Patent Description:
Conventionally, there is known an inkjet printing apparatus that prints an image on a transparent base material by ejecting an ink from a head while conveying the transparent base material. This type of inkjet printing apparatus is used, for example, in the process of manufacturing labels for beverage PET bottles and soft packaging materials. Conventional inkjet printing apparatuses that perform printing on a transparent base material are described in Patent Literatures <NUM> and <NUM>, for example.

Further prior art is known from <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>.

In the process of manufacturing labels and soft packaging materials, it is required to inspect whether or not there is a defect in a printed image after the printed image is printed on a transparent base material. Examples of the types of defects include missing of a portion of a printed image due to clogging of a nozzle or the like, misalignment of a printed image with respect to a transparent base material, dirt due to unnecessary dropping of an ink from the nozzle, and adhesion of foreign matter to the transparent base material.

When a printed image on a transparent base material is inspected, conventionally, in a state where a background plate is disposed on one side of the base material, the base material is imaged while light is emitted from the other side of the base material. Then, the defect is detected by comparing the image obtained by imaging with a normal image. However, in this method, the shadow of the printed image itself is generated on the background plate due to light emission. Therefore, it is necessary to suppress sensitivity of the inspection so as to prevent the shadow from being erroneously detected. Therefore, it is difficult to accurately inspect a printed image printed on a surface of a transparent base material.

Furthermore, conventionally, the color of the background plate is white. However, in printing on a transparent base material, there are cases where not only so-called process color inks such as cyan, magenta, yellow, and black and so-called spot-color inks such as purple/violet and green, but also a white ink are used. In a conventional inspection, it is difficult to accurately distinguish the white background plate and an image formed by the white ink. Therefore, it is difficult to accurately inspect a printed image printed on a surface of a transparent base material.

The present invention has been made in view of these circumstances, and an object of the present invention is to provide an inspection device, and an inspection method capable of accurately inspecting a printed image printed on a surface of a transparent base material.

The above object is achieved by the subject-matters of the independent claims. Preferred embodiments are subject-matters of the dependent claims.

A first aspect of the invention of the present application is the inspection device according to claim <NUM>.

Preferred embodiments of the first aspect of the invention are described by the dependent claims.

A second aspect of the invention of the present application is the inspection method of claim <NUM>.

According to the invention, the first light-emitting unit and the imaging unit are disposed on opposite sides of the transparent base material. As a result, it is possible to suppress generation of the shadow of the printed image itself in the captured image. Therefore, the printed image can be accurately inspected based on the obtained captured image.

According to the invention of the present application, the process-color image covered with the white non process-color image can be satisfactorily imaged with emitted light from the second light-emitting unit.

Hereinafter, embodiments of the present invention will be described with inspecting quality of the printed image based on a captured image obtained in the process a), in which the color of the background plate is a color different from any of the plurality of process colors and the non-process color.

Note that, below, the direction orthogonal to the conveyance direction of a transparent base material and along the surface of the transparent base material is referred to as a "main scanning direction". Furthermore, the conveyance direction of the transparent base material is referred to as a "sub scanning direction".

<FIG> is a diagram illustrating a configuration of an inkjet printing apparatus <NUM> according to a first embodiment of the present invention. The inkjet printing apparatus <NUM> is an apparatus that prints a multicolor image on a surface of the transparent base material <NUM> having a long band shape by an inkjet method while conveying the transparent base material <NUM>. As the transparent base material <NUM>, for example, a colorless and transparent resin film is used. The transparent base material <NUM> after printing is cut into a label for a beverage PET bottle, for example.

As illustrated in <FIG>, the inkjet printing apparatus <NUM> includes a conveyance mechanism <NUM>, a first printing unit <NUM>, a first drying unit <NUM>, a second printing unit <NUM>, a second drying unit <NUM>, an image acquisition unit <NUM>, and a control unit <NUM>.

