JPH10100507A - Printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformize printed density inspite of a simple structure. SOLUTION: A recording paper 1 is pinched between a platen roller 2 and a thermal head 3, and printed with the thermal head 3. An equally distributed load is longitudinally applied to the thermal head 3 from the platen roller 2, and the thermal head 3 is supported at three supporting points B, C, D with a compression coil spring 4. Then, intervals (a) and (b) between both ends of he thermal head 3 and respective supporting points B, C, D are set to almost 0.44:1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing apparatus in which a recording paper is sandwiched between a platen roller or a pressing member and a thermal head and printing is performed on the recording paper by the thermal head.

[0002]

2. Description of the Related Art In general, in this type of apparatus, a platen roller supported on a cover side and a thermal head supported on a housing side are in contact with each other, and the recording paper is sandwiched between the platen roller and the thermal head. Printing was performed on recording paper by a thermal head. Then, the platen roller is configured to be pressed against the thermal head with an even distribution of load in the print line direction of the thermal head, so that the holding force between the platen roller and the thermal head is uniform in the print line direction, and printing is performed. The density was kept constant in the printing line direction.

[0003]

For this reason, in the above-described conventional printing apparatus, an evenly distributed load is applied to the thermal head from the platen roller side, and the thermal head is supported between a plurality of supporting points. Even though the intervals are set to be approximately equal and the same load is applied to each support point, the reaction force at the support point at the center of the thermal head is larger than the reaction force at the support points at both ends,
There was a problem that the print density at both ends was reduced.
To solve this problem, if the load from the platen roller is increased as a whole, an extra load will be applied to the feeding of the recording paper, so it is necessary to increase the driving torque of the platen roller for feeding the recording paper more than necessary. Therefore, there is a problem that the driving motor becomes large and power consumption increases.

Accordingly, the present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a printing apparatus which achieves uniform printing density despite its simple structure. It is in.

[0005]

In order to achieve the above object, a printing apparatus according to the present invention comprises a recording head sandwiched between a rotating platen roller and a thermal head, and printing on the recording paper by the thermal head. A printing device for performing
A uniform load is applied to the platen roller in the direction of the print line of the thermal head with respect to the thermal head, and the thermal head is supported by three support portions which are symmetrical in the print line direction of the thermal head with respect to the evenly distributed load. Support,
The distance between both ends of the thermal head and each support section is approximately 0.4
4: 1. Therefore, the holding force for holding the recording paper between the thermal head and the platen roller in the printing line direction of the thermal head is made uniform.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1A and 1B are configuration diagrams showing a main part of a printing apparatus according to the present invention, in which FIG. 1A is a front view, FIG. 1B is a side view, and FIG. 2 is a distribution of an external force applied to the thermal head. FIG. 3 and FIG. 3 are model diagrams showing the shearing force and the bending moment at the point B. In these drawings, reference numeral 2 denotes a platen roller as a pressing member, which is rotatably supported on a cover (not shown) of the printing apparatus via a bracket (not shown), and a drive motor (not shown). 1 to rotate in the direction indicated by the arrow in FIG.

Reference numeral 3 denotes a thermal head formed in the shape of an elongated flat plate, which has a printing portion (not shown) formed in a linear shape extending in the longitudinal direction on the upper surface, and a lower surface of the printing device on the lower surface. It is supported at three support points B, C, and D by three compression coil springs 4, 4, and 4 attached to the housing body 5. The distance between the support points B, C and D and the distance between the support points B and D and both ends A and E of the thermal head 3 are:
As shown in the figure, a, b, b, and a are set so that the support point B and the support point D are symmetrical about the support point C. In such a configuration, as shown in FIG. 2, a load q [N / m is evenly distributed on the side of the thermal head 3 in the longitudinal direction of the thermal head 3 by a spring means (not shown). Are applied to the thermal head 3, reaction forces RB, RC, RD and bending moments MB, MC, MD are generated at three support points B, C, D of the compression coil spring 4.

