JP2758429B2 - Thermal printer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a thermal printer.

2. Description of the Related Art Conventionally, by holding a leading edge of a sheet by a holding portion provided on an outer periphery of a platen, the sheet is maintained in a state wound around the platen, and printing is performed by pressing a thermal head against the sheet on the platen. In such a thermal printer, a detector is provided to detect the presence or absence of a sheet in a sheet feeding path, and further, it is detected whether or not the sheet is held by a holding unit and wound correctly on a platen. In order to achieve this, a reflection-type photo sensor facing the platen and a mechanical detector that is displaced by the resistance of the sheet are provided.

Problems to be Solved by the Invention In order to detect a sheet on the platen, a type using a reflection type photo sensor is used. Since the above reflectivity does not change, it does not serve as a sensor. Further, in the case of detecting a sheet on the platen with a mechanical detector, the amount of displacement of the detector due to the presence or absence of the sheet is small because the sheet is thin, and a highly reliable detection operation cannot be expected.

Means for Solving the Problems A holding portion for holding a leading edge of a sheet is provided on an outer periphery, and a rotatable platen at least having an outer peripheral surface formed of a conductive material and a thermal head are resiliently contacted to face each other. A plurality of conductive paper presses urged toward the center of the platen are disposed on the outer periphery of the platen, and a power supply is connected to one of the paper presses and one of the platens. In addition, a voltage detector connected to the power supply via the platen and the paper presser is provided.

Function When the outer periphery of the platen comes into contact with the paper presser without paper, there is an energizing action from the power supply to the voltage detector.When paper is interposed between the outer periphery of the platen and the paper presser, the voltage is supplied from the power supply. The operation of supplying electricity to the detection unit is interrupted or significantly impaired, and the change in the detection voltage of the voltage detection unit can reliably detect the presence or absence of a sheet on the platen.

Embodiment An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a side view showing the structure of a thermal printer. In FIG.
The thermal head 5 is pressed against the platen 1 by the urging force. The ink sheet 3 wound around the supply roller 6 is wound around a winding roller 8 with a path defined by a guide roller 7. Further, on the outer periphery of the platen 1, there are provided claws 9 which are holding portions for holding one end edge of the paper 2, and on the outer periphery of the platen 1, there are arranged a plurality of paper pressing rollers 11, 12 as a plurality of paper presses for pressing the paper 2. Have been. Further, the paper feed path 13 is provided with paper feed rollers 14 and 15 and a reflection type optical detector 16 for optically detecting the presence or absence of the paper 2.
Discharge rollers 18 and 19 are provided in the discharge path 17. Further, a battery 20, which is a power source, is connected to the paper pressing roller 12. Further, the outer peripheral surface of the platen 1 is grounded, for example, via a platen shaft 21 to a frame (not shown) holding the platen shaft 21 and is connected to a voltage detecting unit 22.

As shown in FIG. 2, the platen 1 has a conductive rubber 23 on its outer peripheral surface, and the conductive rubber 23 is electrically connected to the platen shaft 21. Further, both ends of the paper pressing roller 12 formed of a conductive material are rotatably supported by a conductive support plate 24, and these support plates 24 are fixed to the tip of an arm 26 via an insulating material 25. . These arms
Reference numeral 26 denotes a shaft 27 rotatably held by a frame holding the platen shaft 21, and is urged in one direction by a spring 28. The battery 20 and the paper pressing roller 12 are connected via a support plate 24, but are insulated from the frame of the thermal printer by an insulating material 25.
The other sheet pressing roller 11 is also rotatably supported by an arm urged in one direction similarly to the arm 26 (not shown), and is brought into elastic contact with the platen 1.

In such a configuration, the paper 2 supplied by the paper feed rollers 14 and 15 is detected by the optical detector 16, and the leading edge is subsequently held by the claw 9 of the platen 1. The sheet 2 wound around the platen 1 is pressed by sheet pressing rollers 11 and 12.
At this time, when the paper 2 is interposed between the platen 1 and the paper pressing roller 12 as shown in FIG. 3A, the paper 2 is insulated from the paper pressing roller 12 and the platen 1. As a result, the energizing operation from the battery 20 to the voltage detection unit 22 is interrupted or significantly impaired. As shown in FIG. 3 (b), when the paper 2 passes through the paper pressing roller 12, the paper pressing roller 12 resiliently comes into contact with the outer peripheral surface of the platen 1, and the voltage of the battery 20 is detected by the voltage detecting unit. Applied to 22. Therefore, the presence or absence of the sheet 2 can be detected based on a change in the detection voltage of the voltage detection unit 22. The same effect can be obtained by using a transparent sheet as the printing sheet. Further, since the relative position between the heat generating element of the thermal head 5 and the paper pressing roller 5 is determined, the thermal head 5 is fixed for a certain period of time based on the time when the trailing edge of the paper 2 passes below the paper pressing roller 12. , It is possible to perform printing up to the trailing edge of the sheet 2 without excess or deficiency.

Effect of the Invention Since the present invention is configured as described above, when the outer periphery of the platen comes into contact with the paper presser without intervening paper, there is an energizing action from the power supply to the voltage detector, and the outer periphery of the platen and the paper presser When paper is interposed between the power supply and the power supply, the power supply from the power supply to the voltage detector is interrupted or significantly damaged, and the change in the voltage detected by the voltage detector can reliably detect the presence or absence of paper on the platen. In addition, there is an effect that the presence or absence of a sheet can be detected even when a transparent sheet is used.

[Brief description of the drawings]

Drawings show an embodiment of the present invention, FIG. 1 is a side view, FIG. 2 is a perspective view showing a support structure of a paper pressing roller,
FIG. 3 is a partial side view showing the sheet detecting operation. 1 ... platen, 2 ... paper, 5 ... thermal head,
9 Holder, 11, 12 Paper presser, 20 Power supply, 22
… Voltage detector

Claims (1)

(57) [Claims] 1. A rotatable platen having a holding portion for holding a leading edge of a sheet on an outer periphery and having at least an outer peripheral surface formed of a conductive material, a thermal head in contact with the platen, A plurality of conductive paper retainers arranged on the outer periphery and urged toward the center of the platen; a power supply connected to one of the paper retainers and the platen; A thermal printer comprising: a voltage detector connected to the power supply via the paper presser.