JPH11272099A - Heat fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat fixing device capable of heat fixing a unfixed toner image on an image supporting body by an appropriate fixing heat quantity by excellently corresponding to the change of conditions imparting the influence to an image fixing property, demonstrating the stable fixing property, preventing the structure from becoming very complex and a large size, and manufacturing simply and compactly. SOLUTION: This heat fixing device, as the heat fixing device capable of making an unfixed toner image Ti heat fixed on an image supporting body 7 holding the unfixed toner image Ti, is provided with the heating roller 1 and a pressure roller 4 (or fixing roller 32 and pressure roller 34) providing a fixing nip part N for heat fixing the image Ti on the image supporting body, a preliminary heating heater 8 mounted on the upstream side of a fixing nip part N in the image supporting body transporting direction (α), a guide member 9 being set opposite to the preliminary heating heater for guiding the image supporting body 7 to the fixing nip part N, and a space adjusting device 18 capable of adjusting the space between the preliminary heating heater and the guide member in accordance with conditions imparting the influence to the image fixing property.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing device for heat fixing an unfixed toner image on an image support holding the image in an image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art A heat roller system is generally used in a heat fixing device in an image forming apparatus such as a copying machine or a printer. In the heat fixing device of the heat roller type, at least one is a heating roller, using a pair of fixing rollers pressed against each other, providing a fixing nip portion for image fixing at a mutual press contact nip portion of the fixing roller pair, The image is heated and fixed to the image support by passing the image support holding the unfixed toner image through the fixing nip. The fixing roller pair usually includes a heating roller and a pressure roller pressed against the heating roller.

However, the following problems have been pointed out with respect to such a heat roller type heat fixing device.
That is, conditions affecting the image fixing performance of the fixing roller pair, in other words, the type (material, thickness, etc.) of the image support, the amount of toner adhered on the image support, the environmental temperature and humidity around the fixing device, the fixing There is a problem that the fixing state of an image fluctuates due to a fusing property variation element such as the temperature of the pressure roller in the roller pair.

For example, in an electrophotographic full-color image forming apparatus, a multi-toner image formed of cyan, magenta, yellow, and black toners formed on an image support is fixed to the image support. When fixing a multi-toner image, a larger amount of heat is required than when fixing is performed on an image support. At this time, assuming that the fixing temperature (heating roller temperature) in the fixing device is the same, even if the monochrome toner image can be fixed without any trouble, the multi-toner image may have a fixing failure due to insufficient heat, or the toner with the fixing failure may be defective. Transfer to the fixing roller may occur. Alternatively, even if a multi-toner image can be fixed without any trouble, a monochrome toner image has too much heat and melts too much toner, thereby causing image defects such as image collapse and unnecessary gloss. In some cases, the toner may transfer to the fixing roller due to excessive melting of the toner.

In order to solve such a problem, the toner and the fixing device conditions must be universally fixed so as to be able to cope with a change in conditions affecting the image fixing property, or the image fixing property must be fixed. It is necessary to change the temperature of the fixing roller according to the conditions that affect the temperature. However, the former is very difficult or almost impossible in practice.

[0006] Further, the change of the fixing roller temperature takes too much time, and it takes time to stabilize the temperature after the change. Therefore, it is not possible to respond quickly to the condition change, and the responsiveness to the condition change cannot be improved. Is bad. JP-A-59-2111072 and JP-A-59-21107.
No. 3 teaches that a pre-heating device for pre-heating an image support and an unfixed toner image held on the image support is provided upstream of the pressure nip portion of the fixing roller pair in the image support transport direction. .

[0007] When such a preheating device is provided, the conditions that affect the image fixing property are more greatly affected by the combination of the temperature control of the preheating device and the control of the fixing roller temperature than when the preheating device is not provided. However, even in this case, it takes time to change the heating temperature and the fixing roller temperature by the pre-heating device, and it takes time to stabilize the temperature after the change. Cannot respond quickly, and the response to a change in conditions is poor.

If the heat capacity of the components of the pre-heating device and the fixing roller is reduced in order to quickly change the temperature, the temperature stability becomes worse and the temperature control becomes complicated. Japanese Patent Application Laid-Open No. 6-230626 discloses a technique for detecting a thickness of an image support and changing an angle of a guide plate at an entrance of a fixing device and a temperature of a fixing roller in accordance with the thickness to perform satisfactory image fixing. is suggesting. However, also in this case, the change in the fixing roller temperature is poor in response to the change in the condition, and the response to the change in the condition affecting the image fixability is limited as compared with the case where the preheating device is employed. .

