Pagewidth printhead assembly incorporating laminated support structure

Abstract

A printhead assembly extending in pagewidth direction includes an elongate support beam; an elongate shell at least partially enclosing and restraining the support beam; and a plurality of printhead integrated circuits mounted to the support beam and substantially aligned with one another in the pagewidth direction. The support beam has formed therein at least one printing fluid reservoir arranged in fluid communication with the plurality of printhead integrated circuits.

Description

FIELD OF THE INVENTION

The present invention relates to printers, and in particular to digital inkjet printers.

BACKGROUND OF THE INVENTION

Recently, inkjet printers have been developed which use printheads manufactured by micro-electro mechanical system(s) (MEMS) techniques. Such printheads have arrays of microscopic ink ejector nozzles formed in a silicon chip using MEMS manufacturing techniques.

Printheads of this type are well suited for use in pagewidth printers. Pagewidth printers have stationary printheads that extend the width of the page to increase printing speeds. Pagewidth printheads do not traverse back and forth across the page like conventional inkjet printheads, which allows the paper to be fed past the printhead more quickly.

To reduce production and operating costs, the printheads are made up of separate printhead modules mounted adjacent each other on a support beam in the printer. To ensure that there are no gaps or overlaps in the printing produced by adjacent printhead modules it is necessary to accurately align the modules after they have been mounted to the support beam. Once aligned, the printing from each module precisely abuts the printing from adjacent modules.

Unfortunately, the alignment of the printhead modules at ambient temperature will change when the support beam expands as it heats up during printhead operation. Furthermore, if the printhead modules are accurately aligned when the support beam is at the equilibrium operating temperature, there may be unacceptable misalignments in any printing before the beam has reached the operating temperature. Even if the printhead is not modularized, thereby making the alignment problem irrelevant, the support beam and printhead may bow because of different thermal expansion characteristics. Bowing across the lateral dimension of the support beam does little to affect the operation of the printhead. However, as the length of the beam is its major dimension, longitudinal bowing is more significant and can affect print quality.

SUMMARY OF THE INVENTION

According to an aspect of the present disclosure, a printhead assembly extending in pagewidth direction includes an elongate support beam; an elongate shell at least partially enclosing and restraining the support beam; and a plurality of printhead integrated circuits mounted to the support beam and substantially aligned with one another in the pagewidth direction. The support beam has formed therein at least one printing fluid reservoir arranged in fluid communication with the plurality of printhead integrated circuits.

BRIEF DESCRIPTION OF THE DRAWING

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawing in which:

FIG. 1 is a schematic cross section of a printhead assembly according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the FIGURE, the printhead assembly 1 includes a printhead 2 mounted to a support member 3. The support member 3 has an outer shell 4 and a core element 5 defining four separate ink reservoirs 6, 7, 8 and 9. The outer shell 4 is a hot rolled trilayer laminate of two different metals. The first metal layer 10 is sandwiched between layers of the second metal 11. The metals forming the trilayer shell are selected such that the effective coefficient of thermal expansion of the shell as a whole is substantially equal to that of silicon even though the coefficients of the core and the individual metals may significantly differ from that of silicon. Provided that the core or one of the metals has a coefficient of thermal expansion greater than that of silicon, and another has a coefficient less than that of silicon, the effective coefficient can be made to match that of silicon by using different layer thicknesses in the laminate.

Typically, the outer layers 11 are made of invar which has a coefficient of thermal expansion of 1.3×10⁻⁶ m/° C. The coefficient of thermal expansion of silicon is about 2.5×10⁻⁶ m/° C. and therefore the central layer must have a coefficient greater than this to give the support beam an overall effective coefficient substantially the same as silicon.

The printhead 2 includes a micro moulding 12 that is bonded to the core element 5. A silicon printhead chip 13 constructed using MEMS techniques provides the ink nozzles, chambers and actuators.

As the effective coefficient of thermal expansion of the support beam is substantially equal to that of the silicon printhead chip, the distortions in the printhead assembly will be minimized as it heats up to operational temperature. Accordingly, if the assembly includes a plurality of aligned printhead modules, the alignment between modules will not change significantly. Furthermore, as the laminated structure of the outer shell is symmetrical in the sense that different metals are symmetrically disposed around a central layer, there is no tendency of the shell to bow because of greater expansion or contraction of any one metal in the laminar structure. Of course, a non-symmetrical laminar structure could also be prevented from bowing by careful design of the lateral cross section of the shell.

The invention has been described herein by way of example only. Skilled workers in this field will readily recognise that the invention may be embodied in many other forms.

Claims

1. A printhead assembly extending in pagewidth direction, the printhead assembly comprising: an elongate support beam;an elongate shell at least partially enclosing and restraining the support beam; anda plurality of printhead integrated circuits mounted to the support beam and substantially aligned with one another in the pagewidth direction, whereinthe support beam has formed therein at least one printing fluid reservoir arranged in fluid communication with the plurality of printhead integrated circuits.

2. A printhead assembly as claimed in claim 1, wherein the laminated structure has an effective coefficient of thermal expansion substantially equal to that of the plurality of printhead integrated circuits.

3. A pagewidth printhead assembly as claimed in claim 1, wherein the shell is a laminated structure.

4. A printhead assembly as claimed in claim 3, wherein the laminated structure has an odd number of laminates arranged so that the outer laminates have the same coefficient of thermal expansion as one another and a different coefficient of thermal expansion to that of the inner laminates.

5. A printhead assembly as claimed in claim 1, wherein the coefficient of thermal expansion of each laminate is different to that of the printhead integrated circuits.

6. A printhead assembly as claimed in claim 1, wherein the outer and inner laminates are formed of different metals.

7. A printhead assembly as claimed in claim 5, wherein the outer laminates are formed of invar.

8. A printhead assembly as claimed in claim 1, wherein the printhead integrated circuits are fabricated from silicon and constructed using micro-electromechanical techniques.