Under actuation detection in a micro electromechanical device
View Patent ↗A method of detecting an under actuation condition within a micro electro-mechanical 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 predetermined level of movement of the actuating arm. A fault is detected to exist by comparing the detected movement with the movement for desired operation, and where a fault is present, at least one further current pulse having an energy level greater than the fault detecting pulse may be passed through the actuating arm in an attempt to clear the fault.
1. A method of detecting under actuation of a micro electro-mechanical 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 for movement of the actuating arm to said predetermined position,
(c) comparing the detected movement of the actuating arm with the movement of desired operation,
wherein under actuation of the device is detected when the detected movement is less than the desired movement.
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 .
7. A method of detecting and remedying an under actuation condition within a micro electro-mechanical 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.