JPS6238148B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal printer that has a plurality of heating elements arranged in a horizontal row and performs printing by selectively energizing these heating elements according to the pattern to be printed, and in particular, a thermal printer that has a plurality of heating elements arranged in a horizontal row and performs printing by selectively energizing these heating elements according to the pattern to be printed. The present invention relates to a thermal printer in which elements are formed on the same head.

The thermal printer described above has heating elements for one dot line in a horizontal row, for example several hundred dots, on the same head board, so if even one of the heating elements is abnormal. If there is, you will have to replace each head board. In such a case, it is good if the head board can be replaced immediately, but if such a situation is not available, the thermal printer must be placed in a dormant state until the head board can be replaced. However, in an environment where thermal printers are frequently used and there is no room for long downtimes, it may be desirable to print even if the print quality is somewhat poor.

Furthermore, since the above-mentioned thermal head is expensive, it is not very economical to replace even one abnormal heating element. Therefore, there is a demand among users of thermal printers to continue printing with a thermal head containing an abnormal heating element, even though some deterioration in printing quality is unavoidable. However, if such a thermal head is allowed to perform the same printing operation as it normally does, there is a risk that characters may be misread due to missing dots or the like.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a thermal printer that can provide a print quality that does not cause misreading even in the presence of an abnormal heating element.

In order to achieve this purpose, a thermal head in which a plurality of heating elements are arranged in a horizontal row, a heating element drive circuit that pairs with these heating elements, a write pulse generation means, and a thermal head for one row of heating elements that are serially inputted are used. and a line buffer for storing print data while shifting it bit by bit by the write pulse supplied from the write pulse generating means, and selectively drives the heating element drive circuit based on the data stored in the line buffer to perform printing. In a thermal printer, the present invention includes an abnormality detecting means for detecting an abnormality in the heating element and the heating element drive circuit, a storage means for storing the position of the abnormal heating element and the heating element driving circuit, and counting the write pulses. a counting means for comparing the counting output of the counting means with the storage output of the storage means, and a comparing means for outputting a correction signal each time the two outputs match, and inputting the print data and the correction signal of the comparing means. If the number of times the correction signal is input while writing the print data for one row of heating elements to the line buffer is zero, the print data is output as is to the line buffer, and if the number of inputs is 1 or more, the print data is and data correction means for shifting the data by an amount corresponding to the number of inputs and outputting the shifted data to the line buffer.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is an explanatory diagram of the printing method of the present invention, and 1 is a thermal head in which a plurality of heating elements 2 are arranged in a horizontal row at equal intervals. _C1 shows an example of printing a dot pattern of the letter "A" by the heating elements 2a to 2e, and particularly shows a printing example in which missing dots occur at the positions of the broken-line circles in the fourth column. d ₁ and d ₂ are the characters "A" stored in the line buffer described later.
The pattern data of the second and fourth lines of the pattern is shown. As shown by d ₁ and d ₂ , the second
The pattern data in the 4th column of the 4th row and 4th row has a binary value of "1", and dots should originally be printed at this position, but the heating element 2d is abnormal and dot printing is not possible. If this happens, missing dots will occur as shown in _C1 above, making it difficult to read the characters.

Therefore, in the present invention, a test mode operation is executed prior to the actual printing operation to detect abnormal heating elements. Of course, abnormalities in the heating element include abnormalities in the driver for driving the heating element. For example, if an abnormality is detected in the heating element 2d, the address of the heating element 2d is stored, and when storing the actual print pattern data in the line buffer, dummy data D is stored at the storage location corresponding to the address.
The pattern data of the column to be printed by the heating element 2d is stored adjacent to the storage position. Then, storage of pattern data for subsequent columns is continued again. As a result, the pattern data in the second and fourth rows in the line buffer become as shown in D ₁ and D ₂ , and dummy data D is stored in the fourth column corresponding to the abnormal heating element 2 d. Accordingly, the pattern data from the fifth column onwards are stored at positions shifted by one bit from the normal positions. Therefore, if the heating element 2 is driven by the pattern data stored in the line buffer in this way, even if the dots in the fourth column are missed, these dots will be printed in the immediately adjacent column, as shown in _C2 .
Character quality improves to the extent that it is not misreadable. Note that in Figure 1, the dots are shown enlarged, so it does not appear that the quality of the characters has improved that much, but since actual printing is done using a large number of dots, even if there are missing dots, they will not be missed. When two dots are printed next to each other, it looks like a continuous line between them.

