JPH0776139A - Thermal printer - Google Patents

Abstract

PURPOSE:To equalize press contact force of a thermal head in a platen by a method wherein a bearing support material wherein a long hole determined to dimensions allowing displacement of an eccentric part in a direction almost in parallel with a contact surface of a thermal head, is formed. CONSTITUTION:When a shaft core 12 is rotated, a shaft center of a platen shaft 2 is displaced around a center of a radius of an outer periphery of an eccentric part 13. Therefore, gaps of, both sides of the outer periphery of a platen 1 to a thermal head 5 can be varied. Then, a flexural amount is adjusted according to each strength of a plurality of compression springs energizing both sides of the thermal head 5, and pressure welding force of the thermal head 5 on both sides of the platen 1 can be equalized. In that case, though the shaft core 12 at the end part of the platen shaft 2 on the right side is displaced around the center of the radius of the outer periphery of the eccentric part 13, the eccentric part 13 can be displaced along a longitudinal direction of a long hole 21, and the core center of the platen 1 can be brought in parallel with the thermal head.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printer which prints on a recording sheet inserted between a platen and a thermal head and conveys the recording sheet by rotating the platen.

[0002]

2. Description of the Related Art First, the structure of a general thermal printer is shown in FIG. 1 is a platen. A bearing 3 for rotatably supporting a platen shaft 2 protruding from the platen 1 is provided on side plates 4 facing each other. A head support 6 that supports a thermal head 5 is rotatably attached to these side plates 4 by a support shaft 7. The thermal head 5 includes a substrate 8 on which a large number of heating elements (not shown) are formed along the axial direction of the platen 1 and a base 9 that holds the substrate 8. The base 9 is rotatably held by the head support 6 by a support shaft 10. Further, a plurality of compression springs 11 are interposed between both sides of the inner surface of the head support 6 and both sides of the base 9. Although not shown, the head support 6 is prevented from moving upward by an opening / closing cover of the printer. In this state, the thermal head 5 is pressed against the platen 1 by the urging force of the compression spring 11.
Therefore, by passing a recording paper and an ink ribbon (not shown) between the platen 1 and the thermal head 5 and causing a desired heating element of the thermal head 5 to generate heat, the ink of the ink ribbon is transferred to the recording paper. .

[0003]

The strength of the compression spring 11 for pressing the thermal head 5 against the platen 1 varies depending on the manufacturing conditions with respect to a desired set value. on the other hand,
Since the thermal head 5 can move a little within the play range around the support shaft 10, if the strength of the compression spring 11 varies, the pressure contact force of the thermal head 5 on both sides of the platen 1 will differ. In this case, there is a problem that the recording paper meanders because the conveyance force applied to the recording paper differs on both sides of the platen 1. Further, there is a possibility that a difference in lightness and darkness of printing may occur on both sides of the recording paper. There is also a method in which the strengths of the compression springs 11 are selected and those having the same strength are set so that the pressure contact forces of the thermal heads 5 on both sides of the platen 1 are made equal, but such work is extremely troublesome, It will be less effective and must be avoided.

[0004]

According to the present invention, there is provided a head support for holding a thermal head in a freely rotatable manner with respect to a rotatable platen, and the head support is interposed between the head support and the thermal head. In a thermal printer in which the thermal head is brought into pressure contact with the platen by the biasing force of a plurality of compression springs, at least one of a plurality of bearings that rotatably support platen shafts projecting from both ends of the platen has an outer peripheral surface. The center of the radius forms an eccentric part that is eccentric with respect to the axis of the platen shaft, the minor axis is sized to rotatably fit and hold the eccentric part, and the major axis contacts the platen with the thermal head. On the axis of the platen shaft, there is provided a bearing support having a long hole defined in a dimension that allows displacement of the eccentric portion in a direction substantially parallel to the plane. A guide portion having a notch to be removably fitted concentrically unit for Oite the axis thereof is disposed on either side of the thermal head.

