JP7547747B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming device.

Image forming devices are known that form images on media by an image forming process that includes a transfer process in which an electrostatic latent image is formed on an image carrier, and an image formed by attaching a visualizing material to the latent image is transferred to the medium. There are several known transfer processes, including one in which the visualizing image formed from the electrostatic latent image is transferred directly from the image carrier to the medium, and one in which the visualizing image is transferred to the medium via a primary transfer to an intermediate transfer belt or the like. In either transfer process, the electrical adsorption force caused by static electricity is used in the process of transferring the image from the components for forming the visualizing image (including the image carrier and intermediate transfer belt, hereinafter referred to as "components") to the medium.

After the image is transferred, the medium needs to separate from the component and move downstream in the transport direction, but if the medium and component cannot be separated from each other due to electrical adhesion, this can cause transport abnormalities. Conventionally, various methods have been used to separate the medium from the component, such as a method in which separation claws are placed around the component and the medium is mechanically separated from the component by the separation claws, or a method in which a separation bias is applied to the component to eliminate the electrical adhesion.

In addition, a technology has been disclosed in which the transfer bias applied to the components is controlled, the medium is divided into multiple regions from the leading edge of the medium in the transport direction to the trailing edge of the medium in the transport direction, and a different transfer bias is applied to each region, making the components easier to separate (see, for example, Patent Document 1).

In recent years, in a situation where global environmental problems have been pointed out, thinner media (low rigidity) are being used for electrophotographic image forming devices in order to reduce the amount of raw materials used. In the future, it is expected that the thickness of the media will become even thinner. In the conventional method of using a separation claw to separate the media from the electrically tight contact state between the structure and the media, there is a possibility that a weakly rigid media will be damaged. Furthermore, even if the technology disclosed in Patent Document 1 is applied and the separation bias value is controlled to be large, the separation bias may affect the image transferred to the media, inducing an abnormal image.

Even if the technology disclosed in Patent Document 1 is used, the leading edge of the medium in the transport direction where the separation bias value is set to a low value generally corresponds to a margin where no image is formed. The width of the margin is narrow (for example, about 2 mm). Therefore, even if the separation bias value is adjusted, the effect of improving separation performance is negligible.

The present invention aims to provide an image forming apparatus capable of executing an image forming process that can improve separation performance even for media with low separation ability against electrical adhesion.

In order to solve the above technical problem, one aspect of the present invention relates to an image forming apparatus, comprising: an image carrier that holds at least a toner; a transfer device that transfers a toner image formed by the toner held on the image carrier from the image carrier to a recording medium; a power supply device that applies a transfer bias to the transfer device; and a control device that controls the application of the transfer bias.
the control device controls to reduce a size of the toner image formed on the image carrier so that the toner image can be transferred to the recording medium without transferring the toner image to the leading region when a margin area set on the recording medium is narrower than a predetermined threshold and a non-image area cannot be expanded beyond the threshold without including a leading region following the margin area , and the control device controls the application timing of a transfer bias for transferring the toner image in accordance with a size of an area where no image is formed and where secondary transfer is not performed, at a leading end portion of the recording medium in a transport direction .

According to the present invention, an image formation process can be performed that can improve separation performance even with media that has low separation ability against electrical contact.

1 is an explanatory side view showing an embodiment of an image forming apparatus according to the present invention; FIG. 2 is an enlarged explanatory diagram illustrating a configuration of a part of the image forming apparatus according to the present embodiment. FIG. 2 is a hardware configuration diagram illustrating the configuration of a control device according to the embodiment. FIG. 2 is a functional configuration diagram illustrating a functional configuration of a control device according to the present embodiment. FIG. 11 is an explanatory diagram illustrating a comparative example to the present embodiment. FIG. 11 is an explanatory diagram illustrating another comparative example to the present embodiment. 5A and 5B are diagrams illustrating an example of transfer bias control according to the embodiment. 5A and 5B are diagrams illustrating examples of nip portions corresponding to transfer bias control according to the embodiment. 8A and 8B are diagrams illustrating another example of transfer bias control according to the embodiment. 8A and 8B are diagrams illustrating another example of transfer bias control according to the embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the configuration of a color printer 200, which is an embodiment of an image forming device according to the present invention. In FIG. 1, the color printer 200 includes a control unit 210. The control unit 210 corresponds to a control device that controls the operation of each component of the color printer 200. The control unit 210 will be described in detail later.

