Patent Publication Number: US-8985759-B2

Title: Image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a power line communication in an image forming apparatus. 
     2. Description of the Related Art 
     In conventional image forming apparatuses, a method of greatly reducing the number of signal lines used for communication and control signal lines by performing data transfer by way of serial communication is implemented in a unit (circuit board) that does not require high data transfer speed. However, a large number of signal lines are provided between the circuit boards in the image forming apparatus as a whole. Further, many power lines are provided for power supply to the circuit boards in addition to the communication and control signal lines. The communication and control signal lines and the power lines occupy a large part of a space in the image forming apparatus. 
     U.S. Patent Application Publication No. 2006/0077046 discusses that, to further reduce the number of communication and signal lines, the number of communication and control signal line bundles is reduced by using a power line as a signal transmission path and performing the communication between a plurality of circuit boards connected to the power line and a control module. 
     In the case of performing signal transmission by using a power line, it is desirable that a transmission path is electrically stable for enabling stable communication. However, in image forming apparatuses, a current supplied from a direct current power source is sometimes changed to a large degree depending on an operational status of a load during an image forming operation. Particularly, a current power source assigned to a driving unit such as a motor and an actuator is greatly fluctuated depending on an operation state. Since impedance in the transmission path is also greatly fluctuated in such a power line, it is sometimes difficult to perform the stable communication depending on the operation status of the image forming apparatus. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an image forming apparatus capable of performing stable power line communication that is suppressed in transmission error. 
     According to an aspect of the present invention, an image forming apparatus includes a first power source configured to supply power for driving a load to be used for image formation via a first power line, a load control circuit configured to control driving of the load, a control circuit configured to output control data for the load control circuit to control the load, a second power source configured to supply power for the load control circuit via a second power line provided separately from the first power line, a superimposing circuit configured to superimpose the control data output from the control circuit onto the second power line, and a separation circuit configured to separate the control data from the second power line, on which the control data is superimposed and sent, and to output the control data to the load control circuit. 
     Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a sectional view illustrating an image forming apparatus according to a first exemplary embodiment of the present invention. 
         FIG. 2  is a block diagram illustrating configurations of a power source and control units of the image forming apparatus according to the first exemplary embodiment. 
         FIG. 3  is a diagram illustrating a configuration of a superimposing circuit. 
         FIG. 4  is a diagram illustrating a configuration of a separation circuit. 
         FIG. 5  is a diagram illustrating a relationship between frequencies of data sent by a power line. 
         FIG. 6  is a block diagram illustrating configurations of a power source and control units of an image forming apparatus according to a second exemplary embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings. 
       FIG. 1  is a sectional view illustrating an entire configuration of an image forming apparatus according to a first exemplary embodiment of the present invention. The image forming apparatus  1  is a full-color printer that forms an image on a recording sheet by employing electrophotography. The image forming apparatus  1  is provided with photosensitive drums  2   a  to  2   d  for four colors, charging devices  3   a  to  3   d , cleaners  4   a  to  4   d , laser scanning units  5   a  to  5   d , transfer blades  6   a  to  6   d , developing units  7   a  to  7   d , an intermediate transfer belt  8 , and a cleaner  12 . The image forming apparatus  1  is further provided with a steering roller  10  supporting the intermediate belt  8  and a belt driving roller  11  for rotating the intermediate transfer belt  8  in a predetermined direction. 
     A plurality of recording sheets S set in a manual feed tray  13  are separated to be fed one by one by a pickup roller  14  and separation rollers  15 . The plurality of recording sheets S housed in a sheet feeding cassette  17  are separated to be fed one by one by a pickup roller  18  and separation rollers  19  and conveyed by feeding rollers  20 . 
     The thus-fed recording sheet S is conveyed to a second transfer roller  22  with timing being adjusted by registration rollers  16 . Here, each of the rollers  14 ,  15 ,  16 ,  18 ,  19 , and  20  for conveying the recording sheet S is driven by an independent stepping motor for realizing a high speed and stable conveyance operation. 
