KR100354734B1 - Image forming device of wet-typed printer - Google Patents

Abstract

PURPOSE: An image forming device of a wet type printer is provided to prevent performance deterioration of squeegee roller by preventing a plastic deformation caused due to the fatigue of the spring. CONSTITUTION: An image forming device comprises a squeegee roller(205) which contacts or is separated from the photosensitive belt of a wet type printer; a sub frame(4010) where the squeegee roller is mounted to be rotatable; a main frame(4000) where the sub frame is supported in such a manner that the sub frame is movable in a vertical direction; a spring(4070) for supporting the sub frame and providing an elastic climbing power to the sub frame; a supporter(4060) for supporting the spring; and an elevating unit for moving the support in a vertical direction with respect to the main frame such that the sub frame elastically moves in a vertical direction by the spring supported by the supporter. The elevating unit moves the sub frame in a vertical direction in such a manner that the sub frame has three stages of different heights with respect to the main frame.

Description

Image forming device of wet-typed printer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for a wet printer, and more particularly, to an image forming apparatus for a wet printer having an improved structure of a squeegee for squeezing a developer applied to a photosensitive belt of a wet printer.

The image forming apparatus is roughly divided into wet and dry depending on the type of developer used. The wet image forming apparatus uses a developer in which powder toner is dispersed in a volatile liquid carrier, and applies a photosensitive belt that circulates an endless orbit image as a medium for image formation.

1 shows a schematic configuration of a conventional image forming apparatus.

Referring to FIG. 1, the photosensitive belt 110 is supported by three rollers 111, 112, and 113. Among the three rollers, reference numeral 111 denotes a backup roller. The toner image formed on the photosensitive belt is pressurized to a certain pressure by the photosensitive belt 110 to the transfer roller 114 installed adjacent thereto. It is to be transferred to. One side of the transfer roller 114 is provided with a pressure roller 115 in contact with the transfer roller 114 at a constant pressure to transfer the recording paper 116 between the transfer roller 114 and the pressure roller 115. The toner image attached to the roller 114 is to be transferred.

An image forming apparatus 200 for forming a toner image on the surface of the photosensitive belt 110 is provided in the transfer section of the photosensitive belt 110 between the steering roller 112 and the driving roller 113. The image forming unit 200 includes an LSU (Line Scanning Unit, 202a, 202b, 202c, 202d) and a developing unit 201a, 201b, 201c, and 201d which are alternately installed. One LSU and a developing unit adjacent to each other form a group to form a unit toner image for each color (Yellow, Magent, Cyan, Black).

The LSUs 202a, 202b, 202c, and 202d form an electrostatic latent image by irradiating a photosensitive surface of the photosensitive belt 110 with a laser beam according to color image signals, and developing units 201a, 201b, 201c, and 201d. Develops an electrostatic latent image formed by LSUs (Line Scanning Units) into a toner image.

The developing units 201a, 201b, 201c, and 201d of the developing apparatus 200 as described above remove the excess amount of the developer applied to the photosensitive belt 110 and the developing roller applied to the photosensitive belt 110. A squeeze roller is provided.

Referring to FIG. 2, the developing parts 201a, 201b, 201c, and 201d may be formed on the upper side of the container 302 storing the developing solution 301, while maintaining a predetermined distance from the photosensitive belt 110 during development. Is applied by the developing roller 205 and the developing roller 205 to apply the developing solution 301 from the developing solution supply device 300 provided on the photosensitive belt 110 to contribute to the development of the toner image and to retain the remaining excess developer. By removing the squeeze roller 204 is provided in contact with the photosensitive belt 110 at a predetermined pressure. The cleaning roller 206 in contact with the development roller 205 is located under the developing roller 205, and the cleaning blade separating the developer attached to the surface of the squeeze roller 204 under the squeeze roller 204. 207 is located. In addition, a backup roller 116 is positioned above the photosensitive belt 110 opposite to the squeeze roller 204. The backup roller 116 supports the back when the squeeze roller 204 is in contact with the photosensitive belt 110.

The developing parts having the structure as described above are maintained as shown in FIG. 2 when the image is formed, and are separated from the photosensitive belt 110 when the idle time, that is, the image forming is not in progress, thus, the image At the time of formation, the phenomenon rollers having a predetermined gap on the photosensitive belt are spaced at even larger intervals, and the squeeze rollers that are in contact with the photosensitive belt are separated. To this end, the developing unit is provided with a lifting device. At this time, the developing parts are lifted up and down simultaneously by one lifting device, or are lifted up and down in two separated states by two separate lifting devices.

