JP7537149B2 - Transfer device and image forming device - Google Patents

Description

The present invention relates to a transfer device and an image forming device.

Conventionally, image forming devices using the intermediate transfer method have been widely used, in which a toner image formed on a photoreceptor (image carrier) is primarily transferred to an intermediate transfer belt (image carrier and intermediate transfer body), and the toner image on the intermediate transfer belt is then secondarily transferred to paper.

In this image forming device, image defects can occur due to discharge between the photoconductor and the primary transfer roller, which are arranged opposite each other via the intermediate transfer belt. For example, image defects such as white spots (white spots) caused by toner that has lost its charge due to discharge and is not transferred, and wavy color unevenness (ripples) caused by toner whose charge polarity has been reversed due to discharge being collected at the downstream primary transfer section.

To prevent such image defects, the primary transfer roller is usually positioned in an image forming apparatus so that it is offset from the photoconductor so that it is downstream in the direction of movement of the intermediate transfer belt. In this position, as shown in FIG. 1A, the primary transfer roller 422 presses the intermediate transfer belt 421 with a predetermined pressure, so that the intermediate transfer belt 421 is wrapped around the photoconductor drum 413, forming a primary transfer nip N1.

In recent years, there has been a demand for such image forming devices to form images on paper with an uneven surface (textured paper), such as embossed paper or rough paper. However, it is known that textured paper has poor secondary transfer properties compared to regular paper, as toner has difficulty reaching the recesses during secondary transfer.

Therefore, a technology has been proposed in which, when forming an image on textured paper, the pressing force of the primary transfer roller against the intermediate transfer belt is made weaker than usual, making it easier for the toner on the intermediate transfer belt to peel off from the belt, thereby improving the secondary transfer properties in the recesses of the textured paper (see, for example, Patent Document 1).

JP 2010-139955 A

However, when the pressing force of the primary transfer roller is weakened, in the above-mentioned arrangement in which the primary transfer roller is shifted so that it is downstream of the photoconductor in the movement direction of the intermediate transfer belt, as shown in FIG. 1B, the tension of the intermediate transfer belt 421 pushes back the primary transfer roller 422, preventing the formation of the primary transfer nip N1, resulting in a significant decrease in primary transferability.

The object of the present invention is to provide a transfer device and an image forming apparatus that can maintain good transferability regardless of the type of paper in an intermediate transfer type image forming apparatus.

The transfer device according to the present invention comprises:
a contact position changing unit that changes a contact position between the image carrier and the transfer roller in a rotation direction of the image carrier according to a type of recording medium on which an image is formed;
a contact pressure changing unit that is operable independently of the contact position changing unit and changes a contact pressure between the image carrier and the transfer roller by changing a pressing force of a pressing member that presses the image carrier;
Equipped with
The pressing member includes a first pressing member and a second pressing member,
the contact pressure changing unit, when the type of the recording medium is textured paper, presses the image carrier with the first pressing member, and when the type of the recording medium is other than textured paper, presses the image carrier with the first pressing member and the second pressing member, holds a shaft of the transfer roller, and includes movable side plates facing both sides in the axial direction of the image carrier;
The movable side plate includes a pressure release portion that releases the pressure of the second pressing member .

The image forming apparatus according to the present invention is equipped with the transfer device described above.

According to the present invention, in an image forming device using an intermediate transfer method, good transferability can be maintained regardless of the type of paper.

1A and 1B are diagrams for explaining the conventional problems in an intermediate transfer type image forming apparatus. 1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention; 1 is a block diagram showing a main functional configuration of an image forming apparatus according to an embodiment of the present invention; FIG. 4A is a diagram for explaining the first nip position and nip pressure in this embodiment, FIG. 4B is a diagram for explaining the problems that arise when the nip pressure is weakened from the state of FIG. 4A, and FIG. 4C is a diagram for explaining the second nip position and nip pressure in this embodiment. FIG. 2 is a perspective view for explaining an overall outline of an intermediate transfer unit according to the present embodiment. FIG. 6 is a partially cutaway view for explaining the configuration of a side plate and the like located on the left side in FIG. 5 . 5 is a perspective view showing the configuration of a contact pressure changing section in the present embodiment. FIG. 13 is a perspective view for explaining the operation of a contact pressure changing portion, etc. FIG. 9A and 9B are diagrams explaining the rotational positions of multiple cams, etc. FIG. 9A is a diagram explaining the state in separation mode or monochrome mode, FIG. 9B is a diagram showing the state during normal pressure contact, and FIG. 9C is a diagram showing the state in textured paper printing mode. 10A and 10B are diagrams illustrating a mechanism for adjusting the nip pressure of the primary transfer roller for black (K). 5 is a transition diagram for explaining the relationship between the rotational positions of the three cams and the contact pressure, etc. FIG.

Below, an embodiment of an image forming device to which the present invention is applied will be described with reference to the drawings.

Figure 2 is a diagram showing the overall configuration of an image forming apparatus 1 according to an embodiment of the present invention. Figure 3 shows the main parts of the control system of the image forming apparatus 1 according to this embodiment.

The image forming device 1 is a color image forming device of the intermediate transfer type that utilizes electrophotographic process technology. That is, the image forming device 1 primarily transfers the Y (yellow), M (magenta), C (cyan), and K (black) color toner images formed on the photosensitive drum 413 onto the intermediate transfer belt 421, superimposes the four color toner images on the intermediate transfer belt 421, and then secondary transfers the toner images onto paper (recording medium), thereby forming a toner image.

The image forming device 1 also employs a tandem system in which photoconductor drums 413 corresponding to the four colors YMCK are arranged in series in the running direction of the intermediate transfer belt 421, and each color toner image is transferred sequentially to the intermediate transfer belt 421 in a single step.

As shown in FIG. 3, the image forming device 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper conveying unit 50, a fixing unit 60, and a control unit 100.

The control unit 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, etc. The CPU 101 reads a program corresponding to the processing contents from the ROM 102, loads it into the RAM 103, and centrally controls the operation of each block of the image forming device 1 in cooperation with the loaded program. At this time, various data stored in the memory unit 72 is referenced. The memory unit 72 is composed of, for example, a non-volatile semiconductor memory (so-called flash memory) or a hard disk drive.

In this embodiment, the control unit 100, together with the intermediate transfer unit 42 described below, constitutes the "transfer device" of the present invention. In addition, the control unit 100, together with mechanisms such as the movable side plate 430 described below, constitutes the "contact position change unit" of the present invention.

The "contact position change unit" here is a function that changes the contact position between the intermediate transfer belt 421 and the primary transfer roller 422 in the rotation direction of the intermediate transfer belt 421 (image carrier) depending on the type of paper (recording medium) on which an image is formed (see Figures 4A to 4C as appropriate), and details will be described later.

The control unit 100 transmits and receives various data to and from an external device (e.g., a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 71. The control unit 100 receives, for example, image data transmitted from an external device, and forms a toner image on paper based on this image data (input image data). The communication unit 71 is composed of, for example, a communication control card such as a LAN card.

The image reading unit 10 is configured with an automatic document feeder 11, also known as an ADF (Auto Document Feeder), and a document image scanning device 12 (scanner), etc.

The automatic document feeder 11 transports the document D placed on the document tray using a transport mechanism and sends it to the document image scanning device 12. The automatic document feeder 11 can continuously read the images (including both sides) of multiple documents D placed on the document tray all at once.

The document image scanning device 12 optically scans the document transported from the automatic document feeder 11 onto the contact glass or the document placed on the contact glass, and forms an image of the reflected light from the document on the light receiving surface of a CCD (Charge Coupled Device) sensor 12a to read the document image. The image reading unit 10 generates input image data based on the results of the reading by the document image scanning device 12. This input image data is subjected to a predetermined image processing in the image processing unit 30.

The operation display unit 20 is composed of, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, image status displays, operation statuses of each function, etc. according to a display control signal input from the control unit 100. The operation unit 22 has various operation keys such as a numeric keypad and a start key, accepts various input operations by the user, and outputs operation signals to the control unit 100.

The image processing unit 30 includes circuits and the like that perform digital image processing on the input image data according to initial settings or user settings. For example, under the control of the control unit 100, the image processing unit 30 performs gradation correction based on gradation correction data (gradation correction table LUT) in the memory unit 72. In addition to gradation correction, the image processing unit 30 also performs various correction processes such as color correction and shading correction, as well as compression processing, on the input image data. The image forming unit 40 is controlled based on the image data that has been subjected to these processes.

The image forming section 40 includes image forming units 41Y, 41M, 41C, and 41K, an intermediate transfer unit 42, and the like for forming images using color toners of the Y, M, C, and K components based on input image data.

