Image forming apparatus and thermal transfer printer

The image forming apparatus has a frame, a head portion pivotably supported on the frame, a platen roller supported on the frame opposite the head portion, an elastic support rod supported on the frame, a rotary member pivotably supported by the support rod and having a pressing member, and a drive mechanism engaged with the rotary member to pivot the rotary member around the support rod. The pressing member presses the head portion against the platen roller with the urging force of the support rod. The image forming apparatus is structured with members that are easy to manufacture.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus and a thermal transfer printer. More specifically, the present invention relates to an image forming apparatus and a thermal transfer printer equipped with a printing head for performing printing.

2. Background Information

An image forming apparatus equipped with a thermal head or other such printing head has been known. For example, Japanese Patent Application Publication 5-85012 discloses such arrangement.

Japanese Patent Application Publication 5-85012 discloses a head pressing apparatus for a thermal printer, which includes a torsion bar having ends that are bent at right angles in opposite directions. The torsion bar is disposed at the top of a thermal head, and the bent ends of the torsion bar are pressed during printing. Therefore, the pressing forces applied to the bent ends of the torsion bar are transmitted to the thermal head in a balanced manner through the torsion bar, which suppresses the difference in the pressing force in the width direction of the thermal head.

Also, thermal transfer printers are known as a type of image forming apparatus.FIGS. 40 and 41are oblique views of the overall structure of a conventional thermal transfer printer.FIGS. 42 and 43are oblique views illustrating the attachment structure of a pressing member and a shaft.FIG. 44is a cross section illustrating the pressing operation of the thermal head on the platen roller in the conventional thermal transfer printer shown inFIGS. 40 and 41. The structure of a conventional thermal transfer printer will now be described through reference toFIGS. 40 to 44.

As shown inFIGS. 40 and 41, this conventional thermal transfer printer includes a metal frame101, a thermal head102for performing printing, a platen roller103, platen roller bearings104that rotatably support the platen roller103, a metal shaft105, pressing members106and107, a drive gear108having a small-diameter gear108aand a large-diameter gear108b, both made of resin, for pivoting the pressing member106, a torsion coil spring109, a motor110, a motor bracket111, and an intermediate gear112.

Also, as shown inFIGS. 40 and 41, an ink sheet insertion portion101cfor attaching an ink sheet (not shown) is provided to a second surface101b, which is located opposite a first surface101aof the frame101to which the motor bracket111is attached. Insertion holes101dinto which the ends of the shaft105are rotatably inserted are provided in the first surface101aand the second surface101bof the frame101. The thermal head102is attached so as to be pivotable around a support shaft102aon the inside of the two side surfaces of the frame101. The torsion coil spring109is attached to the support shaft102aof the thermal head102. The function of this torsion coil spring109is to urge the thermal head102away from the platen roller103. Also, a head component102bprovided to the lower part of the thermal head102is disposed opposite the platen roller103. Bent components102cthat are pressed on by the pressing members106and107are formed above the ends of the head component102bof the thermal head102.

As shown inFIGS. 42 and 43, insertion parts105aare formed near the ends of the shaft105in a flat-sided oval shape, and are non-rotatably inserted in flat-sided oval-shaped insertion holes106aand107aof the pressing members106and107. Bearing supports105bare formed at the ends of the insertion parts105aof the shaft105. The bearing supports105bare rotatably supported in insertion holes101dof the frame101. Pressing springs106band107bthat press on the bent components102cof the thermal head102are attached to the pressing members106and107, respectively. As shown inFIG. 40, the pressing member106is disposed so as to engage with the small-diameter gear108aof the drive gear108. The drive gear108is attached to the first surface101aof the frame101, and transmits drive force from the intermediate gear112to the pressing member106. The drive force of the motor110(seeFIG. 41) attached to the motor bracket111is transmitted through the intermediate gear112(seeFIG. 44) to the large-diameter gear108bof the drive gear108, then to the small-diameter gear108ato the pressing member106.

