JP6094212B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus configured to transfer a developer image onto a recording sheet and thermally fix the image.

  In an image forming apparatus that forms an image on a recording sheet by transferring the developer image onto a recording sheet such as paper and heat-fixing it, the conveyance speed is adjusted according to the thickness of the recording sheet. What is configured to be switchable is known. For example, Patent Document 1 discloses an image forming apparatus that lowers the fixing speed (conveyance speed) when forming an image on thick paper than when forming an image on plain paper.

JP 2001-305825 A

  By the way, in a conventional image forming apparatus, a transfer bias (transfer) applied to a transfer member such as a transfer roller so that an image with a low printing rate such as a document can be satisfactorily transferred when the humidity is high in a mode in which the conveyance speed is low. Current) was set. Therefore, when an image with a high printing rate such as a black solid is to be transferred when the humidity is high in a mode with a low conveyance speed, the current applied to the developer between the image carrier that carries the developer image and the transfer member There is a possibility that transfer defects such as blurring may occur.

  On the other hand, in order to prevent the occurrence of transfer failure, a method of controlling the transfer bias (transfer current) according to the humidity can be considered. Therefore, there is a problem that it is difficult to control the transfer current within the narrow range.

  The present invention has been made in view of the above background, and an object of the present invention is to suppress transfer defects in an image forming apparatus capable of switching a recording sheet conveyance speed.

In order to achieve the above object, the present invention provides an image forming apparatus configured to transfer a developer image onto a recording sheet and thermally fix the image, and to carry the developer image. A transfer member configured to transfer a developer image on the image carrier onto the recording sheet by conveying the recording sheet between the image carrier and the image carrier, and to apply a transfer bias to the transfer member A transfer bias applying apparatus configured to detect a parameter related to humidity in the apparatus main body; and a control apparatus configured to control a conveyance speed of the recording sheet.
The control device controls a first mode for controlling the recording sheet to be transported at a first transport speed, and a second mode for controlling the recording sheet to be transported at a second transport speed that is slower than the first transport speed. Can be selectively executed, and when the parameter detected by the detection unit exceeds the predetermined value when the second mode is selected, the third conveyance speed of the recording sheet is higher than the second conveyance speed. It is controlled so that it is transported.

  According to such a configuration, if the parameter exceeds a predetermined value when the second mode is selected, that is, if the humidity is high in the mode where the conveyance speed is low, the recording sheet conveyance speed is increased. In this case, from the experimental results, the transfer current range in which transfer failure does not occur in a high humidity environment becomes wider than when the conveyance speed is low, and transfer failure can be suppressed. Thus, it is possible to transfer the toner image satisfactorily regardless of the conveyance speed of the recording sheet and the humidity in the apparatus main body.

  In the above-described image forming apparatus, the control device controls the transfer bias applying device to apply the first transfer bias to the transfer member in order to control the recording sheet to be conveyed at the second conveyance speed, and to record the recording sheet. In the case where the sheet is controlled to be conveyed at the third conveying speed, the transfer bias applying device can be controlled to apply a second transfer bias stronger than the first transfer bias to the transfer member. .

  According to this, since the force for attracting the developer image on the image carrier to the recording sheet becomes strong, it is possible to suppress the transfer failure even when the conveyance speed of the recording sheet is increased.

  In the image forming apparatus described above, the second mode may be a mode in which the developer image is transferred to a recording sheet thicker than the first mode and thermally fixed.

  According to this, since the heat fixing time can be extended as compared with the first mode, the developer image can be favorably heat fixed on a thick recording sheet.

  In the above-described image forming apparatus, the third transport speed may be a transport speed that is slower than the first transport speed.

  According to this, even if the conveyance speed of the recording sheet becomes the third conveyance speed that is higher than the second conveyance speed, the conveyance speed is slower than the first conveyance speed, so that the heat fixing time is secured. And fixing failure of a thick recording sheet can be suppressed.

  In the image forming apparatus described above, the detection unit can be configured to detect humidity in the apparatus main body as a parameter. In the above-described image forming apparatus, the detection unit may be configured to detect the resistance value of the transfer member as a parameter.

  According to the present invention, transfer failure can be suppressed in an image forming apparatus capable of switching the conveyance speed of a recording sheet.

1 is a diagram illustrating a schematic configuration of a laser printer as an example of an image forming apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure of a laser printer. It is a flowchart which shows the control by a control apparatus. Results of experiments confirming that when the humidity is high, the range of transfer current where transfer failure does not occur in the mode with low transfer speed becomes narrow, and the range of transfer current where transfer failure does not occur in mode with high transfer speed FIG.

