JP7618223B2 - Automatic print head cleaning system - Google Patents

Description

The present invention relates to a system for automatically cleaning the print head of a continuous inkjet printer.

Inkjet printers (hereafter abbreviated as "IJP") are broadly divided into continuous and on-demand types. Of these, continuous type IJPs use a pump to eject ink from a nozzle, charge the ink droplets with a charging electrode at the point where the ejected ink separates into ink droplets, and then deflect the trajectory of the ink droplets with a deflection electrode, causing them to land at a specified position on the printing surface, forming a print dot.

In the above-mentioned continuous IJP, when printing is repeated, a phenomenon occurs in which the height of the characters printed on the printing surface becomes higher or lower.

There are several possible reasons why the character height increases. One of them is that some of the ink ejected from the nozzle turns into mist and adheres to the surface of the high deflection electrode, reducing the distance between the ink droplets and the electrode, which increases the amount of deflection of the ink droplets.

On the other hand, there are several possible reasons why character height may be reduced. One of these is that the ink droplets come into contact with parts of the high deflection electrode or gutter that have become thicker due to the adhesion of ink, preventing the ink droplets from flying.

If this condition is left unchecked, it can lead to poor printing, so the print head must be cleaned periodically to remove any ink or other substances that may have adhered to the surface of the charging electrode and gutter.

JP 2019-171651 A Patent No. 6391745

Conventionally, print heads were cleaned by an operator who removed the cover of the print head to check the degree of dirt and determined that cleaning was necessary (see Patent Document 1). This required an operator to check the inside of the print head, which was an obstacle to unmanned or automated cleaning processes.

The present invention was made in consideration of these conventional problems, and aims to provide a cleaning system that uses data obtained during IJP operation and data obtained during the inspection process to determine the need for print head cleaning, thereby eliminating the need for an operator to check the degree of dirt.

In order to achieve the above object, the automatic print head cleaning system according to the present invention comprises:
an inkjet printer comprising a print head comprising: a gun which applies a constant periodic vibration to the ejected ink to generate successive ink droplets; a charging electrode which applies a step-wave voltage synchronized with the period of the ink droplets to charge the ink droplets; and a deflection electrode which deflects the charged ink droplets according to the degree of charge and causes the ink droplets to land on a printing surface of a substrate; the ink jet printer causes the ink droplets ejected from the print head to land on a substrate transported by a conveyor, forming characters with multiple rows of printing dots;
an inspection device that photographs the characters printed on the printing medium with a camera and judges whether the printed characters are appropriate;
a cleaning machine for cleaning the print head contaminated by ink with a solvent;
a robot for transferring the print head from a printing position to the cleaning machine;
a general controller for controlling the operations of the inkjet printer, the inspection device, the cleaning device and the robot;
the overall controller further includes a classifier that classifies the cases into cases where cleaning of the print head is required and cases where cleaning of the print head is not required, the classifier being created by performing machine learning using data indicating an operating state obtained from the inkjet printer and data indicating an inspection result obtained from the inspection device;
The general controller includes:
When it is determined that cleaning of the print head is necessary based on a classification result of the classifier using data indicating an operating state obtained from the inkjet printer and data indicating an inspection result obtained from the inspection device as input,
Instructing the inkjet printer to stop operation;
Instructing the robot to move the print head from the printing position to the cleaning machine;
The cleaning device is instructed to clean the print head.

The print head is preferably composed of a head body on which the gun, charging electrode, and deflection electrode are mounted, and a cylindrical head cover in which the gun, charging electrode, and deflection electrode are housed in a hollow portion and in which a slit is formed through which the charged ink droplets pass, and the robot transfers only the head body to the cleaning machine, and the head cover is preferably always held in the printing position.

It is also preferable that the head cover be held at a desired position near the conveyor by a holding means, and that the position in three-dimensional space can be adjusted using the holding means.

The general controller is preferably equipped with a classifier creation device that creates the classifier, and the classifier creation device is preferably configured with a learning data acquisition unit that acquires multiple types of data indicating the operating state from the inkjet printer and multiple types of data indicating the inspection results from the inspection device, a data storage unit that stores the learning data, and a learning unit that uses the learning data stored in the data storage unit as input and performs machine learning using a deep neural network to create the classifier.

The data acquired from the inkjet printer preferably includes the pressure of the ink fed to the gun, the viscosity of the ink ejected from the nozzle of the gun, the detection time from when the ink droplets ejected from the nozzle of the gun are charged to when they are detected by the detection electrode, and a piezoelectric command value, which is the voltage applied to a piezoelectric vibrator built into the gun.

It is also preferable that the data obtained from the inspection device is the suitability of the characters printed on the substrate and the average height of the printed characters that are judged to be suitable.

The automatic print head cleaning system (hereafter abbreviated as "cleaning system") of the present invention uses data obtained during IJP operation and data obtained during the inspection process, which is essential for printing, to automatically determine the need for print head cleaning, and uses a robot to load and unload the print head into the cleaning machine, making it possible to clean the print head without requiring any human labor. As a result, the cleaning process can be unmanned and automated simply by combining existing equipment with a robot.

