Patent Application
20150062245
In some inkjet printers, a media wide arrangement of stationary printheads is used to print on paper or other print media moved past the printheads. In one type of print bar for less expensive media wide inkjet printers for personal and small business users, long narrow molded plastic parts support and carry ink to the printheads.
The same part numbers are used to designate the same or similar parts throughout the figures.
One of the challenges making print bars for less expensive media wide inkjet printers that use molded plastic parts is precisely controlling the position of the printheads on the print bar to maintain the desired spacing and alignment between the printheads and the print media during printing. The length of the print bar corresponds to the width of the print media. Controlling the dimensions of and between plastic parts is more difficult in longer parts. Dimensional control includes not only the initial accuracy of a part for size, position and flatness but also the changes that occur in or between parts during use and over time.
A new print bar structure has been developed to help improve dimensional control in a page wide print bar by introducing a rigid chassis to support and constrain the molded plastic parts that make up other parts of the structure. The chassis is made from die-cast aluminum or another suitably rigid material and serves as a “backbone” for the lower cost plastic parts. Select areas of the chassis may be machined as necessary or desirable to improve dimensional attributes such as size, position, flatness, parallelism, and perpendicularity. The mechanical properties of the aluminum along with the geometry of the chassis enable a part that can span the width of the printed page while maintaining the dimensional stability needed for the print bar. Other parts in the print bar may be mounted to the chassis directly or indirectly to take advantage of its solid structural foundation, enabling the use of lower cost materials and assembly techniques.
This and other examples shown in the figures and described herein are non-limiting examples. Other examples are possible and nothing in this Description should be construed to limit the scope of the invention which is defined in the Claims that follow the Description.
As used in this document, “elongated” means a part is longer than it is wide; and a “printhead” means that part of an inkjet printer or other type of inkjet dispenser that expels fluid from one or more openings. “Printhead” and “print bar” are not limited to printing with ink but also include inkjet type dispensing of other fluids and/or for uses other than printing.
Referring first to
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Referring specifically to
Referring now to the example of print bar 12 shown in
To overcome this difficulty, flat reference surfaces 82, 84 are formed on a metal or other suitably rigid chassis 32. For example, machining datum contact pads 62, 58A-58B, and 46A-46C and reference surfaces 82, 84 on to a cast aluminum chassis 32 enables consistently manufacturing suitably flat print bar structures 14. X, Y, and Z datum contact pads 62, 58A-58B, and 46A-46C are machined flat on chassis 32 after casting to define X datum 64, Y datum 60, and Z datum 48. Reference surfaces 82 and 84 are machined on to flange 40 in X-Y planes parallel to the X-Y plane defined by primary Z datum 48. Chassis flange 40 surrounds an opening 86. In the example shown, flange 40 completely surrounds opening 86. Other configurations are possible. For example, it may be desirable in some implementations to utilize a discontinuous flange 40 that only partially surrounds opening 86. In either case, one or both of manifold front face 76 and substrate rear face 80 extend into or through chassis opening 85. In the example shown, as best seen in
During assembly, an alignment surface 88 on the rear face 80 of mounting substrate 30 is forced against chassis reference surface 82 and an alignment surface 90 on the front face 76 of manifold 28 is forced against chassis reference surface 84. Forcing substrate 30 and manifold 28 against the flat chassis reference surfaces 82, 84 eliminates warp and establishes a uniform gap 92 between the attachment surfaces 94, 96 on the two parts 28, 30. For a glue joint 98, adhesive is used to fill gap 92 to join the two plastic parts 28, 30. For a weld joint 98, plastic flows into gap 92 to join the two parts 28, 30. The biasing force on the plastic parts 28, 30 is maintained until the adhesive cures or until the weld is completed. Once joint 98 is secure, printhead mounting substrate 30 maintains contact with chassis reference surface 82 so that the printhead mounting surfaces 70 on substrate 30 are flatter and more parallel to primary, Z datum 48 than is possible without the “backbone” provided by chassis 32. (The relationship between chassis flange 40, opening 86, alignment surfaces 88, 90, attachment surfaces 94, 96, and joint 98 is also shown in the simplified, diagrammatic view of
A second difficulty constructing a media wide print bar 12 is enabling print bar structure 14 to withstand the dimensional changes that occur as manifold 28, substrate 30, and chassis 32 expand and contract during temperature fluctuations. The stresses associated with dimensional changes in the parts can result in joint failure or permanent dimensional changes that compromise print quality. Examples of the new print bar structure 14 include features that help the structure withstand the stresses of dimensional change without damaging the print bar. To minimize tolerances and improve part-to-part alignment, as described in detail below, the alignment features for both manifold 28 and mounting substrate 30 are located directly adjacent to one another on chassis 32. Also, manifold 28 and substrate 30 are molded from the same plastic to have substantially the same coefficient of thermal expansion (CTE). While the CTE of a plastic manifold 28 and substrate 30 is different from the CTE of chassis 32, and chassis 32 will expand or contract differently than manifold 28 and substrate 30, manifold 28 and substrate 30 are joined to one another but not to chassis 32. Thus, the parts with different CTEs can move relative to one another in the XY plane along chassis flange 40. Allowing the parts to move in the XY plane helps relieve dimensional change stresses without changing the position of substrate 30 (and thus printheads 26) with respect to the primary, Z datum 48.
