JP3187181B2 - Overfixing prevention mechanism of fixing device and overfixing prevention method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for thermally fixing an image formed on a recording sheet by using an electrophotographic method, and more particularly, to separating a heat roller and a press roller from each other when the conveyance of the recording sheet is stopped. The present invention relates to a mechanism for preventing over-fixing of a fixing device and a method for preventing the over-fixing.

[0002]

2. Description of the Related Art Conventionally, a latent image is formed by exposing a photoreceptor on the surface of a photosensitive drum, toner is adhered to the latent image and developed, and a toner image is transferred onto a recording sheet. 2. Description of the Related Art An image forming apparatus using a so-called electrophotographic method in which a toner image is fixed on recording paper by a fixing device is known. 2. Description of the Related Art There is an electrophotographic printer that prints information on a continuous recording sheet with a perforated hole.

In such a printer that forms an image on continuous recording paper, when the transportation of the continuous recording paper is stopped, the continuous recording paper whose transportation is stopped in the fixing device is held between a heat roller and a press roller. Then, the pinched portion of the continuous recording paper is overheated, and there is a risk of generation of kogation and, in the worst case, ignition. For this reason, conventionally, when the conveyance of the continuous recording paper is stopped, the rolling contact state between the heat roller and the press roller is released to prevent the continuous recording paper from being pinched between the two.

[0004]

Therefore, prior to resuming the conveyance of the continuous recording paper, the heat roller and the press roller must be in rolling contact with each other, and the continuous recording paper must be sandwiched between the two. However, in the related art, the heat roller and the press roller are rolled in contact with each other in a state where the conveyance is stopped, so that the conveyance of the continuous recording paper is restarted thereafter. There is a problem that the portion to be pinched by the roller is in an over-fixed state, and the fixed image may be partially thickened.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to separate a heat roller and a press roller from each other when the conveyance of recording paper is stopped, so that the recording paper can be resumed even when conveyance is resumed. It is an object of the present invention to provide an over-fixing prevention mechanism of a fixing device that can surely prevent over-fixing to a fixing device, and an over-fixing prevention method thereof.

[0006]

In order to solve the above-mentioned problems and achieve the object, an over-fixing prevention mechanism of a fixing device according to the present invention comprises a heat roller and a press roller which are provided so as to be able to freely contact and separate from each other. By driving and driving at least one of the heat roller and the press roller, and driving means for driving the contact and separation to the other, heating the heat roller,
And a heating unit for thermally fixing the toner image on the recording paper sandwiched between the heat roller and the press roller. A heat shield member for reducing at least heat transfer from the heat roller to the recording paper in a state where the heat roller is interposed between the heat roller and the heat roller. And a heat-shielding member moving means for moving between a heat-shielding position located between the press rollers and a standby position deviating from the heat-shielding member, and the heat roller and the press roller rolling the heat-shielding member together. And a control means for controlling the heat-insulating member moving means so as to be interposed therebetween.

According to a method for preventing over-fixing of a fixing device according to the present invention, when the conveyance of a recording sheet is stopped, a heat roller and a press roller holding the recording sheet in a rolling contact state are separated from each other. Step 1 and a second step of interposing a heat shielding member between the heat roller and the recording sheet prior to the start of the conveyance of the recording sheet, and rolling the heat roller and the press roller together, A third step of holding the recording paper therebetween, and a fourth step of starting conveyance of the recording paper.
And a step of:

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of an embodiment of an over-fixing prevention mechanism of a fixing device according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows a configuration of a fixing device provided with an over-fixing prevention mechanism of this embodiment and applied to an electrophotographic printer using continuous recording paper, and FIG. 2 shows a swinging and retracting structure of a heat roller. ing. In FIG. 2, the configuration of the over-fixing prevention mechanism, which is a feature of the present invention, is omitted for the sake of illustration.

