Thermal printer

Abstract

The platen bearings 52a, 52b attached to the shaft end parts 51a, 51b of the removable platen roller 5 are pressed by lock levers 8a, 8b to bearing insertion slots 7a, 7b that are formed in the main frame 3 of the thermal printer 1 so that the positions of the platen bearings 52a, 52b are determined by two points A, B on the main frame and one point C on the lock lever.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an oblique view showing the print mechanism unit of a thermal printer according to a preferred embodiment of the present invention.

FIG. 2 is an oblique view showing the print mechanism from a different direction with a portion of the print mechanism removed.

FIG. 3 is a schematic section view of the print mechanism unit.

FIG. 4 shows the lock lever frame and the lock release lever.

FIG. 5 shows the platen roller in the locked position and the unlocked position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention is described below with reference to the accompanying figures.

FIG. 1 is an oblique view showing the print mechanism unit of a thermal printer according to the present invention. FIG. 2 is an oblique view showing the print mechanism from a different direction with a portion of the print mechanism removed. FIG. 3 is a schematic section view of the print mechanism unit.

As shown in these figures, the print mechanism unit 2 of the thermal printer 1 has a main frame 3, a thermal head 4 that is installed to the main frame 3, and a removable platen roller 5 that is removably installed to the main frame 3. The thermal head 4 is a line thermal head disposed extending widthwise to the printer with a print surface 4a that spans the entire printable width of the print head. The platen roller 5 is also installed widthwise to the printer and in contact with the print surface 4a. A head pressure spring 6 pushes the thermal head 4 from behind against the platen roller 5.

The end parts 51a, 51b of the roller shaft 51 protrude coaxially from the opposite end faces of the removable platen roller 5, and cylindrical platen bearings 52a, 52b are attached to these shaft end parts 51a, 51b. These platen bearings 52a, 52b are removably inserted through right and left bearing insertion slots 7a, 7b that are formed in the mainframe 3, and the platen roller 5 is supported freely rotatably on the main frame 3 by these platen bearings 52a, 52b.

The platen bearings 52a, 52b are locked by the right and left lock levers 8a, 8b so that the platen bearings 52a, 52b do not escape from the bearing insertion slots 7a, 7b. The lock levers 8a, 8b are constantly urged by a tension spring 9 in the direction locking the platen bearings 52a, 52b in the bearing insertion slots 7a, 7b.

A manually operated lock release lever 10 for releasing the lock levers 8a, 8b from the locked position is connected to the lock levers 8a, 8b. When the lock release lever 10 is operated against the urging force of the tension spring 9, the lock levers 8a, 8b are released from the locking position and the platen bearings 52a, 52b can be removed from the bearing insertion slots 7a, 7b. As a result, the platen roller 5 can be removed from the main frame 3.

Thermal paper 12a is pulled through the position (the printing position) where the thermal head 4 and the platen roller 5 are pressed together. More specifically, the thermal paper 12a is pulled from a roll paper compartment 13 that holds roll paper 12 having a web of thermal paper 12a wound into a roll, is guided to the printing position by a paper guide 14 disposed on the main frame 3, and is conveyed passed the printing position and discharged from the printer from a paper exit not shown. Content can be printed on the thermal paper 12a by selectively driving the heat elements arrayed on the print surface 4a of the thermal head 4 while rotating the platen roller 5 to advance the thermal paper 12a.

The arrangement of the parts of the print mechanism unit 2 is described next. The main frame 3 has a vertical front panel 31 extending widthwise to the printer, and left and right vertical side panels 32, 33 that extend substantially perpendicularly from the opposite ends of the vertical front panel 31 towards the back of the printer. FIG. 2 shows the print mechanism unit 2 with the one vertical side panel 33 omitted. The paper guide 14 extends widthwise to the printer between the bottom rear end parts of the vertical side panels 32, 33.

A support shaft 15 is disposed widthwise to the printer between the left and right vertical side panels 32, 33. Alternatively, support pins could be affixed at the same positions to the vertical side panels 32, 33. A head support frame 16 is supported on the support shaft 15 so that the head support frame 16 can rock in the front-rear direction of the printer on the support shaft 15.

The head support frame 16 has a head support panel 16a that extends widthwise to the printer, and left and right arm parts 16b, 16c that are bent towards the front of the printer from the opposite ends of the head support panel 16a. The arm parts 16b, 16c (only the one arm part 16c is shown in the figures) are supported rotatably on the support shaft 15. The thermal head 4 is attached to the surface of the head support panel 16a facing the rear of the printer so that the print surface 4a faces the rear of the printer. The head pressure spring 6 is connected extending in the front-rear direction of the printer between the head support panel 16a and the vertical front panel 31 of the main frame 3 at a position above the support shaft 15. Two head pressure springs 6, one each on the left and right sides of the printer, are provided in this embodiment of the invention.

