Image forming apparatus and assembly system of image forming apparatus

An image forming apparatus includes a sheet feed conveying unit having an outlet for a recording medium on one side; at least one image forming unit having an inlet for the recording medium on one side and an outlet for the recording medium on the other side; and a sheet eject conveying unit having an inlet for the recording medium on one side, wherein the sheet feed conveying unit, the image forming unit, and the sheet eject conveying unit are arranged along a conveying direction of the recording medium; the outlet of the sheet feed conveying unit matches the inlet of the image forming unit; the outlet of the image forming unit matches the inlet of the sheet eject conveying unit; and the sheet feed conveying unit, the image forming unit, and the sheet eject conveying unit are connected to each other in a separable manner.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inkjet type image forming apparatus for forming images on a sheet by jetting ink droplets from an inkjet head (hereinafter, also abbreviated as ink head).

2. Description of the Related Art

In recent years, inkjet type image forming apparatuses have been proposed, such as those described in patent documents 1 and 2. Patent document 1 describes an image forming apparatus including plural image forming units connected to each other. Each of the image forming units includes an inkjet engine for jetting ink droplets, which is removably attached to the image forming unit.

Patent document 2 describes an inkjet print system in which plural inkjet print units are disposed at predetermined intervals along a direction of conveying a continuous sheet, so that plural colors can be printed onto both sides of the continuous sheet. The inkjet print system detects marks formed along the continuous sheet, and starts the printing operation performed by the inkjet print units based on detection signals.

FIG. 18is a schematic diagram of the image forming apparatus described in patent document 1,FIG. 19is a perspective view of an image forming unit included in the image forming apparatus shown inFIG. 18, andFIG. 20is a perspective view of an inkjet engine installed in the image forming unit shown inFIG. 19.

The image forming apparatus shown inFIG. 19includes two image forming units101A and101B having substantially the same configuration, which are connected to each other. Each of the image forming units101A and101B includes an inkjet engine102, a sheet feeding cassette103, a supply conveying path104for supplying a recording sheet S in the sheet feeding cassette103to the inkjet engine102, and an eject conveying path105for conveying the recording sheet S on which an image has been formed out from the inkjet engine102.

As shown inFIG. 19, each of the image forming units101A and101B have a substantially cubical shape. A conveying inlet106for the recording sheet S is formed on one side of the image forming unit101B, and a conveying outlet (not shown) for the recording sheet S is formed on the other side of the image forming unit101B.

As shown inFIG. 18, an inkjet engine attachment part107is provided between the supply conveying path104and the eject conveying path105. The inkjet engine102can be removably attached to the inkjet engine attachment part107(seeFIG. 19). On one side of the inkjet engine102, there are provided ink cassettes108for separately storing yellow (Y), magenta (M), cyan (C), and black (K) ink. The ink cassettes108and the inkjet engine102are connected by an ink supplying path109(seeFIG. 18).

As shown inFIG. 20, the inkjet engine102includes a carriage110, a driving motor ill for moving the carriage110in a main scanning direction, a conveying belt112for conveying the recording sheet S, and conveying rollers113.

The carriage110includes ink heads (not shown) each having multiple jetting outlets on the bottom side, for the colors of yellow (Y), magenta (M), cyan (C), and black (K). The conveying belt112is rotated/driven by a driving motor114.

For example, inFIG. 18, the image forming unit101A is used to print line images, and the image forming unit101B located on the downstream side of the image forming unit101A is used to print character images, so that a complete image can be formed. In this manner, the printing operation can be divided between the image forming units101A and101B. Therefore, the printing operation can be accelerated and the degree of freedom in forming images can be enhanced.

In the market of inkjet printers, there is increasing demand for high printing speed, highly precise images, and high image quality, and this demand is made for various types (specifications) of printers. In order to manufacture different machine types to address each of the specifications, complex manufacturing operations and increased development costs for the different machine types will be required. In recent years, there is demand for an image forming apparatus in which functions can be easily expanded or changed. Furthermore, with the increase of printing speed, reduction of the machine downtime has been an issue.

In the image forming apparatus illustrated inFIGS. 18 through 20, units such as the inkjet engine102, the sheet feeding cassette103, the supply conveying path104, and the eject conveying path105are incorporated into a single body in each of the image forming units101. Thus, when considering the various specifications of the image forming apparatus as in the present invention described below, none of the units can be shared by other units in this image forming apparatus. For this reason, the functions cannot be easily expanded or changed.

SUMMARY OF THE INVENTION

The present invention provides an image forming apparatus and an assembly system of the image forming apparatus, in which one or more of the above-described disadvantages are eliminated.

A preferred embodiment of the present invention provides an image forming apparatus and an assembly system of the image forming apparatus, in which the functions can be expanded or changed in accordance with the specifications with a high degree of freedom, the machine downtime can be reduced, and development costs and manufacturing costs can be reduced.

