A CASSETTE WITH A MAGNETIC TAPE BACKING LEAF SPRING ASSEMBLY

Abstract: The invention relates to the technical field of magnetic tape cassette components and the like and specifically to a magnetic tape backing leaf spring particularly for magnetic tape cassettes. The technical problem was to provide a leaf spring which would perform in an optimum way in the tight guide of a tape. The solution to the problem is provided by a magnetic tape backing leaf spring (1) comprising an elastically flexible reed element (2) defining by itself both supporting portions (2b) and a working portion (2a) engageable directly with a tape (3) and being supported by the supporting portions (2b) in a projecting position from the positions of said supporting portions (2b), the working portion (2a) defining stepped zones (2c) with the supporting portion (2b) and being elastically deformable into an arcuate configuration in the operating position.

Description: The invention relates to a cassette with a magnetic tape backing leaf spring assembly of the kind defined in the preamble of the accompanying Claim 1 and disclosed for instance in US-A-3 495 787. As is known, a cassette magnetic tape is held close against the gap of a magnetic recording/playing head by a backing leaf spring arranged to engage whith the tape back side. Prior leaf springs are defined by an elastically flexible, generally metal reed which carries a contact element in direct engagement relationship with the tape. The contact element is everywhere in the form of a felt pad. A disadvantage of prior leaf springs relates to the difficulty of securing the felt pad firmly on the elastic reed. To prevent entrainment by the running tape, some special measures are to be taken, such as disclosed in UK Patent 2 018 492 to this same Applicant. This patent also discloses to select a felt pad having a low frictional resistance, for direct contact with the maqgnetic tape. Also recognized in that felt pads tend to deform and stiffen after a while into a permanent shape which may not conform accurately whit a magnetic head for which they have been intended. Further, felt pads are affected by ambient conditions of humidity and temperature, and the frictional force applid to the tape will vary significantly contingent on such conditions. Another problem, and one of growing weight with the application of magnetic tape cassettes to electronic and other delicate apparatus, in that lint or particles may detach from the felt pads and contaminate apparatus components. In general, moreover, prior leaf spring assemblies insolve significant manufacturing cost and time due to their being made from parts to be formed separately and then assembled together. Also, such leaf spring assemblies have a large volume when stored in coils of leaf spring strings or bands. In fact, the felt pads hold the overlaid leaf spring strings in such coils raised into bulky coil formations of relatively few units. Considering that such coils are to be fed into automated cassette-making equipment, it becomes necessary to arrange for coil changes at frequents intervals, which brings about reiterated shutdowns and increased manufacturing costs. In prior art the US Patent N. 3 495 787 discloses a leaf spring without the felt pad and having configuration where a central portion of a reed element engages the magnetic tape. Said central portion is supported, by thin curved arms, in a projecting position from the positions of the arms. The configuration of said leaf spring is advantageous, owing to the lacking of the felt pad, but a drawback of said configuration is that it may not assure a uniform pressure against a magnetic head: the central portion of the reed element cannot bend to adapt itself to the magnetic head. It is well known that an optimal action of the leaf spring on the magnetic head is an essential feature in all kinds of reed elements, with or without felt pad. US Patents N. 4 293 885 and N. 3 598 339 solve a particular problem of leaf springs: their correct swinging on the fixed elements of the cassette. Said patents show puntiform fulcrums or projections extending out of the leaf springs and in contact with the fixed elements, to allow the swinging of the leaf springs. However, in presence of small fixed elements and of a clearance between the leaf spring and the fixed elements, the cited projections may not contact correctly the fixed elements. The above aim is substantially achieved by a cassette with a magnetic tape backing leaf spring assembly as described in claim 1. The advantages of the invention will be more clearly apparent from the description of preferred embodiments of a magnetic tape backing leaf spring, shown in the accompanying drawings, where: Figure 1 shows in