JP2999933B2 - Ribbon shift mechanism - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ribbon shift mechanism of a serial printer for performing multicolor printing.

[0002]

2. Description of the Related Art When performing color printing in a serial printer, a ribbon cassette containing color ink ribbons of a plurality of colors (generally, four colors of black, cyan, magenta, and yellow) is vertically moved with respect to a print head. , And any color is selectively printed or overprinted. As a ribbon shift mechanism of this type, a mechanism using a camshaft 51 having a spiral cam groove 50 as shown in FIG. 5 is known. A gear 52 is provided at the lower end of the camshaft 51.
The camshaft 51 rotates one shift at a time by the rotational force given via the. The camshaft 51 is fitted to a ribbon holder 53 that holds a ribbon cassette (not shown), and the cam groove 50 is engaged with a projection 54 provided at the fitting portion. In the actual ribbon shift operation, the cam shaft 51 rotates in conjunction with the spacing operation of the carriage (not shown), so that the projection 54 of the ribbon holder 53 is moved to the cam groove 50.
Accordingly, the ribbon holder 53 moves up and down according to the rotation direction of the cam shaft 51, and the color ink ribbon accommodated in the ribbon cassette shifts up and down with respect to the print head.

[0003]

However, in the above-described conventional ribbon shift mechanism, the cam groove 50 of the camshaft 51 is formed spirally with a constant inclination angle in the axial direction as shown in FIG. Because
There were the following inconveniences. That is, when the camshaft 51 is rotated in conjunction with the spacing operation of the carriage, the projection 54 provided on the ribbon holder 53 slides according to the curve of the cam groove 50 shown in FIG. The ribbon holder 53 changes in the vertical direction y according to the rotation angle θ of the cam shaft 51. Therefore,
Even if the rotation stop angle of the camshaft 51 slightly varies, the shift position of the color ink ribbon with respect to the print head is shifted.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned disadvantages, and an object of the present invention is to provide a method for accurately positioning a color ink ribbon with respect to a print head without being affected by variations in a rotation stop angle of a camshaft. An object of the present invention is to provide a ribbon shift mechanism that enables a shift operation.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a ribbon holder for holding a ribbon cassette and a cam groove for engaging a projection provided on the ribbon holder. A camshaft that is rotatably provided in an interlocking manner with the spacing operation of the carriage, and the ribbon holder is moved up and down by rotating the camshaft by one shift to thereby move the color ink stored in the ribbon cassette. In a ribbon shift mechanism of a serial printer that shifts a ribbon up and down with respect to a print head, cam grooves of a cam shaft are formed between a plurality of horizontal portions formed at a predetermined circumferential pitch and each end of the horizontal portions. It is formed in a generally helical shape by an inclined portion that is, double
The horizontal part of the number shifts the color ink ribbon by one.
Position corresponding to the angle of rotation of the camshaft.
One piece of water formed in a line in the axial direction of the camshaft
In order to shift the flat part and the color ink ribbon by one,
Water in a position that does not correspond to the angle at which the
Formed every 180 ° between flat parts, starting from the one horizontal part
And another horizontal portion .

[0006]

In the ribbon shift mechanism of the present invention, since the cam groove of the camshaft is formed in a substantially spiral shape with the horizontal portion and the inclined portion, the cam is not provided when the projection of the ribbon holder is located at the horizontal portion of the cam groove. Even if there is some variation in the rotation stop angle of the shaft, no shift occurs in the shift position of the color ink ribbon with respect to the print head. Also, color incremental
The angle at which the camshaft rotates to shift the bon by one
One horizontal part is formed at the position corresponding to the
The camshaft rotates to shift the ribbon one shift
At a position that does not correspond to the angle
Because other horizontal parts are formed every 80 °,
The center position of the horizontal part is the parting position (parting line)
By adopting the split structure in the molding die,
The product can be easily taken out.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. As shown in FIG. 2, the ribbon shift mechanism in the present embodiment is configured based on a box-shaped gear case 11 having an open top. Gear case 11
A ribbon holder 13 is vertically movably incorporated through three sets of parallel links 12 at the upper part of the printer, and a ribbon cassette (not shown) is mounted on the ribbon holder 13 during printing.

