JP2007310269A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small, inexpensive image forming apparatus by using a common power source, thereby reducing the number of power sources incorporated in the apparatus. <P>SOLUTION: The image forming apparatus forms an image in such a manner that a toner image formed on the surface of a photoreceptor drum and primarily transferred to an intermediate transfer belt is secondarily transferred to recording paper conveyed while held between the intermediate transfer belt and a transfer roller 17 and, then, the transferred toner image is heated and pressed by a pair of fixing rollers, thereby fixing the toner image to the recording paper. In the image forming apparatus, the constant current bias of a secondary transfer bias is applied by connecting a constant current power source 61 to the roller shaft 17b of the transfer roller so that electricity is conducted. On the other hand, a constant voltage bias is applied by bringing an electrode 65, connected to the constant voltage power source 62 for fixing, into contact with the roller shaft by the contact of the transfer roller with the intermediate transfer belt and the separation of the transfer roller from the belt. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an image forming apparatus, and more particularly, to an apparatus that achieves cost reduction and size reduction by sharing a power source that applies a potential to each unit.

2. Description of the Related Art Conventionally, an electrophotographic recording type image forming apparatus that exposes and forms an electrostatic latent image based on image data on the surface of a carrier made of a photosensitive member has been known. A toner image on the surface of the carrier carried by developing the toner with a developing device is transferred and fixed on a recording medium such as recording paper to form an image.

This type of image forming apparatus is equipped with a power supply for applying a transfer bias for transferring a toner image from the surface of a carrier to a recording medium by using toner charging, and fixing by heating and pressing the recording medium. A power supply for applying a fixing bias is also mounted so that the image quality of the toner image to be applied does not deteriorate (see, for example, Patent Document 1).

Also known is an image forming apparatus that employs a configuration in which an intermediate transfer belt is provided as a carrier so that a toner image on the surface of the photosensitive carrier is primarily transferred onto the intermediate transfer belt and then secondarily transferred to a recording medium. In this image forming apparatus, yellow (Y), cyan (C), magenta (M), and black (K) color toners are prepared, and toner images for the respective colors are primarily transferred and overlaid. After a color image is formed on the surface of the transfer belt, the color toner image can be secondarily transferred to a recording medium (see, for example, Patent Documents 2 and 3). In addition,
In the image forming apparatus including the intermediate transfer belt, a power source for applying a transfer bias for transferring the toner image on the surface of the photoreceptor or the intermediate transfer belt is mounted.
JP 2004-138841 A Japanese Patent Laid-Open No. 10-240030 JP 11-288184 A

Accordingly, an object of the present invention is to provide a small and low-cost image forming apparatus by reducing the number of power supplies to be mounted by promoting the common use of power supplies.

A first invention of an image forming apparatus that solves the above problems includes a carrier that carries a toner image obtained by developing an electrostatic latent image based on image data, and a toner that adheres to the electrostatic latent image on the surface of the carrier. A developing device that forms a toner image by developing, a transfer belt that primarily transfers and carries the toner image formed on the surface of the carrier, and a primary transfer unit that primarily transfers the toner image from the surface of the carrier to the surface of the transfer belt And a secondary transfer portion that secondarily transfers the toner image from the surface of the transfer belt to the recording medium, and a fixing portion that fixes the toner image transferred to the recording medium to the recording medium. An image forming apparatus for forming an image by transferring a toner image obtained by developing an electrostatic latent image from a surface of a carrier onto a recording medium via a transfer belt and fixing the toner image on the recording medium. A constant voltage power source and a constant current power source are arranged as means for applying a secondary transfer bias for transferring, and a toner image transferred on the recording medium is stably attached to the surface of the recording medium. A constant voltage power source is arranged as means for applying the fixing bias, and the constant voltage power source is connected in a conductive manner so that a bias can be applied in common use for secondary transfer and fixing, and is synchronized with the secondary transfer operation. A connection / disconnection means for connecting / disconnecting the conduction connection is applied so as to apply the secondary transfer bias.

