Patent Publication Number: US-8983354-B2

Title: Laser fixing device and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2012-228166 filed Oct. 15, 2012. 
     BACKGROUND 
     (i) Technical Field 
     The present invention relates to a fixing device, and an image forming apparatus. 
     (ii) Related Art 
     In an image forming apparatus, there is a technique in which toner is irradiated with laser light and is thus fixed onto a recording medium. 
     SUMMARY 
     According to an aspect of the invention, there is provided a fixing device including: an irradiation section that has plural light emitting elements arranged in a first direction and emits light; a condensing section that condenses the light emitted from the irradiation section in a second direction intersecting the first direction; and a supporter that includes a contact location which supports a recording medium by a surface thereof at a position of a focal length of the condensing section, and a noncontact location which is located outside the contact location in the first direction and has a surface which does not come into contact with the recording medium, wherein a distance between the surface of the noncontact location and the condensing section is different from a distance between the surface of the contact location and the condensing section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a diagram illustrating a configuration of an image forming apparatus according to a first exemplary embodiment; 
         FIG. 2  is a diagram of a fixing device which is viewed from the II direction shown in  FIG. 1 ; 
         FIG. 3  is a diagram illustrating a method of installing a covering member; 
         FIG. 4  is a diagram illustrating that a contact location is irradiated with laser light; 
         FIG. 5  is a diagram illustrating that a noncontact location is irradiated with laser light; 
         FIG. 6  is a diagram of a fixing device according to a second exemplary embodiment which is viewed from the II direction shown in  FIG. 1 ; 
         FIG. 7  is a perspective view of a supporter according to the second exemplary embodiment; 
         FIG. 8  is a diagram illustrating that a noncontact location according to the second exemplary embodiment is irradiated with laser light; 
         FIG. 9  is a diagram illustrating a configuration of a fixing device according to Modification Example 1; 
         FIG. 10  is a perspective view of a supporter according to Modification Example 1; 
         FIG. 11  is a diagram illustrating an operation of a reflection plate according to Modification Example 1; 
         FIG. 12  is a diagram illustrating that a contact location is irradiated with laser light according to Modification Example 2; and 
         FIG. 13  is a diagram illustrating that a noncontact location according to Modification Example 2 is irradiated with laser light. 
     
    
    
     DETAILED DESCRIPTION 
     First Exemplary Embodiment 
       FIG. 1  is a diagram illustrating a configuration of an image forming apparatus  10 . The image forming apparatus  10  has a printer function, and forms an image on continuous paper S according to an electrophotographic method. The continuous paper S is used as a recording medium in the present exemplary embodiment. In addition, the image forming apparatus  10  may have a copy or a facsimile function in addition to the print function. 
     The image forming apparatus  10  includes an incorporation unit  11 , image forming units  12 Y,  12 M,  12 C and  12 K, and a fixing unit  13 . Plural rollers, which transport the continuous paper S in the arrow A direction in the figure when an image is formed, are provided inside each unit. A transport path of the continuous paper S is formed by these rollers or guide members (not shown). In  FIG. 1 , a shape of the transport path is shown by the continuous paper S which extends along the transport path. 
     The incorporation unit  11  incorporates the continuous paper S into the image forming apparatus  10  itself from a paper supply source (not shown). The incorporation unit  11  includes a drive roller  111 , a back tension roller  112 , motors (not shown) which are driving sources rotating the rollers, and plural rollers which rotate according to the transport of the continuous paper S. The drive roller  111  rotates in the arrow a direction in the figure when an image is formed and thereby transports the continuous paper S supplied from the paper supply source to the image forming units  12 Y,  12 M,  12 C and  12 K. The back tension roller  112  is provided further toward the upstream side than the drive roller  111  in the transport direction of the continuous paper S when an image is formed, and gives an appropriate tension to the continuous paper S by rotating in the arrow b direction such that the continuous paper S is transported on the transport path without being loosened. 
     The image forming units  12 Y,  12 M,  12 C and  12 K form toner images on the continuous paper S. The image forming units  12 Y,  12 M,  12 C and  12 K form images by respectively using yellow (Y), magenta (M), cyan (C) and black (K) toners. The image forming units  12 Y,  12 M,  12 C and  12 K are used as an image forming section in the present exemplary embodiment. Configurations of the image forming units  12 Y,  12 M,  12 C and  12 K are the same except that toner colors are different, and, thus, here, a configuration of the image forming unit  12 K will be described as an example. 