Image forming units 41Y, 41M, 41C, and 41K for the Y, M, C, and K components have the same configuration. For ease of illustration and explanation, common components are indicated with the same reference numerals, and when distinguishing between them, the reference numerals are followed by Y, M, C, or K. In FIG. 2, reference numerals are only assigned to the components of image forming unit 41Y for the Y component, and reference numerals are omitted for the components of the other image forming units 41M, 41C, and 41K.

The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, and a drum cleaning device 415.

The photoconductor drum 413 is a negatively charged organic photoconductor (OPC) in which an undercoat layer (UCL), a charge generation layer (CGL), and a charge transport layer (CTL) are sequentially laminated on the circumferential surface of a conductive cylinder (aluminum tube) made of aluminum, for example. The charge generation layer is made of an organic semiconductor in which a charge generation material (e.g., phthalocyanine pigment) is dispersed in a resin binder (e.g., polycarbonate), and generates a pair of positive and negative charges when exposed to light by the exposure device 411. The charge transport layer is made of a hole transport material (electron-donating nitrogen-containing compound) dispersed in a resin binder (e.g., polycarbonate resin), and transports the positive charges generated in the charge generation layer to the surface of the charge transport layer.

The control unit 100 rotates the photoconductor drum 413 at a constant peripheral speed (linear speed) by controlling the drive current supplied to a drive motor (not shown) that rotates the photoconductor drum 413.

The charging device 414 uniformly charges the surface of the photoconductor drum 413, which has photoconductivity, to a negative polarity. The exposure device 411 is composed of, for example, a semiconductor laser, and irradiates the photoconductor drum 413 with laser light corresponding to an image of each color component. Positive charges are generated in the charge generation layer of the photoconductor drum 413, and are transported to the surface of the charge transport layer, thereby neutralizing the surface charge (negative charge) of the photoconductor drum 413. An electrostatic latent image of each color component is formed on the surface of the photoconductor drum 413 due to the potential difference with the surroundings.

The developing device 412 is, for example, a two-component developing device that visualizes the electrostatic latent image by attaching toner of each color component to the surface of the photoconductor drum 413 to form a toner image.

The drum cleaning device 415 has a drum cleaning blade (hereinafter simply referred to as a cleaning blade) as a cleaning member that is brought into sliding contact with the surface of the photosensitive drum 413. The drum cleaning device 415 uses the cleaning blade to remove residual toner remaining on the surface of the photosensitive drum 413 after the primary transfer.

The intermediate transfer unit 42 includes an intermediate transfer belt 421 as an image carrier, a primary transfer roller 422, a number of support rollers 423, a secondary transfer roller 424, and a belt cleaning device 426.

The intermediate transfer belt 421 is an endless belt that is stretched around a number of support rollers 423 in a loop shape. At least one of the support rollers 423 is a drive roller, and the others are driven rollers. For example, it is preferable that roller 423A, which is disposed downstream in the belt running direction from primary transfer roller 422 for K component, is the drive roller. This makes it easier to maintain a constant running speed of the belt in the primary transfer section. As drive roller 423A rotates, intermediate transfer belt 421 runs at a constant speed in the direction of arrow A.

The primary transfer roller 422 is disposed on the inner peripheral side of the intermediate transfer belt 421, facing the photoconductor drum 413 of each color component. The primary transfer roller 422 is pressed against the photoconductor drum 413 with the intermediate transfer belt 421 sandwiched therebetween, thereby forming a primary transfer nip for transferring a toner image from the photoconductor drum 413 to the intermediate transfer belt 421 (see the primary transfer nip portion N1 described above in FIG. 1A).

The secondary transfer roller 424 is disposed on the outer circumferential surface side of the intermediate transfer belt 421, facing the backup roller 423B, which is disposed downstream of the drive roller 423A in the belt running direction. The secondary transfer roller 424 is pressed against the backup roller 423B with the intermediate transfer belt 421 sandwiched therebetween, thereby forming a secondary transfer nip for transferring a toner image from the intermediate transfer belt 421 to the paper S.

When the intermediate transfer belt 421 passes through the primary transfer nip, the toner image on the photoconductor drum 413 is sequentially superimposed and primarily transferred onto the intermediate transfer belt 421. Specifically, a primary transfer bias is applied to the primary transfer roller 422, and a charge of the opposite polarity to the toner is applied to the back side of the intermediate transfer belt 421 (the side that contacts the primary transfer roller 422), so that the toner image is electrostatically transferred to the intermediate transfer belt 421.

Then, when the paper passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the paper. Specifically, a secondary transfer bias is applied to the secondary transfer roller 424, and a charge of the opposite polarity to the toner is applied to the back side of the paper (the side that contacts the secondary transfer roller 424), so that the toner image is electrostatically transferred to the paper. The paper with the transferred toner image is transported toward the fixing unit 60.

The belt cleaning device 426 has a belt cleaning blade that slides against the surface of the intermediate transfer belt 421 and removes residual toner remaining on the surface of the intermediate transfer belt 421 after secondary transfer. Note that instead of the secondary transfer roller 424, a configuration in which the secondary transfer belt is stretched in a loop shape around multiple support rollers including the secondary transfer roller (a so-called belt-type secondary transfer unit) may be used.

The fixing section 60 includes an upper fixing section 60A having a fixing surface side member arranged on the fixing surface side of the paper (the surface on which the toner image is formed), a lower fixing section 60B having a back surface side support member arranged on the back surface side of the paper (the surface opposite the fixing surface), and a heating source 60C. The back surface side support member is pressed against the fixing surface side member to form a fixing nip that holds and transports the paper.

The fixing unit 60 heats and presses the paper that has been transported to it in a fixing nip, fixing the toner image to the paper. The fixing unit 60 is disposed as a unit within the fixing device F. The fixing device F also includes an air separation unit 60D that blows air onto the paper S to separate it from the fixing surface side member.

The paper transport section 50 includes a paper feed section 51, a paper discharge section 52, and a transport path section 53. The three paper feed tray units 51a to 51c that make up the paper feed section 51 store paper S (standard paper, special paper) that is identified based on basis weight (rigidity), size, etc., by preset type. The transport path section 53 includes multiple transport rollers such as a registration roller pair 53a, a double-sided transport path for forming images on both sides of the paper, etc.

The sheets S stored in the paper feed tray units 51a to 51c are sent out one by one from the top and transported to the image forming unit 40 by the transport path unit 53. At this time, the inclination of the fed sheets S is corrected and the transport timing is adjusted by the registration roller unit in which the registration roller pair 53a is arranged. Then, in the image forming unit 40, the toner image on the intermediate transfer belt 421 is secondarily transferred all at once to one side of the sheets S, and the fixing process is performed in the fixing unit 60. The sheets S with the image formed thereon are discharged outside the machine by the paper discharge unit 52 equipped with the paper discharge roller 52a.

In this type of intermediate transfer type image forming device 1, there is a demand to form an image on rough paper with an uneven surface (such as embossed paper or rough paper, hereafter collectively referred to as "uneven paper") as the paper S. On the other hand, with uneven paper, it is difficult for toner to reach the recesses during secondary transfer, and the secondary transferability is often poorer than with normal paper.

Therefore, a technology has been proposed in which, when forming an image on textured paper, the pressing force of the primary transfer roller 422 against the intermediate transfer belt 421 is made weaker than usual, making it easier for the toner on the intermediate transfer belt 421 to peel off from the intermediate transfer belt 421, thereby improving the secondary transfer properties in the recesses of the textured paper.

Here, FIG. 4A shows, in a somewhat exaggerated manner, the position and pressing state of the primary transfer nip portion N1 when forming an image on normal paper S. As shown in FIG. 4A, in order to prevent as much as possible the occurrence of image defects such as the above-mentioned white spots and ripples, each primary transfer roller 422 is shifted and positioned downstream in the movement direction of the intermediate transfer belt 421 relative to the corresponding photoconductor drum 413.

In addition, in FIG. 4A, the pressing force (nip pressure or contact pressure) applied to each primary transfer roller 422 by a pressing member (a coil spring in this example) is indicated by a black arrow. In the setting example shown in FIG. 4A, each primary transfer roller 422 is pressed with a pressing force (nip pressure) sufficient to hold the primary transfer nip portion N1. When the primary transfer nip portion N1 is set in this way, both the primary transferability and secondary transferability of the toner image to regular paper can be ensured.

