Image forming apparatus having abnormality determination function

In an image forming apparatus, a calculation processing portion includes an input portion and an input-portion abnormality determining portion. The input portion is connected to a temperature detection portion. When an abnormality detection circuit has detected that a temperature detected by the temperature detection portion is an abnormally heated temperature, the input-portion abnormality determining portion determines whether or not a first temperature calculated as a temperature of a fixing member is lower than a predetermined second temperature, and upon determining that the first temperature is lower than the second temperature, determines that the input portion is abnormal.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2016-184526 filed on Sep. 21, 2016, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to an image forming apparatus including a fixing member for fixing a toner image to a sheet.

Some image forming apparatuses such as printers include a safety circuit that forcibly stops power supply to a fixing heater when a fixing device is abnormally heated. There is known a temperature control device of this type of image forming apparatus that includes the safety circuit, such as a thermoswitch, that forcibly stops the power supply to the fixing heater, as well as a second safety circuit that maintains an off-state of the fixing heater upon detection of an abnormality of the CPU.

SUMMARY

An image forming apparatus according to an aspect of the present disclosure includes a fixing member, a fixing heater, a temperature detection portion, a driving circuit, an abnormality detection circuit, and a calculation processing portion. The fixing member fixes a toner image to a sheet. The fixing heater heats the fixing member. The temperature detection portion detects a temperature of the fixing member. The driving circuit drives the fixing heater based on the temperature detected by the temperature detection portion. The abnormality detection circuit is connected to the temperature detection portion and detects whether or not the temperature detected by the temperature detection portion is an abnormally heated temperature. The calculation processing portion includes an input portion and an input-portion abnormality determining portion. The input portion is connected to the temperature detection portion. The input-portion abnormality determining portion, when the abnormality detection circuit has detected that the temperature detected by the temperature detection portion is the abnormally heated temperature, determines whether or not a first temperature calculated as the temperature of the fixing member is lower than a predetermined second temperature, and upon determining that the first temperature is lower than the second temperature, determines that the input portion is abnormal.

DETAILED DESCRIPTION

The following describes embodiments of the present disclosure with reference to the accompanying drawings for the understanding of the present disclosure. It should be noted that the following embodiments are examples of specific embodiments of the present disclosure and should not limit the technical scope of the present disclosure.

First, a description is given of an outlined configuration of image forming apparatus10according to a first embodiment of the present disclosure, with reference toFIG. 1andFIG. 2.

As shown inFIG. 1andFIG. 2, the image forming apparatus10is a printer that includes an operation/display portion2, a sheet feed cassette3, and an image forming portion4. It is noted that the image forming apparatus of the present disclosure may be a facsimile device, a copier, or a multifunction peripheral, for example.

The operation display portion2includes a display portion and an operation portion. The display portion is, for example, a liquid crystal display for displaying various types of information such as an error message. The operation portion is composed of, for example, hard keys or a touch panel through which various types of information are input in accordance with user operations.

The sheet feed cassette3stores sheets that are supplied to the image forming portion4.

The image forming portion4forms a color or monochrome image on a sheet by an electrophotographic system, based on image data input from an external information processing apparatus such as a personal computer. Specifically, the image forming portion4includes an engine control portion40, a plurality of image forming units41to44, a laser scanning device (LSU)45, an intermediate transfer belt46, a secondary transfer roller47, a fixing device48, a sheet discharge tray49, and toner containers51to54.

The engine control portion40comprehensively controls the image forming portion4. The engine control portion40is a computer that includes control equipment such as an engine CPU6, a ROM, and a RAM.

The engine CPU6executes a control program by using the RAM or the like as a temporary storage memory (working area), wherein the control program is stored in the ROM in advance. The engine CPU6is an example of the calculation processing portion of the present disclosure. Other examples of the calculation processing portion of the present disclosure include a main CPU of a main control portion that comprehensively controls the image forming apparatus10. It is noted that the engine CPU6is described in detail below.

The plurality of image forming units41to44include an image forming unit41corresponding to cyan, an image forming unit42corresponding to magenta, an image forming unit43corresponding to yellow, and an image forming unit44corresponding to black. Each of the image forming units41to44includes a photoconductor drum411, a charging device412, a developing device413, a primary transfer roller414, and a cleaning portion415.

