THERMAL LINE PRINTER

Abstract: A thermal line printer which further improves printing quality and has a more simplified construction for efficient assembly. The printer comprises a frame (1), a platen (5) rotatably supported on the frame, a thermal head (6) rotatably supported on the frame (1), for printing data to recording paper clamped between the head (6) and the platen while keeping pressure contact with the platen (5), a push plate (4) rotatably supported on the frame (1) and equipped with a head-up lever on a rotating shaft, a leaf spring (7) disposed between the push plate and the thermal head to resiliently press the thermal head against the platen through the push plate, and a motor (14) for suitably rotating the platen through a rotation transmission mechanism disposed on the platen.

Description: TECHNICAL FIELD The present invention relates to a structure of a line type small printer and more particularly to a head-up structure of a thermal head. BACKGROUND ART A prior art example of a general small printer using a line type thermal head will be explained based on a section view shown in FIG. 6. In the figure, the prior art printer comprises a platen 5 provided turnably with respect to a frame 1, a thermal head 6 pressed to the platen 5, a platen spring 19 for pressing the thermal head 6 resiliently to the platen 5, a platen spring receiving plate 20 for receiving resilience of the platen spring 19, a head-up lever 10 having a cam 10a for releasing the thermal head 6 from the platen 5 during maintenance for exchanging sheets of paper or a jammed paper, a head-up pin 8 provided to the thermal head 6 for engaging with the cam 10a to release the thermal head 6 from the platen 5, a thermal head pivot 17 which is a center axis of rotation of the thermal head 6, and others. In the small printer using the line thermal head, it is necessary to press and contact the thermal head to the platen with homogeneous pressure across the whole printing range from the aspect of printing quality and the like. Accordingly, the prior art printer constructed as described above has been adapted such that one coil spring is disposed as the platen spring in a manner capable of freely rocking centering on a fulcrum so that its resilience acts homogeneously between the platen and the thermal head or such that a plurality of coil springs each having homogeneous resilience are disposed at adequate points on the back of the thermal head to eliminate the unevenness of contact of the platen and the thermal head. As a result, although the unevenness of contact of the platen and the thermal head has been improved, there has been a problem that the coil spring is repeatedly stretched and compressed every time when the head is opened and closed, thus causing a degradation of the spring such as settling as a result, because the thermal head has an opening/closing mechanism for maintenance with respect to the platen and the coil spring is designed so that it exerts an adequate resilience when the thermal head abuts with the platen. In case of the printer using the plurality of coil springs in particular, the resilience may vary per each coil spring, thus changing the pressing stress between the platen and the thermal head partially. Accordingly, there have been such problems that it degrades the printing quality and it may cause a failure of the printer itself. There has been also another problem that because the repulsive resilience of the coil spring becomes large when it is compressed during head-up and the mechanical strength of the platen spring receiving plate for receiving such large resilience has to be increased, it has been difficult to design such printer from the aspect of its structure and strength. Further, because the head-up operation carried out by means of the head-up lever has been carried out by abutting the head-up cam only to one side of the head-up pin and resisting to the resilience of the coil spring in general, there has been a problem that the other end of the thermal head which does not engage directly with the head-up cam is inclined largely and it becomes difficult to perform works for recovering a failure such as a paper jam in a printer using a line thermal head having a wider width. There have been also other problems that the use of the coil spring which is cumbersome to assemble drops the efficiency of assembling works and complicates the structure around the head of the printer, thus increasing the cost of the printer. JP-01008055A discloses a thermal head holding device comprising a leaf spring arrangement. JP-62286767A discloses a thermal transfer printer with means for varying the pressing force on a thermal head. Accordingly, it is an object of the present invention to improve the printing quality further as well as to realise a printer having a more simplified structure to improve the efficiency of assembling works. DISCLOSURE OF THE INVENTION According to an aspect of the present invention there is provided a line thermal printer, comprising: a frame; a platen provided with a rotation transmission mechanism at one end