In the present invention, a constant voltage is applied as a transfer bias and a fixing bias from a common constant voltage power source to each of the secondary transfer position and the fixing position, and the application of the transfer bias is unnecessary in synchronization with the secondary transfer operation. The connection is cut so as not to cause a potential difference. Therefore, it is possible to reduce the common constant pressure power source that has been provided for both the secondary transfer and the fixing, thereby reducing the cost and the size.

In addition to the specific matters of the first invention, the second invention of the image forming apparatus that solves the above problems
As the secondary transfer section, a secondary transfer bias is applied to contact and separate the toner image from the surface of the carrier to the transfer belt surface to which the toner image is primarily transferred, and to secondary transfer the toner image on the transfer belt surface to a recording medium. The transfer roller is provided, and as the connection / disconnection means, a contact for connecting / disconnecting the conductive connection with the constant voltage power source by the contact / separation operation of the transfer roller with respect to the transfer belt surface is interposed. It is what.

In the present invention, a secondary transfer bias is applied from a common constant voltage power supply to the transfer roller, and the transfer bias is cut off and connected in accordance with the contact and separation of the transfer roller with respect to the transfer belt. Therefore, the transfer bias of the transfer roller that is separated from the toner image on the surface of the transfer belt does not act to deteriorate the image.

A third invention of an image forming apparatus that solves the above-described problem is in addition to the specific matter of the first invention,
A guide member made of a conductive material for guiding a recording medium is disposed at a secondary transfer position by the secondary transfer unit, and the guide member is electrically connected to a constant voltage power source. The guide member is connected to the recording medium. It functions as a connection / disconnection means for connecting / disconnecting the application of the transfer bias when guiding the image to the secondary transfer location.

In the present invention, a constant voltage from the constant voltage power source is applied as a transfer bias to the recording medium guided by a guide member that is conductively connected to a common constant voltage power source, while the recording medium is When sent further downstream, application of the transfer bias is cut off. Therefore, the application of the transfer bias can be appropriately disconnected without requiring a special mechanism / control synchronized with the secondary transfer operation, and the cost and size can be further reduced.

A fourth invention of an image forming apparatus that solves the above-described problem includes sensor means for acquiring temperature and humidity information in the apparatus main body in addition to the specific matters of any of the first to third inventions, The output voltage of the constant voltage power supply is adjusted based on temperature and humidity information from the sensor means.

According to the present invention, the potential generated at the application location changes according to the resistance component at the location where the constant voltage is applied, in other words, depending on the temperature and humidity, but the output voltage of the constant voltage power supply is adjusted based on the detection information. By doing so, a transfer bias higher than the necessary voltage can be applied. Therefore, the quality of the toner image transferred to the recording medium can be maintained more than desired.

Here, it is needless to say that the common use of the constant voltage power supply can be applied to an image forming apparatus having a configuration that does not include a transfer belt.

As described above, according to the present invention, the constant voltage power source for applying the transfer bias and the fixing bias can be shared, and the transfer bias applied to the transfer position while applying the fixing bias to the fixing position is synchronized with the transfer operation. Therefore, the image forming apparatus can be reduced in cost and size.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, the best embodiment of the invention will be described with reference to the drawings. 1 to 8 are views showing a first embodiment of an image forming apparatus according to the present invention.

1 and 2, the image forming apparatus is a printer that is used by connecting to an external device such as a personal computer PC for creating and outputting an image such as a character. An image recording apparatus 10 that receives image data and records and forms it on one side or both sides of a recording sheet (recording medium) by an electrophotographic method, and transports a plurality of stacked recording sheets to the image recording apparatus 10 and images. An image is recorded on the recording sheet by including a sheet conveying device 30 that unloads the recording sheet that has been recorded and stacked, and a control unit 40 that performs overall control of the image recording device 10 and the sheet conveying device 30. Form and print out.