Color printer 200 uses an image carrier as an intermediate transfer body. Hereinafter, the intermediate transfer body is referred to as intermediate transfer belt 10. Color printer 200 has a photoconductor 1, and around the photoconductor 1, a photoconductor cleaning unit 2, a charger 4, an exposure means 5, intermediate transfer belt 10, etc. are arranged.

The developing means is composed of four developing units, for example, a yellow developing unit 6, a magenta developing unit 7, a cyan developing unit 8, and a black developing unit 9.

When forming a full-color image, a visible image (visible image) is formed in the order of yellow developer 6, magenta developer 7, cyan developer 8, and black developer 9, and the visible images of each color are transferred in order onto intermediate transfer belt 10, forming a full-color image. Note that the order in which the visible images are formed is not limited to this.

A blade 3 is arranged in the photoconductor cleaning unit 2.

The intermediate transfer belt 10 is stretched by a primary transfer bias roller 11, a secondary transfer opposing roller 12, a driven roller 15, and a belt cleaning opposing roller 13, each of which is driven by the driving force of a drive motor. The process speed of these is adjusted to 150 mm/sec. The secondary transfer opposing roller 12 also serves as a drive roller for the intermediate transfer belt 10.

The above rollers are supported on both sides of the intermediate transfer belt 10 by the intermediate transfer belt unit side plates. The primary transfer bias roller 11 is disposed at the contact area between the photoconductor 1 and the intermediate transfer belt 10, and a predetermined transfer bias is applied to the primary transfer bias roller 11.

The intermediate transfer belt 10 is made of a single layer or multiple layers of PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), etc. The intermediate transfer belt 10 has a conductive material such as carbon black dispersed therein, and is adjusted so that its volume resistivity is in the range of 10 ⁸ to 10 ¹² [Ωcm] and its surface resistivity is in the range of 10 ⁹ to 10 ¹³ [Ωcm].

If necessary, a release layer may be coated on the surface of the intermediate transfer belt 10. Materials that can be used for the coating include fluororesins such as ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinylidene fluoride), PEA (perfluoroalkoxy fluororesin), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), and PVF (vinyl fluoride). Note that the materials listed here are not limited to these.

The intermediate transfer belt 10 can be manufactured by a casting method, centrifugal molding method, or the like, and its surface may be polished as necessary.

If the volume resistivity of the intermediate transfer belt 10 exceeds the above-mentioned range, the bias value required for transfer becomes high, which is undesirable since it leads to an increase in power supply costs. In addition, the charged potential of the intermediate transfer belt 10 becomes high during the transfer process, transfer paper peeling process, etc., and self-discharge becomes difficult, so it becomes necessary to provide a charge removal means. In addition, if the volume resistivity and surface resistivity are below the above-mentioned range, the charge potential decays quickly, which is advantageous for charge removal by self-discharge, but the current during transfer flows in the surface direction, causing toner scattering. Therefore, it is assumed that the volume resistivity and surface resistivity of the intermediate transfer belt 10 according to this embodiment are within the above-mentioned range.

The volume resistivity and surface resistivity were measured by connecting an HRS probe (inner electrode diameter 5.9 mm, ring electrode inner diameter 11 mm) to a resistivity meter (Mitsubishi Chemical Corporation: Hiresta IP), applying a voltage of 100 V (surface resistivity of 500 V) to the front and back of the intermediate transfer belt 10, and using the measured value 10 seconds later.

A belt cleaning unit 19 that cleans the intermediate transfer belt 10 is disposed near the belt cleaning opposing roller 13 around which the intermediate transfer belt 10 is stretched.

Figure 2 is an enlarged view of the belt cleaning unit 19 according to this embodiment. As shown in Figure 2, the belt cleaning unit 19 is provided with a cleaning blade 20 made of urethane rubber, which is pressed against the intermediate transfer belt 10 to block and clean the toner.

