JP7793393B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus equipped with electrically driven units or components such as motors and sensors.

Some image forming devices, such as those disclosed in Patent Document 1, have a configuration in which a registration roller, a pre-transfer guide, a post-transfer metal plate, etc. are pressed against a movable support. Both the registration roller and the post-transfer metal plate must be earthed, and when using toner with high charging properties in the image forming device, the pre-transfer guide must also be earthed.

Furthermore, in the image forming device disclosed in Patent Document 2, in a high-humidity environment, the resistance value of the paper may decrease, causing the transfer current from the transfer unit to flow through the paper and into the guide plate. In this case, it is desirable to connect the conductive guide plate and the insulating support member via a non-linear element whose resistance value decreases when a voltage above a predetermined value is applied compared to when no voltage is applied.

Patent Publication No. 2017-151196 Patent Publication No. 2007-298735

As mentioned above, in order to miniaturize the entire image forming apparatus, the sheet transport unit that controls the state and transport of sheets is becoming increasingly smaller. As a result, the distance between the sheet transport unit and units to which high voltage is applied, such as the transfer unit, is becoming shorter. Electrical components or devices such as control boards, motors, and sensors located in the sheet transport unit must be connected to an electrically stable ground metal plate to prevent malfunctions and noise. Meanwhile, a high drive voltage of several kV is applied to the transfer unit that transfers the image. As a result, transfer current from the transfer unit may unintentionally flow into the ground metal plate via the sheet transport unit, which could result in the image not being transferred sufficiently to the sheet, resulting in poor transfer.

In view of the above-mentioned problems, the primary objective of the present invention is to provide an image forming apparatus that can suppress the effects of electrical noise.

The image forming apparatus of the present invention comprises a unit to which voltage is applied, a paper transport section that transports paper to the unit, and an electrical component provided in the paper transport section that operates when current is supplied , wherein the paper transport section is grounded through a first connection section, the electrical component is electrically insulated from the paper transport section and grounded through a second connection section, and the first connection section has a resistance value when a voltage equal to or greater than a predetermined value is applied that is smaller than either the resistance value when a voltage less than the predetermined value is applied or the resistance value when no voltage is applied.

This invention makes it possible to provide an image forming device that can suppress the effects of electrical noise.

FIG. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus. 10A and 10B are explanatory diagrams illustrating a contact state between a transfer unit and a paper transport unit. 10A and 10B are diagrams illustrating the relationship between the operating voltage of the nonlinear element and the grounding state of the transfer unit and the paper transport unit.

The structure and operation of the image forming apparatus 1 of the present invention will be described below.
1 is a cross-sectional view showing the structure of an image forming apparatus 1 of this embodiment. The image forming apparatus 1 includes a paper feed/imaging unit 100 that feeds and transports paper P and transfers images thereto, a fixing/paper discharge unit 200 that fixes images onto paper P and discharges the paper, and an operation unit 400. The operation unit 400 is a user interface and is disposed on the fixing/paper discharge unit 200. The paper feed/imaging unit 100 will now be described. The paper feed/imaging unit 100 includes a paper cassette 110 that stores paper P, a transport path 120, a toner bottle unit 130, a laser scanner 140, image forming units 150, 160, 170, and 180, and a transfer unit 190.

A paper feed mechanism 111 is provided above the paper cassette 110, which feeds the paper P stored in the paper cassette 110 one sheet at a time into the transport path 120. The transport path 120 is equipped with multiple transport rollers 121 and multiple path sensors 122. The paper P fed into the transport path 120 is transported to the transfer unit 190 by the transport rollers 121.

The transport rollers 121 are driven to rotate by an actuator. The position of the paper P on the transport path is detected by on/off information from path sensors 122, which are arranged at various points on the transport path 120 and detect the presence or absence of paper P at their detection positions. Skew correction of the paper P is also performed based on on/off information from a registration sensor 241 arranged in a paper transport section 240 on the transport path, and the state of the paper P on the transport path is detected by on/off information from a paper state detection sensor 242, which acts as an electrical component. Note that electrical components refer to elements, devices, parts, equipment, etc. that operate when supplied with electric current.

Image forming units 150, 160, 170, and 180 each form an image of a different color. Laser scanner 140 is provided above image forming units 150, 160, 170, and 180. In this embodiment, image forming unit 150 forms a yellow image. Image forming unit 160 forms a magenta image.

Image forming unit 170 forms a cyan image. Image forming unit 180 forms a black image. Image forming units 150, 160, 170, and 180 have the same configuration and perform the same operations. Here, we will explain image forming unit 150, which forms a yellow image, and will omit explanations of image forming units 160, 170, and 180, which form images of other colors.