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to heat-fix an unfixed toner image to an image support with an appropriate amount of fixing heat in response to a change in conditions that affect image fixability. It is another object of the present invention to provide a heat fixing device that can be simply and compactly manufactured without causing a significant increase in the structure and complexity of the structure.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is a heat fixing device for heating and fixing an unfixed toner image on an image support holding the image, wherein the unfixed toner image is held. A pair of fixing rollers for providing a fixing nip portion for heating and fixing the image to the image support by passing through the image support, and the unfixed roller disposed upstream of the fixing nip portion in the image support transport direction. A preheating device for a toner image and an image support holding the toner image,
A guide member that is installed to face the preheating device and guides the image support to the fixing nip portion, and adjusts an interval between the preheating device and the guide member according to a condition that affects image fixability. A heating and fixing device, comprising:

The following two types of the heat fixing device according to the present invention can be exemplified. A heat fixing device (heat roller type heat fixing device) in which at least one of the fixing roller pairs is a heating roller, and the fixing roller pairs are directly pressed against each other to form the fixing nip portion. The preheating device winds an endless fixing belt around one of the fixing roller pair and a roller disposed upstream of the roller in the image carrier transport direction, and the two rollers around which the belt is wound. At least one of which is a heating roller, the belt portion being upstream of the fixing roller pair in the image carrier transport direction, and the belt portion on the one roller of the fixing roller pair and the fixing roller pair A heat fixing device in which the other roller is pressed against each other to provide the fixing nip portion, and the guide member faces the fixing belt.

It is assumed that the fixing belt in the belt-type fixing device withstands applied heat. The fixing belt is
It is desirable that the surface is formed of an elastically deformable material having heat resistance. Further, it is still more desirable to have releasability from the toner. In any of the heat fixing devices, each of the fixing rollers has heat resistance enough to withstand applied heat. It is desirable that at least one of the fixing roller pairs has a surface formed of a heat-resistant, elastically deformable material. It is still more desirable that the surface of the roller that comes into contact with the toner has a releasability from the toner.

In any case, the conditions affecting the image fixing property include: a) the type of the image support, b) the environmental temperature around the heat fixing device, c) the environmental humidity around the heat fixing device, and d). E) the temperature of the guide member, e) the temperature of at least one roller constituting the fixing roller pair, and f) the one-side mode in which the image is fixed on one surface of the image support or the two-side mode in which the image is fixed on both surfaces. Paper mode, g) toner adhesion amount on the image support, h) color mode of whether the unfixed toner image is a monochrome image or multiple color image, i) whether or not the image support is passing through the fixing nip portion And j) at least one of the passage time intervals between the image supports when a plurality of image supports are continuously passed through the fixing nip portion.

In the heat-fixing device of the present invention, the distance between the pre-heating device and the guide member may be adjusted according to at least one condition that affects image fixability. The image forming apparatus may further include a control device that controls the interval adjusting device so as to set the direction in which an appropriate amount of fixing heat is applied to the body. In this case, as the control device, a device that controls the interval adjusting device according to at least one of the conditions a) to j) that affect the image fixing property can be exemplified.

The heat fixing apparatus according to the present invention can be used by mounting it on an image forming apparatus such as an electrophotographic system. The unfixed toner image formed on the image support is guided together with the image support by an image support guide member installed on the upstream side in the image support transport direction from the fixing nip portion and can enter the fixing nip portion. When the sheet passes over the guide member, the sheet is preheated by a preheating device installed opposite to the guide member, and then enters the fixing nip portion, where the unfixed toner image is heated and fixed on the image support. .

The preheating device winds an endless fixing belt around one of the fixing roller pair and a roller disposed upstream of the roller in the image support conveying direction, and winds the belt. At least one of the two rollers is a heating roller, and the belt portion on the upstream side of the fixing roller pair in the image support transport direction with respect to the fixing roller pair, the belt portion on the one roller of the fixing roller pair and the fixing roller When the other roller of the pair is pressed against each other to provide the fixing nip portion, the heating roller heats the endless fixing belt, and the heated belt is used for preheating and fixing heating at the fixing nip portion. Contribute.

When the heating temperature of the unfixed toner image is changed in accordance with the above-mentioned change in the condition which affects the image fixability, the pre-heating device and the image are adjusted by the interval adjusting device in accordance with the change in the condition. What is necessary is just to adjust the space | interval with a support body guide member. As a result, the amount of heat applied in the preheating is adjusted, and thus the preheating temperature of the unfixed toner image and the image support is adjusted, whereby the image can be satisfactorily fixed with an appropriate amount of fixing heat as a whole. In addition, the distance between the guide member and the pre-heating device can be quickly changed by the distance adjusting device, so that the amount of heat applied with good responsiveness to changes in conditions can be optimized.

When a control device for controlling the interval adjusting device is provided, the interval adjusting device can properly adjust the interval between the preheating device and the guide member with an appropriate amount of fixing heat under the instruction of the control device. Set the direction to fix the image. Further, since the heat fixing device of the present invention is provided with a preliminary heating device, for example, when heat-fixing a multi-toner image composed of each color toner formed on the image support to the image support in color image formation, By using the pre-heating device, the heat energy given to the fixing nip can be reduced accordingly.Therefore, if there is no such pre-heating device, the fixing roller diameter is increased to increase the fixing nip width, and In order to prevent over-melting of the toner, the required amount of heat must be applied without raising the temperature of the fixing nip too much, and the diameter of the fixing roller does not have to be particularly large, and the thermal energy applied at the fixing nip Overmelting of the toner can be prevented, and the overmelting of the toner on the fixing roller or the endless fixing belt wound around the fixing roller can be prevented. The amount of release agent such as silicone oil that may be applied to the fixing roller or belt to prevent transfer of toner can be small, and the release agent application mechanism can be simplified and downsized. Can be simplified and made compact.

