JP7622501B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming device, and is suitable for use in, for example, electrophotographic printers.

In recent years, there have been image forming devices that use, for example, an image forming unit to generate a toner image (also called a developer image) based on image data using toner (also called a developer), transfer it to paper (also called a medium), and then fix the image by applying heat and pressure to the paper using a fixing unit.

In this image forming unit, a toner image is formed on the peripheral surface of a cylindrical rotating image drum (also called an image carrier), and the toner image is transferred from the photosensitive drum to the paper. This image drum gradually wears down due to friction with the various rollers in the image forming unit and with the paper, so it is replaced every time a replacement condition is met, such as when 30,000 sheets have been printed.

In addition, in an image forming device that supports color printing, image forming units of four colors, for example black, cyan, magenta, and yellow, are arranged along the paper transport path, and a color image can be printed on paper by sequentially transferring and fixing toner images of each color onto the paper.

However, even if an image forming device is capable of such color printing, there are cases where monochrome printing is performed using only black toner, such as when printing a document that consists only of text. In such cases, if the image forming device rotates the image drums for colors other than black (hereinafter referred to as each color) even though a toner image is not being formed, there is a risk of wasting the image drums.

As a result, an image forming device has been proposed that is provided with a mechanism for abutting or separating the image forming units for each color from the paper transport path, and by separating the image forming units for each color from the transport path during monochrome printing and abutting them against the transport path during color printing, unnecessary wear and tear is reduced (see, for example, Patent Document 1).

JP 2020-52298 A (FIGS. 8 to 16, etc.)

However, in an image forming device with this configuration, when the image forming unit is brought into contact with the paper transport path, it is not possible to apply a sufficient force to the image forming unit, and it may not reach the appropriate position. In such cases, the image forming device has a problem in that the quality of the image printed on the paper may deteriorate.

The present invention was made in consideration of the above points, and aims to propose an image forming device that can improve the quality of printed images.

In order to solve the above problem, the image forming apparatus of the present invention includes a device housing having an internal space, an image forming unit provided inside the device housing and forming a developer image on a rotating image carrier by developer, a transport unit that contacts the image carrier and transports the medium in a transport direction, a contact/detachment unit that changes the position of the image forming unit relative to the device housing between a separate position where the image carrier is separated from the medium and a close position where the image carrier is closer to the medium than the separate position, a contact/detachment drive unit that drives the image forming unit to the separate position or the close position, and a contact/detachment drive unit that drives the image forming unit relative to the device housing. A displacement regulating section regulates the image forming section to a transfer position where the developer image is transferred from the image carrier to the medium when the image forming section is displaced in the transport direction, and a control section controls the operation of the image forming section, the transport section and the separation drive section. When the image forming section is displaced to the close position by the separation drive section, the control section starts the transport operation by the transport section, and after a predetermined time has elapsed, starts the rotation operation of the image carrier by the image forming section, and performs a speed difference formation process to make the image carrier speed, which is the linear speed of the image carrier, smaller than the medium speed, which is the linear speed of the medium by the transport section.
The image forming apparatus of the present invention includes a device housing having an internal space, an image forming unit provided inside the device housing and forming a developer image on a rotating image carrier by developer, a transport unit that contacts the image carrier and transports the medium in a transport direction, a contact and separation unit that changes the position of the image forming unit relative to the device housing between a separated position where the image carrier is separated from the medium and a close position where the image carrier is closer to the medium than the separated position, a contact and separation drive unit that drives the image forming unit to the separated position or the close position, and a contact and separation drive unit that changes the position of the image forming unit in the transport direction relative to the device housing. The control unit is provided with a displacement regulating unit which regulates the image carrier to a transfer position where the developer image is transferred from the image carrier to the medium when the image carrier is positioned close to the medium, and a control unit which controls the operations of the image forming unit, the conveying unit and the separation drive unit, and when the image forming unit is displaced to the close position by the separation drive unit, the control unit performs a speed difference forming process to make the image carrier speed, which is the linear speed of the image carrier, smaller than the medium speed, which is the linear speed of the medium by the conveying unit, and then stops the conveying operation by the conveying unit and the rotation operation of the image carrier by the image forming unit, and then performs a printing process to form the developer image on the medium.

In the present invention, when the image forming unit is displaced to a close position by the separation drive unit and then a speed difference forming process is performed, the medium speed is faster than the image carrier speed, so that the image carrier can be urged in the transport direction by the transport unit, and the displacement regulating unit regulates the range of displacement of the image forming unit to reach the transfer position, and the developer image can be transferred to an appropriate position on the medium. At this time, if the rise in the rotation speed of the image carrier in the image forming unit is faster than the rise in the transport speed in the transport unit, and the image carrier speed temporarily becomes higher than the medium speed, there is a risk of the image carrier being displaced in a direction away from the transfer position. However, in the present invention, the rotation operation of the image carrier is started only after the medium speed has sufficiently increased when the speed difference forming process is started, so that the occurrence of such a phenomenon can be prevented in advance.

The present invention makes it possible to realize an image forming device that can improve the quality of printed images.

FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus. FIG. 2 is a schematic diagram illustrating a configuration of an image drum unit. FIG. 2 is a schematic perspective view showing an internal configuration of the image forming apparatus. FIG. 2 is a schematic perspective view showing a configuration of a contact and separation unit. FIG. 4 is a schematic diagram showing a configuration of a contact and separation guide. 5A and 5B are schematic diagrams illustrating a separate state and a close state of the color image drum unit. 3 is a schematic diagram showing a configuration of a drum coupling portion. FIG. FIG. 2 is a schematic perspective view showing a configuration of a coupling slide. FIG. 2 is a schematic block diagram illustrating a circuit configuration of the image forming apparatus. FIG. 4 is a schematic diagram illustrating a configuration of page information. 10 is a flowchart showing a PU print processing procedure according to the first embodiment. 5 is a flowchart showing an image drum up-down process procedure according to the first embodiment. 10 is a flowchart showing a procedure of an image drum stabilization process. 4 is a schematic diagram showing the speeds of an image drum and a conveyor belt. 10 is a flowchart showing a power-on process according to a second embodiment; 13 is a flowchart showing an initial processing procedure according to the second embodiment; 13 is a flowchart showing a PU print processing procedure according to the second embodiment. 10 is a flowchart showing an image drum up-down process procedure according to the second embodiment.

Below, the form for implementing the invention (hereinafter referred to as embodiment) will be explained with reference to the drawings.

1. First embodiment
[1-1. Configuration of Image Forming Apparatus]
1, the image forming apparatus 1 according to the first embodiment is an electrophotographic printer that can form (i.e., print) a monochrome or color image on a medium, such as paper P. Incidentally, the image forming apparatus 1 does not have an image scanner function for reading an original document or a communication function using a telephone line, and is a single-function SFP (Single Function Printer) that has only a printer function.

The image forming device 1 has an internal space 2S formed inside the device housing 2, which is formed in a roughly box shape, and various parts are arranged in the internal space 2S. The device housing 2 also has an upper cover 2C that forms the upper part and is formed so that it can be opened and closed. When the upper cover 2C is opened, the internal space 2S is connected to the external space, allowing the user to easily replace each part and perform various maintenance work. The device housing 2 also has an upper cover sensor 2CS that detects whether the upper cover 2C is opened or closed. Incidentally, in the following description, the left end part in FIG. 1 is the front of the image forming device 1, and the up-down direction, left-right direction, and front-rear direction are defined when viewed from the front.

The image forming device 1 is controlled as a whole by a control unit 3. This control unit 3 is connected wirelessly or by wire to a host device (not shown) such as a computer device. When the control unit 3 is given image data representing an image to be printed from the host device and is instructed to print the image data, it executes a printing process to form a print image on the surface of paper P.

A touch panel 4 is provided near the front of the top surface of the device housing 2. The touch panel 4 is, for example, a combination of a liquid crystal panel and a touch sensor, and displays various information under the control of the control unit 3, and also accepts operational inputs from the user and notifies the control unit 3. In addition, a temperature and humidity sensor 5 is provided near the outside of the device housing 2. This temperature and humidity sensor 5 detects the surrounding temperature and humidity and notifies the control unit 3.

A paper feed tray 6 that stores paper P is provided at the bottom inside the device housing 2. A paper feed section 7 is provided above and in front of the paper feed tray 6. The paper feed section 7 has a paper feed roller 8, a transport roller 9, a paper feed sensor 10, a registration roller 11, etc., arranged in sequence along a transport path U, and also has a transport guide (not shown) and the like arranged along the transport path U.

The paper feed roller 8, the transport roller 9, and the registration roller 11 are all cylindrical with their central axes aligned in the left-right direction, and rotate appropriately when driven by a paper feed motor (not shown). However, the supply of drive force to the paper feed roller 8 and the registration roller 11 is controlled by a paper feed roller clutch and a registration roller clutch (described below). The paper feed sensor 10 is a so-called optical sensor, and is positioned so that the detection light traveling from the light-emitting unit to the light-receiving unit intersects with the transport path U, and supplies the detection results from the light-receiving unit to the control unit 3.

When the paper feed unit 7 receives driving force from the paper feed motor, it rotates the paper feed roller 8 appropriately to separate and send out one of the multiple sheets of paper P stored in the paper feed tray 6. Next, the paper feed unit 7 sends the paper P upwards using the transport roller 9, and causes it to proceed along the transport path U. When the paper feed unit 7 detects the paper P using the paper feed sensor 10, it also rotates the registration roller 11 appropriately in response, corrects any skew in the paper P, and sends it out backwards.

A writing sensor 12 is provided at the rear of the paper feed unit 7 along the transport path U to detect the transport state and size of the paper P. The writing sensor 12 is an optical sensor similar to the paper feed sensor 10, and supplies the detection results to the control unit 3.

Behind the writing sensor 12, the transport path U is inclined so that it slopes slightly upward toward the rear when viewed from the left and right, and the intermediate transport section 13 is located below it. The inclination angle of this transport path U with respect to the horizontal direction is approximately 10°. The intermediate transport section 13 is configured such that a transport belt 15 made of a circular belt is stretched around a front roller 14F located at the front side and a rear roller 14R located at the rear side.

When the driving force is transmitted from the belt motor (described later) to the rear roller 14R, the intermediate conveying unit 13 rotates the rear roller 14R in the direction of the arrow R1, and causes the conveying belt 15 to move accordingly. At this time, the conveying belt 15 moves along a circular path that goes around the front roller 14F and the rear roller 14R, and causes the upper part along the conveying path U, i.e., the part stretched between the front roller 14F and the rear roller 14R, to move in a rear-upward direction. Hereinafter, this direction is also referred to as the conveying direction U1. At this time, when the paper P is delivered from the paper feed unit 7, the intermediate conveying unit 13 applies a force toward the conveying direction U1 to the paper P with the paper P placed on the upper side of the conveying belt 15, and causes the paper P to move in a rear-upward direction, i.e., in the conveying direction U1, as the conveying belt 15 moves.

Above the intermediate conveying section 13, on the opposite side of the conveying path U, four image drum (ID) units 16K, 16C, 16M, and 16Y are arranged in order from the front to the rear. The ID units 16K, 16C, 16M, and 16Y (hereinafter collectively referred to as image drum (ID) units 16) correspond to the colors black (K), cyan (C), magenta (M), and yellow (Y), respectively, but only the colors differ and all are configured the same.