FIGS. 40 and 41show how the thermal head102presses on the platen roller103with the above-mentioned conventional thermal transfer printer. The drive force of the motor110is transmitted through the intermediate gear112and the large-diameter gear108band the small-diameter gear108aof the drive gear108to the pressing member106, which causes the pressing member106to pivot while being supported in the insertion holes101dof the frame101. As a result, the pressing spring106bof the pressing member106presses on the bent component102con the first surface101aside of the frame101. Since the pressing members106and107are non-rotatably attached to the shaft105, pivoting of the pressing member106causes the shaft105and the pressing member107to pivot as well. As a result, the pressing spring107bof the pressing member107presses on the bent component102con the second surface101bside of the frame101. Consequently, the head component102bof the thermal head102is pressed against the platen roller103against the biasing force of the torsion coil spring109.

In the conventional thermal transfer printer shown inFIGS. 40 to 44, the insertion portions105aat the ends of the shaft105are formed in a flat-sided oval shape in order to non-rotatably link the shaft105and the pressing members106and107, which are the components that press on the thermal head102. Obtaining such oval shape requires a time-consuming cutting procedure. Furthermore, since the shaft diameter of the bearing supports105bat the ends of the insertion parts105ahas to be made smaller than the width of the flat-sided portion of the insertion portions105a, it is also necessary to perform a cutting procedure on the insertion portions105a. Therefore, it takes a long time to manufacture the insertion portions105a.

In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for improved thermal transfer printers and image forming apparatuses that overcome the problems of the conventional art. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.

SUMMARY OF THE INVENTION

The present invention was conceived in order to solve the above problem, and it is the first object of the present invention to provide a thermal transfer printer and an image forming apparatus for which it takes less time to manufacture the member used for pressing the printing head portion.

The image forming apparatus according to a first aspect of the present invention includes a frame, a head portion pivotably supported on the frame, a platen roller supported on the frame opposite the head portion, an elastically deformable support rod supported on the frame, a rotary member pivotably supported by the support rod and having a pressing member, the pressing member being adapted to press the head portion against the platen roller with an urging force of the support rod, and a drive mechanism engaged with the rotary member to pivot the rotary member around the support rod.

In this image forming apparatus, by using the rotary member that is pivotably supported by the support rod, it is no longer necessary to form a structure in which the rotary member and the support rod are unrotatably coupled. Therefore, manufacturing of the image forming apparatus can be simplified.

Preferably, in the image forming apparatus, the pressing member is positioned between the support rod and the head portion when the pressing member presses the head portion against the platen roller with the urging force of the support rod.

In this image forming apparatus, since the pressing member is positioned between the support rod and the head portion, the reaction force from the head portion does not pivot the pressing member. Therefore, it is possible to keep the pressing force that is applied to the head portion constant. Thus, it is possible to perform more consistent printing more easily.

Preferably, in the image forming apparatus, the pressing member has a flat bottom surface that comes into contact with the head portion.

In this image forming apparatus, by using the pressing member that has a flat bottom surface, it is possible to prevent pivoting of the pressing member while the pressing member presses on the head portion.

Preferably, in the image forming apparatus, the drive mechanism has a drive gear, and the rotary member has a toothed portion that engages with the drive gear.

Alternatively, in the image forming apparatus, the drive mechanism has a cam groove, and the rotary member has a cam pin that engages with the cam groove.

Preferably, in the image forming apparatus, the pressing member presses the head portion at substantially a width direction center of the head portion.

In this manner, it is possible to press on the head portion with a consistent pressing force in the width direction.

Preferably, in the image forming apparatus, the rotary member includes a first side arm that engages the drive mechanism and a second side arm to which the pressing member is attached, each of the first and second side arms being rotatably supported by the support rod.