In brief, the image recording apparatus 10 irradiates a laser beam scanning apparatus 11 that scans the laser beam L based on image data and a laser beam from the laser beam scanning apparatus 11 that is charged by a charger (not shown). A photosensitive drum (second carrier) 12 on which an electrostatic latent image based on image data is exposed and formed on the surface by scanning, yellow (Y), cyan (C), magenta (
M) Each color that contains toner of black (K) and develops the electrostatic latent image on the surface of the photosensitive drum 12 by the developer roller 14a frictionally charging the toner to selectively adhere (carry) the toner. Each developing cartridge 14 and the developing rotary unit 15 which stores the developing cartridge 14 in the installation space for each color and rotates around the rotation shaft 15a.
And an intermediate transfer belt (first image) that forms and carries a toner image (monochrome image or color image) that can be transferred and recorded on a recording sheet by receiving the toner image developed on the photosensitive drum 12 by primary transfer. The carrier 16) and the conveyed recording paper are transferred to the intermediate transfer belt 1.
The toner image carried by the intermediate transfer belt 16 is secondarily transferred by being pressed (niped) between the transfer roller 17 and the transfer roller 17 that conveys the recording paper to the downstream side, and the toner image. Heat roller (heating roller) on the recording paper that has been transferred and conveyed
A fixing roller pair 18 is provided for fixing the toner image by heating and pressing between the pressure roller 18b and the pressure roller 18b, and for nipping and conveying the recording paper further downstream.

As a result, the image recording apparatus 10 develops the electrostatic latent image based on the image data formed on the surface of the photosensitive drum 12 by the laser beam scanning device 11 in the development rotary unit 15 switched according to the image data. The cartridge 14 is configured to develop toner, and the toner image on the photosensitive drum 12 is subjected to primary transfer by applying a primary transfer bias (giving a potential difference) to the intermediate transfer belt 16, and By applying a secondary transfer bias to the transfer roller 17 on the back side, a secondary transfer potential is applied between the transfer roller 17 and the intermediate transfer belt 16 to perform secondary transfer recording on the recording sheet conveyed by the sheet conveying device 30. After this
The fixing roller pair 18 is heated and pressed to fix the image to form an image. At this time, for example, when the developing rotary unit 15 contains a developing cartridge 14 containing toner of each color of yellow (Y), cyan (C), magenta (M), and black (K), the photosensitive drum By switching the color of the toner that develops the electrostatic latent image on the image 12, the toner of each color is overlaid or selected based on the received image data, and a color image to a single color image is printed on a recording sheet. be able to. Further, when the developing rotary unit 15 contains the developing cartridge 14 containing toner of the same color, for example, black (K), in all the developing cartridges 14, the electrostatic latent image on the photosensitive drum 12. Can be used as a dedicated machine that sequentially switches the developing cartridge 14 that develops the image and continuously prints and forms monochrome images on recording paper.

Briefly, the paper transport device 30 is detachably set at the lower part of the main body of the device, and a paper cassette 31 on which a plurality of recording papers are stacked, and a lifting plate 31 on the bottom surface of the paper cassette 31.
A pickup roller 32 that pulls out the uppermost recording sheet and rotates it to the transport path f by rotating in pressure contact with the recording sheet bundle raised by a, and receives the recording sheet sent out by the pickup roller 32 further downstream A pair of relay transport rollers 33 that are nipped and transported to the transport path f of the paper, and a recording sheet in the transport path f transported by the pair of relay transport rollers 33 to receive an image by the intermediate transfer belt 16 and the transfer roller 17 of the image recording apparatus 10 A pair of registration rollers 34 that are nipped and conveyed to the recording forming position of the recording roller, and a conveyance path f that passes between the intermediate transfer belt 16 and the transfer roller 17 and between the fixing roller pair 18 from the registration roller pair 34 to one side. A switching roller that receives a recording sheet on which a fixed image is formed and nipping and conveying the recording sheet to a downstream conveyance path f. A roller pair 35, conveyance path f of the switching roller pair 35 conveys
And a discharge roller pair 36 that receives the recording paper in the recording medium, carries it out onto the discharge table 39 at the top of the apparatus body, discharges it, and stacks it. Note that the intermediate transfer belt 16 and the transfer roller 17 and the fixing roller pair 18 of the image recording apparatus also have a function of conveying a recording sheet, and thus constitute a part of the sheet conveying apparatus 30.

