The present invention relates to a magnetic tape cassette comprising
an elastic element structure for the reel retention ratchet gear.
As is known, in magnetic tape cassettes, in particular in so-called
videocassettes, a ratchet gear is used which is constituted by a pair of ratchets
oscillating about an axis substantially parallel to the axis of rotation of the
reels, which are pushed elastically against a toothed flange of the reel, so as
to prevent the rotation of the reels, when the cassette is not inserted in the
recording or playback device, to prevent the rotation of said reels in the direction
of unwinding of the tape from the reel.
Various types of elastic elements are currently used which are constituted,
for example, by an elastic leaf spring having a lower flap for coupling to the
cassette shell, to the side whereof two elastic arms are provided which act with
a thrusting action on the thrust branches of the ratchets.
This type of solution has, first of all, the disadvantage of not
allowing packaging of the elastic laminae in reels, since the presence of the small
plate arranged to the side of the elastic arms does not allow the possibility
of unwinding in a tape-like manner the various elastic elements.
Another disadvantage resides in the fact that the elastic preloading
to be imparted to the elastic arms which thrust the ratchets must be performed,
during the step of assembly of the cassette, by performing a composite movement
during the insertion of the ratchets in the cassette, which slows down all the
steps of automatic assembly of the cassette components.
To obviate these disadvantages, springs for videocassette ratchet
gears have already been introduced which are substantially constituted by an elongated
elastic lamina which is provided with a central portion, associable with the cassette
structure, from which there extend two elastic arms, inclined with respect to the
central portion, which act with a thrusting action against the ratchets.
This solution allows to package the various elastic elements in a
continuous tape, but is not conducive to advantages regarding the elastic preloading
of the laminae, which still require a composite movement of insertion of the ratchets.
To try to limit this disadvantage, ratchets have been introduced
which, in their lower part of the thrust arm which engages with the elastic lamination,
are provided with a bevel in the shape of an inclined plane, so that the insertion
of the ratchet along the direction of oscillation of the ratchet itself creates
a component which elastically compresses the elastic lamina.
This solution, though valid from many points of view, has the disadvantage
of possibly creating particles which come loose from the thrust arm and may remain
free within the cassette with the possibility of damage of other component elements.
The elastic laminae are in fact generally obtained by punching and have burr at
their free edges which may scrape the plastic material which constitutes the ratchets,
removing particles of plastic which, by coming loose and remaining within the cassette,
may create a severe detriment to the good quality of the cassette.
Also known from US-A-4,195,797 is a reel retention ratchet gear having
an elastic lamina as defined in the preamble part of claim 1
The aim proposed by the invention is to eliminate the above described
disadvantages by providing an elastic element structure for the reel retention
ratchet gear in magnetic tape cassettes, which allows to obtain the elastic preloading
of the laminae which act on the ratchets, without having to resort to a composite
movement of insertion of the ratchet and without running the risk of scraping or
in any way abrading the surface of the ratchet, with consequent outward dispersion
of plastic particles.
Within the above described aim, a particular object of the invention
is to provide an elastic element structure which may be packaged in a tape-like
manner, thus having the possibility of winding in a reel a large number of elastic
elements.
Another object of the present invention is to provide an elastic
element structure which is configured so as to eliminate practically completely
all of the punching burr which normally occurs during the step of punching of the
individual elastic laminae from a metallic tape or band.
A further object of the present invention is to provide an elastic
element structure which, though being obtainable with a reduced use of material,
is capable of giving the greatest assurances of reliability and safety in use.
Not least object of the present invention is to provide an elastic
element structure which is easily manufacturable from elements and materials commonly
available on the market and which furthermore is competitive from a merely economical
point of view.
The above described aim, as well as the objects mentioned and others
which will become apparent hereinafter, are achieved by a magnetic tape cassette
comprising an elastic lamina as defined in claim 1.
Further characteristics and advantages of the invention will become
apparent from the description of a preferred but not exclusive embodiment of a
structure of an elastic element structure for the reel retention ratchet gear in
magnetic tape cassettes and the like, illustrated only by way of non-limitative
example in the accompanying drawings, wherein:
- figure 1 is a schematic plan view of a magnetic tape cassette with the cover
removed, highlighting the positioning of the elastic element according to the
invention, inside the cassette;
- figure 2 is a sectional view of the cassette, highlighting the detail of the
elastic element acting on the ratchets;
- figure 3 is a schematic perspective view of a ratchet;
- figure 4 is a detail view of the ratchet gear of a cassette with a ratchet
inserted and with the other ratchet in the process of being inserted;
- figure 5 is a schematic view of the step of punching the individual elastic
laminae starting from a metallic band;
- figure 6 is a partial sectional view, in greatly enlarged scale, of the elastic
element according to the invention, highlighting the central portion and one of
the arms which act elastically on the ratchets;
- figure 7 is an end view of the elastic element;
- figures 8 and 9 are schematic views in succession of the step of insertion
of a ratchet with consequent elastic preloading of the lamina at the moment of
the insertion of the ratchets on their oscillation pivot;
- figures 10 and 11 are views of two different embodiments of the free end portion
of the elastic lamina taken along the line X-X of figure 6;
- figure 12 is a view of an elastic lamina with smooth central portion.