Referring to
The slot/pin pair interfaces form a slip joint 118 between printhead mounting substrate 30 and chassis 32 that helps control part-to-part alignment during heating and cooling. Although the part-to-part alignment will change during heating and cooling, slip joint 118 created by the pin/slot interface helps determine how the alignment changes—the slot acts like a track for the pin to follow in the event of a dimensional change during a thermal event. As long as there is contact between the pin and the slot, the path the parts take during expansion (heating) should be the same as the path they take during contraction (cooling). Thus, the parts should return to the same place they were before the thermal event occurred.
A slip joint 120 between ink manifold 28 and chassis 32 is achieved in the same way, but the alignment features are reversed. Alignment slots 122, 124 in manifold 28 fit on corresponding pins 126, 128 on chassis 32. In the example shown, each chassis pin 126, 128 is configured as a continuation of the sidewalls 130 that define chassis slots 110 and 114. This configuration, in which the substrate/chassis and manifold/chassis slip joints are positioned back-to-back, allows forming the plastic joint features by the same side of the mold, reducing positional tolerances and improving alignment between substrate ink slots 66 and manifold ink ports 68. Better alignment, in turn, helps minimize the risk of ink slot/port obstruction during gluing or welding.
As noted above, the CTEs of plastic parts 28, 30 and a metal chassis 32 are not the same. Upon heating or cooling the plastic manifold 28 and substrate 30, which are affixed to one another, will expand or contract about the same but differently than chassis 32. Allowing the parts to slip in the X and Y direction at joints 118 and 120 helps keep the parts from loosening in the Z direction by reducing joint stress during thermal events. Slip joints 118 and 120 allow the parts to expand or contract in the XY plane, minimizing bowing and other distortion in the Z direction. Maintaining a tight fit in the Z direction is desirable because the alignment of printheads 26 to the primary, Z datum helps define the spacing between printheads 26 and print media 16 in print zone 50 during printing (FIG. 4)—properly controlling the printhead-to-media spacing is important to good quality printing.
Reversing the male/female relationship between the parts in slip joints 118 and 120 in print bar structure 114 also helps control part-to-part alignment during both heating and cooling. The pins track in the slots during expansion and contraction. To avoid sloppy tracking, the pins should stay tight in the slots during heating and cooling. This is achieved by reversing the male/female relationship based on the CTEs of the two materials—for example an aluminum chassis 32 with a larger CTE and a plastic manifold 28 and printhead mounting substrate 30 with a smaller CTE. During heating, when the parts expand, the male features on substrate 30 (pins 112, 116) get a little bigger while the female features on chassis 32 (slots 110, 110) get a lot bigger, creating unwanted slop and loosening at slip joint 118. However, the male features on chassis 32 (pins 126, 128) get a lot bigger while the female features on manifold 28 (slots 122, 124) only get a little bigger, tightening slip joint 120. Manifold 28 and substrate 30 are affixed to one other and, consequently, the still tight slip joint 120 maintains control during heating. During cooling, when the parts contract, slip joint 120 may loosen but slip joint 118 will tighten. Thus, by reversing the male/female relationship of the slip joints, one of the two slip joints should remain tight to maintain control during both heating and cooling.
“A” and “an” as used in the claims means one or more.
The examples shown in the Figures and described above illustrate but do not limit the invention. Other forms, details and examples may be made without departing from the spirit and scope of the invention which is defined in the following claims.
