JP2020126203A - Fixing device and image formation device - Google Patents

Abstract

To reduce electric power to be supplied to a heater during image formation.SOLUTION: An engine controller 92, when performing fixing processing on an image whose width is equal to or smaller than a width of a heat generator 54b2 carried on a first recording material whose paper sheet width is greater than the width of the heat generator 54b2, selects whether to perform the fixing process using a heat generator 54b1 or the heat generator 54b2 depending on the temperature in the part of a nip out of a region corresponding to the heat generator 54b2 and within a region where the first recording material passes (S501 to S507).SELECTED DRAWING: Figure 4

Description

The present invention relates to a fixing device and an image forming apparatus, and more particularly to a color image forming apparatus utilizing an electrophotographic process or the like.

Conventionally, a fixing device of an image forming apparatus fixes an unfixed image (toner image) formed on a recording sheet by an image forming unit such as an electrophotographic process onto the recording sheet. In the image forming apparatus, a heat roller type fixing device using a halogen heater as a heat source and a film heating type fixing device using a ceramic heater as a heat source are used. In an image forming apparatus having a fixing device having such a heater as a heat source, a recording paper (hereinafter, referred to as small size paper) having a width shorter than the length of the heating element is passed through the fixing nip portion (hereinafter, referred to as passing paper). ), the following phenomenon may occur. That is, in the area where the heating element is generating heat and the area where the recording paper does not pass (hereinafter referred to as the non-paper passing area), compared to the area where the recording paper passes (hereinafter referred to as the paper passing area). There is a case where a phenomenon in which the temperature rises (hereinafter referred to as non-sheet passing portion temperature rise). If the temperature becomes too high in the non-sheet passing area, it may affect surrounding members such as a member that supports the heater. Therefore, a fixing device is disclosed that includes a plurality of heating elements having different lengths and a switching relay that can exclusively switch between heating elements that generate heat (see, for example, Patent Document 1). With this configuration, the temperature of the non-sheet-passing portion is prevented by selectively using the heating element having a length that matches the width of the recording sheet to be passed.

JP, 2001-100558, A

In the conventional image forming apparatus, the heating element used for the fixing process is selected according to the size of the recording paper in the width direction. Therefore, when printing is performed such that the image size is smaller than the width of the heating element, power is supplied to the heating element even in the sheet passing area and the non-image area where no image is formed. Therefore, the power is excessively consumed in the non-image area where it is not necessary to heat the heating element.

The present invention has been made under such a situation, and an object thereof is to reduce the power supplied to the heater during image formation.

In order to solve the problems described above, the present invention has the following configurations.

(1) A fixing device for fixing an unfixed toner image carried on a recording material, the first heating element and a second heating element having a longitudinal length shorter than that of the first heating element. And a first member heated by the heater, a second member that forms a nip portion together with the first member, the first heating element, or the second heating element. A switching means for switching a power supply path for supplying electric power to the recording medium, and a control means for controlling the switching means, wherein the control means has a width that is a length of the recording material in the longitudinal direction. When the fixing process is performed on the first recording material that is larger than the width of the heating element, the width that is the length in the longitudinal direction of the image formed on the first recording material is the same as that of the second heating element. If the width is equal to or less than the width, the fixing device is characterized in that the fixing process is performed on the first recording material using the second heating element.

(2) An image comprising: an image forming unit that forms an unfixed toner image on a recording material; and the fixing device according to (1) that fixes the unfixed toner image on the recording material. Forming equipment.

According to the present invention, the electric power supplied to the heater during image formation can be reduced.

Sectional drawing which shows the outline of the color image forming apparatus of Examples 1 and 2. Schematic cross-sectional view of the vicinity of the central portion in the longitudinal direction of the fixing device of Examples 1 and 2, schematic diagram of the heater and the power control unit Block diagram of the image forming apparatus of the first embodiment The flowchart which shows the heating element switching control of Example 1. Block diagram of the image forming apparatus of Embodiment 2 Flowchart showing heating element switching control of the second embodiment FIG. 3 is a diagram showing a heater and a heater control circuit according to a third embodiment Flowchart showing heating element switching control of the third embodiment

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, passing the recording paper through the fixing nip portion is called passing the paper. In addition, an area where the recording paper is not passed in the area where the heating element is generating heat is called a non-paper passing area (or a non-paper passing portion), and an area where the recording paper is passing ( Or paper passing section). Furthermore, a phenomenon in which the temperature of the non-sheet passing area becomes higher than that of the sheet passing area is called a non-sheet passing portion temperature rise.

[Image forming device]
FIG. 1 is a configuration diagram of a tandem system (four-drum system) color image forming apparatus according to the first embodiment. Here, the letter a of each code indicates the configuration and unit of yellow (Y), b is magenta (M), c is cyan (C), and d is black (Bk). In the following description, the letters a, b, c, d will be omitted unless a specific unit is described.

The operation of the color image forming apparatus will be described below. The color image forming apparatus includes at least one sheet feeding unit, and in the first embodiment, includes a plurality of sheet feeding units, namely a cassette 16m and a cassette 16n. The cassettes 16m and 16n have width sensors 160m and 160n, paper presence/absence sensors 102m and 102n, and pickup rollers 17m and 17n. The width sensors 160m and 160n are sensors that detect the length (hereinafter, also referred to as size) of the stacked recording paper sheets P in the width direction (direction substantially orthogonal to the transport direction). Based on the detection results of the width sensors 160m and 160n, the engine controller 92, which will be described later, determines whether the size of the paper P stacked in the cassettes 16m and 16n in the width direction is larger than the length L2 (see FIG. 2B). It is possible to determine whether the length is L2 or less (width or less). The paper presence/absence sensors 102m and 102n can detect the presence/absence of the paper P stacked in the cassettes 16m and 16n. The pickup rollers 17m and 17n are rollers for feeding the sheets P stacked in the cassettes 16m and 16n.

