Thermal print head mounting

Abstract: A printer is provided which comprises a frame (1) having rightside and leftside walls separated from each other by a distance equal to the width of a recording medium. A platen (2) is rotatably mounted between both of the side walls, and a printing head (5) is mounted between the side walls such that it faces the platen (2). The printer further comprises a pressure member (7,8,9) rotatably assembled into the frame (1) and adapted to bring the printing head (5) into pressure contact with the platen (2) and a head unit pressure lever (3) rotatably assembled in the frame (1) and adapted to retain the pressure member at a predetermined position by engaging it. With the above structure, the pressure member is fixedly supported by the head unit pressure lever (3) at a predetermined position on the frame (1) at which it compresses the printing head (5) so that the printing head (5) is brought into pressure contact with the platen due to the resilient force of the pressure member.

Description: The present invention relates to a printer provided with a platen and a printing head and more particularly to a printing head support structure. One example of a known printer provided with a platen and a printing head is shown in Figures 4 and 5 of the accompanying drawings. The printer is provided with a platen 2 rotatably mounted along the direction of the width of a recording medium (not shown). The printer is also provided with a head unit 14 having a printing head 5 which is so arranged as to come into pressure contact with the platen 2. Further, the printing head 5 is provided with a pressure member which is integrally attached to the rear surface of the printing head by screws or the like and which causes the printing head to come into pressure contact with the platen 2. The pressure member comprises a resilient member 7 and a head unit pressure plate 8, which are arranged such that the resilient member 7 is interposed between the head unit pressure plate 8 and the head unit 14 so that the pressure member expands and contracts elastically within a predetermined clearance between the two. As a result, when the printing head 5, integrally fixed to the head unit pressure plate 8, is assembled into the predetermined position in the printer together with the pressure member and fixed to the frame 1, the printing head 5 comes into contact with the platen 2 facing the printing head 5 with a predetermined pressure contacting force. In such prior art, as that shown in Figures 4 and 5, the printing head 5 is integrally supported by the head unit pressure plate 8 of the pressure member through the head unit 14 and when the printing head 5 is brought into pressure contact with the platen 2 by the action of the resilient member 7 provided on the pressure member, the resilient member 7 applies a uniform energizing force to the printing head so as to absorb a one-sided or biased contact. However, it has been usual with the above prior art example that, since the pressure member formed integral with the printing head 5 is fixedly supported on the printer body toward one end thereof by a fixing means such as screws 13, when the printing head 5 is replaced with a new one, the troublesome operation of removing the screws is necessary. Further, where it is required to provide a large opening at the pressure contact portion between the platen 2 and the printing head 5 at the time of replacing the printing head 5 with a new one or removing clogged paper, there have been problems that an extremely troublesome operation using tools is required for providing the opening. Consequently, the user of the printer must be skilful at handling the printer and it takes much time for performing the operation. Document JP-A-1 8055 discloses an arrangement for improving print quality and prolonging the life of the thermal head. The thermal head is brought under pressure into contact with a platen by means of a leaf spring fixed to the head that is pressurised by a cam. In view of the above-described prior art problems, an object of the present invention is to provide a printer that has a favourable fabricability allowing easy removal of the printing head. According to one aspect of the present invention, there is provided a printer comprising: a platen; a frame; a printing head for contacting the platen, the head being pivotable between a position in which it is in contact with the platen and a position in which it is free to be withdrawn from the printer; pressure applying means for urging the print head into contact with the platen; and a pressure lever movable between a pressure means retaining position and a pressure means release position, wherein, when in the pressure means retaining position the pressure lever engages with the pressure applying means to apply pressure to the printing head and thus bring the printing head into pressure contact with the platen; and characterised in that: the print head and pressure applying means are independently pivoted to the frame, the pressure applying means being pivotable between a position in which it urges the head into contact with the platen and a position in which it does not apply pressure to the head. According to another aspect of the present invention, there is provided a printer provided with a frame having right and left side walls separated from each other by a distance equal to the width of a recording medium, a platen rotatably disposed between the side walls of the frame, a printing head disposed between said side walls and arranged face to face with said platen, pressure applying means rotatably assembled into said frame and adapted to bring said printing head into pressure contact with said platen; said printing head being pivotable between a position in which it is in contact with said platen and a position in which it is free to be withdrawn from said printer, and a head unit pressure lever rotatably