CARRIAGE TRAVELLING MECHANISM

Abstract: A carriage traveling mechanism according to the pre­ stnt invention includes a carriage (1) movably mounted on a guide shaft (4), a traveling motor (6) fixedly mounted on the carriage (1), the traveling motor (6) including a pinion (8) mounted on a rotary shaft thereof, a rack (10) provided substantially in parallel to the guide shaft (4), the rack (10) being rigid longitudinally and flexible in a perpendicular direction to the longitudinal direction, the rack (10) having longitudinally a tooth part engaged with the pinion (8), the surface of the rack (10) located on the opposite side of the surface of the tooth part being substantially parallel to the guide shaft (4), a roller (9) rotatably mounted on the carriage (1), the roller (9) radially facing the pinion (8) and having contact with the opposite side surface to the tooth surface of the rack (10), the rack (10) being rotatably mounted on the frame in one end thereof and restricted by the frame in the other end thereof in the extent of moving thereof or being fixed directy on the frame in the other end thereof.

Description: The present invention relates to a carriage travelling mechanism for travelling a carriage for use in a printer and the like. A prior art carriage travelling mechanism as disclosed in EP-A 0 117 090 or 0 145 025 can be used in for example an impact type printer, etc., wherein a carriage having a printing head, etc., mounted thereon is movably attached to a guide shaft while a travelling motor such as a brushless motor is fixedly mounted on the lower surface of the carriage with a pinion mounted on a rotary shaft of the travelling motor, the pinion being engaged with a metal rack disposed in parallel to the guide shaft. The carriage travelling mechanism serves to travel the carriage along the guide shaft by thrust force produced due to rotation of the pinion in engagement with the rack, the pinion being fixed on the rotary shaft of the travelling motor, by driving the travelling motor. The carriage travelling mechanism can reciprocate the carriage using the positive and negative two directional rotations of the pinion caused by the travelling motor. However, in the prior art carriage travelling mechanism both ends of the rack must be mounted on a base frame, etc., so as to permit the rack to be parallel to the guide shaft. Accordingly, mounting and adjusting become difficult. In addition, since the rack is made of rigid metal accurate feed of the carriage is difficult due to backlash produced between the rack and the pinion. Furthermore, the travelling motor is likely to be subjected to additional load in travelling of the carriage owing to the backlash as well as an insufficient parallel relation between the guide shaft and the rack. Moreover, since the rack must have a tooth part formed with sufficient accuracy to be engaged with the pinion by cutting a metal raw material, it requires a high level of manufacturing technology therefor at the sacrifice of it being costly. In DE-B-22 39 555, a device for guiding a carriage along guide columns is discussed in which the guide columns can be partly elastically deformed to compensate for tolerances during the movement of the carriage. In view of the drawbacks of the conventional carriage travelling mechanism, it is an object of the present invention to provide a carriage travelling mechanism capable of mounting a rack thereon with ease without requiring adjustment of parallelism of the rack to a guide shaft, while capable of forcing the carriage to travel with use of an inexpensive rack easy to be manufactured as well as reducing any load additionally applied to a travelling motor. The above object is achieved by a carriage travelling mechanism according to claim 1. The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. Fig. 1 is a perspective view, partly fractured, illustrating a carriage travelling mechanism, Fig. 2 is a side elevational view of the same, Fig. 3 is a perspective view showing a parallel link member, Fig. 4 is a perspective view illustrating a mounting portion between a frame and a rack, Fig. 5 (A), (B) are respectively a plan view showing a coil spring, and Fig. 6 is a side elevational view of portions of the rack and the pinion illustrating engagement therebetween. An embodiment of a carriage travelling mechanism according to the present invention will be described with reference to the accompanying drawings. As shown in Figs. 1 and 2 showing a carriage travelling mechanism according to the present invention, designated at 1 is a carriage, and 2 is a cylindrical part provided on the front of the carriage 1 and adapted to have an arm 3 formed thereon as shown in Fig. 2. Designated at 4 is a guide shaft fixedly mounted in its both ends on a side plate, etc., (not shown) adapted to stand on a base plate 5 of a printer, the carriage 1 being movably attached to the guide shaft 4 via the cylindrical portion 2. Likewise, designated at 6 is a travelling motor fixed on the lower surface of the carriage 1 and adapted to have a pinion 8 attached to a rotary shaft 7 of the travelling motor 6, and 9 is a roller rotatably supported on the arm 3 of the carriage 1 radially opposite to the pinion 8 and