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Characterizing Noise in Ink Jet Heads

IP.com Disclosure Number: IPCOM000081055D
Original Publication Date: 1974-Mar-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 3 page(s) / 46K

Publishing Venue

IBM

Related People

Brady, MJ: AUTHOR [+3]

Abstract

Various measurements must be made on an ink jet head (consisting of a piezoelectric or other driver, a fluid chamber, a nozzle or array of nozzles, and possibly an internal filter) to characterize it before it can be used in a printing device. Among these measurements are: (1) jet velocity versus head pressure, (2) frequency dependence associated with head resonance and driver characteristics and (3) print window for satellite formation. Another important measurement, related to the above, is the distance-to-breakoff of the drops, which is also a function of the voltage applied to the driver. Even when no synchronization signal is applied to the driver, randomly spaced drops are still formed at distances which fluctuate randomly in time. The average value of these distances is known as the "natural break-off distance".

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Characterizing Noise in Ink Jet Heads

Various measurements must be made on an ink jet head (consisting of a piezoelectric or other driver, a fluid chamber, a nozzle or array of nozzles, and possibly an internal filter) to characterize it before it can be used in a printing device. Among these measurements are: (1) jet velocity versus head pressure,
(2) frequency dependence associated with head resonance and driver characteristics and (3) print window for satellite formation. Another important measurement, related to the above, is the distance-to-breakoff of the drops, which is also a function of the voltage applied to the driver. Even when no synchronization signal is applied to the driver, randomly spaced drops are still formed at distances which fluctuate randomly in time. The average value of these distances is known as the "natural break-off distance".

The fluctuations in break-off distances are related to the noise characteristics of the head. The observed noise may (1) be of electrical origin in the driver, (2) result from fluid turbulence in the chamber or nozzle, (3) be introduced by an internal filter if one should exist, or (4) be due to air dissolved in the fluid. This noise signal is always present even when the jet is being driven and it results in small displacements from regular, periodic drop placement when the drops are being formed. These small displacements grow as the drops move away from the nozzle due to aerodynamic effects until, at large distances, the noise predominates and the spacing between drops becomes completely random. The noise spectrum is therefore an important characteristic of the head since it determines how well the jet can be synchronized for a given drive voltage. The standard way to measure the noise characteristics is to take a set of photos and to measure from these the average break-off distance or, if desired, the statistical distribution of break-off distances.

The device of Fig. 1 can be used for making this measurement with a very large number of samples (>10/5/) very quickly and easily. The device consists of an ink jet head 12, a special charging electrode 10, a set of deflection plates 14, and a means for real time detection of the drop distribution.

The charging electrode l0 is a novel feature of this system. Rather than forming an equipotential throughout the interior of the electrode, the electrode is constructed as shown in cutout in Fig. 2. The electrode is composed of an outer supporting structure made of an insulating or suitably resistive material 20. If an insulator is used, then the interior of the insulator is coated with a thin resistive film 22 or some other suitably resistive material such as tin oxide. The ends of the cylinder 24 are coated with a metal thin film suc...