Image forming apparatus and method for controlling the image forming apparatus

Abstract

To prevent an increase in cost and detect disconnection of heaters even when a large number of heaters are connected in parallel.SOLUTION: An image forming apparatus comprises: a plurality of heaters that are used for fixing an image to a recording medium and connected in parallel; voltage detection means that detects voltage applied to the plurality of heaters; temperature detection means that is arranged at a position in proximity to a predetermined number of first heaters among the plurality of heaters; current detection means that is connected with a predetermined number of second heaters excluding the first heaters among the plurality of heaters, and detects a current flowing in the predetermined number of second heaters; and a failure determination unit that determines disconnection of the first heaters based on the temperature detected by the temperature detection means, and determines disconnection of the predetermined number of second heaters based on the current detected by the current detection means.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus and a method for controlling the image forming apparatus. [Background technology]

[0002] In an electrophotographic image forming apparatus, after a toner image is transferred onto a recording medium such as transfer paper, the toner image is fixed onto the transfer paper by a fixing device having multiple heaters connected in parallel. For example, a method is known for detecting a fault such as a broken wire in a heater by detecting the value of a current flowing through the heater (for example, Patent Document 1). Summary of the Invention [Problem to be solved by the invention]

[0003] However, since there is variation in the capacity of the heater and the detection accuracy of the current detector that detects the current flowing through the heater, when a large number of heaters are connected in parallel, it becomes difficult to accurately detect a heater breakage based on the current flowing through the heater. For example, if the maximum value of the current when a breakage is detected is greater than the minimum value of the normal current, the breakage of the heater cannot be detected. When a heater with small capacity variation is used, or a current detector with high current detection accuracy is used, or when the number of current detectors is increased according to the number of heaters, the cost of the image forming apparatus increases.

[0004] The disclosed technology has been made in consideration of the above-mentioned problems, and aims to detect heater breakage while suppressing increases in costs even when a large number of heaters are connected in parallel. [Means for solving the problem]

[0005] In order to solve the above technical problems, an image forming apparatus according to one embodiment of the present invention is characterized in that it comprises a plurality of heaters connected in parallel for use in fixing an image on a recording medium, a voltage detection means for detecting a voltage applied to the plurality of heaters, a temperature detection means arranged in a position adjacent to a predetermined number of first heaters among the plurality of heaters, a current detection means connected to a predetermined number of second heaters among the plurality of heaters excluding the first heaters and detecting a current flowing through the predetermined number of second heaters, and a failure judgment unit for judging a break in the first heater based on a temperature detected by the temperature detection means and for judging a break in the predetermined number of second heaters based on a current detected by the current detection means. Effect of the Invention

[0006] Even when a large number of heaters are connected in parallel, heater breaks can be detected while suppressing increases in cost. [Brief description of the drawings]

[0007] [Figure 1] 1 is a side view illustrating an example of an overall configuration of an image forming apparatus according to a first embodiment. [Diagram 2] 2 is a circuit diagram showing an outline of the configuration of the fixing device shown in FIG. 1. [Diagram 3] 3 is a flow chart showing an example of heater disconnection detection control in FIG. 2. [Figure 4] FIG. 11 is a circuit diagram showing an outline of a configuration of a fixing device in an image forming apparatus according to a second embodiment. [Diagram 5] 5 is a flow chart showing an example of heater disconnection detection control in FIG. 4. [Figure 6] FIG. 13 is a circuit diagram showing an outline of a configuration of a fixing device in an image forming apparatus according to a sixth embodiment. [Figure 7] 7 is a flow chart showing an example of heater disconnection detection control in FIG. 6. [Figure 8] FIG. 8 is a flow chart showing a continuation of the operation of FIG. [Figure 9] FIG. 11 is a circuit diagram showing an outline of a configuration of a fixing device in another image forming apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the embodiments will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and duplicated descriptions may be omitted.