spaced away in a prescribed interval. Designated at 10 is a flexible rack comprising polyamide resin and the like and being rigid longitudinally thereof as well as flexible perpendicularly to the longitudinal direction. The rack 10 has a stop pawl 11 elastically displaceable as shown in Fig. 1 (in detail, refer to Fig. 4) on its one end and a stop hole 12 provided therein being I-shaped for example in its cross section. The rack is mounted on the base plate 5 by fitting a projection 13 adapted to stand on the base plate 5 in the stop hole 12 while engaging the stop pawl 11 with a stopper part 14 provided in the vicinity of the projection 13. Hereupon, the stop hole 12 is set to be slightly larger than the thickness and width of the projection 13 whereby the rack 10 is made rotatable horizontally with respect to the projection 13 while being restricted in space to a certain region. In the present embodiment, the rack 10 so made rotatable is put between the pinion 8 and the roller 9 to bring a tooth part of the rack 10 and that of the pinion 8 into engagement with each other, while the rack 10 is pressed to the pinion side 8 owing to the roller 9. Furthermore, with the stop hole 12 being round-shaped, a cylindrical shaft may be provided on the base plate 5 instead of the projection 13 and the cylindrical shaft may be fitted in the round-shaped stop hole 12 for rotatably mounting one end of the rack 10 on the base plate 5. Designated at 15 is a printing head mounted on the carriage 1, the printing head printing any data on a paper (not shown) set on the platen 16 of Fig. 2 following the travelling of the carriage 1. Likewise, designated at 17 is a parallel link member mounted on the rear end of the carriage 1 illustrated in detail in Fig. 3. The parallel link member 17 has a slider 18 and is fixed on the carriage 1 via a screw 19. The slider 18 is engaged slidably with a rail part 20 being formed in or mounted integrally on the base plate 5. Designated at 21 is a platen gap (a gap between the platen 16 and the printing head 15) adjusting screw, whose tip has contact with the upper part of the slider 18. The carriage 1 is rotated on the guide shaft 4 by turning the adjusting screw 21 clockwise or anticlockwise, and thereby the platen gap can be reduced or enlarged. On the other hand, the other end of the rack 10 has a post 22 and a groove 23 in close vicinity of the post 22, and a coil spring 25 is provided between the post 22 and a second projection 24 formed by partly notching the base plate 5 in the close vicinity of the other end of the guide shaft 4. Then, operation of the above arrangement will be described. With the rotary shaft 7 being positively rotated by driving the travelling motor 6, the pinion 8, while engaged with the rack 10, is rotated intrgrally with the rotary shaft 7 to produce thrust force whereby the carriage 1 travels in a prescribed direction along the guide shaft 4. With the travelling motor 6 being driven so as to permit the rotary shaft 7 to be inversely rotated, the pinion 8 is also inversely rotated integrally with the rotary shaft 7 whereby the carriage 1 travels in the opposite direction to the above travelling one. Accordingly, the carriage 1 can be adapted to travel in forward and backward directions along the guide shaft 4 in a reciprocating manner. In the present embodiment, the rack 10 is adapted to be rotatable around one end thereof. Accordingly, although the rack 10 tends to run away owing to the force produced by the rotation of the pinion 8, engagement between the rack 10 and the pinion 8 is assured at all times since a portion at which the rack 10 and the pinion 8 are engaged with each other is pressed against the pinion 8 by the roller 9 supported on the arm 3 of the carriage 1. In addition, since the rack 10 is flexible, an insufficient parallel relation between the guide shaft 4 and the rack 10 and backlash between the rack 10 and the pinion 8 are absorbed. Therefore, it is possible to permit the carriage 1 to travel accurately when any reduced load is applied to the motor 6 upon the travelling of the carriage 1. Next, another embodiment will be described with reference to Figs. 1 to 4 and Figs. 5 and 6. The present example is the same as the previous one except the point in which way the coil spring 25 can be mounted. In the present example, the coil spring 25 shown in Fig. 1 is as follows. Namely, the coil spring 25 is adapted to be previously different, in its angle between a substantially annular stopper part 25a provided on one end of the coil spring 25 and a similar one 25b provided on the other end of the same, from each other by about 90 degrees around the axis of the coil spring. In addition, the stopper part 25b is hung on the post 22 of the rack 10 while a linear part between the stopper part 25b and a helical part is adapted to pass through the groove 23, and further the stopper part 25a , while twisted by about 90 degrees, is hung on the second projection 24 of the base plate 5. Hereby, the coil spring 25 is provided between the post 22 and the second projection 24 whereby the rack 10 is prevented from being horizontally twisted by allowing the spring 25 to pull the other end of the rack 10 while the rack 10 is pressed