     The image forming unit  12 K includes a photoconductor drum  121 K, a charging portion  122 K, an exposure portion  123 K, a developing portion  124 K, and a transfer portion  125 K. The photoconductor drum  121 K is a cylindrical member in which photoconductive films are laminated on an outer circumferential surface. The photoconductor drum  121 K rotates about an axis in the arrow B direction. The charging portion  122 K uniformly charges the surface of the photoconductor drum  121 K. The exposure portion  123 K irradiates the photoconductor drum  121 K with light corresponding to image data of K (black) so as to form an electrostatic latent image. The developing portion  124 K develops the electrostatic latent image with the black toner so as to form a toner image on the surface of the photoconductor drum  121 K. The transfer portion  125 K transfers the toner image onto the continuous paper S. 
     The fixing unit  13  includes a sub-drive roller (or a discharge roller)  131  which is driven by a driver (not shown), a fixing device  133 , and plural rollers which rotate according to the transport of the continuous paper S. The fixing device  133  irradiates the toner image transferred to the continuous paper S with laser light L so as to be fixed to the continuous paper S. The sub-drive roller  131  rotates in the arrow c direction and thereby transports the continuous paper S to outside of the image forming apparatus  10  in the arrow A direction. The continuous paper S discharged by the sub-drive roller  131  is wound by a paper winding device (not shown.). Alternatively, the discharged continuous paper S may be cut out and be accommodated in a stacker (not shown). 
       FIG. 2  is a diagram of the fixing device  133  which is viewed from the II direction shown in  FIG. 1 . The fixing device  133  includes a laser array  31 , a condensing lens  32 , and a supporter  33 . The laser array  31  irradiates the continuous paper S with laser light L with a predefined irradiation width WI. The laser array  31  is used as an irradiation section in the present exemplary embodiment. The laser array  31  includes plural light emitting elements  34  which are disposed so as to be arranged in a line in the width direction (the arrow P direction in the figure) of the continuous paper S. Each of the light emitting elements  34  is, for example, a semiconductor laser element, and applies the laser light L. The irradiation width WI of the laser array  31  has a length corresponding to the maximum paper width used in the image forming apparatus  10 . Therefore, as shown in  FIG. 2 , when the width Ws of the continuous paper S is smaller than the maximum paper width, the laser array  31  applies the laser light L over the irradiation width WI greater than the width Ws of the continuous paper S. The condensing lens  32  is disposed between the laser array  31  and the supporter  33 . The condensing lens  32  collects the laser light L applied from the laser array  31  at a predefined focal position Pf. The condensing lens  32  is used as a condensing section in the present exemplary embodiment. 
     The supporter  33  includes a transport roller  41 , a covering member  42 , and a locknut  43 . The transport roller  41  is a cylindrical member made of a material such as aluminum. The transport roller  41  supports the continuous paper S at the focal position Pf. In other words, the transport roller  41  supports the continuous paper S at a position which is distant from the condensing lens  32  by a focal length F 0  of the laser light L. The “focal length F 0 ” refers to a distance at which the intensity of the laser light L is equal to or more than a threshold value. The threshold value corresponds to an intensity at which, for example, the toner is heated and melted. In addition, in relation to the “position which is distant by the focal length F 0  of the laser light L”, all the laser light beams L applied to the continuous paper S are not necessarily focused, and some of the laser light beams L may be deviated from the focal length F 0 . The transport roller  41  is used as a cylindrical member in the present exemplary embodiment. The transport roller  41  is rotated about an axis in the arrow d direction shown in  FIG. 1  by a driving portion (not shown). Thereby, the transport roller  41  supports and transports the continuous paper S to the sub-drive roller  131 . The transport roller  41  has a length which is equal to or more than the maximum width of the continuous paper S. Therefore, as shown in  FIG. 2 , when the width Ws of the continuous paper S is smaller than the maximum paper width, the transport roller  41  has a part which comes into contact with the continuous paper S and a part which does not come into contact with the continuous paper S. 
