Image forming apparatus and control method

Abstract

To provide an image forming apparatus and a control method that accurately detect a slip state of a fixing belt.SOLUTION: An image forming apparatus includes: a fixing belt; a pressing member that forms a nip part with the fixing belt, and drives the fixing belt; a heating member that is arranged inside the fixing belt; a fixing belt temperature detection unit that acquires fixing belt temperature information based on a temperature of the fixing belt; a pressing member temperature detection unit that acquires pressing member temperature information based on a temperature of the pressing member; and a control unit that, on the basis of a relation between the fixing belt temperature information and the pressing member temperature information, determines whether or not the fixing belt is in a belt slip state where the fixing belt does not follow the movement of the pressure member.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus and a control method thereof. [Background technology]

[0002] Conventionally, image forming apparatuses that form images on print media using an electrophotographic method are known. Methods for detecting slippage of a fixing device included in an image forming apparatus are also known. For example, Patent Document 1 discloses an image forming apparatus that detects an abnormality based on the surface temperature of at least one of a driving unit and a driven unit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-266694 A Summary of the Invention [Problem to be solved by the invention]

[0004] The technique of Patent Document 1 does not take into consideration the relationship between the temperature of the driving part and the temperature of the driven part.

[0005] According to some aspects of the present disclosure, it is possible to provide an image forming apparatus and a control method thereof that accurately detect the slip state of a fixing belt. [Means for solving the problem]

[0006] One aspect of the present disclosure relates to an image forming apparatus including a fixing belt, a pressure member that forms a nip portion with the fixing belt and drives the fixing belt, a heating member arranged inside the fixing belt, a fixing belt temperature detection unit that acquires fixing belt temperature information based on the temperature of the fixing belt, a pressure member temperature detection unit that acquires pressure member temperature information based on the temperature of the pressure member, and a control unit that determines whether the fixing belt is in a belt slip state in which it is not driven by the movement of the pressure member based on the relationship between the fixing belt temperature information and the pressure member temperature information.

[0007] Another aspect of the present disclosure relates to a control method for an image forming device having a fixing belt, a pressure member that forms a nip portion with the fixing belt and drives the fixing belt, and a heating member arranged inside the fixing belt, the control method acquiring fixing belt temperature information based on a temperature of the fixing belt, acquiring pressure member temperature information based on a temperature of the pressure member, and determining whether the fixing belt is in a belt slip state in which it is not driven by the movement of the pressure member based on a relationship between the fixing belt temperature information and the pressure member temperature information. [Brief description of the drawings]

[0008] [Figure 1] 1 is an external view of an image forming apparatus according to an embodiment of the present invention. [Diagram 2] 1 is a configuration example of an image forming apparatus. [Diagram 3] 2 is a configuration example of an image forming unit. [Figure 4] 2 is a cross-sectional view showing a schematic configuration of a fixing device in the image forming apparatus. [Diagram 5] FIG. 2 is a perspective view showing a schematic configuration of a fixing device in the image forming apparatus. [Figure 6A] 4 is an example of temperature changes of a fixing belt and a pressure roller in a normal state. [Figure 6B] 13 is an example of temperature changes of a fixing belt and a pressure roller in a belt slip state. [Figure 6C] 13 is an example of temperature changes of the fixing belt and the pressure roller in another abnormal state. [Figure 7] 5 is a flowchart illustrating a process for determining whether a belt slip state exists. [Figure 8] 5 is a flowchart illustrating a process for determining whether a belt slip state exists. [Figure 9] 10 is a flowchart illustrating another process for determining whether or not a belt slip state has occurred. [Figure 10] 10 is a flowchart illustrating another process for determining whether or not a belt slip state has occurred. [Figure 11] 10 is a flowchart illustrating another process for determining whether or not a belt slip state has occurred. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the present embodiment will be described with reference to the drawings. In the drawings, the same or equivalent elements are given the same reference numerals, and duplicated explanations are omitted. Note that the present embodiment described below does not unduly limit the contents described in the claims. In addition, all of the configurations described in the present embodiment are not necessarily essential configurations of the present disclosure.

[0010] 1. System configuration example FIG. 1 is a diagram showing an example of the appearance of an image forming apparatus 100. The image forming apparatus 100 of this embodiment is a color image forming apparatus that forms multi-color and single-color images on a sheet P such as a recording paper in accordance with, for example, image data. Note that the image forming apparatus 100 may be a monochrome image forming apparatus. The image forming apparatus 100 may also be a printer with a scanning function, or a multifunction peripheral (MFP) having various functions including a printing function. The image forming apparatus 100 may also have, for example, a copy function or a facsimile function.

[0011] Fig. 2 is a diagram showing an example of the configuration of the image forming apparatus 100. As shown in Fig. 2, the image forming apparatus 100 includes a control unit 110, an image forming unit 120, a display unit 130, and a storage unit 140. However, the configuration of the image forming apparatus 100 is not limited to the example shown in Fig. 2, and various modifications are possible, such as omitting some components and adding other components. For example, the image forming apparatus 100 may further include components not shown in Fig. 2, such as an image reading unit that acquires image data by performing a scan process on a document.

[0012] The control unit 110 is configured by the following hardware. The hardware may include at least one of a circuit for processing digital signals and a circuit for processing analog signals. For example, the hardware may be configured by one or more circuit devices or one or more circuit elements mounted on a circuit board. The one or more circuit devices may be, for example, an integrated circuit (IC) or a field-programmable gate array (FPGA). The one or more circuit elements may be, for example, a resistor, a capacitor, etc.

[0013] The control unit 110 may be realized by one or more of the following processors. The image forming apparatus 100 of the present embodiment includes a memory that stores information and a processor that operates based on the information stored in the memory. The information is, for example, a program and various data. The processor includes hardware. The processor can be various processors such as a central processing unit (CPU), a graphics processing unit (GPU), and a digital signal processor (DSP). The memory may be a semiconductor memory such as a static random access memory (SRAM) or a dynamic random access memory (DRAM), a register, a magnetic storage device such as a hard disk drive (HDD), or an optical storage device such as an optical disk device. For example, the memory stores computer-readable instructions, and the function of the control unit 110 is realized as a process by the processor executing the instructions. The instructions here may be instructions of an instruction set constituting a program, or instructions that instruct the hardware circuit of the processor to operate.

