JP2024122470A - Image forming device - Google Patents

Abstract

To provide a technique which can detect the interruption of AC voltage using a configuration provided in an image formation apparatus.SOLUTION: A printer 1 includes: a fuser 7 which has a heater 31 connected via a relay 33 to first and second input terminals T1, T2 that input AC voltage from a commercial power source and fixes a developer on a sheet; and a zero cross circuit 38 which outputs a full-wave zero cross signal indicating a full-wave zero cross of the AC voltage when the first and second input terminals T1, T2 and the heater 31 are turned into the connection state by the relay 33. The zero cross circuit 38, when the first and second input terminals T1, T2 and the heater 31 are turned into the non-connection state by the relay 33, outputs a half-wave zero cross signal indicating a half-wave zero cross of the AC voltage in a case where the AC voltage is input to the first and second input terminals T1, T2, and does not output the half-wave zero cross signal in a case where no AC voltage is input to the first and second input terminals T1, T2.SELECTED DRAWING: Figure 5

Description

This application relates to technology for detecting interruptions in AC voltage input to an image forming device.

Patent document 1 describes a converter device that converts an input AC voltage into a DC voltage, and that includes an AC interruption detection circuit that outputs an AC interruption detection signal when the input AC voltage is interrupted, and a discharge circuit that discharges the residual charge in the X capacitor when the AC interruption detection signal is output from the AC interruption detection circuit.

International Publication No. WO2012/140840 T1

However, since the converter device described in Patent Document 1 is equipped with an AC interruption detection circuit, it can detect when the input AC voltage is interrupted. However, if a converter device that does not have an AC interruption detection circuit is used in an image forming device, it is necessary to add a separate AC interruption detection function, such as an AC interruption detection circuit, to the image forming device.

The present application aims to provide a technology that makes it possible to detect interruptions in AC voltage using a configuration provided in an image forming device.

To achieve the above object, the image forming apparatus of the present application is equipped with a fixing unit having an input terminal for inputting an AC voltage from a commercial power source and a heater connected via a relay, fixing a developer image to a sheet, and a zero-cross circuit that connects the input terminal and the heater by the relay and outputs a full-wave zero-cross signal indicating the zero-cross of a full wave of the AC voltage, and is characterized in that when the input terminal and the heater are disconnected by the relay, the zero-cross circuit outputs a half-wave zero-cross signal indicating the zero-cross of a half wave of the AC voltage when an AC voltage is input to the input terminal, and does not output a half-wave zero-cross signal when no AC voltage is input to the input terminal.

According to the image forming device of the present application, the zero cross circuit outputs a half-wave zero cross signal when an AC voltage is input to the input terminal, even if the relay is in a disconnected state. In this case, the zero cross circuit does not output a half-wave zero cross signal when no AC voltage is input to the input terminal. Therefore, by detecting whether or not a half-wave zero cross signal is being output from the zero cross circuit, it is possible to detect whether or not an AC voltage is being input to the input terminal, and therefore it is possible to detect the interruption of the AC voltage using the zero cross circuit provided in the image forming device.

The zero cross circuit further includes a diode bridge circuit configured by connecting in parallel a first series-connected diode configured by connecting a cathode of a first diode to an anode of a second diode and a second series-connected diode configured by connecting a cathode of a third diode to an anode of a fourth diode, a relay, and a signal output circuit, one end of the input terminal is connected to one end of the heater by a first connection path, the other end of the heater is connected to the anode of the fourth diode by a second connection path, the cathode of the third diode is connected to the other end of the input terminal by a third connection path, a connection point between the cathode of the first diode and the anode of the second diode is connected to the first connection path by a fourth connection path, an input side of the signal output circuit is connected between a connection point between the anode of the second diode and the anode of the fourth diode and a connection point between the cathode of the first diode and the cathode of the third diode, and the relay is disposed between the cathode of the third diode and the anode of the fourth diode.

When the relay is in a connected state, the zero-cross circuit outputs a full-wave zero-cross signal. When the relay is in a disconnected state, the heater is not energized. When the relay is in a disconnected state and an AC voltage is input to the input terminal, a current due to a half-wave component of one pole of the AC voltage flows from one end of the input terminal to the other end of the input terminal via the first connection path, the fourth connection path, the second diode, the signal output circuit, the third diode, and the third connection path. On the other hand, a current due to a half-wave component of the other pole of the AC voltage does not flow from the other end of the input terminal to one end because the relay is in a disconnected state. Therefore, when the relay is in a disconnected state and an AC voltage is input to the input terminal, the zero-cross circuit outputs a half-wave zero-cross signal. On the other hand, when the relay is in a disconnected state and an AC voltage is not input to the input terminal, no current flows between one end and the other end of the input terminal, so the zero-cross circuit does not output a half-wave zero-cross signal. In this way, by detecting whether a half-wave zero-cross signal is being output from the zero-cross circuit, it is possible to detect whether an AC voltage is being input to the input terminal, making it possible to detect the interruption of AC voltage using the zero-cross circuit provided in the image forming device.

