JP2001100548A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate trouble that faulty transfer is caused in the case of transferring a toner image to a thick or thin paper, for example, because transfer efficiency is changed in accordance with the change of the thickness of a transfer sheet if the thickness of the transfer sheet is changed in the case of performing constant-voltage control or constant-current control based on one voltage value or one current value previously set to a transfer means for transferring the toner image on the surface of an image carrier to the transfer sheet. SOLUTION: A pair of detection rollers 3 (detection roller 3a and auxiliary roller 3b) is installed on the upstream side of a transfer part 6. A piezoelectric element layer put between a lower electrode and an upper electrode is provided on the surface of the roller 3a. A voltage detection part 4 detects the voltage value generated by the distortion of the piezoelectric element layer in the case of making transfer paper P pass through space between a pair of rollers 3. The table of optimum transfer voltage in accordance with detected voltage (that is, the thickness of the transfer paper P) by the detection part 4 is previously stored in a transfer bias control part 5. By referring to the table, the optimum transfer voltage value in accordance with the detected voltage by the detection part 4 is acquired and the constant-voltage control of the roller 2 is performed according to the optimum transfer voltage value. Thus, the excellent transfer is always performed even when the thickness of the transfer paper P is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for transferring a toner image on an image bearing member by generating an electric field in the transferring member while passing a transfer sheet through a transfer portion between the image bearing member and the transferring member. The present invention relates to an image forming apparatus that transfers images to a sheet.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer, a facsimile, etc., a photosensitive drum and a transfer means (for example, a transfer roller) provided near or in contact with the photosensitive drum.
The toner image formed on the photosensitive drum is transferred to the transfer sheet by applying a transfer bias having a polarity opposite to that of the toner to the transfer unit while passing the transfer sheet between the transfer sheet and the transfer sheet. It is a target. The transfer bias applied to the transfer unit is usually controlled by constant voltage control or constant current control, and is set to a predetermined voltage value or a predetermined voltage value set in advance so that the transfer efficiency is optimized in a standard transfer sheet. It is maintained at the set current value.

[0003]

Incidentally, the optimum value of the set voltage value in the constant voltage control and the optimum value of the set current value in the constant current control (a value at which the transfer efficiency becomes optimum) are determined, for example, when the thickness of the transfer sheet changes. It changes as the resistance value changes. Therefore, if the constant voltage control or the constant current control is performed based on one voltage value or current value set in advance as in the prior art, if the thickness of the transfer sheet changes, the transfer efficiency changes accordingly. Or transfer failure when transferring to thin paper. Also, when a contact transfer roller that contacts the photosensitive drum is used, the nip width between the photosensitive drum and the transfer roller changes due to a change in the thickness of the transfer sheet and a circumferential difference in the diameter of the transfer roller due to a tolerance. In the constant current control, the current density changes due to the change in the nip width. Therefore, if the constant current control is performed based on one preset current value as in the prior art, if the thickness of the transfer sheet or the diameter of the transfer roller in the circumferential direction changes, the transfer efficiency changes accordingly, resulting in poor transfer. There is a problem that a problem occurs. The present invention has been made in view of the above circumstances, and has as its object to firstly provide an image forming apparatus capable of always performing good transfer even when the thickness of a transfer sheet changes. Second, by providing an image forming apparatus capable of always performing good transfer even when the nip width between the photosensitive drum and the transfer roller changes when a contact transfer roller is used. is there.

[0004]

