Printhead chip incorporating a double action ink ejection mechanism

1. A printhead chip which comprises

a substrate that incorporates a drive circuitry layer;

a plurality of nozzle chamber structures positioned on the substrate, each nozzle chamber structure defining a nozzle chamber and a pair of ink ejection ports in fluid communication with the nozzle chamber;

a plurality of elongate actuators associated with respective nozzle chamber structures, each actuator having one end fast with the substrate to be electrically connected to the drive circuitry layer and to be reciprocally displaced relative to the substrate on receipt of an electrical signal from the drive circuitry layer; and

an ink ejecting member positioned in each nozzle chamber and connected to the associated actuator to be reciprocally displaced by the actuator, the nozzle chamber structure being configured so that as the ink ejecting member is displaced in one direction, ink is ejected from one of the ink ejection ports and as the ink ejecting member is displaced in an opposite direction, ink is ejected from the other ink ejection port.

2. A printhead chip as claimed in claim 1 , in which each actuator comprises an actuator arm of a material capable of thermal expansion to perform work that is anchored to the substrate at one end and a pair of heater elements fast with the actuator arm on respective opposite sides of the arm and connected to the drive circuitry layer to receive alternate heating currents so that the arm experiences alternate thermal differential expansion and is thus reciprocally displaced.

3. A printhead chip as claimed in claim 2 , in which the heater elements are substantially identical.

4. A printhead chip as claimed in claim 2 , in which one of the heater elements is interposed between the actuator arm and the substrate and the arm is interposed between the heater elements so that the arm is displaced reciprocally towards and away from the substrate.

5. A printhead chip as claimed in claim 4 , in which each nozzle chamber structure includes a nozzle chamber wall and a roof that defines the nozzle chamber, each arm being connected to the respective ink ejecting member at the wall, such that the wall acts as a fulcrum, the actuator arm defining an effort member and the ink ejecting member defining a working member.

6. A printhead chip as claimed in claim 4 , in which each nozzle chamber structure includes a partitioning wall that depends from the roof, between the ink ejection ports so that each nozzle chamber is divided into a first part in fluid communication with one of the ink ejection ports and a second part in fluid communication with the other ink ejection port, each ink ejecting member being positioned in a respective first part so that when the ink ejecting member is displaced towards the roof, ink is ejected from the first part and when the ink ejecting member is displaced away from the roof, ink is ejected from the second part.

7. A printhead chip as claimed in claim 6 , in which the substrate defines a plurality of inlet channels in fluid communication with respective first parts of the nozzle chambers.