On the other hand, the squeeze roller which is raised and lowered together with the developing part by the elevating device is installed to be able to be moved up and down elastically in the developing part, and is in contact with the photosensitive belt at different pressure.

Figure 3 shows an example of an image forming apparatus according to the invention filed in 1998 Patent Application No. 7910, the present application.

Referring to FIG. 3, the squeeze roller is rotatably installed in a subframe 401 that is supported to be able to elastically move up and down on the main frame 400. The supporter 406 supporting the subframe 401 and the compression spring 407 providing elasticity to the supporter 406 are located between the mainframe 400 and the subframe 401. In addition, a cam stud 405 guided by the cam groove 404 of the cam slider 403 reciprocating in the horizontal direction is coupled to the subframe 401. On the other hand, one side of the main frame 400, the development roller assembly 402 is coupled to the development roller 205 is coupled.

According to the above structure, even if the developing devices 201a, 201b, 201c, and 201d are lifted by the lifting device, only the developing roller 205 is raised and lowered together, and the cam groove 404 of the cam slider 403 is raised and lowered. The subframe 401 is positioned by overcoming the elasticity of the spring 407 located below the supporter 406 by the cam stud 405 that is restrained by the cam stud 405. Accordingly, the cam slider 403 is properly moved together with the lifting device in forming the image, so that the squeeze roller 204 coupled to the lifting and lowering of the subframe 401 is coupled to the photosensitive belt 110. Contact and disconnection.

In the above structure, the spring 407 serves to apply a contact pressure when the squeeze roller 204 is in contact with the photosensitive belt 110. That is, when the cam slider 403 moves to the right in the drawing, the subframe 401 is raised by the expansion force of the spring 407 with respect to the main frame 400, and thus, the squeeze roller 204 is moved to the photosensitive belt. The spring 407 comes into contact with the 110 at a predetermined pressure. However, the problem is that when the subframe 401 is lowered with respect to the main frame 400, that is, during the idle period in which image formation is not performed, the spring 407 is strongly compressed so that a considerable amount of plastic deformation occurs. In this case, the elasticity of the squeeze roller 204 against the photosensitive belt 110 is not maintained due to the plastic deformation of the spring 407 over time. As such, when the squeeze roller 204 does not come into contact with the photosensitive belt 110 at a given pressure (about 12 to 20 Kgf), the desired squeegeeing action on the photosensitive belt 110 may not be sufficiently achieved. In addition, when the squeeze roller 204 is in contact with the photosensitive belt 110, the spring is made in a state in which the spring is inflated. Therefore, when designing the spring, the strength of the spring should be increased considerably. In this way, when the strength of the spring is increased in consideration of the amount of extension of the spring, the force applied to the cam slider 403 to raise and lower the subframe 401 should be increased by that much. As a result, a power source for operating the cam slider, For example, a high power motor should be used. In addition, elements, such as supporters, mainframes, subframes, etc., which are subject to the force of the reinforced spring, should have high strength, resulting in higher parts manufacturing costs. The technique of providing the contact pressure of the squeeze roller by the compressed spring expanded by a certain amount in the state of being compressed in a certain amount has also been applied to the technology before the applicant's application.

The present invention has a first object to provide an image forming apparatus for a wet printer that can effectively manage the contact pressure of the squeeze roller to the photosensitive belt.

It is a second object of the present invention to provide an image forming apparatus for a wet printer capable of lowering the output of a power source for operating a squeeze roller.

It is a third object of the present invention to provide an image forming apparatus for a wet printer, in which a material having a lower mechanical strength can be used as compared with the prior art, and thus manufacturing cost is reduced.

1 is a schematic configuration diagram of a general wet printer,

2 is a schematic configuration diagram of a conventional image forming apparatus;

3 is a schematic configuration diagram showing an example of an image forming apparatus that can be applied to the wet printer;

4 is a schematic structural diagram of a first embodiment according to an image forming apparatus for a wet printer of the present invention;

5 is a schematic perspective view of a first embodiment according to the image forming apparatus for a wet printer of the present invention shown in FIG.

6 is a view showing an operating state in the first embodiment according to the image forming apparatus for a wet printer of the present invention shown in FIGS.