thereof and turnably supported by said frame; a line thermal head turnably pivoted on said frame and pressed to said platen to record printing data to a recording sheet pinched between it and said platen; a pressing plate turnably pivoted on said frame and provided with a head-up lever fixed at one end of a rotational shaft thereof; a leaf spring disposed between said pressing plate and said thermal head for applying a resilience for resiliently pressing said thermal head to said platen by a pressure of said pressing plate; a motor for turning said platen adequately via said rotation transmission mechanism of said platen; and a head-up switch, and wherein the resilience of said leaf spring does not act on said frame, said pressing plate and said thermal head when the pressing stress of said pressing plate to said leaf spring is released, characterised in that: said pressing plate is turned up via said head-up lever; a cam is formed on part of said head-up lever provided at one end of the rotational centre shaft of said pressing plate and that when said head-up lever is turned, said cam engages with part of said thermal head, thus releasing said thermal head from said platen by the engaging portion thereof; and said leaf spring is positioned by and supported on pins formed on said frame so as to permit freedom of movement of said leaf spring in relation to the pins. In view of the aforementioned problems, according to the present invention, a platen spring for pressing a head is formed by one leaf spring having adequate length and width and the back of the whole leaf spring is pressed by a pressing plate having a width matched with that of the leaf spring to apply a homogeneous resilience to the whole thermal head. Further, a head-up lever is fixed at one end of the pressing plate to head up the main body of the thermal head when the pressure of the thermal head applied by the pressing plate is released, thus realising the printer having such simple structure. According to the present invention, because the leaf spring is used as the platen spring, is disposed between the thermal head and the pressing plate and is pressed by the pressing plate to press the whole thermal head resiliently to the platen, the thermal head may be pressed to the platen homogeneously. Further, the head-up lever is provided at one end of the pressing plate in a body with the pressing plate. When the engagement of the pressing plate with the leaf spring is released by turning the head-up lever, the leaf spring is put into free state and the resilience to the leaf spring is released, thus allowing the degradation and the like of the leaf spring to be reduced. Then, by turning the head-up lever further, the thermal head released from the pressure of the leaf spring may be released in the direction separated from the platen through a cam formed on the head-up lever without resisting to the resilience of the pressing plate . As a result, because the thermal head is not released eccentrically during head-up and the platen spring can be formed simply by one leaf spring, the structure of the printer may be simplified and the assembling efficiency may be improved. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a plan view of a printer of the present invention; FIG. 2 is a section view showing a state in which a thermal head of the inventive printer is pressed; FIG. 3 is a section view showing a state in which the thermal head of the present invention is released; FIG. 4 is a section view of a head-up lever section in the state in which the thermal head of the present invention is pressed; FIG. 5 is a section view of the head-up lever section in the state when the thermal head of the inventive printer is released; and FIG. 6 is a section view of a prior art printer. BEST MODE FOR CARRYING OUT THE INVENTION A preferred embodiment of the present invention will be explained below in detail with reference to the drawings. FIG. 1 is a plan view showing one embodiment of an inventive printer which comprises, at least, a frame 1 which is the base of the printer, a platen 5 turnably pivoted on the frame, a line type thermal head 6 which abuts resiliently with the platen 5 to record printing data on a recording sheet 15 disposed between it and the platen, a leaf spring 7 which corresponds to the prior art platen spring, a pressing plate 4 for resiliently pressing the thermal head 6 to the platen 5 via resilience of the leaf spring 7 by pressing the leaf spring 7, a motor 14 for turning the platen via a gear train 2, a flexible board 11 (hereinafter referred to as FPC) for transmitting driving signals to the thermal head 6, and others. The platen 5 is disposed such that both ends of a rotational center shaft thereof are turnably pivoted at predetermined positions of the frame and a gear composing the gear train 2 is secured at one end of the shaft so as to receive rotational power from the motor 14 and to be able to convey recording sheets pinched between it and the thermal head 6 adequately by the rotational power of the motor 14. The thermal head 6 which is a line type thermal