Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
1997-12-15
2001-01-23
Tran, Thai (Department: 2715)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C386S349000, C360S073050, C360S073080, C318S369000, C318S590000, C318S592000
Reexamination Certificate
active
06178286
ABSTRACT:
The present invention relates to a method and an apparatus for regulating the drive speed of a tape for the recording and/or reproduction of information items, such as with a video recorder, for example, in operating modes in which the tape is supposed to come to a standstill at predetermined positions.
Operating modes of this type are, for example, slow-motion reproduction and still-frame reproduction or freeze-frame reproduction, the tape being scanned by a video head in such a way that individual items of video and/or audio information recorded on this tape are respectively read out for a predetermined time. For this purpose, the tape is wound until a track which is correspondingly assigned to a video head can be scanned by the latter. After a specific time in each case, the tape is wound on in such a way that subsequent tracks can be read.
In the case of slow-motion reproduction, the respective slow-motion speed, which can usually be varied between a fifth, a tenth and also a twenty-fifth of the normal speed, results from the ratio between still-frame time and normal speed. Since slow-motion reproduction is executed by starting and braking, special requirements have to be made of the tape drive. Thus, at the beginning of the play phase, the capstan motor is accelerated by a start pulse to a speed which is to be kept constant for a relatively short time by means of regulation, and is braked again at the beginning of the still-frame phase. The control of the start and stop phases has a very complicated configuration with regard to the equipment technology and, at the same time, equipment and tape tolerances have a certain influence on the respective tracking in these special modes with a corresponding effect on the picture quality.
The object of the present invention, therefore, is to improve the picture reproduction quality for operating modes of the aforementioned type.
The invention is based on the idea, in the context of slow-motion and freeze-frame reproduction, of detecting the rotor movement of the capstan motor and thus the tape drive speed as early as during the start phase characterized by acceleration, and of compensating for any deviations from a desired speed characteristic that occur by means of corresponding changes in the acceleration of the tape drive.
According to the invention, therefore, a tape drive speed measurement is carried out at least once even during the respective start phase and the respective measured value is compared with a corresponding value of the desired speed characteristic, thereby enabling a correction to be carried out by means of corresponding control of the capstan motor in the event of a deviation. This has the advantage that deviations in the start phase can have practically no effect or are compensated for at least to the extent that only slight corrections are necessary for optimum tracking after the start phase. These corrections can then be made in the stop phase if such measures are also provided for this region.
The respective desired speed characteristic for optimum tracking in the operating modes of the aforementioned type is stored in the recorder and is already determined or calculated with the development of the respective equipment type.
The start phase and thus the acceleration of the capstan motor to a specific speed, which is then kept constant by means of corresponding speed regulation until the beginning of the respective stop phase characterized by braking, is effected by a pulse-like exciter current fed to it. This exciter current, which usually represents a maximum value of the current that can be supplied, and is an average value, in this case determines the characteristic of the tape speed in the start phase.
This means that a speed characteristic to be attained can be determined by a corresponding change in the exciter current, something which is utilized, according to the invention, for changes in the acceleration of the tape drive during its start phase in that, in the event of deviations from the respective desired speed characteristic, corresponding changes in the exciter current towards larger values are made in the case of an excessively low tape drive speed and corresponding changes towards smaller values are made in the case of an excessively high speed, it being possible, in an advantageous manner, to carry out the changes during predetermined time windows. By using time windows, relatively large acceleration changes can be made without, in the process, exceeding the value of the already mentioned speed which is to be kept constant between the start and stop phases by means of regulation, or overloading the motor.
Such changes in the pulse-like exciter current can be realized e.g. as corresponding instances of amplitude limiting or, in the case of motor driving by means of PWM signals, by means of corresponding mark-space ratios.
However, the values determined in this way for the respective changes in the exciter current apply, strictly speaking, to the tape used or the recording medium in tape form which is stored in a cassette. In the event of further use of the recording medium, that is to say use that is not interrupted by a cassette change, the exciter current limiting values determined first of all can be stored for renewed activations of special modes of the aforementioned type, with the result that recalculations can advantageously be obviated. Recalculations of corresponding exciter current values are then made only in the event of a cassette change and also in the event of changes in the operating conditions, for example owing to ageing or a considerable temperature change.
REFERENCES:
patent: 4224645 (1980-09-01), Mauch
patent: 4494153 (1985-01-01), Ravizza
patent: 5432419 (1995-07-01), Watanabe et al.
patent: 5473239 (1995-12-01), Kobayashi et al.
patent: 2904009 (1979-08-01), None
Davenport Francis A.
Deutsch Thomson-Brandt GmbH
Laks Joseph J.
Tran Thai
Tripoli Joseph S.
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