JPH01110969A - Thermal printer - Google Patents

Abstract

PURPOSE:To make it possible to obtain favorable printing quality while maintaining printing speed and enable flexible adaptation to variations in printing conditions, by writing driving time control data into a RAM by a microprocessor, reading the driving time control data based on printing history data generated by a printing history data generating circuit, and rewriting the content of the RAM, as required. CONSTITUTION:A printing history date generating circuit 2 receives printing bit data S1-S4, and generates printing history data S10-S13. A RAM 3 is controlled as to reading/writing by a control signal S23 from a microprocessor 1, and driving time control data S14, S15 corresponding to the printing history data S10-S13 outputted from the circuit 2 is written into and read from the RAM 3. A driving time controlling circuit 4 receives the driving time control data S14, S15 read from the RAM 3, and supplies a driving circuit 5 with a driving pulse with a duration corresponding to the data S14, S15. The driving circuit 5 passes an electric current to heat generating elements of a thermal head 6 for the duration of the driving pulse.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal printer having a thermal head composed of a dot heating element.

[Conventional technology]

Conventionally, in this type of thermal printer, the driving time of the heating element is controlled based on the printing history of each dot in order to prevent damage to the thermal head due to heat and to maintain uniform printing results.

FIGS. 6 and 7 are schematic diagrams of the conventional thermal printer described above. In the example shown in FIG. 6, the drive time of the thermal head is controlled entirely by a microprogram, and the drive circuit 72 is turned on/off in order to obtain the optimum drive time taking into consideration the printing history of each dot of the thermal head 73. The timing is directly instructed from the microprocessor 71 to the drive circuit 72. In the example shown in FIG. 7, the microprocessor 71 supplies only information on whether each dot of the thermal head 73 prints (hereinafter referred to as print bit information) to the drive time control circuit 74; Based on this, on/off timing is given to the drive circuit 72 to obtain the optimum drive time.

[Problem that the invention seeks to solve]

The above-mentioned conventional thermal printer has the disadvantage that, in the example shown in Figure 6, all processes such as obtaining the optimal drive time by considering the printing history are performed by a microprogram, which takes time and slows down the printing speed. In the example shown in Figure 7, the drive time is controlled by hardware in consideration of the printing history, so the processing speed is high, but
The circuit size becomes larger, and the control method is fixed, making it impossible to perform fine-grained control such as changing the drive time even for the same printing history in response to changes in printing conditions such as differences in ribbon, paper, or thermal head type. The disadvantage is that there is no flexibility to

[Means for solving problems]

The thermal printer of the present invention includes: a thermal head composed of a dot heating element; a drive circuit that supplies current to the heating element of the thermal head; and a drive circuit that uses printing history information of each dot of the thermal head as an address input. a RAM in which driving time control information for selecting a driving pulse indicating a time width for passing current through the heating element of the thermal head is written and read; A drive time control circuit that selectively outputs a drive pulse indicating a time width for passing a current through the heating element of the thermal head to the drive circuit; and a drive time control circuit that inputs information on whether or not to print each dot of the thermal head to generate printing history information. a print history information generation circuit that generates and outputs to the address input of the RAM; and a print history information generation circuit that operates according to a microprogram and outputs information on whether or not to print each dot of the thermal head to the print history information generation circuit. Generate printing history information and output the printing history information from the printing history information generation circuit to the above-mentioned R.
It has a microprocessor that writes and reads drive time control information to and from the RAM as an address of AM, and causes the drive time control circuit to selectively output drive pulses based on the drive time control information read from the RAM.

[Function] In this way, the print history information generation circuit generates print history information based on the print bit information of each dot of the thermal head from the microprocessor, and the microprocessor uses this print history information as address input to perform optimal drive time control. The processing load of the microprocessor is reduced because the information is written to and read from the RAM and the drive time is controlled so that a current is passed through the heating element in a time width that provides uniform printing results according to the printing history of each dot. High-quality printing results can be obtained without reducing printing speed, and it is also possible to flexibly respond to changes in printing conditions such as the type of ribbon, paper, or thermal head by changing the writing to the RAM at any time.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a thermal printer of the present invention.