The sheets P stacked in the cassettes 16m and 16n are fed from either the cassette 16m or the cassette 16n by the pickup rollers 17m and 17n, and then conveyed by the pair of conveying rollers 140 and 150. The fed sheet P is conveyed to a registration roller (hereinafter referred to as a registration roller) 18 by a pair of conveyance rollers 140 and 150. After that, when the registration sensor 111 detects the leading end position of the paper P, the conveyance of the paper P is temporarily stopped. On the other hand, the exposure device 11 includes a reflection mirror, a laser diode (light emitting element), and the like, and sequentially irradiates the photosensitive drum 1 as a rotationally driven photosensitive member with the scanning beam 12. At this time, the photosensitive drum 1 is previously charged by the charging roller 2. A voltage of, for example, -1200V is output from each charging roller 2, and the surface of the photosensitive drum 1 is charged at, for example, -700V. When an electrostatic latent image is formed by irradiating the scanning beam 12 at this charging potential, the potential of the place where the electrostatic latent image is formed becomes, for example, -100V. The developing roller 4 of the developing unit 8 outputs a voltage of, for example, −350 V, supplies toner to the electrostatic latent image on the photosensitive drum 1, and forms a toner image on the photosensitive drum 1. The primary transfer roller 10 outputs a positive voltage of, for example, +1000V, and transfers the toner image on the photosensitive drum 1 to the intermediate transfer belt 13 (endless belt). Here, the toner not transferred from the photosensitive drum 1 to the intermediate transfer belt 13 is collected by the collecting blade 33 of the cleaning unit 3.

An image forming unit (image forming unit) is a member group including the exposure device 11 and the photosensitive drum 1, which is directly related to the toner image of the charging roller 2, the developing unit 8, the primary transfer roller 10, and the like. ). Further, each member (charging roller 2, developing roller 4, and primary transfer roller 10) that is arranged near the periphery of the photosensitive drum 1 and acts on the photosensitive drum 1 is called a process member that is a process unit. A plurality of types of members can be used as the process member.

The intermediate transfer belt 13 is rotationally driven by the tension roller 14, the auxiliary roller 19, and the secondary transfer counter roller 15, and conveys the toner image to the position of the secondary transfer roller 25 (hereinafter referred to as the secondary transfer position). At this time, at the secondary transfer position of the secondary transfer roller 25, the paper P is restarted to be conveyed in time with the conveyed toner image. Then, the toner image is transferred from the intermediate transfer belt 13 onto the paper P (on the recording material) by the secondary transfer roller 25. Here, the toner not transferred from the intermediate transfer belt 13 to the paper P is collected by the cleaning blade 277 of the cleaning unit 27. After that, the toner image carried on the paper P is heated and fixed by the fixing device 50, which is a fixing unit having the film 51 and the pressure roller 53, and then the paper P is discharged to the outside of the apparatus.

[Fixing device]
Next, the configuration of the fixing device 50 according to the first exemplary embodiment will be described with reference to FIG. Here, the longitudinal direction is the rotation axis direction of the pressure roller 53 that is substantially orthogonal to the conveyance direction of the paper P described later. The length of the paper P in the direction (longitudinal direction) substantially orthogonal to the transport direction is called the width. 2A is a schematic sectional view of the fixing device 50, and FIG. 2B is a schematic diagram of the heater 54 and the electric power control unit 97.

The paper P holding the unfixed toner image Tn from the left side of FIG. 2A is heated while being conveyed from the left to the right in the drawing in the fixing nip portion N, so that the toner image Tn is fixed to the paper P. To be done. The fixing device 50 according to the first exemplary embodiment includes a cylindrical film 51, a nip forming member 52 that holds the film 51, a pressure roller 53 that forms a fixing nip portion N together with the film 51, and a sheet P for heating. And a heater 54.

The film 51, which is the first rotating body, is a fixing film as a heating rotating body. In Example 1, polyimide, for example, is used as the base layer. An elastic layer made of silicone rubber and a release layer made of PFA are used on the base layer. In order to reduce the frictional force generated between the film 51 and the nip forming member 52 and the heater 54 due to the rotation of the film 51, grease is applied to the inner surface of the film 51.

The nip forming member 52 plays a role of guiding the film 51 from the inside and forming a fixing nip portion N between the film 51 and the pressure roller 53. The nip forming member 52 is a member having rigidity, heat resistance, and heat insulation, and is made of liquid crystal polymer or the like. The film 51 is fitted onto the nip forming member 52. The pressure roller 53, which is the second rotating body, is a roller as a pressure rotating body. The pressure roller 53 includes a core metal 53a, an elastic layer 53b, and a release layer 53c. The pressure roller 53 is rotatably held at both ends, and is rotationally driven by a fixing motor (not shown). Further, the film 51 is driven to rotate by the rotation of the pressure roller 53. The heater 54, which is a heating member, is held by the nip forming member 52 and is in contact with the inner surface of the film 51. The substrate 54a, the heating elements 54b1 and 54b2, the protective glass layer 54e, and the fixing temperature sensor 59 will be described later.