The conveyance mechanism <NUM> is a mechanism that conveys the transparent base material <NUM> in the sub scanning direction, which is the longitudinal direction thereof. The conveyance mechanism <NUM> according to the present embodiment includes an unwinding unit <NUM>, a plurality of conveyance rollers <NUM>, and a winding unit <NUM>. The transparent base material <NUM> is unwound from the unwinding unit <NUM> and is conveyed along a conveyance path configured by a plurality of conveyance rollers <NUM>. Each conveyance roller <NUM> rotates about a horizontal axis to guide the transparent base material <NUM> to the downstream side of the conveyance path. Furthermore, the transparent base material <NUM> after having been conveyed is collected by the winding unit <NUM>.

As illustrated in <FIG>, the transparent base material <NUM> moves substantially horizontally at the location under the first printing unit <NUM> and the second printing unit <NUM>. At this time, the print surface of the transparent base material <NUM> is faced up. The transparent base material <NUM> is stretched over the plurality of conveyance rollers <NUM> in a tensioned state. As a result, loosening and a wrinkle of the transparent base material <NUM> during conveyance are suppressed.

The first printing unit <NUM> is a processing unit that ejects so-called process color inks onto the transparent base material <NUM> conveyed by the conveyance mechanism <NUM>. The first printing unit <NUM> of the present embodiment includes four heads <NUM>. The heads <NUM> eject ink droplets of cyan, magenta, yellow, and black, which are process colors, onto the print surface of the transparent base material <NUM>, respectively. Each head <NUM> is fixed to a housing (not illustrated) of the inkjet printing apparatus <NUM>.

<FIG> is a bottom view of the head <NUM>. As illustrated in <FIG>, an ejection surface <NUM> for ejecting ink droplets is provided on a lower part of the head <NUM>. The ejection surface <NUM> covers the entire width of the transparent base material <NUM> in the main scanning direction. As illustrated in an enlarged manner in <FIG>, a plurality of nozzles <NUM> are regularly arranged on the ejection surface <NUM>. The plurality of nozzles <NUM> is arranged so that their positions in the main scanning direction are different from each other.

At the time of printing, ink droplets are ejected from the plurality of nozzles <NUM> of each head <NUM> toward the print surface of the transparent base material <NUM>. That is, ink droplets of cyan, magenta, yellow, and black, which are process colors, are ejected from the plurality of nozzles <NUM> of the heads <NUM>, respectively. As a result, the four heads <NUM> print single-color images of cyan, magenta, yellow, and black on the print surface of the transparent base material <NUM>, respectively. Then, a multicolor image is formed on the print surface of the transparent base material <NUM> by superposing these four single-color images. Hereinafter, the multicolor image printed by the first printing unit <NUM> is referred to as a "process-color image".

The first drying unit <NUM> is disposed on the downstream side of the first printing unit <NUM> in the conveyance path. The first drying unit <NUM> dries the process color inks ejected from the four heads <NUM> of the first printing unit <NUM>. As a result, the process color inks are fixed on the print surface of the transparent base material <NUM>. For example, the first drying unit <NUM> dries the inks by blowing hot air toward the transparent base material <NUM> to vaporize a solvent in the inks that adheres to the transparent base material <NUM>. However, the first drying unit <NUM> may dry or cure the inks by another method such as light emission.

The second printing unit <NUM> is disposed downstream of the first drying unit <NUM> in the conveyance path. The second printing unit <NUM> is a processing unit that ejects an ink of a non-process color different from cyan, magenta, yellow, and black described above onto the transparent base material <NUM> conveyed by the conveyance mechanism <NUM>. The second printing unit <NUM> of the present embodiment includes one head <NUM> that ejects ink droplets of white, which is a non-process color. The head <NUM> is fixed to a housing (not illustrated) of the inkjet printing apparatus <NUM>.

The head <NUM> of the second printing unit <NUM> also includes a plurality of nozzles, similarly to the head <NUM> of the first printing unit <NUM> described above. The head <NUM> ejects white ink droplets from a plurality of nozzles toward the print surface of the transparent base material <NUM>. As a result, a white single-color image is printed on the print surface of the transparent base material <NUM>. Hereinafter, a white single-color image printed by the second printing unit <NUM> is referred to as a "non process-color image".

