JPH0229351A - Thermal recorder - Google Patents

Abstract

PURPOSE:To enable color formation to be effected with a pulse duration with which color formation has not been achieved in a conventional system by providing a means for controlling a power supply so as to set an applied voltage at a raised level for a predetermined period of time after the start of energization of a thermal head. CONSTITUTION:An output (a) is inputted to a thermal head 1, and a voltage is applied from a power supply 6 to heat generating elements of the head 1 according to the pulse duration of the signal (a), whereby heat is generated to heat a thermal recording material, resulting in color formation recording. The voltage Vt of an output (d) from the power supply 6 takes two voltage values Vt1 and Vt2 (Vt1<Vt2). A power supply-controlling circuit 7 controls the voltage Vt to Vt2 for a beginning period of a pulse of the signal (a) (gradation recording signal), and controls the Vt to Vt1 for the other periods. This enables color formation at a part at which color formation has not been achieved on the recording material in a conventional system.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a thermal recording device having a thermal head and capable of performing gradation recording printing.

2. Description of the Related Art A conventional thermosensitive recording apparatus of this type was constructed as shown in FIG. That is, in the figure, 1 is a thermal head, 2 is a thermal head, and 2 is a thermal head.
4 is a memory in which gradation print data is recorded in advance; 3 is a clock generation circuit having a cycle corresponding to the minimum resolution; and 5 is a power source for the thermal head 1.

The operation of the thermal recording apparatus configured as above will be described below. - For example, when printing with 16 steps of pulse width modulation, that is, printing with 16 gradations, the output C from the memory 4 that records gradation print data needs at least 4 bits, and the gradation If the period of the output of the clock generation circuit 3 which determines the time unit of minimum resolution for recording is T, then the gradation recording signal generation section 2 is outputted from the memory 4 in synchronization with the output of the lock generation circuit 3. inputs the gradation print data C, controls the pulse width so that the period T of the output of the clock generation circuit 3 corresponds to the time unit of the minimum resolution, and outputs the recording signal a according to the gradation print data C. do. Since the gradation print data is a 4-bit digital signal, the recording signal a is 0. T, 2T, 3T, ---
This results in 16 types of pulse signals with a width of 15T1. Fifth
The figure is a timing chart showing the above operation.

The recording signal a is input to the thermal head 1, and the heating element of the thermal head 1 has the pulse width of the recording signal a (i.e., the fifth
In the figure, power is supplied from the power supply 5 in accordance with the period "1") to generate heat, and color recording is performed by heating the thermosensitive recording material.

Further, the relationship between the pulse width of the recording signal and the recording density at this time is generally as shown in FIG. In addition, D m in Fig. 6,
ax indicates the saturation density, that is, the maximum density, and Doll indicates the density of the recording paper itself. FIG. 6 shows that 13 tone changes are made between Dθ and Dmax for 16 steps of change in pulse width from O to 15T. That is, when the pulse width is between 0 and 3T, the concentration is De, indicating that there is no change.

Problems to be Solved by the Invention In gradation recording with such a conventional configuration, the relationship between the recording signal pulse width and the recording density is as shown in Figure 6, so the pulse width is narrower than a certain pulse width as described above. The recording material does not develop color with a recording signal having a pulse width of 3T or less. Therefore, the number of stages of pulse width modulation for gradation recording does not directly correspond to the number of gradations, and the number of gradations becomes smaller than the number of stages of pulse width modulation. Furthermore, in order to increase the number of gradations, it is necessary to increase the number of pulse width modulation stages, which requires increasing the clock frequency, resulting in a problem that the processing becomes complicated.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a thermal recording apparatus that is capable of performing gradation recording control without the above-mentioned drawbacks with a simple configuration.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a power supply control means that controls the power supply so that the voltage applied to the thermal head is kept high for a predetermined period after the start of energization of the thermal head. Ta.

Effect of the present invention With the above-described configuration, the amount of energy supplied per unit time increases during a predetermined period after the start of energization to the thermal head, so that color can be generated even with a pulse width that conventionally did not produce color.

Embodiment FIG. 1 is a block diagram of a thermal recording apparatus in an embodiment of the present invention. In the figure, numerals 1 to 4 are the same as those indicated by the same reference numerals in FIG. 4 used in the explanation of the conventional example, so their explanation will be omitted. Reference numeral 6 denotes a power supply for the thermal head 1, the output voltage of which is variable, and 7 a power supply control circuit for controlling the output d of the power supply 6.

The operation of this device will be explained below. It is assumed that the memory 4 contains gradation print data in advance, and that the data is 4-bit data in order to perform 16 steps of pulse width modulation. Further, assuming that the period of the output of the clock signal generating circuit 3 is T, the output a of the gradation recording signal generating section 2 becomes as shown in FIG. 5 in the same manner as in the conventional operation. This output a is input to the thermal head 1, and the thermal head 1
The heating element generates heat when a voltage is applied from the power supply 6 according to the pulse width of the signal a, and performs color recording by heating the thermosensitive recording material.

Here, the voltage Vt of the output d of the power supply 6 is determined from the output e of the power supply control circuit 7 by Vtl and Vt2 (Vtl<Vt
2) Two voltage levels are taken. The power supply control circuit 7 controls the voltage Vt of the output d of the power supply 6 to be Vt2 during the first Tx of the pulse of the gradation recording signal a, and to Vtl during other times.

FIG. 2 shows a timing chart in this case.

Further, the relationship between the recording signal pulse width and the recording density at this time is as shown in FIG. In FIG. 3, D nax is the saturation density, and De is the density of the recording base paper. In Figure 3, a recording signal with a narrow pulse width (for example, a signal with a pulse width of T or 2T) is shown.
Even in the case of , color is developed, indicating that the number of gradations that can be taken between Dθ and D l1ax is increased compared to the conventional example.

In other words, by increasing the voltage applied to the thermal head during the first part of the pulse-width-modulated recording signal, it becomes possible to develop color in areas where the recording material would not develop color in the conventional configuration. In pulse width modulation for comparative gradation recording, it is possible to perform recording without unnecessary steps that do not produce color.

Effects of the Invention As described above, according to the present invention, the number of pulse width modulation stages for gradation recording can be effectively used with an extremely simple configuration, and the number of gradations can be increased even if the number of pulse width modulation stages is the same. be able to. In addition, in order to effectively secure gradation, the memory capacity does not increase, and the basic clock remains unchanged (this is advantageous for high-speed recording without increasing the amount of data processing and transfer.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a thermal recording device according to an embodiment of the present invention, FIG. 2 is a timing chart showing the operation of the device, FIG. 3 is a recording characteristic diagram of the same, and FIG. 4 is a diagram of a conventional thermal recording device. A block diagram, FIG. 5 is a timing chart showing its operation, and FIG. 6 is a recording characteristic diagram. 1... Thermal head 2... Gradation recording signal generation section 3... Clock signal generation circuit 4... Memory 6... Power supply 7 ...Power control circuit

Claims (1)

[Claims] a thermal head having an element that generates heat in accordance with a printing pulse; a power source for supplying power to each element of the thermal head; means for controlling pulse width for gradation recording printing to obtain a gradation printing pulse; A power supply control means for controlling a power supply and increasing the applied voltage for a predetermined period after the start of energization to each element of the thermal head compared to the applied voltage outside the predetermined period. Features of thermal recording device.