On the other hand, in the setting state of the primary transfer nip portion N1 as shown in FIG. 4A, the adhesion of the toner image primarily transferred to the intermediate transfer belt 421 becomes stronger; in other words, the toner image becomes less likely to peel off from the intermediate transfer belt 421. For this reason, if the paper S on which the image is formed is textured paper, the secondary transferability to the textured paper (recording medium) at the secondary transfer nip (i.e., the nip between the intermediate transfer belt 421 and the secondary transfer roller 424) becomes poor.

To address this issue, it is possible to set the pressing force (contact pressure) of the primary transfer rollers 422 against the intermediate transfer belt 421 to be weaker than normal, as shown in FIG. 4B. Note that in FIG. 4B, the pressing force (weaker contact pressure than the example setting in FIG. 4A) with which each primary transfer roller 422 is biased (pressed) by a coil spring is indicated by a dotted arrow, and the same is true for the arrows in FIG. 4C described below.

When the settings shown in FIG. 4B are used, the adhesion of the toner image primarily transferred to the intermediate transfer belt 421 is weaker than when the settings described above in FIG. 4A are used, so the toner on the intermediate transfer belt 421 is more likely to peel off from the intermediate transfer belt 421.

However, when the pressing force of the primary transfer roller 422 is weakened in this way, if the primary transfer roller 422 is shifted so that it is downstream of the photosensitive drum 413 in the movement direction of the intermediate transfer belt 421, the primary transfer roller 422 is pushed back by the tension of the intermediate transfer belt 421 and the primary transfer nip N1 is not formed, as shown in Figures 1B and 4B. In this case, even if the secondary transfer from the intermediate transfer belt 421 to the textured paper can be ensured, the primary transfer from the photosensitive drum 413 to the intermediate transfer belt 421 is significantly reduced.

To solve this problem, as shown in FIG. 4C, it is necessary to lower the pressing force of the primary transfer rollers 422 against the intermediate transfer belt 421 and raise the position of each primary transfer roller 422 in order to maintain close contact with the photosensitive drum 413 via the primary transfer nip portion N1, i.e., the intermediate transfer belt 421.

Thus, as a result of experiments conducted by the inventors, it was found that when the primary transfer nip portion N1 is set as shown in FIG. 4C, it is possible to ensure both primary and secondary transfer properties for textured paper, and it is possible to print without noticeable white spots or ripples. On the other hand, it was confirmed once again that when the primary transfer nip portion N1 is set as shown in FIG. 4C, image defects such as white spots and ripples are noticeable for normal paper.

Furthermore, as a result of various experiments conducted by the inventors, it was confirmed that there is a certain width (range) of the nip position (the position in the vertical direction of the primary transfer roller 422) at which both primary and secondary transfer properties can be ensured for textured paper.

Specifically, in the example shown in FIG. 4C, the axis (center of rotation) (not shown) of the photosensitive drum 413 is aligned horizontally with the axis (center of rotation) (not shown) of the primary transfer roller 422. On the other hand, it has been confirmed that the nip position (in other words, the position of the center of rotation of the primary transfer roller 422) that can ensure both primary and secondary transfer properties for textured paper can be a position slightly lower (or slightly higher) than the position shown in FIG. 4C.

Next, the inventors have considered from various perspectives the specific configuration for changing the nip position, that is, the configuration of a movement mechanism that can move each primary transfer roller 422 back and forth between a first nip position (normal position or initial position shown in FIG. 4A) for forming an image on normal paper and a second nip position (upper position shown in FIG. 4C) for forming an image on textured paper. Such a movement mechanism corresponds to the mechanical configuration of the "contact position change unit" in this invention.

Specifically, the inventors have devised a configuration in which, as a "contact position changing unit," a member that holds the shafts of multiple primary transfer rollers 422 is attached to the movable side plates, and the pair of movable side plates is moved back and forth in a substantially vertical direction. With this configuration, the nip positions of multiple primary transfer rollers 422 can be switched at once.

Based on the configuration of the above-mentioned "contact position change unit," the inventors also designed and studied a mechanism for changing the nip pressure (i.e., the pressure applied to the primary transfer roller 422) in conjunction with a change in the nip position of the primary transfer nip portion N1 (up and down movement of the primary transfer roller 422).

However, when a mechanism is used that links changes in nip position and changes in nip pressure as described above, in other words, when the nip pressure (contact pressure) is changed depending on the contact position between the image carrier (in this example, the photosensitive drum 413 and intermediate transfer belt 421) and the primary transfer roller 422, it has been found that the following problems arise.

In other words, when a mechanism is adopted that links the nip position and nip pressure (contact pressure between the image carrier and the primary transfer roller 422), the two change inseparably, making it difficult to fine-tune the nip position and nip pressure (pressure) individually, and making it difficult to make flexible adjustments during actual maintenance.

In addition, it was found that when trying to realize a mechanism that changes the strength of the nip pressure (contact pressure) in accordance with the positional movement of the pair of movable side plates as described above, the following problems arise:

In other words, a mechanism that changes the nip pressure (contact pressure) according to the position (nip position) of a pair of movable side plates can easily become complicated, and if one tries to realize such a mechanism with as simple a configuration as possible, the amount of movement of the movable side plates increases, which creates a problem of increasing the size of the entire transfer device.

Furthermore, it is considered desirable to provide a separate mechanism for adjusting the position and pressure of the primary transfer roller 422 for colors other than black (in this example, the three colors YMC) used during color printing, and a separate mechanism for adjusting the position and pressure of the primary transfer roller 422 for black (K) used during monochrome printing.

On the other hand, if separate mechanisms are provided for the three colors YMC and black (K), then the mechanisms will be configured separately for the three colors YMC and black (K). Furthermore, normally, two independent drive sources (motors, etc.) would be required to drive the two types of mechanisms for the three colors YMC and black (K) separately. However, using two drive sources would result in an increase in size, weight, and power consumption of the device.

The inventors conducted extensive research to address the various problems described above, and came up with the following configuration.

In this embodiment, a component that changes the pressing force (contact pressure) of the primary transfer roller 422 against the photosensitive drum 413 and a component that changes the contact position of the primary transfer roller 422 against the photosensitive drum 413 are provided separately, and each component operates independently by the transmission of driving force from a single driving source (motor).

Here, as a specific example of a mechanism for transmitting driving force, multiple cams are arranged on the same axis (camshaft), and the driving force of the drive source is transmitted to the camshaft to rotate the multiple cams at once. Then, by pressing (e.g. pushing up) the corresponding parts with each cam, a part that changes the pressing force (contact pressure) of the primary transfer roller 422 against the photosensitive drum 413 and a part that changes the contact position of the primary transfer roller 422 against the photosensitive drum 413 are moved separately (e.g. at different angles (phases) or timing during one revolution of the camshaft).

In this way, by configuring the change in the contact position of the primary transfer roller 422 with respect to the photosensitive drum 413 and the change in the pressing force (contact pressure) of the primary transfer roller 422 with respect to the photosensitive drum 413 to be performed independently through the movement of different parts, the fine adjustment of the contact position and the fine adjustment of the pressing force can be performed separately and easily.

In addition, by adopting the above-described configuration, it is possible to reduce the space occupied by the mechanism that switches the contact position and pressing force (contact pressure), thereby enabling the transfer device (unit) and the main body of the image forming device 1 to be made smaller.

Next, we will explain the above-mentioned configuration in more detail with reference to Figure 5 onwards.

Figure 5 is a perspective view showing the main parts of intermediate transfer unit 42 of image forming apparatus 1 in this embodiment. For ease of understanding, intermediate transfer belt 421 is not shown in Figure 5. The right side in Figure 5 indicates the rear side of the apparatus (the rear side of the paper in Figure 2), and the left side in Figure 5 indicates the front side of the apparatus (the front side of the paper in Figure 2). In this embodiment, the above-mentioned control unit 100 and intermediate transfer unit 42 correspond to the "transfer device" of the present invention.

Referring to FIG. 5, the intermediate transfer unit 42 of this embodiment has a pair of fixed side plates 400 arranged on both sides of the front and rear of the image forming device 1, and a movable side plate 430 movably attached to the inside of each of the fixed side plates 400.

Here, the fixed side plates 400, 400 are arranged approximately parallel to each other with a distance slightly wider than the width of the intermediate transfer belt 421. In order to connect the fixed side plates 400 to each other and maintain (fix) this parallel state, multiple long connecting members (not shown) are provided on the inner surface of the fixed side plates 400, 400 in parallel to the primary transfer roller 422, etc.

The fixed side plates 400, 400 serve to removably fix the entire intermediate transfer unit 42 to the main body of the image forming device 1, to rotatably hold the intermediate transfer belt 421, and to movably hold the movable side plate 430.

The fixed side plate 400 rotatably holds a plurality of support rollers 423 that rotatably support the intermediate transfer belt 421 in order to rotatably hold the intermediate transfer belt 421 (see FIG. 2 as appropriate).

