Anti-static structure for magnetic tape guides

A magnetic tape cassette is provided with shielding means for the guide posts thereof, including a clip member of electrically-conducting material, for preventing build-up of static electrical charges and resultant clinging of the tape to the guide posts, when it is desired to pull the tape from the guide posts by vacuum pressure-differential apparatus, as for threading into a tape transport.

BACKGROUND OF THE INVENTION 
This invention relates to magnetic tape transport, and particularly to tape 
guides therefor. 
Various synthetic or so-called "plastic" materials have found uses in the 
economical manufacture of magnetic tape transport and of components 
therefor, such as the magnetic tape cassette described in U.S. Pat. No. 
3,756,329, which is meant for use in an automatically-threading transport 
mechanism such as the carrousel apparatus disclosed in U.S. Pat. No. 
3,720,794. 
In the machine of this patent, the tape loop that extends between the two 
reels of the cassette is pulled into the transport machine, and into 
contact with the magnetic heads, by means of a vacuum apparatus. 
One problem that has developed in the use of plastic materials for such 
cassettes, is that the surfaces thereof, over which the tape passes in a 
tensioned, rubbing fashion, and particularly surfaces such as those of 
guide posts, tend to collect static charges of electricity, so that the 
tape clings to the guide posts when the tape is at rest. The cassette of 
U.S. Pat. No. 3,756,329, for example, has a pair of guide posts for 
holding the tape that extends between the reels of the cassette in a 
favorable position to be acted upon by the vacuum pressure differential of 
the transport, for threading. However, the build-up of static electrical 
charges between the tape and guide posts, and the resulting clinging of 
the tape to the posts, inhibits and interferes with the desired 
vacuum-threading operation and, on occasion, causes complete malfunction 
of the apparatus. 
Accordingly, it is an object of the present invention to provide 
anti-static protection for magnetic tape and the guide means therefor. 
It is a further object of the present invention to provide an improved 
cassette for the threading of magnetic tape into a tape transport. 
SUMMARY OF THE INVENTION 
A magnetic tape cassette is provided with shielding means for the guide 
posts thereof, including a clip member of electrically-conducting 
material, for preventing build-up of static electrical charges and 
resultant clinging of the tape to the guide posts, when it is desired to 
pull the tape from the guide posts by vacuum pressure-differential 
apparatus, as for threading into a tape transport.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
For convenience of illustration, the invention is shown mounted upon the 
cassette shown in the sole FIGURE of the Drawing, which cassette is 
substantially the same as that shown in U.S. Pat. No. 3,756,329, and is 
described as follows. 
Referring to the sole FIGURE there is shown one of a pair of reels 11 
suitable for winding a short length of magnetic tape of the wide (e.g. 2 
inches, or wider, or narrower) video transverse recording type commonly 
used for "spot announcements" and "commercials" advertisements of several 
minutes' duration in television broadcasting stations. The reels 11 are 
normally enclosed in a cassette housing consisting of two substantially 
equal parts or halves 13,14, which may be broken open for removal or 
exchange of reel-mounted tape. 
To facilitate the opening and closing of the cassette the halves are 
arranged with hinges 16,17 in each of which the leaves are integrally cast 
or molded as portions of the high-strength plastic housing halves 13,14, 
and the knuckles 18,19 define journal means 21,22 for a hinge pin 23. 
To facilitate molding the cassettes from plastic, the hinges 16,17 have an 
unusual construction in that the first or female knuckle 18 is formed as 
part of a re-entrant first wall 24 of the housing half 14 to define a 
recess 26 opening toward the exterior of the housing and toward the second 
or male knuckle 19 on half 13. This construction facilitates the 
production of the knuckle by casting or plastic molding techniques; and 
the male knuckle 19 is also moldable as a protrusion or extension of 
housing portion 13 to fit pivotably within recess 26 in both open and 
closed conditions of the cassette. 
To facilitate both the manufacture and operation of the hinges 16,17, the 
reentrant wall 24 portion of knuckle 18 is slotted to define a pair of 
bearing slots 22 aligned on the hinge axis and opening toward the other 
housing portion 13, so as to permit lateral insertion and removal of the 
hinge pin 23. The pin 23 is formed with its mid-portion fitting in the 
slots 22, and two substantially parallel arms 27 extend orthogonally from 
the mid-portion and along the opposed faces 18 of the reentrant first wall 
portions that face inwardly of the housing. The arms 27 are curved or bent 
as at 28 and have hook portions 29 at the tips to define a springy clip. 
Thus, the clip 23, after having been inserted through the journal 21 of 
male knuckle 19, may be seated in slots 22 of female knuckle 18, and the 
tip hooks 29 are concurrently hooked, by a slight distortion of springy 
bent arms 27, around a pair of shoulders 31 that are cast in the walls 18 
of the female knuckle. This structure not only facilitates manufacture and 
assembly of the hinge, but also its operation, for the springy clip 23 
retains the two cassette halves in tightly clamped together and 
snug-fitting relation both in the closed condition of the cassette and 
during the opening and closing process. 
