Patent Publication Number: US-9411257-B2

Title: Apparatus for increasing the lifespan of light emitting units and image forming apparatus having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is based on and claims priority pursuant to 35 U.S.C. §119(a) to Japanese Patent Application No. 2014-189496, filed on Sep. 17, 2014, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an image forming apparatus and an image forming method. 
     2. Description of the Related Art 
     In some electrophotographic image forming apparatuses, scanning exposure is performed using a light source having a plurality of light emitting units whose lighting is independently controllable. 
     Such an image forming apparatus in which scanning exposure is performed using a light source having a plurality of light emitting units is able to write the same number of line images as the light emitting units on a photoconductor at once. This makes it possible to shorten page printing time and increase printing speed. 
     As the light source, laser diode array (LDA), vertical cavity surface emitting laser (VCSEL), or the like, has been used. 
     Laser diode (LD) gradually deteriorates with use and reaches the end of its life when exceeding the allowable limit. 
     Usually, we replace parts in good time before they deteriorate. Parts are replaced at an appropriate time before they reach the predicted ends of their life. 
     With respect to LD, it is already known that the length of lighting time gives an indication of its lifespan. 
     SUMMARY 
     In accordance with some embodiments of the present invention, an image forming apparatus is provided. The image forming apparatus includes a light source including a plurality of light emitting units to emit light corresponding to image data, and a light source controller to independently control lighting of each one of the light emitting units. The light source controller switches activation and deactivation of one or more of the light emitting units when the number of to-be-used light emitting units is smaller than the total number of the light emitting units included in the light source. 
     In accordance with some embodiments of the present invention, an image forming method is provided. The image forming method includes the steps of emitting light corresponding to image data from a light source including a plurality of light emitting units; and switching activation and deactivation of one or more of the light emitting units when the number of to-be-used light emitting units is smaller than the total number of the light emitting units included in the light source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure 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  is a schematic view of an image forming apparatus according to an embodiment of the present invention which is a laser printer; 
         FIG. 2  is a block diagram of a major part of the optical writing unit illustrated in  FIG. 1 ; 
         FIG. 3  is a timing diagram for explaining switching of light emitting units with respect to 2ch LDA; 
         FIG. 4  is a timing diagram for explaining switching of light emitting units in 1-beam mode with respect to 4ch LDA; 
         FIG. 5  is a timing diagram for explaining switching of light emitting units in 2-beam mode with respect to 4ch LDA; 
         FIG. 6  is a timing diagram for explaining switching of light emitting units per printing job; 
         FIG. 7  is a flowchart illustrating a switching operation of lighting LDs at printing every sheet of paper; and 
         FIG. 8  is a flowchart illustrating a switching operation of lighting LDs at every job. 
     
    
    
     The accompanying drawings are intended to depict example embodiments of the present invention and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DETAILED DESCRIPTION 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     In describing example embodiments shown in the drawings, specific terminology is employed for the sake of clarity. However, the present disclosure is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. 
     In the following description, illustrative embodiments will be described with reference to acts and symbolic representations of operations (e.g., in the form of flowcharts) that may be implemented as program modules or functional processes including routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types and may be implemented using existing hardware at existing network elements or control nodes. Such existing hardware may include one or more Central Processing Units (CPUs), digital signal processors (DSPs), application-specific-integrated-circuits, field programmable gate arrays (FPGAs) computers or the like. These terms in general may be referred to as processors. 
     Unless specifically stated otherwise, or as is apparent from the discussion, terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical, electronic quantities within the computer system&#39;s registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. 
     A conventional image forming apparatus using a light source having a plurality of light emitting units, such as laser diode array, sometimes performs scanning exposure without using all the light emitting units depending on printing mode. For example, in the case of 2ch LDA, scanning exposure may be performed using only one light emitting unit. This causes variation in lifespan among the plurality of light emitting units. 
     In view of this situation, one object of the present invention is to suppress variation in lifespan among a plurality of light emitting units in a light source and extend the lifespan of the light source. 