[0009] (First embodiment) FIG. 1 is a side view showing an example of the overall configuration of an image forming apparatus in the first embodiment. The image forming apparatus 1 shown in FIG. 1 is, for example, a digital multifunction machine having a copy function, a printer function, a scanner function, a facsimile function, and the like. The image forming apparatus 1 can switch its operation mode to any one of the copy function, the printer function, the scanner function, and the facsimile function by an application switching key on an operation unit (not shown). For example, the image forming apparatus 1 goes into the copy mode when the copy function is selected, and goes into the printer mode when the printer function is selected. Also, the image forming apparatus 1 goes into the scanner mode when the scanner mode is selected, and goes into the facsimile mode when the facsimile mode is selected. The image forming apparatus 1 may be a copy machine or a printer.

[0010] For example, the image forming apparatus 1 has an automatic document feeder (ADF) 10, an image reading device 20, a writing unit 30, a printer unit 40, and a power storage device 50. For ease of understanding, the printer unit 40 is shown in a transparent state. The printer unit 40 has a photoconductor drum 41 (photoconductor), a developing device 42, a conveyor belt 43, a fixing device 44, and the like. The printer unit 40 creates a toner image to be transferred to a recording medium such as transfer paper based on image information. The toner image is an example of an image. Below, as an example of the flow of image formation in the image forming apparatus 1, a case where the operation mode is set to the copy mode will be briefly described.

[0011] In the copy mode, multiple documents to be copied are set in the automatic document feeder 10. When a start button on an operation unit (not shown) is pressed, the automatic document feeder 10 sends the documents one by one to the image reading device 20. The image reading device 20 reads image information of the documents sent in order from the automatic document feeder 10. The read image information is processed by the image processing unit 60.

[0012] The writing unit 30 converts the image information processed by the image processing unit 60 into optical information. The photoconductor drum 41 is uniformly charged by a charger (not shown) and then exposed to a laser beam containing the optical information converted by the writing unit 30. An electrostatic latent image is formed on the photoconductor drum 41 by the exposure.

[0013] The developing device 42 develops the electrostatic latent image on the photoreceptor drum 41 to form a toner image on the photoreceptor drum 41. The conveyor belt 43 transfers the toner image onto a recording medium such as transfer paper. The fixing device 44 fixes the toner image onto the transfer paper. Then, the recording medium such as transfer paper onto which the image of the original has been copied is discharged from a discharge section.

[0014] FIG. 2 is a circuit diagram showing an outline of the configuration of the fixing device 44 in FIG. 1. For example, the fixing device 44 has four heaters H1, H2, H3, and H4 connected in parallel and used for fixing the above-mentioned toner image onto a transfer paper. The fixing device 44 also has a CPU (Central Processing Unit) 441, a temperature detector 442, a driving element 443 such as a triac, a current detector A1, a voltage detector V1, and a power source 444. Note that the power source 444 may be disposed in the power storage device 50 in FIG. 1. The CPU 441 is an example of a failure determination unit. The temperature detector 442 is an example of a temperature detection means. The current detector A1 is an example of a current detection means. The voltage detector V1 is an example of a voltage detection means.

[0015] The heaters H1 and H2 have one end connected to a power supply line VDD and the other end connected to a ground line VSS via a current detector A1 and a driving element 443. The heaters H3 and H4 have one end connected to a power supply line VDD and the other end connected to a ground line VSS via a driving element 443. The heaters H1 and H2 are an example of a second heater. The heaters H3 and H4 are an example of a first heater.

[0016] In other words, the heaters H1 and H2 connected in parallel, the current detector A1, and the driving element 443 are connected in series between the power supply line VDD and the ground line VSS, and the heaters H3 and H4 connected in parallel and the driving element 443 are connected in series between the power supply line VDD and the ground line VSS. The driving element 443 controls the current flowing through the heaters H1, H2, H3, and H4. The voltage detector V1 is disposed between the power supply line VDD and the ground line VSS.

[0017] The temperature detector 442 is disposed in close proximity to the heaters H3 and H4 and can detect heat generation from the heaters H3 and H4 due to the current flowing through the heaters H3 and H4. Heat generation from the heaters H1 and H2 due to the current flowing through the heaters H1 and H2, which are distant from the temperature detector 442, cannot be detected by the temperature detector 442. The current flowing through the heaters H1 and H2 can be detected by the current detector A1 disposed on the current path of the heaters H1 and H2. Therefore, the amount of heat generated by the heaters H1 and H2 (i.e., the heater capacity of the heaters H1 and H2) can be detected according to the current detected by the current detector A1 and the voltage detected by the voltage detector V1.