The image forming unit 150 includes a photosensitive drum 153, a charger 152, and a developer 151. The photosensitive drum 153 is a drum-shaped photosensitive element with a photosensitive layer on its surface. The charger 152 uniformly charges the surface of the photosensitive drum 153. The laser scanner 140 scans the charged surface of the photosensitive drum 153 with laser light emitted from a semiconductor laser (not shown). This forms an electrostatic latent image on the surface of the photosensitive drum 153. The developer 151 develops the electrostatic latent image with a developer of the corresponding color, thereby forming an image (toner image) on the surface of the photosensitive drum 153. The developer 151 receives toner replenishment from a toner bottle 131 inserted in the toner bottle unit 130 via a toner pipe (not shown).

The laser scanner 140 has a laser driver (not shown) that drives and controls the laser light based on image data representing the image to be formed, a rotary polygon mirror 142, and a reflecting mirror 141. The laser light emitted from the semiconductor laser is irradiated onto the surface of the photosensitive drum 153 by the rotary polygon mirror 142 and the reflecting mirror 141. The rotation of the rotary polygon mirror 142 changes the reflection angle of the laser light, changing the position at which the laser light irradiates the photosensitive drum 153, thereby scanning the surface of the photosensitive drum 153. In the case of printing, the image data is transmitted from an external device via a specified network or obtained from a portable storage medium. In the case of copying, the image data is generated by an image reading device (not shown) reading an image from a document and input to the image forming apparatus 1.

An intermediate transfer belt 191 is provided below each image forming unit 150, 160, 170, and 180. The toner images formed on the photosensitive drums 153 of each image forming unit 150, 160, 170, and 180 are transferred and superimposed onto the intermediate transfer belt 191, which is applied with a bias voltage of the opposite polarity to that of the toner images. This forms a full-color toner image on the intermediate transfer belt 191. As the intermediate transfer belt 191 rotates, it transports the full-color toner image it carries to the transfer unit 190.

The paper P and the toner image are transported simultaneously to the transfer unit 190, which is a unit to which high voltage is applied. The transfer unit 190 has a transfer belt 192. The transfer belt 192 presses the paper P against the intermediate transfer belt 191 and simultaneously applies a bias voltage of the opposite polarity to that of the toner image, thereby transferring (secondary transfer) the visible image formed on the intermediate transfer belt 191. The paper P with the transferred toner image is transported to the fixing/paper discharge unit 200 by a transport belt 123 located downstream of the transfer unit 190. Note that "downstream" refers to the downstream side in the transport direction of the paper P.

The paper feed and imaging unit 100 also includes a double-sided transport path 124. During double-sided printing, the double-sided transport path 124 retrieves paper P with an image printed on its first side from the fixing and paper discharge unit 200. The paper P with an image printed on its first side is transported to the transport path 120 via the double-sided transport path 124. The paper P then undergoes the same process as the first side, with an image printed on its second side, which is different from the first side.

The fixing and paper discharge unit 200 will now be described. The fixing and paper discharge unit 200 comprises a fixing device 210, a conveying path 220, and a cooler 230. The fixing device 210 heats and fixes the toner image on unfixed paper P, which has been conveyed from the paper feeding and imaging unit 100 and has completed secondary transfer, to the paper P. The conveying path 220 is provided with a conveying roller 221, which is rotated by an actuator, and a path sensor 222. After the paper P has been fixed by the fixing device 210, it is conveyed along the conveying path 220 to the cooler 230. The cooler 230 cools the paper P, which has been heated during the fixing process. In this way, an image is printed on the paper P.

Downstream of the cooler 230 are provided a discharge transport path 224, a reverse transport path 225, and a flapper 223. Paper P is sorted by the flapper 223 into either the discharge transport path 224 or the reverse transport path 225. A double-sided transport switching unit 226 is provided downstream of the discharge transport path 224. A double-sided transport path 227 is connected to the double-sided transport switching unit 226.

In the case of face-up printing, where the paper P is discharged outside the machine with the printed side facing up, the paper P cooled by the cooler 230 is transported to the paper discharge transport path 224 and is then discharged outside the machine. In the case of face-down printing, where the paper P is discharged outside the machine with the printed side facing down, the paper P cooled by the cooler 230 is transported to the reversing transport path 225. The paper P then has its transport direction reversed in the reversing transport path 225 and is transported to the paper discharge transport path 224 and is then discharged outside the machine.