According to another aspect of the present invention, there is provided an image forming apparatus including a sheet feed conveying unit having an outlet for a recording medium on one side; plural image forming units each having an inlet for the recording medium on one side and an outlet for the recording medium on the other side; and a sheet eject conveying unit having an inlet for the recording medium on one side, wherein the sheet feed conveying unit, the plural image forming units, and the sheet eject conveying unit are arranged along a conveying direction of the recording medium; the outlet of the sheet feed conveying unit matches the inlet of one of the plural image forming units located at a most upstream side in the conveying direction of the recording medium; the outlet of one of the plural image forming units located at an upstream side in the conveying direction of the recording medium matches the inlet of one of the plural image forming units located at a downstream side in the conveying direction of the recording medium; the outlet of one of the plural image forming units located at a most downstream side in the conveying direction of the recording medium matches the inlet of the sheet eject conveying unit; and the sheet feed conveying unit, the plural image forming units, and the sheet eject conveying unit are connected to each other in a separable manner.

According to another aspect of the present invention, there is provided an assembly system of an image forming apparatus in which a sheet feed conveying unit, one or more image forming units, and a sheet eject conveying unit are arranged along a conveying direction of a recording medium and connected to each other, wherein a single image forming unit, a twin image forming unit set, and a quadruple image forming unit set are prepared; the single image forming unit includes a first inkjet head filled with ink of a first color, a second inkjet head filled with ink of a second color that is different from the first color, a third inkjet head filled with ink of a third color that is different from the first color or the second color, and a fourth inkjet head filled with ink of a fourth color that is different from the first color, the second color, or the third color; the twin image forming unit set includes a first image forming unit including a first inkjet head filled with ink of a first color and a second inkjet head filled with ink of a second color that is different from the first color, and a second image forming unit including a third inkjet head filled with ink of a third color that is different from the first color or the second color and a fourth inkjet head filled with ink of a fourth color that is different from the first color, the second color, or the third color; the quadruple image forming unit set includes a first image forming unit including a first inkjet head filled with ink of a first color, a second image forming unit including a second inkjet head filled with ink of a second color that is different from the first color, a third image forming unit including a third inkjet head filled with ink of a third color that is different from the first color and the second color, and a fourth image forming unit including a fourth inkjet head filled with ink of a fourth color that is different from the first color, the second color, or the third color; and in accordance with a specification of the image forming apparatus to be assembled, one of the single image forming unit, the twin image forming unit set, or the quadruple image forming unit set is selected as the one or more image forming units, and the selected one or more image forming units is connected to the sheet feed conveying unit and the sheet eject conveying unit in a separable manner.

According to another aspect of the present invention, there is provided an assembly system of an image forming apparatus, the assembly system including the image forming apparatus including a sheet feed conveying unit, plural types of image forming units each including plural ink heads and color information sensors configured to detect colors of ink filled in the ink heads, and a sheet eject conveying unit, wherein the sheet feed conveying unit, one or plural image forming units selected from the plural types of image forming units, and the sheet eject conveying unit are arranged along a conveying direction of a recording medium and connected to each other in a separable manner; and a higher-level apparatus configured to exchange information with the image forming apparatus, wherein the assembly system sends, to the higher-level apparatus, information indicating a color arrangement of the one or plural image forming units detected by the color information sensors; compares the information indicating the color arrangement with color arrangement reference patterns corresponding to different specifications stored in advance in the higher-level apparatus to determine a specification of the image forming apparatus; and outputs driving control data corresponding to the specification of the image forming apparatus to the sheet feed conveying unit and the sheet eject conveying unit to drive/control the sheet feed conveying unit and the sheet eject conveying unit.

According to one embodiment of the present invention, a low-cost image forming apparatus and a low-cost assembly system of the image forming apparatus are provided, with which cost increases can be mitigated when developing multiple machine types, the functions can be expanded or changed in accordance with the specifications with a high degree of freedom, and the machine downtime can be reduced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description is given, with reference to the accompanying drawings, of an inkjet type image forming apparatus and an assembly system of the image forming apparatus according to embodiments of the present invention.

First Embodiment

FIG. 1is a schematic diagram of units of an image forming apparatus according to a first embodiment of the present invention.

The image forming apparatus according to the first embodiment is for forming images by an inkjet recording method.

As shown inFIG. 1, the image forming apparatus includes a sheet feed conveying unit2, plural types of image forming units3A through3C, and a sheet eject conveying unit4. When the image forming apparatus is shipped from the factory or upgraded at the user's site, necessary units are selected from the image forming units3A through3C in accordance with the specification, and a combination of the selected units configure the image forming apparatus. The sheet feed conveying unit2and the sheet eject conveying unit4are commonly used in all of the image forming apparatuses.

Inside the sheet feed conveying unit2, an in feed roller5, a nip roller6, plural guide rollers7, and a motor (not shown) for driving the in feed roller5are provided. A web outlet8is formed on one side of the sheet feed conveying unit2, and casters9with stoppers are provided on the bottom side of the sheet feed conveying unit2. The sheet feed conveying unit2includes various function units such as a web meander correction mechanism, a web discharging mechanism, and a web cleaning mechanism, but these units are not shown as they are not directly related to the present invention.

In the present embodiment, two types of image forming units3are provided; the image forming units3A and3B correspond to the first type and the image forming unit3C corresponds to the second type. The two types of image forming units have the same structure. That is, inside each of the image forming units3A through3C, a cassette attachment part11for attaching four ink cassettes10at the top of each unit, four ink heads12installed at the bottom of the cassette attachment part11, plural platen rollers13for conveying/guiding a web1depicted inFIG. 2so that the web1passes under the ink heads12, an ink receiver14for receiving ink used for test-jetting, and an ink supplying path (not shown) for supplying ink inside the ink cassettes10to the ink heads12are provided.

