JPH02295757A - Thermal print head - Google Patents

Abstract

PURPOSE:To improve print quality and to avoid aging of print quality by arranging the terminal sections of a bead substrate collectively in the longitudinally central section, securing a stop cover to the central section of 8 base substrate and integrally forming bent platen positioning chips at the opposite and sections of the base substrate. CONSTITUTION:Platen positioning chips 12 are formed integrally, while being bent, with a base substrate 1. A bead substrate 5 is secured while being positioned specifically to the base substrate 1 thus automatically ensuring the positional accuracy between a heating dot row 2 and the joint groove 14 in the positioning chip 12 which is critical in the positional relation with respect to the platen. Comb tooth terminal sections 4 are arranged collectively in the longitudinally central section of the bead substrate 5, where a corresponding circuit board 8 for external connection is shortened and the portion for pressing the terminal sections 4, 6 of the head substrate 5 and the circuit board 8 are limited to the longitudinally central section by means of a stop cover 11. When the base substrate is made of ferrous board, for example, and the entire longitudinal region of the print head is energized toward the platen 13 through a plurality of springs 21, the heating dot 2 can be pushed with uniform force against the surface of the platen 13.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a thermal print head.

[Conventional technology and problems to be solved]

In a conventional thermal print head of this type, as shown in FIG. 5, a head substrate b and a substrate C for connection to an external circuit are attached to an aluminum base substrate a that is rectangular in plan view. At the same time, a presser cover d for pressing the overlapping portion of the terminal portion, which will be described later, is superimposed on the base substrate a from above the connection substrate C. The head substrate b has a large number of heat generating doves }e arranged in a row in the longitudinal direction on its surface and a driving circuit f thereof, and a comb-shaped terminal portion is provided on one example part over almost the entire length of the head substrate b. g is formed. On the other hand, the connection board C includes a flexible circuit board i made of a resin film on which a comb-shaped terminal part h corresponding to the terminal part g of the head board b is formed on the back surface of one side, and a flexible circuit board i made of a resin film. Reinforce board i from the back side. It consists of a reinforcing plate j made of glass epoxy, etc. As shown in FIG. 6, the head substrate b and the connection substrate C have the terminal portions g, h
It is electrically connected by polymerizing. The presser cover d also has mounting screws l inserted through mounting holes m provided at predetermined intervals along its entire length.
, the base board a is fastened together with the connection board C.
A string-like pressing rubber k held on the back side presses both terminals g and h against each other. By the way, when the print head configured as described above is installed in a printer, it is used so that the recording paper that is back-amplified by the platen p is fed while being pressed against the heating donut e, and the recording paper is loaded. , and for convenience of maintenance of the head itself, it is common to attach one of the print head and the platen p to the chassis of the printer, and the other to a member that can be rotated to open and close with respect to the chassis. Therefore, a positioning bracket 0 is attached to the print head side so that the side generatrix of the platen p accurately corresponds to the row of heating dots e when the opening/closing member is closed. The positioning bracket 0 stands up in an L-shape from a base S applied to the back surface of the base board a of the print head,
It is made by bending a plate material so as to have a main body part r equipped with a guide #Q that can be engaged with the end of the support shaft of the platen p.
As shown in the figure, the base S is fixed to both ends of the back surface of the base substrate a with screws t, respectively. In the print head to which the positioning bracket 0 as described above is attached, the positioning bracket 0 must be separately formed from iron-based material because mechanical strength is required to repeatedly engage the shaft of the platen. The above positioning bracket 0, which requires a large number of parts in addition to the aluminum base board a, and which requires an accurate positional relationship of the engagement groove q with respect to the heat generating donut }e, is attached to the base board a.
The problem was that it had to be attached to the back side of the machine using screws. In addition, in conventional thermal print heads, the presser cover d is superimposed and fixed over almost the entire length of the base substrate a and the head substrate b with a plurality of screws l, so that the head substrate a is lifted up before the presser cover d. In order to prevent the printing quality from changing due to temporary warping of the entire print head due to heating, it is necessary to increase the thickness of the base substrate a and increase its section modulus as much as possible. This resulted in an increase in the overall thickness and weight of the print head. This invention was devised under the above-mentioned circumstances, and addresses the above-mentioned two problems of the conventional art, namely, the problem of an increase in the number of parts and an increase in work cost due to the installation of the positioning bracket 0.
Another object of the present invention is to provide a thermal print head that can solve the problems of increasing size and weight due to the need to increase the section modulus of the base substrate a with a simple configuration.