perspective a leaf spring for a cassette according to the invention, as inserted into a conventional cassette; Figure 2 shows in plan view the leaf spring of Figure 1 in its rest position, and in dash lines, in its operating position in biased relationship with a recording/playing magnetic head; Figure 3 shows a portion of Figure 2 to an enlarged scale and how the leaf spring is deflected into its operating position; Figure 4 shows how the leaf spring can be provided whit a rigid type magnetic screen; Figure 5 shows how the leaf spring can be cut out and improved at its middle portion; Figure 6 is a plane development of a flattened leaf spring band according to the invention, and Figure 7 shows how the leaf springs overlap one another when completely formed but still held together in a band and coiled up. Whith reference to the drawing figures, a magnetic tape backing leaf for a cassette according to the invention is comprehensively designated 1. It is formed integrally by an elastically flexible reed element 2 defining by itself both a working portion 2a adapted to engage slidingly with a magnetic tape 3 and supporting portions 2b adapted to support the working portion 2a. Between the portions 2a and 2b there extend stepped zones 2c. In the drawings, a working portion 2a is shown inserted centrally in between two supporting portions 2b; this is a typical configuration of cassettes 7 to be used whit a single magnetic head 4 for both playing and recording the tape 3. The working portion 2a of contact with the tape 3 is made quite high to span the full height or transverse width, transversal to the prevalent longitudinal dimension of the reed element 2, of the tape 3 even as the leaf spring 1 oscillates. Furthrmore, it may be variously shaped, for example, it may be made straight, in the rest position, or concave on the side next to the tape 3, to provide an already partarcuate configuration in the rest position. In order for the working portion 2a to deflect arcuately without strain on the head 4 concentrated at the center thereof, where a gap 4a is located, it is envisaged that the middle zone of the working portion 2a be weakened by cutouts to reduce flexural strength locally. In particular, edge cutouts 11 are provided which are made deeper toward the center of said portion and inside cutouts 12 (Figure 5). As brought out in the figures, the stepped zones 2c, located on opposed edges of the working portion 2a, are preferably convergent to each other, toward the tape 3, so as to bring out the working portion 2a into a projection. It is evident from all figures, and demonstrated by the figures 2 and 3, that the stepped zones 2c form, together with the edges of the working portion 2a and of the supporting portions 2b, two Z-shaped zones that substantially retain their initial angles when the leaf spring 2 moves from the free non-operational position shown in solid lines in figure 2 and in dash lines in figure 3, to the deformed operational position shown in dash lines in figure 2 and in solid lines in figure 3. So the center of the working portion 2a is raised arcuately, as evidenced by two thin dash lines converging each other from the stepped zones 2c, in figure 3, and showing how the stepped zones 2c bend the working portion 2a. In other words: the stepped zones 2c enhance their convergence in the operating position, affording an accurate arcuate arrangement of the working portion 2a, with no forcing on the head 4 center. The stepped zones 2c may be variously laid out in varying dimensions and more or less rounded radiusing to the portions 2a, 2b. They are preferably sized to cause the working portion 2a to project by a smaller distance than the width of the portion in the direction of lay of the tape 3. Furthermore, those same stepped zones 2c have a comparable height to the maximum height of the leaf spring 1 in a parallel direction to the tape 3 and across the tape running direction. The supporting portions 2b comprise, in the embodiments shown, two arms 2b spreading from the working portion 2a and extending in a substantially straight direction parallel to the working portion 2a, in the non-operational position, and having a smaller average height than the working portion 2a which grows gradually toward same, as brought out in the drawings. The ends of the supporting portions or arms 2b of the reed element 2 are formed by folded over wings 5 partly surrounding fixed elements or pegs 6 usually provided in the cassette 7. For engaging the reed element 2 with the fixed elements 6, there are support securements having reduced contact zones, These securements are brought out in the various figures and comprise projections such as jutting formations 10 which are rounded and formed by