JP2009042655A - Temperature control device for heated object, fixing device, fixing method, image forming device, and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a temperature control device for heated object which performs temperature control of a traveling endless heating object such as a fixing belt by appropriately using temperature detection means differed in thermal responsiveness, a fixing device and a fixing method using the device to be used for an image forming device such as a copying machine, a facsimile or a printer, and an image forming device and an image forming method using the device and method. <P>SOLUTION: The temperature control device comprises a heating means 25 for heating the traveling endless heated object 21; a plurality of temperature detection means 40 and 41 for detecting a temperature of the heated object 21, which are differed in thermal responsiveness; and a temperature control means which performs heating control of the heated object 21 by the heating means 25 based on the temperature detected by the temperature detection means 40 and 41. The temperature control means switches the temperature detection means 40 and 41 to be used for the control, before and after the temperature of the heated object 21 rises, from the one with low thermal responsiveness to the one with high thermal responsiveness. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a temperature control device for an endless heated body such as a fixing belt and a heating roller, a fixing device and a fixing method used in an image forming apparatus such as a copying machine, a facsimile, and a printer using the same. The present invention also relates to an image forming apparatus and an image forming method using the same.

  2. Description of the Related Art Conventionally, image forming apparatuses such as copiers, facsimile machines, and printers have been provided with a fixing device that fixes an image on a sheet by heating and melting a toner image formed on a sheet such as paper. Such a fixing device performs a process of supplying electric power to the heater to cause the heater to generate heat, and heat and melt the toner image with this heat to fix it on the paper.

  As such a fixing device, a heat roller type fixing device and a belt type fixing device are known. A heat roller type fixing device includes a heating roller having a heater and a pressure roller in pressure contact with the heating roller, and performs fixing by passing a sheet carrying a toner image therebetween. The belt-type fixing device includes an endless fixing belt heated by a heater and a pressure roller pressed against the fixing belt, and performs fixing by passing a sheet carrying a toner image therebetween.

  In these types of fixing devices, as described in [Patent Document 1] to [Patent Document 6], electric power is supplied to the heater in order to keep the temperature when passing the sheet at a temperature suitable for fixing. Then, the temperature is raised to a predetermined temperature so that the fixing is possible, and this temperature is maintained even when the sheet passes.

  Here, the power drive of the heater, that is, the heating control is performed by controlling the power supplied to the heater, and the fixing device is provided with a temperature control means in order to control the power supplied to the heater. It is common. It is known that the temperature control means employs an algorithm for determining the heater lighting duty, represented by PID control, in order to perform accurate and stable temperature control by suppressing the temperature ripple of the heating means. Yes.

  PID control is controlled by three combinations of P: Proportional, I: Integral, and D: Derivative. Optimizing multiple parameters according to the deviation between the target value and the current value. By controlling, As a result, in PID control, when energization time (hereinafter: duty (unit:%)) within a certain control cycle is calculated and controlled, as a result, temperature is maintained by reducing ripple compared to on / off control. Is widely adopted.

  In recent years, belt-type fixing devices have been frequently used with the aim of shortening the warm-up and shortening the first print time. In this type of fixing device, in order to shorten the first print time, when there is no image forming job in the image forming apparatus, the rotation of the fixing belt is stopped, and the fixing belt and the roller around which the belt is wound are preheated to a predetermined temperature. In addition, after the image forming job is generated in the image forming apparatus, the fixing belt starts to rotate so that the amount of heat required when the sheet passes can be supplied promptly.

  Similarly, in the heat roller type fixing device, for the purpose of shortening the first print time or the like, when there is no image forming job in the image forming device, the rotation of the heating roller is stopped and the heating roller is preheated to a predetermined temperature. In addition, a configuration is known in which a heating roller starts rotating after an image forming job is generated in the image forming apparatus, and a necessary amount of heat can be quickly supplied when a sheet passes.

  The state in which the fixing belt and the heating roller stop running and the fixing belt, the roller around which the fixing belt is wound, and the heating roller is preheated to a predetermined temperature is referred to as a preheating mode. This is a typical one that is used to control the surface temperature of the fixing belt inside.

  As described in [Patent Document 4] to [Patent Document 6], as a temperature sensor used for performing the temperature feedback control, a thermopile element having a small thermal time constant and capable of following a rapid temperature rise, In general, a relatively inexpensive thermistor element or the like is used.

  However, in the belt-type fixing device, since the fixing belt is a belt member, the heat capacity is relatively small. Therefore, in the preheating mode, the heated portion of the fixing belt is predetermined when rotation of the fixing belt is stopped. However, the temperature of the non-heated portion of the fixing belt quickly drops, resulting in a large temperature difference in the circumferential direction of the fixing belt and a partial temperature deviation.

  Similarly, even in the heat roller type fixing device, in the preheating mode, the heated roller in the stopped state is in contact with the pressure roller in the stopped state. Temperature deviation occurs.

  In addition, partial temperature deviations of the fixing belt and the heating roller also occur due to heat absorption by the sheet carrying the toner image during the fixing operation.

  The partial temperature deviation of the fixing belt and the heating roller causes fixing unevenness, and thus must be suppressed as much as possible.

  For this reason, various techniques for equalizing the temperature of the fixing belt and the heating roller have been proposed when the driving of the fixing belt and the heating roller is started from the preheating mode or during the fixing operation. In [Patent Document 1] to [Patent Document 3], a so-called on-off control method and a control method such as PID control are performed in order to equalize the temperatures of the fixing belt and the heating roller, particularly when driving is started. And a technique for performing I control, PID control, and P control from on / off control when the detected temperature reaches a threshold value.

