TECHNICAL FIELD

The present invention relates to a device of the kind disclosed in the preamble to the following claim 1.

BACKGROUND ART

Typewriters are normally provided with a platen having the dual task of advancing a sheet of paper past an imprinting location and also constituting backing for a typebar or the like striking the imprinting location. For advancing the paper, the platen coacts with rollers mounted on a shaft known as a bail. In a known embodiment of such a roller, a sleeve-like rubber roller is pressed onto a metal hub, which is in turn mounted on a metal joumalling sleeve displaceable reciprocally on the bail. To provide a certain amount of resistance in the displacing movement and ensure that the roller remains in its set position, there is a leaf spring acting between the jourpalling sleeve and a flat surface on the bail. This spring has bent-up ends serving to retain the roller and the spring itself on the joumalling sleeve.

A drawback with the known roller is the difficulties occurring in its assembly and fitting. The bent-up ends as well as the curved form the spring must have to supply sufficient frictioπal force make it difficult to insert it into the joumalling sleeve. Alternatively, only one end of the spring is bent up, but in this case the other end of the spring must be bent up manually after assembly, e g with the aid of pliers. Furthermore, the different parts must be kept in position during placing the roller on the bail. The different manual assembling operations are time-consuming and thereby expensive.

DISCLOSURE OF INVENTION

It is thus an object of the invention to provide a device for roller mounting, preferably for use in a typewriter or similar office machine, which simply and rapidly can be put together and fitted to its associated shaft. This object is

achieved by a device having the distinguishing features disclosed in the following claims.

BRIEF DESCRIPTION OF DRAWING

An embodiment of the invention, applied to a typewriter, will now be described while referring to the accompanying drawing, on which Figure 1 illustrates in an exploded view the parts forming a roller for a bail on a typewriter, Figure 2 is a cross section of a complete bail roller, Figure 3 is a cross section through ε roller mounted on a bail and finally, Figure 4 is a side view of the device illustrated in Figure 3.

BEST MODE FOR CARRYING OUT THE INVENTION

As will be seen from Figure 1, a bail roller 10 implemented in accordance with the invention solely consists of two parts, namely a plastic sleeve 11 forming the roller itself and a jou alling sleeve 12 on which the plastic sleeve is mounted. The plastic sleeve can be coated witn a layer of rubber, but a layer cf polyurethane 13 is preferred in the example. This layer can be easily applied using a molding technique. The plastic sleeve 11 is formed at its ends with annular recesses 14, 15 defining an interior cylindrical surface 16 for coaction with a corresponding outer cylindrical surface 17 on the journallϊng sleeve 12.

For fixing the sleeve 11 to the joumalling sleeve 12, the latter is provided with an annular flange 18 intended for coaction with one of the recesses 14, 15. The joumalling sleeve 12 is also provided with a resilient tongue 19, the upwardly directed end 19a (as seen in Figures 2 and 3) of this tongue being intended for coaction with the recess in the sleeve 11 opposite it. This is clearly apparent from Figure 3, illustrating the roller mounted on a bail 21 provided with a flat surface 20. A similarly flat surface 22 on the joumalling sleeve 12 coacts with the surface 20 to prevent the joumalling sleeve from being rotated relative the bail 21. Subjecting the resilient tongue to torsional forces is thus avoided.

Assembling the described roller is performed by inserting the joumalling sleeve 12 into the plastic sleeve 11 to an extent such that the flange 18 engages against the recess 14, for example. In an unmounted state, t

projecting part 19a has assumed a position situated inside the cylindrical surface 17, see Figure 2. The amount of the deflection of the resilient tongue in Figure 2, as well as the length of the free end 19a thereof is adjusted such that desired frictional resistance will arise between the tongue and the bail 21, simultaneously as the free end extends in over the recess 15 without its upwardly directed defining surface contacting the plastic sleeve 11, and thereby affecting the free rotation of the latter. Mounting is completed by the assembled roller according to Figure 2 being slipped onto the bail 21, with the end at which the flange 18 is situated coming first. The plastic sleeve 11 and joumalling sleeve 12 are thus automatically kept in their correct mutually relative positions during this operation. At the end of the sllpping-on movement the resilient tongue 19 is moved upward by the flat surface 20 of the bail, and the free end 19a of the tongue assumes its position illustrated in Figure 3, in which it locks the plastic sleeve axially to the joumalling sleeve.

As will be seen from the embodiment, the number of parts incorporated in such a roller has been reduced by the invention, while assembly and mounting have been substantially facilitated at the same time.