In this structure, since both the first and second side arms are pivotably supported by the support rod, the first and second side arms do not rotate relative to one another. Therefore, there is no need to create a separate structure to prevent relative rotation between the first and second side arms.

Preferably, in the image forming apparatus, the support rod is made of a piano wire.

A thermal transfer printer according to a second aspect of the present invention includes a frame, a thermal head pivotably supported on the frame and adapted to perform printing, a platen roller supported on the frame opposite the thermal head, an elastically deformable metal support rod supported on the frame, a rotary member pivotably supported by the support rod and having first and second side arms and a pressing member that is attached to the second side arm and has a flat bottom surface, each of the first and second side arms being rotatably supported by the support rod, a drive mechanism engaged with the first side arm of the rotary member to pivot the second side arm around the support rod. A first distance between the flat bottom surface of the pressing member and where the support rod supports the second side arm is longer than a second distance between where the support rod is supported on the frame and an upper surface of the thermal head when the thermal head is pivoted toward the platen roller the most.

In this thermal transfer printer, since both the first and second side arms are pivotably supported by the support rod, the first and second side arms do not rotate relative to one another. Therefore, there is no need to create a separate structure to prevent relative rotation between the first and second side arms. Therefore, manufacturing of the thermal transfer printer can be simplified. Also in this thermal transfer printer, by using the pressing member that has a flat bottom surface, it is possible to prevent pivoting of the pressing member while the pressing member presses on the thermal head.

Preferably, in the thermal transfer printer, the drive mechanism has a drive gear, and the first side arm of the rotary member has a toothed portion that engages with the drive gear.

Alternatively, in the thermal transfer printer, the drive mechanism includes a cam groove, and the first side arm of the rotary member has a cam pin that engages with the cam groove.

Preferably, in the thermal transfer printer, the pressing member presses the thermal head at substantially a width direction center of the thermal head.

In this manner, it is possible to press on the thermal head with a consistent pressing force in the width direction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIG. 1is an oblique view of the overall structure of the thermal transfer printer in accordance with the first embodiment of the present invention.FIG. 2is a front view of the thermal transfer printer in accordance with the first embodiment shown inFIG. 1.FIGS. 3 to 6are diagrams of the detailed structure of the thermal transfer printer in accordance with the first embodiment shown inFIG. 1.FIGS. 7 to 10are diagrams illustrating how the thermal head presses on the platen roller in the thermal transfer printer shown inFIG. 1in accordance with the first embodiment.

First, the structure of the thermal transfer printer in accordance with the first embodiment of the present invention will be described through reference toFIGS. 1 to 6.

As shown inFIGS. 1 and 2, the thermal transfer printer pertaining to the first embodiment includes a metal frame1; a thermal head2pivotably supported on the frame1for performing printing; a platen roller3rotatably supported on the frame1; a platen roller bearing4for rotatably supporting the platen roller3; an elastically bendable support rod5which is a piano wire with a diameter of approximately 3 mm; a metal rotary member6; a resin pressing member7; a resin drive gear8having a small-diameter gear8aand a large-diameter gear8bfor pivoting the rotary member6; a torsion coil spring9; a motor10having a motor shaft gear10a; a metal motor bracket11; and an intermediate gear12having a large-diameter gear12athat engages with the motor shaft gear10a, and a small-diameter gear12bthat engages with the large-diameter gear8bof the drive gear8. This thermal transfer printer is an example of the “image forming apparatus” of the present invention, and the thermal head2is an example of the “printing head” or “head portion” of the present invention. The drive gear8is an example of the “drive mechanism” of the present invention.