As shown in the schematic cross-sectional view of FIG. 2A, the ID unit 16 as an image forming section is configured such that a toner storage section 21, a supply roller 22, a developing roller 23, a developing blade 24, a charging roller 25, and an image drum 26 (hereinafter also referred to as ID 26) are provided inside an image drum (ID) housing 20. In addition, a transfer roller 27 is provided below the ID 26, i.e., on the opposite side of the conveyor belt 15.

The ID housing 20 is generally formed as a rectangular parallelepiped that is long in the left-right direction, and although most of the outer periphery is covered, a part of the upper side and a part of the lower side are open. The toner storage section 21, which serves as a developer storage section, forms a space inside for storing toner, and stores the toner as developer in this space. A toner remaining amount sensor 21S is provided inside the toner storage section 21. The toner remaining amount sensor 21S, which serves as a remaining amount detection section, detects whether the remaining amount of toner stored in the toner storage section 21 falls below a predetermined reference value and notifies the control section 3.

The supply roller 22, the developing roller 23, the charging roller 25 and the ID 26, and the transfer roller 27 are all cylindrical with their central axes aligned in the left-right direction, and are supported so as to be rotatable about the central axes. The developing blade 24 is a thin plate that is long in the left-right direction, and the rear lower end portion is in contact with the peripheral side of the developing roller 23. The ID 26, which serves as an image carrier, is designed to be charged by a charging layer provided on the outer periphery. Furthermore, a predetermined voltage is applied to the developing roller 23, the developing blade 24, the charging roller 25, and the transfer roller 27.

An LED (Light Emitting Diode) head 28 is provided above the ID 26. The LED head 28 has many light-emitting elements made of LEDs arranged in the left-right direction, which is the main scanning direction, and each light-emitting element is made to emit light appropriately under the control of the control unit 3. Incidentally, a space is formed near the rear of the upper side of the ID housing 20 to position the LED head 28 directly above the ID 26.

As shown in the schematic right side view of FIG. 2B, the ID housing 20 exposes a developing roller connecting portion 24J and an image drum (ID) connecting portion 26J on its right side for receiving a driving force from the device housing 2. A generally flat lower flat portion 20B is formed in the center of the lower surface near the right end of the ID housing 20, and a lower inclined portion 20S is formed on the front side of the lower flat portion 20B. The lower inclined portion 20S is inclined so as to rise as it advances toward the rear with respect to the lower flat portion 20B. Incidentally, the lower flat portion 20B and the lower inclined portion 20S are formed near the left end of the ID housing 20 (not shown) in a generally symmetrical manner with the lower flat portion 20B and the lower inclined portion 20S, respectively. Furthermore, a cylindrical positioning protrusion 29 is provided on the front side of the lower flat portion 20B of the ID housing 20.

The ID unit 16 is also configured to be detachable from the device housing 2. Specifically, when the top cover 2C of the device housing 2 is opened and the internal space 2S is connected to the external space, the ID unit 16 can be taken out of the internal space 2S by the user, and can be inserted into the internal space 2S from the outside and attached. At this time, the ID unit 16 is positioned at a predetermined location in the internal space 2S using a positioning protrusion 29 (described in detail later). When the top cover 2C is closed, the ID unit 16 is urged generally downward by an image drum (ID) unit spring 2G provided on the underside of the top cover 2C, thereby causing the vicinity of the lower end of the ID 26 to abut against the conveyor belt 15.

This ID unit 16 (Fig. 2(A)) rotates each roller appropriately by receiving driving force from an image drum motor described later. This causes the supply roller 22 to supply toner in the toner storage section 21 to the development roller 23. The development roller 23 adheres the toner supplied from the supply roller 22 to its peripheral side. The development blade 24 scrapes off unnecessary toner from the surface of the development roller 23, forming a toner layer of a predetermined thickness on the surface of the development roller 23. The charging roller 25 also uniformly charges the surface of the image drum 26.

The LED head 28 emits light in a light emission pattern based on image data supplied from the control unit 3 (Figure 1), sequentially exposing the peripheral side of the ID 26. This causes the ID 26 to form an electrostatic latent image on the peripheral side in response to the irradiated light. The ID unit 16 then forms a toner image (hereinafter also referred to as a developer image) in response to the electrostatic latent image by adhering toner (developer) to the peripheral side of the ID 26, and the rotation of the ID 26 causes the part on which the toner image is formed to reach the vicinity of the bottom end.

When paper P is being transported along the transport path U by the transport belt 15, the ID unit 16 (Fig. 1) pinches the transport belt 15 and the paper P between the ID 26 and the transfer roller 27, and transfers the toner image from the peripheral side of the ID 26 to the paper P. In this way, each ID unit 16 transfers and overlaps toner images of each color onto the paper P being transported from the front along the transport path U, while moving the paper diagonally upward and rearward.

The fixing unit 17 is provided near the rear end of the intermediate transport unit 13. Fixing rollers 17A and 17B are rotatably provided in the fixing unit 17 on the upper and lower sides of the transport path U. Fixing roller 17A also has a fixing heater 17H built in. When a driving force is supplied from a fixing motor described later, fixing unit 17 rotates fixing roller 17A in the direction of arrow R2 and fixing roller 17B in the direction of arrow R1, and also heats fixing heater 17H in fixing roller 17A under the control of control unit 3. In this way, fixing unit 17 applies heat and pressure to paper P transported along transport path U, fixes the toner image on the paper P, and then advances the paper P diagonally upward and rearward.

The paper discharge section 18 is disposed above and rearward of the fixing section 17. The paper discharge section 18 has a transport guide and multiple transport rollers similar to those of the paper feed section 7, and also has a paper discharge sensor 19 that detects the paper P. The paper discharge sensor 19 is an optical sensor similar to the paper feed sensor 10, and supplies the detection result to the control section 3. By appropriately rotating each transport roller according to the control of the control section 3, the paper discharge section 18 transports the paper P delivered from the fixing section 17 upward and rearward, then turns it around toward the front and discharges it onto the discharge tray 2T formed on the top surface of the device housing 2.

[1-2. Configuration of peripheral parts of image drum unit]
Next, a description will be given of the configuration of the peripheral portion of the ID unit 16. As shown in the schematic perspective view of Fig. 3, inside the device housing 2 of the image forming device 1, a left frame 31 located on the left side, a right frame 32 located on the right side, and a central frame 33 connecting the two are provided, and various parts are attached to each frame.

The left frame 31 is formed as a rectangular parallelepiped that is thin in the left-right direction as a whole, for example, by cutting a specified steel plate into a specified shape and bending it appropriately. This left frame 31 is located inside the device housing 2 (Figure 1) to the left of the paper feed tray 6, intermediate transport section 13, ID unit 16, and fixing section 17, etc.

The right frame 32 is configured generally symmetrically to the left frame 31, and is formed as a rectangular parallelepiped that is thin in the left-right direction as a whole, for example by cutting a specified steel plate into a specified shape and bending it appropriately. This right frame 32 is located to the right of the paper feed tray 6, intermediate transport section 13, ID unit 16, and fixing section 17 inside the device housing 2 (Figure 1).

The central frame 33 is generally formed as a thin plate in the vertical direction, inclined so that the rear side is higher than the front side, and curved so that the area near the rear end rises upward. This central frame 33 is provided at a position corresponding to the lower or rear side of the intermediate conveying section 13 and the fixing section 17 (Figure 1), etc.

A right cover 34 is provided at a position on the right frame 32 that is slightly upward in the vertical direction and near the center in the front-rear direction, i.e., at a position that corresponds to the right side of the ID unit 16 inside the device housing 2 (Fig. 1). The right cover 34 is configured as a thin plate in the left-right direction. This right cover 34 has round holes that penetrate in the left-right direction in a total of eight places, two in each part corresponding to each ID unit 16.

Motors such as a belt motor 35, an image drum (ID) motor 36, a paper feed motor 37, and a fixing motor 38 are attached to the left frame 31 and the right frame 32. The belt motor 35 is a stepping motor that is provided on the left side (i.e., the outside) of the left frame 31 toward the lower rear and supplies driving force to the rear roller 14R (Figure 1) of the intermediate conveying unit 13. The ID motor 36, which serves as an image forming driving unit, is a DC (Direct Current) motor that is provided on the right side (i.e., the outside) of the right frame 32 toward the upper front and supplies driving force to each ID unit 16 (Figures 1 and 2).

The paper feed motor 37 is provided on the right side (i.e., the outside) of the right frame 32, toward the lower front, and supplies driving force to the paper feed rollers 8 of the paper feed unit 7 (Fig. 1). The fixing motor 38, which serves as a contact/separation driving unit, is provided on the right side (i.e., the outside) of the right frame 32, toward the lower rear, and supplies driving force to the fixing rollers 17A and 17B of the fixing unit 17 (Fig. 1).

The right frame 32 is provided with a right contact portion 40R near the lower left side of the right cover 34, and a drum coupling portion 50D and a development coupling portion 50E are provided on the right side (i.e., the outside) of the right cover 34. The left frame 31 is further provided with a left contact portion 40L at a position corresponding to the right contact portion 40R. Hereinafter, the right contact portion 40R and the left contact portion 40L are collectively referred to as contact portions 40, and the drum coupling portion 50D and development coupling portion 50E are collectively referred to as coupling portions 50.

The image forming device 1 is capable of both monochrome printing, which uses only black (K), and color printing, which uses each color. When performing monochrome printing, the image forming device 1 does not use the ID units 16 for colors other than black (K), namely cyan (C), magenta (M), and yellow (Y) (hereinafter, these will be referred to as color image drum (ID) units 16CMY), but only uses the black ID unit 16K.

In the image forming device 1, the contact section 40 changes the position of the color ID unit 16CMY relative to the conveyor belt 15, and the coupling section 50 switches the supply of driving force to the color ID unit 16CMY. Below, the configuration and operation of the right contact section 40R of the contact section 40, and the configuration and operation of the drum coupling section 50D of the coupling section 50 will be described.

[1-2-1. Configuration and operation of the connection/disconnection unit]

As shown in FIG. 4, the right engagement/disengagement unit 40R has a slide guide 41, an engagement/disengagement guide 42 (FIG. 3), a lift-up slide 43, a first lift gear 44, a second lift gear 45, an image drum (ID) up-down clutch 46, and an image drum (ID) up-down sensor 48. Incidentally, in FIG. 4 and FIG. 5, some of the teeth of each gear are omitted, and the external shape of each is shown by a simplified shape.

The slide guide 41 is configured as a long, thin rectangular parallelepiped or rod-like shape overall, and is attached to the left side (i.e., the inner side) of the right frame 32 (Figure 4). Although this slide guide is arranged roughly along the front-to-rear direction, it is arranged in a direction along the transport path U near the ID unit 16 (Figure 1), i.e., parallel to the transport direction U1, and is inclined so that the rear side is higher than the front side. The top surface of the slide guide 41 is formed into a flat, planar shape. Furthermore, a portion of the slide guide 41 is omitted near the rear.

The contact guide 42 (Fig. 3) is configured as a plate that is long in the front-rear direction and thin in the left-right direction as a whole, and is provided on the right side (outside) of the slide guide 41. As shown in Fig. 5 (A), which is a partially enlarged right side view, the contact guide 42 has two protrusions 42A and 42B that are slightly spaced apart in the front-rear direction at four locations corresponding to each ID unit 16. Both protrusions 42A and 42B protrude diagonally upward and forward, and a groove 42D is formed between them. The groove 42D is formed in an arc shape near the bottom end and its upper portion is formed in a straight line. The groove width of the groove 42D is slightly larger than the diameter of the positioning protrusion 29 (Fig. 3) on the ID unit 16.