A web inlet15is formed on one side of the image forming unit3, a web outlet16is formed on the opposite side of the image forming unit3, and casters17with stoppers are provided on the bottom side of the image forming unit3.

The image forming units3A and3B are used together as a set. In the image forming unit3A, two of each of the ink cassettes10storing yellow (Y) ink and the ink cassettes10storing magenta (M) ink are arranged, and two of each of the ink heads12for yellow (Y) ink and the ink heads12for magenta (M) ink are arranged. In the image forming unit3B, two of each of the ink cassettes10storing cyan (C) ink and the ink cassettes10storing black (K) ink are arranged, and two of each of the ink heads12for cyan (C) ink and the ink heads12for black (K) ink are arranged.

Meanwhile, in the image forming unit3C, one of each of the ink cassette10storing yellow (Y) ink, the ink cassette10storing magenta (M) ink, the ink cassette10storing cyan (C) ink, and the ink cassette10storing black (K) ink are arranged, and one of each of the ink head12for yellow (Y) ink, the ink head12for magenta (M) ink, the ink head12for cyan (C) ink, and the ink head12for black (K) ink are arranged.

Inside the sheet eject conveying unit4, an out feed roller18, a nip roller19, plural guide rollers20, and a motor (not shown) for driving the out feed roller18are provided.

A web inlet21is formed on one side of the sheet eject conveying unit4, and casters22with stoppers are provided on the bottom side of the sheet eject conveying unit4. The sheet eject conveying unit4also includes units such as a drying unit for drying the ink; however, these units are not directly related to the present invention, and thus are not shown.

A height H1from a floor23to the web outlet8of the sheet feed conveying unit2, and a height H2of the web inlet15of the image forming unit3A adjacent to the sheet feed conveying unit2, are substantially equal (H1≈H2). A height H3of the web outlet16of the image forming unit3A, and a height H4of the web inlet15of the image forming unit3B, are substantially equal (H3≈H4). A height H5of the web outlet16of the image forming unit3B, and a height H8of the web inlet21of the sheet eject conveying unit4, are substantially equal (H5≈H8). The height H1of the web outlet8of the sheet feed conveying unit2, and a height H6of the web inlet15of the image forming unit3C, are substantially equal (H1≈H6). A height H7of the web outlet16of the image forming unit3C, and the height H8of the web inlet21of the sheet eject conveying unit4, are substantially equal (H7≈H8). All of the heights H1through H8may be substantially equal (H1≈H2≈H3≈H4≈H5≈H6≈H7≈H8).

In order to configure an image forming apparatus having a one-line configuration, the sheet feed conveying unit2and the sheet eject conveying unit4are combined, with the image forming units3disposed therebetween. The following parts are provided for the purpose of determining the positions of units when combining them together. Specifically, protrusion parts24A and24B are respectively formed on the sides of the sheet feed conveying unit2and the sheet eject conveying unit4that are joined with the image forming units3. Recess parts or holes (not shown) for fitting in the protrusion parts24A and24B are respectively formed on the sides of the image forming units3that are joined with the sheet feed conveying unit2and the sheet eject conveying unit4. Conversely, protrusion parts may be formed on the sides of the image forming units3, and recess parts or holes may be formed on the sheet feed conveying unit2and the sheet eject conveying unit4.

FIG. 2is a schematic diagram of an image forming apparatus according to a first specification. In an image forming apparatus201according to this specification, a unit assembly of the image forming units3A and3B is disposed between the sheet feed conveying unit2and the sheet eject conveying unit4. As shown inFIG. 2, the sheet feed conveying unit2, the image forming unit3A, the image forming unit3B, and the sheet eject conveying unit4are arranged in this order along a conveying direction (indicated by an arrow) of the web1. The relative positions of the units are determined, and the units are connected to each other with bolts and nuts (in a separable manner), so that adjacent web outlets and web inlets match each other.

The web1is a long, continuous sheet that is in a form of a roll. The web1is conveyed from the sheet feed conveying unit2to the image forming units3A and3B at a high speed of, for example, 150 m/min., by the collaboration of the in feed roller5and the nip roller6of the sheet feed conveying unit2. The ink color arrangement in the image forming unit3A is Y-Y-M-M along the conveying direction of the web1, and the ink color arrangement in the image forming unit3B is C-C-K-K along the conveying direction of the web1. That is, in each of the image forming units3A and3B, two ink heads12are provided for each of two colors. Furthermore, inside each of the image forming units3A and3B, a mechanism for supplying the ink from each ink cassette10to the corresponding ink head12, and ink paths are provided.

FIG. 3illustrates the connection relationship between the ink cassettes10and the ink heads12in the image forming apparatus201. In the image forming apparatus201, the ink color arrangement of the ink heads12is Y-Y-M-M, C-C-K-K along the conveying direction of the web1, and similarly, the ink color arrangement of the ink cassettes10is Y-Y-M-M, C-C-K-K. Accordingly, two of the ink cassettes10and two of the ink heads12of the same color are disposed close to each other.

As shown inFIG. 3, two ink supplying paths25A and25B extend from a first Y ink cassette10A, and connect with a first Y ink head12A and a second Y ink head12B. Two ink supplying paths25C and25D extend from a second Y ink cassette10B, and connect with the first Y ink head12A and the second Y ink head12B.