     In accordance with some embodiments of the present invention, an image forming apparatus which can suppress variation in lifespan among multiple light emitting units in a light source and extend the lifespan of the light source is provided. 
       FIG. 1  is a schematic view of an image forming apparatus according to an embodiment of the present invention that is a laser printer. 
     The laser printer includes an image forming unit  1  and a fixing unit  2 . The laser printer further includes an image processor that performs necessary image processing for print data, a paper feeder that feeds printing paper to the image forming unit  1 , and a paper ejection unit that ejects the printing paper having an image having been formed in the image forming unit  1  and fixed thereon in the fixing unit  2 . The laser printer further includes a data receiver that receives print data from an external device such as a personal computer or scanner, and an operation display that displays operation keys to set operation mode of the laser printer and other various information. 
     The image forming unit  1  includes a photoconductor  10  in a drum-like shape rotary drivable. Around the photoconductor  1 , a charger  11 , an optical writing unit  12 , a developing unit  13 , a transfer unit  14 , a separation unit  15 , and a cleaner  16  are provided. 
     In the image forming unit  1 , an outer peripheral surface of the photoconductor  10  is uniformly charged by the charger  11  while the photoconductor  10  is rotating, and the charged surface is irradiated with a laser beam modulated based on image data emitted from the optical writing unit  12 , thereby forming an electrostatic latent image on the outer peripheral surface of the photoconductor  10 . 
     The developing unit  13  then supplies toner serving as a developer to the photoconductor  10 , thereby forming a toner image serving as a developer image. 
     The transfer unit  14  then transfers the toner image from the photoconductor  10  onto a printing paper sheet serving as a recording medium having been fed to between the photoconductor  10  and the transfer unit  14  through a paper feeding path  17  from the paper feeder. 
     The separation unit  15  then separates the printing paper sheet having the transferred toner image thereon from the photoconductor  10  and feeds it to the fixing unit  2 . 
     The fixing unit  2  includes a heat roller rotary drivable and heatable to a predetermined fixing temperature, a pressure roller in contact with the heat roller and rotatable along with the heat roller, and a heater to heat the heat roller to a predetermined fixing temperature. The fixing unit  2  feeds the printing paper sheet having the transferred toner image thereon while the heat roller and the pressure roller are applying heat and pressure to it, thereby fixing the toner image on the printing paper sheet. 
     After completion of the transfer of the toner image, the cleaner  16  neutralizes the photoconductor  10  and removes residual toner particles therefrom. The charger  11  then uniformly charges the photoconductor  10  to perform image formation again. 
       FIG. 2  is a block diagram of a major part of the optical writing unit  12 . In  FIG. 2 , each dashed array indicates a laser beam. 
     Upon receipt of image data from an external device such as personal computer or built-in scanner, a controller (such as CPU (central processing unit)) of the laser printer inputs the received image data to the optical writing unit  12 . The optical writing unit  12  generates a laser beam modulated based on the image data. 
     The optical writing unit  12  includes a writing driving unit  20  and a polygon mirror  30 . 
     The writing driving unit  20  includes a light source controller  21 , a light source  22 , and a synchronization detecting sensor  23  having a photodiode. The light source  22  is a laser diode array (hereinafter “LDA”) including two laser diodes (hereinafter “LD”)  22 A and  22 B that emit laser light beams. Hereinafter, LD 22 A and LD 22 B may be referred to as LD 1  and LD 2 , respectively. 
     The writing driving unit  20  further includes an fθ lens, a reflection mirror, a synchronous reflection mirror, or the like. 
     The polygon mirror  30  is a rotary multifaced mirror rotatable by a polygon motor with an angular velocity in accordance with the image density of the laser printer. The polygon mirror  30  illustrated in  FIG. 2  has a regular hexagonal planer shape and six reflection surfaces on its outer periphery. 
     The light source  22 , synchronization detecting sensor  23 , and polygon mirror  30  are controlled by the light source controller  21 . The light source controller  21  independently controls lighting of a plurality of light emitting units LD 22 A and LD 22 B (LD 1  and LD 2 ) in the light source  22 . 