  The technology described in [Patent Document 1] is such that after starting heating, the heater is fully energized continuously until the heating temperature of the heater reaches a switching temperature lower than the control target temperature, and after reaching the switching temperature, I ( The heater energization is controlled by integral control. In addition, the technology described in [Patent Document 2] is such that after starting heating, the heater is fully energized continuously until the heating temperature of the heater reaches a switching temperature lower than the control target temperature, and after reaching the switching temperature, The energization of the heater is controlled by PID control. Furthermore, in the technique described in [Patent Document 3], after the start of heating, the heater is fully energized continuously until the heating temperature of the heater reaches a switching temperature lower than the control target temperature. The energization of the heater is controlled by P (proportional) control.

JP 58-38972 A JP 60-163102 A Japanese Patent Laid-Open No. 3-116208 JP 2003-028721 A Japanese Patent No. 3708834 JP 2005-189900 A

  However, if the sensor for detecting the temperature of the surface of the fixing belt and the heating roller has a small thermal time constant, immediately after the rotation of the fixing belt and the heating roller starts from the preheating mode, these temperature deviations are corrected. As a result, the output value of the temperature sensor greatly fluctuates with the rotation cycle of the fixing belt and the heating roller.

  If the output value of the temperature sensor fluctuates greatly in this way, the mode of the fixing device and the image forming device shifts from the preheating mode to the sheet passing state, and when the rotation of the fixing belt and the heating roller starts, the surface of these devices In spite of the fact that it is desired to make the temperature follow the target temperature quickly, the deviation between the target value and the current value fluctuates greatly, and there is a problem that the duty value is greatly touched accordingly.

  That is, as shown in FIG. 5, when the temperature detected by the temperature sensor, that is, the output value fluctuates greatly as shown by the alternate long and short dash line, the fixing temperature reaches the threshold value at an early timing A that has not yet reached the threshold value. As a result, it is detected that it has reached, resulting in false detection. Therefore, PID control is started earlier than the actual switching timing, and the startup time becomes a time L1 longer than the ideal startup time L0. In the example shown in the figure, the threshold value and the target temperature are different values, but the same phenomenon occurs when these values are the same value.

  Further, in the technology that uses both on / off control and control such as PID control, the on / off control is performed until a predetermined temperature is reached, and then the control such as PID control is performed. Contrary to the above purpose, there also arises a problem that the time until convergence to a predetermined temperature becomes long as follows.

  In the control such as PID control, a certain operation amount is calculated according to the deviation between the target value and the current value, and the operation amount is added / subtracted every control cycle to determine the duty. When the duty is continuously used at the time of switching, the initial value is the maximum value or the minimum value of the duty.

  In other words, if the temperature reaches the target temperature or higher when switching to PID control or the like, the initial duty of PID control or the like is the minimum value. If the temperature is lower than the target temperature when switching to PID control or the like, the duty for PID control or the like is the maximum value.

However, in the case of a system that has a heat capacity, such as a fixing device, has a response delay in the output, that is, the output of the temperature detection means, with respect to the input, that is, the input power to the heater, and has a so-called dead time, the initial value of the duty is set to the maximum value. Alternatively, the minimum value is not always preferable.
The reason for this will be described as follows.

  As shown in FIG. 6, in the on / off control, the PID control or the like is performed in a state where the temperature is equal to or lower than the target temperature and the time-temperature gradient has a positive value and has a deviation extremely smaller than the target temperature. Consider the case of switching.

Since there is a dead time in this system, if the deviation at the moment of switching to PID control or the like is extremely small, the target temperature is reached immediately after the switching of control.
However, if the on / off control is performed even after switching, the duty becomes the minimum value as indicated by the broken line indicated by reference numeral B1 as soon as the target temperature is reached, and the temperature significantly increases from the target temperature as indicated by the broken line indicated by reference numeral C1. Never do.

  However, actually, it switches to PID control or the like. Since the temperature at the time of switching is equal to or lower than the target temperature, the initial value of the duty becomes the maximum value as indicated by the solid line indicated by the symbol D1, and the operation amount such as PID is added or subtracted from this initial value. That is, the operation amount is decreased from the maximum duty. Therefore, as shown by the solid line indicated by reference numeral E1, the overshoot with respect to the target temperature becomes larger than that during the on / off control indicated by reference numeral C1.

  On the other hand, as shown in FIG. 7, in the on / off control, the PID is in a state where the temperature is equal to or higher than the target temperature, the time-temperature gradient has a negative value, and the deviation is extremely smaller than the target temperature. Consider the case of switching to control.

Since there is a dead time in this system, if the deviation at the moment of switching to PID control or the like is extremely small, the target temperature is reached immediately after the switching of control.
However, if the on / off control is performed even after switching, the duty becomes the maximum value as indicated by the broken line indicated by the symbol B2 as soon as the target temperature is reached, and the temperature is greatly reduced from the target temperature as indicated by the broken line indicated by the reference symbol C2. Never do.

  However, actually, it switches to PID control or the like. Since the temperature at the time of switching is equal to or higher than the target temperature, the initial value of the duty becomes the minimum value as indicated by the solid line indicated by the symbol D2, and the operation amount such as PID is added or subtracted from this initial value. That is, the operation amount is increased from the minimum duty. Therefore, as indicated by the solid line indicated by E2, the undershoot with respect to the target temperature is larger than that during the on / off control indicated by C2.

  From these, when switching from on / off control to control such as PID, in order to reduce overshoot and undershoot, the calculation of the manipulated variable is performed from the point where the temperature deviation has occurred to the predetermined temperature. Although it is better to use the same parameters such as PID continuously, the fact is that this is not possible due to the restriction of switching.

  From the above, especially when the output value of the temperature detection means for detecting the temperature of the fixing belt and the heating roller fluctuates greatly, such as at the time of rising, it is better that the thermal response of the temperature detection means is low. On the other hand, when such an output value changes relatively stably, it is better that the temperature responsiveness of the temperature detecting means is high. That is, for temperature control of the fixing device, it is preferable to use temperature detecting means having appropriate thermal response depending on the time. This applies not only to the fixing device but also to general temperature control.

