Vehicles and home entertainment systems commonly use audio cassette tapes for recording and playback of music and other audio recordings. Cassette tape cartridges vary widely in quality of material and design. The best cassette tape cartridges are made from impact and heat resistant materials which are durable and provide thousands of hours of quality playback. However, many manufacturers use inferior cassette tape cartridges due to their low cost. "Bargain" cassettes may not comply with minimum standards for cassette design, testing and manufacturing. If a cassette is not manufactured to precise tolerances, it will not maintain uniform rolling friction of internal parts and may result in improper tape guidance. In severe cases, this may result in tape spilling into the transport mechanism and wrapping around the capstan. A condition commonly referred to as "tape eating" occurs when tape spills from the cassette and wraps onto the capstan, pinch roller or other parts of the cassette player. "Tape eating" occurs relatively frequently in home and vehicle cassette tape players.
Three principal factors are associated with "tape eating": (i) the cassette take-up hub may not rotate freely; (ii) the tape may be loosely wound on the tape reels or separated from the tape pack; (iii) the cassette may have thin tape commonly used in long-playing C-120 cassettes.
When take-up hub rotation is impaired, tape pulled by the capstan from the supply reel does not wind onto the take-up hub. Tape then spills into the tape transport mechanism and wraps onto the capstan or pinch roller. The cause of impaired take-up reel rotation is generally related to one of the following conditions and cassette cartridge defects:
the hub may be dislodged out of position and jammed as a result of the cassette being dropped. PA1 the cassette shell may be made from low-grade plastic which warps upon exposure to high temperatures. PA1 improper sonic welding of a cassette may cause misalignment between the two shell halves which reduces internal dimensional tolerances. PA1 inadequate internal support between the two half shells of the cassette may result in shell deformation when placed in a tape player.
Step formations in the tape pack may cause excessive friction, especially when repeated changes in play and fast forward or rewind modes occur in cassettes having poor internal tape guidance.
"Tape eating" caused by loose tape is more frequently encountered with vehicle cassette tape players than in home tape players due to the extreme conditions in which the tapes are used and stored. When the cassette tapes are stored in the vehicle outside their protective case, vehicle vibrations can be transferred to the cassette and loosen the tape. Upon insertion, the tape may spill into the mechanism, at which time the tape can wrap onto the capstan.
"Tape eating" caused by the use of thin tape, like C-120 and C-90 tapes, can result from an initial formation of a small loop in the tape caused by the tape following the curvature of the capstan upon initial insertion. If a cassette tape cartridge does not have ramps or tape strippers required by the industry standard, a portion of the tape will be able to follow the capstan rotation, catch under the pinch roller, and subsequently wrap around the capstan.
It is estimated that a significant percentage of all cassette system failures in vehicle warranty claims are in some way related to defective or improperly stored cassette cartridges. Cassette system failures are costly to equipment manufacturers, particularly during the warranty period. When a consumer returns a vehicle to the dealer for repair, it is frequently necessary to entirely remove and disassemble the tape player from the vehicle for service leading to consumer dissatisfaction.
Several attempts have been made to prevent "tape eating" in the prior art. One example is disclosed in Taraborrelli U.S. Pat. No. 4,348,702 which describes a device for preventing tape windup on the capstan of a tape deck. The Taraborrelli device incorporates a rotation-sensing switch and switch wiper mounted on the bottom of a take-up spindle. The rotation sensing switch only allows rotation when the take-up spindle rotates in a proper direction. If the take-up spindle changes direction due to tape windup on the capstan, a tab on a rotation-sensing switch engages a vertical edge at the bottom of the take-up spindle and stops the sensor switch from rotating. When the rotation-sensing switch stops, the rotation-sensing circuit disables the drive mechanism to prevent additional tape windup on the capstan. However, the rotation sensing switch is not sensitive enough to detect the tape windup as soon as it happens and additional tape may wind up during the time the switch moves to engage the vertical edge.
Another approach is disclosed Tarpley, Jr. et al U.S. Pat. No. 4,597,547 which describes a logic circuit for detecting reverse rotation of a take-up reel in a tape transport mechanism wherein three motion sensing switches are added to a tape player adjacent the take-up reel to detect a sequence of switch actuation according to the sequence of A-B-C. Subsequent switch activation sequences are then monitored by a logic circuit which can sense and react to an improper switching sequence. The switches and logic circuit are additional elements which must be added to a cassette tape player, thereby increasing cost. Additionally, there is no way to adjust the sensitivity of the motion sensing switches to compensate for changes in the rotational velocity of the take-up reel, making early detection difficult.
In Tarpley, Jr. U.S. Pat. No. 4,632,333 another circuit sensing improper rotation of a take-up reel is disclosed wherein three switches are provided on the cassette player adjacent to the take-up reel. The sensing circuit outputs a pulse each time the sensor switches are actuated. Monostable multivibrators receive the pulses and provide output signals into a gate which responds by providing a control signal to a sensor switch. Improper rotation of the take-up reel interrupts this control signal, causing the sensor switch to respond by stopping or reversing the tape deck mechanism. The need for switches and monostable multivibrators in a special sensing circuit again increase the cost of the cassette tape deck equipped with such a system.
The present invention is directed to overcome the above disadvantages noted in conjunction with prior art systems and to provide a new system which surpasses the prior art in efficiency and simplicity.