PRINTHEAD TEMPERATURE CONTROLLER THAT USES NONPRINTING PULSES

This document discloses a method and apparatus for real-time control of the temperature of thermal ink jet printheads (128) and thermal printheads (128) through the use of nonprinting pulses (142, 144, 148). A closed-loop system (94) produces nonprinting pulses (148) in response to a difference between a reference temperature signal (110) and a printhead temperature signal (100) produced by a temperature sensor (124) on the printhead (128) so that the printhead (128) operates at a constant elevated temperature. The reference temperature signal (110) can specify an operating temperature anywhere between 10 DEG C and 100 DEG C above room temperature. The closed-loop system can have multiple loops (92, 94) with different response times so that complex nonlinear responses to changes in the printhead temperature can be obtained. The open-loop system (96) transmits nonprinting pulses (144) to the printhead (128) for each printing interval that the printer does not eject a drop. Also, this document discloses a method for measuring the energy transfer characteristics of a printhead. This method is used to determine how much energy open-loop nonprinting pulses should transmit within one printing interval to the printhead to prevent fluctuations in the temperature of the printhead caused by variations in the printer output.