[0014] The image forming unit 120 is a mechanical configuration that forms an image on the sheet P. The image forming apparatus 100 according to the present embodiment is, for example, a laser printer, and the image forming unit 120 includes various configurations for performing printing using an electrophotographic method. Details of the image forming unit will be described later with reference to FIGS. 3 to 5.

[0015] The display unit 130 is a display that displays an image. The display unit 130 can be realized by, for example, a liquid crystal display or an organic EL display. The display unit 130 may be a UI (User Interface) for using functions of the image forming apparatus 100, such as a print function or a scan function.

[0016] The storage unit 140 is a work area of ​​the control unit 110, and stores various information. The storage unit 140 can be realized by various memories, and the memories may be semiconductor memories, registers, magnetic storage devices, or optical storage devices. For example, the storage unit 140 may store an algorithm (program) for executing the determination process of the control unit 110, parameters used in the algorithm, and the like. The algorithm here is, for example, an algorithm for executing the process described later with reference to FIG. 7, and the parameters may be, for example, thresholds X and Y shown in FIG. 7.

[0017] 3 is a diagram showing an example of the configuration of the image forming unit 120. The image forming unit 120 includes an optical scanning device 121, a developing device 122, a photoconductor drum 123 acting as an electrostatic latent image carrier, a cleaning device 124, a charging device 125, an intermediate transfer belt device 126, a toner cartridge device 127, and a fixing device 128. The image forming apparatus 100 also includes a paper feed tray and a discharge tray, which are not shown.

[0018] The charging device 125 charges the photosensitive drum 123. The optical scanning device 121 irradiates the charged photosensitive drum 123 with laser light to weaken the charge in an area corresponding to the image data. The developing device 122 causes toner contained in a toner cartridge device 127 to adhere to areas of the photosensitive drum 123 where the charge is relatively weak. The intermediate transfer belt device 126 transfers the toner adhered to the photosensitive drum 123 onto the sheet P. The fixing device 128 fixes the toner adhered to the sheet P. The cleaning device 124 removes the toner remaining on the surface of the photosensitive drum 123.

[0019] For example, when forming an image, the image forming apparatus 100 supplies a sheet P from a paper feed tray and conveys the sheet P by a first conveying roller (not shown) provided along a sheet conveying path. Next, the image forming apparatus 100 conveys the sheet P by a transfer roller (not shown) at a timing when the sheet P and the toner image on the intermediate transfer belt of the intermediate transfer belt device 126 are aligned, thereby transferring a toner image onto the sheet P. Thereafter, the image forming apparatus 100 passes the sheet P through the fixing belt 10 and pressure roller 20 of the fixing device 128, thereby melting and fixing the unfixed toner on the sheet P by heat, and discharges the sheet P onto a discharge tray via a second conveying roller and a discharge roller (not shown).

[0020] The image data handled by the image forming apparatus 100 may correspond to a color image using multiple colors. The multiple colors here are, for example, black (K), cyan (C), magenta (M), and yellow (Y). Therefore, the developing device 122, the photoconductor drum 123, the cleaning device 124, the charging device 125, and the toner cartridge device 127 are each provided in multiple numbers so as to form multiple types of images corresponding to the respective colors, and these constitute multiple image stations.

[0021] 4 and 5 are diagrams illustrating an example of the configuration of the fixing device 128. Fig. 4 is a cross-sectional view illustrating the configuration of the fixing device 128, and Fig. 5 is a perspective view illustrating the configuration of the fixing device 128.

[0022] The fixing device 128 is, for example, a belt fixing type fixing device, and includes a fixing belt 10, a fixing pad 11, a pressure roller 20, a heater 30, a first thermopile 41, a second thermopile 42, a first thermistor 43, and a second thermistor 51.

[0023] The fixing belt 10 is provided so as to be rotatable about a rotation axis. The rotation axis here is an axis along the longitudinal direction of the fixing belt 10, and in a narrow sense, an axis passing through the center of the cross-sectional shape (e.g., circular) of the fixing belt 10. The pressure roller 20 is provided so as to be rotatable about a rotation axis based on the drive of a drive unit (e.g., a drive motor) (not shown). The rotation axis here is an axis along the longitudinal direction of the pressure roller 20, and in a narrow sense, an axis passing through the center of the cross-sectional shape of the pressure roller 20.

[0024] A fixing pad 11 is disposed inside the fixing belt 10. The fixing device 128 is configured such that the pressure roller 20 is pressed against the fixing pad 11 via the fixing belt 10. The pressure roller 20 is pressed against the fixing pad 11, thereby forming a nip portion 12 between the fixing belt 10 and the pressure roller 20. By providing the fixing pad 11, it is possible to increase the nip width (contact width) even when the fixing belt 10 and the pressure roller 20 are thin. The fixing device 128 may include a pressing unit (not shown) that presses the pressure roller 20 against the fixing belt 10, adjusts the pressure, and releases the pressure. In a state in which the nip portion 12 is formed, the pressure roller 20 rotates in accordance with the drive of the drive unit, thereby causing the fixing belt 10 to rotate.

[0025] Moreover, the heater 30 is disposed inside the fixing belt 10, and the heat of the heater 30 is transmitted to the fixing belt 10. Moreover, when the fixing belt 10 is close to (in a narrow sense, in contact with) the pressure roller 20, the heat of the fixing belt 10 is transmitted to the pressure roller 20. The fixing belt 10, together with the pressure roller 20, thermally presses the multi-color toner image transferred onto the sheet P to the sheet P. In this way, the multi-color toner image is melted, mixed, and pressed against the sheet P, thereby being thermally fixed thereto.

[0026] The first thermopile 41, the second thermopile 42, and the first thermistor 43 are sensors that detect fixing belt temperature information based on the temperature of the fixing belt 10. The specific configurations of the thermopile and thermistor are publicly known, so detailed description will be omitted. The first thermopile 41 is a sensor that detects the temperature near the center of the sheet P when the sheet P is transported. The second thermopile 42 is a sensor that detects the temperature near the edge of the sheet P when the sheet P is transported. The first thermistor 43 is a sensor that detects the temperature at a position (near the edge of the fixing belt 10) that does not overlap with the sheet P when the sheet P is transported. The first thermistor 43 is, for example, a contact type thermistor that is disposed at a position that contacts the fixing belt 10. It is not essential that all of the first thermopile 41, the second thermopile 42, and the first thermistor 43 are provided, and some of them may be omitted. The configuration and arrangement of the sensors that detect fixing belt temperature information are not limited to the examples of FIG. 4 and FIG. 5, and various modifications are possible.