  Next, an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. In the following, first, a schematic configuration of the laser printer 1 as an example of the image forming apparatus according to the present embodiment will be described, and then a detailed configuration of the laser printer 1 according to a characteristic part of the present invention will be described. In the following description, the direction will be described with reference to the user who uses the laser printer 1. That is, the right side in FIG. 1 is “front”, the left side is “rear”, the front side is “left”, and the back side is “right”. Also, the vertical direction in FIG.

<Schematic configuration of laser printer>
As shown in FIG. 1, the laser printer 1 is configured to transfer a toner image (developer image) onto a sheet S as an example of a recording sheet and thermally fix it. In the body 2, a paper feed unit 3, an exposure device 4, a process cartridge 5, and a fixing device 8 are mainly provided.

  The paper feed unit 3 is provided in the lower part of the main body housing 2, and includes a paper feed tray 31 that accommodates the paper S, a paper pressing plate 32, and a paper feed mechanism 33 mainly composed of a plurality of paper feed rollers. The registration roller 34 is mainly provided. The sheet S in the sheet feeding tray 31 is moved upward by the sheet pressing plate 32 and supplied to the process cartridge 5 by the sheet feeding mechanism 33 and the registration roller 34.

  The exposure device 4 is disposed in the upper part of the main body housing 2 and includes a laser light source (not shown), a polygon mirror, a lens, a reflecting mirror, and the like that are not shown. In the exposure device 4, the surface of the photosensitive drum 61 after charging is exposed by scanning the surface of the photosensitive drum 61 at high speed with laser light (see a chain line) based on image data emitted from the laser light source.

  The process cartridge 5 is disposed below the exposure apparatus 4 and is detachably mounted on the main body housing 2 through an opening formed when the front cover 21 provided on the main body housing 2 is opened. Yes. The process cartridge 5 includes a drum unit 6 and a developing unit 7.

  The drum unit 6 conveys a sheet S between a photosensitive drum 61 as an example of an image carrier configured to carry a toner image, a charger 62, and the photosensitive drum 61, so that a photosensitive drum is provided. A transfer roller 63 as an example of a transfer member configured to transfer the toner image on 61 to the sheet S is mainly provided. The developing unit 7 is configured to be detachably attached to the drum unit 6, and includes a developing roller 71, a supply roller 72, a layer thickness regulating blade 73, and a toner that contains toner (developer). The housing 74 is mainly provided with an agitator 75.

  In the process cartridge 5, the surface of the photosensitive drum 61 is uniformly charged by the charger 62, and then exposed by the laser beam from the exposure device 4, whereby the photosensitive drum 61 is statically based on image data. An electrostatic latent image is formed. Further, the toner in the toner container 74 is supplied to the developing roller 71 through the supply roller 72 while being stirred by the agitator 75, and the developing roller 71 and the layer thickness regulating blade 73 are rotated as the developing roller 71 rotates. It enters between and is carried on the developing roller 71 as a thin layer having a constant thickness.

  The toner carried on the developing roller 71 is supplied from the developing roller 71 to the electrostatic latent image formed on the photosensitive drum 61. As a result, the electrostatic latent image is visualized and a toner image is formed on the photosensitive drum 61. Thereafter, the paper S supplied from the paper supply unit 3 is conveyed between the photosensitive drum 61 and the transfer roller 63, so that the toner image formed on the photosensitive drum 61 is transferred onto the paper S. .

  The fixing device 8 is disposed behind the process cartridge 5, and mainly includes a heating roller 81 and a pressure roller 82 disposed so as to face the heating roller 81 and press the heating roller 81. In the fixing device 8, the sheet S on which the toner image is transferred is conveyed between the heating roller 81 and the pressure roller 82, so that the toner image is thermally fixed on the sheet S. The paper S on which the toner image has been thermally fixed is discharged onto a paper discharge tray 22 by a paper discharge roller 23.

<Detailed configuration of laser printer>
As shown in FIG. 2, the laser printer 1 further includes a motor 11, a transfer bias application device 12, a resistance value detection unit 13 as an example of a detection unit, and a control device 14.