The spacing adjusting device moves at least one of the preheating device and the image support guide member in a direction for adjusting the spacing. The image support is generally a paper sheet, but other materials and thicknesses such as a synthetic resin overhead projector (OHP) sheet can be used. Various sizes can be used.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic side view showing a configuration of an example of a heat fixing device according to the present invention. This heat fixing device is mounted in a copying machine here. Illustration of the overall configuration of the copying machine is omitted.

The heat fixing device has a fixing roller pair including a heating roller 1 and a pressure roller 4. The heating roller 1 is formed by forming a heat-resistant and releasable elastic material layer 1b on the surface of a metal core roller 1a. The core roller 1a has a heater 2 built therein. The elastic material layer 1b is made of silicone rubber here. A temperature sensor 3 is in contact with the surface of the heating roller 1.

The pressure roller 4 is formed by forming a heat-resistant and releasable elastic material layer 4b on the surface of a metal core roller 4a. The core roller 4a has a heater 5 built therein. The elastic material layer 4b is made of silicone rubber here. The temperature sensor 6 is also in contact with the surface of the pressure roller 4. The pressing roller 4 is pressed against the heating roller 1 by a pressing device including a pressing spring (not shown), so that a pressing nip portion (fixing nip portion) N is formed between the rollers 1 and 4.

The heating roller 1 can receive a driving force from a motor in an image forming apparatus in which the fixing device is mounted via a transmission mechanism (not shown), and can rotate counterclockwise in the drawing. The pressure roller 4 is rotated by the rotation of the heating roller 1 and can rotate clockwise in the drawing. A preliminary heater 8 is disposed upstream of the fixing nip N in the transport direction α of the image support 7. Preheating heater 8
Includes a sheet heating element, which can preheat the image support 7 passing therethrough and the unfixed toner image Ti held thereon. Further, a guide member 9 that guides the image support 7 to the fixing nip portion N facing the preliminary heater 8 is provided.

Although the position of the guide member 9 is fixed, the preliminary heater 8 can be moved up and down with respect to the guide member 9, whereby the distance L between the preliminary heater 8 and the guide member 9 can be adjusted. It has become. That is, FIG.
As shown in FIG. 7, a pair of rack gears 181 are provided upright on the upper surface of the preliminary heater 8, and a pinion gear 182 meshes with each rack gear 181. The pair of pinion gears 182 are fitted and supported on a common shaft 180, and the shaft 17 can be driven forward and reverse by the motor 17. The shaft 180 is rotatably supported by a bearing at a fixed position (not shown), and the motor 17 is fixed to a member (not shown). The rack gear 181, the pinion gear 182, the motor 17, etc.
And an interval adjusting device 18 for adjusting the interval between the two.

The preheater 8 is provided with a temperature sensor 10. Image support transport direction α of fixing nip N
, Sheet discharge guide members 11 and 12 are provided on the downstream side,
Further, a pair of discharge rollers 13 and 14 are provided downstream thereof. An oil application roller 15 is in contact with the heating roller 1 so as to be driven to rotate, and an oil supply rotating member 16 is in contact with the roller 15 so as to be driven to rotate. The oil supply member 16 is formed by winding a heat-resistant paper 16b impregnated with silicone oil on the surface of a cored bar 16a, and providing a synthetic leather layer 16c on the surface for regulating the amount of oil applied. Silicone oil as a release agent is supplied from the oil supply member 16 to the oil application roller 15, and the oil is applied from the roller 15 to the surface of the heating roller 1. The oil supply member 16 is held by a holder (not shown) and can be detached from the fixing device.

FIG. 3 is a block diagram schematically showing a control circuit for adjusting the position of the preliminary heater 8. As shown in FIG. 3, this fixing device utilizes a control unit 19 for controlling the operation of the entire copying machine. The control unit 19 includes a central processing unit CPU, a RAM 20 for storing control information, a ROM 21 for storing control programs and control data, and the like.

The control section 19 includes a heating roller temperature sensor 3, a pressure roller temperature sensor 6, a preliminary heating heater temperature sensor 10, a temperature sensor TS for detecting an environmental temperature, and other sensors 100 in the fixing device. Image support selection key 22 for selecting whether to use plain paper as a signal or an image support or to use an image support other than plain paper such as an overhead projector (OHP) sheet.
, An input signal from a paper-passing mode selection key 23 for selecting one-sided copying, or two-sided copying mode, and a signal such as an input signal from a color mode selection key 24 for selecting a monochrome image forming mode or a color image forming mode. Is input via an input interface (not shown).