The image forming apparatus of the present application further includes a control unit that instructs the relay to be connected or disconnected, and a display unit, and the signal output circuit outputs a full-wave zero-cross signal if an AC voltage is input to the input terminal when the relay is in a connected state, and outputs a half-wave zero-cross signal if an AC voltage is input to the input terminal when the relay is in a disconnected state, and the control unit displays an abnormality on the display unit when it detects a full-wave zero-cross signal from the signal output circuit while instructing the relay to be disconnected.

If the control unit instructs the relay to be disconnected but a full-wave zero-cross signal is detected from the signal output circuit, this means that the relay has welded and the signal output circuit is outputting a full-wave zero-cross signal instead of a half-wave zero-cross signal, so the control unit displays an abnormality on the display unit. This allows the operator to understand that an abnormality has occurred in the image forming device.

The control unit also determines that the cause of the abnormality is that the relay is in a welded state.

This allows the operator to know that the cause of the abnormality is a welded relay.

The image forming apparatus of the present application further includes an AC-DC conversion circuit that converts an AC voltage input to the input terminal into a DC voltage, a capacitor that is disposed between the input terminal and the AC-DC conversion circuit to reduce noise generated between one end and the other end of the input terminal, and a discharge circuit that discharges the charge accumulated in the capacitor, and is characterized in that the control unit instructs the discharge circuit to discharge the capacitor if it does not detect a signal output from the signal output circuit when it has instructed the relay to be disconnected.

When the control unit instructs the relay to be disconnected, not detecting a signal output from the signal output circuit means that no AC voltage is being input to the input terminal, so the control unit instructs the discharge circuit to discharge the capacitor, which makes it possible to quickly remove the residual charge stored in the capacitor.

The control unit also displays an abnormality on the display unit if it detects a signal from the zero-cross circuit that indicates a constant voltage while instructing the relay to be disconnected.

This allows the operator to understand that an abnormality has occurred in the image forming device.

The control unit also determines that the cause of the abnormality is that a DC voltage, rather than an AC voltage, is being input to the input terminal.

This allows the operator to know that the cause of the abnormality is that a DC voltage, rather than an AC voltage, is being input to the input terminal.

The control unit is also characterized in that when it issues an instruction to connect the relay in order to use the fixing unit, if it does not detect a full-wave zero-cross signal from the signal output circuit, it displays an abnormality on the display unit.

This allows the operator to understand that an abnormality has occurred in the image forming device.

The control unit also determines that the cause of the abnormality is a malfunction of the relay.

This allows the operator to know that the cause of the abnormality is a malfunction of the relay.

1 is a side cross-sectional view of a main portion of a monochrome laser printer according to an embodiment of the present application. FIG. 2 is a block diagram showing a control configuration of the monochrome laser printer shown in FIG. 1 . FIG. 2 is a circuit diagram showing a schematic configuration of a heater control device. 1A shows an input voltage waveform, a full-wave rectified voltage waveform, a full-wave zero-cross signal waveform, a half-wave rectified waveform, and a half-wave zero-cross signal waveform, respectively. 3 is a flowchart showing the procedure of an abnormality determination process executed by a control unit, particularly a CPU, in FIG. 2 . 5A shows an input voltage waveform, a zero-cross signal waveform, an input voltage waveform, a waveform after full-wave rectification, and a zero-cross signal waveform, which are different from those shown in FIG. 4 .

The following describes the embodiments of the present application in detail with reference to the drawings.

Figure 1 is a cross-sectional view showing the schematic configuration of a monochrome laser printer 1 according to an embodiment of the present application. The monochrome laser printer 1 is an example of an image forming device. Hereinafter, the monochrome laser printer 1 will be abbreviated to printer 1.

The printer 1 forms a toner image on a sheet S supplied from a supply tray 3 or a manual feed tray 4 disposed in the lower portion of the main body housing 2, using a process unit 6. Thereafter, the printer 1 heats the sheet S on which the toner image has been formed, using a fixing unit 7, thereby carrying out a fixing process.
Furthermore, the printer 1 discharges the sheet S onto a discharge tray 8 located at the top of the main body housing 2 using a discharge roller 24 .

The process unit 6 includes a scanner unit 10, a developing cartridge 13, a photosensitive drum 17, a charger 18, a transfer roller 19, etc.