In the case of double-sided printing, the paper P cooled by the cooler 230 is transported to the double-sided transport switching unit 226 via the reverse transport path 225. The transport direction of the paper P is reversed by the double-sided transport switching unit 226, and the paper P is transported to the double-sided transport path 227. The paper P transported to the double-sided transport path 227 is then transported to the double-sided transport path 124.

The operation unit 400 has an input interface and an output interface that accept various operations, such as the contents of a print job, from the user. The input interface is various buttons and a touch panel. The output interface is a display and speaker. The operation unit 400 accepts various operations, such as the contents of a print job, entered by the user via the input interface. The output interface displays the input screen via the input interface and the status of the image forming device 1. Note that the present invention can also be applied to systems that are connected and process via a network such as a LAN or WAN, as long as the functions of the present invention can be executed.

Figure 2 shows one form of earth connection for the transfer unit 190, paper transport unit 240, and paper condition detection sensor 242 of the image forming apparatus 1. The transfer unit 190, paper transport unit 240, and paper condition detection sensor 242 are each grounded through a common ground G. The ground G can be, for example, an earth plate. The transfer unit 190 applies a bias voltage with opposite characteristics to the toner to the transfer belt 192, thereby transferring the visible image formed on the intermediate transfer belt 191 to the transported paper P. In this case, as shown, a transfer current I1 flows from the transfer unit 190 through the ground line.

However, problems can arise if the transfer unit 190, paper transport unit 240, and paper status detection sensor 242 are simply connected to ground G via conductors without any special circuitry. For example, if paper P comes into contact with the transfer unit 190 and paper transport unit 240 simultaneously, the transfer unit 190 will be electrically connected to ground G via the paper P and paper transport unit 240. This causes an unintended transfer current I0, which is different from transfer current I1, to flow through the paper transport unit 240 and ground G. Therefore, the transfer current I0 may cause image defects or cause the paper status detection sensor 242 to malfunction or fail.

Figures 3(a) and (b) show other forms of grounding between the transfer unit 190 and the paper transport unit 240. In these figures, the transfer unit 190 is connected to the ground G via a connection 250, which serves as a second connection. The connection 250 is preferably made of a material that does not have non-linear characteristics, such as a conductor. The paper transport unit 240 is connected to the ground G via a connection 243, which serves as a first connection and is different from the connection 250. The connection 243 is made of a varistor 245, which serves as an element with non-linear characteristics (hereinafter referred to as a non-linear element), and a bundle of wires (not shown). The paper status detection sensor 242 mounted on the paper transport unit 240 is connected to the ground G via a connection 244, which is different from the connections 250 and 243.

Nonlinear characteristics are characterized by a high resistance value that makes it difficult for current to flow until the voltage reaches a certain value, and then a decrease in resistance value that allows current to flow once the voltage exceeds the certain value. In a nonlinear element, the resistance value when a voltage equal to or greater than the certain value is applied is smaller than either the resistance value when a voltage below that certain value is applied or the resistance value when no voltage is applied.

In this embodiment, a varistor is used as the nonlinear element, and when a voltage equal to or greater than a predetermined value is not applied, the resistance is very high and the element is essentially in an insulating state. Conversely, when a voltage equal to or greater than the predetermined value is applied, the resistance drops nonlinearly and rapidly. Preferably, the resistance of the nonlinear element when a voltage equal to or greater than the predetermined value is applied is small enough to place the connection portion 243 in a conductive state. Furthermore, when a voltage less than the predetermined value is applied or when no voltage is applied, the resistance of the nonlinear element is large enough to place the connection portion 243 in a substantially non-conductive state.

When paper P straddles and contacts the transfer unit 190 and paper transport unit 240, the voltage applied from the transfer unit 190 to the paper transport unit 240 via the paper P is referred to as V1. The above-mentioned predetermined voltage value is referred to as the operating voltage V2. Note that the nonlinear element is not limited to a varistor, and any other element can be used.

Figure 3(a) shows the case where voltage V1 becomes greater than operating voltage V2 of varistor 245 (V1 > V2). In this case, the voltage applied to varistor 245 becomes greater than operating voltage V2, causing the resistance of varistor 245 to suddenly drop. As a result, paper transport section 240 is grounded from connection section 243 via ground section G, and transfer current I0, shown by the solid line in the figure, flows from transfer section 190 for a short period of time. Thereafter, voltage V1 applied to paper transport section 240 decreases and falls below V2, causing the resistance of varistor 245 to rise.

As a result, the connection portion 243 is essentially insulated, and the transfer current I0 does not flow. In this case, the transfer current I0 flows for only a short time, almost the instant that V1 drops below V2, and compared to the example in Figure 2, which does not use the varistor 245, the transfer current I0 flowing from the transfer portion 190 to the ground portion G can be made very small. As a result, transfer defects, such as an image not being sufficiently transferred to the sheet, caused by the transfer current I0 flowing from the transfer portion 190 are suppressed.

