulating member  7   a  comes in contact with the non-photoreceptor application portion  234   a  of the photoreceptor drum  222 . As shown in  FIG. 7B , the interval between the LED head  227  and the photoreceptor drum  222  surface is H=A−B on the side of the first moving member  5   a  at this moment and is smaller than the desired reference interval A by a predetermined value B. Since the first regulating member  7   a  projecting from one end of the LED head  227  contacts with the photoreceptor drum  222  and the second regulating member  7   b  projecting from the other end of the LED head  227  does not contact with the photoreceptor drum  222 , the operation panel displays “pin F: ∘” and “pin R: ×” as shown in  FIG. 8B . 
   (Third Process): Similarly to the second process, the interval adjustment screw  30  is used to move the second moving member  5   b  toward the center of the support shaft  4 ; the second regulating member  7   b  is moved closer to the photoreceptor drum  222 ; and the tip of the second regulating member  7   b  comes in contact with the non-photoreceptor application portion  234   b  of the photoreceptor drum  222 . As shown in  FIG. 7C , the interval between the LED head  227  and the photoreceptor drum  222  surface is H=A−B on the side of the second moving member  5   b  at this moment and is smaller than the reference interval A by the predetermined value B, and the interval between the LED head  227  and the photoreceptor drum  222  surface is A-B over the entire length. Since both the first and second regulating members  7   a ,  7   b  contact with the photoreceptor drum  222  in this state, the operation panel displays “pin F: ∘” and “pin R: ∘” as shown in  FIG. 8C . As described above, the second process and the third process may be performed in reverse order. 
   (Fourth Process): The interval between the LED head  227  and the photoreceptor drum  222  surface is A-B over the entire length as a result of the operation to the third process and is smaller than a design value, i.e., the reference interval A by the distance B. Therefore, the LED head  227  is moved away from the photoreceptor drum  222  by the distance B until the desired reference interval A can be acquired. The interval adjustment screw  30  is tightened again to move the first moving member  5   a  of the LED head  227  toward the end of the support shaft  4  (to the left of  FIG. 2 ) and the interval adjustment screw  30  is tightened again to move the second moving member  5   b  at the other end toward the end of the support shaft  4  (to the right of  FIG. 2 ). 
   In the fourth process, the amount of the tightening of the interval adjustment screw  30  is calculated based on an adjustment interval length B, the shapes of the first and second moving members  5   a ,  5   b  (degree of inclination), and screw pitches of first and second interval adjustment screws  9   a ,  9   b  and, for example, the amount is determined as tightening of the interval adjustment screw  9  by half turn, one turn, etc. For example, if one turn of the first and second interval adjustment screws  9   a ,  9   b  corresponds to a moving distance of 0.2 mm, the process can be achieved by defining the distance B as 0.2 mm. When the fourth process is completed, as shown in  FIG. 7D , the LED head  227  is away from the photoreceptor drum  222  by the distance A over the entire length. Since both the first and second regulating members  7   a ,  7   b  do not contact with the photoreceptor drum  222 , the operation panel displays “pin F: ×” and “pin R: ×” as shown in  FIG. 8D . The operation of separating the first and second regulating members  7   a ,  7   b  may be performed in reverse order. 
     FIG. 9  is a flowchart of a process when adjusting the interval between the write head and the photoreceptor in the image forming apparatus of the first embodiment. 
   After the operation mode of the image forming apparatus is set to a mode of adjusting the interval between the write head  227  and the photoreceptor, the photoreceptor drum  222  is rotated at a low speed (step  1 ). The first regulating member  7   a  is moved closer toward the surface of the photoreceptor drum  222 ; it is checked whether the output of the first output terminal  236   a  of the contact detection mechanism is the low-level signal (step  2 ); if the output is the low-level signal, the display portion of the operation panel displays that the first regulating member  7   a  comes in contact with the non-photoreceptor application portion  234   a  of the photoreceptor drum  222  as shown in  FIG. 8B  (step  3 ); and it is then checked whether the output of the second output terminal  236   b  of the contact detection mechanism is the low-level signal (step  4 ). 