head is disposed near the platen 5 in parallel with the rotational shaft of the platen and a head-up pin 8 is provided at one end of the thermal head in the longitudinal direction thereof in a body with it. Further, the thermal head 6 is provided with a rotational center shaft which becomes the center of rotation during head-up at the both ends in the width direction thereof and is turnably pivoted on the frame via this rotational center shaft. The pressing plate 4 is disposed near the thermal head in parallel with it and its section is formed in a shape of cam. The pressing plate is provided with a rotational center shaft 3 at both ends thereof to be turnably pivoted on the frame. Further, a head-up lever 10 is provided at one end of the rotational center shaft 3 and a cam 10a is formed at part of the head-up lever 10. When the head-up lever 10 is turned, the cam 10a engages with the head-up pin 8 provided to the thermal head 6 depending on its turn position and releases the thermal head 6 from the platen 5. In the same time, the cam 10a contacts with a head-up switch 18 which turns on or off an electrical signal indicating a head-up or head-down state in linkage with the head-up of the thermal head 6. The leaf spring 7 is disposed between the thermal head 6 and the pressing plate 4 while being positioned by pins 13 positioned at adequate spots of the frame 1 and resiliently presses the thermal head 6 in the direction of the platen 5 by means of the pressing plate 4 formed in the shape of cam depending on the turn position of the pressing plate 4 which is turned by the head-up lever 10. In the present embodiment, a portion at the edge of the leaf spring 7 which contacts with the thermal head 6 is formed in a shape of so-called angle in which a cutaway portion is created partly in order to apply a predetermined resilience to the thermal head. Next, the operation of the present invention will be explained below. FIGs. 2 through 5 are diagrammatic section views of the printer of the present embodiment. FIG. 2 shows a state in which the thermal head 6 is resiliently pressed to the platen 5 by the leaf spring 7 and FIG. 3 shows a state in which the resilience of the leaf spring 7 is released from the thermal head. Further, FIG. 4 shows a relationship of position of the head-up switch 18, the head-up lever 10 and the thermal head 6 in the state in which the resilience of the leaf spring 7 is applied to the thermal head 6. FIG. 5 shows a relationship of position and engagement of the head-up switch, the head-up lever and the thermal head in the head-up state in which the head-up lever 10 is turned from the state shown in FIG. 4. In the normal printing states shown in FIGs. 2 and 4, the thermal head 6 is held in the state in which a printing section thereof is pressed to the platen 5 by the resilience of the leaf spring 7 which is pressed by the pressing plate 4 wholly in the longitudinal direction thereof. In this state, the head-up switch 18 is turned on as it contacts with the cam 10a of the head-up lever 10 provided at one end of the pressing plate 4. That is, the on-state of the head-up switch 18 is held and thereby a printer control section not shown acknowledges that the thermal head 6 is pressed to the platen 5 and that the printer is enabled to print. On the other hand, when it becomes necessary to release the press of the thermal head 6 applied to the platen 5 in order to eliminate a failure such as a paper jam occurred during printing operation for example, the head-up lever 10 provided at one end of the pressing plate 4 is turned to release the pressure of the pressing plate 4 applied to the leaf spring 7 at first as shown in FIG. 3 or FIG. 5. In this state, the thermal head 6 will not receive no coercive resilient pressure of the leaf spring 7 and contacts with the platen 5 only by its own weight and the resilience of the FPC connected to one end of the thermal head. In the same time, the head-up switch will not contact with the cam of the head-up lever and the head-up switch is put in a state in which it is shut off. The printer control section not shown which detects that fact detects that the thermal head is in the head-up state at this initial point of time. Then, when the head-up lever is turned further, the cam 10a provided on the head-up lever engages with the head-up pin 8 provided at one end of the thermal head and while holding this engagement, the head-up lever turns the thermal head 6 coercively in the direction of releasing it from the platen 5. At this time, the leaf spring 7 is pushed up in linkage with the thermal head while being positioned by the pins 13 of the frame 1. Further, the pressing plate 4 turns together with the head-up lever formed in a body and during this series of actions, the thermal head is released from the resilient pressure applied by the leaf spring and the pressing plate. Thus, because the thermal head is adapted so that it is pressed by the homogeneous resilience across the whole range in the longitudinal direction thereof by one leaf spring and the pressing plate and so that when the