As a result, the sheet conveying device 30 transfers the recording sheet pulled out from the sheet cassette 31 by the pickup roller 32 to the registration roller pair 34 via the relay conveyance roller pair 33, and then the registration roller pair 34 records the image. To synchronize with the operation of the device 10,
The recording sheet is fed to an image recording position where the intermediate transfer belt 16 and the transfer roller 17 are pressed against each other. A recording sheet on which the toner image on the intermediate transfer belt 16 is transferred and fixed by a pair of fixing rollers 18 is recorded. Are received by the switching roller pair 35 and the paper discharge roller pair 36 and are carried out and discharged onto the paper discharge table 39 to be stacked.

Here, the sheet conveying apparatus 30 reverses the recording sheet on which the image is formed on one side and sends it to the conveying path f on the upstream side of the registration roller pair 34 and its path r.
The pair of intermediate conveyance rollers 37 and 38 disposed on the sheet discharge roller 39 and the switching roller pair 35 are reversed to switch back from the sheet discharge table 39 to be re-conveyance path r.
The recording paper fed in is received by the intermediate conveyance roller pair 37, 38 and the registration roller pair 3
By passing the image to 4, the image can be formed on both sides of the recording paper.

The control unit 40 will be briefly described. The CPU (not shown) executes various processing procedures in accordance with a processing program stored in the memory, so that the personal computer PC
A controller unit 41 for exchanging various types of information such as a print command with the printer driver, receiving image data such as text to form an image on a recording sheet, and temporarily storing it in a memory (not shown); An image recording apparatus using the RAM 45 as a work area in parallel with the CPU 42 receiving, for example, image data from the controller unit 41 according to a control program stored in the ROM 43 and temporarily storing it in the main body memory 44. The engine control unit 46 that forms an image based on the image data on the recording paper by exchanging various information between the printer 10 and the paper transporting device 30 is constructed on a circuit board mounted in the apparatus main body. Yes.

As a result, the control unit 40 receives so-called RGB data of red (R), green (G), and blue (B) from the image data received from the personal computer PC. Therefore, the controller unit 41 can print these yellow data. (Y), magenta (M), cyan (
C), while converting the image data of so-called YMCK data of black (K), for example, it is read out from the memory in units of pages and transferred to the engine control unit 46, and this engine control unit 4
6 forms an image on a recording sheet by controlling the image recording apparatus 10 and the sheet conveying apparatus 30 based on the image data.

The control unit 40 uses the timer function 42a built in the CPU 42 to measure various processing times, etc., so that each part of the apparatus operates optimally and executes this image formation control. The recording device 10 and the paper transport device 30 are connected via an I / O interface 47 so that various types of information can be exchanged with the controller unit 41 and the engine control unit 46, and the engine control unit 46 is connected to the image recording device. 10, the digital signal (D) is converted into an analog signal (A), or the analog signal is converted into a digital signal so that various information exchanged between the paper transport device 30 and the controller unit 41 can be processed respectively. A D / A converter 48 and an A / D converter 49 for conversion are provided.

The intermediate transfer belt 16 of the image forming apparatus is formed in an endless belt shape that is wound around a primary transfer pulley 51, a secondary transfer pulley 52, a driven pulley 53, and tension pulleys 54 and 55. . The primary transfer pulley 51 is the developed photosensitive drum 1.
2 is disposed at a transfer position for primary transfer of the toner image on the intermediate transfer belt 16, and faces the photosensitive drum 12 on the back side of the intermediate transfer belt 16. The secondary transfer pulley 52 is disposed at a recording formation position where the toner image on the intermediate transfer belt 16 subjected to the primary transfer is secondarily transferred to a recording sheet between the transfer roller 17 and an image is recorded. Intermediate transfer belt 1
6 faces the transfer roller 17 on the back side. The driven pulley 53 is a secondary transfer pulley 5.
2 and is rotated by the rotation of the intermediate transfer belt 16. Tension pulleys 54 and 55 are provided between the intermediate transfer belt 16 between the secondary transfer pulley 52 and the driven pulley 53.
The intermediate transfer belt 16 is tensioned from the back side thereof so as not to cause a positional shift or the like.