[0018] For example, the number of heaters H1, H2 connected to the current detector A1 is set to a number that allows the current detected by the current detector A1 to distinguish between a disconnection of one of the heaters H1, H2 and normal operation of the heaters H1, H2 even when the electrical characteristics of the various components vary under the worst conditions. Here, the variation in the electrical characteristics of the various components includes the detection variation of the voltage detector V1, the detection variation of the current detector A1, and the heater capacity variation of the heaters H1, H2.

[0019] The temperature detector 442 has a degree of accuracy that allows it to detect the presence or absence of heat generation from the heaters H3, H4 as a temperature within a range in which the resistance values ​​of the heaters H3, H4 vary normally. The current detector A1 and the voltage detector V1 each have a degree of accuracy that allows it to detect the presence or absence of heat generation from the heaters H1, H2 within a range in which the resistance values ​​of the heaters H1, H2 vary normally. In other words, by setting the number of heaters H1, H2 connected to the current detector A1 in consideration of the worst condition of the variation in the electrical characteristics described above, the temperature detector 442, the current detector A1, and the voltage detector V1 do not need to be highly accurate.

[0020] The CPU 441 controls the on / off of the driving element 443. The CPU 441 also receives current information indicating the current detected by the current detector A1, and voltage information indicating the voltage detected by the voltage detector V1. The CPU 441 also receives temperature information indicating the temperature detected by the temperature detector 442.

[0021] When the driving element 443 is turned on, the CPU 441 detects whether or not the heaters H1, H2 are disconnected by monitoring the current value detected by the current detector A1. For example, the CPU 441 may determine that both the heaters H1, H2 are disconnected when the detected current value is smaller than a first threshold value. The CPU 441 may determine that one of the heaters H1, H2 is disconnected when the calculated current value is equal to or larger than the first threshold value and smaller than a second threshold value. Here, the second threshold value is larger than the first threshold value. The CPU 441 may determine that the heaters H1, H2 are normal when the calculated current value is equal to or larger than the second threshold value.

[0022] The CPU 441 may detect only the presence or absence of disconnection of the heaters H1 and H2 based on whether the current value detected by the current detector A1 is smaller than the second threshold value. In this case, the CPU 441 does not determine which of the heaters H1 and H2 has disconnected.

[0023] On the other hand, when the driving element 443 is turned on, the CPU 441 monitors the temperature detected by the temperature detector 442 to determine whether or not the heaters H3 and H4 are disconnected. When the temperature detected by the temperature detector 442 is lower than a third threshold, the CPU 441 may determine that both the heaters H1 and H2 are disconnected. When the temperature detected by the temperature detector 442 is equal to or higher than the third threshold and lower than a fourth threshold, the CPU 441 may determine that one of the heaters H1 and H2 is disconnected. Here, the fourth threshold is greater than the third threshold. When the temperature detected by the temperature detector 442 is equal to or higher than the fourth threshold, the CPU 441 may determine that the heaters H1 and H2 are normal.

[0024] The CPU 441 may determine whether or not the heaters H3 and H4 are broken based on the time (rise time or rise gradient) from when the driving element 443 is turned on until the temperature detected by the temperature detector 442 exceeds a specified temperature. In this case, the CPU 441 can determine whether both heaters H3 and H4 are broken, one of them is broken, or the heaters H3 and H4 are normal by setting two types of rise time (or rise gradient) as the fifth and sixth thresholds.

[0025] The CPU 441 may detect only the presence or absence of disconnection of the heaters H3 and H4 based on whether or not the temperature detected by the temperature detector 442 is lower than a fourth threshold value. The CPU 441 may detect only the presence or absence of disconnection of the heaters H3 and H4 based on whether or not the rise time or the rise gradient of the temperature detected by the temperature detector 442 is lower than a sixth threshold value. In this case, the CPU 441 does not determine which of the heaters H3 and H4 has disconnected.