[Means to solve the problem]

In order to solve the above problems, the present invention takes the following technical measures. That is, the present invention includes a head substrate having heating dots and their drive circuits arranged in a row on a base substrate, and a terminal portion formed on the back surface of one side portion on the surface of one side portion of the head substrate. a circuit board for external connection that is connected to the terminal portions in an overlapping manner; A thermal print head that prints by guiding recording paper between a platen that is brought into pressure contact with the head substrate with a predetermined pressure, and a presser cover that protects the presser cover when the print head is exposed to the head substrate. By centrally arranging the terminal portions at the center in the longitudinal direction of the head board, the overlapping portion of the external connection circuit board and the terminal portion of the head board is pressed and fixed at the center portion of the base board, and the presser cover can be held there. Positioning pieces are fixed to the base substrate at the center, and are integrally formed at both ends of the base substrate by bending and having engagement grooves that are guided and engaged with the shaft of the platen and members in a constant relationship therewith. It is characterized by

[Action and effect]

In the present invention, positioning pieces for the platen are integrally bent at both ends of the base substrate. Therefore, since the positioning bracket, which was conventionally separate, is integrated into the base board, costs can be reduced by reducing the number of parts. The problem of ensuring positional accuracy between the engagement groove of the positioning piece and the heat-generating dots on the head board can be treated as a problem of positioning accuracy of the head board with respect to the base board. The problem can be solved simply by aligning the substrates using the same conventional method. Therefore, the troublesome work of screwing the bracket from the back side of the base board while recognizing the positional relationship between the heat generating dot on the head board and the guide engagement groove of the positioning bracket from the front side, as in the past, is eliminated. . Next, in the present invention, the terminal portions to be provided on the hard board are concentrated in the longitudinal direction thereof. Therefore, the terminal portion of the external connection circuit board to be overlapped thereon and the pressing portion to which these are to be superimposed and fixed may be only a small portion limited to the longitudinal center portion of the print head. This means that the portion of the presser cover that needs to be fixed to the base board can be limited to the central portion in the longitudinal direction. Therefore, in conventional examples, the base board and the presser cover are fixed to each other over the entire length. This solves the problem of warping due to temperature rise. This eliminates the need to increase the section modulus of the base substrate so much, for example, it becomes possible to form the base substrate from an iron-based plate material, and the print head can be made thinner and lighter. The configuration of the present invention has even more important meaning. That is, conventional thermal print heads are based on the premise that bending rigidity must not be large in order to ensure printing quality, in other words, that they must not be bent by thermal stress or external force, but the present invention overcomes this premise. It is defeating the. As described above, in the present invention, the base substrate and the presser cover are substantially connected to each other only at the central portions in the longitudinal direction. In addition to the first meaning that warping does not occur in the entire head, it does not have any negative effect on the operation as a thermal head, that is, heating a predetermined heating dot according to the printed information. This makes it possible to form the entire head so that it can be bent flexibly. That is, according to the thermal print head of the present invention, the direction of the longitudinal axis of the head with respect to the axis of the platen is defined by the positioning pieces integrally formed at both ends, and the entire head is directed toward the surface of the platen by, for example, a plurality of springs. When pressed, the heating dots are configured so that they can be pressed against the platen surface with a uniform pressing force in all parts in the longitudinal direction of the array, without being affected by the mounting accuracy or surface roundness of the platen. This makes it possible to improve print quality and avoid changes in print quality over time as much as possible.