The intermediate transfer belt 16 is driven to rotate in a state in which the intermediate transfer belt 16 is in close contact with the transfer drum 51 on the back side with respect to the photosensitive drum 12 when a single color monochrome image is formed with black (K) toner, for example. In the same manner as described above, the transfer roller 17 is also driven and rotated in close contact with the surface of the transfer roller 17 to transfer the toner image. On the other hand, as shown in FIG. 3, the transfer roller 17 is rotatable by a rotating member 57 that rotates about a rotating shaft 57a in a direction in which the intermediate transfer belt 16 contacts and separates from the secondary transfer pulley 52. Are supported by yellow (Y), cyan (
C) When a color toner image is formed by superimposing toner images formed of magenta (M) and black (K) toners, the toner image is rotated in a direction away from the intermediate transfer belt 16 and waits. It has become. Needless to say, the transfer roller 17 may be brought into contact with or separated from the surface of the intermediate transfer belt 16 even when a monochrome image such as a monochrome image is formed.

In this image forming apparatus, the toner image on the surface of the photosensitive drum 12 is transferred to the intermediate transfer belt 16.
Therefore, the intermediate transfer belt 16 also has a high-quality toner image formed on the intermediate transfer belt 16 in the same manner as the photosensitive drum 12, and the transfer roller 1 is used.
7 is required to be transferred to the recording paper conveyed between the two.

From this, the photosensitive drum 12 is uniformly charged on the surface of the photosensitive layer by the charger, whereas the intermediate transfer belt 16 has a belt main body 16a and a resistor as shown in FIG. A conductive layer 16c is formed on the entire surface between the layer 16b and an electrode portion 16d that is electrically connected to the conductive layer 16c is formed over the entire circumference instead of the resistor layer 16b on the side. The electrode roller 56 is brought into pressure contact with the electrode portion 16d so as to positively adsorb (adhere) the toner charged to a negative potential by frictional charging in the developing cartridge 14 from the power source portion 21. By applying a positive voltage, it is designed so that the toner can be held evenly over the entire surface. Since the intermediate transfer belt 16 is pressed from the back side to the primary transfer roller 52 and presses against the photosensitive drum 12, the photosensitive drum 12 is connected to the intermediate transfer belt 16 as shown in FIG. Electrode portion 16 exposed on the side side
d is in contact with the photosensitive layer 12b on the surface of the conductive portion 12a, and if there is a pinhole or the like in the photosensitive layer 12b, a current leak occurs with the intermediate transfer belt 16 that is originally insulated. Therefore, the insulating portion 12c that can be interposed in a sufficient area between the electrode portion 16d is formed over the entire circumference.

On the other hand, the transfer roller 17 is produced in a cylindrical shape of a sponge-like resistor elastic body in which a main body portion 17a for bringing a recording sheet into close contact with the intermediate transfer belt 16 is foamed by mixing an additive with a conductive material. The transfer roller 17 includes a metal roller shaft 1 that passes through the axis of the main body 17a.
A secondary transfer bias for transferring the toner image on the surface of the intermediate transfer belt 16 onto the recording paper is applied from the power source unit 7b.

Further, the fixing roller pair 18 tends to disturb the unfixed toner image immediately before the fixing nip because the moisture of the recording sheet is ejected from the fixing nip toward the upstream side in the sheet conveying direction when the recording sheet is heated. Therefore, in order to increase the force for holding the toner on the recording paper, a fixing bias is applied to the pressure roller 18b positioned on the back side of the fixing surface of the toner image while being pressed against the heat roller 18a.

Specifically, a constant voltage and a constant current are applied to the transfer roller 17 in order to transfer the toner image on the surface of the intermediate transfer belt 16 to the recording sheet that is in close contact with the transfer roller 17 with high reliability. Designed to apply a transfer bias, the fixing roller pair 18 is subjected to a fixing operation by being heated and pressed in a stable state by attracting charged toner adhering to one side of the recording paper. It is designed to apply a constant voltage fixing bias to the pressure roller 18b on the back side.

As shown in FIG. 5, the transfer roller 17 is connected to a roller shaft 17 b so that a constant current power supply 61 can apply a constant current transfer bias, and the pressure roller 18 of the fixing roller pair 18.
A constant voltage power source 62 is connected to the roller shaft 18c of b so that a fixing bias of a constant voltage can be applied. The transfer roller 17 only needs to be applied with a constant voltage / constant current transfer bias that is set in advance when the toner image is subjected to secondary transfer while being brought into contact with the intermediate transfer belt 16. The fixing roller having a constant voltage higher than the voltage capable of attracting the charged toner to the recording paper may be applied to the pressure roller 18b.

