Patent Publication Number: US-10310426-B2

Title: Image forming apparatus having switching circuit

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-129699 filed on Jun. 30, 2017, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The technology of the present disclosure relates to an image forming apparatus. 
     In an electrophotographic image forming apparatus, there are some cases where a heater is disposed in the image forming apparatus in order to prevent dew condensation of a photosensitive drum or an exposing device. The heater is provided to machine parts, such as the photosensitive drum and an optical device, in which dew condensation easily occurs. 
     A power supply circuit of the image forming apparatus is connected to either a load system circuit, which supplies power to an image forming apparatus body, or a heat system circuit, which supplies power to the heater, via a changeover switch. The changeover switch can be switched interlocking with a power switch of the image forming apparatus. The changeover switch connects the power supply circuit to a main circuit when the power switch is in an ON state, and connects the power supply circuit to the heat system circuit when the switch is in an OFF state. The power supply circuit is provided with a timer. The timer operates the heater by closing a contact point provided to the heat system circuit when a preset time has come. 
     SUMMARY 
     An image forming apparatus according to one aspect of the present disclosure includes an image forming apparatus body, a power switch, a control unit, and a power supply circuit. The control unit controls an image forming operation in a state in which the power switch is turned on. The power supply circuit supplies power to the control unit. 
     The image forming apparatus further includes a heater, a discharge device, and a humidity detection sensor. The heater heats a predetermined place in the image forming apparatus body. The discharge device discharges water vapor in the image forming apparatus body to an exterior. The humidity detection sensor detects humidity in the aforementioned image forming apparatus body or humidity associated with the humidity and transmits information on the detected humidity to the aforementioned control unit. 
     The power supply circuit includes a power circuit connected to a power supply, a main circuit including the control unit, a sub-circuit including the discharge device and the heater, and a switching circuit. The switching circuit connects the power circuit to the main circuit when the power switch is turned on and connects the power circuit to the sub-circuit when the power switch is turned off. 
     The sub-circuit includes a driving contact point of the heater, a driving contact point of the discharge device, and a timer. The timer performs electrical conduction of the driving contact point of the heater for a first setting time and performs electrical conduction of the driving contact point of the discharge device for a second setting time when the power switch is turned off. 
     The control unit performs timer setting control for determining whether the humidity in the image forming apparatus body is equal to or more than a threshold value on the basis of humidity information received from the humidity detection sensor, for setting the first setting time in the timer to 0 while setting the second setting time to a predetermined time larger than 0 when it is determined that the humidity is equal to or more than the threshold value, and for setting the first setting time in the timer to a predetermined time larger than 0 while setting the second setting time to 0 when it is determined that the humidity is less than the threshold value, in a state in which the power switch is turned on. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view illustrating an image forming apparatus in an embodiment. 
         FIG. 2  is a circuit diagram illustrating an example of a power supply circuit that supplies power to each element of an image forming apparatus. 
         FIG. 3  is a flowchart illustrating content of dew condensation prevention control in a control unit. 
         FIG. 4  is a diagram corresponding to  FIG. 3 , which illustrates an embodiment 2. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, examples of embodiments will be described in detail with reference to the drawings. It is noted that the technical scope of the present disclosure is not limited to the following embodiments. 
     Embodiment 1 
       FIG. 1  is a schematic view illustrating an image forming apparatus  1  in the present embodiment. The image forming apparatus  1  is a laser printer and includes a sheet feeding unit  10 , an image forming unit  20 , a fixing unit  30 , and a sheet discharge unit  40 . The sheet feeding unit  10  is provided at a lower part of an image forming apparatus body  60 , the sheet discharge unit  40  is provided on an upper surface of the image forming apparatus body  60 , and the image forming unit  20  and the fixing unit  30  are provided in the middle of a sheet conveyance path from the sheet feeding unit  10  to the sheet discharge unit  40 . Furthermore, the image forming apparatus body  60  is provided therein with a plurality of conveying roller pairs  11  to  13  along the sheet conveyance path. 
     The sheet feeding unit  10  has a sheet feeding cassette  10   a  in which sheets P are received, and a pick-up roller  10   b  for taking out the sheets P in the sheet feeding cassette  10   a  and sending the sheets P out of the cassette. The sheets P sent out of the cassette by the sheet feeding cassette  10   a  are supplied to the image forming unit  20  via the conveying roller pair  11 . 