assembled into said frame and adapted to retain said pressure applying means at a predetermined position by coming into engagement with said pressure applying means, wherein said pressure applying means is supported by said head unit pressure lever at the predetermined position at which said pressure applying means compresses said printing head so that said printing head is brought into pressure contact with said platen due to a resilient force of said pressure applying means; characterised in that said printing head and said pressure applying means are independently pivoted to said frame, said pressure applying means being pivotable between a position in which it urges said printing head into contact with said platen and a position in which it does not apply pressure to said printing head. The pressure means is preferably supported by a head unit comprising the printing head when the lever is in the pressure means retaining position. If one of the pressure means and the head unit comprises a plate and the other a convex spherical portion, which are arranged to contact at a point, the printer has the added advantage that pressure contact is uniform, and thus the quality of printing and rectilinearity of the recording medium is improved. Further, the pivotal arrangement of the head unit is advantageous in that it readily provides a large opening at the pressure contact portion between the platen and the printing head, for easy accessibility to the printing head. In order to achieve the above-described object, in a preferred embodiment of the present invention, there has been proposed the following measures, namely: The printer according to the present invention is provided, as a basic structure, with a frame, a platen, a printing head and a pressure member. The frame has rightside and leftside walls separated from each other by a distance equal to the width of a recording medium (not shown) and the platen is rotatably mounted between both of the side walls. Likewise, the printing head is mounted between the side walls and located adjacent the platen. The pressure member is assembled into the frame and brings the printing head into pressure contact with the platen. It is characteristic of this preferred embodiment of the present invention, that the printing head can tilt and float forward/rearward and right/left in correspondence to the position of the platen and the pressure member can come into point contact with the printing head so that at the time of printing, the printing head follows the pressure member so as to be brought into pressure contact with the platen. Further, between both of the side walls there is rotatably provided a head unit pressure lever having a head unit pressure shaft and by this head unit pressure lever, the head unit pressure plate is retained from behind the printing head which results in that the heat generating element of the printing head is elastically brought into pressure contact with the platen. In this preferred embodiment, the printing head and the pressure member are formed of different parts, respectively, which can be separably assembled. Further, either the printing head or a head unit pressure plate forming the pressure member is provided with a contact portion such as a convex spherical portion while the other is provided with a flat surface portion and the convex spherical portion and the flat surface portion come into point contact with each other. When the head unit pressure lever is turned toward the platen to separate the head pressure shaft from the head unit pressure plate, the pressure member is freed from the printing head and as a result, the pressure member is also freed from the compression force applied thereto by the pressure member thereby enabling the printing head to be removed from the printer main body. According to this preferred embodiment of the present invention, the printing head and the pressure member are independent of each other and the printing head can be assembled into the frame in such a manner that it is deposited from above so that the printing head replacement operation, such as the assembly and removal of the printing head with, and from, the printer becomes quite easily performed by operating the head unit pressure lever. Further, since the printing head can tilt and float right/left and forward/rearward in correspondence to the position of the platen, and the pressure member is in point contact with the printing head, the printing head is brought into pressure contact with the platen uniformly so that biased or one-sided contact of the printing head can be prevented and the quality of printing and the rectilinearity of the recording medium can be effectively improved. Embodiments of the present invention will now be described with reference to the accompanying drawings, of which: Figure 1 is a schematic side sectional view of the basic structure of a printer according to an embodiment of the present invention; Figure 2 is a schematic side sectional view of the basic structure of the printer of the embodiment of the present invention, showing a pressure member freed from its restricted state by a head unit pressure lever; Figure 3 is a top view of the structure shown in Figure 1; Figure 4 is a schematic sectional view of the general structure of a conventional printer; and Figure 5 is a top view of the general structure of the conventional printer shown in Figure 4. The printer shown in Figure 1 is basically provided with a frame 1, a platen 2, a printing head 5, a pressure member comprising a first head unit pressure plate 9 and a second head unit pressure plate 8, and a head unit pressure lever 3 for retaining the pressure member at a predetermined position on the frame 1 for bringing the printing head 5 into pressure contact with the platen 2. The frame 1 has rightside and leftside walls separated from each other by a distance equal to the width of a recording medium (not shown). The platen 2 is rotatably mounted between both of the side walls of the frame 1. In particular, the platen 2 is provided with a tubular resilient member 2a made of rubber or the like and a rotary shaft 2b passing through the centre of the resilient member with both ends of the rotary shaft 2b being supported by the rightside and leftside walls of the frame 1. Like the platen 2, the printing head 5 is also mounted between the rightside and leftside walls of the frame 1 at a position adjacent the platen 2. The printing head 5 is provided with a heat radiating plate 6 having a thermosensitive element (not shown) mounted thereon and a pair of pins 6b and 6c located one on each side of the head radiating plate 6. The head radiating plate 6 and the pair of pins 6b and 6c may be formed integrally, using a material such as aluminium, and the pins 6b and 6c are respectively inserted into grooves 1a and 1b formed on both side walls of the frame. The pressure member is assembled into the frame 1 to rotate about a pressure member support shaft 9a passing through the frame 1. At the same time, the pressure member is so positioned as to bring the printing head 5 into pressure contact with the platen 2 by means of the head unit pressure lever 5 rotatably provided between the side walls of the frame 1 through the head unit pressure lever 3. The pressure member is formed of the first head unit pressure plate 9, the second unit pressure plate 8 and the spring 7. The first pressure plate 9 and the second pressure plate 8 can elastically expand and contract within a predetermined clearance due to the elastic force of the spring 7 and are rotatably retained by the pressure member support shaft 9a with respect to the frame 1. The spring 7 forming part of the pressure member generates a resilient pressure force for compressing the printing head 5 to integrally retain the heat radiating plate 6 via the head unit pressure plate 9 against the platen 2. In this case, the flat surface portion of the first head unit pressure plate 9 on the side of the head radiating plate comes into point contact with the convex spherical portion 6a formed on the heat radiating plate 6 and as a result, the head radiating plate 6 tilts and floats forward/rearward and right/left with respect to the platen 2 to thereby bring the heat sensitive element on the printing head 5 into pressure contact with the platen 2. Further, the head unit pressure lever 3 comprises a head unit pressure shaft 4 having a width substantially equal to the width of the above-mentioned pressure member and head unit pressure shaft support members 3a and 3b rotatably supported by both side walls of the frame. More concretely, the head radiating plate 6, integral with the printing head 5, is held in engagement with the grooves 1a and 1b on both side walls of the frame 1 through the pair of pins 6b and 6c and then the pressure member is turned to a position at which it comes into contact with the heat radiating plate 6. After that, the above-mentioned head unit pressure lever 3 is turned to a predetermined position in the same direction so that the head unit pressure shaft 4 fixedly supports the pressure member on the frame 1 while the pressure member causes the printing head 5 to elastically contact the platen 2 via the spring 7. Further, a data printing signal is transmitted to the printing head 5 through an FPC 10, which is held by the heat radiating plate 6 through a FPC fixing plate 11. It is a characteristic of the present invention, that the pressure member which elastically compresses the printing head is retained at a predetermined position by means of the head unit pressure lever 3 so that when the pressure lever 3 is released from its pressure member retaining position, the pressure member also releases itself from the printing head and as a result, the printing head 5 including the heat radiating plate 6 can be removed freely from the grooves 1a and 1b of the frame 1 with the printing head 5 in engagement. Further, the printing head 5 is in engagement with both side walls of the frame 1 through the pair of pins 6b and 6c, respectively, and is capable of tilting and floating forward/rearward and right/left in correspondence to the position of the platen 2. On the other hand, the pressure member is in point contact with the convex spherical portion 6a of the heat radiating plate 6 of the printing head 5 so that when a printing operation is performed, the printing head 5 follows the rotation of the platen 2 so as to make pressure contact with the head unit pressure shaft 4 uniformly. The printing head 5 and the pressure member are formed of separate parts which can be assembled together. As described above, according to the preferred embodiment of the present invention, since the head unit pressure lever is rotatably provided with respect to the frame 1, the pressure member rotatably provided on the frame can be retained at a predetermined position by the head unit pressure lever and the pressure contact of the pressure member with the printing head can be easily released by the rotation of the head unit pressure lever. As a result, the printing head can be freely assembled or replaced with a new one with respect to the frame without using any particular tool, thereby simplifying the structure of the printer. Further, since the pressure applying portion with respect to the printing head is a point, the printing head tilts and floats forward/rearward and right/left and consequently the platen and the printing head are uniformly held in pressure contact with each other. Therefore, the present invention is also effective in improving the quality of printing and the rectilinearity of the recording medium. The aforegoing description has been given by way of example only and it will be appreciated by a person skilled in the art that modifications can be made without departing from the scope of the present invention.

