JPH01125182A - Mode changing method for four-frequency pilot system video tape player - Google Patents

Abstract

PURPOSE:To shorten time for mode changing by detecting an on track on the way of a phase trailing even when the phase trailing is generated at the time of shifting from a review mode to a reverse reproducting mode and shifting to a still mode. CONSTITUTION:A capstan motor MC, a capstan motor control circuit 10 and a ATF tracking error signal forming circuit 12 are provided. When the phase trailing is generated at the time of changing from the review mode to the reverse reproducing mode, a microcomputer 10 monitors the ATF tracking error signal to detect the state of the on track in the phase trailing. Within this range and at a prescribed timing synchronizing with a RF switching pulse, the capstan motor MC is stopped to bring the still mode and decide a stop track. Thereby, the time for changing the mode can be shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a mode changing method for a four-frequency pilot type videotape player. Specifically, the present invention relates to an improvement in the method of changing the mode from the review mode (1x reverse playback mode) to the normal playback mode (normal playback mode) during playback of an 8mm VTR.

(b) Conventional technology Playback modes for VTRs include normal playback, in which the tape is transported in the same direction and speed as during recording, reverse playback, in which the tape is moved in the opposite direction and at the same speed, and high-speed playback (for example, 7 times normal, 9
This includes high-speed playback in the forward and reverse directions, where the tape is driven at

And when changing mode between these modes,
The tracking of the rotating head is disrupted, causing noise on the screen. Furthermore, when changing the mode in which the tape running direction is reversed, the mechanical system must be switched.

For this reason, Japanese Patent Application Laid-Open No. 60-20346 (GLIB
15102), when changing the mode in which the playback direction is switched, a stopped playback state (still mode) is provided in between, and in this still mode, the mechanical system is switched and the precision of tape feeding is improved.

However, when changing modes such as changing from -7x review mode to normal playback mode, which requires tape running to be slowed down, the change in speed is large, so simply changing to still mode does not allow playback. There was a problem in that it was not possible to prevent noise bars from appearing on the screen.

For this reason, JP-A-62-198283 (HO4N
5/783), when transitioning from the review mode to the normal playback mode, not only the stealth mode but also the reverse playback mode (reverse 1x speed playback mode) is passed through.

Then, during this reverse playback, tracking control is performed to match the tape running and the tracking of the rotating head, correcting the tracking deviation caused by the rapid deceleration of the tape from review mode to reverse playback mode, and a noise bar is displayed on the screen. This prevents the

The relationship between the amount of tape travel and time at this time is shown in FIG. Points AB indicate review mode, points 80 indicate reverse playback mode, and points CD indicate a predetermined trunk (e.g. rl
The points between the points DE and DE indicate the normal reproduction mode, respectively. Then, in the reverse playback mode between this point 80, tracking is performed.

(c) Problems to be solved by the invention However, in the above conventional example, the reverse playback mode time (
'r+) must be a sufficient time for the tracking 1tIlivi to be completed.

It would be nice if the transition to reverse playback mode (capstan brake) could be done according to theory, but in actual 81DVTR
Naturally, there are cases where the process is performed well according to the above theory, and cases where there are errors.

That is, at the beginning of the reverse playback mode, tape running is considered to include both a phase error (tracking error) and a speed error. The servo circuit of the VTR operates to eliminate this error.

This operation will be conceptually explained using an example of only the phase with reference to FIG. In Figure 3, (1) is the time axis, and (
te) is the point in time when the reverse reproduction mode is changed to 1° from the review mode. The vertical axis represents tracking deviation, and corresponds to an ATF I-racking error signal, which will be described later. In other words, if this mode change is performed properly, tracking will be more quickly adjusted to the servo operation, and tracking deviation will disappear, as shown in FIG. 3, 21. However, if the tracking is largely deviated as shown in FIG. 3, the phase will fluctuate due to the servo operation until the 1-racking is matched. This oscillation is called "phase flow." In reality, it is also affected by speed errors. In the case of a speed error, the speed similarly fluctuates due to the servo operation.

Naturally, when the speed swings at this speed, the phase swing also occurs.

When such oscillation occurs, approximately 2 seconds are required until tracking is correct (until servo operation becomes stable).

That is, the period (T1) in FIG. 4 must be set to about 2 seconds.

This phase shift can be improved to some extent if the discrimination and detection of the front track and back track for trunking, which is unique to BvrnVTRs (specific to four-frequency pilot type videotape players), is performed well.

The present invention provides a mode changing method that allows a quick transition from reverse playback mode to still mode and prevents noise bars from appearing on the screen.

A. Here, detection of front tracks and back tracks will be explained. Note that the following detection of front tracks and back tracks is a well-known and commonly used technique in 8an VTR.

