Thermal printer

Abstract

 To provide a thermal printer in which the number of parts is decreased for the miniaturization and to simplify the assembling work to make it possible to reduce the manufacturing cost.
In a thermal printer including at least: a frame (F) having a pair of side wall portions arranged to face each other at a predetermined interval in a paper width direction; a line thermal head (H) for performing printing; a platen roller (1) having a circumferential surface brought into contact with the thermal head; a pressure means for depressing a back surface of the line thermal head so that the line thermal head is brought into pressing contact with the surface of the platen roller; a motor (M) as a drive source; and a gear transmission mechanism (G1) for transmitting a rotational drive force of the motor to the platen roller, the pressure means is constituted by a part (for example, a pressure portion 10 constituted by a part of the frame) of constituents of the frame brought into pressing contact with a back surface of the head support member.

Description

[0001] The present invention relates to a miniature thermal printer mounted on a variety of portable information equipments or the like and more particularly to a thermal printer provided with a structure in which mounting work for each constituent may readily be performed.

[0002] A general conventional line dot type thermal printer is composed of a line thermal head and a platen roller assembled into a frame to face each other, a drive means therefor, a paper feeding mechanism for feeding of thermal recording paper, and the like.

[0003] A structural example of the conventional thermal printer will herewith be described with reference to Fig. 4 which is an exploded perspective view.

[0004] As shown in Fig. 4, a platen roller 102, a thermal head H, two coil springs 104 for imparting a biasing force for depressing this thermal head H against the platen roller 102, a lock arm member 105 for holding both end portions of a rotary shaft 102A of the platen roller 102, so that they do not separate, a motor M as a drive source, a gear transmission mechanism G2 for transmitting a rotational drive force of the motor M to a driven gear g10 fixed to one end 102A of the platen roller 102, and the like are mounted on a frame 101 molded of resin to form the thermal printer P2.

[0005] In Fig. 4, reference numeral 200 designates a head support member serving also as a heat radiation member of the thermal head H, reference numeral 300 denotes a bearing member of the rotary shaft 102A of the platen roller 102 and reference numeral 400 denotes a sensor for detecting an end portion of the recording paper.

[0006] The lock arm member 105 is formed substantially into a U-shape as a whole and is provided with: a pair of hook-shaped rotary shaft support portions (latch portions) 105a for engaging with and dragging both end portions of the rotary shaft of the platen roller 102 so that the surface of the platen roller 102 is brought into pressing contact with the thermal head H side; a pair of arm portions 105b for leading the latch portions 105a to the back side of the thermal head H through both sides of the head support member 200; and an elastic member support portion 105c arranged in the widthwise direction of the back side of the thermal head H provided with arm portions 105b at both sides thereof for supporting the above-described coil springs 104. Note that the lock arm member 105 and the thermal head H are rotatably supported to both side surfaces of the frame 101 through the rotary shaft 500. Incidentally, reference numeral 700 denotes a screw for fastening the motor M to the frame 101.

[0007] The thermal printer P2 with such a structure is mounted on, for example, a portable information terminal or the like.

[0008] However, as shown in Fig. 4, in the above-described conventional thermal printer P2, mounting positions or mounting directions of respective constituents (a platen roller 102, a thermal head H, a support 200, a gear transmission mechanism G, and the like) with respect to a frame 101 are different from each other. Therefore there was a drawback that the assembling work was complicated and required a skilled artisan.

[0009] That is, for example, in order to mount members in relation with a lock arm member 105, there is needed a work for holding two coil springs 104 between the support member 200 and the lock arm member 105 after a lock arm member 105, a thermal head H, and the support member 200 have been first mounted through a rotary shaft 500 to a frame 101.

[0010] Then, with respect to the mounting work of the platen roller 102, it is necessary to manually move the above-described lock arm member 105 backward and to support both ends of a rotary shaft 102A of the platen roller 102 by latch portions 105a.

[0011] Also, with respect to the mounting work of gears g1 to g3 constituting the gear transmission mechanism G2, it was necessary to mount a gear drop preventing cover 600 for holding gears after gear holes of the respective gears g1 to g3 are fitted in through bearing portions R1 to R3 formed on the side portion of the frame 101.

