A drop on demand inkjet printer which includes a thermal actuator. The thermal actuator is formed of an electrically operable heater element that is encased within actuation material having a high coefficient of thermal expansion. The heater element includes a corugated structure to improve transferral of heat from the heater element to the actuation material and hence increase the speed of actuation of the thermal actuator. The heater element is also of a serpentine or concertina form so as to allow substantially unhindered expansion of the actuation material during heating. One surface of the actuator is hydrophobic and the other surface is hydrophilic, with the heater element constructed form copper encased in polytetrafluoroethylene which is processed to form a hydrophilic surface. The actuator can include a number of layers. One of the layers is conductive material which functions as the heater element. The conductive material is sandwiched between layers of actuation material. The conductive material has a series of slots or holes so as to allow the actuation material to be integrally joined together so as to reduce a likelihood of delamination of the layers.

A method of calibrating a micro electromechanical device in the form of an ink ejection nozzle having an actuating arm that is caused to move an ink displacing paddle when heat inducing electric current is passed through the actuating arm and having also a movement sensor associated with the actuating arm. The method comprises the steps of passing a series of current pulses of successively increasing duration t.sub.p through the actuating arm over a time period t, detecting for a predetermined level of movement of the actuating arm within a predetermined time window t.sub.w, and calibrating the device for subsequent actuation by a current pulse having a duration t.sub.p sufficient to produce the predetermined level of movement within the predetermined time window t.sub.w.

An integral structure within an MEMS device is used to filter out foreign bodies in a fluid supply. The system is initially constructed in a large planar form, and the effect of impurities is reduced by fabricating an integral grill structure in the path of the flow of the liquid so as to filter foreign, bodies in the liquid. Ideally used in an ink jet printing system, the grill forms one wall of a nozzle chamber for filtering ink entering the nozzle chamber to be ejected from the nozzle chamber. The filter can be constructed from nitride as is the nozzle chamber.

A micro electro-mechanical device embodied within an ink ejection nozzle having an actuating arm that is caused to move an ink displacing paddle when heat inducing electric current is passed through the actuating arm. The device incorporates a movement sensor that comprises a moving contact element that is formed integrally with the actuating arm, a fixed contact element that is formed integrally with a support structure of the device and electrical elements formed within the support structure for detecting contact that is made between the fixed contact element and the moving contact element. The movement sensor is provided for the purpose of facilitating testing of the device under various operating conditions.

A method of testing a micro electro-mechanical device in the form of an ink ejection nozzle having an actuating arm that is caused to move an ink displacing paddle when heat inducing electric current is passed through the actuating arm and having also a movement sensor associated with actuating arm. The method comprises the steps of passing a current pulse having a predetermined duration or a series of current pulses having successively increasing durations through the actuating arm, and detecting for a predetermined level of movement of the actuating arm.