[0027] The second thermistor 51 is a sensor that detects pressure member temperature information based on the temperature of the pressure roller 20. The second thermistor 51 is a sensor that detects the temperature near the center of the sheet P when the sheet P is transported. For example, the second thermistor 51 may be disposed at positions that face the fixing belt 10 and the pressure roller 20 in the direction of the rotation axis (positions where the positional deviation in the direction of the rotation axis is equal to or less than a predetermined value). The second thermistor 51 is, for example, a non-contact type thermistor that is disposed at a position that does not contact the pressure roller 20. Note that the configuration and arrangement of the sensor that detects pressure member temperature information are not limited to the examples in FIGS. 4 and 5, and various modifications are possible.

[0028] As described above, the image forming apparatus 100 according to the present embodiment includes the fixing belt 10, the pressure member, the heating member, the fixing belt temperature detector, the pressure member temperature detector, and the controller 110. The pressure member here is a member that forms the nip portion 12 with the fixing belt 10 and drives the fixing belt 10, and corresponds to, for example, the pressure roller 20. The heating member is a member that is disposed in the vicinity of the fixing belt 10 (inside in a narrow sense) and supplies heat to the fixing belt 10, and corresponds to, for example, the heater 30. The fixing belt temperature detector is a sensor that acquires fixing belt temperature information based on the temperature of the fixing belt 10, and includes, for example, one or more of the first thermopile 41, the second thermopile 42, and the first thermistor 43. The pressure member temperature information is a sensor that acquires pressure member temperature information based on the temperature of the pressure member, and corresponds to, for example, the second thermistor 51 that detects information based on the temperature of the pressure roller 20.

[0029] The control unit 110 of the present embodiment determines whether the fixing belt is in a belt slip state based on the relationship between the fixing belt temperature information and the pressure member temperature information. The belt slip state here refers to a state in which the fixing belt 10 does not move (rotate) appropriately with respect to the movement (rotation) of the pressure roller 20. The belt slip state is not limited to a state in which the fixing belt 10 does not move at all, but includes a state in which the actual movement amount of the fixing belt 10 is smaller than the assumed movement amount of the fixing belt 10 assumed based on the movement amount of the pressure roller 20. For example, the belt slip state of the present embodiment may refer to a state in which the difference between the assumed movement amount and the actual movement amount is set as the deviation amount and the deviation amount is equal to or greater than a predetermined threshold value. In addition, when the ratio of the deviation amount to the assumed movement amount is set as a slip index value, the state in which the slip index value is equal to or greater than a predetermined threshold value may be set as the belt slip state. In addition, the belt slip state here refers to a state in which the fixing belt 10 rotates less than expected, but is not limited to this, and may include a state in which the fixing belt 10 rotates excessively more than expected. In other words, the deviation amount is not limited to a value obtained by subtracting the actual movement amount from the estimated movement amount, and may include a value obtained by subtracting the estimated movement amount from the actual movement amount.

[0030] According to the method of the present embodiment, the belt slip state is determined using the relationship between the temperature of the fixing belt 10 and the temperature of the pressure roller 20 that presses the fixing belt 10. Therefore, it is possible to accurately determine the belt slip state.

[0031] For example, when a heater 30 is provided inside the fixing belt 10, the heat of the heater 30 is transferred to the pressure roller 20 via the fixing belt 10. In this case, in the belt slip state, the state of heat transfer from the fixing belt 10 to the pressure roller 20 is different from the normal state (state where belt slip does not occur), so it is considered that the temperature of the pressure roller 20 also behaves differently from the normal state. Specifically, in the normal state, the temperature of the pressure roller 20 follows the temperature of the fixing belt 10 to a high degree, but in the belt slip state, it is assumed that the degree of tracking is lower. Therefore, by using the relationship between the fixing belt temperature information and the pressure member temperature information, it is possible to increase the accuracy of determining the belt slip state.

[0032] Furthermore, when an abnormality other than belt slip occurs, such as excessive heat generation of the heater 30, it is considered that the temperature behaves differently from the normal state when the fixing belt temperature information alone or the pressure member temperature information alone is viewed. Therefore, it may not be easy to distinguish between the belt slip state and other abnormalities by using only one of them or by using the two temperature information independently. In this respect, in this embodiment, the relationship between the fixing belt temperature information and the pressure member temperature information (for example, the degree of tracking) is determined. If there is no belt slip state, it is assumed that the degree of tracking will be high even if other abnormalities occur, so the method of this embodiment makes it possible to appropriately distinguish between the belt slip state and other abnormalities.

[0033] As described above, the method of the present embodiment can improve the accuracy of determining the belt slip state, and therefore can prevent damage to the fixing belt 10 caused by heat concentration on one part of the fixing belt 10, etc.

[0034] The technique of the present embodiment can also be applied to a control method for an image forming apparatus 100 having a fixing belt 10, a pressure member that forms a nip portion 12 with the fixing belt 10 and drives the fixing belt 10, and a heating member disposed inside the fixing belt 10. The control method includes the steps of acquiring fixing belt temperature information based on the temperature of the fixing belt 10, acquiring pressure member temperature information based on the temperature of the pressure member, and determining whether or not the fixing belt 10 is in a belt slip state in which it is not driven by the movement of the pressure member based on the relationship between the fixing belt temperature information and the pressure member temperature information.

[0035] 2. Processing Details 6A to 6C are diagrams showing examples of changes in the fixing belt temperature information and the pressure member temperature information after the start of heating by the heater 30. The horizontal axis of Fig. 6A to 6C represents time, and the vertical axis represents temperature.

