JPS61184968A - Thermal head driving circuit - Google Patents

Abstract

PURPOSE:To suppress fluctuation of recording density and perform heat-sensitive recording of a uniform density, by variably controlling the electric energy to be impressed upon a heating element in accordance with the fluctuation of the characteristics of the driving element of the heating element. CONSTITUTION:Before starting recording operations or whenever recording operations of one line quantity in a main scanning direction are completed, a resistance value measuring circuit 1 measured resistance values of driving elements by impressing recording pulses upon each of plural heat-sensitive elements constituting a thermal head 2. The measured resistance values of the driving elements are stored in a resistance-value memory 4 by each driving element and read out synchronously to the driving timing of each driving element. The read out resistance values are inputted in a pulse width correcting circuit 5 and, after their recording pulse widths are further corrected in accordance with heat accumulation correcting information inputted from a heat accumulation correcting circuit 7, drive desired heating elements of the thermal head 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive circuit for a thermal head used in a thermal recording device.

[Conventional technology]

Thermal heads used for thermal recording usually have a plurality of heating elements corresponding to the number of pixels in the main scanning direction of the thermal recording medium (for example, when recording image information on Japanese Industrial Standards A column No. 4 recording paper, The number of heating elements is 1728, B row 4
(2,048 pieces in the case of No. 1 recording paper), and by generating heat in only the necessary heating elements corresponding to the image information, the heat-sensitive recording paper, ink donor sheet, etc. that comes into contact with the heating element is heated. Colors the recording medium.

By the way, when recording is performed using such a thermal head, if there is variation in the resistance value of the heat-sensitive element, an error occurs in the amount of heat generated, and a variation in recording density occurs.

Therefore, conventionally, a thermal head drive circuit has been used in which the recording pulse width applied to the heating element is changed depending on the variation in the resistance value of the heat-sensitive element, thereby suppressing the variation in recording density.

[Problem that the invention seeks to solve]

However, in the conventional thermal head drive circuit,
Since only the variation in the resistance value of the heating element was considered, K was considered, so if there is variation in the resistance value or response speed of the driving element such as a transistor that drives the heating element, the recording density will vary due to the variation in the characteristics of the driving element. The problem was that it could not be suppressed.

[Means and effects for solving the problems] The present invention aims to solve the above-mentioned problems, and for this purpose, a voltage is applied to the heating elements according to variations in the characteristics of the driving elements of the heating elements. It is configured to variably control electrical energy.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention,
The resistance value measuring circuit 1 applies a recording pulse to each of the plurality of heat-sensitive elements constituting the thermal head 2 before driving the recording operation or each time the recording operation for one line in the main scanning direction is completed. Measure the resistance value of the element.

That is, a voltage is applied to each of the heating elements, and the driving element that drives each heating element is turned on. At this time, the current flowing through the heating element or the driving element is detected, and the applied voltage is determined based on this detected current value. The resistance (on-resistance) of each drive element is measured by dividing the total resistance value of the heat generating element and the drive element, and subtracting the known heat generating element resistance value from this total resistance value.

Note that the resistance value of the heating element is stored in the memory 3 in advance.

The resistance values of the drive elements measured in this manner are stored in the resistance value memory 4 for each drive element, read out in synchronization with the drive timing of each drive element, and sent to the pulse width correction circuit 5.
is input.

In addition to the resistance value r of the drive element, the pulse width correction circuit 5 includes:
The resistance value RH of the heat-sensitive element is input from the memory 3, and the heat storage is performed according to the heat storage history of the heating element calculated by the heat storage correction circuit 7 based on the recorded information of the previous line stored in the recorded data pack memory 6. Correction information is input. Therefore, the pulse width correction circuit 5 calculates the resistance value RH of the heating element and its driving element input from the memories 3 and 4, respectively.
, r, the recording pulse width for each driving element is determined according to the characteristic curve shown in FIG. , to drive the required heating elements of the thermal head 2.

By controlling the recording pulse width variably in accordance with the resistance value of the drive element in this way, variations in recording density due to variations in the resistance value of the drive element can be suppressed. In this case, the recording pulse width may be variably controlled depending on the response speed of the driving element or the combination of the resistance value and the response speed.

By the way, in the case of a thick-film thermal head, a diode is connected in series with the heating element and the driving element, so the minimum value of the forward voltage drop of this diode (■). and on-resistance r
It is necessary to take d into consideration.

In such a case, the voltage drop across the diode ■. After measuring the on-resistance rd and the on-resistance rd in the same manner as when measuring the resistance value r of the driving element, ①. The recording pulse width may be corrected according to the characteristics shown in FIG. 3 according to r rd+r J.

This is the same even when a current adjustment or voltage adjustment element is inserted in addition to the diode.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the electrical energy applied to the heating element is corrected according to the characteristics of the driving element of the heating element, so that variations in recording density due to variations in the characteristics of the driving element are suppressed. Thermosensitive recording with uniform density can be performed.

In particular, as the heat generating element is improved and the variation in its resistance value becomes relatively smaller than the variation in the drive element, the effect becomes more pronounced.

[Brief explanation of drawings]

Fig. gg1 is a block diagram showing an embodiment of the present invention, and Fig. 2 shows the resistance value of the driving element and the recording voltage. FIG. 3 is a characteristic diagram showing the relationship between the resistance value of the driving element including the on-resistance of the diode and the recording pulse width. Explanation of symbols> 1...Resistance value measurement circuit, 2...Thermal head, 3
゜4... Memory, 5... Arm width correction circuit, 6.
...Record data buffer memory, 7...Heat storage correction circuit.

Claims (4)

[Claims] (1) A drive circuit for a thermal head having a plurality of heat generating elements is characterized in that a control means is provided for variably controlling the electrical energy applied to the heat generating elements according to the characteristics of the drive element that drives each heat generating element. Thermal head drive circuit. (2) The thermal head drive circuit according to claim (1), wherein the electrical energy is variably controlled by increasing or decreasing the pulse width of a recording pulse applied to each heating element. (3) The thermal head drive circuit according to claim (1), wherein the characteristic of the drive element is a resistance value of the drive element. (4) The thermal head drive circuit according to claim (1), wherein the characteristic of the drive element is a response speed of the drive element.