deep drawing. Also possible are, for example, projections in the form of lugs formed from cutout and folded over portions of the reed element 2. Said projections are in any case arranged on the remote side of the reed element 2 from the magnetic tape 3 and are so shaped as to allow the leaf spring to swing unrestrictedly about a substantially parallel axis to said arms, and to set itself naturally at the position of best balance of the stresses to which it is subjected. As shown in the figures 1, 2, 4, 5, 6 and 7, the projections 10 have a prevalent dimension parallel to the prevalent longitudinal dimension of the reed element 2, and a reduced dimension transversal to the said prevalent dimension, so as to have a substantially point zone of contact with the pegs 6 even in presence of a clearance between the pegs 6 and the reed element 2, in the prevalent longitudinal dimension of the reed element 2. The reed element 2 may be formed from any suitable fexible, metal or plastics, material having a low frictional coefficient. Experiments have shown that with reed elements 2 of bronze, nickel silver, nickel, non-magnetic stainless steel, berillium copper, leaf springs 1 are obtained which have adequate springiness and a frictional coefficient on magnetic tapes which is equal to or lower than the frictional coefficient between a felt pad and the tape. For example, a frictional coefficient of about 0.12-0.15 has been measured. Much reduced frictional coefficients, e.g. of 0.07-0.08 may be attained by using such valuable materials as oxidized aluminum. Advantageously, the leaf spring of this invention may have at least the working zone 2a treated or lagged with a thin layer of a material having a lower frictional coefficient on magnetic tape 3 than the reed 2 material. In fact, by either galvanic or coating processes, or plastic films, or else, one can treat the leaf spring 1 surface to achieve much reduced frictional coefficients irrespective of the value of the material used to fabricate the reed element 2. Advantageous on the leaf spring 1 is the application of a magnetic shield 8 at the the remote face of the working portion 2a from the tape 3; the shield is close to the tape 3 and the head 4. The magnetic shield 8 may be made very thin and flexible with the working portion 2a, or rigid and attached centrally to that portion, as shown in Figure 4. In the latter case, attachment may be accomplished by either acrylic resins, electric spot welding, or hot melts. Owing to its proximity to the tape 3 and the head 4, a shield applied to the working portion 2a is exceptionally effective even if quite thin. This enables the magnetic shield 8 to be formed from highly expensive materials, such as a particular high-permeability magnetic alloy known as "mumetal" or having an amorphous structure. The magnetic shield 8 may be utilized in combination with a conventional magnetic shield 9, away from the tape 3 (Fig. 1): The reed element 2 itself might form a magnetic shield if made of a high-permeability magnetic material and provided with a surface layer of a non-magnetic material at the face of the working portion 2a next to the magnetic tape. In fact, the magnetic noise fields would close in that case on the reed element 2 itself. In the dreawings, each leaf spring 1 has peduncles 13 for connection to leaf springs 1 in one band 14, still shown in Figure 6 in its flattened condition. Once the leaf springs have set in their final shape they may be supplied in bands which are adapted to be wound into thight coils as shown in Figure 7. The formed coils may have a density which is about four times as high as that of conventional leaf spring coils. It is also envisaged that suitable spacers may be used to avoid interlocking the leaf springs together. Figures 5, 6, 7 show protuberances 15 formed from cut out and folded portions of the reed element 2. The inventive magnetic tape backing leaf spring is used as follows. The leaf spring 1 is insertable into a conventional cassette 7 like known leaf springs. However, it would fit true on the magnetic tape 3 and the contours of the heads 4 without requiring felt pads or the like elements, and this while overcoming all the problems connected with the use of felt pads. In fact, when a magnetic head 4 exerts a bias action on a leaf spring 1, the center zone of the working portion 2a is first deflected where edge cutouts 11 and inside cutouts 12 may be advantageously provided to favor deflection. Then also the edges of the working portion 2a are immediately engaged at the stepped zones 2c. It is the latter that will transfer directly the elastic stresses of the arms 2b to a large extent, preventing enhanced pressures on the gap 4a located centrally to the head 4 and