GB2250270A - Tape cassette: form of tape guides - Google Patents

Abstract

A cassette K. e.g. for a magnetic tape, has pairs 15, 24 and 16, 17 of tape guiding elements in the form of pins and webs, for the tape section on the front side of the cassette. The pairs are symmetrically disposed on either side of centre axis q. One 15, 17 of each pair of guiding elements is moulded on a bottom housing part and the other (hatched) one 16, 24 of each guiding element is moulded on a top housing pant. The effect of thermal deflection of the housing parts is cancelled out by having tape guides S. mounted on both parts. Guiding elements 16, 17 and 22 may be accompanied by adjacent elements 16A, 17A, 22A moulded on the other housing part (Fig. 3). <IMAGE>

Description

Tape Cassette in Particular a Magnetic Tape Cassette This invention relates to a tape cassette, in particular a magnetic tape cassette, having a housing comprising top and bottom parts and having a transverse centre axis, a tape and guide means guiding the tape in the housing and including guiding elements some of which are moulded on the bottom part and some of which are moulded on the top part.

In the front wall of a cassette, three openings are arranged for receiving magnetic heads. Likewise in the region of the front wall of a compact cassette, guiding elements for the magnetic tape are provided, the recording/reproduction quality of the cassette depending very much on these guiding elements. The customary use of relatively cheap plastics material together with the shape of the housing, cause the halves of the housing to bend, in particular under the effect of heat, with the consequent result that the position of the guiding elements is also altered. This results in the production of tape cassettes of inferior quality.

Compact cassettes are known in which tape guiding elements are provided either - on the top part, on the right-hand side and on the left-hand side with respect to the transverse centre axis, or - symmetrically with respect to the transverse centre axis, an inner pair of guide pins being provided on the bottom part and an adjacent outer pair on the top part, all the further guiding elements being moulded on on the bottom part.

This produces either an unsymmetrical arrangement of the guiding elements or an arrangement of the guiding elements which compensates for errors only in the region of the transverse centre axis of the tape cassette.

US-A-3,661,345 discloses the forming of fixed deflecting pins in a compact cassette by fitting together slightly conical cross-shaped elements engaging one in the other from the bottom part and top part and producing for instance an external cylindrical shape. This causes a considerable increase in tape friction and the fitting together of the conical parts makes it more likely that additional stresses will be created than existing stresses will be compensated for with respect to the position of the guiding elements.

It is an object of the present invention to improve the accuracy of tape guidance in tape cassettes.

We have found that this object is achieved by a tape cassette, in particular a magnetic tape cassette, having a housing comprising top and bottom parts and having a transverse center axis, a tape, and guide means guiding the tape in the housing and including pairs of adjacent guiding elements provided symmetrically with respect to the transverse center axis, one guiding element of each pair being moulded on the bottom part and the other guiding element of each pair being moulded on the top part.

A tape cassette according to the invention makes it possible, for example, to compensate for thermally induced slanting of the guiding elements and consequently largely to prevent azimuth errors caused by the cassette Suitably, in particular in the case of cassettes with symmetrical arrangement of deflecting and guiding elements, it is expedient for the pairs of adjacent guiding elements to be arranged between each deflecting element and the transverse centre axis. This equally compensates tape guidance on each cassette side on either side of the transverse centre axis. This is most favourable, in particular, for cassettes which can be operated either way up (e.g. after turning over), such as compact cassettes.

In an advantageous development, at least one pair of adjacent guiding elements is provided in the vicinity of a deflecting element. As a result, it is advantageously possible to compensate for errors in the position of the deflecting roller axes and, if provided, of further guiding pins in the vicinity of the deflecting roller.

It may also be expedient for at least one pair of adjacent guiding elements to comprise guiding elements, arranged closely next to each other, each having a contact surface for the tape. Such closely arranged partial guiding elements have the effect of a single guiding element with automatic compensation if both partial guiding elements slant in opposite directions and the tape bears centrally against both contact surfaces.

It is also expedient for the vertical axes of adjacent guiding elements of a pair to be arranged approximately parallel to each other.

Further features relate to the design of the guiding elements as elongate webs, as cylindrical guide pins or a combination of these two forms.