   If the output of the second output terminal  236   b  is the low-level signal at step  4 , the display portion of the operation panel displays that the second regulating member  7   b  comes in contact with the non-photoreceptor application portion  234   b  of the photoreceptor drum  222  as shown in  FIG. 8C  (step  5 ). When the output of both the first and second output terminals  236   a ,  236   b  becomes the low-level signal and the first half of the adjustment operation is completed (step  6 ), the rotation of the photoreceptor drum  222  is stopped (step  7 ), and the interval adjustment screws  30 ,  30  are tightened again by an amount corresponding to the distance B to terminate the process. If the output of the first and second output terminals is not the low-level signal at steps  2  and  4 , since the display as shown in  FIGS. 8B and 8C  is not performed and the adjustment input is not completed at step  6 , the procedure goes back to step  2  to repeat the same process. 
   In the course of the above process, since the photoreceptor drum  222  is rotated at a low speed during the adjustment process, the tips of the first and second regulating members  7   a ,  7   b  come in contact with conductive areas without the photoreceptor layer (non-photoreceptor application portions  234   a ,  234   b ) of the photoreceptor drum and can remove oxide, etc., from the contact surface to prevent contact failure. 
   (Second Adjusting Mechanism  10 ) 
     FIG. 10  is a perspective view of a second adjusting mechanism that adjusts the scanning inclination of the write head;  FIGS. 1A and 11B  are side views of the write unit disposed on a body frame;  FIG. 11A  depicts movement when adjusting the scanning inclination; and  FIG. 11B  depicts movement when the adjusting mechanism is evacuated. The second adjusting mechanism  10  is a mechanism that adjusts the scanning inclination of the LED head  227  relative to the photoreceptor drum  222 , and a first body frame  45  includes a frame projecting portion  60  that projects outwardly to be opposed to a support plate  40  of the frame member  6 . The frame projecting portion  60  may be integrally configured with the first body frame  45 , and a spring  61  is attached to the frame projecting portion  60  and energizes the frame member  6  in a predetermined direction. The spring  61  disposed on the frame projecting portion  60  of the first body frame  45  energizes the tip of the scanning inclination adjustment screw  42  toward the frame projecting portion  60 . 
   Description will be made of the adjustment of the scanning inclination of the LED head  227  relative to the photoreceptor drum  222  with the use of the second adjusting mechanism  10 . While the other end of the frame member  6  is fixed to the second body frame  50 , a first fixing screw  47  is loosened which fixes one end of the frame member  6  to the first body frame  45 . If the scanning inclination adjustment screw  42  is rotated and advanced toward the frame projecting portion  60 , the scanning inclination adjustment screw  42  is blocked by the frame projecting portion  60 , and an upper end  70  of the frame member  6  is subjected to the action in the direction departing from the frame projecting portion  60 . Since the frame member  6  is rotatably supported by the support shaft  4 , the frame member  6  is torsionally rotated around the support shaft  4  and a lower end  71  of the frame member  6  is subjected to a rotation force in a direction of an arrow F 3  of  FIG. 11A . As a result, the frame member  6  is twisted around the support shaft  4 . 
   When the frame member  6  is torsionally rotated, the LED head  227  held within the frame member  6  swings and rotates around the reference side, which is the side of the second regulating member  7   b . Therefore, the longitudinal direction of the LED head  227  can be made parallel to the axis direction of the photoreceptor drum  222  on a cylindrical surface around the axis of the photoreceptor drum  222 . Although the case of advancing the scanning inclination adjustment screw  42  in the arrow F 1  direction has been described, if the scanning inclination adjustment screw  42  is moved in the counter direction of the arrow F 1  direction, the frame member  6  can inversely be twisted. By torsionally rotating the frame member  6  around the support shaft  4  as above, the second adjusting mechanism  10  can make the longitudinal direction of the LED head  227  parallel to the axis direction of the photoreceptor drum  222  on a cylindrical surface around the axis of the photoreceptor drum  222  and can adjust the scanning inclination of the LED head  227  relative to the photoreceptor drum  222 . 
   Since the support shaft  4  rotatably supports the frame member  6  (the first to third frames  20  to  22 ) holding the write head adjustment apparatus  3  in the first embodiment, a manual lever can be attached to the support shaft  4  to manually rotate to an appropriate angle against the energizing force of the spring  61 . 