As shown in FIG. 5B, which is a further enlargement of a portion of FIG. 5A, the groove portion 42D is formed in a straight line inclined along a diagonal direction connecting the upper front side and the lower rear side. The groove axis XD, which is the imaginary center line of the groove portion 42D, has an inclination angle αV of about 25° with respect to an imaginary vertical axis XV along the vertical direction, and accordingly, an inclination angle βH of about 65° with respect to an imaginary horizontal axis XH along the horizontal direction. In the image forming device 1, the imaginary conveying axis XU along the conveying direction U1 is inclined by about 10° with respect to the horizontal axis XH. Therefore, the groove axis XD has an inclination angle βU of about 75° with respect to the conveying axis XU, and an inclination angle αN of about 15° with respect to a conveying normal XN, which is the imaginary normal to the conveying axis XU.

The lift-up slide 43 (FIGS. 3 and 4) is configured as a rectangular parallelepiped or rod-like shape that is long in the front-rear direction overall, and is placed on the upper side of the slide guide 41. A rack gear 43G is formed facing downwards on the rear side of the underside of the lift-up slide 43, where the slide guide 41 is omitted. Therefore, when a force in the forward or rearward direction is applied to the rack gear 43G, the lift-up slide 43 can move, i.e., slide, along the upper surface of the slide guide 41, i.e., in the conveying direction U1 or the opposite direction. For convenience of explanation, the direction opposite to the conveying direction U1 will be referred to as the counter-conveying direction U2 below.

In addition, on the top surface of the lift-up slide 43, three protrusions 43P are formed that protrude upward at three locations corresponding to the ID units 16C, 16M, and 16Y (i.e., the color ID unit 16CMY). Each protrusion 43P has a close portion 43A that protrudes upwardly relatively little toward the front, an inclined portion 43B that protrudes upwardly more toward the rear, and a distant portion 43C that protrudes upwardly relatively much toward the rear.

Furthermore, the lift-up slide 43 has three protrusions 43P positioned and in contact with the lower flat portion 20B of each of the ID units 16C, 16M, and 16Y. In other words, the protrusions 43P of the lift-up slide 43 support the loads of the ID units 16C, 16M, and 16Y via the lower flat portion 20B.

The first lift gear 44 is a disk-shaped gear with multiple teeth on its circumferential side, and is rotatably supported by the right frame 32. This first lift gear 44 is located directly below the rack gear 43G on the lift-up slide 43, and is engaged with the rack gear 43G. The second lift gear 45, like the first lift gear 44, is a spur gear with multiple teeth on its circumferential side, and is rotatably supported by the right frame 32. This second lift gear 45 is located diagonally below and in front of the first lift gear 44, and is engaged with the first lift gear 44.

The ID up-down clutch 46 is arranged with two gears overlapping in the left-right direction, and a clutch mechanism is provided between the two gears. One gear of the ID up-down clutch 46 meshes with the second lift gear 45, and the other gear meshes with a specified relay gear (not shown), and the driving force from the fixing motor 38 (Figure 3) is transmitted. Based on the control of the control unit 3, the ID up-down clutch 46 can be switched between a transmission state in which the driving force is transmitted between the two gears, and a non-transmission state in which the driving force is not transmitted.

On the other hand, the left separation/removal part 40L (Fig. 3) is configured so that each part, except for the ID up-down clutch 46, is almost symmetrical with respect to the right separation/removal part 40R (Fig. 4). In addition, the second lift gear 45 of the left separation/removal part 40L is connected to the second lift gear 45 of the right separation/removal part 40R by a connecting shaft 47. Therefore, when the second lift gear 45 rotates in the right separation/removal part 40R, the left separation/removal part 40L can rotate the second lift gear 45 of the left separation/removal part 40L integrally therewith.

With this configuration, when the right contact section 40R drives the fixing motor 38 and switches the ID up-down clutch 46 to a transmission state based on the control of the control section 3, it transmits the driving force from the fixing motor 38 to the ID up-down clutch 46, the second lift gear 45, and the first lift gear 44 in that order. The right contact section 40R then transmits this driving force from the first lift gear 44 to the rack gear 43G, and moves the lift-up slide 43 together with the rack gear 43G in the conveying direction U1 or the counter-conveying direction U2. At this time, the left contact section 40L, because the driving force is transmitted from the right contact section 40R to the second lift gear 45 via the connecting shaft 47, moves the lift-up slide 43 in the conveying direction U1 or the counter-conveying direction U2 in the same way as the right contact section 40R.

When the lift-up slide 43 moves in the transport direction U1, it positions the proximal portion 43A of the protrusion 43P directly below the lower flat portion 20B. At this time, as shown in FIG. 6A, the lift-up slide 43 positions the color ID unit 16CMY relatively lower and brings the vicinity of the lower end of the image drum 26 (FIG. 2) close to the transport belt 15. At this time, the positioning protrusion 29 (FIGS. 2 and 4) of the color ID unit 16CMY is located at the lowest end in the groove 42D of the contact guide 42 (FIG. 5). Hereinafter, this state is called the proximity state, the position of the color ID unit 16CMY at this time is called the transfer position, and the position of the positioning protrusion 29 at this time is called the protrusion transfer position Q1. That is, the groove 42D restricts the range in which the positioning protrusion 29 can be displaced in the transport direction U1, and the position of the color ID unit 16CMY when the positioning protrusion 29 is displaced the furthest toward the transport direction U1 is the transfer position. In the following, the positioning protrusion 29 and the groove portion 42D are collectively referred to as the displacement restriction portion 49.

On the other hand, when the lift-up slide 43 is moved from the close state toward the opposite conveying direction U2, the inclined portion 43B abuts against the lower flat portion 20B and the lower inclined portion 20S of the color ID unit 16CMY, gradually lifting the color ID unit 16CMY. At this time, the color ID unit 16CMY moves the positioning protrusion 29 in the groove portion 42D diagonally upward and forward along the groove axis XD.

Eventually, the lift-up slide 43 positions the separation portion 43C of the protrusion 43P directly below the lower flat portion 20B and abuts it. At this time, as shown in FIG. 6B, the lift-up slide 43 positions the color ID unit 16CMY relatively higher, and separates the vicinity of the lower end of the ID 26 (FIG. 2) from the conveyor belt 15. Hereinafter, this state will be referred to as the separated state, and the position of the color ID unit 16CMY at this time will be referred to as the separated position or non-transfer position.

When the lift-up slide 43 is moved from the separated state toward the transport direction U1, the ID unit 16 is gradually lowered while the inclined portion 43B abuts against the lower flat portion 20B and the lower inclined portion 20S of the ID unit 16. At this time, the color ID unit 16CMY moves the positioning protrusion 29 in the groove portion 42D diagonally downward and rearward along the groove axis XD, and eventually reaches the close state (Figure 6 (A)).

The ID up-down sensor 48 (Figure 4) is a so-called optical sensor that has an emitter that emits detection light and a receiver that receives the detection light, and generates a detection signal based on the light reception result by the receiver and notifies the control unit 3. The ID up-down sensor 48 is also mounted in a position such that a part of it blocks the detection light when the lift-up slide 43 moves to the furthest side in the transport direction U1, that is, when the ID units 16 are in close proximity. Therefore, the control unit 3 can recognize whether the ID units 16 are in close proximity based on the detection signal obtained from the ID up-down sensor 48.

In this way, in the separation/contact section 40, the lift-up slide 43 is moved in the conveying direction U1 or the counter conveying direction U2 based on the driving force from the fixing motor 38, so that the color ID unit 16CMY can be switched between a close state (Figure 6 (A)) or a separated state (Figure 6 (B)).

Incidentally, in the image forming device 1, when performing monochrome printing in which only a black (K) toner image is transferred to the paper P, the color ID unit 16CMY is switched to the separated state (Figure 6 (B)) to reduce wear on the ID 26 in the color ID unit 16CMY.

However, in the separation and attachment section 40, when the color ID unit 16CMY is in a close state, as described above, a downward force is applied by the biasing force of the ID unit spring 2G (Figure 1) and the weight of each ID unit 16. Therefore, in the separation and attachment section 40, when switching the color ID unit 16CMY from a close state to a separated state, it is necessary to use the driving force from the fixing motor 38 to apply a force in an upward direction that is greater than the biasing force of the ID unit spring 2G and the weight of each ID unit 16.

At this time, in the separation/contact section 40, the magnitude of the driving force supplied from the fixing motor 38 is limited because the fixing motor 38 is originally a motor for driving the fixing section 17. Therefore, in the image forming device 1, the biasing force of the ID unit spring 2G is kept relatively small so that the driving force supplied from the fixing motor 38 can be used to switch the color ID unit 16CMY from a close state to a separated state.

However, in the contact section 40, because the biasing force of the ID unit spring 2G is relatively small, when the color ID unit 16CMY is switched from the separated state to the close state, the force biasing the color ID unit 16CMY downward may be insufficient. Specifically, in the contact section 40, as shown in FIG. 5(B), when the color ID unit 16CMY is switched to the close state, the positioning protrusion 29 should reach the protrusion transfer position Q1 shown by the solid line in the figure, but due to the influence of friction of each part, etc., it may stop at the protrusion intermediate position Q2, which is slightly above the protrusion transfer position Q1.

When the positioning protrusion 29 is located at the protrusion intermediate position Q2 in this way, the color ID unit 16CMY remains at an intermediate position diagonally above and forward of the transfer position, as shown in FIG. 6C, and is located slightly toward the reverse transport direction U2 from the transfer position. Also, at this time, the color ID unit 16CMY is likely to have a different amount of deviation from the transfer position for each color, rather than a constant amount. For this reason, when the color ID unit 16CMY in the intermediate position transfers a toner image to paper P transported along the transport path U, the position at which the toner image is transferred will be slightly shifted toward the reverse transport direction U2 from the correct position on the paper P, which may cause a misalignment with the toner images of other colors, i.e., a color shift.

In this way, in the image forming device 1, the separation unit 40 may cause the color ID unit 16CMY to be in a proximity state, but to remain at an intermediate position slightly shifted from the transfer position. Therefore, in the image forming device 1, an image drum (ID) stabilization process (described in detail below) is executed as a process for making the color ID unit 16CMY reach the transfer position, as necessary. For ease of explanation, the transfer position and intermediate positions where the color ID unit 16CMY may be located in a proximity state are hereinafter collectively referred to as proximity positions.

In addition, the image forming device 1 can set an "image drum (ID) stabilization request" in a predetermined memory area provided in the control unit 3 as information indicating that this ID stabilization process should be executed. This ID stabilization request is set, for example, when the image forming device 1 is turned on, that is, when there is a possibility that the color ID unit 16CMY has been attached or detached by the user.

[1-2-2. Configuration and operation of coupling unit]
Next, the configuration of the coupling portion 50 (drum coupling portion 50D and development coupling portion 50E) will be described using the drum coupling portion 50D as an example. As shown in a schematic plan view in Fig. 7(A), the drum coupling portion 50D as a transmission switching portion has a drum drive coupler 51, a spring 52, a coupling slide 53, an image drum (ID) coupling clutch 54, and an image drum (ID) coupling sensor 55. Incidentally, Fig. 7(A) mainly shows the portion related to the ID unit 16C, and omits some gears and portions related to the ID units 16M and 16Y.