[0005]

When the bearing having the eccentric portion is rotated, the axis of the platen shaft is displaced around the center of the radius of the outer periphery of the eccentric portion, so that the distance between both sides of the platen outer periphery with respect to the thermal head can be changed. As a result, the amount of bending is adjusted according to the strength of each of the plurality of compression springs that urge both sides of the thermal head, so that the pressure contact force of the thermal head on both sides of the platen can be equalized. . Also, concentric circles on the axis of the platen axis,
By fitting with the notches formed in the guide portions on both sides of the thermal head, the thermal head and the platen are kept parallel to each other when viewed from the direction perpendicular to the conveyed recording paper.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. The same parts as those of the conventional example described with reference to FIG. Figure 1
, A bearing 3 rotatably supporting a platen shaft 2 protruding from the left end of the platen 1 and a bearing 1 rotatably supporting a platen shaft 2 protruding from the right end of the platen 1.
2 is provided on the side plate 4 which is a bearing support. The bearing 12 includes an eccentric portion 13 in which the center of the outer radius is eccentric with respect to the axis of the platen shaft 2, a flange 14 that abuts the outer surface of the side plate 4, and an outer periphery with respect to the axis of the platen shaft 2. Has a concentric portion 15 that is a concentric circle, and an elastic piece 16 that is continuous with the flange 14. A protrusion 17 is formed at the tip of the elastic piece 16.

The bearing 3 is fitted in a circular hole 18 formed in the left side plate 4. The left platen shaft 2 is inserted into the bearing 3 from the inside of the left side plate 4, and an annular groove 20 into which a retaining ring 19 is fixed is formed at the tip thereof. A long hole 21 is formed in the right side plate 4. The short diameter of the long hole 21 is set to a size that rotatably holds the eccentric portion 13 of the bearing 12, and the long diameter of the long hole 21 is in the direction substantially parallel to the contact surface of the thermal head 5 with the platen 1. The size is specified to allow the displacement of the. An annular groove 20 is formed at the end of the platen shaft 2 on the right side, and the retaining ring 19 is fixed to the annular groove 20. Further, on the right side plate 4, the protrusions 17 of the elastic piece 16 are arranged on a radius centered on the center of the elongated hole 21.
Are formed with a plurality of locking holes 22 that are selectively engaged with the. Further, on both sides of the base 9 of the thermal head 5, a guide portion 24 having a notch 23 having an opening at the lower end is bent downward. Right guide 24
The width of the notch 23 is equal to the outer diameter of the concentric circle portion 15 of the bearing 12, and the width of the notch 23 of the left guide portion 24 is
The diameter is the same as the diameter of the concentric circle portion 25 with respect to the axis of the platen shaft 2. In this embodiment, the outer peripheral surface of the platen shaft 2 itself is used as the left concentric circle portion 25.

In such a structure, the shaft center of the bearing 3 supporting the left platen shaft 2 is always constant. Since the elongated hole 21 into which the eccentric portion 13 of the bearing 12 on the right side is fitted is long in the direction substantially parallel to the contact surface of the thermal head 5 with the platen 1 (the direction of arrow A in FIG. 1), the arrow A of the bearing 12 is shown. Although the displacement in the direction is possible, the movement of the bearing 12 in the vertical direction orthogonal to the arrow A is restricted.

Therefore, when the bearing 12 is rotated, the axis of the platen shaft 2 is displaced around the center of the radius of the outer circumference of the eccentric portion 13, so that the platen 1 with respect to the thermal head 5 is displaced.
You can change the spacing on both sides of the outer circumference of the
A plurality of compression springs 11 for urging both sides of the thermal head 5
Adjust the amount of deflection according to the strength of each platen 1
It is possible to equalize the pressure contact forces of the thermal heads 5 on both sides of. In this case, the shaft center of the end portion of the right platen shaft 2 is displaced around the center of the radius of the outer circumference of the eccentric portion 13, but the eccentric portion 13 can be displaced along the longitudinal direction of the elongated hole 21. Therefore, the axis of the platen 1 can be parallel to the thermal head 5 even when viewed from directly above the conveyed recording paper. Moreover, the notch 23 of the guide portion 24 of the thermal head 5 is arranged on the axis of the platen shaft 2 in the concentric circle portion 1.
The position of the eccentric portion 13 in the elongated hole 21 in the direction of the arrow A can be easily determined by fitting it into the slots 5 and 25, so that the adjustment work can be performed very easily. As a result, it is possible to prevent the recording paper from meandering.