With reference to the above described figures, the elastic element
structure for the reel retention ratchet gear in magnetic tape cassettes comprises
an elastic lamina which is generally indicated by the reference numeral 1, which
substantially has a predominantly elongated extension. The elastic lamina 1 is
obtained, as shown in figure 5, by punching from a metallic band or tape, generally
indicated by the reference numeral 2, and is shaped, as will become apparent hereinafter,
so as to have no particular punching burr.
The elastic lamina 1 has a central portion 10 in which insertion
coupling means may be provided, constituted for example by an indentation or possibly
a hole 11 with beading, which has the function of providing the element for insertion
coupling to a corresponding support 12 which is defined by the cassette, generally
indicated by the reference numeral 5.
From the central portion 10 there extend two opposite branches, both
indicated at 15, which are connected to the portion 10 by means of a first folding
line 16; the branches 15 are inclined with respect to the plane of arrangement
of the portion 10 and connect, at the other end, to a terminal portion 17, possibly
connected by means of a second folding line 18, so that the terminal end has a
greater inclination with respect to the central portion 10.
The terminal portions 17 act by contact on the thrust arm 20 of ratchets,
generally indicated by the reference numeral 21, which are rotatable about pivots
22 defined by the cassette and having an axis substantially parallel to the axis
of rotation of the reels 23.
The ratchets 21 have an engagement arm 25 which couples with the
set of teeth 26 defined by the lower flange of the cassette reel.
In a per se known manner, the thrust arms 25 have the function of
locking the rotation of the reels, when these are not used, in the direction of
unwinding of the magnetic tape, while they allow the winding, with a practically
ratchet-like coupling between the end of the thrust arm and the set of teeth 26.
The particularity of the invention resides in the fact that the terminal
portions 17 of the elastic lamina have a convexity, indicated at 30, on the face
directed towards the ratchets 21.
This convexity is extremely important since it defines, on the edges
of the elastic laminae, guiding portions which, upon the insertion of the ratchets
21 with a movement along the direction coinciding with the axis of oscillation
of said ratchets, generate a thrust component on the elastic lamina which in practice
performs the elastic preloading of said lamina.
As schematically indicated in figures 8 and 9, by introducing the
ratchets with a substantially vertical motion the lower edge of the ratchets couples
with the region proximate to the edge of the lamina which is arranged in practice
with an inclined plane, and generates a thrust component on the lamina which elastically
preloads the same.
This type of coupling furthermore prevents the possible burr which
may be present on the edges on the terminal portions from scraping the plastic
material which constitutes the ratchets, with the possibility that particles of
plastic material may become loose and dispersed in the cassette.
For the sake of descriptive completeness, it should be furthermore
added that the central portion 10, on the sides orthogonal to the sides from which
the laminae extend, is provided with expansions 40 which allow in practice to
package the various laminae in the manner of a tape which can be wound in reels;
as the lamina is then gradually inserted, by means of an automatic machine, on
the cassette, the individual lamina is punched in each instance, said expansions
constituting an element which facilitates the grip for their insertion.
Another important aspect of the invention resides in the fact that
the elastic lamina has a width which decreases starting from the central portion
towards the free end, this occurring since the resisting section useful for the
bending torque can decrease as one approaches the free end of said lamina where
contact with the ratchet gears occurs.
This arrangement allows to obtain a significant saving in material,
since it is possible to adopt a configuration, schematically indicated in figure
5, with a substantially rectangular central portion 10 from which there extend
said arms with progressively decreasing width so as to obtain with a punching
operation the execution of a plurality of laminae with no burr whatever, since
the region which is provided between two mutually side-by-side arms in practice
constitutes the useful region for the provision of an arm of another row of laminae.
To what has been described it should be furthermore added that said
convexity may be obtained by means of an inverted-V configuration, as indicated
in figure 10 by the numeral 30a, or possibly with a rounded configuration, indicated
at 30b in figure 11.
In practical use, therefore, once the elastic lamina is positioned
at the support 12 of the cassette it is sufficient to introduce the left and right
ratchets 21 with a substantially vertical translatory motion, so that the lower
edge of the thrust arm of the ratchet couples with the edge part of the convexity
of the terminal portion, so that the successive step of introduction of the ratchet
causes, automatically, the elastic compression of the spring, that is, its preloading,
without resorting, as can be observed in current methods, to composite insertion
movements.
Another important aspect of the invention resides in the fact that
the configuration adopted for the lamina allows its production in tapes wound in
reels, and consequently more easily used on automatic machines, and furthermore
allows to obtain the punching while minimizing burr.