The scanner unit 10 is located at the top of the main body housing 2 and includes a laser emitter (not shown), a polygon mirror 11, multiple reflectors 12, and multiple lenses (not shown). In the scanner unit 10, the laser light emitted from the laser emitter is irradiated by high-speed scanning onto the surface of the photosensitive drum 17 via the polygon mirror 11, reflectors 12, and lenses, as shown by the dashed dotted line.

The developing cartridge 13 is removably attached to the main body housing 2 and contains toner. A developing roller 14 and a supply roller 15 are arranged facing each other at the toner supply port of the developing cartridge 13. The toner in the developing cartridge 13 is supplied to the developing roller 14 by the rotation of the supply roller 15 and is carried by the developing roller 14.

A charger 18 is disposed above the photosensitive drum 17 at a distance. A transfer roller 19 is disposed below the photosensitive drum 17 facing the photosensitive drum 17. While the surface of the photosensitive drum 17 is rotated, it is first uniformly charged, for example, to a positive polarity by the charger 18. Next, an electrostatic latent image is formed on the photosensitive drum 17 by a laser beam from the scanner unit 10.

Then, when the photosensitive drum 17 rotates in contact with the developing roller 14, the toner carried on the developing roller 14 is supplied to the electrostatic latent image on the surface of the photosensitive drum 17, forming a toner image. The toner image is then transferred to the sheet S by the transfer bias applied to the transfer roller 19 while the sheet S passes between the photosensitive drum 17 and the transfer roller 19.

The fixing unit 7 is disposed downstream of the process unit 6 in the sheet conveying direction, and includes a fixing roller 22, a pressure roller 23 that presses the fixing roller 22, and a heater 31 that heats the fixing roller 22. The heater 31 is connected to a power supply board 25, and is controlled by the AC voltage supplied from the power supply board 25. The heater control device 30 includes the heater 31, the power supply board 25, and a main board 40 (see FIG. 3). The printer 1 also includes a display unit 27 that displays printing information, etc.

Figure 2 shows the control configuration of the printer 1. As shown in Figure 2, the printer 1 includes a heater 31, a thermistor 32, a control unit 39, a switching element 34, a zero-cross detection circuit 38, a relay 33, a process unit 6, a conveying unit 5, and a display unit 27. In addition to the discharge rollers 24 (see Figure 1), the conveying unit 5 includes conveying rollers 21 (see Figure 1) that convey the sheet S supplied from the supply tray 3 or the manual feed tray 4 to the process unit 6, a pickup roller (not shown) that picks up the sheet S from the supply tray 3, and a main motor (not shown) that drives various rollers.

As shown in FIG. 2, the control unit 39 includes a CPU 39A, a ROM 39B, a RAM 39C, and an NVRAM 39D. ROM 39B stores various control programs for controlling the heater control device 30, various settings, initial values, and in particular, programs for performing heater control processing, tables for performing heater control processing, etc. In addition, the abnormality determination processing described below with reference to FIG. 5 is also stored in ROM 39B.

RAM 39C and NVRAM 39D are used as working areas from which various control programs are read, or as storage areas for temporarily storing data. CPU 39A controls each component of heater control device 30 according to the control programs read from ROM 39B, while storing the processing results in RAM 39C or NVRAM 39D.

The heater control device 30 includes a heater 31, a thermistor 32, a control unit 39, a switching element 34, and a zero-cross detection circuit 38, as shown in FIG. 2. Furthermore, as shown in FIG. 3, the heater control device 30 includes a pair of first and second input terminals T1, T2 for inputting commercial power from a commercial power source.

The first and second input terminals T1, T2 are connected to a commercial power source (not shown) outside the heater control device 30, and supply AC voltage to the inside of the heater control device 30. One terminal of the commercial power source is connected to the first input terminal T1, and the other terminal of the commercial power source is connected to the second input terminal T2.

A heater 31, a switching element 34, a diode bridge circuit 50, and a relay 33 are connected between the first input terminal T1 and the second input terminal T2. More specifically, the input terminal T1 and one end H1 of the heater 31 are connected via a first connection path L1. The other end H2 of the heater 31 is connected to the anode of the fourth diode D4 that constitutes the diode bridge circuit 50 via a second connection path L2. In addition, the switching element 34 is disposed in the second connection path L2.

The diode bridge circuit 50 has four diodes, the first to fourth diodes D1 to D4, and is configured by connecting in parallel a first series-connected diode configured by connecting the cathode of the first diode D1 to the anode of the second diode D2, and a second series-connected diode configured by connecting the cathode of the third diode D3 to the anode of the fourth diode D4. A relay 33 is disposed between the cathode of the third diode D3 of the second series-connected diodes and the anode of the fourth diode D4. The cathode of the third diode D3, that is, the connection between the cathode of the third diode D3 and the relay 33, is connected to the second input terminal T2 via the third connection path L3. Furthermore, the connection point J1 between the cathode of the first diode D1 and the anode of the second diode D2 is connected to the first connection path L1 via the fourth connection path L4.