1 is a perspective view showing an overall configuration of a cleaning system according to an embodiment of the present invention. 4 is a flowchart showing the process flow of the cleaning system. FIG. 2 is a plan view of an XYZ stage that holds the print head at a desired position on the conveyor. FIG. 2 is a front view showing the configuration of a print head. 1 is a partially cross-sectional front view showing the schematic configuration of a continuous type IJP that constitutes the cleaning system. 2 is a block diagram showing the configuration of a control system of an inspection apparatus that constitutes the cleaning system. FIG. 4 is a flowchart showing a procedure for print inspection in the inspection device. FIG. 13 is a diagram showing an example of print that is a target of print inspection. 4 is a block diagram showing a configuration of a cleaning determination device included in the general controller. FIG. FIG. 2 is a block diagram showing a configuration of a classifier creating device included in the general controller. 1A and 1B are diagrams illustrating examples of printed characters inspected by an inspection device. FIG. 2 is a perspective view showing a state in which a print head is inserted into a head holder of the cleaning machine. FIG. 2 is a front view showing the configuration of a cleaning machine that constitutes the cleaning system.

The following describes an automatic print head cleaning system according to an embodiment of the present invention with reference to the drawings.

<Configuration and operation of the automatic print head cleaning system>
1 shows the overall configuration of an automatic print head cleaning system (hereinafter abbreviated as "cleaning system") 1 according to this embodiment. The flow of processing in the cleaning system 1 is shown in the flowchart of FIG.

The automatic print head cleaning system 1 is composed of an IJP 2, an inspection device 3, a cleaning machine 4, a robot 5 and an overall controller 6.

Although not shown, the IJP 2, inspection device 3, cleaning machine 4, and robot 5 are connected to the general controller 6 via communication cables, and the operating status of each device is reported to the general controller 6 in sequence, and each device operates according to instructions from the general controller 6. Below, the general configuration and operation of each device will be explained according to the flowchart in Figure 2.

The continuous-type IJP2 is used to print the product's manufacturing date, product number, etc. on the top surface of the printing material PT being transported on the conveyor 8. The IJP2 is composed of a print head 20 that performs the printing, and a printer body 21 that controls the operation of the print head 20, and although not shown in the figure, they are connected by a pipe 29. The printer body 21 has a built-in ink tank, and the ink contained in the ink tank is supplied to the print head 20 through the pipe 29.

The print head 20 is held at a predetermined position on the conveyor 8 by the XYZ axis stage 7, and when the printing material PT transported by the conveyor 8 passes under the print head 20, printing is performed on the top surface of the printing material PT (step S1).

A camera 31 of the inspection device 3 is installed on the conveyor 8 downstream of the print head 20, and the characters printed by the print head 20 are photographed by the camera 31, and the controller 34 (see FIG. 7), which will be described later, judges whether the printing is correct or not (step S2). The controller 34 of the inspection device 3 is housed in the control unit 11 installed below the table 12 together with the general controller 6 of the cleaning system 1.

After each printing, the overall controller 6 of the cleaning system 1 estimates the degree of dirt on the print head 20 based on data indicating the printer's operating status obtained from the IJP 2 and data indicating the inspection results obtained from the inspection device 3, and determines the need for cleaning based on the results (step S3).

Summary When the controller 6 determines that cleaning is necessary based on the soiled state of the print head 20 (Yes in step S4), it stops printing by IJP2 (step S5) and instructs the robot 5 to transport the head body 202 of the print head 20 to the cleaning machine 4, attach the head body 202 to the cleaning machine 4, and clean the head body 202 (step S7).

After cleaning, the print head 20 is allowed to air dry for a predetermined period of time (step S8), and then the robot 5 returns the print head 20 to its printing position (step S9). If printing is to continue (Yes in step S10), printing is resumed (step S1).

As mentioned above, with conventional cleaning methods, an operator would visually check the degree of dirt on the print head 20 and only perform cleaning if the dirt was deemed severe, making it difficult to automate the cleaning process.

In contrast, the cleaning system 1 according to the present invention determines the need for cleaning based on data indicating the operating status of IJP2 obtained from IJP2 and data indicating the inspection results obtained from the inspection device 3, and since there is no need for an operator to check the state of dirt, the cleaning process can be easily automated and unmanned.

Next, the configuration and operation of each device that constitutes the cleaning system 1 according to this embodiment will be described in detail with reference to the drawings. First, the configuration and operation of IJP2 will be described.

<IJP Configuration and Operation>
Before describing the configuration of the IJP 2, we will explain the XYZ axis stage 7 that holds the print head 20 facing downward at a predetermined position on the conveyor 8. Figure 3 is a view of the XYZ axis stage 7 as viewed from above.

