Ribbon Platform Mechanism for Extending Ribbon Life

The present invention relates to ribbon feeding mechanisms for printers and typewriters, and more particularly to such mechanisms which extend the useful life of a ribbon.

In the present-day printers such as printers of the short stroke or dot matrix type, after each line of characters is imprinted, the ribbon is caused to increment horizontally. Generally, the ribbon is caused to move in a first horizontal direction then is reversed so that each impacted space along the ribbon provides several printed characters. Since the characters are formed in a relatively small area of the ribbon, full utilization is not made of the ribbon. Attempts have been made to increase the utilization of the ribbon so that the useful life thereof may be extended. For example, a rudimentary approach is to shift the ribbon between two vertical positions so that an upper row of characters is impacted against the ribbon during its travel in a first direction while a lower row of characters is impacted against the ribbon during a reversed direction. Although this essentially doubles the utilized area of the ribbon, there is still a substantial ribbon area that remains unutilized.

A more sophisticated approach to ribbon utilization exists in the prior art. For example, U.S. Pat. No. 2,312,314 includes a ribbon shifting mechanism which causes print characters to impact along gradually sloping paths, first upward and then downward, as the ribbon is moved horizontally. Although this approach increases ribbon utilization, there is still a substantial area of the ribbon which is not used.

U.S. Pat. No. 3,782,521 is directed to a complex ribbon lifting mechanism for a power driven typewriter. The mechanism includes a planetary gearing arrangement and interlocking linkages and camming surfaces which successively move a ribbon to slightly different vertical positions to enable slightly different portions of a ribbon to be successively struck by a type head impacting against a platen. The complexity of the mechanism set forth in this patent increases the cost of a printer or typewriter which is to include the mechanism and also decreases the reliability of such a printer or typewriter due to the inclusion of more mechanical components than is necessary.

The present invention is an improvement over the above-mentioned prior art in that it achieves substantially full utilization of ribbon area thereby substantially increasing ribbon life. A movable platform mounts the ribbon spools and a simple cam moves the platform upwardly and downwardly as a character line is printed. As a result, a printhead is caused to impact against the ribbon in overlapping arched patterns which consume substantially all of the utilizeable space on the ribbon. The present invention provides for longer ribbon life and uniform density. Since the ribbon is raised relative to a printhead, at the initiation of each arched pattern, it becomes easier for a document to be inserted.

The above-mentioned objects and advantages of the present invention will be more clearly understood when considered in conjunction with the accompanying drawing, in which:

FIG. 1 is a schematic illustration depicting the overlapping arched patterns of print cycles on a ribbon.

FIG. 2a is a side elevational view of the ribbon mechanism when the supporting ribbon platform is at its highest point.

FIG. 2b is a partial sectional view taken along section line 2b--2b of FIG. 2a illustrating the driving cam at its high point, relative to the ribbon platform.

FIG. 3a is a view similar to that of FIG. 2a but illustrates the position of the ribbon platform at its lowest point.

FIG. 3b is a figure similar to that of FIG. 2b taken along section line 3b--3b of FIG. 3a showing the cam as it appears at a low point.

FIG. 4 is a top plan view of a ribbon advancing mechanism..

FIG. 5 is an elevational view of the mechanism shown in FIG. 4.

Referring to the figures and more particularly FIG. 1, reference numeral 10 refers to a length of ribbon that is to move vertically upward and downward as it is moved horizontally, relative to a printhead 12 so that arcuate overlapping printing patterns of impacted type are created. For example, the first illustrated arcuate pattern is indicated by reference numeral 1 and is shown to begin with a home position toward the lower edge of the ribbon 10. Slowly, pattern 1 swings upwardly and to the left until a high point is achieved toward the upper edge of the ribbon 10. This is indicated as the center position of the first pattern 1. As the ribbon 10 continues to move horizontally to the right, the pattern 1 of impacting will change so that the arc swings downwardly again toward the lower edge of ribbon 10. As a result, a first cycle of printing occurs whereat an arched printing pattern 1 is effected. It is to be pointed out that the printhead 12 actually moves between the home position, center position and end position of the first cycle or pattern 1. During this time when the printhead 12 travels across the ribbon 10, the ribbon 10 only moves vertically relative to the printhead 12, but does not move horizontally. After the printhead 12 has printed a line and comes to the end position, relative to the ribbon 10, a ribbon moving mechanism is actuated, as will be explained hereinafter, so that the printhead 12 now is located at the home position of printing cycle 2. Again, the printhead 12 is moved from right to left across a section of the ribbon 10 so that the printhead 12 moves from home position to center position and finally end position of the second print cycle 2. In the illustration of FIG. 1, a third cycle 3 is also shown. Of course, the printing cycles go on indefinitely so that a pattern of overlapping arcuate cycles occurs along the length of the ribbon 10. After each successive attainment of an end position, the printhead 12 is returned to a home position to initiate a new cycle.