The second drying unit <NUM> is disposed downstream of the second printing unit <NUM> in the conveyance path. The second drying unit <NUM> dries the non process-color ink ejected from the head <NUM> of the second printing unit <NUM>. As a result, the non process-color ink is fixed on the print surface of the transparent base material <NUM>. For example, the second drying unit <NUM> dries the ink by blowing heated gas toward the transparent base material <NUM> to vaporize a solvent in the ink that adheres to the transparent base material <NUM>. However, the second drying unit <NUM> may dry or cure the ink by another method such as light emission.

<FIG> is a view conceptually illustrating the relationship among the transparent base material <NUM>, a process-color image Ip, and a non process-color image Iw. <FIG> is a view of the transparent base material <NUM> after printing viewed from the non-print surface side (from the direction of arrow A in <FIG>). As described above, in the inkjet printing apparatus <NUM> of the present embodiment, the process-color image Ip is first printed and then the non process-color image Iw is printed on the print surface of the transparent base material <NUM>. Therefore, as illustrated in <FIG>, at least part of the process-color image Ip is covered with the non process-color image Iw. A printed image I is formed on the print surface of the transparent base material <NUM> by the process-color image Ip and the non process-color image Iw.

<FIG> is referred to again. The image acquisition unit <NUM> is disposed downstream of the second drying unit <NUM> in the conveyance path. The image acquisition unit <NUM> captures the printed image I at a predetermined inspection location P on the conveyance path of the transparent base material <NUM>. As illustrated in <FIG>, the image acquisition unit <NUM> includes a first light-emitting unit <NUM>, second light-emitting units <NUM>, and an imaging unit <NUM>. The first light-emitting unit <NUM> is disposed on one side (print-surface side) of the transparent base material <NUM>. The second light-emitting units <NUM> and the imaging unit <NUM> are disposed on the other side (non print-surface side) of the transparent base material <NUM>.

Details of the image acquisition unit <NUM> will be described later.

The control unit <NUM> is a means for controlling operation of each unit in the inkjet printing apparatus <NUM>. The control unit <NUM> of the present embodiment is configured by a computer including a processor <NUM> such as a CPU, a memory <NUM> such as a RAM, and a storage unit <NUM> such as a hard disk drive. As indicated by broken lines in <FIG>, the control unit <NUM> is communicably connected to the conveyance mechanism <NUM>, the four heads <NUM> of the first printing unit <NUM>, the first drying unit <NUM>, the head <NUM> of the second printing unit <NUM>, the second drying unit <NUM>, the first light-emitting unit <NUM>, the second light-emitting units <NUM>, and the imaging unit <NUM> described above. The control unit <NUM> temporarily reads a computer program CP stored in the storage unit <NUM> into the memory <NUM>, and the processor <NUM> performs arithmetic processing based on the computer program CP to control operation of each unit described above. As a result, the printing process in the inkjet printing apparatus <NUM> and an inspection process to be described below advance.

Subsequently, details of the image acquisition unit <NUM> will be described later. <FIG> is a diagram illustrating a configuration of the image acquisition unit <NUM>. As described above, the image acquisition unit <NUM> of the present embodiment includes the first light-emitting unit <NUM>, the second light-emitting units <NUM>, and the imaging unit <NUM>.

The first light-emitting unit <NUM> is located on one side (print-surface side) of the transparent base material <NUM> at the inspection location P. The first light-emitting unit <NUM> includes a plurality of light sources <NUM> arranged in the main scanning direction. As the light source <NUM>, for example, an LED (Light Emitting Diode) is used. When a drive current is supplied to the first light-emitting unit <NUM> according to a command from the control unit <NUM>, each light source <NUM> of the first light-emitting unit <NUM> emits light. As a result, light is emitted from the first light-emitting unit <NUM> toward the transparent base material <NUM>. Light emitted from the first light-emitting unit <NUM> is preferably white light.

The second light-emitting units <NUM> are located on the other side (non print-surface side) of the transparent base material <NUM> at the inspection location P. In the present embodiment, the second light-emitting units <NUM> are provided on the upstream side and the downstream side of the imaging unit <NUM>, respectively. However, the second light-emitting units <NUM> may be installed only on either the upstream side or the downstream side of the imaging unit <NUM>. The second light-emitting unit <NUM> includes a plurality of light sources <NUM> arranged in the main scanning direction. As the light source <NUM>, for example, an LED (Light Emitting Diode) is used. When a drive current is supplied to the second light-emitting unit <NUM> according to a command from the control unit <NUM>, each light source <NUM> of the second light-emitting unit <NUM> emits light. As a result, light is emitted from the second light-emitting unit <NUM> toward the transparent base material <NUM>. Light emitted from the second light-emitting unit <NUM> is preferably white light.