     FIGS. 12A and 12B  depict how the write head adjustment apparatus is rotated and evacuated around the support shaft;  FIG. 12A  is in the case of adjusting the interval between the write head and the photoreceptor drum surface;  FIG. 12B  is in the case of not adjusting the interval. As described above, the write head adjustment apparatus of the embodiment includes the first and second regulating members  7   a ,  7   b  at the head supporting portion  2  of the LED head  227 , and the intervals between the lower ends of the first and second regulating members  7   a ,  7   b  and the photoreceptor drum surface are considerably smaller than the interval between the LED head and the photoreceptor drum. Therefore, at the time of the operation of removing the photoreceptor drum and mounting the new photoreceptor drum  222  when replacing the photoreceptor drum, if the photoreceptor drum comes in contact with the first and second regulating members  7   a ,  7   b , the photoreceptor layer of the photoreceptor drum  222  surface is damaged and/or the regulating member  7  is deformed. 
   Therefore, if the photoreceptor drum  222  is replaced in the write head adjustment apparatus in the first embodiment, the write head adjustment apparatus located as shown in  FIG. 12A  is rotated to an appropriate angle (e.g., 90 degrees) as shown in  FIG. 12B . A mechanism of rotating the write head adjustment apparatus may be electrically or manually operated, and can simply be realized by attaching a manual lever  62   a ,  62   b  to both or one end of the support shaft  4  to manually rotate and drive the support shaft  4 . As a result, when the write head adjustment apparatus is moved to a raised position by the manual lever  62  and is retained at the position by, for example, locking the manual lever  62  to the body frame, the space below the write head adjustment apparatus is wide open, and the damage of the photoreceptor layer of the photoreceptor drum  222  surface and the deformation of the regulating member  7  can be avoided at the time of removing and mounting the photoreceptor drum. 
   Second Embodiment 
     FIGS. 13A to 13D  depict a procedure of adjusting the interval between the write head and the photoreceptor in an image forming apparatus of a second embodiment. In the image forming apparatus of the first embodiment, after the regulating members  7   a ,  7   b  come in contact with the non-photoreceptor application portions  234   a ,  234   b  of the photoreceptor drum, the regulating member  7  is moved together with the LED head  227  in the direction away from the photoreceptor by the predetermined interval (B). On the other hand, the image forming apparatus of the second embodiment includes a mechanism that mounts spacers  235   a ,  235   b  with a thickness (B) corresponding to the predetermined interval described in the image forming apparatus of the first embodiment to a position corresponding to the non-photoreceptor application portion  234  on the photoreceptor drum; a moving mechanism that integrally moves the first and second regulating members  7   a ,  7   b  with the write head toward the photoreceptor to come in contact with the spacers  235   a ,  235   b ; and a mechanism that removes the spacers  235   a ,  235   b  after the regulating members  7   a ,  7   b  come in contact with the spacers  235   a ,  235   b . The contact detection mechanism shown in  FIG. 6  can detect whether the first and second regulating members  7   a ,  7   b  come in contact with the spacers  235   a ,  235   b.    
     FIGS. 14A to 14D  depict screens displayed on the display apparatus in the process of adjusting the interval between the write head and the photoreceptor; a symbol “∘” indicates that the regulating member  7  ( 7   a ,  7   b ) comes in contact with the spacer  235  ( 235   a ,  235   b ); and a symbol “×” indicates that contact is not made. In the following description, constituent elements in common with the image forming apparatus of the first embodiment will not be shown and described. 
   (First Process): To keep a substantially large interval between the LED head  227  and the surface of the photoreceptor drum  222  when adjusting the interval between the LED head  227  and the photoreceptor drum  222 , the interval adjustment screw  30  is used to move the first moving member  5   a  and the second moving member  5   b  toward the ends of the support shaft  4  to hold the LED head  227  at an upper position as shown in  FIG. 13A , and the spacer mounting mechanism mounts the spacer  235   a  with the thickness (B) to the left end of the photoreceptor drum  222 . In the first process, since the first regulating member  7   a  does not contact with the spacer  235   a  and the second regulating member  7   b  does not contact with the spacer  235   b , the adjustment screen displays “pin F: ×” and “pin R: ×” as shown in  FIG. 14A . 
