JPS59119560A - Skew correcting device - Google Patents

Abstract

PURPOSE:To obtain a reproduced picture free from skew by changing the torque of a tape sending out reel motor basing on the detected output in period or phase of the horizontal synchronizing signal of a reproduced video signal, and controlling tension of the tape thereby specially correcting the change of tension in case of the recording device and reproducing device are different. CONSTITUTION:A detected signal of a video head 21 is converted to a video signal in a reproducing circuit 22, and a horizontal synchronizing signal is separated in a horizontal synchronizing signal separating circuit 23. An equivalent pulse in a horizontal synchronizing signal is removed by an equivalent pulse removing circuit 24 and supplied to an AFC circuit 25. A periodic variation or phase variation of the horizontal synchronizing signal detected by a phase detector 25a of the AFU circuit 25 corresponds to the amount of skew on the picture. Accordingly, the output of an amplifier 14, which is the error output of a tension servo system and the output of an amplifier 30 obtained by amplifying the output of an LPF29 are added basing on an AFC error signal. The added output controls rotation torque in the direction reverse to the tape feeding direction of the feeding reel motor 1 through a driver 15.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a skew correction device for a VTR.

BACKGROUND TECHNOLOGY AND PROBLEMS In general, in VTR, during tape recording and playback,
Control is performed to keep the tape tension constant.

Figure 1 shows an example of a conventional tape tension servo system.
)t-, and is then wound onto a take-up reel by a take-up reel motor (4).

To explain the tension servo system in Fig. 1, if there is a change in the tape tension fed out by the feed reel motor (1), the tape tension detected by the tension pickup αυ will change, and this is a movable This appears as a displacement of the iron piece. The displacement of this movable iron piece a is converted into a DC voltage by a magnetoresistive element (tel. This voltage is fed back to the feedback amplifier a4).
- is applied to the motor driver Q5) to control the generated torque of the feed reel motor (]).

Therefore, the tension servo system shown in FIG. 1 keeps the tape tension constant during recording and playback, allowing stable recording and playback.

However, in such conventional devices, the tape tension is adjusted individually for each VTR device even if the same model is used, so that the tape tension varies among the VTR devices. Therefore, if a different VTR device is used for tape playback than for recording, the tape tension will not necessarily be the same during tape recording and playback, and if there is a difference in tape tension between recording and playback, As the tape expands and contracts, the phase of the reproduced horizontal synchronizing signal becomes discontinuous between the end of a track and the beginning of the next track, and a phase shift of the reproduced horizontal synchronizing signal occurs at the time of switching the output of the two rotating heads. For this reason, monitor TV
The horizontal sweep circuit of the receiver is disrupted, and until synchronization is achieved, a so-called skew occurs in which the image that matches the vertical lines at the top of the screen appears to be curved. Furthermore, even if recording and reproduction are performed using the same VTR device and the same tape tension, if the tape is partially expanded or contracted due to physical factors after recording, skew will occur in this portion.

Purpose of the Invention In view of the above-mentioned problems, the present invention corrects the skew caused by changes in the cheese tension between recording and playback, or by expansion and contraction of the cheese, thereby displaying an undisturbed old image at the top of the screen. The purpose is to obtain academic images.

SUMMARY OF THE INVENTION A skew correction device for a rotary head type VTR according to the present invention includes a detection circuit that detects fluctuations in the period or phase of a horizontal synchronizing signal of a reproduced video signal, and a tape feeding system based on the detection output of this detection circuit. +7-Means for controlling the tape tension by changing the torque of the lumo p. With this configuration, a skew-corrected playback screen can be obtained extremely easily.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 2 and 3.

FIG. 2 shows an embodiment of a skew correction device for a VTR according to the present invention, in which the same parts or parts having the same functions as in FIG. 1 are denoted by the same reference numerals.

Further, FIG. 3 is a waveform diagram showing the operation of FIG. 2.

In Figure 2, the running direction of the tape (2) is indicated by the arrow (5).
The torque generation direction of the feed reel motor (1) is indicated by an arrow (6). The signal detected by the video head (2I) is converted into a video signal as shown in FIG. The signals are separated. Note that the horizontal synchronization signal is omitted in Fig. 6(a),
Only the vertical synchronization signal V-8YNO is shown.

