JP2003186264A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device that forms a high quality image without soiling a fixing device. <P>SOLUTION: The device is provided with a sheet thickness detection means 7. The sheet thickness detection means 7 has a light emitting element 71 that emits light to a sheet P between a sheet storage part 40 which stores sheets P and a transfer part 30 which transfers a toner image formed on an image carrier onto the sheet P. The sheet thickness detection means 7 also has a light receiving element 72 that receives transmission light emitted from the light emitting element 71 and passed through the sheet P. The thickness of the sheet is detected by the sheet thickness detection means 7. A control means 6 controls a toner image transfer operation and a toner image fixing operation based upon sheet thickness information transmitted from the sheet thickness detection means 7. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to sheet thickness detection and control based on the detected sheet thickness.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a laser printer, a copying machine, a facsimile, etc. to which an electrophotographic method is applied, a toner image is formed on an image carrier, the toner image is transferred to a sheet, and then the toner image is transferred. I try to fix the image.

Here, FIG. 7 is a diagram showing the structure of an image forming portion of such a conventional image forming apparatus. In FIG. 7, 33 is a photoconductor drum which is an image carrier, and 34 is a photoconductor drum. A charging roller which is a charging member for charging the surface of 33, 35 is a scanner which scans the surface of the photosensitive drum with laser light L, and 36 is a latent image formed on the surface of the photosensitive drum as described later using toner. The developing device 36 includes a developing sleeve 37 containing a cylindrical magnet.

Further, 38 constitutes a transfer portion together with the photosensitive drum 33, and a transfer roller for transferring the toner image onto a sheet such as a transfer paper, 39 a residual toner on the photosensitive drum is cleaned after the transfer of the toner image. Is a cleaning device, 32 is a high-voltage power supply that supplies a high voltage to the charging roller 34 and the developing sleeve 37, and 31 is a controller that controls the electrophotographic process sequence.
Is equipped with.

In the image forming section having such a structure, at the time of image formation, the charging roller 34 first applies a charging voltage of about -600 V to charge the surface of the photosensitive drum, and then, The surface of the photoconductor drum whose surface is charged is scanned by the laser L from the laser scanner 35 based on the image information to form a latent image on the photoconductor drum. Then, after this, the developing sleeve 3 is used by the developing sleeve 37.
The toner stored in 6 is attached to the surface of the photosensitive drum to develop the latent image, and a toner image is formed on the surface of the photosensitive drum.

Next, the toner image thus formed on the photosensitive drum is formed by the photosensitive drum 33 and the transfer roller 38 by applying a transfer bias of about +1 KV to 5 KV to the transfer roller 38. The image is transferred to a sheet (not shown) that has been conveyed to the transfer unit.

After the toner image on the photosensitive drum is transferred in this manner, the sheet is conveyed to a fixing device to fix the toner image, and thereafter, the sheet is discharged by a discharge roller. Further, the toner remaining after being transferred on the photosensitive drum is cleaned by the cleaning unit 39 to prepare for the next image formation again.

[0008]

By the way, in the conventional image forming apparatus provided with the image forming section having such a structure, two or more sheets are double-fed and a toner image is formed on the double-fed sheets. May be transcribed. Then, for example, when the toner image is transferred to the upper sheet thus double-fed, the heat is removed by the lower sheet that is double-fed to fix the toner image during the fixing operation in the fixing device. Insufficient heat may cause insufficient fixing. When such a fixing failure occurs, a problem occurs such that the fixing device is soiled with toner.

The transfer bias required to transfer the toner image varies depending on the thickness of the sheet. That is, the thicker the sheet, the higher the transfer bias required. However, in the conventional image forming apparatus, a constant transfer bias is applied regardless of the thickness of the sheet. Therefore, when the sheets are double-fed, it is possible to sufficiently transfer the toner image from the photosensitive drum. In some cases, the image could not be obtained and a defective image with low image density was obtained.

In a conventional image forming apparatus, a transparent sheet and an opaque sheet are distinguished by providing a light receiving element and a light emitting element with a sheet conveying path sandwiched therebetween, as disclosed in, for example, Japanese Unexamined Patent Publication No. 9-323465. And Japanese Patent Laid-Open Nos. 10-338387 and 1
As described in JP-A-1-109798 and JP-A-11-184317, a reflection type optical sensor is provided with an optical sensor for obtaining information about the surface of a sheet. There was nothing to obtain sheet thickness information.

Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide an image forming apparatus capable of forming a high-quality image without contaminating the fixing device. It is a thing.

