Patent Publication Number: US-7907853-B2

Title: Image forming apparatus executing calibration and service person call

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 USC §119 to Japanese Patent Application No. 2006-169396 filed on Jun. 19, 2006, the entire contents of which are hereby incorporating by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus, such as a printer, a copier, a facsimile, a complex machine including functions of these apparatuses, etc., employing an electro-photographic system. 
     2. Discussion of the Background Art 
     As an electro-photograph engine employed in an image forming apparatus is demanded to have high resolution and to operate at high speed, a plurality of exposure devices are installed or an exposure device having a plurality of emission points is employed. As a result, a number of electronic devices for exposure is necessarily increased, recently. As an exposure device, a semiconductor laser is generally used. 
     However, since being significantly weak, the device is difficult to handle. As prior-arts, JPA Nos. 2000-278471 and 8-336055 are exemplified. 
     SUMMARY OF THE PRESENT INVENTION 
     Accordingly, an object of the present invention is to improve such background arts technologies and provides a new and novel image forming apparatus. Such a new and novel image forming apparatus includes a condition determining device that calculates a deviation amount of image data from a normal condition and determines if the image forming apparatus is in an abnormal condition. An abnormal section specifying device specifies an abnormal section in the image forming apparatus based on a condition of the image forming apparatus. An image processing device executes image processing for abnormal use in accordance with an output of the abnormal section specifying device when the image data condition determining device determines that the image forming apparatus is in an abnormal condition. A service person call output device outputs a service person call signal indicative of calling a service person to a center when the image data condition determining device determines that the image forming apparatus is in an abnormal condition. 
     In another embodiment, the condition determining device determines a deviation amount from the normal condition based on a performance of image color reproduction. The image processing device determines if an abnormality is present in an exposure system of the image forming apparatus when the condition determining device determines that the image forming apparatus is in the abnormal condition. The image processing device executes calibration for abnormal use based on the result of the abnormality presence determination. 
     In yet another embodiment, the condition determining device determines a deviation amount from the normal condition based on granularity of an image. The image processing device determines if an abnormality is present in an exposure system when the condition determining device determines that the image forming apparatus is in the abnormal condition. The image processing device executes halftone processing for abnormal use based on the result of the abnormality presence determination. 
     In yet another embodiment, the calibration includes one of output density correction processing for maintaining a gray balance and correction processing for correcting an exposure position. 
     In yet another embodiment, the halftone processing for abnormal use at least includes one of switching processing for decreasing a frequency of an image to be formed and switching processing for changing a screen angle. 
     In yet another embodiment, a career holding device holds a career of the deviation amount calculated by the condition determining device. The service person call output device outputs service person call information in accordance with the career information of the career holding device. 
     In yet another embodiment, the career information includes one of the deviation amount calculated by the condition determining device, a calibration interval calculated from a date when the image processing device executes previous calibration, and the total number of outputs of recording mediums when the calibration is executed. One of the deviation amount, the calibration interval, and the total number of outputs is segmentized into a prescribed number of groups in an order of a volume of the information, and the service person call is generated when a frequency of a prescribed group exceeds a prescribed reference. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  illustrates an exemplary image forming apparatus according to one embodiment of the present invention; 
         FIG. 2  illustrates an exemplary test pattern image; 
         FIGS. 3A and 3B  collectively illustrates an exemplary manner of reading the test pattern image using an optical sensor; 
         FIGS. 4A and 4B  collectively illustrates an exemplary sequence of a control operation of the image forming apparatus of  FIG. 1 ; 
         FIGS. 5A and 5B  collectively illustrates an exemplary graph showing an exemplary relation between a deviation amount and a frequency; 
         FIGS. 6A and 6B  collectively illustrates an exemplary graph showing an exemplary relation between a number of output sheets and a frequency; 
         FIGS. 7A and 7B  collectively illustrates an exemplary graph showing an exemplary relation between an interval and a frequency; 
         FIG. 8  illustrates an exemplary graph showing an exemplary relation between a driving current and light intensity of an element of a semiconductor laser; 
         FIG. 9  illustrates an exemplary relation between an input and an output of an image; 
         FIG. 10  illustrates an exemplary sequence for determining a manner and a formula of calculating a calculation value (e.g. a Mahalabinos&#39; generalized distance) using a Mahalanobis-Taguchi System (hereinafter “MTS”) method. 