[0026] Fig. 3 is a flow diagram showing an example of disconnection detection control of heaters H1-H4 in Fig. 2. For example, the process shown in Fig. 3 is realized by CPU 441 executing a control program. Fig. 3 also shows an example of a control method for image forming apparatus 1. The process shown in Fig. 3 is started based on the start of fixing control of fixing device 44.

[0027] First, in step S11, the CPU 441 turns on the driving element 443 to pass current through the heaters H1-H4, thereby turning on the heaters H1-H4. Next, in step S12, the CPU 441 monitors the voltage detected by the voltage detector V1, the current detected by the current detector A1, and the temperature detected by the temperature detector 442. For example, the CPU 441 determines that the voltage applied to the heaters H1-H4 is normal based on the voltage detected by the voltage detector V1.

[0028] Next, in step S13, the CPU 441 determines whether the current value detected by the current detector A1 is equal to or greater than a specified value (e.g., equal to or greater than a second threshold) and whether the temperature rise (gradient) detected by the temperature detector 442 is equal to or greater than a specified value (e.g., equal to or greater than a sixth threshold). If the current value is equal to or greater than a specified value and the temperature rise is equal to or greater than a specified value, the CPU 441 determines that the heaters H1-H4 are normally on without disconnection, and proceeds to step S14.

[0029] If the current value is less than the specified value, the CPU 441 determines that at least one of the heaters H1 and H2 has broken down, and shifts the process to step S15. If the temperature rise (slope) is less than the specified value, the CPU 441 determines that at least one of the heaters H3 and H4 has broken down, and shifts the process to step S15. In step S14, the CPU 441 executes normal fixing control, and ends the process shown in FIG. 3.

[0030] In step S15, the CPU 441 turns off the heaters H1-H4 by turning off the driving element 443. Next, in step S16, the CPU 441 notifies a higher-level controller that controls the overall operation of the image forming apparatus 1 that any one of the heaters H1-H4 has been disconnected, and ends the process shown in Fig. 3. The higher-level controller executes anomaly processing based on the disconnection notification.

[0031] In the flow shown in Fig. 3, the CPU 441 detects a disconnection when the current value is less than a preset value, but may also detect a disconnection when the heater capacity calculated from the current value and the voltage value is less than a preset value. In addition, a process for detecting an overcurrent anomaly or a high temperature anomaly may be added to the flow shown in Fig. 3.

[0032] In this case, for example, before step S14, a process for detecting an overcurrent abnormality or a high temperature abnormality is added when the current value or the slope of the temperature rise exceeds an abnormal value that is greater than the respective specified values ​​(overcurrent). This makes it possible to detect a high temperature abnormality in the fixing device 44, and to prevent the occurrence of a malfunction of the image forming apparatus 1 due to the high temperature abnormality. Also, the CPU 441 can detect a high temperature abnormality in the heaters H1 and H2 located away from the temperature detector 442. As a result, the safety and reliability of the image forming apparatus 1 can be improved.

[0033] As described above, in this embodiment, the fixing device 44 is provided with the current detector A1 that detects the current flowing through the heaters H1 and H2, and the temperature detector 442 that detects the heat generated by the heaters H3 and H4. This allows the image forming apparatus 1 to detect breaks in the heaters H1 and H2 and breaks in the heaters H3 and H4 independently. As a result, the image forming apparatus 1 can reliably detect the presence or absence of breaks in the heaters H1-H4 using the voltage detector V1 and current detector A1 with normal detection accuracy.

[0034] In order to detect the presence or absence of disconnection of the heaters H1-H4, the highly accurate temperature detector 442, the highly accurate current detector A1, and the highly accurate voltage detector V1 are not required. Also, for example, it is not necessary to provide a temperature detector 442 or a current detector A1 for each of the heaters H1-H4. Therefore, the parts cost of the fixing device 44 can be reduced, and an increase in the cost of the image forming apparatus 1 can be prevented.

[0035] Second embodiment Fig. 4 is a circuit diagram showing an outline of the configuration of a fixing device in an image forming apparatus according to a second embodiment. Fixing device 44A shown in Fig. 4 is mounted in image forming apparatus 1 in place of fixing device 44 in Fig. 1. Image forming apparatus 1 according to this embodiment has the same configuration and function as image forming apparatus 1 shown in Fig. 1, except that fixing device 44A is mounted instead of fixing device 44.

