Patent Publication Number: US-8532510-B2

Title: Image forming apparatus with image detector

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus employing an electrophotographic system, such as a copy machine, a printer, or a facsimile machine, for example. 
     2. Description of the Related Art 
     As one development system of an image forming apparatus employing an electrophotographic process, there is a contact development system in which development is performed in a state in which a development roller, which is a developer carrier, is rotated in contact with a photosensitive drum, which is an image carrier. In the contact development system, the surface of the photosensitive drum wears due to contact with the development roller and thus performance worsens, leading to a decrease in the quality of formed images. Consequently, technology has been proposed whereby wear of the photosensitive drum due to contact with the development roller is prolonged by performing development by causing the development roller to contact the photosensitive drum only during a time period in which an electrostatic latent image of the photosensitive drum is developed. 
     In Japanese Patent Laid-Open No. 2006-292868, a configuration is proposed in which, in an inline color image forming apparatus, driving and stopping of a development roller, and contact with and separation from the photosensitive drum, are performed in coordination with the timing at which development is performed at respective stations. In an inline system, image forming stations that form images of respective color components are disposed in series on an intermediate transfer belt, and toner images of the respective color components are formed in an image forming region in the order first image forming station (abbreviated below as st 1 )→st 2 →st 3 →st 4  in the conveyance direction of the intermediate transfer belt. In Japanese Patent Laid-Open No. 2006-292868, driving and stopping of the development roller of the respective image forming stations, and contact with and separation from the photosensitive drum, are controlled according to this order. The inline system is also referred to as a tandem system. 
     Here, because the respective image forming stations are provided individually as exchangeable and comparatively inexpensive process cartridges, it is difficult to completely eliminate variation, that is, mechanical variation such as variation in the positional relationship with the main body of the image forming apparatus, variation in drive source control, and so forth. Variation arises in the mechanism for causing contact and separation of a photosensitive drum and a development roller, for example. Assume a mechanism is adopted in which the development roller is biased such that the development roller contacts with the photosensitive drum, and the development roller is caused by a cam mechanism to separate from the photosensitive drum against this biasing force. In this case, assuming that a cam is in the image forming apparatus main body, and a cam follower is in a process cartridge, there is a possibility of variation in the distance between the cam and the cam follower. This variation leads to an offset in the timing of contact and separation of the development roller and the photosensitive drum, the offset occurring between image forming stations or between process cartridges, and the timing offset can cause image defects. For example, when the contact timing of the development roller is later than the leading edge of an image forming region on the photosensitive drum, a leading edge portion of an image is omitted, or image defects occur due to contact shock of the development roller. Also, when the separation timing of the development roller is earlier than the trailing edge of the image forming region on the photosensitive drum, an image defect that the image trailing edge is omitted will occur. Note that the image forming region on the photosensitive drum is a region where a latent image (and eventually a visible image using toner) is formed on the surface of the photosensitive drum according to the size of the recording medium on which printing is performed. 
     In order to prevent these adverse effects arising due to variation in the timing of contact or separation of the development roller and the photosensitive drum, in Japanese Patent Laid-Open No. 2006-292868, control of driving and stoppage, and contact and separation, of the development roller is caused to have a margin preceding an image forming guarantee time, as shown in  FIG. 24 . The margin is, for example, a surplus time for absorbing variation in the time required from the start of movement until actual contact in order to cause the development roller to contact against the photosensitive drum. When the development roller has been moved from a position separated from the photosensitive drum to a position contacted against the photosensitive drum, if the margin time has passed after the start of movement, the development roller is guaranteed to be in a state contacted against the photosensitive drum regardless of variation in timing between image forming stations. Accordingly, the time subsequent to passage of the margin time after the start of movement of the development roller serves as the image forming guarantee time, in which image forming of a visible image by a developer using toner or the like is guaranteed. In the example in  FIG. 24 , the development roller is contacted against the photosensitive drum at a timing t 241 , and this contact is accelerated by the time of an offset  1  relative to the image forming guarantee time. Also, following image forming, in order to guarantee image forming, separation of the development roller contacted against the photosensitive drum is started after passage of the image forming guarantee time. In  FIG. 24 , a time corresponding to an offset  2  is required until actual separation. The occurrence of image forming defects is prevented by performing image forming while allowing for this sort of offset. 
     Therefore, in the example in  FIG. 24 , the development roller and the photosensitive drum are contacted for a time longer than the image forming guarantee time by offset  1 +offset  2 . That is, because an image forming guarantee time allowing for offset is ensured, when performing image forming, in many cases it can be assumed that the development roller and the photosensitive drum are in contact for a long period at least as long as the time necessary and sufficient for image forming. As a result, there is the problem that wear of the photosensitive drum advances due to contact that is not intrinsically necessary for image forming, so the life of the process cartridge is shortened. 
     SUMMARY OF THE INVENTION 
     The present invention was made in view of the problem described above, and relates to providing an image forming apparatus in which it is possible to postpone wear of a process cartridge by adaptively controlling the time that a development roller and a photosensitive drum are in contact. 
     According to an aspect of the present invention, an image forming apparatus comprises: an image carrier on which a latent image is formed; and a developing unit adapted to develop the latent image formed on the image carrier as a toner image; wherein the developing unit includes a developer carrier that is capable of contacting or separating from the image carrier and carries a toner image, and the image forming apparatus has a detector adapted to detect a toner image obtained by starting a contact operation to put the image carrier and the developer carrier in contact to develop the latent image while operating the developing unit in a state in which the image carrier and the developer carrier are separated, and a controller adapted to control the contact operation to put the image carrier and the developer carrier in contact based on the detection results detected by the detector. 
     According to another aspect of the present invention, an image forming apparatus comprises: an image carrier on which a latent image is formed; and a developing unit adapted to develop the latent image formed on the image carrier as a toner image; wherein the developing unit includes a developer carrier that is capable of contacting or separating from the image carrier and carries a toner image, and the image forming apparatus has a detector for detecting a toner image obtained by starting a separation operation to separate the image carrier and the developer carrier to develop the latent image while operating the developing unit in a state in which the image carrier and the developer carrier are in contact, and a controller adapted to control the separation operation to separate the image carrier and the developer carrier based on the detection results detected by the detector. 
     According to still another aspect of the present invention, an image forming apparatus comprises: an image carrier on which a latent image is formed; and a developer carrier that develops the latent image formed on the image carrier; the image forming apparatus being capable of switching between a state in which the image carrier and the developer carrier are separated, and a state in which the image carrier and the developer carrier are in contact and the latent image can be developed; wherein the latent image formed on the image carrier is developed as a detection image for controlling a contact operation or a separation operation of the image carrier and the developer carrier. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of an inline-type full-color printer according to an embodiment. 
         FIG. 2  is a function block diagram of a printer according to an embodiment. 
         FIGS. 3A to 3C  show example contact/separation states of a photosensitive drum and a development roller of an inline-type full-color printer according to an embodiment. 
         FIG. 4  is a cam diagram of a driving cam for causing a development roller of an inline-type full-color printer according to an embodiment to contact with/separate from a photosensitive drum. 
         FIG. 5  is a perspective view of an image forming unit of an inline-type full-color printer according to an embodiment. 
         FIG. 6  is a diagram of detection times of timing of contact of a photosensitive drum and a development roller of an inline-type full-color printer according to an embodiment. 
         FIG. 7  is a diagram of detection times of timing of separation of a photosensitive drum and a development roller of an inline-type full-color printer according to an embodiment. 
         FIG. 8  is a flow diagram of a control program that detects timing of contact/separation of a photosensitive drum and a development roller in a first embodiment. 
         FIG. 9  is a diagram that shows detection states when detecting timing of contact of the photosensitive drum and the development roller in the first embodiment. 
         FIG. 10  is a diagram that shows detection states when detecting timing of separation of the photosensitive drum and the development roller in the first embodiment. 
         FIG. 11  shows example detection patterns for detecting timing of contact/separation of the photosensitive drum and the development roller in the first embodiment. 
         FIG. 12  shows an example of a time when the photosensitive drum and the development roller are contacted in the first embodiment. 
         FIG. 13  is a diagram of timing of detecting contact/separation of a photosensitive drum and a development roller in a second embodiment. 
         FIG. 14  is a flow diagram of a control program that detects timing of contact/separation of a photosensitive drum and a development roller in the second embodiment. 
         FIG. 15  shows example contact/separation states of the photosensitive drum and the development roller in the second embodiment. 
         FIG. 16  is a diagram of the timing of detecting contact/separation of the photosensitive drum and the development roller in the second embodiment. 
         FIG. 17  shows example detection patterns for detecting timing of contact/separation of a photosensitive drum and a development roller in a third embodiment. 
         FIG. 18  is a diagram that shows detection states when detecting timing of separation of the photosensitive drum and the development roller in the third embodiment. 
         FIG. 19  is a flow diagram of a control program that detects timing of contact/separation of the photosensitive drum and the development roller in the third embodiment. 
         FIG. 20  shows a concept of a correction method for correcting timing of contact/separation of the photosensitive drum and the development roller in the third embodiment. 
         FIG. 21  is a timing diagram that shows the timing for applying a charging bias to a photosensitive drum, and applying a transfer bias to a development roller, in a fourth embodiment. 
         FIG. 22  is a timing diagram that shows drive timing and bias application timing of an intermediate transfer belt in the fourth embodiment. 
         FIG. 23  is a flow diagram of a control program that detects timing of contact/separation of the photosensitive drum and the development roller in the fourth embodiment. 
         FIG. 24  shows an example of timing of contact/separation of a photosensitive drum and a development roller relevant to problems in the related art. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     First Embodiment 
     Following is a description of an image forming apparatus according to a first embodiment of the present invention. In this example, as one example of an image forming apparatus, among contact development-type image forming apparatus in which an electrophotographic system is adopted, an inline-type 4-drum full-color image forming apparatus employing an intermediate transfer belt is used.  FIG. 1  is a schematic cross-sectional view that shows the general configuration of this sort of image forming apparatus. 
     Configuration of Image Forming Apparatus 
     As shown in  FIG. 1 , a 4-drum full-color image forming apparatus  1  has a configuration in which process cartridges PY, PM, PC, and PK of the four colors yellow, magenta, cyan, and black are removable from an image forming apparatus main body (referred to below as an apparatus main body)  2 . The process cartridges PY, PM, PC, and PK (below, collectively referred to as P) constitute image forming stations (also referred to as image forming units) of respective color components that have been respectively installed in the apparatus main body. The image forming stations also include development units  63 , photosensitive drums  61 , and so forth, described later. Also provided in the apparatus main body  2  are an intermediate transfer belt unit  5  having an intermediate transfer belt  51  serving as an intermediate transfer member (rotating member), and a fixing unit  7  that thermally fixes toner. The image forming stations are disposed in series in the recording medium conveyance direction. 
     The process cartridges P respectively have photosensitive drums  61 Y,  61 M,  61 C, and  61 K, which are image carriers (photosensitive bodies), and are disposed sequentially in parallel in the movement direction of the intermediate transfer belt  51 , onto which transfer is performed. On the image carrier, that is, on the surface of the image carrier, an electrostatic latent image is formed and developed using toner. Furthermore, each of the process cartridges P integrally has, around the circumference of the respective photosensitive drum  61 , a primary charging unit  62  as a charging means, a development unit  63  as a development means, and a photosensitive member cleaner  65  as a cleaning means. 
     In each process cartridge P, the primary charging unit  62  is disposed on the outer circumferential surface of the photosensitive drum  61 , and uniformly charges the surface of the photosensitive drum  61 . The development unit  63  uses toner of the corresponding color (yellow, magenta, cyan, black) to develop the electrostatic latent image formed on the surface of the photosensitive drum  61  by exposure from respective laser exposure units (exposing means)  21 Y,  21 M,  21 C, and  21 K. A development roller  64  serving as a developer carrier within the development unit  63  is configured such that it is possible to prevent degradation of toner by, in each development unit  63 , separating the development roller  64  from the photosensitive drum  61  and stopping rotation of the development roller  64 . That is, in each development unit  63 , the development roller  64  is configured so as to be capable of contact against or separation from the photosensitive drum  61 . In the description below, a contacted state may also be referred to simply as contact, and a separated state may also be referred to simply as separation. Also, the position where the development roller contacts on the photosensitive drum is referred to as the contact position. After toner images have been sequentially transferred, the photosensitive member cleaner  65  removes toner remaining after transfer that is affixed to the surface of the photosensitive drum  61 . 
     Also, a primary transfer roller  52  that together with the photosensitive drum  61  forms a primary transfer unit is disposed opposing the photosensitive drum  61  at a position where the primary transfer roller  52  together with the photosensitive drum  61  sandwiches the intermediate transfer belt  51 . 
     On the other hand, the intermediate transfer belt unit  5  is provided with the intermediate transfer belt  51 , and three rollers across which the intermediate transfer belt  51  is stretched: a drive roller  53 , a tension roller  54 , and a secondary transfer opposing roller  55 . The intermediate transfer belt  51  is rotationally conveyed by rotationally moving the drive roller  53  with a belt drive motor (not shown). The tension roller  54  is configured so as to be movable in the horizontal direction in  FIG. 1  according to the length of the intermediate transfer belt  51 . 
     Near the drive roller  53 , a registration detection sensor  56  serving as a detection means for detecting a toner patch on the intermediate transfer belt  51  is disposed near both ends in the roller longitudinal direction. This position is a predetermined detection position. A belt cleaner  58  for collecting remaining toner on the intermediate transfer belt is disposed near the tension roller  54 . The longitudinal direction is the roller axial direction, and is the width direction orthogonal to the conveyance direction of the intermediate transfer belt  51 . Furthermore, a secondary transfer roller  82  that together with the secondary transfer opposing roller  55  forms a secondary transfer unit is disposed opposing the secondary transfer opposing roller  55  at a position where the secondary transfer opposing roller  55  sandwiches the intermediate transfer belt  51 . The secondary transfer roller  82  is held by a transfer/conveyance unit  8 . 
     A feed unit  3  that feeds a recording medium (in this apparatus, a print medium such as paper) Q to the secondary transfer unit is disposed in the lower portion of the apparatus main body  2 . The feed unit  3  is provided with a cassette  31  in which a plurality of sheets of the recording medium Q are stored, a feed roller  32 , a retarding roller pair  33  that prevents double feeding, conveying roller pairs  34  and  35 , a registration roller pair  36 , and so forth. Discharge roller pairs  37 ,  38 , and  39  are provided in the conveyance path on the downstream side of the fixing unit  7 . 
     The color image forming apparatus  1  is compatible with duplex printing, and after image forming on a first face of a recording medium Q is finished and that recording medium Q is discharged from the fixing unit  7 , by switching a switching member  41 , the recording medium Q is conveyed to the side of reversing roller pairs  42  and  43 . Once the trailing edge of this recording medium Q has passed over a switching member  44 , at the same time as switching the switching member  44 , the reversing rollers  43  are rotated in reverse to guide the recording medium Q to a duplex conveyance path  45 . Then, by rotationally driving duplex conveyance path roller pairs  46 ,  47 , and  48  to again feed the recording medium Q, printing to a second face is made possible. 
     Furthermore, an image forming control unit (also referred to as simply a control unit)  12  is provided in the image forming apparatus  1 , and with this image forming control unit  12 , output signals of respective sensors are obtained, and image forming operations such as the timing of driving of the drive unit and the timing of latent image formation and so forth are controlled. 
     Configuration of Control Unit 
     Next is a detailed description of the configuration of the image forming control unit  12  disclosed in the first embodiment of the present invention, with reference to  FIG. 2 . The image forming control unit  12  includes a CPU  121  that is a processor that executes a program to execute data processing and input/output processing, and a ROM  122  and a RAM  123  that store data, programs, and so forth. With this configuration, a timer and respective control units that have been mapped to a memory space or IO space, for example, are controlled. As control units, for example, there are an exposure control unit  13 , a high voltage control unit  14 , a drive control unit  15 , a sensor control unit  16 , and so forth. Additionally, a control timer  17  also is used for time measurement and the like. The exposure control unit  13 , in addition to driving the laser exposure unit  21 , drives a scanner motor  182 , performs correction of a laser light amount, and so forth. The high voltage control unit  14  charges and applies a development bias to the photosensitive drum  61 , applies a primary transfer bias to the intermediate transfer belt  51 , applies a secondary transfer bias to the recording medium Q, applies a belt cleaning bias for the belt cleaner, and so forth, necessary for image forming. The drive control unit  15  drives a motor (not shown) of the image forming system of the photosensitive drum  61 , the development roller  64 , and the intermediate transfer belt  51 , and drives a conveyance motor (not shown) that conveys the recording medium Q. The sensor control unit  16  performs detection of the amount of remaining toner and the position of the recording medium Q in the conveyance path. In addition, the sensor control unit  16  performs detection of a toner patch on the intermediate transfer belt  51  using the registration detection sensor  56 , and detection of a position display mark provided on the intermediate transfer belt  51  using a mark sensor  57 . 
     Following is a more detailed description of the above configuration. A pattern detection control unit  181  includes the scanner motor  182 , a charging bias control unit  183 , a development bias control unit  184 , and a primary transfer bias control unit  185 . The charging bias control unit  183  controls the bias applied to the primary charging unit  62 . The development bias control unit  184  controls the bias of a charging unit for charging the development roller  64 . The primary transfer bias control unit  185  controls a charging unit that applies a positive bias to the primary transfer roller  52  when image forming is performed, and applies a negative bias when collecting waste toner. Of course, it is also conceivable that the respective bias control units themselves include a charging unit. 