In order to achieve the above-mentioned object, the present invention provides an image forming apparatus, wherein an electric field is generated in the transfer means while a transfer sheet is passed through a transfer section between the image carrier and the transfer means. In an image forming apparatus for transferring a toner image on an image carrier to the transfer sheet, a detecting means for detecting a thickness of the transfer sheet, and an electric field generated in the transfer means based on a detection signal from the detecting means. The image forming apparatus is provided with control means for controlling the image forming apparatus. The detecting means forms a piezoelectric element layer on at least one of a pair of rollers which are close to or in contact with each other, and allows the transfer sheet to pass between the pair of rollers so that the piezoelectric element at that time is formed. It is conceivable to configure so as to output a signal corresponding to the layer distortion. If such a detecting unit is provided on the upstream side of the transfer unit, any transfer unit such as a contact transfer roller and a non-contact transfer roller can be applied. When the transfer means is a contact transfer roller, a pair of rollers constituting the detection means is constituted by the photosensitive drum and the contact transfer roller, and the piezoelectric element is provided on the surface of the contact transfer roller. It is also possible to provide layers. This makes it possible to accurately detect not only a change in the thickness of the transfer sheet but also a change in the nip width between the photosensitive drum and the transfer roller due to a circumferential change in the diameter of the transfer roller. The transfer can be controlled in accordance with the nip width of the nip, and good transfer can always be performed even if the nip width changes.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments and examples of the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention. The following embodiments and examples are examples embodying the present invention, and do not limit the technical scope of the present invention. Here, FIG. 1 is a schematic diagram showing a schematic configuration of a main part of an image forming apparatus A1 according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a configuration of a detection roller 3a constituting the image forming apparatus A1. FIG. 3 shows the detection roller 3a.
FIG. 4 is a schematic diagram illustrating an electrical connection state at an end of the image forming apparatus, FIG. 4 is a flowchart illustrating an example of a transfer processing procedure by the image forming apparatus A1, and FIG. 5 is a schematic diagram of a main part of an image forming apparatus A2 according to an embodiment of the present invention. FIG. 6 is a schematic cross-sectional view showing the configuration of a transfer roller 2 'constituting the image forming apparatus A2, and FIG. 7 is a schematic view showing an electrical connection state at an end of the transfer roller 2'. is there.

[0006] The image forming apparatus A1 according to the present embodiment comprises:
As shown in the schematic configuration near the transfer section in FIG. 1, the transfer roller 2 is opposed to the photosensitive drum 1 (an example of an image carrier).
(An example of a transfer unit) is provided. The transfer roller 2 may be a contact transfer roller that contacts the photosensitive drum 1 or a non-contact transfer roller that does not contact the photosensitive drum 1. A toner image formed on the surface of the photoconductor drum 1 by a developing device or the like (not shown) is transferred to a transfer sheet P (an example of a transfer sheet) at a portion (transfer section 6) between the photoconductor drum 1 and the transfer roller 2. ), A transfer bias having a polarity opposite to the charge polarity of the toner is applied to the transfer roller 2 to transfer the toner from the surface of the photosensitive drum 1 to the transfer paper P. The application of the transfer bias to the transfer roller 2 and its control (constant voltage control is performed here, but constant current control may be performed) are performed by the transfer bias controller 5.

A pair of detection rollers 3 (detection roller 3a and auxiliary roller 3b) are provided upstream of the transfer section 6. The transfer paper P passes through the space between the detection roller pair 3 and is sent to the transfer unit 6. The above detection roller pair 3
May also serve as, for example, a registration roller. Here, the detection roller 3a is, as shown in FIG.
A piezoelectric element layer 14 sandwiched between a lower electrode 13 and an upper electrode 15 is provided on the outside of a hard roller composed of a hard roller 1 and a hard body 12. As the piezoelectric element layer 14, a general piezoelectric element such as ceramic can be used. For example, PVDF (Physical Vapor Deposition Film)
It is desirable to use a piezoelectric element which has a high elastic modulus and can be applied as described above. A voltage detecting unit 4 is connected to the detecting roller 3a, for example, as shown in FIGS. 1 and 3, and the voltage detecting unit 4 detects a voltage generated by distortion of the piezoelectric element layer 14. The above detection roller 3
The auxiliary roller 3b opposing a is a hard roller having an insulating surface.