[0036] 1, the fixing device 44A has a switch SW1 in addition to the configuration of the fixing device 44. The switch SW1 is connected to the ground line VSS side of the heaters H3 and H4. The switch SW1 is controlled to be turned on / off by the CPU 441. In this embodiment, one end of the heaters H3 and H4 is connected to the power supply line VDD, and the other end is connected to the ground line VSS via the switch SW1, the current detector A1, and the driving element 443.

[0037] Fig. 5 is a flow diagram showing an example of disconnection detection control of heaters H1-H4 in Fig. 4. Detailed description of processes similar to those in Fig. 3 will be omitted. For example, the process shown in Fig. 5 shows an example of a control method for image forming apparatus 1, and is realized by CPU 441 executing a control program. The process shown in Fig. 5 is started based on the start of fixing control of fixing device 44.

[0038] First, in step S21, the CPU 441 turns on the switch SW1, turns on the driving element 443, and passes a current through the heaters H1-H4, thereby turning on the heaters H1-H4. During the period in which the switch SW1 and the driving element 443 are turned on, the CPU 441 can detect the total current flowing through the heaters H1-H4 using the current detector A1. Next, in step S22, the CPU 441 monitors the voltage detected by the voltage detector V1 and the temperature detected by the temperature detector 442.

[0039] Next, in step S23, the CPU 441 determines whether the temperature rise (gradient) detected by the temperature detector 442 is equal to or greater than a specified value (e.g., equal to or greater than a sixth threshold value). If the temperature rise is equal to or greater than the specified value, the CPU 441 determines that the heaters H3 and H4 are normally on without any disconnection, and shifts the process to step S24. If the temperature rise (gradient) is less than the specified value, the CPU 441 determines that at least one of the heaters H3 and H4 has disconnected, and shifts the process to step S29.

[0040] In step S24, the CPU 441 turns off the switch SW1. Next, in step S26, the CPU 441 monitors the current detected by the current detector A1. Next, in step S26, the CPU 441 determines whether or not the current value detected by the current detector A1 is equal to or greater than a specified value (for example, equal to or greater than a second threshold value). If the current value is equal to or greater than the specified value, the CPU 441 determines that the heaters H1 and H2 are normally on without any disconnection, and shifts the process to step S27. That is, if the CPU 441 determines that all the heaters H1-H4 are normal, it shifts the process to step S27. If the current value is less than the specified value, the CPU 441 determines that at least one of the heaters H1 and H2 has disconnected, and shifts the process to step S29.

[0041] In step S27, the CPU 441 turns on the switch SW1. Next, in step S28, the CPU 441 executes normal fixing control and ends the process shown in Fig. 5. The process of step S29 and the process of step S30 executed after step S29 are the same as the processes of steps S15 and S16 in Fig. 3.

[0042] In the flow shown in Fig. 5, the CPU 441 detects a disconnection when the current value is less than a preset value, but may detect a disconnection when the heater capacity calculated from the current value and the voltage value is less than a preset value. Also, a process for detecting an overcurrent anomaly or a high temperature anomaly may be added to the flow shown in Fig. 5.

[0043] In this case, for example, before step S28, a process is added to detect an overcurrent abnormality or a high temperature abnormality when the current value or the slope of the temperature rise exceeds an abnormal value that is greater than the respective specified value. This makes it possible to detect a high temperature abnormality in the fixing device 44A in advance, and to prevent the occurrence of a malfunction of the image forming apparatus 1 due to a high temperature abnormality. As a result, the safety and reliability of the image forming apparatus 1 can be improved.

[0044] As described above, in this embodiment, as in the above-mentioned embodiment, the image forming apparatus 1 can detect breaks in the heaters H1 and H2 and breaks in the heaters H3 and H4 independently. This allows the image forming apparatus 1 to reliably detect the presence or absence of breaks in the heaters H1-H4 using the voltage detector V1 and current detector A1 with normal detection accuracy. As a result, the cost of the parts of the fixing device 44A can be reduced, and an increase in the cost of the image forming apparatus 1 can be prevented.