The cleaning blade 20 is held by a blade holder 22. The blade holder 22 has a tapered end so that residual toner removed by the cleaning blade 20 does not accumulate. Waste toner adhering to the blade holder 22 is caused to fall by applying a voltage from a voltage application device 103. In this embodiment, it is set to apply +1000 [V] and -1000 [V].

The belt cleaning unit 19 applies a solid lubricant 155 to the belt by a lubricant application member 152 to facilitate cleaning. A fatty acid metal salt having a linear hydrocarbon structure is used as the lubricant. Examples of fatty acid metal salts include fatty acid metal salts containing at least one fatty acid selected from stearic acid, palmitic acid, myristic acid, and oleic acid, and containing at least one metal selected from zinc, aluminum, calcium, magnesium, and lithium. Among them, zinc stearate is the most preferable material in terms of cost, quality stability, and reliability, since it is produced on an industrial scale and has a track record of use in many fields. However, the higher fatty acid metal salts generally used industrially are not the simple compound composition of the name, but contain other fatty acid metal salts, metal oxides, and free fatty acids that are more or less similar, and the fatty acid metal salts of the present invention are no exception to this.

These lubricants are supplied in minute amounts in the form of powder, and specific methods include scraping off the lubricant formed into a solid form on a block with a solid lubricant 155 such as a brush and applying it, or adding it to the toner. However, when adding the lubricant to the toner (visualizing material) to apply it, the amount of lubricant supplied depends on the area of the image to be output, and it is not always possible to supply it to the entire belt surface. Therefore, if you want to supply lubricant stably to the entire belt surface with a simple device configuration, it is better to use the method of scraping off the solid lubricant with a brush and applying it as in this embodiment.

In order to scrape off the solid lubricant 155 with the lubricant application member 152, the lubricant pressure means 153, which is an elastic body like a spring, presses the solid lubricant against the lubricant application member 152 with a force of 1 [N] to 4 [N]. The width of the solid lubricant 155 must be set wider than the image width, so it is set to 304 [mm] or more. The width of the lubricant application member 152 must be wider than the width of the solid lubricant 155 in order to scrape off the solid lubricant 155 evenly.

The secondary transfer roller 21 is constructed by covering a metal core such as SUS with an elastic body such as urethane, which is adjusted to a resistance value of 10 ⁶ to 10 ¹⁰ [Ω] using a conductive material. If the resistance value of the secondary transfer roller 21 exceeds the above range, it becomes difficult for current to flow, so a higher voltage must be applied to obtain the required transferability, resulting in increased power supply costs. In addition, since a high voltage is applied, discharge occurs in the gaps before and after the transfer nip, and white spots due to discharge appear on the halftone image.

Conversely, if the resistance value of the secondary transfer roller 21 falls below the above range, it becomes impossible to transfer both the multiple color image portion (e.g., a three-color overlapping image) and the single color image portion present on the same image. This is because, since the resistance value of the secondary transfer roller 21 is low, a current sufficient to transfer the single color image portion flows at a relatively low voltage, but a voltage value higher than the optimal voltage for the single color image portion is required to transfer the multiple color image portion. Therefore, if a voltage is set that allows the multiple color image portion to be transferred, the transfer current becomes excessive for the single color image, resulting in reduced transfer efficiency.

The resistance value of the secondary transfer roller 21 was measured by placing the secondary transfer roller 21 on a conductive metal plate, applying a load of 4.9 [N] on each end of the core metal (a total of 9.8 [N] on both sides), and calculating the current value that flows when a voltage of 1000 [V] is applied between the core metal and the metal plate.

In addition, the secondary transfer roller 21 is driven by a drive gear, and its peripheral speed is adjusted to be approximately the same as the peripheral speed of the intermediate transfer belt 10.

The current applied to the secondary transfer roller 21 is controlled by a constant current, and in this embodiment, the set value is +30 [μA]. Paper P as a sheet-shaped recording medium is transported by the paper feed roller 26, paper transport roller 27, and registration roller 28 in time with the timing when the leading edge of the four-color superimposed image formed on the surface of the intermediate transfer belt 10 reaches the secondary transfer position. The four-color superimposed image transferred to the paper P is discharged by the discharge means as described above, and then transported along the fixing entrance guide 44 to the fixing means 30. After being fixed by the fixing means 30, the paper is discharged by the paper discharge roller 32.

