JPS59101374A - Thermal printer - Google Patents

Abstract

PURPOSE:To prevent the creation of impulsive contact and spring-back of a head by controlling an electric current applied to a salenoid for energizing a type- head in the direction of the platten. CONSTITUTION:When an electric current transmission wave form A is provided from a signal line S1 at the time of starting of head-down (compressive contact) a base current of a switching transistor 8 is allowed to flow to turn the transistor 8 ON, a voltage lower than the source voltage Vb is applied to a solenoid 6 through a resistance 7 causing a slow displacement of armature of the solenoid 6. At the moment when a platten 1 and a thermal head 4 become separated from each other below a certain distance, the signal line S1 is brought to a high level and the transistor turned to OFF and at the same time, a signal line S2 is brought to a low level and a switching transistor 9 to ON and the source voltage Vb is applied directly to the solenoid 6. This source voltage Vb is kept as voltage giving the necessary head-down value for printing.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a thermal printer, and more particularly to a thermal printer having a thermal head that performs a printing operation by lowering the head by driving a solenoid during printing.

Conventional technology Conventional thermal printers mainly print on plain paper by heating an ink ribbon coated with heat-melting ink using a thermal head, and others use thermal paper as the printing paper and do not use an ink ribbon. It can be divided into methods. Normally, in the former type of thermal printer using a heat-melting ink ribbon, printing is performed with a so-called head-down operation in which the thermal head is pressed against the printing paper via the ink ribbon only during printing.

This head-down operation is generally performed by driving a thermal head supported on a certain fulcrum by a solenoid and swinging about the fulcrum, but depending on the pressure setting when the thermal head presses against the printing paper, ,
A bouncing phenomenon occurs in which the thermal head bounces on the platen, and even if no printing current is applied to the thermal head, the impact when the head goes down may cause the ink in the ink ribbon to be transferred to the printing paper, causing the ink at the beginning of the print line to be transferred. There was a drawback that the paper was smudged in some cases.

Purpose The present invention has been made in view of the above-mentioned drawbacks of conventional devices, and provides a thermal printer which has a simple and inexpensive structure and does not cause staining of printing paper due to the above-mentioned impact when the head is down. The purpose is to

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to embodiments shown in the drawings.

FIG. 1 is a schematic diagram showing the structure of a printing section of a thermal printer to which the present invention is applied. In the figure, reference numeral 1 indicates a platen, and a printing paper 2 is wound around this platen l. A shaft 4' provided near this platen l
A thermal head 4 is supported by a bearing provided at one end of the thermal head 4 so as to be swingable in the direction of the arrow in the figure. A printing heat generating part is provided on the surface of the free end of the thermal head 4 facing the printing paper, and when the thermal head 4 swings toward the platen 1 side (head down) during printing, this print heat generating part Printing is performed via an ink ribbon 3 stretched over an ink ribbon cassette (not shown). however,
The head-down mechanism itself is the same as the conventional example.

Under normal conditions, the thermal head 4 is biased to the right in the figure by a spring 5, but when printing, the solenoid 6 is energized, and the armature of the solenoid 6 swings to the left in the figure, causing the printing to occur. When the excitation is completed, the excitation of the solenoid 6 is released and the spring 5 returns to its original position.

FIG. 2 shows a drive control circuit for the solenoid 6 shown in -1-.

As shown in the figure, a driving voltage is applied to the solenoid 6 via a switching transistor 8 or 9. That is, the power supply voltage vb is connected to the solenoid 6 via a switching transistor 9, a series circuit of the switching transistor 8 and a resistor 7, and a parallel circuit consisting of a clamp diode. The drive control of the solenoid 6 is performed by connecting control signal lines s1. to the bases of switching transistors 8.9, respectively. This can be done by applying a control signal from s2.

Next, the operation of the above circuit will be explained with reference to the timing charts of FIGS. 3A and 3B and the diagram of FIG. 4.

First, at the start of head-down, the switching transistor 8 is given the energization waveform shown in FIG. 3(A) from the signal line Sl. As a result, the base current of the switching transistor 8 flows and the switching transistor 8 is turned on, and a voltage smaller than the power supply voltage vb is applied to the solenoid 6 via the resistor 7, and the armature of the solenoid 6 moves slowly. Next, as shown in FIG. 3(B), at a point τl when the distance between the platen l and the thermal head 4 has become less than a certain level, the signal line S is set to high level, the switching transistor is turned off, and at the same time, the signal line S2 is set to low level. level, the switching transistor 9 is turned on, and the power supply voltage vb is directly applied to the solenoid 6. If the power supply voltage vb is set to a voltage that allows the amount of head down necessary for printing, the thermal head 4 will be activated after the head down is completed.
heat generation control can be performed.

FIG. 4 shows changes in head position when this control is performed.

In the figure, the vertical axis represents the displacement amount of the head, and the horizontal axis represents time, and the curve indicated by the symbol lO is the head-down operation according to the conventional method (i.e., when the solenoid 6 is excited directly by the power supply voltage vb at the start of the head-down operation). case)
The amount of displacement of the head during the head-down operation of the present invention, indicated by reference numeral 11, represents the amount of displacement of the head during the head-down operation of the present invention. As is clear from the figure, in the case of the conventional example, a current corresponding to the required pressure is applied to the solenoid 6 at the same time as the head down starts, but when the printing heat generating part of the thermal head 4 reaches the platen 1, In contrast to the bouncing phenomenon in which the head bounces on the platen due to impact force, in the case of the present invention, the thermal head 4 is slowly moved closer to the printing paper 2 on the platen 1'' by a small applied voltage. Since the printing heat generating portion is caused to land with the necessary applied voltage, bouncing does not occur, and inadvertent ink transfer due to impact does not occur.

By adopting the following configuration, it is possible to further increase the head-down stroke, thereby improving maintainability when attaching and detaching the ink ribbon.

In the embodiments described below, a circuit consisting of a switching transistor and a resistor is used as the means for controlling the voltage applied to the solenoid, but it goes without saying that the voltage may be controlled by other circuits.

Effects As is clear from the above description, according to the present invention, means for controlling the voltage applied to the solenoid for head-down operation is provided, and the movement of the thermal head during head-down operation is controlled by this control means. Because it uses a simple and inexpensive structure in the cylinder,
-1- It is possible to provide an excellent thermal printer that does not cause stains on the printing paper due to the impact when the head is down, and furthermore, it is possible to take a large head-down stroke, so it is easy to attach and detach the head. This has the excellent effect of improving maintainability during maintenance.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram illustrating the structure of the printing section of the thermal printer of the present invention, FIG. 2 is a circuit diagram showing an embodiment of the head-down solenoid drive control circuit of the present invention, and FIGS. The figures are a timing chart diagram and a diagram, respectively, explaining the operation of the thermal printer of the present invention. ■...Platen 3...Ink ribbon 4...
...Thermal head 5...Spring 6...Solenoid 7...K Anti-8.9...Switching transistor to, 11...Curve

Claims (2)

[Claims] (1) In a thermal printer having a thermal head that performs printing by moving the head down by driving a solenoid during printing, a means for controlling the voltage applied to the solenoid for the head run operation is provided, and this voltage control means lowers the head. A thermal printer characterized in that the movement of the thermal head is controlled during the operation of the thermal printer. (2) The thermal printer according to claim 1, wherein the voltage control means controls the voltage applied to the head-down operation solenoid in a plurality of stages.