     The image forming unit  20  has a photosensitive drum  21 , a charging device  23 , an exposing device  25 , a developing device  27 , and a transfer unit  29 . At the time of image formation, a peripheral surface of the photosensitive drum  21  is first charged by the charging device  23 , and then laser light based on document image data (for example, image data of a document image received from an external terminal) is irradiated to the surface of the photosensitive drum  21  by the exposing device  25 . By so doing, on the surface of the photosensitive drum  21 , an electrostatic latent image corresponding to the aforementioned image data is formed. The electrostatic latent image formed on the surface of the photosensitive drum  21  is developed by the developing device  27  as a toner image. In this way, the toner image is formed (carried) on the surface of the photosensitive drum  21 . The toner image is transferred to the sheet P, which is supplied from the sheet feeding unit  10 , by the transfer unit  29 . The sheet P with the transferred toner image is supplied to the fixing unit  30  by the rotation of a transfer roller in the transfer unit  29 . 
     The fixing unit  30  heats and presses the sheet P supplied from the transfer unit  29  between a fixing roller  30   a  and a pressure roller  30   b , thereby fixing the toner image to the sheet P. Then, the sheet P with the toner image fixed by the fixing unit  30  is sent to a downstream side in a sheet conveyance direction by the rollers  30   a  and  30   b . The sheet P sent from the fixing unit  30  is discharged to the sheet discharge unit  40  via the plurality of conveying roller pairs  12  and  13 . 
     The image forming apparatus body  60  is provided therein with an optical condensation heater  93   a , a drum heater  93   b , and a cassette heater  93   c . The optical condensation heater  93   a , the drum heater  93   b , and the cassette heater  93   c  are respectively provided in the vicinity of the exposing device  25 , the photosensitive drum  21 , and the sheet feeding cassette  10   a . The optical condensation heater  93   a  prevents dew condensation from occurring in an optical element (a mirror, a lens and the like) in the exposing device  25 . The drum heater  93   b  prevents the occurrence of image defects and jam due to sheet winding by maintaining the temperature of the photosensitive drum  21  and preventing dew condensation of the photosensitive drum  21 . The cassette heater  93   c  prevents the occurrence of paper jam from occurring when dew condensation occurs in the sheet feeding cassette  10   a  of the sheet feeding unit  10  and thus the sheet P becomes wet. These heaters  93   a  to  93   c  prevent dew condensation by raising the temperature of air and thus increasing the amount of saturated water vapor. 
     The image forming apparatus body  60  is further provided with a discharge fan (a discharge device)  94  for preventing dew condensation. The discharge fan  94  is provided to a sidewall adjacent to the image forming unit  20  in the image forming apparatus body  60 . The discharge fan  94  discharges air including water vapor in the image forming apparatus body  60  to an exterior, thereby reducing the amount of water vapor in the image forming apparatus body  60  and thus preventing the occurrence of dew condensation. 
     Next, with reference to  FIG. 2 , a power supply circuit that supplies power to each element of the image forming apparatus  1  will be described. The power supply circuit has a power circuit  70 , a main circuit  80 , a sub-circuit  90 , and a switching circuit  100 . 
     The power circuit  70  includes a power plug  71  which is connected to an outlet of an AC power supply. Two power supply lines of a hot line  72  and a neutral line  73  are connected to the power plug  71 . A fuse  74  is serially connected to the hot line  72 . A timer  75  is connected between the hot line  72  and the neutral line  73 . 
     Changeover switches  100   a  and  100   b  are respectively connected to one end of the hot line  72  and one end of the neutral line  73  of the power circuit  70 . The changeover switches  100   a  and  100   b  constitute a part of the changeover switch  100 . 
     The changeover switches  100   a  and  100   b  are driven by a switch driving circuit  101  to switch a connection destination (the power supply destination) of the power circuit  70  to either the main circuit  80  or the sub-circuit  90 .  FIG. 2  illustrates a state in which the power circuit  70  is connected to the main circuit  80  by the changeover switches  100   a  and  100   b  (corresponding to a first state in which the power circuit  70  supplies power to the main circuit  80 ). When the changeover switches  100   a  and  100   b  are switched to an opposite side of the state illustrated in  FIG. 2  by the switch driving circuit  101 , the power circuit  70  is connected to the sub-circuit  90  and the connection between the power circuit  70  while the main circuit  80  is disconnected (corresponding to a second state in which the power circuit  70  supplies power to the sub-circuit  90 ). 
