METHOD AND APPARATUS FOR CONTROLLING THE TEMPERATURE OF AN ELECTRICALLY-HEATED DISCHARGE NOZZLE
In an embodiment, the disclosure relates to a method and apparatus for fault monitoring and controlling operation of a discharge nozzle in a large array of discharge nozzles. An exemplary apparatus includes a thin, thermally conductive membrane, with an integrated thin-film electrical heater. When a fixed voltage is applied to the heater, and as the heater heats, the resistance of the heater will increase which will cause a concomitant decrease in the electrical current flowing through the heater. By measuring the resistance of the heater it can readily be determined whether the device is functioning properly.
1 . A method for controlling the temperature of a discharge nozzle, the method comprising:
providing a discharge nozzle for dispensing ink, the discharge nozzle having a thermally-conductive membrane with an integrated thin film electric heater and the thin film electric heater defining a resistance;
receiving a quantity of ink in liquid-form at the discharge nozzle;
energizing the thin-film heater by applying a substantially constant current to the thin-film heater;
measuring a voltage across the heater and a current through the heater; and
determining temperature of the heater as a function of the voltage and the current; and
determining the temperature of the ink droplet as a function of the heater temperature.
2 . The method of claim 1 , further comprising energizing the thin-film heater by supplying electric current and measuring the ink quantity by measuring a change in the heater temperature.
3 . The method of claim 1 , further comprising energizing the thin-film heater by applying a plurality of voltage pulses to the thin-film heater, each voltage pulse providing substantially identical voltage and having varying pulse width.
4 . The method of claim 1 , wherein the step of determining temperature of the heater further comprises determining the temperature as a function of the resistance from data specific to said resistor.
5 . The method of claim 1 , further comprising varying the voltage to increase the temperature of the heater.
6 . A control system for controlling temperature of a discharge nozzle, the control system comprising:
a discharge nozzle having a plurality of conduits for receiving a quantity of liquid ink, the discharge nozzle thermally communicating with a heater;
a first metering device for measuring a voltage across the heater;
a second metering device for measuring a current through the heater;
a processor circuit for determining resistance of the heater as a function of the voltage and the current, the processor circuit controlling at least one of voltage or current input to the heater; and
a memory circuit in communication with the processor circuit, the memory containing data associating resistance with the temperature of the conduits of the discharge nozzle;
wherein the processor increases the voltage supplied to the heater to increase the temperature at the conduits of the discharge nozzle.
7 . The control system of claim 6 , wherein the discharge nozzle has a thermally-conductive membrane.
8 . The control system of claim 6 , further comprising a power supply in communication with the processor, the processor controlling at least one of voltage or current supplied to the heater.
9 . The control system of claim 6 , further comprising a power supply in communication with the processor, the power supply supplying voltage pulses to the heater, wherein the voltage pulses have substantially identical pulse height and varying pulse width.
10 . The control system of claim 6 , wherein the resistive heater is integrated with the discharge nozzle.
11 . A discharge system for depositing ink on a substrate, the system comprising:
a chamber having a quantity of ink, the ink defined by a plurality of suspended ink particles in a carrier liquid;
a discharge nozzle for receiving a quantity of liquid ink from the chamber;
a heater in thermal communication with the discharge nozzle, the heater evaporating the carrier liquid at the discharge nozzle to deposit a substantially solid quantity of ink particles from the discharge nozzle; and
a controller in communication with the discharge nozzle, the controller maintaining the heater temperature by varying the voltage while maintaining substantially constant current supplied to the heater.
12 . The system of claim 11 , wherein the controller supplies a plurality of energy pulses to a heater, each of the plurality of pulses having a substantially constant pulse height and varying pulse width.
13 . The system of claim 1 , wherein the controller further comprises a processor circuit programmed with instructions to:
(a) determine one of the amount or the duration of activation required to discharge the quantity of ink particles to the substrate;
(b) energize the discharge nozzle consistent with the amount or duration determined in step (a); and
(c) repeat steps (a) and (b) to discharge additional quantities of ink particles onto the substrate.
14 . The system of claim 1 , wherein the controller further comprises at least one processor circuit in communication with a memory for storing instructions.
15 . The system of claim 1 , wherein the controller tasks the dispenser to provide the metered quantity of ink by providing pulsating energy to the dispenser, the pulsating energy adapted to exact a metered quantity of ink to the discharge nozzle.