Microprocessor 1 operates on a microprogram,
Information on whether or not to print each dot of the thermal head (hereinafter referred to as print bit information) is output to the print history information generation circuit 2. To simplify the explanation, the number of dots in the thermal head 6 is assumed to be four, so the number of print bit information is four, which is referred to as 5L-34. In addition, the microprocessor 1 receives signals 85 to S8, a print cycle timing signal S9, latch pulses 316 to S19, and a control signal S for the RAM 3.
Outputs 23. Print history information generation circuit 2 receives print bit information 81-S4 and generates print history information 5IO-313. The read/write of the RAM 3 is controlled by the control signal S23 from the microprocessor 1, and drive time control information S14. S15 is written,
Read out. The drive time control circuit 4 receives the drive time control information S14. read from the RAM 3. Upon receiving S15, a drive pulse with a corresponding time width is applied to the drive circuit 5.

The drive circuit 5 causes current to flow through the heating element of the thermal head 6 for the duration of the given drive pulse. Here, the time during which the current flows through each heating element is set to a value that allows uniform printing results to be obtained according to the printing history of each head.

FIG. 2 is a circuit diagram of the printing history information generating circuit 2 shown in FIG.

The print history information generation circuit 2 is composed of four shift registers 11 to 14 whose outputs are wired together, and each of the shift registers 11 to 14 receives print bit information 31 to S4 output from the microprocessor 1. The 4-bit printing history information, that is, the next printing bit information 5IO1, is read sequentially in synchronization with the falling edge of the printing cycle timing signal s9 output from
The current print bit information Sll, the previous print bit information S1.2, and the immediately previous print bit information S13 are output. In addition, shift registers 11 to 1
The print history information appears in the outputs of the microprocessor 4 only when the input signals 85 to S8 output from the microprocessor 1 are at a high level. These input signals 8
5 to S8 are controlled so that a plurality of signals do not become high level at the same time.

FIG. 3 is a circuit diagram of the drive time control circuit 4, drive circuit 5, and thermal head 6.

The thermal head 6 is composed of four dot heating elements. The drive circuit 5 includes drivers 31 to 34 that drive (energize) the dot heating elements 41 to 44, respectively.

The drive time control circuit 4 receives a print cycle timing signal S.
Three types of drive pulses S20 with different time widths in synchronization with 9
- Drive pulse generation circuit 21 that generates S22 and RAM
2-bit data (driving time control information) read from S14. S15 from the microprocessor 1 as the signal S
Latch pulse S output in synchronization with 5 to S8, respectively.
The latch circuits 22 to 25 latched by 16 to S19 and the drive pulse 520- output from the drive pulse generation circuit 21 using the outputs of the latch circuits 22 to 25 as selection signals.
322 to the drivers 31 to 34, respectively.

Note that the input terminals D4 of the selectors 26 to 29 are grounded, and when the corresponding dot is not printed, the input terminals D4 of the selectors 26 to 29 are grounded.
29 outputs "O", and at that printing timing, no drive pulse is given to the driver and no current flows to the dot heating element.

FIG. 4 is a diagram showing the timing of the various signals 85 to S22 mentioned above. The print cycle timing signal S9 is a signal that provides basic print cycle timing, and while this signal is at a high level, the drive pulse generation circuit 21 generates drive pulses 320 to S22 having different time widths. The input signals 85 to S8 sequentially become high level after the print cycle timing signal S9 falls, and print history information SIQ to S8
13 is output. Drive time control information S14 read from RAM3. S15 changes corresponding to print history information SIO-S13, and is latched by latch circuits 22-25 by latch pulses S16-S19, respectively.

FIG. 5 is a circuit diagram of another example of the printing history information generating circuit 2 in FIG. 1.