FIG. 7 is a diagram showing a comparison of the amount of deformation of the spring and the force according to the spring in the first embodiment according to the image forming apparatus for a wet printer of the present invention and the conventional image forming apparatus.

8 is a view showing the schematic structure of a cam slider in the second embodiment according to the image forming apparatus for a wet printer of the present invention;

9 is a schematic structural diagram showing an operation state of a second embodiment according to the image forming apparatus for a wet printer of the present invention step by step;

10 is a schematic configuration of a third embodiment according to the image forming apparatus for a wet printer of the present invention.

Figure 10a also shows a state in which the squeeze rollers of the adjacent image forming apparatus are all separated from the photosensitive belt,

10B shows a state when the cam slider is moved left by one step,

10c shows the state when the cam slider is moved to the left by two stages,

10d shows the state when the cam slider is moved to the left by three steps,

10E shows the state when the cam slider of FIG. 10E is moved to the left by four steps.

According to the present invention to achieve the above object, and a squeeze roller contacting and separating the photosensitive belt of the wet printer; A subframe to which the squeeze roller is rotatably mounted; A mail frame in which the subframe is supported to move up and down a predetermined distance; A spring which supports the subframe from below to provide an elastic lifting force to the subframe; A supporter for supporting a lower portion of the spring; An elevating device for elevating the supporter relative to the main frame to allow the subframe to elevate elastically by the spring supported by the supporter; There is provided an image forming apparatus for a wet printer.

In the image forming apparatus of the present invention, the elevating device has a cam stud coupled to the supporter and a cam groove through which the cam stud is guided, and is preferably provided in a cam slider capable of reciprocating in one direction. .

In addition, the lifting device is preferably configured to raise and lower the subframe such that the subframe has a three-step position different from each other with respect to the main frame.

Furthermore, the elevating device for elevating the subframe to have a three-stage position is a cam having a cam groove of a predetermined shape having a three-step height difference by which the cam stud coupled to the supporter and the cam stud are guided. Preferably provided by a slider.

In addition, in order to achieve the above object, according to another type of the invention, the squeeze roller which is in contact with and separated from the photosensitive belt of the wet printer; A subframe to which the squeeze roller is rotatably mounted; A main frame in which the subframe is supported to move up and down a predetermined distance; A spring which supports the subframe from below to provide an elastic lifting force to the subframe; A supporter for supporting a lower portion of the spring; An elevating device for elevating the supporter relative to the main frame to allow the subframe to elevate elastically by the spring supported by the supporter; A plurality of unit image forming apparatuses are provided, and the lifting device of the unit image forming apparatus is provided so as to be shared with an adjacent unit image forming apparatus.

In another type of image forming apparatus of the present invention, the elevating device is provided in a cam slider capable of reciprocating in one direction by having a cam stud coupled to the supporter and a cam groove through which the cam stud is guided. It is preferable.

In addition, the lifting device is preferably configured to raise and lower the subframe such that the subframe has a three-step position different from each other with respect to the main frame.

Furthermore, the elevating device for elevating the subframe to have a three-stage position is a cam having a cam groove of a predetermined shape having a three-step height difference by which the cam stud coupled to the supporter and the cam stud are guided. Preferably provided by a slider.

Hereinafter, preferred embodiments of the image forming apparatus for a wet printer of the present invention will be described in detail with reference to the accompanying drawings.

Example 1

4 and 5, the squeeze roller 205 is rotatably installed in the subframe 4010 which is supported to be able to be lifted and lowered in the main frame 4000. On one side of the main frame 4000, a developing roller assembly 402, to which a developing roller 205 is coupled, is coupled. In addition, a support spring 4060 supporting the subframe 4010 and a compression spring 4070 providing elasticity between the supporters 4060 and the subframe 4010 between the mainframe 4000 and the subframe 4010. ) Is located. Missing portions 4011 of a predetermined height are formed on both lower sides of the subframe 4010. The supporter 4060 is installed to move up and down with respect to the main frame 4000, like the subframe 4010, and is provided at both sides of the subframe 4010 at both sides of the body. An arm 4041 is provided, which is provided with an entry protrusion 4062. Therefore, the subframe 4010 and the arm 4041 are coupled to each other to allow the relative movement of the supporter 4060 by a predetermined distance. At this time, since the spring 407 is located between the supporter 4060 and the subframe 4010, the supporter 4060 and the subframe 4060 receive elasticity in a direction away from each other. The maximum distance between the supporter 4060 and the subframe 4060 is limited to a predetermined range by the protruding portion 4042. Meanwhile, a cam stud 4050 guided by the cam groove 4040 of the cam slider 4030 is coupled to the lower portion of the supporter 4060.

