Abstract:
An image forming apparatus having a load control device which includes a load that executes a job, a relay that selectively connects the load with a power supply, and a central processing unit that outputs a plurality of control signals. Also included is an application specific integrated circuit that outputs a load driving signal to the load in response to a control signal sent from the central processing unit, an output condition observing device that observes an output condition of the application specific integrated circuit and a timer that counts pulses when the output condition is active and does not count pulses when the output condition is not active. In addition, the load stops driving when the timer has counted the prescribed number of pulses.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a load control apparatus for use in an image forming apparatus, such as a copier, a facsimile, a printer and a hybrid machine having a plurality of functions of the image forming apparatus, and in particular, relates to a load control apparatus capable of avoiding damage to a load of the image forming apparatus. 
     2. Discussion of the Background Art 
     A variety of technologies have been developed that avoid damage to a load, such as a motor and so on, by stopping the load in an emergency to keep the load operating safely. For example, the below-described technologies are well known. 
     As described in the Japanese Laid Open Patent Publication No. 5-286642, a sheet cassette in an image forming apparatus is moved by a motor between a setting position and a removing position. A sensor is provided to detect an obstacle that may exist between the setting position and the removing position. The motor is controlled to stop driving when the sensor detects the obstacle. 
     Further, as described in the Japanese Laid Open Patent Publication No. 5-304718, a sensor is provided to measure an amount of current. The sensor outputs a signal when a current larger than a rated current flows. A message or a mark indicating an overload state is displayed when the signal is output. A current fuse is then promoted to melt down, since the current flow is amplified through a safety circuit which avoids problems from occurring with parts of the motor. 
     Further, as described in the Japanese Laid Open Patent Publication No. 6-6996, a sensor is provided to detect a reverse revolution of a motor that drives a reciprocating device. The sensor outputs a signal when the motor does not revolve in a reverse direction within a prescribed time period after the reverse revolution is commanded. The motor is controlled to stop when the sensor does not output the signal. 
     In recent years, a plurality of motors, such as stepping motors, are increasingly employed in an image forming apparatus and so on. A base plate that supports the stepping motor is directly mounted on mold parts of the image forming apparatus. Thus, if for some reason the stepping motor is supplied with power for a long time, the stepping motor may generate heat, thereby having an abnormally high temperature. As a result, the mold parts may melt and become deformed. Further, the operational safety features required of the stepping motor may be lost. 
     In addition, if a central processing unit (hereinafter referred to as a CPU) of a microcomputer of the image forming apparatus controls a plurality of stepping motors by itself, almost all of the operations of the CPU are occupied by control operations for the stepping motors. Thus, a hardware circuit, such as an application specific integrated circuit (hereinafter referred to as an ASIC) has sometimes been recently employed to control the stepping motor for the CPU. 
     In a case of using such an ASIC, no problem occurs when a prescribed allowable amount of power supply voltage is applied having an alternating current (hereinafter referred to as AC), for example, which is more or less 15 percent of a rated voltage for the case of a copier. 
     However, if a plurality of copiers employing the ASIC are connected to an AC power supply constituted by one circuit, electrical power lower than the prescribed allowable range may be supplied to each of the copiers. Accordingly, a voltage, which is outside the allowable range, may be applied to the microcomputer and the ASIC. As a result, the microcomputer and the ASIC sometimes operate in an unexpected manner. For example, the ASIC may unexpectedly continue to output signals for driving the stepping motor. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide an image forming apparatus having a novel load control apparatus. One example of an image forming apparatus having a load control device includes a load that executes a prescribed image forming process, a relay that selectively connects the load with a power supply, and a central processing unit that outputs a plurality of control signals. Also included is an application specific integrated circuit that outputs a load driving signal to the load in response to a control signal sent from the central processing unit, an output condition observing device that observes an output condition of the application specific integrated circuit, and a timer that starts counting pulses when the output condition is active and does not start counting pulses when the output condition is not active. In addition, the load stops driving when the timer has counted a prescribed time period. 
     In another embodiment, a load stops driving when a relay that connects a power supply with the load is turned OFF. The relay is turned OFF when a timer that counts pulses, during an active output condition of an application specific integrated circuit, has counted a prescribed time period. 
     In still another embodiment, a load stops driving when an initializing device initializes an application specific integrated circuit. The initializing device initializes the ASIC when a timer that counts pulses, during an active output condition of the ASIC, has counted a prescribed time period. 