Embodiments of the invention will now be described, by way of example only, with particular reference to the accompanying drawings, in which Figure 1 is a cross-sectional view through a known compact cassette K; Figure 2 is a diagrammatic representation of a tape cassette according to the invention, with tape guiding and deflecting elements; and Figure 3 is an enlarged cassette housing section with a different arrangement of tape guiding elements.

A known, conventional compact cassette K comprises a housing in which are mounted two co-planar, rotatably mounted hubs 1, 2, with magnetic tape 3 able to be wound onto and unwound from the latter. The housing comprises bottom and top halves or parts 4 and 5, respectively, and front, rear and side walls 6, 7 and 8, respectively. Each housing half has a raised part or elevation lOa, lOb which extends from the front wall 6 towards the rear. The front portion of the cassette between these elevations 10a, lOb is intended for receiving at least one recording/playback magnetic head 11 (see Figure 2). The front wall 6 has two more openings for receiving further components such as an erase head 12, a rubber pinch roller 13 for driving the tape by the capstan 19, etc.In order that these components can be brought into the required, precisely defined contact with the magnetic tape 3, the magnetic tape 3 is guided in a free tape loop 3a by deflecting rollers 14 and guiding elements 15, 16 and 17 from the tape roll on the hub 1 along the front wall 6 for winding onto the hub 2, or in the reverse sequence if the cassette is operated in the other direction.

Even slight deviations of about 25 micrometers or more from the perpendicular position cause these guiding elements 14 to 17 to produce distinct azimuth errors, which impair the reproduction of high-frequency sound signals. Ribs or webs 25 extend around the deflecting rollers 14 as far as the side walls, in order to give the cassette housing greater rigidity and stability in this region and in the longitudinal direction.

Due to the steps 18a and 18b produced by the housing elevations and which are of reduced wall thickness, the housing has an inhomogeneity which cannot be compensated by usual design measures. Whereas the wall thicknesses of the bottom and top housing parts 4 and 5 covering the rolls of tape are usually about 1.8 millimetres, the wall thicknesses of the housing elevations 10a and lOb are reduced, at least in the region of the openings in the front wall 6 (referred to hereinafter as front openings), to about 1.0 millimetres.

In production by injection moulding, the inhomogeneity results in material stresses which, for example in the case of exposure to heat, compensate for each other by bending of the parts 10 and lOb in the directions A and A' (Fig. 1).

In Figure 2, there is shown one embodiment of a tape cassette K according to the invention which is designed symmetrically with respect to its transverse centre axis q.

Due to the symmetry of the cassette used as an example, identical parts are provided with the same designations.

The tape 3 runs from the hub 1 via guide pin 22, a deflecting roller 14 mounted on a spindle 23, guiding elements 15 and 24, each designed as an elongate web, then between a pinch roller 13 and a capstan 19, via guide web 16 and guide pin 17 to the transverse centre axis q and via the guiding and deflecting elements of the second half of the cassette in the reverse sequence of designations.

For the purposes of the invention, pairs of adjacent tape guiding elements are considered to be the guide webs 15 and 14, which are arranged very closely together, and the guide web 16 with the guide pin 17, which are spaced a greater distance apart. Thus, on each side of the axis q there are two pairs (15, 24 and 16, 17) of adjacent guiding elements between each deflecting roller 14 and the transverse centre axis q. It is also possible to increase further the number of pairs, as explained below.

Whereas the guiding elements 15 and 17 provided on the bottom part 4 are shown unshaded in plan view in Figure 2, the guiding elements 24 and 16 provided on the top part 5 are shaded, for purposes of differentiation.

The pair of guide webs 15 and 14 are arranged as closely next to each other as troublefree assembly allows, the cross-sections are of a somewhat slender rectangular shape and the forward-facing tape-contacting surfaces lie next to each other and are slightly rounded. The height of the webs 15, 16, 24 is decided according to possible production and assembly tolerances.

The guiding elements 16 and 17 of what is respectively the second pair are further away from each other, but their likewise alternate arrangement on the top part 5 and on the bottom part 4 also achieves in principle the same compensating effect as the pair 15, 24.

