Recorders – Performance of multiple functions of steam and gas engines – Pressure responsive element
Patent
1989-02-27
1991-12-03
Fuller, Benjamin R.
Recorders
Performance of multiple functions of steam and gas engines
Pressure responsive element
346 75, G01D 1518
Patent
active
050703412
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention concerns the control of liquid jets. More particularly, it is concerned with the accurate selection of discrete longitudinal portions of a stream of liquid (hereinafter termed "slugs" of liquid) for printing purposes. It is particularly applicable to the selection of slugs of liquid for printing using jet printers.
BACKGROUND
Jet printers (often called "ink jet printers" because they have been used extensively in the printing of alphanumeric characters on paper with a printing ink) are well known. Such printers usually produce a continuous fine stream of droplets when a pressurised supply of a liquid such as ink or a dye is connected to and issues from a small orifice. The individual droplets in the stream are charged as they leave the orifice. They are then deflected with an electrostatic field so that they strike a surface to be printed at a required point or are directed to a collector without reaching that surface.
The droplet production arrangement most widely used in such printers is that described by R. G. Sweet in the specification of his U.S. Pat. No. 3,596,275. In this arrangement, uniform droplets are formed from a liquid jet as it issues from a fine nozzle. Some of these droplets are charged by a charging electrode at the instant the droplet breaks off from the stream from the nozzle, and are subsequently deflected by an electrostatic field to specific recording sites on a surface to be printed. The amplitude of the deflection of a droplet is in proportion to the charge it has acquired from the charging electrode. Droplets which are not charged at the break off time are not deflected by the electrostatic field and are caught, before hitting the surface to be printed, by a collector (usually called a gutter) and are recycled to the liquid supply.
In practice, when operating this type of jet printer, several difficulties are experienced. These difficulties are mainly related to the correct formation of the droplets, the presence of concurrently formed satellite droplets, and the inducing of the charge on the droplets at the instant of formation (failure to correctly charge the droplets results in inaccurate and unreliable printing).
An alternative arrangement for this type of process has been described by R. G. Sweet and R. C. Cumming in the specification of their U.S. Pat. No. 3,373,437. In this arrangement, multiple streams of liquid issue from orifices arranged in a linear array. As these streams break up into droplets, some of the droplets are charged. Those droplets that are charged are electrostatically deflected to a collector or gutter and the uncharged droplets continue to the surface to be printed. When using this type of jet printer, difficulties similar to those outlined above are experienced, and in addition there are difficulties associated with the provision of a large number of jets and the close spacing of their orifices and charging electrodes. Because the single modulating element used to create the droplets does not impart the same stimulation energy to each liquid stream, the streams break up into droplets at different distances from the orifice and precise charging of individual droplets is impossible.
To some extent these difficulties have been obviated in the apparatus disclosed by C. H. Hertz in the specification of his U.S. Pat. No. 3,416,153 and by R. L. Gamblin in his published UK specification No. 2,108,433. Both of these specifications describe arrangements in which an unstimulated liquid jet is used and the natural breakup of the stream into non-uniform, or randomly sized, droplets is allowed to occur.
In the Hertz process, the droplets are dispersed radially from the projected jet axis in the form of a cone by the mutual repulsion of charge induced by a single annular charging electrode placed in close proximity to the stream at the break off point. The dispersed droplets are prevented from reaching the surface to be printed by an annular collector. The absence of a voltage on the charging electrode leaves the droplets unch
REFERENCES:
patent: 3769625 (1973-10-01), Gunn
patent: 4621268 (1986-11-01), Keeling et al.
Turvey David E.
Wills Leslie J.
Commonwealth Scientific and Industrial Research Organisation
Fuller Benjamin R.
Preston Gerald E.
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