[0036] FIG. 6A is a diagram showing an example of temperature change in a normal state where no abnormality occurs. As shown in FIG. 6A, in a normal state, the heat generated by the heater 30 is transferred to the fixing belt 10 to a certain degree uniformly. Therefore, the temperature of the fixing belt detected by the fixing belt temperature detection unit increases with time at a rate of change close to a certain constant gradient, and becomes almost constant at a desired temperature. In addition, since no belt slip occurs in a normal state, no heat concentration occurs in the fixing belt 10, and the fixing belt 10 and the pressure roller 20 rotate at the same speed. Therefore, as the temperature of the fixing belt 10 increases, the temperature of the pressure roller 20 represented by the pressure member temperature information also increases at a rate of change close to a certain constant gradient. Note that, as shown in FIG. 6A, since the pressure roller 20 is relatively far from the heater 30, the gradient of the temperature change of the pressure roller 20 may be smaller than that of the fixing belt 10.

[0037] 6B is a diagram showing an example of temperature change in a belt slip state. When a belt slip state occurs, there is a period in which the fixing belt 10 does not move as much as expected, and it is considered that heat is concentrated in a part of the fixing belt 10. Therefore, the temperature detected by a fixing belt temperature detection unit such as the first thermistor 43 does not change with a constant slope, and there are periods in which the slope is relatively large and periods in which it is relatively small.

[0038] Also, the temperature of the pressure roller 20 detected by a pressure member temperature detector such as the second thermistor 51 does not change with a constant gradient, and there are periods when the gradient is relatively large and periods when it is relatively small. For example, in a state where the fixing belt 10 is not rotating at all relative to the pressure roller 20, the same position of the fixing belt 10 continues to contact the pressure roller 20, so that the amount of heat conducted from the fixing belt 10 to the pressure roller 20 may be smaller than in the normal state. Specifically, as shown in FIG. 6B, in the belt slip state, heat is not conducted appropriately, so that there is a period when the temperature change of the fixing belt 10 is larger than in the normal state and the temperature change of the pressure roller 20 is smaller than in the normal state.

[0039] Fig. 6C is a diagram showing an example of temperature change when an abnormality other than the belt slip state occurs. Fig. 6C is a diagram showing temperature change when a heater abnormality occurs, for example, when the heater 30 becomes hotter than in the normal state. As shown in Fig. 6C, when a heater abnormality occurs, the amount of heat transferred from the heater 30 to the fixing belt 10 becomes larger than in the normal state, so that the temperature of the fixing belt detected by the fixing belt temperature detection unit increases over time at a steeper slope than in the normal state.

[0040] Even if a heater abnormality occurs, the fixing belt 10 and the pressure roller 20 rotate in a constant relationship unless the belt is slipping. Therefore, although the amount of heat transferred from the fixing belt 10 to the pressure roller 20 is greater than in a normal state, it does not vary greatly from timing to timing. Therefore, the temperature of the pressure roller 20 detected by a pressure member temperature detection unit such as the second thermistor 51 varies with time at a greater rate than in a normal state.

[0041] As can be seen from Figures 6A-6C, in the belt slip state, the fixing belt 10 and pressure roller 20 are not driven, so the degree of tracking of the pressure member temperature information with respect to the fixing belt temperature information is low (Figure 6B). Here, low degree of tracking may also mean a low degree of agreement between the change trend of the fixing belt temperature information and the change trend of the pressure member temperature information. On the other hand, in either the normal state or the abnormal state, if there is no belt slip state, the degree of tracking of the pressure member temperature information with respect to the fixing belt temperature information is high (Figures 6A and 6C).

[0042] Therefore, in the method of the present embodiment, the control unit 110 may determine the degree of tracking of the pressure member temperature information with respect to the fixing belt temperature information, and determine that the belt is slipping when the degree of tracking is determined to be equal to or less than a given threshold value. In this way, it becomes possible to accurately determine whether or not the belt is slipping.

[0043] For example, the control unit 110 may determine whether or not the belt slip state exists based on the change per unit time of the fixing belt temperature information and the change per unit time of the pressure member temperature information. As shown in Fig. 6B, in the belt slip state, compared to the normal state, there are both a time when the temperature of the fixing belt 10 changes rapidly and a time when the temperature of the pressure roller 20 changes rapidly. Therefore, by using both the change per unit time of the fixing belt temperature information and the change per unit time of the pressure member temperature information, it is possible to accurately determine whether or not the belt slip state exists.

[0044] Furthermore, when it is determined that the degree of tracking of the pressure member temperature information with respect to the fixing belt temperature information is greater than a given threshold value, the control unit 110 may determine that an abnormality other than the belt slip state has occurred or that there is no abnormality. In this way, it becomes possible to appropriately distinguish between the belt slip state and other states. An example of a specific process will be described below with reference to Figs. 7 and 8.

[0045] 7 and 8 are flow charts for explaining the determination process for the belt slip state. FIG. 7 is a diagram for explaining the process executed when heating by the heater 30 is started. For example, the control unit 110 repeatedly executes the process shown in FIG. 7 for a predetermined time or a predetermined number of loops when the image forming apparatus 100 is started or when the image forming apparatus 100 returns from a sleep state. After the process shown in FIG. 7 is completed, the control unit 110 may execute the process shown in FIG. 8 to determine whether or not the belt slip state has occurred. Details will be described below.

[0046] 7 starts, first, in step S101, the pressure roller 20 starts rotating while being pressed against the fixing belt 10. In step S102, the heater 30 is activated. In step S103, the fixing belt temperature detection unit starts detecting fixing belt temperature information based on the temperature of the fixing belt 10, and the pressure member temperature detection unit starts detecting pressure member temperature information based on the temperature of the pressure member (pressure roller 20).

[0047] In step S104, the control unit 110 executes slippage judgment on the side of the fixing belt 10 by using the fixing belt temperature information. Specifically, the control unit 110 obtains the change per unit time of the fixing belt temperature information. Here, the change per unit time may be given by the following formula (1) when the value of the fixing belt temperature information acquired at a certain timing t is U(t), the value of the fixing belt temperature information acquired at the next timing t+1 is U(t+1), and the time difference between the timings t and t+1 is Δt. However, the amount of change per unit time is not limited to this, and may be obtained based on the temperature and time difference between two non-adjacent timings, or may be obtained based on three or more timings.

[0048] Change in fixing belt temperature information per unit time ={U(t+1)-U(t)} / Δt …(1)

[0049] The control unit 110 compares the change per unit time of the fixing belt temperature information with a given change amount threshold X. The change amount threshold X here is a threshold for determining whether the degree of deviation from the change amount x in a normal state (for example, the slope of the temperature graph of the fixing belt 10 in FIG. 6A) is large, and may be, for example, X=x+Δx (Δx is a positive number set in advance).

