My U.S. Pat. No. 4,367,850 describes a cartridge including a length of magnetic tape spliced into an endless loop. In one embodiment that cartridge can be made to conform to the standard of the NAB so that it can be used in the types of record/playback machines presently in use in the broadcast industry. That cartridge embodiment causes much less edge wear on the tape and much less change in tension in the tape at a head of a machine in which the cartridge is received than the other types of cartridges presently in use in the broadcast industry.
The cartridge described in U.S. Pat. No. 4,367,850 employs a method for maintaining a uniform high tension in the tape at a head of a machine in which the cartridge is engaged so that the tape can be pressed against the head by tension alone without the use of pressure pads. That method comprises providing a fixed, generally cylindrical hub having a central opening and a slot extending axially across the full width of the hub and communicating with its central opening, and an endless length of magnetic tape; wrapping a major portion of the tape about the hub to form a coil while allowing a minor portion of the tape to extend from the innermost wrap of the coil through the slot into the central opening of the hub, and around the side surface of the coil to the outermost wrap of the coil; pulling the tape from the slot and across a head on a record/playback machine; and applying a light force to tension the minor portion of the tape as it moves onto the outer wrap of the coil which will produce the high, generally uniform tension in the minor portion of the tape being pulled from the coil and across the head.
The embodiment of the cartridge adapted for use in the broadcast industry which employs that method to tension tape across a head comprises a housing adapted to be received in a record/playback machine and having access openings adapted to receive record/playback heads and a tape drive mechanism in the machine. The hub is fixed on the housing at a position spaced from the access openings. Means on the housing define a tape path for, and produce tension in, the minor portion of the tape. Those means comprise means for guiding the minor portion of the tape past the access openings in a predetermined position for engagement by the heads and the drive mechanism of the playback machine, and a guide pin guiding the minor portion of the tape between the access openings and the outermost wrap of the coil. The guide pin is mounted for movement between a first position providing a first path length between the access openings and the outer wrap of the coil and a second position providing a second path length longer than the first path length between the access openings and the outer wrap of the coil (which means preferably is an arm having a first end supporting the guide pin, and a second end pivotably mounted on the housing to afford movement of the pin along an arcuate path adjacent the periphery of the coil between its first and second positions), and means are provided for biasing the guide pin toward its second position.
The pin can move to positions between its first and second positions under the influence of the biasing means to accommodate changes in length of the minor portion of the tape which decreases or increases respectively when the length of the major portion increases or decreases. The major portion of the tape cyclically undergoes its largest change in length by slowly decreasing in length as the splice moves from the coils outer wrap toward its inner wrap and by then suddenly increasing in length as the splice leaves the coil. The means for biasing the guide pin is adapted to apply a small force at the guide pin (e.g., generally in the range of 2 to 14 grams) to lightly tension the tape extending around the pin and moving onto the outermost wrap of the coil, somewhat in the manner of a rope or Proney brake, which light tension produces a significantly higher tension (e.g., generally in the range of 50 to 115 grams or 2 to 4 ounces) in tape leaving the coil. That higher tension is surprisingly uniform despite small changes in the force applied by the guide pin as the length of the minor portion of the tape changes due to the position of the splice along the tape.
The tape is guided so that the quite uniform higher tension thus produced in the minor portion of the tape between the inner wrap of the coil and the drive mechanism of a machine in which the cartridge is engaged presses the tape against the record and playback heads of the machine with sufficient pressure that pressure pads are not required, and the tape is thus not subjected to the abrasion and erratic forces caused by sliding contact between the tape and such pressure pads.
Also, my U.S. Pat. No. 4,394,989 describes a tape cartridge of the type described above in which the length of the minor portion of the tape can be easily adjusted by persons in the field to accommodate changes in the cartridge such as tape wear to ensure that a desired range of guide pin movement will be retained.
In that improved cartridge, the hub comprises a flexible arcuate cantilevered portion having a first end partially defining the slot, a second end that is fixed on the housing, and which is separated from the housing between its ends. Means in the form of a cam rotatably mounted on the housing is provided for changing the position of the cantilevered hub portion radially of the rest of the hub to adjust the effective diameter of the hub and thereby the length of the minor portion of the tape to cause the guide pin to move within a desired range of movement between its first and second positions. The cam has a peripheral surface contacting the inner side of the cantilevered hub portion, and can be manually rotated with a tool such as a screwdriver as the tape is being propelled by a machine so that the effects of cam adjustments on the tape can be observed as they are made. Such adjustability ensures that changes in overall tape length which can occur due to causes such as tape wear can be compensated for. While such adjustments do not need to be made often during the life of a cartridge, they do require attention by technicians, such as each time the tape is re-recorded.
Thus the cartridge described in my U.S. Pat. No. 4,394,989 is not particularly useful in cartridges used in background or foreground music machines where users typically are not trained to or interested in making the occasional cam adjustments needed to maintain the cartridge in its best operating condition.
Another problem that occurs with the cartridge described in U.S. Pat. No. 4,394,989 is that when it is moved from a room at normal temperatures into the cold (e.g., from an area at about 68.degree. F. to an area at below 10.degree. F.) its coil and fixed hub will shrink. When the cartridge is then again brought into a warm room and playing of the cartridge is attempted, its tape coil will seize around the hub which is more exposed and returns to room temperature and thus expands to its original size more quickly than the tape coil. Radio technicians can correct for this problem by adjusting the cam to release the tension in the coil. Again, however, persons involved with background music or foreground machines typically lack the training and desire to perform similar adjustments.