Jet printing apparatus

摘要

The apparatus is of the type wherein a piezoelectric transducer (19) is selectively operated to produce a pressure wave in the ink in a duct (16, 22), which causes a droplet of ink to be expelled from the nozzle (18). In order to absorb the energy of the pressure wave which is directed towards the ink reservoir (47) the duct comprises a portion (22) of viscoelastic material, which is so dimensioned as to damp the resonance of the duct for frequencies higher than a predetermined cut-off frequency. Frequencies which are lower than the cut-off frequency however are damped by an hour-glass shaped constriction (34) in a tube (33) disposed between the viscoelastic portion (22) of the duct and the reservoir (47). The second portion (22) of the duct comprises a polyamide base material, the modulus of elasticity of which is substantially stable over a wide range of possible operating temperatures. The second portion of the duct may comprise a flexible tube (22) or a double spiral passage (not shown) provided between two substantially square plates.