Gear drive mechanism for office products

Abstract: [Object] To provide a gear drive mechanism that contributes to downsize office products and is easily disassembled by thinning the gear drive mechanism. [Arrangement] By a structure such that a plurality of shafts 2 to 8 cantilever from a base plate 18 attached within a label writer X, and gears 9 to 15 are fit in the shafts 2 to 8, respectively, and are engaged with each other, specific shafts that are drive shafts 5, 7, 8, of the shafts 2 to 8 are driven. A groove 23 is formed around an end of at least one of the shafts 2, 4 of the shafts 2, 3, 4, 6, 8, 9 other than the specific shafts. A ring-shaped washer 25 having a slit 26 in a direction of diameter is fit in the groove 23 as a gear removal preventive 17 and a recessed portion 27 is provided to a side surface of the gear 14 throughout the washer 25.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a gear drive mechanism that drives a drive shaft in an office product, more particularly, to a gear drive mechanism that is provided with a removal preventive after a gear is fit to a cantilever-like shaft. 2. Description of the Related Art There has been proposed label writers that print characters and the like on a label tape as conventional office products. In the label writer, a cassette in which the label tape is wound is installed. The label writer feeds the label tape from the cassette to a print head. The label writer prints characters and the like on the label tape by the print head and a platen roller and discharges the printed label tape outside a main body by a nip roller. Such a series of driving in the label writer is performed by a gear drive mechanism provided in the main body of the label writer under the cassette. The gear drive mechanism is structured such that a plurality of shafts including a drive shaft cantilevers from a base plate, gears are fit into the respective shafts, the gears fit into each shafts are engaged with each other, and the gears are prevented from coming off from the shafts. A general method for preventing the gears from coming off is that a groove is formed around an end of the shaft and a removal preventive washer is fit into the groove. In the conventional drive mechanism, as disclosed in closest prior art EP-A-850 771 an E-shaped removal preventive clip that is an elastic metal plate is used for the removal preventive washer. The E-shaped removal preventive clip is shaped like a letter C having a protrusion at the center. The E-shaped removal preventive clip has an opening with respect to the shaft, so that the E-shaped removal preventive clip can be easily attached/detached to/from the shaft. However, size, thickness, material and shape of the E-shaped removal preventive clip are specified in the JIS Standard, so that the size variety of the E-shaped removal preventive clips is small. Therefore, in the conventional gear drive mechanism, the diameter and length of the shaft has been determined based on specifications of the E-shaped removal preventive clip. Small office products, such as the label writers, requires that the gear drive mechanism to be built-in be slim and lightweight. However, there is a problem that the gear drive mechanism is limited to be slimmed and save its weight due to the specifications of the E-shaped removal preventive clip. If the specified E-shaped removal preventive clip is not used, it becomes possible to slim the gear drive mechanism and save its weight. However, there is a problem that it becomes difficult to disassemble the gear drive mechanism. From US 005,762,173 A a gear drive mechanism for office products can be taken which drives a shaft to which a gear is fit. A groove is formed around the shaft. A washer is fitted into the groove. An insertion groove is formed in a side surface of the gear. SUMMARY OF THE INVENTION This invention provides a gear drive mechanism which is easy to be disassembled and contributes to miniaturisation of office products by thinning the gear drive mechanism. In order to achieve such a gear drive mechanism, a gear drive mechanism for office products is provided as is claimed in claim 1. Preferred developments of the invention are defined in the dependent claims. According to the gear drive mechanism of this invention, the gear can be prevented from coming off by using the thin ring-shaped washer having a simple structure and the slit in the direction of diameter. Because the washer has the simple structure, a diameter and length of the shaft can be minimized using the washer conforming to the shaft. Further, the gear drive mechanism can be easily disassembled by which the slit in the washer is aligned with the recessed portion provided to the side surface of the gear and then a tool is inserted in the recessed portion. As described above, according to the gear drive mechanism of this