[0045] (Third embodiment) Fig. 6 is a circuit diagram showing an outline of the configuration of a fixing device in an image forming apparatus according to a third embodiment. Fixing device 44B shown in Fig. 6 is mounted in image forming apparatus 1 in place of fixing device 44 in Fig. 1. Image forming apparatus 1 according to this embodiment has the same configuration and function as image forming apparatus 1 shown in Fig. 1, except that fixing device 44B is mounted instead of fixing device 44.

[0046] Fixing device 44B has switches SW2, SW3 and heaters H5, H6 in addition to the configuration of fixing device 44 in Fig. 1. Heaters H1, H2 and heaters H5, H6 are each an example of a second heater group.

[0047] The switch SW2 is connected to the ground line VSS side of the heaters H1 and H2. The switch SW3 is connected to the ground line VSS side of the heaters H5 and H6. The switches SW2 and SW3 are controlled to be turned on / off by the CPU 441. The heaters H5 and H6 have one end connected to the power supply line VDD and the other end connected to the ground line VSS via the switch SW3, the current detector A1, and the driving element 443.

[0048] 7 and 8 are flow diagrams showing an example of disconnection detection control of heaters H1-H6 in FIG. 6. Detailed description of processes similar to those in FIG. 3 and FIG. 5 will be omitted. For example, the processes shown in FIG. 7 and FIG. 8 show an example of a control method of image forming apparatus 1, and are realized by CPU 441 executing a control program. The process shown in FIG. 7 is started based on the start of fixing control of fixing device 44.

[0049] First, in step S31, the CPU 441 turns on the switches SW2 and SW3, turns on the driving element 443, and passes a current through the heaters H1-H6 to turn on the heaters H1-H6. The processes of steps S32 and S33 executed after step S31 are similar to the processes of steps S22 and S23 in Fig. 5. In step S33, if the temperature rise (slope) is equal to or greater than a specified value, the CPU 441 determines that the heaters H3 and H4 are normally on without disconnection, and shifts the process to step S34. If the temperature rise (slope) is less than a specified value, the CPU 441 determines that at least one of the heaters H3 and H4 has disconnected, and shifts the process to step S42 in Fig. 8.

[0050] In step S34, the CPU 441 turns off the switch SW3. By turning off the switch SW3, the current detector A1 can detect only the current flowing through the heaters H1 and H2. The processes of steps S35 and S36 executed after step S34 are similar to the processes of steps S25 and S26 in FIG. 5. In step S36, if the current value detected by the current detector A1 is equal to or greater than a specified value, the CPU 441 determines that the heaters H1 and H2 are normally on without disconnection, and shifts the process to step S37 in FIG. 8. If the current value is less than the specified value, the CPU 441 determines that at least one of the heaters H1 and H2 has disconnected, and shifts the process to step S42 in FIG. 8.

[0051] In step S37 in Fig. 8, the CPU 441 turns off the switch SW2 and turns on the switch SW3. With the switch SW2 turned off and the switch SW3 turned on, the current detector A1 can detect only the current flowing through the heaters H5 and H6. The processes of steps S38 and S39 executed after step S37 are similar to the processes of steps S35 and S36 in Fig. 7, except that it is determined whether or not the heaters H5 and H6 are disconnected.

[0052] In step S39, if the current value detected by the current detector A1 is equal to or greater than the specified value, the CPU 441 determines that the heaters H5 and H6 are normally on and not disconnected, and proceeds to step S40. If the current value is less than the specified value, the CPU 441 determines that at least one of the heaters H5 and H6 is disconnected, and proceeds to step S42.

[0053] In step S40, the CPU 441 turns on the switch SW2. Next, in step S41, the CPU 441 executes normal fixing control and ends the processing shown in Fig. 7 and Fig. 8. The processing of step S42 and the processing of step S43 executed after step S42 are the same as the processing of steps S15 and S16 in Fig. 3.

[0054] 7 and 8, the CPU 441 detects a disconnection when the current value is less than a preset value, but may detect a disconnection when the heater capacity calculated from the current value and the voltage value is less than a preset value. Also, a process for detecting an overcurrent anomaly or a high temperature anomaly may be added to the flow shown in FIG. 7 and FIG. 8.