The horizontal synchronization signal from the horizontal synchronization signal separation circuit (c) is:

It is supplied to an equivalent pulse removal circuit (24) and the equivalent pulse is removed. The output from the equivalent Hals removal circuit (24) is supplied to the AFU circuit (c). AF' (J circuit ρ9 has a frequency of N based on the output of the equivalent pulse removal circuit (24)
It consists of a PLL loop that forms a signal of fH (hl: horizontal scanning frequency, N: integer), and a voltage-controlled generator (
25c) (V OO) kbi etail. ■C0(25
The output Nf<t of C) is frequency-divided by a frequency divider (25d) and then compared in phase with the output of the equivalent pulse removal circuit (C) in a phase detector (25a). Phase detector (2
The output phase error signal of 5a) is passed through a low-pass filter (2
5b) is applied to the control input of V OO (25c), and one output (
NfH) is obtained from V OO (25c). Note that this output is used in the synchronization system within the VTR.

The period fluctuation or phase fluctuation of the horizontal synchronizing signal detected by the phase detector (25a) of the AFO circuit (c) is the cause of the skew that occurs in the playback screen. The amount of AFO error (phase error) output from the device (25a) corresponds to the amount of skew on the screen.

The AFO error signal shown in FIG. 3 (dl) passes through a low-pass filter (26)' for removing transient components and is supplied to the sample-and-hold circuit (to). This is to sample and hold the AFO error level in the second horizontal synchronization period.
The output of a monostable multivibrator (27) (FIG. 6(C)) which operates in synchronization with the rise of the head switching signal (30 Hz) shown in ) is given. Therefore, from the sample and hold circuit (marked 2), a hold output at l& after the D f pulse is obtained (FIG. 6(c)).

The output of the sample and hold circuit (c) is given to Q low-pass filters, and after the head rotation frequency (30Hz) component is extracted, it is given to an adder (0I) in the form of a DC voltage via an amplifier (to). It will be done. The adder 01) increases the output of the amplifier α, which is the error output of the tension servo system explained in FIG. The output is added. The added output is given to the feed-out motor (1) via the driver aet, thereby controlling the rotational torque of the motor (1) in the direction opposite to the tape feed-out direction. As a result, the tape tension is adjusted so that no skew occurs at the top of the screen.

For example, if the tape tension is low during playback as well as during recording, and this causes sysquiescence, the sample hold value of the AFO error mentioned above will increase, the torque of the feed reel motor will increase, and the tape tension will increase. Tension is increased. As a result, playback is performed with the same tension as during recording, and a playback screen without skew is obtained. It’s time to record υ
The same is true if the tape tension during playback is too high.

In addition, even if the tape has been partially expanded or contracted after recording, and this appears as a skew on the screen, the AFO
By correcting the expansion/contraction f# of the tape by controlling the torque of the feed/output reel motor based on the error sample hold, it is possible to obtain a skew-free screen. Note that skew appears as curved lines to the left or right of the screen. , this is caused by a phase skip (advance or lag) in the positive or negative direction of the phase of the reproduced horizontal synchronization signal immediately after head switching.Therefore, the AFO error is caused by a positive or negative phase skip (advance or lag) in the phase of the reproduced horizontal synchronization signal immediately after switching the head. It is detected as a signal, and its sample hold value has positive or negative polarity.

Therefore, the feed reel motor is controlled such that the torque is increased or decreased from a predetermined reference value depending on the direction in which the skew occurs.

Effects of the Invention As described above, the present invention detects fluctuations in the period or phase of the horizontal synchronizing signal of a reproduced video signal, and changes the torque of the tape feed reel motor based on the detected output to control tape tension. Therefore, when the tape tension changes between recording and playback (especially when the recorder and playback device are different), it is possible to correct this change in tension and obtain a playback screen without skew. Furthermore, even if the tape partially expands or contracts after recording, the tape tension can be controlled to follow the expansion or contraction during playback, and a skew-free playback screen can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a tape tension servo system in a conventional VTR, FIG. 2 is a block diagram showing an embodiment of a skew correction device according to the present invention, and FIG. 6 is an operating waveform of each part of FIG. 2. It is a diagram. In addition, in the symbols used in the drawings - (11......Feeding reel motor (c)......AFO circuit ai) n-
・−・−・ Low pass filter (27>・・・・・・・
...Monostable multivibrator (foundation)...
......This is a sample and hold circuit.

Claims (1)

[Claims] A detection circuit for detecting variations in the period or phase of a horizontal synchronizing signal of a reproduced video signal, and means for controlling tape tension by changing the torque of a tape feed reel motor based on the detection output of this detection circuit. This is a skew correction device for rotating head type VTRs.