As shown inFIGS. 1 and 2, an ink sheet insertion portion1cwhere ink sheets (not shown) are to be inserted is provided to a second surface1bof the frame1, which is located opposite from a first surface1aof the frame1to which the motor bracket11is attached. Insertion holes1dinto which the ends of the support rod5are rotatably inserted are provided on the first surface1aand the second surface1bof the frame1. The thermal head2is attached so as to be pivotable around a support shaft2aon the inside of the two side surfaces of the frame1. The torsion coil spring9is attached to the support shaft2aof the thermal head2. The torsion coil spring9is provided diagonally in the first surface1ato bias the thermal head2away from the platen roller3. As a result, when the pressing member7is not pressing on the thermal head2, there is a gap100(seeFIG. 2) between the lower part of the head portion2bof the thermal head2and the upper part of the platen roller3. The head portion2bof the thermal head2is provided to the lower part of the thermal head102so as to be disposed opposite the platen roller3.

In this first embodiment, the ends of the bendable support rod5are rotatably inserted into insertion holes1don the first surface1aand the second surface1bof the frame1. As shown inFIG. 3, the rotary member6is formed in a square shape with a first side surface6aand a second side surface6bto which the resin pressing member7is attached. Holes6cfor attaching the support rod5are provided in the first side surface6aand the second side surface6bof the rotary member6. A toothed portion6dis provided to the first side surface6aof the rotary member6as seen inFIG. 3. As shown inFIGS. 5 and 6, this toothed portion6dis disposed so as to engage with the drive gear8attached to the first surface1aof the frame1. The above-mentioned resin pressing member7is attached to the second side surface6bof the metal rotary member6. As shown inFIGS. 2-4, the pressing member7has a square shape with a flat bottom pressing surface7ahaving rounded corners. Also, the pressing member7is disposed such that through its pivoting the pressing member7presses the thermal head2at near its width direction center (the direction of arrow A inFIG. 2).

Also, in this first embodiment, as shown inFIG. 4, part of the pressing surface7aat the tip of the pressing member7is formed flat, so that the pressing member7, which is attached to the second side surface6bof the rotary member6, comes into planar contact with the top surface2cof the thermal head2in the course of pressing on the thermal head2. The pressing member7is also disposed so that when the pressing member7presses the thermal head2, the contact position between the pressing member7and the thermal head2is substantially directly beneath the support rod5. In other words, when the pressing member7presses the thermal head2, the pressing member7is between the support rod5and the thermal head2. Furthermore, the supporting rod5is designed to elastically bend upward when the pressing member7presses the thermal head2. The height h1(an example of the first distance, shown inFIG. 4) from the pressing surface7aof the pressing member7to the center of the hole6cin the second side surface6bof the rotary member6is set to be approximately 3 mm greater than the height h2(an example of the second distance, shown inFIG. 8), which is the distance between the top surface2cof the thermal head2and the center of the insertion holes1din the frame1. Therefore, the support rod5is bent upward approximately 3 mm while the pressing member7presses on the thermal head2.

As shown inFIG. 5, the drive gear8is attached to the first surface1aof the frame1and transmits drive force from the intermediate gear12to the rotary member6. The drive force of the motor10(seeFIG. 2) that is attached to the motor bracket11is transmitted from the motor shaft gear10a, through the large-diameter gear12aand the small-diameter gear12bof the intermediate gear12, to the large-diameter gear8bof the drive gear8.

Next, the manner in which the thermal head2presses on the platen roller3in the thermal transfer printer of this first embodiment will be described with reference toFIGS. 1 through 10. First, in the initial state, as shown inFIGS. 1 through 6, the biasing force of the torsion coil spring9causes the thermal head2to pivot away from the platen roller3, and the rotary member6stays in a pivoted position where the pressing member7does not press on the thermal head2. In this state, the drive force of the motor10(seeFIG. 2) is transmitted from the motor shaft gear10a, through the large-diameter gear12aand small-diameter gear12bof the intermediate gear12and the large-diameter gear8band small-diameter gear8aof the drive gear8, to the first side surface6aof the rotary member6. As a result, the first side surface6aof the rotary member6pivots from the state shown inFIG. 1to the state shown inFIG. 7in the direction of arrow C inFIG. 6, so the second side surface6bof the rotary member6is pivoted accordingly, changing from the state shown inFIG. 6to the state shown inFIG. 10. Consequently, the pressing surface7aof the pressing member7attached to the second side surface6bof the rotary member6strikes the top surface2cof the thermal head2as shown inFIGS. 8 and 10. At this point, the pressing member7is positioned between the support rod5and the top surface2cof the thermal head2as shown inFIG. 8, and the height h1, which is the distance between the pressing surface7aof the pressing member7and the center of the hole6cin the second side surface6bof the rotary member6, is set to be approximately 3 mm greater than the height h2, which is the distance between the top surface2cof the thermal head2during pressing operation and the center of the insertion holes1din the frame1. Thus, the support rod5, which is made of a piano wire with a diameter of approximately 3 mm, is elastically bent upward by approximately 3 mm. This generates flexural stress of about 30 to 40 N in the support rod5, and this flexural stress causes the pressing surface7aof the pressing member7to press against the top surface2cof the thermal head2in the direction of arrow B shown inFIG. 8. As a result, the head portion2bof the thermal head2is pressed against the platen roller3at a pressing force of approximately 30 to 40 N.

As discussed above, in the first embodiment, there are provided the bendable support rod5and an open-box-shaped rotary member6that is attached to the support rod5and includes the first side surface6athat engages with the drive gear8and the second side surface6bthat has the pressing member7. The pressing member7of the second side surface6bof the rotary member6uses pressing force produced by the bending of the support rod5to press the thermal head2against the platen roller3. In this manner, the requisite pressing force during the printing operation can be generated by the support rod5and the open-box-shaped rotary member6, by utilizing the biasing force of the bendable support rod5.

Also, in the first embodiment, the open-box-shaped rotary member6includes the first side surface6a, which the drive gear8rotates, and the second side surface6b, which has the pressing member7. Therefore, there is no relative rotation between the first side surface6aand second side surface6b, since they are formed unitarily as the one-piece rotary member6. Accordingly, there is no need to make a D-cut or flat-sided oval shape in order to prevent spinning between the first and second side surfaces6aand6b. In other words, the rotary member6can be formed by press forming, which takes only a short time, without having to perform any time-consuming cutting operations. Thus, in an image forming apparatus having a mechanism that uses the rotary member6to press on the thermal head2, it is possible to reduce the time required to manufacture the rotary member6, which is the member for pressing on the thermal head2.

Also, in the first embodiment, the pressing member7of the second side surface6bof the rotary member6is disposed such that the contact position between the thermal head2and the pressing member7comes substantially directly beneath the support rod5during the pressing operation of the thermal head2. In this manner, even when a reaction force is imparted straight upward from the thermal head2to the pressing member7in the course of pressing on the thermal head2, the reaction force does not cause the second side surface6bof the rotary member6to pivot. Therefore, it is possible to reduce the unevenness in printing since the pressing force applied to the thermal head can be kept constant.

Also, in the first embodiment, since part of the pressing member7that is in contact with the thermal head2is formed as a flat surface, the pressing member7is less likely to pivot relative to the thermal head2during the pressing operation than the case where the pressing surface7aof the pressing member7is formed in a merely curved shape. In this manner, the unevenness in printing can be reduced, since the pressing force applied to the thermal head2can better be kept constant.

Also, in the first embodiment, since the toothed portion6dthat engages with the drive gear8is provided to the first side surface6aof the rotary member6, the drive force of the drive gear8can be transmitted to the rotary member6merely by engaging the drive gear8with the toothed portion6dof the first side surface6aof the rotary member6. Thus, the pressing member7that is attached to the second side surface6bof the rotary member6can be easily pivoted.

Also, in the first embodiment, since the pressing member7that is attached to the second side surface6bof the rotary member6is disposed so as to press on the thermal head2at around the center in the width direction, the thermal head2can be pressed more uniformly in the width direction (direction A inFIG. 2) of the thermal head2. Therefore, the thermal head2can be brought into contact with the platen roller3more uniformly, and the unevenness in printing can be further reduced.