         FIG. 11  illustrates an exemplary sequence for calculating a calculation value at an optional time; 
         FIG. 12  illustrates an exemplary exposure device and its surroundings using dual beams; 
         FIG. 13  illustrates an exemplary adjusting mechanism for a collimator unit shown in  FIG. 12 ; 
         FIGS. 14A and 14B  collectively illustrates an exemplary image processing for abnormal use; 
         FIGS. 15A and 15B  collectively illustrates another exemplary image processing for abnormal use; 
         FIGS. 16 and 17  illustrate exemplary tables each showing configuration of conditional data obtained from an image forming apparatus; 
         FIGS. 18 to 23  illustrate formulas used in calculating the Mahalabinos&#39; generalized distance; and 
         FIGS. 24A and 24B  collectively illustrates exemplary input information used in a MTS method. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawing, wherein like reference numerals designate identical or corresponding parts throughout several views, in particular in  FIG. 1 , the image forming apparatus includes a diagnosis execution instruction device  10 , a test pattern image creating device  11 , an exposure (writing) device  12 , an image carrier  13 , a dev device  14 , and an image quality detection section  15  serving as a condition determination device. Further included are an image processing manner determining device  16 , an image processing device  17 , and an image inputting device  18 . Also included are an image outputting device  19 , a career information holding device  20 , and a service person call output determination device  21 . In addition, a service person call output device  21 , and an abnormal section specifying device  23  are included in the image forming apparatus. 
     When a user is dissatisfied with an image quality and instructs execution of diagnosis, the diagnosis execution instructing device (e.g. an operation section)  10  outputs a signal indicative of execution to the test pattern image creating device  11 . 
     The test pattern image creating device  11  creates and transmits a test pattern signal to the exposure device  12 . For example, as illustrated in  FIG. 2 , a test pattern signal for outputting a pattern including patches per color, such as cyan (C), magenta (M), yellow (Y), black (K), etc., with density changing step by step from high to low. 
     The exposure device  12  forms a latent image on an image bearing member  13  such as a photoconductive member using a laser light modulated in accordance with a test pattern signal inputted thereto. The dev device  14  forms a toner image by developing the latent image formed on the image bearing member  13 . 
     The image quality detection section  15  (serving as a condition determination device) includes a density distribution measurement device  151  and an image quality calculation device  152 . 
     The density distribution measurement device  151  measures a distribution of the test pattern image. The image quality calculation device  152  calculates an amount of deviation from a normal condition with reference to information of a normal condition stored in an internal RAM, not shown. The image quality calculation device  152  determines a condition of the apparatus based on the deviation amount and transmits a determination result to the image processing manner determining device  16  and the abnormal section determination device  23 . 
     The abnormal section determining device  23  determines an abnormal section based on a driving current of the semiconductor laser obtained from the exposure device  12 , light intensity monitor information, and the calculation result obtained from the image quality calculation device  152 . 
     The image processing manner determining device  16  determines an appropriate calibration amount or a halftone processing manner based on a deviation amount calculated by the image quality calculation device  152  and an output of the abnormal section determining device  23 , and then stores such information in a RAM, not shown, in the image processing manner determining device  16 . The image processing device  17  refers to a RAM, not shown, in the image processing manner determining device  16  and applies density correction and halftone processing to image data inputted thereto from the image inputting device  18 . Then, a series of processing, such as transferring, fixing, etc., are executed after operations of the exposure device, the image bearer, and the developing device, and thereby an image is outputted. 