The laser scanning device45irradiates laser light to the photoconductor drums411based on image data so that electrostatic latent images are respectively formed on the photoconductor drums411.

Here,FIG. 3is a block diagram showing the fixing device48of the image forming apparatus10shown inFIG. 2as well as other components such as the engine CPU6.

As shown inFIG. 3, the fixing device48includes a fixing roller481, a fixing heater482, and a fixing thermistor483.

Meanwhile, there may be a case where the image forming process is stopped upon detection of an abnormality of the engine CPU6. The engine CPU6may recover easily from the abnormality if the main power source is turned off and on. However, in general, even in such a case, the image forming process would be stopped to waste time until the repair was done by a service engineer. For example, in a case where the image forming process is stopped after the engine CPU6detects an abnormality of the fixing device48, restarting by turning off and on the main power source may or may not allow the apparatus to recover to a state where the image forming process can be executed. For example, in the case of an erroneous detection of an abnormality of the fixing device48, restarting the image forming apparatus10by turning off and on the main power source may allow the apparatus to recover to a state where the image forming process can be executed. On the other hand, in a case where the fixing device48has been heated abnormally, restarting the apparatus may not allow the apparatus to recover to a state where the image forming process can be executed normally. At this time, for example, if restarting by turning off and on the main power source is prohibited after the engine CPU6detects an abnormally heated state of the fixing device48, the image forming apparatus10is maintained to a state where it cannot be used even when the image forming apparatus10is actually in a state where the image forming process can be executed normally, as when an abnormality of an AID converter61, an input portion, described below is detected. In contrast, in the image forming apparatus10according to the present embodiment, when the fixing roller481is in an abnormally heated state, it is possible to determine whether or not it can recover easily from the abnormally heated state by turning off and on the main power source.

The fixing roller481heats a toner image that has been transferred to a sheet by the secondary transfer roller47, and together with a pressure roller484, fixes the toner image to the sheet (seeFIG. 1). The fixing roller481is an example of the fixing member of the present disclosure.

The fixing heater482heats the fixing roller481. As the fixing heater482, a halogen lamp heater, a ceramic heater, or an inductive heater can be used, for example.

The fixing thermistor483detects the temperature of the fixing roller481. The fixing thermistor483is an example of the temperature detection portion of the present disclosure.

In addition, in the fixing device48, the fixing heater482is connected to a fixing heater driving circuit5, and the fixing thermistor483is connected to the engine CPU6. The fixing heater driving circuit5is controlled by a control signal from the engine CPU6of the engine control portion40, and drives the fixing heater482based on the control signal. The fixing heater driving circuit5is an example of the driving circuit of the present disclosure.

The engine CPU6includes the A/D converter61, an output port62, and an input port63. It is noted that the A/D converter61is used to input analog signals, and is an example of the input portion of the present disclosure. In addition, the output port62and the input port63are general-purpose ports that are used to output and input digital signals, respectively.

As shown inFIG. 4, the A/D converter61includes an A/D conversion circuit611, a multiplexer612, and a channel control circuit613.

The A/D conversion circuit611converts analog data input to the engine CPU6, to digital data. The multiplexer612includes a plurality of input channels, and changes analog data input to the engine CPU6by sequentially changing an input channel that is effective for inputting analog data. The channel control circuit613controls the multiplexer612to change the input channel that is effective for inputting analog data, at predetermined intervals.

The plurality of input channels of the multiplexer612connect to the fixing thermistor483, a position sensor81, an outside air humidity sensor82, and an outside air thermistor83. It is noted that the outside air thermistor83is an example of the ambient-temperature detection portion of the present disclosure. In addition, among the plurality of input ports, an input channel connected to the fixing thermistor483corresponds to the first input channel of the present disclosure, and an input channel connected to the outside air thermistor83corresponds to the second input channel of the present disclosure. Hereinafter, the input channel connected to the fixing thermistor483is referred to as the first input channel, and the input channel connected to the outside air thermistor83is referred to as the second input channel.

Since the fixing thermistor483is connected to the multiplexer612of the A/D converter61, the engine CPU6can monitor the temperature of the fixing roller481. The temperature of the fixing roller481is calculated in synchronization with a timing at which input to the first input channel becomes effective. The engine CPU6generates a control signal to be transmitted to the fixing heater driving circuit5, by comparing a temperature of the fixing roller481that is calculated based on an output from the fixing thermistor483, with a control target temperature of the fixing roller481. That is, the engine CPU6maintains the fixing roller481to the target temperature by transmitting the control signal to the fixing heater driving circuit5. Hereinafter, the timing at which input to the first input channel becomes effective is referred to as a temperature monitoring timing.