B. First, the tracking method of 8+m+VTR will be explained.

The tracking method of Bmm VTR is described in the Japan Broadcasting Publishing Association, 1 edited by Japan Broadcasting Corporation, published on April 20, 1980, NH
Page 130 of ``K Home Video Technology'' and Coronasha 1939
The basic principle is explained on pages 157 to 159 of ``Latest AV Equipment and Digital Technology'' published on December 10, 2015, so a brief explanation will be given here.

FIG. 5 shows the tracks of the tape, and f1 to r4 indicate four pilot signals that have been superimposed and recorded on each track.

FIG. 6 shows a well-known ATF tracking error signal generation circuit (12). (20) is an input terminal for a reproduction signal. (22) is a low-pass filter that extracts pilot signals (r+) to (f4). (24) is a terminal to which reference signals (t4) to (rl) are input, and (26) is a mixing circuit. (28) is a band pass filter that extracts the adjacent leading beat component (16 kHz>), (30) is a band pass filter that extracts the adjacent delayed beat component 47 kHz. (32) and (34) are the detection circuits, and (36) is the detection circuit. It is a differential amplifier circuit.(38) is AT
This is a sample hold circuit for F tracking error, which holds a value at a predetermined timing in one field and outputs an ATF tracking error signal. (40
) is a sample hold circuit for front and back track detection, which holds a value at a predetermined timing in one field and outputs a front and back track detection signal. (42) (4
4) is the control signal (TSA) (SB) input terminal of the sample bold circuit (38) (40). This terminal <4
2) When (44) is at a high level, the sample and hold circuits (38) and (40> are in a hold state, and when they are at a low level, they are conductive.

FIG. 7 shows the principle of the relationship between the pilot signal and the reference signal during normal reproduction, and FIG. 8a shows the relationship between the amount of track deviation and the level of the ATF tracking error signal.

From FIG. 8a, it can be seen that if the tracking deviates by two tracks, the relationship between the level of the ATF tracking error signal and the direction of deviation becomes reversed, and tracking cannot be performed using only the ATF tracking error signal.

The normal case as shown in FIG. 8a is called the front track, and the opposite case is called the back track. In order to always perform good tracking, this back track is detected, and at the time of this back track, the timing of the frequency of the reference signal is advanced by two fields to switch to the front track state.

C1 The idea for detecting this back track is shown in Figure 9. In other words, in the actual 811111 VTR, the switching timing of the reference signal is determined by the RF signal indicating the head rotation phase.
It is delayed by 2 m5ec from the change in switching pulse. The sample and hold circuit (3) of the circuit in Figure 6 is
8) and (40) as shown in FIG. 9 (TSA) and (TSB), this sample hold circuit (3
8) outputs an ATF tracking error signal as in FIG. 7, and the sample hold circuit (40) outputs a signal for front/back track detection (see FIG. 8(b)). The amplifier (46) in FIG. 6 outputs a high-level back track detection signal (see FIG. 8(C)). A servo circuit (not shown) advances the reference signal by two fields based on this back track detection signal to prevent tracking servo malfunction.

D. This back track detection is performed not only during normal playback but also during reverse 1x speed playback (reverse playback). still,
During reverse playback, the head trajectory becomes as shown in FIG. 10, and the playback pilot No. 18 becomes as shown in FIG. 11(b). Therefore, the reference signal is also changed from that during normal reproduction, as shown in FIG. 11(c).

E. Next, stop phase determination in stop playback mode (still mode) will be described. When switching from still mode to normal playback mode, it is desirable to be in the above-mentioned front track state. Therefore, in steal mode,
It is determined in advance which pilot signal track the head is scanning, and the timing of transition to the normal reproduction mode (or the timing of generation of the reference signal) is determined. This stop phase determination is performed using the above-mentioned back track detection signal.
In a type of VTR that scans the same track during still shooting, there is only one type of reproduced pilot signal. Therefore, 4
The scanning track during this still mode is determined based on the phase relationship between the seed reference signal and the back track detection signal.

F. For reference, Fig. 12 shows the head trajectory at the time of review, and Fig. 13 shows the waveform diagram at this time.
TSA) is at low level. Note that, at this time, discrimination between front and back tracks is not performed.

G. Since the above-mentioned detection of the back track is carried out using part of the scanning period, quick detection cannot be performed on an actual 8rm VTR. Therefore, when switching from the above-mentioned review mode to normal playback mode, it is difficult to detect it quickly. In the gnnVTR of the type that uses the reverse playback mode, it takes time to detect front and back tracks at the start of the reverse playback mode, and quick tracking operation cannot be performed.

(d) Means for solving the problem The present invention detects the level of the ATF tracking error signal regardless of the back track or the front track in the reverse playback mode during the transition from the review mode to the normal playback mode. The present invention is characterized in that it detects an on-track state, and upon this detection shifts to a still mode, and also performs stop phase discrimination during this still mode, thereby smoothing the shift to a normal reproduction mode.

