Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-07-31
2001-03-13
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S049000, C347S005000, C324S678000, C324S701000, C324S549000
Reexamination Certificate
active
06199969
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to multi-pass ink jet printing. More particularly, the invention relates to a method and system for detecting one or more failed ink jets in an ink jet printer.
2. Description of the Related Technology
A basic premise of ink jet printers is that all ink jets must “fire” properly (i.e., eject ink droplets) or the quality of the present image may be degraded. The detection of nonfunctional ink jets, otherwise referred to herein as “open jet detection,” is a method of determining which jets within a printhead cartridge are electrically nonfunctional. This electrical non-functionality can result from open traces, damaged drop ejection resistors, changed resistance values, or poor contact between the cartridge and a “flex circuit” which provides control signals to the cartridge. All of these errors may cause one or more jets of a printhead cartridge to not fire, or fire improperly, resulting in anomalies in the printed image.
Defective jets can also result from clogged jet nozzles. Current open jet detection methods are unable to electronically detect clogged jets that are still electrically correct. However, by executing a prime printing pattern using a printhead cartridge under test, and observing the printed results, a user may identify clogged jets and manually input the address or reference designation of each clogged jet into a list of defective or nonfunctional jets. The list of defective or nonfunctional jets, otherwise referred to herein as the “open jet list,” is a record of all nonfunctional jets in the respective printhead cartridge. By updating the open jet list, a user of the ink jet printer may be notified as to when a printhead cartridge has an unacceptable number of nonfunctional jets. Additionally, the open jet list may be utilized to update the print masks, or jet group masks, of a printhead cartridge which is configured for multi-pass mode printing, such that one or more of the remaining functional jets in the printhead cartridge may compensate for the one or more defective jets in that printhead cartridge. This method and system for compensating for defective jets with the remaining functional jets in a printhead cartridge is described in greater detail in a co-pending, commonly-owned U.S. patent application entitled, “Open Jet Compensation During Multi-Pass Printing,” application Ser. No. 09/127,397, filed currently herewith, and which is incorporated by reference herein.
A common way of measuring current in a circuit is to measure the voltage across a resistor in series with the circuit. Prior art methods of detecting nonfunctional jets have utilized this concept to measure current through printhead circuitry as one or more jets in a printhead cartridge are fired. For example, assume that each of four cartridges has four sets of 14 jets. Firing all the jets requires a sequence of 14 separate firings for the 14 jets in each set. During testing, only one jet in each set of jets is turned on at any instant in time. There is a resistor in series with each set of jets for each cartridge for a total of 16 series resistors. The voltage drop across a series resistor is due to a single jet firing. However, if no jet in that set is firing, the voltage drop will be zero. The voltage drop across each of the series resistors is typically connected through a diode to a common point and compared to a reference voltage. The output from the comparison is an indication of whether a jet is properly functioning. By firing each jet one at a time, it can be determined whether each one has electrical continuity.
The above-described method becomes less desirable as the number of jets and, hence, the number of sets of jets, increases, necessitating an increase in the number of series resistors. These series resistors waste energy, generate heat, waste board space and cost money. The prior art method also has limited functionality in that it only indicates that the current through a jet was greater than or less than some predetermined threshold. This type of indication does not distinguish between the different types of problems which may cause an ink jet to misfire, or not fire at all. For example, the prior art method cannot distinguish between a shorted power line, a shorted address line, or a damaged drop ejection resistor in an ink jet.
SUMMARY OF THE INVENTION
The invention provides a method and system in which the current required to fire an ink jet is not measured by measuring the voltage drop across a series resistor, but rather, by measuring the discharge rate of an output capacitor connected to an output of a switching power supply as one or more ink jets are fired. By measuring the discharge rate of the output capacitor after an ink jet has been fired, or after a power line to the ink jet has been turned on, or after an address line to the ink jet has been turned on, and comparing this test discharge rate with a reference discharge rate, the invention provides a very effective and accurate solution to the problem of determining whether there is a defective ink jet, a defective power line, or a defective address line, for example. Once such a determination is made, information regarding a defective element of the printhead may be stored in memory. For example, if a ink jet is determined to be defective, its address may be included in an open jet list which is stored in a memory of the ink jet printer.
As used herein, the term “element” may refer to any component, such as an ink jet, a power line, or an address line within a printhead cartridge, or any other component within an ink jet printhead. Additionally, when an element is said to be “activated,” this term may refer to the turning on of a power line or address line, or the firing of an ink jet, or the turning on of any of the various other components in the ink jet printhead cartridge. As used herein, the terms “element” and “activate”, and any combination or conjugations thereof, should be given their ordinary broad meaning and scope. Additionally, unless otherwise specified, the term “printhead” is used synonymously and interchangeably with the term “printhead cartridge” which is a well-known term of art.
The method and system of the invention measures the time it takes for power supply capacitors supplying power to one or more ink jet cartridges to discharge a small amount of current. The average current supplied by the capacitors during that time is given by the following equation:
I
average
=Cx(dV/dT) Equation 1
where C is the capacitance of the power supply capacitors, dV is the change in voltage across the capacitors, and dT is the time measured for the voltage change to occur. A switching power supply which supplies power to the ink jet cartridges is enhanced to provide this measurement capability by the addition of two functions. In a preferred embodiment, a first function increases the quiescent output voltage by an amount equal to dV and thereafter, decreases the quiescent output voltage level back to its original value. As the output capacitor discharges down to its original quiescent levels, the switching power supply will temporarily cease providing an output pulse waveform to charge to output capacitor. In other words, to allow the output capacitor to discharge, the power supply will interrupt its switching operation. A second function detects when the switching power supply resumes switching after the voltage across the capacitors has decreased to its original level. In this way, the time required for the output capacitor to discharge an amount of current which changes the voltage across the capacitor by an amount equal to dV can be measured.
In order to detect clogged ink jets, the method and system of the invention can also utilize the printing of a prime pattern. Thereafter, an operator can visually examine the prime pattern and determine which ink jets, if any, are nonfunctional. The operator can then manually input the reference designation or address of each nonfunctional ink jet into the open jet list,
Dull David M.
Free Warren
Haflinger James J.
Neese David A.
Barlow John
Encad, Inc.
Knobbe Martens Olson & Bear LLP
Lago Cesar G.
LandOfFree
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