As shown in FIG. 1, this fixing device includes a fixing roller pair 10 in which a heat roller 11 and a press roller 12 are vertically arranged adjacent to each other. In one embodiment, the rotation axes of the heat roller 11 and the press roller 12 are arranged to be orthogonal to the left direction in the figure). That is, in this embodiment, the fanfold paper P is heated by being pinched by the fixing roll pair 10, and as a result, the toner image adhered to the fanhold paper P is fixed.

The upper heat roller 11 is comprised of a cylindrical roller body 18 and a halogen lamp 19 housed in the roller body 18 as a heat generating means. Is heated to a predetermined temperature. Both ends of the heat roller 11 are rotatably supported by a holder 30 pivotally attached to the chassis 1 via the shaft 13. In this manner, the heat roller 11 can swing with respect to the chassis 1. A gear (not shown) is fixed to one end (the right end in FIG. 2) of the heat roller 11, and a driving force from a main motor (not shown) is transmitted through the gear. , Thereby being driven to rotate.

The lower press roller 12 includes a cored bar 20,
An elastic member layer 21 made of silicon rubber or the like having a predetermined hardness and heat resistance is provided around the cored bar 20, and is fixed at a predetermined position on the chassis 1. It is supported rotatably about its own central axis. The support structure is not shown for the sake of illustration.

Holder 30 for supporting heat roller 11
The connecting portion 31 has substantially the same length along the axial direction as the heat roller 11 and is located above the heat roller 11.
And a pair of arm portions 32 extending from both ends of the connecting portion 31 toward the fan hold paper P introduction side (that is, the right side in the drawing). Here, the two arm portions 32 are pivotally supported by the chassis 1 at substantially the center of each of them by a shaft portion 13 having a center axis set in parallel with the rotation axis of the heat roller 11. At the tip of each arm 32, a spring receiver 33 is formed integrally with the upper side rising upward and bent toward the inside (center side of the apparatus).

The shaft 13 has two arm parts 32.
In this state, the lever 40 is pivotally supported at one end of the lever 40 (i.e., the end on the discharge side of the fan hold paper P). A cam follower 4 is provided at the tip of the other end of each lever 40 (that is, the leading end of the fan hold paper P).
1 is provided rotatably. On the other hand, in the lower side portion corresponding to the spring receiver 33 of the holder 30,
The spring holding portion 43 is bent and provided outward (toward the arm portion 32). Further, each spring holding portion 43
A hook 44 is bent and protruded outwardly, adjacent to the shaft portion 13 side.

Here, each arm portion 32 of the shaft portion 13
As shown in FIG. 3, the torsion springs 15 are extrapolated between the and the corresponding levers 40, respectively. One of the extending ends of each torsion spring 15 contacts the upper side of the hook 44 formed on the corresponding lever 40, and the other end contacts the lower surface of the hook portion 1A formed by bending the upper side of the chassis 1 inward. I have. In this way, the return biasing force of each torsion spring 15 causes the corresponding lever 4
0 is urged to swing clockwise about the shaft portion 13. As a result, the cam follower 41 attached to the end of each lever 40 comes into contact with the outer peripheral cam surface of the corresponding eccentric cam 2. In FIG. 3, the illustration of the arm 32 of the holder 30 is omitted for convenience of the drawing.

As shown in FIG. 1 and FIG.
0 between each spring receiver 33 and the corresponding spring holding portion 43 of the lever 40.
Are interposed. The holder 30 is oscillatingly urged against the lever 40 counterclockwise (that is, so that the side holding the heat roller 11 faces downward) by the urging force of each coil spring 14. Also each spring receiver 3
3 is provided with a swing regulating bolt 16 penetrating therethrough and extending vertically. The lower end of each swing regulation bolt 16 is fixed to a spring holding portion 43. In this manner, each swing regulation bolt 16 is
The relative swing amount of the holder 30 with respect to 0 (the spread of the angle between the two) is restricted to a predetermined amount.