Figure 3(b) shows a case where paper P straddles and contacts transfer unit 190 and paper transport unit 240, and the voltage V1 applied from transfer unit 190 to paper transport unit 240 via paper P is equal to or less than the operating voltage V2 of varistor 245. Because V1≦V2, the resistance value of varistor 245 remains high and the device remains essentially in an insulating state, and as a result, transfer current I0 does not flow.

As described above, in this embodiment, the paper transport unit 240 is connected to the grounding portion G via the connection portion 243, which is composed of the varistor 245 and a bundled wire. Furthermore, the paper status detection sensor 242 mounted on the paper transport unit 240 is connected to the grounding portion G via a connection portion 244, which is different from the connection portion 243, and is thus grounded. This prevents unintended transfer current I0 from the transfer unit 190 from flowing to ground via the paper transport unit 240, thereby preventing transfer failures. Furthermore, there are cases where the distance between the sheet transport unit and a unit (e.g., a transfer unit) to which a voltage (e.g., high voltage) is applied is shorter than the length of the transported paper in the transport direction, and the transported paper P may come into contact with both. Even in this case, the current flowing from the unit to which voltage is applied to ground via the grounding portion G can be suppressed. Therefore, it is possible to prevent malfunctions of the unit to which voltage is applied, and to achieve a more compact device. Furthermore, electrical components such as the paper status detection sensor 242 mounted on the paper transport unit 240 are grounded via a connection portion 244, which is separate from the connection portion 243, thereby preventing malfunctions. Furthermore, the electrical component may be a unit to which a low voltage (a voltage lower than the high voltage described above) is applied, which may be affected by the current flowing from a unit to which a high voltage is applied to the paper transport unit 240.

Note that if the operating voltage V2 of the varistor 245 is greater than the maximum voltage generated in the transfer unit 190 when it is operating (i.e., the maximum value of V1), then V1 > V2 does not hold. Therefore, the operating voltage V2 of the varistor 245 is set to a value smaller than the maximum voltage generated in the transfer unit 190 when it is operating. In addition, in this embodiment, the connection unit 243 is constructed using a varistor, which is a non-linear element. As long as the resistance value when a voltage equal to or greater than a predetermined value is applied is smaller than the resistance value when a voltage less than the predetermined value is applied or when no voltage is applied, the connection unit 243 may be constructed using any circuit, etc., instead of a non-linear element.

Furthermore, in the above-described embodiment, the paper feed/imaging unit 100 and the fixing/paper discharge unit 200 are configured in separate frames, but the same effect can be achieved even if the paper feed/imaging unit 100 and the fixing/paper discharge unit 200 are configured in the same frame.

Claims (11)

a unit to which a voltage is applied;
a paper transport unit that transports paper to the unit;
an electric member that is provided in the paper transport unit and operates when an electric current is supplied thereto ;
the paper transport unit is grounded through a first connection unit;
the electrical member is electrically insulated from the paper transport unit and is grounded through a second connection unit;
a resistance value of the first connection portion when a voltage equal to or greater than a predetermined value is applied is smaller than a resistance value when a voltage less than the predetermined value is applied or when no voltage is applied,
Image forming device. The unit is a unit to which high voltage is applied.
The image forming apparatus according to claim 1 . The unit is a transfer unit that transfers an image onto the paper.
3. The image forming apparatus according to claim 1. The distance between the unit and the paper transport section is shorter than the length of the paper in the transport direction.
4. The image forming apparatus according to claim 1. a resistance value when a voltage equal to or greater than the predetermined value is applied is a value small enough to make the first connection portion conductive, and a resistance value when a voltage less than the predetermined value or when no voltage is applied is a value large enough to make the first connection portion substantially non-conductive.
5. The image forming apparatus according to claim 1. The first connection portion has a nonlinear element.
6. The image forming apparatus according to claim 1. The nonlinear element is a varistor.
The image forming apparatus according to claim 6 . The first connection portion and the second connection portion are each connected to a common ground portion and grounded.
The image forming apparatus according to any one of claims 1 to 7. The predetermined value is a value smaller than a maximum voltage generated in the unit during operation of the unit.
The image forming apparatus according to any one of claims 1 to 8. The second connection portion is formed of a conductor that does not have nonlinear characteristics.
The image forming apparatus according to any one of claims 1 to 9. The electrical member is a sensor that detects the state of the paper being transported through the paper transport unit.
The image forming apparatus according to any one of claims 1 to 10.