     Further, the image quality calculation device  152  transmits the deviation amount to the image processing manner determining device  16  and the career information holding device  20 . 
     The career information holding device  20  stores thus inputted information in its internal RAM, not shown. The service person call output determination device  21  refers to the RAM of the career information holding device  20  and determines if a service person call is needed based on the career information stored therein. The service person call output determination device  21  instructs the service person call output device  22  to output a service person call when a service person call is needed. The service person call output device  22  then transmits the service person call to a communication destination via a telephone line or the like. 
     A density distribution measuring device  151  can be an optical sensor  31  as discussed in the jpo2003-219158 or the like. As shown in  FIG. 3A , the optical sensor  31  two-dimensionally measures a density distribution by picking up density data of a toner image on each of the test patches formed on an image bearing member  13  in one dimension in a chronological order as the image bearing member  13  rotates. As shown in  FIG. 3B , the optical sensor  31  includes a CCD line sensor  32 , a light emitting device  33 , and an optical member  34 . Light emitted from the light emitting device  33  reaches a toner image  30  of each of the test patches formed on the image bearing member  13 . Light reflected from the toner image  30  is received and imaged on the CCD line sensor  32  by the optical member  34 . As a result, the two dimensional density distribution of the toner image  30  of each of the test patches can be measured. 
     Now, an exemplary sequence of a control operation of an image forming apparatus of  FIG. 1  according to the first embodiment is described with reference to  FIG. 4 . Initially, when density of a solid toner image on an output decreases in step S 11 , a user instructs execution of calibration using the diagnosis execution instructing device  10  in step S 12 . When the diagnosis execution is thus instructed, the test pattern image creating device  11  transits a signal indicative of a test pattern image including test patches each having a different output density step by step (per mono color in case of a color output apparatus) to the exposure device  12 . Then, the exposure device  12  forms latent images of test patches on the image bearing member  13 , and the developing device  14  then develops the latent images. 
     The density distribution measuring device  151  measures a physical characteristic amount, such as density of a toner image on each of the test patches formed on the image bearing member  13 . 
     A calibration as to density is executed as an image processing manner by the image quality calculation device in this embodiment. Thus, the image quality calculation device  152  uses density measured by the density distribution measuring device  151  as is and compares with density of a normal condition stored in the internal RAM. 
     Then, a deviation amount from the normal condition is calculated, and it is determined if the deviation amount can be corrected by an ordinary calibration in step S 14 . If the determination is positive, the image processing manner determining device  16  calculates and stores a calibration amount based on the deviation amount from the normal condition calculated by the image quality calculation device  152 . Then, the image processing device  17  refers to the internal RAM and executes an ordinary calibration in step S 15 . For example, a correction is executed by changing an amount of supplying mono color toner and thereby adjusting a tone curvature in order to place density in the vicinity of a normal condition where a gray balance can be maintained. 
     Thus, image data inputted from the image inputting device  18  undergoes an appropriate density correction and halftone processing. Then, a series of processing including transferring and fixing is executed in the image outputting device  15  through the exposure device  12 , the image bearing member  13 , and the developing device  14 . Thus, an image is outputted. 
     Further, the image quality calculation device  152  transmits the same information of the deviation amount to the career information holding device  20  as is transmitted to the image processing manner determining device  16 . 
     The career information holding device  20  stores date information or the like in the RAM beside the deviation information transmitted from the image quality calculation device  152  in step S 16 . Then, the service person call output determination device  21  refers to the internal RAM in step S 17  and determines if a condition for transmitting a service person call is met in step S 18 . The service person call output device  22  transmits a service person call signal to a prescribed communication destination via telephone line or the like in accordance with a determination result of the service person call output determination device  21  in step S 119 . As a manner of determination used by the service person call output determination device  21 , various ones can be employed. For example, as shown in  FIGS. 5A and 5B , a deviation amount can be segmented into groups with a prescribed width, and a frequency can be measured per group in accordance with an amount of deviation. 