  In [Patent Document 5] and [Patent Document 6], two types of temperature detecting means are used in combination, and the temperature detected by one temperature detecting means is corrected by the other temperature detecting means to improve the temperature detection accuracy. However, this technology does not focus on the thermal responsiveness of such temperature detection means, and the difference in thermal responsiveness depends on whether the output value of the temperature detection means fluctuates greatly. It is not a technology to use.

  The present invention uses a temperature control device for a heated body that performs temperature control of a traveling endless heated body, such as a fixing belt, by appropriately using temperature detecting means having different thermal responsiveness, It is an object of the present invention to provide a fixing device and a fixing method used in an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and such an image forming apparatus and an image forming method using the same.

  In order to achieve the above object, the invention described in claim 1 includes an endless heated body that travels, a heating unit that heats the heated body, a temperature detection unit that detects the temperature of the heated body, And a temperature control unit for controlling the heating of the object to be heated by the heating unit based on the temperature detected by the temperature detection unit. A plurality of temperature detection means having different properties, and the temperature control means changes the temperature detection means used for performing the control before and after the temperature of the heated body from the low thermal response to the thermal response. It is characterized by switching to a high quality one.

  According to a second aspect of the present invention, in the temperature control device for an object to be heated according to the first aspect, among the plurality of temperature detection means, the maximum and minimum thermal time constants have the same thermal time constant. The ratio is 10 or more.

  According to a third aspect of the present invention, in the temperature control device for a heated object according to claim 1 or 2, at least one of the plurality of temperature detecting means detects a temperature of the heated object by a thermopile element. It is characterized by being.

  According to a fourth aspect of the present invention, in the temperature control device for a heated object according to any one of the first to third aspects, at least one of the plurality of temperature detecting means is a thermistor element. It is characterized in that it detects the temperature.

  According to a fifth aspect of the present invention, in the temperature control apparatus for an object to be heated according to any one of the first to fourth aspects, the temperature control unit is configured to perform the control per unit time of the heating unit. It is characterized by using an algorithm that can change the amount of heat generated at any time.

  The invention according to claim 6 is the temperature control device for a heated object according to claim 5, wherein the algorithm is any one of PID control, PI control, I-PD control, IP control, and PI-D control. It is what is performed.

  According to a seventh aspect of the present invention, there is provided a fixing device comprising the heated body temperature control device according to any one of the first to sixth aspects, wherein the heated body is a fixing belt. A fixing device having a pressure member that presses against the identification belt and passes through the sheet between the identification receiving belt and fixes the sheet.

  According to an eighth aspect of the present invention, in the fixing device according to the seventh aspect, the heating means heats the fixing belt by radiant heat.

  According to a ninth aspect of the present invention, in the fixing device according to the seventh or eighth aspect, the pressure member is indirectly heated by the heating means.

  According to a tenth aspect of the present invention, in the fixing device according to any one of the seventh to ninth aspects, the image forming apparatus includes a cooling unit that cools the pressure member.

  An eleventh aspect of the present invention is a fixing method in which fixing is performed using the fixing device according to any one of the seventh to tenth aspects.

  A twelfth aspect of the invention is an image forming apparatus that forms an image using the fixing device according to any one of the seventh to tenth aspects or the fixing method according to the eleventh aspect.

  According to a thirteenth aspect of the present invention, an image is formed using the fixing device according to any one of the seventh to tenth aspects, the fixing method according to the eleventh aspect, or the image forming apparatus according to the twelfth aspect. There is an image forming method to be performed.

  The present invention is based on a traveling endless heated body, a heating means for heating the heated body, a temperature detecting means for detecting the temperature of the heated body, and a temperature detected by the temperature detecting means. And a temperature control device for a heated body having temperature control means for controlling heating of the heated body by the heating means, wherein the temperature detection means includes a plurality of temperature detection means having different thermal responsiveness. The temperature control means switches the temperature detection means used for performing the control before and after the temperature of the object to be heated from the low thermal responsiveness to the high thermal responsiveness. By properly using different temperature detection means, the temperature of the heated object can be quickly stabilized at the target temperature even with the same temperature control means, and with high accuracy after startup. It is possible to provide a temperature control apparatus of high safety can be performed degree control object to be heated.

  Among the plurality of temperature detection means, if the ratio of the thermal time constant is 10 or more between the maximum and minimum thermal time constants, the temperature detection means having different thermal responsiveness are properly used appropriately. Therefore, even if the same temperature control means is used, the temperature of the object to be heated can be stabilized to the target temperature more quickly, and the temperature can be controlled with high accuracy after the start-up so that the safety is high. A temperature control device for a heating element can be provided.

  If at least one of the plurality of temperature detecting means is to detect the temperature of the object to be heated by a thermopile element, the temperature is accurately detected by a thermopile element having a high thermal response and a small thermal time constant. In addition, by properly using different temperature detection means with different thermal responsiveness, the temperature of the object to be heated can be quickly stabilized at the target temperature even when the same temperature control means is used. After that, it is possible to provide a temperature control device for an object to be heated that can perform temperature control with high accuracy and has high safety.

  If at least one of the plurality of temperature detecting means is to detect the temperature of the object to be heated by a thermistor element, the temperature can be accurately detected with a relatively inexpensive thermistor element, In addition, by properly using different temperature sensing means with different thermal responsiveness, the temperature of the object to be heated can be quickly stabilized at the target temperature even when the same temperature control means is used. It is possible to provide a temperature control device for an object to be heated that can be controlled and is highly safe and inexpensive.

