GB2234713A

GB2234713A - Thermal print head mounting

Info

Publication number: GB2234713A
Application number: GB9014436A
Authority: GB
Inventors: Hiroshi Tabuchi
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1989-07-26
Filing date: 1990-06-28
Publication date: 1991-02-13
Anticipated expiration: 2010-06-28
Also published as: CA2019265A1; DE4023517A1; GB2234713B; CA2019265C; GB9014436D0; JPH0357674A

Abstract

A thermal head device 1, 2 suitable for use on a facsimile machine or the like, including a positioning member 6 for aligning the heating element of the thermal head with the center axis of the platen roller. The thermal head device is preloaded by a spring 10 adapted to urge the positioning member in a predetermined direction into abutting engagement with a collar 5 the shaft 4 of the platen roller to hold the heating element in a constant position relative to the platen roller to ensure production of prints of satisfactory quality. Springs 7 and 10 may be combined as a single inclined spring (7a, fig 3). <IMAGE>

Description

1 .. i --- 1 t 1 ' - THERMAL HEAD DEVICE This invention relates to a

thermal head device for facsimile machines and the like, and more particularly to a thermal head with an improved positioning means.

A conventional thermal head device is shown in schematic sectional and enlarged views in Figs. 1A to 1C. In these figures, numeral 1 designates a thermal head, 2 a heating element of the thermal head 1, 3 a platen roller to be abutted against the heating element 2, 4 the shaft of the platen roller 3, 5 a collar assembled on the roller shaft 4, 6 a positioning member which is fixedly secured to the thermal head 1 and abutted against the collar 5 at its inner surfaces 6a and 6b to position the heating element 2 of the thermal head 1 in alignment with the axis of the platen roller 3, 7 a compression spring serving to press the thermal head 1 against the platen roller 3, 8 a frame, 9 recording paper which is driven by the platen roller 3 and printed by the thermal head 1, W the width of the positioning member 6, dl the outside diameter of the shaft 4, d2 the inside diameter of the collar 5, and d3 the outside diameter of the collar 5. The collar 5 is formed of a material which is softer than the shaft 4, and not rotatable during operation.

- 1 4 Next, the operation will be described. By the pressing force of the spring 7 acting on the thermal head 1, the platen roller 3 and recording paper 9 are held in abutting contact with each other uniformly in the longitudinal direction of the thermal head 1 or in the direction perpendicular to the face of Fig. 1. The spring 7 exerts a pressing force in the direction of r - arrow Y to hold the thermal head 1 and platen roller 3 against fluctuating motions which might results from rotation of the platen roller 3 by a drive source, which is not shown, or from scanning of the recording paper 9, for the purpose of enhancing the printing performance quality together with the above-mentioned uniform abutting contact.

As shown in Fig. 1, when the platen roller 3 is rotated in the direction of arrow Z, the recording paper 9 is driven in the direction of arrow X and printed with characters by the heat which is generated by the heating element 2 according to signals from a heat controller, not shown.

In the drawings, the anti-rotation mechanism for the thermal head 1 is omitted for the sake of simplicity of illustration.

For determining the position of the thermal head, the conventional device resorts to the positioning member 6 which has its inner surfaces 6a and 6b abutted against the collar 5 on the platen roller 4. Due to the 1 existence of gap spaces in the mechanism, this arrangement has a problem that the thermal head 1 is put in fluttering motions during operation as a result of deviations from the center axis of the platen roller 3 by an amount corresponding to:

(1) the difference between the outside diameter dl of the platen roller shaft 4 and the inside diameter d2 of the collar 5; and (2) the difference between the outside diameter d3 of the collar 5 and the width W of the positioning member 6. Consequently, in case of intermittent facsimile recording operations in or the like, the fluttering motions cause fluctuating deviations of the heating element 2 from the -center axis of the platen roller 3, impairing the quality of the print to be produced.

20.

The present invention has been achieved with a view to solving the abovementioned problem of the prior art, and has as its object the provision of a thermal head device which can prevent deviations of the heating element of the thermal head from the center axis of the platen roller to guarantee production of prints of satisfactory quality.

It is another object of the present invention to provide a thermal head device employing a positioning means which is far improved as compared with existing 1 counterparts in positioning accuracy and performance quality and yet feasible at a relatively low cost.

It is a further object of the invention to provide a thermal head device which permits improved positioning accuracy without entailing complication or enlargement of size of the thermal head device itself.

In order to achieve these objectives, the thermal head device according to the present invention includes a thermal head with a heating element, a platen roller held in abutting engagement with the heating element of the thermal head for scanning recording paper fed therebetween, and a positioning means mounted astride of the rotational shaft of the platen roller for positioning the heating element in alignment with the center axis of the platen roller, the thermal head device being characterized by the provision of a preload means adapted to urge the positioning means into abutting engagement with the shaft of the platen roller to preclude fluttering motions or backlashes of the thermal head in 20. operation.