Claims: A printer comprising: a platen (2); a frame (1); a printing head (5) for contacting the platen (2), the head being pivotable between a position in which it is in contact with the platen and a position in which it is free to be withdrawn from the printer; pressure applying means (7,8,9) for urging the print head (5) into contact with the platen (2); and a pressure lever (3) movable between a pressure means retaining position and a pressure means release position, wherein, when in the pressure means retaining position the pressure lever (3) engages with the pressure applying means (7,8,9) to apply pressure to the printing head (5) and thus bring the printing head (5) into pressure contact with the platen (2); and characterised in that: the print head (5) and pressure applying means (7,8,9) are independently pivoted to the frame, the pressure applying means being pivotable between a position in which it urges the head into contact with the platen and a position in which it does not apply pressure to the head. A printer as claimed in claim 1 arranged such that the pressure applying means (7,8,9) is fixedly supported by a head unit (5,6) comprising the printing head (5) when the pressure lever (3) is in the pressure means retaining position. A printer as claimed in claim 2, wherein the pressure applying means (7,8,9) is supported at a point of contact between a plate (9) of the pressure means (7,8,9) and a convex spherical portion (6a) of the head unit (5,6). A printer as claimed in any preceding claim, wherein the pressure lever (3) is arranged to rotate towards the platen (2) when the pressure applying means (7,8,9) is to be retained and away from the platen (2) when the pressure applying means (7,8,9) is to be released. A printer as claimed in any preceding claim, wherein the pressure applying means (7,8,9) is arranged to rotate towards the platen (2) when engaged by the pressure lever (3). A printer as claimed in any of claims 2 to 5, wherein the head unit (5,6) is arranged to pivot towards and away from the platen (2) in accordance with movement of the pressure applying means (7,8,9). A printer as claimed in any preceding claim, wherein the pressure applying means (7,8,9) comprises two plates (8,9) and a resilient member (7) therebetween. A printer provided with a frame (1) having right and left side walls separated from each other by a distance equal to the width of a recording medium, a platen (2) rotatably disposed between the side walls of the frame, a printing head (5) disposed between said side walls and arranged face to face with said platen, pressure applying means (7,8,9) rotatably assembled into said frame and adapted to bring said printing head into pressure contact with said platen; said printing head being pivotable between a position in which it is in contact with said platen and a position in which it is free to be withdrawn from said printer, and a head unit pressure lever (3) rotatably assembled into said frame and adapted to retain said pressure applying means at a predetermined position by coming into engagement with said pressure applying means, wherein said pressure applying means is supported by said head unit pressure lever at the predetermined position at which said pressure applying means compresses said printing head so that said printing head is brought into pressure contact with said platen due to a resilient force of said pressure applying means; characterised in that said printing head (5) and said pressure applying means (7, 8, 9) are independently pivoted to said frame (1), said pressure applying means being pivotable between a position in which it urges said printing head into contact with said platen (2) and a position in which it does not apply pressure to said printing head. A printer as claimed in any preceding claim wherein the printing head (5) and pressure applying means (7,8,9) are separate from each other and the printing head (5) is capable of being disassembled from said frame after the printing head (5) is released from the pressure applied by said pressure applying means (7,8,9). A printer as claimed in any preceding claim, wherein the pressure lever (3) has a head unit pressure shaft (4) which compresses and supports the pressure applying means (7,8,9).

Inventors: KANAI MASASHI, KANAI, MASASHI
Applicants: SEIKO INSTR INC, SEIKO INSTRUMENTS INC.
Application year: 1995
Main classification: B41J25
IPC codes: B41J25