Accordingly, the transfer roller 17 causes the main body portion 17a to contact and separate from the intermediate transfer belt 16 by forward and reverse rotation of the rotation member 57, so that the transfer roller 17 always slides on the end surface of the roller shaft 17b as shown in FIG. A constant current power supply 61 is cable-connected to the electrode 63 that is in contact and in conductive contact via a connector 64 to apply a constant current transfer bias. The roller shaft 17 b is provided with an electrode (contact point) 65 that is brought into contact with and separated from the roller member 17 by a turning operation by the turning member 57, and a fixed roller connected to the pressure roller 18 b of the fixing roller pair 18. A voltage power source 62 is connected to a cable to apply a constant voltage transfer bias, and the application is disconnected. That is, the electrode 65 constitutes a connection / disconnection means.

As a result, as shown in FIG. 7A, the transfer roller 17 forms the toner image on the surface of the intermediate transfer belt 16, particularly yellow (Y), cyan (C), magenta (M).
The toner image formed by each color toner of black (K) is overlapped to form a color toner image, and at the same time as waiting for the main body portion 17a to be separated from the intermediate transfer belt 16, the roller shaft 17b. Thus, the electrode 65 is separated from the constant voltage power supply 62 to block the voltage application. On the other hand, as shown in FIG. 7B, the transfer roller 17 rotates and moves in the direction in which the main body portion 17a is brought into close contact with the timing at which the secondary transfer for receiving the toner image on the surface of the intermediate transfer belt 16 is performed. As a result, the electrode 65 is in conductive contact with the roller shaft 17b, and the constant voltage power source 62
The fixing bias applied to the pressure roller 18b of the fixing roller pair 18 is applied as a constant voltage transfer bias. For this reason, the fixing bias of the constant voltage power supply 62 does not act on the toner image on the surface of the intermediate transfer belt 16 to deteriorate the image quality. The transfer roller 17
The constant current power supply 61 that is conductively connected to the roller shaft 17b may be turned on / off independently according to the application of the transfer bias, and may be conductively connected to the electrode 65 in the same manner as the transfer bias of the constant voltage. Needless to say.

At this time, the CPU 42 of the control unit 40 only needs to apply a fixing bias to the pressure roller 18b of the fixing roller pair 18 so as to attract the charged toner to the recording paper, while the transfer roller 17 has an intermediate transfer. Since it is necessary to apply a constant voltage / constant current transfer bias necessary for transferring the toner image to the recording paper with high quality to the belt 16 side, the output voltage of the constant voltage power source 62 is the ambient temperature. Control to output a lower limit voltage of the transfer bias according to the humidity environment.

Here, the CPU 42 of the control unit 40 detects the temperature of the heat roller 18a of the fixing roller pair 18 and based on the detection information from the detection information of the sensor unit (sensor means) 22 that detects the humidity in the apparatus main body. For example, as shown in FIG. 8, control is performed such that the lower limit voltage set according to the detected temperature sections 0 to 7 and the detected humidity sections 0 to 4 is output from the constant voltage power supply 62. In this embodiment, the case where the temperature and humidity in the apparatus main body is directly detected by the sensor unit 22 will be described. For example, the lower limited voltage output from the constant voltage power supply 62 is controlled only by the temperature or humidity. However, it goes without saying that it is preferable to precisely control the temperature and humidity as in the present embodiment.

Accordingly, a constant voltage fixing bias is applied from the set of constant voltage power sources 62 without preparing a constant voltage power source for each of the transfer roller 17 and the fixing roller pair 18, and a lower limit voltage corresponding to the ambient temperature and humidity is set. A transfer bias can be applied, and the transfer bias can be disconnected by a rotation operation when the transfer roller 17 contacts and separates from the intermediate transfer belt 16.