The light amounts of emitted light from the first light-emitting unit <NUM> and the second light-emitting unit <NUM> of the present embodiment can be individually changed. The light amount is set, for example, by the user inputting a desired value to the control unit <NUM>.

The imaging unit <NUM> is located on the other side (non print-surface side) of the transparent base material <NUM> at the inspection location P. That is, the first light-emitting unit <NUM> and the imaging unit <NUM> are located on the opposite sides of the transparent base material <NUM> with the inspection location P interposed therebetween. The imaging unit <NUM> includes a plurality of imaging elements <NUM> arranged in the main scanning direction. As the imaging element <NUM>, for example, a CCD (Charge-Coupled Device) or a CMOS (Complementary MOS) is used. The imaging unit <NUM> images the transparent base material <NUM> passing through the inspection location P by using these imaging elements <NUM>. As a result, the image of the transparent base material <NUM> passing through the inspection location P is obtained as multi-tone digital data. Hereinafter, an image obtained by the imaging unit <NUM> is referred to as a "captured image D1". The captured image D1 is output from the imaging unit <NUM> to the control unit <NUM>.

Furthermore, as conceptually illustrated in <FIG>, the control unit <NUM> includes an inspection processing unit <NUM>. The inspection processing unit <NUM> is a processing unit for inspecting the quality of the printed image I printed on the transparent base material <NUM> based on the captured image D1 obtained from the imaging unit <NUM>. The function of the inspection processing unit <NUM> is realized by the computer as the control unit <NUM> operating according to the computer program CP described above. In the present embodiment, the first light-emitting unit <NUM>, the second light-emitting units <NUM>, the imaging unit <NUM>, and the inspection processing unit <NUM> constitute an inspection device that inspects the printed image I printed on the surface of the transparent base material <NUM>.

A normal image D2 is stored in advance in the storage unit <NUM> of the control unit <NUM>. The normal image D2 is an image illustrating a state in which the transparent base material <NUM> is normally printed. The normal image D2 is generated in the control unit <NUM> based on print data. The inspection processing unit <NUM> acquires the captured image D1 from the imaging unit <NUM> and reads the normal image D2 from the storage unit <NUM>. Then, the captured image D1 and the normal image D2 are compared. As a result, a portion in which the difference between the captured image D1 and the normal image D2 is greater than a preset threshold is detected as a defect.

Examples of the types of defects include missing of a portion of the printed image I due to clogging of some of the nozzles or the like, misalignment of the printed image I on the print surface of the transparent base material <NUM>, dirt due to unnecessary dropping of ink from the nozzle, and adhesion of foreign matter to the transparent base material <NUM>. Whether or not a character or a code included in the printed image I can be normally identified may also be set as one of the inspection items.

Furthermore, in the present embodiment, the normal image D2 used is an image generated based on the print data; however, the normal image D2 is not limited to this. For example, in a case where an identical image is repeatedly printed, a normal image D2 may be generated from an average image of a plurality of captured images D1, or the like. In this case, it is necessary to confirm that an identical defect does not occur in identical spots; however as compared with a case where the normal image D2 is generated based on the print data, it is possible to suppress the labor of color conversion and resolution conversion and to reduce errors caused by processes of color conversion and resolution conversion.

Subsequently, the inspection procedure of the printed image I in the inkjet printing apparatus <NUM> will be described with reference to the flowchart of <FIG>. The inkjet printing apparatus <NUM> repeatedly executes steps S1 to S3 in <FIG> while executing the printing process on the transparent base material <NUM>.

First, the image acquisition unit <NUM> images the transparent base material <NUM> passing through the inspection location P (step S1). Specifically, the imaging unit <NUM> images the transparent base material <NUM> at the inspection location P while light is emitted toward the transparent base material <NUM> from the first light-emitting unit <NUM> and the second light-emitting units <NUM> described above. As a result, the captured image D1 of the transparent base material <NUM> at the inspection location P is obtained.