To hold the movable side plate 430 movably, multiple (two in this example) fixed shafts 400a are erected (fixed) on the inner surface of the fixed side plate 400 (see FIG. 6 as appropriate). Each fixed shaft 400a of the fixed side plate 400 is fitted with a corresponding groove 430a on the movable side plate 430, allowing the movable side plate 430 to move back and forth in a substantially vertical direction.

On the other hand, the movable side plate 430 rotatably holds three primary transfer rollers 422(Y), 422(M), and 422(C) positioned opposite each photoconductor drum 413 carrying toner images (color images) of three colors (i.e., Y, M, and C) other than black (K).

As shown in Figures 5 and 6, in this embodiment, in order to reduce the weight and size of the entire device, the depth of the movable side plate 430 (width in the left-right direction in Figure 6) is kept to approximately half the depth of the fixed side plate 400.

In addition, to ensure the rigidity of the movable side plate 430, both ends and the lower end of the movable side plate 430 in the depth direction are bent toward the inner surface of the movable side plate 430 to form flanges.

Furthermore, multiple (two in this example) fixed shafts 400b are erected (fixed) on the inner surface of the movable side plate 430. The corresponding guide grooves 450a of the pressure release part 450 are assembled to these fixed shafts 400b, so that the pressure release part 450 can move back and forth in a substantially vertical direction. In other words, the movable side plate 430 has the pressure release part 450 on its inner surface so that it can move up and down.

Here, the pressure release unit 450 is a member having a roughly rod-shaped outer shape that plays a role in changing the contact pressure of the primary transfer roller 422 against the image carrier (in this example, the photosensitive drum 413 and the intermediate transfer belt 421) (releasing the pressure from the coil spring 442, which will be described later). The configuration and operation of the pressure release unit 450 will be described in detail later.

Furthermore, a fixed shaft 403a is erected (fixed) below the pressure release portion 450 on the inner surface of the movable side plate 430, and a push-up member 403 for pushing up the pressure release portion 450 is rotatably attached to the fixed shaft 403a.

In addition, FIG. 6 shows a state in which a plate-shaped cover material 401a, which has a function of preventing the members provided on each shaft (403a, 401) from falling off, is attached to the fixed shaft 403a and the cam shaft 401 described later. On the other hand, in order to make it easier to see the state of the members provided on each shaft (403a, 401), the cover material 401a is removed in the description in FIGS. 9A to 9C described later.

Generally speaking, in this embodiment, by changing the position of the movable side plates 430, 430 that face the pair of fixed side plates 400, 400 (moving the movable side plates 430, 430 in a substantially vertical direction), the contact position (nip position) between the primary transfer rollers 422(Y), 422(M), and 422(C) held on the movable side plate 430 side and the opposing photoconductor drum 413 changes.

More specifically, a block-shaped base material 440A, which will be described later in FIG. 7, is fixed to the inner surface of the movable side plate 430, and the base material 440A holds the shafts of the corresponding primary transfer rollers 422(Y), 422(M), and 422(C) so that they are rotatable and biased in the direction of pressing the intermediate transfer belt 421, etc.

Therefore, when the position of the movable side plate 430 relative to the fixed side plate 400 changes, the positions of the axes of the primary transfer rollers 422(Y), 422(M), and 422(C) held by the substrate 440A change (see Figures 4A and 4C).

When the position of the movable side plate 430 relative to the fixed side plate 400 changes, the position of the fixed shaft 400b erected on the movable side plate 430 also changes.

In contrast, when the pressure release portion 450 is pressed (pushed up) by the tip side of the push-up member 403 described below, it moves regardless of the position of the movable side plate 430. Therefore, in this embodiment, the movable side plate 430 and the pressure release member 450 can move independently of each other relative to the fixed side plate 400.

The pressure release part 450 also moves when the upper end or lower end of the guide groove 450a of the pressure release part 450 is pressed by the fixed shaft 400b of the movable side plate 430. To this extent, the pressure release part 450 moves in accordance with the movement of the movable side plate 430.

To explain in more detail with reference to Figure 6, the movable side plate 430 has multiple guide members 430-1 (two in this example) arranged along the vertical direction to guide the movement of the movable side plate 430 and fixed to the movable side plate 430. The movable side plate 430 and the guide members 430-1 are formed with grooves 430a of the same shape that are bent vertically and diagonally (see also Figure 8).

As described above, multiple (two in this example) fixed shafts 400a are fixed to the inner surface of the fixed side plate 400. Each fixed shaft 400a has a width approximately equal to the horizontal width of the groove 430a described above, and is erected so as to extend perpendicularly from the inner surface of the fixed side plate 400.

Thus, by assembling the grooves 430a of the movable side plates 430 and guide members 430-1 to the fixed shafts 400a of the corresponding fixed side plates 400, the pair of movable side plates 430 and thus the primary transfer rollers 422(Y), 422(M), and 422(C) become movable in a direction that follows the shape defined by the grooves 430a.

In this manner, in this embodiment, the fixed shaft 400a of the fixed side plate 400, the movable side plate 430, and the guide member 430-1 form part of the "contact position changing section" of the present invention. In this embodiment, the movable side plate 430 and thus the primary transfer rollers 422(Y), 422(M), and 422(C) are configured to be separated from the corresponding primary transfer rollers 422 and intermediate transfer belt 421 (image carrier) in response to the movement of the movable side plate 430.

When the movable side plate 430 moves in a generally vertical direction relative to the fixed side plate 400, the members fixed to the movable side plate 430, such as the fixed shaft 400b and the shaft portion of the push-up member 403 for pushing up the pressure release portion 450, also move integrally.

More specifically, when the movable side plate 430 is at the lowest position relative to the fixed side plate 400, in other words when the fixed shaft 400a of the fixed side plate 400 reaches the uppermost position of the groove portion 430a, the pair of movable side plates 430 and thus the primary transfer rollers 422(Y), 422(M), and 422(C) are separated from the opposing photoconductor drums 413(Y)-(C) and the nip is released (see FIG. 4B as appropriate).

The transition to this separated state (nip released state) can be performed under the control of the control unit 100 during monochrome printing, i.e. when forming an image using only black (K) toner, or when maintenance is performed. Note that this separated state corresponds to a state in which the movable side plate 430 and the components attached to the movable side plate 430 have moved diagonally downward to the right in FIG. 9A due to their own weight from the state shown in FIG. 9A.

In other words, Fig. 9A shows the state of each part in an exaggerated manner, and in order to make it easier to see the positions of cams 402-1 to 402-3, which will be described later, the movable side plate 430 and the members attached to the movable side plate 430 are shown as if they were being manually pulled upward. Also, Fig. 9A shows the movable side plate 430 and the like retreated to the right side of the figure from the fixed side plate 400 in order to clearly show the horizontal separation position of the movable side plate 430 and the like relative to the fixed side plate 400 in the actual separation state (see also Fig. 9B or Fig. 9C).

On the other hand, when the movable side plate 430 is at a position somewhat higher than the fixed side plate 400, in other words when the fixed shaft 400a of the fixed side plate 400 is at a position lower than the inclined portion of the groove portion 430a, the pair of movable side plates 430 and thus the primary transfer rollers 422(Y), 422(M), and 422(C) are in a state where they press the opposing image carriers (primary transfer rollers 422(Y)-(C) and intermediate transfer belt 421) (see Figures 9B and 4A).

On the other hand, in the example shown in FIG. 5, the primary transfer roller 422 (K), which faces the photosensitive drum 413 carrying a black (K) toner image (monochrome image), is attached to a block-shaped substrate 440A (see FIG. 7) fixed to the inner surface of the fixed side plate 400.

In other words, in this example, the substrate 440A that rotatably holds the primary transfer roller 422(K) that forms the primary transfer nip portion N1 of the K (black) image is fixed to the fixed side plate 400, not to the movable side plate 430. In contrast, the substrate 440A that rotatably holds the primary transfer rollers 422(Y) to 422(C) that form the primary transfer nip portion N1 of each of the YMC (three color) images is fixed to the movable side plate 430 as described above.

For this reason, in this embodiment, the primary transfer rollers 422(Y), 422(M), and 422(C) move integrally with the movement of the movable side plate 430, and can move to each of the positions of the contact position for normal paper shown in FIG. 4A, the contact-released state shown in FIG. 4B, the contact position for textured paper shown in FIG. 4C, and even a separated position which is a position even higher than the position shown in FIG. 4C.