As described above, in this embodiment, the power supply for applying a constant voltage to the transfer roller 17 and the fixing roller pair 18 can be reduced by using the constant voltage power supply 62 in common, and the surrounding temperature and humidity are given priority to the transfer bias. The lower limit voltage corresponding to the output voltage can be output from the constant voltage power supply 62 and applied, and the toner image can be transferred onto the recording paper from the surface of the intermediate transfer belt 16 with high quality. Accordingly, it is possible to reduce the cost and the size while maintaining the image quality.

Next, FIG. 9 and FIG. 10 are views showing a second embodiment of the image forming apparatus according to the present invention.
Here, since the present embodiment is configured in substantially the same manner as the above-described embodiment, the same reference numerals are given to the same configurations while diverting the drawings, and the characteristic portions will be described.

In FIG. 9, the image forming apparatus includes metal guide members 71 and 72 that guide the recording paper nipped and conveyed by the registration roller pair 34 to the nip portion between the intermediate transfer belt 16 and the transfer roller 17 of the image recording apparatus 10. The guide members 71 and 72 are connected to a constant voltage power source 62 that applies a fixing bias to the pressure roller 18b of the fixing roller pair 18 and is disposed on both sides of the recording paper.

As shown in FIG. 10A, the guide member 71 has an intermediate transfer belt 16 and a transfer roller 17 that are slidably brought into contact with one end of the recording paper P that is nipped and conveyed by the registration roller pair 34. The guide member 72 is laid out so as to guide to the nip portion of
The recording paper P until it is nipped and conveyed by the intermediate transfer belt 16 and the transfer roller 17 and is removed.
It is laid out in sliding contact with the other surface side.

As a result, the guide members 71 and 72 can apply a constant voltage from the constant voltage power supply 62 to the recording paper P to be slidably guided as a transfer bias, and the bias application is cut off at the same time as the recording paper P is separated. can do. That is, the guide members 71 and 72 constitute a connection / disconnection means, and a recording sheet for transferring the toner image on the surface of the intermediate transfer belt 16 without specially installing the electrode 65 or the like as in the above-described embodiment. The fixing bias applied by the constant voltage power supply 62 to the pressure roller 18b of the fixing roller pair 18 is directly applied to the recording paper P as a constant voltage transfer bias via the guide members 71 and 72 at the timing when the transfer roller 17 is brought into close contact with P. Can be applied. Therefore, regardless of the operation of the transfer roller 17, in other words,
Regardless of whether the transfer roller 17 is in contact with or separated from the intermediate transfer belt 16, and the fixing bias of the constant voltage power source 62 does not act on the toner image on the surface of the intermediate transfer belt 16 and does not deteriorate, the recording paper P is high. Can be transferred to quality.

As described above, in the present embodiment, in addition to the operational effects of the above-described embodiment, the existing guide member 71, without installing a mechanism such as the electrode 65 for disconnecting the bias application from the constant voltage power supply 62, By connecting a constant voltage power source 62 that outputs a fixing bias to 72, a constant voltage transfer bias can be applied. Therefore, cost reduction and size reduction can be further promoted.

Although one embodiment of the present invention has been described so far, it is needless to say that the present invention is not limited to the above-described embodiment, and may be implemented in various forms within the scope of the technical idea.

For example, it is devised that the application of the bias from the constant voltage power supply 62 is cut off using the operation when the toner image on the surface of the intermediate transfer belt 16 is transferred to the recording paper, but the invention is not limited to this. Needless to say, a general switch for connecting and disconnecting the output from the constant voltage power supply 62 may be provided.

In this embodiment, an image forming apparatus including the intermediate transfer belt 16 will be described as an example. However, the present invention is not limited to this, and the present invention is applied to an image forming apparatus that employs a structure in which a photosensitive drum is directly transferred onto recording paper. Needless to say.