[0055] In this case, for example, before step S41, a process is added to detect an overcurrent abnormality or a high temperature abnormality when the current value or the slope of the temperature rise exceeds an abnormal value that is greater than the respective specified value. This makes it possible to detect a high temperature abnormality in the fixing device 44B in advance, and to prevent the occurrence of a malfunction of the image forming apparatus 1 due to a high temperature abnormality. As a result, the safety and reliability of the image forming apparatus 1 can be improved.

[0056] As described above, in this embodiment, as in the above-mentioned embodiment, the image forming apparatus 1 can detect breaks in the heaters H1 and H2, H3 and H4, and H5 and H6 independently. This allows the image forming apparatus 1 to reliably detect the presence or absence of breaks in the heaters H1-H6 using the voltage detector V1 and current detector A1 with normal detection accuracy. As a result, the cost of the parts of the fixing device 44B can be reduced, and an increase in the cost of the image forming apparatus 1 can be prevented.

[0057] In addition, when heaters H7 and H8 are further added to the fixing device 44B of FIG. 6, a switch SW4 may be added between the heaters H7 and H8 and the current detector A1. The heaters H7 and H8 are an example of a second heater group. By adding a switch between the heaters and the current detector A1 every time a heater is added, the CPU 441 can reliably determine whether or not the heaters are disconnected by turning on the switches one by one to detect the current even in a configuration with a large number of heaters in parallel. Therefore, even when the number of heaters is large, there is no need to provide a high-precision current detector A1 and voltage detector V1, and there is also no need to provide multiple current detectors A1. As a result, even when the number of heaters is large, the fixing device 44B can be prevented from becoming complicated, and the cost of the image forming apparatus 1 can be prevented from increasing.

[0058] (Comparative Example) Fig. 9 is a circuit diagram showing an outline of the configuration of a fixing device in another image forming apparatus. Fixing device 44C shown in Fig. 9 differs from fixing device 44 in Fig. 1 in that heaters H3 and H4 are connected to driving element 443 without passing through current detector A1. That is, heaters H1-H4 are connected in parallel between power supply line VDD and current detector A1. In this case, current detector A1 constantly detects the current flowing through heaters H1-H4.

[0059] 9, if the accuracy of the current detector A1 and the voltage detector V1 is low, the CPU 441 may not be able to detect disconnections of the heaters H1 and H2 based on the detection of the current value by the current detector A1. For example, assume that the heater capacity variation is ±10%, and the detection variations of the current detector A1 and the voltage detector V1 are each ±5%.

[0060] When three heaters are connected in parallel (3 parallel), the lower limit Rmin1 of the resistance when one of the heaters breaks is given by formula (1). The upper limit Rmax1 of the resistance when the heaters are normal is given by formula (2). The symbol R in the formula indicates the resistance value of the heater (catalog value), and the symbol * indicates the multiplication symbol. Rmin1=R / 2*0.9=0.45R ‥(1) Rmax1=R / 3*1.1*1.05*1.05=0.404R ‥(2)

[0061] The value 0.9 in formula (1) represents the variation on the low side of the heater resistance value. The value 1.1 in formula (2) represents the variation on the high side of the heater resistance value. The value 1.05 in formula (2) represents the variation on the high side of the voltage detection of the voltage detector V1 and the variation on the high side of the current detection of the current detector A1.

[0062] From equations (1) and (2), for up to three parallel heaters, the relationship becomes "the lower limit of the resistance value when one heater breaks, Rmin1">"the upper limit of the resistance value when the heater is normal, Rmax1." Therefore, there is no overlap in the resistance value when a heater breaks and when it is normal, so heater breaks can be reliably detected.

[0063] On the other hand, when four heaters are connected in parallel (four-parallel), the lower limit Rmin2 of the resistance value when one of the heaters breaks is given by formula (3), and the upper limit Rmax2 of the resistance value when the heaters are normal is given by formula (4). Rmin2=R / 3*0.9=0.3R ‥(3) Rmax2=R / 4*1.1*1.05*1.05=0.303R ‥(4)

[0064] From equations (3) and (4), when four or more heaters are connected in parallel, "the lower limit of the resistance value when one heater breaks Rmin2" < "the upper limit of the resistance value when the heater is normal Rmax2". For this reason, there is an overlap between the resistance value when a heater breaks and the resistance value when the heater is normal, and it is not possible to detect a heater break.