     A stepper motor control unit  187  controls a stepper motor  91 , the gist of which is shown by way of example in  FIGS. 3A to 3C . This will be described in detail below with reference to  FIGS. 3A to 3C , but in the present embodiment, the stepper motor  91  is a motor that drives a worm gear that engages with a worm wheel that has been fixed coaxially to a cam for moving the position of the development roller  64  of each color component. In order for the worm gears that drive the respective cams to be coaxially fixed and simultaneously driven by the single stepper motor  91 , the phase difference of the respective cams is fixed. By driving the stepper motor  91  at a timing corresponding to image forming of each color component, the development roller  64  is separated from or contacted against the photosensitive drum  61 . 
     A registration detection sensor  56  (in this embodiment, two sensors  56   a  and  56   b ) of the sensor control unit  16  shown in  FIG. 10  is controlled by the pattern detection control unit  181 . In the pattern detection control unit  181 , a time from starting of the stepper motor  91  until a detection pattern passes directly below the registration detection sensor  56  is measured with the control timer  17 . Also, the pattern detection control unit  181  performs switching control of a detection window for determining the image forming station that formed the detection pattern that passed directly below the registration detection sensor  56 . The timing of starting of the stepper motor  91  can be known from a notification made via the image forming control unit  12 , for example. It is also possible for the detection pattern to be a correction image used for correcting timing. 
     Operation of Image Forming Apparatus 
     Here, an image forming operation of the 4-drum full-color image forming apparatus  1  configured in the above manner will be described. When the image forming operation is started, first, after the recording medium Q in the cassette  31  has been fed by the feed roller  32 , the recording medium Q is separated into individual sheets by the retard roller pair  33 , and then conveyed to the registration roller pair  36  via the conveying roller pairs  34  and  35  and so forth. 
     On the other hand, parallel with the conveyance operation of the recording medium Q, for example in the yellow process cartridge PY, first the surface of the photosensitive drum  61 Y is uniformly negatively charged by the primary charging unit  62 , and then image exposure is performed by the laser exposure unit  21 Y. Thus, an electrostatic latent image corresponding to a yellow image component of an image signal is formed on the surface of the photosensitive drum  61 Y. 
     The development roller  64 Y in the development unit  63 Y, while being rotationally driven, is gradually moved, and approaches and contacts against the photosensitive drum  61 Y, and thus the electrostatic latent image of the photosensitive drum  61 Y is developed using the yellow toner negatively charged by the development unit  63 Y. Thus, the electrostatic latent image is made visible as a yellow toner image. That is, the electrostatic latent image becomes a visible image and appears. Primary transfer of the yellow toner image obtained in this manner onto the intermediate transfer belt  51  is performed by the primary transfer roller  52 , which has been supplied with a primary transfer bias. 
     This sort of one iteration of a toner image forming operation is also sequentially performed in the other process cartridges PM, PC, and PK, at staggered times corresponding to the interval and conveyance speed of those process cartridges. The development roller  64 , while rotating, sequentially contacts against the photosensitive drum  61  in order to prevent degradation of developer. Then, primary transfer is performed with the toner images of each color that have been formed on the respective photosensitive drums  61  sequentially overlaid in the primary transfer unit of each color in a corresponding region on the intermediate transfer belt  51  (referred to as the image forming region on the intermediate transfer belt  51 ). When the development operation is finished, the development rollers  64  are sequentially separated from the photosensitive drums  61  and rotation is stopped in order to prevent degradation of developer, even if primary transfer is currently being performed by a process cartridge on the downstream side. The toner images in four colors that have thus been transferred onto the intermediate transfer belt  51  in a stacked manner are moved to the secondary transfer unit as the intermediate transfer belt  51  rotates. 
     On the other hand, the recording medium Q, after oblique travel thereof has been corrected at the registration roller pair  36 , is fed out to the secondary transfer unit at a timing coordinated with the toner images on the intermediate transfer belt  51 . Secondary transfer of the toner images in four colors on the intermediate transfer belt  51  is collectively performed onto the recording medium Q by the secondary transfer roller  82  contacted against the intermediate transfer belt  51  so as to sandwich the recording medium Q. The recording medium Q to which a toner image has been thus transferred is then conveyed to the fixing unit  7 , and after the toner image has been fixed by applying heat and pressure to the recording medium Q, the recording medium Q is discharged to and stacked on the upper face of the apparatus main body by the discharge roller pairs  37 ,  38 , and  39 . By the above process, a full-color toner image is formed on a recording medium. 
     Operation Switching Contact and Separation of Photosensitive Drum and Development Roller 
     Next is a description of the mechanism that switches contact and separation of the development roller  64  and the photosensitive drum  61 , with reference to  FIGS. 3A to 3C . A worm gear  97  is fixed to an output shaft of the stepper motor  91 , which is the drive source for switching between contact and separation of the development roller  64 , and the stepper motor  91  rotates a drive switching shaft  92 , to which a pinion gear that engages with the worm gear is coaxially fixed. A worm gear  93  for driving cam gears  94  of each color is fixed to the drive switching shaft  92 , and when the drive switching shaft  92  rotates, the phase of a cam  95  fixed coaxially to the cam gear  94  changes. The cam  95  is a plate cam whose circumferential edge is formed such that the radius from the center of rotation differs depending on the phase. The circumferential edge of the cam  95  applies pressure against a side face of the process cartridge P or releases pressure according to the phase of the cam  95 . The side face of the process cartridge P serving as a cam follower is a side face of the case of the development unit  63  that axially supports the development roller, and the case of the development unit  63 , is axially supported near its center by a shaft  99  parallel to the photosensitive drum  61  or the like, to the case supporting the photosensitive drum. The case where the photosensitive drum  61  is axially supported is fixed to the apparatus main body  2 , and between that case and the case of the development unit  63 , an elastic member  98  such as a spring for energizing the case of the development unit  63  to the cam  95  is provided. Thus, the development roller  64  swings, centered on the shaft  99 , according to movement of the case of the development unit  63 , which is driven by the cam  95 . Thus, the development roller  64  contacts against or separates from the photosensitive drum  61  according to the phase of the cam  95 . Note that because the minimum distance between the development roller  64  and the photosensitive drum  61  is 0, the amount of swinging movement of the case of the development unit  63  is regulated not only by the radius of the cam  95 , but also by the photosensitive drum  61 . Thus it is possible to switch between contact and separation of the photosensitive drum  61  and the development roller  64 . 
     The contact and separation states of the development roller  64  and the photosensitive drum  61  in the present embodiment include a standby state (or complete separation state) shown in  FIG. 3A , a full-color contact state shown in  FIG. 3B , and a monochrome contact state shown in  FIG. 3C . In the standby state, all of the cams  95  ( 95 Y,  95 M,  95 C, and  95 K) are contacted against the side face of the process cartridges P (PY, PM, PC, and PK) at the maximum radius, and all of the development rollers  64  ( 64 Y,  64 M,  64 C, and  64 K) are separated from the photosensitive drums  61  ( 61 Y,  61 M,  61 C, and  61 K). The maximum radius is a radius as necessary in order to separate the development roller  64  from the photosensitive drum  61 . In the full-color contact state, all of the cams  95  ( 95 Y,  95 M,  95 C, and  95 K) are contacted against (or separated from) the side face of the process cartridges P (PY, PM, PC, and PK) at approximately a minimum radius. The minimum radius is a radius as necessary for contact of the development roller  64  and the photosensitive drum  61 . As a result, all of the development rollers  64  ( 64 Y,  64 M,  64 C, and  64 K) are contacted against all of the photosensitive drums  61  ( 61 Y,  61 M,  61 C, and  61 K). In the monochrome contact state, the cams  95  ( 95 Y,  95 M, and  95 C) of the three colors yellow (Y), magenta (M), and cyan (C) shown in  FIG. 3C  are contacted against the side face of the process cartridges P (PY, PM, and PC) of the three colors yellow (Y), magenta (M), and cyan (C). Only the cam  95 K for black (K) is separated from (or contacted against at approximately the minimum radius) the side face of the process cartridge PK, and only the black development roller  64 K is contacted against the photosensitive drum  61 K. 
     Next, the relationship between phase changes of the cam  95  and the three selectable states is shown in cam diagrams in  FIG. 4 . In  FIG. 4 , development separation is the side where the development roller  64  and the photosensitive drum  61  separate, and the cam radius is large, and development contact is the side where the development roller  64  and the photosensitive drum  61  are contacted, and the cam radius is small.  FIG. 4  only shows cam profiles, and does not show actual contact and separation of the development roller  64  and the photosensitive drum  61 . As shown in  FIG. 4 , each of the cams  95  ( 95 Y,  95 M,  95 C, and  95 K) have respective profiles, and by staggering the phases of each of the cams  95  ( 95 Y,  95 M,  95 C, and  95 K), switching (mode switching) between the three states shown in  FIGS. 3A to 3C  is possible. Note that in the description below, contact of the photosensitive drum  61  and the development roller  64  may be referred to simply as contact or development contact, and separation of the photosensitive drum  61  and the development roller  64  may be referred to simply as separation or development separation. 
     When performing an ordinary printing operation, the state of the development roller  64  is switched from the standby state to the full-color contact state, or from the standby state to the monochrome contact state, in coordination with the timing at which image forming is started. First, switching of the development contact/separation state in the case of performing full-color printing will be described. The development contact/separation state refers to the state of contact or separation of the development roller  64  and the photosensitive drum  61 , where a state in which the development roller  64  and the photosensitive drum  61  are contacted is referred to as a development contact state (or contact state), and a state in which the development roller  64  and the photosensitive drum  61  are separated is referred to as a development separation state (separation state). The stepper motor  91  is stopped in the standby state. For example, the standby state can be determined for a specific cam by providing a sensor therein that indicates the rotational phase of that cam. Alternatively, the standby state can be determined by once determining the position of the standby state, then measuring the number of steps of one circumference of the cam, and driving the motor while counting the number of steps, or the like. 
     When performing full-color printing, the stepper motor  91  is rotationally driven forward by a predetermined number of steps in coordination with the timing at which image forming is started. When forward rotational driving of the stepper motor  91  is started, the development roller  64  and the photosensitive drum  61  of each image forming station pass through an indefinite state  401  and are contacted, thus establishing the full-color contact state. The order of that contact is image forming station  1 →(yellow)→image forming station  2  (magenta)→image forming station  3  (cyan)→image forming station  4  (black). Image forming is started from the image forming station whose contact is completed. The number of driving steps of the stepper motor  91  at this time is a number of driving steps such that the stepper motor  91  stops in the full-color state with contact completed for all of the image forming stations. When image forming ends, the stepper motor  91  is again rotationally driven forward by a predetermined number of steps. When forward rotational driving of the stepper motor  91  is started, the development roller  64  and the photosensitive drum  61  pass through an indefinite state  402  and separate, thus returning to the standby state. The order of separation is image forming station  1 →(yellow)→image forming station  2  (magenta)→image forming station  3  (cyan)→image forming station  4  (black). Thus image forming is ended. The number of driving steps of the stepper motor  91  at this time is a number of driving steps such that the cam stops in the standby state. That is, the above operation begins from the standby state, passes through stoppage in the full-color state, and returns to the standby state again. 
     Next is a description of switching control of the development contact/separation state when performing monochrome printing. When performing monochrome printing, the stepper motor  91  is rotationally driven in reverse by a predetermined number of steps in coordination with the timing at which image forming is started. When reverse rotational driving of the stepper motor  91  is started, the development roller  64  and the photosensitive drum  61  pass through an indefinite state and are contacted only in the image forming station  4  (black), and image forming in the image forming station  4  (black) is started. The number of driving steps of the stepper motor  91  is a number of driving steps such that the stepper motor  91  stops when contact is completed in only the image forming station  4  (black). When image forming ends, the stepper motor  91  is rotationally driven forward by a predetermined number of steps. When forward rotational driving of the stepper motor  91  is started, the development roller  64 K and the photosensitive drum  61 K of the station  4  (black) separate and printing is ended. The number of driving steps of the stepper motor  91  at this time is a number of driving steps so as to stop when separation of all of the image forming stations is completed. 
     The image forming apparatus  1 , in the process of image forming, switches the development contact/separation state of the development roller  64  and the photosensitive drum  61  from the separation state to the contact state, or from the contact state to the separation state. At that time, the drive start timing (start time) and number of steps of the stepper motor  91  in the standby state, and the drive start timing and number of steps of the stepper motor  91  in the full-color contact state, are predetermined. 
     Here, contact of the development roller  64  and the photosensitive drum  61  is not necessarily started when in the contact state shown in  FIG. 4 . Contact of the development roller  64  and the photosensitive drum  61  may occur before the minimum radius portion of the cam  95  contacts against the case of the development unit, depending on variation in the distance between the cam  95  and the process cartridge provided in the apparatus main body  2 . In this way, variation in the contact timing and the separation timing occurs due to the effects of individual differences between components, installation precision, and so forth. Consequently, in the present embodiment, the contact timing is detected, and the cam drive timing and rotational speed are adjusted such that the development roller  64  and the photosensitive drum  61  contact at nearly an optimal timing. Therefore, next is a description of the principles of a method for detecting the timing of contact of the development roller  64  against the photosensitive drum  61  or the timing of separation. 
     Principles of Detecting Development Contact Timing and Development Separation Timing 
     First, the principles of a method for detecting the timing of contact of the development roller  64  against the photosensitive drum  61  will be described with reference to  FIGS. 5 and 6 . The contact timing (development contact timing) can be specified with the time from starting the stepper motor  91  until completion of contact of the development roller  64  against the photosensitive drum  61 . This time is referred to as a development contact completion passed time, or simply as the movement time of the development roller  64 . In each image forming station, when the stepper motor  91  is started, by this driving the development rollers  64  are sequentially contacted against the photosensitive drums  61 , and thus the development contact/separation state changes from the separation state to the contact state. 
     While the state is transitioning, that is, while the state is indefinite, as shown in  FIG. 5 , an electrostatic latent image  80  is formed on the surface of the photosensitive drum  61  by exposure from the respective laser exposure units (exposing means)  21 Y,  21 M,  21 C, and  21 K. Also, latent image formation is not only performed during the indefinite state, rather, latent image formation is performed such that a continuous latent image in the rotational direction of the photosensitive drum  61  is developed beginning from an intermediate point of the image. In an image forming station where contact of the development roller  64  has been completed, toner is supplied from the development roller  64  to the electrostatic latent image  80  on the drum surface, so that a toner image is formed on the drum surface. The formed toner image is transferred to the intermediate transfer belt  51 , and a detection pattern  81 , which is a detection image, of each color is formed on the intermediate transfer belt  51 . The development contact timing is calculated from the passed time (development contact completion passed time) As(msec) from starting of the stepper motor  91  until detection of the detection pattern  81  formed on the intermediate transfer belt  51  by the registration detection sensor  56 . However, when there are a plurality of image forming stations, the development contact completion passed time will differ for each image forming station depending also on cam phase offset. This is because even in the standby state, which is the state in which measurement is started, there is a phase difference in cams between stations. Therefore, the difference in movement times between respective stations due to phase offset is compensated. The time of movement due to phase offset can be determined by the predetermined phase relationship between stations and the drive speed of the stepper motor  91 . For example, where the phase of each cam is delayed by an angle α in the order that the image forming stations are disposed, and the cam drive angular velocity (uniquely determined from motor drive speed) is Vc, for each subsequent station, α/Vc is subtracted from the measured development contact completion passed time. For example, the phase difference is compensated by subtracting 0 from the measured time of the station  1 , subtracting α/Vc from the measured time of the station  2 , subtracting 2α/Vc from the measured time of the station  3 , and subtracting 3α/Vc from the measured time of the station  4 . In the description hereafter, with respect to the times As and Cs (described below), the phase difference between stations has been compensated. Note that here, an example is described in which the detection pattern  81  is formed on the intermediate transfer belt  51  and detected with the registration detection sensor  56 , but the detection pattern  81  is not limited to being formed on the intermediate transfer belt  51 , and may for example be formed on a recording medium conveyance belt or the like. 
     Here, the method for calculating the development contact timing will be described with reference to the diagram shown in  FIG. 6 .  FIG. 6  shows toner image states up until a toner image that has been formed by the development roller  64  contacting against the photosensitive drum  61  passes by the registration detection sensor  56 . Time is shown on the horizontal axis, and the distance along a path from formation of an electrostatic latent image until a toner image arrives at the position of the registration detection sensor  56  is shown on the vertical axis. The stepper motor  91  is started from the standby state at a timing t 151 , and the development roller  64  contacts against the photosensitive drum  61  at a timing t 152  after passage of a development contact time Xs(msec). The stepper motor  91  stops in the full-color contact state after rotating by the number of steps described above. Latent image formation on the photosensitive drum  61  is started from a timing t 1511 , and that latent image is developed from the timing t 152 . The developed toner image moves to a transfer position with rotation of the photosensitive drum  61 , and primary transfer of that toner image to the intermediate transfer belt  51  is performed at a timing t 1521 . With conveyance of the intermediate transfer belt  51 , the toner image passes by the registration detection sensor  56 , and there the toner image, that is, the detection pattern  81 , is detected. 
     When considering the relationship of measurement times, the calculated development contact time Xs is the difference between the development contact completion passed time As and a passed time Bs from development of the toner image formed on the surface of the photosensitive drum  61  until the toner image is detected by the registration detection sensor  56 . That is, the development contact time Xs can be calculated from formula (1). Here, the suffix s indicates an image forming station, and for example, the development contact completion passed time for the image forming station  1  is A 1  (hereinafter, S means image forming station).
 
