Protective capping apparatus for an ink jet pen

Abstract: An ink pen (14) is provided with a protective capping apparatus (10) to protect against damage caused by the ingress of dirt and debris, the accumulation or solidification of ink, the discharge of static electricity or the like. The protective capping apparatus (10) has a protective cap (12) movable between an open position and a closed position. In the closed position the protective cap (12) shields a portion of an ink pen (14) such as the ink-jets or the electrical contacts.

Description: BACKGROUND INFORMATION The present invention relates to pens for ink-jet printers and, more particularly to a protective capping apparatus for such pens. Ink-jet printers have become widely accepted as a reliable means of performing high quality printing. Such printers have one or more ink-jets which serve to eject, or jet, ink onto a printing medium to form desired characters or images. One type of ink-jet printer is a thermal ink-jet printer. In a typical thermal ink-jet printer, each thermal ink-jet has an orifice, a well for storing a small quantity of ink, and a thermal element such as a resistor. The thermal ink-jet is actuated by heating the thermal element to cause the small quantity of ink within the well to vaporize and be expelled through the orifice. Ink-jet printers often employ ink pens. Such pens commonly have an ink reservoir for containing a supply of ink, a print head having an array of one or more ink-jets, and an electrical contact pad. The electrical contact pad has one or more electrical contacts which, when the ink pen is positioned within a printer, engage with corresponding contacts in the printer to allow electrical connection of the ink-jets to the control system of the printer. In this manner, the printer control system can selectively actuate the ink-jets to print desired images. Ink pens are generally replaceable so that when the supply of ink within the reservoir is depleted or the print head malfunctions, the ink pen can be removed from the printer, discarded, and a new pen inserted into the printer. As can be appreciated ink pens are delicate instruments which must be protected to ensure proper operation. For instance, the tiny orifices of the ink-jets can become plugged or damaged as a result of the accumulation of dust and dirt. This problem is exacerbated because of the abundant amount of dust and small paper fibers that exist in most printing environments. These materials may build up on the print head and clog the ink-jets or may enter an orifice and contaminate the ink within the orifice or the well. Vapor loss may also cause an ink pen to malfunction. Ink is a combination of many different components, some of which evaporate more readily than others. As a result, prolonged exposure of the ink to the ambient atmosphere may cause the easily evaporated components to evaporate while the other components remain. This selective evaporation can alter the composition of the ink to the point where the ink pen can no longer function properly. In extreme cases, the ink within the orifice may thicken or solidify, thereby plugging the orifice. An ink pen may also become inoperable if the electrical contact pad is scratched or if the contacts become obscured with dirt. If the contacts are damaged or obscured, the continuity of the electrical connection between the printer control system and the ink-jets may be broken. This may prevent the proper actuation of the affected ink-jet and require replacement of the entire pen. In addition, ink pens are vulnerable to damage from the discharge of static electricity. A static electrical charge may build up while the ink pen is in service within a printer. This accumulated static charge may discharge when the ink pen comes into contact with a conductive material, either within the printer, during ink pen removal from the printer, or while the ink pen is out of the printer. Such a discharge can seriously damage the sensitive electrical circuits associated with the print head and the contact pads, as well as the orifices on the print head. Thus, to ensure the reliable and efficient operation of an ink pen, it is desirable to protect the sensitive print head and electrical contact pad at all times. In some existing ink pens, the print head is covered with tape during the manufacture of the pen. The tape serves as a vapor barrier to limit vapor loss or evaporation of the ink and covers the print head to help prevent contamination of the print head and ink-jets during shipment and initial storage of the ink pen. However, the tape is removed and discarded prior to placing the ink pen within a printer. As a result, the print head and ink-jets may be left unprotected and without an adequate vapor barrier during use and during any subsequent storage of the ink pen. JP-A-1291947 describes a protective cap for an ink jet pen. The cap is attached to the pen and is movable between an open position, which occurs when the pen is attached to the printer, and a closed position, which occurs when the pen is not attached to the printer. US-A-4 371 881 and DE-U-8205426 describe shields and wipers for ink-jet printing heads. Some printers are provided with built-in capping stations. During printing operations, the printer typically moves the ink pen back and forth over the printing medium to print the desired images. When the ink pen is not in service, the printer moves the ink pen to the capping station where the print head and ink-jets are shielded. However, over time such permanent capping stations can become dirty or wear out. If this occurs, the capping stations no longer perform properly and docking an ink pen at such a capping station may even contribute to the contamination of the print head. Moreover, such built-in capping stations may become obsolete as ink pen designs change. Special storage containers, or ink pen garages, are also available to protect ink pens. However, to place the ink pen within the ink pen garage, the ink pen must be removed from the printer. Consequently, the ink pen must then be removed from the garage and replaced within the printer for use. As a result, the use of such containers is inconvenient and in many circumstances impractical. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a protective capping apparatus for an ink pen that protects the print head, the electrical contacts, or both, from contamination and damage. Another object of the invention is to provide a protective capping apparatus for an ink pen that protects the print head, the electrical contacts, or both, against damage caused by the discharge of static electricity. The present invention provides an ink pen assembly as specified in the claims hereafter. Other aspects of the invention will become apparent to those skilled in the art from the detailed description of the invention which is presented by way of example and not as a limitation of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is perspective view of an ink pen having a protective capping apparatus with a wiper in accordance with a preferred embodiment of the present invention. Figure 2 is a partially exploded perspective view of a print head having a protective capping apparatus in accordance with another preferred embodiment of the present invention. Figure 3 is a cross sectional view taken along line 12-12 in Figure 2. Figure 4 is a partial side view of a print head having a capping mechanism in accordance with another preferred embodiment of the present invention. Figure 1 shows a preferred embodiment of a protective capping apparatus in accordance with the present invention. This embodiment has a sliding cap 68 which slides between an open position in which the ink-jets 20 are exposed and a closed position in which the ink-jets 20 are covered. The sliding cap 68 is provided with legs 70 which are slidably received within guide tracks 72 formed on each side of the support platform 28. An elastomeric gasket (not shown) can be positioned on the sliding cap 68 to form a protective seal around the ink-jets 20 when the sliding cap 68 is in the closed position. This seal acts as a vapor barrier to help prevent the solidification of the ink resulting from evaporation. A wiper 74 can also be provided. The wiper 74 is positioned so that as the sliding cap 68 moves between the open position and the closed position, it wipes across the surface of the ink-jets 20 to remove any dirt, debris or accumulated ink. Figures 2 to 4 show a protective capping mechanism for a page wide print head 78. The illustrated page wide print head 78 has a curved front surface 80 with a number of ink-jets formed therein. A protective cap 82 is pivotable between a closed position in which it shields the front surface 80 and an open position in which the front surface 80 is exposed. The protective cap 82 is provided with a leg 84 at each end. An aperture 86 in each leg 84 is received on a pivot post 88 extending from the page wide print head 78. In this manner, the protective cap can pivot between the closed position and the open position. In the embodiment illustrated in Figure 3, a gasket 90 is positioned on the protective cap 82 to form a protective chamber 91 around ink-jets on the front surface 80. A wiper 92 is positioned so as to wipe across the front surface to remove any accumulated dirt, debris or excess ink. The position of the pivot posts 88 and the length of the legs 84 can be varied to achieve a desired movement of the gasket and wiper across the front surface. For example, if the pivot posts 88 are positioned at the center of curvature of the front surface, as shown in Figures 2 and 3, the wiper and the gasket will wipe across the entire front surface. However, it may be desired that the pivot posts are offset slightly from the center of curvature of the front surface 80 so that the gasket tends to lift from the front surface as the protective cap is pivoted. In the embodiment shown in Figure 4, the pivot posts (not shown) of the cap 82b are offset (in the direction of the open position) from the center of curvature of the front surface 80. To provide for the wiping of the front surface 80, a spring-biased wiper arm 94 is rockably positioned upon the protective cap 82b. The wiper arm 94 has a ledge 96 which extends over the longitudinal edge of the cap opposite the direction of the open position. A wiper 92a is attached to protrude from the ledge 96 and extend longitudinally along the front surface 80. A biasing member 95 urges the wiper 92 into contact with the front surface 80. In a preferred embodiment, the biasing member 95 is a compression spring that interconnects the cap 82b and the wiper arm 94 opposite the ledge 96. The spring 95 is compressed when the cap is in the closed position. As the cap opens, the gasket 90 lifts from the front surface 80, while the spring 95 expands to urge the wiper 92 into sweeping contact with the front surface 80. This embodiment has advantages when, for example, the gasket material is not suitable for wiping, or when an absorbent member not suitable for wiping is installed on the cap. It should be understood that the wiper arm 94 may be biased in a variety of ways. For example, a torsion spring similar to the torsion spring 48 in Figures 1 and 2 may be used. Alternatively, a tension spring positioned adjacent the ledge 96 may be used to urge the wiper 92 into contact with the front surface 80. It should be appreciated that protective cap mechanisms in accordance with the present invention may be actuated by a variety of suitable mechanisms. These mechanisms will be apparent to those skilled in the art. Moreover, the illustrated print heads all have thermal ink-jets. However, it should be appreciated that a capping device in accordance with the present invention may be used beneficially with other types of ink-jets or with other types of print heads. This detailed description is set forth only for purposes of illustrating examples of the present invention and should not be considered to limit the invention in any way. Clearly, numerous additions, substitutions, and modifications can be made to these examples without departing from the scope of the invention which is defined by the appended claims.

