EP0174751A1
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EP
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Apparatus and method for automatically determining defective thermal printhead elements
Assignee: NCR Canada Ltd
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Filing: 1985-08-14
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Granted: —
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Expires: 2005-08-14
Abstract
Abstract In a thermal printer, data in the form of character data separated by gaps is supplied over a data line (38) to a shift register (15). the latched outputs of which cause operation of thermal elements (R 1 -R N ) in a thermal printhead (11 During a test mode of operation, test data is supplied to operate the thermal elements (R 1 -R N ) in succession, a sensing resistor (R s ) providing corresponding test signals which are digitized by an A/D converter (39). Each digitized test signal is compared with an associated initial, stored, digitized test signal, and if the current value deviates by more than a predetermined amount from the initial value, a failure signal is provided. A processor (19) is thereupon effective to cause the subsequent character data to be shifted such that the defective element is aligned with a location which is not used for printing, such as an intercharacter gap. In a modification, the test signals for all the thermal elements (R 1 -R N ) are compared with a common fixed, predetermined reference level.
Inventors
- 👤 Ralf Maynard Brooks
- 👤 Arvindkumar Chunilal Vyas
- 👤 Brian Paul Connell
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-26 22:59
CPC Classifications
B; B41; B41J; B41J2/00; B41J2/315; B41J2/32; B41J2/35; B41J2/355; B41J2/36; B41J2/365; B41J7/00; B41J7/96
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
136 words
Thermal printing apparatus including a linear array (11) of thermal elements (R 1 -RN) and data generating means (19, 38) adapted during a first mode of operation to generate printing data for said thermal elements (R 1 -R N ), characterized in that said data generating means (19, 38) is adapted during a second mode of operation to produce test data, and by test signal developing means (R S , 35, 37) coupled to said thermal elements (R 1 -R N ) and effective during said second mode of operation to provide test signals associated respectively with said thermal elements (R 1 -R N ), and comparing means (21, 23, 29) adapted to compare said test signals with respective predetermined reference values, such that a failure signal is generated whenever a defective thermal element is detected.
Claim 2
Dependent Claim
136 words
Thermal printing apparatus including a linear array (11) of thermal elements (R 1 -RN) and data generating means (19, 38) adapted during a first mode of operation to generate printing data for said thermal elements (R 1 -R N ), characterized in that said data generating means (19, 38) is adapted during a second mode of operation to produce test data, and by test signal developing means (R S , 35, 37) coupled to said thermal elements (R 1 -R N ) and effective during said second mode of operation to provide test signals associated respectively with said thermal elements (R 1 -R N ), and comparing means (21, 23, 29) adapted to compare said test signals with respective predetermined reference values, such that a failure signal is generated whenever a defective thermal element is detected.
Claim 3
Dependent Claim
62 words
Thermal printing apparatus according to claim 1, characterized in that said printing data is formed by character data having a predetermined number of character positions, and by repositioning means (19) adapted to change the character positions with regard to said thermal elements (R 1 -R N ) such that said defective thermal element is not located in any of said character positions.
Claim 4
Dependent Claim
66 words
Thermal printing apparatus according to claim 1, characterized by memory means (43) adapted to store the initial test signals derived by said developing means (R S , 35, 37) for said thermal elements (R 1 -R N ) during an initial second mode of operation, each said initial test signal derived from an associated thermal element being the respective predetermined reference value for that thermal element.
Claim 5
Dependent Claim
18 words
Thermal printing apparatus according to _claim 3, characterized in that said memory means (43) includes a non-volatile memory.
Claim 6
Dependent Claim
24 words
Thermal printing apparatus according to claim 1, characterized in that said respective predetermined reference values are formed by a common, fixed, predetermined reference value.
Claim 7
Dependent Claim
108 words
Thermal printing apparatus according to claim 1, characterized by voltage control means (33) adapted to remove a first voltage from said thermal elements (R l -R N ) during said second mode of operation, thereby preventing said thermal elements (R 1 -R N ) from printing, voltage sensing means (R S ) coupled to said thermal elements (R 1 -R N ) and adapted, in the absence of said first voltage to provide a second voltage dependent on the resistance value of the thermal elements being tested, and conversion means (39) adapted to convert said second voltage to a test signal associated with the thermal element being tested.
Claim 8
Dependent Claim
18 words
Thermal printing apparatus according to claim 6, characterized in that said conversion means includes an analog-to-digital converter (39).
Claim 9
Independent Claim
111 words
A method for automatically detecting any defective thermal element in a linear array (11) of thermal elements (R l -R N ) in a thermal printer, characterized by the steps of: determining an associated reference value for each tnermal element, measuring a test signal for each thermal element during each of a sequence of test modes of operation; comparing each test signal for each thermal element with its associated reference signal during each test mode of operation; and detecting a defective thermal element when a test signal for that thermal element deviates by at least a preselected amount from the associated reference signal for that thermal element during said comparing step.
Claim 10
Independent Claim
111 words
A method for automatically detecting any defective thermal element in a linear array (11) of thermal elements (R l -R N ) in a thermal printer, characterized by the steps of: determining an associated reference value for each tnermal element, measuring a test signal for each thermal element during each of a sequence of test modes of operation; comparing each test signal for each thermal element with its associated reference signal during each test mode of operation; and detecting a defective thermal element when a test signal for that thermal element deviates by at least a preselected amount from the associated reference signal for that thermal element during said comparing step.
Claim 11
Dependent Claim
36 words
A method according to claim 8, characterized by the step of changing the position of serial data bits representing data to be printed such taht the defective thermal element is not utilized during the printing operation.
Claim 12
Dependent Claim
43 words
A method according to claim 8, characterized in that said determining step includes the step of measuring an associated initial test signal for each thermal element during an initial test mode of operation to determine the associated reference signal for each thermal element.
Claim 13
Dependent Claim
32 words
A method according to claim 8, characterized in that said determining step includes the-step of selecting a common, fixed, predetermined value for the associated reference value for all of said thermal elements.
References Cited (Backward Citations)
EP0072224A1
Cited
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