The piezoelectric element layer 14 is provided on the detection roller 3.
The transfer paper P is distorted by being inserted between the transfer paper P and the auxiliary roller 3b, and the amount of distortion is proportional to the thickness of the transfer paper P. Further, the voltage generated by the distortion is also proportional to the thickness of the transfer paper P. Therefore, the voltage value detected by the voltage detection unit 4 is proportional to the thickness of the transfer paper P inserted between the detection roller 3a and the auxiliary roller 3b. Here, the detection roller 3a and the auxiliary roller 3b
This means that the amount of distortion of the piezoelectric element layer 14 differs depending on the thickness of the transfer paper P inserted into the facing portion.
That is, they are installed in a state of contacting each other or maintaining a very small gap so that the output of the voltage detection unit 4 differs depending on the thickness of the transfer paper P. As described above, the detection roller pair 3 (the detection roller 3a and the auxiliary roller 3b) and the voltage detection unit 4 constitute an example of a detection unit that detects the thickness of the transfer sheet.

The voltage detecting section 4 is connected to the transfer bias control section 5 (an example of a control means) for applying a transfer bias to the transfer roller 2 and controlling the transfer bias. The transfer bias control unit 5 previously stores a table (detection voltage) of an optimum transfer voltage (optimal transfer current in the case of constant current control) according to the detection voltage (that is, the thickness of the transfer paper P) detected by the voltage detection unit 4. -Transfer voltage table), and obtains an optimum transfer voltage value corresponding to the voltage detected by the voltage detection unit 4 with reference to the table, and controls the constant voltage of the transfer roller 2 based on the optimum transfer voltage value. I do.

Next, a transfer processing procedure in the image forming apparatus A1 will be described with reference to a flowchart shown in FIG. When the transfer paper P is conveyed and inserted between the pair of detection rollers 3, the piezoelectric element layer 14 of the detection roller 3a is distorted, and the distortion amount (that is, the thickness of the transfer paper P).
Is generated by the voltage detector 4 (step S1). The transfer bias control unit 5 refers to a detection voltage-transfer voltage table stored in advance and acquires an optimum transfer voltage value according to the detection voltage of the voltage detection unit 4 (step S2). When the transfer paper P that has passed between the detection roller pair 3 reaches the transfer unit 6, the transfer bias control unit 5 performs constant voltage control of the transfer roller 2 with the optimum transfer voltage value (step S3). Thereby, an optimal transfer voltage according to the thickness of the transfer paper P is applied to the transfer roller 2, and the toner image on the surface of the photosensitive drum 1 is transferred to the transfer paper P (Step S4).

As described above, in the image forming apparatus A1 according to the present embodiment, the detection roller pair 3 is provided on the upstream side of the transfer unit 6, and the detection roller when passing between the detection roller pair 3 is detected. A voltage generated according to the amount of distortion of the piezoelectric element layer 14 provided on the surface of the transfer sheet 3a (that is, the thickness of the transfer paper P) is detected by the voltage detection unit 4, and the optimum transfer voltage corresponding to the voltage value is determined by the transfer roller 2. And transfer is performed, so that good transfer can always be performed even when the thickness of the transfer paper P changes.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the case where a contact transfer roller that contacts a photosensitive drum is used, the nip width between the photosensitive drum and the transfer roller is changed due to a change in the thickness of the transfer sheet or a circumferential difference in the diameter of the transfer roller due to a tolerance. However, in the constant current control, the current density changes due to the change in the nip width. Therefore, if constant current control is performed based on one preset current value,
If the thickness of the transfer sheet or the diameter of the transfer roller in the circumferential direction changes, the transfer efficiency changes accordingly, resulting in poor transfer. Here, the image forming apparatus A1 according to the above embodiment is described.
As described above, since the transfer control can be performed according to the change in the thickness of the transfer paper as described above, it can be said that the transfer control can be performed according to the change in the nip width due to the change in the thickness of the transfer paper. However, the nip width between the photosensitive drum and the transfer roller is not caused only by a change in the thickness of the transfer paper, but also by a circumferential difference in the diameter of the transfer roller due to, for example, a tolerance. The image forming apparatus A1
In the configuration (1), since the thickness of the transfer paper is detected by the detection roller pair 3 provided on the upstream side of the transfer unit 6, the change in the nip width due to the change in the transfer roller diameter cannot be considered. Therefore, by using the photosensitive drum 1 and the contact transfer roller 2 'as the above-described detection roller pair, it is possible to perform transfer control according to the nip width between the photosensitive drum 1 and the transfer roller 2'. The image forming apparatus A2 will be described.