[Heater and power controller]
(heater)
The heater 54 will be described in detail with reference to FIG. The heater 54 includes a substrate 54a, a plurality of heating elements 54b1 and 54b2, a conductor 54c, contacts 54d1 to 54d3, and a protective glass layer 54e. Heating elements 54b1 and 54b2, conductors 54c, and contacts 54d1 to 54d3 are formed on the substrate 54a, and a protective glass layer 54e is formed thereon to ensure insulation between the heating elements 54b1 and 54b2 and the film 51. .. The heating element 54b1 which is the first heating element and the heating element 54b2 which is the second heating element have different lengths in the longitudinal direction (hereinafter also referred to as sizes). Specifically, the length of the heating element 54b1 in the longitudinal direction is L1, the length of the heating element 54b2 in the longitudinal direction is L2, and the length L1 and the length L2 have a relationship of L1>L2. There is. The length L1 of the heating element 54b1 is a length capable of fixing the sheet P having the maximum width (hereinafter referred to as the maximum sheet passing width) among the sheets P that can be printed (or conveyed) by the image forming apparatus. It is Hereinafter, the paper P having the length L1 is also referred to as the paper P having the L1 width, and the paper P having the length L2 is also referred to as the paper P having the L2 width. The heating element 54b1 is electrically connected to the contacts 54d1 and 54d3 via the conductor 54c, and the heating element 54b2 is electrically connected to the contacts 54d2 and 54d3 via the conductor 54c. That is, the contact 54d3 is a contact commonly connected to the heating elements 54b1 and 54b2.

The fixing temperature sensor 59 is located on the surface opposite to the protective glass layer 54e with respect to the substrate 54a, is installed at the center position in the longitudinal direction of the heating elements 54b1 and 54b2, and is in contact with the substrate 54a. The fixing temperature sensor 59 is, for example, a thermistor, detects the temperature of the heater 54, and outputs the detection result to the engine controller 92. The engine controller 92 controls the temperature during the fixing process based on the detection result of the fixing temperature sensor 59.

(Power control unit)
FIG. 2B also shows a power control unit 97 which is a control circuit of the fixing device 50. The electric power control unit 97 of the fixing device 50 includes heating elements 54b1 and 54b2 (heater 54), an AC power supply 55, a bidirectional thyristor (hereinafter, referred to as a triac) 56, and a heating element switch 57 that is a switching unit. The triac 56 is conductive when power is supplied from the AC power supply 55 to the heating elements 54b1 and 54b2, and is non-conductive when power supply from the AC power supply 55 to the heating elements 54b1 and 54b2 is cut off. The triac 56 functions as a connecting unit that connects or disconnects the supply of electric power to the heater 54. The engine controller 92 calculates the electric power required to control the heating elements 54b1 and 54b2 to the target temperature (target fixing temperature) based on the temperature information which is the detection result of the fixing temperature sensor 59, and turns on the triac 56. Alternatively, it is controlled to be non-conductive.

Further, the heating element switch 57 is, for example, a C contact relay in the first embodiment. The heating element switching device 57 sets an electrical path (power supply path) between the contact 54d1 and the contact 54d to a connection state (hereinafter, also referred to as a short-circuit state) or an open state. Specifically, the heating element switch 57 has a contact 57a connected to the AC power supply 55, a contact 57b1 connected to the contact 54d1, and a contact 57b2 connected to the contact 54d2. Under the control of the engine controller 92, the heating element switch 57 is in one of a state in which the contact 57a and the contact 57b1 are connected and a state in which the contact 57a and the contact 57b2 are connected. By switching the heating element switch 57, which of the heating elements 54b1 and 54b2 is to be supplied with power is exclusively selected. That is, the heating element switch 57 switches the heater 54 to one of the heating element 54b1 and the heating element 54b2. The heating element switch 57 switches a power supply path for supplying power to the heating element 54b1 or the heating element 54b2. The heating element switching unit 57 receives a signal from the engine controller 92 to perform switching. In order to prevent contact welding of the heating element switch 57, which is a C-contact relay, switching of the heating element switch 57 is performed while the triac 56 is in a non-conducting state (power is supplied to the heating element 54b1 or the heating element 54b2). It is performed in the state of being cut off. Hereinafter, the heating elements 54b1 and 54b2 may be collectively referred to as the heating element 54b.

Here, regarding the region between the end of the heating element 54b1 and the end of the heating element 54b2, in FIG. 2B, the left side is an area AL and the right side is an area AR (outside the area corresponding to the heating element 54b2). write. When the sheet P having a width of L2 or less is passed, the heating element switching unit 57 selects the heating element 54b2 and causes the heating element 54b2 to generate heat. Thus, when the heating element 54b2 is heated, the non-sheet passing portion temperature rise is prevented in the areas AL and AR which are the non-sheet passing portion areas when the heating element 54b1 is heated. You can

[Functional block diagram]
FIG. 3 is a diagram showing functional blocks related to the engine controller 92 that is a control unit, the external device 400, the video controller 91, and the hardware 403. In the engine controller 92, the heating element selection unit 421, the heating element control unit 422, the fixing temperature detection unit 423, and the heat storage state determination unit 434 each represent a functional block. Further, each of the triac 56, the heating element switch 57, and the fixing temperature sensor 59 constitutes hardware 403. The triac 56 and the heating element switch 57 are also the power control unit 97. Hereinafter, each will be specifically described.

The video controller 91 receives information necessary for printing from an external device 400 such as a host computer and sends it to the engine controller 92. Here, the information necessary for printing includes, for example, designation information of which paper feed port of the cassette 16 used for printing is used, size information and paper type information of the paper P used for printing, and color mode for printing. The information includes information and image data information to be printed. The video controller 91 can specify a standard size such as A4 or A5, a free size, or an ANY size as the size information of the paper P used for printing. Here, the free size is a size not included in the standard size and the length and width can be freely set, and the ANY size is a size for which size information is not specified.

The fixing temperature detector 423 calculates the temperature of the fixing device 50 (that is, the fixing nip portion N) based on the information acquired from the fixing temperature sensor 59. The heating element control unit 422 turns on the triac 56 when power is supplied to the heating element 54b based on the temperature calculated by the fixing temperature detection unit 423, and turns off the triac 56 when power is not supplied to the heating element 54b. To do. The heat storage status determination unit 434 estimates the temperature of at least one location of the fixing device 50 based on the heating element 54b to which power is being supplied by the heating element control unit 422 and the printing status. The heat storage state determination unit 434 estimates, for example, the temperature of the fixing device 50, more specifically, the temperature of the end portion of the fixing nip portion N in the longitudinal direction.

