Stationary thermal printer for using detachable cassette

Abstract: The present invention provides an improved printer head (2) for using a detachable cassette (A), particularly the printer head stationary mounted on a print station for using a detachably loadable cassette on the station, the cassette integrally having an webbed label together with a platen roller (5) therein. In prior art, however, a conventional printer head is disadvantageous that an webbed label is often broken during the replacement of the cassette due to the absence of suitable locking mechanism to refuge the printer head from a platen roller so as to facilitate and ensure the safe replacement of webbed label when the cassette is replaced. In order to solve such disadvantages, the present invention provides an improved printer head (2) capable of constantly being held at a position apart from a platen roller (5) to refuge in the upper portion as far as no cassette (A) is loaded on the print station. The locking mechanism is released by manually operating a lever (23'), however, even if the manual lever (23') is operated contrary toward wrong direction due to the user's mis-operation, however, the printer head (2) of the present invention will return to a correct direction automatically in response to the absence of the platen roller (5) under the printer head.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stationary thermal printer including a detachable cassette, which cassette a web to be printed and platen against which printing takes place. 2. Description of the Prior Art Japanese Utility Model Provisional Publication No Sho 63-107905 discloses a label printer in which the print work is performed by pressing a thermal print head, onto a platen roller, the thermal head being biased by an elastic member which presses it against the platen roller. It also includes a detachable cassette which embodies the platen roller and also houses the web to be printed. The web may be a web of labels or a printed form. In this conventional printer, when the label cassette (59) is detached from the printer the thermal head is moved away from the platen roller by manually operating a lever. When the cassette is again attached to the printer an end of the web in the cassette is fed into a gap between the thermal head and platen roller. In this arrangement, it is disadvantageous that the web is often broken by it touching the thermal head (which has sharp corners), or the thermal head is damaged by impacting of the cassette against the thermal head during the attachment of the cassette. Also although the thermal head is retracted manually from a lower position to an upper position when the cassette is detached, it may return to the lower position before the cassette attached causing troubles during the replacement work of the cassette. THE INVENTION AND ITS OBJECTIVES It is a general object of the present invention to provide an improved thermal head capable of constantly being held at a position spaced from a platen as the cassette is loaded onto the printer for preventing the print web and thermal from accidental tear damage. It is a more specific object of the present invention to provide an improved thermal head comprising an oprational member provided for selecting alternate positions for the thermal head manely a first position in which the thermal head presses against the platen and a second position in which the thermal head is spaced from the platen; the operational member further being movable by an elastic member in a direction almost at right angles to the direction in which the thermal head is biassed towards the platen; and a means is provided to forceably hold the thermal head at the first position while resisting the bias of the said elastic member and to release the holding action when said holding force does not act. It is another object of the present invention to provide an improved thermal head wherein the operational member consists of a slidable cam plate arranged on a support place of the thermal head, the cam plate having a cam including a first holding section which determines the first position and a second holding section which determines the second position and a cam follower connected with said support plate is engaged with the cam, the cam follower being alternatively positioned between the two holding sections by slidably moving the cam plate, and the first holding section is recessed along the upper edge thereof so that when the cam follower is in the first holding section and is forced against said recessed edge by the biasing force which urges the thermal head against the platen. According to the present invention there is provided a thermal printer of the type comprising a) a detachable cassette (A) which contains the material in web form to be printed, and a platen against which printing takes place; b) a thermal print assembly movably mounted on a printer body and comprising a thermal head adapted to be pressed to the print web and against the platen a support on which the thermal head is movably mounted and a first elastic member acting between the thermal head and the support to urge the thermal head towards the platen; and c) a movable operating member connected to move the thermal print being movable when a cassette is traded on the printer assembly, said operating member between a first position in which the thermal head presses against the platen and a second position in which the thermal head is spaced from the platen, characterised in that a second elastic member is provided biasing the operating member to the second position, and the operating member is connected to the thermal print assembly by means of a coupling arrangement by which the stored energy is the first elastic member when it presses on the platen by reaction on the said coupling arrangement prevents the second elastic member from moving the operating member to the second position, and when the cassette is removed, the release of energy leads to a reduction of the reaction on said coupling arrangement and the second elastic member moves operating member to the second position and keeps it there until the operating member is positively moved against the action of the second elastic member back to the first position. Thus, when the cassette is loaded on the printer, the thermal head can print predetermined data or pattern on the print web whilst the operating member is in the first position and the first elastic member acts to forceably resist the bias force of the second elastic member. In contrast, when the cassette is detached from the printer body, the reaction of the thermal head against the platen is removed and the operational member moves automatically to the second position so that the thermal head is moved away from the position in which it acts against the platen. If the operational member is moved towards the first position due to a user's mistake, when the member is released it will make the automatically return to the second position automatically as long as there is no platen under the thermal head. With the present invention, therefore, the advantage that the platen of a detachable cassette and a stationary thermal head are kept apart when loading the cassette is achieved as the thermal head is always held at the second position when there is no cassette in the printer, which prevents the thermal head from accidentally contacting the print web or platen and damage thereto is avoided. An embodiment of the invention will now be described by way of example, with reference to the accompanying drawings, wherein:- Fig. 1 is a side view illustrating a print section of a thermal printer according to the invention, the view being a section on line I - I of Fig. 2; Fig. 2 is a front view illustrating a vertical section on line II - II of Fig. 1; Fig. 3 is a plan view illustrating a transverse cross section on line III - III of Fig. 1; Fig. 4 and Fig. 5 are sectional side elevations for explaining the operation of the print section of Fig. 1; and Fig. 6 is a side view illustrating the whole printer including a cassette. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in detail to the embodiment of the present invention shown in the drawings, in Figs 1 to 3, reference numberal (1) denotes a base plate mounted of a printer body, reference numeral (2) denotes a thermal head of a thermal printer assembly mounted on the base plate (1) by means of a head support plate (3) of the assembly. The numerals (4) and (4') denote side plates of cassette (A). The cassette (A) is detachably mounted on the base plate (1) so that a platen roller (5) thereof extends between the ends of the side plates (4) and (4'), to define a print section (6) at which the cooperative relative movements of the thermal head (2) and the platen roller (5) take place. The base plate (1) provides a pivot (7) on which the head support plate (3) is pivoted to enable the said assembly to swing up and down. The head support plate (3) has an inverted U-shape provided by bending the sides of the plate (3) downwardly. The bent-down sides (3b) and (3b') bearings provide bearings at the rear thereof by which the support plate (3) is pivoted on the pivot (7) to enable said up and down swinging to take place. The thermal head (2) is connected to the head support plate (3) by a head fixing plate (8). The head support plate (3) includes a pair of bearing brackets (9) and (9') which project upright and are positioned almost centrally of the upper surface of the head support plate (3). A cam follower (10) passes through the bearing brackets (9) and (9') and is in the form of a pivot pin and the plate (3) additionally has a pair of adjusting screws (11) and (11') at the front end portion of the upper surface of the head support plate (3). As shown in Fig. 2, the thermal head (2) is mounted on stepped sides of the fixing plate (8) the head fixing plate (8) also having at, the rear side portions a pair of upwardly bent bearing brackets (8a) and (8a'), and also an upwardly bent bearing bracket (8b) centrally thereof. The pair of bearing brackets (8a) and (8a') and also (8b) extend vertically and have bores which receive a pivot pin (12). The ends of the pivot pin (12) are fixed to the both bearing sides (3b) and (3b') of the head support plate (3) approximately centrally of the bearing sides (3b) and (3b'), which results in that the head fixing plate (8) and therefore the head (2) can pivot on the pivot pin (12) between the both bearing sides (3b) and (3b'). The head fixing plate (8) carries an L-shaped bracket (13) on the upper surface and in the central region thereof, the bracket 13 having a pair of legs to which are fixed a pair of stopper screws (15) and (15') so that the pair of stopper screws (15) and (15') lie above the head support plate (3) in that said legs pass through a slit (14) in the top of the head support plate (3). These stopper screws (15) and (15') serve to restrict the rotation of the head fixing plate (8) relative to the plate (3) in a counter clockwise direction to no greater than a predetermined angle. Further, adjusting screws (11) and (11') of the plate (8) are provided and a pair of coil springs (16) and (16') (forming a first elastic member). These springs lie to the underside of the head fixing plate (8) and press the thermal head (2) onto the platen roller (5) with a predetermined pressure. The base plate (1) carries two spaced mounting pins (20) and (20') which extend horizontally above the upper portion of the head support plate (3). As shown in Fig. 3, a first guide plate (21) extends between the fixing members (20) and (20'), and a second guide plate (21') is fixed to the plate (21) so as to lie parallel with the first guide plate (21) but is spaced therefrom by means of washers or other spacers (22) and (22') and a cam plate (23) lies in the gap between the guide plates (21) and (21'), so as to be slidable therebetween. The cam plate (23) (the operational member) is slidably movable between the plates (21) and (21') towards and away from the members (20) and (20') and the cam plate (23) has a lever (23') which as illustrated in Fig. 2 has an L-shape. The lever (23') is