JPS58159261A - Magnetic tape running speed controller - Google Patents

Abstract

PURPOSE:To attain stable running at an extremely low speed, by detecting the feeding speed of a magnetic tape, detecting the speed error digitally, using an output of speed error detection as a pluse width modulation wave, and pulse- driving a magnetic tape driving means. CONSTITUTION:A capstan 11 is driven with a DC motor 13 and a disc 14 with slits is fixed externally. The DC motor 13 generates a rotating torque T toward the arrow C when an input signal of a driving circuit 23 is at high level, and does not produce the torque T when the level is low. The rotary angle of the capstan 11, i.e., the amount of progress of a magnetic tape 10 is detected at the disc 14 with slits, a light emitting device 15 and a photodetector 16. A light outputted from the light emitting device 15 is intermitted with the revolution of the disc 4, inputted to the photodetector 16 and a pulse signal is outputted. The progressing speed of the magnetic tape 10 is measured by measuring the period of the pulse signal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic tape large running speed control device for a video tape recorder or the like.

In recent years, in video signal magnetic recording/reproducing devices or video signal magnetic reproducing devices using magnetic tape, such as video tape recorders, it has become possible to change the position of the video head by using an electric-position conversion element such as a bimo cliff-type piezoelectric element. As a result, so-called auto-tracking devices that accurately scan recorded tracks have begun to be introduced. This auto-tracking device is capable of producing reproduced images without noise bands during special playback modes such as slow playback, variable speed playback, still playback, fast playback, and reverse playback in which the tape is played back at a running speed different from the tape running speed at the time of recording. It is possible to provide In other words, in order to realize slow playback or variable speed playback, it is necessary to run the magnetic tape at slow or variable speed. However, especially when running at low speeds, the force of the magnetic tape system changes significantly depending on the surrounding conditions, so there is a problem in that it is difficult to stably run at low speeds at a desired speed. It was especially difficult to play back at very low speeds.

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide a magnetic tape running speed control device that can stably run a magnetic tape at a desired speed even when running at extremely low speeds.

That is, the present invention provides a magnetic tape drive means for driving a magnetic tape on which a video signal of a predetermined unit length is recorded as a track having a predetermined angle with respect to the longitudinal direction by a rotating magnetic head, and a magnetic tape drive means Oa! a feed speed detection means for detecting the tape feed speed; a speed error detection means for detecting a speed error based on the speed information from the feed speed detection means; and a speed error signal from the speed error detection means that is pulse width modulated. A pulse width modulation means for supplying this pulse width modulation signal to the magnetic tape drive means is provided, and the device detects the feeding speed of the magnetic tape, performs digital speed error detection, and pulses the speed error detection output. Since the magnetic tape drive means is driven in pulses using a width modulated wave, the magnetic tape can be stably run at a desired speed even when running at extremely low speeds.

Hereinafter, one embodiment of the present invention will be described based on the drawings. In the figure, %(1)(ri) is a video head having an azimuth angle of the same angle (for example, 6＠), and these video heads (1)(2) are composed of laminated piezoelectric elements(3)(
The other end of the piezoelectric element P (3) (4) is attached to the rotating disk (6). (6) is the video head (1) (2)
) is attached to the rotating disk (5), and a rotational phase detection head (7) is installed on the fixed part side corresponding to this magnet (6). The rotating disk (6) is a co-rotating wheel (8).
It is driven by a DC motor (9) via the arrow, and rotates at approximately 80+1z or 251 in the direction of the arrow. (2) is a magnetic tape, and this magnetic tape ring is capstan 0
-1t and the pinch roller (2) in the direction of the arrow @).

The capstan (2) is driven by a DC motor (2), and a disc with a slit (2) is fixedly fitted onto the outside of the capstan (2).

1jff The DC motor (2) generates a rotational torque T in the direction of the arrow when the input signal to the drive circuit is at a high level, and does not generate rotational torque T when it is at a low level. The rotation angle of the capstan Q1, that is, the amount of advance of the magnetic tape (Itl) is detected by the slitted disc α◆, the emitter and the light receiver, as described below. ) The light beam output from ) is interrupted by the rotation of the disc 4 with slits, and is input to the light receiver α peak.The light receiver (to) outputs a pulse signal indicating the above-mentioned interruption.Magnetic tape The traveling speed of Q1m is measured by measuring the period of the pulse signal.The light emitter (2) is composed of, for example, a light emitting diode, and the light receiver (2) is composed of, for example, a light receiving diode. Instead of detecting the rotation angle of the capstan QXl by optical alignment as shown in FIG. good.

