WO2009128572A1

WO2009128572A1 - Printing system

Info

Publication number: WO2009128572A1
Application number: PCT/KR2008/002119
Authority: WO
Inventors: Kye Si Kwon
Original assignee: Soonchunhyang University Industry Academy Cooperation Foundation
Priority date: 2008-04-15
Filing date: 2008-04-15
Publication date: 2009-10-22
Also published as: KR20100136506A; KR101207888B1

Abstract

Techniques for measuring ink motion are provided. In one embodiment, an apparatus includes a pulse generator, a waveform generator, a lighting unit, an image capturing unit, and a controller. The pulse generator is configured to generate a first trigger signal pulse and a second trigger signal pulse based on the control signal, a second control signal pulse being generated after a variable delay to the first trigger signal pulse. The waveform generator is configured to generate a waveform to drive a printing device based on the first trigger signal pulse. The lighting unit is configured to illuminate ink in the printing device based on the second trigger signal pulse. The image capturing unit is configured to capture a plurality of images of the ink, each image captured at a different time point with a different delay between the first and second trigger signal pulses.

Description

PRINTING SYSTEM

Brief Description of the Drawings

[I] The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings.

[2] Figure 1 shows a schematic block diagram of one embodiment of an apparatus capable of measuring ink motion. [3] Figure 2 shows an example of a voltage waveform used to drive a print head in one embodiment. [4] Figure 3 shows an example of an application program display showing the operation of measuring ink motion in one embodiment. [5] Figure 4 shows an example diagram illustrating images of the meniscus of the ink for two different delays, T₁ (upper figure) and T₂ (lower figure), between the first and second control signal pulses.

[6] Figure 5 is a schematic graph illustrating the meniscus motion obtained in one embodiment. [7] Figure 6 is a schematic graph that illustrates one example of a basic waveform used for measuring ink motion in one embodiment. [8] Figure 7 is a schematic graph that illustrates another example of a basic waveform used for measuring ink motion in one embodiment. [9] Figure 8 is a schematic graph that illustrates one example of designing a waveform in one embodiment. [10] Figure 9 is a schematic graph that illustrates another example of designing a waveform in one embodiment.

[I I] Figure 10 is a schematic graph that illustrates still another example of designing a waveform in one embodiment.

[12] Figure 11 is a flow chart that illustrates a method of measuring the motion of an ink, according to one embodiment. [13] Figure 12 is a flow chart that illustrates a method of diagnosing an inkjet printing device, according to one embodiment. [14] Figure 13 is a flow chart that illustrates a method of designing a waveform for driving a printing device, according to one embodiment. [15] BACKGROUND [16] Recent developments in inkjet printing technology have led to the application of the technology to display manufacturing processes, as well as office printers. InkJet printing technology makes use of ink droplets to form specific patterns on a target object, such as a sheet of paper, or other substrate. Using current inkjet printing technology, it is possible to control the volume of a droplet from an inkjet print head to an accuracy of a few picolitres and the location of a droplet on the target object to an accuracy of a few micrometers. Due to these features, inkjet technology has emerged as a powerful tool for patterning electronics devices, such as large area display applications, radio frequency identification (RFID), printed circuit board (PCB) patterning, and the like.

[17] In order for inkjet technology to produce reliable patterning tools, the so-called jetting performance, such as droplet speed and droplet volume, needs to be controlled precisely. The jetting performance of inkjet printing may depend on the viscosity of the ink, print head, printing speed, printing environment, and the like. Thus, extensive research has been conducted to implement a printing head having nozzles that are well calibrated and consistent with jetting performance under a given environment, where uniform patterning is obtained throughout the substrate. For example, the speed of each droplet or the volume of the nozzle can be scanned and the input voltage of each nozzle may be adjusted accordingly before any patterning process is performed.

[18] To conduct a more precise analysis of the jetting performance, it may be necessary to consider the characteristics of the ink contained in the nozzle, such as the motion of the ink (e.g., meniscus motion). Further, the print head may fail to jet the ink from the nozzle, in which case the lack of ink droplets may make it impossible to adjust the nozzle.

[19] SUMMARY

[20] Various embodiments of ink motion measuring techniques are disclosed herein. In accordance with one embodiment by way of non-limiting example, an apparatus includes a controller configured to generate a first control signal, a pulse generator configured to generate a first trigger signal pulse and a second trigger signal pulse based on the first control signal, a second control signal pulse being generated after a variable delay to the first trigger signal pulse, a waveform generator configured to generate a waveform to drive a printing device based on the first trigger signal pulse, a lighting unit configured to illuminate ink in the printing device based on the second trigger signal pulse, and an image capturing unit configured to capture a plurality of images of the ink, each image captured for a different delay between the first and second trigger signal pulses.

[21] The Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[22] DETAILED DESCRIPTION

[23] It will be readily understood that the components of the present disclosure, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of apparatus and methods in accordance with the present disclosure, as represented in the Figures, is not intended to limit the scope of the disclosure, as claimed, but is merely representative of certain examples of embodiments in accordance with the disclosure. The presently described embodiments will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout.

[24] Referring to Figure 1, one embodiment of an apparatus 100 capable of measuring ink motion is illustrated. In certain embodiments, the apparatus 100 includes a print head 102, a lighting unit 104, a lighting unit driver 106, an image capturing unit 108, a controller 110, and a print head driver 112. For example, the lighting unit 104 may include a light emitting diode (LED), a laser diode (LD), or the like, while the image capturing unit 108 may include any type of camera, such as a charge-coupled device (CCD) camera and the like. The print head 102 may include any form of inkjet print head, such as a piezo inkjet head and the like. Each of the components 102, 104, 106, 108, 110, and 112 may be provided on a single device or spread over several devices depending on the implementation. For example, the controller 110, the lighting unit driver 106, and the print head driver 112 may be implemented in a single integrated device with the lighting unit 104 and the image capturing unit 108. Alternatively, the controller 110, the lighting unit driver 106, and the print head driver 112 may be implemented in a separable device detachable from a device or devices embedding the lighting unit 104 and the image capturing unit 108. In both cases, the print head 102 may be installed in a separate device (e.g., a printer) or integrated with the controller 110.

[25] In certain embodiments, the print head driver 112 may include a trigger signal pulse generator 114 and a waveform generator 116. The controller 110 may control the operations of the print head driver 112 by e g., transmitting a control signal to the print head driver 112. Under the control of the controller 110 (e.g., upon receiving the control signal), the print head driver 112 causes the trigger signal pulse generator 114 to generate first and second trigger signal pulses 118 and 120 that are provided to the waveform generator 116 and the lighting unit driver 106, respectively. Alternatively, the trigger signal pulse generator 114 can be installed as a separate unit exterior to the print head driver 112. In this case, the trigger signal pulse generator 114 can link the controller 110 to the print head driver 112 through an interface, such as a wired line connection. The trigger signal pulse generator 114 provides the first trigger signal pulses to the waveform generator 116.

[26] The trigger signal pulse generator 114 may control the first trigger signal pulse 118 to have a certain frequency, e.g., 1 kHz, under the control of the controller 110. For example, the controller 110 may execute an application software program or receive a user input to determine the frequency of the first trigger signal pulse 118. In some embodiments, the trigger signal pulse generator 114 may be implemented with counters in a multi- function Input/Output unit. The trigger signal pulse generator 114 may generate a second trigger signal pulse 120 triggered by the first trigger signal pulse 118. For example, as shown in Figure 1, the second trigger signal pulse 120 is generated to have a delay T₁ relative to the first trigger signal pulse 118. The delay T₁ between the first and second trigger signal pulses 118 and 120 can be variable, e.g., according to the setting provided by a user and/or control by the controller 110. That is, the delay T₁ can be adjusted manually or automatically via an algorithm executed by the controller 110, upon receiving a user input. In this way, the controller 110 can control the operations of the print head 102 and the lighting unit 104 in a time- varying sequential fashion. In other words, the controller 110 may control the lighting unit 104 to operate after the delay T₁ to the operation of the print head 102.

[27] The trigger signal pulse generator 114 delivers the first trigger signal pulse 118 to the waveform generator 116. Triggered by the first trigger signal pulse 118, the waveform generator 116 may generate a waveform for driving the print head 102. Figure 2 shows an example of the voltage waveform used to drive the inkjet print head 102, in one embodiment. The waveform can be characterized by a rising time, a falling time, a dwell time, and the like, where these characteristics may be adjusted according to the requirements of the apparatus 100. For example, the controller 110 may generate waveform data and send the data to the waveform generator 116 through an interface such as a general purpose interface bus (GPIB). The waveform generator 116 may have a sampling frequency of up to, e.g., 15 MHz, in which case the waveform generator 116 may make as many as 15 data points per microsecond (μs) to define the driving waveform voltage. The waveform generator 116 applies the waveform to the print head 102 having a nozzle that contains the ink. The nozzle of the print head 102 may have various diameters depending on its application field and/or design requirements. For example, the nozzle diameter may have the order of approximately tens of μm, such as 50 μm. Various inks, such as a nano silver ink with nanoparticles of approximately 10 nm diameter dissolved in de-ionized water, may be used as the jetting material of the ink. [28] The lighting unit driver 106 receives the second trigger signal pulse 120 to drive the lighting unit 104. For example, when triggered by the second trigger signal pulse 120, the lighting unit driver 106 may control the lighting unit 104 to illuminate the ink contained in the nozzle of the print head 102 and the image capturing unit 108 to start capturing the images of the ink. In this way, the image capturing unit 108 may take a picture of the meniscus motion of the ink when the ink is illuminated by the lighting unit 104. In an example use of the image capturing unit 108, a user may operate the controller 110 to adjust the lighting unit 104 so that the image capturing unit 108 may capture images of the meniscus motion of the ink automatically. The image capturing unit 108 delivers the images to the controller 110 by using various interfaces between the image capturing unit 108 and the controller 110 including, but not limited to, a wired line, a cable, a wireless connection, or any other interface methods. The controller 110 may process the images to generate a graph showing the meniscus motion of the ink and deliver the graph to a display (not shown) that displays the graph, for example, for the user's reference.

[29] In selected embodiments where the image capturing unit 108 is installed in a separate device detachable from the controller 110, the images may be transmitted from the image capturing unit 108 to the controller 110 using a wired communication protocol, a wireless communication protocol, or a combination thereof. For example, the wired or wireless communication protocol may be implemented by employing a digital interface protocol, such as a serial port, parallel port, PS/2 port, universal serial bus (USB) link, firewire/IEEE 1394 link, or a wireless interface connection, such as an infra-red interface, BloothTooth, ZigBee, high definition multimedia interface (HDMI), high-bandwidth digital contents projection (HDCP), wireless fidelity (Wi-Fi), or the like. In one embodiment, the apparatus 100 may be configured with a suitable operating system to install and run executable codes, programs, etc. from one or more computer readable media, such as a floppy disk, CD-ROM, DVD, a detachable memory, a USB memory, a memory stick, a memory card, or the like.

[30] Figure 3 shows an example of an application program display 300 showing the operation of measuring ink motion in one embodiment. The application program display 300 may include an edge coordinate indicator 302, a detected edge display 304, a threshold controller 306, an image viewer 308, a graph viewer 310, a start button 312, an operational interface 314, a save button 316, and an end button 318. In certain embodiments, a user may set the operational parameters through the operational interface 314 to determine the delay T₁ between the first and second trigger signal pulses 118 and 120. For example, as shown in Figure 3, a user may set the start time of the delay T₁ to be 2 μsec, the end time to be 400 μsec, the increment time to be 2 μsec, and the average number of capturing images for one increment time to be 5. The user may initiate the measuring operation by pressing the start button 312. Under the given settings, the controller 110 may generate a control signal to cause the trigger signal pulse generator 114 to variably adjust the delay T₁ between the first and second trigger signal pulses 118 and 120 that are provided to the print head 102 and the lighting unit 104, respectively. In this way, the image capturing unit 108 may capture images of the meniscus motion of the ink when the lighting unit 104 illuminates the ink driven by the second trigger signal pulse 120 having different values of delay T₁ relative to the first trigger signal pulse 118 at a given time. The progress bar indicates the progress of the measuring operation, and the user may save the images by pressing the save button 316 and end the operation by pressing the end button 318.

[31] As illustrated in Figure 3, the image viewer 308 shows each of the images captured at a different delay T₁. The controller 110 may apply a numerical operation (e.g., an edge detection algorithm) to each of the images to detect discontinuities in the pixel intensity of the image along a reference line in the image viewer 308. In other words, the controller 110 uses the edge detection technique to obtain information about the location of the ink boundaries along the reference line. The detected edge display 304 shows the edge boundary of the ink for the image displayed in the image viewer 308, while the edge coordinate indicator 302 displays the X-Y coordinates of the detected edge along the reference line. In certain embodiments, the controller 100 may determine a region of interest (ROI) to confine the target area to be processed in the image. For example, in the edge detection algorithm, the controller 110 may define the ROI by the reference line in the image that selects the pixel data to be analyzed, as shown in Figure 3. Alternatively, the controller 110 may set an area having a certain shape as the ROI, as shown in Figure 4. Although a rectangular shape is illustrated as the ROI in Figure 4, the shape of the ROI can be adjusted according to the implementation requirements and includes, but is not limited to, a circle, an eclipse, a triangle, or the like. For example, the controller 110 may execute a software program that is developed such that the ROI can be specified either interactively or program- matically. The ROI includes image pixels having values that vary, e.g., from 0 to 255, according to the brightness of the image. By using a suitable threshold value, the controller 110 may detect the edge locations of the meniscus of the ink, where the image pixel values cross the threshold value. A user may determine the threshold value by operating the threshold controller 306 of the application program display 300.