The heater 31 serves to heat the fixing roller 22 that constitutes the fixing device 7. The heater 31 is housed inside the fixing roller 22 in a position extending in the direction of the central axis of the fixing roller 22. One example of the heater 31 is a halogen heater. The heater 31 generates heat by passing electricity between one end H1 and the other end H2. The heater 31 heats the fixing roller 22 that constitutes the fixing device 7 to fix the toner to the sheet S.

The thermistor 32 is disposed near the heater 31. The thermistor 32 detects the temperature of the heater 31 and outputs the detected temperature information to the control unit 39.

The switching element 34 switches the AC voltage applied to the heater 31 based on a command from the control unit 39. For example, a triac is an example of the switching element 34. A triac is a semiconductor element that switches an AC voltage that exhibits a voltage waveform that includes positive and negative polarities.

The zero-cross circuit 38 is composed of a diode bridge circuit 50 and a signal output circuit 51. The input side of the signal output circuit 51 is connected between a connection point J2 between the anode of the second diode D2 and the anode of the fourth diode D4, and a connection point J3 between the cathode of the first diode D1 and the cathode of the third diode D3.

The input voltage Vin is a power supply voltage applied between the first input terminal T1 and the second input terminal T2. When the input voltage Vin is applied to the first and second input terminals T1 and T2, the zero-cross circuit 38, particularly the signal output circuit 51, outputs an output signal voltage Vout to the control unit 39. This output signal voltage Vout is the zero-cross signal output by the zero-cross circuit 38.

When the input voltage Vin is an AC voltage, a DC voltage, or there is no input voltage Vin, the zero-cross circuit 38 outputs a corresponding voltage waveform as the output signal voltage Vout. Therefore, the control unit 39 can determine what voltages are applied to the first and second input terminals T1 and T2 by identifying the voltage waveform of the output signal voltage Vout.

The relay 33 has a function of turning on/off the current between the anode of the third diode D3 and the cathode of the fourth diode D4 in response to a command from the control unit 39. An example of the relay 33 is a contact relay.

As part of the heater control process, the control unit 39 ignites the triac (switching element 34) via a known circuit using a triac coupler to perform the required switching operation. At that time, the control unit 39 performs this control based on the temperature information of the heater 31 detected by the thermistor 32 and the output signal voltage Vout of the zero-cross circuit 38.

In areas where the power supply from the commercial power system is not always stable, a power supply using an inverter device may be used as a backup power source to supply power to the printer 1. The voltage applied to the first and second input terminals T1, T2 should be a sine wave AC voltage at the commercial frequency, but due to incorrect settings or a malfunction of the inverter device, a DC voltage or a square wave AC voltage with a fast voltage rise speed may be applied. The zero cross circuit 38 can detect such abnormalities in the voltage applied to the first and second input terminals T1, T2.

Next, the circuit configuration of the zero-cross circuit 38 will be described. The zero-cross circuit 38 switches the zero-cross signal from high level to low level and outputs it when the absolute value of the voltage value falls below the threshold voltage Vth. As described above, the zero-cross circuit 38 is composed of a diode bridge circuit 50 and a signal output circuit 51. The signal output circuit 51 includes a photocoupler 51A, a transistor 51B, and various resistors that are not assigned a sign.

When the control unit 39 outputs an ON command (connection command) to the relay 33 and the relay 33 is in an ON state (connection state), the input voltage Vin is full-wave rectified by the diode bridge circuit 50 to become a rectified signal Vs. The rectified signal Vs is a signal output from the diode bridge circuit 50 of the input voltage Vin. The rectified signal Vs is converted into an optical signal by the light-emitting diode of the photocoupler 51A. When the rectified signal Vs is equal to or higher than the threshold voltage Vth, the light-receiving element of the photocoupler 51A reacts to the optical signal of the light-emitting diode of the photocoupler 51A, and a current flows through the light-receiving element. When a current flows through the photocoupler 51A, no current flows between the emitter and collector of the transistor 51B, and the output signal voltage Vout becomes a high-level voltage. On the other hand, when the rectified signal Vs is smaller than the threshold voltage Vth, the light receiving element of the photocoupler 51A does not react to the optical signal of the light emitting diode of the photocoupler 51A, and no current flows through the light receiving element. As a result, a base current flows through the transistor 51B, and a current flows between the emitter and collector of the transistor 51B, and the output signal voltage V
The output voltage becomes low level.