     The covering member  42  is a cylindrical and hollow member which is made of a material such as aluminum in the same manner as the transport roller  41 . The covering member  42  covers an outer circumferential surface of the part which does not come into contact with the continuous paper S in the transport roller  41 . The diameter D 2  of the covering member  42  is greater than the diameter D 1  of the transport roller  41 . Therefore, the distance F 2  between the surface of the covering member  42  and the condensing lens  32  is smaller than the distance F 1  between the surface of the transport roller  41  and the condensing lens  32 . In addition, an end surface  42   a  of the covering member  42  functions as an edge guide for aligning a position of the side end of the continuous paper S. The locknut  43  is made of a material such as aluminum, and locks and fixes the covering member  42 . 
     As shown in  FIG. 2 , the supporter  33  has a contact location R 1  in which the continuous paper S is on the surface region where a light density is equal to or more than a threshold value and a noncontact location R 2  in which there is no continuous paper S. In the present exemplary embodiment, the part which comes into contact with the continuous paper S in the transport roller  41  is the contact location R 1 . In addition, the part which does not come into contact with the continuous paper S in the transport roller  41  and the covering member  42  are the noncontact location R 2 . 
       FIG. 3  is a diagram illustrating a method of installing the covering member  42 . A worker fits the covering member  42  to the transport roller  41 , and moves the covering member  42  to the position where the end surface  42   a  shown in  FIG. 2  comes into contact with the side end of the continuous paper S. A protrusion  42   c  which has a C shape in the cross-sectional view is provided in an end surface  42   b  of the covering member  42 . After moving the covering member  42 , the worker rotates the locknut  43  in the arrow a direction in the figure and fits the locknut  43  and the protrusion  42   c  to each other. Thereby, the protrusion  42   c  is locked, and the covering member  42  is fixed. 
     In addition, in a case where a paper width of the continuous paper S is changed, the covering member  42  is required to be moved according to the changed paper width. In this case, the worker rotates the locknut  43  in an opposite direction to the arrow e direction in the figure so as to be loosened, and separates the locknut  43  from the protrusion  42   c . After separating the locknut  43 , the worker moves the covering member  42  in the length direction of the transport roller  41 . The worker moves the covering member  42  to a position where the end surface  42   a  shown in  FIG. 2  comes into contact with the side end of the changed continuous paper S in the longitudinal direction, and then fits the locknut  43  and the protrusion  42   c  while rotating the locknut  43  in the arrow e direction in the figure. Thereby, the protrusion  42   c  is locked, and the covering member  42  is fixed. 
       FIG. 4  is a diagram illustrating when the contact location R 1  is irradiated with the laser light L. In addition, in  FIG. 4 , the covering member  42  and the locknut  43  are not shown. Since the continuous paper S is on the surface of the transport roller  41  which is a surface of the contact location R 1 , the laser light L is applied to the surface of the continuous paper S. A distance between the condensing lens  32  and the surface of the continuous paper S is substantially the distance F 1  between the condensing lens  32  and the surface of the transport roller  41 . As described above, the continuous paper S is supported at the focal position Pf, and thus the distance F 1  between the condensing lens  32  and the surface of the continuous paper S is the same as the focal length PC of the laser light L. In this case, the laser light L is applied to the surface of the continuous paper S in a focused state. Thereby, the toner on the continuous paper S is heated and melted and is thus fixed to the continuous paper S. 
       FIG. 5  is a diagram illustrating that the noncontact location R 2  is irradiated with the laser light L.  FIG. 5  is a cross-sectional view of the supporter  33  taken along the line H-H in  FIG. 2 . In addition, in  FIG. 5 , the locknut  43  is not shown. Since there is no continuous paper S on the covering member  42  which is a surface of the noncontact location R 2 , the laser light L is applied to the surface of the covering member  42 . As described above, since the diameter D 2  of the covering member  42  is greater than the diameter D 1  of the transport roller  41 , the distance F 2  between the condensing lens  32  and the covering member  42  is smaller than the distance F 1  between the condensing lens  32  and the surface of the transport roller  41 , that is, the focal length F 0  of the laser light L. In this case, the laser light L is applied to the surface of the covering member  42  in a defocused state. 