Claims: An ink pen assembly having a printhead (20, 80) with a plurality of inkjets and electrical contacts, the assembly further comprising: a protective cap (12, 68, 82, 82b) attached to the ink pen assembly and movable between an open position and a closed position in which the cap shields a portion of the ink pen; a wiper (74, 92, 92a) mounted to the cap to wipe over at least a portion of the printhead and/or the electrical contacts when the cap is moved from one of the open and closed positions to the other position, characterized in that: a gasket (34, 90) is positioned on the cap to form a vapour barrier around at least a part of the shielded portion of the printhead when the cap is in the closed position without the cap itself being in contact with the inkjets. An assembly according to claim 1 further comprising a vent disposed through the cap to maintain an air pressure equilibrium from the ambient through the vapour barrier. An assembly according to claim 1 wherein the wiper is rockably positioned upon the cap (82b), the wiper having a ledge (96) protruding beyond the cap, the ledge supporting a wiper member (92a); and a biasing member (95) situated between the wiper and the cap, the biasing member engaging the wiper to urge the wiper member into sweeping contact with the shielded portion of the ink pen assembly as the cap pivots from the closed to the open position. An assembly according to claim 1 wherein the cap (68) is slidable from the open position to the closed position, and wherein the wiper (74) is positioned on the cap to wipe over at least a portion of the printhead when the cap slides between one of the open and closed positions to the other position.

Inventors: BOHORQUEZ JAIME H, DION JOHN A, HART ARTHUR R, NIELSEN NIELS J, SCHINNER CHARLES E, BOHORQUEZ, JAIME H., DION, JOHN A., HART, ARTHUR R., NIELSEN, NIELS J., SCHINNER, CHARLES E.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1995
Main classification: B41J2
IPC codes: B41J2