[0050] If the change in the fixing belt temperature information per unit time is less than the change amount threshold value X (step S104: No), it is considered that no abnormality has occurred. Therefore, the control unit 110 returns to step S104 and continues the process. In other words, if no abnormality is found in the fixing belt temperature information, the determination process of step S104 is repeatedly executed.

[0051] If the change per unit time of the fixing belt temperature information is equal to or greater than the change amount threshold value X (step S104: Yes), in step S105, the control unit 110 executes slippage judgment on the pressure roller 20 side using the pressure member temperature information. Specifically, the control unit 110 obtains the change per unit time of the pressure member temperature information. Here, the change per unit time may be given by the following formula (2), where the value of the pressure member temperature information acquired at a certain timing t is V(t), the value of the pressure member temperature information acquired at the next timing t+1 is V(t+1), and the time difference between the timings t and t+1 is Δt.

[0052] Change in temperature information of pressurized parts per unit time ={V(t+1)-V(t)} / Δt …(2)

[0053] The control unit 110 compares the change per unit time of the pressure member temperature information with a given change amount threshold Y. The change amount threshold Y here is a threshold for determining whether the degree of deviation from the change amount y in a normal state (for example, the slope of the temperature graph of the pressure roller 20 in FIG. 6A) is large, and may be, for example, Y=y+Δy (Δy is a positive number set in advance). For example, the change amount threshold Y is a value smaller than the change amount threshold X. However, the same value as the change amount threshold X may be used as the change amount threshold Y.

[0054] Note that t in step S104 and t in S105 may be the same timing or different timing. For example, when the control unit 110 determines that the change per unit time of the fixing belt temperature information is equal to or greater than the change amount threshold value X (step S104: Yes), the control unit 110 may set a judgment period of a given length, and execute a process of repeatedly obtaining the change amount per unit time of the pressure member temperature information during the judgment period and comparing it with the change amount threshold value Y. For example, when the change amount per unit time of the pressure member temperature information is equal to or greater than the change amount threshold value Y at least once during the judgment period, the control unit 110 may set the judgment result of step S105 to "Yes". In this way, even when the timing of the sudden rise in temperature is different between the fixing belt 10 and the pressure roller 20 as shown in FIG. 6B, appropriate judgment is possible.

[0055] If the change in the pressure temperature information per unit time is less than the change amount threshold Y (step S105: No), the temperature change in the pressure roller 20 is small and different from the temperature change characteristics shown in Fig. 6B, so there is little possibility of a belt slip state. However, the temperature of the fixing belt 10 is changing rapidly (step S104: Yes), and the temperature change characteristics are different from those shown in Fig. 6A, so an abnormality is suspected. Therefore, the control unit 110 determines whether the situation will be improved by performing a retry operation.

[0056] For example, the control unit 110 counts the number of times that an abnormality is detected on the fixing belt 10 side and no abnormality is detected on the pressure roller 20 side (step S104: Yes and step S105: No), and if the number of times is the first or second, it executes the retry operation of steps S106-S108.

[0057] Specifically, in step S106, the control unit 110 releases the pressure roller 20 from pressing the fixing belt 10 (fixing pad 11). In step S107, the control unit 110 rotates the pressure roller 20 for a predetermined time in a state in which the pressure roller 20 is not applying pressure to the fixing belt 10. In step S108, the control unit 110 stops the rotation of the pressure roller 20 and returns to step S101. Note that in this retry operation, the heater 30 may be kept activated, and the process of step S102 after returning to step S101 may be omitted.

[0058] Furthermore, if the number of times that an abnormality is detected on the fixing belt 10 side and no abnormality is detected on the pressure roller 20 side is the third or subsequent times, the control unit 110 sets an error flag to ON in step S109, indicating that an error other than a belt slip state has occurred, and then executes the retry operation of steps S106-S108.

[0059] If an abnormality is detected on the fixing belt 10 side and also on the pressure roller 20 side (step S104: Yes and step S105: Yes), it is suspected that the belt is slipping. Therefore, the control unit 110 stops the heater 30 and then executes a retry operation.

[0060] Specifically, in step S110, the control unit 110 turns off the heater 30. In step S111, the control unit 110 stops the rotation of the pressure roller 20. Furthermore, in step S112, the control unit 110 counts up a variable M that indicates the number of times that an abnormality is detected on the fixing belt 10 side and on the pressure roller 20 side (step S104: Yes and step S105: Yes). For example, M is a variable that is initialized to 0 when the process shown in FIG. 7 is started. After the process of step S111, the control unit 110 executes the retry operation of steps S106-S108, and returns to step S101 to continue the process.

[0061] After executing the process shown in Fig. 7 for a certain period of time or a certain number of loops, the control unit 110 executes the abnormality determination process shown in Fig. 8. First, in step S201, the control unit 110 determines whether the variable M is equal to or greater than a first number threshold value Th1. Here, the first number threshold value Th1 is, for example, 4, but may be set to another value.

[0062] When the variable M is equal to or greater than the first number threshold Th1, the control unit 110 determines in step S202 that the belt is slipping. In other words, when a state in which the amount of change per unit time of the fixing belt temperature information is determined to be equal to or greater than the first change amount threshold (change amount threshold X) and the amount of change per unit time of the pressure member temperature information is determined to be equal to or greater than the second change amount threshold (change amount threshold Y) is detected a predetermined number of times or more (when M is equal to or greater than the first number threshold Th1), the control unit 110 determines that the belt is slipping.

[0063] 6B, in the belt slip state, abrupt changes in the temperature of the fixing belt 10 and abrupt changes in the temperature of the pressure roller 20 occur repeatedly. Therefore, as shown in steps S201 and S202, by determining the amount of change per unit time and a threshold value for each of the fixing belt temperature information and the pressure member temperature information, it becomes possible to accurately detect the belt slip state.

[0064] Also, in step S201, the control unit 110 determines whether the variable M is equal to or greater than the second count threshold Th2 and less than the first count threshold Th1. The second count threshold Th2 here is a value smaller than the first count threshold Th1. The second count threshold Th2 is, for example, 3, but may be set to another value.