With such a configuration, the ink cassettes10A and10B can be shared by the first Y ink head12A and the second Y ink head12B, and therefore even when the ink cassette10A becomes empty, ink can be supplied from the other ink cassette10B, so that the printing operation can be continued. Accordingly, the machine downtime can be reduced.

The connections between the ink cassettes10and the ink heads12for M, C, and K are the same as that of Y as shown inFIG. 3, and are thus not further described. InFIG. 3, valves are provided in the ink supplying paths and level sensors and empty sensors are provided in the ink cassettes10for detecting the remaining amount of ink; however, these elements are not shown as a matter of simplification.

The web1on which a color image has been formed by the image forming units3A and3B, is ejected from the sheet eject conveying unit4by the collaboration of the out feed roller18and the nip roller19. Then, the web1may be rolled, folded, or cut into sheets according to the final product. While the web1is being conveyed from the sheet feed conveying unit2to the sheet eject conveying unit4, predetermined tension is applied to the web1by a tension applying unit (not shown) for preventing the web1from flapping.

When the web1is being conveyed along the path extending from the sheet feed conveying unit2to the sheet eject conveying unit4through the image forming units3, predetermined tension is applied to the web1, and the web1is guided so as to pass through the image forming units3at a higher position than the position at which the web1passes through the sheet feed conveying unit2and the sheet eject conveying unit4. Accordingly, the web1certainly comes in contact with the platen rollers13. The positions of the platen rollers13can be adjusted in the vertical direction perpendicular to the conveying direction of the web1. Therefore, in accordance with the number of connected image forming units3and the extent of the tension, the positions of the platen rollers13are adjusted in the vertical direction so that the web1certainly comes in contact with the platen rollers13. The platen rollers13are adjusted in the vertical direction by, for example, screws and springs. The image forming apparatuses described below also have the same configuration as that described above.

The web1having tension applied thereto certainly comes in contact with the platen rollers13, and therefore the web1is prevented from flapping and the precision of the gap between the ink heads12and the web1is improved (maintained). Accordingly, the ink lands at highly precise positions so that high-quality images can be formed.

FIG. 4is a schematic diagram of an image forming apparatus according to a second specification. In an image forming apparatus202according to this specification, one image forming unit3C is disposed between the sheet feed conveying unit2and the sheet eject conveying unit4. As shown inFIG. 4, the sheet feed conveying unit2, the image forming unit3C, and the sheet eject conveying unit4are arranged in this order along the conveying direction of the web1. The relative positions of the units are determined, and the units are connected to each other with bolts and nuts (in a separable manner), so that adjacent web outlets and web inlets match each other.

The ink color arrangement of the ink heads12is Y-M-C-K along the conveying direction of the web1, and similarly, the ink color arrangement of the ink cassettes10is Y-M-C-K. Accordingly, the ink cassettes10and the ink heads12of the same color are disposed close to each other.

FIG. 5is a schematic diagram of an image forming apparatus according to a third specification. In an image forming apparatus203according to this specification, two image forming units3C are disposed between the sheet feed conveying unit2and the sheet eject conveying unit4. As shown inFIG. 5, the sheet feed conveying unit2, the first image forming unit3C, the second image forming unit3C, and the sheet eject conveying unit4are arranged in this order along the conveying direction of the web1. The relative positions of the units are determined, and the units are connected to each other with bolts and nuts (in a separable manner), so that adjacent web outlets and web inlets match each other.

When the two image forming units3C and3C have the same color arrangement, i.e., Y-M-C-K and Y-M-C-K as shown inFIG. 5, and an ink cassette10of a certain color is to be shared by two ink heads12, one of the ink paths may need to be extended or cross-over to the other image forming unit3C, and therefore the ink paths may be connected in a complex manner. This disadvantage can be overcome by applying the specification as illustrated inFIGS. 2 and 3.

In each of the image forming apparatuses illustrated inFIGS. 1 through 5, a roll attaching unit for attaching a roll of the web1before image formation is provided separately from the sheet feed conveying unit2. However, the roll attaching unit may be provided in the sheet feed conveying unit2. Furthermore, in the above-described image forming apparatuses, a post-process mechanism for performing a post-process on the web1after image formation, is provided separately from the sheet eject conveying unit4. However, the post-process mechanism may be provided in the sheet eject conveying unit4.

Second Embodiment

FIG. 6is a schematic diagram of units of an image forming apparatus according to a second embodiment of the present invention. In an image forming apparatus204according to the present embodiment, in between the sheet feed conveying unit2and the sheet eject conveying unit4, an image forming unit3D corresponding to special colors used by the user is disposed in addition to the image forming units3A and3B. In the present embodiment, the image forming unit3D of the special colors is disposed on the downstream side of the image forming units3A and3B in the web conveying direction. By using such an image forming unit3D of special colors, a diverse range of colors can be used, thereby forming images of higher quality.

When an increased number of image forming units3are disposed between the sheet feed conveying unit2and the sheet eject conveying unit4, the web1may not contact the platen rollers13or may not stably contact the platen rollers13in one of the image forming units3. In order to overcome this disadvantage, in the present and subsequent embodiments, the vertical positions of the platen rollers13in each of the image forming units3are adjusted so that the trajectory of the web1conveyed through the image forming units3forms a circular arc with the middle portion protruding upward, as shown inFIG. 6.