     As shown in  FIG. 5A , when the sum of the frequency is more than 10 and a peak of the distribution as shown by a slant line in the drawing lowers a prescribed reference value, it is determined that a service person call is not needed. Whereas as shown in  FIG. 5B , when the peak of distribution as shown by the slant line in the drawing exceeds the prescribed reference value, it is determined that a service person call is necessary, and a instruction for issuing a service person call is provided to the service person call output device  22 . Otherwise, as shown in  FIGS. 6A and 6B , a number of output sheets calculated by subtracting a total number of output sheets at the time of the previous calibration from that at the present calibration can be segmentized into groups with a prescribed width in accordance with the number of output sheets, and a frequency can be measured per group. 
     As shown in  FIG. 6A , when the sum of the frequency exceeds 10 and a peak of distribution shown by a slant line in the drawing exceeds a prescribed reference value, it is determined that a service person call is not needed. While, as shown in  FIG. 6B , when the peak of distribution as shown by the slant line in the drawing lowers the prescribed reference value, it is determined that a service person call is necessary, and a instruction for issuing a service person call is provided to the service person call output device  22 . 
     Still otherwise, as shown in  FIGS. 7A and 7B , a time interval calculated by subtracting a date when the previous calibration is executed from a date when calibration is presently executed can be segmentized into groups with a prescribed width in accordance with the length of the interval. Then, a frequency can be measured per group. For example, the time interval can be a prescribed unit time, such as zero to one hour, more than one hour less then 24 hour, more than 24 hour less then one-week, etc. Then, as shown in  FIG. 7A , when the sun of the frequency exceeds more than 10, and the peak of distribution as shown by the slant line in the drawing exceeds the prescribed reference value, it is determined that a service person call is not needed. 
     While as shown in  FIG. 7B , when the peak of distribution as shown by the slant line in the drawing lowers the prescribed reference value, it is determined that a service person call is necessary, and a instruction for issuing a service person call is provided to the service person call output device  22 . 
     In this way, the image forming apparatus of the first embodiment executes an ordinary calibration, in one hand, and on the other hand uses such calibration processing career information. 
     Further, either when a frequency of calibration increases or a number of corrections with a relatively large deviation amount is accumulated to a prescribed level, a service person call is issued. 
     Thus, an erroneous notification not in need of maintenance by a service person is decreased, while maintenance can be timely executed before a serious abnormality occurs in quality of an image. 
     Now, the second embodiment is described. 
     A difference from the first embodiment is that it is assumed that the deviation amount does not fall within the normal adjustable range when an image quality calculation device  152  executes determination if a deviation amount from a normal condition of an apparatus falls within a prescribed ordinal adjustable range in step S 14 . Specifically, when a solid image density decreases on an output material is step S 11 , a user uses the diagnosis execution instructing device  10  and instructs execution of calibration in step S 12 . 
     When diagnosis execution is instructed, the test pattern image creating device  11  transmits a signal indicative of a test pattern image including test patches with different output density step by step (per mono color when a color output apparatus is used) to an exposure device  12 . Then, the exposure device  12  forms latent images of test patches on the image career member  13 , and the developing device  14  then develops a toner image. 
     The density distribution measuring device  151  measures a physical characteristic amount such as density, a granularity level, etc., of the toner image of each of the test patches on the image bearing member  13 . 
     The image quality calculation device  152  calculates a deviation amount from a normal condition by comparing a density of a normal condition stored in internal RAM with the physical characteristic amount measured by the density distribution measuring device  151 . Then, the image quality calculation device  152  determines as being out of the normal adjustable range in step S 114  when the physical characteristic amount deteriorates by 30% than the normal amount stored in the RAM. In such a situation, it is initially determined if there exists abnormality in the exposure system in step S 30 .  FIG. 8  illustrates a relation between a light intensity and a driving current of one element of the semiconductor laser. It is understood in the case of a constant current driving that a light intensity is a level of Pa in relation to an input  10  in a normal condition, but decreases at a time of malfunction. Otherwise, an abnormality in the exposure system can be recognized when the light intensity is controlled to be constant and a current IO needed to obtain the amount of Pa is exceeded. 