[0065] If the variable M is equal to or greater than the second count threshold Th2 and less than the first count threshold Th1, the control unit 110 determines in step S203 that the abnormality is other than the belt slip state. In this case, although there is a history of a sudden change in the temperature of both the fixing belt 10 and the pressure roller 20, the change is not being detected continuously because the number of occurrences is not equal to or greater than the first count threshold Th1. In other words, since the abnormality here has characteristics different from the belt slip state, it is possible to properly isolate the abnormality by determining that the abnormality is other than the belt slip state.

[0066] For example, in the heater abnormality shown in Fig. 6C, there is a period in which the temperature rises rapidly, and during that period, it may be determined that the change per unit time of the fixing belt temperature information is equal to or greater than the change amount threshold value X, and the change per unit time of the pressure member temperature information is equal to or greater than the change amount threshold value Y. However, in the heater abnormality shown in Fig. 6C, the period in which the temperature rises rapidly is relatively short compared to the duration of the belt slip state, so the number of times M is incremented is also small. Therefore, as shown in steps S201-S203, it is possible to identify the type of abnormality by determining the value of M.

[0067] Furthermore, if the variable M is less than the second count threshold Th2, the control unit 110 determines in step S204 whether an error flag is set, which indicates an abnormality other than the belt slip state. If the error flag is ON (step S204: Yes), the control unit 110 determines in step S203 that an abnormality other than the belt slip state has occurred. This corresponds to the case where the process of step S109 is executed in the process of FIG. 7. That is, the error flag being ON corresponds to the case where the number of abnormality detections on the pressure roller 20 side is small, but the number of abnormality detections on the fixing belt 10 side is equal to or greater than a predetermined number, so that there is a high probability that an abnormality other than the belt slip state has occurred.

[0068] An abnormality other than the belt slip state may be a sensor abnormality, which is an abnormality in the fixing belt temperature detection section. When a sensor abnormality occurs, for example, even if the temperature of the fixing belt 10 is actually normal (FIG. 6A), the value of the fixing belt temperature information, which is the detection result, may suddenly change. In this example, there is no heat concentration in the actual fixing belt 10, and there is no belt slip state, so heat is transferred smoothly to the pressure roller 20. Therefore, if there is no abnormality in the pressure member temperature detection section, the pressure member temperature information will behave close to the normal state (FIG. 6A).

[0069] Therefore, when it is determined that the amount of change per unit time of the fixing belt temperature information is equal to or greater than the first change amount threshold (change amount threshold X) and the amount of change per unit time of the pressure member temperature information is less than the second change amount threshold (change amount threshold Y), the control unit 110 may determine that an abnormality other than the belt slip state has occurred. This makes it possible to properly isolate the type of abnormality.

[0070] On the other hand, if the error flag is OFF (step S204: No), the control unit 110 determines in step S205 that the state is normal. This corresponds to a case in which a temperature abnormality of the fixing belt 10 has not been detected in the first place, or a temperature abnormality of the fixing belt 10 has been detected but the number of occurrences is small, in the process of Fig. 7. This corresponds to a case in which, for example, a sudden abnormality has occurred but the abnormality has been eliminated by a retry operation (steps S106-S108), or a case in which a fundamental abnormality has not occurred in the first place and a sudden temperature change due to noise has been detected, etc.

[0071] 7 and 8, when the control unit 110 determines that the belt slip state exists, the control unit 110 may perform control to stop heating by the heating member (heater 30) and control to stop rotation of the fixing belt 10. The control to stop rotation of the fixing belt 10 may be control to stop rotation of the pressure roller 20. In this way, it is possible to prevent the belt slip state from continuing.

[0072] Furthermore, when the belt slip state is suspected, the control unit 110 may perform control to stop heating by the heating member (heater 30) and control to stop rotation of the fixing belt 10. For example, when the belt slip state is suspected, it is when an abnormality occurs in the temperature of both the fixing belt 10 side and the pressure roller 20 side (steps S104 and S105: Yes), and the control to stop heating by the heating unit and the control to stop rotation of the fixing belt 10 may be the retry operation of steps S106-S107. In this way, even when the belt slip state is not confirmed, it is possible to try to resolve the abnormality by the retry operation.

[0073] Although a specific example of the belt slip state determination process has been described above, the process of this embodiment is not limited to the examples shown in FIGS. 7 and 8. For example, the process of FIG. 7 may end at a stage where a given condition is satisfied. For example, when the number of times that it is determined to be No in step S104 is a predetermined number or more, the control unit 110 may determine that it is a normal state and end the process shown in FIG. 7. Also, when the number of times that it is determined to be No in step S105 is three times, the control unit 110 may determine that it is an abnormal state other than the belt slip state and end the process shown in FIG. 7. That is, when a normal state is detected in the fixing belt 10 a certain number of times or more, or when a normal state is detected in the pressure roller 20 a certain number of times or more, it is highly likely that it is not a belt slip state, so it is possible to determine that it is a state other than the belt slip state at that stage.

[0074] 3. Variations Some modified examples will be described below.

[0075] 3.1 Other examples of slip judgment In the example described above with reference to FIG. 7, the slip determination using the fixing belt temperature information (step S104) and the slip determination using the pressure member temperature information (step S105) are described as processes for comparing the amount of change per unit time with the amount of change threshold as shown in the above formulas (1) and (2). The amount of change thresholds X and Y here are, for example, positive values, and the above-mentioned slip determination may be a determination of whether or not the temperature has risen sharply compared to the normal state. However, the slip determination is not limited to this.

[0076] Fig. 9 is a diagram for explaining another determination process regarding the belt slip state. Note that steps S301-S303 and S306-S312 in Fig. 9 are similar to steps S101-S103 and S106-S112 in Fig. 7. Therefore, a description of the overlapping parts will be omitted.

[0077] 6B, when belt slip occurs, the heat transfer from the fixing belt 10 to the pressure roller 20 is hindered, so that the slope of the graph of the fixing belt temperature information may become steeper and the slope of the graph of the pressure member temperature information may become shallower. Therefore, the control unit 110 may perform a slip determination in step S304 for the fixing belt 10 as to whether the amount of temperature change per unit time is equal to or greater than a threshold, and may perform a slip determination in step S305 for the pressure roller 20 as to whether the amount of temperature change per unit time is equal to or less than a threshold.