In this manner, in this embodiment, in order to move each (three) primary transfer rollers 422 facing the photoconductor drums 413 for the three colors YMC at once (collectively) relative to the fixed side plate 400, the base material 440A that holds the shafts of the primary transfer rollers 422 is fixed to the movable side plates 430, 430, which are a single member, and the pair of movable side plates 430, 430 are configured to be movable relative to the opposing fixed side plates 400, 400, and ultimately relative to the intermediate transfer unit 42.

This configuration serves as the basis for a movement mechanism (contact position change unit) that moves between the first nip position (normal position or initial position) shown in FIG. 4A, where image formation is performed on normal paper, and the second nip position (upper position) shown in FIG. 4C, where image formation is performed on textured paper.

Furthermore, when performing monochrome printing of a black (K) toner image, since the YMC color toners are not used, the control unit 100 performs a process of retracting each (three) primary transfer rollers 422 facing the Y, M, and C photoconductor drums 413 when performing monochrome printing.

In this embodiment, the position of the axis (center of rotation) of the primary transfer roller 422(K) relative to the axis (center of rotation) of the photosensitive drum 413(K) is set to a position higher than the position shown in FIG. 4A and lower than the position described above in FIG. 4C.

In general, for the photoconductor drum 413 (K), the position of the roller axis relative to the substrate 440A (position along a substantially horizontal direction) is changed to change (switch) between the nip position (contact position) and nip pressure for normal paper, the nip position (contact position) and nip pressure for textured paper, and even the contact release position (nip release state).

Next, we will explain in more detail the movement mechanism (contact position change unit) that moves the primary transfer rollers 422(Y) to 422(C) for color images collectively.

As shown by the dotted line in FIG. 5, a motor 80 is provided on the outer surface of the fixed side plate 400 at the front of the intermediate transfer unit 42 as a single drive source for moving the movable side plate 430 and various components described below (see FIG. 3 as appropriate).

The motor 80 supplies the driving force to move a pair of movable side plates 430, which hold the primary transfer rollers 422(Y), 422(M), and 422(C), in the vertical direction to change the nip position (contact position with the image carrier).

Motor 80 also supplies a driving force to move pressure release section 450 and switch the pressure (nip pressure) applied by springs 441 and 442 (described later) within substrate 440A on which primary transfer rollers 422(Y), 422(M), and 422(C) are held.

In addition, the motor 80 supplies the driving force to switch the contact pressure (nip pressure) of the primary transfer roller 422 (K), which performs the primary transfer of the K (black) toner image carried on the lowermost photoconductor drum 413 onto the intermediate transfer belt 421.

In this manner, in this embodiment, in which a single motor 80 is used to move various components including the movable side plate 430 and the pressure release portion 450, the intermediate transfer unit 42 and thus the entire image forming device 1 can be made lighter and more compact.

Here, FIG. 6 is a diagram for explaining the mechanism (contact position change unit) that moves the movable side plate 430 in a substantially vertical direction, and shows the normal or default state (see FIG. 9B as appropriate) for forming a color image on paper S (recording medium) other than textured paper.

As shown in Figures 5 and 6, the fixed side plate 400 has a cam shaft 401 in an area below the movable side plate 430, which is parallel to the primary transfer rollers 422 (Y, M, C, K) and rotatably supported. This cam shaft 401 rotates when the driving force of the motor 80 described above is transmitted through a gear (not shown).

The camshaft 401 is equipped with three sets (three pairs) of cams 402 (402-1 to 402-3), which will be described later with reference to FIG. 9 etc.

Generally speaking, in this embodiment, one of these cams (first cams) serves to push the pair of movable side plates 430 upward, changing the nip positions (contact positions with the image carriers) of each of the primary transfer rollers 422(Y), 422(M), and 422(C).

The other set of cams (second cams) plays a role in moving (raising) a pair of pressure release parts 450 to change the pressure (nip pressure) of each of the primary transfer rollers 422(Y), 422(M), and 422(C).

Another set of cams (third cams) plays a role in moving the primary transfer roller 422 (K) that performs the primary transfer of the black (K) toner image onto the intermediate transfer belt 421, thereby changing the nip position and nip pressure.

In this manner, this embodiment, which has multiple cams arranged on the same axis and each cam moving a corresponding part, can reduce the size and weight of the intermediate transfer unit 42 and, ultimately, the entire image forming device 1.

Next, the configuration of the contact pressure change unit 440 that changes the contact pressure of the primary transfer roller 422 will be described with reference to FIG. 7 and other figures. FIG. 7 shows the configuration of the substrate 440A that holds the primary transfer roller 422 for black (K), but the configurations that hold the primary transfer rollers 422 for other colors also have a similar configuration.

On the other hand, FIG. 8 shows the substrate 440A that holds the primary transfer roller 422 for cyan (C). In FIG. 8, in order to make it easier to understand the internal configuration, the fixed side plate 400, the inner bearing 443 and the coil spring 441, which will be described later, have been removed, and only the movable side plate 430, the substrate 440A that holds the primary transfer roller 422 (C), and the pressure release portion 450 are shown.

The base material 440A has a concave recess in the area opposite the side fixed to the movable side plate 430 (see FIG. 8 as appropriate), and the inner bearing 443 and the outer bearing 444 are each movably arranged in this concave area.

Of the above, the inner bearing 443 serves to rotatably hold the base side of the shaft of the primary transfer roller 422, and has an arc-shaped shaft holding surface as shown in FIG. 7.

As shown in FIG. 7, the inner bearing 443 has grooves 443a extending concavely on both the upper and lower ends, and is movably assembled by engaging these grooves 443a with rails (see FIG. 8 as appropriate) that extend to protrude toward the inside of the base material 440A.

As shown in FIG. 7, two coil springs 441 and 442 are arranged inside the base material 440A. The inner bearing 443 is biased to the left in FIG. 7 by the surface opposite to the shaft holding surface being pressed by the coil spring 441 arranged inside the base material 440A.

Here, the coil spring 441 is a spring with a larger diameter and stronger biasing force than the coil spring 442 described below, and corresponds to the "first pressing member" of the present invention. The inner bearing 443 is pressed by the coil spring 441 and also serves as a "first restricting member" that restricts or prevents the coil spring 441 from coming loose.

On the other hand, the outer bearing 444 plays a role of auxiliary pressing against the tip side of the shaft of the primary transfer roller 422, and as shown in Figures 7 and 8, has an outer surface that protrudes in an arc shape, and a shaft pressing portion 445 (see Figure 8) that is continuous with the outer surface and abuts against the tip of the shaft of the primary transfer roller 422.

As shown in FIG. 7, the outer bearing 444 has grooves 444a on the upper and lower ends, and is movably assembled by engaging with rails formed to protrude into the interior of the base material 440A. The surface of the outer bearing 444 opposite the shaft holding surface described above is biased to the left in FIG. 7 by the pressing force of a coil spring 442 arranged inside the base material 440A (see also FIG. 8).

In this example, the coil spring 442 is a spring with a smaller diameter and a weaker biasing force than the coil spring 441 described above, and corresponds to the "second pressing member" of the present invention. The outer bearing 444 is pressed by the coil spring 442 and also serves as a "second restricting member" that restricts or prevents the coil spring 442 from coming loose.

Generally speaking, the primary transfer roller 422 assembled to the substrate 440A is normally biased to the left in FIGS. 7 and 8 by the force (spring force) of two pressing members, coil springs 441 and 442, to form a primary transfer nip between the photoconductor drum 413 and the intermediate transfer belt 421 (image carrier).

In this embodiment, the outer bearing 444 is pressed to the right in Figures 7 and 8, which releases the pressure of the coil spring 442 (second pressing member) applied from the shaft pressing portion 445 to the tip side of the shaft of the primary transfer roller 422, thereby reducing the nip pressure (contact pressure) of the primary transfer nip.

In other words, in this embodiment, the nip pressure (contact pressure) of the primary transfer nip is switched between a normal state for printing on materials other than textured paper and a weak state for printing on textured paper by changing the number of pressing members (coil springs 441, 442) that press the shaft of the primary transfer roller 422 to change the pressing force (spring force).

Next, we will explain the configuration for pressing the outer bearing 444 to the right in Figures 7 and 8 (forcibly moving the outer bearing 444).

Referring to FIG. 8, the base material 440A is fixed to the inner surface of the movable side plate 430. Meanwhile, the pressure release member 450 is attached to the movable side plate 430 so as to be movable in the vertical direction in accordance with the shape of the guide groove 450a extending in the vertical direction, as described above. In other words, the pressure release member 450 is provided so as to be movable in the vertical direction along the side portion of the inner surface of the movable side plate 430 (the side end surface that bends toward the left side in FIG. 8).