     As another determining method of recognizing the abnormality of the exposure system, it is exemplified that no successful result is obtained even after the below described calibration executed in step S 21  for abnormal use is executed for a time or when abnormal use image processing executed in step S 23  is executed. Since various conditions arise when an electro-photographic engine is practically used, and it is difficult to determine every abnormality occurred in an exposure system, leakage of the determination of the abnormality can be reduced if a recovery countermeasure is taken. 
     Now, back to  FIG. 4 , an exemplary sequence after when the abnormality does not exist in the exposure system in step S 30  is described. In such a situation, when a density of a toner image deviates from a normal value by a prescribed amount, it is determined that color reproduction causes a problem in step S 20 . Then, the image processing manner determining device  16  instructs the image processing device  17  in step S 21  to execute an abnormal use calibration in accordance with a result of calculation executed by the image quality calculation device  152 . Simultaneously, the image quality calculation device  152  transmits to the image processing manner determining device  16  a value of the maximum density per mono color (e.g. C, M, C, K) to the image processing manner determining device  16  when a color image forming apparatus is used. As an abnormal use calibration that the image processing device  17  executes, a calibration for maintaining a gray balance as far as possible may be employed as mentioned below. With reference to  FIG. 9B , an exemplary situation when a density of Magenta widely decreases is now described. In such a situation, although it is attempted to create a gray with the same amount of respective toners of C, M, and Y, as usual, an unbalanced gray is obtained with slight green because of decreasing in a density of mono color M. 
     Then, the same density to the maximum density of the mono-color M at the abnormal time as shown in  FIG. 9B  are extracted based on a relation at a normal time between an input density and an output density stored in the RAM of the image quality calculation device  152 . Then, as shown in  FIG. 9C , densities of C, Y, and K in relation to the input at the time are adopted as the maximum densities for the respective mono colors. Thus, a calibration can be achieved even at the abnormal time while keeping the gray balance. In addition, an amount of the calibration is stored in a RAM of the image processing manner determining device  16 . 
     The image processing device  17  refers to the RAM of the image processing manner determining device  16  and executes the abnormal use calibration. As a result, an appropriate density correction and halftone processing can be applied to image date inputted from the image inputting device  18 . Then, an image is outputted when the image outputting device  19  executes transferring and fixing processes after respective operations of the exposure device  12 , the image bearing member  13 , and the developing device  14 . 
     Further, the career information holding device  20  does not store a deviation amount from a normal condition as career information when the deviation amount exceeds a prescribed reference level. 
     The image processing manner determining device  16  directly outputs the deviation amount from the normal condition calculated by the image quality calculation device  152  to the service person call output determination device  21 . 
     The service person call output determination device  21  instructs the service person call output device  22  to issue a service person call because thus received deviation amount from the normal condition exceeds the reference. 
     Thus, the image forming apparatus of the second embodiment executes an abnormal use calibration and outputs a service person call so as to maintain a gray balance when a problem related to image color reproduction arises. 
     Thus, outputs can be continuously obtained before maintenance is executed by a service person. 
     Accordingly, a completely unavailable time impossible for a user to use an image forming apparatus can be reduced. 
     Now, the third embodiment is described. 
     A difference from the second embodiment is that it is assumed that a determination result does not relate to the color production when an image quality calculation device  152  executes determination if a problem relates to color production in step S 20 . 