A drive gear 14 is provided inside the gear case 11 and rotates in conjunction with a spacing operation of a carriage (not shown). The drive gear 14 meshes with a change gear 15. The change gear 15 is vertically movably fitted to a support shaft 16 and is urged downward by an urging member 17 such as a leaf spring. On the other hand, in FIG.
Is a camshaft, a cam groove 19 is formed on the outer peripheral surface of the camshaft 18, and a gear portion 20 is formed at the lower end. The camshaft 18 is attached to the ribbon holder 1
3 and is erected in a state of being fitted to the shaft holder 21. The cam groove 19 is engaged with a projection (not shown) provided on the inner surface of the shaft holder 21. Further, a cam gear 22 is provided between the change gear 15 and the camshaft 18.
2 changes the rotational force of the change gear 15 to the camshaft 1
8.

In addition, a detent spring 23 (see FIG. 3) is provided at the bottom of the gear case 11. The detent spring 23 regulates the stop position of the cam gear 22 in the rotation direction, and is selectively fitted into a recess (not shown) formed at a predetermined circumferential pitch, for example, a 90 ° pitch on the bottom surface of the cam gear 22. Gear case 1
1 is provided with a clutch mechanism for intermittently meshing the change gear 15 and the cam gear 22. This clutch mechanism includes, for example, an electromagnet 24 and an armature 25. The armature 25 is urged toward the change gear 15 by a spring 26 connected to a base end thereof. When the electromagnet 24 is energized by energization, the armature 25 is attracted to the electromagnet 24 against the elastic force of the spring 26. Further, a gear cover 27 is placed over the drive gear 14 and the cam gear 22, and the gear cover 27 prevents the drive gear 14 and the cam gear 22 from floating. Further, a U-shaped notch 28 is formed in the outer portion of the gear cover 27, and the notch 28 engages with the peripheral groove 29 of the camshaft 18, whereby the lower end position of the camshaft 18 is regulated. ing.

Here, the feature of the ribbon shift mechanism according to the present invention is that the camshaft 18 is provided upright to move the ribbon holder 13 up and down during the ribbon shift.
In the structure. FIG. 1 is a diagram illustrating the structure of a camshaft according to the present embodiment. 1A is a two-sided view of the camshaft, FIG.
(C) is the B arrow view.

As shown in FIG. 1, a cam groove 19 is formed on the outer peripheral surface of the camshaft 18 in the axial direction.
a and the inclined portion 19b are formed in a substantially spiral shape.
The horizontal portion 19a is formed on the outer peripheral surface of the camshaft 18 at a predetermined circumferential pitch, for example, at a 180 ° pitch. Further, as shown in FIG. 1C, each horizontal portion 19a has a predetermined angle range α (α ≒ in the illustrated example) between one and the other of the outer peripheral surface of the shaft via the axis of the camshaft 18. 3
0 °). The inclined portion 19b is
a is formed with a certain inclination angle between the respective end portions of the a.
Further, each end of the inclined portion 19b is continuously formed while drawing a smooth curve with respect to each end of the horizontal portion 19a.

Here, the above-mentioned horizontal portion 19a is formed at a circumferential pitch corresponding to the rotation angle of one shift of the camshaft 18. That is, when the rotation angle for one shift of the camshaft 18 is set to 360 °, the circumferential pitch corresponding to the rotation angle is, for example, 90 °, 180 °, 3 °.
The horizontal portions 19a are formed at a circumferential pitch of 60 °. By the way, in this embodiment, the horizontal portion 19a has a half of the rotation angle of one shift of the camshaft 18, that is, 18 degrees.
It is formed at a pitch of 0 °, and the reason will be described in detail later.