[0078] For example, the change threshold Y' may be set based on the change y (for example, the slope of the graph in FIG. 6A) in a normal state, as Y'=y-Δy' (Δy' is a positive number set in advance). In step S305, the control unit 110 determines that there is a possibility of slippage when the change per unit time of the pressure member temperature information is equal to or less than the change threshold Y' (step S305: Yes). As shown in FIG. 6B, the timing when the slope of the graph of the fixing belt temperature information becomes large and the slope of the graph of the pressure member temperature information becomes small is considered to be sufficiently close. Therefore, it is preferable that t and t+1 used in calculating the change per unit time are set to the same values ​​in step S304 and step S305, or to sufficiently close values.

[0079] In this way, the belt slip state can be accurately determined by determining whether the pressure roller 20 behaves differently (changes in the direction of decreasing the inclination) with respect to the temperature change of the fixing belt 10. For example, in the normal state shown in Fig. 6A and the heater abnormality shown in Fig. 6C, the temperature change of the pressure roller 20 follows the temperature change of the fixing belt 10, so the possibility that the two temperatures show changes in opposite directions at close timing is sufficiently low. Therefore, it is possible to properly distinguish between the belt slip state, the normal state, and an abnormal state other than the belt slip state.

[0080] Fig. 10 is a diagram for explaining still another determination process regarding the belt slip state. Note that steps S401-S403 and S406-S412 in Fig. 10 are similar to steps S101-S103 and S106-S112 in Fig. 7. Therefore, a description of the overlapping parts will be omitted.

[0081] As shown in FIG. 6B, in the belt slip state, the degree of tracking is low, so the timing at which the temperature suddenly rises is significantly different between the fixing belt 10 and the pressure roller 20, whereas as shown in FIG. 6C, in the other abnormalities, the degree of tracking is high, so the timing at which the temperature suddenly rises (decreases) is close between the fixing belt 10 and the pressure roller 20.

[0082] Therefore, the control unit 110 may detect abrupt changes in the fixing belt temperature information and the pressure member temperature information in steps S404 and S405, and may further perform a process of calculating the time difference between the detection timings in step S405. If the detection timing difference of the abrupt changes is equal to or greater than a predetermined threshold, the control unit 110 determines that the belt slip state is suspected, and proceeds to the process of step S410. On the other hand, if the pressure member temperature information does not change abruptly in the first place, or if the pressure member temperature information changes abruptly but the timing difference is less than the predetermined threshold, an abnormality other than the belt slip state is suspected. Therefore, the control unit 110 determines No in step S405, and proceeds to the process of step S406 or step S409 depending on the number of times. By determining the timing difference in this way, it is possible to properly isolate the abnormality.

[0083] Fig. 11 is a diagram for explaining still another determination process regarding the belt slip state. Note that steps S501-S503 and S506-S512 in Fig. 11 are similar to steps S101-S103 and S106-S112 in Fig. 7. Therefore, a description of the overlapping parts will be omitted.

[0084] As shown in Fig. 6B, in the belt slip state, the timing at which the temperature suddenly changes is significantly different between the fixing belt 10 and the pressure roller 20, so the temperature difference between the fixing belt 10 and the pressure roller 20 repeatedly increases and decreases. In contrast, as shown in Fig. 6C, in other abnormalities, the degree of tracking is high, so the timing at which the temperature suddenly changes is close between the fixing belt 10 and the pressure roller 20, and the change in the temperature difference is relatively small.

[0085] Therefore, the control unit 110 may determine whether or not the belt is slipping based on the thermal gradient represented by the difference between the fixing belt temperature information and the pressure member temperature information. In this way, it is possible to appropriately distinguish between a normal state, a belt slip state, and an abnormal state other than the belt slip state.

[0086] For example, the control unit 110 may determine whether or not the belt is slipping based on the change in the thermal gradient over time. Specifically, in step S505, the control unit 110 may obtain the difference W between the fixing belt temperature information and the pressure member temperature information, and the change in the difference over time ΔW, using the following formulas (3) and (4). U, V, t, and Δt are the same as those in the above formulas (1) and (2).

[0087] W(t) = U(t) - V(t) … (3) ΔW={W(t+1)-W(t)} / Δt …(4)

[0088] If the value of ΔW is equal to or greater than a given threshold in the determination of step S505, the control unit 110 determines that a belt slip state is suspected, and proceeds to processing of step S510. If the value of ΔW is less than a given threshold, the control unit 110 determines that an abnormality other than a belt slip state is suspected, and proceeds to processing of step S506 or step S509 depending on the number of times. By determining the thermal gradient in this way, it is possible to appropriately isolate the type of abnormality.

[0089] Although some examples of the belt slip state determination process have been described above, the process of this embodiment is not limited to these, and various processes for determining the degree of tracking of the pressure member temperature information with respect to the fixing belt temperature information can be applied. For example, the control unit 110 may obtain the similarity between the waveform representing the time change of the fixing belt temperature information and the waveform representing the time change of the pressure member temperature information, and determine the belt slip state when the similarity is equal to or less than a predetermined threshold value. Note that various methods for obtaining the similarity of waveforms are known, and these methods can be widely applied in this embodiment. In addition, as shown in FIG. 6A, since it is assumed that the temperature of the fixing belt 10 is higher than the temperature of the pressure roller 20, a normalization process (for example, a process for matching the average value) may be performed as a preprocessing when obtaining the similarity of the waveforms.

[0090] 3.2 Fixing belt drive In the above, an example has been shown in which the image forming apparatus 100 does not have a drive unit that directly drives the fixing belt 10, and the fixing belt 10 is driven by the rotation of the pressure member. However, the image forming apparatus 100 of the present embodiment is not limited to this, and may include multiple drive units that can independently drive the pressure member and the fixing belt 10. The multiple drive units fix the toner to the sheet P by rotating the pressure member and the fixing belt 10 at a predetermined speed (in a narrow sense, the same speed).