   (Second Process): The interval adjustment screw  30  is used to move the first moving member  5   a  toward the center of the support shaft  4 ; the first regulating member  7   a  is moved closer to the photoreceptor drum  222 ; and the tip of the first regulating member  7   a  comes in contact with the spacer  235   a  as shown in  FIG. 13B . The interval between the LED head  227  and the photoreceptor drum  222  surface is the desired reference interval A on the side of the first moving member  5   a  at this moment because of the intervention of the spacer  235   a  with the thickness (B). Since the first regulating member  7   a  contacts with the spacer  235   a  and the second regulating member  7   b  does not contact with the spacer  235   b , the liquid crystal panel displays “pin F: ∘” and, “pin R: ×” as shown in  FIG. 14B . Then, the spacer removing mechanism removes the spacer  235   a.    
   (Third Process): After the spacer mounting mechanism mounts the spacer  235   b  to the right end of the photoreceptor drum  222 , the interval adjustment screw  30  is used to move the second moving member  5   b  toward the center of the support shaft  4 ; the second regulating member  7   b  is moved closer to the spacer  235   b ; and the tip of the second regulating member  7   b  comes in contact with the spacer  235   b  as shown in  FIG. 13C . Since the first regulating member  7   a  does not contact with the spacer  235   a  and the second regulating member  7   b  contacts with the spacer  235   b , the liquid crystal panel displays “pin F: ×” and “pin R: ∘” as shown in  FIG. 14C . The interval between the LED head  227  and the photoreceptor drum  222  surface is the desired reference interval A on the side of the second moving member  5   b  at this moment. The second process and the third process may be performed in reverse order. 
   (Fourth Process): The spacer removing mechanism removes the spacer  235   b . The spacers  235   a ,  235   b  are removed as above and the interval between the LED head  227  and the photoreceptor drum  222  surface becomes the reference interval A across the full width as shown in  FIG. 13D . Since the first regulating member  7   a  does not contact with the spacer  235   a  and the second regulating member  7   b  does not contact with the spacer  235   b , the liquid crystal panel displays “pin F: ×” and “pin R: ×” as shown in  FIG. 14D . 
   Third Embodiment 
   An image forming apparatus of a third embodiment relates to adjustment of the mounting position of the write head when eccentricity is generated in the photoreceptor drum  222  for some reason and the interval between the write head  227  and the photoreceptor drum  222  fluctuates periodically in one rotation of the photoreceptor drum. Although it is desirable that the interval between the write head  227  and the photoreceptor drum  222  is not fluctuated during one rotation of the photoreceptor drum  222 , if the fluctuation range falls within a predetermined range, the photoreceptor drum  222  can be used to acquire a predetermined image quality. 
     FIGS. 15A to 15C  depict defective shapes generated in the photoreceptor drum. In the case of the defective shape generated in the photoreceptor drum of  FIG. 15A , although the diameter of the photoreceptor drum  222  should be an ideal shape shown by a dotted line, the diameter is larger (or smaller) as shown by a solid line and does not fall within a predetermined tolerance, and the photoreceptor drum  222  cannot be used in the image forming apparatus in this case. In the case of  FIG. 15B , since a drum rotation shaft  222   a  is eccentrically attached to the photoreceptor drum  222 , regular fluctuations are generated in one rotation of the photoreceptor drum  222 . In the case of  FIG. 15C , since the photoreceptor drum  222  is deformed, the photoreceptor drum  222  is fluctuated in one rotation and if the photoreceptor drum  222  is deformed into a shape of an ellipse as shown, the frequency of fluctuation becomes a half of the case of  FIG. 15B . 
   In the case of  FIGS. 15B and 15C , the write head  227  must be adjusted and mounted such that the interval between the write head  227  and the photoreceptor drum  222  does not become too large or too small during one rotation of the photoreceptor drum  222 . That is, when the interval adjustment is performed between the write head  227  and the photoreceptor drum  222 , the position of the photoreceptor drum  222  must be an intermediate position between the position of the maximum interval and the position of the minimum interval. 
     FIG. 16  is a sectional view of a write head adjustment apparatus in the image forming apparatus of the third embodiment, taken along line P-P of  FIG. 1 . Since the image formation apparatus of the third embodiment is based on an image forming portion that has the same configuration as the image forming portion of the image formation apparatus of the first embodiment shown in  FIGS. 1 and 2 , configurations of other portions will mainly be described. 
