Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
2000-07-13
2001-08-14
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
Reexamination Certificate
active
06273563
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a spring element according to the preamble of claim
1
and to an ink cartridge therewith.
DESCRIPTION OF THE PRIOR ART
Such a spring element for ink cartridges is disclosed in U.S. Pat. No. 5,325,119. Here, the spring element is in the form of a coil and arranged between two plates which control the pressure in the ink cartridge. This is intended to achieve a nonlinear characteristic of the spring function.
U.S. Pat. No. 5,359,353 furthermore describes a compression spring which is composed of spring bows fastened one over the other and which presses two plates apart. For ink reservoirs in printers, this plate and compression-spring arrangement is provided in an ink bag, in which a predetermined negative pressure has to be maintained in order to prevent uncontrolled discharge from the ink bag. The compression spring should also maintain the negative pressure, and keep it as constant as possible, during and after the removal of ink.
The known double bowed spring is not capable of this, since the spring force increases with the compression travel over the strain path of the spring, with the result that the level of negative pressure likewise increases. Furthermore, the double bowed spring is made of metal and must be specially assembled in order to be given its shape and then be fastened to the cover parts.
For the nevertheless unsatisfactory function, the relatively great effort involved in production and assembly is scarcely commercially justifiable.
Ink cartridges of this kind comprise in principle a protective housing with a print head for ink removal and an ink-receiving space which is connected to said print head, is at least partly flexible and in which the spring element maintaining negative pressure is contained.
Spring elements having a relatively constant spring force over a substantial part of the spring travel can also be advantageously used for other applications, for example in measurement and control technology in the automotive sector and generally in pneumatic or hydraulic equipment.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a spring element characterized in this way.
We have found that this object is achieved by a spring element having at least one individual element and having a relatively constant spring force over a substantial part of the overall spring travel, the spring element essentially having an S-bow shape and a spring characteristic which rises and falls over the overall spring travel, and comprising at least one further individual element, which has a single-bow shape and a spring characteristic which rises over the substantial part of the spring travel of the spring element.
This provides a simple, serviceable spring element.
In a practical configuration, the at least one further individual element may be integrated into the S-bow-shape individual elements, in particular as a spring loop within the length of the spring. This reduces the number of individual elements of the spring element and simplifies its production.
The spring travel of the at least one further individual element may expediently be approximately half the overall spring travel, with the result that the substantially constant spring force is realized over the substantial part of the spring travel of the spring element.
It is also conceivable, however, to design other subregions of the overall spring travel with suitable spring characteristics of the individual elements for producing an approximately constant spring force.
In practice, the individual element or elements of the spring element may be arranged and fastened between two frame parts as pressure plates.
It is advantageous in production terms to form the spring element with the frame parts or pressure plates by injection molding.
The individual element or elements may advantageously have over its or their length cross-sectionally differing widths with approximately constant height and consequently have a substantially constant diffusion of stress at the surface of the individual elements.
In an expedient arrangement, the individual elements of S-bow shape may comprise a central element and two side elements spaced equally apart from it, the central element having approximately double the spring force relative to the spring force of each side element.
It is favorable for reasons of symmetry if there are provided two further individual elements which are effective in the substantial part of the spring travel, in particular from about half the overall spring travel of the spring element.
It is likewise favorable if the further individual element or elements are arranged approximately symmetrically with respect to the central element.
It is favorable in terms of injection molding technology if at least one of the frame parts is designed as a cover part with cutouts, which have the shape of the projection of the S-bow-shape individual elements.
A further advantage is obtained if the spring element is composed of a plastics material which has high crystallinity, a high yield point and, below the yield point, high resilience.
This ensures excellent resilient properties over a long service life.
A polyacetal, in particular a polyoxymethylene (POM), which can be processed well by injection molding, may be expediently used for this.
It is advantageously also possible to use other thermoplastics with resilient properties.
The spring element according to the invention can be used advantageously for the production of ink cartridges as mass-produced articles and their function.
The invention furthermore relates to an ink cartridge having the features of claim
17
.
It is also expedient to arrange the individual element or elements of the spring element or elements between two frame parts and to fasten them to the latter.
It is also surprisingly cost-effective if at least one of the frame parts is made with cutouts for forming the shapes of the individual elements and consequently the at least one spring element is produced with at least one frame part in one piece by injection molding, in particular from polyoxymethylene.
It has been found to be decidedly advantageous if the at least one spring element is composed of a plastics material which has high crystallinity, a high yield point and, below the yield point, high resilience, in particular of a polyacetal.
Use of the spring element according to the invention in printing-ink cartridges is also equally advantageous.
REFERENCES:
patent: 4422084 (1983-12-01), Saito
patent: 5325119 (1994-06-01), Fong
patent: 5359353 (1994-10-01), Hunt et al.
patent: 5754207 (1998-05-01), Gragg et al.
patent: 5969734 (1999-10-01), Tamano
patent: 583 154 (1994-02-01), None
patent: 583 153 (1994-02-01), None
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Keil & Weinkauf
Le N.
Vo Anh T. N.
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