The pulse signal thus obtained by the light receiver 0 peak is input to the pulse generating circuit Q. On the other hand, a clock signal is input from the clock signal generation circuit (to) to the pulse generation circuit aη. The pulse generating circuit aη generates a sampling pulse by the rising edge (or falling edge) of pulse width modulation, and generates a preset pulse slightly (several clocks) later than the sampling pulse. These preset pulses, sampling pulses, and clock signals are used by the counter circuit (
2) is input. On the other hand, the speed reference value is input as a digital signal from the speed instruction section (2), is read as an initial value into the counter circuit (to) by a preset pulse, and the contents of the counter circuit (to) are counted up by the clock signal and sampled. The contents of the counter circuit O1l are stored in the memory circuit (b) by the pulse, and the contents of the counter circuit (6) become the initial value by the next preset pulse, and this process is repeated thereafter. The contents of the memory circuit (2) are input to the pulse width modulation circuit, and a pulse width modulated wave is output according to the contents of the memory circuit (2). If the capstan speed is slower than the speed specified by the speed indicator, the high level supplies a wider pulse to the drive circuit (2). Conversely, if the capstan speed is faster than the speed specified by the speed indicator (e), the low level supplies a wider pulse to the drive circuit (to). As a result, a negative feedback path is established, and the magnetic tape OQ is operated at a speed according to the speed specified by the speed indicator (E).
travels in the direction of the arrow). Therefore, by changing the specified speed (in the speed instruction section), variable speed playback is possible.

In this way, even at extremely low speeds, pulses based on the frequency of the carrier wave of the pulse width modulated wave are applied to the drive circuit, so the DC motor generates starting torque based on the frequency of the carrier wave of the pulse width modulated wave. Therefore, the uneven rotation of the DC motor can be reduced, and the running of the magnetic tape can be made extremely stable. Such a magnetic tape running speed control device uses an electrical device such as a bimorph piezoelectric element.
The present invention is particularly effective for video tape recorders having an auto-tracking device that traces recorded tracks at any magnetic tape running speed by changing the position of the video head using a position changing element.

As explained above, according to the magnetic tape running speed control device according to the present invention, the speed error detection is performed digitally by detecting the feeding speed of the magnetic tape, and the speed error detection output is converted into a pulse width modulated wave to control the speed of the magnetic tape. Since the drive means is driven in pulses, the magnetic tape can be stably run at a desired speed even when running at very low speeds.

[Brief explanation of the drawing]

The drawing is a diagram showing the main part of a video tape recorder equipped with a magnetic tape running speed control device in a playback mode according to an embodiment of the present invention. (1) (2)・Video head% (3) (4)...
Piezoelectric element, (5)...rotating disk, exclamation...magnetic tape, 01)...capstan, (to)...pinch roller, (to)...DC motor, (b)... Disc with slit, 0... emitter, (to)... receiver, (b)
...Pulse generation circuit, (To)...Clock signal generation circuit, Ring...Counter circuit, To)...Speed instruction section,
(2)...Memory circuit, Iwa/pulse width modulation circuit, -
...Drive circuit agent Yoshihiro Morimoto

Claims (1)

[Scope of Claims] l A magnetic tape drive means for driving a magnetic tape on which a video signal of a predetermined unit length is recorded as a track at a certain angle with respect to the longitudinal direction by means of a rotating magnet;
A feed speed detection means for detecting the magnetic tape feed speed of this magnetic tape drive means, a speed 1y error detection unit for detecting a speed error based on speed information from this feed speed detection means, and a speed error detection means for detecting a speed error from this speed error detection means. The error signal is pulse width modulated and the pulse width modulated signal is applied to the magnetic tape drive 1.
A magnetic tape running speed control device comprising pulse width modulation means for supplying pulse width to the stages. 2. The magnetic tape running speed control device according to claim 1, wherein the rotating magnetic head is caused to move in a direction approximately at an angle of -C with respect to the track by a wL position conversion element.