formed by partially bending a portion of the cam plate (23) and of the plane of the cam plate (23). The cam plate (23) is of stepped shape in side view, and has three slots namely cam slot (24) of doglegged shape which is located centrally of the plate (23) and second and thirdly a pair of guide slots (25), (26) which extend horizontally and are located at the respective ends of the cam plate (23) on opposite sides of cam slot (24). The cam slot (24) defines two portions namely a lower end portion called herein is "the first holding section" (24a) which receives the cam follower (10) (which is engaged in slot 24) at "the first position " of the head support plate (3), and an upper end portion called herein "the second holding section" (24b) which receives the cam follower (10) at "the second position" of the head support plate (3). The cam guide slit (24) suspends the head support plate (3) through the pair of bearing brackets (9) and (9') and the cam follower (10) so that for example if the cam plate (23) is moved back and forth by manual operation of the lever (23) the print assembly will be pivoted up and down on pivot pin 7. In Fig. 1, in order to ensure that the cam follower (10) can move up and down as said pivoting takes place holes (19) and (19') are provided centrally of the respective guide plates (21) and (21'). Again referring to the cam guid slot (24), the first holding section (24a) and the second holding section (24b) are of substantially equal width which is almost the same as the diameter of the cam follower (10) to ensure the effective and smooth guiding of cam follower (10) between the both holding sections. There is a corner projection (27) at the corner formed between the first holding section (24a) and an upward sloping portion leading to the second holding section (24b) and also the upper edge of the first holding section (24a) is fomred to curve slightly upwardly or lightly recessed to receive the cam follower (10) for a purpose to be explained hereinafter. The guide plates (21) and (21') are connected by a pair of guide pins (28) and (29) which pass through the guide slots (25) and (26) of the cam plate (23) to ensure that the cam plate (23) moves horizontally as it moves between the both first and second positions which are respectively illustrated in Fig. 5 and in Fig. 4. The tension coil spring (30) (the second elastic member) is tensioned between the fixing member (20') and the lever (23') of the cam plate (23) as illustrated in Fig. 1 and Fig. 3, so that the cam plate (23) is constantly biased to the direction of the fixing member (20') [i.e. to the rear direction]. Therefore, as illustrated in Fig. 4, when the cam plate (23) is moved manually by as the second or rear position the cam follower (10) is then positioned in the second holding section (24b) of the cam guide slot (24), and the front assembly is held in the position shown due to the tensile bias of the coil spring (30). On the other hand, as shown, in Fig. 5, when the cam plate (23) is moved to the forward position, the front assembly is pivoted downwards about pin 7 and, if the cassette (A) in position the head 2 is pressed by elastic members 16 onto platen (5) (as shown in Fig. 1) which sets up the storage of energy in springs 16 in turn causing a reaction between the cam follower (10) and the top side of cam slot (24) or section (24a). Due to the fact that the cam follower in this position seats in the recessed upper edge of cam slot section (24b) and due to the friction caused by this spring loaded reaction, the tensile force applied by spring (3) is unable to pull the cam plate (23) to the rearward position, and the mechanism remains locked until the compression of springs 16 is removed, for example by removing the cassette (A). Movement of the mechanism from the Fig. 5 to the Fig. 4 position can be effected manually by movement of plate (23) using lever (23') or by removing the cassette (A) and its platen (5). The latter causes relief of the stored energy in the coil springs (16) removing the reaction between the cam follower (10) and the first holding section (24a) and easily gets over the corner projection (27) of the first holding section (24a) so that spring (30) can easily pull plate (23) so that follower (10) passes the corner (27) of also (24) and the mechanism moves to the Fig. 4 position. Fig. 6 is a general view which illustrates the cassette (A) loaded in position (1). A pair of cassette supporting pins (18) and (18) project from the upper postion of the base plate (1) and are received in apertures (36),(36) of the cassette (A), and a main drive roller (31) and an idle roller (31') are arranged as a roller nip pair at the lower portion of the base plate (1). The main drive roller (31) is driven by a stepping motor mounted on the reverse side of the base plate (1) [not shown in the drawings], and the idle roller (31') is operable by a release lever (33) pivotally mounted on a pivot pin (32) whereby the idle roller (31') can be moved upwardly and away the main drive roller (31) by manually pushing the release lever (33) in a counter clockwise direction. The sides of the cassette (A) are defined by the walls (4) and (4') and a viewing window (34) is provided in the side wall (4). A label detector (35) is arranged in the cassette (A) so that it can be seen through the window (34). To provide engagement of the cassette (A) with the base plate (1), the side wall (4) has said fixing holes (36) and (36) in the upper corner portions of the side wall (4) and additionally, the release lever (33) operates a base plate engaging lock device by means of a linkage when the release lever (33) is operated. [not shown in the drawings] The side wall (4) also carries a reel shaft (37) in the upper portion for supporting a label reel (38') from which a label tape (38) is unwound in use. The label tape (38) consists of a release base sheet carrying plurality of labels which are adhered thereto by an adhesive on the reverse side of the labels. The labels are evenly spaced on the release base sheet. The side wall (4) also carries