JPS58116175A - Heat sensitive printer - Google Patents

Abstract

PURPOSE:To make it possible to prevent a print impressed immediately after the starting of printing from becoming blurred or faint by a method wherein a control circuit adopted to preheat heat generating members in a non-operated condition by the application of a predetermined amount of electric current thereon is provided. CONSTITUTION:The heat generating elements 10 generate heat and enable a recording operation to be made when a drive signal is supplied to input terminals P-P of drive transistors 11 to turn the transistors ON. Resistors 12 constitute control circuits which always preheat the heat generating elements 10 when the drive signal is not supplied. Such preheating may be performed when a heat sensitive head is at its home position or during the return operation of the heat sensitive head. For example, in order to perform the above preheating operation, switching circuits 13 and a gate circuit 14 are provided, a head return signal is supplied to the input terminal CR of the gate circuit 14 and the output of a detecting device for detecting the heat sensitive head being at its home position is supplied to the terminal HP of the gate circuit 14.

Description

[Detailed description of the invention] This FIA relates to thermal printers.

Conventional thermal printers have had the disadvantage that dots are rubbed off immediately after printing starts or near the home position, resulting in unclear characters. The main reason for this is that when the printing operation is stopped, the head cools down during the head return operation, and the heat generation temperature of the heating element is taken away, so that the heating element does not reach the required temperature.

Therefore, the present invention eliminates the above-mentioned drawbacks by preheating the heating element when it is not driven.

An embodiment of the present invention will be described below based on the drawings.

In FIG. 1, a carriage 3 is slidably fitted onto a guide shaft 1.2, and a well-known thermal head 6 is sandwiched between side plates 4 and 5 fixed to the upper surface of the carriage 3.

In front of the thermal head 6, a platen 7 made of relatively hard rubber is formed with a length sufficient to cover the area along the spacing direction of the thermal head 6. 7 is fixed to a metal support plate 8.

As is well known, the thermal head 6 has an insulating base material 9 made of ceramic or the like at one end thereof, and a number of dot-shaped heating elements (not shown) are arranged at the end thereof. A well-known thermal recording paper (not shown) or the like is inserted between the thermal head 6 and the platen 7, and by selectively driving the heating elements during head spacing, the thermal recording paper is formed into a dot shape. The color develops and characters, etc. are formed.

In Fig. 2, numerals 10 to 1υ are heating elements, which generate heat and perform recording when drive signals are supplied to input terminals p and p of drive transistors l] to l], respectively, and drive transistors 11 to 11 are turned on. . The resistors 12 to 12 constitute a control circuit, which always causes a weak current to flow through the heating element 10 to preheat it when no drive signal is supplied.

In the above embodiment, a weak current is constantly applied to each heating element when it is not driven to preheat it, but the invention is not limited to this. For example, preheating may be performed only when the thermal head is at the home position and during head return operation. In this case, as shown in FIG. 3, switching circuits 13 to 13 are provided, and a gate circuit 14 is also provided, the input terminal CRK of the gate circuit 14 supplies a head return signal, and the terminal H1' is connected to the thermal head when the thermal head is at the home position. It supplies the output of a detection device (not shown) that detects this at certain times. As a result, each heating element 10 to 10 is preheated during the head return operation and when the thermal head is at the home position.

Note that by not starting the printing operation immediately after power is turned on, but by delaying the start of the printing operation for a short period of time until each heating element is preheated, clear recording can be performed from the start of the printing operation.

As described above, according to the present invention, by simply adding an extremely simple circuit, the heating element instantly reaches the required temperature, eliminates blurring of characters, and records a constant density by completely destroying the printing area.
Good recording quality can be obtained.

[Brief explanation of the drawing]

Figure 1 is a perspective view of the main parts of an example of a thermal printer;
The figure is an electric circuit diagram showing one embodiment of the present invention, and FIG. 3 is an electric circuit diagram showing another embodiment. 10~1O... Heat generating element 12~12... Control circuit board
Applicant Seikosha Co., Ltd. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] A thermal printer equipped with a control circuit that preheats a heating element by passing a predetermined current through the heating element when the heating element is not driven.