ELECTRICAL TESTING OF INKJET CARTRIDGES

[Anonymous]

Electrical Testing Of Inkjet Cartridges

NuInk Engineering, Inc. (and the recently formed NuInk Engineering Technologies, Inc.) of Overland Park, Kansas is an engineering company applying decades of experience in the disciplines of electrical, mechanical, and chemical engineering to technological problems facing the recharging industry. They remanufacture and sell inkjet and toner cartridges for wholesale and retail customers, and uniquely provide electrical circuit testing services and equipment as well as processing equipment and services to inkjet remanufacturers and cartridge brokers worldwide. While remanufactured inkjet cartridges are routinely print-tested (functional post-test) in the appropriate OEM printer following recharging, they are rarely pre-tested prior to an investment of both labor and materials. Because of internal electronic circuit failures inherent in used cartridges, this often results in low yields of successfully remanufactured products and lost revenue, not to mention frustration on the part of the human operators! Without an electrical circuit tester, it is difficult and sometimes impossible, to differentiate a permanently electrically defective cartridge from one that may only need another cleaning cycle. We don’t waste our time and money on electrically defective cartridges, and neither should you! The First Conception In addition, we have found that internal electrical circuit failures can occur at any time during the remanufacturing process and thus the electrical test can be a valuable troubleshooting aid as well as providing for a decisive final quality determination, or post-test. At NuInk Engineering, our goal is to provide our customers with the highest quality products, to operate efficiently and thus to remain profitable. To that end we apply sound engineering practices to the cartridge remanufacturing process. Let’s use the development of our first cartridge tester as an example: Figure 1 is a sketch of the familiar HP 56 contact pad geometry as viewed with the ink nozzles facing down. The contact pads provide an electro-mechanical interface with the internal cartridge electronic circuits. There is a one-for-one correspondence between 48 of the contact pads and 48 ink jet inducing electronic circuits, in addition to cartridge identification circuits and heating elements. While the details of the electronics and the physics of the internal ink jet producing mechanisms are beyond the scope of this report, the relevant information here is the one-for-one correspondence between contact pads and internal electronic circuits. We refer to this concept as direct-drive, because each ink jet is directly driven by an electronic circuit. Prior to investing a considerable amount of time and money in our own 56 pad cartridge tester, we searched the industry for a tester that we could purchase. The devices we found were simple yet expensive, and often dedicated testers for a single inkjet model number. We called these devices “quadrant” testers because of the simple methodology employed to mate with, test, and report on the health of the internal cartridge electronics. As shown in Figure 2, the quadrant testers typically tie all commonly grounded circuits of the 4 quadrants (A, B, C & D) together to simplify the tester electronics. This results in a gross accept/reject criterion that is, well, gross, and practically useless for judging the health of individual circuits. Why do we care? Because the internal circuits often fail individually and even one bad circuit will affect post print test quality. Again, the typical quadrant tester does not have the resolution necessary to detect a single circuit failure. Ultimately we decided to build a better mousetrap! We successfully developed an electrical circuit tester for all of the HP 56 contact pad inkjet cartridges – the CHiP-56. These are the common HP “direct-drive” cartridges (‘26A, ‘29A, ‘25A & ‘49A, etc.), for the DeskJet 500 and 600 series inkjet printers and various fax machines. Refer to Table 1 for a complete list of the HP 56 contact pad cartridges. Since then, we have tested thousands of “virgin” and remanufactured cartridges. We’ve experienced electrical failure rates as low as 5% for the ‘26A black cartridges and as high as 65% for the less robust ‘49A color cartridges. Equally important from an R&D perspective, we compiled a vast database of circuit measurement data that led to the development of our proprietary cartridge accept/reject criterion. Figure 3 is a photograph of our test lab and an operator using a prototype of the CHiP-56, our 56 contact pad cartridge tester. The major components of the tester are a personal computer (PC) controller with monitor, and graphical user interface (GUI), and a test box providing an electro-mechanical interface, and drive and measurement electronics. The GUI, part of our proprietary software package, provides the test operator with a visual representation of the health of the internal cartridge electronics in addition to accept/reject “bells and whistles.” The electro-mechanical interface of the cartridge/tester provides a precise and robust connection between the cartridge under test and the tester electronics. Early on in the development of the tester we abandoned another common feature of the quadrant testers – an actual cartridge carriage from an OEM printer. We found, as those who perform post-tests on OEM printers will attest to, that the OEM cartridge carriages wear out quickly and must be replaced often. We designed our own cartridge carriage mechanism and it has proven to be very reliable. The results of our cartridge tests are either positive visual and audible feedback, or a negative outcome indication and a failed test report. All test data is stored for statistical analysis. See the sample failed test report of Figure 4. We also provide our cartridge testing service customers with a troubleshooting guide, shown in Figure 5, with each cartridge test order. This guide allows our customers to verify the gross electrical failures themselves with a common electrical continuity checker – note that some failures are more subtle and not identifiable with such common equipment. Also please note our warning about testing good cartridges in this manner, as a simple continuity checker may do damage to internal cartridge electronics. In either case, good or bad, all cartridges are returned to the customer with failure reports attached to the failed cartridges. Down To The More Complex Buoyed by our success with the CHiP-56 tester, we then tackled the more complex 52 and 32 contact pad HP cartridges. See Table 1 for a list of these different cartridges. This endeavor resulted in the development of the CHiP-52 and CHiP-32 testers. While we hold the details of the tester designs as proprietary information, anything more than a cursory look at the complex internal electronics of these cartridges is also beyond the scope of this report. In order to provide greater print resolution for their next generation printers, HP employed many more ink nozzles and significantly increased the complexity of the internal cartridge electronics. To employ the same direct-drive concept as the 56 pad cartridges would have required hundreds of contact pads, resulting in a large and electro-mechanically challenged cartridge. Instead they employed a “row and column” multiplexing concept using embedded electronic switches. Although more electrically complex, this resulted in a simpler electro-mechanical interface with fewer contact pads than the preceding direct-drive cartridges employed. In our survey of commercially available testers, we did not find even the equivalent of a simple quadrant tester for these cartridges. So again we developed our own testers and established our own accept/reject criterion. In conclusion, after satisfying our own internal electrical cartridge testing requirements, we discovered that we had excess tester capacity that might be utilized by others in the industry. We are excited by the opportunity to share our electrical testing expertise with the rest of the remanufacturing industry by offering our equipment for sale, and testing services for pre- and post-testing of inkjet cartridges – any HP 56, 52, 51, or 32 pad cartridge! We offer volume discounts and quick turn-around from our test lab on all orders – and no quantity is too large, or too small!

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December 24, 2003 at 9:40 AM