In this embodiment, in order to print on the top surface of the printing substrate PT being transported on the conveyor 8, the print head 20 must be held facing downward at the desired position on the conveyor. To achieve this, the XYZ axis stage 7 is used.

The XYZ-axis stage 7 is a means used to hold a member attached to an end at a desired position in three-dimensional space, facing in a desired direction, and is composed of an X-axis stage 71 that adjusts the position in the X-axis direction, a Y-axis stage 72 that adjusts the position in the Y-axis direction, and a Z-axis stage 73 that adjusts the position in the Z-axis direction.

The arrangement of stages 71 to 73 can be changed as necessary. In the XYZ-axis stage 7 shown in FIG. 3, the X-axis stage 71, Z-axis stage 73, and Y-axis stage 72 are arranged in this order on top of each other on a base 70 installed close to the conveyor 8, and each stage is provided with handles 74, 76, and 75 for manually adjusting the position.

Figure 4 shows the print head 20 attached to the end of the Y-axis stage 72. A member 77 that supports the cylindrical head cover 201 of the print head 20 is attached to the tip of the Y-axis stage 72, and the head cover 201 is fixed to the support member 77 using a metal band 78.

As shown in FIG. 4, the print head 20 can be separated into a cylindrical head cover 201 and a head body 202 placed inside it. The main components that make up the print head, such as the gun, charging electrode, and deflection electrode, are arranged in close contact with the substrate 203 of the head body 202.

The top of the head body 202 is connected to a tube 205 using a nut 204, and as described below, piping for transporting ink from the printer body 21, piping for supplying air, and cables for transmitting power and signals are inserted into the tube 205.

As shown in FIG. 4, the head body 202 can be separated from the head cover 201. When IJP2 is in operation, the head body 202 is housed inside the cylinder of the head cover 201, but when cleaning the printer head 20, it is removed above the head cover 201 by the robot 5, as shown by the white arrow, and transferred to the cleaning machine 4.

In the present invention, the above-mentioned configuration is effectively utilized as one means for realizing automatic cleaning of the print head 20. That is, all of the components of the print head 20 that require cleaning are mounted on the head body 202, so when printing, only the head body 202 needs to be transferred to the cleaning machine 4.

Therefore, the head cover 201 is always held at the desired position on the conveyor by the XYZ axis stage 7, and if the head body 202 that has been cleaned is inserted into the head cover 201 and integrated, there is no need to adjust the position of the print head 20 using the XYZ axis stage 7 each time printing is performed.

Next, printing on the print substrate PT by the IJP2 will be described with reference to FIG. 5. FIG. 5 is a partial cross-sectional front view showing the schematic configuration of the continuous-type IJP2, including the print head 20.

As shown in FIG. 5, the IJP2 is composed of a print head 20, a controller 21, an ink tank 22, and pumps 23a and 23b. Of these, the print head 20 is composed of a gun 24, a charging electrode 25, a detection electrode 26, deflection electrodes 27a and 27b, a gutter 28, and pipes 29a and 29b, and these components are mounted on a head body 202, and the surrounding area is covered with a cylindrical head cover 201.

As shown in FIG. 4 above, the gun 24 and other components that make up the print head 20 are actually arranged in close contact on the substrate 203 of the head body 202, but FIG. 5 shows a schematic arrangement to easily explain the function of each component. Similarly, while the print head 20 is arranged facing downward in FIG. 1, it is arranged sideways in FIG. 5.

The gun 24 sprays ink droplets ID toward the top surface of the printing substrate PT (e.g., a box in which a product is packed), and is composed of a gun body 241, an ultrasonic vibrator 242, and a nozzle 243. Ink is pumped from the ink tank 22 by the pump 23a and supplied to the gun body 241 through the pipe 29a, and is sprayed from the hole of the nozzle 243 while being vibrated by the piezoelectric vibrator 242.

The ink column IP ejected from the nozzle 243 is separated into individual ink droplets ID by the vibration applied by the piezoelectric vibrator 242, and is then charged by the charging electrode 25. After that, only the ink droplets ID required for printing are deflected by the deflection electrodes 27a and 27b according to the amount of charge, and pass through the slit 206 formed in the front part of the head cover 201, and land on the printing surface of the printing substrate PT.

After food and other items are packed into the box, the printing substrate PT has the manufacturing number, expiration date, etc. printed on the film to form the final product. If the printing substrate PT is moving in a direction perpendicular to the flight direction of the ink droplets ID, changing the deflection amount of the ink droplets ID changes the position at which the ink droplets ID land on the printing surface of the printing substrate PT, and by repeatedly deflecting the ink droplets ID in sync with the movement of the printing substrate PT, letters and symbols are printed.

On the other hand, ink droplets ID that are not charged and ink droplets ID that are charged but are not used for printing are not deflected and jump directly into the gutter 28 for ink recovery and are recovered in the ink tank 22. The ink recovered by the gutter 28 is transferred by the pump 23b through the pipe 29b to the ink tank 22 and is reused.