Second Embodiment

FIG. 11is an oblique view of the overall structure of the thermal transfer printer according to the second embodiment of the present invention.FIGS. 12 and 13are a front view and a plan view of the thermal transfer printer of the second embodiment shown inFIG. 11.FIGS. 14 to 17are diagrams of detailed structure of the thermal transfer printer of the second embodiment shown inFIG. 11.FIGS. 18 to 21are diagrams illustrating how the thermal head presses on the platen roller with the thermal transfer printer of the second embodiment shown inFIG. 11. This second embodiment differs from the first embodiment in that it uses a cam mechanism to pivot the rotary member. The thermal head in this second embodiment is the same as that in the first embodiment except for the structure of the rotary member and the drive gear, and therefore will not be described in detail herein.

As shown inFIGS. 11 and 17, with the thermal transfer printer according to the second embodiment, a thermal head13is attached so as to be pivotable around a support shaft13aon the inside of the side surfaces of the frame1. A head component13bprovided to the lower part of the thermal head13is disposed across from the platen roller3as shown inFIG. 11.

As shown inFIG. 11, a rotary member14is formed with a U-shape and includes a first side surface14aand a second side surface14bwhich is provided with a pressing member14d. Holes14cfor attaching the elastically bendable support rod5are provided in the first side surface14aand the second side surface14bof the rotary member14. The pressing member14dhas a bottom surface having a curved portion14gand a flat portion14f. Before the pressing operation, the tip end of the curved portion14gof the pressing member14dis in contact with the upper surface13eof the thermal head13. As the pressing operation starts, the portion of the pressing member14dthat presses the thermal head13shifts toward the flat portion14f. When the pressing member14dapplies pressure to the thermal head13with the maximum pressure, the pressing member14dpresses the thermal head13with the flat portion14f, as shown inFIGS. 11 and 14. A cam pin14eis provided to the first side surface14aof the rotary member14so as to engage with a cam groove15aof a drive cam15.

The height h3(another example of the first distance, shown inFIG. 21), which is the height from the bottom of the flat portion14fof the pressing member14dto the center of the hole14con the second side surface14bof the rotary member14, is set to be approximately 3 mm greater than the height h4(another example of the second distance, shown inFIG. 18), which is the height from the top surface13eof the thermal head13when the thermal head13is closest to the platen roller3to the center of the insertion hole1din the frame1. Thus, the support rod5is elastically bent upward by approximately 3 mm while the pressing member14dis pressing on the thermal head13with the flat portion14f.

As seen inFIGS. 18-19, the second side surface14bof the rotary member14is positioned approximately at the center of the support rod5. Accordingly, the pressing member14dis positioned to press the thermal head13at approximately the width-direction center of the thermal head13.

Also, as shown inFIG. 13, a drive gear15is attached to the first surface1aof the frame1and engaged with a small-diameter gear22bof an intermediate gear22. As shown inFIG. 15, the cam groove15awhich engages the cam pin14eof the first side surface14aof the rotary member14is formed on the side surface of the drive gear15. The drive gear15and the cam groove15aare another example of the “drive mechanism” of the present invention. As shown inFIG. 17, the cam groove15ais formed such that the pivoting direction (the direction of arrow E) in which the reaction force that is applied from the thermal head13to the pressing member14dcauses the first side surface14ato pivot around the support rod5during the pressing operation is perpendicular to the plane (plane F), which is a tangential plane of the cam groove15aat the point where the cam pin14ecomes into contact with the cam groove15a. The rotational center15bof the drive gear15is disposed on a line G, which is the tangential line of the arrow E. In other words, the direction in which the cam pin14erotates around the support rod5is the direction toward the rotational center15bof the drive gear15.

