The present invention relates to an Endless Ink Ribbon Cassette wherein a ribbon is drawn from a storage void for printing and re-introduced into the storage void after printing. More particularly, the present invention relates to such an endless ink ribbon cassette wherein the ribbon is drawn into the void between first and second induction wheels.
Endless, reusable ink ribbons for computer peripheral printers, typewriters and similar printing devices are known to be provided in a cassette. The cassette typically comprises a pair of arms between which an exposed portion of the ink ribbon is suspended to be struck against paper or other printing material to achieve the printing process and to leave a visible record. As the ribbon is used for printing, so it is caused to move between the arms to present a fresh piece of ink ribbon to the striking device. The ribbon is moved by being drawn into one of the arms by means of a pair of opposed induction wheels inside the cassette between which the endless ink ribbon passes. The induction wheels pay out the ribbon into a storage void within the cassette. The void comprises parallel upper and lower walls separated by a distance equal to the width of the ribbon. The ribbon stacks itself in a serpentine manner against ribbon already within the void and the pack of ribbon in the void moves steadily away from the induction wheels towards an outlet point proximate to the other arm. Ribbon is drawn from the moving pack in the void into the other arm of the cassette and out into the exposed portion to be used in the printing process.
In order for the induction wheels to adequately drive the ribbon they must extend across the full ribbon width and thus occupy the entire height of the void within the cassette. Mounting of the wheels has been achieved by dividing the wheels in two so that they comprise first and second spaced rim portions with a support member passing between the rim portions to hold a central axle.
In the prior art, if the ribbon were to fold slightly into one or other of the spaces between the first and second rim portions on a wheel, the ribbon exiting from between the wheels is folded, has thereby a rigidity imparted by its folded geometric shape, and is not as pliable as an unfolded ribbon, thus preventing the ribbon from adopting the serpentine disposition within the void which in turn causes an irregular packing of the ribbon in the void. This can lead to jamming and discarding of the cassette before all of the ink on the ribbon has been used up.
The present invention comprises an endless ink ribbon cassette wherein a ribbon is drawn from a storage void for printing and reintroduced into the void after printing, the cassette including a first induction wheel having first and second rim portions spaced apart on an axle; a second induction wheel urged against the rim portions, said first and second induction wheels being co-operative to draw the ribbon onto said first induction wheel and between the first and second induction wheels to be introduced into the void; and a fixed insert maintained between the first and second rim portions and operative to prevent entry of the ribbon between the first and second rim portions.
Also in the prior art, the ribbon can fold to such an extent that it passes completely between the first and second spaced rim portions of the induction wheel and become trapped around the axle of the driven induction wheel, thereby causing instant jamming and loss of use of the cassette. In a preferred embodiment of the present invention, the insert is further operative to prevent entry of the ribbon between the insert and the axle.
In the prior art, the driven induction wheel can catch the ribbon as it is introduced into the void and maintain it against its surface, thus causing the ribbon to be wound round the outside of the wheel, again leading to instant jamming as the ribbon piles up between the wheel and the side wall of the cassette whereon the wheel is supported. In the preferred embodiment of the present invention, the insert is provided on an inner surface of a wall of the cassette and is operative to prevent entry of the ribbon when in the void between the induction wheel and the side wall.
In the preferred embodiment of the present invention, the insert is also operative to provide support for the axle of the first or driven induction wheel.
In the preferred embodiment of the present invention, the insert includes a circular portion having an outline including part of the circumference of a circle concentric with the axle of the induction wheel, where the circular portion has a diameter commensurate with the diameter of the first and second rim portions of the induction wheel. Also in the preferred embodiment, the portion of the circumference of the circle of the insert includes the point of contact between the first and second rim portions of the driven induction wheel and the second induction wheel.
A further feature of the preferred embodiment includes the portion of the circumference of a circle of the insert including the point of first contact of the endless ink ribbon with the first or driven induction wheel.
In the preferred embodiment of the present invention the portion of the circumference of a circle of the insert also extends around into the storage void area of the cassette. The commensurate radius of the portion of the circumference of a circle on the insert is preferred to be of the order of 1 mm. less than the radius of the first or driven induction wheel.