Patent Application
20060087526
The invention disclosed herein relates generally to printing systems, and more particularly to a method and system for monitoring the operation of an ink jet print head using a micro-wire array.
Low cost, widely available ink jet printing technologies have enabled many new applications where dynamically varying information must be transmitted in printed form. As used herein, the term “ink jet printing” refers to any form of printing wherein print control signals control a print mechanism to eject ink drops onto a medium to produce a matrix of pixels that represent an image. Many of these applications rely upon a consistent level of print quality over time since the failure to capture the unique information on even a single document can have serious consequences.
A particular example of an application of ink jet printing where a consistent level of print quality is very important is the use of digital print mechanisms in postage meters and mailing machines. Postage meters and mailing machines for printing postage indicia on envelopes and other forms of mail pieces have long been well known and have enjoyed considerable commercial success. There are many different types of mailing machines, ranging from relatively small units that handle only one mail piece at a time, to large, multi-functional units that can process thousands of mail pieces per hour in a continuous stream operation. The larger mailing machines often include different modules that automate the processes of producing mail pieces, each of which performs a different task on the mail piece. The mail piece is conveyed downstream utilizing a transport mechanism, such as rollers or a belt, to each of the modules. Such modules could include, for example, a singulating module, i.e., separating a stack of mail pieces such that the mail pieces are conveyed one at a time along the transport path, a moistening/sealing module, i.e., wetting and closing the glued flap of an envelope, a weighing module, and a metering module, i.e., applying evidence of postage to the mail piece. The exact configuration of the mailing machine is, of course, particular to the needs of the user.
Typically, a control device, such as, for example, a microprocessor, performs user interface and controller functions for the mailing machine. Specifically, the control device provides all user interfaces, executes control of the mailing machine and print operations, calculates postage for debit based upon rate tables, provides the conduit for the Postal Security Device (PSD) to transfer postage indicia to the printer, operates with peripherals for accounting, printing and weighing, and conducts communications with a data center for postage funds refill, software download, rates download, and market-oriented data capture. The control device, in conjunction with an embedded PSD, constitutes the system meter that satisfies U.S. information-based indicia postage meter requirements and other international postal regulations regarding closed system meters. The United States Postal Service (USPS) initiated the Information-Based Indicia Program (IBIP) to enhance the security of postage metering by supporting new methods of applying postage to mail. The USPS has published draft specifications for the IBIP. The requirements for a closed system are defined in the “Performance Criteria for Information-Based Indicia and Security Architecture for Closed IBI Postage Metering System (PCIBI-C), dated Jan. 12, 1999. A closed system is a system whose basic components are dedicated to the production of information-based indicia and related functions, similar to an existing, traditional postage meter. A closed system, which may be a proprietary device used alone or in conjunction with other closely related, specialized equipment, includes the indicia print mechanism.
The PCIBI-C specification defines the requirements for the indicium to be applied to mail produced by closed systems. An example of such an indicium is illustrated in
Since postal services accept indicia printed by postage meters and mailing machines as conclusive proof of payment of the amount of postage indicated, such devices are in effect machines for printing money. As a result postal services have imposed high standards for the print quality of indicia images produced by such machines. Even if an indicium is valid, if the verification equipment is unable to read the indicium due to poor print quality, verification will not be possible. It is therefore necessary to ensure that the printing systems utilized by the mail processing systems are capable of consistently producing high quality images. Ink jet print mechanisms, however, are unable to provide consistent print quality as their mechanisms tend to degrade over time as ink dries up, small print nozzles clog, or one or more of a number of small, rapidly cycling print elements fails. Such a failure can cause substantial losses to a mailer since a large number of mail pieces of substandard print quality may be rejected by a postal service after the cost of the postage has been debited from the funds registers in the mailing machine.
Conventional systems for monitoring the operation of ink jet print heads require expensive imaging or scanning equipment and complicated signal processing techniques. While suitable for use to monitor the operation of ink jet print heads, such equipment is expensive, especially compared with the relatively low cost of available ink jet print heads, and can be very difficult to implement. Thus, there exists a need for a method and system that can monitor the operation of an ink jet print head that is inexpensive and easy to implement.
The present invention alleviates the problems associated with the prior art and provides methods and systems to monitor the operation of ink jet print heads that are easy to implement and inexpensive.
In accordance with embodiments of the present invention, an array of wires is utilized to monitor the operation of an ink jet print head. The print head is positioned over the array, which preferably includes the same number of wires as there are nozzles in the print head, such that each nozzle is located above one of the wires. The array of wires is heated, and the print head is controlled to eject droplets of ink from each nozzle of the print head onto a corresponding wire. Nozzles that are operating properly will eject droplets of ink, which will lower the temperature of the wire when they make contact with the wire. The lowering of the wire temperature will cause a change in resistance of the wire. Nozzles that are not operating properly will not eject droplets of ink, and therefore the temperature of corresponding wires for non-operational nozzles will not be lowered, and the resistance will remain constant. The resistance of each wire is monitored, and if a change in resistance in a wire is not detected, indicating that the ink droplets were not ejected onto that wire, a signal is generated that indicates a non-operational nozzle. Remedial measures can then be taken to fix the non-operational nozzle or to inhibit further printing of postal indicia.