[0012] Thus, the thermal printer P2 involves such a problem that the number of parts of the constituent is large, the mounting work is also complicated and the manufacturing cost is increased.

[0013] Note that, although a printer that is of a type where the platen roller 102 may be removed is shown as the prior art, even if the platen roller is of a fixed type, the problem that the mounting work of the platen roller, the thermal head, the gear transmission mechanism, and the like to the frame is complicated and that the number of parts is relatively large is not solved.

[0014] The present invention has been invented in order to solve the above-described problems and therefore an object of the present invention is to provide a thermal printer in which the assembling work is simplified to thereby make it possible to reduce the manufacturing cost.

[0015] In order to achieve the above-mentioned object, according to the present invention, there is provided a thermal printer including at least: a frame (F) having a pair of side wall portions arranged to face each other at a predetermined interval in a paper width direction; a line thermal head (H) for performing printing; a platen roller (1) whose circumferential surface is brought into contact with the line thermal head; a motor (M) as a drive source; and a plurality of gears (g1, g2, g20) for transmitting a rotational drive force of the motor to the platen roller, in which the frame is composed of a lower frame member (F1) and an upper frame member (F2) which is dividable up and down, and in which receiving portions (receiving portion A, gear receiving portion B) for receiving the line thermal head, the platen roller, the motor and the gears, respectively are formed within the lower frame member, and at the same time, a plurality of holder portions (C1 to C4, D1 to D4) for rotatably holding respective rotary shafts of the platen roller and the motor when the two frame members are coupled with each other are formed in the side wall portion of the lower frame member and the side wall portion of the upper frame member.

[0016] Thus, after the respective rotary shafts of the above-described platen roller and the above-described motor are mounted on the holder portions of the lower frame member side and the thermal head, the motor, and the like are received in the receiving portions, the upper frame member is simply coupled to cover the lower frame member to assemble the printer, which makes it possible to reduce the number of parts and to simplifying the assembling work to reduce the manufacturing cost.

[0017] Also, it is preferable that each of the holder portions formed in the side wall portion of the lower frame member and the side wall portion of the upper frame member has a substantially semicircular shape. Thus, each rotary shaft of the above-described platen roller and the above-described motor may readily be mounted on the lower frame member, and at the same time, when the upper frame member is coupled together, both holder portions per se form the circular bearing portion so that it is unnecessary to form any discrete bearing member to thereby make it possible to simplify the structure.

[0018] Also, a pressure means for depressing a back surface of the line thermal head so that said line thermal head is brought into pressing contact with the surface of the platen roller may be formed in the upper frame member. Thus, it is possible to dispense with the mounting work of the coil springs, which is troublesome in the conventional thermal printer and to simplify the assembling work to make it possible to reduce the manufacturing cost.

[0019] Also, the pressure means may be composed of a planar pressure portion having elasticity and formed integrally with the upper frame member, and the pressure portion may be formed in a position where an end portion of the pressure portion is in contact with the back surface of the line thermal head when the upper frame member is coupled with the lower frame member. Thus, since it is possible to dispense with the coil springs as the pressure means in the prior art, it is possible to reduce the number of parts to make it possible to reduce the cost. Also, since the pressure portion may be formed integrally with the above-described upper frame member, the manufacture is simple. Also, since the assembling work is so simple as to couple with the lower frame so that the line thermal head may be brought into pressing contact with the surface of the platen roller, the structure may be simplified and the manufacturing cost may be reduced.

[0020] Embodiments of the present invention will now be described by way of further example only and with reference to the accompanying drawings, in which:-

Fig. 1 is an exploded perspective view showing an embodiment of a thermal printer P1 to which the present invention is applied;

Fig. 2 is a cross-sectional view of an upper frame member of the thermal printer P1 to which the present invention is applied;

Fig. 3 is a perspective view showing an outer appearance of the thermal printer P1 to which the present invention is applied; and

Fig. 4 is an exploded perspective view of a conventional thermal printer P2.

[0021] A preferred embodiment of the present invention will now be described with reference to the accompanying drawings.

[0022] Fig. 1 is an exploded perspective view showing an embodiment of a thermal printer P1 according to the present invention. Fig. 2 is a cross-sectional view of an upper frame member of the thermal printer P1. Fig. 3 is a perspective view showing an outer appearance of the thermal printer P1 that has been assembled.