     If the covering member  42  is not provided, the distance F 1  between the condensing lens  32  and the surface of the transport roller  41  is substantially the same as the focal length F 0  of the laser light L, and thus the laser light L is applied to the surface of the transport roller  41  in a focused state. In this case, high heat is applied to the surface of the transport roller  41 , and thus there is concern that the transport roller  41  may be thermally deformed or damaged. In contrast, in the present exemplary embodiment, since the laser light L is applied to the surface of the noncontact location R 2  in a defocused state, a temperature of the noncontact location R 2  is suppressed from being increased by the laser light L. As a result, thermal deformation or damage of the noncontact location R 2  is prevented. 
     Second Exemplary Embodiment 
     The second exemplary embodiment is different from the first exemplary embodiment in a configuration of a fixing device  133 A. In addition, the other configurations are the same as in the first exemplary embodiment and are thus given the same reference numerals, and detailed description thereof will be omitted. 
       FIG. 6  is a diagram of the fixing device  133 A which is viewed from the II direction shown in  FIG. 1 . The fixing device  133 A includes a laser array  31  and a condensing lens  32  which are the same as in the first exemplary embodiment, and a supporter  33 A.  FIG. 7  is a perspective view of the supporter  33 A. The supporter  33 A includes a transport roller  41 , a light blocking guide  44 , and a transport portion  45 . The light blocking guide  44  is made of a light blocking material. The light blocking guide  44  is used as a light blocking member in the present exemplary embodiment. The light blocking guide  44  includes an upper surface part  44   a , a side surface part  44   b , and a leg part  44   c . The upper surface part  44   a  is provided between a part which does not come into contact with the continuous paper S in the transport roller  41  and the condensing lens  32 , and blocks the laser light L from being applied to the part. As shown in  FIG. 6 , the upper surface part  44   a  is provided at a position closer to the condensing lens  32  than the surface of the transport roller  41 , and thus a distance F 3  between the surface of the upper surface part  44   a  and the condensing lens  32  is smaller than the distance F 1  between the surface of the transport roller  41  and the condensing lens  32 . Referring to  FIG. 7  again, the side surface part  44   b  supports the upper surface part  44   a . Holes  44   d  are provided in the side surface part  44   b . The transport roller  41  is provided so as to penetrate through the holes  44   d . The leg part  44   c  is fixed to a belt member  46  of the transport portion  45 . 
     The transport portion  45  transports the light blocking guide  44  in the length direction (the arrow P direction) of the transport roller  41 . The transport portion  45  includes the belt member  46 , rollers  47  and  48 , and a driving part  49 . The belt member  46  is an endless belt-shaped member, and is hung over the rollers  47  and  48 . The roller  47  is rotated by the driving part  49  such as a motor. Thereby, the roller  47  rotates the belt member  46 . The roller  48  rotates according to the rotation of the belt member  46 . As described above, the leg part  44   c  of the light blocking guide  44  is fixed to the belt member  46 . Therefore, when the belt member  46  rotates, the light blocking guide  44  moves in the length direction of the transport roller  41 . 
     A controller  14  controls driving of the driving part  49  and moves the light blocking guide  44  depending on a paper width of the continuous paper S. Specifically, the controller  14  moves the light blocking guide  44  to a position where the side surface part  44   b  of the light blocking guide  44  comes into contact with the side end of the continuous paper S, by using the driving part  49 . A paper width of the continuous paper S may be input, for example, through an operation by a worker, and may be detected using a photosensor. 
     As shown in  FIG. 6 , the supporter  33 A has a contact location R 1  in which the continuous paper S on the surface region where a light density is equal to or more than a threshold value and a noncontact location R 2  in which there is no continuous paper S. In the present exemplary embodiment, the part which comes into contact with the continuous paper S in the transport roller  41  is the contact location R 1 . In addition, the part which does not come into contact with the continuous paper S in the transport roller  41  and the light blocking guide  44  is the noncontact location R 2 . 
       FIG. 8  is a diagram illustrating that the noncontact location R 2  is irradiated with the laser light L.  FIG. 8  is a cross-sectional view of the supporter  33 A taken along the line I-I in  FIG. 7 . In addition, in  FIG. 8 , the transport portion  45  and the driving part  49  are not shown. Since there is no continuous paper S on the surface of the upper surface part  44   a  of the light blocking guide  44  which is a surface of the noncontact location R 2 , the laser light L is applied to the surface of the upper surface part  44   a . Since the upper surface part  44   a  is provided at a position closer to the condensing lens  32  than the surface of the transport roller  41 , the distance F 3  between the surface of the upper surface part  44   a  and the condensing lens  32  is smaller than the distance F 1  between the surface of the transport roller  41  and the condensing lens  32 , that is, the focal length F 0  of the laser light L. In this case, the laser light L is applied to the surface of the upper surface part  44   a  in a defocused state in the same manner as the above-described first exemplary embodiment, and thus the same effect as in the first exemplary embodiment can be achieved. 