Subsequently, the camshaft 1 having the above configuration
The operation of the ribbon shift mechanism using No. 8 will be described.
First, in a state where the electromagnet 24 is not energized, FIG.
As shown in (a), the tip of the armature 25 enters the lower end of the change gear 15. In this state,
Change gear 15 urged downward by urging member 17
Are opposed to the toothless portion 30 of the cam gear 22, and the meshing state between them is not obtained. Therefore, even if the drive gear 14 (FIG. 2) rotates in conjunction with the spacing operation of the carriage, only the change gear 15 meshing with the drive gear 14 rotates, and the cam gear 22 and the cam shaft 18 remain stopped. maintain.

On the other hand, when the electromagnet 24 is energized only once,
As shown in FIG. 3B, the armature 25 is
It is sucked to the side 4, whereby the tip of the armature 25 comes off the lower end of the change gear 15. Then,
The change gear 15 is pressed down by the urging member 17, whereby the lower end of the change gear 15 is placed on the cam surface 31 of the cam gear 22, and the change gear 15 meshes with the cam gear 22, and the meshing state of both is obtained. Can be Accordingly, when the driving gear 14 (FIG. 2) rotates in conjunction with the spacing operation of the carriage, the rotation driving force is transmitted to the cam gear 22 via the change gear 15, and thus, via the gear section 20. The camshaft 18 meshing with the cam gear 22 also rotates, and the ribbon holder 13 moves up and down according to the rotation direction. At this time, the tip portion of the detent spring 23 comes off from a concave portion (not shown) provided on the bottom surface of the cam gear 22 as the cam gear 22 rotates. Thereafter, the change gear 15 gradually moves upward following the cam surface 31 while rotating together with the cam gear 22. Then, when reaching the chevron top of the cam surface 31, the tip of the armature 25 enters the lower end of the change gear 15 again, thereby changing the change gear 1.
5 returns to the state where it faces the toothless portion 30 of the cam gear 22.
At this time, the cam gear 22 is
Is rotated to a prescribed position by the action of a force trying to enter into the recess (not shown), and the rotation stop position is regulated by the detent spring 23 being completely fitted into the recess.

As described above, in the above-described ribbon shift mechanism, each time the electromagnet 24 is energized once, the cam gear 22 rotates by a predetermined angle.
Also rotates by a predetermined angle (360 ° in the illustrated example). At this time, a projection (not shown) provided on the shaft holder 21 of the ribbon holder 13 slides along the cam groove 19 as the camshaft 18 rotates. Here, in the present embodiment, the circumferential pitch (18 in the present embodiment) corresponding to the rotation angle of one shift of the camshaft 18 (360 ° in the present embodiment).
The horizontal portion 19a of the cam groove 19 is formed at a pitch of 0 °. Therefore, when the rotation of the camshaft 18 is stopped, the engagement position of the above-mentioned projection is adjusted to the horizontal portion 1 of the cam groove 19.
9a, the camshaft 1
Each time the 8 performs a rotation operation for one shift, the above-mentioned protrusion comes to be located on the horizontal portion 19 a of the cam groove 19. That is, as shown in FIG. 4, the projection 32 provided on the shaft holder 21 slides along the cam groove 19, so that the camshaft 18 is shifted by one shift, that is, 360 °.
When rotated, the protruding portion 32 becomes the inclined portion 19b → the horizontal portion 1
9a → they are again located at the horizontal portion 19a via the inclined portion 19b. When the projection 32 of the shaft holding portion 21 is positioned at the horizontal portion 19a of the cam groove 19 as shown in the drawing by the rotation operation of the cam shaft 18 for one shift, the printing color of the color ink ribbon to the printing head (not shown) is shown. Switches.