As shown inFIG. 3, the output port62of the engine CPU6is connected to the fixing heater driving circuit5. The output port62outputs the control signal that is generated based on an output from the fixing thermistor483, to the fixing heater driving circuit5. The control signal includes an ON signal (high-level signal) and an OFF signal (low-level signal), wherein the ON signal is output to drive the fixing heater482, and the OFF signal is output to stop driving of the fixing heater482. In the present embodiment, the ON signal (high-level signal) is a positive level, and the OFF signal (low-level signal) is a zero level. When the control signal is transmitted to the fixing heater driving circuit5via the output port62, the driving of the fixing heater482is controlled, and the fixing roller481is maintained to the control target temperature. The control target temperature is determined based on, for example, the type of toner that is in use, and is in a range from 100° C. to 200° C. inclusive, for example.

The input port63of the engine CPU6is connected to an abnormality detection circuit7, and receives a determination signal from the abnormality detection circuit7. The abnormality detection circuit7detects, based on an output from the fixing thermistor483, whether or not the fixing roller481has an abnormally heated temperature, namely, is in an abnormally heated state. It is noted that the abnormally heated temperature is set to, for example, a temperature that is higher than a fixing temperature by 25° C. to 100° C. inclusive. The abnormality detection circuit7includes a comparator71and a switching element72.

In the comparator71, a non-inverting input portion is connected to the fixing thermistor483, and an inverting input portion is connected to a reference voltage generating portion (not shown). An output portion of the comparator71is connected to the input port63of the engine CPU6and to the switching element72. The comparator71compares a voltage output from the fixing thermistor483with a reference voltage, and outputs a determination signal based on the comparison result. Here, the reference voltage is set to, for example, a voltage that is output from the fixing thermistor483when the fixing roller481has the abnormally heated temperature. As a result, for example, when a voltage output from the fixing thermistor483is lower than the reference voltage, the comparator71outputs the low-level signal indicating that the temperature of the fixing roller481is normal. On the other hand, when a voltage output from the fixing thermistor483is equal to or higher than the reference voltage, the comparator71outputs the high-level signal indicating that the fixing roller481has the abnormally heated temperature. The determination signal is input to the input port63of the engine CPU6and to the base of the switching element72.

The switching element72is an NPN-type transistor. In the switching element72, the base is connected to the output portion of the comparator71, the collector is connected to a signal line that transmits the control signal from the engine CPU6to the fixing heater driving circuit5, and the emitter is grounded. That is, when the switching element72is in the off-state, it connects the output port62of the engine CPU6to the fixing heater driving circuit5, and when the switching element72is in the on-state, it makes the output port62of the engine CPU6grounded. In a normal state, the switching element72is in the off-state to connect the output port62of the engine CPU6to the fixing heater driving circuit5, and with an input of the high-level signal from the comparator71to the base, the switching element72is switched from the off-state to the on-state. In addition, when the switching element72is in the on-state, with an input of the low-level signal from the comparator71to the base, the switching element72is switched from the on-state to the off-state.

In the abnormality detection circuit7of the above-described configuration, the comparator71makes a comparison between a voltage output from the fixing thermistor483and the reference voltage, and outputs a determination signal indicating whether or not the fixing roller481is in the abnormally heated state. When the high-level signal is input from the comparator71to the base of the switching element72, the switching element72switches to the on-state. This allows the emitter and the collector of the switching element72to be conductive with each other, and the output port62of the engine CPU6is grounded. As a result, the ON signal (high-level signal) is not input to the fixing heater driving circuit5as the control signal. That is, a state that is similar to a state where the OFF signal (low-level signal) of the zero level is input to the fixing heater driving circuit5, is maintained, and the fixing heater482is forcibly stopped. In this way, in the image forming apparatus10, the fixing roller481is forcibly stopped by the abnormality detection circuit7that is different from the engine CPU6. As a result, even if the fixing roller481is in the abnormally heated state due to an abnormality such as a runaway of the engine CPU6, it is possible to reduce the temperature of the fixing roller481appropriately.