[0065] 1 to 8, even when there are four or more heaters, the CPU 441 detects heater breaks in units of two. Therefore, as shown in equations (1) and (2), the relationship Rmin1>Rmax1 can always be satisfied, and the presence or absence of a heater break can be reliably detected. Note that in the embodiment shown in FIGS. 1 to 8, as shown in equations (1) and (2), even under the worst condition of the variation in the electrical characteristics of each component, if Rmin1>Rmax1 is satisfied, breaks in up to three heaters connected in parallel can be detected.

[0066] Although the present invention has been described above based on the embodiments, the present invention is not limited to the requirements shown in the above embodiments. These points can be changed without departing from the spirit of the present invention, and can be appropriately determined according to the application form. [Explanation of symbols]

[0067] 1. Image forming device 20 Image reading device 30 Write Units 40 Printer unit 41 Photoconductor drum 42 Developing device 43 Conveyor Belt 44, 44A, 44B, 44C Fixing device 50 Energy storage device 60 Image Processing Unit 441 CPU 442 Temperature Sensor 443 Drive element 444 Power supply A1 Current detector H1, H2, H3, H4, H5, H6 heaters SW1, SW2, SW3 switches V1 Voltage detector VDD power line VSS ground wire [Prior art documents] [Patent documents]

[0068] [Patent Document 1] JP 2019-159312 A

Claims

1. a plurality of heaters connected in parallel for use in fixing an image on a recording medium; a voltage detection means for detecting a voltage applied to the plurality of heaters; a temperature detection means disposed in proximity to a predetermined number of first heaters among the plurality of heaters; a current detection means connected to a predetermined number of second heaters among the plurality of heaters excluding the first heater, and configured to detect a current flowing through the predetermined number of second heaters; a failure determination unit that determines whether the first heater is disconnected based on the temperature detected by the temperature detection means and determines whether the predetermined number of second heaters are disconnected based on the current detected by the current detection means; An image forming apparatus comprising:

2. a switch for connecting the first heater to the current detection means; The failure determination unit turns off the switch when determining that the second heater is disconnected based on the current detected by the current detection means.

2. The image forming apparatus according to claim 1,

3. a plurality of second heater groups each including the predetermined number of second heaters; a plurality of switches for connecting the plurality of second heater groups to the current detection means, The failure determination unit turns on the plurality of switches one by one, and determines whether or not the second heater group connected to the turned-on switch has been broken based on the current detected by the current detection unit. The image forming apparatus according to claim 1 .

4. the number of the second heaters connected to the current detection means for the failure determination unit to determine whether or not one of the second heaters is disconnected is a number that enables the current detected by the current detection means to distinguish between a disconnection of one of the second heaters and a normal state of the second heaters under a worst-case combination of detection variations of the voltage detection means, detection variations of the current detection means, and variations in heater capacity of the plurality of second heaters; 4. The image forming apparatus according to claim 1, wherein:

5. The failure determination unit determines that the second heater is abnormally high in temperature when a current value detected by the current detection means indicates an overcurrent in order to determine whether the second heater is broken.

5. The image forming apparatus according to claim 1, wherein:

6. A method for controlling an image forming apparatus including a plurality of heaters connected in parallel for use in fixing an image on a recording medium, a voltage detection means for detecting a voltage applied to the plurality of heaters, a temperature detection means arranged in proximity to a predetermined number of first heaters among the plurality of heaters, and a current detection means connected to a predetermined number of second heaters among the plurality of heaters excluding the first heaters and detecting a current flowing through the predetermined number of second heaters, the method comprising the steps of: determining whether the first heater is disconnected based on the temperature detected by the temperature detection means; determining whether or not the predetermined number of second heaters are disconnected based on the current detected by the current detection means; A control method for an image forming apparatus comprising the steps of:

Images