  If the temperature control means uses an algorithm capable of changing the heat generation amount per unit time of the heating means at any time in order to perform the control, the drive duty of the heating means can be appropriately set by such an algorithm. By determining the temperature detection means with different thermal responsiveness as appropriate, the temperature of the object to be heated can be quickly stabilized at the target temperature even when the same temperature control means is used. A temperature control device for an object to be heated that can perform temperature control with high accuracy and has high safety can be provided.

  Assuming that the algorithm performs any one of PID control, PI control, I-PD control, IP control, and PI-D control, the driving duty of the heating means is set by the algorithm such as PID control. By appropriately determining the temperature detection means with different thermal responsiveness as needed, the temperature of the object to be heated can be quickly stabilized at the target temperature even when the same temperature control means is used. Can provide a temperature control device for an object to be heated that can perform temperature control with high accuracy and has high safety.

  The present invention is a fixing device provided with such a temperature control device for a heated body, and the heated body is a fixing belt, and the sheet is passed through the sheet between the fixing belt and the fixing belt. Since the fixing device has a pressure member for fixing the sheet, the fixing belt is particularly susceptible to temperature deviations. A fixing device that can quickly stabilize the temperature of the fixing belt to a target temperature even with the use of the belt, and can control the temperature with high accuracy after startup, has high safety, and prevents uneven fixing. be able to.

  Assuming that the heating means heats the fixing belt by radiant heat, one having a general configuration can be used as the heating means, while the fixing belt is particularly susceptible to temperature deviations. Although the deviation tends to be promoted when the fixing belt is heated by the radiant heat of the heating means, the temperature of the fixing belt can be quickly targeted even if the same temperature control means is used by properly using different temperature detection means with different thermal responsiveness. It is possible to provide a fixing device that can be stabilized at a temperature, that can perform temperature control with high accuracy after startup, has high safety, and prevents uneven fixing.

  If the pressure member is indirectly heated by the heating means, the fixing belt is particularly susceptible to temperature deviation, and if the heating belt is indirectly heated, the deviation is further promoted. Although it is easy to use temperature detection means with different thermal responsiveness as needed, the temperature of the fixing belt can be quickly stabilized at the target temperature even with the same temperature control means, and with high accuracy after startup. It is possible to provide a fixing device that can perform temperature control, has high safety, and prevents uneven fixing.

  If the cooling means for cooling the pressure member is provided, it is possible to prevent or suppress the occurrence of so-called blisters on the sheet. On the other hand, the fixing belt is particularly susceptible to temperature deviations, and is applied by the cooling means. Although it is easy for the deviation to be promoted, the temperature of the fixing belt can be quickly stabilized at the target temperature even if the same temperature control means is used by properly using temperature detection means with different thermal responsiveness. Can provide a fixing device that can perform temperature control with high accuracy, is highly safe, and prevents uneven fixing.

  Since the present invention is in a fixing method in which fixing is performed using such a fixing device, although the fixing belt is particularly susceptible to temperature deviation, the same temperature detection means having different thermal responsiveness can be used appropriately. Fixing method that can stabilize the temperature of the fixing belt quickly to the target temperature even with the temperature control means, and can control the temperature with high accuracy after startup, and is highly safe and prevents uneven fixing. Can be provided.

  The present invention resides in such a fixing device or an image forming apparatus that forms an image using such a fixing method. Therefore, the temperature detection means having different thermal responsiveness even though the fixing belt is particularly susceptible to temperature deviation. By using the same timely, the temperature of the fixing belt can be quickly stabilized at the target temperature even when the same temperature control means is used. Therefore, it is possible to provide an image forming apparatus that can suppress fixing unevenness and perform good image formation.

  The present invention resides in such a fixing device, such a fixing method, or an image forming method for forming an image using such an image forming apparatus. By properly using different temperature sensing means with different responsiveness, the temperature of the fixing belt can be quickly stabilized at the target temperature even when the same temperature control means is used, and temperature control is performed with high accuracy after startup. Therefore, it is possible to provide an image forming method that is high in safety, can suppress fixing unevenness, and can perform good image formation.

  FIG. 1 shows an outline of an image forming apparatus to which the present invention is applied. The image forming apparatus 1 is a complex machine of a copying machine, a printer, and a facsimile machine, and can perform monocolor image formation. When used as a printer, the image forming apparatus 1 performs an image forming process based on an image signal corresponding to image information received from the outside. This is the same when the image forming apparatus 100 is used as a facsimile.

  The image forming apparatus 1 forms a sheet-like recording medium P as a sheet-like recording medium P, which is a plain paper generally used for copying or the like, or an OHP sheet, cardboard, postcard or other thick paper, or an envelope. It is possible to do. The image forming apparatus 1 is also a double-sided image forming apparatus capable of forming images on both sides of the recording medium P.

  The image forming apparatus 1 includes an original reading unit 2 that optically reads the image information of the original D, and a photosensitive drum 5 serving as an image carrier that rotates in the clockwise direction in the figure, and an original reading unit 2. An exposure unit 3 as a writing unit that irradiates the photosensitive drum 5 with the exposure light L based on the image information read in step S3, and a charging process, an exposure process, and a charging process for forming an image consisting of a toner image on the photosensitive drum 5. An image forming unit 4 that performs a developing process and the like, and a transfer unit 7 that transfers a toner image formed on the photosensitive drum 5 to a recording medium P are provided.

  The image forming apparatus 1 also fixes a document conveying unit 10 that conveys a set document D to the document reading unit 2, paper feeding units 12 to 14 that store the recording medium P, and fixing an unfixed image on the recording medium P. A fixing device 20 that performs the operation of the image forming apparatus 1, and a refeeding device that is not shown and that reversely feeds the recording medium P that has passed through the fixing device 20 to the image forming unit 4. And control means (not shown) for controlling the overall operation of the image forming apparatus 1 and a power switch (not shown).