On the other hand, a signal for controlling the preheating heater position variable motor 17 in the fixing device, the heating roller heater 2, the pressure roller heater 5, the preheating heater 8, and other various loads 27 of the copying machine is sent from the control unit 19. It is output via an output interface not shown. According to the heating and fixing device described above, the control unit 19 controls the heating roller heater 2, the pressure roller heater 5 based on the temperature information detected by the heating roller temperature sensor 3, the pressure roller temperature sensor 6, and the preliminary heating heater temperature sensor 10. And the preliminary heater 8 is controlled to set the temperatures of the rollers 1, 4 and the preliminary heater 8 to predetermined temperatures, respectively. Here, the preliminary heater 8 is controlled to a constant surface temperature of 160 ° C. The heating roller 1 is controlled at a constant surface temperature of 150 ° C. The pressure roller 4 is controlled at a constant surface temperature of 150 ° C.

The control unit 19 controls the pre-heater position variable motor 17 in accordance with the type of the image support, which is one of the conditions affecting the image fixing property, so that the pre-heater 8 is shown in FIG. It is arranged at the position A or B. At the position A, the distance L between the preliminary heater 8 and the guide member 9 is 10 mm, and at the position B, the distance L is 15 mm. In addition, in other embodiments described later, the space may be arranged at the position C, but at the position C, the distance L between the preliminary heater 8 and the guide member 9 is 20 mm.

The image support 7 holding the unfixed toner image Ti is conveyed from the left in FIG. 1 and guided by the guide member 9 to the fixing nip N. Image support 7
When the unfixed toner image Ti passes over the guide member 9, the toner image Ti is disposed opposite to the guide member, and the position A is set according to the type of the image support selected by the image support selection key 22. Alternatively, the toner is preheated by the preheater 8 disposed at the position B, and the toner is softened to some extent.
In this state, the image support 7 protrudes into a fixing nip N formed by the heating roller 1 and the pressure roller 4. Then, the toner image is sufficiently softened by the pressure and heat in the nip portion, and is fixed to the image support 7. The image support 7 coming out of the nip portion N is guided to discharge roller pairs 13 and 14 by paper discharge guide members 11 and 12, and is discharged by the roller pairs.

In this fixing process, an interval between the pre-heater 8 and the guide member 9 is set so as to give an appropriate amount of fixing heat to the image support 7 and the toner image Ti supported thereon. You. That is, the preheating heater 8 is quickly set to the position B when plain paper is selected by operating the image support selection key 22, and when an image support other than plain paper such as an OHP sheet is selected,
Quickly set to position A. In this regard, the control unit 19
The operation will be described with reference to the flowchart of FIG. The flowchart shown in FIG. 4 shows a preliminary heating heater position setting routine which is a part of a subroutine in a main control routine for controlling the operation of the entire copying machine by the control unit 19.

As shown in FIG. 4, it is determined in step S11 whether or not the image support is plain paper. If plain paper is selected, in step S12 the distance between the preliminary heater 8 and the guide member 9 is set to B. (Interval L = 15 mm). Assuming that the conveying speed of the image support is 100 mm / sec, an image having sufficient fixability without causing offset of the toner to the heating roller can be obtained under these conditions. If other than plain paper is selected as the image support in Step S11 (for example, when an OHP sheet is used), Step S1
In step 3, the distance between the preliminary heater 8 and the guide member 9 is fixed to the position A (interval L = 10 mm) with the shortest interval,
Return to the main control routine.

Under these conditions, sufficient OHP sheet translucency and fixability can be obtained. If the OHP sheet has a large heat capacity and the toner is not sufficiently melted, the toner layer will not be uniformly melted, and if the OHP sheet is passed at the position B of the plain paper, the light transmittance will deteriorate due to insufficient melting of the toner and the fixing failure will occur. Conversely, when plain paper is passed through the OHP sheet at an appropriate position A, a high-temperature offset occurs due to excessive melting of the toner.

By adjusting the distance between the pre-heater 8 and the guide member 9 according to the type of the image support in this way, it is possible to respond to the type of the image support, which is one of the conditions affecting the image fixing property. It is possible to give an appropriate amount of fixing heat to the image support and the toner image in response to good performance, and to exhibit stable fixing performance. Here, the interval between the preheating heater 8 and the guide member 9 is changed by input of the image support type selection key 22. However, a sensor for detecting the type of the image support is provided, and the interval is changed by a signal thereof. May be.

As described above, the position of the pre-heating heater 8 is set in accordance with the type of the image support, the distance L between the heater 8 and the guide member 9 is adjusted, and an appropriate amount of fixing heat as a whole is determined. Although an example of giving the toner image Ti is described, the position and the interval L of the heater 8 are shown in FIG. 4 by changing the temperature of the preliminary heater 8 and the temperature of the heating roller 1 slightly as necessary. The preheating heater position setting routine can be changed to the preheating heater position setting routine shown in each of FIGS. 5 and 7 to 9 and controlled.
In this case, the control unit 19 and a control circuit including the same are configured to perform such an operation.