As shown inFIG. 3, the engine CPU6further includes an input-portion abnormality determining portion64, an error-handling-process executing portion65, and a power supply control portion66.

When the abnormality detection circuit7has detected that the fixing roller481has the abnormally heated temperature, the input-portion abnormality determining portion64determines whether or not a first temperature calculated as the temperature of the fixing roller481is lower than a predetermined second temperature. When it determines that the first temperature is lower than the second temperature, the input-portion abnormality determining portion64determines that the A/D converter61is abnormal. The second temperature is set to be equal to or lower than the control target temperature that is the fixing temperature to be achieved in the fixing roller481, and the second temperature is preferably the control target temperature.

When the abnormality detection circuit7has detected that the fixing roller481has the abnormally heated temperature and the input-portion abnormality determining portion64has determined that the first temperature is lower than the second temperature, the error-handling-process executing portion65executes a first error handling process that corresponds to an abnormality of the A/D converter61. In addition, when the input-portion abnormality determining portion64has determined that the first temperature is equal to or higher than the second temperature, the error-handling-process executing portion65executes a second error handling process that is different from the first error handling process.

Here, the first error handling process includes, for example, stopping the operation of the image forming portion4, restricting the operation/display portion2from accepting user operations, displaying an error message on the operation/display portion2, and setting a first error control mode to indicate that the first error handling process is being executed. In the first error control mode, in a case where the main power source is turned off during execution of the first error handling process and then turned on again, the error-handling-process executing portion65does not execute the first error handling process. That is, in the image forming apparatus10, in a case where a normal execution of the image forming process becomes available by turning off and on the main power supply, the execution of the image forming process is made available.

On the other hand, the second error handling process includes, for example, stopping the operation of the image forming portion4, restricting the operation/display portion2from accepting user operations, displaying an error message on the operation/display portion2, and setting a second error control mode to indicate that the second error handling process is being executed. In the second error control mode, in a case where the main power source is turned off during execution of the second error handling process, the error-handling-process executing portion65executes the second error handling process. It is noted that the error message displayed on the operation/display portion2in the second error handling process is that, for example, the fixing heater driving circuit5is abnormal, and the fixing heater driving circuit5needs maintenance. That is, in the image forming apparatus10, in a case where a normal execution of the image forming process does not become available by turning off and on the main power supply, the execution of the image forming process is prohibited.

The power supply control portion66controls the stop and start of power supply to the engine CPU6by controlling a switch91provided in a power supply path from the power source portion9to the engine CPU6.

The following describes, with reference to flowcharts ofFIG. 5toFIG. 7, an example of the procedure of a fixing heater control process that is executed by the input-portion abnormality determining portion64and the error-handling-process executing portion65of the engine CPU6. Here, S11, S12and the like in the drawings represent numbers assigned to the processing procedures (steps).

As shown inFIG. 5, in step S11, the engine CPU6determines whether or not the user has turned on the main power source.

Here, upon determining that the user has turned on the main power source (step S11: Yes), the engine CPU6moves the process to step S12. On the other hand, upon determining that the user has not turned on the main power source (step S11: No), the engine CPU6moves the process to step S13.

In step S12, the engine CPU6determines whether or not the second error control mode has been set. The second error control mode is set in step S44(seeFIG. 7) of a driving circuit abnormality handling process that is described below. The second error control mode indicates that an error handling process is being executed, based on a determination result of the engine CPU6that the fixing heater driving circuit5is abnormal (step S19: No). It is noted that the error handling process is described in detail below.

Here, upon determining that the second error control mode has been set (step S12: Yes), the engine CPU6moves the process to step S22. On the other hand, upon determining that the second error control mode has not been set (step S12: No), the engine CPU6moves the process to step S13.

In step S13, the engine CPU6calculates the temperature of the fixing heater482based on the analog data that is input via the multiplexer612. The temperature of the fixing heater482is repeatedly calculated in synchronization with the temperature monitoring timing. With regard to the temperatures calculated in step S13, at least the latest calculated temperature is stored in, for example, the RAM of the engine control portion40. It is noted that the temperature calculated in step S13as the temperature of the fixing heater482corresponds to the first temperature of the present disclosure.

