Printer coil temperature sensor and method

A line printer lot printing data from a host comprising:

• a hammerbank having a plurality of hammers which are retained by magnetism from a permanent magnet;
• means to reciprocally drive said hammerbank across a print media:
• at least one pole magnetically connected to said permanent magnet for retaining each of said hammers;
• coil surrounding said pole pieces;
• electronic drive means for providing a current through said coil for firing said hammers;
• transistor means which turn on during reciprocation of said hammerbank;
• means to provide a pre-established flyback current through said coil equivalent to a first coil temperature;
• means to determine the flyback current through said entire coil after hammer firing with respect to said pre-established current after said transistor means turn on during reciprocation of said hammerbank to determine said coil temperature change with respect to said first coil temperature;
• and,
• means to drive said coil respect to said determined temperature change.

A test circuit for determining the temperature in coils within a line printer wherein said line printer has a hammerbank capable of being driven for reciprocal movement with a plurality of hammers retained by permanent magnetism until released by energizing said coils in associated relationship with said hammers wherein the improvement comprises:

• means to store a pre-established temperature of said coils based upon a first flow of current through said coils;
• means for determining a second current flow through said coil in the entirety during operating conditions of said printer between hammer firings during reciprocation of said hammerbank;
• means for comparing said first and second current flows to determine the difference between said current flows and the corresponding temperature change;
• and,
• means for controlling said printer with respect to said temperatures.

A method of determining temperature of a coil in a hammerbank of a line printer comprising:

• moving said hammerbank in a reciprocating manner;
• providing a first coil resistance value based upon a pre-established temperature of said coil;
• sensing a second coil resistance of said coil in the entirety during the operation of the hammerbank;
• comparing said second coil resistance of said coil during operation with the first coil resistance;
• controlling said printer with respect to the differential between said first and second coil resistances;
• and,
• driving the hammers of said hammerbank during a pre-established direction of movement for printing when said second resistance exceeds said first resistance by a pre-established amount.