[Explanation of Examples]

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. FIG. 1 is an exploded perspective view of an embodiment of a thermal print head according to the present invention. As shown in this figure, on the base substrate 1 of the thermal print head, there are heating pads 2 and their driving circuits 3 arranged in a row, and a comb-shaped terminal portion 4 is formed on the surface of the part. A head substrate 5 made of ceramic, a comb-teeth-shaped terminal portion 6 corresponding to the comb-teeth-shaped terminal portion 4 of the head base 5 on the back surface of one side, and an exterior lined with a reinforcing plate 7 made of glass epoxy. A connecting circuit board 8 is arranged such that both comb-shaped terminal portions 4.6 are overlapped with each other. The both terminal portions 4 are arranged along the green side of the head substrate 5.
．． A presser cover 1 having a cover portion 10 that presses and fixes the overlapping portion 9 of the drive circuit 3 and extends above the drive circuit 3.
1 is fixed to the base substrate 1. As will be described later, in the presser cover 11, since the comb-shaped terminal portions 4.6 are concentrated in the center in the longitudinal direction of the head, the portions fixed to the base board are also shortened accordingly. , only a cover portion 10 extends over both wings so as to protect all drive circuits 3. By devising a circuit pattern built into the head board 5, the comb-like terminal part 6 is concentrated in the center in the longitudinal direction, and correspondingly, the external connection circuit board 8 itself is The length of the head in the longitudinal direction has also been shortened. As clearly shown in FIG. 1, the base substrate 1 is made of, for example, a press-molded iron-based plate member, and positioning pieces 12 are bent and integrally formed at both ends of the base substrate 1. ．． The positioning piece 12 is located at the shaft end of the platen 13,
Alternatively, an engagement groove 14 is formed that can be guided and engaged with a member that is in a fixed positional relationship with the axis of the platen. As explained in the "Prior Art and Problems to be Solved" section, in printers, one of the thermal print head and platen is attached to the printer chassis, and the other is attached to a member that can be rotated to open and close with respect to the chassis. However, the positioning piece 12 is for regulating the positional relationship between the thermal print head and the platen to always be constant when the rotating member is closed. Normally, the above-mentioned positional relationship is determined so that the side generatrix of the platen is precisely along the heat generating dot row 2 of the print head. The attachment of the head substrate 5 to the base substrate 1 is performed by adhesion or the like, and the connection between the base substrate 1 to which the head substrate 5 is fixed in advance, the external connection substrate 8, and the presser cover 11 is performed by the presser cover 11 and the external connection substrate 8. This is done by screwing a fixing screw 16 inserted into a threaded hole 15 formed in a predetermined portion of the board 8 into a threaded hole l7 of the base board l.
At this time, a retaining groove 18 is formed on the back side of the presser cover 11.
A string-shaped elastic body 19 held by the head board 5 elastically presses the overlapping part 9 of the terminal part 4 of the head board 5 and the terminal part 6 of the external connection circuit board 8 from above to ensure electrical continuity between them. do.
In FIG. 1, reference numeral 20 denotes the base substrate 1, which is used for mutual positioning by knock pins (not shown).
The positioning holes provided in the external connection circuit board 8 and the presser cover 11 are shown. In the above configuration, since the base board 1 is integrally formed with the positioning piece l2 for positioning with respect to the platen, a separately formed positioning bracket is screwed to the back surface of the base board 1 as in the conventional case. This is no longer necessary, and by simply fixing the head substrate 5 while performing predetermined positioning with respect to the base substrate l, the problem of the positional relationship between the heating dot row 2 and the engagement groove 14 of the positioning piece 12 with respect to the platen can be eliminated. Positional accuracy between the two locations is automatically ensured. Such positioning of the head substrate 5 with respect to the base substrate 1 can be easily performed from the front side of the print head using, for example, a recognition mark provided on the circuit pattern of the head substrate 5. The comb-teeth terminal portion 4 provided on the head base 5 is centrally arranged in the center in the longitudinal direction of the head substrate 5, and the corresponding external connection circuit board 8 is also shortened. Since the part that presses both the terminal parts 4.6 of the head board 5 and the external connection circuit board 8 is limited to the center in the longitudinal direction of the head, even if the temperature of the base board 1 rises first at the beginning of operation, it will not be affected by thermal stress. It is possible to avoid warping of the entire print head. Therefore, it is no longer necessary to increase the section modulus of the base substrate 1 as in the conventional case, and it is also possible to construct the base substrate 1 from an iron-based plate material as in the embodiment. In this way, the weight of the base substrate 1, which accounts for a large portion of the weight of the print head, can be significantly reduced and the overall weight can be reduced, and at the same time, the print head can be made smaller in the thickness direction. Further, by constructing the base substrate 1 from an iron-based plate material suitable for press molding in this manner, it becomes easier to form the positioning piece 12 which is to be integrally bent. Then, as described above, the overlapping portion 9 of the terminal portions 4 and 6 of the head base 5 and the external connection circuit board 8 is arranged limited to the central portion in the longitudinal direction of the head, and the overlapping portion 9 is covered by the presser cover 11. Limiting the pressing part to the central part in the longitudinal force direction also means that even if the entire head is flexible and can be bent with a relatively small force, it will not have any adverse effect on the electrical characteristics of the head substrate. In other words, if the base substrate 1 is made of an iron-based plate material as in the embodiment, its section modulus will be significantly smaller than that of the conventional one, and it will relatively easily bend elastically and scale due to external force. allows you to configure the printer as follows. That is, as shown in FIG. 4, the entire length of the print head is biased toward the platen 13 by using a plurality of springs 21 or the like. Then, since the entire print head flexes, the heat-generating drift 2 is applied to the surface of the platen 13 with uniform force in all parts of the array in the longitudinal direction, without being affected by the mounting accuracy or surface roundness of the platen 13. Since it can be pressed and there is no deformation due to thermal stress, printing quality is fundamentally improved, and
This change over time can also be avoided.