The drum drive coupler 51 is located to the right of the ID connection part 26J (Fig. 2(B)) of the ID unit 16C in the close proximity state (Fig. 6(A)). This drum drive coupler 51 is formed in a cylindrical shape with its central axis aligned in the left-right direction as a whole, and is composed of a coupler root part 51A on the right side and a coupler tip part 51B on the left side.

The coupler base 51A is a relatively thick cylinder with a gear (not shown) formed on its peripheral side. The coupler tip 51B is a cylinder thinner than the coupler base 51A with a fitting portion formed at its tip (i.e., the left end) that can fit with the ID connection portion 26J of the ID unit 16C. The drum drive coupler 51 is restricted in its movement in the up-down and front-rear directions by the right frame 32 and right cover 34 (Fig. 3) and the like, but is supported so that it can move left-right with its central axis generally aligned left-right and can rotate freely. The drum drive coupler 51 is rotated by the driving force transmitted from the ID motor 36 (Fig. 3) via a transmission gear (not shown) and the like.

The spring 52 is a coil spring with its central axis aligned in the left-right direction, with its right end fixed to the right frame 32 via a specified support member and its left end abutting the right side of the drum drive coupler 51 and compressed from its natural state. As a result, the spring 52 urges the drum drive coupler 51 to the left by the action of its restoring force.

The coupling slide 53 is disposed adjacent to the right side of the right cover 34, and as shown in the schematic perspective view of FIG. 8, has a main body 53M, a hole 53H, and a protrusion 53P. The main body 53M is configured as a thin plate in the left-right direction, and is supported so that it can move (slide) generally in the front-rear direction, specifically in the conveying direction U1 or the counter-conveying direction U2, while its movement in the up-down and left-right directions is restricted by a predetermined support member (not shown) provided on the right cover 34.

The hole 53H penetrates the main body 53M in the left-right direction at a position where it communicates with a hole formed in the right cover 34 (Figure 3), and is an elongated hole that is longer in the front-rear direction than in the up-down direction. The length of the short axis of the hole 53H, i.e., the length in the up-down direction, is larger than the diameter of the coupler tip 51B of the drum drive coupler 51 (Figure 7) and smaller than the diameter of the coupler base 51A. The hole 53H is also provided.

The protrusion 53P protrudes rightward from the right side surface of the main body 53M, and is provided in a range excluding the vicinity of the front end (hereinafter referred to as the connection portion 53A) around the hole 53H. Approximately half of the rear side of the protrusion 53P (hereinafter referred to as the cut portion 53C) has a nearly flat right side surface, and the amount of protrusion to the right from the main body 53M is equal to or greater than the length along the left-right direction of the coupler tip 51B of the drum drive coupler 51. In addition, approximately half of the front side of the protrusion 53P (hereinafter referred to as the inclined portion 53B) is formed with an inclined surface connecting the connection portion 53A and the right side surface of the cut portion 53C. That is, the shape of the coupling slide 53 when viewed from above (FIG. 7(A)) is similar to the shape of the lift-up slide 43 (FIG. 4) of the right contact portion 40R when viewed from the left side.

With this configuration, as shown in FIG. 7(A), when the coupler tip portion 51B of the drum drive coupler 51 is inserted into the hole portion 53H, the left side surface of the coupler base portion 51A can be brought into contact with the connection portion 53A, the inclined portion 53B, or the cutting portion 53C.

The ID coupling clutch 54 is configured similarly to the ID up-down clutch 46 (Fig. 4) of the contact unit 40, with two gears arranged so that they overlap in the left-right direction, and a clutch mechanism provided between the two gears. One gear of this ID coupling clutch 54 meshes with each drum drive coupler 51 via a predetermined relay gear group (not shown), and the driving force from the paper feed motor 37 (Fig. 3) is transmitted to the other gear. Similarly to the ID up-down clutch 46, the ID coupling clutch 54 can be switched between a transmission state in which the driving force is transmitted between both gears and a non-transmission state in which the driving force is not transmitted, based on the control of the control unit 3.

With this configuration, when the drum coupling unit 50D drives the paper feed motor 37 and switches the ID coupling clutch 54 to a transmission state based on the control of the control unit 3, the driving force from the paper feed motor 37 is transmitted to the coupling slide 53 via the ID up-down clutch 46. This causes the coupling slide 53 to move in the conveying direction U1 or the counter-conveying direction U2.

When the coupling slide 53 is moved in the counter-conveying direction U2 as shown in FIG. 7(A), the left side surface of the coupler root portion 51A comes into contact with the connection portion 53A. At this time, the drum drive coupler 51 causes the tip of the coupler tip portion 51B to protrude sufficiently to the left beyond the right cover 34 and engages (i.e., is connected to) the ID connection portion 26J of the ID unit 16C, enabling the drive force to be transmitted to the ID 26. Hereinafter, this state will be referred to as the engaged state or transmission state.

When the coupling slide 53 is moved from the engaged state toward the transport direction U1, it gradually moves the drum drive coupler 51 to the right while abutting the inclined portion 53B against the left side surface of the coupler base portion 51A, releasing the engagement with the ID connection portion 26J and pulling it away.

Eventually, as shown in FIG. 7(B), the coupling slide 53 brings the left side surface of the coupler root portion 51A of the drum drive coupler 51 into contact with the disconnection portion 53C. As a result, the drum drive coupler 51 positions the tip of the coupler tip portion 51B to the right of the right cover 34, and is disconnected (i.e., disconnected) from the ID connection portion 26J of the ID unit 16C, and is no longer able to transmit driving force to the ID 26. Hereinafter, this state will be referred to as the disconnected state or non-transmitting state.

When the coupling slide 53 is moved from the disconnected state to the opposite conveying direction U2, the left side surface of the coupler base portion 51A abuts against the inclined portion 53B, gradually moving the drum drive coupler 51 to the left, and the coupling state is resumed (Figure 7 (A)).

The ID coupling sensor 55 as a transmission state detection unit is a so-called optical sensor, similar to the ID up-down sensor 48 (Figure 4), and has a light-emitting unit that emits detection light and a light-receiving unit that receives this detection light. It generates a detection signal based on the light-receiving result by the light-receiving unit and notifies the control unit 3. The ID coupling sensor 55 is also mounted in a position such that a part of it blocks the detection light when the coupling slide 53 moves to the farthest side in the counter-conveyance direction U2, that is, when each drum drive coupler 51 is in the engaged state (Figure 8 (A)). Therefore, the control unit 3 can recognize whether the drum drive coupler 51 is in the engaged state based on the detection signal obtained from the ID coupling sensor 55.

In this way, in the drum coupling section 50D, the drum drive coupler 51 can be switched between an engaged state (Figure 7(A)) or a disconnected state (Figure 7(B)) by moving the coupling slide 53 in the counter-conveying direction U2 or in the conveying direction U1 based on the driving force from the paper feed motor 37.

Incidentally, in the image forming device 1, a configuration similar to the coupling unit 50 is provided in the location corresponding to the black (K) ID unit 16K, and the drum drive coupler 51 and the like can be switched between an engaged state and a disconnected state. The image forming device 1 is also provided with a linkage mechanism (not shown) that links the opening and closing of the upper cover 2C (Figure 1) with the switching operation of the coupling unit 50 and the like to the engaged state or the disconnected state. For this reason, when the upper cover 2C is opened, the image forming device 1 switches the drum drive couplers 51 and the like in the ID units 16 of all colors to the disconnected state.

[1-3. Circuit configuration of image forming apparatus]
Next, the circuit configuration of the image forming apparatus 1 will be described with reference to the block diagram of Fig. 9. The control unit 3 of the image forming apparatus 1 is roughly divided into a controller unit (CU: Controller Unit) control unit 60 and a print engine unit (PU: Print engine Unit) control unit 70.

The CU control unit 60 has a CPU (Central Processing Unit) 61, a ROM (Read Only Memory) 62, a RAM (Random Access Memory) 63, and an EEPROM (Electronically Erasable and Programmable Read Only Memory) 64. The CU control unit 60 reads out a predetermined program from the ROM 62, EEPROM 64, etc., using the CPU 61, and executes the program using the RAM 63 as a working area, thereby performing various processes related to communication processing with a higher-level device (not shown), displaying information on the touch panel 4, accepting operational input, etc.

The CU control unit 60 is also connected to the touch panel 4 and a host interface (I/F) 65. The host interface 65 is an interface such as a wired LAN (Local Area Network) that complies with the IEEE (Institute of Electrical and Electronics Engineers) 802.3 (IEEE 802.3u/ab/an/ae) standard, and is connected to a higher-level device (not shown).

The CU control unit 60 is further connected to the PU control unit 70 by a video interface (I/F) 67 for transmitting image data and a communication interface (I/F) 68 for transmitting and receiving various information. For example, when the CU control unit 60 acquires print data from a higher-level device via the host interface 65, it starts a print job. Specifically, the CU control unit 60 executes a predetermined processing program, conversion program, etc. to create a print command, and converts this print data into image data by expanding it into a bitmap. The CU control unit 60 then transmits the print command to the PU control unit 70 via the communication interface 68, and transmits the image data to the PU control unit 70 via the video interface 67 using a method such as DMA (Direct Memory Access) transfer.

The PU control unit 70 has a similar configuration to the CU control unit 60, and includes a CPU 71, a ROM 72, a RAM 73, and an EEPROM 74. The PU control unit 70 reads out a predetermined program from the ROM 72, EEPROM 74, etc., using the CPU 71, and executes the program using the RAM 73 as a working area, thereby performing various processes related to each part in the image forming device 1, such as obtaining notifications from various sensors and controlling various motors. The RAM 73 is also capable of storing whether or not the above-mentioned "image drum stabilization request" has been set.

The image processing unit 75 is connected to the PU control unit 70 and the LED heads 28 of each color. This image processing unit 75 acquires image data from the PU control unit 70, adjusts the color of the image data, performs image processing such as splitting it into four colors, and supplies it to the LED heads 28 of each color.

The belt motor 35, ID motor 36, paper feed motor 37, and fixing motor 38 are connected to the PU control unit 70 and operate under the control of the PU control unit 70. The fixing heater 17H generates heat under the control of the PU control unit 70, and heats the fixing roller 17A (FIG. 1) appropriately. The paper feed sensor 10, the writing sensor 12, the paper discharge sensor 19, the temperature and humidity sensor 5, the ID up-down sensor 48, and the ID coupling sensor 55 notify the PU control unit 70 of their respective detection results. The toner remaining sensor 21S detects whether the remaining amount of toner in the toner storage unit 21 has fallen below a predetermined reference value. The upper cover sensor 2CS detects when the upper cover 2C is opened or closed, and notifies the PU control unit 70 of the obtained detection result.

The feed roller clutch 77 switches whether or not to supply driving force from the feed motor 37 to the feed roller 8 (Figure 1) based on the control of the PU control unit 70. The registration roller clutch 78 switches whether or not to supply driving force from the feed motor 37 to the registration roller 11 (Figure 1) based on the control of the PU control unit 70. The ID up-down clutch 46 and the ID coupling clutch 54 each switch whether or not to transmit driving force between two gears based on the control of the PU control unit 70.