[32] Referring to Figure 4, an example diagram illustrating the meniscus motion of the ink for two different delays, T₁ (upper figure) and T₂ (lower figure), between the first and second trigger signal pulses 118 and 120 is illustrated. The trigger signal pulse generator 114 applies the first trigger signal pulse 118 to the waveform generator 116 to generate a waveform for driving the print head 102, and the second trigger signal pulse 120 to the lighting unit driver 106 for driving the lighting unit 104, under the command or instructions of the controller 110. The image capturing unit 108 captures images of the meniscus of the ink at the time when the lighting unit 104 illuminates the ink in the print head 102, and stores the images in a storing unit. The controller 110 may retrieve the stored images and perform the edge detection algorithm on the images. As shown in Figure 4, the controller 110 may display two images of the meniscus of the ink for the delays T₁ and T₂ , where it can be seen that the meniscus of the ink moves downward as the delay changes from T₁ to T₂.

[33] Referring back to Figure 3, the graph viewer 310 displays a graph showing the meniscus motion of the ink as the delay changes as time lapses. For example, the delay may change according to the setting specified by, e.g., a user through the operational interface 314, or by executing a software program that is designed to adjust the meniscus motion measurement process, or the like. The horizontal axis (i.e., the X axis) of the graph indicates the time of the delay (μsec) whereas the vertical axis (i.e., the Y axis) of the graph represents the vibrating amplitude of the meniscus motion of the ink. The amplitude of the meniscus motion may be indicated as having a negative value relative to the predetermined reference amplitude for the convenience of the display. Each point in the graph is linked by collecting boundary locations on the reference line that are detected through the edge detection algorithm by varying the delay between the first and second trigger signal pulses 118 and 120. The fluctuation of the graph displays the meniscus motion of the ink along the reference line. For example, as the graph fluctuates upward in the graph viewer 310, the meniscus of the ink moves downward along the reference line in the image viewer 308, which also means that the detected edge displayed in the detected edge display 304 moves leftward (i.e., the Y coordinate value in the edge coordinate indicator 302 decreases).

[34] Referring to Figure 5, a schematic graph illustrating the meniscus motion obtained in one embodiment is illustrated. As shown in Figure 5, the graph of the meniscus motion may vibrate for a period of time and have an exponentially decaying form as time passes. In selected embodiments, the controller 110 may analyze the graph of the meniscus motion to obtain the characteristics of the meniscus motion, such as damping ratio, peak amplitude, and the like. The controller 110 may perform a numerical analysis on the characteristics of the meniscus motion by modeling the meniscus motion with a mathematical equation, as shown below:

[35] _{y =} Ae^~ξω _" ¹ cos(ω_dt)

[36] where A indicates the peak amplitude, ξ indicates the damping ratio, and and

relate to the period of the graph. By using the above equation, the controller 110 may estimate the status of the ink and the print head 102, based on the characteristics of the meniscus motion of the ink. For example, the controller 110 may interpret the meniscus motion as follows: (i) a larger peak amplitude to mean a stronger pressure (i.e., a larger voltage) for jetting the ink (i.e., easy jetting); (ii) a higher damping ratio (i.e., larger ξ

) to mean a higher viscosity of the ink; and (iii) a smaller period (i.e., larger

) to mean a faster speed of the sound of the ink.

[37] In selected embodiments, the controller 110 may diagnose the operation of the print head 102 and the status of the ink used in the print head 102 from the analyzed results of the graph. In other words, the controller 110 may detect abnormal jetting conditions, such as bubbles trapped in the print head 102, by observing the peak amplitude, and measure the ink material status, such as viscosity, speed of sound, and the like, by observing the damping ratio and the period from the graph. For example, when the controller 110 determines that the peak amplitude is small, the controller 110 may display an indicator showing that the pressure for jetting the ink needs to be increased. Further, when the controller 110 determines that the damping ratio is high, the controller 110 may display an indicator showing that the viscosity of the ink needs to be reduced.

[38] Referring to Figures 6 and 7, schematic graphs that illustrate examples of basic waveforms for measuring the meniscus motion of the ink for waveform designs are illustrated. The controller 110 delivers a control signal to cause the print head driver 112 to generate the basic waveforms for driving the print head 102. An amplitude of the basic waveforms may have negative and positive signs as shown in Figures 6 and 7, respectively. That is, the amplitude of the basic waveforms may be above or below a reference level indicated by a horizontal axis (i.e., X axis) of the graphs. The basic waveforms may have falling and rising times having predetermined values, e.g., 2-10 μsec. To measure the meniscus motions, the waveform generator 116 in the print head driver 112 may generate a basic waveform having a large dwell time, e.g., more than 30 μsec. The positively signed basic waveform of Figure 7 may be generated with a certain delay relative to the negatively signed basic waveform of Figure 6. The controller 110 may measure the meniscus motion of the ink to display graphs of the meniscus motion for the two basic waveforms, as shown in Figures 6 and 7. Further, the controller 110 may use the measured meniscus motions to modify the basic waveforms to design new waveforms. For example, based on the measured meniscus motion, the controller 110 may determine the voltage amplitude and the dwell time of the new waveform. In certain embodiments, the controller 110 measures the characteristics of the meniscus motion of the ink, such as the period, peak amplitude, and damping ratio, and uses the characteristics to design a new waveform. For example, the controller 110 may determine the dwell time of the waveform to be the period of the meniscus motion, and determine the voltage amplitude of the waveform according to the peak amplitude of the meniscus motion.

[39] Referring to Figures 8 to 10, schematic graphs that illustrate examples of designing waveforms are illustrated. From the measured meniscus motion, the controller 110 determines whether the peak amplitude of the meniscus motion will be sufficient to initiate the jetting of ink from the print head 102. Figure 8 shows an example where the controller 110 determines that the amplitude of the meniscus motion will be sufficient for jetting ink from the print head 102. In this case, the controller 110 causes the waveform generator 116 to generate a waveform having a dwell time equal to the period of the meniscus motion T. That is, the controller 110 triggers the waveform generator 116 to generate the basic waveform shown in Figure 6 and, after the delay T, triggers the waveform generator 116 to generate the basic waveform shown in Figure 7 (see upper figure of Figure 8). In this way, the waveform generator 116 may generate a waveform that cancels out the meniscus vibration after jetting ink (see lower figure of Figure 8), while maintaining the peak amplitude of the meniscus motion. By applying the designed waveform, the print head 102 may initiate the jetting of the ink when the voltage level increases.

[40] Figure 9 shows an example where the controller 110 determines that the amplitude of the meniscus motion will not be sufficient for jetting ink from the print head 102. In this case, the controller 110 causes the waveform generator 116 to generate a waveform having a dwell time equal to half the period (772) of the meniscus motion T. That is, the controller 110 triggers the waveform generator 116 to generate the basic waveform shown in Figure 6 with a sign inversion and, after the delay 7/2, triggers the waveform generator 116 to generate the basic waveform shown in Figure 7 with a sign inversion (see upper figure of Figure 9). The sign inversion can be implemented by applying a voltage opposite to the voltage applied to generate the basic waveforms. In this way, the waveform generator 116 may generate a waveform that has an amplified amplitude sufficient to jet ink (see lower figure of Figure 9). The amplified waveform can increase the pressure wave applied to the print head 102. According to the design of the waveform, the pressure wave can be doubled or at least amplified to sufficiently initiate the jetting of the ink from the print head 102.

[41] Figure 10 shows an example where the controller 110 determines that the amplitude of the meniscus motion is not sufficient for jetting ink from the print head 102, and that the meniscus vibration after jetting ink needs to be canceled. In this case, the waveform generator 116 generates a waveform having a dwell time of the period of T/2 in a similar fashion as illustrated in Figure 9, and then generates a waveform having a dwell time of the period of T in a similar fashion as illustrated in Figure 8 (see upper figure of Figure 10). In this way, the waveform generator 116 may generate a waveform that has an amplified amplitude sufficient to jet ink and cancels out the meniscus vibration after jetting ink (see lower figure of Figure 10).

[42] Referring to Figure 11, one embodiment of a method for measuring the motion of an ink is illustrated. Initially at operation 1102, the trigger signal pulse generator 114 in the print head driver 112 applies the first trigger signal pulse 118 to the waveform generator 116 (see also Figure 1). In selected embodiments, a user may use a software program to execute the operations that are run by a computing device. The waveform generator 116 in the print head driver 112 may generate basic waveforms, such as the waveforms shown in Figures 6 and 7. In this way, the print head driver 112 may apply the first trigger signal pulse 118 to the print head 102 to cause the meniscus motion of the ink. To measure the meniscus motion of the ink, the print head driver 112 may adjust the amplitude of the waveform (i.e., the voltage level) not to allow the print head 102 to jet the ink so that no droplets appear from the print head 102 during the measurement of the meniscus motion.

[43] At operation 1104, upon receiving the control signal from the controller 110, the trigger signal pulse generator 114 in the print head driver 112 applies the second trigger signal pulse 120 to the lighting unit driver 106 for driving the lighting unit 104. The trigger signal pulse generator 114 retards the second trigger signal pulse 120 from the first trigger signal pulse 118 by the delay T₁. The trigger signal pulse generator 114 may increase the delay by a unit of, e.g., 2 μsec, based on the input by a user through the software program as shown in Figure 3.

[44] At operation 1106, the image capturing unit 108 captures images of the meniscus motion of the ink that is contained in the print head 102. The image capturing unit 108 captures each image of the ink illuminated by the lighting unit 104 that is driven by the second trigger signal pulse 120 having a given delay T₁ relative to the first control signal pulse 118. In this way, the image capturing unit 108 may obtain a still shot (i.e., a frozen image) of the meniscus motion of the ink. By varying the delay between the first and second control signal pulses 118 and 120, the image capturing unit 108 may capture images of the ink at different time points. The image capturing unit 108 may store the images in a storing unit such as RAM, ROM, CD-ROM, and the like. In certain embodiments, the lighting unit 104 may include a light emitting diode (LED), a laser diode (LD), or the like, while the image capturing unit 108 may include any type of camera, such as a charge-coupled device (CCD) camera.

[45] At operation 1108, the controller 110 carries out an image processing on the images obtained by the image capturing unit 108. The controller 110 may apply a numerical operation (e.g., an edge detection algorithm) to each of the images to detect discontinuities in the pixel intensity of the image along a reference line. In other words, the controller 110 uses edge detection techniques to obtain information about the location of the ink boundaries in each image of the ink. In selected embodiments, the controller 110 may display the image of the ink on a display by using an application program as shown in Figure 3. For example, the detected edge display 304 shows the edge boundary of the ink for the image displayed in the image viewer 308, while the edge coordinate indicator 302 indicates the X-Y coordinates of the detected edge. In certain embodiments, the controller 100 may determine a region of interest (ROI) to confine the target area to be processed in the image. In the edge detection algorithm, the controller 110 may define the ROI by the reference line in the image that selects the pixel data to be analyzed as shown in Figure 3. Alternatively, the controller 110 may set an area having a certain shape as the ROI. Although a rectangular shape is illustrated as the ROI in Figure 4, the shape of the ROI can be adjusted according to the implementation requirements and includes, but is not limited to, a circle, an eclipse, a triangle, or the like. For example, the controller 110 may execute software that is developed such that the ROI line can be specified either interactively or program- matically. The ROI consists of image pixels having values that vary, e.g., from 0 to 255, according to the brightness of the image. By using a suitable threshold value, the controller 110 may detect the edge locations of the meniscus of the ink, where the image pixel values cross the threshold value. A user may determine the threshold value by operating the threshold controller 306 of the application program display 300.

[46] At operation 1110, the controller 110 obtains the meniscus motion graph from the processed images of the ink. The controller 110 collects the locations on the reference line that are detected through the edge detection algorithm by varying the delay between the first and second trigger signal pulses 118 and 120, and links each point to generate the meniscus motion graph as shown in the graph viewer 310 of Figure 3. The graph viewer 310 displays a graph showing the meniscus motion of the ink as the delay changes according to the setting by a user through the operational interface 314.

[47] One skilled in the art will appreciate that, for this and other processes and methods disclosed herein, the functions performed in the processes and methods may be implemented in differing order. Furthermore, the outlined steps and operations are only provided as examples, and some of the steps and operations may be optional, combined into fewer steps and operations, or expanded into additional steps and operations without detracting from the essence of the disclosed embodiments.

[48] Referring to Figure 12, one embodiment of a method for diagnosing an inkjet printing device is illustrated. Initially at operation 1202, the controller controls the trigger signal pulse generator 114 to apply the first control signal pulse 118 to the print head 102 of a printing device in a similar fashion as described with reference to operation 1102 of Figure 11.

[49] At operation 1204, the controller 110 obtains images of the meniscus motion of the ink that are taken by illuminating the ink with the lighting unit 104 driven by the second trigger signal pulse 120. That is, under the control or instruction of the controller 110, the trigger signal pulse generator 114 in the print head driver 112 applies the second trigger signal pulse 120 to the lighting unit driver 106 for driving the lighting unit 104 in a similar fashion as described with reference to operation 1104 of Figure 11. The image capturing unit 108 captures images of the meniscus motion of the ink that is contained in the print head 102 and illuminated by the lighting unit 104 that is driven by the second trigger signal pulse 120 in a similar fashion as described with reference to operation 1106 of Figure 11.

[50] At operation 1206, the controller 110 performs image processing on the images obtained by the image capturing unit 108 in a similar fashion as described with reference to operation 1108 of Figure 11. In this way, the controller 110 may obtain the meniscus motion graph shown in Figure 5 and display the meniscus motion graph on the graph viewer 310 of the application program display 300 as shown in Figure 3.

[51] At operation 1208, the controller 110 may analyze the graph of the meniscus motion to obtain the characteristics of the meniscus motion, such as damping ratio, peak amplitude, and the like. In selected embodiments, the controller 110 may perform a numerical analysis on the characteristics of the meniscus motion by modeling the meniscus motion with a mathematical equation, as follows: y = Ae^~ξω"' cos(ωj) where A indicates the peak amplitude,

indicates the damping ratio, and ω,, and

indicate the period of the graph. By using numerical modeling, the controller 110 may estimate the characteristics of the meniscus motion of the ink. For example, the controller 110 may interpret the meniscus motion as follows: (i) a larger peak amplitude to mean a stronger pressure (i.e., a larger voltage) for jetting the ink (i.e., easy jetting); (ii) a higher damping ratio (i.e., larger

) to mean a faster speed of the sound of the ink.

[52] At operation 1210, the controller 110 outputs diagnosis information on the status of the print head and the material characteristics of the ink based on the analyzed results obtained at operation 1208. The controller 110 may detect abnormal jetting conditions, such as bubbles trapped in the print head, by observing the peak amplitude, and measure the ink material status, such as viscosity, speed of sound, and the like, by observing the damping ratio and the period. For example, when the controller 110 determines that the peak amplitude is small, the controller 100 may display an indication that the pressure for jetting the ink needs to be increased. Further, when the controller 110 determines that the damping ratio is high, the controller 100 may display an indication that the viscosity of the ink needs to be reduced.

[53] Referring to Figure 13, one embodiment of a method for designing a waveform to drive a printing device is illustrated. Through operations 1302 to 1306, the controller 110 may obtain the meniscus motion graph in a similar fashion as described with reference to operations 1202 to 1206 of Figure 12. In particular, the controller 110 delivers a control signal to cause the print head driver 112 to generate the basic waveforms for driving the print head 102, which have negative and positive signs as shown in Figures 6 and 7, respectively. The basic waveforms may have falling and rising times having predetermined values, e.g., 2-10 μsec. The controller 110 may measure the meniscus motions to display graphs of the meniscus motions for the two basic waveforms, as shown in Figures 6 and 7. To measure the meniscus motions, the waveform generator 116 in the print head driver 112 may generate a basic waveform having a large dwell time, e.g., more than 30 μsec.

[54] At operation 1308, the controller 110 may design a waveform based on the meniscus motion graph obtained through operations 1302 to 1306. In particular, the controller 110 may use the measured meniscus motion for determining the voltage amplitude and the dwell time of the waveform. The controller 110 measures the characteristics of the meniscus motion of the ink, such as the period, peak amplitude, and damping ratio, and uses the characteristics to modify the basic waveforms. For example, the controller 110 may determine the dwell time of the waveform to be the period of the meniscus motion, and determine the voltage amplitude of the waveform according to the peak amplitude of the meniscus motion.

[55] At operation 1310, the controller 110 combines the basic waveforms based on the status of the print head 102 and the material status of the ink. From the measured meniscus motion, the controller 110 determines whether the peak amplitude of the meniscus motion is sufficient to initiate the jetting of ink from the print head 102 that is derived by the basic waveforms. If the controller 110 determines that the meniscus motion is sufficient, the controller 110 triggers the waveform generator 116 to generate the basic waveform shown in Figure 6 and after the delay T, triggers the waveform generator 116 to generate the basic waveform shown in Figure 7. In this way, the waveform generator 116 may generate a waveform that has dwell time T (i.e., equal to the period of the meniscus motion) and cancels out the meniscus vibration after jetting ink. If the controller 110 determines that the meniscus motion is not sufficient, the controller 110 triggers the waveform generator 116 to generate the basic waveform shown in Figure 6 with a sign inversion and after the delay T/2, triggers the waveform generator 116 to generate the basic waveform shown in Figure 7 with a sign inversion. The sign inversion can be implemented by applying a voltage opposite to the voltage applied to generate the basic waveforms. In this way, the waveform generator 116 may generate a waveform that has a dwell time T/2 (i.e., equal to half of the period of the meniscus motion) and has an amplified amplitude sufficient to jet ink. In addition to the waveform having the period of T/2, the waveform generator 116 generates a waveform having the period of T and then combines the two waveforms with the periods T/2 and T, respectively, to generate a combined waveform as shown in Figure 10. In this way, the waveform generator 116 may generate a waveform that has amplified amplitude sufficient to jet ink and cancels out the meniscus vibration after jetting ink.

[56] In light of the present disclosure, those skilled in the art will appreciate that the apparatus and methods described herein may be implemented in hardware, software, firmware, middleware, or combinations thereof and utilized in systems, subsystems, components, or sub-components thereof. For example, a method implemented in software may include computer code to perform the operations of the method. This computer code may be stored in a machine-readable medium, such as a processor- readable medium or a computer program product, or transmitted as a computer data signal embodied in a carrier wave, or a signal modulated by a carrier, over a transmission medium or communication link. The machine-readable medium or processor-readable medium may include any medium capable of storing or transferring information in a form readable and executable by a machine (e.g., by a processor, a computer, etc.).

[57] The present disclosure may be embodied in other specific forms without departing from its basic features or characteristics. Thus, the described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the disclosure is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

[I] An apparatus comprising: a controller configured to generate a control signal; a pulse generator configured to generate a first trigger signal pulse and a second trigger signal pulse based on the control signal, the second control signal pulse being generated after a variable delay to the first trigger signal pulse; a waveform generator configured to generate a waveform to drive a printing device based on the first trigger signal pulse; a lighting unit configured to illuminate an ink in the printing device based on the second trigger signal pulse; and an image capturing unit configured to capture a plurality of images of the ink, each image captured for a different delay between the first and second trigger signal pulses. [2] The apparatus of Claim 1, further comprising a memory configured to store the plurality of images of the ink. [3] The apparatus of Claim 1, wherein the waveform generator is configured to drive a printing device to control a motion of the ink contained in a nozzle of the printing device. [4] The apparatus of Claim 1, wherein the controller is further configured to process the plurality of images of the ink to generate information on the ink. [5] The apparatus of Claim 1, wherein the controller is configured to process the plurality of images by applying an edge detection algorithm to the plurality of images. [6] The apparatus of Claim 4, further comprising a display to display the information on the ink. [7] The apparatus of Claim 4, wherein the information on the ink includes a meniscus motion of the ink. [8] The apparatus of Claim 7, wherein the controller is configured to designate a region of interest (ROI) in each of the plurality of images to measure the meniscus motion of the ink. [9] The apparatus of Claim 8, wherein the ROI has a shape selected from the group consisting of a line, a circle, a rectangular, an eclipse, and a triangle. [10] The apparatus of Claim 7, wherein the controller is configured to generate a graph showing the meniscus motion of the ink.

[I I] The apparatus of Claim 8, wherein the controller is configured to apply a suitable threshold value to each of the plurality of the images to determine a meniscus boundary of the ink. [12] The apparatus of Claim 10, wherein the controller is configured to analyze the graph to determine a status of the ink and the printing device. [13] The apparatus of Claim 12, wherein the controller is configured to determine a viscosity of the ink according to a damping ratio of the graph. [14] The apparatus of Claim 10, wherein the controller is configured to modify a dwell time of the waveform according to a period of the graph. [15] The apparatus of Claim 1, wherein the lighting unit comprises a light emitting diode or a laser diode. [16] The apparatus of Claim 1, wherein the image capturing unit comprises a charge coupled device camera. [17] A method comprising : applying a first trigger signal pulse to drive a printing device; applying a second trigger signal pulse to a lighting unit, the second trigger signal pulse being generated after a variable delay to the first trigger signal pulse; capturing a plurality of images of an ink in the printing device, each image captured at a different time point with a different delay between the first and second trigger signal pulses; and processing the plurality of images to generate a graph showing information on the ink. [18] The method of Claim 17, wherein driving a printing device includes controlling a motion of the ink contained in a nozzle of the printing device. [19] The method of Claim 17, wherein processing the plurality of images includes applying an edge detection algorithm to the plurality of images. [20] The method of Claim 17, wherein the information on the ink includes a meniscus motion of the ink. [21] The method of Claim 20, wherein said processing the plurality of images comprises designating a region of interest (ROI) in each of the plurality of images to measure the meniscus motion of the ink. [22] The method of Claim 21, wherein said processing the plurality of images comprises applying a suitable threshold value to each of the plurality of the images to determine a meniscus boundary of the ink. [23] A method comprising: applying a first trigger signal pulse to generate a waveform for driving a printing device; obtaining a plurality of images of an ink contained in a print head by applying a second trigger signal pulse to a lighting unit, the second trigger signal pulse being generated after a variable delay to the first trigger signal pulse; processing the plurality of images to generate a graph showing a meniscus motion of the ink; and analyzing the graph to obtain a status of the printing device and the ink. [24] The method of Claim 23, wherein analyzing the graph includes determining a viscosity of the ink according to a damping ratio of the graph. [25] The method of Claim 23, further comprising adjusting the waveform based on the graph. [26] The method of Claim 25, adjusting the waveform includes determining a dwell time of the waveform according to a period of the graph.

[27] A computer-readable storage medium having stored thereon computer instructions that, when executed by a computer, cause the computer to perform a method comprising: applying a first trigger signal pulse to drive a printing device; applying a second trigger signal pulse to a lighting unit, the second trigger signal pulse being generated after a variable delay to the first trigger signal pulse; capturing a plurality of images of an ink in the printing device, each image captured at a different time point with a different delay between the first and second trigger signal pulses; and processing the plurality of images to generate a graph showing information on the ink.

[28] A computer-readable storage medium having stored thereon computer instructions that, when executed by a computer, cause the computer to perform a method comprising: applying a first trigger signal pulse to generate a waveform for driving a printing device; obtaining a plurality of images of an ink contained in a print head by applying a second trigger signal pulse to a lighting unit, the second trigger signal pulse being generated after a variable delay to the first trigger signal pulse; processing the plurality of images to generate a graph showing a meniscus motion of the ink; and analyzing the graph to obtain a status of the printing device and the ink.