invention, the gear can be prevented from coming off by using the thin ring-shaped washer having a simple structure and the slit in the direction of diameter. Therefore, the gear drive mechanism can be thin, so that the office products can be downsized. Further, the gear drive mechanism can be easily disassembled by which the slit in the washer is aligned with the recessed portion provided to the side surface of the gear and then a tool is inserted in the recessed portion. BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention will be described in detail with reference to the following figures wherein: Fig. 1 is a top view showing a structure of a gear drive mechanism of an embodiment of the invention; Fig. 2 is an enlarged sectional view showing a structure of a gear removal preventive means of the gear drive mechanism of FIG. 1; Fig. 3 is a perspective view of a washer of FIG. 2; Fig. 4 is a perspective view showing a label writer to which the gear drive mechanism of the embodiment of the invention is applied; Fig. 5 is a perspective view showing a state where a lid of the label writer of FIG. 4 is open with respect to a main body; Fig. 6 is a diagram showing an inside of the label writer of FIG. 4; and Fig. 7 is a diagram showing a state where a label cassette is installed inside of the main body of the label writer of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the invention will be described with reference to the drawings. FIG. 1 is a diagram showing a structure of a gear drive mechanism 1 installed in an office product. FIG. 2 is an enlarged sectional view showing a structure of a gear removal preventive 17 of the gear drive mechanism 1. FIG. 3 is a perspective view of a washer 25 used in the gear removal preventive 17. The gear drive mechanism 1 shown in FIG. 1, for example, is applied to a label writer X shown in FIG. 4, which is an office product, as its drive mechanism. The label writer X feeds a label tape from a label cassette and prints characters and the like on the label tape. In FIG. 1, the gear drive mechanism 1 includes a plurality of shafts, a first shaft 2 to a seventh shaft 8; a plurality of gears, a first gear 9 to a seventh gear 15, which are fit into the respective shafts; and the gear removal preventive 17 for the first gear 9 of the first shaft 2 and the third gear 11 of the third gear 4. These members 2 to 15 and 17 are provided on a base plate 18. On the base plate 18, there are a stepping motor 19 driving the gear drive mechanism 1, a swing lever 41 having a platen roller 20 for printing characters and the like on the label tape and a feed roller 21, a print head 42, and a lever 43 moving a cutter for cutting the label tape. The first gear 2 to seventh gear 8 upwardly protrude from the base plate 18 in parallel. Of the gears 2 to 8, the fourth gear 5 is a take-up shaft of the label cassette and a drive shaft. The sixth shaft 7 is a drive shaft for driving a tape feed roller cam 36 provided to the label cassette. The first gear 9 to seventh gear 15 shown in the drawing are fit into the first shaft 2 to the seventh shaft 8, respectively. In the first shaft 2, the first gear 9 including a small-diameter gear 9A and a large-diameter gear 9B integrated in this order from the base plate 18 side is fit and the removal preventive 17 described later is provided to the shaft at its end. The large-diameter gear 9B of the first gear 9 engages an output gear 22 of the DC motor 19. In the second shaft 3, the second gear 10 including a large-diameter gear 10B and a small-diameter gear 10A integrated in this order from the base plate 18 side is fit. The large-diameter gear 10A of the second gear 10 engages the small-diameter 9B of the first gear 9. The large-diameter gear 10A of the second gear 10 is prevented from coming off because the large-diameter gear 10 A is sandwiched between the large-diameter gear 9B of the first gear 9 and the base plate 18. In the third shaft 4, the third gear 11 including a small-diameter gear 11A and a large-diameter gear 11B integrated in this order from the base plate 18 side is fit and the removal preventive 17 is provided to the shaft at its end. The large-diameter gear 11B of the third gear 11 engages the small-diameter gear 10B of the second gear 10. In the fourth shaft 5, the fourth gear 12 and a take-up shaft 28 are fit in this order from the base plate 18 side. The fourth gear 12 engages the large-diameter gear 11B of the third gear 11. The fourth shaft 5 and the take-up shaft 28 protrude toward you and engage the cassette. The E-shaped removal preventive clip described above is fit to the end of the fourth shaft 5. Therefore, the fourth gear 12 and the take-up shaft 28 is prevented from coming off from the forth shaft 5. In the fifth shaft 6, the fifth gear 13 is fit in line with the base plate 18. The fifth gear 13 engages the small-diameter