     The charging devices  3   a  to  3   d  uniformly charge surfaces of the photosensitive drums  2   a  to  2   d . The laser scanning units  5   a  to  5   d , of which light sources are semiconductor lasers, irradiate the photosensitive drums  2   a  to  2   d  with laser beams to form electrostatic latent images on the photosensitive drums  2   a  to  2   d . The developing units  7   a  to  7   d  develop the electrostatic images as toner images. 
     The transfer blades  6   a  to  6   d  transfer the toner images of four colors developed on the photosensitive drums  2   a  to  2   d  onto the intermediate transfer belt  8 . The toner image on the intermediate transfer belt  8  is transferred onto the recording sheet S at a nip portion of a rotation roller  21  and the second transfer roller  22 . A fixing device  23  having heating rollers applies heat to the toner image transferred onto the recording sheet S, so that the toner image is fixed onto the recording sheet. 
     In the case of two-sided printing, the recording sheet S that has passed the fixing device  23  is directed to a direction of a two-sided-reserving path  27  and conveyed in a reverse direction, so that the first side and the second side of the sheet S are reversed when the sheet S is conveyed to a two-sided printing path  28 . The recording sheet S that has passed the two-sided printing path  28  is conveyed to the feeding rollers  20  again, and an image for the second side is formed in the same manner as in the first side. After that, the recording sheet S is discharged by discharge rollers  24  to a sheet discharge tray  25 . 
       FIG. 2  is a block diagram illustrating configurations of a power source and control units of the image forming apparatus  1 . Alternating current power from a commercial power source  102  is input into a switching power source  104  via a filter circuit  103 . The switching power source  104  outputs a constant voltage of 13 V from a power line  107  and outputs a constant voltage of 24 V from a power line  108 . The outputs from the switching power source  104  are supplied to a plurality of circuit boards (units) in the image forming apparatus  1 . In the present exemplary embodiment, the constant voltage of 13 V is supplied to a control unit  105  via the power line  107  serving as a second power line, and the constant voltage 24 V is supplied to a driving unit  106  via the power line  108  serving as a first power line. The second power line outputs 13 V but may output 5 V depending on a type of an element to which the power is supplied. Also, the switching power source  104  outputs the two types of constant voltages in the above-described configuration, but a first power source for outputting 24 V and a second power source for outputting 13 V may be provided. 
     The control unit  105  includes a central processing unit (CPU)  110  for controlling operations of the image forming apparatus  1  and a superimposing circuit  111  for superimposing communication data onto the power line  107  and outputting the communication data. The driving unit  106  includes a pulse motor  117 , a motor driving circuit  116  for driving the pulse motor  117 , a motor control circuit  115  for controlling the motor driving circuit  116 , and a separation circuit  113 . The separation circuit  113  has functions of inputting power from a power line  112  on which motor control data are superimposed from the control unit  105  and separating the motor control data and the power for the separation circuit  113  from each other. The constant voltage of 24 V dedicated to motor driving is connected to the motor driving circuit  116  from the switching power source  104  via the power line  108 , so that the constant voltage of 24 V is supplied as driving power for the pulse motor  117 . The pulse motor  117  is equivalent to a motor for driving the pickup rollers  14  and  18  of the image forming apparatus  1  illustrated in  FIG. 1  and frequently turned on and off during an image forming operation. The pulse motor  117  may be a motor for driving the registration rollers  16  or other feed rollers. 
     Though it is not illustrated, the constant voltage 13 V input into the control unit  105  is input into the superimposing circuit  111 . The superimposing circuit  111  superimposes the motor control data from the CPU  110  onto the power line  112 , so that the motor control data is supplied to the driving unit  106  together with the power. The separation circuit  113  separates the motor control data and the power supplied via the power line  112  from each other. Though it is not illustrated, the constant voltage 13 V input into the control unit  105  is input into a power source circuit not illustrated and converted into a plurality of different voltages to be supplied to the CPU  110  and the superimposing circuit  111  in the control unit  105 , the separation circuit  113  in the driving unit  106 , the motor control circuit  115 , and the like. 
     Hereinafter, the superimposition circuit  111  will be described.  FIG. 3  is a block diagram illustrating a configuration of the superimposing circuit  111 . Here, motor control data including parallel signals and a reference clock for motor driving are superimposed onto the direct current power. 