On the other hand, when the control unit 39 outputs an OFF command (disconnect command) to the relay 33 and the relay 33 is in the OFF state (disconnected state), the input voltage Vin is half-wave rectified by the diode bridge circuit 50 to become the rectified signal Vs. The signal processing in the signal output circuit 51 thereafter is the same as when the rectified signal Vs is full-wave rectified, but the shape of the output signal voltage Vout differs depending on whether the rectified signal Vs is full-wave rectified or half-wave rectified.

Figure 4 shows the waveforms of the rectified signal Vs ((b)) from the diode bridge circuit 50 and the full-wave zero-cross signal Vout ((c)) from the zero-cross circuit 38 when the input voltage Vin is a sine wave ((a)) and the relay 33 is on, and the waveforms of the rectified signal Vs ((d)) from the diode bridge circuit 50 and the half-wave zero-cross signal Vout ((e)) from the zero-cross circuit 38 when the relay 33 is off. The horizontal dotted line in the waveform diagram of the rectified signal Vs indicates the threshold voltage Vth at which the photocoupler 51A operates. When the rectified signal Vs rises from zero to the threshold voltage Vth or less, no current flows through the photocoupler 51A, but when the voltage becomes equal to or greater than the threshold voltage Vth, a current flows through the photocoupler 51A.

As a result, the zero-cross circuit 38 outputs full-wave and half-wave zero-cross signals shown in Figures 4(c) and (e), respectively. Such zero-cross signals indicate that the voltages applied to the first and second input terminals T1 and T2 are normal.

The power supply board 25 is provided with first and second input terminals T1, T2, a switching element 34, a known circuit using a triac coupler, and a zero-cross circuit 38. In addition, the power supply board 25 is also provided with a capacitor 60, a discharge circuit 61, and an AC-DC conversion circuit 62.

The input side of the AC-DC conversion circuit 62 is connected to the first and second input terminals T1, T2, and converts the commercial voltage input from the first and second input terminals T1, T2, for example an AC voltage of 100 V, into a DC voltage of, for example, 24 V, and outputs it to the downstream DC-DC conversion circuit 70.

The capacitor 60 is a so-called X capacitor, and is disposed between the first and second input terminals T1, T2 and the AC-DC conversion circuit 62 to reduce noise generated between the first input terminal T1 and the second input terminal T2.

The discharge circuit 61 is connected in parallel with the capacitor 60, and serves to discharge the residual charge in the capacitor 60 when, for example, the input of commercial voltage to the first and second input terminals T1 and T2 is interrupted. The discharge circuit 61 is instructed to discharge by the control unit 39.

The main board 40 is provided with a control unit 39 and a DC-DC conversion circuit 70. The DC-DC conversion circuit 70 converts the 24V DC voltage from the AC-DC conversion circuit 62 into a DC voltage such as 3.3V or 5V, and supplies it to the control unit 39 and other electronic components.

The control process executed by the printer 1 configured as described above will be described in detail below with reference to Figures 4 to 6.

Figure 5 shows the procedure for the abnormality determination process executed by the control unit 39, particularly the CPU 39A. This abnormality determination process is started when the printer 1 is turned on or when the printer 1 is in standby mode. Hereinafter, in the explanation of each process, steps will be abbreviated as "S".

In FIG. 5, first, the CPU 39A outputs an OFF command to the relay 33 and stops the switching operation of the switching element 34 (S10). As a result, if the relay 33 operates normally, the relay 33 is turned OFF, and the connection between the anode of the third diode D3 and the cathode of the fourth diode D4 of the diode bridge circuit 50 is cut off.

Next, the CPU 39A judges whether or not a half-wave zero-cross signal is detected from the zero-cross circuit 38 (S12). As described above, FIG. 4(e) shows the half-wave zero-cross signal output by the zero-cross circuit 38 when the relay 33 is in the off state. Therefore, if the CPU 39A detects the half-wave zero-cross signal shown in FIG. 4(e), the judgment in S12 is "YES", and if the CPU 39A does not detect the half-wave zero-cross signal shown in FIG. 4(e), the judgment in S12 is "NO". If the judgment in S12 is "YES", the CPU 39A repeats the judgment in S12 until a print command is received (S14: NO), and if a print command is received (S14: YES), the CPU 39A proceeds to the next step S16.

In S16, the CPU 39A outputs an ON command to the relay 33 and starts the switching operation of the switching element 34. Next, the CPU 39A judges whether or not a full-wave zero-cross signal is detected from the zero-cross circuit 38 (S18). As described above, FIG. 4(c) shows the full-wave zero-cross signal output by the zero-cross circuit 38 when the relay 33 is in the ON state. Therefore, if the CPU 39A detects the full-wave zero-cross signal shown in FIG. 4(c), the judgment in S18 is "YES", and if the CPU 39A does not detect the full-wave zero-cross signal shown in FIG. 4(c), the judgment in S18 is "NO". If the judgment in S18 is "YES", the CPU 39A repeats the judgment in S18 until printing is completed (S20: NO), and when printing is completed (S20: YES), the CPU 39A terminates the abnormality determination process.