The operation of IJP2 is controlled by controller 21. The controller is composed of a CPU, memory (ROM, RAM, etc.), a timer, and a display, and controls the operation of piezo transducer 242 of gun 24, pulse power supply 251 of charging electrode 25, detection electrode 26, DC power supply 271 of deflection electrode 27, and pumps 23a and 23b. Note that to avoid complexity, the control wiring is shown only for pumps 23a and 23b in the figure.

To explain the specific operation, the controller 21 applies pressure to the ink contained in the ink tank 22 and supplies it to the gun body 241 by driving the pump 23a. The controller 21 also controls the timing of the pulse voltage applied from the pulse power supply 251 to the charging electrode 25 based on the signal detected by the detection electrode 26, thereby adjusting the number and timing of the ink droplets ID to be charged. Furthermore, the controller 21 adjusts the deflection amount of the ink droplets ID deflected by the deflection electrodes 27a 27b by controlling the voltage of the DC power supply 271.

As mentioned above, in continuous-type IJP, some of the ink ejected from the nozzle 243 floats in the surrounding atmosphere as ink mist and adheres to the surfaces of the components, adversely affecting the flight of ink droplets. For this reason, the main components of the print head 20 are housed inside the head cover 201, and a positive pressure is maintained inside the cover to promote the discharge of ink mist to the outside and prevent dust from outside from entering the cover.

A tube 208 is attached to the bottom plate 207 of the head body 202, and air is supplied from an external compressor through the tube 208 to create positive pressure in the cavity 209 inside the print head 20. The head cover 201 is sealed except for the slits 206 through which the ink droplets ID are ejected, and most of the air AR (indicated by the white arrow) supplied through the tube 208 remains inside the head cover 201, increasing the air pressure.

<Configuration and operation of inspection device>
Next, the configuration and operation of the inspection device 3 will be described with reference to Figures 6 and 7. Figure 6 is a block diagram showing the configuration of a control system of the inspection device 3, and Figure 7 is a flow chart showing the procedure of print inspection.

As shown in FIG. 1 above, a camera 31 is installed above the print head 20 on the downstream side of the conveyor 8 to capture images of characters printed on the printing surface of the printing substrate PT, and lighting fixtures 32 for illuminating the printing surface are arranged around the camera 31, with the camera 31 and lighting fixture 32 being integrated with metal fittings. As mentioned above, the controller 34 that controls the operation of the inspection device 3 is housed in the control unit 11 together with the overall controller 6 of the cleaning system 1.

Although not shown, a photoelectric sensor 33 is installed on the edge of the conveyor 8, and the camera 31 is activated a certain time after the printing object PT blocks the light output from the photoelectric sensor 33, and captures an image of the characters printed on the top surface of the printing object PT.

The controller 34 is composed of a control unit 341, an interface 342, an input/display unit 343, a memory unit 344, a print inspection processing unit 345, and a hard disk drive (hereinafter referred to as "HDD") 346.

In terms of hardware, the controller 34 is equipped with a CPU and RAM, similar to a typical personal computer, and the functions of the control unit 341, interface 342, and print inspection processing unit 345 are realized by reading out a program stored in the HDD 346 and executing it with the microprocessor.

The control unit 341 controls the operation of each part of the camera 31 and the controller 34, as indicated by the dashed lines. Images captured by the camera 31 are input to the controller 34 via the interface 342.

The input/display unit 343 is composed of a touch panel display and is used by the operator to input data necessary for the print inspection, and is also used to display images captured by the camera 31 and the results of the print inspection.

The memory unit 344 is composed of a RAM, and temporarily stores image data captured by the camera 31, and then transfers it to the HDD 346 as necessary. Conversely, it temporarily stores image data read from the HDD 346 and data required to perform the inspection, and transfers it to the print inspection processing unit 345, etc.

The print inspection processing unit 345 performs the processes required for print inspection and setting work, as listed in the block, specifically, parameter setting, binarization, character extraction, similarity calculation, and printing suitability judgment.

Next, the procedure for print inspection will be described with reference to the flowchart in FIG. 7 and the print example in FIG. 8. First, the camera 31 is used to capture an image of the character image printed on the top surface of the printing substrate PT being transported on the conveyor 8 (step S11). As mentioned above, the timing of the capture is such that the shutter of the camera 31 is released a predetermined time after the printing substrate PT blocks the light from the photoelectric sensor 33, so that the printed image is always displayed in the same position on the screen.

The image data captured by the camera 31 is transferred via the interface 342 and the memory unit 344 to the print inspection processing unit 345, where it is subjected to binarization processing (step S12). The binarization processing is a process for converting the image with gradations captured by the camera 31 into a black and white image that can be processed by the CPU, and a threshold value is set according to the brightness of the image, etc. Figure 8 (a) shows an example of binarized printed characters.

Next, the binarized printed characters are extracted (step S13). Extracting characters from the captured image is a process of extracting the printed characters to be inspected by dot connection processing and noise reduction processing. For details on the connection processing and noise reduction processing, please refer to Patent Document 2.

Figure 8 (b) shows the printed characters after the concatenation process and noise cut process have been completed. As shown in the figure, all of the printed characters to be inspected are surrounded by a rectangular frame F, and all of the characters to be inspected for print have been extracted from the captured image.

Next, each character extracted in this manner is compared with a template image of the corresponding character read from HDD 346 to calculate the degree of similarity, i.e., the degree of similarity (step S14).

Next, the calculated similarity is compared with a standard similarity (e.g., 80%) read from HDD 346, and characters with a similarity equal to or higher than this are determined to be appropriate, while characters with a similarity lower than this are determined to be inappropriate (step S15).

In a normal inspection process, a judgment as to whether the printing is appropriate is made for all characters displayed in FIG. 8(b) (Yes in step S16), and the judgment result is displayed on the screen of the input/display unit 343. On the other hand, in this embodiment, the judgment result of the inspection device 3 is used as one of the criteria for deciding whether or not to clean the print head 20, so that the judgment result is sent to the cleaning judgment device 61 described below each time inspection of one character is completed.

<Configuration and Operation of Cleaning Determination Device>
FIG. 9 shows the configuration of a cleaning determination device 61 mounted on the general controller 6 of the cleaning system 1, and FIG. 10 shows the configuration of a classifier creation device 62 that creates a classifier to be incorporated in the cleaning determination device 61.

The classifier creation device 62 shown in FIG. 10 uses machine learning to learn patterns of the degree of dirt on the print head 20 based on data indicating the operating state of the printer 2 obtained from the IJP 21 and data indicating the inspection results obtained from the inspection device 3, and creates a classifier that classifies cases into those in which cleaning is required and those in which it is not.

The classifier program created by the classifier creation device 62 is incorporated into the cleaning determination device 61 of the general controller 6. Four types of data indicating the operating status of the printer obtained from the IJP 2 during operation and two types of data indicating the inspection results obtained from the inspection device 3 are then input to the classifier.

When the cleaning determination device 61 determines that cleaning of the print head 20 is necessary based on the classification results of the classifier, it instructs the controller 21 of the IJP2 to stop operation and instructs the robot controller 54 to transport the print head 20 to the cleaning machine 4.

The configuration and operation of the classifier creation device 62 will be described with reference to FIG. 10. The classifier creation device 62 creates a classifier by machine learning, and is composed of a learning data acquisition unit 621, a data storage unit 622, a learning unit 623, and a classifier 624. The classifier creation device 62 and the cleaning determination device 61 are realized by a personal computer, and the hard disk device stores programs that realize the functions of each of the above-mentioned units.

The learning data acquisition unit 621 acquires the learning data required to create a classifier from the data acquired from IJP2 and the inspection device 3. In this embodiment, seven types of data are used as learning data, of which four types of data are acquired from IJP2 and two types of data are acquired from the inspection device 3. The remaining one type of data is teacher data, and data on whether cleaning is required or not is input directly to the data storage unit 622.

We will explain the four types of learning data obtained from IJP2. The first data is obtained by measuring the pressure of the ink sent to the gun 24 using the pressure sensor 211 built into IJP2.

As the second data, the viscosity of the ink ejected from the nozzle 243 is measured using the viscosity sensor 212 built into the IJP2, and the value is obtained. Specifically, a Zahn cup tank (not shown) is installed separately from the ink tank 22, and when ink falls from a thin tube installed at the bottom of the Zahn cup tank into the ink tank 22, the time it takes for the ink level in the Zahn cup tank to drop by a certain height is measured by the viscosity sensor 212 installed inside the tank, and the viscosity is expressed by that time.

The third data is the time from when the ink droplet ejected from the nozzle 243 becomes charged to when it is detected by the detection electrode 26, which is acquired by the timer 213 and is regarded as the "detection time."

The fourth data is a 12-bit numerical value of the voltage applied to the piezoelectric transducer 242, which is acquired as the "piezo command value" 214. The piezo command value is a parameter for controlling the position at which the ink droplet separates from the ink column, and is used to match the above-mentioned detection time with a target detection time.

For the four learning data items mentioned above, if the ink pressure is within the reference ink pressure ±0.05 MPa, the viscosity is within the reference viscosity ±2.0 s, the detection time is within the reference detection time ±20 μs, and the piezo command value is within the reference piezo command value ±500, this indicates that the condition of the piping, filter, pump, nozzle, and ink is normal. The definition of the above-mentioned "reference" will be explained in the "annotation reference" section below.

Next, two types of data obtained from the inspection device as learning data will be described with reference to FIG. 11. In this embodiment, two types of data created by the inspection device 3 are obtained as learning data.

The first data is data regarding the suitability of printing, and as the method of acquiring this data has been explained above, a detailed explanation will be omitted. Figure 11 shows a specific printing example. The printing example in Figure 11(a) shows a vertically long rectangle that has been printed, and is an example of suitable printing, while Figures 11(b) and (c) show examples of unsuitable printing. In Figure 11(b), the printing dots in the lower row have shifted upward, and in Figure 11(c), the printing dots in the lower row have been formed in a position shifted upward.

The cause of the print examples in Figures 11(b) and (c) is thought to be that ink droplets come into contact with the surface of the gutter 28, particularly the upper surface, causing the ink to solidify, and the ink droplets in flight come into contact with this solid matter, changing their trajectory.

The learning data acquisition unit 621 receives as learning data the value "0" if printing is judged to be appropriate, and the value "1" if printing is judged to be unsuccessful.

The second data obtained from the inspection device 3 is the average character height of the print. The height of the printed characters may become too high or too low, which is a sign of poor printing caused by dirty print heads.

As mentioned above, there are several possible reasons why the character height increases. One of these is that ink or some other conductive material adheres to the high deflection electrode 27a, narrowing the gap between the electrode and the ink droplet, which increases the amount of deflection of the ink droplet.

On the other hand, there are several possible reasons why the character height may be low. One of these is when ink adheres to the surface of the high deflection electrode 27a or the gutter 28, and the ink droplets come into contact with this, preventing them from flying.

Based on the causes of the problem described above, in this embodiment, height data is extracted from the printed characters that are determined to be correct, and if the average character height is greater than or equal to ±20% of the reference character height, it is determined that the print head 20 needs to be cleaned.

As mentioned above, if the print inspection results obtained from the inspection device 3 are appropriate and the average character height is less than ±20% of the reference character height, it is determined that cleaning of the print head 20 is not necessary even if the four data obtained from IJP2 are outside the set range.

The data storage unit 622 stores a large amount of data (approximately 100,000) acquired by the learning data acquisition unit 621. The learning unit 623 reads out the learning data stored in the data storage unit 622 and performs machine learning. In this embodiment, as a machine learning method, a classifier is constructed using a deep neural network, and a ReLU function is used as an activation function in the intermediate layer, and a sigmoid function is used in the output layer. Furthermore, learning is performed by the error backpropagation method using the sum of squares error as the loss function.

The following describes the annotation criteria in the learning unit 623. If the print inspection results are appropriate and the average character height is less than ±20% of the reference character height, it is classified as "0" - no cleaning required.

on the other hand,
(1) If the print inspection result is negative,
(2) If the print inspection result is appropriate, the average character height is 20% or more higher than the reference character height, the ink pressure is within the reference ink pressure ±0.05 MPa, the viscosity is within the reference ink viscosity ±2.0 s, the detection time is within the reference detection time ±20 μs, and the piezo command value is within the reference piezo command value ±500,
(3) If the print inspection result is appropriate, the average character height is 20% or more lower than the reference character height, and further, the ink pressure is within the reference ink pressure ±0.05 MPa, the viscosity is within the reference viscosity ±2.0 s, the detection time is within the reference detection time ±20 μs, and the piezo command value is within the reference piezo command value ±500,
Classify as "1" if cleaning is required. Otherwise, assign an intermediate value.

Here, the reference character height refers to the average character height obtained from over 100,000 pieces of image data stored in the data storage unit 622. Similarly, the reference ink pressure, reference ink viscosity, and reference piezo command value refer to the average values of the respective data stored in the data storage unit 622.

The result of learning based on the above-mentioned annotation criteria constitutes a classifier 624 as a learned model. The program of the classifier 624 created in this way is incorporated into the cleaning determination device 61 built into the general controller 6 of the cleaning system 1.

As shown in FIG. 9, the cleaning judgment device 61 is composed of a data acquisition unit 611, a classifier 624, and a judgment unit 612. The data acquisition unit 611 acquires four pieces of data from the pressure sensor 211, the viscosity sensor 212, the timer 213, and the piezo command value 214 of the IJP 2, and also acquires two pieces of data, the inspection result and the average character height, from the inspection device 3. The six types of data obtained are input to the classifier 624.

Based on the six types of data described above, the classifier 624 estimates whether the print head 20 is closer to class 1 (needs cleaning) or class 0 (no cleaning required) and outputs an intermediate value between 0 and 1.

The determination unit 612 determines whether cleaning is necessary or not based on the output result of the classifier 624. A threshold value is set in advance in the determination unit 612, and for example, if the output of the classifier 624 is 0.5 or more, it determines that cleaning of the print head 20 is necessary, instructs the IJP controller 21 to temporarily stop, and instructs the robot controller 54 to move the print head 20. On the other hand, if the output of the classifier 624 is less than 0.5, no instruction is given to the IJP controller 21 and the robot controller 54. In this case, printing by the IJP 2 and inspection by the inspection device 3 continue.

<Robot configuration and operation>
Next, the transfer of the print head 20 from the printing position to the cleaning machine by the robot 5 will be described.

As shown in FIG. 1 above, the robot 5 is composed of multiple arms 51 and hands 52 that are jointed to each other, and the print head 20 is attached to the tip of the hand 52 via a mounting bracket 53 with a U-shaped cross section. By rotating a servo motor (not shown) housed in each joint of the robot 5, the print head 20 attached to the hand 52 can be moved at any speed along any trajectory.

The movement of the head body 202 of the print head attached to the mounting bracket 53 is controlled using a controller 54. The controller 54 generates data on the movement trajectory and movement speed of the hand 52 as it follows the desired trajectory from the position where it is inserted into the head cover 201 to the position where it is inserted into the head holder 43 of the cleaning machine 3, and stores this data in a memory unit. When an instruction is given to transport the print head 20, the controller 54 reads the data from the memory unit and reproduces the movement trajectory and movement speed.

As mentioned above, the print head 20 is composed of a head body 202 whose main components are closely attached to a substrate 203, and a cylindrical head cover 201 arranged to cover the head body 202, and the head body 202 can be separated from the head cover 201.

Of these, the head cover 201 is attached to the XYZ axis stage 7 via a bracket 77 in a downward facing position and is held at the desired position on the conveyor 8.

In contrast, the head body 202 can be moved freely in three-dimensional space by the robot 5. As shown in FIG. 1, when the printer 2 is in operation, the head body 202 is held inserted in the head cover 201 and is used for printing on the printing substrate PT.

On the other hand, when the cleaning determination device 61 instructs the robot 5 to transfer the head to the cleaner 4, the robot 5 raises the head body 202 and removes it from the head cover 201, as shown by the white arrow in Figure 4, and transfers it to the cleaner 4 and inserts it into the head holder 43.

In this way, the head body 202 and head cover 201 of the print head 20 can be separated, and the head holder 201 is held in the printing position. When cleaning the print head 20, the robot 5 is used to transport only the head body 202 to the cleaning machine 4, making it possible to clean the print head 20 without the need for human labor.

In this embodiment, the case where printing is performed on the top surface of the printing substrate PT transported by the conveyor 8 has been described, but the head body 202 can also be cleaned according to the above-mentioned procedure when printing on the side or bottom surface of the printing substrate PT. In this case, however, the head cover 201 must be held in a horizontal position, and the robot 5 must move the head body 202 horizontally to remove it from the head cover 201, and then move it to the cleaning machine 4 while changing the position of the head body 202 from the horizontal position to a vertical position.

<Configuration and operation of the cleaning machine>
Next, a description will be given of cleaning of the head body 202 by the cleaner 4. The head body 202 of the print head transferred to the cleaner 4 by the robot 5 is inserted into a cylindrical head holder 43 provided on the upper part of the cleaner 4 as shown in Fig. 12, and is cleaned by spraying a solvent onto the dirty parts.

As mentioned above, the charging electrodes and gutters built into the print head 20 become dirty due to the collision of ink mist and ink droplets generated during operation, and ink solids adhere to their surfaces. If this is left unattended, it will affect the flight of the ink droplets, so it is necessary to clean them to remove the ink solids before the dirt becomes too severe.

Figure 13 shows the cleaner 4 with the lid 41 open. The main components of the cleaner 4, the cleaning chamber 42, head holder 43, control box 44, pump unit 45, circulating solvent tank 46, and finishing solvent tank 47, are arranged in a rectangular parallelepiped housing 40. Each component is connected by pipes, and check valves, filters, etc. are attached to the pipes, but their explanation will be omitted here.

The cleaning chamber 42 is a room where the head body 202 is cleaned, and a cylindrical head holder 43 into which the head body 202 is inserted is attached to the top. Although not shown, multiple nozzles are installed inside the cleaning chamber 42 to spray the solvent onto the electrodes of the head body 202, etc.

The control box 44 houses a controller (not shown) that controls the operation of the cleaner 4. When the position sensor detects that the head body 202 has been inserted into the head holder 43, the controller drives the pump unit 45 to start cleaning the head body 202, and ends the cleaning when the time set by the timer has elapsed.

The solvent pumped from the circulating solvent tank 46 by the pump unit 45 is released from a nozzle in the cleaning chamber 42 to wash away solid matter adhering to the surfaces of electrodes, etc. The contaminated solvent from which the solid matter has dissolved is collected in the circulating solvent tank 46 through a pipe attached to the bottom of the cleaning chamber 42.

After the cleaning using the solvent in the circulating solvent tank 46 is completed, the controller sprays clean solvent from the finishing solvent tank 47 from the nozzle to perform finishing cleaning for a specified period of time. The solvent used for the finishing cleaning is collected in the circulating solvent tank 46 by operating the switching valve, so that unused solvent is always stored in the finishing solvent tank 47.

After the cleaning is completed and the ink and other substances that have adhered to the head body 202 have been removed by spraying the solvent, the head body 202 waits for the solvent to evaporate by natural drying for a specified time set by a timer. When the drying is completed, a signal indicating that the cleaning is complete is sent from the controller (not shown) of the cleaner 4 to the general controller 6.