As shown in FIG. 5, the image forming apparatus A2 has
A contact transfer roller 2 ′ (an example of a transfer unit) is provided to face the photosensitive drum 1 (an example of an image carrier). A toner image formed on the surface of the photosensitive drum 1 by the developing device 23 is transferred to a transfer sheet P (an example of a transfer sheet) at a portion (transfer section 6) between the photosensitive drum 1 and the transfer roller 2 '. The transfer roller 2 'is applied with a transfer bias having a polarity opposite to the charge polarity of the toner, so that the toner is transferred from the surface of the photosensitive drum 1 to the transfer paper P. Note that transfer bias is applied to the transfer roller 2 and its control (here, constant current control is performed).
Is performed by the transfer bias controller 5 '. In FIG. 5, reference numeral 21 denotes a charging device, reference numeral 22 denotes an exposure device, reference numeral 24 denotes a charge removing device, reference numeral 25 denotes a cleaning device, and reference numeral 26 denotes a fixing device.

As shown in FIG. 6, the transfer roller 2 'is provided with a piezoelectric element layer 34 sandwiched between a lower conductive layer 33 and an upper conductive layer 35, outside a conductive elastic body 32 covering the metal core 31.
Is provided. In the piezoelectric element layer 34,
Although a piezoelectric element such as a general ceramic can be used, for example, PVDF (Physical Vapor Deposition Filtration) can be used.
It is desirable to use a piezoelectric element that has a high elastic modulus and can be applied as shown in m). Also, as shown in FIG. 7, for example, as shown in FIG.
Are connected, and a voltage generated by the distortion of the piezoelectric element layer 34 is detected by the voltage detecting section 4 '.

The piezoelectric element layer 34 is distorted by the insertion of the transfer paper P into the transfer section 6, and the amount of the distortion is determined by the nip width between the photosensitive drum 1 and the transfer roller 2 '(the thickness of the transfer paper P, (Changes in accordance with a change in the diameter of the transfer roller 2 '). Therefore, the voltage value detected by the voltage detecting section 4 'also changes according to the nip width between the photosensitive drum 1 and the transfer roller 2'. As described above, in the image forming apparatus A2 according to the present embodiment, the photosensitive drum 1, the transfer roller 2 ', and the voltage detecting unit 4' constitute an example of a detecting unit.

The voltage detector 4 'is connected to the transfer bias controller 5' (an example of a control means) for applying a transfer bias to the transfer roller 2 'and controlling the transfer bias. The transfer bias controller 5 'has a voltage detected by the voltage detector 4' (that is, the photosensitive drum 1) in advance.
Table (detection voltage-transfer current table) corresponding to the optimum transfer current corresponding to the nip width between the transfer roller 2 'and the transfer roller 2'. An optimum transfer current value is obtained, and constant current control of the transfer roller 2 'is performed based on the optimum transfer current value.

As described above, the image forming apparatus A2 is provided on the surface of the transfer roller 2 'when the transfer paper passes through the transfer section 6 between the photosensitive drum 1 and the transfer roller 2'. Since the voltage generated in accordance with the amount of distortion of the piezoelectric element layer 34 (ie, the nip width between the photosensitive drum 1 and the transfer roller 2 ') is detected by the voltage detecting unit 4', the change in the thickness of the transfer paper and the transfer The nip width generated due to a difference in the roller diameter in the circumferential direction can be accurately detected, and an optimum transfer current corresponding to the voltage value is applied to the transfer roller 2 'to perform the transfer. , It is possible to always perform good transfer.

(Others) In the image forming apparatus A1 according to the above embodiment, the detection roller 3 having a piezoelectric element layer
Although the transfer paper is passed between a and an auxiliary roller 3b provided opposite thereto, the thickness of the transfer paper is detected by detecting a voltage value caused by distortion of the piezoelectric element layer. The means for detecting the thickness of the paper is not limited to such a configuration. For example, a pair of rollers as electrodes are provided upstream of the transfer section, and when a transfer paper is inserted between the rollers, a current is passed between the electrodes to detect the resistance value of the transfer paper, The thickness of the transfer paper may be detected based on the value. The detection roller 3
The same effect can be expected even if, for example, a piezoelectric element is attached to the bearing portion of one of the rollers constituting the detection roller pair, instead of providing the piezoelectric element layer on the surface of a.