base sheet recovery reel (39) and an idler guide roller (40). The shaft of base sheet recovery reel (39) is driven by a geared motor through a suitable coupling device arranged at the reverse side of the base plate (1). As also shown in Fig. 6, the cassette (A) has another group of idler guide rollers (41), (41') and (41'') arranged along the bottom edge of the cassette (A) in which lie between the side wall (4) and the opposed side wall (4'), and in addition, the platen roller (5) is arranged at the leftmost end of the bottom line of the cassette (A) and there a dispenser (42) is also arranged at just ahead of the platen roller (5). The dispenser (6) enables the separation of printed labels one by one from the base sheet. A further locking mechanism for locking the cassette (A) to the base plate (1) is provided and comprises projection (45) of the head support plate (3) and a slot (44) in a base part (43) of the cassette (A). Thus as described previously in relation to Fig. 2, the head support plate (3) consists of a flat plate portion, and side walls, (3b) and (3b'). The projection (45) is integral with wall (3b) and projects below the bottom edge of the wall (3b) as illustrated in Fig. 1 and Fig. 2. On the other hand, the slit (44) is provided in the upper surface of the base part (43) to receive the projection (45) when the mechanism is in the Fig. 5 position. The base part (43) is formed as a reverse C-shape when viewed as in Fig. 2, and under the projection (45) of the bearing surface (3b) as illustrated in Fig. 1 and Fig. 2. When the cassette (A) is loaded on the base plate (1) and the mechanism is moved to the Fig. 5 position, the projection is squeezed into the slit (44) and simultaneously the platen roller (5) is pressed against the thermal head (2). This engagement is advantageous that it can improve not only the accuracy of print capability of the thermal head (2) but also can prevent the thermal head (2) from any damage caused by careless operation since it is mechanically impossible to remove the cassette (A) as long as the platen roller (5) and thermal head (2) are pushed together even if the printer is carelessly operated by the operator. In use, the label tape (38) is fed from the label web (38') over the guide roller (40), through the label detector (35), and over the guide roller (41) to the print section, and after the separation of the label from the base sheet (38a) by using the despenser (42), the base sheet (38a) passes over rollers (41')(42'') is fed by the nib rollers (31)(31') and finnaly is wound on take up reel (39). When the cassette (A) is to be unloaded from the base plate (1), firstly the release lever (33) is manually rotated counter-clockwise so that the idle roller (31') is spaced the main drive roller (31), to release the drive engagement of the tape by the rollers (31) and (31'). At the same time, the lock device associated with the release level (33) [not shown in the drawings] is also released releasing the further engagement between the cassette side and the base plate side. Next, the cam plate (23) is manually moved rearward by the cam lever (23') so that the cam follower (10) is moved to the second holding section (24b) which causes as explained herein the thermal head (2) to withdraw from the platen roller (5), and the projection (45) of the head support plate (3) to be released from the engage slit (44) of the base part (43). The cassette (A) can now be unloaded from the base plate (1). A summary of the operation apparatus will now be given with particular reference to the movement of the thermal head (2) when a cassette (A) is carried by the plate base (1). Fig. 1 illustrates that the cam follower (10) is in the first holding section (24a) of the cam plate (23) and a cassette (A) is loaded on the base plate (1). In this state, the thermal head (2) enables the printing predetermined data on the labels. Movement of the cam plate (23) by the tensile coil spring (30) is resisted since the cam follower (10) is forced against the arc shaped recess of the first holding section (24a) by the energy stored in coil spring (16). Fig. 4 illustrates that, when the cassette (A) is to be unloaded from the base plate (1) as described previously, the cam plate (23) is moved rearwardly and manually by operating the cam lever (23') which positions the cam follower (10) at the second holding section (24b) the cam follower (10) moving upwardly and along the cam surface (24') during this movement. With the upward movement of the cam follower (10) along the cam surface (24'), the head support plate (3) is slightly rotated clockwise on the pivot (7), and the stop screws (15) and (15) of the head fixing plate (8) are lifted upwardly by the head support plate (3) and through the brackets (13) the thermal head (2) is made to rotate clockwise on pivot (12) causing the thermal head (2) lift from the platen roller (5) and the cassette can be unloaded. Accordingly, the cassette (A) can be loaded on or unloaded from the base plate (1) when the mechanism is in the position of Fig. 4, and this position is maintained by the tensile bias of the coil spring (30), whereby there is no danger of knocking the thermal head (2) against the platen roller (5) or the label tape (38) during loading or unloading of the reel (A). If the cam plate (23) is placed in the first position, due to an erroneous operation of cam lever (23') when there is no cassette (A) on the base plate (1), as shown in Fig. 5, as soon as the cam plate lever (23') is released, the mechanism will automatically return to the Fig. 4 position, due to the tensile bias of the coil spring (30) and the absence of any counter bias from the coil spring (16). The present device ensures that thermal head (2) is always kept at the upper position when there is no cassette (A) on the base plate (1) and there are no additional external influences. As to the structure of the cam plate (23), it is not limited to that described and any other suitable arrangement may optionally be adopted. The invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description.