When the general controller 6 receives a signal from the cleaning device 4 controller indicating that cleaning of the head body 202 is complete, it instructs the robot 5 to move the head body 202 to its initial position, i.e., the position where printing will be performed, in preparation for the next printing. The general controller 6 notifies the IJP controller 21 that preparation for printing is complete. The IJP controller 21 checks whether printing data remains, and if so, resumes printing.

As described above, in the cleaning system according to this embodiment, a classifier is created by performing machine learning using data indicating the operating state obtained from the inkjet printer and data indicating the inspection results obtained from the inspection device, and the classifier is then used to determine whether or not the print head needs to be cleaned. Therefore, since there is no need for an operator to visually check the degree of dirt on the print head, the cleaning process can be easily automated and unmanned.

In the above embodiment, the four types of data obtained from IJP and the two types of data obtained from the inspection device are used as the data to be input to the cleaning determination device, but this is not limited to these. It goes without saying that if, through learning, more appropriate data is found for determining the need for cleaning, this data may be added or replaced.

In addition, in this embodiment, a cylindrical cover is used as the head cover, but this is not limited to this. Depending on the shape and density of the material placed on the head body, a cover with a square or hexagonal cross section may be used.

PT Printed material 1 Cleaning system 2 IJP
3 Inspection device 4 Cleaning machine 5 Robot 6 General controller 7 XYZ-axis stage 8 Conveyor 11 Control box 12 Table 20 Print head 21, 34, 54 Controller 22 Ink tank 23a, 23b Pump 24 Gun 25 Charging electrode 26 Detection electrode 27 Deflection electrode 28 Gutter 31 Camera 32 Illumination 33 Photoelectric sensor 40 Housing 42 Cleaning chamber 43 Head holder 44 Control box 45 Pump unit 46, 47 Solvent tank 51 Arm 52 Hand 53 Mounting bracket 61 Cleaning judgment device 62 Classifier creation device 71 X-axis stage 72 Y-axis stage 73 Z-axis stage 77 Support member

Claims (6)

an inkjet printer comprising a print head comprising: a gun which applies a constant periodic vibration to the ejected ink to generate successive ink droplets; a charging electrode which applies a step-wave voltage synchronized with the period of the ink droplets to charge the ink droplets; and a deflection electrode which deflects the charged ink droplets according to the degree of charge and causes the ink droplets to land on a printing surface of a substrate; the ink jet printer causes the ink droplets ejected from the print head to land on a substrate transported by a conveyor, forming characters with multiple rows of printing dots;
an inspection device that photographs the characters printed on the printing medium with a camera and judges whether the printed characters are appropriate;
a cleaning machine for cleaning the print head contaminated by ink with a solvent;
a robot for transferring the print head from a printing position to the cleaning machine;
a general controller for controlling the operations of the inkjet printer, the inspection device, the cleaning device and the robot;
the overall controller further includes a classifier that classifies the cases into cases where cleaning of the print head is required and cases where cleaning of the print head is not required, the classifier being created by performing machine learning using data indicating an operating state obtained from the inkjet printer and data indicating an inspection result obtained from the inspection device;
The general controller includes:
When it is determined that cleaning of the print head is necessary based on a classification result of the classifier using data indicating an operating state obtained from the inkjet printer and data indicating an inspection result obtained from the inspection device as input,
Instructing the inkjet printer to stop operation;
Instructing the robot to move the print head from the printing position to the cleaning machine;
and an automatic print head cleaning system for instructing the cleaning machine to clean the print head. the print head is comprised of a head body on which the gun, a charging electrode and a deflection electrode are mounted, and a cylindrical head cover in which the gun, the charging electrode and the deflection electrode are housed in a hollow portion and in which a slit is formed through which the charged ink droplets pass;
2. The automatic print head cleaning system according to claim 1, wherein the robot transfers only the head body to the cleaning machine, and the head cover is always held in the printing position. The automatic print head cleaning system according to claim 2, wherein the head cover is held at a desired position near the conveyor by a holding means, and the position in three-dimensional space can be adjusted using the holding means. The general controller includes a classifier creating device that creates the classifier, the classifier creating device comprising:
a learning data acquisition unit that acquires multiple types of data indicating an operating state from the inkjet printer and multiple types of data indicating an inspection result from the inspection device;
A data storage unit that stores the learning data;
a learning unit that uses the learning data stored in the data storage unit as an input and creates the classifier by performing machine learning using a deep neural network. The data obtained from the inkjet printer includes:
the pressure of the ink delivered to the gun;
the viscosity of the ink ejected from the nozzle of said gun;
5. The automatic print head cleaning system according to claim 1, wherein the detection time from when the ink droplets ejected from the nozzle of the gun are charged to when they are detected by a detection electrode, and a piezoelectric command value which is a voltage applied to a piezoelectric vibrator built into the gun. The data acquired from the inspection device includes:
5. The automatic print head cleaning system according to claim 1, wherein the determining step is whether the characters printed on the printing medium are proper or not, and an average height of the printed characters determined to be proper.

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