Thus, the projection 32 on the ribbon holder 13 side
Is located at the horizontal portion 19a of the cam groove 19, the angle range α at which the horizontal portion 19a is formed in the circumferential direction of the shaft.
Even when the camshaft 18 is rotated in the inside (see FIG. 1), the engagement position between the cam groove 19 and the projection 32 in the vertical direction does not change. Therefore, when the camshaft 18 is rotated in conjunction with the spacing operation of the carriage, even if the rotation stop angle of the camshaft 18 slightly varies, the height of the ribbon holder 13 is kept constant. Therefore, no shift occurs in the shift position of the color ink ribbon with respect to the print head.

When the color ink ribbon is shifted upward with respect to the print head, a frictional force due to the load of the ribbon cassette and the ribbon holder 13 also acts on the sliding portion between the cam groove 19 and the projection 32. Therefore, when the rotation of the camshaft 18 is stopped, the detent spring 2
In order to ensure that the distal end of the detent spring 3 is fitted into the concave portion of the cam gear 22, the elastic force of the detent spring 23 must be set large enough to resist the frictional force. In the conventional camshaft structure, the cam groove is formed in a spiral shape with a constant inclination angle over the shaft axis direction.
After the change gear 15 and the cam gear 22 are disengaged from each other, the elastic force of the detent spring 23 causes the cam gear 22 to move.
In order to rotate the ribbon holder to the specified position, an extremely large elastic force is required to lift the ribbon holder 13 on which the ribbon cassette is mounted. Then, in proportion to the elastic force of the detent spring 23, the load on the gear train when the tip of the detent spring 23 is removed from the concave portion of the cam gear 22 at the start of the shift operation also increases, so that the gear life is shortened by wear, and It is extremely difficult to reduce the size of the entire mechanism.

On the other hand, in the camshaft structure of this embodiment,
The cam groove 19 of the camshaft 18 is formed in a substantially spiral shape by the horizontal portion 19a and the inclined portion 19b. In the shift operation, when the rotation of the cam gear 22 is stopped, the projection 32 of the ribbon holder 13 19a. For this reason, the elastic force of the detent spring 23 does not require a large elastic force to lift the ribbon holder 13 on which the ribbon cassette is mounted, and opposes the sliding friction between the cam groove 19 and the projection 32 in the horizontal portion 19a. A sufficient elastic force is sufficient. Therefore, since the elastic force of the detent spring 23 can be reduced as compared with the related art, the load on the gear train when the tip of the detent spring 23 is removed from the concave portion of the cam gear 22 at the start of the shift operation is reduced, thereby prolonging the life of the gear train It is possible to reduce the size and the size of the entire mechanism.

Further, in the conventional camshaft structure, when the color ink ribbon is shifted downward with respect to the print head, the cam groove is uniformly inclined in the shaft axis direction. As a result, the projection of the ribbon holder stops at a position beyond the specified position of the cam groove, which is a structure that is liable to cause a so-called overrun phenomenon. Therefore, if the elastic force of the detent spring 23 is increased in order to surely stop the projection of the ribbon holder at the prescribed position of the cam groove, various problems such as shortening of the life of the gear train and enlargement of the entire mechanism are caused as described above. .

On the other hand, in the camshaft structure of the present embodiment, as described above, since the projection 32 of the ribbon holder 13 is located at the horizontal portion 19a of the cam groove 19 during the shifting operation, the ribbon holder 13 In this case, the inertia force due to the weight of the projections 32 is rapidly attenuated by the sliding friction of the projections 32 in the horizontal portion 19a. At the center).

