Circuit for controlling energization of thermal print head

• US 4,590,488 A
• Filed: 05/28/1985
• Issued: 05/20/1986
• Est. Priority Date: 05/28/1985
• Status: Expired due to Fees

• Current Assignee: Astro-Med Incorporated
• Original Assignee: Astro-Med Incorporated
• Inventors: Sullivan, Michael J.
• Primary Examiner(s): EVANS, ARTHUR G
• Application Number:
  US06/737,921
• Time in Patent Office: 357 Days
• Field of Search: 346/76 R, 346/76 PH, 400/120, 250/317.1, 250/318, 219/216 PH, 219/494, 364/519
• US Class Current: 347/194
• CPC Class Codes: B41J 2/365 by compensation for variation in temperature

Abstract

An electrical circuit for controlling the energization of thermal print head elements on a thermal print head. The circuit is responsive to the overall temperature of a thermal print head for varying the amounts of energy supplied the print head elements thereof so that markings of substantially uniform darkness can be produced on thermally sensitive sheets regardless of the overall head temperature. The circuit is operative in response to a start signal for producing a predetermined number of sequential pulses of substantially uniform duration during a printing cycle to sequentially energize different groups of print head elements at different times during the cycle. The voltage level of the pulses in the cycles is maintained substantially constant, whereas the duration of the pulses in different cycles is varied to vary the amounts of energy supplied to the print head elements.

Claims

1. A circuit for controlling the energization of a plurality of thermal print head elements on a thermal print head comprising:

a. means for sensing the temperature of said head;

b. first signal generating means responsive to said temperature sensing means for generating an electrical signal having a frequency which is proportional to the temperature of said head;

c. second signal generating means communicating with said first signal generating means and actuatable for generating a predetermined number of sequential output pulses of substantially uniform duration during a period of time wherein the temperature of said head remains substantially constant and wherein said duration is substantially proportional to the frequency of said first signal generating means, said second signal generating means communicating with said print head elements for sequentially controlling the energization of different print head elements with sequential pulses; and

d. means for actuating said second signal generating means in response to an input signal to said circuit and for automatically deactuating said second signal generating means after said predetermined number of sequential pulses has been produced therefrom, said means for actuating and deactuating comprising a bistable multivibrator and gate means, said first signal generating means communicating with said second signal generating means through said gate means, said bistable multivibrator being responsive to an input signal to said circuit for actuating said gate means to provide said communication between said first signal generating means and said second signal generating means.

2. A circuit for controlling the energization of a plurality of thermal print head elements on a thermal print head comprising:

a. means for sensing the temperature of said head;

b. first signal generating means responsive to said temperature sensing means for generating an electrical signal having a frequency which is proportional to the temperature of said head;

c. second signal generating means communicating with said first signal generating means and actuatable for generating a predetermined number of sequential output pulses of substantially uniform duration during a period of time wherein the temperature of said head remains substantially constant and wherein said duration is substantially proportional to the frequency of said first signal generating means, said second signal generating means communicating with said print head elements for sequentially controlling the energization of different print head elements with sequential pulses, said second signal generating means comprising counter means, and decoder means, said counter means communicating with said first signal generating means for producing sequential binary signals at intervals which are proportional to the frequency of said first signal generating means signal, said decoder means communicating with said counter means for producing a different one of said sequential output signals in response to each of said sequential binary signals until said predetermined number of sequential output signals has been produced and for thereafter producing a deactuating signal; and

d. means for actuating said second signal generating means in response to an input signal to said circuit and for communicating with said decoder means to automatically deactuate second signal generating means in response to said deactuating signal.