JPH06222700A - Fixing device - Google Patents

Abstract

PURPOSE:To provide a fixing device by which excellent fixing is executed regardless of the thickness of a recording medium and where the recording medium is not curled or wrinkled as a fixing device used in an electrostatic recording system image forming device and fixing a toner image on the recording medium to which the toner image is transferred. CONSTITUTION:This device is provided with a heat roller 11 driven to be rotated so as to heat the toner recording surface of the recording medium (recording paper) 100 where the toner image is formed in a state where it comes in contact with the toner recording surface, a backup roller 12 arranged so that the recording medium 100 may be held between the rollers 11 and 12 and rotatably supported, a pressing means (compression spring) 20 pressing the roller 12 to the roller 11 side, and a pressing force control means (eccentric cam) 22 changing the pressing force of the means 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device which is used in an electrostatic image recording type image forming apparatus or the like to fix a toner image on a recording medium onto which the toner image has been transferred.

In an image forming apparatus such as an electrophotographic apparatus, if a toner image is transferred onto a recording paper (recording medium), the toner may move or drop on the recording paper just by touching something. It is necessary to fix the toner image on the recording paper by pressure contact heating or the like.

[0003]

2. Description of the Related Art Generally, a heat roller, which is rotationally driven in a state of being in contact with the toner recording surface so that the toner recording surface of the recording paper is heated, is arranged so that the recording paper is sandwiched between the heat roller and the heat roller. A backup roller rotatably supported is provided, and the backup roller is biased toward the heat roller by a spring so that the pressing force (nip pressure) of the heat roller is applied to the toner recording surface of the recording paper.

However, the thicker the paper, the stronger the stiffness of the recording paper, so that the contact area of the recording paper with the heat roller becomes smaller at the same nip pressure. Further, since the heat absorption increases as the paper thickness increases, the surface temperature of the heat roller decreases when the fixing operation is continuously performed, resulting in poor fixing.

Therefore, it is necessary to increase the nip pressure as the recording paper becomes thicker. In the conventional fixing device, fixing is performed so that no problem occurs when the thickest recording paper is used. There is.

[0006]

However, when a thin recording paper is applied by applying a nip pressure corresponding to the maximum paper thickness, the nip pressure is too large compared to the stiffness of the recording paper, and the recording paper is curled. Wrinkles may occur. On the contrary, if the nip pressure is insufficient for thick paper, fixing failure occurs due to the above-mentioned phenomenon.

However, in the case of the conventional fixing device in which the backup roller is biased by the spring as described above, the spring is excessively compressed by the thickness of the recording paper, so that if the recording paper is thick, the nip pressure increases, If the recording paper is thin, the nip pressure will be small, but the change will be slight.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a fixing device in which good fixing is performed regardless of the thickness of the recording medium, and curling or wrinkling does not occur on the recording medium.

[0009]

In order to achieve the above-mentioned object, the fixing device of the present invention is shown in FIG.
Recording medium 10 on which a toner image is formed, as shown in FIG.
A heat roller 11 that is rotatably driven in contact with the toner recording surface so as to heat the toner recording surface of No. 0, and the recording medium 100 is disposed between the heat roller 11 and rotatably supported. Backup roller 12 and urging means 2 for urging the backup roller 12 so as to press it against the heat roller 11 side.
0 and an urging force control means 22 for changing the urging force of the urging means 20 are provided.

The urging force control means 22 reduces the urging force of the urging means 20 corresponding to the thickness of the recording medium 100 when the recording medium 100 is thin. Good.

[0011]

The recording medium 100 on which the toner image is formed has the heat roller 11 for heating the toner recording surface and the urging means 20.
The heat roller 1 is sandwiched between the heat roller 11 and the backup roller 12 pressed against the heat roller 11.
Sent by one revolution. The backup roller 12 rotates following it.

Then, when the thickness of the recording medium 100 is changed, the urging means 20 is urged by the urging force control means 22.
The pressing force of the rollers 11 and 12 against the recording medium 100 can be changed by changing the urging force of.

[0013]

Embodiments will be described with reference to the drawings. Figure 3
1 shows an electrophotographic printer used in a printer, a copier, or the like, and 1 in the drawing is a photosensitive drum that is rotationally driven at a constant speed.

Around the photosensitive drum 1, a charging device 2 for uniformly charging the surface of the photosensitive drum 1 is provided, and then the image light is irradiated with a laser beam or a light emitting diode array.
An exposure device 3 for irradiating the surface of the photosensitive drum 1 is arranged, and thereby an electrostatic latent image is formed on the surface of the photosensitive drum 1.