In addition, in the structure of this embodiment, the cam
In forming a plurality of horizontal portions 19a on the shaft 18,
Therefore, as shown in FIG. 1 and FIG.
The camshaft 18 rotates to shift the bon by one.
At a position P1 corresponding to 360 °, that is, 360 °.
One horizontal portion 19a is formed in a line in the axial direction of the shaft 18.
To shift the color ink ribbon by one
Corresponds to the angle at which the camshaft 18 rotates, ie, 360 °
Also at the position P2 which is not performed, the one
The other horizontal portion 1 is set every 180 ° with the horizontal portion 19a as a base point.
9a and the horizontal portions 19a are formed on the outer peripheral surface of the camshaft 18 at a pitch of 180 °, so that the following advantages can be obtained. That is, in actual manufacture of the camshaft, it is more preferable to perform processing by resin molding using a mold than performing cutting processing on a metal or resin bar in consideration of mass productivity in particular. With the conventional camshaft structure, the molding groove is uniformly inclined because the cam groove is uniformly inclined.When removing the molded product from the mold, it must be removed while rotating the molded product along the cam groove shape In addition, the molding operation becomes complicated and the mold structure becomes complicated. On the other hand, in the camshaft structure according to the present embodiment, the horizontal portion 19a is formed at a position that is inverted by 180 ° on the circumferential surface of the camshaft 18, so that the center position of the horizontal portion 19a is determined by the parting line Position) and a groove shape without undercut, a divided structure is adopted for the molding die, so that the molded product can be easily taken out, and the camshaft 18 can be easily manufactured with a simple mold structure. Becomes possible.

[0022]

As described above, according to the present invention,
Since the cam groove of the camshaft for moving the ribbon holder up and down is formed in a substantially spiral shape with the horizontal part and the inclined part, the camshaft rotation stop angle is set with the protrusion of the ribbon holder positioned in the horizontal part of the cam groove. Even if a slight variation occurs, the ribbon holder does not fluctuate in the vertical direction, so that the shift position of the color ink ribbon with respect to the print head does not shift. This makes it possible to accurately shift the color ink ribbon with respect to the print head without being affected by variations in the rotation stop angle of the camshaft. Also, shift the color ink ribbon by one
To a position corresponding to the angle at which the camshaft rotates
One horizontal part, and one color ink ribbon
The angle at which the camshaft rotates to
Every other 180 ° with one horizontal part as the base point.
Since the flat parts are formed, the center position of those horizontal parts
By setting the parting position (parting line)
Easily take out molded products by adopting a split structure in the molding die
The camshaft can be easily manufactured with a simple mold structure.
It becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a structure of a camshaft according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view showing an example of a ribbon shift mechanism.

FIG. 3 is a diagram illustrating the operation of a ribbon shift mechanism.

FIG. 4 is a developed view of a cam groove curve of a cam shaft in the embodiment.

FIG. 5 is a sectional view of a main part of a conventional ribbon shift mechanism.

FIG. 6 illustrates a structure of a conventional camshaft.
FIG.

FIG. 7 is a developed view of a cam groove curve of a conventional camshaft.

[Explanation of symbols]

 18 Camshaft 19 Cam groove 19a Horizontal portion 19b Inclined portion

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 35/20 B41J 35/18

Claims (1)

(57) [Claims] 1. A cam having a ribbon holder for holding a ribbon cassette and a cam groove for engaging with a projection provided on the ribbon holder, the cam being rotatably provided in an interlocking manner with a spacing operation of a carriage. A ribbon shifter for a serial printer, wherein the ribbon holder is moved up and down by rotating the camshaft by one shift to shift the color ink ribbon accommodated in the ribbon cassette up and down with respect to a print head. In the mechanism, the cam groove of the camshaft is formed in a substantially spiral shape by a plurality of horizontal portions formed at a predetermined circumferential pitch and an inclined portion formed between each end of the horizontal portion , The plurality of horizontal portions shift the color ink ribbon by one shift.
Corresponding to the angle of rotation of the camshaft to rotate
In a line in the axial direction of the camshaft.
One horizontal portion formed and one color ink ribbon
The angle at which the camshaft rotates to shift
In a position that does not respond to the one horizontal part.
With other horizontal parts formed every 180 ° as points
Ribbon shift mechanism, characterized in that that.