The platen roller 5 is pressed from the rear side of the printer to the print surface 4a of the thermal head 4. The platen roller 5 includes a cylindrical roller 50 made from an elastic material, and a roller shaft 51 that is attached to the roller 50 and passes coaxially through the roller 50. The shaft end parts 51a, 51b at the opposite ends of the roller shaft 51 protrude from the end surfaces of the roller 50, and a cylindrical platen bearing 52a, 52b is mounted on each of the shaft end parts 51a, 51b.

In this aspect of the invention the platen roller 5 is assembled to a unit frame 55. The unit frame 55 has a connecting plate 55c extending widthwise to the printer, and arm parts 55a, 55b bent downward perpendicularly from the opposite ends of the connecting plate 55c. The platen bearings 52a, 52b on the opposite ends of the platen roller 5 are held so that the platen bearings 52a, 52b can slide in the front-rear direction of the printer on the distal end parts of the arm parts 55a, 55b. The unit frame 55, the platen roller 5, and the left and right platen bearings 52a, 52b form a platen roller unit 56, and this platen roller unit 56 is removably installed to the main frame 3.

The driven gear 18 is fixed coaxially to the platen roller 5 on the end of one shaft end part 51a. This driven gear 18 meshes with the compound drive gear 19, which is attached freely rotatably on the vertical side panel 32 of the main frame 3. The compound drive gear 19 is connected to the output shaft of a paper feed motor not shown by means of an intervening speed reducing gear train not shown.

FIG. 4 is a parts diagram showing the part to which the lock levers 8a, 8b are formed and the lock release lever 10. The lock levers 8a, 8b are formed at the left and right ends of the lock lever frame 8. More specifically, the lock lever frame 8 has a connecting plate 8c extending widthwise to the printer, and the lock levers 8a, 8b are bent towards the rear of the printer from the opposite ends of the connecting plate 8c. Shaft holes 8d, 8e are formed in the left and right lock levers 8a, 8b at an appropriate position towards the front of the printer, and the support shaft 15 (denoted by the imaginary line in FIG. 4) disposed to the main frame 3 passes freely rotatably through these holes 8d, 8e. The lock lever frame 8 is thus supported by the support shaft 15 so that the lock lever frame 8 can rock vertically to the printer on the support shaft 15. A spring catch 8f is formed on the connecting plate 8c, which is positioned to the front of the printer from the support shaft 15, in the width wise center of the printer. Another spring catch 3a is formed at a position on the main frame 3 below the spring catch 8f, and the tension spring 9 is connected between these catches as shown in FIG. 3.

Hooks 8g, 8h are formed curving upward from the parts of the lock lever 8b toward the rear of the printer from the support shaft 15. The left and right platen bearings 52a, 52b are pushed towards the front of the printer by the edges of the hooks 8g, 8h facing the front of the printer, thus rendering a locked position in which the platen bearings 52a, 52b cannot escape from the bearing insertion slots 7a, 7b.

As will be known from FIG. 2 and FIG. 4, the lock release lever 10 is supported by the support shaft 15 so that the lock release lever 10 can rock vertically relative to the printer on the support shaft 15. An engaging member 10a that contacts the connecting plate 8c of the lock lever frame 8 from the front is formed on the lock release lever 10 towards the front of the printer from the support shaft 15. A manual operating member lob is formed bent to the outside widthwise to the printer at a part of the lock release lever 10 to the rear of the printer from the support shaft 15. The center of gravity of the lock release lever 10 is to the rear of the printer from the support shaft 15, and the engaging member 10a at the front of the printer therefore always contacts the front side of the connecting plate 8c of the lock lever frame 8.

FIG. 5A shows the platen roller 5 in the locked position, and FIG. 5B shows the platen roller 5 in the unlocked position. The profiles of the bearing insertion slots 7a, 7b and the front edges of the hooks 8g, 8h of the lock levers 8a, 8b in this embodiment of the invention are described next with reference to these figures.

The bottom 71 of each of the bearing insertion slots 7a, 7b is a flat surface extending substantially horizontally in the front-rear direction of the printer. A front slot side 72 and a rear slot side 73 extend from the front and back ends of each slot bottom 71.

Each front slot side 72 has a concave surface part 72a that curves toward the front of the printer, and a convex surface part 72b that continues smoothly from the top end of the concave surface part 72a and projects slightly towards the rear of the printer. The profiles of the slot bottom 71 and the front slot side 72 are set so that the slot bottom 71 and the front slot side 72 respectively contact the outside of the platen bearings 52a, 52b at points A and B.