[0023] As shown in Fig. 1, the thermal printer P1 according to a first embodiment is provided with a frame F composed of a lower frame member F1 and an upper frame member F2 having a pair of side wall portions arranged to face each other in a paper width direction at a predetermined interval.

[0024] The frame F is comprised of, for example, the injection-molded products of plastic such as a polycarbonate.

[0025] An upper surface of the lower frame member F1 and a lower surface of the upper frame member F2 are formed into a coupling structure (that is, a structure in which end faces correspond to each other and when coupled, there is generated no gap) and in the coupled condition shown in Fig. 2, both frame members F1 and F2 are fixed together by engagement claws or screws which can be fitted in.

[0026] In the lower frame member F1, a receiving portion A for receiving a platen roller 1, a thermal head H, a motor M as a drive source, and the like is formed. Although not shown in the drawing, a groove, a cutaway portion, or the like for positioning the thermal head H is formed in the receiving portion A. Also, a support portion El for fixing a rear end portion of the motor M is formed in the receiving portion A.

[0027] Also, a connector 30 connected to signal lines for transmitting printing signals is provided in the thermal head H.

[0028] A divisional surface is determined in the lower frame member F1 and the upper frame member F2 so that it is divided through a plane passing through each bearing portion. In the case where each bearing portion is completely overlapped in the vertical direction, it is impossible to cope with the divisional structure of the lower frame member F1 and the upper frame member F2. Accordingly, the structure is designed so that each rotary shaft of each gear g1, g2 is not overlapped in the vertical direction and displaced in the horizontal direction.

[0029] A gear receiving portion B for receiving each gear g1, g2 of a gear transmission mechanism G1 for transmitting a rotational drive force of the motor M to a driven gear g20 fixed at one end of the rotary shaft 1A of the platen roller 1 and for receiving the driven gear g20 is formed on one side wall side (on the right side wall side in Fig. 1) of the lower frame member F1.

[0030] Semicircular holder portions C1 to C3 for rotatably holding the rotary shaft 1A of the platen roller 1 and the rotary shafts g1a and g2a of the respective gears g1 and g2 and a semicircular holder portion C4 for holding the bearing portion Ma of the motor M are formed on the upper edge side of the gear receiving portion B and the side wall of the lower frame member F1. In the lower frame member F1, reference numeral 20 denotes a guide portion that serves as a guide when a roll paper (not shown) as the recording paper is fed.

[0031] Also, semicircular holder portions D1 to D3 (incidentally, D4 does not appear in the drawing) formed in confronting positions with the holder portions C1 to C3 of the lower frame member F1 are formed in the lower surface side of the upper frame member F2.

[0032] In Fig. 2, a portion indicated by reference numeral 10 is a V-shaped pressure portion having elasticity for depressing a back surface of the thermal head H so that the line thermal head H is brought into pressing contact with the surface of the platen roller 1 when the upper frame member F2 is coupled with the lower frame member F1.

[0033] Also, reference numeral 11 denotes a heat radiation portion for performing the heat radiation of the thermal head H, which is formed integrally with the pressure portion 10 and is provided in a position where an end face of the heat radiation portion 11 is brought into contact with the back surface of the thermal head H when the upper frame member F2 is fitted with the lower frame member F1.

[0034] Hereby, the assembling order of the thermal printer P1 with the above-described structure will be described.

[0035] First of all, the motor M of the lower frame member F1 is mounted on the receiving portion A, and the rotary shafts g1a and g2a of the gears g1 and g2 are mounted on the holding portions C3 and C2 of the gear receiving portion B.

[0036] Subsequently, the driven gear g20 is mounted at one end portion of the rotary shaft 1A of the platen roller 1 and both end portions of the rotary shaft 1A of the platen roller 1 are mounted on the holder portion C1 of the lower frame member F1. In this case, the driven gear g20 is received on the gear receiving portion B.

[0037] Subsequently, the thermal head H provided with the line thermal head H is mounted on the receiving portion A. Finally, the upper frame member F2 is fitted with the lower frame member F1. Thus, the platen roller 1 and the rotary shafts of the gears g1 and g2, and the like are rotatably held by the holder portions D1 to D4 and the holder portions C1 to C4.