[0019]

As described above, according to the present invention, the toner on the image carrier is generated by generating an electric field in the transfer device while passing the transfer sheet through the transfer section between the image carrier and the transfer device. In an image forming apparatus for transferring an image to the transfer sheet, detection means for detecting the thickness of the transfer sheet and control means for controlling an electric field generated in the transfer means based on a detection signal from the detection means are provided. Since the image forming apparatus is provided as an image forming apparatus, good transfer can always be performed even when the thickness of the transfer sheet changes. The detecting means forms a piezoelectric element layer on at least one of a pair of rollers which are close to or in contact with each other, and allows the transfer sheet to pass between the pair of rollers so that the piezoelectric element at that time is formed. It is conceivable to output a signal corresponding to the distortion of the layer. However, if such a detecting means is provided on the upstream side of the transfer portion, the transfer means can be a contact transfer roller, a non-contact transfer roller, or the like. Anything is applicable. When the transfer means is a contact transfer roller, a pair of rollers constituting the detection means is constituted by the photosensitive drum and the contact transfer roller, and the piezoelectric element is provided on the surface of the contact transfer roller. It is also possible to provide layers. This makes it possible to accurately detect not only a change in the thickness of the transfer sheet but also a change in the nip width between the photosensitive drum and the transfer roller due to a circumferential change in the diameter of the transfer roller. The transfer can be controlled in accordance with the nip width of the nip, and good transfer can always be performed even if the nip width changes.

[Brief description of the drawings]

FIG. 1 is an image forming apparatus A1 according to an embodiment of the present invention.
The schematic diagram which shows the schematic structure of the principal part of FIG.

FIG. 2 is a cross-sectional view illustrating a configuration of a detection roller 3a included in the image forming apparatus A1.

FIG. 3 is a schematic diagram showing an electrical connection state at an end of the detection roller 3a.

FIG. 4 is a flowchart illustrating an example of a transfer processing procedure performed by the image forming apparatus A1.

FIG. 5 is a schematic diagram illustrating a schematic configuration of a main part of an image forming apparatus A2 according to the embodiment of the present invention.

FIG. 6 is a cross-sectional view illustrating a configuration of a transfer roller 2 ′ included in the image forming apparatus A2.

FIG. 7 is a schematic diagram showing an electrical connection state at an end of the transfer roller 2 '.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum (example of an image carrier) 2: Transfer roller 2 '... Contact transfer roller 3 ... Detection roller pair 3a ... Detection roller 3b ... Auxiliary roller 4, 4' ... Voltage detection part 5, 5 '... Transfer bias Control part (an example of control means) 14, 34 ... piezoelectric element layer

Claims (4)

[Claims] 1. An image forming apparatus for transferring a toner image on the image carrier to the transfer sheet by generating an electric field in the transfer unit while passing the transfer sheet through a transfer section between the image carrier and the transfer unit. An image forming apparatus, comprising: a detecting means for detecting a thickness of the transfer sheet; and a control means for controlling an electric field generated in the transferring means based on a detection signal from the detecting means. Forming equipment. 2. The method according to claim 1, wherein the detecting means includes a piezoelectric element layer formed on a surface of at least one of a pair of rollers which are close to or in contact with each other, and the transfer sheet is passed between the pair of rollers. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to output a signal corresponding to the distortion of the piezoelectric element layer. 3. The image forming apparatus according to claim 2, wherein said detecting means is provided upstream of said transfer section. 4. The transfer device according to claim 1, wherein the transfer unit is a contact transfer roller provided in contact with a photosensitive drum serving as the image bearing member, and a pair of rollers constituting the detection unit is configured to contact the photosensitive drum with the contact member. 3. The image forming apparatus according to claim 2, further comprising a transfer roller, wherein the piezoelectric element layer is provided on a surface of the contact transfer roller.