     Hereinbelow, only sequences after a step S 22  are described, since operational sequences up to a step S 20  are the same as in the second embodiment. The image quality calculation device  152  calculates a deviation amount by comparing a granularity level transmitted from the density distribution measuring device  151  with a normal value stored in the RAM, and then transfer the deviation amount to the image processing manner determining device  16 . The image processing manner determination device  16  determines that a problem relates to granularity in step S 22  when the deviation amount from the normal granularity exceeds the prescribed reference value, and forcibly switches to an abnormal use image processing manner in step S 23 . 
     For example, processing with a dither method is switched to a low line number dither processing method. Then, the image quality calculation device  152  transfers a deviation amount from a normal granularity to the service person call output determination device  21 . The service person call output determination device  21  transmits an instruction to create a service person call to the service person call output device  22 . 
     The above-mentioned deviation amount calculated by the image quality calculation device  152  can employ a Mahalanobis&#39; generalized distance in relation to a reference space constructed by using a MTS manner. 
     Now, the MTS method is described in detail. 
     According to the method, a distance from a homogenous data group as a reference is calculated. An average of the Mahalanobis&#39; generalized distance of data belonging to a reference space is one, and the distance becomes longer as a difference from reference data increases. Thus, when it is supposed that a data group outputted when an image forming apparatus normally operates is supposed to be a reference space and the Mahalanobis&#39; generalized distance is around one, the image forming apparatus represents a performance almost as same as a normal condition. Specifically, the larger the Mahalanobis&#39; generalized distance, the more serious abnormal level. 
     A sequence of determining a manner of calculating a calculation value (i.e., a distance of Maharanobis) and a calculation formula in accordance with a MTS manner is described with reference to a flowchart of  FIG. 10 . 
     Initially, n-group of k-number of information considered to be related to a condition of the image forming apparatus are obtained during an operation of the image forming apparatus in step S 37 . Herein, the table  1  illustrated in  FIG. 16  represents a configuration of data thus obtained. 
     A shown, K-number of data are obtained in the first condition (e.g. a first day, a first unit or the like), and y1l to y1k are assigned thereto, respectively. 
     Similarly, data are obtained in the next condition (e.g. a second day, a second unit or the like) and are assigned with y2l to y2k, respectively. Thus, n-group of data can be obtained. 
     Then, raw (fresh) data (e.g. yij) are standardized using an average value (yj) and a standard deviation (σj) in step S 38  using the first formula as shown in  FIG. 18  per type (j) of information. 
     The table  2  illustrated in  FIG. 19  represents a result of the standardization using the data shown in the table  1 . 
     Then, all of correlation efficient rpq (=rqp) between data of the two groups among the k types are calculated using the second formula, and thereby a matrix R is obtained as the third formula as shown in  FIG. 20  in step S 39 . 
     A reverse matrix of a correlation coefficient to the matrix R is then obtained as a matrix A as shown in the fourth formula in step S 40 . 
     As shown in the second formula, symbol Σ represents the total of suffix i. 
     Thus, a value of a calculation parameter used when a single calculation value is calculated can be determined. 
     Since the data group handled here represents those in a normal condition, the correlation is interrupted and the distance becomes larger when an abnormality such as a malfunction almost arises separated from the normal condition. 
     Now, an exemplary sequence for calculating a calculation value at an optional time is described with reference to  FIG. 11 . 
     A calculation value can be obtained at the optional time as follows: 
     Initially, k-types of data xl to xk are obtained at an optional condition in step S 41 . The data type corresponds to y1l to y1k or the like. Then, the data thus obtained are standardized in step S 42  using the represented by the number 5. The standardized data are assigned xl to xk. Then, a calculation value D 2  is calculated in step S 43  using the sixth calculation formula shown in  FIG. 23  as determined using elements akk of the reverse matrix A already sought. “D” as a square root of this value is called the Mahalanobis&#39; generalized distance, and is regarded as a calculation value. Further, Σ in the sixth formula represents the total related to suffixes p and q. 
     In this embodiment, as shown in the table  1 , a plurality of output values outputted from various sensors employed in the image forming apparatus are obtained during a normal operation, and a reference space is constructed based on the output values. 
