Methods and apparatus for control of a signal in a printing apparatus
View Patent ↗A printing apparatus is provided that precisely control the transition of an electrical signal that causes a printing substance to be deposited. In particular, in some embodiments, a circuit is configured to control the application of a firing pulse to a printing element, and the printing element is configured to control the application of a printing substance. The circuit in this embodiment is configured to condition or control the transition of the firing pulse from the first state to the second state such that current through the printing element dissipates to zero over a period of tine that is neither too fast nor too slow.
1. A circuit for controlling current to an actuator element configured to deposit ink in a printing apparatus, the circuit comprising:
at least one circuit component configured to cause current through an actuator element to dissipate in a controlled manner by controlling at least one edge of a firing signal pulse, wherein the edge comprises a transition from a first state to a second state.
2. The circuit as recited in claim 1 , wherein the component is configured to dissipate current caused by the firing signal pulse rapidly to an initial level and then more slowly to a zero level.
3. The circuit as recited in claim 1 , wherein the at least one circuit component comprises a circuit component that dissipates current according to a characteristic that approximates resistor, and a circuit component that dissipates current according to a characteristic that approximates a diode.
4. The circuit as recited in claim 1 , wherein the circuit resides on a chip on a printhead, wherein the printhead includes an ink chamber, nozzles configured to allows ink to exit the printhead, and connectors to receive address signals from a controller, and wherein the actuator element comprises a heater element configured to heat the ink to cause it to exit the printhead.
5. The circuit as recited in claim 1 , wherein the actuator element comprises a heater, wherein the circuit includes a switching device that is switched by the controlled firing pulse signal to cause current to be delivered to the actuator element, and wherein the controlled dissipation of the current controls the magnitude of back EMF such that the back EMF is below a level that would cause damage to components in the circuit.