JPH022431B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method for driving a thermal recording head, and particularly to a driving circuit for a thermal recording head used as a recording device of an information output apparatus.

(Prior art) Conventionally, to compensate for the darkness of the recorded image due to the thermal response delay of the thermal recording element, the printing pulse width is controlled by the time from the previous line printing timing to the current line printing timing, but this method , is insufficient as information on the number of black pixels of the previous line, that is, as temperature information on the amount of residual heat generated by the driving recording element. Therefore, for a black line after a continuous white line, a sufficient black density cannot be ensured because the recording element is cooled. An example of this problem is that for a document such as that shown in FIG. 6a, the horizontal hanging lines tend to become thinner in the recorded image, resulting in a recorded image such as that shown in b.

(Objective of the Invention) The present invention uses the time from the previous line printing timing to the current line printing timing as a control parameter for the printing pulse width, as well as the time from the last line where the number of black pixels in the past line is greater than a certain value to the current line. Depending on the time, the printing time is controlled to be longer than the normal printing pulse only when there is a transition from a line with few black pixels to a line with many black pixels, and black information that comes after white information such as horizontal lines such as in hanging line originals is controlled. The present invention provides a driving circuit for a thermal recording head that improves reproducibility.

(Structure of the Invention) According to the present invention, there is provided a first timer that measures the time from the previous line printing timing to the current line printing timing, and a final line printing timing that satisfies the condition that the number of black pixels in the past line is larger than a certain value. A second timer measures the time from the current line printing timing to the current line printing timing, and if the number of black pixels on the current line is smaller than a predetermined value, the printing pulse width is controlled by the timer value of the first timer. If the number of black pixels is equal to or greater than a predetermined value, a driving circuit for the thermal recording head is obtained, which includes a circuit for controlling the print pulse width with the clock value of the second timer.

That is, in the thermal recording type line recording device of the present invention, the first timer measures the time from the previous line printing timing to the current line printing timing, and the number n of black pixels in the past line is nn ₁ ,
A second timer measures the time from the last line printing timing that satisfies the condition (n ₁ : constant value) to the current line printing timing, and the printing pulse width is controlled by these two parameters. When the number of black pixels on the current line is small (n<n ₂ , where n ₂ is a constant value), there are few sudden changes from white to black, so the first timer from the previous line to the current line printing timing is The printing pulse width is controlled by the clock time, and when the number of black pixels on the current line is large (nn ₂ ), there may be a sudden transition from white to black, and the temperature information of the recording element has a large effect, so the number of pixels from this line The line is controlled so that black density can be ensured by making the printing pulse width larger than usual based on the time value of the second timer.

(Principle of the Invention) In general, thermal recording elements have a thermal response delay, and when driven at high speed, the black density is higher when no heat remains in the recording element than when there is no heat remaining in the recording element. We cannot secure enough. Therefore, only when there is no heat remaining in the recording element, that is, when there is a transition from a continuous line with few black pixels to a line with many black pixels, the printing pulse width is made larger than the normal printing pulse width. The aim is to ensure the concentration of

(Example) Next, an example of the present invention will be described with reference to the drawings. Figure 1 is a circuit diagram of a thermal recording head, in which one line of thermal recording elements 11 is divided into a matrix of 416 pixels x 4 blocks, and each block is sequentially driven with enable signals EN1 to EN4. There is. In addition, this thermal recording head is configured with a double buffer of a shift register circuit 12 and a latch circuit 13 for one line in order to temporally parallelize the image information transfer timing and the print timing and enable high-speed driving. The data is transferred by the data transfer clock DCP and the recording data DATA (here, black pixels are "1" and white pixels are "0"), and output by the latch pulse LATCH. In FIG. 1, 14 is a NAND circuit (AND inversion output circuit), and 15 is a recording element driver.
FIG. 2 is a time chart corresponding to each terminal in FIG. 1.

In the embodiment of FIG. 3, this enable signal EN1
~The purpose is achieved by controlling the pulse width of EN4, and a block diagram of one example is shown in Figure 3.
The time chart corresponding to this block diagram is shown in the fourth section.
As shown in the figure.