     The switch driving circuit  101  is connected to a power switch  102  provided to an operation unit of the image forming apparatus body  60 . When a signal indicating the turning-on of the power switch  102  is received, the switch driving circuit  101  switches the changeover switches  100   a  and  100   b  to the main circuit  80  side as illustrated in  FIG. 2 . On the other hand, when a signal indicating the turning-off of the power switch  102  is received, the switch driving circuit  101  switches the changeover switches  100   a  and  100   b  to the sub-circuit  90  side. 
     The main circuit  80  includes a hot line  81 , a neutral line  82 , a DC power supply  83 , and an AC load  84 . The hot line  81  is connected to the hot line  72  of the power circuit  70  via the changeover switch  100   a  so as to be electrically connectable/disconnectable, and the neutral line  82  is connected to the neutral line  73  of the power circuit  70  via the changeover switch  100   b  so as to be electrically connectable/disconnectable. The DC power supply  83  and the AC load  84  are connected between the hot line  81  and the neutral line  82 . A control unit  85  is connected to the DC power supply  83  to control an image forming operation which is performed by the image forming apparatus  1 . 
     The control unit  85 , for example, is configured by a microcomputer including a CPU, a ROM, a RAM and the like. A DC load and various sensors are connected to the control unit  85 .  FIG. 2  illustrates only a humidity detection sensor  87 , which measures humidity in the image forming apparatus body  60 , as an example of the sensor. 
     The sub-circuit  90  includes a hot line  91 , a neutral line  92 , the three heaters  93   a  to  93   c , and the discharge fan  94 . The hot line  91  is connected to the hot line  72  of the power circuit  70  via the changeover switch  100   a  so as to be electrically connectable/disconnectable, and the neutral line  92  is connected to the neutral line  73  of the power circuit  70  via the changeover switch  100   b  so as to be electrically connectable/disconnectable. The three heaters  93   a  to  93   c  are disposed in parallel to one another and are connected to a first line  96  across between the hot line  91  and the neutral line  92 . The discharge fan  94  is connected to a second line  97  across between the hot line  91  and the neutral line  92 . A reference number  95  of the drawing indicates a diode for counter electromotive voltage protection, which is disposed in parallel to the discharge fan  94 . 
     The first line  96  and second line  97  are respectively provided with contact points A ( 75   a  and  75   b ) which are driven by the timer  75 . In a state in which the power circuit  70  has been connected to the sub-circuit  90 , when the A ( 75   a  and  75   b ) are closed, the heaters  93   a  to  93   c  and the discharge fan  94 , which are disposed on the first line  96  and second line  97 , operate. The two contact points A ( 75   a  and  75   b ) can be driven by the timer  75  independently from each other. Consequently, it is possible to operate the heaters  93   a  to  93   c  and the discharge fan  94  independently from each other in accordance with setting content of the timer  75 . In the following description, the contact point A ( 75   a ) provided on the first line  96  will be referred to as a heater driving contact point, and the contact point A ( 75   b ) provided on the second line  97  will be referred to as a fan driving contact point. 
     The timer  75  is connected to the control unit  85  so as to be able to transmit and receive signals. The timer  75  stores an ON time (a conduction time) of the heater driving contact point  75   a  as a first setting time T 1 , and stores an ON time of the fan driving contact point  75   b  as a second setting time T 2 . The setting times T 1  and T 2  stored in the timer  75  are set by the control unit  85 . The control unit  85  updates (sets) the setting times T 1  and T 2  at predetermined time intervals in accordance with humidity detected by the humidity detection sensor  87  as will be described later. 
     With reference to  FIG. 3 , details of the setting control of the first and second setting times T 1  and T 2  by the control unit  85  will be described. 
     In step SA 1 , the control unit  85  calculates humidity in the image forming apparatus body  60  on the basis of a detection signal (humidity information) of the humidity detection sensor  87 , and determines whether the calculated humidity is equal to or more than a threshold value set in advance. When the determination is NO, the control unit  85  proceeds to step SA 3 , and when the determination is YES, the control unit  85  proceeds to step SA 2 . 