Therefore, it should now be apparent that the invention substantially achieves all the above aspects and advantages. Additional aspects and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. Moreover, the aspects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
The accompanying drawings illustrate a presently preferred embodiment of the invention, and together with the general description given above and the detailed description given below, serve to explain the principles of the invention. As shown throughout the drawings, like reference numerals designate like or corresponding parts.
In describing the present invention, reference is made to the drawings, wherein there is seen in
Printer 22 includes a print head controller (PHC) 30 that is coupled to the controller 24. PHC 30 controls the operation of a print head (PH) 32. The PHC 30 can cause the print head 32 to move between a plurality of positions, including, for example, a printing position 36 (as illustrated in
According to embodiments of the present invention, PHC 30 will periodically move the print head 32 to the test position 40 to monitor the operation of the print head 32 to ensure that all nozzles are operating correctly. For example, a monitoring operation could be performed on a periodic basis based upon a number of mail pieces processed, e.g., every fifty mail pieces. Alternatively, a monitoring operation could also be performed as part of a standard print head maintenance routine.
Referring now to
The wires also preferably have a small enough diameter such that (i) each wire in the array 52 will align with a corresponding nozzle in the print head 32; and (ii) it does not require a large amount of ink droplets from each nozzle to cause a sufficient temperature change in each wire to change the resistance of the wire significantly enough to be detected. To satisfy the second requirement, it is preferable to select a diameter of wire based on the size of each drop such that the wire will be coated with only a few drops. Thus, the diameter of the wire is preferably selected based on the diameter of each drop of ink. Assuming that each ink droplet is a sphere, the diameter, D, of each droplet can be calculated from the following formula:
D=(6 V/π)1/3
where V is the volume. The volume of each drop is approximately 20 picoLiters (1.22×10−9 in3). Thus, using the above equation, the diameter of each drop is approximately 0.0013 in. Based on the diameter of each drop being approximately 0.0013 inches, a suitable diameter for each wire is approximately 0.002 inches. This will allow each wire to be surrounded by ink with relatively few droplets. If the ink droplets arrive at a frequency of 14 kHz, the wire will be surrounded by ink within a time frame in the order of microseconds. It should be understood, of course, that the above description is exemplary in nature only and other types and diameters of wire can also be used.
The wire array 52 is coupled, by, for example, a bus 54, to a resistance measuring device 56, such as, for example, a Wheatstone Bridge circuit, or any other type of suitable device that can either measure the actual resistance or detect changes in resistance of each of the wires in the array 52. While only a single device 56 for all of the wires in the array 52 is illustrated in
The operation of the device 50 is as follows. When it is desired to monitor the operation of the print head 32, the PHC 30 moves the print head 32 to the test position 40.
For those nozzles 60 that are operating properly, upon firing ink will be expelled from the nozzle 60 and deposited onto the corresponding wire of the array 52. The ink droplets making contact with the wires will cause the temperature of the heated wires to decrease, which in turn will cause a corresponding change in resistance of the wires. For those nozzles 60 that are not operating properly, e.g., the nozzle is clogged, a print element has failed, etc., upon firing ink will not be expelled from the nozzle 60 and therefore no ink will be deposited onto the corresponding wire of the array 52. The temperature of the wires where no ink is deposited will remain relatively constant, and therefore there will be no change in resistance of the wires where no ink is deposited. The resistance of the wires is monitored by the resistance measuring device 56. If no change of resistance is measured for a wire in the array 52, a signal is sent to the PHC 30 indicating that a nozzle 60 is not operating properly. PHC 30 can then take remedial measures to try and correct the problem that is causing the nozzle to be inoperative, such as, for example, by performing a nozzle cleaning operation. Alternatively, the PHC 30 can provide a signal to the controller 24 indicating that one or more of the nozzles 60 in the print head 32 are not operating properly, and controller 24 in response can inhibit further printing. Optionally, the PHC 30 can receive a separate signal for each nozzle 60 of the print head 32, and only after some predetermined minimum number of nozzles 60 are determined to be inoperative will some remedial action be taken or the controller 24 notified of the inoperative nozzles.
Thus, methods and systems to monitor the operation of ink jet print heads that are easy to implement and inexpensive are provided. The print head is positioned over an array of wires. The array of wires is heated, and the print head is controlled to eject droplets of ink from each nozzle of the print head onto a corresponding wire. Nozzles that are operating properly will eject droplets of ink, which will lower the temperature of the wire when they make contact with the wire. The lowering of the wire temperature will cause a change in resistance of the wire. Nozzles that are not operating properly will not eject droplets of ink, and therefore the temperature of corresponding wires for non-operational nozzles will not be lowered, and the resistance will remain constant. The resistance of each wire is monitored, and if a change in resistance in a wire is not detected, indicating that the ink droplets were not ejected onto that wire, a signal is generated that indicates a non-operational nozzle.
While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Those skilled in the art will also recognize that various modifications can be made without departing from the spirit of the present invention. For example, the number of wires n in the array of wires 52 can be less than the number of nozzles 60 in the print head 32, and the array 52 (or the print head 32) can be moved to position each of the nozzles 60 over a wire in the array 52 at some point for testing. Thus, a single wire can be used with more than one nozzle 60, or even a single wire can be used for every nozzle 60. Therefore, the inventive concept in its broader aspects is not limited to the specific details of the preferred embodiments but is defined by the appended claims and their equivalents.