 Xs=As−Bs (msec)  (1)
 
     The time As can be measured by the control timer  17 . The time Bs is the time needed for the developed toner image to move from the development position on the photosensitive drum  61  to the position of the registration detection sensor  56 , and is a constant provided by the conveyance speed and conveyance distance of the toner image. 
     Next is a description of principles of a method for detecting the timing of separation of the development roller  64  from the photosensitive drum  61 . The development separation timing can be specified with the time from starting the stepper motor  91  in the full-color contact state until completion of separation of the development roller  64  from the photosensitive drum  61 . This time is referred to as the development separation completion passed time. In the respective image forming stations, when the stepper motor  91  is started, the development rollers  64  are sequentially separated from the photosensitive drums  61 , so that the development contact/separation state is switched to the separation state. The development separation timing is calculated from a development separation completion passed time Cs(msec) from starting of the stepper motor  91  until the detection pattern  81  formed on the intermediate transfer belt  51  can no longer be detected by the registration detection sensor  56 . 
     Here, the method for calculating the development separation timing will be described with reference to the diagram shown in  FIG. 7 .  FIG. 7  shows toner image states up until a toner image that has been no longer formed due to the development roller  64  separating from the photosensitive drum  61  passes by the registration detection sensor  56 . Time is shown on the horizontal axis, and the distance along a path from formation of an electrostatic latent image until a toner image arrives at the position of the registration detection sensor  56  is shown on the vertical axis. The stepper motor  91  is started at a timing t 154 , and arrives at the standby state at a timing t 155 . At a timing t 1541  therebetween, the development roller  64  and the photosensitive drum  61  separate. Primary transfer of the trailing edge of the toner image formed immediately before separation to the intermediate transfer belt  51 , is performed at a timing t 1551 , and the toner image is conveyed and arrives at the position of the registration detection sensor  56  at a timing t 156 . A development separation time Ys(msec) is the difference between the above-described development separation completion passed time Cs(msec) and the fixed time Bs(msec), and can be calculated from formula (2).
 