More specifically, the pressure release unit 450 is a generally rod-shaped member that is made up of multiple members and extends in the vertical direction, and is provided with tapered protruding pressure units 450b at positions corresponding to the respective substrates 440A that hold the primary transfer rollers 422 (Y, M, C) (see also FIG. 6).

When the pressure release portion 450 is gradually pushed upward from the state shown in FIG. 8, the inclined portion of the pressure portion 450b of the pressure release portion 450 comes into contact with the outer bearing 444, and the outer bearing 444 is, so to speak, forcibly moved to the right in FIG. 8 (see FIG. 9C as appropriate). The amount of movement of the outer bearing 444 is maximum when the thickness (protrusion amount) of the opposing pressure portion 450b is maximum.

On the other hand, when the force pushing the pressure release portion 450 upward is released from the state in which the outer bearing 444 has moved to the right in FIG. 8, the pressure release portion 450 moves downward under its own weight, and as a result, the outer bearing 444 returns to the state shown in FIG. 8 due to the pressing force of the coil spring 442.

Thus, according to this embodiment, the pressure release portion 450 moves vertically relative to the movable side plate 430, thereby changing the pressure (spring force) of the pressure members (coil springs 441, 442) and switching the nip pressure (contact pressure) of the primary transfer nip in the primary transfer rollers 422(Y), 422(M), and 422(C).

Next, the configuration and operation of the three cams arranged on the camshaft 401 described above will be explained with reference to Figures 9A to 9C.

As shown in Figures 9A to 9C, the cam shaft 401, which is rotatably supported on the fixed side plate 400, is provided with three sets (three pairs) of cams 402-1, 402-2, and 402-3.

Of the above, the outermost cam 402-1 faces the flange portion at the lower end of the movable side plate 430 described above, and serves to push the movable side plate 430 upward. In other words, when the main body of the cam 402-1 pushes the movable side plate 430 upward (see FIG. 9B, etc.), the three primary transfer rollers 422 (Y, M, C) rise and each nip position changes.

Thus, the above cam 402-1 is responsible for moving the movable side plate 430, and corresponds to the "first cam" of the present invention, and is therefore referred to as the first cam 402-1 below.

Of the above, the innermost cam 402-2 faces the push-up member 403 attached to the movable side plate 430, and serves to push the pressure release portion 450 upward via the push-up member 403 (see Figure 9C).

The above cam 402-2 is responsible for moving the pressure release portion 450, and corresponds to the "second cam" of the present invention, and is therefore referred to as the second cam 402-2 below.

The push-up member 403 has an axis 403a, which serves as the center of rotation, provided on the movable side plate 430, and the tip side of the push-up member 403 faces the lower end surface of the pressure release portion 450 described above.

In this embodiment, when the tip side of the push-up member 403 and the pressure release portion 450 are pushed upward by the main body portion of the second cam 402-2 (see FIG. 8), the pressing portion 450b of each of the pressure release portions 450 abuts against the outer bearing 444, and then moves the outer bearing 444 in a direction against the pressing force of the coil spring 442 (to the right in FIG. 8).

By this action, the shaft pressing portion 445 of the outer bearing 444 moves away (retracts) from the tip side of the shaft of the corresponding primary transfer roller 422, thereby preventing the pressure of the coil spring 442 (second pressing member) from being transmitted to the shaft of the primary transfer roller 422.

As a result, the only member pressing the primary transfer roller 422 is the coil spring 441 (first pressing member), and the nip pressure (contact pressure) of the primary transfer nip is reduced. Thus, the above-described series of operations completes the change (switching) to a nip pressure (contact pressure) suitable for transferring the toner image to the textured paper.

If it becomes necessary to fine-tune the contact pressure or contact position of the primary transfer nip during maintenance, you can perform the following procedure, for example.

When fine-tuning the contact pressure of the primary transfer nip, the second cam 402-2 currently in use is replaced with one having a different radius or cam shape. In general, when the radius of the second cam 402-2 is reduced, the amount of upward pressure from the tip side of the push-up member 403 and the pressure release section 450 decreases. In this case, in the mode for printing on textured paper (see Figure 9C), the nip pressure (contact pressure) of the primary transfer nip can be made slightly higher than before by leaving a small amount of pressure from the spring 442 (second pressure member).

On the other hand, in contrast to the above, if the second cam 402-2 is changed (replaced) with a cam having a larger radius, the pressing force of the spring 442 (second pressing member) and therefore the nip pressure (contact pressure) of the primary transfer nip can be further reduced in the mode for printing on textured paper (see FIG. 9C).

Therefore, for example, if the nip pressure of the temporary transfer nip in the mode for printing on textured paper (see Figure 9C) is slightly insufficient or slightly excessive overall due to durability, it is possible to fine-tune only the nip pressure without changing the nip position.

Furthermore, by changing (replacing) the second cam 402-2 with a different shape, it is possible to modify or fine-tune the timing (angle) at which the change (switch) to the nip pressure (contact pressure) suitable for transferring the toner image to the textured paper is completed.

On the other hand, when fine-tuning the contact position of the primary transfer nip, the first cam 402-1 currently in use is replaced with one having a different radius. In general, if the radius of the first cam 402-1 is made smaller, the amount of lift of the movable side plate 430 becomes smaller, and conversely, if it is made larger, the amount of lift becomes larger.

Therefore, for example, if the position where the temporary transfer nip is formed in the mode for printing on textured paper (see Figure 9C) has shifted slightly above or below the reference position (see Figure 4C) due to durability, it is possible to fine-tune only the nip position without changing the nip pressure.

In addition, by changing (replacing) the first cam 402-1 with one having a different shape, it is possible to modify or fine-tune the timing (angle) at which the change (switching) to the nip position suitable for transferring the toner image to the textured paper is completed.

In this manner, in this embodiment, the mechanism for changing the nip position of the primary transfer nip (contact position changing unit) and the mechanism for changing the nip pressure (contact pressure) of the primary transfer nip (contact pressure changing unit) are configured as independent mechanisms. With this configuration, this embodiment makes it possible to adjust the nip position and nip pressure of the primary transfer nip separately, and both adjustment operations can be easily performed.

In other words, in this embodiment, the movable side plate 430 is provided so as to be movable relative to the fixed side plate 400, and the pressure release member 450 is provided on the movable side plate 430, and the pressure release member 450 is configured so as to be movable relative to the movable side plate 430.

With this configuration, by adjusting the amount of movement (relative movement) of the pressure release member 450 with respect to the movable side plate 430 when the movable side plate 430 moves with respect to the fixed side plate 400, the biasing force of the second pressure spring 422 can be adjusted separately regardless of the movement mode of the movable side plate 430 (the movement mode of the primary transfer roller 422).

Next, referring to Figures 10A and 10B, we will explain the mechanism for adjusting the nip pressure of the primary transfer roller 422 for black (K).

Figures 10A and 10B are perspective and side views of the pressure spring release member 451, a portion of which (only the upper portion) is shown in Figures 9A to 9C (see also Figure 5 as appropriate). Hereinafter, the pressure spring release member 451 will be referred to as the "pressure spring release member 451 for black" to distinguish it from the pressure spring release mechanism for YMC described above.

In the example shown in FIG. 10A, the black pressure spring release member 451 has a substantially circular bearing 451c provided in the center of the member, and the shaft 460 is inserted into the bearing 451c, so that the member is rotatably supported.

The black pressure spring release member 451 also has a pressure section 452 at the tip of the member that extends downward from the bearing 451c for pressing the bearing.

As shown in Figures 10A and 10B, this pressing portion 452 includes a first spring pressing release portion 452-1 that faces the pressing surface 443b (see Figure 7) of the inner bearing 443, and a second spring pressing release portion 452-2 that faces the outer surface of the outer bearing 444.

The state (position) of the black pressure spring release member 451 shown in Figures 10A and 10B corresponds to the print mode for normal paper described above in Figures 4A and 9B. The black pressure spring release member 451 is similarly arranged on the fixed side plate 400 on the opposite side (see Figure 5 as appropriate).

Thus, when transitioning from the printing mode for normal paper shown in Figures 10A and 9B to the printing mode for textured paper, the motor 80 is driven under the control of the control unit 100, causing the above-mentioned cam shaft 401 and the three cams 402 (402-1 to 3) to rotate integrally in the counterclockwise direction in the figure by a predetermined angle.

As a result of this cam action, as shown in FIG. 9C, the first cam 402-1 pushes up the movable side plate 430 to change (raise) the nip position, while the second cam 402-2 raises the pressure release portion 450 by pushing up the push-up member 403, thereby reducing the nip pressure. This completes the transition (switching) to the printing mode for textured paper for the primary transfer rollers 422 for the YMC colors.