   The write head adjustment apparatus  3  shown in  FIG. 16  includes the support shaft  4  located substantially in parallel with the photoreceptor drum  222 , the moving member  5  that is movably disposed along the support shaft  4  to move substantially parallel to the axis of the photoreceptor drum  222 , the frame member  6  supported by the support shaft  4  and including the first to third frames  20  to  22 , moving guide pins  21   a ,  11   b  disposed at both ends of the LED head  227 , which is in contact with the moving member  5 , and which is locked and guided by the first locking portions  25   a ,  25   b  of the third frame  22 , and the spring  8  that energizes the moving guide pins  11   a ,  11   b  toward the moving member  5  and the frame member  6 . The write head adjustment apparatus  3  includes the first adjusting mechanism  9  including the interval adjustment screw  30  near the frame of the image forming apparatus  1 , i.e., at the both longitudinal ends of the frame member  6  to adjust the interval H between the LED head  227  and the photoreceptor drum  222 , and the second adjusting mechanism  10  including the scanning inclination adjustment screw to adjust the scanning inclination of the LED head  227  relative to the photoreceptor drum  222 . The head supporting portion  2  of the LED head  227  is disposed with movable pins  12   a ,  12   b  that can freely move in the axis direction, adjacent to the moving guide pins  11   a ,  11   b.    
     FIGS. 17A and 17B  depict a configuration of the movable pin and a relationship between the movable pin and the photoreceptor drum surface. The movable pin  12   a ,  12   b  is formed as a conductive member, and the upper expanded portion thereof is mounted to a movable pin mounting portion  13  formed in the head supporting portion  2  of the LED head  227  by a spring and is energized in the protruding direction. The length of the movable pin  12   a ,  12   b  is set such that the interval between the LED head  227  and the photoreceptor drum  222  surface becomes A-B when the pin protrudes to a maximum extent as shown in  FIG. 17A . Therefore, the movable pin  12   a ,  12   b  can move depending on the position of the photoreceptor drum  222  surface (interval between the LED head  227  and the photoreceptor drum  222  surface), and the tip thereof is in contact with the non-photoreceptor application portion of the photoreceptor drum  222  as shown in  FIG. 17A  or  17 B. The contact detection mechanism shown in  FIG. 6  can be used to detect whether the movable pin  12   a ,  12   b  comes in contact with the non-photoreceptor application portion of the photoreceptor drum  222 . 
     FIGS. 18A to 18C  depict a method of adjusting a mounting position of the write head in the image forming apparatus of the third embodiment. In  FIGS. 18A to 18C , a circle C 1  depicted with a dotted line is an ideal photoreceptor drum, and an ellipse depicted with a solid line is the photoreceptor drum  222 , which shows an example of an ellipse photoreceptor drum attached eccentrically. In  FIG. 18A , a circle C 2  depicted with a virtual line is a circle around the rotation shaft  222   a  of the photoreceptor drum  222 , which has a radius of a distance L between the movable pin and the rotation shaft  222   a , and the movable pin  12  comes in contact with a portion located outside of the circle C 2  in the photoreceptor drum  222 . Description will hereinafter be made of a method of adjusting the mounting position of the write head with the use of a conductive time display mechanism calculating and displaying a percentage of a conducting (contact) time per rotation of the photoreceptor drum relative to a time required for one rotation of the photoreceptor drum. 
   (First Process) 
   While the photoreceptor drum  222  is slowly rotated, the interval adjustment screw  30  is tightened to slowly move the movable pin  12  toward the photoreceptor drum  222 . When the movable pin  12  comes in contact with a portion with the largest diameter of the photoreceptor drum  222  as shown in  FIG. 18A , the conductive time display mechanism displays that one conductive period exists during one rotation of the photoreceptor drum  222  as shown in the left part of  FIG. 18A . 
   (Second Process) 
   The interval adjustment screw  30  is further tightened to move the movable pin  12  closer toward the photoreceptor drum  222 , and the display indicates that two conductive periods exist during one rotation of the photoreceptor drum  222  as shown in the left part of  FIG. 18B . 