FIG. 5 shows an example of control in accordance with the sheet passing mode of single-sided copying or double-sided copying selected by the sheet passing mode selection key 23. When this control is performed, the temperatures of the preliminary heater 8, the heating roller 1, and the pressure roller 4 are controlled to the same constant temperatures as in the control of FIG. In this control,
In step S21, it is determined whether or not the sheet passing mode is duplex copying. If single-sided copying is selected, the process proceeds to step S22 and the distance between the preliminary heater 8 and the guide member 9 is set to the position B (interval L = 15 mm). Fixed to. If double-sided copying has been selected, the process proceeds to step S23 if it is the first side in step S23.
At 22, the distance between the preliminary heater 8 and the guide member 9 is fixed to the position B (interval L = 15 mm). In the case of the second surface, the distance between the preliminary heater 8 and the guide member 9 is set to C in step S24.
(Interval L = 20 mm). As a result, in the case of double-sided copying, an image having no difference in toner image quality between the first side and the second side is obtained. Since heat is applied to the image support 7 once on the second side during double-sided copying, if the same amount of heat is applied as the fixing energy (the amount of fixing heat) applied to the first side, the toner is over-melted and the gloss becomes excessive. If worse, a hot offset occurs. According to the position control of the preliminary heater, the problem is solved.

As a method of changing the fixing energy,
It is conceivable to lower the temperature of the heating roller 1 or the temperature of the preliminary heater 8, but it is difficult to lower the temperature with good responsiveness due to the problem of the heat capacity, and a waiting time until the temperature lowers occurs. It is also conceivable to change the fixing speed, but this is also a change in the system speed of the copying machine, and it is not easy because there is a relationship between the speed of the image forming system on the upstream side of the fixing device.

According to the control shown in FIG. 5, by adjusting the interval between the pre-heater 8 and the guide member 9 in accordance with the paper passing mode, it is possible to switch to the paper passing mode which is one of the conditions affecting the image fixing property. An appropriate amount of fixing heat can be given to the image support and the toner image in response to good responsiveness, and stable fixing performance can be exhibited. FIG. 7 shows an example of control according to the surface temperature of the pressure roller when the heater is not built in the pressure roller 4 in the fixing device of FIG. 1 as shown in FIG.

When the pressure roller 4 is not provided with the heater 5, the temperature of the roller rises due to heat conduction from the heating roller 1 by rotation of the fixing roller pair including the heating roller 1 and the pressure roller 4, and the image support 7 and the rotation time of the fixing roller pair. The temperature rises as the image support 7 is passed. Since the heating roller 1 is controlled at a constant temperature, the fixing property changes in proportion to the temperature of the pressure roller 4.

The pre-heater 8 is arranged at any one of the positions A, B and C. Further, since no heater is provided on the pressure roller 4, in this control, the preliminary heater 8
Is controlled at a constant surface temperature of 170 ° C., and the heating roller 1 is controlled at a constant surface temperature of 160 ° C. In this control based on the pressure roller surface temperature, as shown in FIG.
At 31 it is determined whether or not the pressure roller temperature T is T <100 ° C. If T <100 ° C., the position of the preliminary heater 8 is changed to the position A (interval L = 10) shown in FIG.
mm), and returns to the main control routine.
If T <100 ° C. in step S31, step S3
In step 2, it is determined whether the pressure roller temperature T satisfies 100 ° C. ≦ T <120 ° C. If 100 ° C. ≦ T <120 ° C., the position of the preliminary heater 8 is set to B (interval L = 1) in step S34.
5 mm), and returns to the main control routine. If the pressure roller temperature T is 120 ° C. ≦ T, the position of the preliminary heater 8 is set to C (interval L =
20 mm), and returns to the main control routine.

By adjusting the distance between the preliminary heater 8 and the guide member 9 in accordance with the change in the temperature of the pressure roller, one of the conditions affecting the image fixability is the change in the temperature of the pressure roller without a heater. In this case, an appropriate amount of fixing heat can be given to the image support and the toner image in response to the above-mentioned responsiveness, and stable fixing performance can be exhibited. FIG. 8 shows a control example according to the environmental temperature around the fixing device in the fixing device shown in FIG. In this case, an environmental temperature sensor TS (see FIG. 3) is used to detect the environmental temperature. The pre-heater 8 is controlled at a constant surface temperature of 160 ° C., the heating roller 1 is controlled at a constant surface temperature of 150 ° C., and the pressure roller 4 is controlled at a constant surface temperature of 150 ° C.

In this control, as shown in FIG. 8, it is determined in step S41 whether or not the environmental temperature T is T <10 ° C. If T <10 ° C., the position of the preliminary heater 8 is changed in step S43. Move to the position A (L = 10 mm) shown in FIG. 1 and return to the main control routine. T <10
If not, the environmental temperature T is set to 10 ° C. ≦ at step S42.
It is determined whether T <25 ° C., and 10 ° C. ≦ T <25 ° C.
If so, the position of the preliminary heater 8 is set to B in step S44.
(L = 15 mm) and returns to the main control routine. If the environmental temperature T is 25 ° C. ≦ T, the position of the preliminary heater 8 is set to C (L = 20) in step S45.
mm), and returns to the main control routine.

In a low temperature environment (lower than 10 ° C.), the temperature of the image support does not rise, and sufficient fixability cannot be obtained. Conversely, under a high temperature environment (25 ° C. or higher), the toner is in an over-melted state. Therefore, the preliminary heater 8 is adapted to the change of the environmental temperature.
By changing the distance between the guide member 9 and the responsiveness, it is possible to provide appropriate fixing energy to the image support and the toner image in response to the environmental temperature which affects the image fixing property with good responsiveness, and to exhibit stable fixing performance. it can.