In addition, due to the above cam action, as shown in FIG. 9C, the third cam 402-3 presses and moves the upper part of the black pressure spring release member 451 to the left in FIG. 9C.

At this time, the black pressure spring release member 451 rotates counterclockwise around the shaft 460 shown in FIG. 10A, and the lower pressure part 452 moves to the right in FIG. 10A and FIG. 10B, thereby performing the following operation.

That is, the black pressure spring release member 451 reduces the nip pressure (contact pressure) between the image carrier and the black (K) primary transfer roller 422 by pressing the outer bearing 444 (second pressure spring regulating member) with the second spring pressure release portion 452-2 of the pressing portion 452.

Thus, the transition (switching) to the printing mode for textured paper for the primary transfer roller 422 for monochrome print images (K, i.e. black) is completed.

In general, in the printing mode for textured paper, the intermediate transfer unit 42 in this embodiment can print toner images in both YMCK (color images) or K (monochrome images), as well as full color using these five colors.

In addition, in this embodiment, for example, during maintenance or when the device is turned off, the motor 80 is driven under the control of the control unit 100, causing the above-mentioned camshaft 401 and the three cams 402 (402-1 to 3) to rotate to the state (rotation angle) shown in Figure 9A.

At this time, the black pressure spring release member 451 presses the outer bearing 444 (second pressure spring regulating member) with the second spring pressure release portion 452-2 of the pressing portion 452, thereby reducing the nip pressure (contact pressure) between the image carrier and the black (K) primary transfer roller 422.

The black pressure spring release member 451 also presses the pressure surface 443b (see FIG. 7) with the first spring pressure release portion 452-1 of the pressure portion 452, forcibly moving the inner bearing 443 and thus the black (K) primary transfer roller 422, thereby releasing the nip with the image carrier.

The sequence of changes in each of the cams 402-1 to 402-3 and the primary transfer nip that accompany the rotation of the cam shaft 401 will be described below with reference to the cam curve diagram in Figure 11 and Figures 9A to 9C.

Here, FIG. 11 is a diagram showing a specific example of the pressing state according to the rotation angle of the three cams 402-1 to 402-3 arranged side by side on the above-mentioned cam shaft 401.

In FIG. 11, the vertical axis indicates the radius of the cam, and the higher up on the vertical axis, the greater the cam radius and therefore the amount of movement of the opposing member.

On the other hand, in Figure 11, the horizontal axis indicates the rotation angle of the camshaft 401, which indicates the rotation angle from the state shown in Figure 9A (0° position) until the camshaft 401 rotates 360° counterclockwise in Figures 9 (A to C).

Thus, the state of each of the cams 402-1 to 402-3 shown in FIG. 9A corresponds to the range of rotation angles of the dotted rectangle indicated by "(1) HP" in FIG. 11.

At this rotation angle of the camshaft 401 (around 0°), the inner second cam 402-2 and the outer first cam 402-1 do not press against the opposing members (i.e., the push-up member 403 and the movable side plate 430).

As a result, the primary transfer roller 422 for YMC held by the movable side plate 430 descends from the state shown in FIG. 9A according to the shape of the groove portion 430a under its own weight, and becomes separated from the intermediate transfer belt 421 (see FIG. 4B and the cam radii at a cam angle of 0° in FIG. 11 for the second cam 402-2 and the first cam 402-1 as appropriate).

On the other hand, the third cam 402-3 shown in FIG. 9A has the maximum cam radius and presses the opposing member (the portion above the black pressure spring release member 451) with the greatest force.

Therefore, the black pressure spring release member 451 presses the outer bearing 444 with the second spring pressure release portion 452-2, and presses the pressure surface 443b (see FIG. 7) with the first spring pressure release portion 452-1, forcibly moving the inner bearing 443. As a result, the black (K) primary transfer roller 422 is also separated from the intermediate transfer belt 421.

Next, under the control of the control unit 100, the motor 80 is driven, causing the above-mentioned camshaft 401 and the three cams 402 (402-1 to 3) to rotate slightly counterclockwise from the state (rotation angle) shown in Figure 9A, and the cam radii of all the cams (402-1 to 3) become minimum (see the radii of each cam in the "(2) Monochrome" area in Figure 11 as appropriate).

As a result, while the primary transfer roller 422 for YMC remains separated from the intermediate transfer belt 421, the pressure of the black pressure spring release member 451 is released, and the above-mentioned pressure portion 452 of the black pressure spring release member 451 is no longer pressing against either the outer bearing 444 or the inner bearing 443.

Therefore, in monochrome (K only) mode, the primary transfer roller 422 for black (K) contacts the image carrier with a contact force (pressing force) for normal paper. In other words, the primary transfer nip of the primary transfer roller 422 for black (K) is set to a nip pressure for printing a black image on paper S other than textured paper.

Thus, in this example, monochrome printing of black images only can be performed stably in the cam angle range of 50° to 70° (reference angle: 60°) in the "(2) Monochrome" area in Figure 11.

Next, under the control of the control unit 100, the motor 80 is driven, causing the cam shaft 401 and the three cams 402 (402-1 to 402-3) to rotate counterclockwise from the "(2) Monochrome" cam angle (approximately 60°) in FIG. 11 to the "(3) Color" cam angle (reference angle: 165°).

When transitioning to the above cam angle, as shown in Figures 9B and 11, the bottom of the movable side plate 430 is pushed up by the first cam 402-1, causing the primary transfer roller 422 for the colors (Y, M, C) to move according to the shape of the groove 430a described above and come into contact with the image carrier to form a primary transfer nip.

That is, the movable side plate 430 rises in the upper left direction in FIG. 9B according to the shape defined by the groove portion 430a. As a result, the position of the primary transfer nip portion N1 of the primary transfer roller 422 for the colors (YMC) held by the movable side plate 430 is set to the normal position shown in FIG. 4A.

In this example, the second cam 402-2 pushes up the corresponding push-up member 403 when the cam angle in FIG. 11 becomes equal to or greater than approximately 190°, so no action to reduce the nip pressure occurs until that point.

Therefore, at the cam angle "(3) Color" in FIG. 11 (reference angle: 165°), the primary transfer nip of the primary transfer rollers 422 for the colors (YMC) and black (K) is set to a nip pressure for printing a black image on paper S other than textured paper.

Furthermore, when the motor 80 is driven to rotate under the control of the control unit 100, causing the camshaft 401 to rotate counterclockwise from the state shown in FIG. 9B, the second inner cam 402-2 pushes up the tip side of the opposing push-up member 403, thereby raising the pressure release portion 450, as shown in FIG. 9C.

As a result, the primary transfer nip of the primary transfer roller 422 for the colors (YMC) is set to a weak nip pressure for printing a color (YMC) image on paper S that is textured paper such as embossed paper, as shown in FIG. 4C (see the cam angle area of around 250° for "(4) Emboss" in FIG. 11 as appropriate).

At this time, the outer first cam 402-1 also pushes the opposing movable side plate 430 further upward than the position described above in FIG. 9B.

As a result, the nip position (contact position) of the primary transfer nip portion N1 of the primary transfer roller 422 for the colors (YMC) is set to an elevated position for printing a color (YMC) image on the paper S, which is textured paper such as embossed paper, as shown in FIG. 4C.

The third cam 402-3 also presses the opposing member (the portion above the black pressure spring release member 451) (see the cam angle in the "(4) Emboss" area shown in Figure 11 as appropriate).

As a result, the primary transfer nip of the primary transfer roller 422 for black (K) is set to a weak nip pressure for printing color (YMC) images on textured paper S such as embossed paper, as shown in FIG. 4C (see the cam angle in the "(4) Embossed" area in FIG. 11 as appropriate).

As described above, in this embodiment, when the type of paper S to be printed is other than textured paper, the configuration is such that only the movable side plate 430 moves without pushing up the pressure release portion 450. On the other hand, when the type of paper S to be printed is textured paper, the movable side plate 430, the pressure release portion 450, and the member that presses the primary transfer roller 422 (K) for black (K) images (such as the black pressure spring release member 451) move, thereby changing the contact position and contact pressure of the primary transfer roller 422 (YMC) that transfers the color image, and changing the contact pressure of the primary transfer roller 422 (K) for black (K) images.

This configuration ensures the durability of the image carriers (intermediate transfer belt 421 and multiple primary transfer rollers 422), while allowing for image formation on textured paper in monochrome, color, and even full color YMCK, and allows for good image transfer.