[Explanation of Embodiment 1]
In the first embodiment, when the width of the image transferred to the paper P (hereinafter, referred to as printing) is narrow (hereinafter, referred to as image width) even if the paper P is wide, the heater 54 having a narrow width corresponding to the image width is used. The method of switching to is explained. FIG. 4 is a flowchart showing the heating element switching control of the first embodiment. In step (hereinafter referred to as S) 500, the engine controller 92 determines whether the print information of the page to be printed next is received from the video controller 91. The print information here includes the image size to be printed on the paper P and the size of the paper P. The size of the paper P may be information based on the detection results of the width sensors 160m and 160n.

If the engine controller 92 determines in step S500 that the next print information has been received, the process proceeds to step S501, and if it determines that the next print information has not been received, the process ends. In S501, the engine controller 92 refers to the print information received in S500, and determines whether or not the paper width Lp, which is the length of the paper P in the width direction, is less than or equal to the length L2 of the heating element 54b2 (Lp≦L2). .. When the engine controller 92 determines in S501 that the sheet width Lp is the second recording material having the length L2 or less (Lp≦L2), the process proceeds to S505. In S505, the engine controller 92 selects the heating element 54b2 corresponding to the width (Lp≦L2) of the sheet P as the heating element 54b used for fixing the sheet P. If the engine controller 92 determines in S501 that the paper width Lp is the first recording material that is greater than the length L2 (Lp>L2), the process proceeds to S503.

In step S<b>503, the engine controller 92 refers to the print information received in step S<b>500, and determines whether the image width Li, which is the size in the width direction of the image transferred onto the sheet P, that is, the image fixed on the sheet P, is the length L<b>2 or less. Determine whether or not. When the engine controller 92 determines in S503 that the image width Li is equal to or less than the length L2 (Li≦L2), the process proceeds to S504. In S504, when the engine controller 92 selects the heating element 54b2 having a width narrower than that of the sheet P based on the heat storage states of the film 51, the pressure roller 53, and the heater 54, the temperature of the non-sheet passing portion is a predetermined temperature. It is determined whether or not a certain TD or more. That is, the engine controller 92 determines whether or not the temperature (TD) at which the fixing device 50 is damaged in the non-sheet passing portion is equal to or higher than the temperature (TD).

(About the temperature at the end of the fixing temperature)
The engine controller 92 estimates the temperature of the end portion of the fixing device 50 by the heat storage status determination unit 434 based on the heat storage status of the non-sheet passing portion in the printing status before the (current) printing. When the engine controller 92 estimates that the temperature of the end portion of the fixing device 50 is equal to or higher than the predetermined temperature, the engine controller 92 determines that the fixing device 50 is not damaged, advances the process to S505, and removes the heating element 54b2. select. That is, in the first embodiment, the heating element 54b2 is used for the fixing process of the sheet P when it can be determined that the fixing device 50 is not damaged even if the sheet width Lp is larger than the length L2.

Here, as an example of damage that occurs in the fixing device 50, buckling failure that occurs in the film 51 can be cited. Buckling breakdown is damage that occurs due to a temperature difference between the end portion and the central portion of the fixing device 50 when printing is continued in a state where the end portion of the fixing device 50 is cold and the central portion of the fixing device 50 is hot. .. Therefore, the engine controller 92 does not damage the fixing device 50 if the end portion of the fixing device 50 is higher than or equal to the temperature TD, but damages the fixing device 50 if the temperature is lower than the temperature TD (below a predetermined temperature). Determine that there is a risk of

To determine whether or not the fixing device 50 may be damaged, the end of the fixing nip portion N after the sheet P having a width larger than the length L2 has passed through the fixing nip portion N using the heating element 54b2. It is determined by the temperature TEE of the part. It is assumed that the engine controller 92 controls the heat generating element 54b to the temperature TS during image formation (that is, during fixing processing). The temperature TSC of the central portion of the fixing nip portion N and the temperature TSE of the end portion of the fixing nip portion N before the sheet P passes through the fixing nip portion N are within the length L2 when the heating element 54b2 is selected. It is controlled by 92 to maintain the temperature TS. Therefore, the temperature TEC of the central portion of the fixing nip portion N after the sheet P has passed through the fixing nip portion N is represented by the following equation (1). That is, in the central portion of the fixing nip portion N, the temperature TSC before passing the sheet P and the temperature TEC after passing the sheet P are both maintained at the temperature TS.
TEC=TSC=TS... Formula (1)

On the other hand, outside the length L2, the temperature is not controlled by the engine controller 92, the heat is taken by the paper P, and the temperature drops to TEE. Therefore, hereinafter, when the term is referred to as an end of the fixing nip portion N (or the fixing device 50), the end means an area outside the length L2 of the heating element 54b2. At this time, it is necessary to prevent the temperature TEE from falling below the temperature TD at which the fixing device 50 may be damaged. Therefore, the temperature TEE is calculated by using the temperature change amount TF (hereinafter referred to as a temperature gradient) TF in consideration of the degree of the heat being deprived by the paper P passing through the fixing nip portion N, that is, the temperature drop. It is represented by (2). That is, at the end portions (both end portions) of the fixing nip portion N, heat is taken by the paper P, and the temperature decreases by the temperature gradient TF from the temperature TSE before the paper P passes, and after the paper P passes. Temperature TEE.
TEE=TSE-TF... Formula (2)

The engine controller 92 estimates the temperature TEE of the end portion of the fixing nip portion N from the equation (2) by the heat storage state determination unit 434 and determines whether the fixing device 50 is damaged or not. In this way, the engine controller 92 estimates the temperature TEE of the end portion of the fixing nip portion N when performing the fixing process on the sheet P having a width wider than that of the heating element 54b2 by using the heating element 54b2. The presence or absence of damage to the fixing device 50 is determined.