 Ys=Cs−Bs (msec)  (2)
 
     Ordinarily, when detecting the development contact timing and the development separation timing of the development rollers  64  to the photosensitive drums  61  of all of the image forming stations, the development contact timing or the development separation timing of all four image forming stations is detected with a single registration detection sensor  56 . Therefore, in the present embodiment, it is necessary to perform four development contact operations and four development separation operations for each of the colors. 
     Development Contact Time and Development Separation Time Determination Processing 
     Next is a detailed description of a method for detecting development contact and separation times according to the present embodiment, with reference to  FIGS. 8 ,  9 ,  10 ,  11 , and  12 .  FIG. 8  is a flowchart of a control program that detects development contact and separation times. The procedure in  FIG. 8  is realized by, for example, the CPU  121  executing a program stored in the ROM  122 .  FIG. 9  shows an overview of, when detecting the development contact timing, states on the intermediate transfer belt  51 , detection signals of the registration detection sensor  56 , and main body sequence operation timing.  FIG. 10  shows an overview of, when detecting the development separation timing, states of the detection pattern  81  on the intermediate transfer belt  51 , detection signals of the registration detection sensor  56 , and main body sequence operation timing.  FIG. 11  shows an overview of the detection pattern  81  used to detect the development contact timing and separation timing. 
     In  FIG. 8 , first detection of whether or not a process cartridge has been exchanged is performed (S 1 ), and when determined that a process cartridge has been exchanged, the stepper motor  91  is started (S 2 ). At this time a timer is also started. The meaning of Step S 1  is that processing is started from Step S 2 , triggered by exchange of a process cartridge. Next, formation of a predetermined detection pattern  81  is started (S 3 ). That is, formation of a latent image of the detection pattern  81  is started. Note that the detection pattern  81  has a width in the main scanning direction that is at least detectable by the registration detection sensor  56 . 
     Parallel with formation of the detection pattern  81 , detection of the detection pattern  81 , which has been made visible by the development roller  64  contacting against the photosensitive drum  61 , is attempted by the registration detection sensor  56  (S 4 ). Detection is “attempted” because the detection pattern  81  is not developed, and cannot be detected, until the development roller  64  contacts against the photosensitive drum  61 . That is, part of the latent image of the detection pattern  81  is developed. If the detection pattern  81  is successfully detected, the timer started in Step S 2  is immediately stopped. Then, once the stepper motor  91  has been rotated by the predetermined number of steps to the full-color contact state, the stepper motor  91  is stopped in that state (S 5 ). Next, the development contact completion passed time As measured by the timer is stored in a memory or the like (S 6 ). With the above processing, the leading edge of the detection pattern  81  is detected, the development contact completion passed time As is measured, and so the development contact time Xs can be obtained. 
     Next, from the full-color contact state, the stepper motor  91 , which changes the position of the development roller  64 , is started (S 7 ), and parallel with this, formation of the latent image of the detection pattern  81  is started (S 8 ). Note that the stepper motor  91  may also be continuously driven, and formation of the detection pattern  81  continued, from the prior step S 3 , and in that case S 7  and S 8  can be omitted. Parallel with this, detection of the trailing edge of the visible image of the detection pattern  81  by the registration detection sensor  56  is attempted (S 9 ). The trailing edge of the detection pattern  81  indicates the position, in other words, the timing, at which development of the electrostatic latent image of the detection pattern  81  is no longer possible due to the development roller  64  separating from the photosensitive drum  61 . Then, once the relationship of the photosensitive drum  61  and the development roller  64  has reached the standby state, the stepper motor  91  is stopped (S 10 ). Based on the signal of the registration detection sensor  56  that performed the detection above, the development separation completion passed time (separation time) Cs from starting of the stepper motor  91  until the detection pattern  81  can no longer be detected is stored (S 11 ). With the above processing, the trailing edge of the detection pattern is detected, the development separation completion passed time Cs is measured, and so the development separation time Ys can be obtained. 
     As described above, measurement of the contact time As and the separation time Cs is carried out in each station S (S 12 ). When measurement is finished, based on the longest development contact time max (Xs) among all stations, the drive timing at which the stepper motor  91  is started from the standby state and the drive speed of the stepper motor  91  are adjusted. This adjustment is performed specifically by adjusting the drive speed of the stepper motor  91  such that the max (Xs) becomes the margin time shown in  FIG. 24 . However, because there is a range of speeds that can be adopted for the stepper motor  91 , when it is necessary to deviate from that range and set a slower or faster speed, the drive start timing also is controlled to correspond to that speed (S 13 ). 
     Specifically, where the margin time is Tm 1 , and the ordinary drive speed of the stepper motor  91  during contact is Vr 1 , a relationship Vr=(Vr 1 ×Tm 1 )/max(Xs) may be adopted as a post-adjustment driving speed Vr. However, when the motor speed range is set to at least Vmn and not more than Vmx, if Vr&lt;Vmn, the speed of the stepper motor  91  is set to a minimum speed of Vmn. In that case, the development roller contacts at a timing earlier by (Vmn×max(Xs)−Vr 1 ×Tm 1 )/Vmn. This is not a problem for image forming and therefore may be allowed, but it is desirable that the start of driving of the stepper motor  91  is delayed by this amount of time. The reason for this is that such a scheme is suitable for the initial objective of preventing wearing out of the photosensitive drum  61 . 
     Also, based on the shortest development separation time min (Ys) among all stations, the drive timing at which the stepper motor  91  is started from the full-color contact state and the drive speed of the stepper motor  91  are both adjusted (S 13 ). 
     Specifically, the time needed from starting driving of the motor for separation until separation is complete is Tm 2 , and the ordinary drive speed of the stepper motor  91  during separation is Vr 2 . With the drive speed Vr after adjustment set to Vr 2 , the start timing is made earlier. The new start timing is adjusted such that the development roller  64  of the station that separates earliest (that is, with the shortest development separation time) separates at the timing that the image forming guarantee time ends. That is, the new start timing is adjusted such that the start timing of the stepper motor  91  is made earlier by a time obtained by subtracting from min(Ys) the time from starting driving of the stepper motor  91  in the full-color contact state until the timing that the color image forming guarantee time ends. Of course, the time that the development roller  64  and the photosensitive drum  61  are in contact is shorter as the motor drive speed increases, so Vr may also be set to Vmx. In that case, the start timing of the stepper motor  91  will be accelerated by a lesser amount, to the extent of that difference in speed. 
     Detection and Adjustment of Development Contact Time 
     Control to detect the development contact timing and measure the development contact time will be described in detail with reference to  FIG. 9 . In cam diagram  1204  in  FIG. 9 , the difference in detection times caused by the phase difference between the cams of each station is compensated. That is, in this diagram the phases of other stations are matched to the phase of the station  1  in the standby state. As shown in  FIG. 9 , a signal that starts driving of the stepper motor  91 , which is the drive source of the contact/separation mechanism of the development roller  64 , is output (t 11 ). Afterward, in the period until contact completes (t 14 ) (interval A) in the cam diagram, the electrostatic latent image of the detection pattern  81  is formed on the photosensitive drum  61 . In  FIG. 9 , in the cam diagram, latent image formation is started at the timing of contact start (t 12 ), but also may be started at timing t 11 . This detection pattern  81  is formed on the photosensitive drum  61  as an electrostatic latent image, but when the development roller  64  contacts against the photosensitive drum  61  (t 131 , t 132 , t 133 , and t 134 ), the electrostatic latent image on the photosensitive drum  61  is made visible as a visible image. The detection pattern  81  made visible is detected with the registration detection sensor  56 . The development contact time (As) from the start of stepper motor  91  driving until the detection pattern  81  is detected by the registration detection sensor  56  is measured for the process cartridge of each station, and the respective development contact times As are fed back to the image forming control unit  12 . The start timing of the stepper motor  91  is determined according to the longest time among the respective development contact times. In  FIG. 9 , the development contact time A 4  of the station  4  is longest. Consequently, using station  4  as a reference, the speed and if necessary the start timing of the stepper motor  91  is adjusted so as to shift the timing t 134  when the development roller  64  contacts in the station  4  to the image forming guarantee time start timing t 14 . That is, the cam diagram  1204  is shifted to the dotted line  1204 ′. Therefore, in the cam diagram, because development contact is completed at the timing t 16 , the stepper motor  91  stops at the subsequent timing t 17 . Since the number of driving steps determines the timing of stoppage, the stoppage timing changes according to speed adjustment, but there is no particular change in control. 
     Detection and Adjustment of Development Separation Time 
     Control to detect the development separation timing will be described in detail with reference to  FIG. 10 . Detection of the development separation timing is performed immediately after the development contact time is measured, so the state in which the development roller  64  has contacted against the photosensitive drum  61  (the full-color state) is the state when started. In cam diagram  1304  in  FIG. 10  as well, the difference in detection times caused by the phase difference between the cams of each station is compensated. When a signal that starts driving of the stepper motor  91  is output (t 21 ), in the period from the start of separation of the development roller  64  (t 22 ) until separation completes (t 24 ) (interval B) in the cam diagram, the detection pattern  81  is formed as an electrostatic latent image on the photosensitive drum  61 . The detection pattern  81  is made visible as a visible image (a toner-developed image), but when the development roller  64  separates from the photosensitive drum  61  the detection pattern  81  becomes an electrostatic latent image, and can no longer be detected by the registration detection sensor  56 . Consequently, the development contact time (Cs) from the start of driving of the stepper motor  91 , which is the drive source, until the registration detection sensor  56  can no longer detect the detection pattern  81  is measured for the process cartridge of each station. Then, both or either one of the start timing and the drive speed of the stepper motor  91  is adjusted in coordination with the station having the longest measured time. In the example in  FIG. 10 , the detection timing of the trailing edge of the detection pattern  81  is, in order from the station  1 , timings t 221 , t 222 , t 223 , and t 23 . The detection pattern  81  of the station  4  is shown by way of example. Using the shortest development separation time C 4  as a reference, the drive start timing of the stepper motor  91  is advanced by time P 3  such that the timing t 221  moves to the timing t 22 . However, in the example in  FIG. 10  the drive speed of the stepper motor  91  also is increased. 
     Next is a detailed description of the detection pattern  81  used when measuring the development contact time and the development separation time, with reference to  FIG. 11 . As shown in  FIG. 11 , it is sufficient that the width of the detection pattern  81  is in a range detectable by the registration detection sensor  56  (about 10 mm), and the length of the detection pattern  81  includes the range of interval A on the development contact side, and includes the range of interval B on the development separation side. Also, the detection pattern  81  is preferably a solid image in the forming range of the detection pattern  81  such that the development contact timing and the separation timing can be precisely detected. 
     As described above, in the combination of the main body and the process cartridge that is actually used, it is possible to measure the development contact time and the development separation time. Therefore, when an image signal has been sent out to the main body, by starting the stepper motor  91  at a timing based on the measured development contact time and development separation time, it is possible to perform control at an optimal timing for an image guarantee region ( FIG. 12 ). In the example in  FIG. 12 , an optimal variation in the timing absorbed by the margin before and after the image forming guarantee time is adopted, and so the time during which the development roller  64  is actually contacted against the photosensitive drum  61  can be brought near the image forming guarantee time. 
     As described above, in the combination of the main body and the process cartridge that is actually used, development contact and separation are performed, and the leading edge and trailing edge of the detection pattern  81  transferred to the intermediate transfer belt  51  are detected with the registration detection sensor  56 . Thus, the development contact timing and the development separation timing in each image forming station can be adaptively controlled for each image forming apparatus. 
     Thus, the margin before and after the image forming guarantee period, which was a problem in the conventional technology, can be shortened, and so shortening of the process cartridge life due to unnecessary contact of the development roller  64  and the photosensitive drum  61  can be prevented. 
     Second Embodiment 
     In the first embodiment, detection patterns  81  of each color are respectively formed on the intermediate transfer belt  51  and detected, and by performing this for each color, a development contact time and a development separation time are measured for each color. Thus, the drive timing and the drive speed of the stepper motor  91  are adjusted. That is, formation and detection of a detection pattern  81  is repeated four times. In the present embodiment, an example is disclosed in which by forming detection patterns  81  of each color on the intermediate transfer belt  51 , and detecting them in windows of each color, the time needed to adjust the drive timing and the drive speed of the stepper motor  91  is shortened. The configuration of the image forming apparatus according to the present embodiment is the same as in the first embodiment, but differs in the procedure for forming and detecting the detection patterns  81  of each color. Accordingly, below mainly those differences will be described. 
     Method for Detecting and Adjusting Development Contact Timing and Separation Timing 
     The method for detecting and adjusting the development contact timing and separation timing in the present embodiment will be described with reference to  FIG. 13 .  FIG. 13  shows detection patterns  81  for detecting contact or separation timing, laser emitting timings when forming the detection patterns  81 , separation cam states, and output waveforms of image detection sensors. In  FIG. 13 , the timings in cam diagrams and so forth are shown without compensation of the phase difference between cams of the respective stations. 
     When control of detection of the development contact timing and the separation timing is started, the stepper motor  91 , which is the drive source of the mechanism for separation from the standby state, is started, and the state changes from development separation to the contact state. The stepper motor  91  stops in the full-color contact state. In coordination with the timing of starting of the stepper motor  91 , the lasers of each image forming station are turned on after passage of respective periods Ty 1 , Tm 1 , Tc 1 , and Tk 1 , and the photosensitive drum  61  is scanned with a laser beam according to the shape of the detection pattern  81 . The shape of the detection pattern  81 , particularly the length in the sub-scanning direction, is the same for each color. This length corresponds to the shape of the latent image, not the visible image developed with toner. The periods Ty 2 , Tm 2 , Tc 2 , and Tk 2  during which the lasers of each image forming station are scanning the photosensitive drum  61  are indefinite periods of the change from the separation state to the contact state, and are predetermined according to the cam diagrams. 
     Next, from the full-color contact state, the stepper motor  91  starts and in each station the development roller  64  sequentially separates, thus changing to the standby state. In coordination with the timing of starting of the stepper motor  91 , the lasers of each image forming station are irradiated onto the photosensitive drum  61  at timings Ty 3 , Tm 3 , Tc 3 , and Tk 3 . Likewise for periods Ty 4 , Tm 4 , Tc 4 , and Tk 4  during which the lasers of each image forming station are on, these are periods in which the separation cam state is in an indefinite region, and are predetermined according to the cam diagrams. 
     As shown in  FIG. 13 , the detection patterns  81  are configured with vertical strip-like patterns disposed in the order Y (yellow), M (magenta), C (cyan), K (black) so as to pass directly below the registration detection sensors  56   a  and  56   b . The diagonal line portions in  FIG. 13  indicate regions where only an electrostatic latent image is formed on the photosensitive drum  61 , and the image is not developed because the development roller  64  has been separated. The detection pattern  81  is formed at a darkness of 100% for each color. 
     In the present embodiment, in order to shorten the time needed for detection of the development contact timing and the separation timing, the development contact and separation timing of each color is detected in one development contact and separation operation. When performing ordinary printing, when development contact is started, the development rollers  64  contact in the order that the stations are disposed, beginning from the upstream side of the intermediate transfer belt  51 . The development rollers  64  contact against the photosensitive drums  61  in the order yellow (Y) image forming station (1st)→magenta (M) image forming station (2nd)→cyan (C) image forming station (3rd)→black (K) image forming station (4th). The timing at which the development roller  64  of each image forming station contacts is controlled such that the leading edges of the image forming regions formed in the image forming units of each color are aligned. That is, the images formed immediately after sequential development contact in each image station are transferred at approximately the same position on the intermediate transfer belt  51 . Consequently, in order to detect the development contact and separation timing of each color in one development contact and separation operation, the rotational speed of the stepper motor  91  is changed. Thus, the ratio of the conveyance speed of the intermediate transfer belt  51  and the drive speed of the stepper motor  91  at which development contact and development separation are performed is changed to a different ratio than when performing ordinary printing. Thus, the position of the detection pattern  81  of each color is offset on the intermediate transfer belt  51 . For example, where only the speed of the stepper motor  91  is set to half to the ordinary speed, twice as much time as in the ordinary case is taken from when development contact occurs in a particular station to when development contact occurs in the next station. During that time, the intermediate transfer belt  51 , which is being conveyed at the ordinary speed, is conveyed past the ordinary transfer position. Therefore, the position of the detection pattern  81  of each color is offset. This position offset occurs even when only increasing the speed of the stepper motor  91 . 
     Note that in the control of detection of the development contact timing and separation timing, the rotational speed of the stepper motor  91  is controlled to be slower than when a printing operation is performed, and in the present embodiment the stepper motor  91  rotates at ½ the rotational speed during a printing operation. Accordingly, it takes twice as much time as in an ordinary case for each development contact completion passed time and separation completion passed time, and this is indicated by the equation stepper motor  91  rotational speed relative value Rv=2. 
     In  FIG. 13 , registration detection sensor output  1301  is the output waveform when the registration detection sensor  56  has detected the detection pattern  81 . The registration detection sensor  56 , by detecting the detection pattern  81 , is able to detect times Ty 5 *, Tm 5 *, Tc 5 *, and Tk 5 * when development contact occurs prior to the contact timing on the cam diagrams. The contact timing on the cam diagrams corresponds to the image forming guarantee time start timing after the margin shown in  FIG. 24 . Also, the registration detection sensor  56  is able to detect times Ty 6 *, Tm 6 *, Tc 6 *, and Tk 6 * (*=a, b) when development separation occurs subsequent to the separation timing on the cam diagrams. The separation timing on the cam diagrams corresponds to the image forming guarantee time end timing shown in  FIG. 24 . Here, * corresponds to detection results by the registration detection sensor  56   a  or  56   b , and in  FIG. 13  indicates detection results common to both registration detection sensors. 
     In the control of detection of the development contact timing and the separation timing, the rotational speed of the stepper motor  91  is changed. Therefore, it is necessary to determine the development contact timing and the separation timing after correcting the detected times Ty 5 *, Tm 5 *, Tc 5 *, and Tk 5 *, and Ty 6 *, Tm 6 *, Tc 6 *, and Tk 6 * (*=a, b). A development contact timing correction amount Tt and a development separation timing correction amount Tr can be calculated from the below formulas.
 