  The motor 11 is a driving source for applying a driving force for transporting the paper S to the paper feed unit 3, the process cartridge 5, the fixing device 8, the paper discharge roller 23, and the like, and is configured to be able to change its rotation speed. Yes. The laser printer 1 according to this embodiment includes a known driving force transmission mechanism including a plurality of gears (not shown), and the driving force of the motor 11 is supplied to the paper feeding unit 3 and the process via the driving force transmission mechanism. It is transmitted to the cartridge 5, the fixing device 8, the paper discharge roller 23, and the like.

  The transfer bias applying device 12 is a device (power supply) configured to apply a transfer bias to the transfer roller 63, and is connected to the transfer roller 63. As the specific configuration of the transfer bias applying device 12, a widely known configuration can be adopted, and detailed description thereof will be omitted in this specification.

  The resistance value detecting means 13 is configured to detect a parameter related to the humidity in the main body housing 2, specifically, a resistance value of the transfer roller 63 as an example of the parameter. The resistance value of the transfer roller 63 decreases as the humidity in the main body housing 2 increases, and increases as the humidity in the main body housing 2 decreases. As a specific configuration for detecting the resistance value of the transfer roller 63, a widely known configuration can be adopted, and thus detailed description thereof is omitted in this specification. In the present embodiment, the resistance value detection unit 13 may be provided as one of functional units of the control device 14.

  The control device 14 is configured to control the operation of the laser printer 1 by controlling each part of the laser printer 1, such as controlling the conveyance speed of the paper S by controlling the rotation speed of the motor 11, for example. Device. The control device 14 includes a CPU, a RAM, a ROM, an input / output interface, and the like (not shown), and executes control by performing arithmetic processing based on preset programs and detection results of various sensors (not shown).

  In the present embodiment, the control device 14 is configured to selectively execute a plain paper printing mode as an example of the first mode and a thick paper printing mode as an example of the second mode. Each print mode can be selected by, for example, operating a control panel (not shown) provided in the main body housing 2 by the user.

The plain paper printing mode is a mode in which a toner image is transferred to plain paper and thermally fixed to form an image on the plain paper (printing mode suitable for image formation on plain paper). When the plain paper printing mode is selected, the control device 14 controls the rotational speed of the motor 11 so as to transport the paper S at the first transport speed V _fast . On the other hand, the thick paper printing mode is a mode in which a toner image is transferred to a paper thicker than the plain paper used in the plain paper printing mode, for example, a postcard or an envelope, and heat-fixed to form an image on the thick paper (thick paper). Printing mode suitable for image formation). When the thick paper printing mode is selected, the control device 14 controls the rotational speed of the motor 11 to transport the paper S (thick paper) at a second transport speed V _slow that is slower than the first transport speed V _fast. To control.

In addition, when the thick paper printing mode is selected and the humidity in the main body housing 2 is high, the control device 14 specifically decreases the resistance value R of the transfer roller 63 detected by the resistance value detection unit 13. When the threshold value _Rth for the resistance value of the transfer roller 63 as an example of a predetermined value set in advance is exceeded (below), the rotational speed of the motor 11 is controlled so that the sheet S (thick paper) is moved to the third position. It controls so that it may convey with the conveyance speed _Vmiddle .

In the present embodiment, the third transport speed V _middle is a transport speed that is faster than the second transport speed V _slow and is slower than the first transport speed V _fast (in order of speed). : _Vfast > _Vmiddle > _Vslow ).

In addition, when the thick paper printing mode is selected, the control device 14 controls the transfer bias applying device 12 to transfer the paper S at the second transport speed V _slow to control the transfer roller. A first transfer bias B _low is applied to 63. On the other hand, when the thick paper printing mode is selected, the control device 14 controls the transfer bias applying device 12 to transfer the paper S at the third transport speed V _middle to control the transfer roller. A second transfer bias B _medium is applied to 63. Further, the control device 14 controls the transfer bias applying device 12 to control the transfer roller when the plain paper printing mode is selected (when the paper S is controlled to be transported at the first transport speed V _fast ). A third transfer bias B _high stronger than the first transfer bias B _low is applied to 63.

In the present embodiment, the second transfer bias B _medium is a transfer bias stronger than the first transfer bias B _low and weaker than the third transfer bias B _high . Here, the strong transfer bias means a transfer bias that increases the force of attracting the toner on the photosensitive drum 61 to the paper S (in order of increasing force of attracting the toner: B _high > B _medium > B _low ). .

Next, the control by the control device 14 will be described in more detail with reference to the flowchart shown in FIG.
When a job including image data, a print start command, and the like is input, the control device 14 starts the process of the flowchart shown in FIG. 3 and determines whether or not the currently selected print mode is a cardboard print mode. Determine (S101).