     In still another embodiment, a load stops driving when a main power supply stops applying power to an application specific integrated circuit. The main power is stopped when a timer that counts pulses, during an active output condition of an ASIC, has counted a prescribed time period. 
     In still another embodiment, provided is an output condition observing device having a function of observing an operation condition of the image forming apparatus. A relay quickly disconnects the load with a power supply when a timer that counts pulses, during an active output condition of the application specific integrated circuit, has counted a prescribed time period and an image formation is not executing, or after the timer has counted the prescribed time period and the image formation has completed. 
     In still another embodiment, an initializing device initializes an application specific integrated circuit and a load stops driving only when a timer that counts pulses, during an active output condition of the application specific integrated circuit, has counted a prescribed time period and an image formation is not executing, or after the timer has counted the prescribed time period and the image formation has completed. 
     In still another embodiment, provided is an output condition observing device including a function of observing an operation condition of the image forming apparatus. A load stops driving only when a main power supply is not applied to the application specified integrated circuit, a timer that counts pulses, during an active output condition of the application specific integrated circuit, has counted a prescribed time period, and an image formation is not executing, or after the timer has counted the prescribed time period and the image formation has completed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention as well as other objects and features thereof, reference is made to the following detailed description to be read in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a block diagram that illustrates a load control apparatus of the present invention; 
     FIG. 2 is a timing diagram that illustrates timing of a reset signal generation by a reset circuit illustrated in FIG. 1; 
     FIG. 3A and 3B are timing diagram that illustrates an output timing of each series of a rectangular wave signal for the driving motors illustrated in FIG. 1; 
     FIG. 4 is a schematic view that illustrates a sheet feeding unit having motors illustrated in FIG. 1, which is used in a duplex copier; 
     FIG. 5 is a flowchart that illustrates a process of determining if electrical power is applied to the motors illustrated in FIG. 1 by observing a signal output condition of an ASIC using an observation function of the reset circuit illustrated in FIG. 1; 
     FIG. 6 is a flowchart that illustrates a control process of an output of a rectangular wave from an ASIC to the reset circuit illustrated in FIG. 1 depending on a determination if a flag is set as illustrated in FIG. 5; 
     FIG. 7 is a flowchart that illustrates a control process of applying a power supply to motors by controlling a first relay that selectively connects a power supplying line with the motors depending on the determination of a flag as illustrated in FIG. 5, 
     FIG. 8 is a flowchart that illustrates a control process of applying a power supply to motors, which slightly modifies the control process illustrated in FIG. 7, by adding a step which determines if a copier is at work; 
     FIG. 9 is a flowchart that illustrates a control process of applying a power supply to a copier by selectively activating a second relay that may connect a power supplying line with the copier depending on the determination of a flag as illustrated in FIG. 5; 
     FIG. 10 is a flowchart that illustrates a control process of applying a power supply to a copier, which slightly modifies the control process illustrated in FIG. 9, by adding a step which determines if the copier is at work; and 
     FIG. 11 is a flowchart that illustrates a control process of applying a power supply to motors by selectively stopping an output of a rectangular wave from an ASIC to a reset circuit illustrated in FIG. 1, which may reset the ASIC depending on the determination of a flag as illustrated in FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the present invention will now be explained, in which like reference numerals designate identical or corresponding parts throughout the several views. 
     An outline of a constitution of a load control apparatus of the present invention is illustrated in FIG.  1 . The load control apparatus includes a microcomputer unit  3  having at least a CPU  1  and an ASIC  2 . The ASIC  2  may receive signals for driving a stepping motor, indicating a revolution direction of the stepping motor, indicating a number of rounds per minutes (hereinafter referred to as rpm) of the stepping motor, and indicating an amount of moving distance of the stepping motor from the CPU  1 . The ASIC  2  outputs a plurality of series of a rectangular wave signal to each of four coils of the stepping motor to keep the coils supplied with electrical power from their corresponding ports A 1 , A 2 , B 1  and B 2  to drive the stepping motor. 
