Testing of a micro-electromechanical device for under actuation

1. A method of detecting under actuation of a micro electromechanical device of a type having a support structure, an actuating arm that is movable relative to the support structure between a rest position and an operating position under the influence of heat inducing current flow through the actuating arm and a movement sensor associated with the actuating arm, said movement sensor being activated by movement of the actuating arm to a predetermined position beyond said operating position; the method comprising the steps of:

(a) passing a series of current pulses of varying magnitude and/or duration through the actuating arm,

(b) determining the minimum magnitude and/or duration of the current pulse required to move the actuating arm to the predetermined position, and

(c) comparing said determined magnitude and/or duration with a desired magnitude and/or duration characteristic,

wherein under actuation of the device is detected when the detected movement is less than the desired magnitude and/or duration characteristic.

2. A method of detecting and remedying an under actuation condition within a micro electromechanical device of a type having a support structure, an actuating arm that is movable relative to the support structure between a rest position and an operating position under the influence of heat inducing current flow through the actuating arm and a movement sensor associated with the actuating arm, said movement sensor being activated by movement of the actuating arm to a predetermined position beyond said operating position; the method comprising the steps of:

(a) detecting the fault in the manner as claimed in claim 1 , and

(b) remedying the fault by passing at least one further current pulse through the actuating arm at an energy level greater than that of the fault detecting current pulse.

3. The method as claimed in claim 1 when employed in relation to a liquid ejection nozzle having a liquid receiving chamber from which the liquid is ejected with movement of the actuating arm to said operating position.

4. The method as claimed in claim 1 when employed in relation to an ink ejection nozzle having an ink receiving chamber from which the ink is ejected with movement of the actuating arm to said operating position.

5. The method as claimed in claim 4 wherein the movement sensor comprises a moving contact element formed integrally with the actuating arm, a fixed contact element formed integrally with the support structure and electric circuit elements formed within the support structure, and wherein contact is made between the fixed and moving contact elements at said predetermined position of the operating arm.

6. The method as claimed in claim 4 wherein a single current pulse having the predetermined pulse t p is induced to pass through the actuating arm and detection is made for movement of the actuating arm to said predetermined position consequential on the passage of the single current pulse.

7. The method as claimed in claim 4 wherein a series of current pulses of successively increasing duration t p are induced to pass through the actuating arm over a time period t and detection is made for movement of the actuating arm to said predetermined position within a predetermined time window t w where t>t w >t p .