In the first embodiment, the fixing temperature sensor 59 is provided in the central portion of the heater 54, but not provided at the end portion of the heater 54. Therefore, the temperature TEE of the end portion of the fixing nip portion N uses the estimated temperature experimentally determined from the printing information performed before printing the paper P. As another embodiment, a temperature sensor is provided at the end of the heater 54, and the engine controller 92 determines whether or not the fixing device 50 may be damaged based on the temperature detected by the temperature sensor. Good.

Returning to the explanation of FIG. When the engine controller 92 determines in S503 that the image width Li is longer than the length L2 (Li>L2), the process proceeds to S506. In S506, the engine controller 92 selects the heating element 54b1 as the heating element 54b used when performing the fixing process on the sheet P, and advances the process to S507.

If the engine controller 92 determines in S504 that the temperature TEE at the end of the fixing nip portion N is lower than the temperature TD (TEE<TD), the process proceeds to S506. In this case, the engine controller 92 determines that if the narrow heating element 54b2 is selected, some damage may occur in the area outside the heating element 54b2, and selects the heating element 54b1 in S506. , And advances the processing to S507.

In S507, the engine controller 92 switches to the heating element 54b2 or the heating element 54b1 selected in S505 or S506, or one of the heating elements 54b. In addition, it is preferable that the execution timing of the first exemplary embodiment is performed before the sheet P currently being printed is conveyed to the fixing device 50. Further, the processing of the first embodiment may be performed at the start of printing, may be performed during continuous printing, or may be performed when the next print instruction is given during the print end operation. Good.

From the above, when the width of the paper P is wide and the width of the image to be printed is narrow, the heating element 54b is selected according to the degree of warming of the fixing device 50 and the size of the image to be printed. As a result, the toner image is fixed by heating by the heater 54 in the image area, and the paper P can be conveyed in the non-image area without damaging the fixing device 50 due to the residual heat of the fixing device 50. As a result, it is possible to reduce the electric power supplied to the heater at the time of image formation while preventing the occurrence of an image defect due to the defective fixing of the unfixed toner image.

As described above, according to the first embodiment, it is possible to reduce the power supplied to the heater during image formation.

In the first embodiment, when the width of the sheet P is wide and the width of the image to be printed on the sheet P is narrow, if the fixing device 50 is in a warm state, the heating element 54b2 having a smaller width is switched to reduce the width. The method of using the narrower heating element 54b2 for the fixing process has been described. However, the amount of change in temperature (that is, the temperature gradient) when the sheet P is nipped and conveyed in the fixing nip portion N differs depending on the type of the sheet P that is actually conveyed. For example, when the paper P is thick paper (for example, paper having a grammage of 120 [g/m ² ] or more), the fixing device is larger than standard paper (for example, paper having a grammage of 75 [g/m ² ]). Absorbs a lot of heat from 50. On the other hand, when the paper P is a thin paper (for example, paper having a basis weight of 60 [g/m ² ] or less), the rate of absorbing heat from the fixing device 50 is smaller than that of standard paper. That is, the temperature gradient TF is larger in thick paper than in standard paper, and smaller in thin paper than in standard paper. Therefore, it is desirable to consider the type of the paper P as the temperature gradient TF when the heat is taken away by the paper P passing through the fixing nip portion N.

If the temperature gradient TF is assumed to be thick paper in advance, the number of cases of selecting the heating element 54b2 that reduces power consumption when transporting thin paper is reduced. On the other hand, if the temperature gradient TF assuming thin paper is used in advance, the actual temperature change amount becomes large when thick paper is conveyed, and the temperature TEE at the end of the fixing nip portion N may damage the fixing device 50. It may fall below a certain temperature TD. Therefore, in the second embodiment, the temperature gradient TF is set for each type of the sheet P by considering the type of the sheet P. Then, a method of increasing the accuracy in estimating the end portion TEE using the above-described formula (2) and selecting the heating element 54b that reduces power consumption will be described.

[Explanation of functional block diagram]
FIG. 5 is a diagram showing functional blocks related to the engine controller 92, the external device 400, the video controller 91, and the hardware 403. The engine controller 92 has a temperature estimation unit 620 and a paper type identification unit 621 in addition to the functional blocks described in the first embodiment. The temperature estimation unit 620 estimates the temperature of the end portion of the fixing device 50 after the paper P is conveyed in the fixing nip portion N. Further, the hardware 403 has a paper type identification sensor 60 in addition to the hardware of the first embodiment. Regarding FIG. 5, the same components as those in FIG. 3 of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. The points different from the first embodiment will be specifically described below.

A paper type identification sensor 60, which is a detection unit that detects the type of recording material, is provided between the registration roller 18 and the secondary transfer roller 25, for example. The paper type identification sensor 60 irradiates the first surface (hereinafter, referred to as the front surface) side of the paper P sent from the cassette 16 and conveyed with light from a light source such as a light emitting diode (hereinafter, referred to as LED). The paper type identification sensor 60 measures light reflected from the front surface of the paper P (hereinafter referred to as reflected light), and then irradiates light from the second surface (hereinafter referred to as back surface) side of the paper P to transmit the paper P. Measure the light. The paper type identification sensor 60 outputs a signal corresponding to the measurement result (hereinafter, also referred to as a detection result).

