Patent Application
20070145636
Micro-fluid ejection heads, such as inkjet print cartridges, may include a disposable ink supply tank for supplying ink to permanent or semi-permanent printheads. Such tanks may include a transparent lens in the tank that is used to reflect light to a sensor for optically sensing the presence or absence of ink in the tank. When an absence of ink is detected, a command signal is generated to limit operation of the printhead so that damage to the printhead is avoided. Fabrication of tanks having suitable lenses is challenging and improvement is needed.
Accordingly, the disclosure relates to a tank for a micro-fluid ejection device and methods for making the tank containing a liquid level lens. In some embodiments, the tank includes a tank body made of a first material defining a lens aperture, and a lens made of a second material that is different from the first material is disposed within the lens aperture.
In other embodiments, there is provided a method for making a tank containing a fluid level lens therein. The method includes providing a lens made of a lens material having a first melting point. The lens is placed within a mold configured to provide a tank body having a lens aperture therein. A tank material is introduced into the mold containing the lens to yield a tank having the lens bonded within the lens aperture of the tank body. The tank material used for making the tank body has a second melting point less than the first melting point of the lens material.
An advantage of exemplary embodiments described herein is the provision of a tank/lens assembly having improved lens and tank properties as compared to conventional structures.
Further advantages of the exemplary embodiments will become apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale, wherein like reference numbers indicate like elements through the several views, and wherein:
With reference to
The tank/lens assembly 10 is particularly suitable for use as a disposable fluid supply to supply fluid, such as ink, to a micro-fluid ejection device, such as a permanent or a semi-permanent printhead utilized by an inkjet printer, as described in more detail below in connection with
The assembly 10 is made by providing the lens 14 and the tank body 12 in separate forming steps. The tank 12 and the lens 14 being made of different but chemically compatible materials, with the pre-formed lens 14 being integrated into the tank body 12. The lens 14 may be integrated into the tank body 12 during formation of the tank body 12 or after formation of the tank body 12. Separate formation of the lens 14 enables both the tank body 12 and the lens 14 to each be made of a material suitable for their purpose. Conventional constructions provide a tank body and a lens in a single molding step, with the tank body and the lens being simultaneously formed of the same material that is a compromise to the desired performance of at least the lens. That is, materials that facilitate the molding of the tank body typically have disadvantages for use as lens materials, such as low scratch resistance or a high shrinkage rate, poor transparency, and the like which compromises the formation of the desired lens shape for fluid level sensing or detection applications. Likewise, materials suitable for forming the transparent lens may be more costly to use for the entire tank material and may have poorer compatibility with the fluid contained in the tank body.
With continuing reference to
With reference to
The lens aperture 16 is defined on the side wall 33, so that the lens 14 may be located in the aperture 16 adjacent to the chamber 20. As depicted in
The sensor 34 may include a source of light 36, such as a light emitting diode, positioned so as to direct light angularly toward the lens 14. If the chamber 20 contains sufficient ink to cover the lens 14, then a low to medium amount of light will be reflected for detection by a detector 38. If the chamber 20 is empty or otherwise does not contain sufficient ink to cover the lens 14, then a medium to high amount of light will be reflected back to the detector 38, as depicted in
To enable the desired light reflection function, the lens 14 may include a stepped configuration as seen in
It has been observed that lens structures made using materials such as clear polypropylene or HDPE have disadvantages such as poor optical properties and low scratch resistance. Accordingly, the lens 14 is suitably made using a material having desirable optical and mechanical properties. For there to be sufficient internal reflection when no fluid is present above the lens, the refiactive index may be selected so that the light incident on the lens/air interface is at an angle greater than the critical angle associated with the two mediums. To achieve this, with the given sensor configuration where light is incident on the lens surface at a 45 degree angle, the material is selected to have a refractive index greater than about 1.445. The lens material must also be chemically compatible with the tank material. Accordingly, suitable lens materials may be selected from polypropylene (PP), polymethylmethacrylate (PMMA), polycarbonate (PC), and styrene-acrylonitrile. The following Table 1 provides the melting points of the lens and tank materials that may be used. Table 2 provides a selection chart for selecting suitable lens materials for the tank materials and vice versa.
As seen by table 2, materials that are compatible with a PP lens material, for example, include PP and PP/EPDM. In another example, a lens material made of SAN may be compatible with a tank material selected from SAN, PBT, PMMA, PVC-W, and TPU.
Various methods may be used to fixedly attach the lens 14 in the aperture 16 of the tank 10. In one manner of attachment, the lens 14 may be mechanically secured within the aperture 16 of the tank body 12 as by a friction fit and a suitable adhesive or the like to provide a hermetic seal at an interface between the lens 14 and the body 12 so that air does not enter chambers 20 or 22 and fluid does not escape therefrom. Other means for securing the lens 14 in the aperture 16 include, but are not limited to, ultrasonic welding, laser welding, and the like.
In another method of manufacture, the lens 14 may be provided, as by conventional injection molding techniques, and the lens subsequently incorporated into the tank body 12 during manufacture of the tank body 12. For example, the formed lens 14 may be installed in a mold configured to provide the tank body 12 depicted in
During the foregoing tank molding procedure, it is desirable that the lens material have a melting point that is sufficiently greater than the melting point of the tank material so that the lens 14 does not deform under the thermal conditions associated with molding the tank body 12 so that the lens 14 substantially retains its shape and optical properties. For example, a suitable tank material, such as PP/EPDM has a lower melting point of 220° C., and a suitable lens material for the tank material is a lens material such as polypropylene having an upper melting point 280° C.
Use of a lens 14 made of one of the foregoing lens materials in the above described integrated molding step desirably results in the formation of a chemical and mechanical bond between the lens material and the tank material that creates a hermetic seal between the tank body 12 and the lens 14, while the lens 14 substantially retains its shape and optical properties. Without being bound by theory, it is believed that during the body molding step for integrating the lens 14 in the body 12, some of the boundary regions of the lens 14 soften under frictional and thermal forces associated with the molding process to promote bonding between the lens 14 and body 12 without altering the optical properties of the relevant surfaces of the lens 14.
With reference to
Having described various aspects and exemplary embodiments and several advantages thereof, it will be recognized by those of ordinary skills that the disclosed embodiments is susceptible to various modifications, substitutions and revisions within the spirit and scope of the appended claims.
