Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Synchronizing moving-head moving-record recorders
Reexamination Certificate
1998-07-22
2001-03-20
Faber, Alan T. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Synchronizing moving-head moving-record recorders
C386S349000
Reexamination Certificate
active
06204986
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a magnetic recording and reproducing apparatus such as a videotape recorder (VTR).
BACKGROUND ART
For intermittent slow reproduction in which activating and braking pulses are alternately supplied to a capstan motor for tape feed of a VTR to repeat a still status and a two-field standard traveling status, if a head drum is rotated at the same speed for still and standard reproduction, lateral vibration (jitter) of an image is caused by the change in the relative speed of a video head and the tape.
To prevent such jitter of the image, as described in Japanese Utility Model Laying-Open No.4-35234, acceleration of the capstan motor is detected to increase the speed of the speed control data of the rotating drum, or deceleration of the capstan motor is detected to decrease the speed of the speed control data of the rotating drum for braking.
In this method, however, a sufficient effect cannot be ensured to reduce the jitter as time delay is caused for the actual control voltage applied to the drum motor when the capstan motor is activated, as shown in FIG.
2
.
Then, common practice is to employ a method of directly applying a pulse voltage to a rotating drum control voltage together with the method described above.
FIG. 3
shows a block diagram of a conventional rotating speed control circuit for a head.
In the activation process for intermittent driving, the activating pulse is generated in a capstan intermittent driving control circuit (
2
) in accordance with a head switching signal generated in a head switching signal generating circuit (
1
) and is supplied to a capstan control PWM output generating means (
3
).
In capstan control PWM (Pulse Width Modulation) output generating means (
3
), a PWM output signal at H (at high level) is generated for a prescribed period of time, which is then smoothed by a low pass filter (LPF) and converted to a direct-current voltage signal for driving a capstan motor (
4
).
Thereafter, an error with respect to a target speed is calculated in accordance with an FG pulse output from capstan motor (
4
) in a capstan controlling means (
5
), a calculation result is transmitted to capstan control PWM output generating circuit (
3
), and the PWM output signal is output in accordance with the calculation result from capstan control PWM output generating circuit (
3
), so that rotation control of the capstan motor is performed.
Then, a control signal recorded on a magnetic tape is reproduced by a CTL head (
6
) and, a braking pulse is generated in capstan intermittent driving control circuit (
2
) delayed by a prescribed period of time with respect to the reproduced control signal, thereby braking capstan motor (
4
).
Intermittent slow reproduction is performed by a series of above described operations.
In activating capstan motor (
4
) (denoted by A in FIG.
4
), however, a relative speed a drum motor (
7
) and the magnetic tape, that is, the relative speed of the rotary video head and the video signal recorded on the magnetic tape, is rapidly changed, thereby causing lateral vibration of the reproduced image.
To solve this problem, a correction pulse is generated in a drum correcting output generating circuit (
8
) and directly applied to a voltage which drives drum motor (
7
) through a diode (
9
) when the drum motor is activated.
In this method, a dedicated output port must be provided in a control microcomputer and a circuit component such as a diode is required, which may considerably increase a substrate mounting space and material cost.
DISCLOSURE OF THE INVENTION
The present invention is an intermittent slow controller of a magnetic recording and reproducing apparatus for intermittently driving a magnetic tape by alternately supplying activating and braking pulses to a capstan motor and reading a video signal by a magnetic head mounted to a rotating drum. The intermittent slow controller is characterized in that a drum controlling means for controlling a voltage driving the rotating drum is provided and that the drum controlling means increases the voltage driving the drum by a prescribed value in activating the capstan motor and decreases the voltage driving the drum by the prescribed value in braking the capstan motor.
Further, a drum control PWM output generating portion outputting a signal having a pulse width in accordance with an output from the drum controlling means is provided, whereby the output from the drum controlling means increases the pulse width of the drum control PWM output generating portion by a prescribed value in activating the capstan motor, and decreases the voltage driving the drum by a prescribed value in braking the capstan motor.
In addition, the output pulse width of the PWM output generating portion is set by supplying PWM data which has been corrected by the drum control PWM output generating portion, where the setting of the drum control PWM output generating portion and the output pulse width is performed within the microcomputer.
Thus, using the intermittent slow controller according to the present invention, jitter of the image at the time of intermittent slow reproduction can be corrected without the need for a dedicated output port or circuit component and constant correction can always be performed without being affected by the difference of operating points of the rotating drum motor.
REFERENCES:
patent: 5548455 (1996-08-01), Sato
patent: 5777814 (1998-07-01), Park et al.
patent: 2-299489 (1990-12-01), None
patent: 4-35234 (1992-03-01), None
patent: 7-312003 (1995-11-01), None
Faber Alan T.
Michaelson Peter L.
Michaelson & Wallace
Sanyo Electric Co,. Ltd.
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