Method and apparatus for locating the edge of a magnetic tape

#This invention relates to a method and apparatus for defining a reference location of a magnetic recording and playback unit which corresponds to an edge of a magnetic recording tape so that the unit may be subsequently moved transversely to the edge of the tape precise distances from the reference location to enable information to be recorded and played back from any one of a plurality of longitudinal tracks on the tape.

#A variety of techniques for controlling the transverse position of a magnetic recording/playback head relative to a magnetic tape have been proposed and used in the past. For example, simple mechanical detents have been employed for positioning the heads at a series of transverse positions relative to a tape transport path defined by tape guide members. Such a technique may be suitable for systems such as those designed for use with eight track audio cartridges in which only eight tracks are recorded on one-quarter inch wide tapes. In most current systems, the recording tape is contained within some type of cartridge or cassette which also includes tape guide members. These members, either solely, or in combination with other members forming a part of the tape drive, control the transverse position of the tape such that any variation in the positioning of the cartridge within the drive or in the tolerances of the cartridges themselves will result in a variation in the final transverse position of the tape. Such a final position will vary even as the same cartridge is repeatedly removed and reinserted in the same drive. Such variations can be tolerated in systems in which each track is relatively wide and is separated by a similarly wide space from an adjacent track, such as in the eight track audio cartridge system.

#Newer systems, in which significantly narrower tracks are desirably used and in which the tracks are placed much closer together, such as when over twenty tracks are to be recorded on 6.4 mm wide tape, have been found to require a much tighter control over the transverse position of the heads relative to the tape. Accordingly, methods have been developed for sensing the actual tape edge, apart from the specific positioning of a cartridge or cassette within which the tape is located. Thus, for example, optical and mechanical sensors have been so employed, with such additional components contributing to the complexity and expense of the drive and providing additional sources of malfunction.

#FIG. 1 is a block diagram of the system of the present invention;

#FIG. 2 is a flow sheet showing the sequence of operations desirably performed while fixing the gain according to the present invention;

#FIG. 3 is a representation of signal waveforms typically present while performing certain steps set forth in FIG. 2;

#The dynamic gain set and edge seek features of the present invention are particularly desirably implemented in a drive adapted for use with a belt-driven tape cartridge of the sort disclosed in U.S. Pat. No. 3,692,255 (VonBehren) and 3,861,619 (Wolff). As particularly set forth in the latter patent, such a cartridge is desirably provided with a tape containing a series of hole patterns to enable detection of particular regions of the tape. Thus, for example, as shown in FIG. 1, a tape 10 contained within such a cartridge will have a pattern of double holes 12 indicative of the beginning of tape (BOT) and spaced a predetermined distance therefrom a single hole 14 indicative of the load point (LP), i.e., the point at which normal recording operations may begin. Thus, for example, if the cartridge is of a type generally identified as a type DC-1000 cartridge, there will be approximately 18 inches (48 cm) of tape between the BOT and LP identification holes 12 and 14 respectively, whereas if it is a type DC-2000 cartridge approximately 30 inches (76 cm) of tape will be present between those respective points.

#Such a cartridge is adapted for recording and playing back of data on a plurality of parallel tracks extending longitudinally along the length of the tape while the tape is driven via a brushless DC motor 16 which is coupled to a drive puck 18 in contact with a capstan (not shown) within the cartridge. Recording and playback of the respective tracks is enabled by a record and playback unit 20 within which are mounted a record head 22 and a playback head 24. In a preferred embodiment, an inexpensive unicore dual gap wide write (8 mils, 203 .mu.m) and narrow read head (5 mils, 127 .mu.m) is employed. The record/playback head unit 20 is mounted so as to be transversely movable across the 5 width of the tape by means of a lead screw 26 and stepper motor mechanism 28.

#The longitudinal motion of the tape 10 is, as noted above, under control of a motor 16, which motor is energized by signals from a drive motor commutation logic circuit 30. The motor further includes sensors which provide a tachometer signal on lead 32 which is coupled to a motor speed control processor 34. The processor 34 is in turn controlled by general command instructions from a command capture processor 36 and by time control signals from a timer circuit 38. Thus, depending upon the desired tape speed, such as 60 inches per second (152 cm/sec) for normal recording and playback operations or 90 inches per second (229 cm/sec) for high speed fast forward or reverse operation, the processor 34 responds to input signals from the timer 38 and the tachometer pulses on lead 32 to provide a speed control signal to the drive motor commutation logic circuit 30, which in turn provides motor drive signals to the motor 16.