That is, each lever 40 is oscillated in a clockwise direction by the corresponding torsion spring 15, and
Each cam follower 41 is in contact with the corresponding eccentric cam 2. As a result, according to the displacement of the outer peripheral cam surface (the amount of eccentricity from the center of rotation) due to the rotation of each eccentric cam 2, each lever 40
Is driven to swing around the shaft portion 13, and as a result, the holder 30
Swings in a state of interlocking with the swing of each lever 40 via the coil spring 14 or the swing regulating bolt 16. Then, as shown in FIG.
Is in contact with a position where the amount of displacement of the outer peripheral cam surface of the eccentric cam 2 from the rotation center is the largest (that is, the cam follower 41).
Is located at the uppermost position), and the outer periphery of the heat roller 11 is set in contact with the outer periphery of the press roller 12. Further swinging of the lever 40 after the heat roller 11 comes into contact with the press roller 12 causes the coil spring 14 to be compressed and deformed by a predetermined amount. In this manner, the heat roller 11 is pressed against the press roller 12 with a predetermined pressing force by the elastic restoring force of each coil spring 14, and the fixing operation state is defined.

On the other hand, in the state where each cam follower 41 abuts on the position where the amount of displacement of the outer peripheral cam surface of the corresponding eccentric cam 2 from the center of rotation is smallest (ie, the state where the cam follower 41 is located at the lowest position), Due to the clockwise swing of FIG. 40, the holder 30 also swings in a state interlocked with the clockwise direction in the figure via the swing regulation bolt 16, and as a result, the heat roller 11 held by the holder 30 is Separated from the press roller 12 upward by a predetermined interval,
The evacuation state is defined.

The rotational drive of the eccentric cam 2 is controlled by a control device (not shown) of an electrophotographic printer having the heat roll fixing device. Specifically, the control device controls the press roller 12 to perform printing (at the time of image formation).
As shown in FIG. 1, the pressing roller 12 has a predetermined pressing force.
When the printer is in a standby state for printing, the operation is controlled so as to be released upward from the press roller 12 to be in a retracted state.

Further, as shown in FIG. 1, a paper discharge cover 70 is attached to a main body (not shown) of the electrophotographic printer to which the fixing device of the embodiment is applied so that the upper end thereof can be opened. That is, the paper discharge cover 70 swings counterclockwise in the drawing around its lower end so that the upper end is opened. Also, this paper ejection cover 70
The shaft 50 is disposed in a state where the shaft 50 has a central axis parallel to the rotation axis of the heat roller 11 in a state where the shaft 50 is positioned on the sheet discharge side (left side in the figure) of the heat roller 11. Jam prevention claws 60 are fixed to both sides of the outer periphery of the shaft 50, respectively.

As shown in FIG. 2, the shaft 50 is
It is rotationally urged in a counterclockwise direction in the figure by a spring 51 wound around one end (the right side in the figure) of the above.

On the other hand, the tips of these jam prevention claws 60
Regardless of the state of contact with or separation from the press roller 12, the fan-hold paper P that has always contacted the outer peripheral surface of the heat roller 11 and passed between the fixing roller pair 10, for example, the outer peripheral surface of the heat roller 11. Even when the fan is in close contact with the heat roller 11, it is reliably peeled off from the outer peripheral surface of the heat roller 11, and the jam of the fan hold paper P is reliably prevented.

Here, each jam prevention claw 60 comprises a cylindrical base 61 through which the shaft 50 is inserted and fixed, and a claw 62 extending integrally from the base 60 and having a sharp end. ing.

As shown in FIG. 1, a lower discharge guide 17 is provided below the shaft 50 (that is, on the discharge side of the press roller 12). The fan-hold paper P, which has passed through the fixing roller pair 10 and has undergone the fixing operation, is separated from the outer periphery of the heat roller 11 by the jam prevention claw 60, and is discharged onto the lower discharge guide 17 on a lower discharge guide 17 (not shown). It will be conveyed to the mouth.

