Over actuation detection in a micro electromechanical device
View Patent ↗A method of detecting an over actuation condition within a micro electromechanical device in the form of an ink ejection nozzle having an actuating arm that moves an ink displacing paddle when heat inducing electric current is passed through the actuating arm and having a movement sensor associated with the actuating arm. The method comprises the steps of passing at least one current pulse having a predetermined duration through the actuating arm and detecting for a rate of movement of the actuating arm. A fault condition is detected to exist where the detected rate of movement is in excess of the rate for normal operation.
1. A method of detecting an over-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) passing at least one current pulse having a predetermined duration t p through the actuating arm, and
(b) detecting the rate of movement of the actuating arm to said predetermined position, and
(c) comparing the detected rate with the rate for desired actuation of the actuating arm,
wherein the over-actuation condition is detected when the detected rate is in excess of the normal rate.
2. 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.
3. 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.
4. The method as claimed in claim 3 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.
5. The method as claimed in claim 3 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.
6. The method as claimed in claim 3 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 .