At this time, the first light-emitting unit <NUM> emits light from one side of the transparent base material <NUM>, and the light is incident on the imaging unit <NUM> located on the other side of the transparent base material <NUM>. That is, the imaging unit <NUM> receives light emitted from the back of the transparent base material <NUM>. Accordingly, it is possible to suppress generation of the shadow of the printed image I itself in the vicinity of the printed image I by emitted light from the second light-emitting units <NUM>. Therefore, the imaging unit <NUM> can obtain a clear captured image D1 in which shadow is suppressed. The captured image D1 obtained is output from the imaging unit <NUM> to the control unit <NUM>.

When the captured image D1 is input to the control unit <NUM>, the inspection processing unit <NUM> in the control unit <NUM> compares the captured image D1 with the normal image D2 read from the storage unit <NUM>. Then, it is judged whether or not there is a defective portion having a large difference from the normal image D2 in the captured image D1 (step S2). As a result, the quality of the printed image I formed on the print surface of the transparent base material <NUM> is inspected. Specifically, it is judged for each pixel whether or not the difference in pixel value between the captured image D1 and the normal image D2 exceeds a preset threshold value, and the pixel with the difference exceeding the threshold value is set as a defective portion.

Thereafter, the control unit <NUM> outputs the inspection result obtained by the inspection processing unit <NUM> (step S3). For example, the inspection result is displayed on a display connected to the control unit <NUM>. The user of the inkjet printing apparatus <NUM> can recognize a defect included in the printed image I by checking the inspection result displayed on the display. However, the control unit <NUM> does not necessarily have to display the inspection result. The control unit <NUM> may sequentially accumulate the inspection results in a specific storage area in the storage unit <NUM>.

As described above, in step S1 of the present embodiment, the captured image D1 in which generation of the shadow of the printed image I itself is suppressed is obtained by emitting light from the first light-emitting unit <NUM>. Therefore, in step S2 of the present embodiment, the defect in the printed image I can be accurately inspected based on the obtained captured image D1.

Note that as illustrated in <FIG>, in a case where a portion of the process-color image Ip is covered with the non process-color image Iw, emitted light from the first light-emitting unit <NUM> is blocked by the non process-color image Iw, and sufficient light is not emitted to the portion of the process-color image Ip. However, in step S1 of the present embodiment, not only the first light-emitting unit <NUM> located on one side of the transparent base material <NUM> but also the second light-emitting units <NUM> located on the other side of the transparent base material <NUM> emit light. As a result, sufficient light is emitted also to the portion of the process-color image Ip covered with the non process-color image Iw. Therefore, the imaging unit <NUM> can image the entire printed image I more clearly. Therefore, in step S2 of the present embodiment, the defect in the printed image I can be inspected more accurately based on the obtained captured image D1.

Furthermore, the light amounts of emitted light from the first light-emitting unit <NUM> and the second light-emitting unit <NUM> of the present embodiment can be individually changed. Therefore, the light amounts of the first light-emitting unit <NUM> and the second light-emitting unit <NUM> and the balance of the light amounts can be adjusted as desired. As a result, it is possible to prevent a problem such as so-called lens flare due to an inappropriate amount of light from occurring in the captured image D1. Particularly, in a case where the area ratio of the non process-color image Iw is small, lens flare is likely to occur due to emitted light from the first light-emitting unit <NUM>. Therefore, the control unit <NUM> may automatically reduce the light amount of the first light-emitting unit <NUM> more as the area ratio of the non process-color image Iw in the printed image I is smaller. Note that the light amount of only one of the first light-emitting unit <NUM> and the second light-emitting units <NUM> may be able to be changed.

Subsequently, a second embodiment of the present invention will be described. <FIG> is a diagram illustrating a configuration of an image acquisition unit <NUM> according to the second embodiment. As illustrated in <FIG>, the image acquisition unit <NUM> of the present embodiment includes a first light-emitting unit <NUM>, second light-emitting units <NUM>, an imaging unit <NUM>, and a background plate <NUM>.