     Parallel motor control data  201  generated by the CPU  110  is converted into serial data  212  by a parallel/serial conversion circuit  202  to be input into a data modulation circuit  203 . The serial data  212  is converted into modulated data  207  having a carrier wave of a frequency fc 1  by the data modulation circuit  203 . A reference clock  205  for driving the pulse motor  117  is converted into modulated data  211  having a carrier wave of a frequency fc 2  by a clock modulation circuit  206  in the same manner. 
     The modulated data  207  and  211  are superimposed onto the constant voltage 13 V by a data superimposing circuit  204  via an inductor  210  to be output via the power line  112 . The inductor  210  has impedance that is satisfactorily high for the modulated data  207  and  211  and prevents the modulated data from leaking to the power line  107 . 
       FIG. 5  is a diagram illustrating a relationship between the frequencies of the data contained in the power line  112 . In the present exemplary embodiment, the modulation frequency fc 2  of the motor reference clock  205  is set higher than the modulation frequency fc 1  of the motor control data  201 , but an inverted relationship does not cause any issue. 
     In the case of sending the motor control data by using a power line, the use of the power line  108  to the motor driving circuit  116  may be considered. However, since the pulse motor  117  is frequently turned on and off during an image forming operation, it is highly possible that a power fluctuation is caused at the moment of turning on or off. Accordingly, the data sent by the power source can be inaccurate. The same applies to the power line for a driving circuit for an actuator not illustrated, other than the power line for a motor. Therefore, in the present exemplary embodiment, accurate data transmission is realized by performing a power line communication by using the power line to the control unit  105  that is suppressed in load fluctuation, not the power line for the driving circuit for operating a movable member such as the motor and the actuator. 
     Hereinafter, the separation circuit  113  will be described.  FIG. 4  is a block diagram illustrating functions of the separation circuit  113 . The power onto which modulated motor control data and the modulated reference clock are superimposed via the power line  112  is separated by a data separation circuit  301  into power  118 , motor control data  302  modulated with the frequency fc 1 , and a reference clock  303  modulated with the frequency fc 2 . An inductor  310  prevents the modulated data from leaking to the power  118 . 
     The motor control data  302  is converted into serial digital data  306  by a data demodulation circuit  304  to be converted into motor control data of parallel system via a serial/parallel conversion circuit  308 . The reference clock  303  is converted into a clock  307  by a clock demodulation circuit  305  to be input into the motor control circuit  115  together with the motor control data  302 . 
     In the present exemplary embodiment, the power line for driving, which is subject to the large load fluctuation, is not used as the communication line, and the power line for the control unit which is suppressed in load fluctuation is used. However, other power lines may be used insofar as the power line is suppressed in voltage fluctuation. 
     A voltage value other than a direct current voltage value generated by a switching power source is sometimes required depending on a unit in the image forming apparatus. In such case, a direct current/direct current (DC/DC) convertor is provided for the purpose of generating a necessary voltage value. It is possible to attain the same effect by superimposing control data onto an output of the DC/DC converter. 
       FIG. 6  is a block diagram illustrating configurations of a power source and control units of an image forming apparatus  501  according to a second exemplary embodiment of the present invention. A predetermined constant voltage is supplied from a switching power source  104  to a DC/DC convertor  509  inside a control unit  505  via a power line  507  to be converted into another constant voltage. The converted constant voltage is supplied to a superimposing circuit  511  via a power line  514 . The superimposing circuit  511  superimposes control data from a CPU  510  onto the supplied constant voltage to supply the data and voltage to a separation circuit  113  of a driving unit  106  via a power line  512 . Since other parts of the configuration are the same as those of the first exemplary embodiment, descriptions thereof are not repeated. As another configuration, the other parts may, for example, be similar to those of the first exemplary embodiment without departing from the scope of the present invention. 
     As described above, it is possible to reduce the number of bundles of signal lines and to perform stable communication by performing signal communication via the power line having the small load fluctuation. 
     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 modifications, equivalent structures, and functions. 
     This application claims priority from Japanese Patent Application No. 2009-285751 filed Dec. 16, 2009, which is hereby incorporated by reference herein in its entirety.