     In step SA 2 , the control unit  85  sets the first setting time T 1 , which is the ON time of the heater driving contact point  75   a  stored in the timer  75 , to 0, sets the second setting time T 2 , which is the ON time of the fan driving contact point  75   b , to a predetermined time Tf larger than 0, and then proceeds to step SA 4 . The predetermined time Tf is preferably a sufficient time capable of lowering the humidity in the image forming apparatus body  60  to be less than the threshold value, and for example, is set to 30 minutes to one hour. The predetermined time Tf may be a constant value or may be longer as the humidity detected by the humidity detection sensor  87  is higher. 
     In step SA 3  performed when the determination of step SA 1  is NO, the control unit  85  sets the first setting time T 1 , which is the ON time of the heater driving contact point  75   a  stored in the timer  75 , to a predetermined time Th larger than 0, sets the second setting time T 2 , which is the ON time of the fan driving contact point  75   b , to 0, and then proceeds to step SA 4 . The predetermined time Th is preferably an average value of times from an OFF operation of the power switch  102  of the image forming apparatus  1  to an ON operation of the power switch  102 . It is sufficient if the average value is calculated by the control unit  85 . The predetermined time Th may not be based on such an average value and may be set by predicting an OFF time of the power switch  102  of the image forming apparatus  1 . That is, for example, when it is assumed that the power switch  102  of the image forming apparatus  1  is in an OFF state from 9:00 PM to 9:00 AM of the following day, it is sufficient if the predetermined time Th is set to 12 hours. The predetermined time Th is sufficiently longer than the predetermined time Tf described in the step SA 2 . 
     In step SA 4 , the control unit  85  determines whether a predetermined time (for example, 10 minutes) has passed after the determination process of step SA 1  is performed. When the determination is NO, the control unit  85  performs the process of the present step SA 4  again, and when the determination is YES, the control unit  85  returns. 
     In the image forming apparatus  1  configured as above, when the power switch  102  is turned on, the power circuit  70  is connected to the main circuit  80  via the changeover switches  100   a  and  100   b . Then, power is supplied to each element of the image forming apparatus  1  and a print process and the like are performed, so that temperature in the image forming apparatus body  60  rises. When the temperature in the image forming apparatus body  60  is high, dew condensation does not occur, but when the power switch  102  is turned off and the temperature in the image forming apparatus body  60  is reduced, dew condensation may occur. 
     In order to solve the problem, in the conventional image forming apparatus, a heater is disposed at a place where image defects or failure of the apparatus may occur due to the occurrence of dew condensation, and is operated even after a power switch is turned off to maintain the amount of saturated water vapor in the air to be high, thereby preventing the occurrence of the dew condensation. However, in a case where humidity in the image forming apparatus is high, since the amount of water vapor in the air is large, it is not possible to completely suppress the occurrence of the dew condensation even after the heater is operated. In this regard, it is considered to suppress the occurrence of the dew condensation by reducing the amount of water vapor in the image forming apparatus. As a method for reducing the amount of water vapor, there is a method for forcibly discharging air including water vapor in the image forming apparatus out of the apparatus by a discharge fan. However, power for generally driving the discharge fan is considerably larger than power for driving the heater. Consequently, when the discharge fan is simply operated, there is a problem that an energy saving property is reduced. 
     However, in the present embodiment, in a state in which the power switch  102  is turned on, the control unit  85  determines whether humidity in the image forming apparatus body  60  is equal to or more than a threshold value on the basis of humidity information received from the humidity detection sensor  87 . When it is determined that the humidity is equal to or more than the threshold value, the control unit  85  is configured to set the first setting time T 1  (the ON time of the heater driving contact point  75   a ) in the timer  75 , to 0 and set the second setting time T 2  (the ON time of the fan driving contact point  75   b ) to the predetermined time Tf larger than 0. However, when it is determined that the aforementioned humidity is less than the aforementioned threshold value, the control unit  85  is configured to set the aforementioned first setting time in the timer  75 , to the predetermined time Th larger than 0 and set the aforementioned second setting time to 0. 
     According to the configuration, when the humidity in the image forming apparatus body  60  is equal to or more than the threshold value, after the power switch  102  is turned off, since the discharge fan  94  is driven by the timer  75  during only the predetermined time Tf (=the second setting time), the heaters  93   a  to  93   c  do not operate. 
     Consequently, when the humidity in the image forming apparatus body  60  is high (when the amount of water vapor is large), the discharge fan  94  capable of reducing the amount of water vapor is operated, so that it is possible to reliably suppress the occurrence of dew condensation. 