The rear slot side 73 of each of the bearing insertion slots 7a, 7b has an incline part 731 and a incline part 732. The one incline part 731 extends at an angle of greater than 90 degrees from the slot bottom 71. The other incline part 732 curves upward continuously from the top of the first incline part 731. The gap between the front and rear slot sides 72, 73 is greater than the outside diameter of the platen bearings 52a, 52b, and increases gradually to the top, that is, to the open side of the slot.

The front edge 81 of each of the hooks 8g, 8h of the lock levers 8a, 8b has a concave profile that curves slightly towards the rear of the printer and encroaches the front of the printer from the bottom to the top of the curve. The curvature of this concave surface is less than the curvature of the outside diameter of the platen bearings 52a, 52b. This concave surface is set to contact the outside surface of one of the platen bearings at one point C from the rear of the printer.

In the locked position as shown in FIG. 5A, the lock levers 8a, 8b are urged upward by the tension spring 9 so that the front edges 81 of the hooks 8g, 8h of the lock levers 8a, 8b push the platen bearings 52a, 52b inserted in the bearing insertion slots 7a, 7b towards the front of the printer. The platen bearings 52a, 52b are therefore pushed against the front side 72 and the bottom 71 of the bearing insertion slots 7a, 7b, and the platen bearings 52a, 52b are thus positioned by contact at the three points A, B, and C. The platen roller 5 is thus precisely positioned to the main frame 3 when in the locked position.

The thermal head 4 is pressed by the force of the head pressure spring 6 from the front of the printer against the platen roller 5. This pressure pushes the platen roller 5 to the rear of the printer, and pushes the platen bearings 52a, 52b on the ends of the platen roller 5 in the direction separating from the front slot side 72 of the bearing insertion slots 7a, 7b of the main frame 3. The tension of the tension spring 9 is therefore set so that when the lock levers 8a, 8b are in the locked position the hooks 8g, 8h can hold the platen bearings 52a, 52b against the front slot side 72 in resistance to the force of the head pressure spring 6.

More specifically, the strength of the tension spring 9 relative to the force of the head pressure spring 6 is set so that when the lock levers 8a, 8b are in the locked position, the force of the head pressure spring 6 asserted through the platen bearings 52a, 52b does not cause the lock levers 8a, 8b to move from the locked position toward the unlocked position.

The lock release lever 10 is operated to remove the platen roller 5 from the main frame 3. Referring to FIG. 5B, when the manual operating member 10b of the lock release lever 10 is pushed down using a finger, for example, the engaging member 10a of the lock release lever 10 pushes the lock lever frame 8 up as indicated by arrow D. This causes the left and right lock levers 8a, 8b to pivot down to the unlocked position separated from the outside surface of the platen bearings 52a, 52b.

The head pressure spring 6 urges the thermal head 4 from the front of the printer to the platen roller 5 as indicated by arrow F in FIG. 5B. As a result, when the lock levers 8a, 8b separate from the platen bearings 52a, 52b, the head pressure spring 6 pushes the platen bearings 52a, 52b toward the rear of the printer inside the bearing insertion slots 7a, 7b. Because the rear slot side 73 of the bearing insertion slots 7a, 7b is an incline 731 that slopes upward toward the rear of the printer, the platen bearings 52a, 52b are pushed upward from the bearing insertion slots 7a, 7b along the incline part 731 as indicated by arrow E. As a result, when the lock release lever 10 is operated, the force of the head pressure spring 6 automatically pushes the platen roller 5 out from the bearing insertion slots 7a, 7b. The platen roller 5 can thus be easily removed.

The operation for installing the removed platen roller 5 to the main frame 3 is the same. More specifically, the lock release lever 10 is operated to move the lock levers 8a, 8b to the unlocked position. The platen bearings 52a, 52b on the opposite ends of the platen roller 5 are then inserted to the bearing insertion slots 7a, 7b in the main frame 3. The lock release lever 10 is then released to automatically restore the locked position shown in FIG. 5A.

A lock release lever 10 is provided in this aspect of the invention, but the lock lever frame 8 could instead be used as the lock release lever by disposing a manual operating member to the lock lever frame 8. For example, a manual operating tab 80 could be formed extending upward at the middle of the connecting plate 8c of the lock lever frame 8 as indicated by the imaginary lines in FIG. 1, FIG. 2, and FIG. 4. Pushing this manual operating tab 80 to the rear of the printer moves the lock levers 8a, 8b to the unlocked position.

