JPS5987183A - Controller for printing thermal head - Google Patents

Abstract

PURPOSE:To lessen a dispersion of printing density during the acceleration and deceleration of speed by switching by using a system in which in the switching of the time-division drive and the single drive, the driving of a heating resistor immediately after switching is made during driving time immediately before switching. CONSTITUTION:When ratio of black dots is 25% or less, pulse of time limit t1 is concurrently applied to the terminals (a)-(d) of AND circuits 3, whereupon receording signal converted from serial to parallel in a shift register 4 is added to the base of a transistor 2 and a heating resistor 1 is heated by the recording signal. When the ratio of the black dots exceeds 25%, pulse t1 of single drive period is orderly applied to the terminals (a)-(d) of AND circuit 3, and the terminals are heated in the order of (a)-(d) in comply with the recording signals. From the second period of the time-division drive, pulse of longer time limit t3 than t1 is put in (a)-(d) in a time-division manner and the heating resistors 1 are energized in the order of (a)-(d) in comply with the recording signals (e). The dispersion of printing density during the switching period can thus be lessened.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a printing thermal head that reduces unevenness in printing density.

Conventional printing thermal heads, for example, count the number of black dots in one line to prevent the power supply capacity from increasing, and if the ratio is less than 25, all dots (black) are driven at once. However, when it reaches 25% or more, one line is divided into a predetermined number of parts and driven in time division. Figure 1 (I) shows that when the proportion of black dots in one line is less than 25 pixels, t 2 = 2.5 m5ec.
Fig. 1 (I[) shows that when the proportion of black dots in one line is 25% or more, one line is driven as shown in (a). (b) (C) Divide into 4 blocks of (d) at t4-5 and t3 at a period of 0 m5ec, respectively.
= 1.1 This indicates that the drive is performed in a time-division manner over a time period of 1.1 m5ec.

According to this thermal head for printing, since the j drive mode is changed according to the proportion of black dots, it is possible to prevent the power supply capacity from increasing even if the thermal head is made to be denser, and it is possible to increase the speed of printing. In addition, in the case of time-division driving in which the cooling time of the heating resistor becomes longer depending on the off time, the driving time is kept short, so that it is possible to prevent the concentration from decreasing.

However, according to the conventional printing thermal head, the off time (t2 tx) at the time of batch rot is hours; ■IMg
Since it is shorter than the off time (t4 ts) at M, il+, the proportion of black dots increases and when switching from batch 4 drive to time division 111 drive (Fig. 2), the on time decreases. To be long! ; There is a risk that the dot density immediately after changing the rl will become uneven, resulting in uneven print density (time division j
Printing unevenness may occur in the same way when switching from drive to drive all at once, or when speeding up by switching to drive.)

The present invention has been made in consideration of the above-mentioned problems.- In order to prevent uneven print density from occurring when the print speed is slowed down or increased between finger drive and time-division 1 drive, the 1 The present invention provides a control device for a printing thermal head that performs driving for 111 operating hours immediately before switching.

The control device for a thermal print head according to the present invention will be described in detail below.

Fig. 3 shows an embodiment of the present invention during deceleration, and the same can be considered when increasing speed), blocks a+t)
A heating resistor 1 divided into 1 e g d, a switching transistor 2 that controls the energization of the heating resistor l,
An AND circuit 3 that controls the operation of the switching transistor 2 and a shift register 4 that inputs a serial recording signal from a terminal e and outputs it as a parallel signal to each AND circuit 3 are set to =g.

In the above structure, the operation will be explained with reference to the time chart of FIG. 4. When the proportion of black dots is less than 25, terminal a of the AND circuit 3 is activated.

At the same time, b+e+d is converted from 7 real to parallel by the shift register 4 and applied to the base of the transistor 2. The transistor 2 that receives the recording signal "1" turns on, and the transistor 2 that receives the recording signal "0" remains off.
The heating resistor 1 that has been turned off generates heat. Next, when the ratio of black dots becomes 25 or more, the terminal &
) b r Cr d K time limit tl for sequential batch drive
pulses are applied in time division (period, 1iJJt4).

As a result, the heating resistors 1 generate heat in the order of block fL+by(!yd) in accordance with the recording signal.
From the cycle period, the pulse of time t3 is sent to the terminals a r b HC.
! Time division input to Hd and block a1 of heating resistor 1
It is energized in the order of b+c*d according to the recording signal. Similarly, apart from the embodiment, only the driving time of blocks a and b may be set at 1° in one cycle, and blocks c and df may be set to t3.

As explained above, according to the control device for a thermal head for printing according to the present invention, when switching between -finger drive and time-division Jtty; drive, one drive immediately after switching is performed during the drive time immediately before switching. It is possible to reduce unevenness in print density when the printing speed is slowed down or increased due to printing speed.

[Brief explanation of the drawing]

εshi! 11≦41(1), (10 and FIG. 2 are explanatory diagrams showing drive modes of a conventional thermal head. FIG. 3 is an explanatory diagram showing an embodiment of the present invention. FIG. 4 is an explanatory diagram showing the drive mode of a conventional thermal head. Time chart showing the operation. Code explanation: 1: Heat generating resistor, 2: Switching transistor, 3: AND circuit, 4: Shift register. Patent applicant: Fuji Xerox Co., Ltd. Agent, Patent attorney Shin Matsubara 2

Claims (1)

[Claims] A heating resistor is energized according to the recording signal, and a flIIJ control section that controls the printing speed according to the proportion of black dots and also controls the energization time of the front m1 heating resistor according to the printing speed. The controller is characterized in that when the printing speed is decelerated or increased, the energizing time of the heating resistor immediately after decelerating or immediately after increasing the speed is equal to the energizing time before decelerating or before speeding up. '+IjU control device for thermal head for printing.