JPS6089378A - Driving of thermal head - Google Patents

Abstract

PURPOSE:To uniformize the printing density by driving a thermal head employing a bidirectional print system so that one line of print is completed by printing at an alternate heat cycle covering given portion in the outgoing operation and the rest in the incoming operation likewise. CONSTITUTION:A carriage 1 is driven reciprocatively along a guide shaft 6 with a pulse motor 4 through gears 7, 8 and 9. In this case, printing is performed at an alternate heat cycle covering the odd rows in the outgoing of the thermal head 2 and even rows reversely in the incoming thereof to complete one line of print. This can increase the ratio of the cooling time significantly with respect to the heat generation time in heat generating elements DT1-DT8 without lowering the printing speed and eliminate heat accumulation thereby preventing variations in the printing density associated with a rise in the temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for driving a thermal head, and more particularly to a method for driving a thermal head that performs printing with uniform density by completely alleviating heat accumulation during continuous printing.

[Prior art]

2. Description of the Related Art In thermal printers used as output devices of information devices, a method is widely adopted in which printing is performed by moving a thermal head in which heating elements are arranged in a vertical line in the entire scanning direction.

This type of thermal printer is required not only to perform all character printing such as letters and symbols, but also to perform all image printing, such as printing an image displayed on a monitor screen such as a CRT or a complete copy of a printer.

In particular, for such image glint, so-called peta-black printing or similar printing is often used, in which printing is performed while generating heat from all the dot heating elements arranged in a vertical row. On the other hand, the density of each printed dot is most affected by the temperature rise of the heating element.

For this reason, in printing that generates heat continuously during each heat cycle, such as peta black printing, the temperature is not initialized.
The problem that the element temperature gradually rises due to heat accumulation and the printing density gradually becomes darker, that is, the problem of density non-uniformity, becomes important.

FIGS. 1A and 1B are explanatory diagrams illustrating all the ways in which non-uniformity of print density occurs during continuous peta black printing. In these figures, if you print one line of peta black starting at heat cycle 1 and ending at heat cycle n,
As shown in FIG. 1(B), the dot surface temperature increases, and as shown in FIG. 1(5), the print density gradually becomes darker, resulting in uneven density.

〔the purpose〕

The purpose of the present invention is to eliminate all the drawbacks of the prior art,
It is an object of the present invention to provide a method for driving a thermal head that can completely equalize printing density.

The feature of the present invention is that it adopts a bidirectional printing method, in which it performs IJ with every other heat cycle during the forward movement, and prints with the remaining every other heat cycle during the backward movement to print one line. The above objective is achieved by fully driving the thermal head to complete the process.

[Explanation of Examples] The present invention will be described in detail below with reference to all the drawings.

FIG. 2 shows the control s' of the thermal printer according to the present invention.
FIG.

The host computer 21, which controls the entire thermal printer as a peripheral device, connects the central processing unit (hereinafter referred to as CPU) 2, which performs the main control of the printer, via the signal 1s1'r.
Connected to 2. This CPU 22 includes a random access memory (RAM) used by the CPU.
26 and a read-only memory (ROM) 27 containing all the printer control programs are provided.

On the other hand, the CPU 22 controls the driver 23 through the signal lines S2 and 83. This driver 23 includes each heating element DTI-DT8 of the thermal head 2, and an excitation phase Sφ1 of a pulse motor 4 that drives the thermal head in all scanning directions.
- Sφ4 and excitation phases Fφ1 to Fφ4 of the pulse motor 5 for fully driving the paper feed roller and feeding the paper are connected. In this way, the heating element and each pulse motor are driven under the control of the CPU 22, and predetermined printing is performed.

Reference numeral 28 is a power switch for the thermal printer, and when the power is fully turned on, the CPU 22, driver 23,
The thermal head 2 and the nozzle motors 4 and 5 are now ready for operation. Also, CPU22, b source bxo
At the time of N, the heat cycle counter and line counter provided in the RAM 26 are reset.

143 Figures (A) and (B) show the entire schematic structure of a thermal printer. A carriage 1 carrying a thermal head 2 performs a printing operation while moving along a guide shaft 6 arranged parallel to and facing a platen 12. In this embodiment, the carriage 1 is driven reciprocally along the guide shaft 6 by a Noculus motor 4 via gears 7, 8, 9, and when moving forward from left to right in the figure and from right to left. During the backward movement, printing is performed every alternate heat cycle, and printing for one line is completely completed each time one reciprocating movement is completed. In this case, an end switch 3 is provided to detect the return position W''r of the carriage 1, and a return signal 't can be input to the CPU 22 when the carriage 1 returns after printing for one line is completely completed.

Furthermore, gears 10, 11, 13'! The feed feed operation is performed by driving the paper through the paper r and feeding the paper.

According to the thermal printer configured as described above, the thermal head 2 in which a plurality of heat generating elements, that is, eight heating elements DT1 to DT8 are arranged in a vertical line, is reciprocated, and the forward and backward movements are performed in a reciprocating manner. It is possible to print based on print data while energizing a predetermined heating element to generate heat in each heat cycle in both directions.

According to the method for driving a thermal head according to the present invention, as shown in FIG. 4, when the thermal head 2 moves forward (from left to right in FIG. 4), the heat cycle is performed every other odd row. Printing is completed for one line by printing all lines and printing from the opposite direction with a heat cycle of 1a for every even numbered column (remaining columns) during the backward motion. The mark ◎ in Figure 4 indicates the printing driver during forward movement)? The ○ marks indicate all printed dots during double movement. Conversely, it is also possible to print all even-numbered cycles during forward movement and print odd-numbered cycles during backward movement.