Third Embodiment

FIG. 7is a schematic diagram of units in an image forming apparatus according to a third embodiment of the present invention. In an image forming apparatus205according to the present embodiment, four image forming units3E through3H are disposed between the sheet feed conveying unit2and the sheet eject conveying unit4.

The ink color arrangement of the ink heads12in the image forming unit3E is Y-Y-Y-Y, the ink color arrangement of the ink heads12in the image forming unit3F is M-M-M-M, the ink color arrangement of the ink heads12in the image forming unit3G is C-C-C-C, and the ink color arrangement of the ink heads12in the image forming unit3H is K-K-K-K, i.e., four ink heads12are provided for each color. The printing speed of the image forming apparatus205according to the present embodiment is set at approximately 210 m/min.

Although not shown, in the image forming apparatus205according to the present embodiment, an ink cassette10of a certain color is shared by two ink heads12, and the ink supplying paths between the ink cassettes10and the ink heads12are substantially the same as those shown inFIG. 3.

With respect to the image forming apparatus202shown inFIG. 4, the image forming apparatus201shown inFIG. 2has two times as many ink heads12of the same color, and the image forming apparatus205shown inFIG. 7has four times as many ink heads12of the same color. Therefore, assuming that the printing resolution in the web conveying direction is the same, theoretically, the printing speed of the image forming apparatus201is two times as fast as that of the image forming apparatus202, and the printing speed of the image forming apparatus205is four times as fast as that of the image forming apparatus202.

Accordingly, for a user that does not require such a high printing speed (for example, when the desired speed is approximately 70 m/min.), the image forming apparatus202shown inFIG. 4may be provided, so that the cost and space used can be reduced. Meanwhile, for a user that desires a high printing speed (for example, when the desired speed is approximately 150 m/min. or 210 m/min.), the image forming apparatus201shown inFIG. 2, the image forming apparatus203shown inFIG. 5, or the image forming apparatus205shown inFIG. 7may be provided according to the desired specifications.

Furthermore, when the user using the image forming apparatus202desires a higher printing speed, additional image forming units3may be selected and connected, while using the same sheet feed conveying unit2and sheet eject conveying unit4. Accordingly, the image forming apparatus202can be upgraded to any of the image forming apparatuses201,203, and205. In this case, there is no need for replacing the entire apparatus. Therefore, costs can be reduced, the time required for installment can be reduced, the machine downtime can be reduced, and the degree of freedom can be enhanced in expanding and changing the functions in accordance with the specifications.

As shown inFIGS. 2,4, and7, the same ink color arrangement information (order of printing colors) is used when one image forming unit3is provided and when plural image forming units3are provided (in the above embodiment, the order is Y, M, C, and K). Accordingly, the appropriate printing color order can be maintained in consideration of image quality, and a common color imaging process can be performed when one image forming unit3is provided and when plural image forming units3are provided.

Next, the precision of relative positions of the ink heads12of the same color is described with reference toFIGS. 8 and 9.FIG. 8is a schematic diagram illustrating the nozzle surfaces of the ink heads12used in the image forming apparatus201shown inFIG. 2. As shown inFIG. 8, the first Y ink head12A and the second Y ink head12B are fixed adjacent to each other in parallel, on a single base26A. In each ink head12, multiple nozzles27are arranged along a width direction (main scanning direction) that is perpendicular to the conveying direction of the web1, thereby configuring a line head.

The position of each ink head12with respect to the base26may determined by fitting together surfaces that have been worked for the purpose of positioning, or fitting positioning pins into positioning holes (not shown). In the case ofFIG. 8, the ink heads12of the same color are juxtaposed and fixed on the same base26A, and therefore relative positional errors between the nozzles27of the first Y ink head12A and the second Y ink head12B can be prevented. As a result, the positional errors δ between the nozzles27in the main scanning direction (width direction of web1) are reduced. The same applies to the relationships between the other ink heads12.

FIG. 9is a schematic diagram illustrating the nozzle surfaces of the ink heads12used in the image forming apparatus202shown inFIG. 4. As shown inFIG. 9, the first Y ink head12A is fixed on one base26A, while the second Y ink head12B is fixed on the other base263. Therefore, the positional error δ′ between the base26A and the base26B is added, consequently increasing the positional errors δ between the nozzles27in the main scanning direction. The same applies to the relationships between the other ink heads12.

When the temperature in the apparatus increases due to continuous printing, the larger the interval between the ink heads12A and12B, the larger the differences in temperature and in thermal expansion between the ink heads12A and12B. As a result, the positional errors δ in the main scanning direction are apt to increase.

InFIG. 8, the positional errors in the main scanning direction between the nozzles27of the ink heads12of the same color are small, and therefore compensatory effects can be expected. For example, among two nozzles27on the same line in the main scanning direction, one of the nozzles27may become unable to strike a pixel while the other nozzle27strikes a corresponding pixel. In this case, nozzles27of different ink heads12will be used to strike adjacent pixels, but the pitch error between these pixels can be mitigated.

Furthermore, two different nozzles27can be used to strike liquid droplets at the same pixel position, so that multi-valued liquid droplets can be provided. For example, assuming that each of the nozzles can strike liquid droplets of two different sizes (large and small), and two different nozzles27are used to strike the same pixel, the sizes of the liquid droplets jetted from the nozzles27can be controlled (for example, large-large, large-small (small-large), and small-small). Accordingly, the sizes of the pixels can be optionally controlled.

