System for aligning a plurality of printhead modules

1. A method of aligning individual printhead modules in a pagewidth printer, the printhead modules being mounted adjacent each other along an elongate support, the elongate support having a higher coefficient of thermal expansion than the modules such that during use the temperature of the elongate support raises from ambient to an operating temperature, wherein the elongate support lengthens and the modules displace relative to each other, the method of aligning comprising the steps of:

forming fiducial marks on each of the printhead modules;

providing a microscope for viewing the fiducial marks as the printhead modules are positioned on the elongate support;

positioning reference marks on the microscope such that bringing the fiducial marks of adjacent printhead modules into registration with the reference marks aligns the modules; and,

calibrating the reference marks to incorporate an alignment error that is equal and opposite to the relative displacement of adjacent printhead modules from ambient temperature to the operating temperature.

2. A method according to claim 1 wherein the elongate support is a beam with a core of silicon and an outer metal shell.

3. A method according to claim 2 wherein the beam is adapted to allow limited relative movement between the silicon core and the metal shell.

4. A method according to claim 3 wherein the beam has an elastomeric layer between the silicon core and metal shell to permit the limited relative movement.

5. A method according to claim 4 wherein the outer shell is formed from laminated layers of at least two different metals.