against the pinion 8 to permit the rack 10 and the pinion 8 to be engaged with each other without any backlash due to reaction force produced by the horizontal twisting as described before, as shown by the arrow in Fig. 6. Hereupon, provided that the second projection 24 is perpendicular to the post 22, i.e., the post 22 and the second projection 24 are formed vertically or horizontally respectively, the same effect can be assured by a procedure as described below. Namely, first the spring 25 is formed as shown in Fig. 5 (B) and the stopper 25a is provided, by twisting it about 90 degrees as shown in Fig. 5 (A), upon hanging the stopper part 25a on the second projection 24. Then, effect of the arrangement described above will be described. With the rotary shaft 7 being positivly rotate by driving the travelling motor 6, the pinion 8 , while engaged with the rack, is rotated integrally with the rotary shaft 7 to produce thrust force whereby the carriage 1 travels in a prescribed direction along the guide shaft 4. While, with the travelling motor 8 being driven so as to permit the rotary shaft 7 to be inversely rotated, the pinion 8 is also inversely rotated integrally with the rotary shaft 7. Accordingly, the carriage 1 travels in the opposite direction to the above travelling one thereof owing to the thrust force produced as described above. As a result, the carriage 1 can be travelled in forward and backward directions along the guide shaft 4. In the present embodiment, although the rack 10 is adapted to be rotatable around one end thereof within the prescribed limit, the other end is prevented from being horizontally twisted due to tensile force of the coil spring if provided between the post 22 and the projection 24, and an engagement portion between the rack 10 and the pinion 8 and the roller 9 supported on the arm 3 of the carriage 1 in a sandwiching relation, whereby the engagement between the rack 10 and the pinion 8 can be assured at all time. In addition, since the rack 10 is flexibly constructed, and the rack 10 is pressed against the pinion side 8 due to reaction force yielded by twisting one end of the coil spring 25, an insufficient parallel relation of the guide shaft 4 to the rack 10 and any backlash between the rack 10 and the pinion 8 are both moderated. Consequently, the rack 10 and the pinion 8 are engaged with each other without producing any backlash therebetween, whereby the carriage 1 can be travelled accurately when any reduced load is applied to the travelling motor 6 upon travelling of the carriage 1. Hereupon, although the above embodiment is described as a carriage travelling mechanism in a printer, it goes without saying that any apparatus having a carriage function may be applied without any limitation on the present invention. Although certain preferred embodiments have been shown and described, it should be understood that many changes and modifications may be made therein without departing from the scope of the appended claims.

Claims: A carriage travelling mechanism comprising: (a) a carriage (1) movably mounted on a guide shaft (4); (b) a travelling motor (6) fixedly mounted on said carriage (1), said travelling motor (6) including a pinion (8) mounted on a rotary shaft (7) thereof; (c) a rack (10) provided substantially in parallel to said guide shaft (4), said rack (10) having longitudinally a tooth part engaged with said pinion (8), the surface of said rack (10) located on the opposite side of said tooth surface being substantially parallel to said guide shaft; and the mechanism being characterised in that said rack (10) is rigid longitudinally and flexible in a direction perpendicular to said longitudinal direction, and in that (d) a roller (9) rotatably mounted on said carriage (1), said roller (9) radially facing said pinion (8) and having contact with the side surface opposite to the tooth surface of said rack; said rack (10) being rotatably mounted on a frame in one end thereof and being fixed on said frame in the other end thereof either directly or via an elastic member. A carriage travelling mechanism according to claim 1, wherein said carriage travelling mechanism has a stop pawl (11) and a stop hole (12) provided on and in one end of said rack (10), a projection (13) and a stopper part (14) provided on said frame, said projection (13) of the frame being fitted in said stop hole (12) of said rack (10) while said stop pawl (11) of the rack (10) is engaged with said stopper part (14) of the frame, one end of said rack (10) being rotatably mounted on the frame. A carriage travelling mechanism according to claim 1 or 2, wherein said elastic member for mounting said rack (10) on said frame is a coil spring (25). A carriage travelling mechanism according to claim 3, wherein said coil spring (25) is mounted while being twisted by about 90 degrees around an axis of said spring (25).

Inventors: HAYASHI, KUNIHARU OKI ELECTRIC IND. CO. LTD., ISOBE, MINORU OKI ELECTRIC IND. CO. LTD., KIKUCHI, HIROSHI OKI ELECTRIC IND. CO. LTD., MAEKAWA, MASANORI OKI ELECTRIC IND. CO. LTD., TANUMA, JIRO OKI ELECTRIC IND. CO. LTD.
Applicants: OKI ELECTRIC INDUSTRY COMPANY, LIMITED
Application year: 1986
Main classification: B41J19
IPC codes: B41J19