First, enable signal with differentiator circuit (DIV1) 40
When DEN becomes "0", the timing is shifted and pulses φ ₁ , φ ₂ , and φ ₃ are output. A black pixel counter (C1) 38 counts black pixels from DATA synchronized with the data clock DCP, and when the count values reach _n1 and _n2 , respectively,
1, N2 is set to "1" and cleared at the timing of pulse _φ3 . (Here, n ₁ = 100, n ₂ = 200.) T0 timer (C4) 42 is clock SCP
is counted and cleared at the timing of pulse _φ2 . Further, the T1 timer (C3) 41 counts the clock SCP and is cleared by the output pulse of the ant circuit (AND1) 35 of N1 and _φ2 . T0
Output B of timer (C4) 42 and T1 timer (C3) 4
The output A of 1 is the data select circuit (DS1) 34. When the select signal S (S=N2) is "0", the T0 timer 42 is selected, B is output to the output terminal Y, and when S is "1" T1 timer 41 is selected and output A is output to output terminal Y.

The counter (C2) 39 counts the pulses φ ₂ using the pulse of the output b of the AND circuit (AND2) 36 using φ 2 and _N2 as a start pulse. This count (C2) 39 output has a φ ₂ count value l (here, l = 2) after the start pulse.
The gate (AND3) 37 of the latch pulse _φ1 of the latch circuit (LAT2) 33 is closed. That is, the output Y' of the latch circuit (LAT2) 33 is latched every line when the T0 timer 42 is applied, and is latched for 1+1 lines when the T1 timer 41 is applied.

When this T1 timer 41 is applied, the latch process is not performed, and T1 timer 41 is simply used when recording hanging lines with steps.
When the timer 41 is applied, as shown in FIG.
For the k line, the T1 timer value T1k is applied, and the k line is clearly recorded as black, but for the k+
1, k+2 line is T0 by clearing T1 timer
The value is the same as that of a timer, and clear black cannot be recorded on lines k+1 and k+2 because the printing pulse width is insufficient. Therefore, sufficient black density is ensured by applying T1k as the printing pulse width from line k to line l by the latch process when the T1 timer is applied as described above.

Returning to FIG. 3 again, the latched output Y' of the latch circuit (LAT2) 33 is input to the address terminal of the memory circuit (ROM) 32 containing the print pulse width data table, and the table is read at the timing of _φ2 . Output data. Counter (C5) 3
1 reads this output at the timing of _φ3 , starts counting by the clock SCP, and outputs " ₁ " to Q1 until the data value is reached. When the output of Q ₁ is completed, the count timer is operated in the same manner for Q ₂ to Q ₄ to form print pulses like enable signals EN1 to EN4 in FIG. 2.

Through the above series of circuit operations, lines with a small number of black pixels (n<n ₂ ) to lines with a large number of black pixels (n
n ₂ ), the printing pulse width of the l+1 line after the transition can be made larger than usual, and a sufficient density of black pixels can be ensured.

In this way, when transitioning from a line with a small number of black pixels (n<n ₂ ) to a line with a large number of black pixels (n>n ₂ ), high-speed driving is achieved by increasing the printing pulse width for l+1 lines after the transition. As shown in FIG. 6(c), this method has the effect of making parts that were not previously clear, such as hanging lines, clear.

(Effects of the Invention) According to the present invention, as described above, there is an effect that the reproducibility of the black information that follows the white information can be improved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional double buffer type thermal recording head, FIG. 2 is a control time chart for driving the thermal recording head, and FIG. 3 is a block diagram of an embodiment of the thermal recording head driving circuit according to the present invention. Fig. 4 is the time chart, Fig. 5 is a correspondence diagram of two timers on hanging lines with steps, and Fig. 6 a, b, c.
FIG. 2 is an explanatory diagram of the effects of the present invention. 12... Shift register equivalent to one line of pixels, 13... Latch circuit equivalent to one line of pixels, 14... AND inversion output circuit, 15... Recording element driver, 31, 38, 39, 41, 42
... Counter circuit, 32 ... Data table memory, 33 ... Latch circuit, 34 ... Data select circuit, 40 ... Pulse generation differentiation circuit, 35, 3
6, 37...Logic product circuit, _VTH ...Thermal recording head drive power supply, EN1 to EN4...Recording element drive pulse, LATCH...Latch pulse, DATA...Recording data, DCP...Data clock, SCP
...Sample clock, DEN...Data enable signal.

Claims (1)

[Claims] 1. A first timer that measures the time from the previous line print timing to the current line print timing, and a time from the last line print timing to the current line print timing that satisfies the condition that the number of black pixels in the past line is greater than a certain value. and a second timer for timing the number of black pixels of the current line, and if the number of black pixels of the current line is smaller than a predetermined value, the printing pulse width is controlled by the time value of the first timer, and the number of black pixels of the current line is set to the predetermined value. and a circuit for controlling a print pulse width by the time value of the second timer when the print pulse width is equal to or larger than the second timer.