The paper type identification unit 621 identifies the type of the paper P from at least two types of paper such as plain paper, thick paper, thin paper, and glossy paper based on the detection result input from the paper type identification sensor 60. To do. The heat storage state determination unit 434 estimates the heat storage state in the fixing device 50 from the target temperature determined based on the type of the paper P identified by the paper type identification unit 621 and the size information of the paper P. The temperature estimation unit 620 makes the next determination from the temperature TEE of the end portion of the fixing device 50 determined by the heat storage state determination unit 434 and the gradient temperature TF generated according to the type of the sheet P identified by the sheet type identification unit 621. To do. That is, the temperature estimation unit 620 determines whether or not the temperature at the end of the fixing device 50 after the paper P is conveyed is equal to or higher than the temperature TD at which the fixing device 50 may be damaged.

[Explanation of Example 2]
The flow of the heating element switching process in the second embodiment will be described with reference to the flowchart of FIG. The same steps as those in the first embodiment are designated by the same step numbers and the description thereof is omitted. When the engine controller 92 determines in S501 that the paper width Lp is greater than the length L2 of the heating element 54b2 (Lp>L2), and determines in S503 that the image width Li is less than or equal to the length L2 (Li≦L2). , The process proceeds to S710. In S710, the engine controller 92 estimates the temperature TSE of the end portion of the fixing device 50 outside the heating element 54b2 from the heat storage state of the film 51, the pressure roller 53, and the heater 54. At this time, the engine controller 92 uses the temperature gradient TFP of the fixing device 50 according to the type (type) of the paper P identified by the paper type identification unit 621 to determine the temperature TEE of the end portion of the fixing device 50 after the paper P is conveyed. Is calculated using the following equation (3).
TEE=TSE-TFP... Formula (3)
In the second embodiment, the temperature gradient TFP is classified for each paper type according to, for example, plain paper, thin paper, thick paper, glossy paper, etc., but at least two or more kinds may be used regardless of such classification. Good.

In S711, the engine controller 92 determines whether or not the temperature TEE of the end portion of the fixing device 50 calculated in S710 is equal to or higher than the temperature TD, that is, the temperature TEE of the end portion of the fixing device 50 may damage the fixing device 50. Determine if there is a certain temperature. If the engine controller 92 determines in step S711 that the temperature TEE of the end portion of the fixing device 50 is equal to or higher than the temperature TD (TEE≧TD), the process proceeds to step S505, and in step S505 it is determined that the fixing device 50 is not damaged. Then, the heating element 54b2 is selected. When the engine controller 92 determines in S711 that the temperature TEE of the end portion of the fixing device 50 is lower than the temperature TD, the process proceeds to S506. In this case, the engine controller 92 determines that the fixing device 50 may be damaged if the heating element 54b2 is used in the fixing process, selects the heating element 54b1 in S506, and advances the process to S507.

From the above, when the width Lp of the paper P is wide and the image width Li to be printed is narrow, whether to select the heating element 54b according to the image size to be printed is switched according to the type of the paper P to be conveyed. As a result, it is possible to reduce the electric power supplied to the heater at the time of image formation while preventing the occurrence of an image defect due to the defective fixing of the unfixed toner image.

As described above, according to the second embodiment, the electric power supplied to the heater during image formation can be reduced.

The image forming apparatuses of Examples 1 and 2 have been described as having a configuration including two types of heating elements having different lengths in the longitudinal direction. In the third embodiment, there are three types of heating elements having different lengths in the longitudinal direction. In the third embodiment, when the width of the sheet P is wide and the width of the image printed on the sheet P is narrow, the width is narrower than that of the wider heating element 54m1 if the fixing device 50 is in a warm state. A method of switching to the heating element and used for the fixing process will be described. The image forming apparatus according to the third embodiment has the same configuration as that of the first embodiment, and only different parts will be described.

[Explanation of heater and power controller]
(heater)
The heater 54 will be described in detail with reference to FIG. 7. The heater 54 includes a substrate 54a, a plurality of heat generating elements 54m1 to 54m3, contacts 54n1 to 54n4, and a protective glass layer 54e. Heating elements 54m1 to 54m3 and contacts 54n1 to 54n4 are formed on the substrate 54a, and a protective glass layer 54e is formed on the heating elements 54m1 to 54n4 to secure insulation between the heating elements 54m1 to 54m3 and the film 51. The heating element 54m1 which is the first heating element, the heating element 54m2 which is the second heating element, and the heating element 54m3 which is the third heating element have different lengths in the longitudinal direction. Specifically, the length of the heating element 54m1 in the longitudinal direction is L1, the length of the heating element 54m2 in the longitudinal direction is L2, and the length of the heating element 54m3 in the longitudinal direction is L3. The length L1, the length L2, and the length L3 have a relationship of L1>L2>L3. The length L1 of the heating element 54m1 is a length capable of fixing the sheet P having the maximum width (hereinafter referred to as the maximum sheet passing width) among the sheets P that can be printed (or conveyed) by the image forming apparatus. It is Hereinafter, the paper P having the length L1 is also referred to as a paper P having an L1 width, the paper P having a length L2 is also referred to as a paper P having an L2 width, and the paper P having a length L3 is also referred to as a paper P having an L3 width. The heating element 54m1 is electrically connected to the contacts 54n1 and 54n4, the heating element 54m2 is electrically connected to the contacts 54n2 and 54n4, and the heating element 54m3 is electrically connected to the contacts 54n2 and 54n3. .. That is, the contact 54n2 is a contact commonly connected to the heating elements 54m2 and 54m3, and the contact 54n4 is a contact commonly connected to the heating element 54m1 and the heating element 54m2.

The heating elements 54m1 are one heating element 54m1 arranged at one end of the substrate 54a in the lateral direction and the other heating element 54m1 arranged at the other end. These heating elements 54m are arranged in the lateral direction in the order of one heating element 54m1, heating element 54m2, heating element 54m3, and the other heating element 54m1.