Each print history information generation circuit 2 generates print bit information 81.
- Four shift registers 15 to 18 that take in S4 in synchronization with the falling edge of print cycle timing signal S9, and shift registers 15 to 18 that take in input signals 85 to s8 as control signals.
16 outputs 4-bit printing history information, that is, the next printing bit information Sll, the current printing bit information S12, and the next printing bit information SIO and S13 of the adjacent dots on both sides. It is composed of 3-state buffers 51 to 66.

Note that since the dot heating elements 41 and 44 are located at both ends, the inputs of the three-state buffers 51 and 66 are grounded. Depending on the characteristics of the thermal head, it may be necessary to consider the printing history information of adjacent dots as in this example, or it may be possible to use even more past printing bit information by increasing the number of shift register stages and 3-state buffers. By increasing the number of bits of printing history information, it is possible to support even more detailed control.

〔Effect of the invention〕

As explained above, the present invention allows the microprocessor to write the drive time control information to the RAM, and read out the drive time control information based on the print history information generated from the print history information generation circuit. Because the processing is reduced, the printing speed does not decrease, and by rewriting the content written to RAM as needed, the same print quality can be maintained in response to changes in printing conditions, such as differences in the type of ribbon, paper, or thermal head. This has the effect of making it possible to realize a flexible thermal printer that can perform detailed control such as changing the drive time even in the case of printing history.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the thermal printer of the present invention, FIG. 2 is a circuit diagram of the print history information generation circuit 2 in FIG. 1, and FIG. 4 is a circuit diagram of the thermal head 6; FIG. 4 is a timing diagram of signals S5 to S22 in FIGS. 1 and 3; FIG. 5 is a circuit diagram of another example of the printing history information generating circuit 2 in FIG. Figure 6 is a block diagram of a conventional thermal printer in which the drive time of the thermal head is controlled entirely by a microprocessor, and Figure 7 is a block diagram of a conventional thermal printer in which the drive time of the thermal head is controlled by a drive time control circuit based on information from the microprocessor. 1 is a block diagram of a conventional example of a printer. 1...Microprocessor, 2...Print history information generation circuit, 3...RAM. 4... Drive time control circuit, 5... Drive circuit, 6... Thermal head, 11.12, 13, 14, 15, 16, 17°18...
・Shift register, 21... Drive pulse generation circuit, 22.23, 24.25... Latch circuit, 26.27
．． 28.29...Selector, 31.32.33.34
... Driver, 41.42.43.44 ... Dot heating element, 51.52, 53. ..., 66 ... 3-state buffer, SL, S2. S3. S4--Print bit information, S5,
36. S7. S8...Input signal, S9...Print cycle timing signal, SIO, Sl 1. S12
．． S13...Printing history information, S14. S15... Drive time control information, S16. S1
7. S18. S19...Latch pulse, S20,321. S22... Drive pulse, S23...
·Control signal.

Claims (1)

[Scope of Claims] A thermal head configured with a dot heating element; a drive circuit that causes current to flow through the heating element of the thermal head; and a drive circuit that uses printing history information of each dot of the thermal head as an address input. a RAM in which driving time control information for selecting a driving pulse indicating a time width for passing a current through the heating element of the thermal head is written and read; A drive time control circuit that selectively outputs a drive pulse indicating a time width for passing a current through the heating element of the thermal head; and a drive time control circuit that inputs information on whether to print each dot of the thermal head or not to print history information. a print history information generation circuit that generates information and outputs it to the address input of the RAM; and a print history information generation circuit that is operated by a microprogram and outputs information on whether or not to print each dot of the thermal head to the print history information generation circuit to print. The printing history information generated from the printing history information generation circuit is
A thermal printer comprising a microprocessor that writes and reads drive time control information to and from the RAM as an AM address, and causes the drive time control circuit to selectively output drive pulses based on the drive time control information read from the RAM.