Patent GB-1152801-A (GB)
Title: Improvements in or relating to Electric Signal Transducer Apparatus
IPC: G11B5/41
Filed: 1966-05-16
Abstract: 1,152,801. Tape recorder. IIT RESEARCH INSTITUTE. 16 May, 1966 [17 May, 1965], No. 21722/66. Heading G5R. A multi-channel tape recorder, in which the head contacts the tape at the capstan position, comprises a switching arrangement whereby the recorder may be operated at a fast speed for video recording and a slow speed for audio recording; an arrangement which on completion of record/playback on one channel automatically moves the transducer head to the next channel during which movement the tape drive is reversed and the head is cleaned and de-magnetized and in which the head is returned to the first channel position after completion of recording/playback of the last channel; a capstan which may be formed with a circumferentially grooved tape-engaging surface and an arrangement for bulk demagnetization of the tape on one of the spools. Capstan.-The capstan 74 is formed with grooves 94 having a centre-centre spacing which is equal to the spacing between the tape channels and the magnetic head 85, which is resiliently urged towards the capstan, depresses the tape channel being recorded or played back into the corresponding capstan groove. The head is moved away from the capstan during change of channel. The capstan grooves may be filled with a resilient material, e.g. rubber, Fig. 4 (not shown) or the capstan may have a single groove containing resilient material opposite a fixed head position, for which arrangement guide shifting means are provided for moving the tape transversely to engage the tape channels with the head, Fig. 2 (not shown). Alternatively the capstan may be provided without grooves with a plain resilient surface, Fig. 5 (not shown), or with a non-resilient surface coated with a magnetic material which acts as a keeper and reduces cross-talk between channels, Fig. 2 (not shown). Two-speed drive.-The capstan 74 is secured to a flywheel 96 and is directly driven by motor 98. The motor is supplied for high speed operation from an A.C. mains supply and for low speed operation from a low frequency oscillator 405. During low speed operation a second flywheel 392 is coupled to the main flywheel 96. The motor may be reversed by switch 384. In a second arrangement, Fig. 12 (not shown), which additionally shows the switching circuits for connecting the audio or video circuits to the head, the capstan is directly driven for video recording and driven for audio operation from a low speed drive motor via a mechanical coupling. Fig. 12 (not shown) indicates how reverse drive is obtained when the capstan is mechanically driven in audio operation from the low speed motor. Head shift.-On completion of recording or play-back of one channel a switch 122 is operated, e.g. by a tape foil or the like. This energizes motor 117 which drives gear 115 coupled to gear 112. On rotation of gear 112 cam 90 moves member 88a out of slot 89 so that arm 88 is pivoted about pin 126 against the action of spring 125. Movement of the arm moves the head 85 away from the capstan and additionally a member 88b on the arm operates switch 127 in parallel with switch 122. Gear 112 also rotates gear 91 to which a threaded shaft 83 engaging the head block 82 is fastened. One rotation of the gear 91 brings the head to a position opposite the next track and at this position member 88a drops back into the slot 89 in the cam 90 and the head re-engages the new track on the tape and the movement of member 88b switches off the motor 117. Rotation of gear 112 also operates a gear train which actuates an indicator 100 to show the new track number. Between the final track number and the first track number on the indicator wheel a pin 102 is provided which actuates a lever 103 of a reversing switch which actuates the motor 117 in the reverse direction. The motor drives the head back to a position opposite the first track in which position the pin returns the reversing switch to its initial position. Demagnetization.-Coils 25, 27, Fig. 10, are disposed below one of the tape spools 12 and energized via a potentiometer 137 when a button 143 is pressed to actuate switch 139. The moving arm of the potentiometer is connected to a bi-metallic element 148 which turns the arm when the strip is heated by resistor 14 also connected across the supply via switch 139. The spool is rotated so that successive sectors of the coil of tape are influenced by the erase field from the coils. When the moving arm reaches the end of its traverse it engages switch arm 139a and push-rod 150 which switch off the supply and restore button 143 respectively. In a second arrangement, Fig. 11 (not shown), the potentiometer arm is motordriven. A demagnetizing signal may also be applied to the head 440 by means of a pick-up winding 437 on the common core of the bulk erase windings 25 and 27. The picked up energy is applied to the head winding 439. Brush means 442 for cleaning the head gap are also shown. Head cleaning.-The head may also be cleaned by brush 346 driven by motor 347 which are both mounted on a slidable plate 350. As this is moved downwardly edge 350a contacts a portion 360 of the head assembly to pivot arm 88 and allow the brush to engage the head. This cleaning action may take place automatically each time the head is moved to a new channel and where the demagnetizing supply to the head winding is obtained from a source other than the winding 437, the head may be demagnetized at the same time.