FIG. 9 shows the interval between the preliminary heater 8 and the guide member 9 in the fixing device shown in FIG. 1 according to the monochrome image forming mode or the color image forming mode selected by the color mode selection key 24 (see FIG. 3). 9 shows an example of control to be determined. In this case, the preliminary heater 8 has a surface temperature of 16
The temperature is controlled to be constant at 0 ° C.
And the pressure roller 4 is controlled at a constant surface temperature of 150 ° C.

In this control, it is determined in step S51 whether or not the mode is the color image forming mode. If the mode is the color image forming mode, the position of the preliminary heater 8 is determined in step S53 in FIG.
(L = 10 mm), and returns to the main control routine. In the monochrome image forming mode, the position of the preliminary heater 8 is set to B (L = 15) in step S52.
mm), and returns to the main control routine.

In the color image forming mode, toner layers of two or more colors may overlap in order to reproduce colors, and it is necessary to apply more fixing energy than in the case of a single toner layer in monochrome image formation in order to uniformly develop colors. is there.
By changing the interval between the pre-heater 8 and the guide member 9 according to such a mode difference, it is possible to obtain appropriate fixing energy for the image support and the toner image with good responsiveness according to the amount of toner adhering on the image support. And stable fixing performance can be exhibited.

FIG. 10 shows another example of the heat fixing device according to the present invention. FIG. 10 is a schematic side view of the device. This heat fixing device is mounted in a copying machine here. Illustration of the overall configuration of the copying machine is omitted. The fixing device shown in FIG. 10 includes a pair of fixing rollers 32 and 34. An upper fixing roller 32 of the fixing roller pair;
The endless fixing belt 31 is wound around a roller 33 disposed upstream of the roller 32 in the image support conveying direction α. The upstream roller 33 is a heating roller having a built-in heater 330. The heating roller 33 is provided with a spring force in a direction away from the fixing roller 32 by a pressing device including a pressing spring (not shown), whereby a constant tension is applied to the belt 31. Endless fixing belt 3
1 is a portion 311 on the upstream side of the fixing roller pairs 32 and 34
Constitutes a preliminary heater. Outside the portion 312 of the fixing belt 31 wound around the heating roller 33, a temperature sensor 35 for detecting a belt temperature is arranged.

The lower fixing roller 34 is pressed against a portion 313 of the belt 31 wound around the upper fixing roller 32 by a pressing device including a pressing spring (not shown). The lower fixing roller is a pressure roller. As a result, the transfer nip portion N is formed between the pair of fixing rollers 32 and 34 such that the lower fixing roller 34 is pressed against the belt portion 313 on the upper fixing roller.

A guide member 38 for the image support is provided below the belt portion 311 constituting the preliminary heater of the belt 31 and faces the belt portion 311. The guide member 38 can be moved up and down as described later. The guide member is provided with a temperature sensor 42 for detecting the temperature of the guide member. Discharge guide members 40 and 41 are provided on the downstream side of the fixing nip portion N in the image support transport direction, and further on the downstream side, a discharge roller pair (not shown) is provided.

The oil application roller 3 is provided on a portion 314 of the belt 31 opposite to the side on which the guide member 38 faces.
6 is in contact with the application roller 36 so that the oil supply rotating member 37 is in contact with the application roller 36 so as to be driven and rotatable. The upper fixing roller 32 of the rollers can receive a driving force from a motor in an image forming apparatus in which the fixing device is mounted via a transmission mechanism (not shown), so that the upper fixing roller 32 can rotate counterclockwise in the drawing. . As a result, the fixing belt 31 runs, and the heating roller 33 and the pressure roller 34
Can be driven to rotate.

The upper fixing roller 32 is formed by covering a metal core roller with a heat-resistant and elastic silicone sponge layer. The lower fixing roller (pressure roller) 34 is formed by forming a silicone rubber layer on a metal shaft. The heating roller 33 is made of an aluminum pipe, and is subjected to an alumite treatment to prevent abrasion.

The fixing belt 31 is made of nickel and has a thickness of 4 mm.
The surface of a 0 μm endless belt is coated with a 150 μm thick silicone rubber layer having heat resistance and release properties. The oil application roller 36 has a configuration in which the surface is coated with silicone rubber having a good affinity for silicone oil as a release agent, and the silicone oil is supplied by an oil supply rotating member 37.
It is applied more uniformly. The oil supply rotating member 37 is formed by winding a heat-resistant paper impregnated with silicone oil on the surface of a metal core, and providing a heat-resistant nomex paper layer on the surface.

