JPS58211471A - Thermal head driving device - Google Patents

Abstract

PURPOSE:To reduce load on an element like an electric power source circuit etc. in a thermosensitive recording device etc. by calculating energy supplied to each heating segment and applying voltage to the thermal head until the result take an intended value. CONSTITUTION:The instant that the initializing signal A is turned off the pulse generator 14 generates a pulse signal C, supplies it to the source driver 4, applies a voltage from the power source 6 to the thermal head 1 and current supply control is initiated to the heating body 2 according to picture element data to each sink driver 8. This applied voltage V is calculated in the integrator 13 to output an integrated value Vt, multiplied by V in the multiplier 15 to be entered to the operational amplifier 16. Here, this integrated value is compared with the reference voltage Vo<2> to from the generator 17 that is the reference applied energy. When it exceeds the reference voltage, the output signal is supplied to the integrator 13 and the pulse generating circuit 14 through the OR circuit 12 and reset respectively. In this manner, since the heat quantity is controlled without further applied voltage, load on elements is small and reliability is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal head drive device used in a thermal recording device. , records image information.

FIG. 1 shows the general configuration of the recording section of such a conventionally used apparatus. One end of each heating element 20) of the thermal head 1 is connected to a common source driver (switching 1 to transistor) 4 via a die A-3 (), and is connected to a common source driver (switching 1 to transistor) 4 with a predetermined pulse width. When the pulse signal C is supplied, a DC voltage is applied from the power supply (constant voltage power supply) 6 to one end of each heat generating element 20 via the r-twirer 77 and the (dense driver 4). On the other hand, the other end of each heating element 2 is grounded via an independently installed sink driver (switching transistor) 8. Therefore, both data 9 are supplied to each sink driver 8. When the source driver 4 is activated, the heating element 2 selectively generates heat according to the content of the image data 9, and thermal recording is performed.

By the way, as shown above, the current flowing through the source driver 1 and the wire 17 increases or decreases depending on the number of heat generating elements 2 that are energized at the same time. Assuming that a current of A flows, for example, if one line consisting of 1728 dots 1~ is divided into two times and recorded, these will be recorded when the black ratio (ratio of the drum h to print) is 100%. The current flowing through is as follows.

1 (1 (10%) = 0.04 x 1728÷2
= 34.6 (A) That is, when the black ratio in image data 9 changes from 0% to 100%, the current becomes O
This results in a significant change to 634.6△.

FIG. 2 shows the change in the voltage applied to the heating element due to the 41 current change. As the black ratio increases, the resistance valve of the wire 7 and the V of the transistor constituting the source driver 4. The voltage drop caused by 5 is alarming. As a result, the electric current applied to the heat generating element 2 decreases from Vo to (Vo-2) volts.As shown in Fig. 3, the pulse width of the applied pulse applied to the heat generating element 2 Since t. is always constant, the applied voltage ICE changes from Vo to (Vo-2)
As the temperature changes up to 1-, the amount of heat generated by the heat-generating element 2 changes accordingly. Print density was different for each bundled scanning line, resulting in uneven printing.

The present invention has been made in view of the above circumstances.The present invention has been made in view of the above circumstances.The pulse width of the pulse signal supplied to the source driver is changed in accordance with the fluctuation of the voltage applied to the thermal head, and the power supplied to each heat generating element is changed. It is an object of the present invention to provide a thermal head drive device which can maintain a substantially constant value.

In the present invention, each heating element (heating element) of +J-maru head
The above object is achieved by applying a voltage to the thermal head until the calculation result reaches a predetermined value using a calculation means for calculating the energy to be supplied to the thermal head.

The present invention will be described in detail below with reference to Examples.

FIG. 4 shows the glue head driving device of this embodiment. The image signal is supplied line by line as a serial signal to a shift register (not shown) of this device. 3-1 to signal line 11 is 1-1 (high) until time 1 (Figure 5) when the image signal to the shift 1 register ends.
A level initialization signal (a) is supplied to the level initialization signal.