[0012]

The present invention provides an image forming apparatus in which a toner image is formed on an image carrier, the toner image is transferred to a sheet, and then the toner image is fixed. Based on sheet thickness information from the sheet thickness detecting means provided between the sheet storing portion for storing the sheet and the transfer portion for transferring the toner image formed on the image carrier onto the sheet. And a control means for controlling the toner image transfer operation and the toner image fixing operation. The sheet thickness detecting means emits light to the sheet, and the sheet thickness detection means is irradiated from the light emitting element and transmitted through the sheet. And a light receiving element for receiving transmitted light.

Further, the invention is characterized in that the control means controls a transfer bias at the time of transferring the toner image to the sheet based on the sheet thickness information from the sheet thickness detecting means.

Further, the invention is characterized in that the control means controls a fixing temperature at which the toner image is fixed on the sheet based on the sheet thickness information from the sheet thickness detecting means.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a view showing the arrangement of an image forming apparatus according to the first embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 7 indicate the same or corresponding portions.

In FIG. 1, 1 is an image forming apparatus, and 2 is an image forming apparatus main body (hereinafter referred to as an apparatus main body). Further, 3 is an image forming section, 4 is a sheet feeding section for feeding the sheet P to the image forming section 3, and 6 is a control section which is a control means for controlling the electrophotographic process sequence. The image forming apparatus 1 is connected to a computer (not shown) via a network or the like.

Further, the sheet feeding section 4 has a pickup roller 41 for picking up the sheet P stored in the cassette 40, which is a sheet storage section, and the pickup roller 4.
A registration roller 42 is provided that conveys the sheet P sent out by No. 1 to the transfer portion 30 including the photosensitive drum 33 and the transfer roller 38 at a predetermined timing.

Then, the image forming apparatus 1 having such a configuration.
In the above, when the image forming operation is started, the surface of the photosensitive drum is first charged by the charging roller 34, and then the surface of the photosensitive drum is charged from the laser scanner 35 based on the image information. The laser L scans to form a latent image on the photosensitive drum. And after this,
The toner accommodated in the developing device 36 is attached to the surface of the photoconductor drum by the developing sleeve 37 to develop the latent image, and a toner image is formed on the surface of the photoconductor drum.

On the other hand, in parallel with this toner image forming operation, the sheet P stored in the cassette 40 is picked up by the pickup roller 41, and the picked up sheet P is thereafter exposed by the registration roller 42 at a predetermined timing. The sheet is conveyed to the transfer unit 30 configured by the body drum 33 and the transfer roller 38.

Next, when the sheet P is conveyed to the transfer section 30 as described above, a transfer bias is applied to the transfer roller 38, whereby the toner image formed on the photosensitive drum 33 is transferred to the sheet P. It

Next, the sheet P on which the toner image has been transferred in this way is conveyed to the fixing device 5 and the toner image is fixed thereon, and thereafter, the sheet P is provided on the upper surface of the apparatus main body 2 by the paper discharge rollers 81 and 82. The sheet is discharged to the discharged sheet stacking unit 21. Also,
The toner remaining after being transferred on the photosensitive drum is cleaned by the cleaning unit 39 to prepare for the next image formation again.

On the other hand, in the figure, reference numeral 7 designates, for example, a registration roller 42 located downstream of the cassette 40 and a transfer portion 30.
A thickness detection sensor that is a sheet thickness detection unit that is provided between the sheet and the sheet P and detects the thickness of the conveyed sheet P. Here, FIG. 2 shows the arrangement of the thickness detection sensor 7 in the sheet conveying path. As shown in FIG. 2, the thickness detection sensor 7 is illuminated by the light emitting element 71 and the light emitting element 71.
The light receiving element 72 receives light transmitted through the sheet P.

Here, the output of the light emitting element 71 may be as bright as white light used in a normal room, and is about 2000 to 6000 lux when measured by an illuminance meter in a pure state. Further, the light is condensed on the light-receiving side in a defocused manner so that the light is not focused.

In the present embodiment, the light emitting element 7
1 is MAG INSTRUMENT, CALIF
An ORNIA-USA product was used, and the light emitting element 71 was turned on indoors, and the illuminance of 4000 to 6000 lux was measured.

On the other hand, as the light receiving element 72, a light receiving element which easily reacts to infrared light, for example, a photodiode (model TPS706) manufactured by Toshiba Corp. is used.
Can be detected with a light amount of about 3500 lux.

As shown in the figure, the light emitting element 71 and the light receiving element 72 are installed with a space of 35 mm, and the sheet P is about 30 mm from the light emitting element 71 and the light receiving element 7 is provided.
It is set to pass a position separated by about 5 mm from 2. As a result, the light receiving element 72 can reliably receive the transmitted light emitted from the light emitting element 71 and transmitted through the sheet P.

Under these conditions, the thickness of the two types of sheets, that is, the ordinary sheet which is a normal sheet and the rough sheet which has a rough surface, and the thickness detection sensor 7 (light receiving element 7)
The relationship between the detection output (voltage value V) in 2) is as shown in Table 1 below, and FIG. 3 is a plot of the relationship. In the figure, the vertical axis represents the light receiving sensor output, and the horizontal axis represents the sheet thickness.

[0029]

[Table 1]

Here, the sheet P is usually 80 to 120.
Many of them have a thickness of about μm, and in terms of the surface condition and thickness of the sheet, for example, Xerox 4024-75
What is called g detects an output of about 2.1 V on plain paper. In the case of rough paper, an output of about 1.8V is detected.

On the other hand, when two sheets are double-fed,
As shown in the figure, the light receiving sensor output is 1.3V. Therefore, in the present embodiment, a table showing the relationship between the sheet thickness shown in Table 1 and the detection output (voltage value V) by the thickness detection sensor 7 is stored in a memory (not shown), and the control unit 6 is also provided. Is configured to detect the occurrence of double feeding based on the detection output (voltage value V) from the thickness detection sensor 7.

For example, when an image is formed on plain paper and a value of 1.3 V or less is detected as a detection output from the thickness detection sensor 7, it is determined that double feeding has occurred. When it is determined that the double feeding of the sheet P has occurred in this way, the image forming operation is stopped, and at the same time, the host computer connected via a network or the like is notified of the occurrence of the double feeding to notify the user. .

Thus, the light emitting element 71 and the light emitting element 7
The double feed of the sheet P is detected by comparing the detection output from the thickness detection sensor 7 having the light receiving element 72 that receives the transmitted light emitted from the sheet 1 and transmitted through the sheet P with the threshold value (1.3 V). In addition, when the double feed is detected, the image forming operation is stopped to prevent the double feed sheet P from entering the fixing device 5.

As a result, it is possible to prevent a problem such as a fixing failure due to insufficient heat due to double feeding, and the fixing device 5 being soiled with toner. Moreover, since the thickness of the sheet P can be detected in a non-contact manner by using the thickness detection sensor 7 having the above-described configuration, the sheet thickness can be detected without hindering the conveyance of the sheet P. it can.

By the way, in the above description, the case where the double feed is detected based on the detection output from the thickness detection sensor 7 has been described, but the present invention is not limited to this.
The transfer bias may be controlled based on the sheet thickness detected by the thickness detection sensor 7. Further, the roughness of the sheet surface may be detected based on the detection output from the detection sensor 7, and the fixing temperature of the fixing device 5 may be controlled based on the detected surface roughness.

Next, a second embodiment of the present invention in which the transfer bias is controlled based on the sheet thickness detected by the thickness detecting sensor 7 will be described.

In this embodiment, the transfer bias corresponding to the value detected by the thickness detection sensor 7 is applied to the transfer roller 38 based on the following relational expression.

Vtr = 1.5 * Vin-1 (Vtr: transfer bias V, Vin: thickness detection sensor detection value V)

Table 2 below is a table showing the relationship between the transfer bias V and the detection value of the thickness detection sensor, and FIG. 4 is a plot of it.

In the present embodiment, a table showing this relationship or the above relational expression is stored in a memory (not shown), and the control unit 6 controls the table or the relational expression and the thickness detection sensor. The transfer bias value is changed based on the detection output (voltage value V) from 7.

[0041]

[Table 2]

For example, based on the characteristics shown in FIG. 3, a value of 1.8V to 2.2V corresponding to a thickness of plain paper of 80 to 120 μm is set in the main body as a default state (detection value V of the light receiving sensor).
Is input, 1.7 KV to 2.3 KV is applied as a transfer bias value to the transfer roller 38 as a transfer bias value.

By applying a proper transfer bias according to the sheet thickness to the transfer roller 38 in this manner, a clear image of good quality without image distortion can be obtained on the sheet P.
Can be formed.

Next, the roughness of the sheet surface is detected based on the detection output from the thickness detection sensor 7, and the fixing temperature of the fixing device 5 is controlled based on the detected surface roughness. A third embodiment of the invention will be described.

By the way, as the fixing device 5, a heat roller type device using a general halogen lamp as a light source or an on-demand type device as shown in FIG. 5 is used. In the figure, 51 is a heater that generates heat, and 52 is a heater.
Is a pressure roller, 53 is a film, 54 is a pressure roller 52
Alternatively, an iron stay for supporting the film 53 and 55 are resin guides for supporting the film 53.

