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Chopped Current Circuit - Resistance Compensated Flight Time

IP.com Disclosure Number: IPCOM000034156D
Original Publication Date: 1989-Jan-01
Included in the Prior Art Database: 2005-Jan-26
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Wallace, JE: AUTHOR [+2]

Abstract

When a print actuator coil is energized, much of the energy is dissipated as heat, thereby increasing the printer temperature. The increased temperature causes thermal expansion of the print actuator parts and also increases the coil resistance. While the thermal expansion of the print actuator parts causes a decrease in the flight time of the actuator, the increased coil resistance causes an increase in the flight time. In general, the effects of increased coil resistance do not completely offset the effects of thermal expansion. Consequently, as the printer heats up, the flight time decreases. A new print actuator design adds an external resistor to a chopped current circuit which powers the actuator coil. The added resistor is located near the actuator coil to provide temperature compensation.

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Chopped Current Circuit - Resistance Compensated Flight Time

When a print actuator coil is energized, much of the energy is dissipated as heat, thereby increasing the printer temperature. The increased temperature causes thermal expansion of the print actuator parts and also increases the coil resistance. While the thermal expansion of the print actuator parts causes a decrease in the flight time of the actuator, the increased coil resistance causes an increase in the flight time. In general, the effects of increased coil resistance do not completely offset the effects of thermal expansion. Consequently, as the printer heats up, the flight time decreases. A new print actuator design adds an external resistor to a chopped current circuit which powers the actuator coil. The added resistor is located near the actuator coil to provide temperature compensation. The added external resistor is connected in series with the coil. The purpose of this resistor is to increase the difference in the current rise time between the cold and the hot condition (see the figure). By adding an external resistor, rather than adding resistance to the coil, the power dissipation of the coil remains approximately constant. It is preferable that the external resistor be a material with a relatively high temperature coefficient of resistance (TCR), such as copper. A high TCR maximizes the resistance change as a function of temperature. In the ideal case, it is desirable to have the added ex...