Reference numeral 4 denotes a developing device for developing the electrostatic latent image formed on the surface of the photosensitive drum 1 into a toner image.
The toner image formed there is transferred to the recording paper 100 by the transfer device 5. Reference numeral 7 is a cleaner for cleaning the toner remaining on the surface of the photosensitive drum 1.

A large number of recording papers 100 are arranged in a paper cassette 31 and are picked up by a pickup roller 32 in order from the uppermost recording paper 100. Then, the recording sheet 100 is conveyed by the sheet conveying roller 33, and a toner image is transferred when the recording sheet 100 passes between the photosensitive drum 1 and the transfer device 5, and then is transferred to the heating roller 11 and the backup roller 12 of the fixing device 10. The toner image is fixed on the recording paper 100 by being sandwiched and heated and pressed against each other. The recording paper 100 that has passed through the fixing device 10 in this manner is discharged to the stacker 35 by the discharging roller 34 and is stacked there.

FIGS. 1 and 2 show the fixing device 10. The heat roller 11 is formed of a metal material having a small heat capacity and a high thermal conductivity, such as an aluminum alloy, into a cylindrical shape, and is rotatably supported by the frame 14. A heater (not shown) including, for example, a halogen lamp is disposed inside the heater.

The heat roller 11 is rotationally driven in conjunction with the photosensitive drum 1 and the like by a recording paper conveying motor (not shown) via a gear 15 connected to the end portion.
As a result, the heat roller 11 is rotationally driven in contact with the toner recording surface so as to heat the toner recording surface of the recording paper 100 on which the toner image is formed.

The backup roller is made of a heat-resistant elastic material such as heat-resistant rubber, and its both ends are rotatably supported by a pair of bearings 17. The pair of bearings 17 is arranged so as to be movable in a direction toward and away from the heat roller 11 along a guide hole 18 formed in the frame 14.

Reference numeral 20 is a compression coil spring for urging the bearing 17 toward the central axis of the heat roller 11. This causes the backup roller 12 to move the recording paper 1
It is urged so as to be pressed against the heat roller 11 with 00 sandwiched therebetween.

The spring bearing portion for supporting the other end of the compression coil spring 20 is formed on the surface of the spring bearing plate 21 facing the backup roller 12, and the eccentric cam 22 is provided on the surface opposite to the spring bearing plate 21. The cam surface of is in sliding contact.

As shown in FIG. 2, both ends of the spring receiving plate 21 are slidably engaged with the guide holes 18, and both ends of the cam shaft 23 to which the eccentric cam 22 is fixed are connected to the frame 14. It is rotatably supported by.

The cam shaft 23 is rotationally driven by a step motor 25 via a reduction gear 24, and the rotational position of the eccentric cam 22 can be arbitrarily changed by the step motor 25.

Therefore, by controlling the rotation angle of the step motor 25, the eccentric cam 22 rotates and the spring receiving plate 21 is displaced, whereby the compression coil spring 20 urges the backup roller 12 against the heat roller 11. Can be changed.

The rotation operation of the step motor 25 is controlled by the operation of the operation switch 27.
It is controlled by the control unit 28 including (central processing unit).

In this embodiment, the thickness of the recording paper 100 is input from the operation switch 27. Then, when the recording paper 100 is thick, the control unit 28 exerts a large urging force of the compression coil spring 20, and the recording paper 10 has a large urging force.
When 0 is small, the step motor 25 controls the rotation angle of the eccentric cam 22 so that the biasing force becomes small.

FIG. 4 is a flow chart of the control process, S
Indicates a processing step. Here, it is first determined in S1 whether or not the panel switch 27 for inputting the paper thickness has been operated. If the paper thickness input operation has not been performed, the determination in S1 is repeated.

When the paper thickness input operation is performed in S1, the paper thickness is input in S2, and in S3, it is necessary to stop the step motor 25 at a rotation position where an appropriate nip pressure corresponding to the paper thickness is obtained. The number of steps required.

Then, in S4, a control signal for rotating the step motor 25 by the number of steps is output, and the process returns to S1. FIG. 5 shows the relationship between the paper thickness and the nip pressure controlled by the controller 28. Here, for example, recording paper 1
When the thickness of 00 is 0.18 mm (equivalent to 135 kg of fine quality), the nip pressure (linear pressure) is 0.6 kg / cm, and the recording paper 100
When the thickness is 0.08 mm (equivalent to 55 kg of fine quality), the nip pressure (line pressure) is controlled to be 0.25 kg / cm.