 Tt =MIN( Ty 5 *,Tm 5 *,Tc 5 *,Tk 5*)/ Rv   (2-1)
 
 Tr =MIN( Ty 6 *,Tm 6 *,Tc 6 *,Tk 6*)/ Rv   (2-2)
 
Rv: stepper motor  91  rotational speed relative value *=a, b
 
     As indicated by the above formulas, for the development contact timing, the development contact timing correction amount Tt is calculated from the detected times Ty 5 *, Tm 5 *, Tc 5 *, and Tk 5 * (*=a, b), using the image forming station having the shortest development contact time as a reference. When performing printing, the start timing of the contact/separation mechanism when changing from the standby state to the full-color contact state is delayed by the calculated development contact timing correction amount Tt. 
     For the development separation timing, the development separation timing correction amount Tr is calculated from the detected times Ty 6 *, Tm 6 *, Tc 6 *, and Tk 6 * (*=a, b), using the image forming station having the shortest development contact time as a reference. When performing printing, the start timing of the contact/separation mechanism when changing from the full-color contact state to the standby state is accelerated by the calculated development separation timing correction amount Tr. By starting the contact/separation mechanism at an optimal development contact timing and separation timing, the development contact time can be adjusted to be as short as possible. 
     Note that in the first embodiment, in  FIG. 13 , the timer is started from a timing t 1301 , and for example with respect to the station Y, the time until a timing t 1302  is measured. Here, the time t 1301  to t 1303  is determined by the mechanism or motor drive speed. Accordingly, the same value is obtained by measuring the time t 1301  to t 1302  and by measuring the time t 1302  to t 1303 , as in the present embodiment. Therefore, in the present embodiment, the time t 1301  to t 1302  may be measured as in the first embodiment, or conversely, in the first embodiment the time t 1302  to t 1303  may be measured. Of course, this is also true with respect to a station of a color component other than Y. 
     Next,  FIG. 14  shows a flowchart of the control to detect the development contact timing and the separation timing according to the present embodiment. For example, the CPU  121  of the image forming control unit  12  executing a program stored in the ROM  122  realizes the procedure in  FIG. 14 . As shown in  FIG. 14 , first detection of whether or not a process cartridge has been exchanged is performed (S 1401 ), and when determined that a process cartridge has been exchanged, the processing proceeds to S 1402 . Processing may also be started from S 1402 , triggered by exchange of a process cartridge. In S 1402 , in order to detect the development contact timing and the separation timing, the registration detection sensor  56  or the like is started, and a drive source (excluding the stepper motor  91 ) of the photosensitive drum  61  and the intermediate transfer belt  51  and the like is started (S 1402 ). Then, the detection pattern  81  is formed (S 1403 ), and the stepper motor  91  is driven to start the contact operation of the development roller  64  and the photosensitive drum  61  (S 1404 ). During this step as well, the registration detection sensor  56  attempts to detect the detection pattern  81 . The detection pattern  81  has a width in the sub-scanning direction such that laser scanning ends at the timing (for example, t 1303 ) that the development roller  64  contacts against the photosensitive drum  61  in the cam diagram in  FIG. 13 . When the development roller  64  contacts against the photosensitive drum  61  and the registration detection sensor  56  detects an edge portion, for example the leading edge and the trailing edge, of the detection pattern  81  that has been made visible, the development contact timing correction amount Tt is calculated from a detection result Tx 5  (where x represents Y, M, C, or K), and stored (S 1405 ). Here, as shown in  FIG. 13 , the detection patterns  81  of each color are each isolated patterns, so the respective patterns can be independently measured. 
     Next, the development separation operation is started (S 1406 ), the detection pattern  81 , which has become an electrostatic latent image due to separation of the development roller  64 , is detected by the registration detection sensor  56 , and the development separation timing correction amount Tr is calculated from the detection results, and stored (S 1407 ). An optimal contact timing and separation timing are determined from the detected development contact timing correction amount and development separation timing correction amount (S 1408 ). Here, as shown in  FIG. 13 , the detection patterns  81  of each color are each isolated patterns, so the respective patterns can be independently measured. 
     That is, Tt=MIN(Ty 5 *,Tm 5 *,Tc 5 *,Tk 5 *)/Rv is calculated. The stepper motor  91  is controlled such that the start timing of the contact/separation mechanism when changing from the standby state to the full-color contact state when printing is delayed from the presently set value by the correction value Tt. Also, Tr=MIN(Ty 6 *,Tm 6 *,Tc 6 *,Tk 6 *)/Rv is calculated. The stepper motor  91  is controlled such that the start timing of the contact/separation mechanism when changing from the full-color contact state to the standby state when printing is accelerated from the presently set value by the correction value Tr. 
     Note that in the present embodiment, when performing ordinary printing, only the start timing is changed and not the speed of the stepper motor  91 , but of course the speed may be changed as in the first embodiment. 
     As described above, in the actually used combination of the main body and a process cartridge, development contact and separation are performed, and the leading edge and trailing edge of the detection pattern  81  transferred to the intermediate transfer belt  51  is detected with the registration detection sensor  56 . By doing so, it is possible to accurately know the development contact timing and the development separation timing in each combination. Also, it is possible to detect the contact timing and the separation timing in one development and separation operation, and thus possible to shorten the detection time. Thus, it is possible to optimally correct the development contact timing and the development separation timing in each detected process cartridge. As a result, it is possible to set the time that the development roller  64  is contacted against the photosensitive drum  61  to as short a time as possible, and therefore planing of the photosensitive drum  61  by the development roller  64  can be reduced, and so an image forming apparatus can be provided that is advantageous with respect to process cartridge life. 
     Furthermore, measurement of the stations of each color of a full-color image forming apparatus can be accomplished in a single image forming operation, so it is possible to shorten the adjustment time of development contact and development separation. 
     Modified Example of Second Embodiment 
     Following is a description of a variation of the second embodiment of the image forming apparatus according to the present invention. In the present embodiment, a description is given of a configuration of an image forming apparatus in which the timing of contact or separation of the development roller  64  and the photosensitive drum  61  at a position determined in the main scanning direction is delayed, and development contact timing and separation timing are detected using a detection pattern  81  in which the amount of toner consumption is small. Descriptions given in the first and second embodiments are not repeated here. 
       15   a  to  15   h  in  FIG. 15  show contact and separation states of the photosensitive drum  61  and the development roller  64  in the present example.  15   a  to  15   d  in  FIG. 15  show states of switching from separation to contact.  15   e  to  15   h  in  FIG. 15  show states of switching from contact to separation. As shown in  15   a  to  15   d  in  FIG. 15 , during switching from separation to contact, the photosensitive drum  61  and the development roller  64  abut later at the leading edge side than the trailing edge side in the main scanning direction. The trailing edge side is the side pressed against by the cam  95 , and is the side where the registration detection sensor  56   b  is disposed. Also, as shown  15   e  to  15   h  in  FIG. 15 , during switching from contact to separation, the photosensitive drum  61  and the development roller  64  contact later at the trailing edge side than the leading edge side in the main scanning direction. These slight delays in the development contact and separation timing are determined by the mechanical configuration of the process cartridges and the printer main body. In the present embodiment, the position where the development contact timing is delayed is the leading edge side in the main scanning direction, and the position where the development separation timing is delayed is the trailing edge side in the main scanning direction. 
     Method for Detecting and Optimizing Development Contact Timing and Separation Timing 
     A method for detecting and optimizing the development contact timing and the separation timing in this modified example of the present embodiment will be described with reference to  FIG. 16 .  FIG. 16  shows detection patterns  81  for detecting contact or separation timing, laser emitting timings when forming the detection patterns  81 , cam diagrams, and output waveforms of the registration detection sensors  56 . Compared to the detection patterns  81  in  FIG. 13 , a pattern that passes directly under the registration detection sensor  56   b  is deleted; there is only a pattern that passes directly under the registration detection sensor  56   a  disposed on the leading edge side. 
     Operation itself is substantially the same as in the second embodiment. However, because a detection pattern  81  can only be detected with the registration detection sensor  56   a , only detection results from the registration detection sensor  56   a  are used for determining a correction amount. Accordingly, the correction amounts Tt and Tr are given by the below formulas.
 