  Although details of the fixing device 20 will be described later, generally, an endless fixing belt 21 which is a heated body as a fixing member, and a pressure roller 31 as a pressure member pressed against the fixing belt 21. have. The fixing belt 21 is driven to rotate so as to convey the recording medium P in the direction indicated by the arrow in the figure, and the pressure roller 31 rotates following the rotation of the fixing belt 21.

  The operation panel includes a start button for starting copying and the like, and a numeric keypad for inputting the number of copies. When the start button is pressed, an image formation start instruction signal is input to the control means.

  The control means includes a CPU, a memory as a storage means, and the like. The control unit causes the image forming apparatus 1 to shift to a standby mode when a predetermined time elapses without input of a predetermined signal such as an image formation instruction from when the image forming apparatus 1 is turned on or when the previous image formation is completed. Then, processing such as stopping the rotation of the fixing belt 21 is performed. In the standby mode, the fixing device 20 is in the preheating mode.

An operation during normal image formation in the image forming apparatus 1 will be described.
When the document D is set on the document transport unit 10 and the start button is pressed, the document D is transported from the document table in the direction of the arrow by the transport roller of the document transport unit 10 and passes over the document reading unit 2. To do. At this time, the document reading unit 2 optically reads the image information of the document D passing above.

  The optical image information read by the document reading unit 2 is transmitted to the exposure unit 3 after being converted into an electrical signal. From the exposure unit 3, exposure light L such as laser light based on the image information of the electric signal is emitted toward the photosensitive drum 5 of the image forming unit 4.

  On the other hand, in the image forming unit 4, an image including a toner image corresponding to the exposure light L is formed on the photosensitive drum 5 by a predetermined image forming process such as a charging process, an exposure process, and a development process. The toner image formed on the photosensitive drum 5 is transferred by the transfer unit 7 onto the recording medium P fed by a registration roller.

  The recording medium P fed to the transfer unit 7 by the registration roller is transported to the registration roller and fed to the transfer unit 7 as follows. That is, one of the paper feeding units 12, 13, and 14 is automatically or manually selected, and the uppermost sheet of the recording medium P in the selected paper feeding unit is positioned at the position of the conveyance path K. It is conveyed toward. The recording medium P passes through the conveyance path K and reaches the position of the registration roller. The recording medium P that has reached the position of the registration roller is conveyed toward the transfer unit 7 at a predetermined timing that is aligned with the image formed on the photosensitive drum 5.

  The recording medium P after the transfer process reaches the fixing device 20, and is sent between the fixing belt 21 and the pressure roller 31 in the fixing device 20 and receives heat from the fixing belt 21 and both members 21, 31. The toner image is fixed as an image by the pressure received from the toner. The recording medium P on which the image has been fixed is delivered from the nip portion between the fixing belt 21 and the pressure roller 31 and then discharged to the outside of the image forming apparatus 1.

Thus, a series of image forming processes is completed.
Note that the recording medium P on which the image has been fixed may be discharged to the outside of the image forming apparatus 1 after the image is formed on the back surface through the refeeding device.

The configuration and operation of the fixing device 20 will be described in detail with reference to FIG.
As shown in the figure, the fixing device 20 includes a fixing auxiliary roller 22 and a heating roller 23, which are two roller members around which the fixing belt 21 is wound, in addition to the fixing belt 21 and the pressure roller 31. Two temperature sensors 40 and 41 are provided on the outside as opposed to the heating roller 23 so as to detect the surface temperature of the fixing belt 21.
Since the temperature sensors 40 and 41 are provided side by side in the width direction of the fixing belt 21 which is a direction perpendicular to the paper surface in the figure, the temperature sensors 40 and 41 are illustrated as being disposed at the same position in the figure. .

  The fixing device 20 also includes a cooling unit 60 that is pressed against the pressure roller 31 from below, an entrance guide plate 35 that guides the recording medium P to the nip portion between the fixing belt 21 and the pressure roller 31, and a nip portion. And an exit guide plate 36 for guiding the conveyance of the recording medium P that has passed.

  The fixing device 20 also includes a pressure mechanism (not shown) that urges the pressure roller 31 so as to come into pressure contact with the auxiliary fixing roller 22 via the fixing belt 21, and an outer peripheral surface of the fixing belt 21 in the vicinity of the exit side of the nip portion. And a separating plate (not shown) for separating the recording medium P from the fixing belt 21 and a driving means (not shown) for driving the auxiliary fixing roller 22 in the direction of the arrow in the drawing. . In the figure, the symbol T indicates the toner carried on the recording medium P.

  The fixing belt 21 is an endless belt having a multilayer structure in which an elastic layer and a release layer are sequentially laminated on a base layer made of a resin material. The elastic layer of the fixing belt 21 is formed of an elastic material such as fluorine rubber, silicone rubber, or foamable silicone rubber. The release layer of the fixing belt 21 is formed of PFA (tetrafluoroethylene barfluoroalkyl vinyl ether copolymer resin), polyimide, polyetherimide, PES (polyether sulfide), or the like. By providing a release layer on the surface layer of the fixing belt 21, the release property for the toner T or the toner image formed by this, in other words, the releasability is ensured.

The fixing belt 21 is driven to rotate following the direction of the arrow in FIG. Driving control of the auxiliary fixing roller 22 is performed by a control unit.
By using the fixing belt 21 having a low heat capacity as the fixing member, the temperature rise characteristic of the apparatus is improved.

  The fixing auxiliary roller 22 has an elastic layer 22b made of fluorine rubber, silicone rubber, foamable silicone rubber or the like formed on a core metal 22a such as SUS304, and the fixing belt 21 is attached to a pressure roller 31 as a pressure member. To form a nip portion.

  The heating roller 23 includes a thin cylindrical body 24 made of a metal material, and a heater 25 that is a heat source as a heating unit fixed inside the cylindrical body 24. The heating roller 23 rotates following the fixing belt 21 as the fixing belt 21 rotates.