For example, when the PU control unit 70 obtains a print command and image data from the CU control unit 60, it creates the page information shown in FIG. 10 for each page of the image data. This page information has the major items "page ID," "parameters," and "control information." Of these, the "page ID" item contains information indicating the number of pages in the print job, expressed, for example, as a numerical value.

The "Parameter" item is information that represents adjustment values and setting values related to various print setting information. This "Parameter" item has sub-items such as "Paper size," "Paper feed tray," "Print DPI (dots per inch)," "Media type," "Color/monochrome," "Double-sided/single-sided," "Paper size check," and "Darkness." In addition to these, the "Parameter" item has sub-items such as "Paper length," "Paper width," "Paper thickness," "Stacker," "Soft 4-tone," "Left margin length," "Right margin length," "Top margin length," and "Bottom margin length."

The "control information" item is information that represents adjustment values and setting values related to various print controls. This "control information" item has sub-items such as "print speed," "heater temperature," "development voltage," and "transfer voltage." Each adjustment value of this "control information" is set based on each adjustment value of the "parameters" and values obtained from various sensors, etc.

[1-4. Processing Procedure]
Next, a printing process executed by the PU control unit 70 after the image forming apparatus 1 acquires print data from a higher-level device and the CU control unit 60 creates a print command and converts the data into image data will be described.

[1-4-1. Printing process procedure]
When the PU control unit 70 is notified by the CU control unit 60 that print data has been acquired from a higher-level device, it reads out a predetermined program from the EEPROM 74 and executes it to start the PU print processing procedure RT1 shown in Fig. 11, and proceeds to the first step SP1. In step SP1, the PU control unit 70 receives image data and a print command from the CU control unit 60 via the video interface 67 and the communication interface 68, and proceeds to the next step SP2.

In step SP2, the PU control unit 70 stores adjustment values, etc. in each sub-item of "parameter" in the page information (Figure 10), creates adjustment values for each "control information" based on the adjustment values of the "parameter" and values obtained from various sensors, sets these in the page information, and proceeds to the next step SP3. In step SP3, the PU control unit 70 executes an ID up-down process (described in detail below) as a subroutine to raise and lower the color ID unit 16 CMY, and proceeds to the next step SP4.

In step SP4, the PU control unit 70 performs a print transport process, and then proceeds to the next step SP5. This print transport process is a process in which, for example, a sheet of paper P is transported along the transport path U, a toner image is generated by the ID unit 16 and transferred to the paper P, and the toner image is then fixed by the fixing unit 17, thereby printing an image on the paper P. In step SP5, the PU control unit 70 ends the PU print process procedure RT1.

[1-4-2. Image drum up/down processing procedure]
Next, an image drum (ID) up-down process executed as a subroutine in step SP3 of the PU print process procedure RT1 (FIG. 11) will be described. When the PU control unit 70 advances to step SP4 in the PU print process procedure RT1, it reads out a predetermined program from the EEPROM 74 and executes it to start the ID up-down process procedure RT2 shown in FIG. 12, and then advances to the first step SP21.

In step SP21, the PU control unit 70 determines whether or not color printing is to be performed by referring to the page information (Figure 10). If a positive result is obtained here, this indicates that a color toner image needs to be generated using the color ID unit 16CMY and transferred to the paper P. At this time, the PU control unit 70 proceeds to the next step SP22.

In step SP22, the PU control unit 70 determines whether the color ID unit 16CMY is in a separated state (FIG. 6B) based on the detection result obtained from the ID up-down sensor 48 (FIG. 4). If a positive result is obtained here, this indicates that the color ID unit 16CMY needs to be lowered (down) to transition to a close state and moved to the transfer position. At this time, the PU control unit 70 proceeds to the next step SP23.

In step SP23, the PU control unit 70 determines whether or not the coupling unit 50 is in an engaged state (FIG. 7(A)) based on the detection result obtained from the ID coupling sensor 55 (FIG. 7). If a positive result is obtained here, this indicates that the coupling unit 50 is in an engaged state, and if the color ID unit 16CMY is transitioned from a separated state to a close state in this state, there is a possibility that the drum drive coupler 51, etc. may be damaged. At this time, the PU control unit 70 proceeds to the next step SP24.

Incidentally, in the image forming device 1, when the color ID unit 16CMY is in the separated state (FIG. 6B), the coupling portion 50 should be in the disconnected state (FIG. 7B), but due to some malfunction, the coupling slide 53 may be in the engaged state. For this reason, the PU control unit 70 performs a determination process such as step SP23.

In step SP24, the PU control unit 70 controls the feed motor 37 (Figure 3) and the ID coupling clutch 54 (Figure 7) to switch the coupling unit 50 from the engaged state to the disengaged state, and then proceeds to the next step SP25.

On the other hand, if a negative result is obtained in step SP23, this indicates that the coupling unit 50 is already in a disconnected state (Figure 7 (B)) and there is no need to operate the coupling unit 50. At this time, the PU control unit 70 proceeds to the next step SP25. In step SP25, the PU control unit 70 operates the separation unit 40 by controlling the fixing motor 38 (Figure 3) and the ID up-down clutch 46 (Figure 4), lowers the color ID unit 16CMY from the separated state to switch it to the close state, and proceeds to the next step SP27. At this time, the color ID unit 16CMY may or may not have reached the transfer position.

On the other hand, if a negative result is obtained in step SP22, this indicates that the color ID unit 16CMY is in a close proximity state. At this time, the PU control unit 70 proceeds to the next step SP26, and, similar to step SP23, determines whether the coupling unit 50 is in an engaged state (FIG. 7(A)) based on the detection result obtained from the ID coupling sensor 55 (FIG. 7). If a negative result is obtained here, the PU control unit 70 proceeds to the next step SP27.

In step SP27, the PU control unit 70 controls the feed motor 37 (Figure 3) and the ID coupling clutch 54 (Figure 7) to switch the coupling unit 50 from a disconnected state to an engaged state, and then proceeds to the next step SP29.

On the other hand, if a positive result is obtained in step SP26, this indicates that the color ID unit 16CMY is in a close proximity state and the coupling unit 50 is in an engaged state. At this time, the PU control unit 70 proceeds to the next step SP28. In step SP28, the PU control unit 70 determines whether an ID stabilization request has been set by referring to the RAM 73. If a positive result is obtained here, this indicates that the color ID unit 16CMY may be in an intermediate position (Figure 6 (C)) due to reasons such as the user having detached the color ID unit 16CMY, and therefore ID stabilization processing must be performed. At this time, the PU control unit 70 proceeds to the next step SP29.

In step SP29, the PU control unit 70 performs ID stabilization processing as a subroutine (described in detail later), and moves to the next step SP30 after the color ID unit 16CMY reaches the transfer position (Figure 6(A)). In step SP30, the PU control unit 70 clears (deletes) the ID stabilization request set in the RAM 73, and moves to the next step SP35.

Also, if a negative result is obtained in step SP28, this indicates that there is a possibility that the color ID unit 16CMY has already reached the transfer position (Figure 6(A)), and therefore there is no need to perform ID stabilization processing. In this case, the PU control unit 70 proceeds to the next step SP35.

On the other hand, if a negative result is obtained in step SP21, this indicates that monochrome printing is required and that the color ID unit 16CMY must be in the separated state (Figure 6(B)). At this time, the PU control unit 70 proceeds to the next step SP31.

In step SP31, the PU control unit 70, similar to step SP23, determines whether the coupling unit 50 is in the engaged state (FIG. 7(A)) based on the detection result obtained from the ID coupling sensor 55 (FIG. 7). If a positive result is obtained here, this indicates that the coupling unit 50 is in the engaged state, and that the coupling unit 50 needs to be transitioned to the disconnected state before transitioning the color ID unit 16CMY from the close state to the separated state. At this time, the PU control unit 70 proceeds to the next step SP32.

In step SP32, the PU control unit 70 controls the feed motor 37 (FIG. 3) and the ID coupling clutch 54 (FIG. 7) to switch the coupling unit 50 from the engaged state to the disengaged state, similar to step SP24, and then proceeds to the next step SP33.

On the other hand, if a negative result is obtained in step SP31, this indicates that the coupling unit 50 is already in a disconnected state. In this case, the PU control unit 70 proceeds to the next step SP33.

In step SP33, the PU control unit 70, similar to step SP22, determines whether the color ID unit 16CMY is in the separated state (FIG. 6B) based on the detection result obtained from the ID up-down sensor 48 (FIG. 4). If a negative result is obtained here, this indicates that the color ID unit 16CMY needs to be raised (up) and transitioned to the separated state. At this time, the PU control unit 70 proceeds to the next step SP34.

In step SP34, the PU control unit 70 operates the contact unit 40 by controlling the fixing motor 38 (Figure 3) and the ID up-down clutch 46 (Figure 4), raises (up) the color ID unit 16CMY from the close state to switch it to the separated state, and proceeds to the next step SP35.

On the other hand, if a positive result is obtained in step SP33, this indicates that the color ID unit 16CMY is already in a separated state and should be maintained in this state. In this case, the PU control unit 70 proceeds to the next step SP35.

In step SP35, the PU control unit 70 ends the ID up/down processing procedure RT2 and returns to step SP3 of the original PU print processing procedure RT1 (Figure 11).

[1-4-3. Image drum stabilization process procedure]
Next, the image drum (ID) stabilization process executed as a subroutine in step SP29 of the ID up-down process procedure RT2 will be described. When the PU control unit 70 proceeds to step SP29 in the ID up-down process procedure RT2, it starts the image drum (ID) stabilization process procedure RT4 shown in Fig. 13 by reading and executing a predetermined program from the EEPROM 74, and proceeds to the first step SP41. In step SP41, the PU control unit 70 reads the first waiting time T1 and the second waiting time T2 from the EEPROM 74, and proceeds to the next step SP42. The first waiting time T1 and the second waiting time T2 are preset values.

In step SP42, the PU control unit 70 determines whether the amount of toner contained in the toner storage unit 21 (i.e., the remaining amount) is below a reference value, i.e., a toner-low state, based on the detection result obtained from the toner remaining sensor 21S.

If a positive result is obtained here, this indicates that the weight of the ID unit 16 is relatively small (i.e. light) because the amount of toner contained in the toner storage unit 21 is relatively small. This also indicates that when the separation/attachment unit 40 transitions the color ID unit 16CMY from the separated state to the adjacent state, the color ID unit 16CMY may remain in an intermediate position and the distance from the transfer position may be relatively large. At this time, the PU control unit 70 proceeds to the next step SP43. In step SP43, the PU control unit 70 increases the second waiting time T2 by adding a predetermined correction value to it, and proceeds to the next step SP44.

On the other hand, if a negative result is obtained in step SP42, this indicates that the amount of toner contained in the toner storage unit 21 is relatively large, and therefore the weight of the ID unit 16 is relatively large (i.e., heavy). In this case, the PU control unit 70 proceeds to the next step SP44 without correcting the second standby time T2.

In step SP44, the PU control unit 70 starts driving the belt motor 35 (FIG. 3) and proceeds to the next step SP45. At this time, as shown in FIG. 14, the PU control unit 70 controls the running speed (i.e., linear speed) of the conveyor belt 15 (FIGS. 1 and 2) to a predetermined speed VB1. Specifically, the PU control unit 70 controls the rotation speed of the belt motor 35 so that the speed VB1 of the conveyor belt 15 is 96 mm/s, which corresponds to 16 PPM (Page Per Minute). Hereinafter, the speed VB1 is also referred to as the media speed.