The alternate arrangement of the adjacent guiding elements on the top and bottom parts compensates for housing deformation. For example, thermally initiated deflections of the housing elevation 10 in the direction A (Figure 1) and of the housing elevation lOb in the direction A', causes the two guiding elements of each adjacent pair to deflect, in relation to the tape 3, by the same amount (if the material of top and bottom parts is the same) but in opposite directions. The above deflections in directions A and A' have the following effects on the running of the tape: Above (as viewed in Figure 2) the transverse centre axis q, the tape 3 is deflected, at each first guiding element 17 and 15 moulded on the bottom part 4 (or, to be more precise, on the elevation lOa), in the same direction A.However, at the following, second guiding element 16 and 24 of each pair moulded on the elevation lOb, the tape 3 is immediately deflected back in the opposite direction At.

The consequence is that the tape 3 retains a central position at each pair of adjacent guiding elements (17 and 16) and (15 and 24), and this central position is maintained by the use of a plurality of symmetrically arranged pairs also along the front side 6 of the cassette.

Of course, it is also advantageous to double the guiding elements 16, 17 and 22 by means of corresponding counter-pieces 16A, 17A and 22A moulded-on on what is respectively the other part of the housing, and consequently by use of double guiding elements, such as 15, 24, to ensure self-compensation at each pair of guiding elements. This variant is diagrammatically represented in Figure 3.

As a result of this design according to the invention, it is possible to achieve the following measurable advantages in comparison with commercially available compact cassettes.

Commercially available compact cassettes of the applicants were compared in comparative tests with compact cassettes according to the invention, with the following results. Both compact cassettes were subjected to heat aging (HA) for 8 hours at 850C and the azimuth angle ( < ) of a magnetic head gap in relation to the tape of each compact cassette (CC) was measured before and after.

The values in the following table were obtained: TABLE Type of CC Azimuth < before HA Azimuth < [ angular minutes ] * after HA commercially available CC < 3 5 < 5' CC according to the invention < 1.9' < 2.8' *1 angular minute is equal to one sixtieth of a degree.

Consequently, the following is found if the invention is applied: Improvement in the azimuth angle of > factor 2, i.e. a reduction in the azimuth errors caused by the cassette by at least half.

No comparable measures are known for commercially available compact cassettes allowing such an improvement in the azimuth angle and the accuracy of tape guidance to be achieved for such a comparably low outlay.

For the purposes of this invention, magnetic tape cassettes are all types of audio, video, data and instrumentation tape cassettes to which the measures of the invention can be applied.

Claims (9)

1. A tape cassette, in particular a magnetic tape cassette, having a housing comprising top and bottom parts and having a transverse centre axis, a tape, and guide means guiding the tape in the housing and including pairs of adjacent guiding elements provided symmetrically with respect to the transverse centre axis, one guiding element of each #pair being moulded on the bottom part and the other guiding element of each pair being moulded on the top part.

2. A tape cassette according to claim 1, wherein said guide means include deflecting elements on opposite sides of the transverse centre axis, the pairs of adjacent guiding elements being arranged between each deflecting element and the transverse centre axis.

3. A tape cassette according to 2, wherein at least one pair of adjacent guiding elements is provided in the vicinity of each deflecting element.

4. A tape cassette as claimed in any one of claims 1 to 3, wherein at least one pair of adjacent guiding elements comprises guiding members arranged closely next to each other and each having a contact surface for the tape.

5. A tape cassette as claimed in any one of claims 1 to 4, wherein vertical axes of the adjacent guiding elements of a pair are at least approximately parallel to each other.

6. A tape cassette as claimed in any one of claims 1 to 5, wherein the guiding elements of at least some of said pairs are designed as cross-sectionally elongate webs having tape contacting surfaces arranged on narrow sides of the webs.

7. A tape cassette as claimed in any one of claims 1 to 6, wherein the guiding elements of at least some pairs comprise cylindrical guide pins.

8. A tape cassette substantially as herein described with reference to, and as illustrated in, Figures 2 or 3 of the accompanying drawings.

9. A tape cassette, in particular a magnetic tape cassette, having a housing comprising bottom and top parts and a tape guided therein by means of deflecting elements and further guiding elements, the guiding elements being moulded on, some on the bottom part and some on the top part, and the housing having a transverse centre axis, wherein pairs of adjacent guiding elements are provided symmetrically with respect to the transverse centre axis, the one guiding element of each pair being moulded-on on the bottom part and the other guiding element of the same pair being moulded-on on the top part.