The above description is given for the main scanning direction; the same applies to the sub scanning direction. Accordingly, with the ink color arrangement ofFIG. 8, higher precision can be achieved and images of higher quality can be recorded, compared to that ofFIG. 9.

In the above examples, each ink head12corresponds to one color, and different ink color arrangements may be provided by switching the positions of the ink heads12. In another example, there may be ink heads each including plural nozzle rows (for example, four rows) and image forming units having separate ink supplying paths for each of the nozzle rows. In this case, the ink color arrangement can be changed in units of nozzle rows in each ink head to achieve the same effects as the above examples.

Fourth Embodiment

FIG. 10illustrates a modification (fourth embodiment) of the connection relationship between the ink cassettes10and the ink heads12shown inFIG. 3.

This modification is described by taking as an example the ink supplying path for yellow (Y). First and second Y sub ink cassettes28A and28B are disposed between the first and second Y ink cassettes10A and10B and the first and second Y ink heads12A and12B.

A first ink supplying path29A extends from the first Y ink cassette10A and branches midway to connect to the first and second Y sub ink cassettes28A and28B which then connects to the first and second Y ink heads12A and12B. Valves30are provided on the branched supplying paths. Similarly, a second ink supplying path29B extends from the first Y ink cassette10A and branches midway to connect to the first and second Y sub ink cassettes28A and28B which then connects to the first and second Y ink heads12A and12B. The valves30are provided on the branched supplying paths.

Furthermore, a third ink supplying path29C extends from the first Y sub ink cassette28A to the first Y ink head12A, and a fourth ink supplying path29D extends from the second Y sub ink cassette28B to the second Y ink head12B.

Ink cassette empty sensors31are provided in the Y ink cassettes10A and10B. Sub ink cassette level sensors32(for detecting remaining amount) and sub ink cassette empty sensors33are provided in the Y sub ink cassettes28A and28B.

For example, when the sub ink cassette level sensor32detects that the remaining amount of ink is small as shown in the first Y sub ink cassette28A, the corresponding valve30is opened so that ink can be supplied from the Y ink cassette10A.FIG. 10illustrates a state where ink is supplied to the first Y sub ink cassette28A. Accordingly, the valve30on the far right is open, while the other valves30are closed.

Furthermore, when the ink cassette empty sensor31detects that the ink cassette is empty as shown in the first Y ink cassette10A, the ink cassette to be used is switched to another ink cassette of the same color (in this case, the second Y ink cassette10B). With regard to the empty ink cassette (in this case, the first Y ink cassette10A), an empty alarm is displayed on an operations panel (not shown) of the image forming apparatus. The operator replaces the first Y ink cassette10A with a new one in response to this alarm.

Each ink cassette is continuously used until it becomes empty. That is, the ink cassettes of the same color are sequentially used until each are finished. For example, even after the empty state of an ink cassette (first Y ink cassette10A) has been cancelled by replacing it with a new one, the new one will not be used unless the ink cassette that is presently used for supplying ink (second Y ink cassette10B) becomes empty.

By sequentially switching the ink cassette to be used for supplying ink, it is possible to prevent plural (all of the) ink cassettes from becoming empty at the same time. Therefore, it is possible to minimize situations where the printing operation stops because of empty ink cassettes. Accordingly, the machine downtime can be reduced.

Even when all of the ink cassette empty sensors31of the same color detect ink cassette empty states, as long as there is ink of the same color in the sub ink cassette28, compensatory printing can be performed by decreasing the printing speed.

When all of the ink cassette empty sensors31and all of the sub ink cassette empty sensors33of the same color detect ink cassette empty states, an ink empty error (stop printing) is displayed on the operations panel of the image forming apparatus, and the printing operation of the image forming apparatus is automatically stopped.

Fifth Embodiment

FIG. 11is a schematic diagram of an image forming apparatus according to a fifth embodiment of the present invention.FIG. 12is a block diagram indicating the relationships between the image forming units and a higher-level device.

As shown inFIG. 12, each of the ink cassettes10includes a chip34recording color information of the ink stored in the corresponding cassette. Furthermore, a color information detecting sensor35is set in advance at a position that is near/faces the chip34when the ink cassette10is attached to the cassette attachment part11of the image forming apparatus.

The means for detecting color information is not limited to a chip. Various methods are applicable, such as a method of detecting the color of the ink or the color of the label of the ink cassette, and a method of forming the ink cassettes so as to have different shapes according to the colors and detecting the differences in the shapes with a photo sensor or a micro switch.

In the present embodiment, four ink cassettes10storing yellow (Y) ink can be attached in the first image forming unit3E, four ink cassettes10storing magenta (M) ink can be attached in the second image forming unit3F, four ink cassettes10storing cyan (C) ink can be attached in the third image forming unit3G, and four ink cassettes10storing black (K) ink can be attached in the fourth image forming unit3H.

Each color information detecting sensor35detects whether the ink cassette10has been attached/detached, and detects the color information of the chip34. It can be determined whether the ink cassette10has been attached/detached according to a detection signal from the color information detecting sensor35. In the present embodiment, the color information detecting sensor35also serves as a detection sensor for detecting whether the ink cassette10has been attached/detached. However, another sensor can be provided for detecting whether the ink cassette10has been attached/detached. The number of components and costs can be reduced by having the color information detecting sensor35serve as both a color sensor and a sensor for detecting whether the ink cassette10has been attached/detached, as described in the present embodiment.