     More specifically, upon input of image data, the light source controller  21  controls lightings of the LD 22 A and LD 22 B by means of a writing clock or timing control signal based on the image data. The light source controller  21  is implemented by, for example, a control board, memory, LD driver, or the like. 
     Laser beams emitted from LD 22 A and/or LD 22 B in the light source  22  are reflected by the polygon mirror  30  and become a laser beam used for optical scanning. The laser beam then passes through the fθ lens and is reflected by the reflection mirror, thereby forming an image on the photoconductor  10 . 
     As the polygon mirror  30  rotates, the incident position (reflection position) of the laser beam on the reflection mirror moves in the direction of arrow S, and the imaging position on the photoconductor  10  also moves in the direction of arrow S. The direction of arrow S is coincident with the generating line of the cylinder of the photoconductor  10  and the main scanning direction. 
     A part of the laser beam having passed through the fθ lens enters the synchronous reflection mirror disposed near a position on the scanning line of the laser beam on the photoconductor  10  deviated from the image forming area. The synchronous reflection mirror reflects the entered laser beam toward the synchronization detecting sensor  23 . 
     As the reflected laser beam enters, the synchronization detecting sensor  23  generates a synchronization detecting signal that is a pulse output. The light source controller  21  sets an effective scanning period during which an image is written on the photoconductor  10  based on the synchronization detecting signal. 
       FIGS. 3 to 6  are timing diagrams for explaining switching of activation and deactivation of light emitting units in the light source  22 . In  FIGS. 3 to 6 , image area signal represents a signal showing a writing area in a sub-scanning direction. One assertion period of the image area signal coincides with a period of printing on one sheet of paper. 
     LD 1  lighting signal and LD 2  lighting signal represent signals for controlling lighting of LD 22 A (LD 1 ) and LD 22 B (LD 2 ), respectively, in the light source  22 . Both of them are output from the light source controller  21 . 
     During each assertion period of the image area signal, each LD lighting signal includes multiple main scanning lines. Each main scanning line includes synchronization lighting, APC (Auto Power Control) lighting, and main scanning image area lighting. Here, these lightings are omitted from the figures for the sake of simplicity. During a negation period between successive assertion periods of the image area signal, each LD lighting signal performs synchronization lighting and APC lighting. These lightings are also omitted from the figures for the sake of simplicity. 
       FIG. 3  shows a case in which 2ch LDA is used as the light source  22  in the optical writing unit  12  and 4-sheet continuous printing is performed in 1-beam mode. The 2ch LDA represents a 2-channel laser diode array having 2 laser diodes serving as light emitting units. 
     The image area signal is asserted (put into an active state) for every one sheet of paper. Once printing is started, an assertion of the image area signal corresponding to the first sheet of paper triggers an assertion of the LD 1  lighting signal. 
     An assertion of the image area signal corresponding to the second sheet of paper triggers a negation (an inactive state) of the LD 1  lighting signal and an assertion of the LD 2  lighting signal. Namely, the LD 1  lighting signal is asserted when printing an odd-numbered sheet of paper, and the LD 2  lighting signal is asserted when printing an even-numbered sheet of paper. Lighting is alternately switched between LD 1  and LD 2  every time the sheet of paper for printing is changed. 
     This operation makes it possible to eliminate deviation in the operating time between LD 1  and LD 2 , i.e., two light emitting units in the light source  22 , and to extend the lifespan of the light source  22 . 
       FIG. 4  shows a case in which 4ch LDA is used as a light source in an optical writing unit and 4-sheet continuous printing is performed in 1-beam mode. 
     The optical writing unit in this case has the same configuration as the optical writing unit  12  illustrated in  FIG. 2  except for replacing the light source  22  with a 4-channel laser diode array having 4 laser diodes serving as light emitting units. 
     LD 1  lighting signal, LD 2  lighting signal, LD 3  lighting signal, and LD 4  lighting signal represent signals for controlling lighting of LD 1 , LD 2 , LD 3 , and LD 4 , respectively. 