 Tt =MIN( Ty 5 a,Tm 5 a,Tc 5 a,Tk 5 a )/ Rv   (2-1′)
 
 Tr =MIN( Ty 6 a,Tm 6 a,Tc 6 a,Tk 6 a )/ Rv   (2-2′)
 
Rv: stepper motor  91  rotational speed relative value
 
     The stepper motor  91  is controlled such that when performing printing, the start timing of the contact/separation mechanism when changing from the standby state to the full-color contact state is delayed from the presently set value by the correction amount Tt. Also, the stepper motor  91  is controlled such that when performing printing, the start timing of the contact/separation mechanism when changing from the full-color contact state to the standby state is accelerated from the presently set value by the correction amount Tr. Otherwise, this modified example is the same as the second embodiment. 
     The reason for adopting such a configuration is that it is sufficient to only detect the development contact timing and the separation timing at the main scanning position, where the margin time is short for image omission. A short margin time for image omission means that there is a greater delay of contact for the development contact time, and a greater acceleration of separation for the development separation time. Accordingly, among the detection patterns  81  in the second embodiment, the pattern on the side where the margin time is long relative to image omission, that is, the pattern on the side of the sensor  56   b , can be omitted. 
     Thus, in an image forming apparatus in which the position where the development contact or separation timing is delayed is determined in the main scanning direction, the detection pattern  81  used to detect the development contact timing, in the region detectable by the registration detection sensor  56 , is formed only at the main scanning position where development contact is most delayed. Also, the detection pattern  81  used to detect the development separation timing, in the region detectable by the registration detection sensor  56 , is formed only at the main scanning position where development separation is most accelerated. By adopting such a configuration, it is possible to reduce the amount of toner consumed, and while losing as little precision as possible, the time that the development roller  64  is contacted against the photosensitive drum  61  can be made as short as possible. 
     Second Modified Example of Second Embodiment 
     Here, a modified example will be disclosed in which only the correction method is changed from the above modified example of the second embodiment. In control of detection of the development contact timing and separation timing, the rotational speed of the stepper motor  91  is changed. Therefore, it is necessary to determine the development contact timing and the separation timing after optimizing the detected times Ty 5   a , Tm 5   a , Tc 5   a , and Tk 5   a , and Ty 6   a , Tm 6   a , Tc 6   a , and Tk 6   a . The development contact timing correction amount Tt and the development separation timing correction amount Tr can be calculated from the below formulas.
 
 Tt =MIN( Ty 5 a,Tm 5 a,Tc 5 a,Tk 5 a )/ Rv−α   (2-1″)
 
 Tr =MIN( Ty 6 a,Tm 6 a,Tc 6 a,Tk 6 a )/ Rv+β   (2-2″)
 
Rv: stepper motor  91  rotational speed relative value
 
     Here, α and β in the formulas represent margin times in consideration of effects of sensor output response and variation in control, variation in development contact and separation delay times, and the like. As in this modified example, some additional time may be considered as a margin for omission of the leading edge and trailing edge of an image. Also, addition and subtraction of this margin time may be likewise applied to other embodiments. 
     Thus, in an image forming apparatus in which the position where the development contact or separation timing is delayed is determined in the main scanning direction, the detection pattern  81  used to detect the development contact timing, in the region detectable by the registration detection sensor  56 , is formed only at the main scanning position where development contact is most delayed. Also, the detection pattern  81  used to detect the development separation timing, in the region detectable by the registration detection sensor  56 , is formed only at the main scanning position where development separation is most accelerated. By adopting such a configuration, it is possible to reduce the amount of toner consumed, and while losing as little precision as possible, the time that the development roller  64  is contacted against the photosensitive drum  61  can be made as short as possible. 
     Third Embodiment 
     Next is a description of an image forming apparatus in which development contact timing and separation timing are detected in a short required time, the time that the development roller  64  is contacted against the photosensitive drum  61  during an image forming operation is kept as short as possible, and thus shortening of the life of a process cartridge is prevented. The configuration of the present embodiment and the principles of control of the start timing and speed of the stepper motor  91  are the same as in the first embodiment and the second embodiment. However, in the present embodiment, the detection pattern  81  is different, and the method for detecting this detection pattern  81  also differs from the other embodiments. Mainly those differences will be described below. 
     Principles of Detecting Development Contact Timing and Development Separation Timing in Present Embodiment 
     Following is a description of a method for detecting the development contact timing and the development separation timing of the development rollers  64  ( 64 Y,  64 M,  64 C, and  64 K) to the photosensitive drums  61  ( 61 Y,  61 M,  61 C, and  61 K) for each image forming station by one development contact and separation operation. 
     First, the detection patterns  81  for detecting the development contact timing and the development separation timing for each image forming station by one development contact operation and separation operation will be described with reference to  FIG. 17 . In order to detect the development contact timing and the development separation timing for each image forming station by one development contact operation and separation operation, it is necessary to start latent image formation of the detection patterns  81  as shown in  FIG. 17  while the development separation state is indefinite, that is, while contact or separation is not yet completed.  FIG. 17  shows the detection patterns  81  formed on the intermediate transfer belt  51 . In the development contact/separation mechanism in the present embodiment, when performing the contact and separation operations of the development roller  64  to the photosensitive drum  61 , contact does not occur throughout the width of the photosensitive drum  61  at the same time, rather, first the trailing edge side of the photosensitive drum  61  contacts, and lastly the leading edge side contacts. That is, when an electrostatic latent image is formed on the photosensitive drum  61  during the indefinite state of the development separation state prior to contact completion, in the detection patterns  81  on the intermediate transfer belt  51  formed due to completion of contact of the development roller  64 , the leading edge side is formed later than the trailing edge side. Since a reliable contact completion timing can be detected by detecting the leading edge side pattern, the detection patterns  81  are formed only on the leading edge side. Accordingly, also with respect to the registration detection sensor  56 , it is sufficient to use only the sensor  56   a . The detection patterns  81  are formed at a position so as to pass directly below the registration detection sensor  56   a  on the leading edge side. One set of detection patterns is configured in the order first image forming station (yellow), second image forming station (magenta), third image forming station (cyan), fourth image forming station (black). This one set of the detection patterns  81  are repeatedly and periodically formed. Note that in the present embodiment, an example is disclosed in which the detection patterns  81  for detecting the timing at which the contact operation and the separation operation complete are formed at a position as described above, but this is only an example, and it is desirable to change this formation according to the configuration of the registration detection sensor  56  or the configuration of the image forming apparatus. 
     Next is a description of principles whereby it is possible to detect the development contact timing and the development separation timing of the development rollers  64  ( 64 Y,  64 M,  64 C, and  64 K) to the photosensitive drums  61  ( 61 Y,  61 M,  61 C, and  61 K) for each image forming station by one development contact and separation operation, with reference to the diagram shown in  FIG. 18 . The diagram in  FIG. 18  shows the process from formation of an electrostatic latent image on the photosensitive drum  61  corresponding to the detection patterns  81  shown in  FIG. 17  on the intermediate transfer belt  51 , to detection with the registration detection sensor  56  of the detection patterns  81  on the intermediate transfer belt  51  formed due to contact. Time is shown on the horizontal axis, and the distance along a path from formation of an electrostatic latent image until a toner image arrives at the position of the registration detection sensor  56  is shown on the vertical axis. Here, taking as an example a method for detecting the development contact timing of the image forming station  1 , is a description of principles for detecting the development contact timing of each image forming station with one development contact operation. 
     When switching the contact/separation state from the separation state (standby state) to the contact state, the stepper motor  91  is started. While the development contact/separation state is indefinite after starting the stepper motor  91 , the electrostatic latent image of the detection patterns  81  shown in  FIG. 17  is repeatedly formed on the photosensitive drum  61 . Where the first exposure start timing of the detection pattern  81  of the image forming station  1  is N 1 , when an electrostatic latent image whose formation was started at timing N 1  has been developed, the toner image thereof passes directly under the registration detection sensor  56  at a timing O 1 , where a time Q 1  has passed since Q 1 . Consequently, a detection window of the image forming station  1  is set before the timing O 1 , for determining that the detection patterns  81  of the image forming station  1  have passed directly under the registration detection sensor  56 . However, the electrostatic latent image that has been exposed on the photosensitive drum  61  at the timing N 1  is not developed, because contact has not been completed at the development timing. Therefore, the detection patterns  81  are not formed on the intermediate transfer belt  51 , and thus cannot be detected by the registration detection sensor  56 . Where the exposure start timing of the detection patterns  81  of the image forming station  1  formed second is N 2 , when the electrostatic latent image formed at timing N 2  has been developed, the toner image thereof passes directly under the registration detection sensor  56  at a timing O 2 , where a time Q 2  has passed since N 2 . Consequently, a detection window of the image forming station  1  is set before the timing O 2 , for determining that the detection patterns  81  of the image forming station  1  have passed directly under the registration detection sensor  56 . The electrostatic latent image exposed on the photosensitive drum  61  at the timing N 2 , because contact is completed at the development timing, is supplied with toner from the development roller  64  and becomes a toner image. The toner image formed on the photosensitive drum  61  is transferred onto the intermediate transfer belt  51 , and detected by the registration detection sensor  56  at timing O 2 . Thus, the development contact timing X 1  of the image forming station  1  is the difference between a passed time A 1  from starting of the stepper motor  91  until the timing O 2  where a detection pattern  81  is detected by the registration detection sensor  56 , and a time B 1 . The time B 1  is the time until the toner image developed in the first station reaches the registration detection sensor  56 , and is given as a fixed value based on the distance and conveyance speed during that period. The time X 1  can be calculated from formula (1) in the first embodiment, in other words:
 
 Xs=As−Bs (msec)  (1)
 
In the present example, the value of s is 1.
 
     While switching detection windows based on the same principle for the remaining image forming stations, development contact timings X 2 , X 3 , and X 4  are calculated by detecting the detection patterns  81 . Thus, the timing detection principle is the same as in the first embodiment. The separation timing also can be determined in the same manner as in the first embodiment, by measuring the development separation completion passed time Cs.
 
 Ys=Cs−Bs (msec)  (2)
 
     In the present embodiment, a detection window for detecting the detection pattern  81  of each toner color is set. The detection window is switched before passing directly under the registration detection sensor  56 . Thus, it is possible to detect the development contact timing of the development rollers  64  ( 64 Y,  64 M,  64 C, and  64 K) to the photosensitive drums  61  ( 61 Y,  61 M,  61 C, and  61 K) for each image forming station by one development contact operation. The separation timing of each image forming station also can be detected by the same principle. That is, it is possible to detect the development contact timing of the development rollers  64  ( 64 Y,  64 M,  64 C, and  64 K) to the photosensitive drums  61  ( 61 Y,  61 M,  61 C, and  61 K) for each image forming station by one development separation operation. Note that “before passing” needs to be determined in advance. Since the timing at which the detection pattern  81  is expected to pass can be roughly estimated, a window of a predetermined time is provided based on that rough estimation, and a timing for that window is determined. Since there may be instances where detection still is not possible, the window is closed after passage of the predetermined time even if detection cannot be performed. This window is a window in figurative terms, and actually, for example, the period in which output signals of the registration detection sensor  56  are monitored serves as a window. 
     Next is a description of the precision of detection of the development contact timing and the development separation timing when using a detection pattern  81 , with reference to  FIG. 18 . A pattern interval H(mm) of the above-described one set is the sum of the pattern width W(mm) and the pattern interval I(mm) of each toner color, and can be calculated from formula (3-1).
 