[Hardware configuration of control unit 210]
Next, the control unit 210 of the color printer 200 will be described. Fig. 3 is a diagram showing the hardware configuration of the control unit 210. As shown in Fig. 3, the control unit 210 includes the same configuration as a general information processing device. The control unit 210 of the color printer 200 according to this embodiment includes a CPU (Central Processing Unit) 211, a RAM (Random Access Memory) 212, a ROM (Read Only Memory) 213, a HDD (Hard Disk Drive) 214, and an I/F 215, which are connected via a bus 219. In addition, a display unit 216, an operation unit 217, and a dedicated device 218 are connected to the I/F 215.

The CPU 211 is a computing means and controls the operation of the entire color printer 200. The RAM 212 is a volatile storage medium capable of reading and writing information at high speed, and is used as a working area when the CPU 211 processes information. The ROM 213 is a read-only non-volatile storage medium in which programs such as firmware are stored. The HDD 214 is a non-volatile storage medium in which information can be read and written, and in which an OS (Operating System), various control programs such as an image formation control program and a transfer bias control program, application programs, etc. are stored.

The I/F 215 connects the bus 219 to various hardware devices, networks, etc. Information communication with the outside world is performed via the I/F 215. The display unit 216 is a visual user interface that allows the user to check the status of the color printer 200 and the operating mode that has been set, and is realized by a display device such as an LCD (Liquid Crystal Display). The operation unit 217 is a user interface that allows the user to input the operating mode settings of the color printer 200.

The dedicated device 218 is hardware for implementing a function that performs a dedicated operation in the color printer 200. The dedicated device 218 includes, for example, a secondary bias power supply 102 that serves as a power supply device that applies a secondary transfer bias to the secondary transfer roller 21, a paper detection sensor that detects the type of paper P to which the secondary bias is applied, and a drive motor that controls the rotation of the photoconductor 1.

The control unit 210 constitutes a software control unit that realizes a predetermined function by using each hardware configuration included in the dedicated device 218 to read programs stored in the ROM 213, HDD 214, etc. into the RAM 212 and executes them with the CPU 211.

[Functional configuration of control unit 210]
Fig. 4 is a functional block diagram illustrating the configuration of a software control unit according to this embodiment. As shown in Fig. 4, the software control unit is realized by the hardware resources of the control unit 210 and the control program according to this embodiment. The software control unit includes an image data acquisition unit 221, a non-image area determination unit 222, a bias voltage control unit 224, a medium information storage unit 225, an image formation size change unit 226, an image formation position change unit 227, and an image formation control unit 228.

The image data acquisition unit 221 executes processing to input data (image data) for forming an image in the color printer 200 to the color printer 200. The image data includes information that is the basis of the image 310 (described later) to be formed in the image formation area of the paper P, and information that specifies the formation position of the image 310.

The non-image area determination unit 222 acquires a "non-image area" that is an area in which an image 310 is not formed based on image data from the image formation area 302 (see FIG. 7) of the paper P that is the image formation target. The non-image area determination unit 222 also acquires the width of the margin area 301 set on the paper P based on the attribute information of the paper P included in the image data or based on the attribute information of the paper P stored in the medium information storage unit 225. The non-image area determination unit 222 also acquires the width of the "leading area 303" that is the image formation area 302 following the margin area 301 and is an area up to a distance D as a predetermined distance. The leading area 303 is, for example, 10 mm from the leading edge of the paper P in the transport direction, regardless of the width of the margin area 301. Furthermore, the non-image area determination unit 222 determines whether the margin area 301 is large enough to ensure the separability described below, and if the margin area 301 is not large enough to ensure separability, it determines whether the image 310 is included in the area of the image formation area 302 following the margin area 301, which is included in the leading area 303.

In addition, when the width of the margin area 301 is insufficient to ensure separation and an image 310 is not formed in the leading area 303, the non-image area determination unit 222 determines that the leading area 303 is a "non-image area" that is not included in the area to which the transfer bias is applied, and notifies the bias voltage control unit 224 of the determination result.