Information from the color information detecting sensor35is first stored in a data processing unit39provided in each image forming unit3. Based on the stored color information, ink color arrangement information for the corresponding image forming unit3is created. For example, when four ink cassettes10storing yellow (Y) ink are normally attached in the first image forming unit3E, the ink color arrangement information is Y-Y-Y-Y; however, when an ink cassette10storing ink of a different color is erroneously attached, the ink color arrangement information will be, for example, Y-M-Y-Y. Information indicating whether the ink cassette10has been attached/detached and ink color arrangement information is sent from the data processing unit39to a higher-level apparatus36, starting from the first image forming unit3E.

In the higher-level apparatus36, based on the ink color arrangement information and the printing data, separate driving control data items are created for the each of the image forming units3, and the created driving control data items are sent to each of the image forming units3. In each of the image forming units3, the ink heads12are driven based on the corresponding driving control data item to jet ink droplets onto a conveyed web1, thereby forming a color image with the ink droplets that have landed on the conveyed web1.

When the ink color arrangement information received by the higher-level apparatus36is Y-M-C-K, the higher-level apparatus36determines that the ink color arrangement information corresponds to a specification of the image forming apparatus202(seeFIG. 4) in which only one image forming unit3is connected. Accordingly, the higher-level apparatus36creates driving control data corresponding to this specification, and sends the driving control data to the image forming unit3.

When the ink color arrangement information received by the higher-level apparatus36is Y-Y, M-M, C-C, K-K, the higher-level apparatus36determines that the ink color arrangement information corresponds to a specification of the high-speed image forming apparatus201(seeFIG. 2) in which two image forming units3are connected. Accordingly, the higher-level apparatus36creates driving control data corresponding to this specification, and sends the driving control data to the image forming units3.

When the ink color arrangement information received by the higher-level apparatus36is Y-Y-M-M, C-C-K-K, S1-S1-S2-S2, the higher-level apparatus36determines that the ink color arrangement information corresponds to a specification of the image forming apparatus204(seeFIG. 6) in which an image forming unit3of a special color is connected. Accordingly, the higher-level apparatus36creates driving control data corresponding to this specification, and sends the driving control data to the image forming units3.

When the ink color arrangement information received by the higher-level apparatus36is Y-Y-Y-Y, M-M-M-M, C-C-C-C, K-K-K-K, the higher-level apparatus36determines that the ink color arrangement information corresponds to a specification of the super high-speed image forming apparatus205(seeFIG. 7) in which four image forming units3are connected. Accordingly, the higher-level apparatus36creates driving control data corresponding to this specification, and sends the driving control data to the image forming units3.

In embodiments of the present invention, the printing speed is divided into three levels, i.e., low speed (for example, 70 m/min.), high speed (for example, 150 m/min.), and super high speed (for example, 210 m/min.).

The sheet feed conveying unit2and the sheet eject conveying unit4are controlled by the higher-level apparatus36, and the in feed roller5and the out feed roller18are controlled so that the web1is conveyed at a speed corresponding to each of the specifications.

The image forming apparatus according to an embodiment of the present invention may have various specifications according to the number of connected image forming units3. The color information of the ink filled in the ink heads12does not need to be set in the higher-level apparatus36when the image forming apparatus is shipped from the factory or upgraded at the user's site. Accordingly, working hours can be reduced.

In the embodiment illustrated inFIGS. 11 and 12, the information items of the image forming units3are separately sent to the higher-level apparatus36. Thus, each image forming unit3has a single output connector, and the higher-level apparatus36has plural input connectors (four in the case ofFIG. 11) corresponding to the number of connected image forming units3. The higher-level apparatus36can analyze the received information to recognize the ink color arrangement information of the image forming units3and the specifications of the image forming apparatus.

The sheet feed conveying unit2and the sheet eject conveying unit4send, to the higher-level apparatus36, information pertaining to the web1such as information indicating whether the web1is present (whether the web1is set, whether a paper jam has occurred), information indicating the width size of the web1, information indicating the thickness of the web1, information indicating the position (edges) of the web1(in the scanning direction), and information indicating the conveying speed of the web1, as well as error information indicating a failure of the corresponding device or line disconnection.

As described above, each image forming unit3only needs to be provided with one connector for outputting information to the higher-level apparatus36, and therefore the configuration and control circuit are simple and costs can be reduced. Furthermore, the image forming units3have the same information transmitting system, and therefore development costs can be reduced.

Sixth Embodiment

FIG. 13is a schematic diagram of an image forming apparatus according to a sixth embodiment of the present invention.FIG. 14is a block diagram indicating the relationship between the image forming units and a higher-level device. The difference between the sixth embodiment and the fifth embodiment shown inFIG. 11is that in the sixth embodiment, the information items of the image forming units3are transmitted among the image forming units3and collected in one of the image forming units3. Then, the collected information items are transmitted to the higher-level apparatus36from one of the image forming units3.