[0038] Then, the upper frame member F2 is fixed to the lower frame member F1 by engagement with engagement claws or screw fastening with screws so that the thermal printer P1 as shown in Fig. 2 may be assembled.

[0039] Thus, in the thermal printer P1 according to this embodiment, since only a simple assembling work for mounting each constituent on the lower frame member F1 and coupling the upper frame member therewith is sufficient to assemble the thermal printer P1, it is not necessary to provide skill for the complicated assembling work like the conventional thermal printer P2, to thereby make it possible to shorten the assembling time and to reduce the manufacturing cost of the printer.

[0040] Also, since the members such as a lock arm member and coil springs as the pressure means or the like are dispensed with, the number of parts is decreased to thereby make it possible to further reduce the cost.

[0041] The invention made by the present inventors has been described specifically based upon the embodiments. However, the present invention is not limited to the above-described embodiments and it is possible to effect the change within the scope of the claims.

[0042] For example, although in this embodiment, the case where the gear transmission mechanism G1 is composed of the two gears g1 and g2, the invention may be applied to the case where it is composed of three or more gears. In this case, the holder portions formed in the lower frame member F1 and the upper frame member F2 are provided in conformity with the arrangement positions and the number of the gears.

[0043] Also, in this embodiment, although the case where the planar pressure portion 10 as the pressure means is formed in the upper frame member F2 has been described, the invention is not limited to this. For example, it is possible to interpose the leaf springs or the like between the thermal head H and the upper frame member F2.

[0044] Also, in this embodiment, although the case where the thermal head H is mounted on the lower frame member F1 in assembling has been described, it is possible to attach the thermal head H onto the heat radiation portion 11 of the upper frame member F2 in advance. Thus, it is possible to effectively perform the assembling work.

[0045] As described above, since a thermal printer according to the present invention includes at least: a frame having a pair of side wall portions arranged to face each other at a predetermined interval in a paper width direction; a line thermal head for performing printing; a platen roller having a circumferential surface brought into contact with the thermal head; a motor as a drive source; and a plurality of gears for transmitting a rotational drive force of the motor to the platen roller, in which the frame is composed of a lower frame member and an upper frame member which is dividable up and down and receiving portions for receiving the line thermal head, the platen roller, the motor and the gears, respectively are formed within the lower frame member, and at the same time, a plurality of holder portions for rotatably clamping respective rotary shafts of the platen roller and the motor when the two frame members are coupled with each other are formed in the side wall portion of the lower frame member and the side wall portion of the upper frame member. Thus, after the respective rotary shafts of the above-described platen roller and the motor are mounted on the holder portions of the lower frame member side and the thermal head, the motor, and the like are received in the receiving portions, the upper frame member is simply coupled to cover the lower frame member to assemble the printer which makes it possible to reduce the number of parts while simplifying the assembling work to reduce the manufacturing cost.

Claims

1. A thermal printer comprising:

a frame having a pair of side wall portions arranged to face each other at a predetermined interval in a paper width direction;

a line thermal head for performing printing;

a platen roller having a circumferential surface brought into contact with the line thermal head;

a motor as a drive source; and

a plurality of gears for transmitting a rotational drive force of the motor to the platen roller,

   wherein the frame is composed of a lower frame member and an upper frame member being dividable up and down,
   receiving portions for receiving the line thermal head, the platen roller, the motor and the gears, respectively are formed within the lower frame member, and at the same time, a plurality of holder portions for rotatably holding respective rotary shafts of the platen roller and the motor when the two frame members are coupled with each other are formed in the side wall portion of the lower frame member and the side wall portion of the upper frame member.

2. The thermal printer according to claim 1, wherein each of the holder portions formed in the side wall portion of the lower frame member and the side wall portion of the upper frame member has a substantially semicircular shape.

3. The thermal printer according to claim 1, further comprising a pressure means for depressing a back surface of the line thermal head and formed in the upper frame member so that the line thermal head is brought into pressing contact with the surface of the platen roller.

4. The thermal printer according to claim 1, wherein the pressure means is composed of a planar pressure portion having elasticity and formed integrally with the upper frame member, and
   the pressure portion is formed in a position where an end portion of the pressure portion is in contact with the back surface of the line thermal head when the upper frame member is fitted with the lower frame member.

Drawing