Here, in step S13, even in a case where an error has occurred to the switching between the input channels of the multiplexer612and the first input channel has not been selected, the temperature of the fixing roller481is calculated in synchronization with the temperature monitoring timing. That is, in a case where an error has occurred to the switching between the input channels of the multiplexer612, in step S13, the temperature of the fixing roller481may be calculated based on analog data from an input channel that is different from the first input channel. In that case, the temperature calculated as the temperature of the fixing heater482is different from the actual temperature of the fixing heater482. For example, when the input channel of the multiplexer612is fixed to the second input channel, the temperature calculated in step S13becomes an ambient temperature, and is calculated as a temperature that is extremely lower than the actual temperature of the fixing heater482.

In step S14, the engine CPU6determines whether or not the temperature of the fixing heater482is the abnormally heated temperature based on the determination signal from the abnormality detection circuit7.

Here, upon determining that the temperature of the fixing heater482is not the abnormally heated temperature (step S14: No), the engine CPU6moves the process to step S15. On the other hand, upon determining that the temperature of the fixing heater482is the abnormally heated temperature (step S14: Yes), the engine CPU6moves the process to step S19.

It is noted that in a state where the temperature of the fixing heater482exceeds the abnormally heated temperature, the high-level signal (ON signal) is continuously transmitted from the comparator71to the switching element72, and the on-state of the switching element72is maintained. While the switching element72is in the on-state, no control signal is transmitted to the fixing heater driving circuit5, and the off-state of the fixing heater482is maintained.

In step S15, the engine CPU6releases the first error control mode. The first error control mode is set in step S34of an A/D converter abnormality handling process that is described below. The first error control mode indicates that an error handling process is being executed, based on a determination result of the engine CPU6that the A/D converter61is abnormal (step S19: Yes). That is, in a case where the engine CPU6determines that the temperature of the fixing heater482is not the abnormally heated temperature (step S14: No), the engine CPU6determines that the A/D converter61is not abnormal, and thus when an error handling process is executed to handle an abnormality of the A/D converter61, the engine CPU6ends the error handling process.

In step S16, the engine CPU6determines whether or not the temperature calculated in step S13is lower than the control target temperature. It is noted that the control target temperature corresponds to the fixing temperature that is to be achieved in the fixing roller481.

Here, upon determining that the temperature of the fixing roller481is lower than the control target temperature (step S16: Yes), the engine CPU6outputs the ON signal to the fixing heater driving circuit5(step S17). This allows the fixing heater482to be driven to increase the temperature of the fixing roller481. On the other hand, upon determining that the temperature of the fixing roller481is equal to or higher than the control target temperature (step S16: No), the engine CPU6outputs the OFF signal to the fixing heater driving circuit5(step S18). This allows the driving of the fixing heater482to be stopped to decrease the temperature of the fixing roller481.

In step S19, the engine CPU6determines whether or not the temperature calculated in step S13is lower than the reference temperature. Upon determining that the temperature calculated in step S13is lower than the reference temperature (step S19: Yes), the engine CPU6moves the process to step S20. On the other hand, upon determining that the temperature calculated in step S13is equal to or higher than the reference temperature (step S19: No), the engine CPU6moves the process to step S21.

It is noted that the reference temperature is set to a temperature that is lower than the abnormally heated temperature, and is set to a temperature that is equal to or lower than the control target temperature of step S16. However, from the viewpoint of reducing the load on the fixing heater control process, the reference temperature is preferably the same as the control target temperature. The reference temperature is an example of the second temperature of the present disclosure.

In step S20, the engine CPU6determines that the A/D converter61is abnormal, and executes the A/D converter abnormality handling process. As shown inFIG. 6, the engine CPU6stops the operation of the image forming portion4(step S31), restricts the operation/display portion2from accepting user operations (step S32), and displays an error message on the operation/display portion2(step S33). The processes of steps S31to S33are an example of the first error handling process of the present disclosure.

As the stopping of the operation of the image forming portion4executed in step S31, for example, the power supply control portion66stops the power supply to the image forming portion4by switching the switch91to the off-state, and the engine CPU6transmits a driving stop signal to components of the image forming portion4.

As the restriction on the operation/display portion2accepting user operations, for example, when a user operation is performed on the operation/display portion2, a control is made to disregard the user operation.