In this way, when the recording paper 100 is thick, a large nip pressure sufficient for good fixing is applied, and when the recording paper 100 is thin, the nip pressure is reduced to curl or wrinkle the recording paper 100. Etc. does not occur.

FIG. 6 shows a second embodiment of the present invention, in which the thickness of the recording paper is automatically detected and the nip pressure is automatically changed in response to the detection signal. It is a thing. In FIG. 6, reference numeral 33 denotes a pair of sheet conveying rollers, which are provided to face each other and are driven to rotate, as in the first embodiment, and the recording sheet 100 is sandwiched and conveyed between them.

The drive roller 33 of the paper transport rollers 33
The a is rotatably supported by the frame 40, and is rotationally driven by a carrying motor (not shown). The bearing 37 that rotatably supports the driven roller 33b is movably arranged on a straight line toward the axis of the drive roller 33a, and is biased by the compression coil spring 38 in the axial direction of the drive roller 33a.

The urging force of the compression coil spring 38 is detected by the pressure sensor 39 arranged between the bearing 37 and the frame 40. However, when the recording paper 100 is passed between the pair of paper transport rollers 33, the driven roller 33b retracts by the thickness of the paper, and the compression coil spring 38 is compressed and the urging force thereof changes.

Therefore, the detection signal from the pressure sensor 39 changes according to the thickness of the recording paper 100 passing therethrough,
The paper thickness of the recording paper 100 can be calculated from the pressure value. The output signal from the pressure sensor 39 is input to the control unit 28 similar to that of the first embodiment, and the step motor 25 for controlling the nip pressure of the fixing device 10 is controlled by the output signal from the control unit 28. It Other configurations are not shown, but are the same as in the first embodiment.

Next, the operation of the second embodiment will be described with reference to the control processing flow chart of FIG. Here, the output signal from the pressure sensor 39 is first input to the control unit 28 (S
11), the signal value changes as the recording paper 100 is picked up from the paper cassette by the pickup roller and is sandwiched between the pair of paper transport rollers 33.

The control unit 28 calculates the paper thickness at that time from the pressure value input from the pressure sensor 39. However, the actual calculation can be omitted and the input pressure value can be used as it is. Then, the number of steps required to stop the step motor 25 at the rotational position where an appropriate nip pressure (see FIG. 5) corresponding to the paper thickness at that time is obtained is calculated (S12).

Then, the control signal for rotating the step motor 25 by the number of steps is output from the control section 28 to the step motor 25 (S13) so that the nip pressure in the fixing device 10 is automatically adjusted according to the paper thickness. Controlled.

[0038]

According to the fixing device of the present invention, by providing the biasing force control means for changing the biasing force of the biasing means for pressing the backup roller to the heat roller side, the thickness of the recording medium used Since the nip pressure can be changed in accordance with the above, good fixing can be performed even if the recording medium is thick, and good fixing can be performed even if the recording medium is thin so that curling and wrinkles do not occur on the recording medium. You can

When the thickness of the recording medium is thin, the optimum nip pressure is automatically obtained by performing control corresponding to the thickness of the recording medium so that the urging force of the urging means is reduced. Therefore, good fixing can be performed.

[Brief description of drawings]

FIG. 1 is a front view of a first embodiment.

FIG. 2 is a side view of the first embodiment.

FIG. 3 is a configuration diagram of a printer according to a first embodiment.

FIG. 4 is a flow chart of control processing of the first embodiment.

FIG. 5 is a diagram showing the operation of the first embodiment.

FIG. 6 is a partial configuration diagram of a second embodiment.

FIG. 7 is a control processing flowchart of the second embodiment.

[Explanation of symbols]

 11 Heat Roller 12 Backup Roller 20 Compression Coil Spring (Biasing Means) 22 Eccentric Cam (Biasing Force Controlling Means) 25 Step Motor 28 Control Section

Claims (2)

[Claims] 1. A recording medium (100) having a toner image formed thereon.
Of the recording medium (10) between the heat roller (11) and the heat roller (11) which are rotatably driven in a state of contacting the toner recording surface so as to heat the toner recording surface.
0) and a rotatably supported backup roller (12), and urging means (2) for urging the backup roller (12) to press it toward the heat roller (11).
0) and an urging force control means (22) for changing the urging force of the urging means (20). 2. The biasing force control means (22) corresponds to the thickness of the recording medium (100), and the recording medium (10).
The fixing device according to claim 1, wherein the biasing force of the biasing means (20) is reduced when the thickness of (0) is thin.