 H =( W+I )×4(mm)  (3-1)
 
     The interval H(mm) of one set of patterns is the interval (pitch) from detection of the yellow toner pattern of the first set to detection of the yellow toner pattern of the second set, and so the pitch of the patterns of each toner color is the detection precision of the patterns of each color. That is, the detection precision of the development contact timing and the development separation timing of each image forming station corresponds to the pattern interval. For example, when the pattern width is 1 mm and the pattern interval is 1 mm for each color, the detection precision of the development contact timing and the development separation timing of each image forming station is, in terms of conveyance distance, (1+1)×4=8 mm. In this case, if the conveyance speed of the intermediate transfer belt  51  is 16 mm/sec, the detection precision is 0.5 seconds when converted to time. Therefore, in this example, the speed and start timing of the stepper motor  91  can be controlled in 0.5 sec units, and the time that the development roller  64  is contacted against the photosensitive drum  61  can be reduced in 0.5 sec units. 
     Flowchart of Control for Detecting Development Separation Timing 
     Next is a description of the method for controlling detection of the development contact timing and the development separation timing of the development rollers  64  ( 64 Y,  64 M,  64 C, and  64 K) to the photosensitive drums  61  ( 61 Y,  61 M,  61 C, and  61 K) for each image forming station by one development contact and separation operation. 
       FIG. 19  shows a flowchart of control for detecting the development contact timing and the development separation timing for each image forming station by one development contact and separation operation. The sequence (hereinafter, the development contact timing and separation timing detection sequence) shown in  FIG. 19  is executed when a door whereby a process cartridge can be exchanged is closed or when power is turned on. 
     The development contact timing and separation timing detection sequence is stored in the ROM  122  as a control sequence program for detecting the development contact timing and the development separation timing. When the development contact timing and separation timing detection sequence is started, the CPU  121  starts a motor that drives the photosensitive drum  61  and the intermediate transfer belt  51 , and the scanner motor  182 . Also, bias application and the like of the charging bias control unit  183 , the development bias control unit  184 , and the primary transfer bias control unit  185  is performed to start image forming preparation. Next, the stepper motor  91  is rotationally driven forward by a predetermined number of steps in order to start the development contact operation (S 1901 ). When forward rotational driving of the stepper motor  91  starts, the control timer  17  is started (S 1902 ). The stepper motor  91  is started, and while the development contact/separation state is indefinite, repeated formation of an electrostatic latent image of the detection patterns  81  on the photosensitive drum  61  is started (S 1903 ). The detection window of the image forming station  1  is set to immediately before the timing when the electrostatic latent image formed on the photosensitive drum  61  of the image forming station  1  arrives directly below the registration detection sensor  56  (S 1904 ). This timing is determined in advance. Next, the sequence awaits passage of the predetermined time set as the detection window of the image forming station  1  (S 1905 ). 
     After the predetermined time has passed, the electrostatic latent image of the detection pattern  81  formed on the photosensitive drum  61  of the image forming station  1  is expected to arrive directly under the registration detection sensor  56 . Consequently, when the detection pattern  81  is not detected at this timing (S 1906 ), setting is switched to the detection window of the image forming station  2 . Switching is performed after a predetermined time following the window. After setting is switched to the detection window of the image forming station  2 , likewise in the image forming station  2 , when the detection pattern  81  cannot be detected within the detection window, setting is switched to the detection window of the image forming station  3 . After setting is switched to the detection window of the image forming station  3 , likewise in the image forming station  3 , when the detection pattern  81  cannot be detected within the detection window, setting is switched to the detection window of the image forming station  4 . In this way, steps S 1904  to S 1906  are repeatedly executed until the detection pattern  81  is detected within the detection window. 
     When the detection pattern  81  was detected at the timing that the electrostatic latent image of the detection pattern  81  formed on the photosensitive drum  61  of the image forming station  1  arrives directly under the registration detection sensor  56  after passage of the predetermined time (S 1906 ), the sequence moves to S 1907 . In Step S 1907 , a development contact completion passed time A 1 (msec) from starting of the control timer  17  until the detection pattern  81  of the image forming station  1  is detected in the detection window of the image forming station  1  by the registration detection sensor  56  is acquired. When the development contact completion passed time As(msec) of each image forming station is not detected (S 1908 ), setting is switched to the detection window of the image forming station  2 . In this way, switching of the detection window is repeatedly executed in steps S 1904  to S 1908  until the development contact completion passed time As(msec) of each image forming station is detected. When the development contact completion passed time As(msec) of each image forming station is detected (S 1908 ), the stepper motor  91  is again rotationally driven forward by a predetermined number of steps in order to switch the development contact/separation state from the contact state to the separation state (S 1909 ). 
     When forward rotational driving of the stepper motor  91  starts, the control timer  17  is started (S 1910 ). For this principle, the detection pattern  81  of  FIG. 17  is applied to the procedure of separation timing detection in the first embodiment. The detection window of the image forming station  1  is set to immediately before the timing when the electrostatic latent image formed on the photosensitive drum  61  of the image forming station  1  arrives directly below the registration detection sensor  56  (S 1911 ). Next, the sequence awaits passage of the predetermined time set as the detection window of the image forming station  1  (S 1912 ). After passage of the predetermined time, the electrostatic latent image of the detection pattern  81  formed on the photosensitive drum  61  of the image forming station  1  arrives directly under the registration detection sensor  56 . When the detection pattern  81  is detected at that timing (S 1913 ), the setting is switched to the detection window of the image forming station  2 . After the setting is switched to the detection window of the image forming station  2 , likewise in the image forming station  2 , when the detection pattern  81  is detected within the detection window, the setting is switched to the detection window of the image forming station  3 . After the setting is switched to the detection window of the image forming station  3 , likewise in the image forming station  3 , when the detection pattern  81  is detected within the detection window, the setting is switched to the detection window of the image forming station  4 . In this way, steps S 1911  to S 1913  are repeatedly executed until the detection pattern  81  is no longer detected within the detection window. 
     When the detection pattern  81  is not detected at the timing that the electrostatic latent image of the detection pattern  81  formed on the photosensitive drum  61  of the image forming station  1  arrives directly under the registration detection sensor  56  after passage of the predetermined time (S 1913 ), the sequence moves to S 1914 . In step S 1914 , a development contact/separation passed time C 1 (msec) is acquired. The development contact/separation passed time C 1  is the time from starting the control timer  17  to the timing when the detection pattern  81  of the image forming station  1  is finally detected with the registration detection sensor  56  in the detection window of the image forming station  1 . When the development contact/separation passed time Cs(msec) for each image forming station is not detected (S 1915 ), the setting is switched to the detection window of the image forming station  2 . In this way, switching of the detection window in steps S 1911  to S 1915  is repeatedly executed until the development contact/separation passed time Cs(msec) for each image forming station is detected. When the development contact/separation passed time Cs(msec) for each image forming station is detected (S 1915 ), the development contact timing Xs(msec) is calculated from formula (1) and stored in the RAM (S 1916 ). Also, the development separation timing Ys(msec) is calculated from formula (2) and stored in the RAM (S 1917 ). With this processing, it is possible to detect the development contact timing and the development separation timing of the development rollers  64  ( 64 Y,  64 M,  64 C, and  64 K) to the photosensitive drums  61  ( 61 Y,  61 M,  61 C, and  61 K) for each image forming station by one development contact and separation operation. 
     Correction of Development Contact/Separation Timing 
     Next is a description of a method for correcting the development contact/separation timing when printing, based on the development contact timing Xs and the development separation timing Ys of each image forming station calculated by the development contact timing and separation timing detection sequence. This description is given with reference to the timing chart in  FIG. 20 . 
     The broken lines in  FIG. 20  indicate the timing when the development roller  64  and the photosensitive drum  61  are contacted and separated for each image forming station when the development contact timing and separation timing detection sequence has been performed. The solid lines indicate the latest timing when the development roller  64  and the photosensitive drum  61  contact when variation has been considered, and the earliest timing when the development roller  64  and the photosensitive drum  61  separate when variation has been considered. Xs and Xy prior to correction in  FIG. 20  indicate the development contact timing Xs(msec) and the development separation timing Ys(msec) of each image forming station calculated by the development contact timing and separation timing detection sequence. Ls (where the value of s is 1 to 4) prior to correction in  FIG. 20  indicates the latest timing when the development roller  64  and the photosensitive drum  61  contact when variation has been considered. Ps indicates the earliest timing when the development roller  64  and the photosensitive drum  61  separate when variation has been considered. 
     Below is a method for correcting the development contact timing in a printing operation. 
     (1) A variation error Ds for each image forming station is calculated from the difference of the development contact timing Xs(msec) and Ls(msec) calculated by the development contact timing and separation timing detection sequence. 
     (2) Among the variation errors Ds for each image forming station, a development contact correction time Dmin(msec) serving as the smallest variation error is determined. 
     (3) The start timing of the stepper motor  91  is delayed by the development contact correction time Dmin(msec). 
     By delaying the start timing of the stepper motor  91  as described above, it is possible to adopt an optimal contact timing for each station. In  FIG. 20 , an error variation D 1 (msec) of the image forming station  1  is smallest, so by delaying the start timing (contact start) of the stepper motor  91  by D 1 (msec), contact can be completed at an optimal timing. 
     Next, below is a method for correcting the development separation timing in a printing operation. 
     (4) A variation error Es for each image forming station is calculated from the difference of the development separation timing Ys(msec) and Ps(msec) calculated by the development contact timing and separation timing detection sequence. 
     (5) Among the variation errors Es for each image forming station, a development contact correction time Emin(msec) serving as the smallest variation error is determined. 
     (6) The start timing of the stepper motor  91  is accelerated by the development contact correction time Emin(msec). 
     By accelerating the start timing of the stepper motor  91  as described above, it is possible to adopt an optimal separation timing for each station. In  FIG. 20 , an error variation E 4 (msec) of the image forming station  4  is smallest, so be delaying the start timing (contact start) of the stepper motor  91  by E 4 (msec), contact can be completed at an optimal timing. 
     Here, a plurality of stations are controlled with one drive source, so the contact timing is controlled in coordination with the smallest error variation D 1 (msec), but when the respective stations have independent drive sources, control of an optimal contact timing in coordination with the detection results of the respective stations is possible. Likewise, the separation timing is controlled in coordination with the smallest error variation E 4 (msec), but when the respective stations have independent drive sources, control of an optimal contact timing in coordination with the detection results of the respective stations is possible. 
     Furthermore, coordination of the contact timing and the separation timing with the image forming guarantee time was described, but it is possible, for example, to have a receiving means for receiving information regarding the size of an image formed from a controller, and when an engine knows the size of images to be formed in each color, to coordinate the contact timing and the separation timing with the size of the images to be formed in the respective colors, rather than with the image forming guarantee time. 
     When the respective stations can be independently driven in this way, the contact time can be optimally controlled in each station, so wear of the development roller  64  and the photosensitive drum  61  can be reduced. Also, because the size of the images to be formed in the respective colors is known, the contact time can be controlled in coordination with the images to be formed, so wear of the development roller  64  and the photosensitive drum  61  can be reduced even further. 
     As described above, in any combination of the development contact/separation mechanism and process cartridges P (PY, PM, PC, and PK) included in the main body apparatus  2 , latent image patterns are repeatedly formed such that the detection patterns  81  of different colors are in contact without overlapping. The registration detection sensor  56  can detect the patterns on the intermediate transfer belt  51  after contact and separation are completed. The time between the start timing of the stepper motor  91  and the detection timing of the detection pattern  81  is measured in windows of the respective stations. Thus, it is possible to detect an optimal development contact timing and separation start timing in a minimal amount of required time. Thus, the development contact timing and the separation start timing can be corrected such that the time of contact is no longer than necessary. As a result, it is possible to provide an image forming apparatus in which wear of the development roller  64  and the photosensitive drum  61  can be reduced, and thus shortening of the life of process cartridges can be prevented. 
     Fourth Embodiment 