The error message is displayed on the operation/display portion2to notify the user that an error has occurred due to an abnormality of the engine CPU6. The error message, for example, indicates that an error has occurred in the engine CPU6, and urges the user to turn on the main power source again. In addition, the error message may notify that the image forming operation has stopped, or the error message may be an error code corresponding to the abnormality of the engine CPU6.

Subsequently, the engine CPU6sets the first error control mode (step S34). The first error control mode indicates that the error handling process of steps S31to S33is being executed. The setting of the first error control mode is executed by, for example, setting a flag on a register. The setting of the first error control mode is an example of the first error handling process of the present disclosure.

It is noted that the error handling process of steps S31to S34differs from the error handling process of steps S41to S44at least in part of the driving circuit abnormality handling process that is described below. Specifically, in the present embodiment, the error handling process of step S33differs from the error handling process of step S43in that the error message of step S33indicates that an error has occurred in the engine CPU6, and urges the user to turn on the main power source again. In addition, in the present embodiment, the error handling process of step S34differs from the error handling process of step S44in that in step S34, the first error control mode is set, and the error handling process is regarded not to have been continued after the power source was turned on again.

As shown inFIG. 5, in step S21, the engine CPU6executes the driving circuit abnormality handling process. As shown inFIG. 7, the engine CPU6executes an error handling process that is the same as the A/D converter abnormality handling process shown inFIG. 6. That is, the engine CPU6stops the operation of the image forming portion4(step S41), restricts the operation/display portion2from accepting user operations (step S42), and displays an error message on the operation/display portion2(step S43). The error message displayed on the operation/display portion2indicates, for example, that an abnormality has occurred in the fixing heater driving circuit5, and the fixing heater driving circuit5needs maintenance. In addition, the error message may notify that the image forming operation has stopped, or the error message may be an error code corresponding to the abnormality of the fixing heater driving circuit5. The processes of steps S41to S43are an example of the second error handling process of the present disclosure.

Subsequently, the engine CPU6sets the second error control mode (step S44). The second error control mode indicates that the error handling process of steps S41to S43is being executed. The setting of the second error control mode is executed by, for example, setting a flag on a register. The setting of the second error control mode is an example of the second error handling process of the present disclosure.

As shown inFIG. 5, the engine CPU6executes steps S22to S24as the error handling process. Specifically, the engine CPU6stops the operation of the image forming portion4(step S22), restricts the operation/display portion2from accepting user operations (step S23), and displays an error message on the operation/display portion2(step S24). That is, upon determining that the second error control mode has been set (step S12: Yes), the engine CPU6executes the error handling process (steps S41to S43) in the driving circuit abnormality handling process of step S21, even after the main power source is turned on again. It is noted that the error handling process (steps S31to S33) in the A/D converter abnormality handling process of step S20is not executed after the main power source is turned on again, and is released when the main power source is turned off.

As described above, in the image forming apparatus10, in a case where the abnormality detection circuit7detects that the fixing roller has the abnormally heated temperature, when the engine CPU6determines that the temperature of the fixing heater482is lower than the reference temperature, it is determined that the A/D converter61of the engine CPU6is abnormal.

Here, among causes of the abnormally heated temperature of the fixing roller481, some causes can be eliminated easily by turning off and on the main power source, and some causes cannot be eliminated easily and need a repair by a service engineer. An example of a cause that cannot be eliminated easily, is an abnormality of the fixing heater driving circuit5. On the other hand, an example of a cause that can be eliminated easily, is a latchup between input channels of the A/D converter61of the engine CPU6. The latchup may be solved by turning off the main power source. In many cases, the latchup can be solved by turning off the main power source a plurality of times.

On the other hand, in the image forming apparatus10, it is possible to determine whether or not the A/D converter61of the engine CPU6is abnormal. As a result, when the fixing roller481is in the abnormally heated state, it is possible to determine whether or not there is a possibility that the abnormally heated state can be solved easily by turning off and on (turning on again) the main power source. With this configuration, in the image forming apparatus10, when there is a possibility that the abnormally heated state can be solved easily, a repair by a service engineer is not required, and the time is not wasted identifying the cause of the abnormality. As a result, in the image forming apparatus10, in a case where the cause of an abnormal heating of the fixing roller481is an abnormality of the A/D converter61, a state where the image forming process cannot be executed due to a repair by a service engineer or the like is avoided, and the convenience of the user is improved.