The background plate <NUM> is located on one side (print-surface side) of a transparent base material <NUM> at an inspection location P. The background plate <NUM> has a background surface <NUM> that extends in parallel to the print surface of the transparent base material <NUM> and faces the print surface. The background surface <NUM> covers the entire width of the transparent base material <NUM> in the main scanning direction. The color of the background surface <NUM> of the background plate <NUM> is a color different from any of the colors of inks ejected from heads <NUM> of a first printing unit <NUM> (process colors) and the color of ink ejected from a head <NUM> of a second printing unit <NUM> (non-process color). For example, the color of the background plate <NUM> is gray.

The first light-emitting unit <NUM> is disposed on one side (print-surface side) of the transparent base material <NUM>. The emission direction of light from the first light-emitting unit <NUM> of the present embodiment is directed not to the transparent base material <NUM> but to the background plate <NUM>. The first light-emitting unit <NUM> includes a plurality of light sources <NUM> arranged in the main scanning direction. As the light source <NUM>, for example, an LED (Light Emitting Diode) is used. When a drive current is supplied to the first light-emitting unit <NUM> according to a command from the control unit <NUM>, each light source <NUM> of the first light-emitting unit <NUM> emits light. As a result, light is emitted from the first light-emitting unit <NUM> toward the background plate <NUM>. Light emitted from the first light-emitting unit <NUM> is preferably white light.

Second light-emitting units <NUM>, an imaging unit <NUM>, and an inspection processing unit <NUM> are equal to those in the above-described first embodiment, and thus overlapping description will be omitted. In the present embodiment, the first light-emitting unit <NUM>, the second light-emitting units <NUM>, the imaging unit <NUM>, the background plate <NUM>, and the inspection processing unit <NUM> constitute an inspection device that inspects a printed image I printed on the surface of the transparent base material <NUM>.

Also in the second embodiment, inspection of the printed image I is executed by the procedure similar to the flowchart of <FIG>. However, in step S1, imaging is performed with the background plate <NUM> disposed on one side of the transparent base material <NUM>. The first light-emitting unit <NUM> emits light not to the transparent base material <NUM> but to the background plate <NUM>. Then, light reflected by the background surface <NUM> of the background plate <NUM> passes through the transparent base material <NUM> and is incident on the imaging unit <NUM>. By emitting light to the background plate <NUM> as described, generation of a shadow on the background plate <NUM> is suppressed.

That is, in the present embodiment, in step S1, it is possible to acquire a captured image D1 in which the shadow of the printed image I itself is suppressed by light emitted from the first light-emitting unit <NUM> and reflected by the background plate <NUM>. Therefore, in step S2 of the present embodiment, the defect in the printed image I can be accurately inspected based on the obtained captured image D1.

The captured image D1 obtained in step S1 includes a portion corresponding to the background surface <NUM> of the background plate <NUM> and a portion corresponding to the printed image I located in front of the background surface <NUM>. As described, the color of the background plate <NUM> is a color different from any of the colors of inks ejected from the heads <NUM> of the first printing unit <NUM> (process colors) and the color of ink ejected from the head <NUM> of the second printing unit <NUM> (non-process color). Therefore, in the obtained captured image D1, a process-color image Ip and a non process-color image Iw appear clearly distinguishably from the background surface <NUM>. Therefore, the printed image I can be accurately inspected based on the captured image D1.

The color of the background surface <NUM> of the background plate <NUM> (hereinafter referred to as a "background color") may be a color corresponding to a multi-primary color including two or more color components of the plurality of process colors and the non-process color. For example, in a case where the background color is gray, it is preferable to use gray corresponding to a multi-primary color including color components of cyan, magenta, and yellow, rather than gray corresponding to low-density black. This is because multi-primary color is less likely to match a color used in the printed image than a single color does.

<FIG> is a flowchart illustrating an example of a background color determination method. When the background color is determined, first, a plurality of candidate colors that are candidates for the background color are prepared. Each candidate color is a multi-primary color including two or more color components of the plurality of process colors and the non-process color. As illustrated in <FIG>, first, the plurality of process colors, the non-process color, and the plurality of candidate colors are printed on the transparent base material <NUM> (step S11). Next, the process colors, the non-process color, and the plurality of candidate colors that are printed are imaged by the imaging unit <NUM> (step S12).