     In the fourth embodiment, a description is given of an image forming apparatus and control method thereof in which wear of the photosensitive drum  61  that contacts the intermediate transfer belt  51  due to attractive force occurring between the intermediate transfer belt  51  and the photosensitive drum  61  is prevented, thus extending the life of the photosensitive drum  61 . A charging bias is applied to the photosensitive drum  61  prior to image forming (including a margin) to charge the photosensitive drum  61  even while not contacted with the development roller  64 . The intermediate transfer belt  51  is also charged by a transfer bias applied during transfer of a toner image. Since these loads act in the direction of attraction to each other, even when image forming is not being performed, the intermediate transfer belt  51  and the photosensitive drum  61  contact each other due to charging, causing wear of the surface of the photosensitive drum  61  if there is a speed difference between them. In the present embodiment, this is prevented. Also, the present embodiment may be combined with the first to third embodiments, but here, by way of example, a description is given of an image forming apparatus operating in the development contact/separation state as shown in  FIG. 24 . 
     Timing of Application of Transfer Bias and Charging Bias 
     The timing of application of the transfer bias and the charging bias according to the present embodiment will be described in detail with reference to  FIG. 21 .  FIG. 21  shows an overview of a separation cam  80   a  in the yellow (Y) image forming station (1st), and the timing at which the transfer bias and the charging bias are applied. 
     As shown in  FIG. 21 , the separation cam  80   a  is rotationally driven, and the region while the development roller  64  is moving from the separation state to the contact state with the photosensitive drum  61  is in a so-called indefinite state. In the indefinite state, the contact timing becomes offset. Thus, it is necessary to apply the transfer bias and the charging bias early, with some margin (timing e) from the time (c) when the indefinite region is started. This is in order to prevent toner from being transferred to the photosensitive drum  61  when the development roller  64  is contacted against the photosensitive drum  61 . In the main body and process cartridge where variation in components or assembly actually occurs, development contact occurs (g) after passage of a fixed time from the time (c) when the indefinite region is started. Therefore, the time (e to g) from application of the transfer bias and the charging bias to contact of the development roller  64  against the photosensitive drum  61  becomes long, and during that time, a large attractive force occurs between the intermediate transfer belt  51  and the photosensitive drum  61 . This accelerates planing of the photosensitive drum  61 . 
     Also, the same sort of variation is present in the region in which the development roller  64  is moving from the contact state to the separation state from the photosensitive drum  61 . Therefore, it is necessary to stop the transfer bias and the charging bias with some margin (timing f) from the time (d) when the indefinite region is completed. In the main body and process cartridge where variation in components or assembly actually occurs, development separation occurs (h) after passage of a fixed time from the time (b) when the indefinite region is started. Therefore, the time (h to f) from separation of the development roller  64  from the photosensitive drum  61  to stopping of the transfer bias and the charging bias becomes long, and during that time, a large attractive force occurs between the intermediate transfer belt  51  and the photosensitive drum  61 . This accelerates planing of the photosensitive drum  61 . 
     When the transfer bias and the charging bias are applied in the state in which the development roller  64  is separated from the photosensitive drum  61 , a large attractive force occurs between the intermediate transfer belt  51  and the photosensitive drum  61 . This phenomenon will be described with focus on a torque change of the drive source of the intermediate transfer belt  51 .  FIG. 22  shows an overview of the torque change of the drive source of the intermediate transfer belt  51 , the contact timing and separation timing of the development roller  64 , the timing of application of the transfer bias and charging bias, and the start state of the drive source of the intermediate transfer belt  51 , process cartridge, and contact/separation mechanism. 
       FIG. 22  illustrates operation from sending of an image signal to the main body to printing of an image. As shown in  FIG. 22 , when the drive source of the intermediate transfer belt  51  and a drive motor provided for each process cartridge are started (p), a small amount of torque occurs in the drive source of the intermediate transfer belt  51 . When the transfer bias and the charging bias are applied (e), a large attractive force occurs between the intermediate transfer belt  51  and the photosensitive drum  61 , a large torque occurs in the drive source of the intermediate transfer belt  51 , and planing of the photosensitive drum  61  is accelerated. Even when a large attractive force occurs in the intermediate transfer belt  51  and the photosensitive drum  61 , if the speed of the intermediate transfer belt  51  and the photosensitive drum  61  is the same, a large torque will not occur and so planing of the photosensitive drum  61  will not occur. However, a speed difference in the drive speed of the intermediate transfer belt  51  and the photosensitive drum  61  occurs due to variation in the diameter of the photosensitive drum  61 , variation in thickness of the intermediate transfer belt  51 , variation in the diameter of the drive roller  53  of the intermediate transfer belt  51 , and so forth. Therefore a large torque occurs, and so planing of the photosensitive drum  61  occurs. In a state in which this large torque is occurring, the stepper motor  91  serving as the drive source of the contact/separation mechanism is driven, and the development roller  64  contacts against the photosensitive drum  61  ( g ). Thus, because a low-friction substance such as toner is present between the intermediate transfer belt  51  and the photosensitive drum  61 , the torque occurring in the drive source of the intermediate transfer belt  51  is small. That is, in a state in which the development roller  64  is contacted against the photosensitive drum  61 , even if there is a speed difference between the intermediate transfer belt  51  and the photosensitive drum  61 , the intermediate transfer belt  51  and the photosensitive drum  61  slide due to the presence of toner therebetween, and so there is little occurrence of planing of the photosensitive drum  61 . 
     Next is a description of operation from when printing of an image is ended to stoppage of the main body. In a state in which the development roller  64  is contacted against the photosensitive drum  61 , the stepper motor  91  is driven, and the development roller  64  separates from the photosensitive drum  61  ( h ). As a result, there is no longer a low-friction substance such as toner interposed between the intermediate transfer belt  51  and the photosensitive drum  61 , so a large torque occurs in the drive source of the intermediate transfer belt  51 , and planing of the photosensitive drum  61  is accelerated. When the transfer bias and the charging bias are stopped (f), there is no longer an attractive force between the intermediate transfer belt  51  and the photosensitive drum  61 , so there is little torque in the drive source of the intermediate transfer belt  51 . Finally, the drive source of the intermediate transfer belt  51  and the drive motor of the process cartridge are stopped. 
     In the periods (interval X and interval Y) in which a large torque is occurring in the drive source of the intermediate transfer belt  51 , a speed difference exists in the state in which the intermediate transfer belt  51  and the photosensitive drum  61  are attracted. Therefore, sliding wear occurs between the intermediate transfer belt  51  and the photosensitive drum  61 , so planing of the photosensitive drum  61  is accelerated. Also, the problem of the time that the transfer bias and the charging bias are applied being longer than the time that the development roller  64  is contacted against the photosensitive drum  61  occurs similarly in each image forming station. Consequently, the development contact or separation timing in each image forming station is detected, and the application time of the transfer bias and the charging bias in each image forming station are respectively adaptively adjusted. 
     Detection of Development Contact Timing and Separation Timing, and Bias Application Timing Method 
     Next is a detailed description of method for detecting and optimizing the development contact timing and separation timing according to the present example, with reference to  FIG. 23 .  FIG. 23  is a flowchart of a control program for detecting the development contact timing and separation timing. In the present embodiment, the bias application timing is adjusted in the same manner as in the first embodiment. That is, in the second and third embodiments, the margin of the development contact/separation timing was shortened, and here, in the same manner the margin of the timing for application of the charging bias and the transfer bias is shortened. 
     As shown in  FIG. 23 , first detection of whether or not a process cartridge has been exchanged is performed (S 2301 ). When determined that a process cartridge has been exchanged, control to detect the development contact timing and separation timing is started, and a drive source (excluding the stepper motor  91 ) of the photosensitive drum  61  and the intermediate transfer belt  51  and the like is started (S 2302 ). Then, the detection pattern  81  is formed (S 2303 ), and by starting the stepper motor  91 , the operation of contacting the development roller  64  against the photosensitive drum  61  is started (S 2304 ). At this time, a timer is started at the drive start timing of the stepper motor  91 . The detection pattern  81  made visible by the development roller  64  contacting against the photosensitive drum  61  is detected by the registration detection sensor  56  (S 2305 ), and the stepper motor  91  is stopped in the full-color state (S 2306 ). The timer is stopped when the leading edge of the detection pattern  81  is detected. The time (contact time) thus measured from starting the stepper motor  91  to detection is stored (S 2307 ). 
     On the other hand, the stepper motor  91  is started from the full-color contact state, in which the development roller  64  is contacted (S 2308 ). Here a timer is started at the drive start timing of the stepper motor  91 . The detection pattern  81  that has become an electrostatic latent image due to the development roller  64  separating is detected by the registration detection sensor  56  (S 2309 ), and the stepper motor  91  is stopped in the standby state (S 2310 ). The timer is stopped when the trailing edge of the detection pattern  81  is detected. The time (separation time) thus measured from starting the stepper motor  91  until detection is no longer possible is stored (S 2311 ). 
     Thus, the contact time and the separation time are detected in each station (S 2312 ). The manner of this operation is the same as in the first embodiment. The timing when the transfer bias and the charging bias are applied is changed in accordance with the contact time of each station. 
     The timing is determined such that in each station, the time from application of the transfer bias and the charging bias to contact of the development roller  64  against the photosensitive drum  61  is as short as possible. The timing when the transfer bias and the charging bias are stopped is changed in accordance with the separation time of each station. The timing is determined such that in each station, the time from separation of the development roller  64  from the photosensitive drum  61  to stoppage of the transfer bias and the charging bias is as short as possible (S 2313 ). That is, this timing adjustment is performed such that the intervals X and Y in  FIG. 22  are as short as possible. In order to do so, in the same manner as in the first and third embodiments, the development contact timing and the development separation timing are determined, and application and stoppage of bias are respectively performed in accordance with that timing. 
     For example, the values Xs=As−Bs and Ys=Cs−Bs calculated in the first embodiment can be used for the bias timing offset amount. That is, Xs can delay the bias application timing from the predetermined timing e in  FIG. 22 . Also, the bias application timing can be accelerated by Ys from the predetermined timing f in  FIG. 22 . That is, the bias timing is adjusted by the adjustment amount obtained when adjusting the drive timing of the development roller  64  (or by the same control amount, or by the same time). 
     Therefore, rather than performing the time measurement only for control in the present embodiment, it is possible to use the times As and Cs measured by control of the drive timing of the stepper motor  91  for adjustment of the development contact timing and the development separation timing performed in the first to third embodiments. Also, the time measurement according to the second embodiment is the time itself of the detection pattern  81 , and thus differs from the first embodiment, but as described in the second embodiment, these are values that can be converted to each other, so it is also possible to use the time measured in the manner described in the second embodiment. 
     As described above, in the combination of the main body and the process cartridge that is actually used, development contact and separation are performed, and the leading edge and trailing edge of the detection pattern  81  transferred onto the intermediate transfer belt  51  are detected with the registration detection sensor  56 . By adopting such a configuration, it is possible to accurately know the development contact time and the development separation time in each combination. Thus, when an image signal has been sent to the main body, it is possible to apply the transfer bias and the charging bias such that the transfer bias and the charging bias are applied for as short a time as possible relative to the detected development contact time of each station. 
     Thus, it is possible to optimally correct the application timing and the stop timing of the transfer bias and the charging bias according to the development separation timing. As a result, it is possible to apply the transfer bias and the charging bias for a minimal amount of time relative to the time that the development roller  64  is contacted against the photosensitive drum  61 . Therefore, it is possible to provide a means whereby it is possible to reduce planing of the photosensitive drum  61 , which is beneficial for the process cartridge life. 
     In the description of the present example, the detection pattern  81  is formed as an electrostatic latent image on the photosensitive drum  61 , in the period from the start of contact of the development roller  64  to completion of contact, and in the period from the start of separation of the development roller  64  to completion of separation. However, the detection pattern  81  may also be formed as an electrostatic latent image on the photosensitive drum  61  in the period from the start of contact to completion of separation. 
     The present invention is also applicable to a system configured with a plurality of devices (for example, such as a host computer, an interface device, a reader, a printer, and so forth), and also applicable to an apparatus constituted of single device (for example, such as a copier or a facsimile apparatus). Each step of the present invention can be realized by executing software (a program) acquired via a network or various recording media with a processing apparatus (such as a CPU or processor) such as a personal computer. 
     Other Embodiments 
     Aspects of the present invention can also be realized by a computer of a system or apparatus (or devices such as a CPU or MPU) that reads out and executes a program recorded on a memory device to perform the functions of the above-described embodiment(s), and by a method, the steps of which are performed by a computer of a system or apparatus by, for example, reading out and executing a program recorded on a memory device to perform the functions of the above-described embodiment(s). For this purpose, the program is provided to the computer for example via a network or from a recording medium of various types serving as the memory device (for example, computer-readable medium). 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application Nos. 2009-141621, filed Jun. 12, 2009 and 2010-041005, filed Feb. 25, 2010, which are hereby incorporated by reference herein in their entirety.