FIG. 2a illustrates the components necessary to achieve the vertical displacement of a ribbon 10 during horizontal movement of a printhead 12. The printhead 12 has its printing elements at 14 in proximity with a printing plane against which a document is positioned during a printing operation. As is the case with most dot matrix printers, used herein for illustrative purposes, a platen stop 18 is provided to ensure that a document (not shown) is properly positioned in the print plane. A ribbon platform 20 supports the ribbon 10 and moves the ribbon 10 vertically due to the pivotal connection of the ribbon platform 20 at pivot point 22. The ribbon platform 20 and the pivot point 22 are supported by support members 24, which may be positioned at opposite ends of the ribbon platform 20.

The means for vertically displacing the ribbon platform 20 is an eccentrically mounted cam 26 which has a camming surface in engagement with a cam follower 28, the latter being attached to the underside of the ribbon platform 20. The cam 26 is secured to a shaft 30 which is driven by a motor (not shown) during scanning motion of the printhead 12. An opposite end of the shaft 30 is journalled within block 32.

The ribbon carrying components are conventional. They include a spindle 34 which mounts a spool of ribbon 38. On the underside of the spool 38 and coaxial with the spindle 34 is a ratchet gear 36 which increments the horizontal motion of ribbon 10. As is shown in FIGS. 4 and 5 and included in conventional printers of this type, two such spindles 34 and 56, spools 38 and 55 and ratchet gears 36 and 54 are included at opposite ends of a length of ribbon 10 across which the printhead 12 scans.

FIG. 2b, taken along section line 2b of FIG. 2a, illustrates the high point position of cam 26, the high point being indicated at reference numeral 40. When the cam 26 is in this position, the ribbon platform 20 and the ribbon components mounted thereabove are shown in the elevated position of FIG. 2a. This will be the position of the ribbon platform 20 and cam 26 in the home and end positions previously explained in connection with FIG. 1.

FIG. 3b, taken along section line 3b of FIG. 3a, illustrates the disposition of cam 26 at a low point 42. The ribbon mechanism components are shifted downwardly, relative to the printhead 12, as shown in FIG. 3a. This is the position of the ribbon platform 20 and cam 26 when the ribbon mechanism components are in a center position as previously explained in connection with FIG. 1. Of course, other points along the camming surface will be engaged by the cam follower 28 at points between the high and low points 40 and 42, respectively, just explained.

FIG. 4 illustrates a pawl-ratchet mechanism for advancing the ribbon 10 after each cycle which occurs at the end position of each arc pattern generated between the ribbon 10 and printhead 12 as explained in connection with FIG. 1. A bifurcated pawl is generally indicated by reference numeral 44. This pawl 44 is centrally mounted on a pivot 46. The central portion 48 of the pawl 44 extends outwardly to the left to a ratchet engaging end 50. The ribbon 10 as illustrated will remain in place between the left and right spools 38 and 55 during traversal of the printhead 12 from the home position at the right end of the platen 51 to a leftmost position. The printhead 12 will then return to a home position during which time the ribbon 10 will advance so that a second print cycle will be displaced from the first print cycle as shown and described in connection with FIG. 1. The sequential incrementing of the ribbon 10 between the spool 38 and 55 occurs as the ratchet engaging end 50 is incrementally moved between adjacent teeth of ratchet gear 36. Notice that during a presumed motion of the ribbon 10 from left to right, an opposite ratchet engaging end 52 remains clear from engaging the ratchet 54 associated with the right ribbon spool 55 which is mounted on its own spindle 56.

Referring to FIG. 5, a pivotal actuator 58, shown in block diagram form, is used to disengage ratchet engaging end 50 and ratchet gear 36 when the left end of a ribbon 10 is sensed. In order to reverse the direction of ribbon incrementation and repeat the printing cycles from an opposite direction, the pivotal actuator 58 must then engage the ratchet engaging end 52 and its associated ratchet 54. The pivotal actuator 58 does not, per se, form part of the present invention but may be made from conventional components such as solenoid-linkage components connected to the pivot 46. A support member 60 permits the connection of springs 62 and 64 between the central portion 48 of pawl 44 and left and right off-center points 63 and 65 on either side of pivot 46. These springs 62 and 64 resiliently engage the selected ratchet engaging end 50 or 52 of the pawl 44 with either ratchet 36 or 54. Winding mechanisms 66 and 68 are shown in block diagram form and indicated as being connected with the left and right spools 38 and 55, respectively. These winding mechanisms 66 and 68 may simply be stepping motors or another conventional type of electromechanical mechanism for permitting the spools 38 and 55 to turn each time a print cycle is completed. This approach is conventional.

To further round out the disclosed embodiment, the ribbon 10 is seen to be guided by rollers 70 and 72 which are positioned at opposite points along the sections of a ribbon 10 to be impacted against. A ribbon guide 67 is also included.

From an explanation of the invention, it will be appreciated that the combination of components set forth herein operate in a synergistic fashion to achieve an unusual overlapping arcuate printing pattern across a ribbon 10 which extends ribbon life and ensures uniform print density. In addition, since the ribbon 10 is raised by the platform 20 when the printhead 12 is in the home position, there is more clearance generated for document insertion.

It should be understood that the invention is not limited to the exact details of construction shown and described herein for obvious modifications will occur to persons skilled in the art.