The fixing belt 31 has a fixed position, but the guide member 38 can be moved up and down with respect to the fixing belt portion 311 constituting the pre-heating heater, whereby the fixing belt constituting the pre-heating heater is formed. The distance between the portion 311 and the guide member 38 can be adjusted. That is, the guide member 38 can swing up and down about a fulcrum shaft 381 at an end near the fixing nip portion N, and an upstream end 382 remote from the nip portion N.
The upper link 391 of the links 391 and 392 that are flexibly connected to each other is pin-connected. The lower link 392 is connected to the fixing member 43 with a pin. Also,
The tension spring 4 is attached to one link 392 and the fixing member 43.
4 are connected to each other, and a solenoid SOL is further connected to the link 392. The solenoid SOL is supported by the fixing member 43.

When the solenoid SOL is off, the spring 44
As a result, the links 391 and 392 are pulled and bent, whereby the guide member 38 moves down to the position B ′ (sheet passing position).
Take. When solenoid SOL is turned on, link 39
1, 392 is pulled toward the solenoid side against the spring 44,
As a result, the links 391 and 392 are extended, and the guide member 38 is extended.
Rises to the position A ′ (guide member heating position).

The links 391 and 392, the spring 44, the solenoid SOL, and the like constitute an interval adjusting device 390 between the guide member 38 and the preheating heater (belt portion 311). FIG. 11 is a block diagram of a control circuit for adjusting the position of the guide member 38. As shown in FIG. 11, this fixing device utilizes a control unit 50 for controlling the operation of the entire copying machine.

The control unit 50 includes a central processing unit CPU, a RAM 51 for storing control information, a ROM 52 for storing control programs and control data, and the like. The control unit 50 includes a fixing belt temperature sensor 35, a guide member temperature sensor 42, and other sensors 4 in the fixing device.
A signal such as a detection signal from 00 is input via an input interface (not shown).

On the other hand, a signal for controlling the guide member position variable solenoid SOL, the heating roller heater 330, and other various loads 53 of the copying machine is output from the control unit 50 through an output interface (not shown). According to the heating and fixing device shown in FIG. 10, the control unit 50 sets the temperature of the heating roller heater 330 to a predetermined temperature based on the temperature information detected by the fixing belt temperature sensor 35, whereby the preliminary heating of the fixing belt 31 is performed. Is controlled to be constant at 165 ° C., and the temperature of the fixing nip N is controlled to be constant at 160 ° C.

The controller 50 controls the solenoid S in accordance with the temperature of the guide member 38 (the temperature detected by the guide member temperature sensor 42), which is one of the conditions affecting the image fixability.
By controlling OL, the guide member 38 is arranged at the position A 'or B' shown in FIG. The position A 'is a position closer to the fixing belt 31 and the position B' is a position farther from the fixing belt 31 than the position A '.

According to the fixing device shown in FIG. 10, the image support 7 holding the unfixed toner image Ti is conveyed from the left in FIG. 10 and guided by the guide member 38 to the fixing nip N. Heading. When the image support 7 and the unfixed toner image Ti pass over the guide member 38, the heat from the portion 311 serving as a preheater of the fixing belt 31 heated by the heating roller 33 passes through the image support. When the guide member 38 is heated by being exposed to the belt 31 when the belt 31 is not heated, the toner is softened to some extent. In this state, the image support 7 enters the fixing nip N, and the toner image Ti is further softened and melted by the pressure and heat there, and is fixed to the image support 7. The image support 7 coming out of the nip portion N is guided to a discharge roller pair (not shown) by the paper discharge guide members 40 and 41, and is discharged by the roller pair.

In this fixing process, the control unit 50 controls the solenoid SOL so that the guide member 38 is arranged at the position B '(sheet passing position) when the image support is passed through the fixing nip N. In order to give an appropriate amount of fixing heat to the image support 7 and the toner image Ti supported on the image support 7 as a whole, the temperature of the guide member 38 detected by the temperature sensor 42 when the image support 7 does not pass through the image support 7 When the temperature is lower than the predetermined temperature for
Position (guide member heating position).

This will be described with reference to the flowchart of FIG. The flowchart shown in FIG. 12 shows a guide member position setting routine which is a part of a subroutine in a main control routine for controlling the operation of the entire copying machine by the control unit 50. As shown in FIG. 12, in a step S61, it is determined whether or not the temperature T of the guide member 38 is lower than 70 ° C.
If the temperature is lower, the guide member 38 is arranged at the position A 'in step S63, and the fixing device is operated in step S64.
Thereby, when the temperature of the guide member 38 becomes 70 ° C. or more,
In step S62, the guide member 38 is arranged at the position B ', and the process returns to the main control routine.

By maintaining the temperature of the guide member 38 at 70 ° C. or higher, appropriate fixing heat energy can be applied to the toner image Ti and the image support 7 supporting the toner image Ti, and stable fixing performance can be obtained.

[0063]

As described above, according to the present invention, an unfixed toner image is heated and fixed on an image support with an appropriate amount of fixing heat in response to a change in conditions affecting the image fixability with good responsiveness. Thus, it is possible to provide a heat fixing device which can exhibit stable fixing performance, and can be simply and compactly manufactured without remarkably complicating the structure and increasing its size.

[Brief description of the drawings]

FIG. 1 is a schematic side view of an example of a heat fixing device according to the present invention.