Therefore, the supporter 4060 is moved up and down relative to the main frame 4000 by the cam slider 4030 separately from the lifting operation of the main frame 4000. Therefore, when the image forming apparatus is coupled to the main frame 4000 as the apparatus for raising and lowering the main frame 4000 and the apparatus for horizontally moving the cam slider 4030 operate in a sequence of operations. The developing roller 205 and the squeeze roller 204 are raised so that the developing roller 205 is positioned close to the photosensitive belt at a predetermined interval, and the photosensitive belt is at a predetermined pressure of the squeeze roller 204. Contact 110. In the above structure, the device for elevating the mainframe 4000 may be provided by the cam slider 4030, which is the same structure as elevating the subframe 4010, that is, one side of the mainframe. A cam stud is provided in the cam slider 4030, and a cam groove corresponding to the cam stud is provided in the cam slider 4030 so that the cam slider 4030 moves up and down preliminarily and the main frame 4000 by the cam slider 4030. The lifting motion of the subframe 4010 is possible.

When the cam slider 4030 moves to the left in the drawing, the supporter 4060 is moved upward by the cam stud 4050 guided by the cam groove 4040, and at this time, the subframe is supported by the spring 4070. Lift force is generated by the spring force of the spring 4070 in the 4010, and therefore, the squeeze roller 204 supported by the subframe 4010 is in contact with the photosensitive belt 110 at a constant pressure. At this time, the spring 4070 is maintained in a compressed amount.

According to the above structure, the contact pressure of the squeeze roller 204 is provided by the spring 4070 compressed by a certain amount. That is, the spring 4070 is inflated a certain amount within the maximum distance allowed between the supporter 4060 and the subframe 4010 when the idle time is not an image forming time, that is, when the supporter 4060 does not rise. When it is formed, that is, when the supporter 4060 is raised, a certain amount of compression is provided, thereby providing a contact pressure of the squeeze roller 204.

Therefore, according to the image forming apparatus of the present invention, since the spring is sufficiently inflated during the normal idle time, plastic deformation does not occur through this period, and this period is compressed only for a short time during the image forming period. Plastic deformation through not much occur. This feature is contrasted with the case in the conventional image forming apparatus. That is, in the conventional image forming apparatus, the spring is compressed during the idle time, and the contact pressure is generated as the spring is expanded to form the image, thus causing large plastic deformation during the compressed idle time, in particular, the spring is compressed. Since the contact pressure is generated while changing from the expanded state to the expanded state, a spring having a strength considering the amount of expansion from the compressed state to the expanded state, that is, a spring having a high elasticity, should be applied.

6A to 6B, in the image forming apparatus of the present invention, the compression change of the squeeze roller according to the compression expansion stage of the spring will be described.

Fig. 6A shows a state in which the spring is sufficiently inflated within a limited range as mechanically so as to easily understand the state in the idle time. That is, the squeeze roller 2040 is separated from the photosensitive belt 110 and the spring 4070 is inflated to the maximum range allowed by the subframe 4010 and the supporter 4060. This state is a time when image formation is not performed, and thus, the spring 4070 is inflated to the maximum and thus has low fatigue.

FIG. 6B shows a state in the image forming time, and the spring 4070 is compressed greatly as the interval between the subframe 4010 and the supporter 4060 is narrowed. As the supporter 4060 is raised, the subframe 4060 supported by the spring 4070 also rises, so that the squeeze roller 204 comes into contact with the photosensitive belt 110. When the squeeze roller 204 is in contact with the photosensitive belt 110, the backup roller 116 supports the sub-frame 4010 no longer as the supporter 4060 rises and thus interposes therebetween. The spring 4070 is compressed, and a contact pressure corresponding to the amount of the spring 4070 is compressed is applied to the squeeze roller 204.

FIG. 7 is a diagram showing the amount of spring deformation and the force of the spring in the image forming apparatus of the present invention and the conventional image forming apparatus.

In Fig. 7 f ₀ is the target value of the force to be applied to the squeeze roller, f ₁ represents the force during the idle period of the spring in the present invention, and f ₂ is during the idle period of the spring in the conventional device Indicates the power of And x ₀ is the amount of deformation of the spring to obtain the target value of force f ₀ , f ₁ is the amount of deformation during the idle period of the spring in the present invention, and f ₂ is the period of idleness of the spring in the conventional apparatus. Shows the amount of deformation.