Further, since the substrate 8 of the thermal head 5 can be brought into close contact with the outer periphery of the platen 1 evenly, it is possible to prevent a difference in the density of printing on both sides of the recording paper.

When the eccentric portion 13 is rotated, the projection 17 of the elastic piece 16 is elastically locked in any one of the locking holes 22 of the side plate 4, so that the position of the eccentric portion 13 in the rotational direction is changed. Can be fixed. In this case, as described above, by fitting the notch 23 of the guide portion 24 on the right side and the concentric circle portion 15,
In order to allow displacement of the eccentric portion 13 in the elongated hole 21 in the arrow A direction, it is effective to make each of the locking holes 22 slightly longer along the arrow A.

Next, a second embodiment of the present invention will be described with reference to FIG. The bearing 26 for supporting the platen shaft 2 on the right side is the same as the bearing 12 in the above-described embodiment except that the bearing 26 is not provided with the concentric circle portion 15. For this purpose, the guide portion 24 on the right side of the thermal head 5 is
The notch 23 is defined to have a width that allows the right outer platen shaft 2 to be fitted to the outer peripheral surface (concentric circle portion 25) without play. As a result, the same effect as that of the above-described embodiment can be obtained.

The platen shafts 2 protruding from both ends of the platen 1 may be supported by bearings 12 or 26 having an eccentric portion 13.

[0014]

As described above, according to the present invention, in the thermal printer in which the thermal head is pressed against the platen by the biasing force of the plurality of compression springs, the plurality of platen shafts projecting from both ends of the platen are rotatably supported. On at least one of the bearings, an eccentric part whose center of the outer circumference is eccentric with respect to the axis of the platen shaft is formed, and the minor axis is determined to have a dimension that rotatably fits and holds the eccentric part, and the major axis is the platen. Is provided with a bearing support body having a long hole defined in a dimension that allows the displacement of the eccentric portion in a direction substantially parallel to the contact surface of the thermal head with respect to the concentric circle with respect to the axis of the platen shaft. Since the guide portion having the notch that is detachably fitted to the portion is arranged on both sides of the thermal head, when the bearing having the eccentric portion is rotated,
Since the axis of the platen shaft is displaced around the center of the radius of the outer periphery of the eccentric part, the distance between both sides of the outer periphery of the platen with respect to the thermal head can be changed. Since the amount of bending is adjusted according to the strength of each compression spring, the pressure contact force of the thermal heads on both sides of the platen can be equalized, and the thermal heads can be attached to the concentric circles on the axis of the platen shaft. By fitting the notches formed in the guide portions on both sides, it is possible to maintain the thermal head and the platen in a parallel state very easily when viewed from the direction perpendicular to the recording paper being conveyed. The recording paper can be prevented from meandering, and the thermal head can be evenly attached to the outer periphery of the platen. It is possible to prevent the shading difference of printing occurs.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a first embodiment of the present invention.

FIG. 2 is a vertical sectional front view.

FIG. 3 is a side view.

FIG. 4 is a vertical sectional front view showing a second embodiment of the present invention.

FIG. 5 is a side view showing a conventional example.

[Explanation of symbols]

 1 platen 2 platen shaft 3 bearing 4 bearing support 5 thermal head 6 head support 11 compression spring 12 bearing 13 eccentric part 15 concentric part 21 long hole 23 notch 24 guide part 25 concentric part 26 bearing

Claims (1)

[Claims] 1. A head support for holding a thermal head so that it can be brought into contact with and separated from a rotatable platen, and a biasing force of a plurality of compression springs interposed between the head support and the thermal head. In the thermal printer in which the thermal head is brought into pressure contact with the platen by at least one of a plurality of bearings that rotatably support the platen shafts protruding from both ends of the platen, the center of the radius of the outer periphery is the platen shaft. An eccentric portion that is eccentric to the axis is formed, and a minor axis of the eccentric portion is sized to rotatably fit and hold the eccentric portion and a major axis of the eccentric portion in a direction substantially parallel to a contact surface of the thermal head with respect to the platen A bearing support body having a long hole defined to allow displacement of the eccentric portion is provided, and the bearing support body is provided on the axis of the platen shaft with respect to the axis. A thermal printer, characterized in that guide portions having notches that are detachably fitted to the core portion are arranged on both sides of the thermal head.