On the other hand, if the determination in S18 is "NO", CPU 39A displays the abnormality (S22), stops printing (S24), and then ends the abnormality determination process. If the determination in S18 is "NO", this is the case when CPU 39A detects a half-wave zero-cross signal. In this case, even though CPU 39A has output an ON command to relay 33, it is considered that relay 33 is not in the ON state. Therefore, in S22, CPU 39A displays on display unit 27 that an abnormality has occurred that can be determined to be a malfunction of relay 33.

On the other hand, if the half-wave zero-cross signal is not detected in the judgment of S12 (S12: NO), the CPU 39A judges whether or not a full-wave zero-cross signal is detected in the same manner as in S18 (S30). If the full-wave zero-cross signal is detected in this judgment (S30: YES), the CPU 39A proceeds to S32, and if the full-wave zero-cross signal is not detected (S30: NO), the CPU 39A proceeds to S40. Here, when the CPU 39A detects a full-wave zero-cross signal, if the relay 33 is operating normally, the CPU 39A should detect a half-wave zero-cross signal, so it can be determined that the relay 33 is not operating normally. Therefore, in S32, the CPU 39A judges that the contact of the relay 33 is welded, and in the following S34, the CPU 39A displays on the display unit 27 that an abnormality that can be determined as a weld of the contact of the relay 33 has occurred, and then ends the abnormality judgment process.

On the other hand, when the CPU 39A does not detect a full-wave zero-cross signal in S30, the CPU 39A detects the output signal voltage Vout shown in Fig. 6(b). In this case, as shown in Fig. 6(a), it can be determined that a commercial power source (AC voltage) is not being input to the first and second input terminals T1 and T2. Therefore, the CPU 39A determines that an AC voltage is not being input (S40) and outputs a signal to operate the discharge circuit 61 to discharge the residual charge in the capacitor 60 (S40).
42), the abnormality determination process is then terminated.

As described above, the printer 1 of this embodiment includes a fuser 7 having a heater 31 connected via a relay 33 to the first and second input terminals T1, T2 that input AC voltage from a commercial power source, and fuses a developer image onto a sheet; and a zero-cross circuit 38 that connects the first and second input terminals T1, T2 and the heater 31 via the relay 33 and outputs a full-wave zero-cross signal indicating a zero-cross of a full wave of the AC voltage. When the first and second input terminals T1, T2 and the heater 31 are disconnected by the relay 33, the zero-cross circuit 38 outputs a half-wave zero-cross signal indicating a zero-cross of a half wave of the AC voltage when an AC voltage is input to the first and second input terminals T1, T2, and does not output a half-wave zero-cross signal when no AC voltage is input to the first and second input terminals T1, T2.

In this way, in the printer 1 of this embodiment, the zero-cross circuit 38 outputs a half-wave zero-cross signal when an AC voltage is input to the first and second input terminals T1 and T2, even if the relay 33 is in a disconnected state. At this time, the zero-cross circuit 38 does not output a half-wave zero-cross signal when no AC voltage is input to the first and second input terminals T1 and T2. Therefore, by detecting whether or not a half-wave zero-cross signal is being output from the zero-cross circuit 38, it is possible to detect whether or not an AC voltage is being input to the first and second input terminals T1 and T2, so that it is possible to detect the interruption of the AC voltage using the zero-cross circuit 38 provided in the printer 1.

The zero-cross circuit 38 includes a diode bridge circuit formed by connecting in parallel a first series-connected diode formed by connecting the cathode of the first diode D1 to the anode of the second diode D2 and a second series-connected diode formed by connecting the cathode of the third diode D3 to the anode of the fourth diode D4, a relay 33, and a signal output circuit 51. The first input terminal T1 of the first and second input terminals T1 and T2 is connected to one end H1 of the heater 31 by a first connection path L1, and the other end H2 of the heater 31 is connected to the anode of the fourth diode D4 by a second connection path L2. The cathode of D3 is connected to the second input terminal T2 of the first and second input terminals T1 and T2 by the third connection path L3, the connection point between the cathode of the first diode D1 and the anode of the second diode D2 is connected to the first connection path L1 by the fourth connection path L4, the input side of the signal output circuit 51 is connected between the connection point between the anode of the second diode D2 and the anode of the fourth diode D4 and the connection point between the cathode of the first diode D1 and the cathode of the third diode D3, and the relay 33 is disposed between the cathode of the third diode D3 and the anode of the fourth diode D4.