   (Third Process) 
   When the movable pin  12  is further moved closer to the photoreceptor drum  222 , a large portion of one rotation of the photoreceptor drum  222  becomes the conductive period, and the display indicates that only the portion with the minimum diameter of the photoreceptor drum  222  does not contact with the movable pin  12  as shown in the left part of  FIG. 18C . The moving distance of the movable pin  12 , i.e., the amount of rotation for tightening the interval adjustment screw  30  to move the movable pin  12  is recorded with regard to the first process to the third process. 
   (Fourth Process) 
   Since the interval between the movable pin  12  and the photoreceptor drum  222  is a minimum distance when the third process is completed, the movable pin  12  is moved in the opposite direction by a half of the moving distance of the movable pin  12  and is held at an intermediate point. That is, if the interval adjustment screw  30  is tightened by ten turns in the first process to the third process, the interval adjustment screw  30  is loosened by five turns. 
   Fourth Embodiment 
   In the description of the image forming apparatuses of the first to third embodiments, when adjusting the interval between the LED head  227  and the photoreceptor drum  222 , the rotation shaft  222   a  of the photoreceptor drum has been an extension of the center axis of the regulating member  7 . However, if the center line of the photoreceptor drum is shifted and is not an extension of the center axis of the regulating member  7 , the interval between the LED head  227  and the photoreceptor drum  222  is set smaller than a desired interval as the shift amount increases. Therefore, an image forming apparatus of a fourth embodiment provides a mechanism that eliminates the positional shift between the regulating member  7  and the photoreceptor drum when adjusting the interval between the LED head  227  and the photoreceptor drum  222 . 
     FIG. 19  depicts a relationship among the regulating member, a positioning member, and the photoreceptor drum in the image forming apparatus of the fourth embodiment. The regulating member  7  of the LED head  227  is disposed with a positioning member  14  integrated with the regulating member  7 . As shown in  FIG. 19 , the regulating member  7  and the positioning member  14  are in a positional relationship such that a distance D exists between one side surface of the positioning member  14  and the rotation shaft  222   a  when the rotation shaft  222   a  of the photoreceptor drum  222  is an extension of the regulating member  7 . 
     FIG. 20  depicts a contact detection mechanism for the regulating member and the positioning member used in the image forming apparatus of the fourth embodiment. The contact detection mechanism shown in  FIG. 20  can detect whether the one side surface of the positioning member  14  comes in contact with the rotation shaft  222   a  of the photoreceptor drum  222 . When adjusting the interval between the LED head  227  and the photoreceptor drum  222  to a desired interval, adjustment is firstly performed with the use of a mechanism that shifts the positioning member  14  and the LED head  227  in the sub-scanning direction, and the interval between the LED head  227  and the photoreceptor drum  222  is then adjusted to a desired interval as described in the first and second embodiments. 
     FIGS. 21A and 21B  are side views of operation of shifting the write head in the sub-scanning direction;  FIG. 21A  is a diagram corresponding to a sectional view taken along line P-P of  FIG. 16 ; and  FIG. 21B  is a diagram corresponding to a sectional view taken along line Q-Q of  FIG. 16 . The LED head  227  is rotatably attached to the inside of the frame member  6  including the first to third frames  20  to  22  by the support shaft  4 , and the frame member  6  is rotatably attached to the first and second body frames  45 ,  50  of the image forming apparatus by the support shaft  4 . The position adjustment can be performed in the sub-scanning direction relative to the photoreceptor drum  222  by loosening the first and second fixing screws  47 ,  52  movably attaching the frame member  6  to the first and second body frames  45 ,  50 , by adjusting the position in a substantially elliptical elongate hole  48 , and by tightening the screws. 
     FIGS. 22A to 22E  depict a method of correcting a shift between the regulating member and the rotation shaft of the photoreceptor drum. 
   (First Process) 
   If the rotation shaft  222   a  of the photoreceptor drum  222  is not an extension of the regulating member  7  as shown in  FIG. 22A , the contact detection mechanism shown in  FIG. 20  detects that the positioning member  14  does not contact with the rotation shaft  222   a  of the photoreceptor drum  222 . 