  The heater 25 is a halogen heater, and both ends thereof are fixed to a side plate (not shown) of the fixing device 20. The heater 25 is output controlled by a power supply unit (not shown) of the image forming apparatus 1 that is an AC power supply, generates heat, the heating roller 23 is heated by the radiant heat, and the fixing belt 21 is further heated by the heating roller 23. Output control from the power supply unit to the heater 25, that is, power supply control is performed by the control means.

  The pressure roller 31 mainly includes a cored bar 32 and an elastic layer 33 formed on the outer peripheral surface of the cored bar 32 via an adhesive layer. The elastic layer 33 is made of a material such as fluorine rubber, silicone rubber, or foamable silicone rubber. A thin release layer made of PFA or the like may be provided on the surface layer of the elastic layer 33.

  A desired nip portion is formed between the pressure roller 31 and the fixing belt 21 by the pressure roller 31 being pressed against the auxiliary fixing roller 22 via the fixing belt 21 by a pressure mechanism. The pressure roller 31 is driven by the fixing belt 21 as the fixing belt 21 rotates, and rotates in the direction of the arrow in FIG.

  In this embodiment, the pressure roller 31 is configured to receive the heating by the heater 25 indirectly, and does not have a heating means such as a heater for directly heating the pressure roller 31. This prevents an increase in the cost of the fixing device 20 and prevents an increase in the heat consumption of the entire device. However, such heating means is provided so that the temperature of the entire fixing device 20 can be raised quickly. You may comprise.

The entrance guide plate 35 and the exit guide plate 36 are fixed to a side plate (not shown) of the fixing device 20.
The separation plate is for suppressing a problem that the recording medium P after the fixing process is wound around the fixing belt 21 along the travel of the fixing belt 21.

  The temperature sensors 40 and 41 are separated from the fixing belt 21 and are disposed in a non-contact manner with respect to the fixing belt 21. A signal relating to the surface temperature of the fixing belt 21 is output to the control means. Details of the temperature sensors 40 and 41 will be described later.

  The cooling means 60 has a cooling roller 61 having substantially the same length as the pressure roller 31 and abutted against the pressure roller 31, and urges the cooling roller 61 toward the pressure roller 31 to press the pressure roller 31. An urging means (not shown) is provided, a heat sink (not shown) provided at both ends of the cooling roller 61, and a fan (not shown) for blowing air to the heat sink.

The cooling means 60 prevents the temperature of the pressure roller 31 from becoming excessive, so that the moisture contained in the recording medium P is pressurized even when the recording medium P is coated paper. Occurrence of blistering, which is a blistering phenomenon caused by thermal expansion due to heating from the roller 31, and occurrence of undulation of the recording medium P are suppressed.
The cooling means 60 may have a configuration different from the configuration as long as it has such a function. For example, the cooling unit 60 may include a Peltier element instead of the heat sink.

  The control means determines the energization time of the AC voltage to be applied to the heater 25 based on the signal relating to the temperature of the surface of the fixing belt 21 input from the temperature sensors 40 and 41, and based on the determination, the control unit determines from the power supply section the heater 25. Is energized and an AC voltage is applied.

  As described above, the control unit functions as a temperature control unit that controls the heating of the fixing belt 21 by the heater 25 based on the temperature detected by the temperature sensors 40 and 41. The control means functioning as the temperature control means controls the output of the heater 25 by such output control of the fixing belt 21 during warm-up, image formation including when paper is passed to the fixing device 20, in other words, during printing and during standby. The temperature, that is, the fixing temperature is adjusted and controlled to a desired temperature, that is, a target control temperature. The warm-up time refers to the time from the start of power supply to the heater 25 to the time when the fixing belt 21 travels and reaches the target control temperature for the first time. The image formation time refers to the time when the last recording medium P is nipped. The time until it finishes passing through the section is referred to, and the standby time refers to the time when the standby mode is entered and the preheating mode is set.

The fixing device 20 configured as described above operates as follows.
When the power switch is turned on and the start button is pressed on the operation panel, an AC voltage is applied to the heater 25 from the power supply unit to supply power, and then the fixing belt 21 and the fixing assistance are supplied on condition that an image formation start instruction signal is input. The rotational drive of the roller 22, the heating roller 23, and the pressure roller 31 is started.

  Further, the recording medium P fed from any one of the paper feeding units 12 to 14 and carrying an unfixed image in the image forming unit 4 is guided by an entrance guide plate 35 as indicated by reference numeral Y1 in FIG. It is fed into the nip portion between the fixing belt 21 and the pressure roller 31. The recording medium P has a toner image fixed at the nip portion by heating by the fixing belt 21 and pressing force between the fixing belt 21 or the auxiliary fixing roller 22 and the pressure roller 31. The recording medium P on which the toner image is fixed is sent out from the nip portion by the rotating fixing belt 21 and the pressure roller 31 and is conveyed in the direction indicated by the reference numeral Y2 in FIG.

  In such a fixing process, as described above, in order to perform stable fixing without fixing unevenness, it is necessary to suppress the temperature fluctuation of the fixing belt 21. In this case, FIGS. As described above, it is necessary to stabilize the output value from the temperature detection means. For this purpose, it is effective to properly use temperature detection means having different thermal responsiveness in a timely manner.

  Therefore, the temperature sensors 40 and 41 of this embodiment have different thermal time constants, in other words, thermal time constants. Specifically, as the temperature sensor 40, a responsive thermopile element having high sensitivity is used, and as the temperature sensor 41, a thermistor element having lower sensitivity than the temperature sensor 40 is used.