The thermal printer 1 according to this embodiment of the invention thus presses the platen bearings 52a, 52b on the opposite ends of the platen roller 5 against the bearing insertion slots 7a, 7b formed in the main frame 3 to lock and prevent the platen bearings 52a, 52b from leaving the bearing insertion slots 7a, 7b. The platen roller 5 can thus be precisely positioned to the main frame 3 because the platen bearings 52a, 52b are pressed directly against the main frame 3. As a result, the driven gear 18 attached to the shaft end part 51a, 51b always meshes reliably with the compound drive gear 19 disposed to the main frame 3.

When the lock levers 8a, 8b move to the unlocked position, the force of the head pressure spring 6 pushes the platen bearings 52a, 52b along the rear slot sides 73 of the bearing insertion slots 7a, 7b in the direction leaving the bearing insertion slots 7a, 7b. The platen roller 5 can therefore be easily removed.

The lock levers 8a, 8b can also be moved with little force to the unlocked position by using the lock release lever 10. This also simplifies the task of removing the platen roller 5.

Although the present invention has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims, unless they depart therefrom.

Claims

1. A thermal printer comprising: a main frame;a thermal head;a platen roller;a head urging member that urges the thermal head to the platen roller;platen bearings attached to each end of a roller shaft that protrudes coaxially from both ends of the platen roller;bearing insertion slots that are formed in the main frame and in which the platen bearings are removably inserted;a lock lever that can move from a locked position for locking and preventing the platen bearings from leaving the bearing insertion slots to an unlocked position enabling removal of the platen bearings from the bearing insertion slots; anda lever urging member that constantly urges the lock lever to the locked position;wherein the platen bearings are pressed against the bearing insertion slots and positioned against the main frame by the lock lever when the lock lever is in the locked position.

2. The thermal printer described in claim 1, wherein: a contour of the inside edge of each of the bearing insertion slots is shaped to contact an outside diameter surface of each of the platen bearings at two points; anda contour of the contact surface of the lock lever that contacts the platen bearing is shaped to contact the outside diameter surface of the platen bearing at one point.

3. The thermal printer described in claim 1, wherein: the head urging member urges the platen roller by means of the thermal head in the direction in which the platen bearings separate from the inside edge of the bearing insertion slot; andthe urging force of the lever urging member is set so that when the lock lever is in the locked position, the urging force of the head urging member does not cause the lock lever to move from the locked position.

4. The thermal printer described in claim 3, wherein: the shape of the bearing insertion slot is set so that when the lock lever moves to the unlocked position, the platen bearings are pushed from the bearing insertion slot by the urging force of the head urging member.

5. The thermal printer described in claim 1, further comprising: a manually operated lock release lever for moving the lock lever to the unlocked position.

6. The thermal printer described in claim 1, wherein: the lock lever is disposed to the main frame so that the lock lever can pivot on a support shaft extending parallel to a platen roller shaft;the lock lever has a connecting plate for the lever urging member formed on one side of the support shaft, and on the other side of the support shaft has a hook for pushing the platen bearing into the bearing insertion slot;the thermal head is attached to the main frame on the opposite side of the platen roller as the hook so that the thermal head can pivot on the support shaft; andwhen the lock lever is in the locked position, a bottom of the bearing insertion slot, a side surface of the bearing insertion slot on the thermal head side, and an edge of the hook of the lock lever each contact the outside of the platen roller shaft.

7. The thermal printer described in claim 6, wherein: the urging force of the lever urging member is set so that when the lock lever is in the locked position, the urging force of the head urging member does not cause the lock lever to move from the locked position.

8. The thermal printer described in claim 7, wherein: a rear slot side of the bearing insertions lots includes an inclined surface forming an angle of 90 degrees or more relative to a bottom surface of the bearing insertion slots; andwhen the lock lever moves to the unlocked position, the urging force of the head urging member pushes the platen bearing along the inclined surface from the bearing insertion slot.

9. The thermal printer described in claim 1, further comprising: a lock lever frame formed on the lock lever; anda manual operating member that is disposed on the lock lever frame and is operated to move the lock lever to the unlocked position.

10. The thermal printer described in claim 1, further comprising: a manually operated lock release lever for moving the lock lever to the unlocked position;wherein the lock release lever is attached to the main frame so that the lock release lever can pivot on the support shaft.

11. The thermal printer described in claim 1, wherein a gap between a front slot side and a rear slot side of the bearing insertion slots is greater than an outside diameter of said platen bearings.

12. The thermal printer described in claim 11, wherein the gap increases in the direction toward an open end of said bearing insertion slots.

13. The thermal printer described in claim 6, wherein the hook has a concave surface that curves towards a rear of the printer.

14. The thermal printer described in claim 6, wherein a curvature of said concave surface is less than a curvature of an outside diameter of said platen bearings.