     On the other hand, when the humidity in the image forming apparatus body  60  is less than the threshold value, after the power switch  102  is turned off, since the heaters  93   a  to  93   c  are driven by the timer  75  during only the predetermined time (=the first setting time T 1 ), the discharge fan  94  does not operate. 
     Consequently, when the humidity in the image forming apparatus body  60  is low, since the amount of water vapor in the air is small, the discharge fan  94  is not operated and the heaters  93   a  to  93   c  consuming low power are operated, so that it is possible to prevent the occurrence of dew condensation. 
     Thus, in the present embodiment, it is possible to reliably prevent dew condensation from occurring in the image forming apparatus body  60  after the power switch  102  is turned off without reducing an energy saving property. Furthermore, it is possible to prevent operation noise of the discharge fan  94  from being unnecessarily generated. 
     Furthermore, in the present embodiment, the control unit  85  is configured to perform timer setting control (the processes of steps SA 1  to SA 3 ) at predetermined time intervals. 
     In this way, it is possible to set the setting times T 1  and T 2  of the timer  75  by maximally reflecting humidity in the image forming apparatus body  60  at a current time point. 
     Embodiment 2 
       FIG. 4  illustrates an embodiment 2. In the present embodiment, setting timings of the setting times T 1  and T 2  of the timer  75  by the control unit  85  are different from those of the embodiment 1. That is, in the present embodiment, the setting times T 1  and T 2  of the timer  75  are set only immediately after the power switch  102  is turned off. 
     Specifically, in step SB 1 , on the basis of an operation signal of the power switch  102 , the control unit  85  determines whether the power switch  102  is turned off. When the determination is NO, the control unit  85  returns without setting the setting times T 1  and T 2  of the timer  75 , and when the determination is YES, the control unit  85  proceeds to step SB 2 . 
     Processes of steps SB 2  to SB 4  are similar to those of steps SA 1  to SA 3  in the embodiment 1. 
     In step SB 5 , the control unit  85  drives the changeover switches  100   a  and  100   b  (the switching circuit  100 ) by the switch driving circuit  101  to switch a connection destination of the power circuit  70  from the main circuit  80  to the sub-circuit  90 , and then returns. 
     According to the configuration, in the present embodiment, immediately after the power switch  102  is turned off and before a connection destination of the power switch  102  is switched from the main circuit  80  to the sub-circuit  90  by the switching circuit  100 , timer setting control (steps SB 2  to SB 4 ) is performed. Consequently, as compared with the case where the setting times T 1  and T 2  of the timer  75  are set at predetermined time intervals during the operation of the image forming apparatus  1 , it is possible to reduce an arithmetic load of the control unit  85 . 
     Furthermore, humidity in the image forming apparatus body  60  is measured by the humidity detection sensor  87  at the nearest time at which the heaters  93   a  to  93   c  or the discharge fan  94  is operated, so that it is possible to set the setting times T 1  and T 2  of the timer  75  by maximally reflecting humidity in the image forming apparatus body  60  at a current time point. 
     Other Embodiments 
     In the aforementioned each embodiment, humidity in the image forming apparatus body  60  is detected by the humidity detection sensor  87 ; however, the technology of the present disclosure is not limited thereto. For example, the humidity detection sensor  87  may be allowed to detect humidity of an interior in which the image forming apparatus body  60  is installed. That is, it is sufficient if humidity detected by the humidity detection sensor  87  is humidity correlated (that is, associated) with humidity in the image forming apparatus body  60 . 
     Furthermore, in the aforementioned each embodiment, even when it is determined that humidity in the image forming apparatus body  60  is equal to or more than the threshold value, when a silent mode (a mode for prioritizing suppression of noise) is set, the first setting time (the ON time of the heater driving contact point  75   a ) in the timer  75  may be set to the predetermined time Th larger than 0 and the second setting time (the ON time of the fan driving contact point  75   b ) may be set to 0. In this way, it is possible to prevent silence performance from being impaired due to the operation of the discharge fan  94  even when a user has set an operation mode of the image forming apparatus  1  as a silent mode. 
     Furthermore, in the aforementioned each embodiment, the discharge fan  94  is used as a discharge device for discharging water vapor in the image forming apparatus body  60  to an exterior; however, the technology of the present disclosure is not limited thereto and for example, a heat exchanger may be used. 
     It should be noted that the technical scope of the present disclosure is not limited to the aforementioned each embodiment and includes configurations obtained by appropriately combining the embodiments with each other.