  The control means functioning as the temperature control means is a heater that is used before and after the fixing belt 21 starts running, at the time when the temperature of the fixing belt 21 is stabilized and is set to the target temperature, that is, before and after the temperature of the fixing belt 21 rises. The temperature sensors 40 and 41 used for controlling the heating of the fixing belt 21 by supplying power to 25 are changed from the temperature sensor 41 having a low thermal response, that is, a large thermal time constant, to a temperature response having a high thermal response, that is, a thermal time constant. Switch to a smaller temperature sensor 40.

  Note that the timing of this switching is the time when the temperature of the fixing belt 21 reaches the target control temperature for the first time, that is, a temperature having a sufficiently large thermal time constant with respect to the temperature change period of the fixing belt 21 and having a low thermal response. This is a time when the sensor 41 detects that the temperature of the fixing belt 21 has reached the target control temperature for the first time.

  The ratio of the thermal time constant between the temperature sensor 40 and the temperature sensor 41 is 10 or more so that the temperature sensor 41 has a sufficiently large thermal time constant with respect to the temperature change of the fixing belt 21. The temperature sensor 40 and the temperature sensor 41 are selected so that becomes 10 times or more the thermal time constant of the temperature sensor 41.

  Specifically, in this embodiment, the thermal time constant of the temperature sensor 40 using the thermopile element is about 100 ms including the time required for A / D conversion, D / A conversion and signal processing, Similarly, the thermal time constant of the temperature sensor 41 using the thermistor element is about 3000 ms, which is a difference of about 30 times.

  Here, having a sufficiently large thermal time constant with respect to the temperature change of the fixing belt 21 means that even if a temperature deviation occurs in the circumferential direction of the fixing belt 21 while the rotation of the fixing belt 21 is stopped, It means that the temperature of the part exceeding the target control temperature is not detected. Therefore, such a thermal time constant depends on the heat capacity of the fixing belt 21 and the target control temperature.

  When the control means functions as the temperature control means, the circuit 25 shown in FIG. 3 controls the heater 25 based on the temperature of the fixing belt 21 measured by the temperature sensors 40 and 41 so that the fixing belt 21 has an optimum temperature. It is controlled to become.

  As shown in the figure, the control means as the temperature control means constitutes a temperature control circuit 50, and has a PID controller 51 and a PWM drive circuit 52. The temperature control circuit 50 controls the duty of energizing the heater 25. Specifically, the duty of energization is a predetermined energization time, in other words, the lighting rate of the heater that is lit per control cycle, and is equal to the energization time of the heater 25 or the amount of heat generated per unit time.

  The PID controller 51 calculates a duty from a predetermined target control temperature and a temperature deviation of the fixing belt 21 detected by the temperature sensors 40 and 41 based on a PID control algorithm. Then, the heater 25 is turned on through the PWM drive circuit 52 based on the calculated duty. Specifically, the rate at which the rated AC voltage per control cycle is applied to both ends of the heater 25 is controlled.

  By the fixing belt 21, the heater 25, the temperature sensors 40 and 41, and the control means functioning as the temperature control means having the above-described configuration, the temperature control device (hereinafter referred to as “temperature”) according to the present invention shown in FIG. Control device ") 53 is formed.

The operation of the temperature control device 53 will be described as follows.
In general, the temperature control unit 53 feeds back the temperature of the temperature sensor 40 having a small thermal time constant and inputs the temperature to the temperature control circuit 50 to improve the accuracy of the fixing temperature control.

  However, if the thermal response is too high, as described above, the temperature deviation in the circumferential direction of the fixing belt 21 is remarkably read, and the deviation from the target temperature may greatly vary. Since the fixing device 20 of the present embodiment includes the cooling unit 60, the temperature deviation is particularly likely to occur.

  For this reason, the temperature control device 53 has a configuration in which a temperature sensor 41 having a slow response is also provided, and the temperature control is performed by feeding back the output of the temperature sensor 41 only when the temperature deviation of the fixing belt 21 is determined to be large. To do.

  A specific example of this will be described with reference to FIG. This figure shows the profile of the fixing device 20 with the horizontal axis representing time and the vertical axis representing the temperature of the fixing belt 21, that is, the fixing temperature or the duty of the heater 25.

  In the figure, time T is when an image formation start instruction signal is input in the preheating mode, and the fixing belt 21 starts to warm up in the fixing device 20 and shifts to warm-up.

  When the preheating mode is long, the temperature of only the portion of the fixing belt 21 wound around the heating roller 23 having the heater 25 is maintained at, for example, near 160 ° C., and other portions are reduced to near the ambient temperature, for example, 50 ° C. Therefore, when the rotation is started, the thermopile element 40 shows the reading of the alternate long and short dash line in the figure.

  When this value is input to the temperature control device 53, the duty fluctuates greatly as shown by a two-dot chain line, and it becomes difficult to supply a sufficient amount of heat for quickly raising the temperature to a predetermined temperature. Time T1 is required as the rise time when the signal rises.

  On the other hand, the thick line in the figure indicates the reading value of the thermistor 41, and since the temperature deviation in the circumferential direction of the fixing belt 21 cannot be read due to the large thermal time constant, the detected temperature fluctuates greatly. There is no.

  Therefore, the detected value of the temperature sensor 41 is used to input to the temperature control device 53. As a result, the duty becomes as shown by a thick line 64, and the power supply amount is appropriately output as compared with the case indicated by the two-dot chain line using the detection value of the temperature sensor 40, and as a result, the rise time rises to the target control temperature. Takes only a time T2 shorter than the above-described time T1, and rises to a predetermined temperature more quickly than when the temperature sensor 40 is used, and the first print time is shortened.

  After rising to the target control temperature, the value input to the temperature control device 53 is switched from the temperature sensor 41 to the reading value of the temperature sensor 40 and returned to the original value.

  The value of the temperature sensor 41 is used from the preheating mode until the temperature rising phase from the start of rotation of the fixing belt 21 until the sheet can be passed. In other aspects, the value of the temperature sensor 40 is input to fix the fixing temperature. There is provided a safe fixing device 20 in which the control is highly accurate, an image having no fixing unevenness between the images is obtained, and a sudden temperature change due to runaway can be detected.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.