In step SP45, the PU control unit 70 waits for a predetermined first waiting time T1, and then proceeds to the next step SP46. This first waiting time T1 is set because, as described above, the ID motor 36 is a DC motor and can start driving immediately, whereas the belt motor 35 is a stepping motor and requires a certain amount of time for the stabilization process when driving starts.

In step SP46, the PU control unit 70 starts driving the ID motor 36 (FIG. 3) and proceeds to the next step SP47. At this time, the PU control unit 70 controls the running speed (i.e., linear speed) on the circumferential side of the ID 26 (FIG. 2) to be a predetermined speed VD1. Specifically, the PU control unit 70 controls the rotation speed of the ID motor 36 so that the speed VD1 on the circumferential side of the ID 26 is 72 [mm/s], which corresponds to 12 PPM. That is, the speed VD1 forms a speed difference with the speed VB1, and is a smaller value than the speed VB1. The speed ratio, which is the ratio of the speed VB1 to the speed VD1, is 1.33. In the following, the speed VD1 is also referred to as the image carrier speed. In the following, the ID stabilization process is also referred to as the speed difference formation process.

At this time, in the image forming device 1, the linear velocity VD1 in the transport direction U1 near the bottom end of ID26 in the color ID unit 16CMY is smaller than the linear velocity VB1 in the transport direction U1 of the conveyor belt 15. Therefore, at the point of contact with the conveyor belt 15, a force in the transport direction U1 is applied by the conveyor belt 15 to ID26, and the ID26 is pulled in the transport direction U1.

Now, let us consider a case where the color ID unit 16CMY is located at the intermediate position. At this time, as shown in FIG. 5, the positioning protrusion 29 of the color ID unit 16CMY is located at the protrusion intermediate position Q2 within the groove portion 42D of the contact guide 42, and the color ID unit 16CMY is in a state where it can only move in a direction along the groove axis XD. Therefore, when a force in the conveying direction U1 acts on the ID 26, the color ID unit 16CMY displaces the positioning protrusion 29 diagonally downward and backward so as to align with the groove axis XD, eventually reaching the protrusion transfer position Q1 and being positioned at the transfer position.

In step SP47 (FIG. 12), the PU control unit 70 waits for a predetermined second waiting time T2, and then proceeds to the next step SP48. This second waiting time T2 is set in advance, for example, within the range of 100 ms to 10 seconds. If a correction value was added to the second waiting time T2 in step SP43, the PU control unit 70 will wait for the corrected second waiting time T2. In step SP48, the PU control unit 70 stops the belt motor 35 and the ID motor 36, and then proceeds to the next step SP49, where the ID stabilization processing procedure RT4 ends.

[1-5. Effects, etc.]
In the above configuration, the image forming apparatus 1 according to the first embodiment switches the color ID units 16CMY between a close state or a separated state using the contact/separation unit 40, and at this time moves the positioning protrusions 29 of each ID unit 16 in a direction along the groove axis XD within the groove portion 42D of the contact/separation guide 42 (Figures 5 and 6).

Then, when performing color printing in the printing process, if certain conditions are met, the image forming device 1 performs ID stabilization processing, rotates the ID 26, and runs the conveyor belt 15 at a higher speed (Figures 13 and 14).

At this time, in the ID stabilization process, the image forming device 1 can apply a force to the color ID unit 16CMY in the transport direction U1 by intentionally creating a speed difference between the ID 26 and the transport belt 15. Here, in the image forming device 1, the groove axis XD of the separation guide 42 is inclined with respect to the transport normal XN, and descends as it proceeds in the transport direction U1, approaching the transport path U. Therefore, the image forming device 1 can move the positioning protrusion 29 diagonally downward and rearward along the groove portion 42D, and as a result, the color ID unit 16CMY can reach the transfer position.

In this way, even if the color ID unit 16CMY is located in the intermediate position, the image forming device 1 can move the color ID unit 16CMY to the transfer position by performing ID stabilization processing. This allows the image forming device 1 to print high-quality images with significantly reduced color misalignment.

However, in the image forming device 1, if only the conveyor belt 15 is run during the ID stabilization process, there is a risk that the belt motor 35, which is a stepping motor, will go out of step. In this case, only certain points of the ID 26 in the image forming device 1 will slide against the conveyor belt 15, causing localized wear, which may lead to deterioration in the image quality of the toner image. Therefore, in the ID stabilization process, the image forming device 1 does not operate only one of the ID 26 and the conveyor belt 15, but operates both and provides a predetermined speed difference between the two to avoid problems such as out-of-step and deterioration in image quality.

Furthermore, in step SP47 of the ID stabilization process (FIG. 13), the image forming device 1 presets the second waiting time T2 to be greater than or equal to 100 ms and less than or equal to 10 seconds. This enables the image forming device 1 to reliably move the color ID unit 16CMY from the intermediate position to the transfer position, and also prevents the time required to start the print transport process (FIG. 11, step SP4) from becoming excessively long.

From another perspective, the image forming device 1 can move the color ID unit 16CMY from the intermediate position to the transfer position by utilizing the frictional force generated based on the speed difference between the ID 26 and the conveyor belt 15 during the ID stabilization process, without providing a separate biasing means such as an actuator.

From another perspective, in the image forming apparatus 1, the fixing motor 38 is kept relatively small in size in order to reduce size and cost, and as a result, the driving force of the fixing motor 38 is also relatively small. The contact section 40 (FIG. 4) uses the driving force from the fixing motor 38 to switch the color ID unit 16CMY from the close state to the separated state. For this reason, in the image forming apparatus 1, it is necessary to keep the biasing force of the ID unit spring 2G relatively small. However, in the image forming apparatus 1, when the contact section 40 switches the color ID unit 16CMY from the separated state to the close state, the biasing force of the ID unit spring 2G is relatively small, so the color ID unit 16CMY cannot be biased to the transfer position and may stop at an intermediate position. Therefore, in the image forming apparatus 1, by performing ID stabilization processing using the ID 26 and the conveyor belt 15, it is possible to effectively suppress deterioration of image quality due to color shift while realizing reduction in size and cost.

In addition, in the ID stabilization process procedure RT4 (FIG. 13), the image forming device 1 corrects the second waiting time T2 according to the amount of toner remaining in the toner storage unit 21. Therefore, in the image forming device 1, even if the amount of toner remaining in the toner storage unit 21 is relatively small and the weight of the color ID unit 16CMY is relatively small, and therefore the original second waiting time T2 alone is not sufficient to move the color ID unit 16CMY to the transfer position, the second waiting time T2 is increased by correction, so it can be expected that the color ID unit 16CMY will move to the transfer position.

Furthermore, in the ID up-down processing procedure RT2 (FIG. 12), the image forming device 1 performs ID stabilization processing when starting color printing, except when the color ID unit 16CMY is in a close state and the coupling section 50 is in an engaged state. This allows the image forming device 1 to reliably perform the ID stabilization processing in cases where the color ID unit 16CMY may have been in a separated state after the ID stabilization processing was previously performed, and the color ID unit 16CMY may have stopped in an intermediate position.

Furthermore, in the ID up/down processing procedure RT2 (Figure 12), the image forming device 1 sets an ID stabilization request when the power is turned on, etc., and performs ID stabilization even when the color ID unit 16CMY is in a close proximity state and the coupling section 50 is in an engaged state. This allows the image forming device 1 to reliably execute ID stabilization processing when the color ID unit 16CMY may have been attached or detached and each ID unit 16 may be stuck in an intermediate position.

Looking at this from another perspective, the image forming device 1 does not always perform ID stabilization processing when, for example, color printing is performed, but performs the ID stabilization processing only when there is a possibility that the color ID unit 16CMY is stopped in an intermediate position, such as after the color ID unit 16CMY has transitioned from a distant state to a close state. This allows the image forming device 1 to avoid performing a wasteful operation, such as performing ID stabilization processing even when the color ID unit 16CMY is already in the transfer position.

According to the above configuration, the image forming device 1 according to the first embodiment moves the positioning protrusion 29 of the ID unit 16 in the groove portion 42D of the contact guide 42 in a direction along the groove axis XD inclined with respect to the transport direction U1. When performing color printing, the image forming device 1 performs an ID stabilization process when the color ID unit 16CMY is lowered, rotates the ID 26, and runs the transport belt 15 at a higher speed than its peripheral side, applying a force toward the transport direction U1 to the color ID unit 16CMY to reach the transfer position. This allows the image forming device 1 to print high-quality images with significantly reduced color shift.

2. Second embodiment
An image forming apparatus 201 (FIG. 1) according to the second embodiment differs from the image forming apparatus 1 according to the first embodiment in that it has a control unit 203 instead of the control unit 3, but is otherwise configured in the same manner.

The control unit 203 differs from the control unit 3 (FIG. 9) according to the first embodiment in that it has a PU control unit 270 instead of the PU control unit 70, but is otherwise configured similarly. The PU control unit 270 differs from the PU control unit 70 according to the first embodiment in that it has an EEPROM 274 instead of the EEPROM 74, but is otherwise configured similarly. This EEPROM 274 stores a program that is partially different from that stored in the EEPROM 74.

Next, we will explain the power-on process when the image forming device 201 is powered on, and the print process that is executed by the PU control unit 270 after the image forming device 201 acquires print data from a higher-level device and the CU control unit 60 creates a print command and converts it into image data.

[2-1. Power-on procedure]
When the power is turned on, the PU control unit 70 starts the power-on processing procedure RT20 shown in Fig. 15 by reading and executing a predetermined program from the EEPROM 274, and proceeds to the first step SP201. In step SP201, the PU control unit 70 performs a predetermined power-on initialization process, such as initializing various setting values, and proceeds to the next step SP202. In step SP202, the PU control unit 270 sets an ID stabilization request in the RAM 73, and proceeds to the next step SP203. This enables the PU control unit 270 to reliably perform ID stabilization processing when starting color printing processing later.

In step SP203, the PU control unit 270 determines whether or not a predetermined initial processing condition is satisfied. The initial processing condition here is a condition necessary for executing the initial processing described below. Specifically, the initial processing condition is set to be that no error has occurred, such as an error indicating that the LED head 28 (FIG. 2) is not installed, or an error indicating that the detection result by the temperature and humidity sensor 5 (FIG. 1) is outside a predetermined normal range.

If a positive result is obtained in step SP203, the PU control unit 270 proceeds to the next step SP204, executes initial processing (described in detail below) as a subroutine, and proceeds to the next step SP205. On the other hand, if a negative result is obtained in step SP203, this indicates that some kind of error has occurred, or the initial processing cannot be performed normally. In this case, the PU control unit 270 proceeds to the next step SP205 without performing initial processing. In step SP205, the PU control unit 270 ends the power-on processing procedure RT20.

[2-2. Initial Processing Procedure]
Next, the initial processing executed as a subroutine in step SP204 of the power-on processing procedure RT20 (FIG. 15) will be described. When the PU control unit 270 advances to step SP204 in the power-on processing procedure RT20, it starts the initial processing procedure RT21 shown in FIG. 16 by reading and executing a predetermined program from the EEPROM 274, and then advances to the first step SP211.