resilience of the leaf spring is released, no load is applied to the other components of the printer by the resilience of the leaf spring, the high precision printer may be realised with the simple structure. Further, the realisation of the press-contact of the thermal head to the platen by means of the leaf spring allows the structure to be simplified as compared to the prior art thermal head press-contact structure. For example, it becomes possible to construct a printer having a different size in the width direction by the same components, design and specification just by changing the width of the thermal head in accordance with a width of a recording sheet. Therefore, it becomes unnecessary to design accommodating to the size of the printer due to the spring for pressing the thermal head. It is also noted that a support frame 12 of the FPC connected to transmit driving signals for printing to the thermal head is formed at part of the frame to support the FPC by the printer frame and to take a countermeasure to static electricity of an IC for driving the head provided on part of the FPC. INDUSTRIAL APPLICABILITY As described above, according to the present invention, because the leaf spring and the pressing plate for wholly pressing the leaf spring are provided, the resilience may be applied to the thermal head with a homogeneous pressure. Further, because the head-up lever is provided at one end of the rotational shaft of the pressing plate to release the resilience of the leaf spring, to coercively cause the thermal head to head up and to turn on/off the head-up switch by part of the head-up lever, the printer which has the very simple structure, whose assembling efficiency is improved and whose printing quality is stable may be realized.

Claims: A line thermal printer, comprising: a frame (1); a platen (5) provided with a rotation transmission mechanism at one end thereof and turnably supported by said frame; a line thermal head (6) turnably pivoted on said frame and pressed to said platen to record printing data to a recording sheet (15) pinched between it and said platen; a pressing plate (4) turnably pivoted on said frame and provided with a head-up lever (10) fixed at one end of a rotational shaft thereof; a leaf spring (7) disposed between said pressing plate and said thermal head for applying a resilience for resiliently pressing said thermal head to said platen by a pressure of said pressing plate; a motor (14) for turning said platen adequately via said rotation transmission mechanism of said platen; and a head-up switch (18), and wherein the resilience of said leaf spring does not act on said frame, said pressing plate and said thermal head when the pressing stress of said pressing plate to said leaf spring is released, characterised in that : said pressing plate is turned up via said head-up lever; a cam (10a) is formed on part of said head-up lever provided at one end of the rotational centre shaft of said pressing plate and that when said head-up lever is turned, said cam engages with part of said thermal head, thus releasing said thermal head from said platen by the engaging portion thereof; and said leaf spring is positioned by and supported on pins (13) formed on said frame so as to permit freedom of movement of said leaf spring in relation to the pins. The line thermal printer according to claim 1, characterised in that said pressing plate has a rotational centre shaft (3) turnably pivoted on said frame and that a press-contact portion of said leaf spring formed eccentrically to said shaft is formed in parallel along the length of said leaf spring. The line thermal printer according to claim 1, characterised in that the cam of said head-up lever contacts with a head-up switch provided near said head-up lever, thus indicating a head-down state in which said thermal head is pressed to and contacts with said platen and printing is enabled, and said cam is disconnected from said head-up switch, indicating that it has turned to a head-up state, when said head-up lever is turned and the pressure of said thermal head to said platen is released. The line thermal printer according to claim 1, characterised in that said leaf spring resiliently presses said thermal head to said platen by own resilience when it is pressed by a leaf spring pressing portion (4a) of said pressing plate. The line thermal printer according to claim 4, characterised in that a plurality of cutaway portions are formed on a whole contact portion of said leaf spring in the longitudinal direction which contacts with said thermal head in order to apply a homogeneous resilience to said thermal head. The line thermal printer according to claim 1, characterised in that a frame for pressing a flexible printed board connected to said thermal head is formed on part of said frame.

Inventors: IMAI SABURO, TAKEUCHI KIYOKAZU, IMAI, SABURO, TAKEUCHI, KIYOKAZU, IMAI, Saburo, Seiko Instruments Inc., TAKEUCHI, Kiyokazu, Seiko Instruments Inc.
Applicants: SEIKO INSTR INC, SEIKO INSTRUMENTS INC.
Application year: 1996
Main classification: B41J25
IPC codes: B41J2, B41J25