[Brief explanation of drawings]

Fig. 1 is an exploded perspective view of the thermal print head of the present invention, Fig. 2 is an assembled cross-sectional view corresponding to the cross section taken along the line ■-■ in Fig. 1, and Fig. 3 is a cross-sectional view corresponding to the line ■-■ in Fig. 1. FIG. 4 is a cross-sectional view showing an example of how it is assembled into the printer head, FIG. 5 is an exploded perspective view of the conventional example, and FIG. 6 is an assembly corresponding to the Vl-VT line cross section in FIG. 5. FIG.

Claims (1)

[Claims] (1) A head substrate having heat-generating dots arranged in a row and a driving circuit thereof on a base substrate, a terminal portion formed on the back surface of one side, and a terminal portion formed on the surface of one side of the head substrate. an external connection circuit board which is connected to the external connection circuit board so as to be overlapped with the head board; and a circuit board formed along the side edge of the head board, which presses and fixes the overlapping part of both the terminal parts, and which extends above the drive circuit. In a thermal print head that prints by guiding recording paper between a platen that is pressed into contact with the head substrate at a predetermined pressure and is provided with a presser cover that protects the head substrate, the terminal portion of the head substrate is connected to the By arranging them centrally in the longitudinal direction of the board, while pressing and fixing the overlapping part of the external connection circuit board and the terminal part of the head board in the center part of the base board, the presser cover can be fixed in the central part of the base board. The present invention is characterized in that positioning pieces are bent and integrally fixed to the base substrate and have engagement grooves that are guided and engaged with the shaft of the platen and a member that is in a certain relationship with the axis of the platen, at both ends of the base substrate. , thermal print head.