     The ASIC  2  may change a form of the rectangular wave signal to change a revolution direction corresponding to the signal applied from the CPU  1 . The ASIC  2  may also change a cycle of the rectangular wave in accordance with the signal indicating the number of rpm. The load control apparatus also includes a read only memory  4  (hereinafter referred to as a ROM  4 ) and a random access memory  5  (hereinafter referred to as a RAM  5 ), each connected to the microcomputer unit  3  by an address bus and a data bus. 
     The load control apparatus further includes a reset circuit  6  connected to both an input port P 1  and an output port P 3 . In addition, the load control apparatus includes first and second stepping motors  7  and  8 , and a driver  9  connected to both output ports A 1 , A 2 , B 1  and B 2  and the first and second stepping motors  7  and  8 . The driver  9  drives the stepping motors  7  and  8 . Also included are first and second relays  10  and  11  each respectively connected to output ports P 2  and P 4  of the microcomputer unit  3 . Each of the first and the second relays  10  and  11  respectively turn a motor power supply and an AC power supply (not shown) ON and OFF for the image forming apparatus. 
     The ROM  4  may store a program that controls the load control apparatus. The RAM  5  may be used when handling and storing data during execution of the program&#39;s commands. The ASIC  2  outputs a rectangular wave signal to the driver  9  when driving the motors  7  and  8 . The first relay  10  may close and open a contact point  10   a  of the relay under control of the microcomputer  3  to selectively connect a power supply line with the stepping motors  7  and  8 . The second relay  11  may close and open a contact point of the relay, not shown, under a control of the microcomputer  3  to selectively connect an AC power supply line with the image forming apparatus. 
     The reset circuit  6  may have a function of observing a condition of the microcomputer  3  and a function of a reset timer. The observing function includes a function of determining if the ASIC  2  outputs a rectangular wave signal from its output ports and a function of determining if an image forming apparatus is at work. If the ASIC  2  outputs the signal from one of the ports, the observing function recognizes an output condition of the ASIC as active. If the ASIC  2  does not output any signal from each of the ports, the observing function recognizes the output condition as non-active. 
     When the microcomputer  3  normally operates, a rectangular wave P 11  having a prescribed cycle, as illustrated in FIG. 2, may be output from the output port P 1  to the reset circuit  6 . If the microcomputer  3  abnormally operates in such a manner that the CPU  1  does not operate in accordance with a program stored in the ROM  4 , the rectangular wave P 11  is not output from the output port P 1 . 
     The reset timer installed in the reset circuit  6  may generate an exponential curve of voltage or current when the microcomputer unit  3  normally operates, and reset an amount of the voltage or current using the rectangular wave P 11  as illustrated in FIG.  2 . The reset timer may output a reset signal when the voltage or the current of the exponential curve is not reset by the rectangular wave P 11 . The reset signal is input to the input port P 3  and then resets a status of the microcomputer unit  3  so that it may start from an initial state. The microcomputer unit  3  is also initialized by a reset signal when electrical power is first supplied from an AC power supply. 
     Since an amount the voltage or current of the exponential curve is reset by a rising portion or a dropping portion of the rectangular wave P 11 , as illustrated in FIG. 2, a reset signal is not output from the reset circuit  6  as long as the microcomputer unit  3  normally operates. A cycle of the rectangular wave P 11  may be determined to be smaller than a time when the exponential curve reaches a threshold level illustrated in FIG.  2 . 
     A four-phase type stepping motor having four coils is utilized for each of the motors  7  and  8 . The stepping motor is driven when four series of a rectangular wave signal are respectively input to the corresponding four coils. To output four series of a rectangular wave signal, four output ports A 1 , A 2 , B 1  and B 2  of the ASIC  2  may be respectively connected to a plurality of stepping motors. A timing diagram that illustrates an output timing of the rectangular wave signal for driving the stepping motors  7  and  8  is illustrated in FIGS. 3A and 3B. A waveform of the rectangular wave illustrated in FIG. 3A is generally called a two phase excitation driving waveform. A one-two phase excitation driving waveform, as illustrated in FIG. 3B, can be used for the two phase excitation driving. 
     A current may flow through the first relay  10  when a high value signal is generated by a logic circuit, not shown, disposed in the microcomputer  1 , and is output from the port P 2 . The contact point of the relay  10   a  then closes the power supply line so that a 24 volt power supply may supply direct current (hereinafter referred to as DC) to the stepping motors  7  and  8 . Thus, the stepping motors  7  and  8  are ready to be driven. When, the output signal from the port P 2  has a low value, the contact point of the relay  10   a  opens the power supply line, since current does not flow through the first relay  10 , and accordingly, the stepping motors  7  and  8  are not ready to be driven. 
     One example of using stepping motors is illustrated in FIG.  4 . The stepping motors may be employed in a duplex copysheet feeding unit  12  of an image forming apparatus, which includes side fences and an end fence each for aligning side edges of a received copysheet having a toner image on one side. 
     When the first motor  7  is driven, a side fence moving belt  13  wound around an axis of the first motor  7  rotates a side fence driving gear  14  in a specified direction. A pair of racks  16  mount the side fences  15  and mesh with the side fence driving gear  14  from an opposite side. 
     Thus, when the stepping motor  7  is driven, the pair of the side fences  15  may simultaneously move in opposite directions. The side fences  15  may narrow and expand a distance between both side fences corresponding to rotational directions of the stepping motor  7 . 
     When the second motor  8  is driven, an end fence moving belt  18  wound around an axis of an end fence driving pulley  17  moves the end fence  19  in a specified direction. Thus, when the stepping motor  8  is driven, the end fence  19  may move back and forth corresponding to rotational directions of the stepping motor  8 . 
     Hereinbelow, embodiments of the load control apparatus of the present invention are explained in detail referring to FIGS. 5 through 11. First, FIG. 5 explains a determination process that determines if electrical power is supplied to the first and second stepping motors  7  and  8  using an observing function of the reset circuit  6 . As illustrated in FIG. 5, it is determined in step S 1  if at least one of the output ports A 1 , A 2 , B 1  and B 2  of the ASIC  2  outputs a rectangular wave signal. 
     If none of the ports A 1 , A 2 , B 1  and B 2  output a rectangular wave signal, a motor power supply timer included in the CPU  1 , as illustrated in FIG. 1, is reset in step S 2 . This is because a problem likely has not occurred in the microcomputer  3 . If at least one port outputs a rectangular wave signal, a motor power-supply timer starts counting pulses output from a clock generator illustrated in FIG.  2 . 
     In step S 4  it is determined if the motor power supply timer has counted, for example, up to three minutes, that is regarded as an upper limit for the ASIC  2  to be normally operating. If the motor power supply timer has counted up to three minutes, a flag that demands a stop of an output of a rectangular wave P 11  from the output port P 1  to the reset circuit  6  is set in step S 5 . This is because a problem may have occurred in the microcomputer unit  3 , and accordingly the loads may be damaged. The step then returns to a main routine in a step indicated by “RET” illustrated in FIG. 5 (hereinafter, a step indicated by “RET” in the Figures means the same thing). The above-mentioned determining process is repeated as long as the electrical power supply continues to be applied to the image forming apparatus. 
     When a prescribed job to be performed by the stepping motors  7  and  8  is completed, and accordingly electrical power is stopped from being supplied to the stepping motors  7  and  8  before elapsing of three minutes, the motor power supply timer is reset. This means that the prescribed job has safely completed. The above-mentioned reset operation is executed, for example, by a program stored in the ROM  4  by rewriting a time value of zero on a prescribed amount of time value stored in the RAM  5 . A length of time of the motor power supply timer can be determined at a level longer than a time period required for the load to complete its job. 
     A control process after the determination if the flag is set in step S 5  is illustrated in FIG.  6 . As illustrated in FIG. 6, it is determined in step S 6  if the flag is set. If the flag is not set, the rectangular wave P 11  continues to be output from the ASIC  2  to the reset circuit  6  in step S 7 . If the flag is set, the output of the rectangular wave P 11  is stopped in step S 8 . The reset circuit  6  then generates and outputs a reset signal as illustrated in FIG. 2 to the microcomputer unit  3  through the port P 3 . Both the ASIC  2  and the CPU  1  are then reset and restart operations. Since the ASIC  2  is reset when the reset signal is input to the microcomputer unit  3 , a rectangular wave signal that drives the driver  9  is not output from each of the ports A 1 , A 2 , B 1  and B 2 . Each of the stepping motors  7  and  8  then stop, even if the DC power supply is applied to the motors, since the signal is not applied to the driver  9 . The above-mentioned process is repeated as long as the electrical power is supplied to the image forming apparatus. 
     Hereinbelow, a slightly modified embodiment of the load control apparatus is explained referring to FIG.  7 . 