When the margin area 301 is insufficient to ensure separation and the leading area 303 contains an image 310, the non-image area determination unit 222 issues an instruction to change the image formation to either the image formation size change unit 226 or the image formation position change unit 227, or both. In this case, the non-image area determination unit 222 determines the area that will become a "non-image area" due to the change in image formation size, or determines the area that will become a "non-image area" due to the change in image formation position, and notifies the bias voltage control unit 224 of the determination result.

The bias voltage control unit 224 controls the application timing of the secondary transfer bias to the paper P based on the judgment result of the non-image area judgment unit 222. The application timing of the secondary transfer bias includes an "application start timing" and an "application end timing." The "application start timing" is the timing at which the application of the secondary transfer bias to the paper P starts in response to the timing at which the area judged as a "non-image area" in the non-image area judgment unit 222 to ensure separability passes the secondary transfer position. The "application end timing" is the timing at which the application of the secondary transfer bias ends after passing the position where the secondary bias needs to be applied to form the image 310 as a toner image based on the image data.

The application start timing is earlier than the timing when the position where the image 310 is transferred reaches the nip, taking into account the time it takes for the transfer bias to rise to a predetermined value when the transfer bias is turned ON when the trailing end of the non-image area in the transport direction passes the secondary transfer position (nip).

The bias voltage control unit 224 may control the application timing and bias value based on information about the paper P stored in the medium information storage unit 225. For example, a more appropriate application timing (timing for starting application of the transfer bias) and bias value may be selected based on the thickness (thinness) of the paper P, and the secondary bias power supply 102 may be controlled based on this. The bias voltage control unit 224 also constitutes a medium information recognition unit that recognizes information necessary for bias control from information about the paper P stored in the medium information storage unit 225.

The medium information storage unit 225 stores the type of paper P used in the image formation process in the color printer 200. The user operates the setting screen via the operation unit 217 to input information into the medium information storage unit 225 that can identify the thickness (thinness) of the paper P to be used.

When the non-image area determination unit 222 determines that the width of the margin area 301 set at the leading edge of the paper P in the transport direction is insufficient to ensure separation, the image formation size change unit 226 notifies the image formation control unit 228 to reduce the image 310 toward the trailing edge in the transport direction. In other words, when the margin area 301 is narrower than a predetermined threshold, the image formation control unit 228 is controlled to perform processing to expand the area (non-transfer area) to which the secondary transfer bias is not applied up to the leading area 303 including the margin area 301. Then, even if the non-transfer area is expanded to the leading area 303, the image formation control unit 228 controls processing to reduce the image 310 toward the trailing edge in the transport direction so that the image 310 is transferred within the image formation area 302. For example, as a toner image reduction process, the size of the electrostatic latent image formed on the photoconductor 1 is controlled to be changed.

When the size of the electrostatic latent image is reduced, the timing for starting application of the transfer bias to the paper P in the subsequent transfer process can be determined based on the reduced toner image, so the specified image 310 can be formed (transferred) on the paper P even if the "non-transfer area" where the secondary transfer bias is not applied to the leading portion of the paper P in the transport direction is expanded.

When the non-image area determination unit 222 determines that the width of the margin area 301 set at the leading edge of the paper P in the transport direction is insufficient to ensure separation, the image formation position change unit 227 controls to change the formation position of the image 310 to the trailing edge in the transport direction. In other words, when the margin area 301 is narrower than a predetermined threshold, the image formation control unit 228 controls to perform processing to expand the area (non-transfer area) to which the secondary transfer bias is not applied to the leading area 303 including the margin area 301. Then, even if the non-transfer area is expanded to the leading area 303, the image formation control unit 228 controls to move the image 310 to the trailing edge in the transport direction so that the image 310 is transferred within the image formation area 302. For example, as a toner image movement process, the image formation control unit 228 controls to change the position of the electrostatic latent image formed on the photoconductor 1.

The image formation control unit 228 controls the formation of an electrostatic latent image on the photoconductor 1 to coincide with the timing of the secondary transfer to the paper P based on the control of the image formation size change unit 226 and the image formation position change unit 227 to change the size and position of the image 310, and also controls the visible image and primary transfer.