Here, in the case of rough paper having a rough surface, the light from the light emitting element 71 is diffusely reflected on the surface, so that the amount of transmitted light decreases. Therefore, the amount of light detected by the light receiving element 72 decreases, and the value of the detection output from the thickness detection sensor 7 decreases accordingly. Therefore, if the fixing temperature is controlled according to this value, the fixing property will be poor. That is, a sheet having a rough surface tends to have poor fixability.

Therefore, in the present embodiment, the fixing temperature is changed according to the thickness of the sheet and the roughness of the surface. For example, when the detected light receiving sensor output is lower than a predetermined threshold value, The fixing temperature is raised based on the formula.

T = -18.75 * Vin + 226.25 (T: fixing device temperature control temperature ° C, Vin: light receiving sensor detection value V)

FIG. 6 is a plot of the relationship between the fixing temperature and the thickness detection sensor detection value shown in Table 2 described above. Then, the table showing this relationship or the above relational expression is stored in a memory (not shown), and the control unit 6 controls the table or the relational expression and the detection output (voltage value V) from the thickness detection sensor 7. ), The fixing temperature T of the fixing device 5 is set.

By properly controlling the fixing temperature in accordance with the sheet thickness and the surface roughness in this manner, a clear image of good quality without any problem such as offset can be obtained on the sheet P.
Can be formed.

In the above description, the MAG INSTRUMENT, CALIF is used as the light emitting element 71.
Although the case where the light emitting element 71 made by ORNIA-USA is used has been described, the present invention is not limited to this, and the light emitting element 7 is not limited thereto.
You may make it use a red LED lamp as 1.

As an example of such a red LED lamp, an infrared light having a wavelength of 760 nm is used, the distance between the light receiving element 72 and the light receiving element 72 is 7 mm, and the distance between the light receiving element surface and the sheet is 3.5 mm. Even in this case, the same effect as that described above was obtained.

[0053]

As described above, as in the present invention, the sheet thickness detecting means is provided between the sheet storage portion and the transfer portion,
By controlling the toner image transfer operation and the toner image fixing operation based on the sheet thickness information from the sheet thickness detecting means, it is possible to form a high quality image without polluting the fixing device.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a thickness detection sensor provided in the image forming apparatus.

FIG. 3 is a diagram showing a relationship between a sheet thickness and a detection output of the thickness detection sensor.

FIG. 4 is a diagram showing a relationship between a transfer bias value and the output of the thickness detection sensor.

FIG. 5 is a diagram showing a configuration of a fixing device provided in the image forming apparatus.

FIG. 6 is a diagram showing a relationship between a fixing temperature control temperature and an output of the thickness detection sensor.

FIG. 7 is a diagram showing a configuration of an image forming unit of a conventional image forming apparatus.

[Explanation of symbols]

1 Image forming device 2 device body 3 Image forming section 6 control unit 7 Thickness detection sensor 71 light emitting element 72 Light receiving element 30 transfer part 33 photoconductor drum 40 cassettes

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H027 DC02 DE02 DE07 DE10 EA03                       EA12 EC06 EF09                 2H033 AA02 AA47 BA08 BA25 BA30                       BA59 BB01 BB28 BE03 CA07                       CA16 CA30                 2H200 FA08 FA09 GA04 GA10 GA23                       GA34 GA44 GB12 GB22 GB25                       GB26 GB44 HA02 HB12 JA02                       JA29 PA05 PA15 PB25 PB39                 3F048 AA02 AA04 AA05 AB01 BA06                       BA28 BB05 BD02 BD07 CA02                       DA06 DC13 EB37

Claims (3)

[Claims] 1. An image forming apparatus in which a toner image is formed on an image carrier, the toner image is transferred to a sheet, and then the toner image is fixed. A sheet thickness detecting unit provided between a transfer unit that transfers the toner image formed on the image carrier to a sheet, and a toner image transfer operation and a toner image based on the sheet thickness information from the sheet thickness detecting unit. Control means for controlling a fixing operation; and the sheet thickness detecting means, a light emitting element for irradiating the sheet with light, and a light receiving element for receiving transmitted light emitted from the light emitting element and transmitted through the sheet. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the control unit controls a transfer bias when the toner image is transferred to a sheet based on the sheet thickness information from the sheet thickness detecting unit. apparatus. 3. The control unit controls the fixing temperature when fixing the toner image on the sheet based on the sheet thickness information from the sheet thickness detecting unit. Image forming apparatus.