Epson used a presentation at the recent Advanced Inkjet Technology conference in Switzerland to introduce its Nozzle Verification Technology, which can give feedback on potential nozzle blockages within inkjet printheads before they start to become a problem.
Asami Okamoto from Seiko Epson’s inkjet R&D department, who holds a number of patents around nozzle sensing technology, noted, “A nozzle might suddenly stop firing and create white streaks, which leads to production stops, so dealing with this issue is very important.”
Readers may remember that I’ve already covered a similar technology from Meteor Inkjet earlier this year. However, Kan Igarashi, director of Epson Europe’s IJS printhead business, told me that Epson had been looking at this approach for more than 10 years, adding, “As a printer supplier, we want to add value to the products that we offer to improve the ROI for the entire system that the competition can’t offer.”
All piezo printheads work by applying a voltage pulse to a piezoelectric actuator, which forces the actuator to move, firstly to push the ink or fluid out of a given nozzle, and then to return to its starting position. This movement is very precisely controlled through an electronic signal or waveform.
Okamoto explained that the Nozzle Verification Technology builds on this. “We are using the piezo actuator not only to jet the ink but also as a sensor. By analyzing this signal, we can determine the condition of the nozzle. The actuator can be used for both jetting and sensing, and so no additional cost is required.”
The system works by detecting pressure changes inside the ink cavity through residual vibrations from the actuator movement, with the pressure variations converted into electrical signals through an integrated circuit embedded in the printhead.
However, this does not work when the nozzles are actually printing. But given that most printheads fire thousands of droplets per second, it’s relatively straightforward to run the test signal through nozzles when they are not being used for printing. Okamoto added, “As a head manufacturer, we can optimize timing control to allow high diagnostic accuracy.” The test signal itself only needs a fraction of a second. Igarishi told me that for a head such as the D3000, it’s possible to test all 3000 nozzles within a second.
Okamoto says that apart from the day-to-day running of a print device, the system can also be used in the development of inks and fluids to be jetted. Typically, ink developers use rheometers to test their ink. But as Okamoto points out, the ink performance is different in a real printhead because there are more variables like the temperature of the ink, the speed that the ink dries at (because the surface area is different), and variations in pressure (with negative pressure changes during ejection), which a rheometer can’t mimic. Normally, a printhead can’t provide the viscosity measurements that a rheometer can, but she says, “You can use NVT to measure viscosity from residual vibration.”
Epson validated this by testing the NVT approach against a rheometer and found that the results matched very closely. Using the NVT in this way has the advantage of allowing simultaneous testing of both the jetting performance and the dynamic viscosity of a fluid, which should reduce the time needed to optimise those fluids and lead to a faster time to market.
Okamoto also outlined a case study in which a customer created a print device to produce printed circuit boards using 20 Epson D3000 printheads to jet a copper-based ink. She noted this was the first time Epson had used the NVT with a copper-based ink, adding: “We optimized the algorithm for this ink.”
Some customers want to use the NVT to replace the need for optical inspection, which Epson is currently reviewing, though Okamoto says the NVT approach can achieve 99.5 percent accuracy in this regard. This shouldn’t add any extra cost to the printhead, but would reduce the overall cost of the printer.
To help its OEM customers, Epson has created a test rig, the KSCAN D3000, which has the NVT approach built in. This should make it easier for those customers to test the performance of the printhead for their intended fluids, media and ambient conditions.
Drive electronics
Epson initially developed this technology for its home and office printers. Okamoto explained, “To move into industrial, we first developed an Epson genuine board. We engineered the diagnostic capability into the board itself.” That was necessary because although the actuator is being used both for jetting and sensing, there’s still a need to control the NVT pulse and to interpret the results, as well as to amplify the signal and separate it from the signal used for jetting.
Okamoto says that Epson is now exploring ways to offer NVT functions to its OEM printhead customers by separating this function from Epson’s own electronic boards. Igarashi says, “The first NVT only uses Epson drive electronics. But we want to embed it to third party boards, which we will start with a partner this year.” However, this is not Meteor Inkjet, though the two companies are talking and aware of what the other is doing.
Igarashi says that Epson is now trying to spread awareness of this technology to see what the feedback is. “We have started to install the NVT for some customers already and have started to validate how much value this technology can create. This year, we would like to introduce it to more customers.”
For now, the nozzle verification technology is built into the D3000 printheads, and Epson is looking at adding it to some variants within its S-series printheads, especially the SI variants that were designed for aggressive solvents, such as the S3200-S1, the S800-S1, and the i3200-S1HD. These are used for printed electronics, with Igarashi noting: “So this ink is very expensive and some customers want the NVT for this.”
The NVT system is also used in Epson’s robotic direct-to-shape printer, which I’ve previously covered here, and in the SurePress L5034 Label press that I’ve covered here.
The iPrint institute, which hosted the AIT conference, is also developing its own nozzle verification system, which I’ll come back to in another story. Epson also has an office at the iPrint lab in Marly, Switzerland, and will use NVT in Epson’s Marly lab to evaluate machine performance in development, as it gives them a quicker testing workflow.
Epson will continue to develop its NVT approach, particularly its ability to measure ink viscosity, as well as being able to support a wider range of inks. Epson is also testing greyscale NVT to predictively detect nozzle clogging before failures occur.
I’ll cover the AIT conference in further stories later this month. In the meantime, you can find further details on Epson’s PrecisionCore printheads from corporate.epson.