When the selected print mode is not the thick paper print mode (No in S101), that is, when the selected print mode is the plain paper print mode, the control device 14 performs control so that the paper S is conveyed at the first conveyance speed V _fast. At the same time, image formation on the sheet S is executed while controlling to apply the third transfer bias B _high to the transfer roller 63 (S103). Then, when the image formation is completed, the control device 14 ends the processing of the flowchart shown in FIG.

On the other hand, when the selected printing mode is the cardboard printing mode (S101, Yes), the control device 14 acquires the resistance value R of the transfer roller 63 from the resistance value detection unit 13 (S105), and acquires the acquired resistance value R. Is lower than the threshold value _Rth , that is, whether the humidity in the main body housing 2 is high is determined (S107).

When the resistance value R is not lower than the threshold value _Rth (S107, No), that is, when the humidity in the main body housing 2 is low, the control device 14 conveys the sheet S at the second conveyance speed _Vslow. In addition to the control, image formation on the sheet S is executed while controlling to apply the first transfer bias B _low to the transfer roller 63 (S109). Then, when the image formation is completed, the control device 14 ends the processing of the flowchart shown in FIG.

When the resistance value R is lower than the threshold value _Rth (S107, Yes), that is, when the humidity in the main body housing 2 is high, the control device 14 is configured to convey the sheet S at the third conveyance speed _Vmiddle. In addition to the control, image formation on the sheet S is executed while controlling to apply the second transfer bias B _medium to the transfer roller 63 (S111). Then, when the image formation is completed, the control device 14 ends the processing of the flowchart shown in FIG.

According to the present embodiment described above, when the humidity is high in the thick paper printing mode in which the transport speed of the paper S is low, the transport speed of the paper S is changed from the second transport speed V _slow to the third transport speed V _middle . In this case, the range of transfer current that does not cause transfer failure in a high humidity environment is wider than when the transport speed is slow, so that the transfer current is set within the range. And transfer defects can be suppressed. Thereby, in the laser printer 1, it is possible to transfer the toner image satisfactorily regardless of the conveyance speed of the paper S and the humidity in the main body housing 2.

When the transport speed of the paper S is increased from the second transport speed V _slow to the third transport speed V _middle when the thick paper printing mode is selected, the transfer bias applied to the transfer roller 63 is set. Since the first transfer bias B _low is strengthened from the second transfer bias B _medium , the force for attracting the toner image on the photosensitive drum 61 to the sheet S is increased, and the conveyance speed of the sheet S is increased. Also, transfer defects can be suppressed.

  In the thick paper printing mode, the transport speed of the paper S is slower than in the plain paper printing mode, so that the time for passing through the fixing device 8, that is, the time for thermal fixing can be lengthened. As a result, the toner image can be satisfactorily heat-fixed on the thick paper.

Further, even when the transport speed of the paper S is changed to the third transport speed V _middle higher than the second transport speed V _slow when the thick paper printing mode is selected, the third transport speed V _middle is normal. Since it is slower than the first transport speed V _{fast in the} paper printing mode, it is possible to secure a heat fixing time. Thereby, even when the humidity is high in the thick paper printing mode, fixing failure of the thick paper can be suppressed.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. About a concrete structure, it can change suitably in the range which does not deviate from the meaning of this invention as follows.

In the above-described embodiment, the resistance value detection unit 13 that detects the resistance value R of the transfer roller 63 is exemplified as the detection unit that detects the parameter related to the humidity in the main body housing 2, but the present invention is not limited to this. It is not something. For example, the detection unit may be a humidity sensor that detects the humidity H in the main body housing 2 as another example of the parameter related to the humidity in the main body housing 2. When a humidity sensor is employed as the detecting means, the control device 14 causes the humidity H to exceed a threshold value H _th for humidity as another example of a predetermined value set in advance when the cardboard printing mode is selected. In this case, the sheet S is controlled to be conveyed at the third conveyance speed V _middle .

In the above embodiment, the third transport speed V _middle is a transport speed that is faster than the second transport speed V _slow and is slower than the first transport speed V _fast. Is not limited to this. For example, the third conveyance speed and the first conveyance speed may be the same conveyance speed. In the above embodiment, the second transfer bias B _medium is a transfer bias stronger than the first transfer bias B _low and weaker than the third transfer bias B _high. The invention is not limited to this. For example, the second transfer bias and the third transfer bias may be the same transfer bias.