  For example, the number of temperature detection means may be three or more as long as it is plural. Also at this time, the thermal responsiveness is different from each other, and is sequentially switched from a low thermal responsiveness to a high thermal responsiveness before and after the heating target is raised.

  It is desirable that at least one of the temperature detecting means uses a thermopile element. This is because the thermopile element has high thermal responsiveness and good followability to the temperature change of the heated object.

  It is desirable that at least one of the temperature detecting means uses a thermistor element. This is because the thermistor element is relatively inexpensive and is provided in a fixing device having a plurality of temperature detecting means, and its cost can be reduced.

  However, as long as the thermal responsiveness and the thermal time constant are different from each other and the control is not hindered, all temperature detecting means can be made using a thermopile element or a thermistor.

  The algorithm that allows the temperature control means to change the amount of heat generated per unit time of the heating means used at any time to control the heating of the object to be heated by the heating means is not limited to the above-described PID control, but PI control , I-PD control, IP control, or PI-D control.

In addition to such an algorithm, on / off control may be used in combination.
The fixing device is not limited to a belt type and may be a heat roller type. In this case, the heating roller becomes a member to be heated that is heated by the heating means, and also becomes a heating member that heats the sheet.
The temperature control device for an object to be heated according to the present invention can be applied to devices other than the fixing device of the image forming apparatus.

  The present invention may be applied not only to an image forming apparatus capable of forming only a mono color but also to an image forming apparatus capable of forming a color image including a full color. The image forming apparatus in this case may be a so-called tandem type image forming apparatus, or a color image obtained by sequentially forming toner images of respective colors on one image carrier and sequentially superimposing the respective color toner images. The present invention can be similarly applied to a so-called one-drum image forming apparatus.

In any type of image forming apparatus, an intermediate transfer method using an intermediate transfer member may be employed, or a direct transfer method in which each color toner image is directly transferred to a recording medium may be employed.
The image forming apparatus may not be a copier, a printer, and a facsimile machine, but may be a single unit thereof, or may be a multi-function machine of another combination such as a copier and printer.

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

1 is a schematic front view of an image forming apparatus to which the present invention is applied. FIG. 2 is a schematic front view of a fixing device provided in the image forming apparatus illustrated in FIG. 1. FIG. 2 is a block diagram of a temperature control device for an object to be heated according to the present invention provided in the image forming apparatus shown in FIG. 1. 3 is a profile showing a fixing temperature and a duty of the fixing device shown in FIG. 2. It is the profile of the fixing temperature in the conventional temperature control apparatus of a to-be-heated body. It is another profile of the fixing temperature in the temperature control apparatus of the conventional to-be-heated body. It is another profile of the fixing temperature in the temperature control apparatus of the conventional to-be-heated body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 20 Fixing apparatus 21 To-be-heated body 25 Heating means 31 Pressure member 40, 41 Temperature detection means 40 Temperature detection means with high heat responsiveness, Temperature detection means to detect the temperature of to-be-heated body with a thermopile element 41 Heat Temperature detecting means having low responsiveness, temperature detecting means for detecting the temperature of the object to be heated by the thermistor element 50 temperature control means 53 temperature control device for the object to be heated 60 cooling means P sheet

Claims (13)

An endless heated body that travels,
Heating means for heating the object to be heated;
Temperature detecting means for detecting the temperature of the heated object;
In the temperature control device for a heated object, comprising: a temperature control means for controlling the heating of the heated object by the heating means based on the temperature detected by the temperature detection means,
The temperature detection means has a plurality of temperature detection means having different thermal responsiveness from each other,
The temperature control means switches the temperature detection means used for performing the control before and after the temperature of the object to be heated from a low thermal responsiveness to a high thermal responsiveness. Temperature control device for heating element. In the temperature control apparatus of the to-be-heated body of Claim 1,
A temperature control device for a heated object, wherein the ratio of the thermal time constant is 10 or more between the maximum and minimum thermal time constants among the plurality of temperature detecting means. In the temperature control apparatus of the to-be-heated body of Claim 1 or 2,
At least one of the plurality of temperature detecting means detects a temperature of the heated object by a thermopile element, and the temperature control apparatus for the heated object is characterized in that: In the temperature control apparatus of the to-be-heated body as described in any one of Claim 1 thru | or 3,
At least one of the plurality of temperature detecting means detects the temperature of the heated body by a thermistor element. In the temperature control apparatus of the to-be-heated body as described in any one of Claim 1 thru | or 4,
In order to perform the control, the temperature control means uses an algorithm that can change the amount of heat generated per unit time of the heating means as needed. In the temperature control apparatus of the to-be-heated body of Claim 5,
The temperature control device for an object to be heated is characterized in that the algorithm performs any one of PID control, PI control, I-PD control, IP control, and PI-D control.   A fixing device comprising the temperature control device for a heated object according to any one of claims 1 to 6, wherein the heated object is a fixing belt, and is in pressure contact with the fixing belt. A fixing device having a pressure member that passes through the sheet and fixes the sheet. The fixing device according to claim 7.
The fixing device is characterized in that the heating means heats the fixing belt by radiant heat. The fixing device according to claim 7 or 8,
The fixing device, wherein the pressure member is indirectly heated by the heating means. The fixing device according to any one of claims 7 to 9,
A fixing device comprising cooling means for cooling the pressure member.   A fixing method in which fixing is performed using the fixing device according to claim 7.   An image forming apparatus that forms an image using the fixing device according to claim 7 or the fixing method according to claim 11.   An image forming method for forming an image using the fixing device according to any one of claims 7 to 10, the fixing method according to claim 11, or the image forming device according to claim 12.

Images