Function: Since the present invention has the above-mentioned configuration, when transitioning from review mode to reverse playback mode, the ATF tracking error level is detected and turned on even when the tracking of the tape and head is in the process of being retracted. If it is determined to be a track, it immediately shifts to still mode, reducing the time it takes to change modes.

(f) Embodiment An embodiment of the present invention will be described with reference to FIGS. 1 and 2.

(Mc) in FIG. 1 is a cab stan motor.

(10) is a cab stan motor control circuit, which is composed of a microcomputer. (12) is the ATF tracking error number generation circuit shown in FIG.

(10a) is an A/D conversion terminal into which an ATF tracking error signal is input, and the ATF tracking error signal is A/D converted and processed by the microcomputer (10). (
14) is a hysteresis circuit for shaping ATF tracking error No. 18, and (10b) is a high/low signal input terminal. In addition, in Fig. 1, other capstan control circuits (RF switching pulse signal, FG multiplication signal P)
Conventional control circuits such as G-type etc. have been omitted.

FIG. 2 shows the relationship between the amount of tape travel and time at this time, and FIG. 14 shows the operation of the microcomputer (10) at this time.

When the user presses the playback button during review playback (AB), the VTR changes from the tape's 17x review mode to reverse playback mode (BC) by applying a brake on the tape in synchronization with the RF switching pulse. do,
In this reverse playback mode, if the ATF tracking error signal shown in FIG. 8(a) is in the range of ±0.5cm, the device is substantially on-track. Here, the microcomputer (10) in Fig. 1 detects that when the ATF tracking error signal input from the A/D input terminal (10a) is within the range of ±0.5V, the head traces a track of a predetermined azimuth during still shooting. Turn on the carburetor brake in synchronization with the RF switching pulse to stop the tape. The VTR goes into still mode. At this time, the head is stopped regardless of the front or back trunk, so the scanning track at this time is 0, which is one of the tracks with the same azimuth (for example, the pilot signal is rl or f'p). , if the stop track is rl or f3, the stop track is determined whether the ATF tracking error signal (input signal at terminal 10b) when the reference signal is 12 is high (at f'3) or low (at f'+). Determine.

It should be noted that when changing from review mode to reverse playback mode, as shown in FIG. 3, ``phase flow.''

The same applies if this occurs. The microcomputer (10) is A
TF I-Monitor the racking error signal and check that it is within the range of ±0.5V during "phase flow" (in the middle of fluctuation) (
(on-track state in the middle of fluctuation) is detected. Then, within this range, at a predetermined timing synchronized with the RF switching pulse (timing when the head is on track in still mode), the capstan motor (MC> is stopped, the still mode is entered, and the stop track is started as described above. Determine.

In this way, since the stopped track is determined, the MyFun determines the timing of transition from still mode to normal playback mode according to this trunk, and at this determined timing, the capstan ( MC).

Note that when changing from the review mode to the reverse playback mode, there is a period (approximately 176 seconds) in which the tape speed is reduced from 17x to 11x. Naturally, the microcomputer (10) detects the level of the ATF tracking error signal after completing this deceleration period.

Incidentally, in the above embodiment, the stop track is determined by the tracking error signal, but in addition to this, as in the conventional case, the stop phase is determined as described in the above section E, and the start timing of the tape is set. You may then shift to normal playback mode.

(G) Effects of the Invention As described above, according to the present invention, even if a phase flow occurs when transitioning from the review mode to the reverse playback mode, on-track in the middle of this phase flow is detected and the transition to the ester mode is performed. Therefore, the transition from still mode to 1 can be performed quickly, and the mode can be changed quickly.

[Brief explanation of the drawing]

FIGS. 1 and 2 are diagrams for explaining one embodiment of the present invention. Figure 3 is a diagram for explaining phase flow, Figure 4 is a diagram showing Dave feeding, Figure 5 is a diagram showing tape, and Figure 6 is a diagram showing AT.
Figure 7 is a diagram showing the F tracking error signal generation circuit; Figure 7 is a diagram for explaining the operation in normal playback mode; Figure 8
The diagram shows the operation in Figure 6. FIG. 9 is a diagram showing the waveforms of various parts in the actual normal playback mode, FIGS. 10 and 11 are diagrams to explain the river playback mode, and FIGS. 12 and 1.
FIG. 3 is a diagram for explaining the review mode. FIG. 14 is a diagram for explaining the operation of FIG. 1.

Claims (1)

[Claims] (1) When changing from high-speed reverse playback mode to normal playback mode, in the mode change method of a 4-frequency pilot type videotape player via reverse 1x playback mode and stop playback mode, when in the reverse 1x playback mode, The on-track state is detected by the ATF tracking error signal regardless of the back track or the front track, and upon this detection, the system shifts to the stop playback mode, and after detecting the tape stop position in the stop playback mode, shifts to the normal playback mode. A method for changing the mode of a four-frequency pilot type videotape player, characterized in that: