Abstract:
Drop detection are disclosed. An example liquid dispensing device includes a controller to control dispensing of a first drop from a first orifice and a second drop from a second orifice, a sensor to monitor the first orifice to detect at least one of a presence or an absence of a drop from the first orifice and, in response to the sensor detecting an absence of the first drop, the controller is to classify the first orifice as at least one of occluded or non-functioning.

Description:
RELATED APPLICATION 
     This patent arises from a continuation of U.S. patent application Ser. No. 13/123,804, which was filed on Apr. 12, 2011, which claims priority to International Patent Application Ser. No. PCT/US08/11809, filed Oct. 15, 2008, both of which are hereby incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     Liquid dispensing devices, such as thermal ink jet printers, may be utilized to dispense precise and minute amounts of liquid, such as droplets of liquid, into individual wells of a multiple-well tray, such as in pharmaceutical testing, for example. Precise numbers of drops should be dispensed into the individual wells in order to ensure accurate test results. There is a need, therefore, to detect the number of drops dispensed from a liquid dispensing device. Moreover, there is a need for detecting the presence of drops from a liquid dispensing device to determine if the orifices of the device are functioning. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side cross-sectional view of one example embodiment of a liquid dispensing device. 
         FIG. 2  is a table showing a correlation between the intended total volume and the total number of drops to achieve the intended total volume for a particular drop volume. 
         FIG. 3  is an exemplary plot showing dependency of signal strength versus number of simultaneously exposed drops. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic side cross-sectional view of one example embodiment of a liquid dispensing device  10 , which in the embodiment shown may include a drop ejection device  12 . Drop ejection device  12  may be a printing or an imaging device, and in the example embodiment shown, may be a thermal ink jet device. Drop ejection device  12  may include a printhead or multiple printheads  14  that may each include an orifice layer  16 , such as an orifice plate, for example, including multiple orifices  18  therein for ejecting fluid  20  therefrom. Drop ejection device  12  may be one of a thermal ejection device, and a piezo ejection device, for example. 
     Orifice layer  16  may include one or several orifices  18  or may include thousands of orifices  18 , as may be suited for a particular application. Fluid  20  may be any fluid as desired for a particular liquid dispensing application. The drop ejection device  12  generates droplets  38  of fluid  20  of differing drop volumes depending on fluid  20  and construction details of device  12 . In the field of pharmaceutical testing, fluid  20  may primarily be any water-miscible organic solvent, such as dimethyl sulfoxide (DMSO), for example. In other embodiments, fluid  20  may be primarily water, methanol, isopropanol, ethanol, glycerol, acetone, pyridine, tetrahydrofuran, acetonitrile, and dimethylformamide, for example. 
     Liquid dispensing device  10  may be utilized to dispense precise and minute amounts of liquid into a liquid receiving device  22 , such as into individual wells  24  of a multiple-well tray  26 , as used in pharmaceutical testing, for example. In some example embodiments liquid receiving device  22  may be a biochemical testing device, a diagnostic strip device, or a device to receive a coating, for example. Precise volume amounts should be dispensed into the individual wells  24  in order to ensure accurate test results. There is a need, therefore, to increase the reliability and/or predictability of the volume of fluid  20 , such as the predictability of the number of drops  38 , dispensed into each of the individual wells  24 . 
     Liquid dispensing device  10  may include a drop detection device  28 . The drop detection device may be chosen from one of an electrostatic detection device, a capacitive detection device, an acoustic drop detection device, and an optical detection device, for example. In the embodiment shown, drop detection device  28  may include a light emitting device  30  that emits a light  32 , such as a laser, and a single light detecting device  34  positioned with respect to orifice layer  16  such that light detecting device  34  receives light  36  reflected, scattered or otherwise emanating from drops  38  of fluid  20  ejected from orifice  18  and illuminated by light  32 . Light detecting device  34  may be a photodetector chosen from one of a photo diode, a CMOS, a charge-coupled device, a photo multiplying tube, and any other photodetector. Light emitting device  30  may be chosen from one of a laser, a light emitting diode, an arc discharge lamp, and any other high intensity light source. 
     Light detecting device  34  may be connected to a controller  40  that may use the light information received from light  36  by detecting device  34 , so as to determine the number of drops ejected into, or to be ejected into, each compartment of liquid receiving device  22 , such as into each of the individual wells  24  of a well tray  26 , with each well  24  receiving different intended volumes, as one example. 
     Controller  40  may include a database of information such as electronically or otherwise stored formulas, graphs, tables, and the like that correlate different types of information, such as a correlation of drop volume for individual drops for a variety of fluid solutions, for example. Controller  40  may also include a means for determining the number of drops  38  of particular volume that are required for an intended dispense volume into an individual well  24 . In the embodiment shown, drop detection device  28  is a light based detection device. However, drop detection device  28  may be an electrostatic device, a capacitive device, an acoustic device, a magnetic detection device, an optical device, or any other drop detection device that will function for a particular application. 
     In one example embodiment, drop detection device  28  may be a light scattering drop detector including a light emitting device  30 , with a 1 millimeter) laser beam waist (the critical dimension in a drop&#39;s trajectory direction). Light detecting device  34  may be a single channel photocell or a photocell array that is capable of detecting up to 5,000 to 8,000 drop-events per second at a nominal drop velocity &gt;10 m/s, which is typical for both thermal and piezo-ink jet technologies. Using a 0.1 mm laser beam waist, the same detector may be capable of detecting up to 50,000 to 80,000 drop-events per second at the same drop ejecting conditions. As the drops  38  fall, light  32  from laser diode  30  illuminates the drop  38 , and light  36  scattered from the drops is detected by photo cell  34 . At a drop velocity at 10 m/second, the expected time-of-flight (TOF) of the drops is 10 micro seconds (μsec). The single channel light detection device  34  may be positioned at a single, predetermined angle  34   a  relative to the direction of incident light  32  from laser diode  30 . Accordingly, angle  34   a  is shown as the angle between incident light  32  and scattered light  36 . In the embodiment shown in  FIG. 1 , angle  34   a  is near 0°, i.e., device  34  is positioned almost in line with the path of light  32  from light emitting device  30 . At angle of 0° a shadow effect by obscuring light by the drop will occur. The device will detect scattering light from near 0° up to 180°, which corresponds to complete back scattering/retro reflection. For typical inkjet drop sizes &gt;10 μm a diffraction is significant at low angles (close to 0°) and may have a significant contribution at higher angles only for small particles and long light wavelengths such as when the particle size is comparable and even smaller than the wavelength. In one preferred embodiment, an angle of 10-45° is utilized for light scattering. In general, angles of 10-90 degrees are readily useable, with large signals closer to 0 degrees, although there is a decrease of light intensity at exactly zero degrees because of superposition of the shadow effect and low angular diffraction contributions. Accordingly, an angle  34   a  of 20 degrees for particular implementation may be desirable. 
     In one embodiment the drops  38  may continue to fall into a drop collection reservoir (not shown) for later use in liquid dispensing device  10 , such that the fluid is not wasted, or drops  38  may fall into a separate reservoir (not shown) to be collected for disposal. However, in the embodiment shown the drops  38  fall directly into a predetermined individual well, such as a well  24   a , for example, of well tray  26  and real time processing is conducted to determine the exact number of drops to be dispensed into the particular well  24   a  so that well  24   a  will contain a minute, precise, predetermined and known volume of fluid  20 . 
     In a simple embodiment, light emitting device  30  may be a laser diode or a light emitting diode (LED) and light detecting device  34  may be a single photodiode, which may be interfaced via a preamplifier to a pulse counter on a single personal computer or a controller device such as an FPGA or PLC for example. In more sophisticated implementations, a peak detector may be used to measure a value of the amplitude signal, which will be used for number of drops evaluation as well (see  FIG. 3 ). This versatile system could be used to count drops that are being generated up to 100 KHz and accomplish the counting in real time, as opposed to offline precalibration methods such as optical or gravimetric methods currently utilized. Accordingly, the current device provides extremely rapid feedback to the dispense system. Moreover, because every drop is counted, the precision and accuracy of the disclosed method is better than gravimetric or optical methods currently in use. Furthermore, use of a single light detection device  34 , positioned at a single angle  34   a  with respect to light emitting device  30 , greatly simplifies the device operation and lowers the cost of device  1 , and greatly simplifies the mathematical calculations that may be conducted by controller  40  in determining a drop count of drops  38  from printhead  14 . 
     In another embodiment, drop detection device  28  may be utilized to determine a health of individual ones of orifices  18  of orifice layer  16 . In particular, drop detection device  28  may be utilized to determine the presence or absence of a drop ejected from a particular orifice of multiple orifices  18 . The absence of a drop ejected from a particular orifice when a drop is attempted to be ejected from that orifice, will be determined by the controller  40  to indicate that the particular orifice is occluded or otherwise is in a state of bad health. Conversely, the presence of a drop ejected from a particular orifice when a drop is attempted to be ejected from that orifice, may be determined by the controller  40  to indicate that the particular orifice is not occluded or otherwise is in a state of good health. If a particular orifice is determined to be occluded or otherwise in bad health, controller  40  may control ejection of fluid  20  from one or more healthy orifices to compensate for the occlusion of the particular orifice. If more than a specified threshold number of orifices  18  are determined to be in had health, controller  40  may notify the operator that drop ejection device  12  is not useful to dispense the required dispense volume and prompt the operator and use a different drop ejection device  12 . 
     In another implementation the peak detector signal may be used to evaluate a real number of dispensed drops from simultaneously firing nozzles. The method enables high throughput and high precision. 
       FIG. 2  is a table  66  showing a correlation, at a particular total intended volume of 1,000 picoliters, between a particular drop volume  68 , determined by or stored in controller  40 , in picoliters of drops  38  from printhead  14 , and the total number of drops  70  that should be ejected to ensure the intended total volume within an individual well  24   a  of wall tray  26 . For example, a desired total intended volume in a well  24   a  of 1,000 picoliters is achieved by ejecting a total of forty drops  38  into well  24   a  from printhead  14  when the drop volume is 25 pL. The total of forty drops may be calculated to include drops that previously have been dispensed into well  24   a , such as during a setup or calibration step such as orifice health determinations or drop volume determinations by controller  40 . For this method, the drops ejected for the orifice health or drop volume determination would be counted as they are dispensed into a well  24   a  which is later intended to have a sufficiently large dispensed volume. The number of drops dispensed into this well during the orifice health or drop volume determination steps may be subtracted from the intended number of drops for well  24   a  to determine the correct number of drops remaining to be dispensed. After the correct number of drops required for each individual well  24   a  are determined, the dispensing into well tray  26  may proceed, including real time drop counting to dispense the exact number of drops required. 
     In this manner, a quick, efficient and accurate total number of drops  70  may be placed into multiple individual liquid receiving compartments  24  of a liquid receiving device on a large scale to achieve multiple intended total volumes. For example, minute and precise volumes of liquid  20  may be dispensed into the individual wells  24  of a well tray  26  that may include hundreds or thousands of individual wells  24 , for example. 
     Advantages of the drop count determination of the process described herein include the lack of use of fluid additives to enable drop detection, improved accuracy and precision of dispensed volumes, the speed of the drop volume calculation method, and the lack of use of expensive detection hardware. Moreover, this method may be used “on-line” or in “real-time” during filling of a well tray, or before filling a well tray during a set-up or calibration routine. 
     The information contained in  FIG. 2  is a very small sample shown for ease of illustration. In practice, much more information may be contained within the database or databases of controller  40  to allow the precise calculation of desired dispense volumes. 
       FIG. 3  shows an exemplary plot showing dependency of signal strength versus number of simultaneously exposed drops. 
     An example liquid dispensing device ( 10 ) disclosed herein includes a drop ejection device ( 12 ) including an orifice ( 18 ) adapted for ejecting drops therefrom, a single detection device ( 28 ) positioned to receive drop information from the ejected drops of the drop ejection device, and a controller ( 40 ) that receives the drop information and uses the drop information to determine a number of drops ejected from the drop ejection device. In some examples, the drop ejection device ( 12 ) is one of a thermal ejection device, and a piezo ejection device and the single detection device ( 28 ) is one of an electrostatic detection device, a capacitive detection device, an acoustic drop detection device, and an optical detection device. 
     In some examples, the single detection device including a light scattering drop detection device including a light source such as a laser, a light emitting diode, or an arc discharge lamp. In some examples, the detection device also includes a photodetector chosen such as a photo diode, a CMOS, a charge-coupled device, or a photo multiplying tube. In some examples, the controller ( 40 ) uses the light scattering information to determine a health of individual orifices of the drop ejection device. 
     An example method of dispensing liquid disclosed herein includes ejecting drops ( 20 ) from at least one orifice ( 18 ), counting a number of the ejected drops using a single detection device, and calculating a dispensed volume of the ejected drops from the counted number of drops. In some examples, the method also includes ejecting drops from multiple orifices ( 18 ) simultaneously. In some examples, the calculating includes correlating the counted number of drops with a drop volume of each drop to determine the dispensed volume. In some examples, counting the number of ejected drops is conducted utilizing electrostatic detection, capacitive detection, acoustic drop detection, or optical detection. In some examples, counting the number of ejected drops is conducted with a light scattering drop detection device ( 28 ) including a light source such as a laser, a light emitting diode, or an arc discharge lamp. Sin some examples, the counting is performed using a photodetector such as a photo diode, a CMOS, a charge-coupled device, or a photo multiplying tube. In some examples, the calculating a dispensed volume is conducted during real time filling of a multiple-well liquid receptacle ( 26 ), and drops ejected during the counting are subtracted from the total dispense volume required for each wells. In some examples, the counting is conducted prior to real time filling of a receptacle. In some examples, the method includes positioning a liquid receiving device to receive an intended volume of the ejected drops. In some examples, the liquid receiving device is a biochemical testing device or a diagnostic strip device. In some examples, the drops exhibit an absence of a light detection reagent added to the drops. 
     Other variations and modifications of the concepts described herein may be utilized and fall within the scope of the claims below.