Next, the manner in which the thermal head13of the thermal transfer printer of the thermal transfer printer presses on the platen roller3in this second embodiment of the present invention will be described through reference toFIGS. 11 to 16andFIGS. 17 to 21. First, in the initial state, as shown inFIGS. 11 to 16, the biasing force of the torsion coil spring9is causing the thermal head13to stay away from the platen roller3, and the rotary member14to pivot to a position where the pressing member14ddoes not press on the thermal head13.

In this state, the drive force of the motor10(seeFIG. 13) is transmitted from the motor shaft gear10ato the first side surface14aof the rotary member14, through a large-diameter gear22aand a small-diameter gear22bof an intermediate gear22, the drive gear15, and the cam pin14eof the rotary member14that engages with the cam groove15aof the drive gear15. As a result, the first side surface14aof the rotary member14pivots from the state shown inFIG. 15to the state shown inFIG. 20in the direction of arrow I inFIG. 20. Accordingly, the second side surface14bof the rotary member14also pivots in the direction of arrow J inFIG. 16, from the state shown inFIG. 16to the state shown inFIG. 21.

Consequently, the pressing member14dstarts pressing the thermal head13with the flat portion14f. Here, since the height h3from the bottom of the flat portion14fof the pressing member14dto the center of the hole14con the second side surface14bof the rotary member14is set to be approximately 3 mm greater than the height h4, which is the height from the top surface13eof the thermal head13when the thermal head13is closest to the platen roller3to the center of the insertion hole1din the frame1, the support rod5, which is a piano wire with a diameter of approximately 3 mm, is elastically bent upward by approximately 3 mm during the pressing operation of the pressing member14d. This generates flexural stress of about 30 to 40 N in the support rod5, and this flexural stress causes the pressing member14dto press against the upper surface13eof the thermal head13in the direction of arrow H (seeFIG. 18). As a result, the head component13bof the thermal head13is pressed against the platen roller3at a pressing force of approximately 30 to 40 N.

In the second embodiment, as discussed above, the cam groove15ais formed in the drive gear15, and the cam pin14ethat engages with the cam groove15ais provided in the first side surface14aof the rotary member14. In this manner, the drive force of the drive gear15is transmitted to the rotary member14using the cam groove15aand the cam pin14e, so that the pressing member14dof the second side surface14bof the rotary member14can easily pivot.

Also, in the second embodiment, the cam groove15ais formed such that the direction in which the reaction force applied from the thermal head13to the pressing member14dduring the pressing operation pivots the first side surface14aaround the support rod5(the direction of arrow E inFIG. 17) is perpendicular to the plane F, which is a tangential plane of the cam groove15aat the point where the cam pin14ecomes into contact with the cam groove15a. Also, the rotational center15bof the drive gear15is disposed on the line G, which is tangential to the arrow E. Since the direction in which the cam pin14erotates around the support rod5is the direction toward the rotational center15bof the drive gear15, even though the contact position between the thermal head13and the pressing member14dof the second side surface14bof the rotary member14is not directly beneath the support rod5, the reaction force from the thermal head13to the pressing member14dgenerated during the pressing operation does not pivot the first side surface14aor second side surface14bof the rotary member14. Accordingly, there is no need for the contact position between the thermal head13and the second side surface14bof the rotary member14to be disposed directly beneath the support rod5. As a result, there are fewer restrictions imposed on the design of the thermal transfer printer according to the second embodiment. Thus, a greater degree of freedom is accorded in the design of the thermal transfer printer.

The other effects of the second embodiment of the present invention are the same as those of the first embodiment.

The embodiments disclosed here are in all respects examples, and should not be construed as a limitation to the scope of the invention. The scope of the present invention is defined by the claims, and not limited by the above descriptions of embodiments, and furthermore encompasses all modifications within a scope and meaning equivalent to the claims.

Other Embodiments

(a) In the above embodiments, a thermal transfer printer is given as an example of the image forming apparatus. However, the present invention is not limited to thermal transfer printers, and can also be applied to other kinds of image forming apparatus besides a thermal transfer printer, as long as the image forming apparatus has a printing head.