Next, FIG. 2 is a block diagram schematically showing the circuit configuration of an embodiment for performing the above-described printing operation.

When a test command TS is given to the test mode control circuit 3 by an external command source such as a manual switch or by turning on the power prior to the actual printing operation, the test mode control circuit 3 first turns off the drivers of all heating elements. A detection command is issued to the abnormal element detection circuit 4 under the following conditions, and the presence or absence of current flowing through all heating elements is checked. If a current is detected, pattern data is given to the line buffer 5 so that the drivers of all heating elements are turned on, and then pattern data is given in which the drivers that are turned off are sequentially switched from those in the first row. , the abnormal element detection circuit 4 monitors the current value and detects the address of the abnormal heating element. Furthermore, if no current flowing through the heating elements is detected under the condition that all the drivers are off, the test mode control circuit 3 sends pattern data to the line buffer 5 such that the drivers in the first row are turned on one by one. The abnormal element detection circuit 4 detects the address of an abnormal heating element that is not driven.

In this way, if there is an abnormal heating element in which dots are constantly printed and an abnormal heating element in which dots are always missing, the addresses of these abnormal heating elements are detected, and this address is stored in the abnormal element address storage circuit 6. .

When the test mode operation is completed, the actual printing operation begins. The pattern data PD to be printed is serially transferred bit by bit and stored in the line buffer 5 via the data correction circuit 7. The line buffer 5 stores the entire line of dot pattern data while shifting it bit by bit in response to the write pulse WP supplied from the write pulse generating circuit 8. The address counter 9 counts the write pulse WP and indicates up to which column of pattern data is currently stored. The contents of this address counter 9 are given to a comparison circuit 10 and compared with the address of the abnormal heating element stored in the abnormal element address storage circuit 6. When the difference between the address and the contents of the address counter 9 becomes 1, a correction signal S is supplied from the comparison circuit 10 to the data correction circuit 7.

FIG. 3 shows an embodiment of the data correction circuit, in which the correction signal S is applied to the correction number counter 12. The correction number counter 12 counts up in response to the correction signal S, and its contents are decoded by the decoder 13. Pattern data to be printed on the other hand
PD is input to the OR gate 14. The other input of this OR gate 14 is test data TD given from the test mode control circuit 3. The output of the OR gate 14 is supplied to a shift register 15 and an AND gate _AG0 . The output of each stage of the shift register 15 is connected to one input of AND gates AG ₁ to AG _o , respectively. The other inputs of these AND gates AG ₀ to AG _o are connected to each output of the decoder 13 described above.

The operation of the data correction circuit in Figure 3 is shown in Figures 4 and 5.
This will be explained below using the time chart shown in the figure.

The OR gate 14 in FIG. 3 has pattern data PD of 1, 2, 3...1 as shown in FIGS. 4 and 5.
0, 11, etc. are supplied sequentially. Further, a write pulse WP is supplied from the write pulse generating circuit 8 of FIG. 2 to the shift register 15 as shown in the figure. Therefore, the first stage of the shift register 15 contains pattern data.
PD1, 2, 3...10, 11... are write pulses WP
They are set as 1', 2', 3'...10'...in synchronization with . Similarly, in the second stage, 1'', 2'', 3'', etc. are set. Items with the same numbers are the same data. Therefore, the address counter 9 in Figure 2 counts as shown in the figure. A case where an abnormality occurs in heating elements 5 and 6, and a case where an abnormality occurs in heating elements 5 and 7 will be explained with reference to FIGS. 4 and 5, respectively.

When there is an abnormality in the heating elements 5 and 6 as shown in FIG. 4, the correction signal S is supplied to the correction number counter 12 in FIG.
Outputs as shown in the figure can be obtained from output terminals 0, 1, and 2 of 3.