Therefore, according to the color printer 200 of this embodiment, the timing of application of the transfer bias for transferring the visible image is controlled according to the size (width) of the area (non-transfer area) where no image is formed and where secondary transfer is not performed at the leading portion of the paper P in the transport direction. This makes it possible to prevent the paper P after transfer from electrically adhering to the secondary transfer section. Furthermore, by controlling the timing of application of the transfer bias according to the size (width) and position of the non-transfer area, the secondary transfer process can be completed with greater precision. This makes it easier for the paper P to peel off from the structure with which it is in close contact during the transfer process, improving the quality of image formation.

[Description of Comparative Example]
Here, in order to clarify the effect of the transfer bias control by the color printer 200 according to the present embodiment, an example of the prior art will be described as a comparative example. FIG. 5 is a diagram for explaining an example of a transfer bias application method according to the prior art. In the example of FIG. 5, the transfer bias is applied (turned ON) when the paper P passes through the configuration corresponding to the secondary transfer roller 21 of the present embodiment. FIG. 5(a) shows the application area of the transfer bias in the conveying direction of the paper P. Also, in FIG. 5(b), the horizontal axis represents the application time of the transfer bias to the paper P, and the vertical axis represents the bias value of the transfer bias. Note that the paper P has a "blank area 301" where the image 310 is not formed, and an "image forming area 302" where the image 310 can be formed, which are set in advance according to the attributes (mainly size) of the paper P. FIG. 5(a) illustrates an example where the image 310 is formed so as to fill the image forming area 302.

As shown in FIG. 5, in the comparative example, image 310 is formed up to the leading edge of image formation area 302 in the transport direction (the boundary with margin area 301), so application of transfer bias is started before paper P reaches secondary transfer roller 21. In addition, application of transfer bias is terminated after the rear end of paper P passes secondary transfer roller 21.

Figure 6 is another comparative example. The example in Figure 6 is an example in which the transfer bias is controlled to be applied (on) when the leading edge of the paper P in the transport direction reaches a transfer device in which a transfer nip is formed by the secondary transfer opposing roller 12 and the secondary transfer roller 21. Figure 6 also shows an example in which an image 310 is formed to fill the image formation area 302.

At this time, the timing of application of the transfer bias is the same as in the example of Figure 5. However, taking into consideration the separability described below, a specific area following the leading edge of the paper P in the transport direction is distinguished as a first area, and its transfer bias value is set to Va [v]. After that, when the paper P is transported to a second area following the first area, the transfer bias value is set to Vb [v]. Then, in the third area following the second area, the transfer bias value is set to Vc [v], and the transfer bias value for the final fourth area is set to Vd [v].

Here, Va<Vb<Vc, and Vd=Va. That is, in this comparative example, the transfer bias value is set low at the leading edge and trailing edge of the paper P in the transport direction to facilitate separation from the components that make up the transfer section. However, when the paper P is thin, even if the transfer bias value at the leading edge in the transport direction is low, there is a high possibility that separation will not be stable.

[First embodiment]
Hereinafter, in an embodiment of the present invention, an example of a method for controlling a transfer bias that improves the separation of the paper P during secondary transfer and contributes to image formation quality will be described. In order to improve the separation of the paper P with respect to electrical adhesion to the components that make up the transfer section, it is important to reduce the electrical adhesion of the end of the paper P in the transport direction, particularly the end on the downstream side in the transport direction (the leading portion during transport).

Therefore, in this embodiment, the image data acquisition unit 221 of the control unit 210 acquires image data that is the basis of the image 310 as a toner image to be transferred to the paper P. Based on the acquired image data, the non-image area determination unit 222 determines the size of the margin area 301 at the beginning of the paper P, which is the object on which the image formation using the image data will be performed. Then, if the margin area 301 is sufficient to ensure separability, normal image formation processing can be performed.

When the non-image area determination unit 222 determines that the result of the determination is "insufficient," the non-image area determination unit 222 determines whether the area of the image forming area 302 following the margin area 301 to which the secondary transfer bias is applied based on the image data (to which the image 310 is transferred) is included in the leading area 303. The leading area 303 is the area of the image forming area 302 following the margin area 301, within a range of distance D from the boundary with the margin area 301 toward the upstream side in the conveying direction.