Also, as shown in FIG. 11, in this embodiment, when the type of paper S to be printed is textured paper, the first cam 402-1 moves the movable side plate 430 to complete the change in the contact position of the primary transfer nip (cam angle: approximately 200°), the second cam 402-2 moves the pressure release section 450 to complete the change in the contact pressure of the primary transfer nip (cam angle: approximately 210°), and then the third cam 402-3 completes the change in the contact pressure of the primary transfer nip of the black (K) primary transfer roller 422 (K) (cam angle: approximately 240°).

As described above, this embodiment has the following advantages: The rotation angle at which the change in the contact position or contact pressure of the primary transfer nip is completed is staggered, in other words, the timing at which the contact position or contact pressure is changed is staggered.

In other words, in this embodiment, by shifting the timing at which the radius of each of the cams 402-1 to 402-3 is maximized, in other words the rotation angle at which the mechanical load is maximized, it is possible to distribute or equalize the load when driving and rotating the camshaft 401 provided with multiple cams (in this example, the first cam 402-1 to the third cam 402-3).

As described above in detail, the intermediate transfer unit 42 in the image forming apparatus 1 of this embodiment includes a contact position changer that changes the contact position (nip position) between the intermediate transfer belt 421 and the photosensitive drum 413 and the primary transfer roller 422 in the rotation direction of the intermediate transfer belt 421 etc. (image carrier) depending on the type of paper S (recording medium) on which an image is formed, and a contact pressure changer that changes the primary transfer nip pressure (contact pressure) by changing the pressure of the pressing member (springs 441, 442) that presses the photosensitive drum 413 etc. regardless of the contact position.

The intermediate transfer unit 42 of this embodiment, which has such a configuration, can independently change the position of the primary transfer nip portion N1 via the intermediate transfer belt 421 and change the nip pressure (contact pressure) of the primary transfer nip portion N1 depending on the type of paper S to be printed.

More specifically, in this embodiment, under the control of the control unit 100, the cam shaft 401 is rotated, and the movable side plate 430, which holds the shafts of the multiple primary transfer rollers 422, moves (rises) from its normal position relative to the fixed side plate 400, which rotatably supports the intermediate transfer belt 421, by the action of the cam 402-1 (first cam), changing the nip position (see the cam angle range of 100° to 250° in Figures 4A, 4C, 9C, and 11).

In addition, when the nip position is changed, the pressure release section 450 moves (rises) due to the action of cam 402-2 (second cam) provided on the same camshaft 401, and the nip pressure (contact pressure) is weakened by reducing the number of pressing members pressing the shaft of the primary transfer roller 422 (leaving only the coil spring 401) (see the same figure).

With this configuration, even when forming an image on textured paper, which generally has poor transferability, it is possible to maintain good transferability of the image onto the textured paper. Therefore, according to this embodiment, regardless of the type of paper S, it is possible to maintain good transferability, i.e., good primary transferability onto the intermediate transfer belt 421 and therefore good secondary transferability onto the paper S.

In addition, according to this embodiment, the change in the contact position of the primary transfer roller 422 with respect to the photosensitive drum 413 and the change in the pressing force (contact pressure) of the primary transfer roller 422 with respect to the photosensitive drum 413 are performed by moving different parts (such as rotating a cam), so that the fine adjustment of the contact position and the fine adjustment of the pressing force can be performed separately and easily.

Furthermore, according to the present embodiment having the above configuration, it is possible to reduce the space required for the mechanism for switching the contact position and the pressing force (contact pressure), thereby enabling the transfer device (intermediate transfer unit 42) and ultimately the main body of the image forming device 1 to be made smaller.

The above-mentioned embodiments and modifications are merely examples of the realization of the present invention, and the technical scope of the present invention should not be interpreted in a limiting manner based on them. In other words, the present invention can be implemented in various forms without departing from its gist or main characteristics.

REFERENCE SIGNS LIST 1 Image forming apparatus 10 Image reading section 20 Operation display section 30 Image processing section 40 Image forming section 42 Intermediate transfer unit (transfer device)
50 Paper transport section 51 Paper feed section 52 Paper discharge section 53 Transport path section 60 Fixing section 80 Motor (driving source, contact position changing section)
100 Control unit (transfer device, contact position changing unit)
413 Photoconductor drum (image carrier)
400 Fixed side plate 400a Fixed shaft (contact position change part)
400b Fixed shaft 401 Cam shaft 401a Lid member 402 (402-1, 402-2, 402-3) Cam 402-1 First cam 402-2 Second cam 402-3 Third cam 403 Push-up member (contact pressure change section)
403a Fixed shaft 421 Intermediate transfer belt (image carrier)
422 Primary transfer roller (transfer roller)
430 Movable side plate (contact position change part)
430a Groove portion 430-1 Guide member (contact position change portion)
440: Contact pressure change portion 440A: Base material 441: Coil spring (first pressing member)
442 Coil spring (second pressing member)
443 Inner bearing (first restricting member)
443a Groove portion 443b Pressing surface 444 Outer bearing (second restricting member)
444a Groove portion 444b Locking portion (first restricting member)
445 Shaft pressing portion 450 Pressing release member 450a Guide groove 450b Pressing portion 451 Black pressing spring release member 451a Upper end portion 451c Bearing 452 Pressing portion 452-1 First spring pressing release portion 452-2 Second spring pressing release portion 460 Shaft N1 Primary transfer nip portion S Paper (recording medium)

Claims (16)

a contact position changing unit that changes a contact position between the image carrier and the transfer roller in a rotation direction of the image carrier according to a type of recording medium on which an image is formed;
a contact pressure changing unit that is operable independently of the contact position changing unit and changes a contact pressure between the image carrier and the transfer roller by changing a pressing force of a pressing member that presses the image carrier;
Equipped with
The pressing member includes a first pressing member and a second pressing member,
the contact pressure changing unit, when the type of the recording medium is textured paper, presses the image carrier with the first pressing member, and when the type of the recording medium is other than textured paper, presses the image carrier with the first pressing member and the second pressing member, holds a shaft of the transfer roller, and includes movable side plates facing both sides in the axial direction of the image carrier;
The movable side plate includes a pressure release portion that releases the pressure of the second pressing member .
Transcription device. the contact position changing unit changes the position of the transfer roller by moving the movable side plate in accordance with a rotation angle of a cam.
The transfer device according to claim 1 . the contact position changing unit moves the movable side plate away from the image carrier in response to the movement of the movable side plate.
The transfer device according to claim 2 . The movable side plate and the pressure release portion move independently of each other.
The transfer device according to claim 1 . the movable side plate holds a shaft of the transfer roller that transfers an image of a color other than a black image;
the contact position changing unit separates the movable side plate from the image carrier during monochrome printing.
The transfer device according to claim 1 . When the type of the recording medium is textured paper, the contact pressure changing unit changes the contact pressure of the transfer rollers other than the transfer roller that transfers the black image by moving the pressure releasing unit to release the pressure of the second pressing member.
The transfer device according to claim 1 . The movable side plate and the pressure release portion are moved by the same driving source.
The transfer device according to claim 1 . a first cam that moves the movable side plate, and a second cam that is provided on the same axis as the first cam and moves the pressure release portion,
the movable side plate and the pressure release portion move independently of each other in accordance with the rotation angles of the first cam and the second cam.
The transfer device according to claim 1 . When the type of the recording medium is textured paper, the contact pressure of the transfer roller that transfers the black image is made smaller than when the type of the recording medium is other than textured paper.
The transfer device according to claim 6 . a third cam for changing the pressing force of a member that presses the transfer roller for transferring a black image in accordance with a rotation angle;
The transfer device according to claim 8 . The third cam is provided on the same axis as the first cam and the second cam.
The transfer device according to claim 10 . When the type of the recording medium is other than textured paper, the movable side plate moves without the pressure release portion moving,
when the type of the recording medium is textured paper, the movable side plate, the pressure release portion, and a member that presses the transfer roller that transfers the black image are moved to change the contact position and the contact pressure of the transfer roller that transfers an image of a color other than the black image, and to change the contact pressure of the transfer roller that transfers the black image.
The transfer device according to claim 11 . When the type of the recording medium is textured paper, the first cam moves the movable side plate to complete the change of the contact position, and then the second cam moves the pressure release portion to complete the change of the contact pressure, and then the third cam changes the contact pressure of the transfer roller that transfers the black image.
The transfer device according to claim 12 . the contact pressure changing unit prevents the pressing force of the second pressing member from being transmitted to the transfer roller by pressing a second regulating member that regulates the second pressing member from coming off.
The transfer device according to claim 1 . the contact pressure changing unit further presses a first regulating member that regulates the first pressing member from coming off, thereby preventing the pressing force of the first pressing member from being transmitted to the transfer roller.
The transfer device according to claim 14 . An image forming apparatus comprising the transfer device according to claim 1 .

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