(b) Also, in the above embodiments, the pressing members that press on the thermal head at near its width direction center. However, the present invention is not limited to such construction. The pressing member may press on any other portion other than the width direction center of the thermal head.

(c) Also, the above embodiments use as an example the flexural stress produced by the bending of the support rod to press on the thermal head with the pressing member. However, the present invention is not limited to such construction. The rotary member may be constituted by a leaf spring or other such member that can be twisted easily. In such cases the pressing member may be made to press against the thermal head by using both the torsional stress of the leaf spring and the flexural stress produced by the bending of the support rod.

(d) Also, in the first embodiment, the thermal transfer printer has the lower part of the pressing member that has one distal end. However, the present invention is not limited to such construction. For example, the lower part of the pressing member can be formed into two branches, as shown inFIGS. 22-30. In this case, the pressing member207has two pressing surfaces207athat press the thermal head3as the toothed portion6dof the first side surface6aof the rotary member6engages the drive gear8and the second surface6bpivots from the state shown inFIGS. 22 and 26to the state shown inFIGS. 27 and 30. Other structure of the thermal transfer printer according to this embodiment is the same as that the first embodiment. Therefore, further detailed explanation will be omitted herein.

Furthermore, the lower part of the pressing member can be divided into three or more branches.

(e) In the above embodiments, the torsion springs9are used to bring the thermal heads2and13away from the platen rollers3while the pressing members7and14dare not pressing the thermal heads2and13. However, the present invention is not limited to such construction. Instead, the present invention can have a structure shown inFIGS. 31-39, where the second side surface314bis provided with a pressing pin314das shown inFIG. 34, and the thermal head313has an engagement portion313con its upper surface313eas shown inFIG. 35, at approximately the center of the thermal head313in the width direction (the direction of arrow D inFIGS. 32-33). The engagement portion313chas an engagement hole313das shown inFIG. 35, such that the second side surface314bengages with the engagement portion313cthrough the engagement of the pressing pin314dwith the engagement hole313d. As shown inFIG. 36, the pressing pin314dstays engaged with the upper portion of the engagement hole313dwhen the pressing pin314dis not pressing the thermal head313. During the pressing operation, the pressing pin314dstrikes the lower portion of the engagement hole313dof the engagement portion313c, as shown inFIG. 39, and thereby presses the thermal head313.

The height h5, (still another example of the first distance) which is the height from the center of the pressing pin314dof the second side surface314bto the center of the hole314cof the rotary member314, is set to be approximately 3 mm greater than the height h6(still another example of the second distance, shown inFIG. 37), which is the height from the center of the pressing pin314dof the second side surface314bof the rotary member314to the center of the insertion holes1din the frame1. Thus, the support rod5, which is a piano wire with a diameter of approximately 3 mm, is elastically bent upward by approximately 3 mm while the pressing pin314dis in engagement with the lower portion of the engagement hole313dand pressing on the thermal head313. The structure of the drive gear15, the cam groove15a, and the first side surface314ais the same as that of the drive gear15, the cam groove15a, and the first side surface14aof the second embodiment. Therefore, their detailed explanation will be omitted herein.

(f) Also, in the above embodiments, the pressing members7and14dare formed separately from the second side surfaces6band206b. However, the present invention is not limited to such construction. Instead, the pressing member may be constituted integrally with the second side surface of the rotary member.

As used herein, the following directional terms “forward, rearward, above, downward, vertical, horizontal, below and transverse” as well as any other similar directional terms refer to those directions of a device equipped with the present invention. Accordingly, these terms, as utilized to describe the present invention should be interpreted relative to a device equipped with the present invention.

This application claims priority to Japanese Patent Application No. 2004-117988. The entire disclosure of Japanese Patent Application No. 2004-117988 is hereby incorporated herein by reference.