   (Second Process) 
   If it is detected that the rotation shaft  222   a  of the photoreceptor drum  222  is not an extension of the regulating member  7  in the first process, the mechanism of shifting the LED head in the sub-scanning direction as shown in  FIGS. 21A  and  21 B is used to move the LED head  227  until the positioning member  14  comes in contact with the rotation shaft  222   a  with the use of the adjustment screws  47 ,  52  as shown in  FIG. 22B . 
   (Third Process) 
   As shown in  FIG. 22C , the LED head is then moved away from the rotation shaft  222   a  such that the distance D exists between one side surface of the positioning member  14  and the rotation shaft  222   a  of the photoreceptor drum  222 . 
   (Fourth Process) 
   Since the predetermined relationship is established in the positional relationship between the LED head  227  and the photoreceptor drum  222  when the third process is completed, the method goes to a process of adjusting the interval between the LED head  227  and the photoreceptor drum  222  to a desired interval, and the regulating member  7  and the contact detection mechanism shown in  FIG. 20  are used to set the interval H between the LED head  227  and the photoreceptor drum  222  to A-B with the same adjusting method as that performed in the image forming apparatus of the first and second embodiments as shown in  FIG. 22D . 
   (Fifth Process) 
   To set the interval H between the LED head  227  and the photoreceptor drum  222  to the desired reference interval A, the LED head  227  is moved away from the photoreceptor drum  222  by the distance B with the same adjusting method as that performed in the image forming apparatus of the first and second embodiments as shown in  FIG. 22E . 
   Fifth Embodiment 
     FIG. 23  depicts an image forming apparatus of a fifth embodiment. The image forming apparatus of the fifth embodiment is an image forming apparatus using a photoreceptor belt and an intermediate transfer belt, instead of the image forming apparatus of the first or second embodiment including the photoreceptor drum. In the image forming apparatus of the fifth embodiment, the LED head  227  emits light based on print image data after an imaging process; each developing unit  241  of yellow, magenta, cyan, and black forms a toner image on a photoreceptor belt  244  stretched between belt support rollers  242 ,  243 ; the toner images are sequentially transferred to an intermediate transfer belt  245  for each color; after all the toner images are overlapped and transferred, batch transfer is performed onto the recording paper fed from a paper feed cassette; and after the batch transfer, a fixing device fixes the images to complete a full-color image. The image forming apparatus includes the same write head adjustment apparatus  3  as that of the image forming apparatuses of the first and second embodiments; the built-in LED head  227  includes the regulating member  7  (the first and second regulating members  7   a ,  7   b ); and the interval between the LED head  227  and the photoreceptor belt  244  surface can be adjusted by using the regulating member  7  as follows. 
   The regulating member  7  with the LED head  227  attached is moved toward and brought into contact with the photoreceptor belt  244 , and the interval between the LED head  227  and the photoreceptor belt  244  is set to A-B, which is smaller than the reference interval A by the predetermined interval B. The contact detection apparatus shown in  FIG. 6  detects that the regulating member  7  comes in contact with the photoreceptor belt  244 . The regulating member  7  is moved along with the LED head  227  in the direction opposite to the photoreceptor belt  244  by the predetermined interval B. By performing the above operation for the first and second regulating members  7  disposed on the both sides of the photoreceptor belt  244 , the interval between the LED head  227  and the photoreceptor belt  244  can be set to the reference interval A across the full width of the photoreceptor belt. 
     FIG. 24  depicts a modified image forming apparatus of the fifth embodiment. As compared to the image forming apparatus of the fifth embodiment shown in  FIG. 23 , the modified image forming apparatus is different in the mechanism and method of adjusting the interval between the LED head  227  and the photoreceptor belt  244  surface. In the image forming apparatus of this example, a belt-backside pressing support member  246  is disposed at the backside of a part of the photo-receptor belt  244  at which the LED head  227  is located such that the photoreceptor belt  244  is pressed from the backside in the direction of the photoreceptor belt  244 . The interval between the LED head  227  and the photoreceptor belt  244  surface can be adjusted by using the regulating member  7  (the first and second regulating members  7   a ,  7   b ) and the belt-backside pressing support member  246  as follows. 
