Patent Publication Number: US-8529011-B2

Title: Drop detection mechanism and a method of use thereof

Description:
BACKGROUND 
     Generally, drop detection devices are used to detect ink drops ejected by printhead nozzles. Based on the detection of ink drops, the status of a particular nozzle may be diagnosed. Typically, a printhead ejects ink drops in response to drive signals generated by print control circuitry in a printer. A printhead that ejects ink drops in response to drive signals may be referred to as a drop on demand printhead. Typically, there are two commonly used drop on demand technologies. These technologies are thermal (or bubble-jet) inkjet printing and piezo-electric (or impulse) inkjet printing. In thermal inkjet printing, the energy for ink drop ejection is generated by resistor elements, which are electrically heated. Such elements heat rapidly in response to electrical signals controlled by a microprocessor and creates a vapor bubble that expels ink through one or more nozzles associated with the resistor elements. In piezo-electric inkjet printing, ink drops are ejected in response to the vibrations of a piezo-electric crystal. The piezo-electric crystal responds to an electrical signal controlled by a microprocessor. 
     Nozzles through which ink drops are ejected may become clogged with paper fibers or other debris during normal operation. The nozzles may also become clogged with dry ink during prolonged idle periods. Generally, printhead service stations are used for wiping the printhead and applying suction to the printhead to clear out any blocked nozzles. The ink drop detectors may be used to determine whether a printhead actually requires cleaning. Additionally the detectors may be used to detect permanent failures of individual nozzles that may be caused, for example, by the failure of heating elements (in thermal ink jets) or by the failure in the piezo-electric crystals (in impulse printers). Other examples are related to detection of nozzles which have failed to eject drops because of de-priming (losing detection devices may also be used to calibrate the nozzle position relative to other parts of the printing machine. 
     Typically only high end printing systems have a drop detection system due to cost constraints. Consequently, growing complexity of printheads and harsh competition in printer costs and performance require new solutions for improvement in speed and printed image quality. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a high-level flowchart of a method in accordance with an embodiment. 
         FIG. 2  is an exemplary drop ejection system in accordance with an embodiment. 
         FIG. 3  is a drop detector arrangement in accordance with an embodiment. 
         FIG. 4  shows an exemplary view of the drop detector arrangement in accordance with an alternate embodiment. 
         FIG. 5  shows an exemplary view of the drop detector arrangement in accordance with an alternate embodiment. 
         FIG. 6  shows an exemplary view of the drop detector arrangement in accordance with an alternate embodiment. 
         FIG. 7  shows an exemplary view of the drop detector arrangement in accordance with an alternate embodiment. 
         FIG. 8  shows an exemplary view of the drop detector arrangement in accordance with an alternate embodiment. 
         FIG. 9  shows an exemplary view of the drop detector arrangement in accordance with an alternate embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in the drawings for purposes of illustration, a drop detection mechanism and method of use thereof is disclosed. In an embodiment, a shaped laser beam is employed to scatter light off of ink drops that are fired from a plurality of nozzles. A low cost, high throughput detector is utilized to detect the individual drops and thereby calculate the drop count, drop velocity and other drop characteristics. Consequently, through the use of the below described embodiments, new levels of print image quality are enabled on a broad range of inkjet printers, including industrial and web printers. 
       FIG. 1  is a flowchart of a method in accordance with an embodiment. A first step  101  involves ejecting at least one drop from the drop ejector. A second step  102  involves utilizing a collimated light source to scatter light off of the at least one drop. A next step  103  includes utilizing at least one photo detector to detect the scattered light. Step  104  includes converting a signal from the least one photo detector into an electrical signal the signal being associated with the detected scattered light. A final step  105  includes transmitting the electrical signal to the drop ejection system. 
     Referring to  FIG. 2 , an exemplary drop ejection system  200  is illustrated. The depicted drop ejection system  200  includes an input/output (I/O) port  202 , print engine  204 , input tray  206 , output tray  208  and a drop detector arrangement  210 . System  200  additionally includes a processor  212 , such as a microprocessor, configured to control functions of drop ejection system  200 . Processor  212  communicates with other hardware elements of drop ejection system  200  via bus  214 . 
     I/O port  202  includes an input/output device adapted to couple with a host computer  250 . Print engine  204  is coupled to bus  214  and provide print output capability for the system  200 . Sheet media is pulled from input tray  206  into print engine  204  and subsequently directed to output tray  208 . 
     During a print operation, the processor  212  determines the location where the ink drops are to be deposited on the underlying print media and sends this data to the print engine  204 . The print engine controller  204  receives the data associated with the print operation from the processor  212  and controls the print engine  206 . The print engine  206  controls a print carriage (not shown) based on the data received. The exact location information of the ink droplets is contained in the print data. Accordingly, the print carriage deposits ink droplets on an underlying print media based on the print data received from the processor  212 . 
     In an embodiment, the system  200  also includes a drop detector arrangement  210 . For a better understanding of the drop detector arrangement  210 , please refer now to  FIG. 3 . The drop detector arrangement  210  includes a plurality of drop ejectors  211 , each ejector capable of dispensing an ink droplet  213  and a collimated light source  215  for dispensing a beam of light  217 . Also shown is a service station  219  for receiving the ink droplets  213 . In an embodiment, the drop ejectors  211  are print head nozzles or the like. 
     In an embodiment, the collimated light source  215  is a laser diode device or the like. The shape of the light beam  217  can be circular, elliptical, rectangular or any other of a variety of shapes. Furthermore, the collimated light source  215  may work in conjunction with a light collection device and photo detector in an alternate embodiment shown in  FIG. 4 . 
       FIG. 4  shows an exemplary view of the alternate embodiment of the drop detector arrangement  210 .  FIG. 4  shows the drop ejector  211 , the ink droplet  213 , the light beam  217 , and the service station  219 . Also shown is a photodetector  220  and a light collection device  230 . The light collection device  230  can be a lens, a mirror or the like capable of directing (e.g. reflecting) the light scattered off of the droplet  213  to the photodetector  220 . 
     In an alternate embodiment, a refractive lens can be used to direct the light scattered off of the droplet.  FIG. 5  shows the drop ejector  211 , the ink droplet  213 , the light beam  217 , and the service station  219 . Also shown is a photodetector  220  and a refractive lens  232 . 
     In yet another embodiment, a combination of reflective and refractive optics can be employed.  FIG. 6  shows the drop ejector  211 , the ink droplet  213 , the light beam  217 , and the service station  219 . Also shown is a photodetector  220 , a reflective lens  230  and a refractive lens  232 . 
     In an embodiment, the photodetector  220  may be a CCD array. Typically the CCD array  220  may have a plurality of cells that provide the sensing functions. The CCD array  220  by means of the plurality of cells detects the light in its various intensities. Each ink drop  213  is identified from the detected light intensity of a group of one or more cells of the CCD array  220 . 
     Based on the various light intensities the CCD electronics determines ink drop characteristics such as the presence and/or absence of ink drops, the size of the drops, and the falling angle of the ink drops. A predetermined low threshold light intensity may indicate the presence of an ink drop  213 . Similarly, a predetermined high threshold may indicate the absence of an ink drop  213 . Light intensities may also indicate other ink drop characteristics such as, size, position and speed. 
     Accordingly, the microprocessor  212  associated with the CCD array  220  may determine the status of the drop ejectors  211  based on the characteristics of the ink drops  213 . For instance, the absence of an ink drop  213  may indicate that a nozzle failed to fire or is misfiring. The presence an ink drop  213  may indicate that the nozzle is firing. The size of the ink drop provides further information pertaining to the working status of the nozzle. An ink drop  213  that is smaller than usual indicates that a particular nozzle may be partially clogged or misfiring. The location of an ink drop  213  may also provide further information. An ink drop  213  that is in an unusual position or angle may suggest that the nozzle is skewed. 
     An ink drop flying across a laser beam generates a continuous optical signal with time proportional to beam width and reciprocal of drop speed. For a typical drop speed of approximately 10 m/sec and a 1 mm laser beam, the drop&#39;s time of flight is 100 μsec. Consequently, a single channel photocell is capable of detecting between 5,000-8,000 drop events per second. With a 0.1 mm laser beam, the same detector is capable of detecting between 50,000-80,000 drop-events per second. Accordingly, the servicing of a typical printhead may be accomplished in 5-10 seconds. The implementation of a photocell array could further decrease the service time. 
     Although the system  200  is described in conjunction with above-delineated components, it should be noted that the system  200  is an exemplary system. One of ordinary skill in the art will readily recognize that a variety of different components could be employed while remaining within the spirit and scope of the inventive concepts. For example, the drop detector arrangement  210  is illustrated in conjunction with a computer printer, however the drop detector arrangement  210  could be implemented with any of a variety of drop ejection systems while remaining within the spirit and scope of the present invention. 
     In another embodiment, the drop detector arrangement includes multiple laser sources.  FIGS. 7-9  show varying embodiments of a drop detector arrangement that includes a multiple laser sources.  FIG. 7  shows an embodiment whereby the laser source  215  includes an integrated beam splitter  218  thereby creating multiple light beams  217   a ,  217   b .  FIG. 8  shows an embodiment that incorporates a stand-alone beam splitter  218  for creating multiple light beams  217   a ,  217   b .  FIG. 9  shows an embodiment that incorporates two lasers sources  215   a ,  215   b  whereby each laser source  215   a ,  217   a  emits a respective laser beam  217   a ,  217   b.    
     A drop detection mechanism and method of use thereof is disclosed. In an embodiment, a shaped laser beam is employed to scatter light off of ink drops that are fired from a plurality of nozzles. A low cost, high throughput detector is utilized to detect the individual drops and thereby calculate the drop count, drop velocity, turn on energy and other drop characteristics. The drop detector may even enable optimization of driving conditions for every nozzle by creating of printhead lookup table. Consequently, through the use of the below described embodiments, new levels of print image quality are enabled on a broad range of inkjet printers, including industrial and web printers. 
     Without further analysis, the foregoing so fully reveals the gist of the present inventive concepts that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention. Therefore, such applications should and are intended to be comprehended within the meaning and range of equivalents of the following claims. Although this invention has been described in terms of certain embodiments, other embodiments that are apparent to those of ordinary skill in the art are also within the scope of this invention, as defined in the claims that follow.