The fixing temperature sensor 59 is located on the surface opposite to the protective glass layer 54e with respect to the substrate 54a, is installed at the center position in the longitudinal direction of the heating elements 54m1 to 54m3, and is in contact with the substrate 54a. The fixing temperature sensor 59 is, for example, a thermistor, detects the temperature of the heater 54, and outputs the detection result to the engine controller 92. The engine controller 92 controls the temperature during the fixing process based on the detection result of the fixing temperature sensor 59.

(Power control unit)
FIG. 7 also shows a power control unit 97 which is a control circuit of the fixing device 50. The electric power control unit 97 of the fixing device 50 includes heating elements 54m1 to 54m3 (heater 54), an AC power supply 55, bidirectional thyristors (hereinafter referred to as triacs) 56a and 56b, and a heating element switch 57 that is a switching unit.

The heating element switching unit 57 has a contact 57a connected to the contact 54n2, a contact 57b1 connected to the triac 56b and the contact 54n3, and a contact 57b2 connected to the AC power supply 55 and the contact 54n4. When the contact 57a and the contact 57b1 are connected to each other, the heating element switching unit 57 is in a state in which power can be supplied to the heating element 54m2, and when the contact 57a and the contact 57b2 are connected, heat is generated. Electric power can be supplied to the body 54m3.

The triac 56a has one end connected to the contact 54n1 and the other end connected to the AC power supply 55 and the triac 56b. When the triac 56a conducts, electric power is supplied to the heating element 54m1. The triac 56b has one end connected to the AC power supply 55 and the triac 56a, and the other end connected to the contact 57b1 and the contact 54n3 of the heating element switch 57. When the triac 56b becomes conductive, electric power is supplied to one of the heating element 54m2 and the heating element 54m3 depending on the state of the heating element switching device.

[Explanation of Example 3]
FIG. 8 is a flowchart showing the heating element switching control of the third embodiment. In S800, the engine controller 92 determines whether the print information of the page to be printed next is received from the video controller 91. The print information here includes the image size to be printed on the paper P and the size of the paper P. The size of the paper P may be information based on the detection results of the width sensors 160m and 160n. If the engine controller 92 determines in step S800 that the next print information is received, the process proceeds to step S801. If it is determined that the next print information is not received, the process ends.

In step S801, the engine controller 92 refers to the print information received in step S800, and determines whether the paper width Lp, which is the length of the paper P in the width direction, is less than or equal to the length L2 of the heating element 54m2 (Lp≦L2). .. When the engine controller 92 determines in S801 that the sheet width Lp is the second recording material having the length L2 or less (Lp≦L2), the process proceeds to S810. When the engine controller 92 determines in S801 that the paper width Lp is the first recording material larger than the length L2 (Lp>L2), the process proceeds to S803.

In step S810, the engine controller 92 refers to the print information received in step S800, and determines whether the paper width Lp, which is the length of the paper P in the width direction, is less than or equal to the length L3 of the heating element 54m3 (Lp≦L3). .. When the engine controller 92 determines in S810 that the paper width Lp is the third recording material having the length L3 or less (Lp≦L3), the process proceeds to S813. When the engine controller 92 determines in S810 that the paper width Lp is the second recording material larger than the length L3 (L3<Lp), the process proceeds to S811. In S813, the engine controller 92 selects the heating element 54b3 according to the width (Lp≦L3) of the sheet P as the heating element 54b used for fixing the sheet P.

In step S803, the engine controller 92 refers to the print information received in step S800, and determines whether the image width Li, which is the size in the width direction of the image transferred onto the sheet P, that is, the image fixed on the sheet P, is the length L2 or less. Determine whether or not. If the engine controller 92 determines in S803 that the image width Li is equal to or less than the length L2 (Li≦L2), the process proceeds to S804. When the engine controller 92 determines in S803 that the image width Li is longer than the length L2 (Li>L2), the process proceeds to S806.

In S804, when the engine controller 92 selects the heating element 54b2 having a width narrower than that of the sheet P based on the heat storage states of the film 51, the pressure roller 53, and the heater 54, the temperature of the non-sheet passing portion is a predetermined temperature. It is determined whether or not it becomes a certain TD1 or more. That is, the engine controller 92 determines whether or not the temperature is higher than the temperature (TD1) at which the fixing device 50 is damaged in the non-sheet passing portion. When the engine controller 92 determines in S804 that the temperature TEE at the end of the fixing nip portion N is lower than the temperature TD (TEE<TD), the process proceeds to S806. In this case, the engine controller 92 determines that if the narrow heating element 54b2 is selected, some damage may occur in the area outside the heating element 54b2, and selects the heating element 54b1 in S806. , And advances the processing to S807.

If the engine controller 92 determines in step S804 that the temperature TEE at the end of the fixing nip portion N is lower than the temperature TD1 (TEEE≧TD1), the process advances to step S811. In this case, the engine controller 92 determines that even if the narrow heating element 54b2 is selected, some damage does not occur in the area outside the heating element 54b2.

In step S811, the engine controller 92 refers to the print information received in step S800, and determines whether the image width Li, which is the size in the width direction of the image transferred onto the sheet P, that is, the image fixed on the sheet P, is the length L3 or less. Determine whether or not. When the engine controller 92 determines in S811 that the image width Li is less than or equal to the length L3 (Li≦L3), the process proceeds to S812. If the engine controller 92 determines in S811 that the image width Li is longer than the length L3 (Li>L3), the process proceeds to S805.