gear 11A of the third gear 11. The fifth gear 13 is prevented from coming off because the fifth gear 13 is sandwiched between the large-diameter gear 11B of the third gear 11 and the base plate 18. In the sixth shaft 7, the sixth gear 14 is fit in line with the base plate 18. In the seventh shaft 8, the seventh gear 15 is fit in line with the base plate 18. The sixth gear 14 and the seventh gear 15 engage the fifth gear 13. The sixth gear 14 and the seventh gear 15 each has collar 16, 16. The sixth gear 14 and the seventh gear 15 are prevented from coming off because the collars 16, 16 of the sixth gear 14 and the seventh gear 15 are sandwiched between the lower surface of the fifth gear 13 and the base plate 18. The gear drive mechanism 1 transmits rotation of the DC motor 19 to the gear 12 via the gears 9, 10, 11 while reducing its speed, and rotates and drives the tape feed roller cam 36 and the seventh gear 15 via the gears 11 to 13 while rotating and driving the take-up shaft 28. The seventh gear 15 rotates and drives the platen roller 20 via a gear not shown which is provided under the platen roller 20 on the same shaft as the platen roller 20 so that the gear can rotate together with the platen roller 20. The gear removal preventive 17 is applied to the first shaft 2 and the third shaft 4 that are countershafts and prevent the gear from coming out at the end. As shown in FIG. 2, the gear removal preventive 17 for the third shaft 4 includes a removal preventive groove 23, an insertion groove 24, and a washer 25. The removal preventive groove 23 is a circular groove formed around the end of the third shaft 4. The insertion groove 24 is formed in a side surface of the large-diameter gear 11B of the fourth gear 11. The insertion groove 24 is formed around the third shaft 4, extending in a direction of the diameter. As shown in FIG. 3, the washer 25 is formed in a ring shape and has a slit 26 extending in the direction of diameter. The washer 25 is made of resin, such as plastic material, so that the thickness of the washer 25 can be 0.25 mm or less. The width of the removal preventive groove 23 and the insertion groove 24 of FIG. 2 is also formed so as to be the same dimension as the thickness of the washer 25. The washer 25 is fit in the removal preventive groove 23 using the slit 26 with elastically deformed as shown by double dashed chain line. At the same time, the washer is installed in the insertion groove 24 by releasing the elastic deformation. The removal preventive 17 for the first shaft 2 has the same structure as that of the removal preventive 17 for the third shaft 4, except that the removal preventive 17 for the first shaft 2 has no insertion groove 24. Therefore, the first gear 9 and the forth gear 11 are prevented from coming off from the first shaft 2 and the third shaft 4, respectively. Because the fourth gear 11 is prevented from coming off, the second gear 10 and the fifth gear 13 provided under the fourth gear 11 are also prevented from coming off the shafts. The washer 25 is detachable from the fourth gear 11 using a recessed portion 27. The recessed portion 27 is formed within the insertion groove 24 provided in the side surface of the fourth gear 12 and outwardly extends in the direction of diameter of the fourth gear 11 from the third shaft 4. By rotating the washer 25 around the third shaft 4, the slot 26 is positioned over/near the recessed portion 27. In this state, a slim tool is inserted into the recessed portion 27 and the washer 25 is lifted from the fourth gear 11. By doing so, the washer 25 is vertically stretched at the slit 26 as a boundary. In this state, the washer 25 can be removed from the removal preventive groove 23 by moving the tool along the shaft. The washer 25 for the first gear 9 can be also removed from the first shaft 2 in the same manner. As described above, according to the gear drive mechanism 1 of the embodiment of the invention, the gears 9 to 15 can be prevented from coming off using the thin washer 25. When the washer 25 is made of plastic material, the washer can be thin, that is, the thickness of the washer can be 0.25 mm or less. Therefore, the removal prevention groove 23 of the third shaft 4 and the first shaft 2 can be also narrow conforming to the thickness of the washer 25. The amount of protrusion of the third shaft 4 and the first shaft 2 from the fourth gear 11 and the first gear 9 can be restricted to a minimum. Accordingly, the thickness of the gear drive mechanism 1 can be reduced. By inserting the slim tool into the recessed portion 27, the washer 25 can be easily removed from the fourth gear 12 and the first gear 9 and the gears 9 to 15 can be disassembled. As shown in FIGS. 4 and 5, the gear drive mechanism 1 is applied to the label writer X, which is the office product, as a drive mechanism. The label writer X includes