Control circuit for regulating temperature in an ink-jet print head

A temperature control circuit for regulating temperature in an ink-jet print head, the print head having multiple nozzles and associated drivers, individual drivers providing energy pulses to controllably deposit ink drops from associated individual nozzles to form a desired image, the temperature control circuit comprising:

• a thermal sensor mounted on the print head to measure temperature of the print head, the thermal sensor generating a voltage indicative of the temperature of the print head;
• a programmable voltage source for establishing a threshold voltage level representative of a threshold temperature;
• a comparator to compare the voltage produced by the thermal sensor with the threshold voltage level from the programmable voltage source, the comparator outputting a first signal when the voltage exceeds the threshold voltage level and a second signal when the voltage does not exceed the threshold voltage level;
• a flip-flop memory coupled to the comparator to sample and store the first or second signal output from the comparator, the flip-flop memory sampling the comparator during periods when the print head is not depositing ink drops;
• a warming pulse generator for producing a continuous series of warming pulses, individual warming pulses having a pulse width of an effective short duration which is insufficient to cause a deposition of an ink drop when applied to the print head;
• a firing pulse generator for selectively producing firing pulses, individual firing pulses having a pulse width of a duration longer than the short duration of one of the warming pulses which is effective to cause a deposition of an ink drop when applied to the print head;
• first logic circuitry having one input operatively connected to the flip-flop memory, another input connected to the warming pulse generator, and an output, the first logic circuitry providing at the output of the first logic circuitry the warming pulses received from the warming pulse generator when the flip-flop memory stores the second signal from the comparator;
• and
• second logic circuitry having one input connected to the output of the first logic circuitry, another input connected to the firing pulse generator, and an output connected to a nozzle driver of the print head, the second logic circuitry providing at the output of the second logic circuitry at least one of (1) the warming pulses to warm the print head and (2) the firing pulses to cause deposition of ink drops from the print head.

An ink-jet print head comprising:

• multiple nozzles arranged in a predetermined configuration;
• a plurality of drivers for corresponding nozzles, individual drivers providing energy pulses to controllably deposit ink drops from the associated individual nozzles;
• a thermal sensor mounted to measure temperature of the print head, the thermal sensor generating a voltage indicative of the temperature of the print head;
• a programmable voltage source for establishing a threshold voltage level representative of a threshold temperature;
• a comparator coupled to compare the voltage from the thermal sensor with the threshold voltage level from the programmable voltage source, the comparator outputting a first signal when the voltage exceeds the threshold voltage level indicating that the print head temperature exceeds the threshold temperature and a second signal when the voltage does not exceed the threshold voltage level indicating that the print head temperature does not exceed the threshold temperature;
• a warming pulse generator for producing a continuous series of warming pulses, individual warming pulses having a pulse width of an effective short duration which is insufficient to cause a deposition of an ink drop when applied to one of the drivers;
• a firing pulse generator for selectively producing firing pulses, individual firing pulses having a pulse width of a duration longer than the short duration of one of the warming pulses which is effective to cause a deposition of an ink drop when applied to one of the drivers;
• first logic circuitry having one input connected to the comparator, another input connected to the warming pulse generator, and an output, the first logic circuitry providing at the output of the first logic circuitry the warming pulses received from the warming pulse generator upon receipt of the second signal from the comparator indicating that the measured print head temperature does not exceed the threshold temperature;
• and
• second logic circuitry having one input connected to the output of the first logic circuitry, another input connected to the firing pulse generator, and an output connected to a nozzle driver of the print head, the second logic circuitry providing at the output connected to the nozzle driver (1) the firing pulses for depositing ink drops from selected nozzles of the print head and (2) the warming pulses for warming non-selected nozzles of the print head.

A temperature control circuit for regulating temperature in an ink-jet print head, the temperature control circuit comprising:

• a thermal sensor to measure temperature of the print head and thereby provide a measured print head temperature;
• a temperature level detector coupled to the thermal sensor to determine whether the measured print head temperature exceeds a threshold temperature;
• a warming pulse generator for producing a series of warming pulses, individual warming pulses having a pulse width of an effective short duration which is insufficient to cause a deposition of an ink drop when applied to the print head;
• a firing pulse generator for selectively producing firing pulses, individual firing pulses having a pulse width of a duration longer than the short duration of one of the warming pulses which is effective to cause a deposition of an ink drop when applied to the print head;
• and
• logic circuitry coupled to the temperature level detector, the warming pulse generator, and the firing pulse generator to (1) simultaneously pass both the warming pulses and the firing pulses to the print head when the temperature level detector determines that the measured print head temperature does not exceed the threshold temperature and (2) pass only the firing pulses to the print head when temperature level detector determines that the measured print head temperature exceeds the threshold temperature.