In the fixing device configured as described above, as described above, the rotation of the lever 40 and the holder 30 by the rotation of the eccentric cam 2 causes the heat roller 11 to rotate during printing.
Is brought into a fixing operation state, and is rolled to the press roller 12 to perform a fixing operation.
Is brought into a retracted state in which it is retracted upward by a predetermined amount.

In the fixing operation state, the heat roller 11 is pressed against the press roller 12 with a predetermined pressing force, and
The heat roller 11 is driven to rotate, and both rollers 11 and 12 are rotated.
The fan hold paper P is conveyed and driven and discharged while the fixing operation is performed by pressurizing and heating the fan hold paper P sandwiched therebetween.

Here, when the heat roller 11 is in the fixing operation state, the jam prevention claw 60 is moved as shown in FIG.
The heat roller 11 is pressed by a predetermined pressing force by the urging force of the spring 51. Accordingly, even when the fan-hold paper P that has completed the fixing operation adheres to the heat roller 11 due to the welding force of the toner or the like,
The paper is peeled off by the jam prevention claw 60 and is discharged without being jammed.

On the other hand, at the time of printing standby, when the heat roller 11 is retracted upward from the fixing action position and the retracted state is defined, the shaft 50 rotates counterclockwise in the figure by the urging force of the spring 51. . The rotation of the shaft 50 causes the jam prevention claw 60 to rotate counterclockwise in the drawing, and as a result, the state of being pressed against the heat roller 1 is maintained as shown in FIG. As a result, the fan hold paper P is conveyed in the paper discharge direction without being caught by the jam prevention attachment 60.

When a new fan-hold sheet P is set, the heat roller 11 is returned to the fixing operation position before the fan-hold sheet P is conveyed and its front end reaches the fixing roll pair 10, whereby The jam prevention claw 60 is pressed by the heat roller 11, thereby preventing the front end of the fan-hold paper P from bending toward the heat roller 11 due to the applied heat and winding around the heat roller 11. .

Next, an over-fixing prevention mechanism and an over-fixing prevention method which characterize the present invention will be described with reference to FIGS. First, the configuration of the over-fixing prevention mechanism of this embodiment will be described with reference to FIG.

In this embodiment, the over-fixing prevention mechanism 80 is disposed so as to be interposed between the heat roller 11 and the fan-folded paper P at the rolling contact portion of the heat roller 11 and the press roller 12. In a state interposed therebetween, a heat-shielding sheet 82 as a heat-shielding member for at least reducing heat transfer from the heat roller 11 to the fan hold paper P, and the heat-shielding sheet 82 is connected to the heat roller 11 and the press roller. 12 and a moving mechanism 84 as a heat-insulating member moving means for moving between a heat-shielding position between the heat roller 11 and the standby position. The moving mechanism 84 is interposed between the two before they come into contact with each other.
And a control mechanism 86 as control means for controlling the control. The axial length of the heat shield sheet 82 is defined so as to cover the rolling contact portion (that is, the lower part in the figure) of the heat roller 11 with the press roller 12 over the entire area in the axial direction.

The moving mechanism 84 described above is disposed on the right side of the heat roller 11 and is provided with an electromagnetic solenoid 90 for pulling in and driving the plunger 88 in an excited state, and for always projecting the plunger 88 outward. A biasing coil spring 92 is connected to the tip of the plunger 88, and in accordance with the retraction / projection of the plunger 88,
A connecting member 96 is provided at one end and is swingably driven around a support shaft 94. Here, the above-described plunger 88 is driven to be pulled in above the heat roller 11 in accordance with the excitation of the electromagnetic solenoid 90, and protrudes outward due to the urging force of the coil spring 92 when the electromagnetic solenoid 90 is demagnetized. Is driven in the following manner.