  In the above embodiment, the control device 14 is configured to control the conveyance speed of the paper S by controlling the rotation speed of the motor 11, but the present invention is not limited to this. For example, when the image forming apparatus includes a speed change mechanism including a plurality of gears, the control device may be configured to control the paper transport speed by controlling the speed change mechanism.

  In the embodiment, the photosensitive drum 61 is exemplified as the image carrier. However, the present invention is not limited to this, and may be a photosensitive belt, an intermediate transfer drum, an intermediate transfer belt, or the like.

  In the embodiment, the laser printer 1 capable of forming only a monochrome image is exemplified as the image forming apparatus, but the present invention is not limited to this. For example, the image forming apparatus may be a printer capable of forming a color image, or may be a printer capable of forming an image on both sides of a sheet. The image forming apparatus is not limited to a printer, and may be, for example, a copier or a multi-function machine including a document reading apparatus such as a flat bed scanner.

  Next, it was confirmed that when humidity is high, the range of transfer current where transfer failure does not occur in the mode with low conveyance speed becomes narrow, and the range of transfer current where transfer failure does not occur in mode with high transfer speed is confirmed. The experiment will be described.

<Experiment method>
Under the following experimental conditions, using a laser printer equipped with a toner cartridge (development unit) after printing 1,000 sheets, changing the transfer current (transfer bias applied to the transfer roller) flowing through the transfer roller to each sheet (thick paper) Printing was performed, and the state of the image formed on each sheet, specifically, the presence or absence of ghost or fading was confirmed. Then, the range of the transfer current in which the state of the image was good (no ghosting or blurring occurred) was examined.

<Experimental conditions>
Environmental temperature: 32.5 ° C
Environmental humidity: 80% RH
Laser printer: HL-2130 (manufactured by Brother Industries, Ltd.)
Paper: Wausau Exact Index 110lb LTR
Paper transport speed: Full-speed mode or Half-speed mode Here, the half-speed mode is a half-speed transport speed of the full-speed mode.

<Experimental result>
In FIG. 4, the range indicated by the vertical bars is the range of the transfer current in which the image state was good, and the range outside the range indicated by the vertical bars is the range of the transfer current in which ghost or blur occurred in the image.
As shown in FIG. 4, in a high humidity environment, the transfer speed range in which the image state was better in the full speed mode with a high transport speed than in the half speed mode with a low transport speed, ie, transfer It was confirmed that the range of transfer current that does not cause defects is wide.

DESCRIPTION OF SYMBOLS 1 Laser printer 2 Main body housing | casing 12 Transfer bias application apparatus 13 Resistance value detection means 14 Control apparatus 61 Photosensitive drum 63 Transfer roller S Paper

Claims (3)

An image forming apparatus configured to transfer a developer image to a recording sheet and thermally fix the image,
An image carrier configured to carry a developer image;
A transfer member configured to transfer a developer image on the image carrier to the recording sheet by conveying the recording sheet to and from the image carrier;
A transfer bias applying device configured to apply a transfer bias to the transfer member;
Detection means configured to detect a parameter related to humidity in the apparatus body;
A control device configured to control the conveyance speed of the recording sheet,
In an environment where the parameter detected by the detection unit exceeds a predetermined value, the transfer in which the transfer speed of the recording sheet is higher in the mode in which the transfer speed of the recording sheet is higher than in the mode in which the transfer speed of the recording sheet is lower. It has the characteristic that the current range is wide,
The controller is
A first mode in which the recording sheet is controlled to be conveyed at a first conveying speed; and a mode in which a developer image is transferred to a recording sheet thicker than the first mode and heat-fixed; A second mode in which control is performed so as to transport at a second transport speed that is slower than the transport speed of 1;
If the parameter detected by the detection means when the second mode is selected exceeds a predetermined value, rather faster than the recording sheet second conveying speed, and, from the first transport speed also controlled so as to transport at a third transportation speed slow,
When the recording sheet is controlled to be conveyed at the second conveying speed, the transfer bias applying device is controlled to apply a first transfer bias to the transfer member, and the recording sheet is conveyed to the third conveying speed. In the image forming apparatus, the transfer bias applying device is controlled to apply a second transfer bias stronger than the first transfer bias to the transfer member in the case of controlling the transfer to be carried by the printer . The image forming apparatus according to claim 1 , wherein the detection unit detects humidity in the apparatus main body as the parameter. The image forming apparatus according to claim 1 , wherein the detection unit detects a resistance value of the transfer member as the parameter.

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