When the non-image area determination unit 222 determines that the margin area 301 alone is "insufficient" but determines that the image 310 will not be transferred to the leading area 303, the margin area 301 and leading area 303 are combined and set as a "non-image area."

This makes it possible to set an area where no image is formed (non-transfer area). For example, in the case illustrated in FIG. 7(a), when image 310 as a toner image to be transferred to paper P is formed at the rear side of paper P but not at the front side, the front area 303 following margin area 301 becomes a non-image area (non-transfer area). Bias voltage control unit 224 does not apply transfer bias to the non-transfer area, and therefore controls the application timing according to the timing at which this non-transfer area reaches the secondary transfer position.

An example of the application timing in this case is shown in FIG. 7(b). That is, the timing at which the transfer bias starts to be applied (the time at which application starts) is delayed compared to the comparative examples (FIGS. 5 and 6). In other words, taking advantage of the fact that the transfer area of image 310 is not at the leading edge of paper P, the transfer bias is applied (on) after paper P passes through the transfer nip area formed by secondary transfer roller 21. By controlling the application timing of the transfer bias in this way, a sufficient non-transfer area can be secured at the leading edge of paper P, and since a sufficient non-charged area can be secured at the leading edge of paper P, the separation of paper P from photoconductor 1 or intermediate transfer belt 10 can be improved.

When the application of the transfer bias is controlled as described above, an example of the positional relationship between the paper P and the secondary transfer roller 21 when the transfer bias is turned ON is shown in Figure 8. That is, the application of the transfer bias begins when the leading edge of the paper P has passed the transfer nip of the secondary transfer roller 21, so the paper P is not electrically attracted to the intermediate transfer belt 10 and is transported downstream in the transport direction. In other words, the application of the transfer bias begins when the separation of the paper P is ensured.

[Second embodiment]
Next, in another embodiment of the present invention, another example of a method for controlling a transfer bias that improves the separation of the paper P during secondary transfer and contributes to the quality of image formation will be described.

As in the first embodiment already described, the non-image area determination unit 222 determines the size of the margin area 301 based on the image data acquired in the image data acquisition unit 221 of the control unit 210. Then, if the margin area 301 is sufficient to ensure separation, normal image formation processing may be executed.

When the non-image area determination unit 222 determines that the result of the determination is "insufficient," the non-image area determination unit 222 determines whether the area of the image forming area 302 following the margin area 301 to which the secondary transfer bias is applied based on the image data (to which the image 310 is transferred) is included in the leading area 303.

When the non-image area determination unit 222 determines that the margin area 301 alone is "insufficient" and determines that the image 310 will be transferred to the leading area 303, as shown in FIG. 9(a), the non-image area determination unit 222 issues an instruction to the image formation size change unit 226 to reduce the image 310.

Based on the instruction from the non-image area determination unit 222, the image formation size change unit 226 notifies the image formation control unit 228 to reduce the image 310 toward the rear end in the transport direction. As a result, the image formation control unit 228 executes the image formation process so that the image 310 is formed as shown in FIG. 9B, for example.

In this case, the image formation control unit 228 controls the timing to start applying the transfer bias so as to transfer the reduced image 310 onto the paper P. This control ensures that a sufficient non-charged area is provided at the leading edge of the paper P, as shown in FIG. 9(b), improving the separation of the paper P from the photoconductor 1 or intermediate transfer belt 10.

[Third embodiment]
Next, in another embodiment of the present invention, still another example of a method for controlling a transfer bias that improves the separation of the paper P during secondary transfer and contributes to the quality of image formation will be described.

As in the first and second embodiments already described, the non-image area determination unit 222 determines the size of the margin area 301 based on the image data acquired in the image data acquisition unit 221 of the control unit 210. Then, if the margin area 301 is sufficient to ensure separation, normal image formation processing may be executed.

When the non-image area determination unit 222 determines that the result of the determination is "insufficient," the non-image area determination unit 222 determines whether the area of the image forming area 302 following the margin area 301 to which the secondary transfer bias is applied based on the image data (to which the image 310 is transferred) is included in the leading area 303.