     Objective to establish a system using the MTS method is not limited to the input information of the table  3 , and includes a combination of the other information. 
     However, it is limited to a few types of input information. 
     In this way, according to the image forming apparatus of the third embodiment, when a problem related to granularity occurs, an operation is switched to an abnormal use halftone processing manner, and a service person call is outputted. 
     Thus, the output can be continued until the service person arrives, and thus, a completely unavailable time for the image forming apparatus can be reduced. 
     Now, the fourth embodiment is described with reference to  FIG. 4 , wherein it is supposed that a problem neither relates to image color reproduction nor granularity occurs in step S 22  in  FIG. 4 . In such a situation, a user is highly probably dissatisfied with a problem impossible for a sensor or the like included in the image forming apparatus to detect. Thus, the image processing manner determining device  16  directly transmits information of both of deviation of density less than a reference value and granularity to the service person call output determination device  21 . Upon receiving the information from the image processing manner determining device  16 , the service person call output determination device  21  instructs the service person call output device  22  to output a service person call without any condition. Upon receiving the instruction, the service person call output device  22  issues a service person call in step S 19 . Thus, even when a problem other than the image color reproduction and the image granularity occurs, the image forming apparatus of  FIG. 4  can allow a service person to execute maintenance at an early stage. 
     Now, the fifth embodiment is described wherein it is supposed that a problem related an exposure system occurs during processing in step S 30  in  FIG. 4 . When the exposure system causes a problem (i.e., Yes, in step S 30 ), it is determined in step S 31  if color reproduction causes a problem in step S 31 . Specifically, a density distribution measuring device  151  measures a physical performance of a toner image of respective test patches, such as density, granularity, etc. When the density of the toner image deviates from the normal value by more than a prescribed value, it is determined that the color reproduction causes a problem in step S 31 . In such a situation, the exposure device  12  is instructed to execute calibration for abnormal use in step S 32 . A calibration for the abnormal use, calibration for a light intensity in a multiple beam system is exemplified. Specifically, as shown in  FIG. 8 , each of driving currents supplied to each of laser elements to execute constant current driving is separately calibrated again, and a light intensity of a target is lowered down to Pb, for example, so that light intensity of the respective elements can become substantially the same, even decreased. 
     As a result, a problem related to color reproduction can be suppressed. Since the maximum density decreases when the light intensity decreases, it is more preferable if the same calibration as the abnormal use calibration executed in step S 21  of the second embodiment is executed, simultaneously. 
     Now, an exposure device is described with reference to  FIG. 12  before the other abnormal use calibration in the exposure device  12  is explained. As shown, an exposure device and surroundings operating with dual beams are illustrated in  FIG. 12 . 
     The reference number  61  denotes a collimator unit as a light source section. The collimator unit  61  includes a plurality of collimator lenses  613  and  614 , a plurality of semiconductor lasers  615  and  616 , and a prism  617  for almost approximating light paths of the laser beams. The laser beams emitted from the collimator unit  61  become almost parallel to each other after passing through a cylindrical lens  62 . The light is then scanned in a horizontal direction by a polygon  63 . The light thus scanned is concentrated on the image bearing member  13  and scanned in a main scanning direction through a f-theta lens  64  and a Troidal lens  65 . A horizontal synchronization sensor  69  is arranged on the scan starting side and outputs a trigger signal. Based on the trigger signal, a phase synchronization signal generation circuit  70  outputs a synchronization signal representing scanning start. The synchronization signal is transmitted to a video control section  71 . 
     The video control section  71  includes a ROM  72  for creating a test pattern, and is connected to an operation panel  73 , and an interface circuit  74  for image data. An image signal from the video control section  71  is transmitted to a LD driving circuit  75  so as to drive the semiconductor lasers  615  and  616 . 
     An exemplary adjustment mechanism for the collimator unit shown in  FIG. 12  is described with reference to  FIG. 13 . 
