US Patent 7878629 Stackable printer module with two pairs of printheads

A printer module includes a housing. The housing surrounds a frame and defines footing holes. A print engine is housed within the housing and includes a pair of opposed print head assemblies for enabling double-sided printing on print media to be effected. Each printhead assembly includes a print media engaging roller and a pair of adjacent printheads configured to eject ink. Feet extend from the housing and are spaced apart to engage in respective footing holes defined in the housing of another printer module so that the printer modules can be stacked together.