   The belt-backside pressing support member  246  is used to push out the photoreceptor belt  244  toward the LED head  227  for a distance corresponding to the interval B described above. The regulating member  7  is then moved along with the LED head  227  in the direction of the photoreceptor belt  244  to bring the regulating member  7  into contact with the photoreceptor belt  244 . The contact detection apparatus shown in  FIG. 6  detects that the regulating member  7  comes into contact with the photoreceptor belt  244 . The interval between the LED head  227  and the photoreceptor belt  244  surface can be set to the reference interval A by restoring the belt-backside pressing support member  246  to return the photoreceptor belt  244  to the original state. 
   According to the present invention, the following advantages can be acquired. 
   In the image forming apparatus and the adjusting method of the image forming apparatus of the present invention, since the adjusting mechanism adjusts the interval of the write head and the photoreceptor to the reference interval (A) and includes the regulating member that integrally moves with the write head for a predetermined distance to regulate the interval between the write head and the photoreceptor, even an unskilled user can easily check and adjust the interval between the write head and the photoreceptor highly accurately. 
   In the present invention, the interval between the write head and the photoreceptor is set to be smaller than the reference interval (A) by the predetermined dimension (B) when the regulating member comes into contact with the photoreceptor; a moving mechanism is included to integrally move the regulating member along with the write head and to bring the regulating member into contact with the photoreceptor; a reverse-moving mechanism is included to integrally move the regulating member along with the write head in the direction opposite to the photoreceptor by the predetermined dimension (B) after the regulating member comes into contact with the photoreceptor; and, therefore, even an unskilled user can easily check and adjust the interval between the write head and the photoreceptor. 
   In the present invention, the interval between the write head and the photoreceptor is set to a length of the reference interval (A) when the regulating member comes into contact with the spacer mounted to the photoreceptor, which has a thickness of the predetermined dimension (B); a mechanism is included to mount the spacer to the photoreceptor; a moving mechanism is included to integrally move the regulating member along with the write head and to bring the regulating member into contact with the spacer; a mechanism is included to remove the spacer after the regulating member comes into contact with the spacer; and, therefore, even an unskilled user can easily check and adjust the interval between the write head and the photoreceptor. 
   In the present invention, the contact detection mechanism electrically detects that the regulating member comes into contact with the photoreceptor or the spacer to perform notification of the detection result and, therefore, even an unskilled user can easily detect the contact between the regulating member and the photoreceptor or the spacer and can easily check and adjust the interval between the write head and the photoreceptor. 
   In the present invention, an evacuation mechanism is included to evacuate the regulating member and, therefore, the pin-shaped regulating member can be prevented from contacting and damaging the photoreceptor surface or from being deformed at the time of replacing the photoreceptor. 
   In the present invention, when adjusting the interval between the write head and the photoreceptor, the regulating member is brought into contact with the photoreceptor holding member while the photoreceptor is rotated and, therefore, contact failure can be prevented from occurring due to oxide, foreign matters, etc., attached to the surfaces of the photoreceptor holding member and the regulating member. 
   In the present invention, when adjusting the interval between the write head and the photoreceptor, the interval adjustment is performed at an intermediate rotation position between a rotation position of the photoreceptor drum where the distance between the write head and the photoreceptor is maximized and a rotation position of the photoreceptor drum where the distance between the write head and the photoreceptor is minimized and, therefore, the photoreceptor surface can be adjusted to be within the range of the focal depth of the write head during one rotation of the photoreceptor drum. 
   In the present invention, when adjusting the interval between the write head and the photoreceptor, the interval between the write head and the photoreceptor can be accurately adjusted by adjusting the interval between the write head and the photoreceptor after correcting the shift in the sub-scanning direction between the regulating member and the photoreceptor drum such that the shape of the exposure spot applied to the photoreceptor is adjusted to a perfect circle. 
   In the present invention, a distance between the center axis line of the regulating member and the contact position that brings a sub-scanning direction position detecting member into contact with the rotation shaft of the photoreceptor is set larger than the radius (C) of the rotation shaft of the photoreceptor drum by the predetermined distance (D); when detecting contact with the rotation shaft, the sub-scanning direction position detecting member is moved away from the contact position by the predetermined distance (D); and, therefore, both sides can be prevented from wearing to highly accurately adjust the interval between the write head and the photoreceptor for a long period.