FIG. 2 is a perspective view showing an interval adjusting device for adjusting an interval between a preliminary heater and a guide member shown in FIG. 1;

FIG. 3 is a block diagram schematically showing a control circuit of the fixing device shown in FIG.

FIG. 4 is a flowchart showing a preliminary heater position setting routine among operations of a control unit in the control circuit shown in FIG. 3;

FIG. 5 is a flowchart illustrating another example of a preliminary heater position setting routine.

FIG. 6 is a schematic side view of a modification of the heat fixing device shown in FIG.

FIG. 7 is a flowchart showing a preliminary heater position setting routine among operations of a control unit in a control circuit in the apparatus shown in FIG. 6;

FIG. 8 is a flowchart illustrating still another example of a preliminary heater position setting routine.

FIG. 9 is a flowchart illustrating still another example of a pre-heating heater position setting routine.

FIG. 10 is a schematic side view of another example of the heat fixing device according to the present invention.

11 is a block diagram schematically showing a control circuit of the fixing device shown in FIG.

12 is a flowchart illustrating a guide member position setting routine among operations of a control unit in the control circuit illustrated in FIG. 11;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 heating roller 2 heating roller heater 3 heating roller temperature sensor 4 pressure roller 5 pressure roller heater 6 pressure roller temperature sensor N pressure contact nip (fixing nip) Ti toner image 7 image support 8 preheater A, B, C Preheating heater position L Spacing between preheating heater and guide member 9 Guide member 10 Preheating heater temperature sensor 11, 12 Discharge guide member 13, 14 Discharge roller pair 15 Oil application roller 16 Oil supply rotating member 18 Interval adjustment device 180 Shaft 181 Rack gear 182 Pinion gear 19 Control unit CPU Central processing unit 20 RAM 21 ROM TS Environmental temperature sensor 22 Image support selection key 23 Paper passing mode selection key 24 Color mode selection key 31 Endless fixing belt 311 In charge of preheating device Fusing belt part 31 2, 313, 314 Fixing belt portion 32, 34 Fixing roller pair 33 Heating roller 330 Heating roller heater 35 Temperature sensor 36 Oil application roller 37 Oil supply rotating member 38 Guide member 390 Interval adjustment device 391, 392 Link 43 Fixing member 44 Tension spring 42 Temperature sensor SOL solenoid A ', B' Guide member position 40, 41 Discharge guide member 50 Control unit 51 RAM 52 ROM

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Takashi Yamada 2-3-113 Azuchicho, Chuo-ku, Osaka City Inside Osaka International Building Minolta Co., Ltd. (72) Noboru Yonekawa 2-3-3 Azuchicho, Chuo-ku, Osaka-shi No. 13 Osaka International Building Minolta Co., Ltd.

Claims (5)

[Claims] An image fixing device for heating and fixing an unfixed toner image to an image support holding the image, wherein the image fixing device fixes the image by passing the image support holding the unfixed toner image. A pair of fixing rollers for providing a fixing nip for heating and fixing an image, a preheating device for the unfixed toner image installed upstream of the fixing nip in the image support transport direction, and an image support holding the image A guide member installed opposite to the preheating device and guiding the image support to the fixing nip portion; and a distance between the preheating device and the guide member according to a condition that affects image fixing property. A heating and fixing device, comprising: 2. The heat fixing device according to claim 1, wherein at least one of the fixing roller pairs is a heating roller, and the fixing roller pairs are directly pressed against each other to form the fixing nip portion. 3. The preheating apparatus according to claim 1, wherein the preheating device winds an endless fixing belt around one of the fixing roller pair and a roller disposed upstream of the roller in the image support conveying direction. The belt portion on the one roller of the fixing roller pair is constituted by the belt portion on the upstream side of the fixing roller pair in the image support transport direction with at least one of the wound rollers as a heating roller. And the other roller of the fixing roller pair are pressed against each other to provide the fixing nip portion,
2. The image forming apparatus according to claim 1, wherein the guide member faces the fixing belt.
The fixing device according to claim 1. 4. An apparatus according to claim 1, wherein the distance between said preheating device and said guide member is determined by adjusting at least one condition affecting the image fixing property to an appropriate amount of fixing heat for the unfixed toner image and the image support holding the image. 4. The heat fixing device according to claim 1, further comprising a control device for controlling the gap adjusting device so as to set the direction to be given. 5. The image forming apparatus according to claim 1, wherein the control device has a function of affecting the image fixing property, a) a type of the image support, b) an environmental temperature around the heat fixing device, c) an environmental humidity around the heat fixing device, and d) the guide member. E) the temperature of at least one roller constituting the fixing roller pair; f) a single-side mode in which an image is fixed on one side of the image support or a duplex mode in which an image is fixed on both sides; g) a toner adhesion amount on the image support; h) a color mode of whether the unfixed toner image is a monochrome image or a multi-color image; i) whether or not the image support is passing through the fixing nip; 5. The image forming apparatus according to claim 4, wherein the interval adjusting device is controlled in accordance with at least one of conditions of a passage time interval between the image supports when a plurality of image supports are continuously passed through the fixing nip portion. Heat fixing as described Location.