When the non-image area determination unit 222 determines that the margin area 301 alone is "insufficient" and determines that the image 310 will be transferred to the leading area 303, as shown in FIG. 10(a), the non-image area determination unit 222 issues an instruction to the image formation position change unit 227 to move the image 310.

Based on the instruction from the non-image area determination unit 222, the image formation position change unit 227 notifies the image formation control unit 228 to move the image 310 toward the rear end side in the transport direction. As a result, the image formation control unit 228 executes the image formation process so that the image 310 is formed as shown in FIG. 10(b), for example.

In this case, the image formation control unit 228 controls the timing to start applying the transfer bias so as to change the transfer position of the image 310 onto the paper P. This control ensures that there is a sufficient non-charged area at the leading edge of the paper P, as shown in FIG. 10(b), improving the separation of the paper P from the photoconductor 1 or intermediate transfer belt 10.

As described above, in this embodiment, in order to delay the application timing of the transfer bias from the normal timing, the image formation control unit 228 controls to change the transfer timing of the toner image transferred to the intermediate transfer belt 10. This makes it possible to effectively delay the arrival timing of the image relative to the timing at which the paper P reaches the secondary transfer roller 21. Then, the bias voltage control unit 224 controls the application timing of the transfer bias so that the secondary transfer bias is applied in accordance with the arrival timing of the image.

This ensures that the leading edge of the paper P is left uncharged, improving the separation of the paper P from the photoreceptor 1 or intermediate transfer belt 10.

The present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the technical gist of the invention. All technical matters included in the technical ideas described in the claims are covered by the present invention. The above-described embodiments are preferred examples, but a person skilled in the art can realize various modifications from the disclosed contents. Such modifications are also included in the technical scope described in the claims.

1: photoconductor 2: photoconductor cleaning unit 3: blade 4: charger 5: exposure means 6: yellow developer 7: magenta developer 8: cyan developer 9: black developer 10: intermediate transfer belt 11: primary transfer bias roller 12: secondary transfer opposing roller 13: belt cleaning opposing roller 15: driven roller 19: belt cleaning unit 20: cleaning blade 21: secondary transfer roller 22: blade holder 26: paper feed roller 27: paper transport roller 28: registration roller 30: fixing means 32: paper discharge roller 44: fixing entrance guide 102: secondary bias power supply 103: voltage application device 152: lubricant application member 153: lubricant pressure means 155: solid lubricant 200: color printer 210: control unit 211: CPU
212: RAM
213: ROM
214: HDD
215: I/F
216: Display unit 217: Operation unit 218: Dedicated device 219: Bus 221: Image data acquisition unit 222: Non-image area determination unit 224: Bias voltage control unit 225: Medium information storage unit 226: Image formation size change unit 227: Image formation position change unit 228: Image formation control unit 301: Margin area 302: Image formation area 303: Leading area 310: Image

JP 2019-107876 A

Claims (3)

an image carrier that holds at least a toner;
a transfer device that transfers a toner image formed by the toner held on the image carrier from the image carrier to a recording medium;
a power supply device that applies a transfer bias to the transfer device;
A control device for controlling application of the transfer bias;
Equipped with
The control device includes:
when a marginal area set on the recording medium is narrower than a predetermined threshold value and a non-image area cannot be expanded beyond the threshold value unless a leading area following the marginal area is included, a control is performed to reduce the size of the toner image formed on the image carrier so that the toner image can be transferred to the recording medium without transferring the toner image to the leading area ,
The control device includes:
An image forming apparatus characterized in that the timing of application of a transfer bias for transferring the toner image is controlled in accordance with the size of an area where an image is not formed and where secondary transfer is not performed at the leading end portion of the recording medium in the transport direction . The control device includes:
a medium information storage unit for storing medium information that is information related to the recording medium,
controlling a start timing of application of the transfer bias in accordance with the information stored in the medium information storage unit;
The image forming apparatus according to claim 1 . The control device includes:
a non-image area determination unit that determines a non-image area to which the toner image is not transferred in an image forming area including the leading area of the recording medium,
controlling the application timing of the transfer bias in accordance with the size or position of the non-image area;
3. The image forming apparatus according to claim 1 or 2.