[0091] In this case, the belt slip state may represent a state in which a speed difference occurs, which is the difference between the rotation speed of the fixing belt 10 and the pressure roller 20. In this case, too, since one of the fixing belt 10 and the pressure roller 20 cannot rotate sufficiently while the other rotates, heat concentration may occur on the fixing belt 10. According to the method of the present embodiment, even when both the fixing belt 10 and the pressure roller 20 are driven in this way, it is possible to appropriately detect a state in which the two are not moving in conjunction with each other (a state in which the speed difference is large) as the belt slip state.

[0092] 3.3 Sensor placement In the image forming apparatus 100 of this embodiment, the pressure member temperature detection unit (second thermistor 51) may be a non-contact temperature sensor arranged at a position not in contact with the pressure member, as shown in Figures 4 and 5. In this way, it is possible to increase the degree of freedom in the arrangement of the pressure member detection unit.

[0093] However, the pressure member temperature detection unit is not limited to a non-contact temperature sensor, and may be a contact temperature sensor. In addition, although an example of a contact temperature sensor is shown as the first thermistor 43 of the fixing belt temperature detection unit in Fig. 4 and Fig. 5, the first thermistor 43 may be a non-contact temperature sensor.

[0094] In addition, the pressure member temperature detector and the fixing belt temperature detector are preferably arranged so that the temperatures of the fixing belt 10 and the pressure roller 20 facing each other can be obtained in the main scanning direction (the front / back direction in FIG. 4, the direction along the longitudinal direction of the fixing belt 10 and the pressure roller 20) perpendicular to the paper conveying direction. By arranging the temperature detectors at the opposing positions in this way, it is possible to detect the relationship between the temperatures of the fixing belt 10 and the pressure roller 20 at the positions where they come into contact and directly transfer heat. As a result, it is possible to prevent the degree of tracking of the pressure member temperature information to the fixing belt temperature information from being reduced due to the difference in position in the main scanning direction. In other words, it is possible to prevent factors other than the belt slip state from being involved in the degree of tracking of the pressure member temperature information to the fixing belt temperature information, and therefore it is possible to increase the accuracy of determining the belt slip state. For example, in FIG. 5, the fixing belt temperature detector may be the first thermopile 41, and the pressure member temperature detector may be the second thermistor 51.

[0095] Although the present embodiment has been described in detail as above, it will be easily understood by those skilled in the art that many modifications are possible without substantially departing from the novel matters and effects of the present embodiment. Therefore, all such modifications are intended to be included in the scope of the present disclosure. For example, a term described at least once in the specification or drawings together with a different term having a broader meaning or synonymy can be replaced with that different term anywhere in the specification or drawings. In addition, all combinations of the present embodiment and modifications are also included in the scope of the present disclosure. In addition, the configurations and operations of the image forming apparatus, image forming unit, fixing device, etc. are not limited to those described in the present embodiment, and various modifications are possible. [Explanation of symbols]

[0096] 10...fixing belt, 11...fixing pad, 12...nip portion, 20...pressure roller, 30...heater, 41...first thermopile, 42...second thermopile, 43...first thermistor, 51...second thermistor, 100...image forming apparatus, 110...control portion, 120...image forming portion, 121...optical scanning device, 122...developing device, 123...photosensitive drum, 124...cleaning device, 125...charging device, 126...intermediate transfer belt device, 127...toner cartridge device, 128...fixing device, 130...display portion, 140...storage portion

Claims

1. A fixing belt; a pressing member that forms a nip portion with the fixing belt and drives the fixing belt; a heating member disposed inside the fixing belt; a fixing belt temperature detection unit that acquires fixing belt temperature information based on the temperature of the fixing belt; a pressure member temperature detection unit that acquires pressure member temperature information based on a temperature of the pressure member; a control unit that determines whether or not the fixing belt is in a belt slip state, that is, is not moved by the movement of the pressure member, based on a relationship between the fixing belt temperature information and the pressure member temperature information; An image forming apparatus comprising:

2. In claim 1, The control unit is The image forming apparatus determines whether or not the belt is in a slip state based on a change per unit time in the fixing belt temperature information and a change per unit time in the pressure member temperature information.

3. In claim 2, The control unit is An image forming apparatus which determines that the belt is in a slip state when a state in which the amount of change per unit time of the fixing belt temperature information is determined to be equal to or greater than a first change amount threshold and the amount of change per unit time of the pressure member temperature information is determined to be equal to or greater than a second change amount threshold is detected a predetermined number of times or more.

4. In claim 3, The control unit is An image forming apparatus that determines that an abnormality other than the belt slip state has occurred when it is determined that the amount of change per unit time of the fixing belt temperature information is greater than or equal to the first change amount threshold and when it is determined that the amount of change per unit time of the pressure member temperature information is less than the second change amount threshold.

5. In claim 1, The control unit is the image forming apparatus determines a degree of tracking of the pressure member temperature information with respect to the fixing belt temperature information, and determines that the belt is in a slip state when the degree of tracking is determined to be equal to or less than a given threshold value.

6. In claim 5, The control unit is When it is determined that the degree of tracking of the pressure member temperature information with respect to the fixing belt temperature information is greater than the given threshold value, the image forming apparatus determines that an abnormality other than the belt slip state has occurred or that no abnormality exists.

7. In claim 1, The control unit is The image forming apparatus determines whether or not the belt is in a slip state based on a thermal gradient represented by a difference between the fixing belt temperature information and the pressure member temperature information.

8. In claim 7, The control unit is The image forming apparatus determines whether or not the belt is in a slip state based on a time change in the thermal gradient.

9. In any one of claims 1 to 8, The control unit is When it is determined that the belt is in a slip state, the image forming apparatus performs control to stop the heating by the heating member and control to stop the rotation of the fixing belt.

10. In any one of claims 1 to 8, The pressure member temperature detection unit is The image forming apparatus includes a non-contact temperature sensor disposed at a position not in contact with the pressure member.

11. A method for controlling an image forming apparatus having a fixing belt, a pressure member that forms a nip portion with the fixing belt and drives the fixing belt, and a heating member that is disposed inside the fixing belt, comprising the steps of: acquiring fixing belt temperature information based on the temperature of the fixing belt; obtaining pressure member temperature information based on the temperature of the pressure member; determining whether or not the fixing belt is in a belt slip state, that is, the fixing belt is not moved by the movement of the pressing member, based on a relationship between the fixing belt temperature information and the pressing member temperature information; Control methods.

Images