The zero-cross circuit 38 outputs a full-wave zero-cross signal when the relay 33 is in a connected state. When the relay 33 is in a disconnected state, the heater 31 is not energized. When the relay 33 is in a disconnected state and an AC voltage is input to the first and second input terminals T1 and T2, a current due to a half-wave component of one pole of the AC voltage flows from the first input terminal T1 of the first and second input terminals T1 and T2 through the first connection path L1, the fourth connection path L4, the second diode D2, the signal output circuit 51, the third diode D3, and the third connection path L3 to the second input terminal T2 of the first and second input terminals T1 and T2. On the other hand, a current due to a half-wave component of the other pole of the AC voltage does not flow from the second input terminal T2 of the first and second input terminals T1 and T2 to the first input terminal T1 because the relay 33 is in a disconnected state. Therefore, when the relay 33 is in a disconnected state and an AC voltage is input to the first and second input terminals T1 and T2, the zero-cross circuit 38 outputs a half-wave zero-cross signal.
Since no current flows between the input terminal T2, the zero-cross circuit 38 does not output a half-wave zero-cross signal. In this way, by detecting whether or not a half-wave zero-cross signal is being output from the zero-cross circuit 38, it is possible to detect whether or not an AC voltage is being input to the first and second input terminals T1, T2, so it is possible to detect interruption of the AC voltage using the zero-cross circuit 38 provided in the printer 1.

The printer 1 further includes a CPU 39A that instructs the relay 33 to be connected or disconnected, and a display unit 27. When the relay 33 is in a connected state, the signal output circuit 51 outputs a full-wave zero-cross signal if an AC voltage is input to the first and second input terminals T1, T2, and when the relay 33 is in a disconnected state, the signal output circuit 51 outputs a half-wave zero-cross signal if an AC voltage is input to the first and second input terminals T1, T2. When the CPU 39A instructs the relay 33 to be disconnected, it displays an abnormality on the display unit 27 if it detects a full-wave zero-cross signal from the signal output circuit 51.

If the CPU 39A detects a full-wave zero-cross signal from the signal output circuit 51 even though the CPU 39A has instructed the relay 33 to be disconnected, this means that the relay 33 has welded and the signal output circuit 51 is outputting a full-wave zero-cross signal instead of a half-wave zero-cross signal, so the CPU 39A displays an abnormality on the display unit 27. This allows the operator to know that an abnormality has occurred in the printer 1.

The CPU 39A also determines that the cause of the abnormality is that the relay 33 is in a welded state.

This allows the operator to know that the cause of the abnormality is that relay 33 is in a welded state.

The printer 1 further includes an AC-DC conversion circuit 62 that converts the AC voltage input to the first and second input terminals T1, T2 into a DC voltage, a capacitor 60 that is disposed between the first and second input terminals T1, T2 and the AC-DC conversion circuit 62 to reduce noise generated between the first input terminal T1 and the second input terminal T2 of the first and second input terminals T1, T2, and a discharge circuit 61 that discharges the charge accumulated in the capacitor 60. The CPU 39A is characterized in that, when it has instructed the relay 33 to be disconnected, if it does not detect a signal output from the signal output circuit 51, it instructs the discharge circuit 61 to discharge the capacitor 60.

When the CPU 39A instructs the relay 33 to be disconnected, not detecting a signal output from the signal output circuit 51 means that no AC voltage is being input to the first and second input terminals T1 and T2, so the CPU 39A instructs the discharge circuit 61 to discharge the capacitor 60. This makes it possible to quickly remove the residual charge that has accumulated in the capacitor 60 from the capacitor 60.

The CPU 39A is also characterized in that if it detects a signal from the zero-cross circuit 38 indicating that a constant voltage continues while instructing the relay 33 to be disconnected, it displays an abnormality on the display unit 27.

This allows the operator to understand that an abnormality has occurred in Printer 1.

The CPU 39A also determines that the cause of the abnormality is that a DC voltage, rather than an AC voltage, is being input to the first and second input terminals T1 and T2.

This allows the operator to know that a DC voltage, not an AC voltage, is being input to the first and second input terminals T1 and T2.

In addition, when the CPU 39A instructs the relay 33 to connect in order to use the fixing unit 7, if the CPU 39A does not detect a full-wave zero-cross signal from the signal output circuit 51, it displays an abnormality on the display unit 27.

This allows the operator to understand that an abnormality has occurred in Printer 1.

The CPU 39A also determines that the cause of the abnormality is a malfunction of the relay 33.

This allows the operator to know that the cause of the abnormality is a malfunction of relay 33.

The present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the invention.

(1) In the above embodiment, a halogen heater that uses radiant heat is used as the heater 31, but the heater is not limited to this and may be, for example, a ceramic heater or a carbon heater that uses heat generated by a resistor. In addition, the heater may be disposed outside the heating element, rather than inside the heating element.