Here, the captured image obtained by the imaging unit <NUM> is data defined not by CMYK but by RGB. That is, the colors in the captured image are represented by combinations of R (red), G (green), and B (blue) values. After the captured image is obtained in step S12, the RGB values of the plurality of process colors and the non-process color are compared with the RGB values of each candidate color (step S13). Then, the candidate color with largest difference in RGB value from the plurality of process colors and the non-process color is determined as the background color (step S14).

By using the background color determined as described, the background surface <NUM> of the background plate <NUM> and the printed image I can be more clearly distinguished in the captured image D1. Therefore, the printed image I can be accurately inspected based on the captured image D1.

Subsequently, a third embodiment of the present invention will be described. <FIG> is a diagram illustrating a configuration of an image acquisition unit <NUM> according to a third embodiment. As illustrated in <FIG>, an image acquisition unit <NUM> of the present embodiment is different from the second embodiment in that the image acquisition unit <NUM> includes a projection unit <NUM> in lieu of the first light-emitting unit <NUM>. That is, the image acquisition unit <NUM> of the present embodiment includes second light-emitting units <NUM>, an imaging unit <NUM>, a background plate <NUM>, and the projection unit <NUM>. The color of a background surface <NUM> of the background plate <NUM> in the present embodiment is white.

The projection unit <NUM> is located on one side (print-surface side) of a transparent base material <NUM>. The projection unit <NUM> is directed to the background surface <NUM> of the background plate <NUM>. The projection unit <NUM> includes a plurality of rows of light sources <NUM> arranged in the main scanning direction. The light sources <NUM> in each row emit different colors. As the light source <NUM>, for example, an LED (Light Emitting Diode) is used. The projection unit <NUM> causes the light sources <NUM> in any row to emit light in response to a command from the control unit <NUM>. As a result, light in a plurality of colors is selectively emitted from the projection unit <NUM> toward the background surface <NUM> of the background plate <NUM>.

The second light-emitting units <NUM>, the imaging unit <NUM>, and an inspection processing unit <NUM> are equal to those in the above-described first and second embodiments, and thus overlapping description will be omitted. In the present embodiment, the second light-emitting units <NUM>, the imaging unit <NUM>, the background plate <NUM>, the projection unit <NUM>, and the inspection processing unit <NUM> constitute an inspection device that inspects a printed image I printed on the surface of the transparent base material <NUM>.

Also in the third embodiment, inspection of the printed image I is executed by the procedure similar to the flowchart of <FIG>. However, in step S1, imaging is performed with the background plate <NUM> disposed on one side of the transparent base material <NUM>. At this time, the projection unit <NUM> emits light in a predetermined color to the background plate <NUM>. Then, light reflected by the background surface <NUM> of the background plate <NUM> passes through the transparent base material <NUM> and is incident on the imaging unit <NUM>. By emitting light to the background plate <NUM> as described, generation of a shadow on the background plate <NUM> is suppressed.

That is, in the present embodiment, in step S1, it is possible to acquire a captured image D1 in which the shadow of the printed image I itself is suppressed by light emitted from the projection unit <NUM> and reflected by the background plate <NUM>. Therefore, in step S2 of the present embodiment, the defect in the printed image I can be accurately inspected based on the obtained captured image D1.

The captured image D1 obtained in step S1 includes a portion corresponding to the background surface <NUM> of the background plate <NUM> and a portion corresponding to the printed image I located in front of the background surface <NUM>. Here, the color of the light emitted from the projection unit <NUM> to the background plate <NUM> is, for example, a color different from any of the colors of inks ejected from heads <NUM> of a first printing unit <NUM> (process colors) and the color of ink ejected from a head <NUM> of a second printing unit <NUM> (non-process color). Therefore, in the obtained captured image D1, a process-color image Ip and a non process-color image Iw, and the background surface <NUM> appear clearly distinguishably. Therefore, the printed image I can be accurately inspected based on the captured image D1.