In addition, in the image forming apparatus10, the engine CPU6distinguishes between an abnormality of the A/D converter61and an abnormality of the fixing heater driving circuit5, and executes different error handling processes upon detection of their abnormalities. Furthermore, the error handling process for the abnormality of the A/D converter61(first error control mode) can be released by turning on the main power source again. On the other hand, release of the error handling process for the abnormality of the fixing heater driving circuit5(second error control mode) is restricted even if the main power source is turned on again. That is, in the image forming apparatus10, with respect to an abnormality that can be easily solved by turning on the main power source again, it is made possible to release the error handling process, and with respect to an abnormality that cannot be solved easily, release of the error handling process is restricted. With this configuration, in a case where there is a possibility that a serious abnormality has occurred, the image forming process continues to be stopped, and in a case where an abnormality that can be easily solved has occurred, a resumption of the image forming process is made possible. Accordingly, in the image forming apparatus10, it is possible to avoid a state where the image forming process cannot be executed more than necessary, and the convenience of the user is improved.

In addition, it is possible to determine whether or not the A/D converter61is abnormal only by determining whether or not the temperature of the fixing heater482is lower than the reference temperature after the abnormality detection circuit7detects that the fixing roller has the abnormally heated temperature. Accordingly, in the image forming apparatus10, the cause of the abnormality is determined by a simple process, and it is possible to transfer to the error handling process in a short time. As a result, it is possible to restrict a wasteful printing from being continued while an abnormality is determined to execute an error handling process. This reduces an economic loss due to wastefully formed defective printed matter.

Next, a description is given of an image forming apparatus according to a second embodiment of the present disclosure, with reference toFIG. 8andFIG. 9. The image forming apparatus according to the second embodiment of the present disclosure is the same as that of the first embodiment in the basic configuration, except for the configuration of the engine CPU (an example of the calculation processing portion of the present disclosure).

An engine CPU6A shown inFIG. 8includes the A/D converter61, the output port62, the input port63, a power supply control portion66A, an input-portion abnormality determining portion64A, an error-handling-process executing portion65A, and a number-of-times determination processing portion67A. It is noted that a description of the A/D converter61, the output port62, and the input port63is omitted since they are the same as those described in the first embodiment.

The power supply control portion66A controls a stop and a start of a power supply to the engine CPU6A by controlling the switch91provided in a power supply path from the power source portion9to the engine CPU6A. For example, in a case where the input-portion abnormality determining portion64A has determined that the A/D converter61is abnormal, the power supply control portion66A stops the power supply to the engine CPU6A by switching the switch91to the off-state, and then resumes the power supply to the engine CPU6A by switching the switch91to the on-state. That is, the power supply control portion66A restarts the engine CPU6A in a case where the input-portion abnormality determining portion64A determines that the A/D converter61is abnormal.

The input-portion abnormality determining portion64A determines whether or not the first temperature is lower than the second temperature after the power supply control portion66A stops and resumes the power supply to the engine CPU6A.

When the input-portion abnormality determining portion64A has determined that the A/D converter61is abnormal, the number-of-times determination processing portion67A determines whether or not the number of times that the power supply control portion66A stopped and resumed the power supply to the engine CPU6A is equal to a predetermined reference number of times.

The error-handling-process executing portion65A executes an error handling process when the number-of-times determination processing portion67A has determined that the number of times that the power supply control portion66A stopped and resumed the power supply to the engine CPU6A is equal to the reference number of times.

Next, with reference toFIG. 9, a description is given of another example of the A/D converter abnormality handling process in the fixing heater control process executed by the input-portion abnormality determining portion64A, the error-handling-process executing portion65A, the power supply control portion66A, and the number-of-times determination processing portion67A of the engine CPU6A.

As shown inFIG. 9, the engine CPU6stops the operation of the image forming portion4(step S51), and then restarts the image forming apparatus10(step S52). At this time, in a case where the input-portion abnormality determining portion64A has determined that the A/D converter61is abnormal, the power supply control portion66A stops the power supply to the engine CPU6A by switching the switch91to the off-state, and then resumes the power supply to the engine CPU6A by switching the switch91to the on-state. Subsequently, the engine CPU6A counts the number of restarts since the engine CPU6determined that the temperature was lower than the reference temperature in step S19ofFIG. 5(step S53).

