Drive Units Provided With Driving Rollers

This invention relates to an improvement in drive units provided with driving rollers and more particularly in such units where the rotating rollers cause an elongated member associated thereto and engaged with the rollers to be moved longitudinally in both directions and where this elongated member can move independently of the rollers which do not rotate, frictionally sliding in respect thereto.

A unit of this type is particlarly, if not exclusively, applied in tuning apparatus, particularly in car radio apparatus, which are provided with a mechanical tuning device having a plurality of push buttons, in which device a plurality of stations can be stored. The apparatus is readily and precisely tuned on each station by pushing the associated push button.

Among known units, a more commonly used unit comprises a resilient and flexible metal strip inserted between two rollers elastically pushed against each other. One of these two rollers is idle while the second roller is keyed on the shaft of the tuning knob of the apparatus. The metal strip is connected to a longitudinally movable rod whose position controls the tuning circuit of the radio apparatus thus controlling the frequency on which the apparatus is tuned. With such an arrangement the rotation of the knob in one or the other direction transmitted to the rollers determines the longitudinal movement of the strip engaged with the rollers and accordingly the tuning of the apparatus by means of the rod connected to the strip.

Furthermore, this rod and the strip associated thereto must move also when any tuning push button is actuated upon and thereupon the necessity rises that the rod and strip be moved in respect to the rollers being stationary and namely that a relative frictional movement takes place.

The above described units have the drawback that the driving action exerted on the strip by the roller is discontinuous.

From a geometric point of view, an optimal driving action on the strip by means of two rollers engaging the strip gripped therebetween can be obtained only if the portion of plane defined by the strip is always perfectly tangent to the cylindrical surface of a roller with which the strip is engaged. In practice, however, this is impossible since, both for the inevitable unevenness of this cylindrical surface and for the tolerance in manufacturing and assembling the knob shaft on which the driving roller is mounted, the generating lines of the cylindrical surface of the rotating roller do not remain parallel to the plane of the strip. These generating lines describe an approximately conic surface to which the strip cannot remain tangent because, for operation requirements, the longitudinally movable rod to which the strip is connected is rigid and forced by guides to move longitudinally yet remaining in the same plane.

This means that the strip cannot engage the rotating roller throughout the width thereof and accordingly the driving action is irregular and this affects the precise tuning of the apparatus by the knob.

Accordingly, it is a main object of the invention to provide a driving unit of the above described type wherein the driven element continously engages the roller throughout the width thereof, that is geometrically speaking a unit wherein the driven element surface engaging the roller surface is continuously tangent to the corresponding generating line of the cylindrical surface of the roller itself.

According to the invention, in order to obtain this tangency allowing the best engagement condition between the driving roller and the driven element, the unit comprises: a composite driven elongated element comprising a rigid bar of a certain thickness and a particular cross section and a thin flat strip backed thereby; a roller engaging this strip and a wheel engaging this backing bar. The roller is keyed on the shaft of the operating knob while the wheel is idle on an elastic support urging it against the roller.

This arrangement always ensures the best engagement conditions between the driving rollers and the driven element since the strip can take different positions in respect to the bar through torsional movements about its axis and transverse slant movements in respect to the bar, yet remaining tangent to the generating line of the cylindrical surface of the roller engaging it.

The invention will be now described in detail with reference to the annexed drawing, wherein:

FIG. 1 is a perspective view of the improved unit according to the invention; and

FIG. 2 is a detail showing the cross section of the driven element and the engagement thereof with the driving roller.

With reference to FIG. 1, reference P indicates a supporting plate of the driving unit according to the invention provided with a vertical wall A integral therewith.

The composite driven element, generally designated by 10, is connected to tuning bar B of the apparatus at one of its ends, as described above. Element 10 is positioned between a roller 11 keyed to shaft 12 of knob M, supported by wall A, and a wheel 13 whose hub 14 is received within a saddle 15 shaped on an elastic supporting plate element 16 secured to plate P at its end 18. As clearly seen in FIG. 1, the elastic support 16 has a slot 19 wherein wheel 13 can rotate and furthermore its end 20 is fork-shaped and a pin 22 integral with plate P is inserted between branches 21 of fork-shaped end 20.

As clearly seen in FIG. 2, composite element 10 comprises an elongated bar 25 having a substantially rectangular cross section but with a slightly rounded upper face 26 and a strip 27 secured to upper face 26 at its ends 28 by means of two rivets 29. Furthermore, strip 27 is "unloaded" at each end thereof, that is it has two "neck" portions 31 obtained by means of pairs of corresponding notches 30.

With such a construction and arrangement, strip 27, which is of a width identical with the axial length of roller 11, can rotate about its longitudinal axis which is perpendicular to the plane of the drawing of FIG. 2, rolling on rounded upper surface 26 of bar 25 through torsional movements in correspondence with necks 31. Accordingly, strip 27 can always accommodate the inevitable slight variations of the position of roller 11, yet remaining constantly tangent to the cylindrical surface thereof. On the contrary, rigid element 25 associated to movable rod B of the tuning device (not shown) does not rotate and it remains constantly tangent to and engaged with wheel 13 owing to elastic support 18 of wheel 13.

As for the material used, and particularly for strip 27 and roller 11, it should be noted that the material of the roller must be softer than the material of strip 27. For example, a strip 27 of stainless steel requires a roller 11 of phosphor bronze.