Battery operated thermal printer with means to optimize battery life

• US 6,095,700 A
• Filed: 07/17/1997
• Issued: 08/01/2000
• Est. Priority Date: 10/30/1993
• Status: Expired due to Term

• Current Assignee: Brother Kogyo Kabushiki Kaisha
• Original Assignee: Asahi Kogaku Kogyo Kabushiki Kaisha
• Inventors: Orita, Hiroshi, Suzuki, Minoru, Suzuki, Katsuyoshi, Negishi, Kiyoshi, Kawamura, Katsumi
• Primary Examiner(s): Burr, Edgar
• Assistant Examiner(s): Nolan, Jr., Charles H.
• Application Number:
  US08/895,814
• Time in Patent Office: 1,111 Days
• Field of Search: 400/120.05, 400/120.01, 400/120.2, 347/192, 347/9
• US Class Current: 400/120.02
• CPC Class Codes: B41J 2/355 Control circuits for heating-element selection
• CPC Class Codes: B41J 29/393 Devices for controlling or analysing the entire machine ; Controlling or analysing mechanical parameters involving printing of test patterns

Abstract

In a thermal printer having a plurality of thermal elements arranged in a line, voltage of a battery which is to be applied to the thermal elements is detected. Based on the detected voltage, the period of time during which the thermal elements are driven is determined.

Claims

1. A thermal printer having a thermal head provided with a plurality of thermal elements arranged in a line, said printer comprising:

a feeding mechanism for feeding a recording medium;

a battery;

an A/D convertor for converting a voltage V of said battery to a digital value;

a microprocessor having a strobe pulse width calculator and data representative of a heat equation stored therein, said heat equation including a relation;

space="preserve" listing-type="equation">T=Q/(V*V/R),

said relation relating a heat output Q of said thermal elements to said digital value representing V, a resistance value R of said thermal elements, and a strobe pulse width value T, said strobe pulse width calculator calculating said strobe pulse width according to said relation of said heat equation, said microprocessor having at least one data output for outputting printing data and at least one strobe output for outputting strobe data having said strobe pulse width;

a sensor for detecting the presence of the recording medium in the printer; and

a thermal head driver connected to said plurality of thermal elements, to said at least one data output, and to said at least one strobe output, said thermal head driver driving the thermal elements in accordance with the printing data and said at least one strobe output having said strobe pulse width,

said microprocessor including means for determining a feeding speed of said recording medium in accordance with said digital value of the voltage V of said battery, and means for setting said feeding mechanism to a synchronous feeding speed so that said recording medium is fed at the synchronous feeding speed corresponding to said strobe pulse width of said thermal elements.

2. The thermal printer according to claim 1, which further comprises means for feeding a recording sheet, and wherein said microprocessor varies the feeding speed of said recording sheet in accordance with said digital value so that said recording sheet is fed synchronously with a driving of said thermal elements.

3. The thermal printer according to claim 1, wherein said strobe pulse width calculator of said microprocessor calculates said strobe pulse width according to said heat equation such that said heat generated by said thermal elements is substantially constant at each operation, regardless of said voltage of said battery.

4. The thermal printer according to claim 1, which further comprises:

a connector to which an external voltage source is connected; and

a connection detector for detecting that said external voltage source is connected, and wherein said strobe pulse width calculator of said microprocessor calculates said strobe pulse according to said heat equation upon connection of said external voltage source.

5. The thermal printer according to claim 1, further comprising means, responsive to said voltage detected by a voltage detector, for actuating an indicator when a detected voltage is below a first predetermined value, and for terminating driving of said thermal elements when said detected voltage is below a second predetermined value.

6. The thermal printer according to claim 5, said first predetermined value corresponding to 12 volts.

7. The thermal printer according to claim 5, said indicator comprising a light emitting diode.

8. The thermal printer according to claim 5, wherein printer operation continues when said digital value is between said first predetermined value and said second predetermined value.

9. A method for controlling a thermal printer which has a thermal head provided with a plurality of thermal elements arranged in a line and a feeding mechanism for feeding a recording medium, a voltage V of a battery being applied to said thermal elements for driving said thermal elements to generate heat, said method comprising the steps of:

detecting the presence of the recording medium in the printer;

converting the voltage V of said battery to a digital value;

relating a heat output value of said thermal elements to at least said digital value, a resistance value R of said thermal elements, and a strobe pulse width value T according to a heat equation including a relation T=Q/(V*V/R);

calculating said strobe pulse width according to said heat equation;

outputting a printing data output;

outputting at least one strobe output having said strobe pulse width;

driving the thermal elements in accordance with the printing data and said at least one strobe pulse output to heat said thermal elements;

determining a feeding speed of said recording medium in accordance with said digital value of the voltage V of said battery;

setting a synchronous feeding speed; and

feeding said recording medium at the synchronous feeding speed corresponding to said strobe pulse width of said thermal elements.

10. The method according to claim 9, further comprising the steps of:

detecting a voltage of said battery;

warning a user when said detected voltage is less than a first predetermined value; and

terminating printer operation when said detected voltage is less than a second predetermined value,

wherein said second predetermined value is less than said first predetermined value.

11. The method according to claim 10, wherein said warning to the user is provided by a light emitting diode.

12. The method according to claim 10, said first predetermined value corresponding to 12 volts.