In the present embodiment, the information of the image forming unit3H is sent to the image forming unit3G, and the image forming unit3G stores this information in a memory in its data processing unit39. The image forming unit3G sends the information of the image forming units3H and3G to the image forming unit3F, and the image forming unit3F stores this information in a memory in its data processing unit39. The image forming unit3F sends the information of the image forming units3H,3G, and3F to the image forming unit3E, and the image forming unit3E stores this information in a memory in its data processing unit39. The image forming unit3E collects all the information including its own, analyzes the information, recognizes attachment/detachment information, color arrangement information, and the specification of the image forming apparatus, and then sends this information to the higher-level apparatus36.

In the present embodiment, information is sequentially added starting from the image forming unit3H, the information is collected in the image forming unit3E, and the collected information is sent to the higher-level apparatus36. In another example, at the same time as sending the information of the image forming unit3H to the image forming unit3G, the information of the image forming unit3E may be sent to the image forming unit3F. Then, the image forming unit3F incorporates the information of itself into the information of the image forming unit3E and sends this information to the image forming unit3G. The image forming unit3G collects the information including the information of itself, and sends the collected information to the higher-level apparatus36. Accordingly, the information can be sent in a parallel manner.

Seventh Embodiment

FIG. 15is a schematic diagram of an image forming apparatus according to a seventh embodiment of the present invention. In the present embodiment, the information is sequentially added starting from the sheet eject conveying unit4disposed on the far downstream end in the web1conveying direction. The information is collected at the sheet feed conveying unit2disposed on the far upstream end in the web1conveying direction. The collected information is sent to the higher-level apparatus36.

Transmission of the information is not so limited. For example, the information may be collected in the order of the sheet eject conveying unit4, the image forming unit3H, and the image forming unit3G, and at the same time, the information may be collected in the order of the sheet feed conveying unit2, the image forming unit3E, and the image forming unit3F. Then, the information may be collected at the image forming unit3F or the image forming unit3G, and the collected information may be sent from the image forming unit3F or the image forming unit3G to the higher-level apparatus36. Accordingly, the information can be sent in a parallel manner.

In the sixth and seventh embodiments, information can be sent among the image forming units3by providing input/output connecters in each of the image forming units3and connecting the connectors with signal lines, or by providing input/output connecters on the side surfaces of each of the image forming units3and directly fitting together (inserting) the connectors.

In the sixth and seventh embodiments, test printing can be performed for the purpose of recognizing and determining the specifications of the image forming apparatus, even when there is no higher-level apparatus. Accordingly, maintenance properties can be improved. Furthermore, wires used for sending information can be shortened, thereby reducing cost and eliminating complex wiring.

In the image forming system according to an embodiment of the present invention, the patterns of the ink color arrangement information of the image forming units3may correspond to various specifications according to the connected image forming units3. Thus, predefined color arrangement reference patterns of different specifications (different machine types) are stored in the memory of the higher-level apparatus36in advance. Examples of the arrangement reference patterns are Y-M-C-K, Y-Y-M-M, C-C-K-K, Y-Y-Y-Y, M-M-M-M, C-C-C-C, K-K-K-K.

The ink color arrangement information sent from the image forming apparatus is compared with color arrangement reference patterns at the higher-level apparatus36. When the ink color arrangement information is different from the color arrangement reference patterns, or when the ink cassettes10are not attached to the cassette attachment parts11, an error is displayed (see, for example,FIG. 12) to send a notice to the operator, and the printing operation is automatically stopped.

Accordingly, when the image forming apparatus is shipped from the factory or upgraded at the user's site, it is possible to prevent paper sheets from being wasted as a result of printing errors due to erroneous ink color arrangements (the ink cassettes10are attached to wrong positions) or erroneous wiring, and to reduce the time required for recovering from failures. Accordingly, costs can be reduced and the productivity can be enhanced.

FIGS. 16 and 17respectively show a schematic top view and a schematic side view of the image forming apparatus shown inFIG. 10.

InFIGS. 16 and 17,37denotes a power source and38denotes a maintenance mechanism provided on the rear side of the image forming apparatus. As indicated by an arrow, the base26provided with plural ink heads12is configured to move back-and-forth between a printing position facing the web1and the platen rollers13, and a standby position facing the maintenance mechanism38. When maintenance operations are to be performed for the ink heads12(e.g., wiping the ink heads12and detecting ink jetting properties), the ink heads12(base26) move toward the maintenance mechanism38. This configuration is also provided in other image forming apparatuses.

In the above embodiments, regular ink is used in the ink-jet type image forming apparatus; however, the present invention is not so limited. For example, the present invention is also applicable to another type of image forming apparatus, such as an ultraviolet curing ink-jet type image forming apparatus that uses ultraviolet curing type ink. In this case, it is necessary to provide an ultraviolet ray emitting unit for curing the ink by radiating ultraviolet rays toward the downstream side of the ink heads in the web conveying direction.

In the above embodiments, the image forming apparatus forms images on one side of the recording medium such as a web; however, the present invention is not so limited. For example, the present invention is also applicable to an image forming apparatus that forms images on both sides of the recording medium with a reverse mechanism provided on the conveying path of the recording medium such as a web for reversing the recording medium.

In the above embodiments, an ink-jet type image forming apparatus is described; however, the present invention is not so limited. The present invention is also applicable to other image forming apparatuses such as an electrophotographic image forming apparatus.

The present application is based on Japanese Priority Patent Application No. 2008-281845, filed on Oct. 31, 2008, the entire contents of which are hereby incorporated herein by reference.