By the way, line battle 5 has orgate 16.
The output of the OR gate 14 and the shift register 15 are supplied by the decoder 13.
Since the outputs of each stage are selectively ORed and supplied, print data is set as shown in FIG. In other words, the pattern data PD1, 2, 3, 4, 5 while the output of the output terminal 0 of the decoder 13 is "1" are first set in the line buffer 5, and then while the output of the output terminal 1 of the decoder 13 is "1". The output 5' of the first stage of the shift register 15 is set,
After that, the output of the output terminal 2 of the decoder 13 becomes “1”
The output 5″ of the second stage of the shift register 15 between
6'', 7'', 8''... are set sequentially.

Therefore, dummy data 5, 5' are set at the address corresponding to the abnormal heating element (in the case of FIG. 4, the address indicated by the mark "▽"), and when this dummy data is removed, the line buffer 5 has 1, 1, 2,
Pattern data PD is set in the given order of 3, 4, 5'', 6'', 7'', 8''...

FIG. 5 shows a case where there is an abnormality in the heating elements 5 and 7, and since the operation can be fully understood from the explanation of FIG. 4 above, the explanation will be omitted. In Fig. 5, 5 and 6' marked with "▽" are dummy data, and line buffer 5 has 1, 2, 3, 4, 5', 6'',
Pattern data PD in the given order as 7″, 8″…
is set.

Note that dummy data is “1” even if it is “0”.
This means that it may be , and cannot be used as print data. In other words, if there is an abnormality in the heating element that causes dots to be printed all the time, dots will be printed no matter what this dummy data is, and if dots are always missing, then dots will be printed no matter what this dummy data is. However, no dots are printed.

In this way, the pattern data PD to be printed is corrected by the data correction circuit 7 so as to print with the adjacent heating element each time the pattern data PD to be printed with an abnormal heating element arrives and is stored in the line buffer 5. When one line of pattern data is stored in the line buffer 5, the drivers 11 are driven all at once according to the pattern data by a drive timing control circuit (not shown) to print one line of dots.

In the data correction circuit 7, the correction number counter 12 and shift register 15 are cleared at the same time as the one line of dots is printed, and return to the initial state.

As explained above with reference to the drawings, according to the present invention, in a thermal printer in which a plurality of heating elements are arranged in a horizontal row on the same head, even if there is an abnormal one among the heating elements, it is possible to read the thermal printer. This has the effect that it is possible to obtain print quality that does not cause errors, and that there is no need to replace the head every time a failure such as a missing dot or a dot appears.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the printing method of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, FIG. 3 is a diagram showing a part of the circuit configuration of FIG. 2, FIGS. This figure is a time chart explaining the operation of the data correction circuit of FIG. 3. DESCRIPTION OF SYMBOLS 1...Thermal head, 2...Heating element, 3...Test mode control circuit, 4...Abnormal element detection circuit, 5...
Line buffer, 6... Abnormal element address storage circuit, 7... Data correction circuit.

Claims (1)

[Scope of Claims] 1. A thermal head in which a plurality of heating elements are arranged in a horizontal line, a heating element driving circuit that pairs with these heating elements, a write pulse generating means, and a serially input pulse generator for one row of heating elements. and a line buffer for storing print data while shifting it bit by bit by a write pulse supplied from the write pulse generating means, and selectively drives the heating element drive circuit based on the data stored in the line buffer to perform printing. In a thermal printer, the following are provided: an abnormality detecting means for detecting an abnormality in the heating element and the heating element drive circuit; a storage means for storing the position of the abnormal heating element and the heating element driving circuit; and a counting means for counting the write pulses. and a comparison means that compares the count output of the counting means and the storage output of the storage means and outputs a correction signal every time the two outputs match, and inputs the print data and the correction signal of the comparison means, If the number of inputs of the correction signal while writing the print data for one row of elements to the line buffer is zero, the print data is output as is to the line buffer, and if the number of inputs is 1 or more, the print data is input the number of times. A thermal printer comprising: data correction means for shifting the data by an amount corresponding to the amount and outputting the shifted data to the line buffer.