In step SP211, the PU control unit 270 determines whether or not color shift correction processing is necessary. Specifically, the PU control unit 270 makes this determination based on, for example, the values of various variables stored in the RAM 73 and information stored in the EEPROM 274. If a positive result is obtained here, this indicates that color shift correction processing is necessary, that ID up/down processing is necessary before the color shift correction processing, and in some cases, that ID stabilization processing is necessary. At this time, the PU control unit 270 proceeds to the next step SP212.

In step SP212, the PU control unit 270 performs an image drum (ID) up-down process (described in detail later) as a subroutine, and then proceeds to the next step SP213. As a result, the PU control unit 270 places the color ID unit 16CMY in a proximity state and places the drum drive coupler 51 and the like in an engaged state, but there is a possibility that the color ID unit 16CMY will stop in an intermediate position.

In step SP213, the PU control unit 270 refers to the RAM 73 to determine whether an ID stabilization request has been set. If a positive result is obtained here, the PU control unit 270 proceeds to the next step SP214, performs ID stabilization processing as in the first embodiment, and proceeds to the next step SP215. Specifically, the PU control unit 270 positions the color ID unit 16CMY at the transfer position (FIG. 6B) by performing the ID stabilization processing procedure RT4 (FIG. 13) as a subroutine. In step SP215, the PU control unit 270 clears (deletes) the ID stabilization request set in the RAM 73, and proceeds to the next step SP216.

On the other hand, if a negative result is obtained in step SP213, this indicates that there is a possibility that the color ID unit 16CMY is already positioned at the transfer position (Figure 6(B)), and therefore there is no need to perform ID stabilization processing. In this case, the PU control unit 270 proceeds to the next step SP216. In step SP216, the PU control unit 270 executes color misregistration correction processing to appropriately correct the misregistration in the toner images of each color transferred to the paper P, and proceeds to the next step SP217.

Also, if a negative result is obtained in step SP211, the PU control unit 270 proceeds to step SP217. In step SP217, the PU control unit 270 ends the initial processing procedure RT21 and returns to the original power-on processing procedure RT20 (Figure 15).

[2-3. PU Printing Processing Procedure]
Next, a printing process executed by the PU control unit 270 after the image forming apparatus 201 acquires print data from a higher-level device and the CU control unit 60 creates a print command and converts the data into image data will be described.

When the PU control unit 270 is notified by the CU control unit 60 that print data has been acquired from a higher-level device, it starts the PU print processing procedure RT22 shown in FIG. 17 by reading and executing a specific program from the EEPROM 274, and proceeds to the first step SP221. Incidentally, the PU print processing procedure RT22 (FIG. 17) is a processing procedure that is partially similar to the PU print processing procedure RT1 (FIG. 11) in the first embodiment.

In steps SP221 to SP223, the PU control unit 270 performs the same processing as steps SP1 to SP3 of the PU print processing procedure RT1 (FIG. 11) in the first embodiment, thereby performing ID up/down processing, and then proceeds to the next step SP224.

In step SP224, the PU control unit 270 determines whether the color ID unit 16CMY is in a separated state (FIG. 6B) based on the detection result obtained from the ID up-down sensor 48 (FIG. 4). If a negative result is obtained here, this indicates that the color ID unit 16CMY has been lowered (down) to a close state in order to perform color printing, but has not necessarily reached the transfer position and may be located in an intermediate position. In this case, the PU control unit 270 proceeds to the next step SP225.

In step SP225, the PU control unit 270 determines whether an ID stabilization request is set by referring to the RAM 73. If a positive result is obtained here, the PU control unit 270 proceeds to the next step SP226.

In step SP226, the PU control unit 270 performs the ID stabilization processing procedure RT4 (FIG. 13) as a subroutine to position the color ID unit 16CMY at the transfer position (FIG. 7B), and proceeds to the next step SP227. In step SP227, the PU control unit 270 clears (deletes) the ID stabilization request set in the RAM 73, and proceeds to the next step SP228.

On the other hand, if a positive result is obtained in step SP224, this indicates that the color ID unit 16CMY is in a separated state to perform monochrome printing, and there is no need to perform ID stabilization processing. At this time, the PU control unit 270 proceeds to the next step SP228.

Also, if a negative result is obtained in step SP225, this indicates that the ID stabilization request has not been set because it has been determined that ID stabilization processing is unnecessary because the color ID unit 16CMY is already positioned at the transfer position. In this case, the PU control unit 270 proceeds to the next step SP228.

In step SP228, the PU control unit 270 performs a print transport process similar to step SP4 of the PU print processing procedure RT1 (Figure 12) in the first embodiment, and then proceeds to the next step SP229 to end the PU print processing procedure RT22.

[2-4. Image drum up/down processing procedure]
Next, the image drum (ID) up-down processing executed as a subroutine in step SP212 of the initial processing procedure RT21 (FIG. 16) and in step SP223 of the PU print processing procedure RT22 will be described. When the PU control unit 270 proceeds to step SP212 or step SP223, it reads out a predetermined program from the EEPROM 274 and executes it to start the ID up-down processing procedure RT23 shown in FIG. 18, and proceeds to the first step SP231. Incidentally, the ID up-down processing procedure RT23 (FIG. 17) is a processing procedure that is partially similar to the ID up-down processing procedure RT2 (FIG. 12) in the first embodiment.

In step SP231, the PU control unit 270 determines whether there is a request to switch the color ID unit 16CMY to the proximity state, for example, when performing color misregistration correction in the initial process or when performing color printing in the PU print process. If a positive result is obtained here, the PU control unit 270 proceeds to the next step SP232.

In steps SP232 to SP237, the PU control unit 270 performs the same processing as steps SP22 to SP27 of the ID up/down processing procedure RT2 (FIG. 12) in the first embodiment. Then, in step SP237, the PU control unit 270 switches the coupling unit 50 to the engaged state, and proceeds to the next step SP238. In step SP238, the PU control unit 270 sets an ID stabilization request in the RAM 73, and proceeds to the next step SP243. This enables the PU control unit 270 to reliably execute ID stabilization processing in the subsequent processing.

Also, if a positive result is obtained in step SP236, this indicates that the color ID unit 16CMY is in a proximity state and the coupling unit 50 is in an engaged state, so that the color ID unit 16CMY should have already reached the transfer position, and there is no need to perform ID stabilization processing. At this time, the PU control unit 270 proceeds to the next step SP243.

On the other hand, if a negative result is obtained in step SP231, this indicates that it is necessary to switch the color ID unit 16CMY to the separated state, for example when performing monochrome printing. In this case, the PU control unit 270 proceeds to the next step SP239. In steps SP239 to SP242, the PU control unit 270 performs the same processing as steps SP31 to SP34 of the ID up/down processing procedure RT2 (Figure 12) in the first embodiment, and then proceeds to the next step SP243.

In step SP243, the PU control unit 270 ends the ID up/down processing procedure RT23 and returns to the original processing procedure (initial processing procedure RT21 or PU printing processing procedure RT22).

[2-5. Effects, etc.]
In the above configuration, the image forming apparatus 201 according to the second embodiment, like the first embodiment, switches the color ID units 16CMY between a close state or a separated state using the contact/separation unit 40, and at this time moves the positioning protrusions 29 of each ID unit 16 in the direction along the groove axis XD within the groove portion 42D of the contact/separation guide 42 (Figures 5 and 6).

When color printing is performed in the printing process, the image forming device 201 performs ID stabilization processing if certain conditions are met, rotating the ID 26 and running the conveyor belt 15 at a higher speed (FIGS. 13 and 14). As a result, the image forming device 201, like the first embodiment, moves the positioning protrusion 29 diagonally downward and rearward along the groove 42D, and as a result, the color ID unit 16CMY reaches the transfer position, making it possible to print a high-quality image with significantly reduced color shift.

The image forming device 201 also performs ID stabilization processing when performing color printing according to the PU print processing procedure RT22 (Figure 17) as well as when performing color shift correction processing in the initial processing procedure RT21 (Figure 16). This allows the image forming device 201 to perform color shift correction processing with the color ID unit 16CMY reliably positioned at the transfer position, significantly improving accuracy and ultimately allowing printing of high-quality images with significantly reduced color shift.

In other respects, the image forming device 201 can achieve the same effects as the image forming device 1 according to the first embodiment.

According to the above configuration, the image forming apparatus 201 according to the second embodiment moves the positioning protrusion 29 of the ID unit 16 in the groove portion 42D of the contact guide 42 in a direction along the groove axis XD inclined with respect to the transport direction U1. The image forming apparatus 201 performs an ID stabilization process before performing a printing process or a color shift correction process, rotates the ID 26, and runs the transport belt 15 at a higher speed than its peripheral surface, applying a force toward the transport direction U1 to the color ID unit 16CMY to reach the transfer position. This allows the image forming apparatus 201 to print high-quality images with significantly reduced color shift.

3. Other embodiments
In the above embodiment, in the ID stabilization process procedure RT4 (FIG. 13), the speed VB1, which is the running speed of the conveyor belt 15, is set to 96 [mm/s], the speed VD1 on the circumferential side of the ID 26 is set to 72 [mm/s], and the speed ratio, which is the ratio of the speed VB1 to the speed VD1, is set to 1.33. However, the present invention is not limited to this, and the speed ratio may be set to various other values, such as 1.25 or 1.60. In this case, by setting the speed ratio within a range of 1.2 to 2.0, it is expected that an appropriate force will be applied to the color ID unit 16CMY in the conveying direction U1. The same applies to the second embodiment.

In the first embodiment described above, the lift-up slide 43 is moved in the conveying direction U1 or the counter conveying direction U2 in the contact section 40 (FIG. 4) to bring the adjacent section 43A or the separated section 43C into contact with the lower flat section 20B of the color ID unit 16CMY, thereby lifting or lowering the color ID unit 16CMY. However, the present invention is not limited to this, and for example, a support section for supporting the color ID unit 16CMY may be provided in the device housing 2, and the color ID unit 16CMY may be lifted or lowered by moving the support section in the vertical direction by an actuator or the like. In addition, the configuration is not limited to lifting or lowering the three color ID units 16CMY together, and each color ID unit 16 may be lifted or lowered individually, for example. In short, the color ID unit 16CMY can be lifted or lowered by using various well-known methods. The same applies to the second embodiment.

Furthermore, in the first embodiment described above, the groove portion 42D provided in the contact guide 42 (FIG. 5) of the contact portion 40 has been described as having an inclination angle αN of the groove axis XD relative to the conveyance normal XN of about 15°. However, the present invention is not limited to this, and the inclination angle αN may be various other angles, such as about 30° or about 10°. In this case, the inclination angle αN should at least satisfy 0<αN<90°. The same applies to the second embodiment.

Furthermore, in the first embodiment described above, the groove portion 42D provided in the contact guide 42 (Figure 5) of the contact portion 40 is formed in a straight line along the groove axis XD. However, the present invention is not limited to this, and the groove portion 42D may have various shapes, such as a curved shape or a shape in which a straight line and a curved line are joined. In these cases, it is sufficient that at least a part of the groove portion 42D has an inclined portion so as to proceed in the conveying direction U1 as it approaches the conveying path U (i.e., descends). The same applies to the second embodiment.