1 is a perspective front view illustrating a schematic overall configuration of a first embodiment of an image forming apparatus according to the present invention. It is a related block diagram explaining the control. It is a partially enlarged view for explaining the operation of the transfer roller. 2A and 2B are diagrams illustrating the structure of the intermediate transfer belt, wherein FIG. 1A is a partial cross-sectional configuration diagram illustrating a structure for supplying voltage, and FIG. 2B is a cross-sectional configuration illustrating a structure of a photosensitive drum corresponding to the structure. FIG. FIG. 4 is a conceptual configuration diagram showing a power supply for applying a bias to the transfer roller and fixing roller pair. It is a block diagram which shows the mechanism which applies a bias to the transfer roller. It is a figure explaining the timing which applies a bias to the transfer roller, (a) is a state figure which shows when a bias is not applied, (b) is a state figure which shows when the bias is applied. It is a table | surface which shows the lower limit voltage value applied to the transfer roller according to the temperature and humidity of ambient environment. It is a figure which shows 2nd Embodiment of the image forming apparatus which concerns on this invention, and is a block diagram which shows the mechanism which applies a bias at the time of transcription | transfer. It is a figure explaining the bias application at the time of the transfer by the transfer roller, (a) is a state diagram showing the start of bias application, (b) is a state diagram showing the end of the bias application.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Image recording device 11 ... Laser beam scanning device 12 ... Photosensitive drum 1
4. Development cartridge 15 ... Development rotary unit 16 ... Intermediate transfer belt 17 ... Transfer roller 17a ... Body 17b ... Roller shaft 18 ... Fixing roller pair 18 ... Transfer roller 18a ... Heat roller 18b ... ... Pressure roller 18c ... Roller shaft
21 …… Power supply unit 22 …… Sensor unit 30 …… Paper transport device 31 …… Paper cassette 32 …… Pickup roller 34 …… Registration roller pair 35 …… Switching roller pair 36 …… Discharge roller pair 39 …… Discharge Table 40 …… Control unit
41 …… Controller unit 46 …… Engine control unit 57 …… Rotating member 57a…
... Rotating shaft 61 ... Constant current power source 62 ... Constant voltage power source 63, 65 ... Electrode 7
1, 72 …… Guide member

Claims (4)

A carrier that carries a toner image obtained by developing an electrostatic latent image based on image data, a developing unit that forms a toner image by attaching toner to the electrostatic latent image on the surface of the carrier, and a carrier. A transfer belt that primarily transfers and carries a toner image formed on the surface, a primary transfer portion that primarily transfers the toner image from the surface of the carrier to the transfer belt surface, and a secondary transfer of the toner image from the transfer belt surface to the recording medium. A transfer belt for transferring a toner image obtained by developing an electrostatic latent image based on image data from the surface of the carrier, and a secondary transfer portion for fixing the toner image transferred to the recording medium to a fixing portion for fixing the toner image to the recording medium. An image forming apparatus for forming an image by transferring and fixing to a recording medium via
A constant voltage power source and a constant current power source are arranged as means for applying a secondary transfer bias for secondary transfer of the toner image from the transfer belt surface to the recording medium, and the toner image transferred on the recording medium is transferred to the recording medium. A constant voltage power source is arranged as a means for applying a fixing bias for adhering to the surface of the recording medium in a stable state,
The constant voltage power supply is connected in a conductive manner so that a bias can be applied in common use for secondary transfer and fixing, and the conductive connection is disconnected so as to apply a secondary transfer bias in synchronization with the secondary transfer operation. An image forming apparatus comprising a connecting / disconnecting means. As the secondary transfer section, a secondary transfer bias is applied to contact and separate the toner image from the surface of the carrier to the transfer belt surface to which the toner image is primarily transferred, and to secondary transfer the toner image on the transfer belt surface to a recording medium. Equipped with a transfer roller
2. The image according to claim 1, wherein a contact for disconnecting a conductive connection with a constant voltage power source by a contact / separation operation of the transfer roller with respect to a transfer belt surface is interposed as the connection / disconnection unit. Forming equipment. A guide member made of a conductive material for guiding a recording medium is disposed at a secondary transfer position by the secondary transfer unit, and the guide member is electrically connected to a constant voltage power source;
The image forming apparatus according to claim 1, wherein the guide member functions as a connection / disconnection unit that disconnects application of a transfer bias when the recording medium is guided to a secondary transfer portion. It is equipped with sensor means for acquiring temperature and humidity information in the device body,
4. The image forming apparatus according to claim 1, wherein the output voltage of the constant voltage power source is adjusted based on temperature and humidity information from the sensor means.

Images