holding the tape 3 close against the working portion 2a over the entire length thereof. The stepped zones 2c tend to retain the initial angles to the working portion 2a and accordingly , on increasing their mutual convergence, they tend to raise arcuately the center of the working portion 2a, as shown in Figure 3, avoiding high pressures on the gap 4a. Precise positioning of the working portion 2a is also determined by the projections 10 enabling the reed element 2 to swing freely about an axis close to the line of lay of the leaf spring and to arrange itself naturally in the position of least forcing. Said projections are particularly important to the operability of the leaf spring and may be advantageously implemented with various leaf spring designs. In fact, the projections serve the purpose of accommodating any imperfections in the positions and shapes of the pegs 6, which engage with the leaf springs, and of also accommodating small errors in the positiong of the head 4 relatively to the cassette 7. Precise positioning of the leaf spring 1 and the absence of overpressures on the gap 4a acquire basic importance when it is considered that many of the currently available magnetic tapes contain such particular materials as chromium oxide, chromiumiron, and "metal", which are apt to increase wear of the magnetic heads. Also revealed is a reduced frictional coefficient, which can be brought down to very low values by said surface treatments, and optimum magnetic shielding is provided by the magnetic shield 8 being adjacent the magnetic tape and the magnetic head. Actual tests have also brought out minimization of electrostatic discharges because of the low average resistivity of the system. The leaf spring 1 further enables compact high-density rolls to be formed, and is simple construction-wise and easily implemented.

Claims: A cassette with a magnetic tape backing leaf spring assembly, comprising: a cassette (7) and an elastically flexible reed element (2) having a prevalent longitudinal dimension and defining by itself supporting portions (2b) and a working portion (2a) engageable with a magnetic tape (3) and supported by said supporting portions (2b) in a projecting position from the positions of said supporting portions (2b), the free ends of each supporting portions (2b) being attached to fixed elements (6) positioned in the cassette (7) and wherein said reed element (2) further comprises: stepped zones (2c) crosswise interposed between said working portion (2a) and said supporting portions (2b) and having a transverse width, transversal to said prevalent longitudinal dimension, comparable to the maximum transverse width of said reed element (2), to form areas of maximum rigidity on said reed element and wherein said supporting portions (2b) have a transverse width, at ends close to said stepped zones (2c), comparable to said transverse width of said stepped zones (2c), and extend from said stepped zones (2c) in a substantially straight direction, substantially parallel to said working portion (2a), in a non-operational position of said reed element (2), characterized in that the free ends of said supporting portions (2b) are folded over wings (3) partially surrounding said fixed elements (6) in the cassette (7), whereby in operational position of said stepped zones (2c) are rotated and said working portion (2a) are elastically deformed by said stepped zones (2c) into a substantially arcuate configuration. A cassette with a magnetic tape backing leaf spring assembly according to Claim 1, in which said supporting portions (2b) include: projections (10) close to end portions of said supporting portions (2b) and jutting out of a side of said reed element (2) not facing said magnetic tape (3), said projections (10) forming reduced contact zones with the fixed elements (6) and said reduced contact zones having a prevalent dimension parallel to said prevalent longitudinal dimension of said reed element (2), and a reduced dimension transversally to said prevalent dimension. A cassette with a magnetic tape backing leaf spring assembly according to Claim 1, in which said reed element (2) has at least one portion of at least said working portion (2a) faced with a layer of a material having a lower frictional coefficient on said tape (3) than the material forming said reed element (2). A cassette with a magnetic tape backing leaf spring assembly according to Claim 1, in which, in a non-operational position of said reed element (2), said stepped zones (2c) converging together toward said tape (3) and are increasing their convergence in an operational position.

Inventors: BORDIGNON, ABRAMO
Applicants: A.T.B. S.P.A.
Application year: 1986
Main classification: G11B23
IPC codes: G11B15, G11B23