Apparatus for reproducing information at variable speeds from a

Details Apparatus for reproducing information at variable speeds from a Apparatus for reproducing information at variable speeds from a

1985-12-30

1988-12-13

Faber, Alan

Dynamic magnetic information storage or retrieval

Automatic control of a recorder mechanism

Controlling the head

360 102, 360 7308, G11B 5584, G11B 5592, H04N 5783

Patent

active

047915072

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to tracking control for a magnetic recording/playback apparatus (which will be termed simply "VTR" hereinafter) and, particularly, to a method of tracking control for realizing variable-speed playback at arbitrary playback tape speeds in a VTR using four kinds of tracking control pilot signals and an electromechanical transducer for moving the head.
A method of noise-free variable-speed playback using an electromechanical transducer such as a piezoelectric element has been realized in VTRs of the VHS system. In this method, the capstan FG (frequency generator) signal, which virtually represents the tape speed is counted to produce a sawtooth wave. The difference between this sawtooth wave and the sawtooth wave necessary for still picture reproduction is used to produce an actual preset voltage waveform to be supplied to the electromechanical transducer. The capstan FG signal does not indicate the exact tape speed due to slippage of the tape between the capstan and pinch roller, and therefore the preset voltage waveform is corrected by being reset by a playback control signal.
Although the above-mentioned method is effective for VTRs having the control signal, it cannot be applied directly to VTRs using tracking control pilot signals (which will be termed simply "pilot signals" hereinafter) instead of the control signal. The reason is that there is no control signal to be reset and that pilot signals, when four kind of signals are used, recorded on the scanning track need to be identified, as will be described in detail later, which necessitates the introduction of a new method.
Next, the four-frequency pilot system will be summarized, and a conceivable variable-speed playback system and its problems will be described.
FIG. 1 shows magnetic recording traces of the pilot signals. In the figure, A.sub.1, B.sub.1, A.sub.2, and so on are magnetized traces produced by head A and head B, and each recording track has a record of a video signal of one-field length. The pilot signals indicated by f.sub.1 through f.sub.4 are recorded over the video signal and arranged orderly for each field. The pilot signals have frequencies as listed in Table 1, in which f.sub.H denotes the frequency of the horizontal sync signal.


TABLE 1 ______________________________________ f.sub.1 = 102.5 (kHz) .apprxeq. 6.5 f.sub.H f.sub.2 = 118.9 (kHz) .apprxeq. 7.5 f.sub.H f.sub.3 = 165.2 (kHz) .apprxeq. 10.5 f.sub.H f.sub.4 = 148.7 (kHz) .apprxeq. 9.5 f.sub.H ______________________________________
Pilot signals of adjacent tracks have a difference of frequencies of f.sub.H or 3f.sub.H as shown in FIG. 1. Accordingly, by extracting each frequency difference and comparing the levels, a tracking error signal related to the tracking deviation can be obtained.
FIG. 2 is a block diagram of a circuit for producing the tracking error signal. In the figure, a terminal 1 receives the reproduced RF signal, and a lowpass filter 2 extracts only pilot signals. A balanced modulation (BM) circuit 3 produces the difference of frequencies of the pilot signal received and a reference signal received at terminal 4. For example, the pilot signal reproduced when the head scans the track A.sub.2 in FIG. 1 includes f.sub.3 which is reproduced on the main scanning track and a composite signal of f.sub.2 and f.sub.4 which is reproduced as a crosstalk signal. The reference signal at this time is the pilot signal f.sub.3 recorded on the main scanning track. The BM circuit 3 at this time provides outputs having frequency differences between f.sub.3 and each of f.sub.2, f.sub.3 and f.sub.4, and they include signals of f.sub.H and 3f.sub.H. These differential frequency signals are picked up by a tuning circuit 5 which extracts f.sub.H and a tuning circuit 6 which extracts 3f.sub.H , and fed through detecting circuits 7 and 8, respectively, to a comparison circuit 9, which is followed by an analog inverting circuit 10 and an electronic analog switch 11. The switch 11 operates in response to the

REFERENCES:
patent: 4287538 (1981-09-01), Sakamoto et al.
patent: 4521815 (1985-06-01), Tokuyama
patent: 4558382 (1985-12-01), Edakubo et al.
patent: 4566045 (1986-01-01), Weissensteiner
patent: 4568986 (1986-02-01), Furuhata et al.
patent: 4581658 (1986-04-01), Azuma et al.
patent: 4581659 (1986-04-01), Azuma et al.
patent: 4594615 (1986-06-01), Nemoto et al.
patent: 4644413 (1987-02-01), Takayama

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