Furthermore, in the above-mentioned first embodiment, a positioning protrusion 29 is provided on the ID housing 20 side of the ID unit 16, and a groove 42D is formed in the contact guide 42 on the device housing 2 side (Figures 2, 3, and 5). However, the present invention is not limited to this, and for example, a groove may be formed on the ID housing 20 side of the ID unit 16, and a positioning protrusion may be provided on the contact guide 42 on the device housing 2 side. The point is that it is sufficient to be able to move the ID 26 closer to or farther away from the transport path U while regulating the position of the ID unit 16 in the device housing 2 in the transport direction U1. The same applies to the second embodiment.

Furthermore, in the first embodiment described above, in the ID stabilization processing procedure RT4 (FIG. 13), a correction value is added to the second waiting time T2 depending on the amount of toner remaining in the toner storage section 21 in the ID unit 16. However, the present invention is not limited to this, and for example, the second waiting time T2 may be used as is without correction, regardless of the amount of toner remaining. The same applies to the second embodiment.

Furthermore, in the above-described first embodiment, a case has been described in which, in steps SP26 and SP28 of the ID up/down processing procedure RT2 (FIG. 12), if the coupling unit 50 is in a mated state and the ID stabilization request is not set, the ID stabilization processing is not performed. However, the present invention is not limited to this, and, for example, the ID stabilization processing may be performed even if the coupling unit 50 is in a mated state and the ID stabilization request is not set.

Furthermore, in the second embodiment described above, in step SP236 of the ID up/down processing procedure RT23 (FIG. 18), if the coupling unit 50 is in a mated state, the ID stabilization request is not set and the ID stabilization processing is not performed. However, the present invention is not limited to this, and for example, even if the coupling unit 50 is in a mated state, the ID stabilization request may be set and the ID stabilization processing may be performed.

Furthermore, in the above-mentioned first embodiment, various programs are stored in advance in the EEPROM 74 of the PU control unit 70 in the control unit 3 (Figure 9), and the programs are read and executed. However, the present invention is not limited to this, and for example, a program obtained from a server device (not shown) via the CU control unit 60 and the host interface 65 may be executed. The same applies to the second embodiment.

Furthermore, in the first embodiment described above, a case has been described in which the image forming apparatus 1 (FIG. 1) is provided with ID units 16 for four colors. However, the present invention is not limited to this, and one or more ID units 16 may be provided to form toner images of colors called spot colors, such as white, transparent (clear), gold, silver, etc., for a total of five or more ID units 16. In this case, when performing printing processing using spot colors, the ID unit 16 for that spot color can be placed in a proximity state together with the color ID unit 16CMY to perform ID stabilization processing. The same applies to the second embodiment.

Furthermore, in the above-mentioned first embodiment, the image drum 26 is exposed by an LED head 28 (FIG. 2) having an LED element. However, the present invention is not limited to this, and the image drum 26 may be exposed by, for example, a laser head that emits laser light. The same applies to the second embodiment.

Furthermore, in the first embodiment described above, the upper portion of the conveyor belt 15 in the intermediate conveyor section 13, i.e., a portion of the conveyor path U, is inclined at about 10° with respect to the horizontal direction (FIG. 1). However, the present invention is not limited to this, and the upper portion of the conveyor belt 15 in the intermediate conveyor section 13 may be inclined at another angle, or may be horizontal without being inclined. The same applies to the second embodiment.

Furthermore, in the first embodiment described above, the present invention has been described as being applied to a so-called direct transfer type image forming apparatus 1 in which the ID unit 16 is disposed at a location where it abuts against the transport path U, and a toner image is directly transferred from the ID 26 of the ID unit 16 to the paper P on the transport path U (FIG. 1). However, the present invention is not limited to this, and the present invention may also be applied to an intermediate transfer type image forming apparatus in which, for example, each toner image is transferred from each ID unit 16 to an intermediate transfer belt in sequence and superimposed, and the superimposed toner images are transferred from the intermediate transfer belt to the paper P. The same applies to the second embodiment.

Furthermore, in the first embodiment described above, the case has been described where the left frame 31 and right frame 32 (FIG. 3) in the image forming apparatus 1 are provided with the contact guide 42 and lift-up slide 43 of the contact unit 40, and the ID unit 16 is attached. However, the present invention is not limited to this, and for example, as in Patent Document 1, a basket that can slide relative to the device housing 2 may be provided, and the contact guide 42 and lift-up slide 43 of the contact unit 40 may be provided on the basket. The same applies to the second embodiment.

Furthermore, the present invention is not limited to the above-mentioned embodiments and other embodiments. In other words, the scope of application of the present invention extends to embodiments that arbitrarily combine the above-mentioned embodiments with part or all of the other embodiments described above, or to embodiments that extract parts of the above-mentioned embodiments.

Furthermore, in the above-mentioned embodiment, the present invention has been described as being applied to an image forming device 1 that is a single-function printer (i.e., an SFP). However, the present invention is not limited to this, and may be applied to, for example, a multifunction device that has an image scanner function and a communication function in addition to a printer function and can also operate as a copier (copy machine) or facsimile machine, that is, a so-called MFP (Multi Function Peripheral/Printer). The present invention may also be applied to various devices that have an electrophotographic printing function, such as a facsimile machine or copier. The same applies to the second embodiment.

Furthermore, in the above-mentioned embodiment, the image forming apparatus is configured with the device housing 2 as the device housing, the image drum 26 as the image forming unit, the intermediate conveying unit 13 as the conveying unit, the contact unit 40 as the contact unit, the fixing motor 38 as the contact drive unit, the displacement regulating unit 49 as the displacement regulating unit, and the control unit 3 as the control unit. However, the present invention is not limited to this, and the image forming apparatus may be configured with a device housing having various other configurations, an image forming unit, a conveying unit, a contact unit, a contact drive unit, a displacement regulating unit, and a control unit.

The present invention can be used, for example, in image forming devices capable of color printing and monochrome printing using electrophotography.

1, 201: image forming apparatus, 2: apparatus housing, 2S: internal space, 3, 203: control section, 13: intermediate conveying section, 15: conveying belt, 16: ID unit, 16CMY: color ID unit, 20: ID housing, 21: toner storage section, 21S: toner remaining amount sensor, 26: image drum, 26J: ID connection section, 29: positioning protrusion, 37: paper feed motor, 38: fixing motor, 40: contact section, 42: contact guide, 42D: groove section, 48 ......ID up/down sensor, 49...displacement regulating section, 50...coupling section, 51...drum drive coupler, 55...ID coupling sensor, 70, 270...PU control section, T1...first waiting time, T2...second waiting time, U...conveying path, U1...conveying direction, U2...counter-conveying direction, VB1...speed, VD1...speed, XD...groove axis, XH...horizontal axis, XN...conveying normal, XU...conveying axis, XV...vertical axis, αN, αV, βH, βU...tilt angle.

Claims (12)

An apparatus housing having an internal space;
an image forming unit provided inside the device housing and forming a developer image on a rotating image carrier using a developer;
a conveying section that contacts the image carrier and conveys the medium in a conveying direction;
a separation unit that displaces a position of the image forming unit with respect to the device housing between a separate position where the image carrier is separated from the medium and a close position where the image carrier is closer to the medium than the separate position;
a separation/communication driving unit that drives the image forming unit to the separated position or the adjacent position;
a displacement regulating portion that regulates the image forming portion to a transfer position where the developer image is transferred from the image carrier to the medium when the image forming portion is displaced in the transport direction with respect to the device housing;
a control unit that controls operations of the image forming unit, the conveying unit, and the contact/separation drive unit,
The control unit, when displacing the image forming unit to the close position by the separation drive unit, starts a transport operation by the transport unit, and after a predetermined time has elapsed, starts a rotation operation of the image carrier by the image forming unit, and performs a speed difference formation process to make the image carrier speed, which is the linear velocity of the image carrier, slower than the media speed, which is the linear velocity of the medium by the transport unit. The control unit, after performing the speed difference forming process, stops a conveying operation by the conveying unit and a rotating operation of the image carrier by the image forming unit, and then performs a printing process to form the developer image on the medium.
2. The image forming apparatus according to claim 1, The image forming apparatus according to claim 1 , wherein the displacement regulating portion regulates the displacement of the image forming portion in the transport direction as the image carrier approaches the medium when the image forming portion is displaced relative to the apparatus housing. The displacement regulating portion is
a positioning protrusion provided on one of the image forming unit and the device housing;
4. The image forming apparatus according to claim 1, further comprising: a groove portion provided on the other of the image forming unit and the apparatus housing, the groove portion guiding a position of the positioning protrusion. 5. The image forming apparatus according to claim 1 , wherein the transport section is a circular belt that runs along a circular path, or a sheet transported by the circular belt, as the medium. 6. The image forming apparatus according to claim 1 , wherein the control unit sets a speed ratio, which is a ratio of the medium speed to the image carrier speed when performing the speed difference forming process, to 1.2 or more and 2.0 or less. 7. The image forming apparatus according to claim 1 , wherein the control unit sets a period for performing the speed difference forming process to be 100 ms or more and 10 seconds or less. The image forming unit includes:
a developer container that contains the developer;
a remaining amount detection unit that detects a remaining amount of the developer,
8. The image forming apparatus according to claim 1, wherein the control unit extends a period for performing the speed difference forming process when the remaining amount of the developer is less than a predetermined reference value, compared to when the remaining amount is equal to or greater than the reference value . 9. The image forming apparatus according to claim 1, wherein the control unit controls the speed difference forming process to be performed if the speed difference forming process has not been performed after the separation driving unit displaces the image forming unit from the separated position to the close position. an image forming driving unit provided in the device housing and generating a driving force for driving the image forming unit;
a transmission switching unit provided in the apparatus housing, the transmission switching unit switching between a transmission state in which the driving force is transmitted to the image forming unit and a non-transmission state in which the driving force is not transmitted to the image forming unit;
a transmission state detection unit that detects whether the transmission switching unit is in the transmission state or the non-transmission state,
The image forming apparatus according to any one of claims 1 to 9, characterized in that, when the control unit detects that the transmission switching unit is in the non-transmitted state while the image forming unit is displaced to the close position by the separation driving unit, the control unit controls the transmission switching unit to switch to the transmitted state and perform the speed difference formation process. 11. The image forming apparatus according to claim 10, wherein the control unit controls not to perform the speed difference forming process when the control unit detects that the transmission switching unit is in the transmitted state and the image forming unit is located at the adjacent position. An apparatus housing having an internal space;
an image forming unit provided inside the device housing and configured to form a developer image on a rotating image carrier using a developer;
a conveying section that contacts the image carrier and conveys the medium in a conveying direction;
a separation unit that displaces a position of the image forming unit with respect to the device housing between a distant position where the image carrier is distant from the medium and a close position where the image carrier is closer to the medium than the distant position;
a separation/communication driving unit that drives the image forming unit to the separated position or the adjacent position;
a displacement regulating portion that regulates the image forming portion to a transfer position where the developer image is transferred from the image carrier to the medium when the image forming portion is displaced in the transport direction with respect to the device housing;
a control unit that controls operations of the image forming unit, the conveying unit, and the contact/separation drive unit;
Equipped with
When the image forming unit is displaced to the approaching position by the separation driving unit, the control unit performs a speed difference forming process of making an image carrier speed, which is a linear velocity of the image carrier, smaller than a medium speed, which is a linear velocity of the medium by the transport unit, and then stops a transport operation by the transport unit and a rotation operation of the image carrier by the image forming unit, and then performs a printing process of forming the developer image on the medium.
1. An image forming apparatus comprising:

Images