Printing Apparatus With Inked Ribbon Lift Restrainer

The present invention relates in general to printing apparatus of the type having a horizontally movable type-carrier, a horizontally movable ink ribbon and a plurality of print hammers, and more particularly to a printing apparatus in which unwanted lifting of the ink ribbon is prevented to eliminate loss of print characters.

It is an object of the present invention to provide a printing apparatus having a ribbon lift restrainer which limits undesirable upward movement of an ink ribbon to prevent loss of print characters.

It is another object of the present invention to provide an improved printing apparatus which can be constructed by slightly modifying a part in existing printing apparatus.

According to the present invention, there is provided a printing apparatus having a printing zone where printing action is made and comprising a type-carrier running horizontally along the printing zone and having characters formed thereon; a plurality of print hammers juxtaposed in a row along the printing zone; a platen straightly extending along the printing zone at a position behind the type-carrier with respect to the row of the print hammers; and an ink ribbon running parallel with the typecarrier along the printing zone at a position between the type-carrier and the row of the print hammers. A print sheet runs vertically between the ink ribbon and the row of the print hammers in a direction parallel with the face of the ink ribbon.

A separating member is provided to maintain a distance between the ribbon and the print sheet to prevent smearing of the latter by the ribbon ink. This separating member has a cutout portion to define a print zone to allow print hammers to make impact therethrough on the ink ribbon. A folded portion of the print sheet has a tendency to extend through the print zone into contact with the ribbon as sheet 32 is advanced to a new print line position thereby dragging the ribbon upwardly. This causes the ribbon to displace from the print position and a loss of print characters will result if the ribbon fails to return to the print position before a hammer is subsequently activated. A restraining member is mounted above the ink ribbon to limit its undesirable upward movement.

Other objects and advantages of the present invention will become clear from the following description when taken in conjunction with the accompanying drawing.

FIG. 1 is a schematic plan view of a prior art printing apparatus;

FIG. 2 is a cross sectional view of an existing printing apparatus taken along the line 2--2 of FIG. 1;

FIG. 3 is a partial front view of the printing apparatus of FIG. 1, showing positional relationship between a ribbon separator and an inked ribbon;

FIG. 4 is a view similar to FIG. 2, but shows a first embodiment of the present invention and

FIGS. 5 and 6 are views similar to FIG. 2, but show second and third embodiments of the present invention, respectively.

Prior to describing the invention, reference is first made to FIGS. 1 to 3 in which a prior art printing apparatus is illustrated. This type of printing apparatus is clearly described in U.S. patent application Ser. No. 909,106 filed May 24, 1978 by Takahiro Yamamoto et al. and assigned to the same assignee as the present invention, now U.S. Pat. No. 4,210,076.

The printing apparatus 10, shown in FIG. 1, comprises a type-carrier 12 having, for example, a flexible endless belt having formed thereon a series of type characters. The type-carrier 12 is supported by a driving pulley 14 and a driven pulley 16 to move along a horizontal path. Inside the endless type-carrier 12 is located a platen 18 which extends parallel with a straight section of the endless type-carrier 12. Located opposite the platen 18 and parallel with the straight section of the endless type-carrier 12 is a plurality of print hammers 20 (only one is numbered) which are juxtaposed in a row facing the platen 18.

Between type-carrier 12 and the row of hammers 20 is a section of an endless ink ribbon 26 which is slidably supported by a pair of guides 22 and 24. The ink ribbon 26 is engaged between pinch rollers 28 and stored within cassette 30. Between the row of hammers 20 and the ink ribbon 26, there is a print sheet 32 which is arranged to move in a direction normal to the plane of FIG. 1. As is seen in FIG. 2, a hammer plate 34 is provided which serves as a guide for sheet 32 and between the print sheet 32 and the ink ribbon 26 is arranged a ribbon separator 36 which functions to prevent the portions of print sheet 32 which are outside a printing zone (see FIG. 3) from touching the ink ribbon 26. This printing zone is defined by an elongated cutout portion 36a of ribbon separator 36.

Print sheet 32 is formed with a longitudinally spaced transverse series of cuts along which the sheet 32 is successively folded in opposite directions and stored in a stack relation as illustrated in FIG. 2, so that the sheet 32 may be manually separated apart into forms after printing. The folded edges of the stacked sheets 32 tend to extend through the cutout portion 36a into contact with the ink ribbon 26 as the sheet 32 is advanced upward to a new line position. This drags the print section of ribbon 26 upwardly. If ribbon 26 fails to return to the original position before the next printing action occurs, the ribbon 26 will be displaced from the print position resulting in a loss of a character print on sheet 32.

Referring now to FIG. 4, there is shown a first embodiment of the invention in which the same parts as those of FIG. 2 are designated by corresponding numerals. In this first embodiment, a stopper 38 for restraining upward movement of the ink ribbon 26 is employed, which is constructed from aluminium, plastics or the like and is firmly mounted on the platen 18 by suitable fastening means. The stopper 38 extends along the longitudinal length of the platen 18 and consists of a base 38a attached to the platen 18 and a projection 38b protruding toward the print hammers 20. The projection 38b has a generally bill-shaped cross section and is positioned at the inside upper ridge section of the base 38a, extending along the same. The projection 38b is sized and constructed so that at least a part thereof, such as a leading end thereof, protrudes toward the print hammers 20 beyond an imaginary plane which includes the face of the ink ribbon 26 which assumes its normal position. The base 38a has an inclined flat inside surface 38c terminating at the foot of the projection 38b. The inclination angle of the surface 38c relative to the imaginary plane is selected to have a value in a range from approximately 3.degree. to approximately 10.degree..

The tendency of print sheet 32 to shift toward ink ribbon 26 is restricted therefore by projection 38b reducing the possibility of sheet 32 contacting with ribbon 26. Furthermore, even if the ink ribbon 26 is forced to lift by undesirable contact with the folded portion of sheet 32 when the latter is advanced upwardly to a new line position this lifting movement of the ribbon 26 is limited by the inclined flat surface 38c of the stopper 38. In fact, experiments show that the ink ribbon 26 is brought into contact with the surface 38c upon lifting thereof and returns to its normal position quickly by the time the following hammering action of the print hammers 20 starts. Even if the lift of the ribbon 26 further proceeds, the projection 38b will surely stop lifting of the ribbon 26 by a downward facing flat surface 38d. It should be noted that since the flat inside surface 38c of the base 38a which the ink ribbon 26 is to contact is inclined with respect to the imaginary plane which includes the face of the ribbon 26 taking the normally operating position, the ribbon 26 will never be flexed upon contact with surface 38c.

Experiments show that substantially the same effect is achieved if surface 38c is convexed or concaved.

In FIG. 5, a second embodiment of the invention is shown, which is substantially the same as the first embodiment except that a high friction member 40, such as emery paper, is bonded to the inclined flat surface 38c of the base 38a.

In a third embodiment of the invention shown in FIG. 6, the restraining member 38' is shaped so that the inclined surface equivalent to surface 38c has plural step portions 42 extending parallel with the longitudinal length of the stopper 38'.

With the second and third embodiments, the lifting of the ink ribbon 26 is much more restricted in comparison with the first embodiment.

Although shown and described as a separate element the restraining member 38 (38') can be constructed integrally with platen 18 as a one piece unit.

With the above, it will be appreciated that in accordance with the present invention, the displacement of ribbon 26 from print position is prevented when a hammer 20 is operated to provide an impression on sheet 32.