Namely, the thermal head device according to the invention is provided with a preload means which holds the positioning means in abutting engagement with the platen roller in operation thereby maintaining the heating element in a constant position relative to the axis of the platen roller to ensure prints of satisfactory quality.

a The above and other objects, features and advantages of the invention will be more fully understood from the following particular description of the invention and the appended claims, taken in conjunction with the accompanying drawings, which are given for the purpose of illustration only and therefore should not be construed as limitative of the scope of the invention.

p In the accompanying drawings:

Figs. 1A to 1C are schematic sectional and enlarged views of a conventional thermal head device; Figs. 2A to 2C are schematic sectional and enlarged views of a thermal head device according to one embodiment of the present invention; and Fig. 3 is a schematic sectional view of a thermal head device according to another embodiment of the invention.

A preferred embodiment of the invention will now be 20. described in detail referring to accompanying the drawings.

Referring to Figs. 2A to 2C, there is shown an embodiment of the thermal head device according to the invention in schematic sectional and enlarged fragmentary views, in which the component parts common to the prior art counterpart of Fig. 1 are designated by common reference numerals and their description is omitted to avoid repetitions.

A In these figures, numeral 8b designates a frame, and 10 a spring which is employed as a preload means for biasing the thermal head 1 in the direction of arrow X. The spring 10 which is provided between the frame 8b and thermal head 1 pushes the thermal head 1 in the direction of arrow X in such a manner as to substantially zeroing gap spaces in the mechanism including the gap space 1 between shaft 4 and the collar 5 and the gap spaces between the collar 5 and the positioning member 6. As a result of application of the pressing force of the spring 10 urging the thermal head 1 in the rightward direction in the drawing, the inner surface 6b of the positioning member 6, collar 5 and platen roller shaft 4 are tightly abutted against each other without leaving a play gap therqbetween. Namely, the pressing force of the spring 10 directly acts on the thermal head 1 to hold same against the shaft 4 of the platen roller 3 through the collar 5 for positioning the heating element 2 relative to the platen roller 5.

Next, operation of this thermal head with the above-described construction will be described.

If the platen roller 3 is turned in the direction of arrow Z by a drive source which is not shownt the recording paper 9 is driven in the direction of arrow X since the thermal head 1 is pressed in the direction of arrow Y by the spring 7. At this time, as the thermal head 1 which is preloaded in the direction of arrow X F 1 by the spring 10, the inner surface 6b of the positioning member 6 is tightly abutted against the platen roller shaft as explained hereinbefore. Accordingly, even in intermittent recording operations, the preload means suppresses the fluctuating deviations of the heating element 2 of the thermal head 1 from the center axis of the platen roller 3, holding the heating element 2 in a constant position relative to the platen roller 3 to ensure prints of satisfactory quality.

Instead of applying the thermal head 1 with a preload in the direction of arrow X by the spring 10 as in the foregoing embodiment, there may be employed an arrangement in which the thermal head 1 is preloaded in an oblique direction (in the direction of arrow H) as -shown in Fig. 3 by the use of a spring 7a. In this case, the thermal head 1 is preloaded in the direction of arrow X by the component force I of the spring 7a to produce the same effects as in the first embodiment.

Further, a tension spring may be employed as a preload means in place of the compression spring 7a or 10 in the foregoing embodiments. Similar effects can be obtained by a preload means in the form of a tensile or compression spring which is provided in the first quadrant instead of locating same in the second quadrant as in the particular embodiments shown.

As clear from the foregoing description, the thermal head according to the present invention ensures

1 production of prints of satisfactory quality by the provision of the preload means which is adapted to abut the head positioning means against the platen roller shaft in such a manner as to maintain the heating element of the thermal head in a constant position relative to the center axis of tfie platen roller.

The preload means which suffices to have simply a function of biasing the head positioning means in a predetermined direction can be realized at a low cost.

For the reasons stated above, the present invention makes it possible to provide a simple and compact thermal head.

It will of course be understood that the present invention has been described'above purely by way of example, and that modifications of detail can be made within the scope of the invention.

f

Claims

WHAT IS CLAIMED IS:

1. A thermal head device including a thermal head with a heating element, a platen roller held in abutting engagement with the heating element of the thermal head for scanning recording paper being fed therebetween, and a head positioning means mounted astride of the rotational shaft of said platen roller for positioning said heating element in alignment with the center axis of said platen roller, said thermal head assembly comprising: a preload means for urging said positioning means in a predetermined direction into abutting engagement with said rotational shaft of said platen roller.

2. A thermal head device as claimed in claim 1, wherein said preload means is located at an angle of about 101 to about 901 with the direction of the abutting engagement of said heating element with said platen roller and on the paper charging side of said platen roller.

3. A thermal head device as claimed in claim 1, wherein said preload means is located at an angle of about 10 to about 90 with the direction of the abutting engagement of said heating element with the platen roller and on the paper discharging side of said platen roller.

4.

A thermal head device as claimed in claim 2 or 3, wherein said preload means is adapted to push said positioning means in said predetermined direction.

A thermal head device as claimed in claim 2 or wherein said preload means is in the form of a tension spring.

0.

6. A thermal head device substantially as hereinbefore described with reference to and as shown in Figure 2 or Figure 3 of the accompanying drawin95.

a Published 1991 at 7be Patent Office. State House. 66/71 High Holborn, London WC I R47P. Further copies Tnay be obtained from Sales Branch, Unit 6, Nina! Mile Point. Cwmfelinfach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.