     The image area signal is asserted for every one sheet of paper. Once printing is started, an assertion of the image area signal corresponding to the first sheet of paper triggers an assertion of the LD 1  lighting signal. An assertion of the image area signal corresponding to the second sheet of paper triggers a negation of the LD 1  lighting signal and an assertion of the LD 2  lighting signal. An assertion of the image area signal corresponding to the third sheet of paper triggers a negation of the LD 2  lighting signal and an assertion of the LD 3  lighting signal. An assertion of the image area signal corresponding to the fourth sheet of paper triggers a negation of the LD 3  lighting signal and an assertion of the LD 4  lighting signal. 
     Lighting is successively switched among LD 1  to LD 4  in the order of LD 1 , LD 2 , LD 3 , and LD 4  every time the sheet of paper for printing is changed. After termination of lighting of LD 4 , LD 1  is put into a lighting state. This operation is repeated until the printing operation is completed. 
     This operation makes it possible to eliminate deviation in the operating time among LD 1  to LD 4 , i.e., four light emitting units in the light source, and to extend the lifespan of the light source. 
       FIG. 5  shows a case in which 4ch LDA is used as a light source in an optical writing unit and 4-sheet continuous printing is performed in 2-beam mode. 
     The optical writing unit in this case has the same configuration as that in the case of  FIG. 4 . Namely, a 4-channel laser diode array having 4 laser diodes serving as light emitting units is used as the light source. 
     The image area signal is asserted for every one sheet of paper. Once printing is started, an assertion of the image area signal corresponding to the first sheet of paper triggers assertions of the LD 1  lighting signal and LD 2  lighting signal. An assertion of the image area signal corresponding to the second sheet of paper triggers negations of the LD 1  lighting signal and LD 2  lighting signal and assertions of the LD 3  lighting signal and LD 4  lighting signal. Lighting is alternately switched between a pair of LD 1  and LD 2  and another pair of LD 3  and LD 4  every time the sheet of paper for printing is changed. 
     This operation makes it possible to eliminate deviation in the operating time among LD 1  to LD 4 , i.e., four light emitting units in the light source, and to extend the lifespan of the light source. 
     A pair of LDs to be simultaneously put into a lighting state is not limited to the above-described combinations. However, it is necessary that any combination of LDs simultaneously put into a lighting state provide lines adjacent to each other in a sub-scanning direction. 
       FIG. 6  is a timing diagram for explaining switching operation of lighting LDs at every job, while  FIGS. 3 to 5  are those for explaining switching operation of lighting LDs at printing every sheet of paper. 
       FIG. 6  shows a case in which 2ch LDA is used as a light source in an optical writing unit in 1-beam mode, and 2-sheet continuous printing is performed in the first job and the second job. 
     The image area signal is asserted for every one sheet of paper. Once the first job is started, an assertion of the image area signal corresponding to the first sheet of paper triggers an assertion of the LD 1  lighting signal, and the LD 1  lighting signal is negated upon completion of the first job. 
     An assertion of the image area signal corresponding to the sheet of paper in the second job triggers an assertion of the LD 2  lighting signal, and the LD 2  lighting signal is negated upon completion of the second job. Lighting is switched between LD 1  and LD 2  at every job. 
     This operation makes it possible to eliminate deviation in the operating time between LD 1  and LD 2 , i.e., two light emitting units in the light source, through the jobs, and to extend the lifespan of the light source. 
     The same control can be applied to another case in which 4ch LDA is used as a light source in an optical writing unit in 2-beam mode. 
       FIG. 7  is a flowchart illustrating a switching operation of lighting LDs performed by the light source controller  21  at printing every sheet of paper. 
     In S 101 , the light source controller  21  detects an assertion of a job start signal (STTRIG signal) and enters a printing operation state. 
     In S 102 , the light source controller  21  detects an assertion of an image area signal (FGATE signal), sets a LD switching flag, and enters an image generation state. 
     In S 103 , the light source controller  21  determines printing mode and the number of LDs to light required in the printing operation. For example, in the case where 4ch LDA is used, it is determined that one LD is required to light. 
     In S 104 , the light source controller  21  selects LDs to light based on the flag set in S 102  and the required number of lighting LDs determined in S 103 . When the processing has proceeded to S 104  through a loop, the light source controller  21  selects LDs to light other than those selected in the previous determination. (For example, in the case where the printing operation uses 4ch LDA and one LD, LD to light is selected in the following manner: LD 1 →LD 2 →LD 3 →LD 4 →LD 1 → . . . ) 
     In S 105 , the light source controller  21  transmits data to drivers of the selected LDs. 
     In S 106 , the light source controller  21  detects a negation of the FGATE signal, removes the LD switching flag, and enters an image generation waiting state. In the case where the FGATE signal is input again, the processing goes back to S 102 . 
     In S 107 , the light source controller  21  detects a negation of the STTRIG signal and enters a printing operation waiting state. 
       FIG. 8  is a flowchart illustrating a switching operation of lighting LDs performed by the light source controller  21  at every job. 
     In S 201 , the light source controller  21  detects an assertion of a job start signal (STTRIG signal), sets a LD switching flag, and enters a printing operation state. 
     In S 202 , the light source controller  21  detects an assertion of an image area signal (FGATE signal) and enters an image generation state. 
     In S 203 , the light source controller  21  determines printing mode and the number of LDs to light required in the printing operation. For example, in the case where 4ch LDA is used, it is determined that one LD is required to light. 
     In S 204 , the light source controller  21  selects LDs to light based on the flag set in S 201  and the required number of lighting LDs determined in S 203 . When the processing has proceeded to S 204  through a loop, the light source controller  21  selects LDs to light other than those selected in the previous determination. (For example, in the case where the printing operation uses 4ch LDA and one LD, LD to light is selected in the following manner: LD 1 →LD 2 →LD 3 →LD 4 →LD 1 → . . . ) 
     In S 205 , the light source controller  21  transmits data to drivers of the selected LDs. 
     In S 206 , the light source controller  21  detects a negation of the FGATE signal and enters an image generation waiting state. 
     In S 107 , the light source controller  21  detects a negation of the STTRIG signal, removes the LD switching flag, and enters a printing operation waiting state. In the case where the STTRIG signal is input again, the processing goes back to S 202 . 
     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of the present invention may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. 
     Each of the functions of the described embodiments may be implemented by one or more processing circuits or circuitry. Processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC) and conventional circuit components arranged to perform the recited functions. 
     The present invention can be implemented in any convenient form, for example using dedicated hardware, or a mixture of dedicated hardware and software. The present invention may be implemented as computer software implemented by one or more networked processing apparatuses. The network can comprise any conventional terrestrial or wireless communications network, such as the Internet. The processing apparatuses can compromise any suitably programmed apparatuses such as a general purpose computer, personal digital assistant, mobile telephone (such as a WAP or 3G-compliant phone) and so on. Since the present invention can be implemented as software, each and every aspect of the present invention thus encompasses computer software implementable on a programmable device. The computer software can be provided to the programmable device using any storage medium for storing processor readable code such as a floppy disk, hard disk, CD ROM, magnetic tape device or solid state memory device. 
     The hardware platform includes any desired kind of hardware resources including, for example, a central processing unit (CPU), a random access memory (RAM), and a hard disk drive (HDD). The CPU may be implemented by any desired kind of any desired number of processor. The RAM may be implemented by any desired kind of volatile or non-volatile memory. The HDD may be implemented by any desired kind of non-volatile memory capable of storing a large amount of data. The hardware resources may additionally include an input device, an output device, or a network device, depending on the type of the apparatus. Alternatively, the HDD may be provided outside of the apparatus as long as the HDD is accessible. In this example, the CPU, such as a cache memory of the CPU, and the RAM may function as a physical memory or a primary memory of the apparatus, while the HDD may function as a secondary memory of the apparatus.