Therefore, these loads q and reaction forces RB, R
C, RD, the platen roller 2 and the thermal head 3 contact each other with a pressing force, and the recording paper 1 is sandwiched between the platen roller 2 and the thermal head 3, printed by the printing portion of the thermal head 3, and printed. The paper is fed by the rotation of. Here, as conditions for making the print density printed by the thermal head 3 uniform in the longitudinal direction of the thermal head 3, each of the support points B,
The reaction force at the points C and D should be RB = RC = RD, and the bending moment should be MB = MC = MD. Therefore, the support points B, C, D and both ends of the thermal head 3 satisfying this condition are required. And the relationship between a and b are determined.

First, the relationship between the bending moments MB, MC, MD generated around the support points B, C, D and the distances a, b will be described. As in the present embodiment, the thermal head 3 to which the load q and the reaction forces RB, RC, and RD, which are equal distributions as external forces, are applied and which bends and bends, is called a “beam” in material mechanics, and has a stress inside. Has occurred. Further, beams in which the thermal head 3 is supported at three or more support points (B, C, D) as in the present embodiment are referred to as continuous beams.

In such a continuous beam, the formula of three moments is established at three adjacent fulcrums B, C, and D, and MB · b + 2MC (b + b) + MD · b = − (q / 4) · (B ³ + b ³ ) Equation (1) Also, the bending moment M at the point B
Is B, MB = represented by -q · a · (a / 2 ) = -q · a 2/2 ... Equation (2), since the bending moment is equal at the point B and the point D from the symmetry of the beam MB = MD: Equation (3) is obtained.

By substituting equations (2) and (3) into equation (1), M
When determining the ^{C, -q · a 2/2} · b + 2MC · 2b-q · a 2/2 · b =
-Q · b ^3/2 becomes, 4MC · b-q · a 2 · b = -q · b 3/2 becomes, ∴MC = (1 / 4b) · (q · a 2 · b-q · b 3 / 2) = (q / 8) · (2a ² −b ² ) Equation (4)

Next, as shown in FIG. 3, the shearing forces FB _{+ 0} , FB _-0 , FC _{+ 0} , and FC _-0 at the supporting points B and C, and the reaction force RB,
The relationship between RCs will be described. First, the shearing force of the supporting point B on the supporting point C side is represented by FB _{+ 0} = (MC-MB) /b+q.b/2 FB _-0 = -q.a. The shear force is represented by F _{C + 0} = (MD−MC) / b + q · b / 2 F _C−0 = F _{B + 0} −q · b,

Reaction force RB at support points B and C
And RC have the relationship of RB = FB _{+ 0-} FB _-0 RC = FC _{+ 0-} FC _-0, and since RB = RC, FB _{+ 0-} FB _-0 = FC _{+ 0} −FC _-0 .

Therefore, (MC−MB) / b + q · b / 2 + q · a = (MD−M
C) / b + q · b / 2 − ｛(MC-MB) / b + q · b
/ 2−q · b｝ Since MB = MD, (MC−MB) / b + q · b / 2 + q · a = (MB−M
C) / b + q · b / 2− (MC-MB) / b−q · b /
2 + q · b, and (MC−MB) / b + q · b / 2 + q · a = (MB−M
C) / b- (MC + MB) / b + q · b, and (MC + MC + MC-MB-MB-MB) / b = q · b
/ 2−q · a, and 3 (MC−MB) = q · b ² / 2−q · a · b, 6 (MC−MB) = q · b ² −2q · a · b Equation (5) ).

By substituting the equations (2) and (4) into the equation (5), 6 ｛(q / 8) · (2a ² −b ² ) − (− q · a ² /
2)｝ = q (b ² −2 · a · b), and 3/4 ｛(2a ² −b ² ) -4a ² ｝ = (b ² −2 · a · b)
b) 18a ² −3b ² = 4b ² −8a · b and 18a ² + 8a · b−7b ² = 0 Here, when the relationship between a and b is obtained, a = ｛− 4 ± (16 + 126) ^1/2} · b / 18 = - a ^{(4 ± 142 1/2) · b} / 18 ≒ 0.44b.

Therefore, by setting the interval of the relationship: a: b ≒ 0.44: 1...
The reaction forces RB, RC, and RD at C and D are the same. In other words, by setting the relationship represented by Expression (6), the pinching force between the thermal head 3 and the platen roller 2 in the longitudinal direction becomes uniform, and the print density printed on the recording paper 1 by the thermal head 3 is reduced. The thermal head 3 becomes uniform in the longitudinal direction.