As shown in Fig. 7, the spring in the conventional apparatus is deformed during the idle period by x ₂ and crack-cracked with a force of f ₂ , but in the present invention the spring is deformed very small by x ₁ . It is slightly compressed with the smallest force f ₁ . At the time of image formation, the conventional spring is lowered to a target value f ₀ , which is a force smaller than f ₂ , while its deformation amount is lowered from x ₂ to x ₀ . However, the spring in the device of the present invention has a larger value of the target value f ₀ as it is more deformed from x ₁ to x ₀ . That is, as described above, the spring in the conventional apparatus is compressed with a very large deformation amount during the idle period, so that the plastic deformation is largely increased by the fatigue increase, and the spring of the image forming apparatus of the present invention is the lowest deformation during the idle period Due to the deformation, plastic deformation due to fatigue accumulation is very small. In addition, since a spring of lower elasticity is used as compared to the conventional method according to the present invention, the strength of a component applied by the spring can be lowered compared with the conventional, and thus the cost of parts is lowered.

Example 2

In the first embodiment, the cam groove of the cam slider has two positions, but the structure of the cam groove of the cam slider is changed in order to multiply the contact pressure on the photosensitive belt of the wet color printer (two steps in this embodiment). . This embodiment includes a cam slider having the basic structure in Embodiment 1 and having a cam groove of the modified structure.

8 schematically shows the structure of the cam slider 4031 according to the present embodiment.

Referring to FIG. 8, the cam groove 4041 formed in the cam slider 4031 has a structure that allows the cam stud 4050 to be positioned at three upper and lower positions A, B, and C. Accordingly, according to the positions A, B, and C of the cam stud 4041 guided by the cam groove 4041, the compression amount of the spring compressed by the supporter is three-stage, and thus the squeeze roller of the subframe The contact pressure will be different. At this time, the C position of the cam groove is a position where the squeeze roller is separated from the photosensitive belt, and the A and B positions are positions where the squeeze roller contacts the photosensitive belt, and the contact pressure of the squeeze roller at the B position is the C position. This is higher than the contact pressure of the squeeze roller at. This difference in contact pressure is applied to the so-called image development step and the removal of the drip line in the wet printer, thereby making it possible to form a high quality image during image formation. That is, during the image development step, the squeeze roller contacts the photosensitive belt with the first pressure and performs the rolling motion together, squeezes the excess of the developer attached to the photosensitive belt in this process, and removes the squeeze roller during the removal of the drip dry. The reverse rotation in the state in which the contact with the photosensitive belt at a second pressure lower than the first pressure to remove the drip line generated in the photosensitive belt.

Example 3

The image forming apparatus according to the present invention as described above is provided with a plurality of, for example, four color printers in one wet printer. Therefore, each image forming apparatus has a first raising and lowering means for raising and lowering a main frame and a second raising and lowering means for raising and lowering a squeeze roller of each image forming apparatus, wherein each of the image forming apparatuses has the first and second gains. Providing the lowering means not only increases manufacturing cost but also makes the internal structure of the printer very complicated.

Therefore, when one lifting device operates a plurality of image forming apparatuses, for example, two image forming apparatuses, the two lifting devices can lift and lower the squeeze rollers of the four image forming apparatuses.

In particular, the elevating device is to provide a cam groove of a predetermined shape to the elevating the main frame and the squeeze roller in the cam slider to enable the cam slider to raise and lower the main frame, the elevating and lifting of the subframe. Can be. However, in some cases, the first elevating means for elevating the main frame and the second elevating means for elevating the subframe may be provided as separate devices. In this embodiment, only a portion of the structure for elevating the subframe is described, and the structure for elevating the mainframe is omitted.

Preferably, when the squeeze rollers of the two image forming apparatuses are moved up and down by one cam slider, the operation of each image forming apparatus at a time difference may reduce the load of the power source for driving the cam sliders.

That is, two cam grooves for guiding the cam studs of the two image forming apparatuses are provided in one cam slider as shown in FIGS. 10A to 10E, and the cam grooves guide the cam studs of the two image forming apparatuses at a time difference. Let's do it. 10A to 10E sequentially show the trajectories of the positions of the cam studs provided on the supporters of both image forming apparatuses and the relative positions of the squeeze rollers relative to the photosensitive belt during the cam slider moving from right to left in the drawing. .