To hold the cassette halves together at points remote from the hinges, 
there are provided three key-type fasteners 36, each having an enlarged 
head 37 and a single bit 38. Each of the corresponding keyholes 39 (in 
part 14 e.g.) is warded to permit insertion and removal axial passage of 
the key only in a first predetermined orientation, i.e., the orientation 
illustrated in the FIGURE, which corresponds with a ward slot 41 that 
passes the entire length of keyhole 39 in part 14. However, once inserted, 
the key may be turned 90 degrees to a second orientation corresponding 
with a slot 42 which extends axially along the side of the keyhole only 
far enough to seat the axial length of bit 38. Thus, in the second 
orientation the key cannot be removed; and a helical compression spring 43 
is provided to seat against a shoulder 44 forming part of the enlarged 
head portion of the key, and a shoulder 46 on the interior of the keyhole, 
to urge the key in a removal direction and thus retain it securely with 
the bit in slot 42. 
To fasten the housing parts together by means of the keys 36, the other 
housing part 13 is provided with matching keyholes 49 that are warded to 
accept the key bit only in the second orientation thereof, as by means of 
a single ward slot 51, which passes to an enlarged interior chamber 
defined in part by a shoulder 52, having a shallow slot 53 therein at a 
different orientation than slot 51, so that when the key is pushed more 
deeply inwardly against the resistance of spring 43, it may be rotated to 
the orientation of slot 53 and seated therein, thus locking the two 
cassette halves together. 
A key type structure is also used for function lockout buttons, such as 
record lockout and erase lockout, commonly provided in cassettes in the 
form of punchout holes in the casing, the related function being permitted 
(or conversely, prevented) by a sensing lever on the transport controls 
when the punch-out is missing, permitting the sensing lever to intrude 
into the punch-out recess. In the present invention, no punch-outs are 
provided, but rather a pair of depressable and restorable keys 61 having 
enlarged heads 62, single bits 63, and springs 64, fitting in keyholes 66 
in a first orientation, as illustrated, corresponding to full-length slots 
67, and being seatable in a second orientation in part-length slots 68 
with the heads 62 coplanar with the outer surface of the cassette, 
representing the function-permitted position (or the opposite in some 
applications). Part-length slots 69 are also provided at a third 
orientation and at a depth such that when the key is further depressed and 
the bit is seated in slot 69, the head 62 is recessed substantially below 
the outer surface of the cassette, this being the function-forbidden 
position (or the reverse). 
Both key heads 37 and 62 may be slotted to aid the use of screwdrivers in 
operation. 
The cassette, of course, contains two reels 11, which may be identical, and 
only one of which is shown in the drawing, fitting between the upper 
cassette openings 98, 114. The other reel fits between the lower openings 
98, 114. Each reel has a hub spindle 84, a brake member 94 springloaded by 
a helical compression spring (not shown) to be urged against the portion 
of the inner face of the wall of cassette half 14 that is peripheral to 
opening 98, such portion being chamfered to mate with and to centralizing 
seat a correspondingly bevelled portion 97 of the brake member 94. The 
reel flange 108 has a stepped extension (not shown) fitting loosely within 
the opening 114 for centralizing the flange 108 with respect to the 
opening 114. 
In operation, the reels 11 serve to mount a magnetic tape 121, with the 
reel-to-reel run 122a of tape (shown in phantom lines) looped over a pair 
of guide posts 132 and exposed to the operation of an air pressure 
differential, as described in U.S. Pat. No. 3,756,329 previously referred 
to. Recessed portions 133,134 are provided beneath the tape run 122 to 
ensure the communication of atmospheric pressure to the tape and to thus 
assist in the establishment of the required air pressure differential. 
When the run 122a of tape is pulled from the cassette by the pressure 
differential, the tape loses, or should lose, its contact with the guide 
posts 132, and thereafter, for play-record operation, does not contact any 
portion of the cassette except the reels 11. 
However, during the fast-wind and fast-rewind modes of operation, and to 
some extent during the un-threading mode, the tape does run frictionally 
against the guide posts 132, which, as integral parts of the cassette, 
have been found to be very economically manufacturable, as by molding 
processes, from hard synthetic or so-called "plastic" substances, which 
are characterized by the common feature that they collect static electric 
charges from the frictional running of the tape. Thus when the tape is 
stopped against the posts 132 it tends to cling to the posts, and often 
cannot be pulled successfully away by the differential air pressure 
forces. 
To remedy this problem, the present invention provides an anti-static 
shield in the form of metal or other electrically conducting material to 
cover the tape bearing portions of the guide posts 132, so as to engage 
the tape and bleed away static electrical charges before they can build 
up. 
The clip 141 is arrange to enclasp more than a 180-degree sector of the 
assembly of the two posts 132, so as to be retained thereon without the 
need for fasteners or adhesives, and means are provided for preventing the 
clip 141 from rotating on the post assembly, in that the clip 141 is 
formed to conform to the generally triangular cross-section of the post 
assembly, and has one flat side 142 for spanning the space between the 
posts 132 on the tape-confronting side of the post assembly; and the clip 
also has two rounded apex portions 143 adjacent to the flat side 142, so 
as to define with the flat side 142 a non-rotating bearing element for 
engaging the tape. 
The shield clip 141 may be made of springy material so as to snap on to the 
post assembly; but it is here shown as being slipped on to the post 
assembly from the free end thereof. 
Thus there has been described the following apparatus: A magnetic tape 
cassette, provided with shielding means for the guide posts thereof, 
including a clip member of electrically-conducting material, for 
preventing build-up of static electrical charges and resultant clinging of 
the tape to the guide posts, when it is desired to pull the tape from the 
guide posts by vacuum pressure-differential apparatus, as for threading 
into a tape transport.