The initialization signal Δ passes through the OR circuit 12 and is supplied to the integrator 13 and the pulse generator 14. The contents of the integrator 13 are thereby cleared. Furthermore, the pulse generator 14 receives an H-level pulse signal 0 (
Avoid generating C) in the same figure. The pulse signal C is supplied to the base of a transistor constituting the source driver 4. At the same time, a voltage is applied from the power supply 6 to the thermal head 1 via the wire A 77, the collector/X-mitter of the source driver 4, and the diode 3. At this time, since the image data 9 is supplied to each sink driver 8 connected to the other end of the thermal head 1, these sink drivers are selectively driven according to the contents, and the heating element 2 is energized. Control begins. As described above, the power on the emitter side of the source driver 4 varies depending on the number of heat generating elements 2 that are energized at the same time. This voltage L'-(applied voltage) is expressed as V1
I'll decide.

The applied voltage V is applied to both the input terminal I of the integrator 13 and the first input terminal 11 of the multiplier 15 .

The integrator 133 starts integrating the applied voltage V at time 1, and outputs an integrated value Vt from its output terminal O. The integral value Vt is supplied to the second input terminal I2 of the multiplier 15, and multiplied with the applied voltage V. The output V,2 t (FIG. 5d) thus obtained is supplied to the ■ terminal of the operational amplifier 16.

On the other hand, the reference voltage generation circuit 1 is connected to the e terminal of the operational amplifier 16.
7 to the reference voltage V. 2[o is applied. As shown in FIG. 6, a pulse P is applied to the thermal head 1 in a state where no voltage drop occurs. The voltage is V.

If the pulse width is (.), then the energy applied to each heating element 2 is expressed by the following equation.

Applied energy ccVo2to... (1) Generally, if the voltage of the applied pulse P is V, and the pulse width t at this time satisfies the following formula, the applied energy of each heating element 2 is always It's constant.

Vo 2t O=V2t ””...(2),', t
= Vn 2 t o /V2 - - - (3) The comparator circuit constituted by the operational amplifier 16 determines this time [. Therefore, the reference voltage V21o input to the θ terminal has an experimentally determined value C.

The Δ pair knob 16 outputs a comparison output signal 1' (FIG. 5e) of the level 2 to 1 from time 2 to 1, which satisfies the equation (2). Comparison output signal 1: (Yo-OR circuit 12 is integrator 1
3 and the pulse generator 14, which connects them to the relay l-
Cane. Since the pulse signal C is cut off at this time T2, the source driver 4 stops applying the voltage to the normal driver 1 at this point.

Once one line has been recorded in this way, the recorded operation is repeated and the next line is recorded. The same goes for the following. In this way, even if the number of energized photothermal elements 2 changes, the same energy is always supplied to them, thereby ensuring a uniform printing operation.

Jmata-1 As explained above, according to the present invention, the heat generation ω of each heating element can be controlled without increasing the applied voltage (...
There is less burden on elements such as the power supply circuit, and 1) the R reliability of the multi-head drive device can be improved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional legal head driving device, and FIG. 2 is a characteristic diagram showing an example of changes in the black ratio of both data and the application type B- to each heating element in this device.
Figure 3 is a waveform explanatory diagram showing the relationship between the voltage and pulse width of the pulse applied to the heating element in this device.
The drawings are for explaining one embodiment of the present invention, and Fig. 4 is a circuit diagram of the beam-maru head drive device, Fig. 5 is various waveform diagrams for explaining the circuit operation of each part, and Fig. 6 is 1-
Showing the waveform change of the applied pulse to keep the energy constant 1
It is a waveform explanatory diagram. 1... Thermal head 2... Heat generating element 6... Power supply 7- 13... Integrator 14... Pulse generator 15... ... Multiplier 16 ... Operational amplifier ■ Mr. Yamanouchi, Patent Attorney, Fuji Xerox Co., Ltd. @) It ε and ■ 0 8- 6 ′ Ward 3 Figure □, ′” 1st Figure 2

Claims (1)

[Claims] As the number of heating elements of the legal head that are energized at the same time increases, the voltage drop across the line from the constant voltage power supply to the current head increases, and the voltage drop across the line from the constant voltage power supply to the legal head increases. In a recording device in which the applied voltage decreases, there is a means for integrating the voltage application time per printing operation to the square of the applied voltage, and a means for integrating the calculation result of the means into each heating element. and a voltage application time adjusting means for adjusting the voltage application time to stop the printing operation when the comparison means detects a match. A thermal head driving device characterized in that a decrease in the heat generating capacity of each heat generating element due to a decrease in the applied voltage is compensated for by increasing the energization time.