In S812, when the engine controller 92 selects the heating element 54b3 having a width narrower than that of the sheet P based on the heat storage states of the film 51, the pressure roller 53, and the heater 54, the temperature of the non-sheet passing portion is a predetermined temperature. It is determined whether or not it becomes a certain TD2 or more. That is, the engine controller 92 determines whether or not the temperature is higher than the temperature (TD2) at which the fixing device 50 is damaged in the non-sheet passing portion. If the engine controller 92 determines in S812 that the temperature TEE at the end of the fixing nip portion N is lower than the temperature TD2 (TEE<TD2), the process proceeds to S805. In this case, the engine controller 92 determines that if the narrow heating element 54b3 is selected, some damage may occur in the area outside the heating element 54b3, and selects the heating element 54b2 in S805. , And advances the processing to S807. If the engine controller 92 determines in step S812 that the temperature TEE at the end of the fixing nip portion N is equal to or higher than the temperature TD2 (TEE≧TD2), the process advances to step S813. In this case, the engine controller 92 determines that even if the narrow heating element 54b3 is selected, some damage does not occur in the area outside the heating element 54b3.

In S807, the engine controller 92 switches to the heating element 54b2, the heating element 54b1, or the heating element 54b3 selected in S805, S806 or S813. In addition, it is desirable that the implementation timing of the third embodiment is performed before the sheet P currently being printed is conveyed to the fixing device 50. Further, the processing of the third embodiment may be performed at the start of printing, may be performed during continuous printing, or may be performed when the next print instruction is issued during the print end operation. Good.

(About the temperature at the end of the fixing temperature)
Here, as an example of damage that occurs in the fixing device 50, there is buckling failure that occurs in the film 51 as in the first embodiment. The temperature at which buckling failure occurs may change depending on the temperature distribution in the longitudinal direction. Therefore, the temperature TD1 when the heating element 54b2 is selected and the temperature TD2 when the heating element 54b3 is selected may change.

From the above, when the width of the paper P is wide and the width of the image to be printed is narrow, the heating element 54b is selected according to the warming degree of the fixing device 50 and the size of the image to be printed. As a result, the toner image is fixed by heating by the heater 54 in the image area, and the paper P can be conveyed in the non-image area without damaging the fixing device 50 due to the residual heat of the fixing device 50. As a result, it is possible to reduce the electric power supplied to the heater at the time of image formation while preventing the occurrence of an image defect due to the defective fixing of the unfixed toner image.

As described above, according to the third embodiment, the electric power supplied to the heater during image formation can be reduced.

50 fixing device 51 film 53 pressure roller 54 heaters 54b1 and 54b2 heating element 57 heating element switching device 92 engine controller

Claims (12)

A heater having at least a first heating element and a second heating element having a width that is a longitudinal length shorter than that of the first heating element;
A first rotating body heated by the heater;
A second rotating body that forms a nip portion together with the first rotating body;
Switching means for switching a power supply path for supplying power to the first heating element or the second heating element;
Control means for controlling the switching means,
A fixing device for fixing an unfixed toner image carried on a recording material in the nip portion by heat when the recording material passes through the nip portion,
The control means carries the width, which is the length in the longitudinal direction, carried by the first recording material, the width being the length in the longitudinal direction of the recording material, which is longer than the width of the second heating element. When the fixing process is performed on an image having a width equal to or smaller than the width of the second heating element, the temperature of the area outside the area corresponding to the second heating element in the nip portion and through which the first recording material passes. The fixing device is configured to select whether to perform the fixing process using the first heating element or the fixing process using the second heating element. The control means fixes the image formed on the first recording material to the first recording material by using the second heating element, and the width of the image is equal to or less than the width of the second heating element. When the temperature of the end portion in the longitudinal direction of the nip portion after the processing is equal to or higher than a predetermined temperature, the fixing processing to the first recording material is performed using the second heating element. The fixing device according to claim 1, wherein: Even if the width of the image formed on the first recording material is equal to or smaller than the width of the second heating element, the control means fixes the image on the first recording material using the second heating element. When the temperature of the end portion of the nip portion after the processing is lower than the predetermined temperature, it is possible to perform the fixing processing on the first recording material using the first heating element. The fixing device according to claim 2, wherein the fixing device is a fixing device. The controller controls the temperature of the central portion and the temperature of the end portion of the nip portion in the longitudinal direction before and after the first recording material passes through the nip portion, and the first recording material is The nip after the fixing process is performed on the first recording material using the second heating element based on the degree of the temperature drop at the end of the nip due to passing through the nip. The fixing device according to claim 3, wherein the temperature of the end portion of the portion is estimated. Equipped with detection means to detect the type of recording material,
The fixing device according to claim 4, wherein the control unit sets the degree based on a result detected by the detection unit. The fixing device according to claim 2, wherein the end portion of the nip portion is a region outside the second heating element in the longitudinal direction. When the fixing process is performed on the second recording material in which the width of the recording material is equal to or less than the width of the second heating element, the control unit uses the second heating element to perform the second recording material. The fixing device according to any one of claims 1 to 6, wherein a fixing process is performed on the fixing device. The fixing device according to any one of claims 1 to 7, further comprising a third heating element having a width shorter than that of the second heating element. A substrate on which the first heating element, the second heating element, and the third heating element are arranged,
The first heating element includes one of the first heating elements arranged at one end portion in the lateral direction of the substrate and the other of the first heating element arranged at the other end portion. And
The one first heating element, the second heating element, the third heating element, and the other first heating element are arranged in this order in the lateral direction. The fixing device according to item 8. The fixing device according to any one of claims 1 to 9, wherein the first rotating body is a film. The heater is provided so as to contact the inner surface of the film,
The fixing device according to claim 10, wherein the nip portion is formed by the heater and the second rotating body via the film. Image forming means for forming an unfixed toner image on the recording material,
The fixing device according to any one of claims 1 to 11, which fixes an unfixed toner image on a recording material,
An image forming apparatus comprising:

Images