     As illustrated in FIG. 7, it is determined in step S 9  if the flag is set in step S 5 . If the flag is not set, the first relay  10  is turned ON so that the contact point  10   a  closes, and accordingly the electrical power supply line is connected with the motors  7  and  8  in step S 10 . If the flag is set, the first relay  10  is turned OFF so that the contact point  10   a  opens, and accordingly the electrical power supplying line is disconnected with the motors  7  and  8  in step S 11 . Thus, when the ASIC  2  or CPU  1  abnormally operates, namely, the motor power supply timer has counted up to three minutes, the motors  7  and  8  stop driving. 
     Hereinbelow, another embodiment of the load control apparatus is explained referring to FIG. 8. A control process illustrated in FIG. 8 is similar to that of FIG. 7 except for a step S 12 . As illustrated in FIG. 8, it is determined in step S 12  if an image forming apparatus, such as a copier, is at work. If the image forming apparatus is at work, the first relay  10  is not turned OFF in step S 10 , even if the flag is set in step S 9 . This is because a sheet may jam, for example, in the duplex sheet-feeding tray if the motors  7  and  8  quickly stop. When the image formation is then completed, the motors  7  and  8  may stop. If it is determined that the image forming apparatus is not at work in step S 12 , the first relay  10  is turned OFF in step S 11 . The determination if the copier is at work may be executed, for example, by a program stored in the ROM  4  by determining a condition, for example, of a display of a copy start key, not shown, that differently displays something depending on operational conditions. The copy start key generally is displayed in red when the copier is at work and in blue when in a copy waiting mode. 
     Hereinbelow, still another embodiment of the load control apparatus is explained referring to FIG.  9 . Since a control process of this embodiment is similar to the control process using the first relay  10  illustrated in FIG. 7, a second relay  11  is controlled almost in a same manner as the first relay  10  as explained earlier referring to FIG.  7 . Therefore, if the flag is set in step S 9 , the second relay  11  is turned ON in step S 10 . Thus, electrical power is applied to the image forming apparatus, and accordingly the stepping motors  7  and  8  are driven. If the flag is not set in step S 9 , the second relay  11  is turned OFF in step S 11 . Thus, the electrical power is stopped from being supplied to the image forming apparatus, and accordingly the stepping motors  7  and  8  stop driving. 
     Hereinbelow, still another embodiment of the load control apparatus is explained referring to FIG.  10 . Since, a control process of this embodiment is similar to the control process illustrated in FIG. 8, the second relay  11  is controlled almost in a same manner as the first relay  10  illustrated in FIG.  8 . Thus, if it is determined that the copier is at work in step S 12 , electrical power is not stopped from being supplied to the image forming apparatus in step S 10 . When the copier completes its work, the stepping motors  7  and  8  stop driving. Further, if it is determined that the copier is not at work in step S 12 , the electrical power is stopped from being supplied to the image forming apparatus in step S 11 . 
     Hereinbelow, still another embodiment of the load control apparatus is explained referring to FIG. 11. A control process that controls an output of the rectangular wave P 11  from the ASIC  2  is illustrated in FIG. 11. A control process of this embodiment is similar to the control process illustrated in FIG. 9 except for steps S 10  and S 11 . If it is determined that the copier is at work in step S 12 , a rectangular wave continues to be output to the reset circuit  6  in step S 10 , even when the flag is set in step S 9 . The reason why the rectangular wave P 11  continues to be output even when the flag is set is the same as mentioned earlier. If it is determined that the copier is not at work in step S 12 , the rectangular wave P 11  may be discontinued from being output from the microcomputer  3  to the reset circuit  6  in step S 11 . The reset circuit  6  then outputs a reset signal to the microcomputer unit  3 , thereby stopping output from the microcomputer to the driver  9 , and stopping the driving motors  7  and  8 . If it is determined that the copier is at work in step S 12 , the rectangular wave P 11  may continue to be output from the microcomputer  3  to the reset circuit  6  in step S 10 . Thus, the stepping motors  7  and  8  continue a prescribed job. When the copier completes the prescribed job, the rectangular wave P 11  is stopped from being output. 
     Obviously, numerous additional modifications and variations of the present invention are possible in light of the 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. The present application is based on Japanese priority document 10-21500, the contents of which are incorporated by reference.