As described above, the print density on the thermal head 3 becomes uniform only by setting the distances a and b between both ends of the thermal head 3 and the support points B, C and D as described above. Therefore, there is no need to increase the pressing force of the platen roller 2 against the thermal head 3 as in the related art, and it is not necessary to increase the rotational torque of the platen roller 2.
A small drive motor can be used,
The device can be miniaturized.

In the present embodiment, the member in contact with the thermal head 3 is the platen roller 2 which also serves to feed the recording paper. However, if a recording paper feeding means is provided separately, the platen roller 2 is simply pressed. It may be a pressing member that does nothing. In that case, bending or bending of the pressing member occurs,
A “beam” is used for material mechanics, and the thermal head or the bracket member holding the thermal head is moved closer to a rigid body.
A load is applied to the thermal head in the printing line direction of the thermal head with respect to the pressing member, and the pressing member is supported at three positions symmetrical in the printing line direction of the thermal head with respect to the load. We support in part. Accordingly, similarly to the above-described embodiment, the holding force for holding the recording paper by the thermal head and the pressing member in the print line direction of the thermal head is made uniform. Also,
In the present embodiment, the platen roller 2 and the thermal head 3 are both elastically supported. However, either one of them may be supported by a rigid support.

[0019]

As described above, according to the present invention, in a printing apparatus in which recording paper is sandwiched between a platen roller and a thermal head which are driven to rotate and printing is performed on the recording paper by the thermal head, A uniform load is applied to the thermal head in the print line direction of the thermal head, and the thermal head is supported by three support portions that are symmetrical in the print line direction of the thermal head with respect to the uniform load and pressed. By setting the distance between both ends of the member and each supporting portion to be approximately 0.44: 1, a uniform print density can be obtained in the print line direction of the thermal head, so that print quality is improved. Further, since it is not necessary to increase the pressing force of the platen roller against the thermal head as in the related art, a small driving motor for feeding the recording paper can be used, and the apparatus can be downsized. .

Further, according to the present invention, a uniform load is applied to the thermal head in the printing line direction of the thermal head with respect to the pressing member, and the pressing member is moved in the printing line direction of the thermal head with respect to the uniform distribution load. The support member is supported by three symmetrical support portions, and both ends of the pressing member and the distance between the supporting portions are set to approximately 0.44: 1, so that the pressing member is bent or bent. If the thermal head or the bracket member holding the thermal head is brought closer to a rigid body, the clamping force for clamping the recording paper by the thermal head and the pressing member in the print line direction of the thermal head becomes uniform. For this reason, a uniform print density can be obtained in the print line direction of the thermal head.
Printing quality is improved. Further, since it is not necessary to increase the pressing force of the pressing member against the thermal head as in the related art, a small driving motor for feeding the recording paper can be used, and the apparatus can be downsized. .

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a main part of a printing apparatus according to the present invention, in which (a) is a view from the front and (b) is a view from the side.

FIG. 2 is a distribution diagram of an external force applied to a thermal head in the printing apparatus according to the present invention.

FIG. 3 is a model diagram showing a shearing force and a bending moment at a point B in the printing apparatus according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Recording paper, 2 ... Platen roller, 3 ... Thermal head, 4 ... Compression coil spring.

Claims (2)

[Claims] 1. A printing apparatus for printing on a recording sheet by a thermal head by sandwiching the recording sheet between a platen roller and a thermal head that are driven to rotate, the printing line direction of the thermal head relative to the thermal head and the platen roller. The thermal head is supported by three support parts which are symmetrical in the print line direction of the thermal head with respect to the uniform distribution load, and both ends of the thermal head and the distance between the support parts are adjusted. A printing apparatus characterized by being approximately 0.44: 1. 2. A printing apparatus in which a recording sheet is sandwiched between a pressing member and a thermal head and printing is performed on the recording sheet by the thermal head. In addition to this, the pressing member is supported by three support portions which are symmetrical in the printing line direction of the thermal head with respect to the uniformly distributed load, and both ends of the pressing member and the distance between the support portions are set to about 0.44. :
1. A printing device, characterized in that: