KR100209135B1 - Method for auto-tracking in vcr at double speed play mode - Google Patents

Abstract

The present invention relates to an autotracking method in double speed reproduction on a video cassette recorder for obtaining an optimal reproduction screen in double speed reproduction in a video cassette recorder having a standard play (EP) head and an EP (extended play) Determining whether the video tape to be recorded is recorded in the SP mode or the EP mode, and then running the video tape at the double speed playback speed; If the envelope waveform of the video signal read out to the EP head is recorded in the EP mode, the envelope waveform of the video signal read out to the SP head is switched in the diagonal direction on the drum if the envelope waveform is recorded in the SP mode And a second step of performing autotracking by adaptively controlling the traveling speed of the video tape so as to be located at the center between the edges of the head switching signal for the EP mode. When the EP mode is recorded in the SP mode, It is possible to select the SP head to perform double speed playback, so that a high quality playback screen can be obtained at the time of double speed playback.

Description

Auto Tracking Method at Double Speed Playback on Video Cassette Recorder

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an auto-tracking method during double speed reproduction in a video cassette recorder, and more particularly to a method and apparatus for minimizing noise that may occur in a double- And more particularly, to an auto-tracking method for speed-up reproduction in a video cassette recorder for auto-tracking.

In general, a video cassette recorder has a special playback function, and this special playback is to reproduce the moving speed of the cassette tape by varying the speed.

However, if the running speed of the cassette tape is changed and regenerated, the track trace of the head changes corresponding to the running speed of the cassette tape, and deviates from the track at the time of recording. Therefore, as the reproducing head moves out of the normal track trajectory at the time of recording, the reproduction output is reduced, and at the same time, it is invited to the adjacent track, so that a cross talk occurs in the adjacent track.

On the other hand, the crosstalk of the luminance signal is generally negligible because it adopts the sloped edge recording method and the crosstalk of the color signal is phase shift (PS) or phase invert : PI) method.

However, when the reproducing head is further shifted by the track width, effective reproduction output can not be obtained, and a noise bar due to noise band is generated on the reproduction screen. Therefore, control is performed such that the occurrence of noise bars is minimized by making the head switching points coincide with the intervals in which such noise bars occur.

FIG. 2 is a schematic view of a head drum to which four video heads used in the present invention are attached. As shown in FIG. 2, the SP (Standard Play) head SPR ' (SPL ') and an EP (Extended Play) head (EPR, EPL), and the SP head SPR' and the EP head EPL are positioned at a '2H' The head EPR is also located at '2H' intervals.

On the other hand, as shown in FIG. 3, a solid line shown in the video tape represents a regular track, and a dotted line represents a trace track at the time of double-speed reproduction. Therefore, when the 2x speed reproduction is performed, the lower portion of the normal track and the black region which is the upper portion of the track track at the time of 2x speed reproduction are reproduced and the 2x speed reproduction is performed. As shown in Fig.

On the other hand, the envelope comparison signal (Enve-Comp) is a signal for comparing the envelope level of the reproduction signal read from the SP (Standard Play) head and the EP (Extended Play) head and outputting the comparison result. When the envelope level read by the EP head is large (SPR ', SPL') and EP heads (EPR, EPL) are selectively switched in the video cassette recorder having four heads by using the envelope comparison signal (Enve-Comp) Can be obtained.

However, the edge area of the envelope comparison signal (Enve-Comp), that is, the chattering section, is a case in which the playback signal read by the SP head and the EP head has similar envelope levels. At this time, The playback screen has a noise bar even if the SP head and the EP head are selectively switched by using the head amplifier switch signal (Head-Amp SW) based on the Enve-Comp signal. Therefore, When a section where the head is switched is the middle portion of the reproduction screen, even if the head amplifier switch signal (Head-Amp SW) is forcibly switched from the solid line waveform to the dotted line waveform and reproduced as shown in the drawing, So that the chattering section is positioned in the middle of the head switching signal V.SW as shown in FIG. 3A, and a noise bar is placed on the upper and lower edges of the playback screen To control the running speed of the video tape rock was sought to auto-tracking.

It is an object of the present invention to provide an auto tracking method in double speed reproduction in a video cassette recorder in which a noise-free picture can be reproduced in a video cassette recorder having four video heads during double speed reproduction.

An auto-tracking method for double speed reproduction in a video cassette recorder according to the present invention is a method for autotracking during double speed reproduction in a video cassette recorder having an SP (Standard Play) head and an EP (Extended Play) A first step of determining whether the video tape is recorded in the SP mode or the EP mode and then running the video tape at the double speed reproduction speed; If the envelope waveform of the video signal read out to the EP head is recorded in the EP mode, the envelope waveform of the video signal read out to the SP head is switched in the diagonal direction on the drum if the envelope waveform is recorded in the SP mode And a second step of performing autotracking by adaptively controlling the traveling speed of the video tape so as to be located at the center between the edges of the head switching signal for the EP mode. When the EP mode is recorded in the SP mode, The SP head can be selected and the double speed reproduction can be performed.

The second step is to compare the envelope level of the video signal reproduced from the SP head and the EP head with reference to the edge of the head switching signal when the SP mode is recorded so that the video signal reproduced from the EP head The first time Tl from the low level to the high level is generated when the video signal reproduced from the SP head is high at a high level and when the level of the video signal reproduced from the SP head is high A third step of detecting a second time (T2) from a first time (T1) to a time point when chattering is generated from a high level to a low level; and a third step of detecting an edge of the head switching signal The first time T1 from the high level to the low level of chattering is detected as the reference, and from the first time T1 again A fourth step of detecting a second time (T2) from a high level to a low level until chattering occurs; The second time T2 is subtracted from the time T0 between the edges of the head switching signal so that the third divided time T3 does not coincide with the first time T1 within a predetermined tolerance range If the first time period T1 and the third time period T3 coincide with each other within the predetermined tolerance range, it is determined that the running speed of the video tape is adaptively controlled and the auto- And a fifth step of terminating the process.

FIG. 1 is a schematic block diagram of a video cassette recorder for applying the present invention; FIG.

FIG. 2 is a schematic view of a head drum with four video heads used in the present invention; FIG.

Figures 3a and 3b and 3c are waveform diagrams for explaining the present invention.

FIG. 4 is a flow chart showing an auto-tracking process in the double speed reproduction according to the present invention;

DESCRIPTION OF THE REFERENCE NUMERALS

10: key input unit 20:

30: Deck section 40: Enbe detecting section

50: comparator 60: signal processor

These and other objects and advantages of the present invention will become more apparent from the following description of the preferred embodiments of the present invention with reference to the accompanying drawings.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic block diagram of a video cassette recorder for applying the present invention and includes a key input unit 10, a microcomputer 20, a deck unit 30, an envelope detection unit 40, a comparison unit 50, And a processing unit (60).

In the figure, the key input unit 10 is an input means for operating the video cassette recorder. The key input unit 10 includes a plurality of keys including a double speed playback key to output a key signal corresponding to a user's key operation, Detects the key signal on the infrared carrier wave from the remote controller and outputs the detected key signal.

The microcomputer 20 controls the overall operation of the video cassette recorder on the basis of the key signal from the key input unit 10 and controls the envelope comparison signal applied from the deck unit 30 and the head switching signal for video head switching And controls the auto-tracking operation at the time of the double speed reproduction as described later.

Further, the deck unit 30 selectively reads out the video signal recorded on the video tape under the control of the microcomputer 20 by the video head (SP, EP head) and outputs it.

The envelope detector 40 detects the envelopes of the video signals reproduced by the SP head and EP head respectively read out from the deck unit 30 and outputs them to the DC level respectively. The comparator 50 compares the envelope of the video signal reproduced by the envelope detector 40, And outputs an envelope comparison signal having a high level to the microcomputer 20 when the envelope detection signal read out to the EP head is large.

Next, the signal processing unit 60 selects the video signals SP and EP from the deck unit 30 based on the control of the microcomputer 20, processes them into signals easy to display, and outputs them to the monitor.

Next, the video cassette recorder including the above-described components will be described in detail with reference to a waveform diagram of FIG. 3C and a flowchart of FIG. 4, which shows an auto-tracking process in the double speed reproduction according to the preferred embodiment of the present invention.

The microcomputer 20 controls the auto tracking process at the time of the double speed reproduction according to the present invention when a double speed reproduction key signal from the key input unit 10 or a predetermined key signal for auto tracking at the double speed reproduction is applied, It is determined whether the video tape is recorded in the SP mode or in the EP mode by using the control pulse or the like applied from the deck unit 30 during playback and the deck unit 30 is controlled to record the video The video signal is simultaneously read out from the SP head and the EP head (for example, SPR 'and EPL or SPL' and EPR) while the tape is running.

The video signals SP and EP read out from the deck unit 30 are outputted to the comparator 50 at the DC level detected by the envelope detector 40 and the comparator 50 Compares the applied envelope detection signals SP and EP and applies an envelope comparison signal Enve-Comp having a high level to the microcomputer 20 when the envelope detection signal from the EP head is large.

On the other hand, if the recording in the SP mode is performed in step 400, a rise of the head switching signal V.SW, which is generated to switch the video heads (EPL, SPR ', SPL', and EPR) symmetrically positioned on the drum, The first time T1 from the comparison unit 50 until the rising edge of the envelope comparison signal Enve-Comp is detected is counted as the reference time (step 402).

Next, when the first time T1 described above is counted, the second time T2 from the point in time when the falling edge of the envelope comparison signal (Enve-Comp) is detected is counted (step 404).

The reason for this is that when the video tape is recorded in the SP mode, it is possible to obtain a better picture quality by reading the EP head on the head position on the drum during double speed reproduction. Therefore, when the video signal level read from the EP head is large The high level section of the envelope comparison signal Enve-Comp having the high level is set to the high level of the head switching signal V.SW (in the preferred embodiment of the present invention, To match the center.

If the EP mode is recorded in the step 400, conversely, reading out to the SP head results in a better picture quality. Therefore, the low level section of the envelope comparison signal (Enve-Comp) From the rising edge of the head switching signal V.SW to the falling edge of the envelope comparison signal Enve-Comp applied from the comparator 50 to match the center of the high level section of the head switching signal V.SW One hour T1 is counted (step 406).

Next, the second time T2 until the rising edge of the envelope comparison signal (Enve-Comp) is detected is counted (step 408).

On the other hand, when the first time T1 and the second time T2 are counted based on the steps 402, 404, 406, and 408, the head switching signal V.SW is preset A third time T3 is subtracted by the second time T2 from the time T0 between edges and again divided by '2' (step 410).

The calculated third time T3 is a high level in which the envelope comparison signal Enve-Comp is an effective period of the video signal reproduced by the EP head (in the present invention, It can be seen that the section where the reproduction signal from the EP head has a higher level is based on the high level section) is located at the middle portion of the head switching signal V.SW and is left on both sides .

Therefore, if the third time T3 coincides with the first time T1, a valid video signal read by the EP head is matched to the middle position of the head switching signal V.SW, and the SP head and the EP head Compared with the phase of the envelope comparison signal (Enve-Comp), the head amplifier switch signal (Head-Amp SW) to be selected is reproduced in a more noise-free manner.

Therefore, after the step 410, the microcomputer 20 determines whether the absolute value of the difference obtained by subtracting the first time T1 from the third time T3 is less than the predetermined tolerance (step 412) When the absolute value of the difference obtained by subtracting the first time T1 from the third time T3 is greater than the first time T1, the deck unit 30 is controlled in accordance with the difference value to control the traveling speed of the video tape, The process returns to step 400 and proceeds to step 410. Again, the absolute value and the tolerance are compared.

If the absolute value of the difference obtained by subtracting the first time T1 from the third time T3 in step 412 is smaller than the predetermined tolerance, the auto tracking operation is terminated.

As described above, according to the present invention, a video cassette recorder having four heads can reproduce noise-free image quality during double speed reproduction.

Claims (2)

A method for autotracking during double speed reproduction on a video cassette recorder having an SP (Standard Play) head and an EP (Extended Play) head, comprising the steps of: judging whether a video tape to be reproduced is recorded in the SP mode or EP mode A first step of running the video tape at a speed of double speed reproduction; If the envelope waveform of the video signal read out to the EP head is recorded in the EP mode, the envelope waveform of the video signal read out to the SP head is switched in the diagonal direction on the drum if the envelope waveform is recorded in the SP mode And a second step of performing autotracking by adaptively controlling the traveling speed of the video tape so as to be located at the center between the edges of the head switching signal for the EP mode. When the EP mode is recorded in the SP mode, , The SP head is selected so that double speed reproduction can be performed. ≪ Desc / Clms Page number 19 > The method as claimed in claim 1, wherein the second step is a step of comparing the envelope level of the video signal reproduced from the SP head and the EP head based on the edge of the head switching signal when recording is performed in the SP mode, A first time T1 from the low level to the high level when chattering is generated when the video signal reproduced from the SP head is high and the envelope comparison signal having the low level is high A third step of detecting a second time (T2) from the first time (T1) to the time when chattering is generated from the high level to the low level; The first time T1 is detected when the envelope comparison signal is changed from the high level to the low level on the basis of the edge of the head switching signal, A fourth step of detecting a second time T2 from a high level to a point at which chattering is generated at a low level; The second time T2 is subtracted from the time T0 between the edges of the head switching signal so that the third divided time T3 does not coincide with the first time T1 within a predetermined tolerance range If the first time period T1 and the third time period T3 coincide with each other within the predetermined tolerance range, it is determined that the running speed of the video tape is adaptively controlled and the auto- And a fifth step of terminating the video cassette recorder.