     MODIFICATION EXAMPLES 
     The above-described exemplary embodiments are examples of the invention, and the invention is not limited to the exemplary embodiments. The above-described exemplary embodiments may be modified as follows. In addition, the following Modification Examples may be combined. 
     (1) Modification Example 1 
     In the second exemplary embodiment, the laser light L which is reflected by the continuous paper S or the laser light L which is applied to the light blocking guide  44  may be applied to the continuous paper S through reflection.  FIG. 9  is a diagram illustrating a configuration of a fixing device  131 B according to Modification Example 1. The fixing device  131 B includes a semicircular reflection member  35  which is made of a material which reflects light. The reflection member  35  is provided so as to surround a region which is irradiated with the laser light L. An opening portion  35   a  is provided in an upper end of the reflection member  35 . The laser array  31  irradiates the continuous paper S with the laser light L via the opening portion  35   a . The laser light L applied from the laser array  31  is applied to the continuous paper S via the opening portion  35   a . At this time, some of the laser light L applied to the continuous paper S is reflected by the continuous paper S. The reflection member  35  reflects the laser light L reflected by the continuous paper S so as to be applied to the continuous paper S again. 
       FIG. 10  is a perspective view of a supporter  333  according to Modification Example 1. In the supporter  33 B, a reflection plate  50  is provided in the light blocking guide  44 . The reflection plate  50  is made of a material reflecting light and is disposed at the end of the upper surface part  44   a . The reflection plate  50  reflects light which is applied to the noncontact location R 2  from the laser array  31 , toward the contact location R 1  side. 
       FIG. 11  is a diagram illustrating an operation of the reflection plate  50 . In Modification Example 1, the controller  14  controls the laser array  31  so as to turn on only the light emitting elements  34  corresponding to the contact location R 1 . Thereby, basically, the laser light L is applied to only the continuous paper S on the contact location RI. However, practically, it is difficult to completely match an irradiation width of the laser light L with a width of the continuous paper S. For this reason, even in a case where this control is performed, some of laser light L may be applied to the noncontact location R 2 . The reflection plate  50  plays a part of guiding the laser light L applied to the noncontact location R 2 , to the continuous paper S. 
     When the laser array  31  irradiates the noncontact location R 2  with the laser light L, the reflection plate  50  reflects the laser light L toward the contact location R 1  side. The light reflected by the reflection plate  50  is reflected by the reflection member  35  and is applied to the continuous paper S again. According to Modification Example 1, a light amount of the laser light L applied to the continuous paper S increases, and even the laser light L applied to the noncontact location R 2  is appropriately used to fix a toner image. 
     (2) Modification Example 2 
     In the first exemplary embodiment, the covering member  42  is provided in the part which does not come into contact with the continuous paper S in the transport roller  41 . Alternatively, the covering member  42  may be provided in the part which comes into contact with the continuous paper S in the transport roller  41 . In this case, the covering member  42  supports the continuous paper S at the focal position Pf. In this Modification Example, the part which comes into contact with the continuous paper S in the transport roller  41  and the covering member  42  are the contact location R 1 . In addition, the part which does not come into contact with the continuous paper S in the transport roller  41  is the noncontact location R 2 . 
       FIG. 12  is a diagram illustrating that the contact location R 1  is irradiated with the laser light L according to Modification Example 2. In addition, in  FIG. 12 , the locknut  43  is not shown. Since the continuous paper S is on the surface of the covering member  42  which is a surface of the contact location R 1 , the laser light L is applied to the surface of the continuous paper S. A distance between the condensing lens  32  and the continuous paper S is substantially a distance F 11  between the condensing lens  32  and the surface of the covering member  42 . As described above, the continuous paper S is supported at the focal position Pf, and thus the distance F 11  between the condensing lens  32  and the surface of the continuous paper S is the same as the focal length F 10  of the laser light L. In this case, the laser light L is applied to the surface of the continuous paper S in a focused state. Thereby, the toner on the continuous paper S is heated and melted and is thus fixed to the continuous paper S. 
