Patent Application
20060176326
The invention relates to fluid injection, and more particularly, to fluid injector devices and methods for improving injection performance by adjusting output parameters according to resistance of each heater of the fluid injector devices.
Typically, fluid injectors are employed in inkjet printers, fuel injectors, biomedical chips and other devices. Among inkjet printers presently known and used, injection by thermally driven bubbles has been most successful due to reliability, simplicity and relatively low cost.
The conventional monolithic fluid injector 1 using bubbles as a virtual valve is advantageous due to reliability, high performance, high nozzle density and low heat loss. As inkjet chambers are integrated in a monolithic silicon wafer and arranged in a tight array to provide high device spatial resolution, no additional nozzle plate is needed.
Heaters for conventional monolithic fluid injector 1, however, are critical for fluid injection. The resistive layer formed during front-end processes may cause uniform resistance distribution and variation of each heater across different regions of the monolithic silicon wafer. Resistance in some heaters may even exceed limitation such that injection quality is affected leading to overshooting and/or satellite droplets.
U.S. Pat. No. 6,244,682, the entirety of which is hereby incorporated by reference, discloses a method and apparatus using an optical scanning device to analyze a graph printed by an inkjet printer. By comparing printing results with the predetermined standard driving parameters, subsequent operating printing parameters are calibrated and optimized.
The aforementioned methods are applied to inkjet printers in which the resistances of each heater are within a specific range. If the resistance of each heater deviates from standard operating settings due to front-end process variation, deterioration of printing performance occurs and calibration may be required.
Fluid injector devices and methods for utilizing the same are provided to improve printing performance by measuring resistance of each heater of fluid injectors and comparing with standard operating resistance as reference for adjusting output operating parameters.
Embodiments of the invention provide a method for inkjet injection, comprising providing a fluid injector device with a plurality of heaters for bubble generation, measuring resistance of each heater, comparing the resistance of each heater with a standard operating resistance, and adjusting output signals to heaters with resistance exceeding the standard operating resistance.
Embodiments of the invention also provide a method for inkjet injection, comprising providing a fluid injector with a plurality of heaters for bubble generation, measuring resistance of each heater, comparing the resistance of each heater with a standard operating resistance, and adjusting output signals to heaters with resistance exceeding the standard operating resistance, while maintaining, standard output signal to heaters having the standard operating resistance.
Embodiments of the invention also provide a fluid injector device, comprising a plurality of heaters for bubble generation, a sensor connecting each heater for measuring resistance of heaters, a comparator comparing resistance of each heater with a standard operating resistance, and a controller adjusting output signal to heaters with resistance exceeding the standard operating resistance.
The invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein:
Generally, resistances of heaters of thermally driven inkjet injectors dramatically affect the results of fluid injection. According to embodiments of the invention, each fluid injector comprises approximately 100-200 sets of bubble generators such as resistive heaters. In one exemplary embodiment, fluid injectors S1-S5 comprise heaters with resistance within a standard range of about 60-65 Ohm. When each heater of the fluid injectors S1-S5 is biased at 12V, the equivalent resistance of the entire interconnect of the fluid injector is about 10 Ohm with current through each heater about 160-170 mA. Thus, by heating 1.2 μs as well as selecting appropriate dimensional design of orifices, e.g., diameter of 16-18 μm, the volume of each injection droplet is within a desired range of about 5-6 pl. The density of the fluid is assumed to be equal to that of water with surface tension in a range of about 26-30 dyne/cm and viscosity in a range of about 1-2 cp.
Fluid injectors S6-S12 comprise heaters with resistance exceeding the standard range, such as about 60-95 Ohm. Heaters with resistance exceeding 65 Ohm are about 5%-22% of the total, and with resistance 100%-160% of the standard range of about 60-65 Ohm. According to an embodiment of the invention, fluid injectors S1-12 all function under the same driving parameters such as at 12V and 1.2 μs, whereby equivalent resistance of the entire interconnection is about 10 Ohm and current through each heater is about 160-170 mA. The results of each set of injectors are shown in table 1, where droplets with 95% standard volume (i.e., 5-6 pl) are indicated by “◯”, droplets with 90%-94% standard volume are indicated by “Δ”, droplets with 80%-89% standard volume are indicated by “⋆” and droplets with 80%-84% standard volume are indicated by “⋆⋆”.
According to Table 1, the difference between resistances of each heater can thus be determined, with corresponding effects on injecting quality.
Table 2 shows results on printing of adjusting driving parameters according to resistance of each set of fluid injectors S6-S12. For example, the driving parameters can be adjusted by increasing heating time. By incrementally adding 0.2 μs each injection, printing quality is improved. Although the present disclosure provides a method for improving print performance by incrementally increasing heating time, it should be noted that other parameters such as operating voltage or driving current may also be adjusted within the scope of embodiments of the invention. For example, increasing 100-120% of the standard operating voltage of about 12V may also improve droplet injecting performance.
Although by increasing heating time of each set of fluid injectors can improve injection performance, it is critical for the increase to be incremental since overheating can affect operating frequency of the injectors as well as lifetime thereof. Heater overheating can cause overshoot and/or satellite droplets. Table 3 shows the relationship between injectors with normal resistance and injection performance with different heating time. Injector S5 may overshoot at heating time of 2 μs, as shown in Table 3.
While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