a lid 31 and a main body 32. The lid 31 is provided to the main body 32 by hinges and freely covers and uncovers the main body 32. The lid 31 is provided with a keyboard for inputting data of characters. In the main body 32, a control circuit board that processes the data, the gear drive mechanism 1, the DC motor 19, the platen roller 20 and the print head 42 are provided. As shown in FIGS. 6 and 7, the gear drive mechanism 1 is attached to the bottom of the main body 32 so as to be under a cover 33 provided in the main body 32. In the cover 33, an opening 34 is formed so that the take-up shaft 28 of the fourth shaft 5 passes therethrough. The label cassette 35 is installed on the upper side of the cover 33. The label cassette 35 is engaged with the take-up shaft 28 protruding from the cover 33 and then installed in the main body 32. The label tape is housed in the label cassette 35 in a wound state. The label writer X feeds the label tape to the print head 42 from the label cassette 35 and prints input characters and the like onto the label tape using the print head 42 and the platen roller 20 by driving the gear drive mechanism 1 by the DC motor 19. Then, the label writer X discharges the printed label tape outside of the main body 32 by the tape feed roller cam 36 provided to the end of the sixth shaft 7 and the feed roller 21 and cuts the label tape by pressing the lever 43 for moving the cutter. As described above, when the gear drive mechanism 1 of the embodiment of the invention is applied to the label writer X that is the office product, the gear drive mechanism 1 can become thin so that the label writer X can be also thin. Therefore, a downsizing of the label writer X can be achieved. The ends of the shafts, except for the fourth shaft 5 that is the take-up shaft, are covered with the cover 33. Therefore, the ends of the shafts are hidden, so that the inside of the main body 32 of the label writer X is visually simplified. Further, the gear drive mechanism 1 is thin, so that the space for the cassette installation is provided over the gear drive mechanism 1 and the cover 33. The gear drive mechanism 1 of the embodiment of the invention has been described using an example that the gear drive mechanism 1 is applied to the label writer X. However, the invention is not restricted to the embodiment described above. The gear drive mechanism 1 can be also applied to other office products, such as printers and facsimile machines. In particular, when the gear drive mechanism 1 is applied to the small office products, the internal space in the main body can be made effective use. Further, in the gear drive mechanism 1 of the embodiment described above, the removal preventive 17 including the washer 25 is applied to the first shaft 2 and the third shaft 4. Because the largest gear is fit into the third shaft 4, the removal preventive 17 using the washer 25 is applied to only the third shaft 4. As a result, the thickness of the gear fit to the first shaft 2 becomes thin, so that the removal preventive 17 using the specified E-shaped removal preventive washer can be used. Further, the number of shafts and gears structuring the gear drive mechanism 1 and an arrangement are not restricted to the structure of FIG. 1. Further, the use of plastic material is the best way to thin the washer 25. However, the use of metals is not precluded to thin the washer 25.

Claims: A gear drive mechanism (1) for office products that drives a specific shaft (5,7,8) of a plurality of shafts (2 to 8) which cantilever from a base plate (18) attached within the office product, and gears (9 to 15) are fit to the shafts (2 to 8) and engaged with each other; wherein a groove (23) is formed around an end of at least one of the shaft (4) other than the specific shaft (5,7,8); a washer (25) having a ring-shape and a slit (26) in a direction of diameter is fit in the groove (23) as a removal preventive (17) of the gear (11); characterized in that an insertion groove (24) is formed in a side surface of the gear (11) of the at least one of the shaft (4) other than the specific shaft (5,7,8); and a recessed portion (27) is provided in a part of a side surface of the gear (11) in the insertion groove (24). The gear drive mechanism for the office products claimed in claim 1, characterized in that the washer (25) is made of plastic and is 0.25 mm or less in thickness. The gear drive mechanism for the office products claimed in claim 1 or 2, characterized in that a cover (33) having an opening (34) through which the drive shaft (5) passes is attached so as to be opposed to the base plate (18).

Inventors: SUGIMOTO KIYOSHI, TAKAHASHI TOSHIHIRO, SUGIMOTO, KIYOSHI, TAKAHASHI, TOSHIHIRO
Applicants: BROTHER IND LTD, BROTHER KOGYO KABUSHIKI KAISHA
Application year: 2001
Main classification: F16H57
IPC codes: F16H1, F16H55, F16H57, B41J29, B41J3