10A shows a state in which both the squeeze rollers of both image forming apparatuses are separated from the photosensitive belt.

Fig. 10B is a state when the cam slider is moved to the left by one step. The squeeze roller of the left image forming apparatus is in contact with the photosensitive belt at low pressure, and the squeeze roller of the right image forming apparatus maintains its initial state. It shows the state.

FIG. 10C shows a state in which the cam slider is moved to the left by two stages, and the squeeze rollers of both image forming apparatuses are contacted with the photosensitive belt at low pressure.

FIG. 10D is a state in which the cam slider is moved to the left by three stages. The squeeze roller of the left image forming apparatus is in contact with the photosensitive belt at high pressure, and the squeeze roller of the right image forming apparatus is directly in contact with the photosensitive belt at low pressure. I see a state becoming.

As the cam slider in Fig. 10E moves to the left by four steps, the squeeze rollers of both image forming apparatuses are in contact with the photosensitive belt at high pressure.

The position change of the squeeze roller through the above process is to operate in the reverse order of the above-described sequence when the cam slider is moved to the right step by step.

In the above operation, the state of e) is applied to the position of the squeeze roller in the so-called image development step, and the state of c) is preferably applied to the squeeze roller position in the drip line removal step.

As described above, according to the image forming apparatus of the present invention, it is possible to effectively control the contact pressure of the squeeze roller to the photosensitive belt, in particular to prevent plastic deformation due to fatigue accumulation of the spring providing the contact pressure, It is possible to prevent deterioration of the function of the squeegee roller due to a change in contact pressure, in particular a decrease. In addition, by multi-stage the contact pressure of the squeeze roller, it is possible to reduce the load of the power source that operates the squeeze roller, and in particular, by appropriately adjusting the contact pressure of the squeeze roller during the image formation process and the removal of the drip line, it effectively squeezes the photosensitive belt. The drip line can be removed as well as the gong. In addition, since the output of the power source for operating the squeeze roller can be lowered, the cost of parts can be reduced by the power source with low output, and the production cost can be reduced because a material having a lower mechanical strength can be used as compared with the conventional art.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention should be defined only in the appended claims.

Claims (6)

A squeeze roller contacting and separating the photosensitive belt of the wet printer; A subframe to which the squeeze roller is rotatably mounted; A main frame in which the subframe is supported to move up and down a predetermined distance; A spring which supports the subframe from below to provide an elastic lifting force to the subframe; A supporter for supporting a lower portion of the spring; An elevating device for elevating the supporter relative to the main frame to allow the subframe to elevate elastically by the spring supported by the supporter; Equipped, And the elevating device is configured to elevate the subframe to raise and lower the subframe so that the subframe has three positions of different heights relative to the main frame. The wet printer of claim 1, wherein the elevating device includes a cam stud coupled to the supporter, and a cam slider for reciprocating in one direction, having a cam groove through which the cam stud is guided. Image forming apparatus. The cam lifting device according to claim 2, wherein the elevating device for elevating the subframe includes: a cam stud coupled to the supporter; and a cam slider having a predetermined cam groove having a three-step height difference by which the cam stud is guided. An image forming apparatus of a wet printer, characterized in that provided by. A squeeze roller contacting and separating the photosensitive belt of the wet printer; A subframe to which the squeeze roller is rotatably mounted; A mail frame in which the subframe is supported to move up and down a predetermined distance; A spring which supports the subframe from below to provide an elastic lifting force to the subframe; A supporter for supporting a lower portion of the spring; An elevating device for elevating the supporter relative to the main frame to allow the subframe to elevate elastically by the spring supported by the supporter; A plurality of unit image forming apparatuses are provided, The lifting device of the unit image forming apparatus is configured to share with an adjacent unit image forming apparatus. And the elevating device is configured to elevate the subframe to elevate the subframe such that the subframe has three positions with different heights relative to the mainframe. 5. The wet printer according to claim 4, wherein the elevating device includes a cam stud coupled to the supporter, and a cam slider for reciprocating in one direction by having a cam groove through which the cam stud is guided. Image forming apparatus. According to claim 4, The elevating device for elevating the sub-frame to have a three-step position is a predetermined shape having a three-step height difference that the cam stud coupled to the supporter and the cam stud is guided An image forming apparatus of a wet printer, characterized by being provided by a cam slider having a cam groove.