     A beam pitch is adjusted by moving the collimator unit  61  by means of an adjusting mechanism  68 . Specifically, when a region impossible to execute scanning (i.e., exposure) is created due to a deviation of a scanning pitch, such scanning is recovered to be uniform by adjusting a pitch again. Such an adjustment of the exposure pitch can be executed using an evaluation chart as described in the Japanese Patent Registration No. 3254392 and the optical sensor  31  as described with reference to  FIG. 3 . When the abnormal use calibration step in step S 32  is completed, a test pattern is created again after the calibration, and then it is determined as to a problem related to granularity is executed in step S 33 . The same manner to that used in step S 22  can be used. When it is determined that there exists a problem related to granularity performance, an operation is switched to an abnormal use image processing in step S 34 . If it is not determined that there exists a problem related to granularity in step S 33 , the step S 34  is not executed. Then, the image quality calculation device  152  transmits a deviation amount from a normal granularity to the service person call output determination device  21 . The service person call output determination device  21  then transmits an instruction to the service person call output device  22  to issue a service person call. 
     Now an exemplary image processing for abnormal use performed in step S 34  is described with reference to  FIG. 14 , wherein a number of processing lines in a dither method is decreased. 
     Specifically, when a high line number dither is used and scanning is executed by a polygon while a laser includes a problem, a problem is caused as to a scanning line as shown in  FIG. 14A . 
     Such affection is serious in the high line number dither, because a small number of dots form a grid. However, since a number of dots forming a grid increases in case of using a low line number dither as shown in  FIG. 14B , in proportion to a number of multiple beams, a level of a dot formation problem caused by a light emission error can be decreased. 
     Another exemplary image processing for abnormal use to be performed in step S 34  is now described with reference to  FIG. 15 , wherein a screen angle of processing is changed in a dither method. In a color electro-photographic engine, a screen angle is added in a dither method. However, abnormality in an exposure device  12  readily causes affection when a difference between screen and scanning line angles is small as shown in  FIG. 15A . 
     Thus, when the screen angle is changed as shown in  FIG. 15B , such affection of the abnormality can be suppressed not to be prominent. 
     Now, the sixth embodiment is described, wherein an exemplary sequence is described when it is determined in step S 31  that a problem relates to color reproduction different from the fifth embodiment. The image quality calculation device  152  calculates a deviation amount by comparing a normal value stored in a RAM with a granularity transmitted from the density distribution measuring device  151 , and transmits the deviation amount to the image processing manner determining device  16 . 
     The image processing manner determining device  16  determines that a problem relates to a granularity when the deviation amount from the normal one exceeds a prescribed reference value in step S 35 , and forcibly switches a manner to the abnormal use image processing manner in step S 36 . Such an abnormal use image processing manner can be the same to that executed in step S 34 . 
     The image quality calculation device  152  then transmits the deviation amount from the normal granularity to the service person call output determination device  21 . The service person call output determination device  21  then transmits an instruction to the service person call output device  22  to issue a service person call. 
     Now, the seventh embodiment is described, wherein it is supposed in step S 35  that a problem does not relate to image color reproduction and granularity. In such a situation, it is recognized that the exposure device  12  causes some problem. 
     Specifically, a problem impossible for a sensor included in the image forming apparatus to detect occur. Accordingly, a user highly probably feels complaint about it. Then, the image processing manner determining device  16  directly transmits information such as a density deviation amount less than a reference value, a granularity level, etc., to the service person call output determination device  21 . The service person call output determination device  21  instructs the service person call output device  22  to issue a service person call without any condition upon receiving the information from the image processing manner determining device  16 . The service person call output device  22  issues a service person call in accordance with the instruction. 
     In this way, the image forming apparatus according to the seventh embodiment, maintenance can be executed by a service person at an earlier stage even when a problem unrelated to image color reproduction and image granularity occurs. 
     Further, a downtime of the apparatus can be minimized. 
     Obviously, numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.