Pen positioning in page wide array printers

#The present invention relates to the art of fluid ejection devices and, more particularly, to inkjet printers which use a plurality of pens supported in a page wide array in a frame referred to herein as a printbar which extends across a path of movement of media on which printing is to take place. The individual pens used in this field usually comprise generally rectangular configured fluid containing housings of molded plastic or other suitable material so that a number of pens can be aligned end-to-end in the printbar. Maximization of the size of the pens for ease of manufacture and close positioning of the pens in the printbar without pen-to-pen contact is important for accurate ink drop placement and in keeping size of the printer footprint to a minimum. For these reasons it is considered particularly advantageous to utilize pens which have protruding fore and aft lower orifice array portions on opposite sides of the lower portion of the pen so that the pens can be aligned with the fore and aft portions of adjacent pens in a side-to-side or nested relationship. These pens are rotationally symmetrical about a vertical axis. Electrical interconnects comprising conductive contacts arranged in a pattern are provided on opposite sides of the pen and mating electrical contacts are mounted on the frame for engagement with the interconnects on the pens for transmitting power to control the ejection of fluid from the pens. The pens must be closely and accurately positioned without contacting each other and they must each be stabilized against linear and rotational movement in the spaces on the printbar in which they are mounted.

#Microscopic fluid droplets are ejected usually downwardly from thermal or piezoelectric printheads onto media on which a print pattern is to be produced from orifice plates mounted on the lower surfaces of the pens. The need for precise alignment of the pens relative to the frame or printbar on which they are supported is apparent to those skilled in the art.

#The present invention therefore provides a method of positioning one or more fluid ejection devices such as an inkjet pen which ejects fluid in a first (Z) direction in a support, said device having electrical interconnects on opposite sides of said device which resiliently engage spaced electrical interconnects on said support which are spaced in a second (X) direction substantially orthogonal to said first direction, comprising inserting said device in said first direction into a mounting location in said support until said device engages said support and engaging datum surfaces on said opposite sides of said device located proximate opposite ends of said device with datum surfaces on said support during insertion of said device to resist rotation of said device about an axis parallel to said first direction.

#FIG. 1 is a perspective view of a printbar which holds a plurality of inkjet pens for a page wide array printer.

#FIG. 2 is a top plan view of an inkjet pen.

#FIGS. 3A and 3B respectively comprise left and right side elevation views of the pen of FIG. 2.

#The invention will be described with reference to a rectangular coordinate system in which the X, Y and Z directions extend as seen in FIG. 1. A frame or printbar 100, elongated in the Y direction, is shown for supporting an aligned plurality of fluid ejection devices such as inkjet pens includes spaced end pieces 102, 104 each having supporting feet 106 with apertures 108 for attaching of the printbar 100 to printer chassis structure. The exemplary printbar shown in the drawings includes a pair of spaced side frames 110, 120 each having elongated lower beams 112, 122 and upper beams 114, 124 connected by spaced columns 130 which extend in the Z direction which is generally vertical as shown. The spaced columns 130 define windows 132 therebetween for reception of electrical interconnects (not shown) assembled onto the printbar which mate with electrical interconnects on the inkjet pens when installed in the respective pen locations in the printbar 100. As seen when comparing thee top plan view of FIG. 6 with the bottom plan view of FIG. 7, the columns 130 and windows 132 are not directly aligned with each other on opposite sides of the printbar. A rectangular cover 140 may be provided and affixed to the upper beams 114, 124 and to the end pieces 102, 104 by a plurality of fasteners 142 or any other suitable means.

#Spaced generally horizontally extending Z-datum supports 150 protrude inwardly of the frame in the X direction from the lower ends of the columns 130 for supporting the fluid ejection devices.

#One or more fluid ejection devices such as inkjet pens 200 are received in individual mounting locations or pockets (four are shown in the illustrated example) in the printbar 100. Each pen 200 is comprised of a generally rectangular plastic housing 210 having protruding fore and aft portions 212, 214 at the lower portion of each pen so that the lower portion of each pen can be said to define a generally offset or S configuration as best seen in FIGS. 2 and 4. The bottom plan view of the pen seen in FIG. 4 shows four elongated overlapping (in the Y direction) nozzle arrays 220, 222, 224, 226 which each contain inkjet orifices 228 through which ink may be fired by electrical activation of fluid vaporizing resistors or by piezoelectric firing as is conventional. Each pen housing 210 may contain a supply of ink and may also be provided with a fill port 230 for replenishment of ink in the housing from remote sources of ink, not shown.