       FIG. 13  is a diagram illustrating that the noncontact location R 2  is irradiated with the laser light L according to Modification Example 2.  FIG. 13  is a cross-sectional view of the supporter  33  taken along the line H-H in  FIG. 2  in the same manner as  FIG. 5 . In addition, in  FIG. 13 , the locknut  43  is not shown. Since there is no continuous paper S on the transport roller  41  which is a surface of the noncontact location R 2 , the laser light L is applied to the surface of the transport roller  41 . As described above, since the diameter D 1  of the transport roller  41  is smaller than the diameter D 2  of the covering member  42 , the distance F 12  between the condensing lens  32  and the surface of the transport roller  41  is greater than the distance F 11  between the condensing lens  32  and the surface of the covering member  42 , that is, the focal length F 10  of the laser light L. In this case, the laser light L is applied to the surface of the transport roller  41  in a defocused state, and thus the same effects as in the above-described first exemplary embodiment can be achieved. 
     (3) Modification Example 3 
     In the second exemplary embodiment, the transport portion  45  transports the light blocking guide  44  by using a belt feeding mechanism. However, the transport portion  45  is not limited to using a belt feeding mechanism. For example, the transport portion  45  may transport the light blocking guide  44  by using a screw feeding mechanism. 
     (4) Modification Example 4 
     In the first and second exemplary embodiments, the controller  14  may control the laser array  31  so as to turn on only the light emitting elements  34  corresponding to the contact location R 1  as in the above-described Modification Example 1. Thereby, basically, the laser light L is applied to only the continuous paper S on the contact location R 1  from the laser array  31 . However, practically, it is difficult to completely match an irradiation width of the laser light L with a width of the continuous paper S. For this reason, even in a case where this control is performed, some of laser light L may be applied to the noncontact location R 2 . Therefore, the invention may be appropriately carried out through a combination with this control. 
     (5) Modification Example 5 
     In the first and second embodiments, the reflection member  35  may be provided so as to surround a region which is irradiated with the laser light L as in the above-described Modification Example 1. Thereby, a light amount of the laser light L applied to the continuous paper S increases. 
     (6) Modification Example 6 
     In the first exemplary embodiment, the covering member  42  may be made of a material absorbing the laser light L. Similarly, in the second exemplary embodiment, the light blocking guide  44  may be made of a material absorbing the laser light L. Thereby, an influence of the laser light L exerted on the noncontact location R 2  is further suppressed. 
     (7) Modification Example 7 
     In the first exemplary embodiment, the covering member  42  is provided in the transport roller  41 , and thereby the distance F 2  between the surface of the noncontact location R 2  and the condensing lens  32  is different from the distance F 1  between the surface of the contact location R 1  and the condensing lens  32 . However, for example, when a width of the continuous paper S is fixed, the contact location R 1  and the noncontact location R 2  do not vary. In this case, a shape of the transport roller  41  itself may be changed. For example, the transport roller  41  may be formed such that a diameter of the part which comes into contact with the continuous paper S in the transport roller  41  is greater or smaller than a diameter of the part which does not come into contact with the continuous paper S. In this case, the part which comes into contact with the continuous paper S in the transport roller  41  is the contact location R 1 , and the part which does not come into contact with the continuous paper S is the noncontact location R 2 . 
     (8) Modification Example 8 
     In the first and second embodiments, toner is used as a color material for forming an image. However, a color material is not limited to the toner. For example, a color material may be ink which is of a heated and melted type used for an ink jet method. 
     (9) Modification Example 9 
     In the first and second exemplary embodiments, the continuous paper S is used as a recording medium on which an image is formed. However, a recording medium is not limited to the continuous paper S. For example, a recording medium maybe a cut paper sheet which is cut out to a determined size in advance. 
     (10) Modification Example 10 
     In the first and second embodiments, the image forming apparatus  10  forms a color image, but may form a monochrome image. In this case, the image forming apparatus  10  may include only the image forming unit  12 K among the image forming units  12 Y,  12 M,  120  and  12 K. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.