(2) In the above embodiment, a printer that forms a monochrome image on a sheet is given as an example of an image forming device, but the image forming device is not limited to this and may be, for example, a printer configured to form a color image on a sheet. In addition, the image forming device is not limited to a printer and may be, for example, a copier or multifunction device equipped with a document reading device such as a flatbed scanner.

1... monochrome laser printer (image forming apparatus), 7... fixing unit, 25... power supply board, 27... display unit, 30... heater control device, 31... heater, 33... relay, 34... switching element, 38... zero cross circuit, 39... control unit, 39A... CPU (control unit), 39B... ROM, 39C... RAM, 39D... NVRAM, 40... main board, 50... diode bridge circuit, 51... signal output circuit, 51A... photocoupler, 51B... transistor, 60... con condenser, 61...discharge circuit, 62...AC-DC conversion circuit, 70...DC-DC conversion circuit, D1...first diode, D2...second diode, D3...third diode, D4...fourth diode, L1...first connection path, L2...second connection path, L3...third connection path, L4...fourth connection path, S...sheet, T1...first input terminal (input terminal), T2...second input terminal (input terminal), Vin...input voltage, Vout...output signal voltage, Vs...rectified signal, Vth...threshold voltage.

Claims (9)

a fixing unit having a heater connected via a relay to an input terminal for inputting an AC voltage from a commercial power source, and fixing the developer image onto a sheet;
a zero-cross circuit that outputs a full-wave zero-cross signal indicating a zero-cross of a full wave of the AC voltage when the input terminal and the heater are connected to each other by the relay;
Equipped with
The zero cross circuit is
When the input terminal and the heater are disconnected by the relay,
When the AC voltage is input to the input terminal, a half-wave zero-cross signal indicating a zero-cross of a half-wave of the AC voltage is output;
When the AC voltage is not input to the input terminal, the half-wave zero-cross signal is not output.
1. An image forming apparatus comprising: The zero cross circuit is
a diode bridge circuit configured by connecting in parallel a first series-connected diode configured by connecting a cathode of a first diode to an anode of a second diode and a second series-connected diode configured by connecting a cathode of a third diode to an anode of a fourth diode, the relay, and a signal output circuit;
one end of the input terminal is connected to one end of the heater by a first connection path;
the other end of the heater is connected to the anode of the fourth diode by a second connection path;
a cathode of the third diode is connected to the other end of the input terminal by a third connection path;
a connection point between the cathode of the first diode and the anode of the second diode is connected to the first connection path by a fourth connection path;
an input side of the signal output circuit is connected between a connection point between the anode of the second diode and the anode of the fourth diode and a connection point between the cathode of the first diode and the cathode of the third diode,
the relay is disposed between the cathode of the third diode and the anode of the fourth diode.
2. The image forming apparatus according to claim 1, A control unit that instructs the relay to be connected or disconnected;
A display unit;
Further equipped with
The signal output circuit includes:
When the relay is in the connected state, if the AC voltage is input to the input terminal, the full-wave zero-cross signal is output;
When the relay is in the non-connected state, if the AC voltage is input to the input terminal, the half-wave zero-cross signal is output;
The control unit is
when the full-wave zero-cross signal is detected from the signal output circuit while the relay is being instructed to be disconnected, an abnormality is displayed on the display unit.
3. The image forming apparatus according to claim 2, The control unit is
determining that the cause of the abnormality is that the relay is in a welded state;
4. The image forming apparatus according to claim 3. an AC-DC conversion circuit for converting the AC voltage input to the input terminal into a DC voltage;
a capacitor disposed between the input terminal and the AC-DC conversion circuit for reducing noise generated between the one end and the other end of the input terminal;
a discharge circuit for discharging the charge stored in the capacitor;
Further equipped with
The control unit is
when the relay is instructed to be disconnected and a signal output from the signal output circuit is not detected, the discharge circuit is instructed to discharge the capacitor.
4. The image forming apparatus according to claim 3. The control unit is
When a signal indicating that a constant voltage continues is detected from the zero cross circuit while the relay is being instructed to be disconnected, an abnormality is displayed on the display unit.
4. The image forming apparatus according to claim 3. The control unit is
determining that the cause of the abnormality is that a DC voltage, rather than the AC voltage, is being input to the input terminal;
7. The image forming apparatus according to claim 6, The control unit is
When the relay is instructed to make the connection in order to use the fixing unit,
When the full-wave zero-cross signal is not detected from the signal output circuit, an abnormality is displayed on the display unit.
4. The image forming apparatus according to claim 3. The control unit is
determining that the cause of the abnormality is a malfunction of the relay;
9. The image forming apparatus according to claim 8,

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