Claims: A thermal printer of the type comprising a) a detachable cassette (A) which contains the material in web form (38a) to be printed, and a platen (5) against which printing takes place; b) a thermal print assembly movably mounted on a printer body (1) and comprising a thermal head (2) adapted to be pressed to the print web (38a) and against the platen (5), a support (3) in which the thermal head is movably mounted and a first elastic member (16) acting between the thermal head (2) and the support (3) to urge the thermal head (2) towards the platen (5); and c) a movable operating member (23) connected to move the thermal print assembly, said operating member (23) being movable when a cassette is traded on the printer between a first position in which the thermal head (2) presses against the platen (5) and a second position in which the thermal head (2) is spaced from the platen (5), characterised in that a second elastic member (30) is provided biasing the operating member (23) to the second position, and the operating member (23) is connected to the thermal print assembly by means of a coupling arrangement (10,24) by which the stored energy in the first elastic member (16) when it presses on the platen (5) by reaction on the said coupling arrangement (10,24) prevents the second elastic member (30) from moving the operating member (23) to the second position, and when the cassette (A) is removed, the release of energy leads to a reduction of the reaction on said coupling arrangement (10,24) and the second elastic member (30) moves the operating member (23) to the second position and keeps it there until the operating member (23) is positively moved against the action of the second elastic member (30) back to the first position. A thermal printer according to claim 1, characterised in that the said first elastic member (16) acts in a direction which is substantially at right angles to the direction in which the second elastic member (30) acts. A thermal printer according to claim 1 or 2, characterised in that the operating member (23) is mounted for linear sliding movement between said first and second positions. A thermal printer according to claim 3 characterised in that said coupling arrangement (10,24) comprises a cam slot (24) in said operating member (23) and a cam follower (10) on said thermal print assembly, said thermal print assembly being mounted for pivotal movement on the printer body (1) and the cam slot (24) having a first portion (24a) lying in the direction of sliding movement of the operating member and a second portion (24b) offset from the first portion (24a) and connected thereto by an inclined portion so that as the cam follower (10) moves along the inclined portion the thermal print assembly pivots on the body (1) to move the thermal print head (2) away from the platen (5) releasing the energy in the first elastic member (16). A thermal printer according to claim 4 characterised in that the said reaction of the first elastic member to prevent the operating member (23) from moving to the second position is through said cam follower (10) reacting against a side of said cam slot (24) in the first portion (24a) and said side of said side of said slot (24) is recessed to enable the cam follower (10) to lock therein when under said reaction. A thermal printer according to claim 4 or 5, characterised in that said cam follower (10) comprises a pin (10) passing through said cam slot (24) and being supported at its ends in bearing brackets (9,9') carried by said support (3). A thermal printer according to any preceding claims, characterised in that the operating member (23) is movable located between a pair of guide plates (21,21'), said plates (21,21') being carried by the printer body (1) and said operating member (23) has a manually operable arm (23') for moving the operating member (23). A thermal printer according to claim 7, characterised in that said second elastic member (30) is tensioned between said manually operable arm (23') and one said body (1). A thermal printer according to any one of the preceding claims, characterised in that the thermal head (2) is pivotally mounted on the support.

Inventors: SEYASU SHIRO, SEYASU, SHIRO
Applicants: TERAOKA SEIKO KK, TERAOKA SEIKO CO., LTD.
Application year: 1991
Main classification: B41J2
IPC codes: B65C9, B41J25, E04D1, B41J2