The connecting member 96 described above is attached below the heat roller 11 with the support shaft 94 attached to one end and wrapping around the paper discharge side (left side in the figure) of the heat roller 11. The heat shield sheet 82 is attached to the lower end thereof. More specifically, the connecting member 96 is driven to be pushed out by the urging force of the coil spring 92 as shown in FIG. 7 in a state where the electromagnetic solenoid 90 is demagnetized. With the electromagnetic solenoid 90 being excited, as shown in FIG. 9, the heat shield sheet 82 is driven to be pulled away against the urging force of the coil spring 92 so that the heat shield sheet 82 is separated from the sheet discharge side and the electromagnetic solenoid 90 is excited. Heat roller 11
Side, and a part thereof is brought to a heat shielding position covering at least a rolling contact portion of the heat roller 11 to the press roller 12.

A driving source for generating a driving force transmitted through a gear fixed to one end (the right end in FIG. 2) of the heat roller 11 is driven when the warm-up operation of the electrophotographic printer is completed. Although not shown, a main motor (not shown) is provided, and when the main motor is started, a photosensitive drum (not shown), a developing roller in a developing unit, a tractor of a paper transport mechanism,
The heat roller 11 and the like in the fixing device are driven.

Here, a clutch mechanism (not shown) is provided between the tractor and the heat roller 11 of the paper transport mechanism and the main motor, and the driving force of the main motor is transmitted when the clutch mechanism is on. In the off state, transmission is not performed. That is, in a state where the main motor is activated, the fan mechanism sheet is driven to be conveyed while the clutch mechanism is in the on state, and the heat roller 11 is driven to rotate and is turned off so that the conveying operation of the fan hold sheet P is performed. Is interrupted, and the heat roller 11 is stopped and turned on again,
The transport operation of the fan hold paper P is restarted, and the heat roller 11 is driven to rotate.

The eccentric cam 2 is connected to an up / down motor (not shown), and is configured to be driven to rotate by rotation of the up / down motor. Further, although not shown, a down sensor (not shown) that is turned on when the heat roller 11 is lowered to a lower position where the heat roller 11 rolls on the press roller 12 in response to the driving of the up-down motor is provided.

Next, the control operation of one embodiment of the over-fixing prevention method, which is a feature of the present invention, in the over-fixing prevention mechanism 80 configured as described above will be described with reference to a timing chart shown in FIG. 8 and FIGS. The operation will be described in detail with reference to operation mode diagrams shown in FIGS. First, as described above, in a state where the warming-up operation of the electrophotographic printer is being performed, in other words, in a standby state of the electrophotographic printer, the up-down motor causes the heat roller 12 to retreat above the press roller 11. It has been brought to the retracted state, and the electromagnetic solenoid 90 has been demagnetized. Further, the fan hold paper P is taken out from a paper feed table (not shown), passes between a photosensitive drum (not shown) and a transfer charger, and is engaged with a tractor of a paper transport mechanism (not shown). And the leading end is taken out of the paper discharge port.

When the warm-up operation is completed in such a standby state, the control mechanism 86 activates the main motor to turn on the main motor, and also causes the halogen lamp such as the halogen lamp incorporated in the heat roller 11 to generate heat. Thereafter, the operation of applying the voltage power to the charging charger (not shown) is started within the elapse of the predetermined first management time T1.

On the other hand, when the operation of applying the high-voltage power supply to the charging charger is started, the electromagnetic solenoid 90 is excited when a predetermined second set time T2 has elapsed from the start. As a result, the plunger 88 is drawn inward against the urging force of the coil spring 92, and as a result, the heat shield sheet 82 connected to the plunger 88 via the connecting member 96 is moved from the standby position to the heat shield sheet. As shown in FIG. 9, the lower part of the heat roller 11, which is separated upward from the press roller 12, is covered.

Further, in synchronization with the excitation operation of the electromagnetic solenoid 90, the up-down motor is started, and the lowering operation of the heat roller 11 is started. When the down sensor is turned on along with the lowering operation of the heat roller 12 and it is detected that the heat roller 11 abuts on the press roller 12, the driving of the up-down motor is stopped in synchronization with the on operation. Then, the electromagnetic solenoid 90 is demagnetized in synchronization with the drive stop of the up-down motor. That is, in a state where the heat roller 11 is lowered to the down position in this manner, FIG.
As shown in FIG. 0, a fan hold sheet P is sandwiched between the heat roller 11 and the press roller 12, and a heat shield sheet 82 is interposed between the fan hold sheet P and the heat roller 11. Will be.