By implementing all of these drive methods, the ratio of the cooling time to the heat generation time of the heat generating elements DTI to DT8 can be increased to 1 by a large amount without reducing the printing speed, thereby reducing heat accumulation. This makes it possible to achieve uniform printing density.

FIG. 5 is a flowchart showing a specific example of the operating procedure when carrying out the entire thermal head driving method according to the present invention. The operating procedure will be explained below with reference to this footchard.

In FIG. 5, when the received data is input to the print buffer and the print buffer becomes full (MAX) and preparation for printing is completed (step 100), the next step 101 determines whether the print is in image mode. It is fully determined whether it is normal character printing, and if it is the image mode, it is determined in the next step 102 whether rightward (forward) printing has been completed.

If the right direction printing is not completed, in step 103, the right direction excitation sound O of the excitation phase Sφ1-8φ4 of the pulse motor 4 is output.
N, and in step 104, the timer 2 stops energizing the dot heating element during a set cooling period time-divided for each cycle, and during this period, in step 105, it is determined whether the cycle in question is an odd cycle or not.

If it is an odd number cycle, the print pattern is set on the signal line S2 in the next step 106, and in step 107, a predetermined dot heating element (all of DTL to DT8 in the case of peta black printing) is energized to generate heat. In step 108, the timer 2 is used to turn on electricity for a set heat generation period, and then in step 109, the electricity is turned off to complete one heat cycle, and the process returns to step 102 again.

If Stella 7'105 determines that it is an even cycle rather than an odd cycle, the dot heating element is not heated and is kept in a cooling state during the period set by the timer 2, and after the cycle is completed, the process returns to step 102.

In this way, all of the above operations are repeated until the printing in the right direction is completed, and printing is performed while generating heat only in odd-numbered cycles for all printing operations and cooling in even-numbered cycles, that is, while generating heat every 1 cycle.

When it is determined in step 102 that rightward printing is completed, in step 110 the excitation phases Sφ1 to Sφ4 of the motor 4 are
All 1 to Sφ magnets are turned ON, and in step 111, the timer 2 stops energization for the set cooling period (time-divided period in each cycle), and during that time, in step 112, it is determined whether the cycle in question is an even cycle or not. Determine whether

If it is an even number cycle, the Stella 7'j13 sets all the print patterns to the signal lines S2, and the Stella 7'l14 energizes a predetermined dot heating element to generate heat.

In step 115, the timer 2 is used to energize the set heat generation period, and then the Stella fl16 stops the energization to complete one heat cycle. Thereafter, in step 117, a full judgment is made as to whether or not leftward printing has been completed, and if it has not been completed, the process returns to step 110 to perform the next odd cycle operation.

In this odd number cycle, it is determined in step 112 that it is not an odd number cycle, so the process jumps to step 115 without energizing the dot heating element, and leftward printing is completed when one cycle period has elapsed with the timer (step 117). Determine whether or not.

If not completed, the process returns to step 110 and the above operations are repeated alternately until all leftward printing is completed.

If it has been completed, it means that printing for one line has been completed, and the process returns to step 100 to start printing the next line. In step 101, it is determined whether or not to print the entire image mode.
If this line is also in the image mode, bidirectional printing is performed using the same operating procedure as described above.

Note that if it is not image mode printing, step 101
Then, the character is printed based on another control code.

According to the method of driving the thermal head explained above, during forward movement (during conventional printing operation), one of the odd number columns (even number columns is also possible)
Generate heat with alternating heat cycles to print all lines, and during backward movement (conventional gear rigid return) generate heat with heat cycles of 1" to print all lines, bidirectional print for 1 line. Since the operation is performed so as to completely complete printing, a cooling period of one heat cycle or more can be provided between one heat generation period of the element and the next heat generation period.

Therefore, all the heat accumulation in the dot heating elements can be almost completely eliminated without reducing the printing speed.
Changes in print density due to temperature rise can be completely prevented.

In addition, it is possible to reliably prevent heat accumulation with a simple control mode, without requiring complicated control such as correcting heat cycle control by checking the history of each dot heating element, such as the number of times it heats up or whether or not it generated heat last time. [Effects] As is clear from the above explanation, according to the present invention, with relatively simple control operations, it is possible to completely prevent heat accumulation in the thermal head, thereby reducing density during peta black printing, etc. A method of driving a thermal head that can prevent changes is provided.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram illustrating all the states of heat accumulation and density changes when solid black printing is performed using a conventional thermal head driving method, and FIG. 2 is a diagram showing a control suitable for implementing the entire thermal head driving method according to the present invention. 3(A) and 3) are a block diagram illustrating the configuration of the parts, and FIGS. FIG. 4 is an explanatory diagram illustrating a state in which the method for driving a thermal head according to the present invention is implemented to perform solid black printing, and FIG. It is an illustrative flowchart. 1... Carriage, 2... Thermal head, 4, 5.
... Yarus motor, 6... Guide shaft, 21... Host computer, 22... Thermal printer CPU
, 23...Driver, DT1-DT8...Dot heating element, Sφ1-Sφ4...Excitation phase of the reciprocating motor for the thermal head, Fφ1-Fφ4...Excitation phase of the A pulse motor for paper feeding. Figure 813 (A) (B) Figure 114

Claims (1)

[Claims] (1) In a method of driving a thermal head in which all print data is printed by moving the entire thermal head having a plurality of heating elements and energizing the heating elements to generate heat, when the thermal head moves forward, an odd column or an even column is printed. Print with a heat cycle for every other row, and print the remaining one during the return run.
A method for driving a thermal head, characterized in that printing is completed in an alternating heat cycle to completely complete printing.