In step S54, the engine CPU6A repeatedly calculates the temperature of the fixing heater482in synchronization with the temperature monitoring timing. With regard to the temperatures calculated in step S54, at least the latest calculated temperature is stored in the RAM of the engine control portion40or the like.

In step S55, the engine CPU6A determines whether or not the temperature calculated in step S54is lower than the reference temperature. That is, the engine CPU6A determines whether or not the abnormality of the A/D converter61has been solved by the restart in step S52.

Here, upon determining that the temperature calculated in step S54is lower than the reference temperature (step S55: Yes), the engine CPU6A moves the process to step S57. On the other hand, upon determining that the temperature calculated in step S54is equal to or higher than the reference temperature (step S55: No), the engine CPU6A moves the process to step S56.

In step S56, the engine CPU6A releases the stop of the operation of the image forming portion4, and ends the A/D converter abnormality handling process. That is, since it has been determined in step S55that the temperature calculated in step S54is equal to or higher than the reference temperature, the engine CPU6A determines that the abnormality of the A/D converter61has been solved by the restart in step S52. This makes it possible for the image forming portion4to execute the image forming process.

In step S57, the engine CPU6A determines whether or not the restart of the image forming apparatus10has been executed a predetermined number of times. For example, the predetermined number of times is selected from a range from 1 (once) to 5 (five times), and is preferably set to 2 (twice) or 3 (three times).

Here, upon determining that the restart of the image forming apparatus10has been executed the predetermined number of times (step S57: Yes), the engine CPU6A moves the process to step58. On the other hand, upon determining that the restart of the image forming apparatus10has not been executed the predetermined number of times (step S57: No), the engine CPU6A moves the process to step52.

Upon determining that the restart of the image forming apparatus10has been executed the predetermined number of times (step S57: Yes), the engine CPU6A determines that the abnormality of the A/D converter61is not solved, and executes the error handling process in steps S58to S60. Specifically, the engine CPU6A stops the operation of the image forming portion4(step S58), restricts the operation/display portion2from accepting user operations (step S59), and displays an error message on the operation/display portion2(step S60).

In step S61, the engine CPU6A sets the second error control mode. In the second error control mode, the error handling process is not released even when the user turns on the main power source again (seeFIG. 5). In other words, in a case where the abnormality of the A/D converter61is not solved even if the restart of the image forming apparatus10is executed the predetermined number of times, the engine CPU6A, when the main power source is turned on again by the user, stops the operation of the image forming portion4, restricts the operation/display portion2from accepting user operations, and displays an error message on the operation/display portion2(steps S22to S24ofFIG. 5).

As described above, in the image forming apparatus10, it is determined whether or not the abnormality of the A/D converter61is solved after restarting the image forming apparatus10by turning off and on the main power source a predetermined number of times. As a result, in the image forming apparatus10, in a case where an abnormality that may be easily solved occurs in the A/D converter61, it is determined whether or not the abnormality is solved by a simple operation of restarting the image forming apparatus10. In case of an abnormality that may be easily solved, after the abnormality is solved, execution of the image forming operation by the image forming portion4is made available. As a result, in the image forming apparatus10, it is possible to avoid a state where the image forming process cannot be executed more than necessary due to a repair by a service engineer, and the convenience of the user is improved. On the other hand, with respect to an abnormality that cannot be solved easily, releasing the error handling process is restricted by setting the second error control mode. With this configuration, in a case where a serious abnormality has occurred in the A/D converter61, execution of the image forming process is restricted, the abnormality of the A/D converter61is restricted from becoming more serious, and a failure such as a seizure of the fixing roller481is restricted.

It is noted that in step S52of the A/D converter abnormality handling process shown inFIG. 9, instead of the image forming apparatus10, the engine control portion40may be restarted. That is, in step S52, portions other than the engine CPU6A may not be restarted, but the power supply to the engine CPU6A may be stopped and resumed. In this case, in step S53, the number of restarts of the fixing device6A is counted, and in step S57, it is determined whether or not the engine CPU6A has been restarted a predetermined number of times.

In step S21of the fixing heater control process, instead of the driving circuit abnormality handling process, the A/D converter abnormality handling process and an abnormality handling process other than the driving circuit abnormality handling process may be executed. Also, in the step S21, in addition to the driving circuit abnormality handling process, the other abnormality handling process may be executed.