Thus, in this embodiment,
In a state before the conveyance of the fan hold paper P is started, that is, in a state in which the fan hold paper P is stopped, the heat roller 11 is in contact with the press roller 12 so as to pinch the fan hold paper P therebetween. Therefore, even if the toner image before fixing is formed on the fan hold paper P, the toner image is not disturbed and the heat roller 11 By passing between the press roller 12 and the press roller 12 in a rolling contact state, the toner image is reliably fixed.

In particular, in this embodiment, when the fan hold paper P is stopped, it is held between the heat roller 11 and the press roller 12 and the heat roller 11 is held until the fan hold paper P is conveyed. Of the fan hold paper P as described above.
Since the heat shield sheet 82 is interposed between the heat roller 11 and the heat roller 11, the heat influence of the heat roller 11 is reduced, the overfixing is reliably prevented, and the kogation on the fan hold paper P is surely prevented. Will be prevented.

As described above, in this state, since the electromagnetic solenoid 90 is already demagnetized, the heat shield sheet 82 is urged toward the standby position shown in FIG. ing. However, in this state, the heat shield sheet 82 is sandwiched between the heat roller 11 and the press roller 12, and is held at the heat shield position by this sandwiching force, and is prevented from returning to the standby position. Have been. After that, it waits for the start of laser exposure.

On the other hand, when a fourth set time T4 has elapsed from the start of the laser exposure operation, the clutch mechanism interposed between the main motor and the tractor is turned on (connection operation), and The driving force of the motor is transmitted to the tractor and the heat roller 11. As a result,
From the state shown in FIG. 10, the tractor is started, and the rotational drive of the heat roller 11 is also started.

When the rotation of the heat roller 11 is restarted, the heat shield sheet 82 is pushed forward along the conveying direction. Here, as described above, since the heat shielding sheet 82 is urged from the heat shielding position toward the standby position by the urging force of the coil spring 92, the heat shielding sheet 82 is pushed forward in the transport direction, so that the heat shielding sheet 82 is pushed forward. Removed from position, Figure 1
As shown in FIG. 1, it will be moved to the standby position. When the heat shield sheet 82 is extruded from between the fixing roller pair 10, the heat roller 11 comes into contact with the fan-hold paper P, whereby the fixing and conveying operation is restarted.

On the other hand, if the printing operation is interrupted (finished) while such a fixing operation is being performed,
As shown in FIG. 12, the laser exposure is stopped, and after a lapse of a predetermined time T5 from the stop of the laser exposure, the above-described clutch mechanism is turned off (cutoff operation) to stop driving the tractor and rotate the heat roller 11. Stop driving. In this way, the transport operation of the fan hold paper P is interrupted. In synchronization with this off operation, while stopping the driving of the main motor and the application operation to the high voltage power supply,
The up-down motor is restarted, and the heat roller 11 is pulled up so as to be separated from the press roller 12. When the completion of the lifting operation is detected by turning off the down sensor, the up / down motor is stopped. In this way, a standby state for the next printing operation is established.

During the period from the stoppage of printing to the standby state, the state in which the fixing roller pair 10 holds the fan hold paper P is continued, and heat is supplied from the heat roller 11 to the fan hold paper P. A situation occurs that can be continued. However, in this embodiment, the drive of the up / down motor for pulling up the heat roller 11 is restarted along the biasing direction of the spring 14 shown in FIG. Is not necessary to wait, the time required for the fixing roller pair 10 to hold the fan-hold paper P stopped during the print start operation is sufficiently shorter, and there is no problem with over-fixing.

Here, when the conveyance of the fan hold paper P is interrupted, the application of the high-voltage power supply is cut off. Then, prior to the restart of the transport operation, the application operation of the high-voltage power supply is first started.

As described above, in this embodiment, the electromagnetic solenoid 90 is applied after the second set time T2 has elapsed from the start of the application based on the operation of applying the high-voltage power supply performed before the restart of the transport operation. Is to be excited.
As a result, even when the transport operation is restarted, over-fixing to the fan-hold paper P is prevented as in the above-described start of the transport operation. A situation in which an image is partially thickened due to overfixing is surely suppressed.

[0049]

As described above, the over-fixing prevention mechanism of the fixing device according to the present invention moves the heat roller and the press roller provided so as to be able to contact and separate from each other and at least one of the heat roller and the press roller. A driving means for driving and driving to contact / separate from the other, and heating for heating the heat roller and thermally fixing the toner image on the recording paper sandwiched between the heat roller and the press roller. Means for preventing over-fixing of the fixing device, wherein the mechanism is disposed between the heat roller and the recording paper at a rolling contact portion of the heat roller and the press roller, and is interposed between the heat roller and the recording paper. A heat-shielding member for at least reducing heat transfer from the heat roller to the recording paper in the state, and positioning the heat-shielding member between the heat roller and the press roller. A heat-shielding member moving means for moving between a heat-shielding position and a standby position deviating from the heat-shielding member, and interposing the heat-shielding member between the heat roller and the press roller before the heat roller and the press roller come into contact with each other. Control means for controlling the heat-insulating member moving means.

Further, in the method for preventing over-fixing of the fixing device according to the present invention, when the conveyance of the recording paper is stopped, the heat roller and the press roller holding the recording paper in a rolling contact state are separated from each other. Step 1 and a second step of interposing a heat shielding member between the heat roller and the recording sheet prior to the start of the conveyance of the recording sheet, and rolling the heat roller and the press roller together, A third step of holding the recording paper therebetween, and a fourth step of starting conveyance of the recording paper.
And a step of: Therefore, according to the present invention, when the conveyance of the recording paper is stopped, the heat roller and the press roller are separated from each other, and even when the conveyance is restarted, the over-fixing of the fixing device that can reliably prevent the over-fixation on the recording paper can be prevented. A prevention mechanism and an over-fixing prevention method thereof are provided.

[Brief description of the drawings]

FIG. 1 is a front sectional view schematically showing a configuration of an embodiment of an over-fixing prevention mechanism of a fixing device according to the present invention.

FIG. 2 is a perspective view showing a swing retreat structure of a heat roller.

FIG. 3 is a perspective view showing a swing biasing structure of a lever.

FIG. 4 is a plan view showing a configuration of a jam prevention claw.

FIG. 5 is a front front view for explaining an operation state of the jam prevention claw in a fixing operation state.

FIG. 6 is a front elevational view for explaining an operation state of the jam prevention claw in a retracted state.

FIG. 7 is a front sectional view showing a configuration of an over-fixing prevention mechanism.

FIG. 8 is a timing chart for explaining a print control operation in the control mechanism.

FIG. 9 is a front cross-sectional view showing a state in which a heat shielding sheet is interposed between the heat roller and the press roller immediately before the heat roller comes into contact with the press roller.

FIG. 10 is a front cross-sectional view showing a state in which the heat roller is in contact with the press roller with the heat shield sheet interposed therebetween immediately before restarting the conveyance of the fan hold paper.

FIG. 11 is a front cross-sectional view showing a state where conveyance on the fan hold is resumed and the heat shield sheet is taken out from between the heat roller and the press roller.

FIG. 12 is a timing chart for explaining a control operation for ending printing in the control mechanism.

[Explanation of symbols]

 P: Fan hold paper (recording paper) 10: Fixing roller pair 11: Heat roller 12: Press roller 60: Jam prevention claw 80: Over-fixing prevention mechanism 82: Heat shielding sheet 84: Moving mechanism 86: Control mechanism 88: Plunger 90 ... Electromagnetic solenoid 92 ... Coil spring 94 ... Support shaft 96 ... Connecting member.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G03G 13/20 G03G 15/20

Claims (11)

(57) [Claims] A heat roller and a press roller which are provided so as to be able to freely contact and separate from each other; and a driving means for moving and driving at least one of the heat roller and the press roller so as to move toward and away from the other; Heating means for heating the heat roller and thermally fixing the toner image on the continuous recording paper sandwiched between the press roller and the press roller; and When stopped, the fixing device drives the heat roller and the press roller so that the heat roller and the press roller are separated from each other and prior to the start of the conveyance of the continuous recording paper, so that the heat roller and the press roller are in rolling contact with each other. Disposed between the heat roller and the recording paper at the rolling contact portion of the roller and the press roller,
A heat shield member for at least reducing heat transfer from the heat roller to the recording paper in a state interposed between the heat roller and the heat roller; and a heat shield positioned between the heat roller and the press roller. A heat-shielding member moving means for moving between a position and a standby position deviating from the position, and the heat-shielding member is interposed between the heat roller and the press roller until the start of conveyance of the continuous recording paper. And a control means for controlling the heat-insulating member moving means so as to separate from the heat roller and the press roller with the start of conveyance of the continuous recording paper. Over-fixing prevention mechanism. 2. The fixing device according to claim 1, wherein the heat-shielding member is detached by the rotation of the heat roller or the press roller in response to the start of conveyance of the continuous recording paper. mechanism. 3. The heat shielding member moving means interposes the heat shielding member between the heat roller and the recording paper from a direction opposite to a direction in which the recording paper is transported. An over-fixing prevention mechanism of the fixing device described in the above. 4. An urging member for urging the heat shielding member in a direction in which the heat shielding member is taken out from between the heat roller and the recording paper in a direction in which the recording paper is transported. 4. An over-fixing prevention mechanism for a fixing device according to claim 3, further comprising an intervening means for interposing the heat shielding member between the heat roller and the recording sheet against the urging force of the urging member. . 5. The intervening means includes an electromagnetic solenoid for interposing the heat shielding member between the heat roller and the recording sheet against an urging force of the urging member in response to an input of a start signal. The over-fixing prevention mechanism of the fixing device according to claim 4, wherein: 6. When the conveyance of the recording paper is stopped, a separating means for separating the heat roller and the press roller which hold the recording paper in a rolling contact state from each other, and prior to the start of the conveyance of the recording paper, A heat shielding means interposed between the heat roller and the recording paper, a rolling contact means for rolling the heat roller and the press roller to each other, and sandwiching the recording paper between the heat roller and the press roller, An over-fixing prevention mechanism for a fixing device, comprising: a conveying unit that conveys the recording paper with the heat shielding unit interposed therebetween. 7. When the conveyance of the recording paper is stopped, a first step of separating a heat roller and a press roller holding the recording paper in a rolling contact state from each other, and starting the conveyance of the recording paper. Prior to this, a second step of interposing a heat shield member between the heat roller and the recording paper, a third step of rolling the heat roller and the press roller together to sandwich the recording paper therebetween, And a fourth step of starting the conveyance of the recording paper. 8. The method according to claim 7, wherein the recording paper is made of continuous paper. 9. The fixing device according to claim 7, wherein the fourth step is performed after the heat roller and the press roller in the third step have completed rolling contact with each other. Fixing prevention method. 10. The heat treatment apparatus according to claim 3, wherein the heat-insulating member is interposed between the heat roller and the recording paper in the second step, and then the heat roller and the press roller are brought into rolling contact with each other. The method for preventing over-fixing of a fixing device according to claim 7, wherein: 11. The method according to claim 7, wherein in the second step, the heat shielding member is inserted between the heat roller and the press roller from a direction opposite to a recording paper conveyance direction. 3. The method for preventing over-fixing of a fixing device according to item 1.