Furthermore, in the present embodiment, the control unit <NUM> switches the color of light emitted from the projection unit <NUM> depending on the printed image I. Specifically, the projection unit <NUM> emits light in a color with the greatest difference in RGB value from the colors included in the printed image I, among the colors of light that can be emitted from the projection unit <NUM>. For example, in the case of a printed image I having a large proportion of green, such as a label for a green tea beverage, light in a red color in contrast to green is emitted. Furthermore, for example, in the case of a printed image I having a large proportion of blue, such as a label for a sports drink, light in an orange color in contrast to blue is emitted. Moreover, in the case of a test chart in which a printed image I is printed for each color of cyan, magenta, yellow, black, and white for nozzle inspection, the color of light emitted from the projection unit <NUM> may be changed for each color of the test chart. In this way, the printed image I and the background surface <NUM> can be more clearly distinguished in the captured image D1. Therefore, the printed image I can be inspected more accurately based on the captured image D1.

The first to third embodiments of the present invention have been described above; however, the present invention is not limited to these embodiments.

According to a configuration not according to the invention, the second light-emitting units <NUM> may be omitted in the configuration of the image acquisition unit <NUM> of the first embodiment. In a configuration not according to the invention, the first light-emitting unit <NUM> may be omitted in the configuration of the image acquisition unit <NUM> of the second embodiment. In a configuration not according to the invention, the second light-emitting unit <NUM> may be omitted in the configuration of the image acquisition unit <NUM> of the second embodiment. In a configuration not according to the invention, the second light-emitting unit <NUM> may be omitted in the configuration of the image acquisition unit <NUM> of the third embodiment.

Furthermore, in the configuration of the image acquisition unit <NUM> of the first embodiment, light emitted from the first light-emitting unit <NUM> may be light other than white light. For example, the color of light emitted from the first light-emitting unit <NUM> may be a color different from any of the colors of inks ejected from the heads <NUM> of the first printing unit <NUM> (process colors) and the color of ink ejected from the head <NUM> of the second printing unit <NUM> (non-process color). Furthermore, the color of light emitted from the first light-emitting unit <NUM> may be switched depending on the printed image I.

Moreover, in the above embodiments, the first printing unit <NUM> includes the four heads <NUM>. However, the number of heads <NUM> included in the first printing unit <NUM> may be one to three, or may be five or more. For example, heads <NUM> that eject inks of spot colors such as purple/violet and green in addition to inks of cyan, magenta, yellow, and black may be provided.

Furthermore, in the embodiments described above, printing is performed on the continuous transparent base material <NUM> having a long strip shape. However, an inkjet printing apparatus of the present invention may perform printing on each of a plurality of transparent base materials while sequentially conveying the plurality of transparent base materials in the sub scanning direction.

Claim 1:
An inspection device configured to inspect a printed image printed on a surface of a transparent base material (<NUM>), the device comprising:
a first light-emitting unit (<NUM>) configured to emit light from a print-surface side of the transparent base material toward the transparent base material (<NUM>);
an imaging unit (<NUM>) configured to image the transparent base material (<NUM>) from an opposite side of the print-surface side of the transparent base material (<NUM>);
an inspection processing unit (<NUM>) configured to inspect quality of the printed image based on a captured image obtained by the imaging unit (<NUM>); and
a second light-emitting unit (<NUM>) configured to emit light from the opposite side of the print-surface side of the transparent base material toward the transparent base material, wherein
light emitted from the first light-emitting unit (<NUM>) is transmitted through the transparent base material (<NUM>) and incident on the imaging unit (<NUM>),
light emitted from the second light-emitting unit (<NUM>) is reflected by the transparent base material (<NUM>) and incident on the imaging unit (<NUM>),
the imaging unit (<NUM>) is configured to image the transparent base material (<NUM>) from the opposite side of the print-surface side of the transparent base material (<NUM>) while the first light-emitting unit (<NUM>) and the second light-emitting unit (<NUM>) emit light,
the printed image includes
a process-color image that is formed by inks of a plurality of process colors, and
a non process-color image that is formed by an ink of a non -process color different from the plurality of process colors and that covers the print-surface side of the process-color image,
the plurality of process colors includes cyan, magenta, yellow, and black, and
the non-process color is white.